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astro-ph/0001001 | Alex Lazarian | A. Lazarian | Statistics of Turbulence from Spectral-Line Data Cubes | 21 pages, 1 figure, review for "Plasma Turbulence and Energetic
Particles in Astrophysics", eds.M. Ostrowski & R. Schlickeiser, Cracow (1999) | null | null | null | astro-ph cond-mat.stat-mech physics.ao-ph physics.flu-dyn physics.plasm-ph physics.space-ph | null | Emission in spectral lines can provide unique information on interstellar
turbulence. Doppler shifts due to supersonic motions contain information on
turbulent velocity field which is otherwise difficult to measure. However, the
problem of separation of velocity and density fluctuations is far from being
trivial. Using atomic hydrogen (HI) as a test case, I review techniques
applicable to emission line studies with the emphasis on those that can provide
information on the underlying power spectra of velocity and density. I show
that recently developed mathematical machinery is promising for the purpose.
Its application to HI shows that in cold neutral hydrogen the velocity
fluctuations dominate the small scale structures observed in spectral-line data
cubes and this result is very important for the interpretation of observational
data, including the identification of clouds. Velocity fluctuations are shown
to dominate the formation of small scale structures that can be erroneously
identified as diffuse clouds. One may argue that the HI data is consistent with
the Goldreich-Shridhar picture of magnetohydrodynamic turbulence, but the
cascade from the scales of several kpc that this interpretation involves does
not fit well in the current paradigm of energy injection. The issue whether
magnetic field does make the turbulence anisotropic is still open, but if this
is the case, I show that studies of emission lines can provide a reliable way
of determining magnetic field direction. I discuss various techniques for
studying interstellar turbulence using emission lines, e.g. spectral
correlation functions, genus statistics and principal component analysis.
| [
{
"created": "Sat, 1 Jan 2000 02:05:30 GMT",
"version": "v1"
}
] | 2016-08-30 | [
[
"Lazarian",
"A.",
""
]
] |
astro-ph/0001002 | Renxin Xu | G.J. Qiao, R.X. Xu, J.F. Liu, J.L. Han, B. Zhang (CAS-PKU BAC &
Astronomy Department, PKU) | On the inverse Compton scattering model of radio pulsars | 5 pages, no figures, LaTeX, a proceeding paper for Pacific Rim
Conference on Stellar Astrophysics, Aug. 1999, HongKong, China | null | 10.1007/978-94-010-0878-5_44 | null | astro-ph | null | Some characteristics of the inverse Compton scattering (ICS) model are
reviewed. At least the following properties of radio pulsars can be reproduced
in the model: core or central emission beam, one or two hollow emission cones,
different emission heights of these components, diverse pulse profiles at
various frequencies, linear and circular polarization features of core and
cones.
| [
{
"created": "Sat, 1 Jan 2000 11:08:49 GMT",
"version": "v1"
}
] | 2016-01-27 | [
[
"Qiao",
"G. J.",
"",
"CAS-PKU BAC &\n Astronomy Department, PKU"
],
[
"Xu",
"R. X.",
"",
"CAS-PKU BAC &\n Astronomy Department, PKU"
],
[
"Liu",
"J. F.",
"",
"CAS-PKU BAC &\n Astronomy Department, PKU"
],
[
"Han",
"J. L.",
"",
"CAS-PKU BAC &\n Astronomy Department, PKU"
],
[
"Zhang",
"B.",
"",
"CAS-PKU BAC &\n Astronomy Department, PKU"
]
] |
astro-ph/0001003 | Matthias Steinmetz | Julio F. Navarro (University of Victoria) and Matthias Steinmetz
(University of Arizona) | Dark Halo and Disk Galaxy Scaling Laws in Hierarchical Universes | submitted to The Astrophysical Journal | Astrophys.J.538:477-488,2000 | 10.1086/309175 | null | astro-ph | null | We use cosmological N-body/gasdynamical simulations that include star
formation and feedback to examine the proposal that scaling laws between the
total luminosity, rotation speed, and angular momentum of disk galaxies reflect
analogous correlations between the structural parameters of their surrounding
dark matter halos. The numerical experiments follow the formation of
galaxy-sized halos in two Cold Dark Matter dominated universes: the standard
Omega=1 CDM scenario and the currently popular LCDM model. We find that the
slope and scatter of the I-band Tully-Fisher relation are well reproduced in
the simulations, although not, as proposed in recent work, as a result of the
cosmological equivalence between halo mass and circular velocity: large
systematic variations in the fraction of baryons that collapse to form galaxies
and in the ratio between halo and disk circular velocities are observed in our
numerical experiments. The Tully-Fisher slope and scatter are recovered in this
model as a direct result of the dynamical response of the halo to the assembly
of the luminous component of the galaxy. We conclude that models that neglect
the self-gravity of the disk and its influence on the detailed structure of the
halo cannot be used to derive meaningful estimates of the scatter or slope of
the Tully-Fisher relation. Our models fail, however, to match the zero-point of
the Tully-Fisher relation, as well as that of the relation linking disk
rotation speed and angular momentum. These failures can be traced,
respectively, to the excessive central concentration of dark halos formed in
the Cold Dark Matter cosmogonies we explore and to the formation of galaxy
disks as the final outcome of a sequence of merger events. (abridged)
| [
{
"created": "Sun, 2 Jan 2000 01:09:29 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Jan 2000 21:59:55 GMT",
"version": "v2"
}
] | 2012-06-01 | [
[
"Navarro",
"Julio F.",
"",
"University of Victoria"
],
[
"Steinmetz",
"Matthias",
"",
"University of Arizona"
]
] |
astro-ph/0001004 | Ruth Dgani | Ruth Dgani | Theory of the Interaction of Planetary Nebulae with the Interstellar
Medium | To appear in ``Asymmetrical Planetary Nebulae II: from Origins to
Microstructures, '' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N.
Soker & S.A. Rappaport, eds | null | null | null | astro-ph | null | The theory of the interaction of planetary nebulae with the interstellar
medium is important for the interpretation of nebular morphologies that deviate
from point symmetry. It can be used to probe the interstellar medium and its
magnetic field. We emphasize in this review the role of hydrodynamical
instabilities in the interaction.
| [
{
"created": "Sun, 2 Jan 2000 01:22:49 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Dgani",
"Ruth",
""
]
] |
astro-ph/0001005 | Sergei B. Popov | S.B. Popov and M.E. Prokhorov (Sternberg Astronomical Institute) | Restrictions on parameters of power-law magnetic field decay for
accreting isolated neutron stars | 8 pages including 3 PostScript figures | null | 10.1080/10556790108221135 | null | astro-ph | null | In this short note we discuss the influence of power-law magnetic field decay
on the evolution of old accreting isolated neutron stars. We show, that,
contrary to exponential field decay (Popov & Prokhorov 2000), no additional
restrictions can be made for the parameters of power-law decay from the
statistics of isolated neutron star candidates in ROSAT observations.
We also briefly discuss the fate of old magnetars with and without field
decay, and describe parameters of old accreting magnetars.
| [
{
"created": "Sun, 2 Jan 2000 10:34:46 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Popov",
"S. B.",
"",
"Sternberg Astronomical Institute"
],
[
"Prokhorov",
"M. E.",
"",
"Sternberg Astronomical Institute"
]
] |
astro-ph/0001006 | Shiv Kumar Sethi | Shiv K. Sethi, S. G. Bhargavi, Jochen Greiner | On the Clustering of GRBs on the Sky | 5 pages, Latex with aipproc.sty, incl. 1 ps-Fig., Proc. of the 5th
Huntsville Gamma Ray Burst Symposium, Oct. 1999, ed. R.M. Kippen, AIP | null | 10.1063/1.1361517 | null | astro-ph | null | The two-point correlation of the 4th (current) BATSE catalog (2494 objects)
is calculated. It is shown to be consistent with zero at nearly all angular
scales of interest. Assuming that GRBs trace the large scale structure in the
universe we calculate the angular correlation function for the standard CDM
(sCDM) model. It is shown to be $\le 10^{-4}$ at $\theta \simeq 5^\circ$ if the
BATSE catalog is assumed to be a volume-limited sample up to $z \simeq 1$.
Combined with the error analysis on the BATSE catalog this suggests that nearly
$10^5$ GRBs will be needed to make a positive detection of the two-point
angular correlation function at this angular scale.
| [
{
"created": "Sun, 2 Jan 2000 17:19:00 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Sethi",
"Shiv K.",
""
],
[
"Bhargavi",
"S. G.",
""
],
[
"Greiner",
"Jochen",
""
]
] |
astro-ph/0001007 | Kim Eunhyeuk | Eunhyeuk Kim (1), Myung Gyoon Lee, (1), and Doug Geisler (2) ((1)
Seoul National University, Korea (2) Universidad de Concepcion, Chile) | Wide Field CCD Surface Photometry of the Giant Elliptical Galaxy NGC
4472 in the Virgo Cluster | 8 pages(mnrasLaTeX), 8 Postscript figures, Accepted for publication
in MNRAS, 2000) | null | 10.1046/j.1365-8711.2000.03356.x | SNU-ASTRO-00-001 | astro-ph | null | We present deep wide field (16'.4 x 16'.4) Washington CT1 CCD surface
photometry of the giant elliptical galaxy NGC 4472, the brightest member in the
Virgo cluster. Our data cover a wider field than any previous CCD photometry as
well as going deeper. Surface brightness profiles of NGC 4472 are not well fit
by a single King model, but they can be fit approximately by two King models:
with separate models for the inner and outer regions. Surface brightness
profiles for the outer region can also be fit approximately by a deVaucouleurs
law. There is clearly a negative color gradient within 3' of NGC 4472, in the
sense that the color gets bluer with increasing radius. The slope of the color
gradient for this region is derived to be $\Delta \mu (C-T_1)$ = -0.08 mag
arcsec$^{-2}$ for $\Delta \log r =1$, which corresponds to a metallicity
gradient of $\Delta$ [Fe/H] $= -0.2$ dex. However, the surface color gets
redder slowly with increasing radius beyond 3'. A comparison of the structural
parameters of NGC 4472 in C and T1 images has shown that there is little
difference in the ellipse shapes between isochromes and isophotes. In addition,
photometric and structural parameters of NGC 4472 have been determined.
| [
{
"created": "Mon, 3 Jan 2000 05:18:47 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Kim",
"Eunhyeuk",
""
],
[
"Lee",
"Myung Gyoon",
""
],
[
"Geisler",
"Doug",
""
]
] |
astro-ph/0001008 | Sylvio Klose | Sylvio Klose | Gamma-Ray Bursts in the 1990's - a Multi-wavelengths Scientific
Adventure | 22 pages, Latex; added references for section 2.1 | null | null | null | astro-ph | null | In 1997 the first optical afterglow of a cosmic Gamma-Ray Burst was
discovered, and substantial progress has been achieved since then. Here we
present a short review of some recent developments in this field, with emphasis
on observational aspects of the GRB phenomenon.
| [
{
"created": "Mon, 3 Jan 2000 10:01:25 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Feb 2000 13:57:33 GMT",
"version": "v2"
}
] | 2016-08-30 | [
[
"Klose",
"Sylvio",
""
]
] |
astro-ph/0001009 | Aya Kubota | Kazuo Makishima (1), Aya Kubota (1), Tsunefumi Mizuno (1), Tomohisa
Ohnishi(1), Makoto Tashiro(1), Yoichi Aruga(2), Kazumi Asai(2), Tadayasu
Dotani(2), Kazuhisa Mitsuda(2), Yoshihiro Ueda(2), Shin'ichiro Uno(2),
Kazutaka Yamaoka(2), Ken Ebisawa(3), Yoshiki Kohmura(4) and Kyoko Okada(4)
((1)University of Tokyo, (2) Institute of Space and Astronautical Science,
(3)NASA/Goddard Space Flight Center, (4)Harima Institute) | The Nature of Ultra-Luminous Compact X-Ray Sources in Nearby Spiral
Galaxies | submitted to ApJ, December 1999 | Astrophys.J.535:632,2000 | 10.1086/308868 | RESCEU 48/99 | astro-ph | null | Studies were made of ASCA spectra of seven ultra-luminous compact X-ray
sources (ULXs) in nearby spiral galaxies; M33 X-8 (Takano et al. 1994), M81 X-6
(Fabbiano 1988b; Kohmura et al. 1994; Uno 1997), IC 342 Source 1 (Okada et al.
1998), Dwingeloo 1 X-1 (Reynolds et al. 1997), NGC 1313 Source B (Fabbiano &
Trinchieri 1987; Petre et al. 1994), and two sources in NGC 4565 (Mizuno et al.
1999). With the 0.5--10 keV luminosities in the range 10^{39-40} ergs/s, they
are thought to represent a class of enigmatic X-ray sources often found in
spiral galaxies. For some of them, the ASCA data are newly processed, or the
published spectra are reanalyzed. For others, the published results are quoted.
The ASCA spectra of all these seven sources have been described successfully
with so called multi-color disk blackbody (MCD) emission arising from
optically-thick standard accretion disks around black holes. Except the case of
M33 X-8, the spectra do not exhibit hard tails. For the source luminosities not
to exceed the Eddington limits, the black holes are inferred to have rather
high masses, up to ~100 solar masses. However, the observed innermost disk
temperatures of these objects, Tin = 1.1--1.8 keV, are too high to be
compatible with the required high black-hole masses, as long as the standard
accretion disks around Schwarzschild black holes are assumed. Similarly high
disk temperatures are also observed from two Galactic transients with
superluminal motions, GRO 1655-40 and GRS 1915+105. The issue of unusually high
disk temperature may be explained by the black hole rotation, which makes the
disk get closer to the black hole, and hence hotter.
| [
{
"created": "Mon, 3 Jan 2000 10:06:13 GMT",
"version": "v1"
}
] | 2011-05-10 | [
[
"Makishima",
"Kazuo",
""
],
[
"Kubota",
"Aya",
""
],
[
"Mizuno",
"Tsunefumi",
""
],
[
"Ohnishi",
"Tomohisa",
""
],
[
"Tashiro",
"Makoto",
""
],
[
"Aruga",
"Yoichi",
""
],
[
"Asai",
"Kazumi",
""
],
[
"Dotani",
"Tadayasu",
""
],
[
"Mitsuda",
"Kazuhisa",
""
],
[
"Ueda",
"Yoshihiro",
""
],
[
"Uno",
"Shin'ichiro",
""
],
[
"Yamaoka",
"Kazutaka",
""
],
[
"Ebisawa",
"Ken",
""
],
[
"Kohmura",
"Yoshiki",
""
],
[
"Okada",
"Kyoko",
""
]
] |
astro-ph/0001010 | Ferrara Andrea | A. Ferrara, B. Ciardi, S. Marri, and P. Todini | Feedback Processes in the Early Universe | 8 pages, EslabStyle.cls, LaTeX, 7 figures | Invited Review at the 33rd ESLAB Symp. "Star Formation from the
Small to the Large Scale", ed. F. Favata et al | null | OAA-001 | astro-ph | null | Feedback effects due to massive stars and supernovae in the first objects are
shown to strongly regulate both galaxy formation/evolution and the reionization
process. Here we review the most important ones in some detail. We discuss how
Type II supernovae can be used as tracers of the first objects and detected
with NGST, for which we predict supernova number counts including the effects
of gravitational lensing. Preliminary results on the formation of dust in the
ejecta of supernovae of primordial composition are also presented. We finally
turn to the consideration of the process of inhomogeneous reionization due to
primordial stellar sources by means of high resolution numerical simulations,
allowing for a self-consistent treatment of the above feedback processes. These
simulations allow us to draw conclusions on the evolution and epoch of
reionization and about the fate of reionizing objects. We conclude that a large
fraction (~ 99%) of collapsed objects must be dark at redshift around eight.
| [
{
"created": "Mon, 3 Jan 2000 10:17:25 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Ferrara",
"A.",
""
],
[
"Ciardi",
"B.",
""
],
[
"Marri",
"S.",
""
],
[
"Todini",
"P.",
""
]
] |
astro-ph/0001011 | Giangiacomo Gandolfi | G. Gandolfi, M. Feroci, E. Costa, L. Piro (IAS/CNR), M.J.S. Smith,
J.M. Muller (SRON), A. Coletta, G. Celidonio, L. Di Ciolo, A. Paolino, G.
Tarei, G. Tassone (TELESPAZIO) and F. Frontera(ITESRE/CNR) | What can BeppoSAX tell us about short GRBs: An update from the Subsecond
GRB Project | Proc. 5th Huntsville GRB Symposium | null | 10.1063/1.1361500 | null | astro-ph | null | We present some statistical considerations on the BeppoSAX hunt for subsecond
GRBs at the Scientific Operation Center. Archive analysis of a BATSE/SAX
sub-sample of bursts indicates that the GRB Monitor is sensitive to short (< 2
sec) events, that are in fact about 22% of the total. The non-detection of
corresponding prompt X-ray counterparts to short bursts in the Wide Field
Cameras, in about 3 years of operations, is discussed: with present data no
implications on the X-to-gamma-ray spectra of short vs long GRBs may be
inferred. Finally, the status of searching procedures at SOC is reviewed.
| [
{
"created": "Mon, 3 Jan 2000 11:32:23 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Gandolfi",
"G.",
"",
"IAS/CNR"
],
[
"Feroci",
"M.",
"",
"IAS/CNR"
],
[
"Costa",
"E.",
"",
"IAS/CNR"
],
[
"Piro",
"L.",
"",
"IAS/CNR"
],
[
"Smith",
"M. J. S.",
"",
"SRON"
],
[
"Muller",
"J. M.",
"",
"SRON"
],
[
"Coletta",
"A.",
"",
"TELESPAZIO"
],
[
"Celidonio",
"G.",
"",
"TELESPAZIO"
],
[
"Di Ciolo",
"L.",
"",
"TELESPAZIO"
],
[
"Paolino",
"A.",
"",
"TELESPAZIO"
],
[
"Tarei",
"G.",
"",
"TELESPAZIO"
],
[
"Tassone",
"G.",
"",
"TELESPAZIO"
],
[
"Frontera",
"F.",
"",
"ITESRE/CNR"
]
] |
astro-ph/0001012 | Joanna Mikolajewska | Joanna Mikolajewska | Observed Properties of Mass Loss in Symbiotic Binaries | To appear in ``Asymmetrical Planetary Nebulae II: from Origins to
Microstructures'', ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N.
Soker, & S.A. Rappaport, eds | null | null | null | astro-ph | null | Both the red giants and the Mira variables in symbiotic systems have
systematically higher mass-loss rates than do typical galactic giants and
Miras, which suggests that only very evolved giants, and so those with highest
mass-loss rates, can support symbiotic behaviour in widely separated binary
systems. They often show a flattened mass-loss geometry due to an intrinsically
inhomogeneous mass loss and/or tidal interactions between the binary
components. The main body of a symbiotic nebula is thus formed from material
lost in the giant wind, while the hot component is responsible for its
ionization and excitation. In addition, the fast wind and/or jet ejection from
the hot component, whenever occur, give rise to the complex, often bipolar,
shape of symbiotic nebulae. Observations of resolved nebulae also suggest that
the binary geometry and nebular structure are aligned but the bipolar outflow
may be not orthogonal to the orbital plane in all cases.
| [
{
"created": "Mon, 3 Jan 2000 14:38:11 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mikolajewska",
"Joanna",
""
]
] |
astro-ph/0001013 | Thomas Michael Tauris | T.M. Tauris, E.P.J. van den Heuvel, G.J. Savonije | Formation of Millisecond Pulsars with Heavy White Dwarf Companions -
Extreme Mass Transfer on Sub-Thermal Timescales | Accepted for publication in The Astrophysical Journal Letters | null | 10.1086/312496 | null | astro-ph | null | We have performed detailed numerical calculations of the non-conservative
evolution of close X-ray binary systems with intermediate-mass (2.0-6.0 M_sun)
donor stars and a 1.3 M_sun accreting neutron star. We calculated the thermal
response of the donor star to mass loss, in order to determine its stability
and follow the evolution of the mass transfer. Under the assumption of the
"isotropic re-emission model" we demonstrate that in many cases it is possible
for the binary to prevent a spiral-in and survive a highly super-Eddington
mass-transfer phase (1 << M_dot/M_Edd < 10^5) on a sub-thermal timescale, if
the convective envelope of the donor star is not too deep. These systems thus
provide a new formation channel for binary millisecond pulsars with heavy CO
white dwarfs and relatively short orbital periods (3-50 days). However, we
conclude that to produce a binary pulsar with a O-Ne-Mg white dwarf or P_orb ~1
day (e.g. PSR B0655+64) the above scenario does not work, and a spiral-in phase
is still considered the most plausible scenario for the formation of such a
system.
| [
{
"created": "Mon, 3 Jan 2000 15:42:00 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Tauris",
"T. M.",
""
],
[
"Heuvel",
"E. P. J. van den",
""
],
[
"Savonije",
"G. J.",
""
]
] |
astro-ph/0001014 | Thomas Michael Tauris | T.M. Tauris, G.J. Savonije | Spin-Orbit Couplings in X-ray Binaries | 6 pages, to appear in the proceedings of the NATO ASI "The Neutron
Star - Black Hole Connection" | null | null | null | astro-ph | null | We discuss the influence of tidal spin-orbit interactions on the orbital
dynamics of close intermediate-mass X-ray binaries. In particular we consider
here a process in which spin angular momentum of a contracting RLO donor star,
in a synchronous orbit, is converted into orbital angular momentum and thus
helps to stabilize the mass transfer by widening the orbit. Binaries which
would otherwise suffer from dynamically unstable mass transfer (leading to the
formation of a common envelope and spiral-in evolution) are thus shown to
survive a phase of extreme mass transfer on a sub-thermal timescale.
Furthermore, we discuss the orbital evolution prior to RLO in X-ray binaries
with low-mass donors, caused by the competing effects of wind mass loss and
tidal effects due to expansion of the (sub)giant.
| [
{
"created": "Mon, 3 Jan 2000 15:52:07 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Tauris",
"T. M.",
""
],
[
"Savonije",
"G. J.",
""
]
] |
astro-ph/0001015 | Thomas Michael Tauris | T.M. Tauris, E.P.J. van den Heuvel | New Direct Observational Evidence for Kicks in SNe | 2 pages, to appear in the proceedings of the IAU Colloq. 177 "Pulsar
Astronomy - 2000 and beyond" | null | null | null | astro-ph | null | We present an updated list of direct strong evidence in favour of kicks being
imparted to newborn neutron stars. In particular we discuss the new cases of
evidence resulting from recent observations of the X-ray binary Circinus X-1
and the newly discovered binary radio pulsar PSR J1141-6545. We conclude that
the assumption that neutron stars receive a kick velocity at their formation is
unavoidable (van den Heuvel & van Paradijs 1997).
| [
{
"created": "Mon, 3 Jan 2000 15:57:14 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Tauris",
"T. M.",
""
],
[
"Heuvel",
"E. P. J. van den",
""
]
] |
astro-ph/0001016 | Martin Zwaan | M. A. Zwaan and F. H. Briggs (Kapteyn Astronomical Institute,
Groningen) | The Space Density of Primordial Gas Clouds near Galaxies and Groups and
their Relation to Galactic HVCs | Accepted for publication in ApJL. 7 pages, 2 figures | null | 10.1086/312488 | null | astro-ph | null | The Arecibo HI Strip Survey probed the halos of ~300 cataloged galaxies and
the environments of ~14 groups with sensitivity to neutral hydrogen masses >
10^7 M_sun. The survey detected no objects with properties resembling the High
Velocity Clouds (HVCs) associated with the Milky Way or Local Group. If the
HVCs were typically M_HI=10^{7.5} M_sun objects distributed throughout groups
and galaxy halos at distances of 1 Mpc, the survey should have made ~70 HVC
detections in groups and ~250 detections around galaxies. The null detection
implies that HVCs are deployed at typical distances of <200 kpc from the
galaxies or group barycenters. If the clouds are in virial equilibrium, their
average dark matter fraction must be 98% or higher.
| [
{
"created": "Mon, 3 Jan 2000 16:53:45 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Zwaan",
"M. A.",
"",
"Kapteyn Astronomical Institute,\n Groningen"
],
[
"Briggs",
"F. H.",
"",
"Kapteyn Astronomical Institute,\n Groningen"
]
] |
astro-ph/0001017 | Herpin | F. Herpin (Dept. Fisica Molecular, IEM, CSIC, Madrid, Spain),
J.Cernicharo (same address), and A. Heras (Space Science Dept. of ESA, ESTEC,
Netherlands) | H2 emission from CRL 618 | 4 pages, 3 figures, proceeding of the "H2 in Space" conference,
Paris, September 1999 | null | null | null | astro-ph | null | We present a complete study of the H2 infrared emission, including the pure
rotational lines, of the proto Planetary Nebulae CRL 618 with the ISO SWS. A
large number of lines are detected. The analysis of our observations shows: (i)
an OTP ratio very different from the classical value of 3, probably around
1.76-1.87; (ii) a stratification of the emitting region, and more precisely
different regions of emission, plausibly located in the lobes, in an
intermediate zone, and close to the torus; (iii) different excitation
mechanisms, collisions and fluorescence.
| [
{
"created": "Mon, 3 Jan 2000 17:19:55 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Herpin",
"F.",
"",
"Dept. Fisica Molecular, IEM, CSIC, Madrid, Spain"
],
[
"Cernicharo",
"J.",
"",
"same address"
],
[
"Heras",
"A.",
"",
"Space Science Dept. of ESA, ESTEC,\n Netherlands"
]
] |
astro-ph/0001018 | Inese I. Ivans | Christopher Sneden (1), Inese I. Ivans (1), Robert P. Kraft (2) ((1)
McDonald Observatory and Univ. of Texas at Austin (2) UCO/Lick Observatory
and Univ. of California at Santa Cruz) | Do AGB Stars Differ Chemically from RGB Stars in Globular Clusters? | 9 pages, 2 figures (memsait.sty, epsf.sty) to appear in Workshop
Proceedings of "The Changes in Abundances in Asymptotic Giant Branch Stars",
held in Monteporzio Catone (Italy), September 1999, to be published by
Mem.Soc.Astron.It., eds. F. D'Antona and R. Gallino | null | null | null | astro-ph | null | Recent improvements in globular cluster colour-magnitude diagrams, coupled
with an increase in large-sample spectroscopic abundance studies of cluster
giants, finally allow some attempts at a statistically meaningful comparison of
the chemical compositions of red giant branch (RGB) and asymptotic branch (AGB)
cluster stars. We review some of the extant data here, concluding that in a few
clusters the AGB stars show on average smaller amounts of high-temperature
proton-capture synthesis products (low oxygen, high sodium and aluminum) at
their surfaces than do the first-ascent RGB stars. This suggests that those RGB
stars with envelopes that have been enriched with proton-capture material also
have high helium contents. Such stars after the He-flash then take up residence
on the bluest parts of the horizontal branch (as a consequence of their high
envelope helium), probably never to return to the AGB during subsequent
evolutionary stages.
| [
{
"created": "Mon, 3 Jan 2000 19:12:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sneden",
"Christopher",
""
],
[
"Ivans",
"Inese I.",
""
],
[
"Kraft",
"Robert P.",
""
]
] |
astro-ph/0001019 | Kevin Hurley | K. Hurley, N. Lund, S. Brandt, C. Barat, T. Cline, R. Sunyaev, O.
Terekhov, A. Kuznetsov, S. Sazonov, A. Castro-Tirado | The Ulysses Supplement to the GRANAT/WATCH Catalog of Cosmic Gamma-Ray
Bursts | 26 pages, plus 25 gif figures; submitted to the Astrophysical Journal
Supplements | Astrophys.J.Suppl. 128 (2000) 549-560 | 10.1086/313400 | null | astro-ph | null | We present 3rd interplanetary network (IPN) localization data for 56
gamma-ray bursts in the GRANAT/ WATCH catalog which occurred between 1990
November and 1994 September. These localizations are obtained by triangulation
using various combinations of spacecraft in the IPN, which consisted of
Ulysses, BATSE, Pioneer Venus Orbiter (PVO), Mars Observer (MO), WATCH, and
PHEBUS. The intersections of the triangulation annuli with the WATCH error
circles produce error boxes with areas as small as 16 sq. arcmin., reducing the
sizes of the error circles by up to a factor of 800.
| [
{
"created": "Mon, 3 Jan 2000 19:08:23 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Hurley",
"K.",
""
],
[
"Lund",
"N.",
""
],
[
"Brandt",
"S.",
""
],
[
"Barat",
"C.",
""
],
[
"Cline",
"T.",
""
],
[
"Sunyaev",
"R.",
""
],
[
"Terekhov",
"O.",
""
],
[
"Kuznetsov",
"A.",
""
],
[
"Sazonov",
"S.",
""
],
[
"Castro-Tirado",
"A.",
""
]
] |
astro-ph/0001020 | J. A. Lopez | J.A. Lopez, J. Meaburn, L.F. Rodriguez, R. Vazquez, W. Steffen and M.
Bryce | HST/WFPC2 observations of the core of KjPn 8 | 4 pages, 1 figure. To appear in ``Asymmetrical Planetary Nebulae II:
from Origins to Microstructures'' ASP Conference Series, Vol. 199, 2000; J.H.
Kastner, N. Soker and S.A. Rappaport, eds | null | null | null | astro-ph | null | Narrow-band images of the core of the extraordinary poly-polar planetary
nebula KjPn 8 have been obtained with the WFPC2 camera on board the Hubble
Space Telescope. Spasmodic bipolar ejections, in changing directions have
occurred over thousands of years to create KjPn 8. The central star is finally
revealed in these observations and its compact nebular core is resolved into a
remarkably young, aprox. 500 years old, elliptical ring. The highest speed
bipolar outflows are perpendicular to this central ring which is identified as
the latest event in the creation of this nebula. The formation history of KjPn
8 has involved two distinct planetary nebula-like events, probably originating
froma a binary core evolution with components of similar mass.
| [
{
"created": "Mon, 3 Jan 2000 19:42:35 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Lopez",
"J. A.",
""
],
[
"Meaburn",
"J.",
""
],
[
"Rodriguez",
"L. F.",
""
],
[
"Vazquez",
"R.",
""
],
[
"Steffen",
"W.",
""
],
[
"Bryce",
"M.",
""
]
] |
astro-ph/0001021 | Michiel R. Hogerheijde | Michiel R. Hogerheijde (1), Goeran Sandell (2) ((1) Radio Astronomy
Laboratory, Astronomy Department, University of California, Berkeley; (2)
NRAO Greenbank) | Testing envelope models of young stellar objects with submillimeter
continuum and molecular-line observation | 35 pages incl. 9 figures. Uses AAS LaTeX v5.0 and psfig | null | 10.1086/308795 | null | astro-ph | null | This paper examines the density and velocity structure of envelopes around
young stellar objects through submillimeter continuum imaging of four objects
in Taurus and previously obtained molecular-line data. Observations carried out
with the SCUBA on the JCMT at 850 and 450 micron of L1489 IRS, L1535 IRS, L1527
IRS, and TMC 1 reveal ~2000 AU elongated structures embedded in extended
envelopes. The density distribution in these envelopes is equally well fit by a
radial power-law of index p=1.0-2.0 or with a collapse model such as that of
Shu (1997: ApJ, 214, 488). This inside-out collapse model predicts 13CO, C18O,
HCO+, and H13CO+ line profiles which closely match observed spectra toward
three of our four sources. This shows that the inside-out collapse model offers
a good description of YSO envelopes, but also that reliable constraints on its
parameters require independent measurements of the density and the velocity
structure, e.g., through continuum and line observations. For the remaining
source, L1489 IRS, we find that a model consisting of a 2000 AU radius,
rotating, disk-like structure better describes the data. Possibly, this source
is in transition between the embedded Class I and the optically revealed T
Tauri phases. Two apparently starless cores are found at ~10,000 AU from L1489
IRS and L1535 IRS. They are cold, 10-15 K, contain 0.5-3.0 M_sol, and have flat
density distributions characterized by a Gaussian of ~10,000 AU FWHM. The
proximity of these cores shows that star formation in truly isolated cores is
rare even in Taurus.
| [
{
"created": "Mon, 3 Jan 2000 20:10:38 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Hogerheijde",
"Michiel R.",
""
],
[
"Sandell",
"Goeran",
""
]
] |
astro-ph/0001022 | Joshua N. Winn | Catherine S. Trotter, Joshua N. Winn and Jacqueline N. Hewitt (MIT) | A multipole-Taylor expansion for the potential of gravitational lens MG
J0414+0534 | 44 pages, 5 figures, 11 tables, accepted for publication in ApJ | null | 10.1086/308861 | null | astro-ph | null | We employ a multipole-Taylor expansion to investigate how tightly the
gravitational potential of the quadruple-image lens MG J0414+0534 is
constrained by recent VLBI observations. These observations revealed that each
of the four images of the background radio source contains four distinct
components, thereby providing more numerous and more precise constraints on the
lens potential than were previously available. We expand the two-dimensional
lens potential using multipoles for the angular coordinate and a modified
Taylor series for the radial coordinate. After discussing the physical
significance of each term, we compute models of MG J0414+0534 using only VLBI
positions as constraints. The best-fit model has both interior and exterior
quadrupole moments as well as exterior m=3 and m=4 multipole moments. The
deflector centroid in the models matches the optical galaxy position, and the
quadrupoles are aligned with the optical isophotes. The radial distribution of
mass could not be well constrained. We discuss the implications of these models
for the deflector mass distribution and for the predicted time delays between
lensed components.
| [
{
"created": "Mon, 3 Jan 2000 21:54:25 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Trotter",
"Catherine S.",
"",
"MIT"
],
[
"Winn",
"Joshua N.",
"",
"MIT"
],
[
"Hewitt",
"Jacqueline N.",
"",
"MIT"
]
] |
astro-ph/0001023 | Neal J. Evans II | Neal J. Evans II | Studies of Low-Mass Star Formation with ALMA | 10 pg., 4 figs | null | null | null | astro-ph | null | ALMA will revolutionize the study of star formation by providing a
combination of angular resolution and sensitivity that far exceeds that of
present instruments. I will focus on studies of relatively isolated cores that
are forming low-mass stars. There is a general paradigm for the formation of
such stars, and there are detailed theoretical predictions for the evolution of
the density and velocity fields for different assumptions about the initial
conditions. Because the theory is well developed, observational tests are
particularly revealing. The primary probes of physical conditions in these
regions are discussed and the sensitivity of ALMA to these probes is shown and
compared to the current state of the art. The consequences for the ALMA
requirements are discussed.
| [
{
"created": "Mon, 3 Jan 2000 22:17:58 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Evans",
"Neal J.",
"II"
]
] |
astro-ph/0001024 | Carl Heiles | Carl Heiles, L.M. Haffner, R.J. Reynolds, S.L. Tufte | Physical Conditions, Grain Temperatures, and Enhanced Very Small Grains
in the Barnard Loop | 21 pages, 6 figures. Accepted by Astrophysical Journal | null | 10.1086/308935 | null | astro-ph | null | We derive the radio spectral index of the Barnard Loop (BL) from large-scale
radio surveys at four frequencies and find it to be a thermal source. We use
the radio data together with H-alpha data to determine the electron temperature
in BL, the lambda-Ori HII region, and a high-latitude filament; all of these
regions are somewhat cooler than typical HII regions.
We perform least squares fits of the DIRBE diffuse IR intensities to the
21-cm line and radio continuum intensities. After the resolution of a
``geometrical conundrum'', this allows us to derive the electron density n_e;
we find n_e ~ 2.0 cm^{-3} and pressure (P/k) ~ 24000 cm^{-3} K.
Grains within BL are warmer than in HI regions. Trapped L-alpha accounts for
the extra heating that is required. This is a general effect that needs to be
accounted for in all analyses that examine IR emission from H^+ regions. Very
small grains that emit 60 micron radiation are enhanced in BL relative to HI by
a factor of 2-3, while PAH's that emit 12 micron are probably deficient by a
factor ~2.
| [
{
"created": "Mon, 3 Jan 2000 23:46:33 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Heiles",
"Carl",
""
],
[
"Haffner",
"L. M.",
""
],
[
"Reynolds",
"R. J.",
""
],
[
"Tufte",
"S. L.",
""
]
] |
astro-ph/0001025 | Qingjuan Yu | Scott Tremaine, Qingjuan Yu (Princeton University Observatory) | Resonant capture, counter-rotating disks, and polar rings | 10 pages, 6 figures, Latex. Submitted to MNRAS | Mon.Not.Roy.Astron.Soc. 319 (2000) 1 | 10.1046/j.1365-8711.2000.03653.x | null | astro-ph | null | We suggest that polar rings and/or counter-rotating disks in flattened
galaxies can be formed from stars captured at the Binney resonance, where the
rate of precession of the angular momentum vector of a disk star equals the
pattern speed of a triaxial halo. If the halo pattern speed is initially
retrograde and slowly decays to zero, stars can be trapped as the Binney
resonance sweeps past them, and levitated into polar orbits. If the halo
pattern speed is initially retrograde and slowly changes to prograde, trapped
stars can evolve from prograde to retrograde disk orbits. The stellar
components of polar rings formed by this process should consist of two equal,
counter-rotating star streams.
| [
{
"created": "Tue, 4 Jan 2000 00:15:10 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Tremaine",
"Scott",
"",
"Princeton University Observatory"
],
[
"Yu",
"Qingjuan",
"",
"Princeton University Observatory"
]
] |
astro-ph/0001026 | Deepto Chakrabarty | Deepto Chakrabarty (MIT), Michael J. Pivovaroff (MIT), Lars E.
Hernquist (CfA), Jeremy S. Heyl (CfA/Caltech), Ramesh Narayan (CfA) | The Central X-Ray Point Source in Cassiopeia A | 17 pages including 2 figs. To appear in ApJ, Vol. 546 (Jan 10, 2001).
Minor revisions per referee. Pulsation limits revised in light of HRC wiring
problem. Typos corrected | null | 10.1086/318994 | null | astro-ph | null | The spectacular first light observation by the Chandra X-Ray Observatory
revealed an X-ray point source near the center of the 300 yr old Cas A
supernova remnant. We present an analysis of the public X-ray spectral and
timing data. No coherent pulsations were detected in the Chandra/HRC data. The
3-sigma upper limit on the pulsed fraction is <35% for P>20 ms. The
Chandra/ACIS spectrum of the point source may be fit with an ideal blackbody
(kT=0.5 keV), or with BB models modified by the presence of a NS atmosphere
(kT=0.25-0.35 keV), but the temperature is higher and the inferred emitting
area lower than expected for a 300 yr old NS according to standard cooling
models. The spectrum may also be fit with a power law model (photon index
2.8-3.6). Both the spectral properties and the timing limits of the point
source are inconsistent with a young Crab-like pulsar, but are quite similar to
the properties of the anomalous X-ray pulsars. The spectral parameters are also
very similar to those of the other radio-quiet X-ray point sources in the
supernova remnants Pup A, RCW 103, and PKS 1209-52. Current limits on an
optical counterpart for the Cas A point source rule out models that invoke
fallback accretion onto a compact object if fallback disk properties are
similar to those in quiescent low-mass X-ray binaries. However, the optical
limits are marginally consistent with plausible alternative assumptions for a
fallback disk. In this case, accreting NS models can explain the X-ray data,
but an accreting BH model is not promising.
| [
{
"created": "Tue, 4 Jan 2000 00:16:35 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Aug 2000 22:35:54 GMT",
"version": "v2"
},
{
"created": "Sun, 10 Sep 2000 16:01:02 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Chakrabarty",
"Deepto",
"",
"MIT"
],
[
"Pivovaroff",
"Michael J.",
"",
"MIT"
],
[
"Hernquist",
"Lars E.",
"",
"CfA"
],
[
"Heyl",
"Jeremy S.",
"",
"CfA/Caltech"
],
[
"Narayan",
"Ramesh",
"",
"CfA"
]
] |
astro-ph/0001027 | Enrique Vazquez-Semadeni | Enrique V\'azquez-Semadeni, Adriana Gazol (Instituto de Astronomia,
UNAM) and John Scalo (U. of Texas) | Is Thermal Instability Significant in Turbulent Galactic Gas? | 18 pages, 11 figures. Submitted to ApJ | null | 10.1086/309318 | null | astro-ph | null | We investigate numerically the role of thermal instability (TI) as a
generator of density structures in the interstellar medium (ISM), both by
itself and in the context of a globally turbulent medium. Simulations of the
instability alone show that the condenstion process which forms a dense phase
(``clouds'') is highly dynamical, and that the boundaries of the clouds are
accretion shocks, rather than static density discontinuities. The density
histograms (PDFs) of these runs exhibit either bimodal shapes or a single peak
at low densities plus a slope change at high densities. Final static situations
may be established, but the equilibrium is very fragile: small density
fluctuations in the warm phase require large variations in the density of the
cold phase, probably inducing shocks into the clouds. This result suggests that
such configurations are highly unlikely. Simulations including turbulent
forcing show that large- scale forcing is incapable of erasing the signature of
the TI in the density PDFs, but small-scale, stellar-like forcing causes
erasure of the signature of the instability. However, these simulations do not
reach stationary regimes, TI driving an ever-increasing star formation rate.
Simulations including magnetic fields, self-gravity and the Coriolis force show
no significant difference between the PDFs of stable and unstable cases, and
reach stationary regimes, suggesting that the combination of the stellar
forcing and the extra effective pressure provided by the magnetic field and the
Coriolis force overwhelm TI as a density-structure generator in the ISM. We
emphasize that a multi-modal temperature PDF is not necessarily an indication
of a multi-phase medium, which must contain clearly distinct thermal
equilibrium phases.
| [
{
"created": "Tue, 4 Jan 2000 02:56:40 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Vázquez-Semadeni",
"Enrique",
"",
"Instituto de Astronomia,\n UNAM"
],
[
"Gazol",
"Adriana",
"",
"Instituto de Astronomia,\n UNAM"
],
[
"Scalo",
"John",
"",
"U. of Texas"
]
] |
astro-ph/0001028 | Fan Junhui | J.H. Fan (CfA, Gnu, Cas-Pku.Bac) and R.G. Lin (CfA, Gnu) | The variability analysis of PKS 2155-304 | 11 pages, 4 figures, A&A (accepted) | null | null | null | astro-ph | null | In this paper, the post-1977 photometric observations of PKS 2155-304 are
compiled and used to discuss the variation periodicity. Largest amplitude
variations ($\Delta U = 1^{m}.5$; $\Delta B = 1^{m}.65$;
$\Delta V = 1^{m}.85 $; $\Delta R = 1^{m}.25$; $\Delta I = 1^{m}.14 $) and
color indices ($(B-V) = 0.30\pm 0.06$; $(U-B) = -0.72\pm 0.08$;
$(B-R) = 0.62\pm 0.07$; $(V-R) = 0.32\pm 0.04$) are found.
The Jurkevich's method and DCF (Discrete Correlation Function) method
indicate possible periods of 4.16-year and 7.0-year in the V light curve.
| [
{
"created": "Tue, 4 Jan 2000 06:55:17 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Fan",
"J. H.",
"",
"CfA, Gnu, Cas-Pku.Bac"
],
[
"Lin",
"R. G.",
"",
"CfA, Gnu"
]
] |
astro-ph/0001029 | Fan Junhui | J.H. Fan (CfA, Gnu, Cas-Pku.Bac) | Long-term Variability Properties and Periodicity Analysis for Blazars | 10 pages, 2 table, no figure, a proceeding paper for Pacific Rim
Conference on Stellar Astrophysics, Aug. 1999, HongKong, China | null | 10.1007/978-94-010-0878-5_38 | null | astro-ph | null | In this paper, the compiled long-term optical and infrared measurements of
some blazars are used to analyze the variation properties and the optical data
are used to search for periodicity evidence in the lightcurve by means of the
Jurkevich technique and the discrete correlation function (DCF) method.
Following periods are found: 4.52-year for 3C 66A; 1.56 and 2.95 years for AO
0235+164;
14.4, 18.6 years for PKS 0735+178; 17.85 and 24.7 years for PKS 0754+100;
5.53 and 11.75 for OJ 287. 4.45, and 6.89 years for PKS 1215; 9 and 14.84 years
for PKS 1219+285;
2.0, 13.5 and 22.5 for 3C273; 7.1 year for 3C279;
6.07 for PKS 1308+326; 3.0 and 16.5 years for PKS 1418+546;
2.0 and 9.35 years for PKS 1514-241; 18.18 for PKS 1807+698;
4.16 and 7.0 for 2155-304; 14 and 20 years for BL Lacertae. Some explanations
have been discussed.
| [
{
"created": "Tue, 4 Jan 2000 08:29:59 GMT",
"version": "v1"
}
] | 2016-01-27 | [
[
"Fan",
"J. H.",
"",
"CfA, Gnu, Cas-Pku.Bac"
]
] |
astro-ph/0001030 | Roberto Della Ceca | R. Della Ceca, T. Maccacaro, P. Rosati, and V. Braito | A Hard Medium Survey with ASCA. III.: a Type 2 AGN revealed from X-ray
Spectroscopy | 8 pages, 6 figures, Latex manuscript, Accepted for publication in the
Astronomy and Astrophysics - Main Journal | null | null | null | astro-ph | null | In this paper we report the discovery of an hard X-ray selected Type 2
Seyfert galaxy and we present and discuss its X-ray and optical spectrum
together with the radio to X-ray energy distribution. The X-ray source -
AXJ2254+1146 - is part of the ASCA Hard Serendipitous Survey (HSS). What makes
this discovery particularly noteworthy is the fact that the Type 2
classification of this Seyfert galaxy has resulted directly from the X-ray data
and has been confirmed by optical spectroscopy only subsequently. The X-ray
spectrum of AXJ2254+1146 is best described by a model consisting of an
unresolved Gaussian line at $6.43\pm 0.1$ keV plus the so called
"leaky-absorber" continua having an intrinsic power law photon index of
$\Gamma$ = $2.51^{2.76}_{2.17}$ (1 $\sigma$ confidence interval). The best fit
values of the absorbing column density ($N_H$ = $1.85^{2.24}_{1.47} \times
10^{23}$ cm$^{-2}$), of the line equivalent width ($0.6^{0.84}_{0.36}$ keV) and
of the scattering fraction ($0.7^{1.4}_{0.1} %$), lead us to classify it as a
Type 2 AGN from an X-ray point of view. Inspection of the POSS II image reveals
the presence, within the ASCA X-ray error circle, of the nearby Sbc spiral
galaxy UGC 12237 ($m_{B_o}=14.26$) that, even on positional ground
considerations alone, is the most likely optical counterpart of AXJ2254+1146.
Subsequent optical spectroscopy of UGC 12237 has confirmed its Seyfert 2
optical nature.
| [
{
"created": "Tue, 4 Jan 2000 10:45:13 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Della Ceca",
"R.",
""
],
[
"Maccacaro",
"T.",
""
],
[
"Rosati",
"P.",
""
],
[
"Braito",
"V.",
""
]
] |
astro-ph/0001031 | Robert Lucas | Robert Lucas (1), Pierre Cox (2) and Patrick J. Huggins (3) ((1)
Institut de RadioAstronomie Millimetrique, (2) Institut d'Astrophysique
Spatiale, (3) Physics Department, New York University) | Multiple Outflows in AFGL 2688 | To appear in ``Asymmetrical Planetary Nebulae II: from Origins to
Microstructures,'' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N.
Soker, & S.A. Rappaport, eds | null | null | null | astro-ph | null | We present high resolution (1.1x0.9'') imaging of the proto-planetary nebula
AFGL 2688 in the CO (J=2-1) line using the IRAM interferometer. The
observations reveal with unprecedented detail the structure and the kinematics
of the gas ejected by the star over the past few hundred years and exemplify
the mechanism by which point symmetries are imprinted on the structure of
planetary nebulae at early stages of their formation.
| [
{
"created": "Tue, 4 Jan 2000 11:00:43 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Lucas",
"Robert",
""
],
[
"Cox",
"Pierre",
""
],
[
"Huggins",
"Patrick J.",
""
]
] |
astro-ph/0001032 | Richard Hook | Richard N. Hook, Ethan J. Schreier and George Miley | Limits on the Spatial Extent of AGN Measured with the Fine Guidance
Sensors of the HST | 33 pages, 24 figures, 6 tables, accepted for publication in the
Astrophysical Journal | null | null | null | astro-ph | null | The optical structure of several AGN has been studied using the Fine Guidance
Sensors (FGS) on the Hubble Space Telescope (HST). The FGSs are interferometric
devices which can resolve structure on scales of 20 milliarcsecs or less and
hence have the potential to improve on the resolution attainable by HST's
cameras. The FGSs produce interferometric fringes known as S-curves which are
related to the intensity profile of the object on the sky. These have been
analyzed using a simple model for the radial intensity distribution and
strength of the underlying background illumination of the observed objects.
Eight different observations of six different AGN have been analyzed. No
statistically significant differences from point sources are detected but
significant upper limits of order 20 milliarcseconds are placed on any spatial
extent. Systematic effects limiting the resolution are discussed and some
simple conclusions about the physical size and luminosity densities of the
emitting regions of the AGN implied by the data are given.
| [
{
"created": "Tue, 4 Jan 2000 11:44:39 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Hook",
"Richard N.",
""
],
[
"Schreier",
"Ethan J.",
""
],
[
"Miley",
"George",
""
]
] |
astro-ph/0001033 | Sergei A. Trushkin | S.A. Trushkin (SAO RAS, Russia) | Radio emission of the Galactic X-rays binaries with relativistic jets | 10 pages, LaTeX, 14 Postscript figures, talk given at the Gamov
Memorial International Conference (GMIC'99) "Early Universe: Cosmological
Problems and Instrumental Technologies" in St.Petersburg, 23-27 August, 1999,
to appear in Astron. Astrophys. Trans., 2000 | null | 10.1080/10556790008238598 | SAO 99-T | astro-ph | null | Variable non-thermal radio emission from Galactic X-ray binaries is a trace
of relativistic jets, created near accretion disks. The spectral
characteristics of a lot of radio flares in the X-ray binaries with jets (RJXB)
is discussed in this report. We carried out several long daily monitoring
programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3,
LSI+61o303, GRS 1915+10 and some others. We also reviewed some data from the
GBI monitoring program at two frequencies and hard X-ray BATSE (20-100 keV) and
soft X-ray RTXE (2-12 keV) ASM data. We confirmed that flaring radio emission
of Cyg X-3 correlated with hard and anti-correlated with soft X-ray emission
during the strong flare (>$ Jy) in May 1997. During two orbital periods we
investigated radio light curves of the remarkable X-binary LSI+61o303. Two
flaring events near a phase 0.6 of the 26.5-day orbital period have been
detected for first time at four frequencies simultaneously. Powerful flaring
events of SS433 were detected at six frequencies in May 1996 and in May 1999.
The decay of the flare is exactly fitted by an exponential law and the rate of
the decay $\tau$ depends upon frequency as tau \propto \nu^{-0.4} in the first
flare and does not depend upon frequency in the second flare, and is equal to
\tau=6+-1 days at frequencies from 0.96 to 21.7 GHz in the last flare in May
1999. Many flaring RJXB show two, exponential and power, laws of flare decay.
Moreover, these different laws could be present in one or several flares and
commonly flare decays are faster at a higher frequency. The decay law seems to
change because of geometric form of the conical hollow jets. The synchrotron
and inverse Compton losses could explain general frequency dependences in flare
evolution. In conclusion we summarized the general radio properties of RJXB.
| [
{
"created": "Tue, 4 Jan 2000 14:21:35 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Trushkin",
"S. A.",
"",
"SAO RAS, Russia"
]
] |
astro-ph/0001034 | R. L. J. van der Meer | A. C. Brinkman, C. J. T. Gunsing, J. S. Kaastra, R. L. J. van der
Meer, R. Mewe, F. Paerels, A. J. J. Raassen, J. J. van Rooijen (SRON), H.
Br\"auninger, W. Burkert, V. Burwitz, G. Hartner, P. Predehl (MPE), J.-U.
Ness, J. H. M. M. Schmitt (Uni Hamburg), J. J. Drake, O. Johnson, M. Juda, V.
Kashyap, S. S. Murray, D. Pease, P. Ratzlaff, B. J. Wargelin (Harvard-CFA) | First Light Measurements of Capella with the Low Energy Transmission
Grating Spectrometer aboard the Chandra X-ray Observatory | 4 pages (ApJ letter LaTeX), 2 PostScript figures, accepted for
publication in ApJ Letters, 2000 | null | 10.1086/312504 | null | astro-ph | null | We present the first X-ray spectrum obtained by the Low Energy Transmission
Grating Spectrometer (LETGS) aboard the Chandra X-ray Observatory. The spectrum
is of Capella and covers a wavelength range of 5-175 A (2.5-0.07 keV). The
measured wavelength resolution, which is in good agreement with ground
calibration, is $\Delta \lambda \simeq$ 0.06 A (FWHM). Although in-flight
calibration of the LETGS is in progress, the high spectral resolution and
unique wavelength coverage of the LETGS are well demonstrated by the results
from Capella, a coronal source rich in spectral emission lines. While the
primary purpose of this letter is to demonstrate the spectroscopic potential of
the LETGS, we also briefly present some preliminary astrophysical results. We
discuss plasma parameters derived from line ratios in narrow spectral bands,
such as the electron density diagnostics of the He-like triplets of carbon,
nitrogen, and oxygen, as well as resonance scattering of the strong Fe XVII
line at 15.014 A.
| [
{
"created": "Tue, 4 Jan 2000 15:03:31 GMT",
"version": "v1"
}
] | 2016-08-15 | [
[
"Brinkman",
"A. C.",
"",
"SRON"
],
[
"Gunsing",
"C. J. T.",
"",
"SRON"
],
[
"Kaastra",
"J. S.",
"",
"SRON"
],
[
"van der Meer",
"R. L. J.",
"",
"SRON"
],
[
"Mewe",
"R.",
"",
"SRON"
],
[
"Paerels",
"F.",
"",
"SRON"
],
[
"Raassen",
"A. J. J.",
"",
"SRON"
],
[
"van Rooijen",
"J. J.",
"",
"SRON"
],
[
"Bräuninger",
"H.",
"",
"MPE"
],
[
"Burkert",
"W.",
"",
"MPE"
],
[
"Burwitz",
"V.",
"",
"MPE"
],
[
"Hartner",
"G.",
"",
"MPE"
],
[
"Predehl",
"P.",
"",
"MPE"
],
[
"Ness",
"J. -U.",
"",
"Uni Hamburg"
],
[
"Schmitt",
"J. H. M. M.",
"",
"Uni Hamburg"
],
[
"Drake",
"J. J.",
"",
"Harvard-CFA"
],
[
"Johnson",
"O.",
"",
"Harvard-CFA"
],
[
"Juda",
"M.",
"",
"Harvard-CFA"
],
[
"Kashyap",
"V.",
"",
"Harvard-CFA"
],
[
"Murray",
"S. S.",
"",
"Harvard-CFA"
],
[
"Pease",
"D.",
"",
"Harvard-CFA"
],
[
"Ratzlaff",
"P.",
"",
"Harvard-CFA"
],
[
"Wargelin",
"B. J.",
"",
"Harvard-CFA"
]
] |
astro-ph/0001035 | Herpin | F. Herpin (Dept Fisica Molecular, I.E.M., C.S.I.C., Madrid, Spain),
and J. Cernicharo (same address) | O-bearing Molecules in Carbon-rich Proto-Planetary Objects | 16 pages, 3 figures, accepted in Astrophys. Journal Letters | null | 10.1086/312507 | null | astro-ph | null | We present ISO LWS observations of the proto-planetary nebula CRL 618, a star
evolving very fast to the planetary nebula stage. In addition to the lines of
12CO, 13CO, HCN and HNC, we report on the detection of H2O and OH emission
together with the fine structure lines of [OI] at 63 and 145 um. The abundance
of the latter three species relative to 12CO are 4 10^{-2}, 8 10^{-4} and 4.5
(approximate value) in the regions where they are produced. We suggest that
O-bearing species other than CO are produced in the innermost region of the
circumstellar envelope. The UV photons from the central star photodissociate
most of the molecular species produced in the AGB phase and allow a chemistry
dominated by standard ion-neutral reactions. Not only allow these reactions the
formation of O-bearing species, but they also modify the abundances of C-rich
molecules like HCN and HNC for which we found an abundance ratio of roughly 1,
much lower than in AGB stars. The molecular abundances in the different regions
of the circumstellar envelope have been derived from radiative transfer models
and our knowledge of its physical structure.
| [
{
"created": "Tue, 4 Jan 2000 15:23:16 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Herpin",
"F.",
"",
"Dept Fisica Molecular, I.E.M., C.S.I.C., Madrid, Spain"
],
[
"Cernicharo",
"J.",
"",
"same address"
]
] |
astro-ph/0001036 | Martin Kerscher | Claus Beisbart, Martin Kerscher (University of Munich) | On Luminosity and morphology segregation in the Southern Sky Redshift
Survey 2 | O pages, superceeded by arXiv:astro-ph/0003358 | null | null | null | astro-ph | null | The results are still valid, however this letter is superceeded by a
significantly extended version which is available at astro-ph/0003358 and is
scheduled for publication in the ApJ Dec. 10, 2000. We have withdrawn this
letter to avoid confusion.
| [
{
"created": "Tue, 4 Jan 2000 15:26:14 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Oct 2000 16:04:12 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Beisbart",
"Claus",
"",
"University of Munich"
],
[
"Kerscher",
"Martin",
"",
"University of Munich"
]
] |
astro-ph/0001037 | Andrea Comastri | A. Comastri, F. Fiore, C. Vignali, F. La Franca, G. Matt | The BeppoSAX High Energy Large Area Survey (HELLAS): a progress Report | Invited talk, to appear in the Proceedings of the Conference: ``Large
Scale Structure in the X-ray Universe" Santorini, Greece, 20-22 September
1999, 8 pages, 4 figures. Added references | null | null | null | astro-ph | null | The integrated emission of highly obscured AGN is expected to provide a major
contribution to the X-ray energy density in the Universe: the X-ray background
(XRB). The study of these objects is possible only at energies where the
effects of absorption are less severe. For this reason we have carried out the
BeppoSAX High Energy LLarge Area Survey in the hardest band (5-10 keV)
accessible so far with imaging X-ray instruments. The source surface density at
the survey limiting flux accounts for a significant fraction (20-30%) of the
hard XRB. The X-ray data complemented by multiwavelength follow--up
observations suggest that a large fraction of the hard sources are AGN and that
X-ray absorption with column densities in the range 10^22-23.5 cm-2 is common
among them. The great diversity in their optical-near-IR properties suggests
that the optical appearance of obscured sources is a function of the X-ray
luminosity. We briefly discuss the implications of these findings for the XRB
models.
| [
{
"created": "Tue, 4 Jan 2000 15:53:10 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Jan 2000 13:42:48 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Comastri",
"A.",
""
],
[
"Fiore",
"F.",
""
],
[
"Vignali",
"C.",
""
],
[
"La Franca",
"F.",
""
],
[
"Matt",
"G.",
""
]
] |
astro-ph/0001038 | Riccardo Valdarnini | R.Valdarnini, S. Ghizzardi, S. Bonometto | Morphological evolution of X-ray clusters using hydrodynamical
simulations | 4 pages, To appear in "LSS in the X-ray Universe", Santorini 20-22
September 1999 | null | null | null | astro-ph | null | A large set of TREESPH simulations is used to test the global morphology of
galaxy clusters and its evolution against X-ray data. A powerful method to
investigate substructures in galaxy clusters are the power ratios introduced by
Buote & Tsai. We consider three flat cosmological models: CDM,
LCDM($\Omega_\Lambda = 0.7$) and CHDM($\Omega_h = 0.2$, 1 massive $\nu$), all
normalized so to fit the observed number of clusters. For each model we built
40 clusters, using a TREESPH code, and performed a statistical comparison with
a data sample including nearby clusters observed with ROSAT PSPC instrument.
The comparison disfavors the LCDM model, as clusters appear too relaxed, while
CDM and CHDM clusters, in which a higher degree of complexity occurs, seem to
be closer to observations. A better fit of data can be expected for some
different DM mix. If DM distributions are used instead of baryons, we find
substructures more pronounced than in gas and models have a different score.
Using hydrodynamical simulations is therefore essential to our aims.
| [
{
"created": "Tue, 4 Jan 2000 16:08:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Valdarnini",
"R.",
""
],
[
"Ghizzardi",
"S.",
""
],
[
"Bonometto",
"S.",
""
]
] |
astro-ph/0001039 | Subrata Pal | Subrata Pal, Debades Bandyopadhyay and Walter Greiner | Antikaon condensation in neutron stars | 34 pages;13 figs;Revtex; change of title; a figure added; version to
appear in Nucl. Phys. A | Nucl.Phys. A674 (2000) 553-577 | 10.1016/S0375-9474(00)00175-5 | null | astro-ph nucl-th | null | We investigate the condensation of charged $K^-$ meson and neutral $\bar K^0$
meson in dense neutron star matter. Calculations are performed in relativistic
mean field models in which both the baryon-baryon and (anti)kaon-baryon
interactions are mediated by meson exchange. It is found that $\bar K^0$
condensation is quite sensitive to the antikaon optical potential and depends
more strongly on the nucleonic equation of state. For moderate values of
antikaon potential and a rather stiff equation of state, a significant region
of maximum mass star will contain $\bar K^0$ meson. The critical density of
$\bar K^0$ condensation is always higher than that of $K^-$ condensation. With
the appearance of $K^-$ and $\bar K^0$ condensates, pairs of $p-K^-$ and
$n-\bar K^0$ are produced with equal proportion leading to a perfectly
symmetric matter of nucleons and antikaons in neutron stars. Along with $K^-$
condensate, $\bar K^0$ condensate makes the equation of state much softer
resulting in smaller maximum mass stars compared to the case without any
condensate.
| [
{
"created": "Tue, 4 Jan 2000 16:50:32 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Mar 2000 14:02:57 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Pal",
"Subrata",
""
],
[
"Bandyopadhyay",
"Debades",
""
],
[
"Greiner",
"Walter",
""
]
] |
astro-ph/0001040 | Elizabeth J. Barton | Sidney van den Bergh (DAO/HIA/NRC) | Updated Information on the Local Group | 19 pages, 1 figure, to be published in the April 2000 issue of PASP | Publ.Astron.Soc.Pac.112:529-536,2000 | 10.1086/316548 | null | astro-ph | null | The present note updates the information published in my recent monograph on
\underline{The Galaxies of the Local Group}. Highlights include (1) the
addition of the newly discovered Cetus dwarf spheroidal as a certain member of
the Local Group, (2) an improved distance for SagDIG, which now places this
object very close to the edge of the Local Group zero-velocity surface, (3)
more information on the evolutionary histories of some individual Local Group
members, and (4) improved distance determinations to, and luminosities for, a
number of Local Group members. These data increase the number of certain (or
probable) Local Group members to 36. The spatial distribution of these galaxies
supports Hubble's claim that the Local Group ``is isolated in the general
field.'' Presently available evidence suggests that star formation continued
much longer in many dwarf spheroidals than it did in the main body of the
Galactic halo. It is suggested that ``young'' globular clusters, such as
Ruprecht 106, might have formed in now defunct dwarf spheroidals. Assuming
SagDIG, which is the most remote Local Group galaxy, to lie on, or just inside,
the zero-velocity surface of the Local Group yields a dynamical age \gtrsim
17.9 \pm 2.7 Gyr.
| [
{
"created": "Tue, 4 Jan 2000 17:51:48 GMT",
"version": "v1"
}
] | 2010-11-09 | [
[
"Bergh",
"Sidney van den",
"",
"DAO/HIA/NRC"
]
] |
astro-ph/0001041 | Roman Juszkiewicz | R. Juszkiewicz, P.G. Ferreira, H.A. Feldman, A.H. Jaffe, M. Davis | Evidence for a low-density Universe from the relative velocities of
galaxies | 12 pages, 2 figures, to appear in the Jan.7 issue of ``Science''; In
the original version, the title appeared twice. This problem has now been
corrected. No other changes were made | Science 287 (2000) 109-112 | 10.1126/science.287.5450.109 | null | astro-ph | null | The motions of galaxies can be used to constrain the cosmological density
parameter Omega and the clustering amplitude of matter on large scales. The
mean relative velocity of galaxy pairs, estimated from the Mark III survey,
indicates that Omega = 0.35 +0.35/-0.25. If the clustering of galaxies is
unbiased on large scales, Omega = 0.35 +/- 0.15, so that an unbiased
Einstein-de Sitter model (Omega = 1) is inconsistent with the data.
| [
{
"created": "Tue, 4 Jan 2000 18:17:05 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Jan 2000 13:59:33 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Juszkiewicz",
"R.",
""
],
[
"Ferreira",
"P. G.",
""
],
[
"Feldman",
"H. A.",
""
],
[
"Jaffe",
"A. H.",
""
],
[
"Davis",
"M.",
""
]
] |
astro-ph/0001042 | Mir Abbas Jalali | M. A. Jalali and A. R. Rafiee | Eccentric Stellar Discs with Strong Density Cusps and Separable
Potentials | 5 pages, submitted to MNRAS | null | null | null | astro-ph | null | We introduce a class of eccentric discs with "strong" density cusps whose
potentials are of St\"ackel form in elliptic coordinates. Our models exhibit
some striking features: sufficiently close to the location of the cusp, the
potential and surface density distribution diverge as $\Phi \propto r^{-1}$ and
$\Sigma \propto r^{-2}$, respectively. As we move outward from the centre, the
model takes a non-axisymmetric, lopsided structure. In the limit, when $r$
tends to infinity, the isocontours of $\Phi$ and $\Sigma$ become spherically
symmetric. It is shown that the configuration space is occupied by three
families of regular orbits: {\it eccentric butterfly}, {\it aligned loop} and
{\it horseshoe} orbits. These orbits are properly aligned with the surface
density distribution and can be used to construct self-consistent equilibrium
states.
| [
{
"created": "Tue, 4 Jan 2000 19:10:34 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Jalali",
"M. A.",
""
],
[
"Rafiee",
"A. R.",
""
]
] |
astro-ph/0001043 | Vera Ellinger Margoniner | V. E. Margoniner & R. R. de Carvalho | Photometric Properties of 47 Clusters of Galaxies: I. The Butcher-Oemler
Effect | 35 pages including 8 figures, submitted to AJ | null | 10.1086/301318 | null | astro-ph | null | We present gri CCD photometry of 44 Abell clusters and 4 cluster candidates.
Twenty one clusters in our sample have spectroscopic redshifts. Fitting a
relation between mean g, r and i magnitudes, and redshift for this subsample,
we have calculated photometric redshifts for the remainder with an estimated
accuracy of 0.03. The resulting redshift range for the sample is 0.03<z<0.38.
Color-magnitude diagrams are presented for the complete sample and used to
study evolution of the galaxy population in the cluster environment. Our
observations show a strong Butcher-Oemler effect (Butcher & Oemler 1978, 1984),
with an increase in the fraction of blue galaxies (f_B) with redshift that
seems more consistent with the steeper relation estimated by Rakos and
Schombert (1995) than with the original one by Butcher & Oemler (1984).
However, in the redshift range between ~ 0.08 and 0.2, where most of our
clusters lie, there is a wide range of f_B values, consistent with no redshift
evolution of the cluster galaxy population. A large range of f_B values is also
seen between ~ 0.2 and 0.3, when Smail at al. (1998) x-ray clusters are added
to our sample. The discrepancies between samples underscore the need for an
unbiased sample to understand how much of the Butcher-Oemler effect is due to
evolution, and how much to selection effects. We also tested the idea proposed
by Garilli et al. (1996) that there is a population of unusually red galaxies
which could be associated either with the field or clusters, but we find that
these objects are all near the limiting magnitude of the images (20.5<r<22) and
have colors that are consistent with those expected for stars or field galaxies
at z ~ 0.7.
| [
{
"created": "Tue, 4 Jan 2000 23:36:38 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Margoniner",
"V. E.",
""
],
[
"de Carvalho",
"R. R.",
""
]
] |
astro-ph/0001044 | Richard J. Rand | Richard J. Rand | Interferometric 12CO Observations of the Central Disk of NGC 4631: An
Energetic Molecular Outflow | Accepted for publication in The Astrophysical Journal. LaTex
manuscript 12 pages, 7 ps files of figures. Also available at
http://www.phys.unm.edu/~rjr/rjrhome.html | null | 10.1086/308869 | null | astro-ph | null | We present interferometric observations of CO J=1-0 emission in the central
regions of the edge-on galaxy NGC 4631, known for its extended gaseous halo and
its tidal interactions. Previous single-dish observations revealed that almost
all of the CO emission arises from a central ring or bar-like structure of
length $\sim$ 4 kpc. We confirm this structure at higher resolution, and find
that it is bent at the center, reflecting the overall bend in this galaxy
apparent from optical images. The kinematic evidence favors a rigidly rotating
ring over a bar. The gaseous halo emission in several tracers is concentrated
above and below this molecular structure. To the north of an emission peak at
the eastern end of the structure is an extraplanar feature showing filamentary
and shell-like properties which we interpret as an energetic molecular outflow.
The energies involved are difficult to estimate, but are probably of order
10$^{54}$ ergs or more. The CO concentration in the disk below this structure
coincides with a bright HII region complex, a peak of radio emission, and the
brightest X-ray feature in the inner disk of the galaxy seen in a ROSAT HRI
map, all suggesting intense star formation. A filament of radio continuum
emission may also have a footprint in this region of the disk. The origin of
the outflow is unclear.
| [
{
"created": "Wed, 5 Jan 2000 00:03:20 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Rand",
"Richard J.",
""
]
] |
astro-ph/0001045 | Marc Kamionkowski | Marc Kamionkowski and Ari Buchalter | The Second Peak: The Dark-Energy Density and the Cosmic Microwave
Background | 4 pages, 3 PostScript figures | null | null | CALT-68-2253 | astro-ph hep-ph | null | Supernova evidence for a negative-pressure dark energy (e.g., cosmological
constant or quintessence) that contributes a fraction $\Omega_\Lambda\simeq0.7$
of closure density has been bolstered by the discrepancy between the total
density, $\Omega_{\rm tot}\simeq1$, suggested by the location of the first peak
in the cosmic microwave background (CMB) power spectrum and the
nonrelativistic-matter density $\Omega_m\simeq0.3$ obtained from dynamical
measurements. Here we show that the impending identification of the location of
the {\it second} peak in the CMB power spectrum will provide an immediate and
independent probe of the dark-energy density. As an aside, we show how the
measured height of the first peak probably already points toward a low matter
density and places upper limits to the reionization optical depth and
gravitational-wave amplitude.
| [
{
"created": "Wed, 5 Jan 2000 00:04:50 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kamionkowski",
"Marc",
""
],
[
"Buchalter",
"Ari",
""
]
] |
astro-ph/0001046 | Motokazu Takizawa | Motokazu Takizawa (Univ. of Tokyo), Tsuguya Naito (Yamanashi Gakuin
Univ.) | Non-Thermal Emission from Relativistic Electrons in Clusters of
Galaxies: A Merger Shock Acceleration Model | 19 pages, 5 figures, accepted for publication in ApJ | null | 10.1086/308894 | Kyoto 99-19 | astro-ph | null | We have investigated evolution of non-thermal emission from relativistic
electrons accelerated at around the shock fronts during merger of clusters of
galaxies. We estimate synchrotron radio emission and inverse Compton scattering
of cosmic microwave background photons from extreme ultraviolet (EUV) to hard
X-ray range. The hard X-ray emission is most luminous in the later stage of
merger. Both hard X-ray and radio emissions are luminous only while signatures
of merging events are clearly seen in thermal intracluster medium (ICM). On the
other hand, EUV radiation is still luminous after the system has relaxed.
Propagation of shock waves and bulk-flow motion of ICM play crucial roles to
extend radio halos. In the contracting phase, radio halos are located at the
hot region of ICM, or between two substructures. In the expanding phase, on the
other hand, radio halos are located between two ICM hot regions and shows
rather diffuse distribution.
| [
{
"created": "Wed, 5 Jan 2000 04:30:31 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Takizawa",
"Motokazu",
"",
"Univ. of Tokyo"
],
[
"Naito",
"Tsuguya",
"",
"Yamanashi Gakuin\n Univ."
]
] |
astro-ph/0001047 | Hiroshi Muraishi | H. Muraishi, T. Tanimori, S. Yanagita, T. Yoshida, M. Moriya, T.
Kifune, S. A. Dazeley, P. G. Edwards, S. Gunji, S. Hara, T. Hara, A. Kawachi,
H. Kubo, Y. Matsubara, Y. Mizumoto, M. Mori, Y. Muraki, T. Naito, K.
Nishijima, J. R. Patterson, G. P. Rowell, T. Sako, K. Sakurazawa, R.
Susukita, T. Tamura, and T. Yoshikoshi | Evidence for TeV gamma-ray emission from the shell type SNR
RXJ1713.7-3946 | Accepted for publication by Astronomy and Astrophysics (5 pages, 2
figures) | null | null | null | astro-ph | null | We report the results of TeV gamma-ray observations of the shell type SNR
RXJ1713.7-3946 (G347.3-0.5). The discovery of strong non-thermal X-ray emission
from the northwest part of the remnant strongly suggests the existence of
electrons with energies up to 100 TeV in the remnant, making the SNR a good
candidate TeV gamma-ray source. We observed RXJ1713.7-3946 from May to August
1998 with the CANGAROO 3.8m atmospheric imaging Cerenkov telescope and obtained
evidence for TeV gamma-ray emission from the NW rim of the remnant with the
significance of 5.6 sigma. The observed TeV gamma-ray flux from the NW rim
region was estimated to be (5.3 +/- 0.9[statistical] +/- 1.6[systematic]) *
10^{-12} photons cm^{-2} s^{-1} at energies >= 1.8 +/- 0.9 TeV. The data
indicate that the emitting region is much broader than the point spread
function of our telescope. The extent of the emission is consistent with that
of hard X-rays observed by ASCA. This TeV gamma-ray emission can be attributed
to the Inverse Compton scattering of the Cosmic Microwave Background Radiation
by shock accelerated ultra-relativistic electrons. Under this assumption, a
rather low magnetic field of 11 micro gauss is deduced for the remnant from our
observation.
| [
{
"created": "Wed, 5 Jan 2000 05:31:25 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Muraishi",
"H.",
""
],
[
"Tanimori",
"T.",
""
],
[
"Yanagita",
"S.",
""
],
[
"Yoshida",
"T.",
""
],
[
"Moriya",
"M.",
""
],
[
"Kifune",
"T.",
""
],
[
"Dazeley",
"S. A.",
""
],
[
"Edwards",
"P. G.",
""
],
[
"Gunji",
"S.",
""
],
[
"Hara",
"S.",
""
],
[
"Hara",
"T.",
""
],
[
"Kawachi",
"A.",
""
],
[
"Kubo",
"H.",
""
],
[
"Matsubara",
"Y.",
""
],
[
"Mizumoto",
"Y.",
""
],
[
"Mori",
"M.",
""
],
[
"Muraki",
"Y.",
""
],
[
"Naito",
"T.",
""
],
[
"Nishijima",
"K.",
""
],
[
"Patterson",
"J. R.",
""
],
[
"Rowell",
"G. P.",
""
],
[
"Sako",
"T.",
""
],
[
"Sakurazawa",
"K.",
""
],
[
"Susukita",
"R.",
""
],
[
"Tamura",
"T.",
""
],
[
"Yoshikoshi",
"T.",
""
]
] |
astro-ph/0001048 | Penny D. Sackett | Penny D. Sackett | The 24-Hour Night Shift: Astronomy from Microlensing Monitoring Networks | Invited Targeted Talk at ``Gravitational Lensing: Recent Progress and
Future Goals,'' 28 July 1999, Boston. To appear in the ASP Conference Series,
eds. T.G. Brainerd and C.S. Kochanek. 8 postscript pages, LaTex requires
paspconf.sty | null | null | null | astro-ph | null | Scores of on-going microlensing events are now announced yearly by the
microlensing discovery teams OGLE, MACHO and EROS. These early warning systems
have allowed other international microlensing networks to focus considerable
resources on intense photometric - and occasionally spectroscopic - monitoring
of microlensing events. Early results include: metallicity measurements of main
sequence Galactic bulge stars; limb darkening determinations for stars in the
Bulge and Small Magellanic Cloud; proper motion measurements that constrain
microlens identity; and constraints on Jovian-mass planets orbiting (presumably
stellar) lenses. These results and auxiliary science such as variable star
studies and optical identification of gamma ray bursts are reviewed.
| [
{
"created": "Wed, 5 Jan 2000 05:42:54 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sackett",
"Penny D.",
""
]
] |
astro-ph/0001049 | Peter Nugent | Greg Aldering, Robert Knop and Peter Nugent | The Rise Times of High and Low Redshift Type Ia Supernovae are
Consistent | 18 pages, 4 figures, Accepted for publication in the Astronomical
Journal. Also available at http://www.lbl.gov/~nugent/papers.html Typos were
corrected and a few sentences were added for improved clarity | null | 10.1086/301344 | LBNL-44232 | astro-ph | null | We present a self-consistent comparison of the rise times for low- and
high-redshift Type Ia supernovae. Following previous studies, the early light
curve is modeled using a t-squared law, which is then mated with a modified
Leibundgut template light curve. The best-fit t-squared law is determined for
ensemble samples of low- and high-redshift supernovae by fitting simultaneously
for all light curve parameters for all supernovae in each sample. Our method
fully accounts for the non-negligible covariance amongst the light curve
fitting parameters, which previous analyses have neglected. Contrary to Riess
et al. (1999), we find fair to good agreement between the rise times of the
low- and high-redshift Type Ia supernovae. The uncertainty in the rise time of
the high-redshift Type Ia supernovae is presently quite large (roughly +/- 1.2
days statistical), making any search for evidence of evolution based on a
comparison of rise times premature. Furthermore, systematic effects on rise
time determinations from the high-redshift observations, due to the form of the
late-time light curve and the manner in which the light curves of these
supernovae were sampled, can bias the high-redshift rise time determinations by
up to +3.6/-1.9 days under extreme situations. The peak brightnesses - used for
cosmology - do not suffer any significant bias, nor any significant increase in
uncertainty.
| [
{
"created": "Wed, 5 Jan 2000 07:29:54 GMT",
"version": "v1"
},
{
"created": "Sat, 29 Jan 2000 16:25:09 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Aldering",
"Greg",
""
],
[
"Knop",
"Robert",
""
],
[
"Nugent",
"Peter",
""
]
] |
astro-ph/0001050 | Fumihide Iwamuro | F. Iwamuro, K. Motohara, T. Maihara, J. Iwai, H. Tanabe, T. Taguchi,
R. Hata, H. Terada, M. Goto, S. Oya, M. Iye, M. Yoshida, H. Karoji, R.
Ogasawara, K. Sekiguchi | Near-infrared emission-line galaxies in the Hubble Deep Field North | 12 pages, 7 figures. Accepted for publication in PASJ(2000) | null | 10.1093/pasj/52.1.73 | null | astro-ph | null | We present the 2.12~$\mu$m narrow-band image of the Hubble Deep Field North
taken with the near-infrared camera (CISCO) on the Subaru telescope. Among five
targets whose H$\alpha$ or [O~{\sc iii}] emission lines are redshifted into our
narrow-band range expected from their spectroscopic redshift, four of them have
strong emission lines, especially for the two [O~{\sc iii}] emission-line
objects. The remaining one target shows no H$\alpha$ emission in spite of its
bright rest-UV luminosity, indicating that this object is already under the
post-starburst phase. The volume-averaged $SFR$ derived from the detected two
H$\alpha$ emission is roughly consistent with that evaluated from the rest-UV
continuum.
| [
{
"created": "Wed, 5 Jan 2000 08:10:20 GMT",
"version": "v1"
},
{
"created": "Fri, 7 Jan 2000 06:19:49 GMT",
"version": "v2"
},
{
"created": "Mon, 24 Jan 2000 03:58:16 GMT",
"version": "v3"
}
] | 2015-06-24 | [
[
"Iwamuro",
"F.",
""
],
[
"Motohara",
"K.",
""
],
[
"Maihara",
"T.",
""
],
[
"Iwai",
"J.",
""
],
[
"Tanabe",
"H.",
""
],
[
"Taguchi",
"T.",
""
],
[
"Hata",
"R.",
""
],
[
"Terada",
"H.",
""
],
[
"Goto",
"M.",
""
],
[
"Oya",
"S.",
""
],
[
"Iye",
"M.",
""
],
[
"Yoshida",
"M.",
""
],
[
"Karoji",
"H.",
""
],
[
"Ogasawara",
"R.",
""
],
[
"Sekiguchi",
"K.",
""
]
] |
astro-ph/0001051 | Fumihide Iwamuro | F. Iwamuro, K. Motohara, T. Maihara, J. Iwai, H. Tanabe, T. Taguchi,
R. Hata, T. Terada, M. Goto, S. Oya, Subaru project team | Infrared Imaging of the Gravitational Lens PG 1115+080 with the Subaru
Telescope | 11 pages, 6 figures. Accepted for publication in PASJ(2000) | null | 10.1093/pasj/52.1.25 | null | astro-ph | null | We present high spatial resolution images of the gravitational-lens system PG
1115+080 taken with the near-infrared camera (CISCO) on the Subaru telescope.
The FWHM of the combined image is $0.''32$ in the $K'$-band, yielding spatial
resolution of $0.''14$ after a deconvolution procedure. This is a first
detection of an extended emission adjacent to the A1/A2 components, indicating
the presence of a fairly bright emission region with a characteristic angular
radius of $\sim$ 5 mas (40 pc). The near-infrared image of the Einstein ring
was extracted in both the $J$ and $K'$ bands. The $J-K'$ color is found to be
significantly redder than that of a synthetic model galaxy with an age of 3
Gyr, the age of the universe at the quasar redshift.
| [
{
"created": "Wed, 5 Jan 2000 08:40:24 GMT",
"version": "v1"
}
] | 2015-06-24 | [
[
"Iwamuro",
"F.",
""
],
[
"Motohara",
"K.",
""
],
[
"Maihara",
"T.",
""
],
[
"Iwai",
"J.",
""
],
[
"Tanabe",
"H.",
""
],
[
"Taguchi",
"T.",
""
],
[
"Hata",
"R.",
""
],
[
"Terada",
"T.",
""
],
[
"Goto",
"M.",
""
],
[
"Oya",
"S.",
""
],
[
"team",
"Subaru project",
""
]
] |
astro-ph/0001052 | Eleonore Paul | Alfred Krabbe, Bruce J. Sams III, Reinhard Genzel, Niranjan Thatte,
Francisco Prada | Near infrared imaging spectroscopy of NGC1275 | 16 pages, LaTex, 15 gif figures, aa.cls required, accepted for A&A,
high resolution images at http://astro1.ws.ba.dlr.de | null | null | null | astro-ph | null | We present H and K band imaging spectroscopy of the core regions of the
cD/AGN galaxy NGC1275. The spectra, including lines from H2, H, 12CO bandheads,
[FeII], and [FeIII], are exploited to constrain the star formation and
excitation mechanisms in the galaxy's nucleus. The near-infrared properties can
largely be accounted for by ionized gas in the NLR, dense molecular gas, and
hot dust concentrated near the active nucleus of NGC1275. The strong and
compact H2 emission is mostly from circumnuclear gas excited by the AGN and not
from the cooling flow. The extended emission of latetype stars is diluted in
the center by the thermal emission of hot dust.
| [
{
"created": "Wed, 5 Jan 2000 08:42:54 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Krabbe",
"Alfred",
""
],
[
"Sams",
"Bruce J.",
"III"
],
[
"Genzel",
"Reinhard",
""
],
[
"Thatte",
"Niranjan",
""
],
[
"Prada",
"Francisco",
""
]
] |
astro-ph/0001053 | C. C. Popescu | Cristina C. Popescu, Richard J. Tuffs, Joerg Fischera, Heinrich Voelk
(MPIK Heidelberg) | On the FIR emission from intracluster dust | 19 pages, accepted for publication in Astronomy and Astrophysics | null | null | null | astro-ph | null | We make predictions for the diffuse far-infrared (FIR) emission from dust in
the intracluster medium (ICM) of the Virgo cluster using detailed information
on potential dust sources, grain heating and sputtering rates available for
this cluster from recent optical and X-ray studies. We show that the infrared
emission from dust injected by sources inside the core region of the Virgo
cluster is a factor of 10 below the detection limit of currently available
telescopes. The outer regions of dynamically young clusters like the Virgo
cluster have a further potential source of intracluster grains since they are
still accreting freshly infalling spiral galaxies which are presumably
contained in an accreting intergalactic medium (IGM). We show that cosmic ray
driven winds from the infalling spirals can inject grains into a subvirial IGM
that is external to the observed X-ray-emitting ICM. Sputtering during the
injection process and in the IGM is weak, so that the injected grains should
accumulate in the IGM until the infall brings them into contact with the hot
ICM. This effect dominates the dust injection rate from known sources embedded
in the hot Virgo ICM. Thus, any detection of diffuse IR emission would probe
the current dust accretion rate for the cluster, acting as an indicator of the
youth and the dynamical state of the cluster. The predictions for the Virgo
cluster are generalised to other clusters and the possibility of detection of
dynamically young clusters at cosmological distances is discussed.
| [
{
"created": "Wed, 5 Jan 2000 09:36:37 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Popescu",
"Cristina C.",
"",
"MPIK Heidelberg"
],
[
"Tuffs",
"Richard J.",
"",
"MPIK Heidelberg"
],
[
"Fischera",
"Joerg",
"",
"MPIK Heidelberg"
],
[
"Voelk",
"Heinrich",
"",
"MPIK Heidelberg"
]
] |
astro-ph/0001054 | Ulrich Hopp | U. Hopp, D. Engels, R.F. Green, A.V. Ugryumov, Y.I. Izotov, H.-J.
Hagen, A.Y. Kniazev, V.A. Lipovetsky, S.A. Pustilnik, N. Brosch, J. Masegosa,
J.-M. M artin, I. M'arquez | The Hamburg/SAO Survey for Emission-Line Galaxies. III. The Third List
of 81 Galaxies | A&A latex file with 8 tables and one figure. Astron. Astrophys.
Suppl. accepted 2000 | null | 10.1051/aas:2000162 | null | astro-ph | null | We present the third list with results {Tables 2 to 6 are available only in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html. Figures A1 to
A9 will be made available only in the electronic version of the journal.} of
the Hamburg/SAO Survey for Emission-Line Galaxies (HSS therein, SAO - Special
Astrophysical Observatory, Russia). This survey is based on the digitized
objective-prism photoplate database of the Hamburg Quasar Survey (HQS).
Here, we present new spectroscopic results of candidates which were obtained
in 1998 with the 2.1 m KPNO and the 2.2 m Calar Alto telescopes. All candidates
are selected in the declination band +35$^{\circ}$ to +40$^{\circ}$.
The follow-up spectroscopy with the 2 m class telescopes confirmed 85
emission-line objects out of 113 observed candidates and allowed their
quantitative spectral classification. For 80 of them, the redshifts are
determined for the first time. For 5 previously known ELGs, line ratios are
presented for the first time. We could classify 55 out of the 85 emission-line
objects as BCG/H{\sc ii} galaxies or probable BCGs, 4 - as QSOs, 6 - as Seyfert
galaxies, 1 - as super-association in a subluminous spiral galaxy, and 11 are
low-excitation objects - either starburst nuclear (SBN), or dwarf amorphous
nuclear starburst galaxies (DANS). We could not classify 8 ELGs. Further, for 8
more galaxies we did not detect any significant emission lines.
| [
{
"created": "Wed, 5 Jan 2000 11:37:56 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Hopp",
"U.",
""
],
[
"Engels",
"D.",
""
],
[
"Green",
"R. F.",
""
],
[
"Ugryumov",
"A. V.",
""
],
[
"Izotov",
"Y. I.",
""
],
[
"Hagen",
"H. -J.",
""
],
[
"Kniazev",
"A. Y.",
""
],
[
"Lipovetsky",
"V. A.",
""
],
[
"Pustilnik",
"S. A.",
""
],
[
"Brosch",
"N.",
""
],
[
"Masegosa",
"J.",
""
],
[
"artin",
"J. -M. M",
""
],
[
"M'arquez",
"I.",
""
]
] |
astro-ph/0001055 | Leonid Piyugin | L.S. Pilyugin (Main Astron. Obs. of Nat. Academy of Sc. of Ukraine),
F.Ferrini (University of Pisa, Italy) | The oxygen abundance deficiency in irregular galaxies | 8 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics | New Astron.Rev. 44 (2000) 335-339 | 10.1016/S1387-6473(00)00057-9 | null | astro-ph | null | The observed oxygen abundances in a number of irregular galaxies have been
compared with predictions of the closed-box model of chemical and photometric
evolution of galaxies. Oxygen is found to be deficient with respect to the
predicted abundances. This is an indicator in favor of loss of heavy elements
via galactic winds or/and of infall of low--abundance gas onto the galaxy.
The oxygen abundance deficiency observed within the optical edge of a galaxy
cannot be explained by mixing with the gas envelope observed outside the
optical limit. We confirm the widespread idea that a significant part of the
heavy elements is ejected by irregular galaxies in the intergalactic medium.
| [
{
"created": "Wed, 5 Jan 2000 12:04:57 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Pilyugin",
"L. S.",
"",
"Main Astron. Obs. of Nat. Academy of Sc. of Ukraine"
],
[
"Ferrini",
"F.",
"",
"University of Pisa, Italy"
]
] |
astro-ph/0001056 | Annalisa Celotti | Annalisa Celotti (1) and Roger D. Blandford (2) ((1) SISSA, Trieste,
Italy, (2) Caltech, Pasadena, USA) | On the Formation of Jets | 10 pages, Springer-Verlag LaTex style. To appear in Proc. ESO
Workshop on "Black Holes in Binaries and Galactic Nuclei", Garching (Sept.
1999), L. Kaper, E.P.J. van den Heuvel, P.A. Woudt eds., Springer-Verlag | null | 10.1007/10720995_43 | null | astro-ph | null | The phenomenology of jets associated with a variety of black hole systems is
summarized, emphasizing the constraints imposed on their origin. Models of jet
formation are reviewed, focusing in particular on recent ideas concerning MHD
models. Finally, the potential for advancing our understanding of jets both
through future observations - especially forthcoming X-ray missions - and for
elucidating some crucial theoretical questions is highlighted.
| [
{
"created": "Wed, 5 Jan 2000 12:30:38 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Celotti",
"Annalisa",
""
],
[
"Blandford",
"Roger D.",
""
]
] |
astro-ph/0001057 | Leonid Piyugin | L.S. Pilyugin (Main Astron. Obs. of Nat. Academy of Sc. of Ukraine),
F.Ferrini (University of Pisa, Italy) | On the origin of the luminosity - metallicity relation for late-type
galaxies: Spirals to irregulars transition | 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics | Astrophys.Space Sci. 277 (2001) 441-444 | null | null | astro-ph | null | We consider the roles of two widely invoked mechanisms for the
metallicity-luminosity correlation among late-type galaxies: higher astration
level and decreasing efficiency of heavy-element loss with increasing
luminosity. We find that both mechanisms contribute about equally to the range
in oxygen abundance between low (logL_B = 8) and high (logL_B = 10.5)
luminosity galaxies.
We also consider the transition from spirals to irregulars, finding that both
the oxygen abundance deficiency (indicating the degree of mass exchange between
a galaxy and its environment) and the gas fraction vary smoothly along the
sequence. Thus we find no "irregular versus spiral dichotomy".
| [
{
"created": "Wed, 5 Jan 2000 12:32:39 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Pilyugin",
"L. S.",
"",
"Main Astron. Obs. of Nat. Academy of Sc. of Ukraine"
],
[
"Ferrini",
"F.",
"",
"University of Pisa, Italy"
]
] |
astro-ph/0001058 | Cecile Gry | Edward B. Jenkins, Cecile Gry, Olivier Dupin | Electron densities, temperatures and ionization rates in two
interstellar clouds in front of beta Canis Majoris, as revealed by UV
absorption lines observed with IMAPS | 17 pages, 2 figures, to be published in Astronomy & Astrophysics | Astron. Astrophys. 354,253 (2000) | null | null | astro-ph | null | The spectrum of beta CMa (Mirzam) between 1000 and 1200 A was recorded at a
wavelength resolving power ~ 60 000 by the Interstellar Medium Absorption
Profile Spectrograph (IMAPS) during its orbital flight on the ORFEUS-SPAS II
mission in 1996. New information about interstellar absorption lines of CII,
CII*, NI and OI from this spectrum are combined with the HST results reported
by Dupin & Gry (1998) to arrive at new conclusions about the physical
properties of the absorbing gas in front of beta CMa. For two prominent
velocity components centered at heliocentric velocities of +20.0 and +30.5
km/s, designated by Dupin & Gry as Components C and D respectively, we use
determinations of N(CII*)/N(CII) and N(MgI)/N(MgII) to solve for temperatures
and electron densities. From our knowledge that oxygen and nitrogen have their
ionizations coupled to that of hydrogen through charge exchange reactions, we
can derive the hydrogen ionizations by comparing these elements to sulfur,
which is likely not to be depleted onto dust grains. For Component C with an
approximate column density of neutral and ionized hydrogen N(Htotal)=6 10^{18}
cm^-2, we find that the neutral fraction n(HI)/n(Htotal)=0.25, 400<T<6500 K,
and 0.08<n(e)<0.6 cm^-3, while for Component D with N(Htotal)=1.2 10^{19}cm^-2,
we arrive at n(HI)/n(Htotal)=0.035, 8000<T<14000 K, and 0.09<n(e)<0.2cm^-3. The
relatively large ionization fractions of H can arise if the clouds are about
130 pc away from us, so that they are exposed to the strong, ionizing radiation
fields from epsilon and beta CMa. The presence of SiIII indicates the existence
of additional gas with even higher levels of ionization.
| [
{
"created": "Wed, 5 Jan 2000 12:43:37 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Jenkins",
"Edward B.",
""
],
[
"Gry",
"Cecile",
""
],
[
"Dupin",
"Olivier",
""
]
] |
astro-ph/0001059 | Gurin | Alexander M. Ilyanok | Quantum Astronomy. Part II | in Russian, 29 pages | Vesti of the Institute of Modern Knowledge, 1999, vol. 2-3,
p.71-102 | null | null | astro-ph | null | A new method of fundamental quantum data sampling on basis of an optimum
measuring scale has been designed. The method was applied for minimization of
redundant experimental data in different fields of physics. Basing of this
method there has been found the laws of binding electromagnetic, strong and
gravitational interaction. It is shown that the laws of quantizing of physical
quantities are the effect of space fibering. Moreover the said laws have a
general electromagnetic nature as well. They are related to dimensionless
electromagnetic constants - Na =861 and a-1=137,0360547255. These constants
cover both the atomic and the space scales.
| [
{
"created": "Wed, 5 Jan 2000 13:48:39 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Ilyanok",
"Alexander M.",
""
]
] |
astro-ph/0001060 | Maria Rosa Zapatero Osorio | Ya. Pavlenko (MAO, Ukraine), M. R. Zapatero Osorio, R. Rebolo (IAC,
Spain) | On the Interpretation of the Optical Spectra of L-type Dwarfs | Accepted for publication in A&A. 12 pages (figures included) | null | null | null | astro-ph | null | We present synthetic optical spectra in the range 640-930 nm of a sample of
field L dwarfs and the brown dwarf GL229B. Our computations show that Li, Na,
K, Rb, and Cs govern the spectra of these objects, with Na and K contributing
significantly to block the optical emergent radiation. Molecular absorptions of
TiO, VO, CrH, FeH and CaH also dominate in the early L-types showing a strength
that progressively decreases for later types. We find that the densities of
these molecules in the atmospheres are considerably smaller by larger factors
than those predicted by the chemical equilibrium. In order to reproduce the
overall shape of the optical spectra an additional opacity (AdO) is required to
be implemented in the computations. We have modelled it with a simple law [a0
(nu / nu0)^N, N=4], and found that this provides a good fit to the data. This
AdO could be due to molecular/dust absorption or to dust scattering. The EWs
and intensities of the alkali lines are highly affected by this opacity. The Li
line at 670.8 nm, widely used as a substellarity discriminator, is more
affected by the AdO than by the natural depletion of neutral Li. Our
computations display a rather strong feature even at Teffs around 1000 K;
depending on the Teff and on the amount of dust in the atmospheres of very cool
dwarfs, it might be possible to detect Li even at temperatures this cool.
Changes in the physical conditions of dust formation in L-type dwarfs will
cause variability of the alkali lines.
| [
{
"created": "Wed, 5 Jan 2000 14:42:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Pavlenko",
"Ya.",
"",
"MAO, Ukraine"
],
[
"Osorio",
"M. R. Zapatero",
"",
"IAC,\n Spain"
],
[
"Rebolo",
"R.",
"",
"IAC,\n Spain"
]
] |
astro-ph/0001061 | Ofer Lahav | Ofer Lahav (Institute of Astronomy, Cambridge, UK) | Observational Tests for the Cosmological Principle and World Models | Review talk, to appear in the proceedings of the NATO ASI `Structure
Formation in the Universe', Isaac Newton Institute, Cambridge, July 1999, ed.
R. Crritenden & N, Turok. Kluwer; 12 pages Latex, with 3 embedded figures.
Uses crckapb.sty | null | null | null | astro-ph | null | We review observational tests for the homogeneity of the Universe on large
scales. Redshift and peculiar velocity surveys, radio sources, the X-Ray
Background, the Lyman-$\alpha$ forest and the Cosmic Microwave Background are
used to set constraints on inhomogeneous models and in particular on
fractal-like models.
Assuming the Cosmological Principle and the FRW metric, we estimate
cosmological parameters by joint analysis of peculiar velocities, the CMB,
cluster abundance, IRAS and Supernovae.
Under certain assumptions the best fit density parameter is Omega_m = 1 -
lambda \approx 0.4 .
We present a new method for joint estimation by combining different data sets
in a Bayesian way, and utilising `Hyper-Parameters'.
| [
{
"created": "Wed, 5 Jan 2000 14:44:20 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Lahav",
"Ofer",
"",
"Institute of Astronomy, Cambridge, UK"
]
] |
astro-ph/0001062 | Zlatan Tsvetanov | SDSS Collaboration, Zlatan I. Tsvetanov, et al | The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital
Sky Survey Commissioning Data | 9 pages, 3 figures, AASTeX, to appear in ApJ Letters, authors list
updated | Astrophys.J.531:L61-L65,2000 | 10.1086/312515 | null | astro-ph | null | We report the discovery of a second field methane brown dwarf from the
commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS
J134646.45-003150.4 (SDSS 1346-00), was selected because of its very red color
and stellar appearance. Its spectrum between 0.8-2.5 mic is dominated by strong
absorption bands of H_2O and CH_4 and closely mimics those of Gliese 229B and
SDSS 162414.37+002915.6 (SDSS 1624+00), two other known methane brown dwarfs.
SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that
it lies about 11 pc from the sun. The ratio of flux at 2.1 mic to that at 1.27
mic is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which
suggests that SDSS 1346-00 has a slightly higher effective temperature than the
others. Based on a search area of 130 sq. deg. and a detection limit of z* =
19.8, we estimate a space density of 0.05 pc^-3 for methane brown dwarfs with
T_eff ~ 1000 K in the 40 pc^3 volume of our search. This estimate is based on
small-sample statistics and should be treated with appropriate caution.
| [
{
"created": "Wed, 5 Jan 2000 15:25:32 GMT",
"version": "v1"
},
{
"created": "Sun, 9 Jan 2000 19:57:41 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"SDSS Collaboration",
"",
""
],
[
"Tsvetanov",
"Zlatan I.",
""
]
] |
astro-ph/0001063 | Peter Kahabka | P. Kahabka (University of Bonn) | The nature of RXJ0052.1-7319 | 5 pages, accepted by A&A December 30th 1999 | null | null | null | astro-ph | null | The nature of the X-ray source RXJ0052.1-7319 is discussed from observational
data obtained from ROSAT observations performed in 1995 and 1996. An accurate
position is derived from ROSAT HRI observations performed in 1995. The 6" error
circle contains two OGLE microlensing optical variables of which one has
previously been identified with a 14.5 mag Be-type star in the Small Magellanic
Cloud. During the October 1996 observation RXJ0052.1-7319 was found to be
extremely bright (with a count rate of ~1.1+/-0.1 s^-1) and 15.3 second X-ray
pulsations have been discovered during this observation. This indicates for a
high-mass X-ray binary nature of the source. During the 1995 observation the
X-ray source detected at the position of RXJ0052.1-7319 was a factor 200
fainter. The corresponding luminosity has changed from 5.2x10^37 erg s^-1 to
2.6x10^35 erg s^-1 assuming SMC membership of the source. It is unclear whether
the so-far unidentified second optical variable contributes to the X-ray flux
of the source.
| [
{
"created": "Wed, 5 Jan 2000 15:40:17 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kahabka",
"P.",
"",
"University of Bonn"
]
] |
astro-ph/0001064 | Rafael Garrido | Rafael Garrido (Instituto de Astrofisica de Andalucia, CSIC, Granada,
Spain) | Photometric modal discrimination in Delta Scuti and Gamma Doradus stars | 6th Vienna Workshop in Astrophysics on Delta Scuti and Related stars.
ASP Conference Series. M. Breger & M. Montgomery eds. 32 pages, 23 figures,
newpasp style | null | null | null | astro-ph | null | The potential of photometric methods for the identification of l, the degree
of spherical surface harmonic of a pulsating star, is investigated with special
emphasis on Stromgren photometry applied to delta Scuti and gamma Dor
variables. Limitations of actual model atmospheres when fine precision is
required for the calculations of partial derivatives and integrals, which
depend on limb darkening coefficients, are discussed. Two methods are discussed
to calculate the phase lags, the angle between maximum temperature and minimum
radius, and R, a parameter which describes departure from adiabaticity of the
atmospheres of these pulsating stars. These quantities appear to be very
dependent on the convection as parametrized by the mixing length theory. When
one of the methods is applied to the gamma Dor stars gives phase lags close to
0 degrees, which are 90-180 degrees out of phase from typical delta Scuti
stars. Examples are given for some High Amplitude Delta Scuti Stars (HADS)
where the method can be easily applied and gives results consistent to
interpret them as radial (l=0) pulsating stars. Other low amplitude delta Scuti
stars could be oscillating in a non-radial (l=1, 2) mode. Multi-band photometry
is concluded to be a very powerful tool for mode identification of delta Scuti
and gamma Dor stars, specially with the more accurate photometry that will be
achieved in the near future with the asteroseismological space missions now in
progress.
| [
{
"created": "Wed, 5 Jan 2000 17:52:31 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Garrido",
"Rafael",
"",
"Instituto de Astrofisica de Andalucia, CSIC, Granada,\n Spain"
]
] |
astro-ph/0001065 | Alison Sills | Alison Sills, M. H. Pinsonneault, D. M. Terndrup (OSU) | The Angular Momentum Evolution of Very Low Mass Stars | To appear in the May 10, 2000 ApJ | Astrophys.J.534:335-347,2000 | 10.1086/308739 | null | astro-ph | null | We present theoretical models of the angular momentum evolution of very low
mass stars (0.1 - 0.5 M_sun) and solar analogues (0.6 - 1.1 M_sun). We
investigate the effect of rotation on the effective temperature and luminosity
of these stars. We find that the decrease in T_eff and L can be significant at
the higher end of our mass range, but becomes negligible below 0.4 M_sun.
Formulae for relating T_eff to mass and v_rot are presented.
We compare our models to rotational data from young open clusters of
different ages to infer the rotational history of low mass stars, and the
dependence of initial conditions and rotational evolution on mass. We find that
the qualitative conclusions for stars below 0.6 M_sun do not depend on the
assumptions about internal angular momentum transport, which makes these low
mass stars ideal candidates for the study of the angular momentum loss law and
distribution of initial conditions. We find that neither models with solid body
nor differential rotation can simultaneously reproduce the observed stellar
spin down in the 0.6 to 1.1 M_sun mass range and for stars between 0.1 and 0.6
M_sun. The most likely explanation is that the saturation threshold drops more
steeply at low masses than would be predicted with a simple Rossby scaling. In
young clusters there is a systematic increase in the mean rotation rate with
decreased temperature below 3500 K (0.4 M_sun). This suggests either
inefficient angular momentum loss or mass-dependent initial conditions for
stars near the fully convective boundary. (abridged)
| [
{
"created": "Wed, 5 Jan 2000 18:21:49 GMT",
"version": "v1"
}
] | 2009-07-28 | [
[
"Sills",
"Alison",
"",
"OSU"
],
[
"Pinsonneault",
"M. H.",
"",
"OSU"
],
[
"Terndrup",
"D. M.",
"",
"OSU"
]
] |
astro-ph/0001066 | Nick Gnedin | Nickolay Y. Gnedin, Andrea Ferrara, and Ellen G. Zweibel | Generation of the Primordial Magnetic Fields during Cosmological
Reionization | accepted for publication in ApJ. MPEG movies and color versions of
figures are available at
http://casa.colorado.edu/~gnedin/GALLERY/magfi_p.html | Astrophys.J. 539 (2000) 505-516 | 10.1086/309272 | null | astro-ph | null | We investigate the generation of magnetic field by the Biermann battery in
cosmological ionization fronts, using new simulations of the reionization of
the universe by stars in protogalaxies. Two mechanisms are primarily
responsible for magnetogenesis: i) the breakout of I-fronts from protogalaxies,
and ii) the propagation of I-fronts through the high density neutral filaments
which are part of the cosmic web. The first mechanism is dominant prior to
overlapping of ionized regions (z ~ 7), whereas the second continues to operate
even after that epoch. However, after overlap the field strength increase is
largely due to the gas compression occurring as cosmic structures form. As a
consequence, the magnetic field at z ~ 5 closely traces the gas density, and it
is highly ordered on megaparsec scales. The mean mass-weighted field strength
is B_0 ~ 10^{-19} G in the simulation box. There is a relatively well-defined,
nearly linear correlation between B_0 and the baryonic mass of virialized
objects, with B_0 ~ 10^{-18} G in the most massive objects (M ~ 10^9 M_sun) in
our simulations. This is a lower limit, as lack of numerical resolution
prevents us from following small scale dynamical processes which could amplify
the field in protogalaxies. Although the field strengths we compute are
probably adequate as seed fields for a galactic dynamo, the field is too small
to have had significant effects on galaxy formation, on thermal conduction, or
on cosmic ray transport in the intergalactic medium. It could, however, be
observed in the intergalactic medium through innovative methods based on
analysis of gamma-ray burst photon arrival times.
| [
{
"created": "Wed, 5 Jan 2000 19:26:13 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Mar 2000 17:12:14 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Gnedin",
"Nickolay Y.",
""
],
[
"Ferrara",
"Andrea",
""
],
[
"Zweibel",
"Ellen G.",
""
]
] |
astro-ph/0001067 | Tigran G. Arshakian | T. G. Arshakian (1 and 2) and M. S. Longair (1) ((1) Cavendish
Laboratory, (2) Byurakan Observatory) | An asymmetric relativistic model for classical double radio sources | 16 pages LaTeX, including 10 figures. Accepted for publication in
MNRAS | null | 10.1046/j.1365-8711.2000.03098.x | null | astro-ph | null | There is substantial observational evidence against the symmetric
relativistic model of FRII radio sources. An asymmetric relativistic model is
proposed which takes account of both relativistic effects and
intrinsic/environmental asymmetries to explain the structural asymmetries of
their radio lobes. A key parameter of the model is the jet-side of the double
sources, which is estimated for 80% of the FRII sources in the 3CRR complete
sample. Statistical analyses of the properties of these sources show that the
asymmetric model is in agreement with a wide range of observational data, and
that the relativistic and intrinsic asymmetry effects are of comparable
importance. Intrinsic/environmental asymmetry effects are more important at
high radio luminosities and small physical scales. The mean translational speed
of the lobes is found to be 0.11c, consistent with the speeds found from
spectral ageing arguments. According to a Gaussian model, the standard
deviation of lobe speeds is 0.04c. The results are in agreement with an
orientation-based unification scheme in which the critical angle separating the
radio galaxies from quasars is about 45 degrees.
| [
{
"created": "Wed, 5 Jan 2000 19:35:21 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Arshakian",
"T. G.",
"",
"1 and 2"
],
[
"Longair",
"M. S.",
""
]
] |
astro-ph/0001068 | Leo Alberto Girardi | L. Girardi, J.-C. Mermilliod, G. Carraro | On the peculiar red clump morphology in the open clusters NGC 752 and
NGC 7789 | 10 pages, 7 figures, accepted by Astronomy & Astrophysics | A&A 354, 892 | null | null | astro-ph | null | The red clump stars in the open cluster NGC 752 present a peculiar
distribution in the colour-magnitude diagran (CMD): the clump is observed to
present a faint extension, slightly to the blue of the main concentration of
clump stars. We point out that a similar structure is present in the CMD of NGC
7789, and discuss their possible origins. This feature may be understood as the
result of having, at the same time, stars of low-mass which undergo the
helium-flash, and those just massive enough for avoiding it. The ages of both
clusters are compatible with this interpretation. Similar features can be
produced in theoretical models which assume a non-negligible mass spread for
clump stars, of about 0.2 Mo. However, one can probably exclude that the
observed effect is due to the natural mass range of core helium burning stars
found in single isochrones, although present models do not present the level of
detail necessary to completely explore this possibility. Also the possibility
of a large age spread among cluster stars can be refuted on observational
grounds. We then suggest a few alternatives. This spread may be resulting
either from star-to-star variations in the mass-loss rates during the RGB
phase. Alternatively, effects sush as stellar rotation or convective core
overshooting, could be causing a significant spread in the core mass at
He-ignition for star of similar mass. Finally, we point out that similar
effects could also help to understand the distribution of clump stars in the
CMDs of the clusters NGC 2660 and NGC 2204.
| [
{
"created": "Wed, 5 Jan 2000 22:22:27 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Girardi",
"L.",
""
],
[
"Mermilliod",
"J. -C.",
""
],
[
"Carraro",
"G.",
""
]
] |
astro-ph/0001069 | Kate Y. L. Su | K. Y. L. Su, K. Volk and S. Kwok (University of Calgary) | 2-D Radiation Transfer Model of Non-Spherically Symmetric Dust Shell in
P roto-Planetary Nebulae | To appear in ``Asymmetrical Planetary Nebulae II: from Origins to
Microstructures,'' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N.
Soker, & S.A. Rappaport, eds | null | null | null | astro-ph | null | We have fitted the HST images and the spectral energy distributions (SEDs) of
three proto-planetary nebulae (PPN) with a 2-D radiation transfer model. The
geometric and mass loss properties of these PPN are also derived.
| [
{
"created": "Wed, 5 Jan 2000 21:02:15 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Su",
"K. Y. L.",
"",
"University of Calgary"
],
[
"Volk",
"K.",
"",
"University of Calgary"
],
[
"Kwok",
"S.",
"",
"University of Calgary"
]
] |
astro-ph/0001070 | F. H. Briggs | F.H. Briggs | Cold gas, the HI 21cm line and evolving galactic potentials | 8 pages, 2 figures. Invited review to appear in Proceedings of the
XIXth Recontres de Moriond, on "Building the Galaxies: from the Primordial
Universe to the Present," Editors F. Hammer, T.X. Thuan, V. Cayatte, B.
Guiderdoni and J. Tran Thanh Van, Editions Frontieres | null | null | null | astro-ph | null | Neutral hydrogen traces gravitational potentials. In the nearby universe,
21cm emission-line surveys show that the bulk of the HI resides in well-formed,
optically-luminous galaxies. At high redshift, 21cm line absorption against
background radio quasars occurs in gas-rich systems identified with the highest
HI column densities -- the ``damped Lyman alpha'' quasar absorption-line
systems. High spatial-resolution observations of the redshifted 21cm line
absorbers measure sizes and kinematics of the neutral absorbers.
| [
{
"created": "Wed, 5 Jan 2000 21:59:42 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Briggs",
"F. H.",
""
]
] |
astro-ph/0001071 | Takashi Murayama | Takashi Murayama, Shingo Nishiura, Tohru Nagao, Yasunori Sato,
Yoshiaki Taniguchi, D. B. Sanders | Discovery of a Low Surface Brightness Object near Seyfert's Sextet | 4 pages, 3 figures, to appear in the April 2000 issue of The
Astronomical Journal | Astron.J. 119 (2000) 1691-1694 | 10.1086/301320 | null | astro-ph | null | We report the discovery of a low surface brightness (LSB) object
serendipitously found during deep CCD imaging of a compact group of galaxies,
Seyfert's Sextet, in VR and I bands. The LSB object is located 2.3 arcmin
southwest from the group center. Its surface brightness within the angular
effective radii of r_e(VR)=4.8 arcsec and r_e(I)=4.8 arcsec is very low ---
mu_e(VR)=25.28 mag arcsec-2 and mu_e(I)=24.47 mag arcsec-2, respectively. The
apparent magnitudes are m_AB(VR)=19.87 mag and m(I)=19.06 mag. The object is
most likely a LSB dwarf galaxy, but other possibilities are also discussed.
| [
{
"created": "Wed, 5 Jan 2000 22:57:25 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Murayama",
"Takashi",
""
],
[
"Nishiura",
"Shingo",
""
],
[
"Nagao",
"Tohru",
""
],
[
"Sato",
"Yasunori",
""
],
[
"Taniguchi",
"Yoshiaki",
""
],
[
"Sanders",
"D. B.",
""
]
] |
astro-ph/0001072 | Scott C. Trager | S. C. Trager (1), S. M. Faber (2), Guy Worthey (3), J. Jesus Gonzalez
(4) ((1) OCIW, (2) UCO/Lick Observatory, (3) St. Ambrose, (4) IA-UNAM) | The Stellar Population Histories of Local Early-Type Galaxies. I.
Population Parameters | Accepted to the Astronomical Journal, April 2000. 35 pages, 15
figures. Uses emulateapj.sty | Astron.J.119:1645-1676,2000 | 10.1086/301299 | null | astro-ph | null | We present single stellar population (SSP) equivalent ages, metallicities,
and abundance ratios for local elliptical galaxies derived from Hbeta, Mgb, and
<Fe> absorption line strengths. We use an extension of the Worthey (1994)
stellar population models that incorporates non-solar line-strength "response
functions" by Tripicco & Bell (1995), allowing us to correct the models for the
enhancements of Mg and other alpha-like elements relative to the Fe-peak
elements. SSP-equivalent ages of local ellipticals from Gonzalez (1993) are
found to vary widely, 1.5 < t < 18 Gyr, while metallicities [Z/H] and
enhancement ratios [E/Fe] are strongly peaked around <[Z/H]>=+0.26 and
<[E/Fe]>=+0.20 (in an aperture of radius Re/8). The enhancement ratios are
milder than previous estimates, owing to the application of non-solar abundance
corrections to both Mgb and <Fe> for the first time. Gradients in stellar
populations within galaxies are found to be mild, with SSP-equivalent age
decreasing by 25%, metallicity decreasing by <[Z/H]>=0.20 dex, and [E/Fe]
remaining nearly constant out to an aperture of radius Re/2 for nearly all
systems. Our ages have an overall zeropoint uncertainty of at least 25% due to
uncertainties in the stellar evolution prescription, the oxygen abundance, the
effect of non-solar abundances on the isochrones, and other unknowns. However,
the relative age rankings of stellar populations should be largely unaffected
by these errors. In particular, the large spread in ages appears to be real and
cannot be explained by contamination of Hbeta by blue stragglers or hot
horizontal branch stars, or by fill-in of Hbeta by emission. Correlations
between these derived SSP-equivalent parameters and other galaxy observables
will be discussed in future papers. (Abridged)
| [
{
"created": "Thu, 6 Jan 2000 02:21:49 GMT",
"version": "v1"
}
] | 2011-05-05 | [
[
"Trager",
"S. C.",
"",
"OCIW"
],
[
"Faber",
"S. M.",
"",
"UCO/Lick Observatory"
],
[
"Worthey",
"Guy",
"",
"St. Ambrose"
],
[
"Gonzalez",
"J. Jesus",
"",
"IA-UNAM"
]
] |
astro-ph/0001073 | Maartje Sevenster | M.Sevenster, H.Dejonghe, K.Van Caelenberg, H.J. Habing | Distribution functions for evolved stars in the inner galactic Plane | 23 pages, 20 figures, LaTeX, accepted for publication in A+A | null | null | null | astro-ph | null | We present dynamical distribution functions for evolved stars in the inner
galactic plane. We use an axisymmetric, two-component Stackel potential that
satisfies recent constraints on the galactic potential, amongst others a
slightly declining local rotation curve. We show that this potential is
adequate to model stellar-kinematic samples with radial extent ranging from
\~100 pc to ~5 kpc in the Galaxy. The two-integral model that gives the best
fit to the first three projected moments provides a very good global
representation of the data but fails to reproduce the central dispersion, the
central apparent scaleheight and the cylindrical rotation at intermediate
longitudes. All these features are fitted well by a three--integral model. We
discuss various properties of the 2I- and 3I models and the implications for
galactic structure. A somewhat thicker disk component is needed to explain the
distribution of older AGB stars in the plane; this component also fits the
kinematics at higher latitudes better. We find that the Disk and the Bulge, as
traced by AGB stars, are very similar dynamically and could well be one and the
same component. There is a dynamically distinct component in the inner 100 pc
of the Bulge, however.
| [
{
"created": "Thu, 6 Jan 2000 03:03:13 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sevenster",
"M.",
""
],
[
"Dejonghe",
"H.",
""
],
[
"Van Caelenberg",
"K.",
""
],
[
"Habing",
"H. J.",
""
]
] |
astro-ph/0001074 | Dwarkadas | Vikram Dwarkadas (1), Lewis Ball (1), James Caswell (2), Anne Green
(3), Simon Johnston (1), Brian Schmidt (4), Mark Wardle (1) ((1) SRCfTA, (2)
ATNF, (3) Astrophysics, U Sydney, (4) RSAA, ANU) | Supernova Remnants, Pulsars and the Interstellar Medium - Summary of a
Workshop Held at U Sydney, March 1999 | 13 pages, Latex. To be published in the Publications of the
Astronomical Society of Australia, 2000, Vol 17, No 1 | null | 10.1071/AS00083 | null | astro-ph | null | We summarise the proceedings of the SRCfTA workshop on ``Supernova Remnants,
Pulsars and the Interstellar Medium'' that was held at the University of Sydney
on Mar 18 and 19, 1999.
| [
{
"created": "Thu, 6 Jan 2000 06:57:08 GMT",
"version": "v1"
}
] | 2015-06-24 | [
[
"Dwarkadas",
"Vikram",
""
],
[
"Ball",
"Lewis",
""
],
[
"Caswell",
"James",
""
],
[
"Green",
"Anne",
""
],
[
"Johnston",
"Simon",
""
],
[
"Schmidt",
"Brian",
""
],
[
"Wardle",
"Mark",
""
]
] |
astro-ph/0001075 | Max Pettini | Max Pettini (Institute of Astronomy, Cambridge) | The First Galaxies: Clues from Element Abundances | 15 pages, LaTex, 8 Postscript Figures. To appear in the Philosophical
Transactions of The Royal Society, Series A | null | 10.1098/rsta.2000.0628 | null | astro-ph | null | It has recently become possible to measure directly the abundances of several
chemical elements in a variety of environments at redshifts up to z = 5. In
this review I summarise the latest observations of Lyman break galaxies, damped
Lyman alpha systems and the Lyman alpha forest with a view to uncovering any
clues which these data may offer to the first episodes of star formation. The
picture which is emerging is one where the universe at z = 3 already included
many of the components of today's galaxies--even at these early times we see
evidence for Populations I and II stars, while the `smoking gun' for Population
III objects may be hidden in the chemical composition of the lowest density
regions of the IGM, yet to be deciphered.
| [
{
"created": "Thu, 6 Jan 2000 08:48:14 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Pettini",
"Max",
"",
"Institute of Astronomy, Cambridge"
]
] |
astro-ph/0001076 | Kohji Yoshikawa | Kohji Yoshikawa (1), Y.P. Jing (2) and Yasushi Suto (2) ((1)
Department of Astronomy, Kyoto University, (2) Department of Physics and
RESCEU, University of Tokyo) | Cosmological SPH simulations with four million particles: statistical
properties of X-ray clusters in a low-density universe | Accepted for publication in The Astrophysical Journal. 18 pages with
7 embedded figures | The Astrophysical Journal 535 (2000) 593-601 | 10.1086/308895 | null | astro-ph | null | We present results from a series of cosmological SPH (smoothed particle
hydrodynamics) simulations coupled with the P3M
(Particle-Particle-Particle-Mesh) solver for the gravitational force. The
simulations are designed to predict the statistical properties of X-ray
clusters of galaxies as well as to study the formation of galaxies. We have
seven simulation runs with different assumptions on the thermal state of the
intracluster gas. Following the recent work by Pearce et al., we modify our SPH
algorithm so as to phenomenologically incorporate the galaxy formation by
decoupling the cooled gas particles from the hot gas particles. All the
simulations employ 128^3 particles both for dark matter and for gas components,
and thus constitute the largest systematic catalogues of simulated clusters in
the SPH method performed so far. These enable us to compare the analytical
predictions on statistical properties of X-ray clusters against our direct
simulation results in an unbiased manner. We find that the luminosities of the
simulated clusters are quite sensitive to the thermal history and also to the
numerical resolution of the simulations, and thus are not reliable. On the
other hand, the mass-temperature relation for the simulated clusters is fairly
insensitive to the assumptions of the thermal state of the intracluster gas,
robust against the numerical resolution, and in fact agrees well with the
analytic prediction. Therefore the prediction for the X-ray temperature
function of clusters on the basis of the Press-Schechter mass function and the
virial equilibrium is fairly reliable.
| [
{
"created": "Thu, 6 Jan 2000 10:22:29 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Yoshikawa",
"Kohji",
""
],
[
"Jing",
"Y. P.",
""
],
[
"Suto",
"Yasushi",
""
]
] |
astro-ph/0001077 | Marten van Kerkwijk | M. H. van Kerkwijk (Utrecht University) | Neutron Star Mass Determinations | 6 pages, 3 figures, to appear in Proc. ESO Workshop on "Black Holes
in Binaries and Galactic Nuclei", Garching (Sept. 1999), L. Kaper, E.P.J. van
den Heuvel, P.A. Woudt eds., Springer-Verlag | null | 10.1007/10720995_4 | null | astro-ph | null | I review attempts made to determine the properties of neutron stars. The
focus is on the maximum mass that a neutron star can have, or, conversely, the
minimum mass required for the formation of a black hole. There appears to be
only one neutron star for which there is strong evidence that its mass is above
the canonical 1.4 solar masses, viz., Vela X-1, for which a mass close to 1.9
solar masses is found. Prospects for progress appear brightest for studies of
systems in which the neutron star should have accreted substantial amounts of
matter.
| [
{
"created": "Thu, 6 Jan 2000 10:26:50 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"van Kerkwijk",
"M. H.",
"",
"Utrecht University"
]
] |
astro-ph/0001078 | Andrzej A. Zdziarski | Andrzej A. Zdziarski (Copernicus Ctr., Warsaw) | Radiative Processes and Geometry of Spectral States of Black-Hole
Binaries | Invited review for IAU Symp. 195, Highly Energetic Physical Processes
and Mechanisms for Emission from Astrophysical Plasmas, P. C. H. Martens, S.
Tsuruta, & M. A. Weber, eds., ASP, pp. 153-170 (2000) | 2000, IAU Symp. 195, P. C. H. Martens et al, eds, (San Francisco:
ASP), 153 | null | null | astro-ph | null | I review radiative processes responsible for X-ray emission in the hard (low)
and soft (high) spectral states of black-hole binaries. The main process in the
hard state appears to be thermal Comptonization (in a hot plasma) of blackbody
photons emitted by a cold disk. This is supported by correlations between the
spectral index, the strength of Compton reflection, and the peak frequencies in
the power density spectrum, as well as by the frequency-dependence of
Fourier-resolved spectra. Spectral variability may then be driven by the
variable truncation radius of the disk. The soft state appears to correspond to
the smallest truncation radii. However, the lack of high-energy cutoffs
observed in the soft state implies that its main radiative process is Compton
scattering of disk photons by non-thermal electrons. The bulk-motion
Componization model for the soft state is shown to be ruled out by the data.
| [
{
"created": "Thu, 6 Jan 2000 11:20:51 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Jan 2000 10:24:45 GMT",
"version": "v2"
},
{
"created": "Sun, 11 Jun 2000 09:27:46 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Zdziarski",
"Andrzej A.",
"",
"Copernicus Ctr., Warsaw"
]
] |
astro-ph/0001079 | Sandip Kumar Chakrabarti | Sonali Chakrabarti and Sandip K. Chakrabarti | Can DNA bases be produced during molecular cloud collapse? | 4 pages including Figures; Accepted in Astronomy and Astrophysics
Letters | null | null | null | astro-ph | null | Using a reasonably large chemical reaction network consisting of 421 species,
we show that along with normal chemical evolution of molecular cloud during
collapse and star formation, significant amount of adenine, a DNA base, may be
produced after an evolution of 10^{6-7} years. This findings may shed light on
whether life on earth had to begin from scratch or these molecules could have
contaminated the earth from the beginning.
| [
{
"created": "Thu, 6 Jan 2000 13:12:47 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Chakrabarti",
"Sonali",
""
],
[
"Chakrabarti",
"Sandip K.",
""
]
] |
astro-ph/0001080 | Sabine Schindler | Sabine Schindler (Liverpool John Moores University) | X-ray and optical observations of three clusters of galaxies: Abell 901,
Abell 1437, and Abell 3570 | 8 pages (incl. 6 figures), accepted for publication in A&A (Suppl.) | null | 10.1051/aas:2000161 | null | astro-ph | null | We analyse three clusters of galaxies, Abell 901 (z=0.17), Abell 1437
(z=0.13) and Abell 3570 (z=0.037). They have low to intermediate X-ray fluxes
and an irregular morphology in the ROSAT All-Sky Survey (RASS). These clusters
are chosen to test the abilities and limitations of the RASS in terms of
cluster fluxes and cluster morphologies. Therefore some ``worst'' cases are
used here. X-ray observations with the ROSAT/HRI and optical spectroscopic
observations are carried out. The ROSAT/HRI observations, which have a much
better spatial resolution than the RASS, reveal in two of the three cases a
significantly different morphology than seen in the RASS. The reasons are point
sources which could not be resolved in the RASS and were therefore confused
with the cluster emission. For A3570 we could confirm the relaxed state of the
cluster by the optical determination of a small velocity dispersion. In the
cluster with the lowest flux (Abell 901) the countrate measurement is strongly
affected by point sources, in the two other cases the countrate measurements of
the RASS are reliable, i.e. they are reproduced by the ROSAT/HRI measurement.
We conclude that for clusters with a flux of a few times 10^{-12} erg/cm^2/s or
smaller, which show at the same time a non-relaxed morphology, the flux
measurement of the RASS can be seriously affected by fore- or background
sources. We point out that an all-sky survey of a second ABRIXAS mission would
provide a much clearer source distinction for low-flux clusters and thus a much
improved countrate determination.
| [
{
"created": "Thu, 6 Jan 2000 13:44:52 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Schindler",
"Sabine",
"",
"Liverpool John Moores University"
]
] |
astro-ph/0001081 | Klaus Reinsch | K. Reinsch, A. van Teeseling, A. R. King, K. Beuermann | A limit-cycle model for the binary supersoft X-ray source RX
J0513.9-6951 | 4 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics Letters | null | null | null | astro-ph | null | We present new results of our X-ray monitoring of the transient binary
supersoft X-ray source RX J0513.9-6951 in the LMC and of our re-analysis of
optical light curves obtained during the MACHO project. We have covered a
complete X-ray outburst cycle with the ROSAT HRI detector. From the amplitude
and timescale of the soft X-ray variability, tight limits are derived for the
temporal behaviour of the white-dwarf radius and the effective temperature of
its envelope. A limit-cycle model is proposed to explain the observed optical
and X-ray variability, the characteristic timescales of the durations of the
X-ray on and off states, and those of the transitions between both states. Our
observations confirm that the radius changes of the white-dwarf envelope occur
on the Kelvin-Helmholtz timescale. The duration of the X-ray on and off states
is compatible with the viscous timescales of the inner and outer accretion
disk, respectively.
| [
{
"created": "Thu, 6 Jan 2000 14:55:26 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Reinsch",
"K.",
""
],
[
"van Teeseling",
"A.",
""
],
[
"King",
"A. R.",
""
],
[
"Beuermann",
"K.",
""
]
] |
astro-ph/0001082 | Paolo Salucci | A. Borriello and P. Salucci | The Dark Matter Distribution in Disk Galaxies | 8 pages, 6 figures, MNRAS accepted. New section and figures added,
concerning CDM mass models. Minor changes to the rest of the paper | Mon.Not.Roy.Astron.Soc. 323 (2001) 285 | 10.1046/j.1365-8711.2001.04077.x | null | astro-ph | null | We use high-quality optical rotation curves of 9 low-luminosity disk galaxies
to obtain the velocity profile of the surrounding dark matter halos. We find
that they increase linearly with radius at least out to the stellar disk edge,
implying that, over the entire region where the stars reside, the density of
the dark halo is constant. The properties of the halo mass structure found are
similar to that claimed for a number of dwarf and low surface brightness
galaxies, but provide a more substantial evidence of the discrepancy between
the halo mass distribution predicted in standard cold dark matter scenario and
those actually detected around galaxies. We find that the density profile
proposed by Burkert (1995) reproduces the halo rotation curves, with halo
central densities and core radii scaling as $\rho_0 \propto r_0^{-2/3}$.
| [
{
"created": "Thu, 6 Jan 2000 14:56:28 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Sep 2000 14:11:29 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Borriello",
"A.",
""
],
[
"Salucci",
"P.",
""
]
] |
astro-ph/0001083 | Reza Ansari | EROS Collaboration | Observation of Microlensing towards the Galactic Spiral Arms. EROS II 3
year survey | 4 pages, 3 figures, submitted for publication in A&A Letters | null | null | LAL 00-02 | astro-ph | null | We present an analysis of the light curves of 9.1 million stars observed
during three seasons by EROS (Experience de Recherche d'Objets Sombres), in the
Galactic plane away from the bulge. Seven stars exhibit luminosity variations
compatible with gravitational microlensing effects due to unseen objects. The
corresponding optical depth, averaged over four directions, is tau = 0.45 +0.24
-0.11 x 10^-6. While this value is compatible with expectations from simple
galactic models under reasonable assumptions on the target distances, we find
an excess of events with short timescale towards the direction closest to the
Galactic Centre.
| [
{
"created": "Thu, 6 Jan 2000 15:13:53 GMT",
"version": "v1"
}
] | 2012-08-27 | [
[
"EROS Collaboration",
"",
""
]
] |
astro-ph/0001084 | Diego Harari | Diego Harari, Silvia Mollerach, Esteban Roulet | Signatures of galactic magnetic lensing upon ultra high energy cosmic
rays | 18 pages, 7 figures, uses JHEP.cls | JHEP 0002 (2000) 035 | 10.1088/1126-6708/2000/02/035 | null | astro-ph hep-ph | null | We analyse several implications of lensing by the regular component of the
galactic magnetic field upon the observed properties of ultra high energy
cosmic rays. Magnetic fields deflect cosmic ray trajectories, causing flux
(de)magnification, formation of multiple images of a single source, and time
delays. We derive the energy dependence of these effects near the caustics at
which the flux amplification of a point source diverges. We show that the large
magnification of images around caustics leads to an amplification bias, which
can make them dominate the flux in some energy ranges. We argue that clustering
in the arrival directions of UHECRs of comparable energy may be due to magnetic
lensing around caustics. We show that magnetic lensing can also significantly
alter the observed composition of cosmic rays at the highest energies. We also
show that the time delay between events from a single image may monotonically
decrease with decreasing energy in the neighborhood of a caustic, opposite to
its behaviour in normal regions.
| [
{
"created": "Thu, 6 Jan 2000 15:43:59 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Harari",
"Diego",
""
],
[
"Mollerach",
"Silvia",
""
],
[
"Roulet",
"Esteban",
""
]
] |
astro-ph/0001085 | Israel | G.L. Israel, S. Covino, S. Campana, V.F. Polcaro, P. Roche, L. Stella,
A. Di Paola, D. Lazzati, S. Mereghetti, E. Giallongo, A. Fontana and F.
Verrecchia | The discovery of the optical/IR counterpart of the 12s transient X-ray
pulsar GS 0834-43 | 6 pages. Accepted for publication in MNRAS | null | 10.1046/j.1365-8711.2000.03404.x | null | astro-ph | null | We report the discovery of the optical/infra-red counterpart of the 12.3s
transient X-ray pulsar GS0834-43. We re-analysed archival ROSAT PSPC
observations of GS0834-43, obtaining two new refined positions, about 14" and
18" away from the previously published one, and a new spin period measurement.
Within the new error circles we found a relatively faint (V=20.1) early type
reddened star (V-R=2.24). The optical spectrum shows a strong Halpha emission
line. The IR observations of the field confirm the presence of an IR excess for
the Halpha-emitting star (K'=11.4, J-K'=1.94) which is likely surrounded by a
conspicuous circumstellar envelope. Spectroscopic and photometric data indicate
a B0-2 V-IIIe spectral-type star located at a distance of 3-5kpc and confirm
the Be-star/X-ray binary nature of GS0834-43.
| [
{
"created": "Thu, 6 Jan 2000 16:16:10 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Israel",
"G. L.",
""
],
[
"Covino",
"S.",
""
],
[
"Campana",
"S.",
""
],
[
"Polcaro",
"V. F.",
""
],
[
"Roche",
"P.",
""
],
[
"Stella",
"L.",
""
],
[
"Di Paola",
"A.",
""
],
[
"Lazzati",
"D.",
""
],
[
"Mereghetti",
"S.",
""
],
[
"Giallongo",
"E.",
""
],
[
"Fontana",
"A.",
""
],
[
"Verrecchia",
"F.",
""
]
] |
astro-ph/0001086 | Anil K. Pradhan | Guo Xin Chen and Anil K. Pradhan (Department of Astronomy, The Ohio
State University, Columbus, OH) | Fluorescent Excitation of Spectral Lines in Planetary Nebulae | 5 pages, 4 figures (fig.4 in color), ApJ (in press) | null | 10.1086/308941 | null | astro-ph | null | Fluorescent excitation of spectral lines is demonstrated as a function of
temperature-luminosity and the distance of the emitting region from the central
stars of planetary nebulae. The electron densities and temperatures are
determined, and the method is exemplified through a detailed analysis of
spectral observations of a high excitation PN, NGC 6741, observed by Hyung and
Aller(1997). Fluorescence should also be important in the determination of
element abundances. It is suggested that the method could be generally applied
to determine or constrain the luminosity and the region of spectral emission in
other intensively radiative sources such as novae, supernovae, and active
galactic nuclei.
| [
{
"created": "Thu, 6 Jan 2000 16:38:42 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Chen",
"Guo Xin",
"",
"Department of Astronomy, The Ohio\n State University, Columbus, OH"
],
[
"Pradhan",
"Anil K.",
"",
"Department of Astronomy, The Ohio\n State University, Columbus, OH"
]
] |
astro-ph/0001087 | Pauline Barmby | Pauline Barmby & John P. Huchra | Testing population synthesis models with globular cluster colors | To appear in ApJ Letters; 8 pages including 3 figures and 1 table | Astrophys.J. 531 (2000) L29 | 10.1086/312511 | null | astro-ph | null | We have measured an extensive set of UBVRIJHK colors for M31 globular
clusters [Barmby et al. 2000]. We compare the predicted simple stellar
population colors of three population synthesis models to the intrinsic colors
of Galactic and M31 globular clusters. The best-fitting models fit the cluster
colors very well -- the weighted mean color offsets are all < 0.05 mag. The
most significant offsets between model and data are in the U and B passbands;
these are not unexpected and are likely due to problems with the spectral
libraries used by the models. The metal-rich clusters ([Fe/H] > -0.8) are best
fit by young (8 Gyr) models, while the metal-poor clusters are best fit by
older (12--16 Gyr) models. If this range of globular cluster ages is correct,
it implies that conditions for cluster formation must have existed for a
substantial fraction of the galaxies' lifetimes.
| [
{
"created": "Thu, 6 Jan 2000 17:18:48 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Barmby",
"Pauline",
""
],
[
"Huchra",
"John P.",
""
]
] |
astro-ph/0001088 | Tkashi Okamoto | Takashi Okamoto and Asao Habe | Evolution of Cluster Galaxies in Hierarchical Clustering Universes | accepted for publication in PASJ | Publ.Astron.Soc.Jap. 52 (2000) 457-463 | 10.1093/pasj/52.3.457 | null | astro-ph | null | Using cosmological N-body simulations of critical (SCDM) and open ($\Omega =
0.3$, OCDM) cold dark matter models, we investigate evolution of cluster
galaxies. From our numerical simulation, we construct merging history trees of
the galaxies. By following their merging history, we show major merger
fractions of the galaxies in cluster forming regions is roughly proportional to
(1+z)^{4.5} at low redshifts (z < 2) and has a steep peak at $z \simeq 2.5$ and
$z \simeq 3$ in SCDM and OCDM, respectively. We also show that the cluster
galaxies are affected by tidal interaction after the clusters formed. Because
the formation redshift of the cluster in SCDM, z_{form} = 0.15, is much more
recent than that of the cluster in OCDM, z_{form} = 1.6, the cluster galaxies
in SCDM show more rapid evolution by tidal interactions from z = 0.5 than those
in OCDM.
| [
{
"created": "Thu, 6 Jan 2000 17:55:36 GMT",
"version": "v1"
},
{
"created": "Tue, 2 May 2000 09:35:42 GMT",
"version": "v2"
}
] | 2015-06-24 | [
[
"Okamoto",
"Takashi",
""
],
[
"Habe",
"Asao",
""
]
] |
astro-ph/0001089 | David H. Weinberg | John Phillips, David H. Weinberg, Rupert A. C. Croft, Lars Hernquist,
Neal Katz and Max Pettini | Constraints on Cosmological Parameters from the Lyman-alpha Forest Power
Spectrum and COBE-DMR | 26 pages, 6 figs, ApJ, in press (10/01). New version corrects some
numerical results for Lambda-CDM models, updates discussion in light of new
observational developments (especially CMB). Main conclusions unchanged | Astrophys.J. 560 (2001) 15-27 | 10.1086/322369 | null | astro-ph | null | We combine COBE-DMR measurements of cosmic microwave background anisotropy
with a recent measurement of the mass power spectrum at redshift z=2.5 from Lya
forest data to derive constraints on cosmological parameters and test the
inflation+CDM scenario of structure formation. By treating the inflationary
spectral index n as a free parameter, we can find successful fits to the COBE
and Lya forest constraints in Omega_m=1 models with and without massive
neutrinos and in low-Omega_m models with and without a cosmological constant.
Within each class of model, the combination of COBE and the Lya forest P(k)
constrains a parameter combination of the form (Omega_m h^a n^b Omega_b^c),
with different indices for each case. This new constraint breaks some of the
degeneracies in cosmological parameter determinations from other measurements.
The Lya forest P(k) provides the first measurement of the slope of the linear
mass power spectrum on ~Mpc scales, and it confirms a basic prediction of the
inflationary CDM scenario: a nearly scale-invariant spectrum of primeval
fluctuations (n~1) that bends towards k^{n-4} on small scales. Considering
additional observational data, we find that COBE-normalized, Omega_m=1 models
that match the Lya forest P(k) do not match the observed masses of rich galaxy
clusters and that a low-Omega_m model with a cosmological constant provides the
best overall fit, even without the direct evidence for cosmic acceleration from
supernovae. Modest improvements in the Lya forest P(k) measurement could
greatly restrict the allowable region of parameter space for CDM models,
constrain the contribution of tensor fluctuations to CMB anisotropy, and
achieve a more stringent test of the current consensus model of structure
formation.
| [
{
"created": "Thu, 6 Jan 2000 18:13:07 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Jun 2001 18:24:17 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Phillips",
"John",
""
],
[
"Weinberg",
"David H.",
""
],
[
"Croft",
"Rupert A. C.",
""
],
[
"Hernquist",
"Lars",
""
],
[
"Katz",
"Neal",
""
],
[
"Pettini",
"Max",
""
]
] |
astro-ph/0001090 | T. A. Aaron Sigut | T.A.A. Sigut, J.D. Landstreet, S.L.S. Shorlin | Emission Lines in the Spectrum of the 3He Star 3 Cen A | 16 pages, 3 figures | null | 10.1086/312499 | null | astro-ph | null | Emission in the 4d - 4f transitions of MnII (multiplet 13, 6122-6132 Ang), in
the 4f - 6g transitions of PII, and in 6149.5 Ang of HgII has been detected in
the spectrum of the helium weak star 3 Centauri A (B5 III-IVp). Weaker emission
from the same MnII multiplet is also seen in the hot, mild HgMn star 46 Aquila
(B9 III).It is suggested that the emission is of photospheric origin and may be
evidence for the stratification of manganese, phosphorus and mercury in the
photosphere of 3 CenA, and of manganese in 46Aql.
| [
{
"created": "Thu, 6 Jan 2000 18:33:44 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Sigut",
"T. A. A.",
""
],
[
"Landstreet",
"J. D.",
""
],
[
"Shorlin",
"S. L. S.",
""
]
] |
astro-ph/0001091 | Michael Pivovaroff | M. J. Pivovaroff (MIT), V. M. Kaspi (MIT), and F. Camilo (Columbia) | X-ray observations of the high magnetic field radio pulsar PSR
J1814-1744 | 11 pages, including 2 embedded figures. Accepted by ApJ | null | 10.1086/308848 | null | astro-ph | null | PSR J1814-1744 is a 4 s radio pulsar with surface dipole magnetic field
strength 5.5*10^13 G, inferred assuming simple magnetic dipole braking. This
pulsar's spin parameters are very similar to those of anomalous X-ray pulsars
(AXPs), suggesting that this may be a transition object between the radio
pulsar and AXP population, if AXPs are isolated, high magnetic field neutron
stars as has recently been hypothesized. We present archival X-ray observations
of PSR J1814-1744 made with ROSAT and ASCA. X-ray emission is not detected from
the position of the radio pulsar. The derived upper flux limit implies an X-ray
luminosity significantly smaller than those of all known AXPs. This conclusion
is insensitive to the possibility that X-ray emission from PSR J1814-1744 is
beamed or that it undergoes modest variability. When interpreted in the context
of the magnetar mechanism, these results argue that X-ray emission from AXPs
must depend on more than merely the inferred surface magnetic field strength.
This suggests distinct evolutionary paths for radio pulsars and AXP, despite
their proximity in period--period derivative phase space.
| [
{
"created": "Thu, 6 Jan 2000 18:45:03 GMT",
"version": "v1"
}
] | 2016-08-30 | [
[
"Pivovaroff",
"M. J.",
"",
"MIT"
],
[
"Kaspi",
"V. M.",
"",
"MIT"
],
[
"Camilo",
"F.",
"",
"Columbia"
]
] |
astro-ph/0001092 | Tim O'Brien | C. D. Gill, T.J. O'Brien | Hubble Space Telescope imaging and ground-based spectroscopy of old nova
shells - I. FH Ser, V533 Her, BT Mon, DK Lac, V476 Cyg | Accepted by MNRAS, 10 pages, 7 figures | null | 10.1046/j.1365-8711.2000.03342.x | null | astro-ph | null | In this paper we report on the first five out of eleven observations in our
programme of Hubble Space Telescope (HST) imaging of old nova shells. We
present new WFPC2 images of the shells around FH Ser and V533 Her taken in the
F656N (Halpha+[NII]) filter. We also show long-slit spectra taken using the
William Herschel Telescope (WHT) in La Palma for these objects in the same
spectral range. The shell around FH Ser is found to be a prolate ellipsoid of
ellipticity 1.3 +/- 0.1 inclined at 62 +/- 4 deg to the line of sight. The
shell has an equatorial ring which is found to be due to increased emission in
the two [NII] lines rather than Halpha. The expansion velocity, systemic
velocity and distance are found to be 490 +/- 20 km/s, -45 km/s and 950 +/- 50
pc. The origin of the [NII] equatorial ring is discussed in the context of a
photoionization feature resulting from aspherical illumination by the central
source rather than a simple density enhancement. It is possible however that
the ring is also in part due to an extremely localised increase in the nitrogen
abundance. Similar imaging and spectroscopy of the nova V533 Her reveal a shell
of radius 5 +/- 0.7 arcsec with an axial ratio of 1.2 +/- 0.2, expansion
velocity of 850 +/- 150 km/s and distance 1250 +/- 300 pc. The shells around BT
Mon, DK Lac and V476 Cyg were not detected with HST.
| [
{
"created": "Thu, 6 Jan 2000 18:49:55 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Gill",
"C. D.",
""
],
[
"O'Brien",
"T. J.",
""
]
] |
astro-ph/0001093 | Peter Berczik | Peter Berczik (Main Astronomical Observatory of Ukrainian National
Academy of Sciences) | Chemo - Photometric evolution of star forming disk galaxy | 4 pages, LaTeX2e, using the eslab.cls file, presented as a poster in
the 33rd ESLAB Symp. "Star formation from the small to the large scale",
Noordwijk, The Netherlands, 2-5 November 1999, (F. Favata, A.A. Kaas & A.
Wilson eds, ESA SP-445, 2000) | null | null | null | astro-ph | null | The chemical and photometric evolution of star forming disk galaxies is
investigated. Numerical simulations of the complex gasdynamical flows are based
on our own coding of the Chemo - Dynamical Smoothed Particle Hydrodynamical (CD
- SPH) approach, which incorporates the effects of star formation. As a first
application, the model is used to describe the chemical and photometric
evolution of a disk galaxy like the Milky Way.
| [
{
"created": "Thu, 6 Jan 2000 19:13:48 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Berczik",
"Peter",
"",
"Main Astronomical Observatory of Ukrainian National\n Academy of Sciences"
]
] |
astro-ph/0001094 | Jonathan Slavin | Jonathan D. Slavin, Christopher F. McKee, and David J. Hollenbach | Photoionization of Galactic Halo Gas by Old Supernova Remnants | AASTeX 5.01; 34 pages, 2 figures; submitted to Astrophysical Journal | null | 10.1086/309409 | null | astro-ph | null | We present new calculations on the contribution from cooling hot gas to the
photoionization of warm ionized gas in the Galaxy. We show that hot gas in
cooling supernova remnants (SNRs) is an important source of photoionization,
particularly for gas in the halo. We find that in many regions at high latitude
this source is adequate to account for the observed ionization so there is no
need to find ways to transport stellar photons from the disk. The flux from
cooling SNRs sets a floor on the ionization along any line of sight. Our model
flux is also shown to be consistent with the diffuse soft X-ray background and
with soft X-ray observations of external galaxies.
We consider the ionization of the clouds observed towards the halo star HD
93521, for which there are no O stars close to the line of sight. We show that
the observed ionization can be explained successfully by our model EUV/soft
X-ray flux from cooling hot gas. In particular, we can match the H alpha
intensity, the S++/S+ ratio, and the C+* column. From observations of the
ratios of columns of C+* and either S+ or H0, we are able to estimate the
thermal pressure in the clouds. The slow clouds require high (~10^4 cm^-3 K)
thermal pressures to match the N(C+*)/N(S+) ratio. Additional heating sources
are required for the slow clouds to maintain their ~7000 K temperatures at
these pressures, as found by Reynolds, Hausen & Tufte (1999).
| [
{
"created": "Thu, 6 Jan 2000 19:49:46 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Slavin",
"Jonathan D.",
""
],
[
"McKee",
"Christopher F.",
""
],
[
"Hollenbach",
"David J.",
""
]
] |
astro-ph/0001095 | Wei Cui | Wei Cui (MIT), Shuang Nan Zhang (UAH), and Wan Chen (UMd/GSFC) | Phase Lag and Coherence Function of X-ray emission from Black Hole
Candidate XTE J1550-564 | To appear in ApJ Letters | null | 10.1086/312520 | null | astro-ph | null | We report the results from measuring the phase lag and coherence function of
X-ray emission from black hole candidate (BHC) XTE J1550-564. These X-ray
temporal properties have been recognized to be increasingly important in
providing important diagnostics of the dynamics of accretion flows around black
holes. For XTE J1550-564, we found significant hard lag --- the X-ray
variability in high energy bands {\em lags} behind that in low energy bands ---
associated both with broad-band variability and quasi-periodic oscillation
(QPO). However, the situation is more complicated for the QPO: while hard lag
was measured for the first harmonic of the signal, the fundamental component
showed significant {\em soft} lag. Such behavior is remarkably similar to what
was observed of microquasar GRS 1915+105. The phase lag evolved during the
initial rising phase of the 1998 outburst. The magnitude of both the soft and
hard lags of the QPO increases with X-ray flux, while the Fourier spectrum of
the broad-band lag varies significantly in shape. The coherence function is
relatively high and roughly constant at low frequencies, and begins to drop
almost right after the first harmonic of the QPO. It is near unity at the
beginning and decreases rapidly during the rising phase. Also observed is that
the more widely separated the two energy bands are the less the coherence
function between the two. It is interesting that the coherence function
increases significantly at the frequencies of the QPO and its harmonics. We
discuss the implications of the results on the models proposed for BHCs.
| [
{
"created": "Thu, 6 Jan 2000 22:03:16 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Cui",
"Wei",
"",
"MIT"
],
[
"Zhang",
"Shuang Nan",
"",
"UAH"
],
[
"Chen",
"Wan",
"",
"UMd/GSFC"
]
] |
astro-ph/0001096 | Amy Barger | A.J. Barger, L.L. Cowie, E.A. Richards | Mapping the Evolution of High Redshift Dusty Galaxies with Submillimeter
Observations of a Radio-Selected Sample | 18 pages, accepted by The Astronomical Journal for April 2000 issue | Astron.J. 119 (2000) 2092-2109 | 10.1086/301341 | null | astro-ph | null | Direct submm imaging has recently revealed the 850-micron background to be
mostly composed of a population of distant ultraluminous infrared galaxies, but
identifying the optical/NIR counterparts to these sources has proved difficult
due to the poor submm spatial resolution. However, the proportionality of both
cm and submm data to the star formation rate suggests that high resolution
radio continuum maps with subarcsecond positional accuracy can be exploited to
locate submm sources. In this paper we present results from a targeted SCUBA
survey of micro-Jansky radio sources in the flanking fields of the Hubble Deep
Field. Even with relatively shallow 850-micron SCUBA observations (>6 mJy at
3-sigma), we were successful at making submm detections of optical/NIR-faint
(I>24 and K~21-22) radio sources, and our counts closely match the bright
counts from submm surveys. Redshift estimates can be made from the ratio of the
submm flux to the radio flux across the 100 GHz break in the spectral energy
distribution. This millimetric redshift estimation places the bright submm
population at z=1-3 where it forms the high redshift tail of the faint radio
population. The star formation rate density (SFRD) due to ultraluminous
infrared galaxies increases by more than two orders of magnitude from z~0 to
z~1-3. The SFRD at high redshift inferred from our >6 mJy submm observations is
comparable to that observed in the UV/optical. (Abridged)
| [
{
"created": "Thu, 6 Jan 2000 23:03:23 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Barger",
"A. J.",
""
],
[
"Cowie",
"L. L.",
""
],
[
"Richards",
"E. A.",
""
]
] |
astro-ph/0001097 | Kate Y. L. Su | K. Y. L. Su (1), S. Kwok (1), B. J. Hrivnak (2), R. Sahai (3) ((1)
University of Calgary, (2) Valparaiso University, (3) JPL/Caltech) | HST NICMOS Observation of Proto-Planetary Nebulae | To appear in ``Asymmetrical Planetary Nebulae II: from Origins to
Microstructures,'' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N.
Soker, & S.A. Rappaport, eds | null | null | null | astro-ph | null | We report NICMOS wide-band and polarimetric observations of four
proto-planetary nebulae. Molecular hydrogen emission is detected near the ends
of the bipolar lobes of IRAS 17150-3224, which is evidence for the interaction
of a fast, collimated outflow with the remnant of the asymptotic giant branch
wind.
| [
{
"created": "Thu, 6 Jan 2000 23:16:14 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Su",
"K. Y. L.",
""
],
[
"Kwok",
"S.",
""
],
[
"Hrivnak",
"B. J.",
""
],
[
"Sahai",
"R.",
""
]
] |
astro-ph/0001098 | Omar Almaini | O. Almaini (University of Edinburgh) | The X-ray/submillimetre link | Invited review, to appear in proceedings of the ``Large Scale
Structure in the X-ray Universe'' conference, held in Santorini, Greece,
September 1999, eds. M. Plionis and I. Georgantopoulos (Editions Frontieres),
8 pages, 2 figures. Also available at http://www.roe.ac.uk/~omar/astro.html | null | null | null | astro-ph | null | It is widely believed that most of the cosmic X-ray background (XRB) is
produced by a vast, hitherto undetected population of obscured AGN. Deep X-ray
surveys with Chandra and XMM will soon test this hypothesis. Similarly, recent
sub-mm surveys with SCUBA have revealed an analogous population of
exceptionally luminous, dust-enshrouded {\em star-forming} galaxies at high
redshift. There is now growing evidence for an intimate link between these
obscured populations. There are currently large uncertainties in the models,
but several independent arguments lead to the conclusion that a significant
fraction of the SCUBA sources ($10-30% $) will contain quasars. Recent
observational studies of SCUBA survey sources appear to confirm these
predictions, although the relative roles of AGN and star-forming activity in
heating the dust are unclear. Forthcoming surveys combining X-ray and sub-mm
observations will provide a very powerful tool for disentangling these
processes.
| [
{
"created": "Fri, 7 Jan 2000 17:54:41 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Almaini",
"O.",
"",
"University of Edinburgh"
]
] |
astro-ph/0001099 | Andreas A. Berlind | Andreas A. Berlind (1), Vijay K. Narayanan (1 and 2), David H.
Weinberg (1) .((1) The Ohio State University, (2) Princeton University) | Biased Estimates of Omega from Comparing Smoothed Predicted Velocity
Fields to Unsmoothed Peculiar Velocity Measurements | 11 pages including 2 eps figures. Submitted to ApJ | null | 10.1086/309085 | null | astro-ph | null | We show that a regression of unsmoothed peculiar velocity measurements
against peculiar velocities predicted from a smoothed galaxy density field
leads to a biased estimate of the cosmological density parameter Omega, even
when galaxies trace the underlying mass distribution and galaxy positions and
velocities are known perfectly. The bias arises because the errors in the
predicted velocities are correlated with the predicted velocities themselves.
We investigate this bias using cosmological N-body simulations and analytic
arguments. In linear perturbation theory, for cold dark matter power spectra
and Gaussian or top hat smoothing filters, the bias in Omega is always
positive, and its magnitude increases with increasing smoothing scale. This
linear calculation reproduces the N-body results for Gaussian smoothing radii
R_s > 10 Mpc/h, while non-linear effects lower the bias on smaller smoothing
scales, and for R_s < 3 Mpc/h Omega is underestimated rather than
overestimated. The net bias in Omega for a given smoothing filter depends on
the underlying cosmological model. The effect on current estimates of Omega
from velocity-velocity comparisons is probably small relative to other
uncertainties, but taking full advantage of the statistical precision of future
peculiar velocity data sets will require either equal smoothing of the
predicted and measured velocity fields or careful accounting for the biases
discussed here.
| [
{
"created": "Fri, 7 Jan 2000 01:04:31 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Berlind",
"Andreas A.",
"",
"The Ohio State University"
],
[
"Narayanan",
"Vijay K.",
"",
"1 and 2"
],
[
"Weinberg",
"David H.",
"",
"The Ohio State University"
],
[
".",
"",
""
]
] |
astro-ph/0001100 | Sandy Leggett | S. K. Leggett, F. Allard, Conard Dahn, P. H. Hauschildt, T. H. Kerr,
J. Rayner | Spectral Energy Distributions for Disk and Halo M--Dwarfs | 24 pages including 13 figures, 4 Tables; accepted by ApJ | Astrophys.J.535:965-974,2000 | 10.1086/308887 | null | astro-ph | null | We have obtained infrared (1 to 2.5 micron) spectroscopy for 42 halo and disk
dwarfs with spectral type M1 to M6.5. These data are compared to synthetic
spectra generated by the latest model atmospheres of Allard & Hauschildt.
Photospheric parameters metallicity, effective temperature and radius are
determined for the sample. We find good agreement between observation and
theory except for known problems due to incomplete molecular data for metal
hydrides and water. The metal-poor M subdwarfs are well matched by the models
as oxide opacity sources are less important in this case. The derived effective
temperatures for the sample range from 3600K to 2600K; at these temperatures
grain formation and extinction are not significant in the photosphere. The
derived metallicities range from solar to one-tenth solar. The radii and
effective temperatures derived agree well with recent models of low mass stars.
| [
{
"created": "Fri, 7 Jan 2000 01:21:50 GMT",
"version": "v1"
}
] | 2009-05-29 | [
[
"Leggett",
"S. K.",
""
],
[
"Allard",
"F.",
""
],
[
"Dahn",
"Conard",
""
],
[
"Hauschildt",
"P. H.",
""
],
[
"Kerr",
"T. H.",
""
],
[
"Rayner",
"J.",
""
]
] |
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