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astro-ph/0001401

Andrei Beloborodov

A.M. Beloborodov, B.E. Stern, R. Svensson

Power Density Spectra of GRBs

9 pages, accepted to ApJ

Astrophys.J. 535 (2000) 158-166

10.1063/1.1361535

astro-ph

Power density spectra (PDSs) of long gamma-ray bursts (GRBs) provide useful information on GRBs, indicating their self-similar temporal structure. The best power-law PDSs are displayed by the longest bursts (T_90>100 s) in which the range of self-similar time scales covers more than 2 decades. Shorter bursts have apparent PDS slopes more strongly affected by statistical fluctuations. The underlying power law can then be reproduced with high accuracy by averaging the PDSs for a large sample of bursts. This power law has a slope approximately equal to -5/3 and a sharp break at about 1 Hz. The power-law PDS provides a new sensitive tool for studies of GRBs. In particular, we calculate the PDSs of bright bursts in separate energy channels. The PDS flattens in the hard channel (h\nu>300 keV) and steepens in the soft channel (h\nu<50 keV), while the PDS of bolometric light curves approximately follows the -5/3 law. We then study dim bursts and compare them to the bright ones. We find a strong correlation between the burst brightness and the PDS slope. This correlation shows that the bursts are far from being standard candles and dim bursts should be intrinsically weak. The time dilation of dim bursts is probably related to physical processes occurring in the burst rather than to a cosmological redshift.

2009-10-31

astro-ph/0001402

Brian McNamara

B.R. McNamara (CfA), M. Wise (MIT/CSR), P.E.J. Nulsen (U. Wollongong),L.P. David (CfA), C.L. Sarazin (U. Virginia), M. Bautz (MIT/CSR), M. Markevitch (CfA), A. Vikhlinin (CfA), W.R. Forman (CfA), C. Jones (CfA), D.E. Harris (CfA)

Chandra X-ray Observations of the Hydra A Cluster: An Interaction Between the Radio Source and the X-Ray-Emitting Gas

4 pages, 3 figures; submitted to ApJ Letters

Astrophys.J.534:L 135,2000

10.1086/312662

astro-ph

We present Chandra X-ray Observations of the Hydra A cluster of galaxies, and we report the discovery of structure in the central 80 kpc of the cluster's X-ray-emitting gas. The most remarkable structures are depressions in the X-ray surface brightness, $\sim 25-35$ kpc diameter, that are coincident with Hydra A's radio lobes. The depressions are nearly devoid of X-ray-emitting gas, and there is no evidence for shock-heated gas surrounding the radio lobes. We suggest the gas within the surface brightness depressions was displaced as the radio lobes expanded subsonically, leaving cavities in the hot atmosphere. The gas temperature declines from 4 keV at 70 kpc to 3 keV in the inner 20 kpc of the brightest cluster galaxy (BCG), and the cooling time of the gas is $\sim 600$ Myr in the inner 10 kpc. These properties are consistent with the presence of a $\sim 34 \msunyr$ cooling flow within a 70 kpc radius. Bright X-ray emission is present in the BCG surrounding a recently-accreted disk of nebular emission and young stars. The star formation rate is commensurate with the cooling rate of the hot gas within the volume of the disk, although the sink for the material cooling at larger radii remains elusive.

2011-05-05

astro-ph/0001403

Vladimir Avila-Reese

V. Avila-Reese (1), C. Firmani (1,2) ((1) Instituto de Astronomia, UNAM, Mexico (2) Osservatorio Astronomico di Brera, Italy)

Properties of disk galaxies in a hierarchical formation scenario

24 pages, includes figures, uses rmaa.cls. Accepted for publication in RevMexAA, Vol. 36, No. 1 (April 2000)

Rev. Mex. Astron. Astrofis., V. 36, N. 1, pp. 23-42 (2000)

astro-ph

We used galaxy evolutionary models in a hierarchical inside-out formation scenario to study the origin of the main properties and correlations of disk galaxies. We found that most of these properties and correlations are the result of three (cosmological) initial factors and their dispersions: the virial mass, the halo mass aggregation history (MAH), and the angular momentum given through the spin parameter \lambda. The MAH determines mainly the halo structure and the color indexes while \lambda determines mainly the surface brightness and the bulge-to-disk ratio. We calculated star formation (SF) using a gravitational instability criterion and a self-regulation mechanism in the turbulent ISM. The efficiency of SF in this model is almost independent from the mass. We show that the luminosity-dependent dust absorption empirically determined by Wang & Heckman explains the observed color-magnitude and color Tully-Fisher (TF) relations without the necessity of introducing a mass-dependent SF efficiency. The disks in centrifugal equilibrium form within growing CDM halos with a gas accretion rate proportional to the MAH. The disks present exponential surface density and brightness profiles, negative radial color index gradients, and nearly flat rotation curves. We also calculated the secular formation of a bulge due to gravitational instabilities in the stellar disk. The intensive properties of our models agree with the observational data and the trends of the Hubble sequence are reproduced. The predicted infrared TF and luminosity-radius relations also agree with observations. The main shortcomings of our inside-out hierarchical models are the excessive radial color gradients and the dark halo dominion in the rotation curve decompositions.

2007-05-23

astro-ph/0001404

Martin A. Guerrero

Martin A. Guerrero, You-Hua Chu and Robert A. Gruendl (Department of Astronomy, University of Illinois at Urbana-Champaign)

ROSAT observations of X-ray emission from planetary nebulae

To be published in The Astrophysical Journal Supplement Series. 21 pages, 7 figures, 5 tables

Astrophys.J.Suppl. 129 (2000) 295

10.1086/313415

astro-ph

We have searched the entire ROSAT archive for useful observations to study X-ray emission from Galactic planetary nebulae (PNs). The search yields a sample of 63 PNs, which we call the ROSAT PN sample. About 20-25% of this sample show X-ray emission; these include 13 definite detections and three possible detections (at a 2-sigma level). All X-ray sources in these PNs are concentrated near the central stars. Only A 30, BD+30 3639, and NGC 6543 are marginally resolved by the ROSAT instruments. Three types of X-ray spectra are seen in PNs. Type 1 consists of only soft X-ray emission (<0.5 keV), peaks at 0.1-0.2 keV, and can be fitted by blackbody models at temperatures 1-2 10^5 K. Type 2 consists of harder X-ray emission, peaks at >0.5 keV, and can be fitted by thin plasma emission models at temperatures of a few 10^6 K. Type 3 is a composite of a bright Type 1 component and a fainter Type 2 component. Unresolved soft sources with Type 1 spectra or the soft component of Type 3 spectra are most likely photospheric emission from the hot central stars. Absorption cross sections are large for these soft-energy photons; therefore, only large, tenuous, evolved PNs with hot central stars and small absorption column densities have been detected. The origin of hard X-ray emission from PNs is uncertain. PNs with Type 2 spectra are small, dense, young nebulae with relatively cool (<<10^5 K) central stars, while PNs with Type 3 X-ray spectra are large, tenuous, evolved nebulae with hot central stars. The hard X-ray luminosities are also different between these two types of PNs, indicating perhaps different origins of their hard X-ray emission. Future Chandra and XMM observations with high spatial and spectral resolution will help to understand the origin of hard X-ray emission from PNs.

2009-10-31

astro-ph/0001405

Amir Levinson

A. Levinson (TAU), D. Eichler (BGU)

Hydrodymanic collimation of GRB fireballs

8 pages, uses REVTEX, submitted to Phys. Rev. Lett

10.1103/PhysRevLett.85.236

astro-ph

Analytic solutions are presented for the hydrodynamic collimation of a relativistic fireball by a surrounding baryonic wind emanating from a torus. The opening angle is shown to be the ratio of the power output of the inner fireball to that of the exterior baryonic wind. The gamma ray burst 990123 might thus be interpreted as a baryon-pure jet with an energy output of order 10$^{50}$ erg or less, collimated by a baryonic wind from a torus with an energy output of order $10^{52}$ erg.

2009-10-31

astro-ph/0001406

S. A. Levshakov

Sergei A. Levshakov (Ioffe Institute, St.Petersburg, Russia)

The deuterium abundance in QSO absorption systems: a mesoturbulent approach

6 pages, 2 eps figures, newpasp.sty file, to appear in the Proceedings of the IAU Symposium 198 "The light elements and their evolution", November 22-27, 1999, Natal, Brazil

astro-ph

A new method, based on simulated annealing technique and aimed at the inverse problem in the analysis of intergalactic or interstellar complex spectra of hydrogen and metal lines, is outlined. We consider the process of line formation in clumpy stochastic media accounting for fluctuating velocity and density fields self-consistently. Two examples of the analysis of `H+D'-like absorptions seen at z = 3.514 and 3.378 towards APM 08279+5255 are presented.

2007-05-23

astro-ph/0001407

Arvind Parmar

A.N. Parmar (1), T. Oosterbroek (1), S. Del Sordo (2), A. Segreto (2), A. Santangelo (2), D. Dal Fiume(3), M. Orlandini (3) ((1) ESA/ESTEC, (2) IFCAI/Palermo, (3) ITESRE/Bologna)

Broad-band BeppoSAX observation of the low-mass X-ray binary X1822-371

7 pages. To appear in A&A

astro-ph

Results of a 1997 September 9-10 BeppoSAX observation of the 5.57 hr low-mass X-ray binary (LMXRB) X1822-371 are presented. The 0.3-40 keV spectrum is unusually complex and cannot be fit by any of the standard models applied to other LMXRB. At least two components are required. One component has a shape consistent with that expected from the Comptonization of an input soft (Wein) spectrum while the other, contributing ~40% of the 1-10 keV flux, is consistent with being a blackbody. In addition, there is a ``dip'' in the spectrum which can be modeled by a 1.33 +0.05 -0.11 keV absorption edge with an optical depth, tau, of 0.28 +/- 0.06. If the same model is fit to ASCA Solid-State Imaging Spectrometer spectra obtained in 1993 and 1996, then reasonable fits are also obtained, with a similar absorption feature required. The nature of this feature is highly uncertain; its energy corresponds to the K-edges of highly ionized Ne x and neutral Mg, or to an L-edge of moderately ionized Fe. Surprisingly, no strong (tau > 0.05) Fe-K or (tau > 0.18) O-K edges are visible. The folded lightcurve of X1822-371 is similar to previous observations, except that no strong softening is seen near the eclipse. An updated orbital ephemeris is provided.

2007-05-23

astro-ph/0001408

Origlia Livia

Livia Origlia and Claus Leitherer

Transformations between the theoretical and observational planes in the HST-NICMOS and WFPC2 photometric systems

22 pages, 14 figures

10.1086/301284

astro-ph

Color-temperature relations and bolometric corrections in the HST-NICMOS F1110W, F160W and F222M and in the WFPC2 F439W, F555W and F814W photometric systems, using two different sets of model atmospheres, have been derived. This database of homogeneous, self-consistent transformations between the theoretical and observational planes also allows combinations of visual and infrared quantities, without any further transformation between the two different photometric systems. The behavior of the inferred quantities with varying the stellar parameters, the adopted model atmospheres and the instrumental configurations are investigated. Suitable relations to transform colors and bolometric corrections from HST to ground-based photometric systems are also provided.

2009-10-31

astro-ph/0001409

Monica Tosi (Osservatorio Astronomico di Bologna, Italy)

Evolution of D and 3He in the Galaxy

10 pages including 7 figs, to appear in "The Light Elements and Their Evolution", IAU Symp.198, L. Da Silva, M. Spite, J.R. Medeiros eds, ASP Conf. Ser., in press

BAP01-2000-03-OAB

astro-ph

The predictions of Galactic chemical evolution models for D and $^3$He are described in connection with those on the other Galactic quantities for which observational constraints are available. Models in agreement with the largest set of data predict deuterium depletions from the Big Bang to the present epoch smaller than a factor of 3 and do not allow for D/H primordial abundances larger than $\sim4\times10^{-5}$. Models predicting higher D consumption do not reproduce other observed features of our Galaxy. If both the primordial D and $^3$He are low, models assuming that 90% of low-mass stars experience an extra-mixing during the red giant phase reproduce all the $^3$He observed abundances. The same percentage allows to fit also the observed carbon isotopic ratios, thus supporting the self-consistency of the extra-mixing mechanism.

2007-05-23

astro-ph/0001410

Luigi Costamante

L. Costamante, G. Ghisellini, P. Giommi, G. Tagliaferri, A. Celotti, M. Chiaberge, L. Chiappetti, G. Fossati, L. Maraschi, E. Pian, F. Tavecchio, A. Treves, A. Wolter

New Extreme Synchrotron BL Lac Objects

To appear in the proceedings of the conference "X-Ray Astronomy '99", Bologna, Italy, September 1999; 4 pages, 3 figures, uses bo99.sty. Corrected authors' list

10.1063/1.1434692

astro-ph

We report on the BeppoSAX observations of four "extreme" BL Lacs, selected to have high synchrotron peak frequencies. All have been detected also in the PDS band. For 1ES 0120+340, PKS 0548-322 and H 2356-309 the spectrum is well fitted by a convex broken power-law, thus locating the synchrotron peak around 1 - 4 keV. 1ES 1426+428 presents a flat energy spectral index (alpha_x= 0.92) up to 100 keV, thus constraining the synchrotron peak to lie near or above that value. For their extreme properties, all sources could be strong TeV emitters.

2009-10-31

astro-ph/0001411

Querci

F. R. Querci (Obs. Midi-Pyrenees, Toulouse), M. Querci (Obs. Midi-Pyrenees, Toulouse)

Search for Astronomical Sites in Developing Countries and their Preventive Protection

in Proc. IAU Symposium 196 on "Preserving the Astronomical Sky", held in Vienna (Austria), 12-16 July 1999, in conjunction with UNISPACE III, to be published in A.S.P. Conf. Series (eds. R.J. Cohen and W.T. Sullivan)

astro-ph

The archives of meteorological satellites permit to find around the world dry sites well adapted to astronomical observations (in the visible, IR, and millimetric ranges), as a pre-selection of sites. The GSM (Grating Scale Monitor) technique permits to qualify some of them as astronomical sites for a future setting-up of astronomical observatories. Such sites are found in new astronomical countries or in Developing Countries. At the same time, their preventive protection from light pollution and/or radio interference has to be viewed. In practice, once the pre-selection is made, the government of these countries ought to be alerted for example by IAU and/or UN Office for Outer Space Affairs. The local site testing through GSM should be carried out in cooperation with astronomers or scientists of these countries under the umbrella of IAU. This should be an approach to help to introduce astronomy and astrophysics in Developing Countries.

2007-05-23

astro-ph/0001412

Dirk Grupe

D. Grupe, K.M. Leighly, H.-C. Thomas, and S.A. Laurent-Muehleisen

The enigmatic Soft X-ray AGN RX J0134.2--4258

13 pages (including 13 Figures), accepted for in A&A (main journal), also available at http://www.xray.mpe.mpg.de/~dgrupe/research/refereed.html

astro-ph

We report the discovery and analysis of the follow-up ROSAT pointed observation, an ASCA observation and optical and radio observations of the enigmatic soft X-ray AGN RX J0134.2-4258. In the optical, RX J0134.2-4258 appears as an extreme 'Narrow-Line Seyfert 1 galaxy' (NLS1), with very strong FeII emission, very blue optical continuum spectrum and almost no Narrow Line Region emission. While its spectrum was one of the softest observed from an AGN during the ROSAT All-Sky Survey, its spectrum was found to be dramatically harder during a pointed observation although the count rate remained constant. We found in the pointed observation that the spectrum is softer when it is fainter and spectral fitting demonstrates that it is the hard component that is variable. The ASCA observation confirms the presence of a hard X-ray power law, the slope of which is rather flat compared with other NLS1s. Survey and followup radio observations reveal that RX J0134.2-4258 is also unusual in that it is a member of the rare class of radio-loud NLS1s, and, with R=71, it holds the current record for largest radio-to-optical ratio in NLS1s. We discuss possible scenarios to explain its strange behaviour.

2007-05-23

astro-ph/0001413

Andrew Hopkins

A. Hopkins, A. Georgakakis, L. Cram, J. Afonso, and B. Mobasher

Microjansky radio sources in DC0107-46 (Abell 2877)

14 pages, 3 figures, Accepted by ApJS (v128n2p JUN 2000 issue)

Astrophys.J.Suppl.128:469-478,2000

10.1086/313399

astro-ph

The cluster DC0107-46 (Abell 2877) lies within the Phoenix Deep Survey, made at 1.4 GHz with the Australia Telescope Compact Array. Of 89 known optical cluster members, 70 lie within the radio survey area. Of these 70 galaxies, 15 (21%) are detected, with luminosities as faint as 10^20 W/Hz. Spectroscopic observations are available for 14/15 of the radio-detected cluster galaxies. Six galaxies show only absorption features and are typical low-luminosity AGN radio sources. One galaxy hosts a Seyfert 2 nucleus, two are star-forming galaxies, and the remaining five may be star-forming galaxies, AGNs, or both.

2008-12-18

astro-ph/0001414

Carlton M. Caves

Carlton M. Caves (University of New Mexico)

Predicting Future Duration from Present Age: A Critical Assessment

17 pages, standard LaTeX; to be published in Contemporary Physics

Contemp.Phys. 41 (2000) 143-153

10.1080/001075100181105

astro-ph gr-qc physics.data-an

Using a temporal version of the Copernican principle, Gott has proposed a statistical predictor of future longevity based on present age [J. R. Gott III, Nature 363, 315 (1993)] and applied the predictor to a variety of examples, including the longevity of the human species. Though Gott's proposal contains a grain of truth, it does not have the universal predictive power that he attributes to it.

2009-10-31

astro-ph/0001415

Anthony H. Gonzalez

Anthony H. Gonzalez, Ann I. Zabludoff, Dennis Zaritsky, Julianne J. Dalcanton

Measuring the Diffuse Optical Light in Abell 1651

28 pages including 8 figures. Color version of figure 6 available at http://www.ucolick.org/~anthonyg/work/a1651/fig6.color.eps . Accepted to ApJ

Erratum-ibid. 611 (2004) 1208

10.1086/308985

astro-ph

Using drift scan data, a new approach to determining surface brightness profiles, and techniques for detecting low surface brightness signals, we fit the light profile of the brightest cluster galaxy (BCG) in the rich cluster Abell 1651 out to 670 h^{-1} kpc. This radius is a significant fraction of the virial radius of the cluster (2 h^{-1} Mpc; Girardi et al. 1998), indicating that the sizes of the BCG and the cluster are comparable. We find that the profile is consistent with a de Vaucouleurs profile over the radial range probed. We also find that the integrated light profile of the BCG in Abell 1651 contributes 36% of the total cluster light within 500 h^{-1} kpc. Including all luminous components, we obtain M/L_I~160 h for the cluster, which would be overestimated by ~20% without the BCG halo. Furthermore, the relatively red color of the BCG at large radii suggests that recent disruption and tidal stripping of spirals and dwarf ellipticals do not contribute significantly to the halo luminosity. The color and the form of the profile are consistent with a scenario in which the BCG forms from filamentary collapse during the epoch of cluster formation, with relatively little evolution in the past 5 Gyrs (Dubinski 1998). We remove the BCG and other detected galaxies from the image and construct a two dimensional surface brightness map of the cluster core. Several knots of excess emission are found, but the total diffuse component is constrained to contribute less than 5% of the cluster light.

2009-10-31

astro-ph/0001416

J. M. Bonnet-Bidaud

J.M. Bonnet-Bidaud (1), M. Mouchet (2,3), N.M. Shakhovskoy (4), T.A. Somova(5), N.N. Somov(5), I.L. Andronov(6), D. de Martino(7), S.V. Kolesnikov(6), Z. Kraicheva(8) ((1)Service d'Astrophysique, DSM/DAPNIA/SAp, CE Saclay, (2)DAEC, Observatoire de Paris Section de Meudon, (3)Universit\'e Denis Diderot, (4)Crimean Astrophysical Observatory, (5)Special Astrophysical Observatory, (6)Department of Astronomy Odessa University, (7)Osservatorio Astronomico di Capodimonte, (8)Institute of Astronomy Bulgaria)

Magnetic field and unstable accretion during AM Herculis low states

accepted in Astronomy & Astrophysics (Main Journal), 10 pages, 6 Figures, Latex

astro-ph

A study of AM Her low states in September 1990 and 1991 and June-July 1997 is reported from a coordinated campaign with observations obtained at the Haute-Provence observatory, at the 6-m telescope of the Special Astrophysical Observatory and at the 2.6m and 1.25m telescopes of the Crimean observatory. Spectra obtained at different dates when the source was in low states at a comparable V magnitude, show the presence of strong Zeeman absorption features and marked changes in emission lines with a day-to-day reappearance of the HeII (4686\AA) emission lines in 1991. Despite this variability, the magnetic field inferred from the fitting of the absorption spectrum with Zeeman hydrogen splitting, is remarkably constant with a best value of (12.5$\pm$0.5)MG. Detailed analysis of the UBVRI light curves shows the presence of repetitive moderate amplitude ($\sim$ 0.3-0.5 mag) flares predominantly red in colour. These flares are attributed to small accretion events and are compared to the large ($\sim$ 2 mag.) blue flare reported by Shakhovskoy et al. (1993). We suggest that the general flaring activity observed during the low states is generated by accretion events. The different characteristics of the flares (colour and polarization) are the results of different shock geometries depending on the net mass accretion flux.

2016-08-15

astro-ph/0001417

Bohdan Paczynski

Bohdan Paczynski and Bart Pindor

OGLE Cepheids have Lower Amplitudes in SMC than in LMC

5 pages with 1 figure, AASTex latex, submitted on January 24, 2000 to The Astrophysical Journal Letters

astro-ph

We selected cepheids from the OGLE database for the Magellanic Clouds in the period range 10^{1.1} < P < 10^{1.4} days. There were 33 objects in the LMC and 35 in the SMC. We find that the median amplitude of cepheids in the LMC is 18% larger than in the SMC, a 4 sigma effect. This implies that the period - flux amplitude relation is not universal, and cannot be used to measure distances accurately.

2007-05-23

astro-ph/0001418

Hui Li

Stirling A. Colgate & Hui Li (LANL)

The Magnetic Fields of the Universe and Their Origin

10 pages, 1 figure (figures.png), invited talk at IAU 195

LAUR 00-180

astro-ph

Recent rotation measure observations of a dozen or so galaxy clusters have revealed a surprisingly large amount of magnetic fields, whose estimated energy and flux are, on average, $\sim 10^{58}$ ergs and $\sim 10^{41}$ G cm$^2$, respectively. These quantities are so much larger than any coherent sums of individual galaxies within the cluster that an efficient galactic dynamo is required. We associate these fields with single AGNs within the cluster and therefore with all galaxies during their AGN phase. Only the central, massive black hole (BH) has the necessary binding energy, $\sim 10^{61}$ ergs. Only the accretion disk during the BH formation has the winding number, $\sim 10^{11}$ turns, necessary to make the gain and magnetic flux. We present a model of the BH accretion disk dynamo that might create these magnetic fields, where the helicity of the $\alpha - \Omega$ dynamo is driven by star-disk collisions. The back reaction of the saturated dynamo forms a force-free field helix that carries the energy and flux of the dynamo and redistributes them within the clusters.

2007-05-23

astro-ph/0001419

David Hogg

David W. Hogg (IAS)

Constraints on Photometric Calibration from Observations of High-Redshift Type Ia Supernovae

Submitted to AJ. Comments greatly appreciated

astro-ph

The good match of the type Ia supernova (SNIa) Hubble Diagram to the prediction of a not-unreasonable cosmological world model shows that measurements of standard stars and their comparison with point sources down to m=25 mag is good to better than +/-0.5 mag over an 11 mag range. It also shows that the true spectral energy distribution (SED) shapes of standard stars are known to better than +/-0.5 mag over an octave in wavelength. On the other hand, the SNIa argument for an accelerating Universe assumes that the magnitude system is good to much better than ~0.1 mag over the 11 mag range, and that SED shapes are known to much better than ~10 percent over an octave in wavelength. There is no independent empirical evidence for these plausible assumptions.

2007-05-23

astro-ph/0001420

Li-Xin Li

Li-Xin Li

Screw Instability and Blandford-Znajek Mechanism

10 pages, 1 figure

Astrophys.J. 531 (2000) L111

10.1086/312538

POPe-811

astro-ph

When magnetic field lines thread a rotating black hole's horizon and connect with remote astrophysical loads, the rotational energy of the black hole can be extracted through the Blandford-Znajek mechanism. Due to the rotation of the black hole, the magnetic field lines are twisted and toroidal components are generated. So poloidal electric currents are induced and the black hole's rotational energy is transported to the astrophysical loads through Poynting flux. The Blandford-Znajek mechanism has been considered to be a possible process for powering extragalactic jets. In this paper we show that due to the screw instability of magnetic field, the toroidal components of the magnetic field, and thus the poloidal currents, cannot exceed the limits given by the Kruskal-Shafranov criterion. This significantly lowers the power of the Blandford-Znajek mechanism when the loads are far from the black hole. So the Blandford-Znajek mechanism can only work efficiently within the neighborhood of the black hole. The implications of the results for the scenario of extragalactic jets powered by the Blandford-Znajek mechanism are discussed.

2009-10-31

astro-ph/0001421

Andrew P. Gould

Andrew Gould (Ohio State University)

A Natural Formalism for Microlensing

8 pages, 1 figure tells all. Interested parties are requested to vote on a proposed standard for microlensing notation given in the appendix. Submitted to ApJ

10.1086/317037

astro-ph

If the standard microlensing geometry is inverted so that the Einstein ring is projected onto the observer plane rather than the source plane, then the relations between the observables (\theta_E,\tilde r_E) and the underlying physical quantities (M,\pi_rel) become immediately obvious. Here \theta_E and \tilde r_E are the angular and projected Einstein radii, M is the mass of the lens, and \pi_rel is the lens-source relative parallax. I recast the basic formalism of microlensing in light of this more natural geometry and in terms of observables. I then find that the relations between observable and physical quantities assume an exceptionally simple form. In an appendix, I propose a set of notational conventions for microlensing.

2009-10-31

astro-ph/0001422

Masao Mori

Masao Mori (University of Tokyo), Andreas Burkert (Max-Planck-Institut fuer Astronomie)

Gas Stripping of Dwarf Galaxies in Clusters of Galaxies

9 pages, 6 figures; accepted for publication in ApJ

10.1086/309140

astro-ph

Many clusters of galaxies contain an appreciable amount of hot gas, the intracluster medium. As a consequence, gas will be stripped from galaxies that move through the inter cluster medium, if the ram pressure exceeds the internal gravitational force. We study the interaction between the intracluster medium and an extended gas component of dwarf galaxies confined by a surrounding cold dark matter halo analytically and numerically, using axisymmetric two-dimensional hydrodynamical simulations at high resolution. The results show that the gas within the dark matter halo is totally stripped in a typical galactic cluster. The process of ram pressure stripping therefore must have played an important role during the chemo-dynamical evolution of dwarf galaxies in galactic clusters. Our results predict that most of the chemical evolution of dwarf galaxies must have occurred at high redshift, before the virialized cluster had formed.

2009-10-31

astro-ph/0001423

Israel

G.L. Israel, S. Campana, S. Covino, D. Dal Fiume, T.J. Gaetz, S. Mereghetti, T. Oosterbroek, M. Orlandini, A.N. Parmar, D. Ricci and L. Stella

BeppoSAX and Chandra Observations of SAXJ0103.2-7209=2E0101.5-7225: a new Persistent 345s X-ray Pulsar in the SMC

4 pages. Accepted for publication in ApJ Letters. Emulateapj style used

10.1086/312546

astro-ph

We report the results of a 1998 July BeppoSAX observation of a field in the SMC which led to the discovery of 345s pulsations in the X-ray flux of SAXJ0103.2-7209. The BeppoSAX X-ray spectrum is well fit by an absorbed power-law with photon index 1.0 plus a black body component with kT=0.1keV. The unabsorbed luminosity in the 2-10 keV energy range is 1.2x10^{36} erg/s. In a very recent Chandra observation the 345s pulsations are also detected. The available period measurements provide a constant period derivative of -1.7s/yr over the last three years making SAXJ0103.2-7209 one of the most rapidly spinning-up X-ray pulsars known. The BeppoSAX position is consistent with that of the Einstein source 2E0101.5-7225 and the ROSAT source RXJ0103.2-7209. This source was detected at a luminosity level of few 10^{35}-10^{36} erg/s in all datasets of past X-ray missions since 1979. The ROSAT HRI and Chandra positions are consistent with that of a m_V=14.8 Be spectral type star already proposed as the likely optical counterpart of 2E0101.5-7225. We conclude that SAXJ0103.2-7209 and 2E0101.5-7225 are the same source, a relatively young and persistent X-ray pulsar in the SMC.

2009-10-31

astro-ph/0001424

Matthias Tecza

M. Tecza, R. Genzel, L. J. Tacconi, S. Anders, L. E. Tacconi-Garman and N. Thatte

Stellar Dynamics and the implications on the merger evolution in NGC6240

34 pages, 11 figures, using AASTEX 5.0rc3.1, paper submitted to the Astrophysical Journal, revised version

10.1086/309021

astro-ph

We report near-infrared integral field spectroscopy of the luminous merging galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by 1.6arcsec are the central parts of inclined, rotating disk galaxies with equal mass bulges. The dynamical masses of the nuclei are much larger than the stellar mass derived from the K-band light, implying that the progenitor galaxies were galaxies with massive bulges. The K-band light is dominated by red supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 years ago, possibly by the most recent perigalactic approach. Strong feedback effects of a superwind and supernovae are responsible for a short duration burst (~5x10^6 years) which is already decaying. The two galaxies form a prograde-retrograde rotating system and from the stellar velocity field it seems that one of the two interacting galaxies is subject to a prograde encounter. Between the stellar nuclei is a prominent peak of molecular gas (H_2, CO). The stellar velocity dispersion peaks there indicating that the gas has formed a local, self-gravitating concentration decoupled from the stellar gravitational potential. NGC 6240 has previously been reported to fit the paradigm of an elliptical galaxy formed through the merger of two galaxies. This was based on the near-infrared light distribution which follows a r^1/4-law. Our data cast strong doubt on this conclusion: the system is by far not relaxed, rotation plays an important role, as does self-gravitating gas, and the near-infrared light is dominated by young stars.

2009-10-31

astro-ph/0001425

Remo Ruffini

Remo Ruffini

Black Hole Formation and Gamma Ray Bursts

10 pages, 4 figures, to appear in the proceedings of the ESO workshop on "Black Holes in Binaries and Galactic Nuclei", in honour of Prof. R. Giacconi, edited by L. Kaper, E.P.J. van den Heuvel, and P.A. Woudt, and printed in the series ESO Astrophysics Symposia by Springer (2000)

10.1007/10720995_73

astro-ph

Recent work on the dyadosphere of a black hole is reviewed with special emphasis on the explanation of gamma ray bursts. A change of paradigm in the observations of black holes is presented.

2009-10-31

astro-ph/0001426

Garik Israelian

G. Israelian, R. Garcia Lopez and Rafael Rebolo

Early Galactic Evolution of Carbon, Nitrogen and Oxygen

10 pages, 3 figures, To appear in the proceedings of the conference "The Chemical Evolution of The Milky Way: Stars versus Clusters", eds. F. Matteucci and F. Giovannelli, Vulcano, Italy, September 20-24 1999

10.1007/978-94-010-0938-6_4

astro-ph

We present results on carbon, nitrogen, and oxygen abundances for a sample of unevolved metal-poor stars with metallicities in the range -0.3< [Fe/H]< -3. Oxygen abundances derived from different indicators are compared showing consistently that in the range 0.3 >[Fe/H]>-3.0, the [O/Fe] ratio increases from approximately 0 to 1. We find a good agreement between abundances based on the forbidden line, the OH and IR triplet lines when gravities based on Hipparcos} parallaxes are considered for the sample stars. Gravities derived from LTE ionization balance in metal-poor stars with [Fe/H]< -1 are likely too low, and could be responsible for an underestimation of the oxygen abundances derived using the [OI] line. [C/Fe] and [N/Fe] ratios appear to be constant, independently of metallicity, in the same range. However, they show larger scatter than oxygen at a given metallicity, which could reflect the larger variety of stellar production sites for these other elements.

2016-01-27

astro-ph/0001427

Pierre Billoir

Pierre Billoir, Antoine Letessier-Selvon (LPNHE Paris)

Note on the Origin of the Highest Energy Cosmic Rays

3 pages, 2 figures

astro-ph

In this note we argue that the galactic model chosen by E.-J. Ahn, G. Medina-Tanco, P.L. Bierman and T. Stanev in their paper discussing the origin of the highest energy cosmic rays, is alone responsible for the focussing of positive particles towards the North galactic pole. We discuss the validity of this model, in particular in terms of field reversals and radial extensions. We conclude that with such a model one cannot retreive any directional information from the observed direction of the cosmic rays. In particular one cannot identify point sources at least up to energies of about 200 EeV. Therefore the apparent clustering of the back-traced highest energy cosmic rays observed to date cannot be interpreted as an evidence for a point source nor for the identification of M87, which happens to be close to the North pole, as being such a source.

2007-05-23

astro-ph/0001428

L. E. Tacconi-Garman

R. Genzel (1), C. Pichon (2 and 3), A. Eckart (1), O.E. Gerhard (2), T. Ott (1) ((1) MPE, (2) Univ. Basel, (3) Obs. de Strasbourg)

Stellar Dynamics in the Galactic centre: Proper Motions and Anisotropy

35 pages, 17 figures, submitted to M.N.R.A.S

Mon.Not.Roy.Astron.Soc. 317 (2000) 348

10.1046/j.1365-8711.2000.03582.x

astro-ph

We report a new analysis of stellar dynamics in the Galactic centre, based on improved sky and LOS velocities for >100 stars within a few arcsec of SgrA*. Overall the motions do not deviate strongly from isotropy. For 32 stars with all 3 components determined the absolute, LOS and sky velocities agree well, as for a spherical cluster. The projected radial and tangential motions of all 104 pm stars are also consistent with overall isotropy. However, the projected velocities of the young, early type stars have a strong radial dependence. Most of the bright HeI stars 1-10" from SgrA* are on tangential orbits. This anisotropy of the HeI stars and most of the brighter IRS16 complex members is largely caused by a CW and counter-rotating, coherent rotation pattern. The overall rotation of the young star cluster probably is a remnant of the angular momentum in the cloud these stars formed from. The fainter, fast stars within \~1" of SgrA* appear to be largely moving on radial or very elliptical orbits. We have not detected nonlinear motion for any of them. Most of the SgrA* cluster members also are on CW orbits. Spectroscopy shows them to be early type stars. We propose that the SgrA* cluster stars are those members of the early type cluster with small angular momentum which can plunge to the vicinity of SgrA*. Our anisotropy-independent estimate of the Sun-GC distance is 7.8-8.2 kpc (+/- 0.9 kpc). We include velocity anisotropy in estimating the central mass distribution. We confirm previous conclusions that a compact central mass concentration is present and dominates the potential from 0.01-1 pc. The central mass ranges from 2.6-3.3E6 M_sun. (abridged)

2009-10-31

astro-ph/0001429

Torsten Ensslin

Torsten A. Ensslin, Christian R. Kaiser (MPI fuer Astrophysik, Garching)

Comptonization of the Cosmic Microwave Background by Relativistic Plasma

15 pages, 9 figures, Accepted by Astronomy & Astrophysics; corrected Planck sensitivity in Fig. 9; added Appendix about detectability of the Cluster rSZ Effect; added paragraph about electron cooling in radio plasma

Astron.Astrophys.360:417-430,2000

astro-ph

(Abridged) We investigate the spectral distortion of the cosmic microwave background (CMB) caused by relativistic plasma. Within the Thomson regime, an exact analytic expression for the photon scattering kernel of a momentum power-law electron distribution is given. The ultra-relativistic Sunyaev-Zeldovich (SZ) decrement measures the electron number and not the energy content. On the other hand, the relativistic SZ increment at higher frequencies depends strongly on the spectral shape of the electrons. We calculate the expected Comptonization due to the energy release of radio galaxies, which we estimate to be 3 10^66 erg Gpc^-3. We investigate Comptonization from (a) the part of the released energy which is thermalized and (b) the relativistic, remnant radio plasma, which may form a second, relativistic phase in the inter galactic medium, nearly unobservable for present day instruments (presence of so called 'radio ghosts'). We find a thermal Comptonization parameter due to (a) of y = 10^-6 and (b) an optical depth of relativistic electrons in old radio plasma of tau_rel < 10^-7. If a substantial fraction of the volume of clusters of galaxies is filled with such old radio plasma the SZ effect based determination of the Hubble constant is biased to lower values. Finally, it is shown that a supra-thermal population of electrons in the Coma cluster would produce a signature in the Wien-tail of the CMB, which is marginally detectable with a multifrequency measurement by the Planck satellite. Such a population is expected to exist, since its bremsstrahlung would explain Coma's recently reported high energy X-ray excess.

2011-05-23

astro-ph/0001430

Coel Hellier

Coel Hellier (Keele University), Jonathan Kemp, T. Naylor, Frank M. Bateson, Albert Jones, Danie Overbeek, Rod Stubbings and Koji Mukai

Outbursts of EX Hydrae: mass-transfer events or disc instabilities?

To appear in MNRAS (8 pages; 9 figs)

10.1046/j.1365-8711.2000.03301.x

astro-ph

We present the 45-yr record of EX Hya's lightcurve and discuss the characteristics of its 15 observed outbursts. We then concentrate on the 1998 outburst, reporting the first outburst X-ray observations. We discover an X-ray beat-cycle modulation, indicating that an enhanced accretion stream couples directly with the magnetosphere in outburst, confirming our previous prediction. Optical eclipse profiles late in outburst show that the visible light is dominated by an enhanced mass-transfer stream overflowing the accretion disc. We are uncertain whether the enhanced mass transfer is triggered by a disc instability, or by some other cause. While in outburst, EX Hya shows some of the characteristics of SW Sex stars.

2009-10-31

astro-ph/0001431

Jon Hakkila

David J. Haglin (1), Richard J. Roiger (1), Jon Hakkila (1), Geoffrey Pendleton (2), Robert Mallozzi (2) ((1) Minnesota State University, Mankato, (2) University of Alabam in Huntsville)

A GRB Tool Shed

5 pages, 1 figure, presented at the 5th Huntsville Gamma-Ray Burst Symposium

10.1063/1.1361659

astro-ph

We describe the design of a suite of software tools to allow users to query Gamma-Ray Burst (GRB) data and perform data mining expeditions. We call this suite of tools a shed (SHell for Expeditions using Datamining). Our schedule is to have a completed prototype (funded via the NASA AISRP) by February, 2002. Meanwhile, interested users will find a partially functioning tool shed at http://grb.mankato.msus.edu.

2009-10-31

astro-ph/0001432

Eleonora Kotok

D. Novikov (1,2,3,4), P. Naselsky (5,6), H.E. Jorgensen (3), P.R. Christensen(5,7), I. Novikov(3,4,5,8), H.U. Norgaard-Nielsen(9) ((1) Ludwig Maximilians Universitat, (2) University of Oxford,(3)Copenhagen University Observatory, (4) Astro-Space Center of P.N. Lebedev Physical Institute, (5) Theoretical Astrophysics Center,(6)Rostov State University, (7) Niels Bohr Institute, (8) NORDITA,(9) Danish Space Research Institute)

Power filtration of CMB observational data

17 pages; 4 figures; submitted to International Journal of Modern Physics

10.1142/S0218271801000950

astro-ph

We propose a power filter Gp for linear reconstruction of the CMB signal from observational maps. This Gp filter preserves the power spectrum of the CMB signal in contrast to the Wiener filter which diminishes the power spectrum of the reconstructed CMB signal. We demonstrate how peak statistics and a cluster analysis can be used to estimate the probability of the presence of a CMB signal in observational records. The efficiency of the Gp filter is demonstrated on a toy model of an observational record consisting of a CMB signal and noise in the form of foreground point sources.

2016-08-16

astro-ph/0001433

Torsten Ensslin

Torsten A. Ensslin (MPI fuer Astrophysik, Garching)

Theoretical Implications of Diffuse Non-Thermal Emission from Clusters of Galaxies

8 pages, 2 figures, LaTeX, uses newpasp.sty, invited talk at IAU 199 `The Universe at Low Radio Frequencies' in Pune, India, 1999

astro-ph

A short review on theoretical implications of non-thermal emission (radio, extreme ultraviolet, high energy X-ray) from the intra-cluster medium is given. The origin of cluster radio halos and cluster radio relics is discussed within the framework of a network of processes producing a non-thermal electron population. Emphasis is given to the role of old, remnant, presently invisible relativistic plasma released by former radio galaxies.

2007-05-23

astro-ph/0001434

Leo Alberto Girardi

Leo Girardi (Padova)

Broad-band colour evolution of star clusters

6 pages, to appear in proc. of Strasbourg workshop "Massive Stellar Clusters", ASP Conf. Ser., eds. A. Lancon, C. Boily

astro-ph

We briefly review the main features in the broad-band colour evolution of star clusters, over the complete age interval from 10^7 to 10^(10) yr. The emphasis is in the problem of age-dating distant young clusters (<2 Gyr) from their integrated colours. It is shown that U-B and B-V are less sensitive to metallicity than colours involving red pass-bands, like V-I, at least up to ages of some few Gyr. Since U-B and B-V are determined by well-understood and well-populated evolutionary stages, they are also less affected by theoretical uncertainties and by the ubiquitous effect of stochastic colour dispersion. The latter effects become important for the V-K colour. Thus, we argue that U-B and B-V are, presently, the more suitable broad-band colours for age-dating distant clusters. For other potentially useful colours like V-R and V-I, empirical tests of their evolution are still missing.

2007-05-23

astro-ph/0001435

David R. Alves

C. Alcock, R.A. Allsman, D.R. Alves, T.S. Axelrod, A. Basu, A.C. Becker, D.P. Bennett, K.H. Cook, A.J. Drake, K.C. Freeman, M. Geha, K. Griest, L. King, M.J. Lehner, S.L. Marshall, D. Minniti, C. Nelson, B.A. Peterson, P. Popowski, M.R. Pratt, P.J. Quinn, C.W. Stubbs, W. Sutherland, A.B. Tomaney, T. Vandehei, D.L. Welch (The MACHO Collaboration)

The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud

to appear in the Astronomical Journal, 49 pages, 12 figures, aaspp4.sty

10.1086/301326

astro-ph

We present a 9 million star color-magnitude diagram (9M CMD) of the LMC bar. The 9M CMD reveals a complex superposition of different age and metallicity stellar populations, with important stellar evolutionary phases occurring over 3 orders of magnitude in number density. First, we count the non-variable supergiants, the associated Cepheids, and measure the effective temperatures defining the instability strip. Lifetime predictions of stellar evolution theory are tested, with implications for the origin of low-luminosity Cepheids. The highly-evolved AGB stars have a bimodal distribution in brightness, which we interpret as discrete old populations (>1 Gyr). The faint AGB may be metal-poor and very old. We identify the clusters NGC 411 and M3 as templates for the admixture of old stellar populations. However, there are indications that the old and metal-poor field population has a red HB morphology: the RR Lyraes lie on the red edge of the instability strip, the AGB-bump is very red, and the ratio of AGB-bump stars to RR Lyraes is quite large. If the HB second parameter is age, the old and metal-poor field population likely formed after the oldest clusters. Lifetime predictions of stellar evolution theory lead us to associate a significant fraction of the red HB clump giants with the same old and metal-poor population producing the RR Lyraes and the AGB-bump. In this case, compared to the age-dependent luminosity predictions of stellar evolution theory, the red HB clump is too bright relative to the RR Lyraes and AGB-bump. Last, the surface density profile of RR Lyraes is fit by an exponential, favoring a disk-like rather than spheroidal distribution. We conclude that the age of the LMC disk is probably similar to the age of the Galactic disk. (ABRIDGED)

2009-10-31

astro-ph/0001436

Luigi Piro

Luigi Piro (IAS/CNR, Roma)

X-Ray Afterglows of Gamma-Ray Bursts

14 pages, 8 figures, Proc.s. of "X-Ray Astronomy '99:Stellar Endpoints, AGN and the Diffuse X-ray Background", September 6-10, 1999, CNR Bologna

10.1063/1.1434643

astro-ph

The afterglow emission has become the main stream of Gamma-Ray burst research since its discovery three years ago. With the distance-scale enigma solved, the study of the late-time GRB emission is now the most promising approach to disclose the origin of these explosions and their relationship with the environment of the host galaxy in the early phase of the Universe. In this contribution I will review X-ray observations and their implication on our undertstanding on the GRB phenomenon. These measurements are providing a direct probe into the nature of the progenitor and a measurement of the GRB beaming properties, crucial to establish the total energy output. Some evidence of iron lines connects the GRB explosion with massive progenitors, thence with star-forming regions. Furthermore a comparison of the spectral properties with the temporal evolution indicates that the fireball expansion should not be - on average - highly collimated, with a jet angle $>10 \deg$.

2009-10-31

astro-ph/0001437

Lorenzo Natalucci

L. Natalucci, A. Bazzano, M. Cocchi, P. Ubertini, J. Heise, E. Kuulkers, J.J.M. in 't Zand, M.J.S. Smith

SAX J1810.8-2609: A New Hard X-ray Bursting Transient

15 pages, 4 figures, accepted for publication in ApJ

10.1086/308987

astro-ph

The transient X-ray source SAX J1810.8-2609 was discovered on 1998, March 10 with the Wide Field Cameras on board the BeppoSAX satellite, while observing the Galactic Bulge in the 2-28 keV energy range. On March 11, a strong type-I X-ray burst was detected with evidence of photospheric radius expansion. A follow-up target of opportunity observation with the Narrow-Field Instruments (NFI) was performed on March 11 and 12, for a total elapsed time of 8.51 x 10^{4} s. The wide band spectral data (0.1-200 keV) obtained with the NFI show a remarkable hard X-ray spectrum detected up to ~200 keV, which can be described by a power law with photon spectral index Gamma=1.96\pm0.04, plus a soft component which is compatible with blackbody radiation of temperature kT~0.5 keV. The detection of the type-I X-ray burst is a strong indication that the compact object is a neutron star in a low mass X-ray binary system. Assuming standard burst parameters and attributing the photospheric radius expansion to near Eddington luminosity, we estimate a distance of ~5 kpc. The inferred 2-10 keV X-ray luminosity is ~ 9 x 10^{35} erg/s at the time of the discovery.

2009-10-31

astro-ph/0001438

Robert L. Kehoe

Carl Akerlof, Richard Balsano, Scott Barthelmy, Jeff Bloch, Paul Butterworth, Don Casperson, Tom Cline, Sandra Fletcher, Fillippo Frontera, Galen Gisler, John Heise, Jack Hills, Kevin Hurley, Robert Kehoe, Brian Lee, Stuart Marshall, Tim McKay, Andrew Pawl, Luigi Piro, John Szymanski and Jim Wren

Prompt Optical Observations of Gamma-ray Bursts

4 pages, 3 figures, submitted to ApJ Letters

10.1086/312567

astro-ph

The Robotic Optical Transient Search Experiment (ROTSE) seeks to measure simultaneous and early afterglow optical emission from gamma-ray bursts (GRBs). A search for optical counterparts to six GRBs with localization errors of 1 square degree or better produced no detections. The earliest limiting sensitivity is m(ROTSE) > 13.1 at 10.85 seconds (5 second exposure) after the gamma-ray rise, and the best limit is m(ROTSE) > 16.0 at 62 minutes (897 second exposure). These are the most stringent limits obtained for GRB optical counterpart brightness in the first hour after the burst. Consideration of the gamma-ray fluence and peak flux for these bursts and for GRB990123 indicates that there is not a strong positive correlation between optical flux and gamma-ray emission.

2009-10-31

astro-ph/0001439

Richard P. Nelson

Richard P. Nelson & John C.B. Papaloizou

Hydrodynamic Simulations of the Bardeen-Petterson Effect

18 pages, 14 figures. Accepted for publication in M.N.R.A.S. A version with posctcript figures included can be obtained from http://www.maths.qmw.ac.uk/~rpn

Mon.Not.Roy.Astron.Soc. 315 (2000) 570

10.1046/j.1365-8711.2000.03478.x

astro-ph

We present SPH simulations of accretion discs in orbit about rotating compact objects such as black holes and neutron stars, and study the structure of warped discs produced by the Bardeen-Petterson effect. We calculate the transition radius out to which the disc specific angular momentum vector is aligned with that of the black hole. We focus on the parameter regime where the warp dynamics are controlled by bending wave propagation, but also consider models in which warps are subject to diffusion rather than wave transport, and are able to consider the fully nonlinear regime. Because of hydrodynamic or pressure effects, for the parameter range investigated, the transition radius is always found to be much smaller than that obtained by Bardeen & Petterson (1975). For discs with midplane Mach numbers of about 10, the transition occurs between 10 - 16 gravitational radii, whereas for a Mach number of about 30 it occurs at around 30 gravitational radii. A thicker disc with a Mach number of 5 is found to produce no discernible warped structure. The rate of black hole - disc alignment is found to be consistent with the ideas of Ress (1978), with the alignment torque behaving as if it arises from the accreted material transferring its misaligned component of angular momentum at the larger transition radius of Bardeen & Petterson (1975). The inclusion of Einstein precession in the calculations modified both the warped disc structure and, consistent with linear analysis, produced an increased alignment rate by up to a factor of 4 because of the effect that a non Keplerian potential has on the propagation of warps.

2009-10-31

astro-ph/0001440

Kenneth M. Nollett

Kenneth M. Nollett and Scott Burles

Estimating reaction rates and uncertainties for primordial nucleosynthesis

20 pages, 17 figures, accepted for publication in Physical Review D

Phys.Rev. D61 (2000) 123505

10.1103/PhysRevD.61.123505

astro-ph

We present a Monte Carlo method for direct incorporation of nuclear inputs in primordial nucleosynthesis calculations. This method is intended to remedy shortcomings of current error estimation, by eliminating intermediate data evaluations and working directly with experimental data, allowing error estimation based solely on published experimental uncertainties. This technique also allows simple incorporation of new data and reduction of errors with the introduction of more precise data. Application of our method indicates that previous error estimates on the calculated abundances were too large by as much as a factor of three. Since uncertainties in the BBN calculation currently dominate inferences drawn from light-element abundances, the re-estimated errors have important consequences for cosmic baryon density, neutrino physics, and lithium depletion in halo stars. Our direct method allows detailed discussion of the status of the nuclear inputs, by identifying clearly the places where improved cross section measurements would be most useful.

2009-10-31

astro-ph/0001441

Matt Visser

Bruce A. Bassett (University of Oxford, Portsmouth University), Stefano Liberati (SISSA, INFN; Trieste), Carmen Molina-Paris (Los Alamos), Matt Visser (Washington University in Saint Louis)

Geometrodynamics of Variable-Speed-of-Light Cosmologies

19 pages, latex 209, revtex 3.1; To appear in Physical Review D; Numerous small changes of presentation and emphasis; new section on the entropy problem; references updated; central results unaffected

Phys.Rev.D62:103518,2000

10.1103/PhysRevD.62.103518

PU-RCG-99/25

astro-ph gr-qc hep-ph

This paper is dedicated to the memory of Dennis Sciama. Variable-Speed-of-Light (VSL) cosmologies are currently attracting interest as an alternative to inflation. We investigate the fundamental geometrodynamic aspects of VSL cosmologies and provide several implementations which do not explicitly break Lorentz invariance (no "hard" breaking). These "soft" implementations of Lorentz symmetry breaking provide particularly clean answers to the question "VSL with respect to what?". The class of VSL cosmologies we consider are compatible with both classical Einstein gravity and low-energy particle physics. These models solve the "kinematic" puzzles of cosmology as well as inflation does, but cannot by themselves solve the flatness problem, since in their purest form no violation of the strong energy condition occurs. We also consider a heterotic model (VSL plus inflation) which provides a number of observational implications for the low-redshift universe if chi contributes to the "dark energy" either as CDM or quintessence. These implications include modified gravitational lensing, birefringence, variation of fundamental constants and rotation of the plane of polarization of light from distant sources.

2014-10-13

astro-ph/0001442

J. Robert Buchler

Zoltan Kollath, J. Robert Buchler & Michael Feuchtinger

RR Lyrae - Theory vs Observation

6 pages, 5 figures (revised april 2000, revisions relatively minor)

ApJ, Vol. 540, p. 468-473 (2000)

10.1086/309330

astro-ph

The luminosities, effective temperatures and metallicities that are derived empirically by Kovacs and Jurcsik from the light curves of a large number of globular cluster and field RRab and RRc stars are compared to theoretical RR Lyrae models. The strong luminosity dependence of the empirical blue and red edges (Log L vs Log Teff diagram) is in disagreement with that of both radiative and convective models. A reexamination of the theoretical uncertainties in the modelling leads us to conclude that the disagreement is irreconcilable.

2009-10-31

astro-ph/0001443

Kan Chen

Per Bak and Kan Chen

Scale Dependent Dimension of Luminous Matter in the Universe

6 pages, 2 figures

10.1103/PhysRevLett.86.4215

astro-ph cond-mat.stat-mech nlin.AO

We present a geometrical model of the distribution of luminous matter in the universe, derived from a very simple reaction-diffusion model of turbulent phenomena. The apparent dimension of luminous matter, $D(l)$, depends linearly on the logarithm of the scale $l$ under which the universe is viewed: $D(l) \sim 3\log(l/l_0)/\log(\xi/l_0)$, where $\xi$ is a correlation length. Comparison with data from the SARS red-shift catalogue, and the LEDA database provides a good fit with a correlation length $\xi \sim 300$ Mpc. The geometrical interpretation is clear: At small distances, the universe is zero-dimensional and point-like. At distances of the order of 1 Mpc the dimension is unity, indicating a filamentary, string-like structure; when viewed at larger scales it gradually becomes 2-dimensional wall-like, and finally, at and beyond the correlation length, it becomes uniform.

2009-10-31

astro-ph/0001444

Sarbani Basu

Sarbani Basu and H. M. Antia

Possible solar cycle variations in the convection zone

To appear in Solar Physics

Solar Phys. 192 (2000) 449

10.1023/A:1005232901528

astro-ph

Using data from the Global Oscillations Network Group (GONG) that covers the period from 1995 to 1998 we study the change in frequencies of solar oscillations with solar activity. From these frequencies we attempt to determine any possible variation in solar structure with solar activity. We do not find any evidence of a change in the convection zone depth or extent of overshoot below the convection zone during the solar cycle.

2015-06-24

astro-ph/0001445

JieHao Huang

L. Ji, Y. Chen, J. H. Huang, Q. S. Gu, S. J. Lei (Department of Astronomy, Nanjing University, Nanjing, China)

The FIR-Radio Correlation of Wolf-Rayet Galaxies and the Role of Star Formation in LINERs

9 pages, 4 figures, to be published in Astronomy & Astrophysics

astro-ph

We find that a preliminary classification of LINERs' energetics may be made in terms of the FIR-radio correlation of Wolf-Rayet galaxies. The AGN- or starburst-supported LINERs can be distinguished by their FIR-to-radio ratio, $Q\equiv L(1.4{\rm GHz})/$ $L(60\mu{\rm m})>$ or $<0.01$. It is interesting to note that almost all the LINERs with inner rings might be starburst- supported, indicating reduced AGN activities compared with those of the AGN-supported ones. We also find that a shock-heating phase for the warm dust component might be important for some starbursts at the burst age of $\ge 10^{7}$ yr, with $Q<0.001$.

2007-05-23

astro-ph/0001446

Myeong-Gu Park

Myeong-Gu Park (1) and Jeremiah P. Ostriker (2) ((1) Kyungpook National University, Korea, (2) Princeton University)

Preheated Advection Dominated Accretion Flow

41 pages with 10 postscript figures (aastex5). Submitted to ApJ

10.1086/319042

KNUAST-00-01-01

astro-ph

All high temperature accretion solutions including ADAF are physically thick, so outgoing radiation interacts with the incoming flow, sharing as much or more resemblance with classical spherical accretion flows as with disk flows. We examine this interaction for the popular ADAF case. We find that without allowance for Compton preheating, a very restricted domain of ADAF solution is permitted and with Compton preheating included a new high temperature PADAF branch appears in the solution space. In the absence of preheating, high temperature flows do not exist when the mass accretion rate mdot == Mdot c^2 / L_E >~ 10^-1.5. Below this mass accretion rate, a roughly conical region around the hole cannot sustain high temperature ions and electrons for all flows having mdot >~ 10^-4, which may lead to a funnel possibly filled with a tenuous hot outgoing wind. If the flow starts at large radii with the usual equilibrium temperature ~10^4 K, the critical mass accretion rate is much lower, mdot \~10^-3.7 above which level no self-consistent ADAF (without preheating) can exist. However, above this critical mass accretion rate, the flow can be self-consistently maintained at high temperature if Compton preheating is considered. These solutions constitute a new branch of solutions as in spherical accretion flows. High temperature PADAF flows can exist above the critical mass accretion rate in addition to the usual cold thin disk solutions. We also find solutions where the flow near the equatorial plane accretes normally while the flow near the pole is overheated by Compton preheating, possibly becoming, a polar wind, solutions which we designate WADAF.

2009-10-31

astro-ph/0001447

Tomoyuki Hanawa

Tomoyuki Hanawa and Tomoaki Matsumoto

Growth of a Vortex Mode during Gravitational Collapse Resulting in Type II Supernova

AAS LaTeX, 14 pages including 6 figures, submitted to Astrophysical Journal in January

10.1086/309370

DPNU-00-03

astro-ph

We investigate stability of a gravitationally collapsing iron core against non-spherical perturbation. The gravitationally collapsing iron core is approximated by a similarity solution for dynamically collapsing polytropic gas sphere. We find that the similarity solution is unstable against non-spherical perturbations. The perturbation grows in proportion to $ (t - t_0) ^{-\sigma} $ while the the central density increases in proportion to $ (t - t_0) ^{-2} $. The growth rate is $ \sigma = 1/3 + \ell (\gamma - 4/3) $, where $ \gamma $ and $ \ell $ denote the polytropic index and the parameter $ \ell $ of the spherical harmonics, $ Y_{\ell} ^m (\theta, \phi) $, respectively. The growing perturbation is dominated by vortex motion. Thus it excites global convection during the collapse and may contribute to material mixing in a type II supernova.

2009-10-31

astro-ph/0001448

Wolfgang Vieser

Wolfgang Vieser and Gerhard Hensler

Evaporation and Condensation Processes of Giant Molecular Clouds in a Hot Plasma

to appear in: 1999, Proc. "Astrophysical Dynamics", eds. D. Berry et al., Astroph. Sp. Sci., in press

Astrophys.Space Sci. 272 (2000) 189-196

10.1023/A:1002684126855

astro-ph

2d hydrodynamical simulations are performed to examine the evaporation and condensation processes of giant molecular clouds in the hot phase of the interstellar medium. The evolution of cold and dense clouds is calculated in the subsonic stream of a hot tenuous plasma. Our code includes self-gravity, heating and cooling processes and heat conduction by electrons. Significant differences occur between simulations with and without heat conduction.

2009-10-31

astro-ph/0001449

Federica Govoni

F. Govoni, R. Falomo, G. Fasano, R. Scarpa

Optical surface photometry of radio galaxies - II. Observations and data analysis

9 pages, plus 17 .gif figures, accepted by Astronomy and Astrophysics, Supplement Series

10.1051/aas:2000338

astro-ph

Optical imaging observations for 50 radio galaxies are presented. For each object isophotal contours, photometric profiles, structural parameters (position angle, ellipticity, Fourier coefficients), and total magnitudes are given. These observations, obtained in the Cousins R band, complement the data presented in a previous paper and are part of a larger project aimed at studying the optical properties of low redshift (z<0.12) radio galaxies (Govoni et al. 1999). Comments for each individual source are reported.

2009-10-31

astro-ph/0001450

Marat Gilfanov

M. Gilfanov (1,2), E.Churazov (1,2) and M. Revnivtsev (2,1) ((1) MPA, Garching; (2)IKI, Moscow)

Frequency resolved spectroscopy of Cyg X-1: fast variability of the reflected emission in the soft state

submitted to MNRAS

Mon.Not.Roy.Astron.Soc. 316 (2000) 923

10.1046/j.1365-8711.2000.03686.x

astro-ph

Using the RXTE/PCA data we study the fast variability of the reflected emission in the soft spectral state of Cyg X-1 by means of Fourier frequency resolved spectroscopy. We find that the rms amplitude of variations of the reflected emission has the same frequency dependence as the primary radiation down to time scales of <30-50 msec. This might indicate that the reflected flux reproduces, with nearly flat response, variations of the primary emission. Such behavior differs notably from the hard spectral state, in which variations of the reflected flux are significantly suppressed in comparison with the primary emission, on time scales shorter than ~0.5-1 sec. If related to the finite light crossing time of the reflector, these results suggest that the characteristic size of the reflector -- presumably an optically thick accretion disk, in the hard spectral state is larger by a factor of >5-10 than in the soft spectral state. Modeling the transfer function of the disk, we estimate the inner radius of the accretion disk R_in~100R_g in the hard and R_in<10R_g in the soft state for a 10M_sun black hole.

2009-10-31

astro-ph/0001451

Youichi Ohyama

Youichi Ohyama, Michitoshi Yoshida, Tadafumi Takata, Masatoshi Imanishi, Tomonori Usuda, Yoshihiko Saito, Hiroko Taguchi, Noboru Ebizuka, Fumihide Iwamuro, Kentaro Motohara, Tomoyuki Taguchi, Takashi Hata, Toshinori Maihara, Masanori Iye, Toshiyuki Sasaki, George Kosugi, Ryusuke Ogasawara, Junichi Noumaru, Yoshihiko Mizumoto, Masafumi Yagi, Yoshihiro Chikada

Superwind-Driven Intense H_2 Emission in NGC 6240

33 pages, 9 figures, accepted for publication in PASJ

10.1093/pasj/52.4.563

astro-ph

We have performed a long-slit K band spectroscopic observation of the luminous infrared galaxy NGC 6240. The peak position of the H_2 v=1-0 S(1) emission in the slit is located ~0.3" - 0.4" north of the southern nucleus. It is almost the midpoint between the southern nucleus and the peak position of the ^12CO J=1-0 emission. Based on the line-ratio analyses, we suggest the excitation mechanism of H_2 is pure thermal at most positions. In the southern region we find the following three velocity components in the H_2 emission: the blueshifted shell component (~-250 km s^-1 with respect to V_sys) which is recognized as a distinct C-shape distortion in the velocity field around the southern nucleus, the high-velocity blueshifted ``wing'' component (~-1000 km s^-1 with respect to V_sys), and the component indicating possible line splitting of ~500 km s^-1. The latter two components are extended to the south from the southern nucleus. We show that the kinematic properties of these three components can be reproduced by expanding motion of a shell-like structure around the southern nucleus. The offset peak position of the H_2 emission can be understood if we assume that the shell expanding to the north interacts with the extragalactic molecular gas. At the interface between the shell and the molecular gas concentration the cloud-crushing mechanism proposed by Cowie et al. (1981) may work efficiently, and the intense H_2 emission is thus expected there. All these findings lead us to propose a model that the most H_2 emission is attributed to the shock excitation driven by the superwind activity of the southern nucleus.

2015-06-24

astro-ph/0001452

Takashi Murayama

Yoshiaki Taniguchi, Takashi Murayama, Hideaki Mouri

Dusty Tori of Seyfert Nuclei

8 pages, to appear in `ASCA/ROSAT Workshop on AGN and the X-ray Background', Tokyo, Nov. 1-3, 1999, eds. T. Takahashi and H. Inoue

astro-ph

Dusty tori around active galactic nuclei (AGNs) play an important role in the classification of Seyfert galaxies. Therefore, physical properties of dusty tori are of great interest. We briefly introduce three statistical studies investigating properties of dusty tori; 1) physical sizes of dusty tori based on water-vapor maser emission, 2) ionization condition of the inner wall of tori based on high-ionization emission lines, and 3) viewing angle toward dusty tori based on mid-infrared color.

2007-05-23

astro-ph/0001453

Angelo Loinger

A.Loinger (Dipartimento di Fisica, Universita' di Milano, Italy)

On continued gravitational collapse

5 pages, PDF, submitted to Il Nuovo Cimento

astro-ph gr-qc

According to a widespread idee fixe, the spherically-symmetric collapse of a sufficiently massive celestial body of spherical shape should generate a black hole. I prove that this process generates simply an ordinary point mass. My argument is model-independent.

2007-05-23

astro-ph/0001454

Frank Eisenhauer

F. Eisenhauer, M. Tecza, N. Thatte, S. Mengel, R. Hofmann and R. Genzel

Near-Infrared-Spectroscopy with Extremely Large Telescopes: Integral-Field- versus Multi-Object-Instruments

8 pages, 4 figures (converted to bitmap), to appear in the proceedings of the Workshop on Extremely Large Telescopes, Sweden, June 1-2, 1999, uses spie.sty (V0.91) and spiebib.bst (V0.91)

astro-ph

Integral-field-spectroscopy and multi-object-spectroscopy provide the high multiplex gain required for efficient use of the upcoming generation of extremely large telescopes. We present instrument developments and designs for both concepts, and how these designs can be applied to cryogenic near-infrared instrumentation. Specifically, the fiber-based concept stands out the possibility to expand it to any number of image points, and its modularity predestines it to become the new concept for multi-field-spectroscopy. Which of the three concepts --- integral-field-, multi-object-, or multi-field-spectroscopy --- is best suited for the largest telescopes is discussed considering the size of the objects and their density on the sky.

2007-05-23

astro-ph/0001455

Kristy K. Dyer

Kristy K. Dyer, Stephen P. Reynolds, Kazik J. Borkowski

Low Frequency Insights Into Supernova Remnants

To appear in conference proceedings for "The Universe at Low Frequencies" IAU 199 ASP

astro-ph

Low frequency observations at 330 and 74 MHz can provide new insights into supernova remnants (SNR). We can test theoretical predictions for spectral index variations. Nonlinear models of shock acceleration predict that the spectra from young SNR should be slightly concave rather than power laws -- flattening toward higher energies. However, few SNR are bright and compact enough to be studied at millimeter wavelengths, restricting studies to the small range from 6 to 20 cm (a factor of 1.7 in electron energies). Observations at 330 MHz increase the electron energy baseline to a factor of 4, while providing sensitivity to larger spatial scales that are resolved out by centimeter-wavelength interferometers. Such observations can also separate thermal from nonthermal emission and detect excess free-free absorption associated with cool gas in remnants. Wide field images also provide an efficient census of both thermal and nonthermal sources over a large region.

2007-05-23

astro-ph/0001456

Fronefield Crawford

Fronefield Crawford (MIT), Victoria M. Kaspi (MIT), Jon F. Bell (ATNF)

A Search for Sub-millisecond Pulsations in Unidentified FIRST and NVSS Radio Sources

8 pages, including 2 tables and 1 figure. Accepted for publication in AJ

Astron.J.119:2376-2381,2000

10.1086/301329

astro-ph

We have searched 92 unidentified sources from the FIRST and NVSS 1400 MHz radio survey catalogs for radio pulsations at 610 MHz. The selected radio sources are bright, have no identification with extragalactic objects, are point-like and are more than 5% linearly polarized. Our search was sensitive to sub-millisecond pulsations from pulsars with dispersion measures (DMs) less than 500 pc cm-3 in the absence of scattering. We have detected no pulsations from these sources and consider possible effects which might prevent detection. We conclude that as a population, these sources are unlikely to be pulsars.

2008-11-26

astro-ph/0001457

Massimo Turatto

Massimo Turatto (Osservatorio di Padova)

The present rate of Supernovae

9 pages, Latex, 1 figure, To appear in the proceedings of the conference "The Chemical Evolution of The Milky Way: Stars versus Clusters", eds. F. Matteucci and F. Giovannelli, Vulcano, Italy, September 20-24 1999

10.1007/978-94-010-0938-6_36

astro-ph

We present and discuss the most recent determination of the rate of Supernovae in the local Universe. A comparison with other results shows a general agreement on the gross values but still significant differences on the values of the rates of various SN rates in different kinds of galaxies. The rate of SNe, used as a probe of Star Formation, confirms the young progenitor scenario for SNII+Ib/c. The increasing diversity of SNe reflects also in the SN yields which may affect the chemical evolution of the Galaxy but, because of the limited statistics, we cannot estimate the contributions of the new subtypes yet. It is also expected that in a few years observational determinations of the SN rates at various look-back times will be available.

2016-01-27

astro-ph/0001458

H. C. Spruit

H.C. Spruit and F. Haardt

The X-ray spectrum of a disk illuminated by ions

7p, to appear in Monthly Notices

Mon.Not.Roy.Astron.Soc. 315 (2000) 751

10.1046/j.1365-8711.2000.03483.x

astro-ph

The X-ray spectrum from a cool disk embedded in an ion supported torus is computed. The interaction of the hot ions with the disk increases the hard X-ray luminosity of the system}. A surface layer of the disk is heated by the protons from the torus. The Comptonized spectrum produced by this layer has a shape that depends only weakly on the incident energy flux and the distance from the accreting compact object. It consists of a `blue bump' of unComptonized soft photons and a flat high energy tail, reminiscent of the observed spectra. The hard tail becomes flatter as the thermalization depth in the cool disk is increased. Further evidence for ion illumination are the Li abundance in the secondaries of low mass X-ray binaries and the 450 keV lines sometimes seen in black-hole transient spectra.

2009-10-31

astro-ph/0001459

Andrew Thean

Andy Thean (1,2), Alan Pedlar (2), Marek J. Kukula (3), Stefi A. Baum (4) and Christopher P. O'Dea (4) ((1) Istituto di Radioastronomia, Bologna, (2) Jodrell Bank, Cheshire, (3) Royal Observatory, Edinburgh, (4) Space Telescope Science Institute, Baltimore)

High-resolution radio observations of Seyfert galaxies in the extended 12-micron sample - I. The observations

(17 pages) For full image quality and ascii data lists see http://www.jb.man.ac.uk/~ahct/database.html

10.1046/j.1365-8711.2000.03401.x

astro-ph

We present 8.4 GHz VLA A-configuration observations of 87 sources from the mid-infrared-selected AGN sample of Rush et al (1993). These 0.25 arcsec resolution observations allow elongated radio structures tens of parsecs in size to be resolved and enable radio components smaller than 3.5 arcsec to be isolated from diffuse galactic disc emission. When combined with previous data, matched radio observations covering ninety percent of the sample have been collected and these represent the largest sub-arcsecond-resolution radio imaging survey of a homogeneously-selected sample of Seyfert galaxies to date. We use our observations to identify 5 radio-loud AGN in the sample. The nature of the radio emission from Seyfert nuclei will be discussed in subsequent papers.

2009-10-31

astro-ph/0001460

Donald A. Smith

Hale Bradt, Alan M. Levine, Ronald A. Remillard, Donald A. Smith (MIT)

Transient X--Ray Sources Observed with the Rxte All-Sky Monitor after 3.5 Years

16 Pages, 6 Figures, To appear in the proceedings of the Vulcano May 1999 Workshop: Multifrequency Behaviour of High Energy Cosmic Sources: III, F. Giovannelli and Lola Sabau-Graziati (eds.), Mem SAIt, Vol 71, (2000)

astro-ph

We present light curves of a sample of "transient" sources observed with the All-Sky Monitor (ASM) of the Rossi X-ray Timing Explorer (RXTE). The light curves extend over 3.5 years. They are presented in three groups: six neutron-star systems, eight black-hole-candidate systems, and an additional diverse set of six objects that are either transient sources (in the sense of usually being undetectable) or persistent sources showing transient behavior. The outburst profiles of these sources show reproducible characteristics within one source and from source to source, as well as large variations. These profiles together with the profiles of the hardness ratios from the ASM are a valuable resource for the understanding of accretion instabilities. We summarize briefly some recent work by observers on these somewhat arbitrarily selected sources.

2007-05-23

astro-ph/0001461

G. Helou, N. Y. Lu (1), M. W. Werner (2), S. Malhotra and N. Silbermann (1) ((1) IPAC/Caltech, (2) JPL)

The Mid-Infrared Spectra of Normal Galaxies

10 pages, 2 figures, uses AAS LaTeX; to appear in the Astrophysical Journal Letters

10.1086/312549

astro-ph

The mid-infrared spectra (2.5 to 5 and 5.7 to 11.6 mu) obtained by ISO-PHOT reveal the interstellar medium emission from galaxies powered by star formation to be strongly dominated by the aromatic features at 6.2, 7.7, 8.6 and 11.3 mu. Additional emission appears in-between the features, and an underlying continuum is clearly evident at 3-5 mu. This continuum would contribute about a third of the luminosity in the 3 to 13 mu range. The features together carry 5 to 30% of the 40-to-120 mu `FIR' luminosity. The relative fluxes in individual features depend very weakly on galaxy parameters such as the far-infrared colors, direct evidence that the emitting particles are not in thermal equilibrium. The dip at 10 mu is unlikely to result from silicate absorption, since its shape is invariant among galaxies. The continuum component has a f_nu \~ nu^{0.65} shape between 3 and 5 mu and carries 1 to 4% of the FIR luminosity; its extrapolation to longer wavelengths falls well below the spectrum in the 6 to 12 mu range. This continuum component is almost certainly of non-stellar origin, and is probably due to fluctuating grains without aromatic features. The spectra reported here typify the integrated emission from the interstellar medium of the majority of star-forming galaxies, and could thus be used to obtain redshifts of highly extincted galaxies up to z=3 with SIRTF.

2009-10-31

astro-ph/0001462

Matthew Bate

Ian A. Bonnell

Competitive Accretion in Clusters and the IMF

Proc. of 33rd ESLAB Symp. "Star Formation from the Small to the Large Scale" (F. Favato, A.A. Laas & A. Wilson Eds, ESA SP-445, 2000). 10 pages, incl. 5 figures

astro-ph

Observations have revealed that most stars are born in clusters. As these clusters typically contain more mass in gas than in stars, accretion can play an important role in determining the final stellar masses. Numerical simulations of gas accretion in stellar clusters have found that the stars compete for the available reservoir of gas. The accretion rates are highly nonuniform and are determined primarily by each star's position in the cluster. Stars in the centre accrete more gas, resulting in initial mass segregation. This competitive accretion naturally results in a mass spectrum and is potentially the dominant mechanism for producing the initial mass function. Furthermore, accretion on to the core of a cluster forces it to shrink, which may result in formation of massive stars through collisions.

2007-05-23

astro-ph/0001463

Emanuele Berti

Valeria Ferrari, Marco D'Andrea, Emanuele Berti

Gravitational waves emitted by extrasolar planetary systems

14 pages, 5 figures. Accepted for publication on International Journal of Modern Physics D. Table 6 and minor typos corrected

Int.J.Mod.Phys. D9 (2000) 495-509

10.1142/S0218271800000530

astro-ph gr-qc

In this paper we consider the Extra-solar Planetary Systems recently discovered in our Galaxy as potential sources of gravitational waves. We estimate the frequency and characteristic amplitude of the radiation they emit due to the orbital motion, using the quadrupole formalism. In addition, we check whether the conditions needed for the resonant excitation of the f- and g-modes of the central star can be fulfilled. By a Roche-lobe analysis, we show that there could exist systems in which the low-order g-modes could be excited, although this does not happen in the systems discovered up to now.

2009-10-31

astro-ph/0001464

Franziska Brachwitz

Franziska Brachwitz, David J. Dean, W. Raphael Hix, Koichi Iwamoto, Karlheinz Langanke, Gabriel Martinez-Pinedo, Ken'ichi Nomoto, Michael R. Strayer, Friedrich-K. Thielemann, Hideyuki Umeda

The Role of Electron Captures in Chandrasekhar Mass Models for Type Ia Supernovae

26 pages, 8 figures, submitted to ApJ

10.1086/308968

astro-ph

The Chandrasekhar mass model for Type Ia Supernovae (SNe Ia) has received increasing support from recent comparisons of observations with light curve predictions and modeling of synthetic spectra. It explains SN Ia events via thermonuclear explosions of accreting white dwarfs in binary stellar systems, being caused by central carbon ignition when the white dwarf approaches the Chandrasekhar mass. As the electron gas in white dwarfs is degenerate, characterized by high Fermi energies for the high density regions in the center, electron capture on intermediate mass and Fe-group nuclei plays an important role in explosive burning. Electron capture affects the central electron fraction Y_e, which determines the composition of the ejecta from such explosions. Up to the present, astrophysical tabulations based on shell model matrix elements were only available for light nuclei in the sd-shell. Recently new Shell Model Monte Carlo (SMMC) and large-scale shell model diagonalization calculations have also been performed for pf-shell nuclei. These lead in general to a reduction of electron capture rates in comparison with previous, more phenomenological, approaches. Making use of these new shell model based rates, we present the first results for the composition of Fe-group nuclei produced in the central regions of SNe Ia and possible changes in the constraints on model parameters like ignition densities and burning front speeds.

2009-10-31

astro-ph/0001465

Titus J. Galama

Titus J. Galama (CalTech)

Optical/Multiwavelength Observations of GRB Afterglows

10 pages, 4 figures; invited review for the 5th Huntsville Gamma-Ray Burst Workshop, eds. M. Kippen, R. Mallozzi, and G. Fishman

10.1063/1.1361551

astro-ph

I review gamma-ray burst optical/multiwavelength afterglow observations since 1997, when the first counterparts to GRBs were discovered. I discuss what we have learned from multiwavelength observations of GRB afterglows in relation to the `standard' fireball plus relativistic blast-wave models. To first order the `standard' model describes the afterglow observations well, but a wealth of information can be gathered from the deviations of GRB afterglow observations from this `standard' model. These deviations provide information on the nature of the progenitor and on the physics of GRB production. In particular I focus on the possible connection of GRBs to supernovae, on jet and circumstellar wind models, on the early-time afterglow, and on the emission from the reverse shock.

2009-10-31

astro-ph/0001466

Reuven Ramaty

R. Ramaty, R. E. Lingenfelter, B. Kozlovsky

LiBeB Evolution: Three Models

latex 10 pages, 7 double panel figures, uses newpasp.sty To appear in The Light Elements and Their Evolution, IAU Symp. 198, L. da Silva, M. Spite and R. de Medeiros, eds., ASP

astro-ph

We consider the three principal LiBeB evolutionary models, CRI in which the cosmic-ray source at all epochs of Galactic evolution is the average ISM, CRI+LECR in which metal enriched low energy cosmic rays (LECRs) are superimposed onto the CRI cosmic rays, and CRS in which the cosmic-ray source, accelerated in superbubbles, is constant, independent of the ISM metallicity. By considering the evolutionary trend of log(Be/H) vs. both [Fe/H] and [O/H], we demonstrate that the CRI model is energetically untenable. We present evolutionary trends for B-11/B-10 and B/Be which, combined with future precision measurements, could distinguish between the CRS and CRI+LECR models. We show that delayed LiBeB synthesis in the CRS model, due to the transport of the cosmic rays, could explain why log(Be/H) is steeper vs. [O/H] than vs. [Fe/H]. We also show that delayed deposition of Fe into star forming regions, due to its incorporation into high velocity dust, could provide an explanation for the possible rise of [O/Fe] with decreasing [Fe/H]. Observations of refractory and volatile alpha-elements could test this scenario. There seems to be a need for pregalactic or extragalactic Li-6 sources.

2007-05-23

astro-ph/0001467

Klaus Schertler

K. Schertler, C. Greiner, J. Schaffner-Bielich, and M.H. Thoma

Quark phases in neutron stars and a "third family" of compact stars as a signature for phase transitions

37 pages, 18 eps-figures included, LaTeX

Nucl.Phys.A677:463-490,2000

10.1016/S0375-9474(00)00305-5

astro-ph hep-ph nucl-th

The appearance of quark phases in the dense interior of neutron stars provides one possibility to soften the equation of state (EOS) of neutron star matter at high densities. This softening leads to more compact equilibrium configurations of neutron stars compared to pure hadronic stars of the same mass. We investigate the question to which amount the compactness of a neutron star can be attributed to the presence of a quark phase. For this purpose we employ several hadronic EOS in the framework of the relativistic mean-field (RMF) model and an extended MIT bag model to describe the quark phase. We find that - almost independent of the model parameters - the radius of a pure hadronic neutron star gets typically reduced by 20-30% if a pure quark phase in the center of the star does exist. For some EOS we furthermore find the possibility of a "third family" of compact stars which may exist besides the two known families of white dwarfs and neutron stars. We show how an experimental proof of the existence of a third family by mass and radius measurements may provide a unique signature for a phase transition inside neutron stars.

2008-11-26

astro-ph/0001468

Antonio Aparicio

A. Aparicio (Instituto de Astrofisica de Canarias) & N. Tikhonov (Special Astrophysical Observatory)

The spatial and age distribution of stellar populations in DDO 190

To be published in the AJ. 29 pages, 13 figures

10.1086/301360

astro-ph

The spatial distribution of stellar populations, the star formation history, and other properties of the dIrr galaxy DDO 190 have been analyzed using color--magnitude diagrams (CMDs) of about 3900 resolved stars and the Ha fluxes of HII regions. From the mean color index of the red giant branch, a mean metallicity [Fe/H]=-2.0 is obtained. The I magnitude of the TRGB has been used to estimate the distance. DDO 190 is 2.9+/-0.2 Mpc from the Milky Way, 2.1 Mpc from the M 94 group (CnV-I), 2.4 Mpc from the M 81 group and 2.9 Mpc from the barycenter of the Local Group, all indicating that it is an isolated, field galaxy. The surface-brightness distribution of the galaxy is well fitted by ellipses of ellipticity e=1-a/b=0.1 and P.A.=82deg. The radial star density distribution follows an exponential law of scale length a=43."4, corresponding to 611 pc. The Holmberg semi-major axis to mu_B=26.5 is estimated to be r^B_(26.5)=3.'0. Stellar populations of different ages in DDO 190 show strong spatial decoupling, the oldest population appearing much more extended than the youngest. Stars younger than 0.1 Gyr occupy only the central 40'' (0.55 kpc); stars younger than a few (~4) Gyr extend out to ~80'' (125 kpc), and for larger galactocentric distances only older stars seem to be present. This behavior is found in all the dIrr galaxies for which spatially extended studies have been performed and could be related with the kinematical history of the galaxy.

2009-10-31

astro-ph/0001469

Simone Marri

Simone Marri, Andrea Ferrara and Lucia Pozzetti

Gravitational Lensing Effects on High Redshift Type II Supernova Studies with NGST

19 pages including 6 figures. Accepted for publication in MNRAS

Mon.Not.Roy.Astron.Soc.317:265,2000

10.1046/j.1365-8711.2000.03493.x

astro-ph

We derive the expected Type II SN differential number counts, N(m), and Hubble diagram for SCDM and LCDM cosmological models, taking into account the effects of gravitational lensing (GL) produced by the intervening cosmological mass. The mass distribution of dark matter halos (ie the lenses) is obtained by means of a Monte Carlo method applied to the Press-Schechter mass function. The halos are assumed to have a NFW density profile, in agreement with recent simulations of hierarchical cosmological models. Up to z=15, the (SCDM, LCDM) models predict a total number of (857, 3656) SNII/yr in 100 surveyed 4' times 4' fields of the Next Generation Space Telescope. NGST will be able to reach the peak of the N(m) curve, located at AB approx 30(31) for SCDM(LCDM) in J and K wavelength bands and detect (75%, 51%) of the above SN events. This will allow a detailed study of the early cosmic star formation history, as traced by SNIIe. N(m) is only very mildly affected by the inclusion of lensing effects. In addition, GL introduces a moderate uncertainty in the determination of cosmological parameters from Hubble diagrams, when these are pushed to higher $z$. For example, for a ``true'' LCDM with (Omega_M= 0.4, Omega_Lambda=0.6), without proper account of GL, one would instead derive (Omega_{M}=0.36^{+0.15}_{-0.12}, Omega_{Lambda}=0.60^{+0.12}_{-0.24}). We briefly compare our results with previous similar work and discuss the limitations of the model.

2011-08-23

astro-ph/0001470

Piotr Popowski

Piotr Popowski (IGPP/LLNL)

Harmonizing the RR Lyrae and Clump Distance Scales - Stretching the Short Distance Scale to Intermediate Ranges?

version accepted to MNRAS, added discussion about the dependence of the results on theoretical assumptions and observational input, stressed that the derived range of the LMC distance modulus between 18.24 and 18.44 is insensitive to the controversial dereddened I-magnitude of the LMC clump giants

Mon.Not.Roy.Astron.Soc. 321 (2001) 502

10.1046/j.1365-8711.2001.04046.x

astro-ph

I explore the consequences of making the RR Lyrae and clump giant distance scales consistent in the solar neighborhood, Galactic bulge and Large Magellanic Cloud (LMC). I employ two major assumptions: 1) that the absolute magnitude - metallicity, M_V(RR) - [Fe/H], relation for RR Lyrae stars is universal, and 2) that absolute I-magnitudes of clump giants, M_I(RC), in Baade's Window are known (e.g., can be inferred from the local Hipparcos-based calibration or theoretical modeling). A comparison between the solar neighborhood and Baade's Window sets M_V(RR) at [Fe/H] = -1.6 in the range (0.59 +/- 0.05, 0.70 +/- 0.05), somewhat brighter than the statistical parallax solution. More luminous RR Lyrae stars imply younger ages of globular cluster, which would be in better agreement with the conclusions from the currently favored stellar evolution and cosmological models. A comparison between Baade's Window and the LMC sets the M_I^{LMC}(RC) in the range (-0.33 +/- 0.09, -0.53 +/- 0.09). The distance modulus to the LMC, mu^{LMC}, is between 18.24 +/- 0.08 and 18.44 +/- 0.07. Unlike M_I^{LMC}(RC), this range in mu^{LMC} does NOT depend on the adopted value of the dereddened LMC clump magnitude, I_0^{LMC}(RC). I argue that the currently available information is insufficient to select the correct distance scale with high confidence.

2009-10-31

astro-ph/0001471

Pasquale Blasi

P. Blasi (Fermilab), A.V. Olinto (U. Chicago), A. Stebbins (Fermilab)

The Effect of a Non-Thermal Tail on the Sunyaev-Zeldovich Effect in clusters of galaxies

14 pages, 3 figures, version to be published in ApJ. Lett

Astrophys.J.535:L71,2000

10.1086/312706

Fermilab/Pub-00/050

astro-ph

We study the spectral distortions of the cosmic microwave background radiation induced by the Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies when the target electrons have a modified Maxwell-Boltzmann distribution with a high-energy non-thermal tail. Bremsstrahlung radiation from this type of \\ electron distribution may explain the supra-thermal X-ray emission observed in some clusters such as the Coma cluster and A2199 and serve as an alternative to the classical but problematic inverse Compton scattering interpretation. We show that the SZ effect can be used as a powerful tool to probe the electron distribution in clusters of galaxies and discriminate among these different interpretations of the X-ray excess. The existence of a non-thermal tail can have important consequences for cluster based estimators of cosmological parameters.

2009-10-31

astro-ph/0001472

Stephen S. Eikenberry

S. Eikenberry (Cornell), K. Matthews (Caltech), M. Muno (MIT), P. Blanco (UCSD), E. Morgan (MIT), R. Remillard (MIT)

Faint Infrared Flares from the Microquasar GRS 1915+105

10 pages, 4 figures Accepted for publication in ApJ Letters

10.1086/312559

astro-ph

We present simultaneous infrared and X-ray observations of the Galactic microquasar GRS 1915+105 using the Palomar 5-m telescope and Rossi X-ray Timing Explorer on July 10, 1998 UT. Over the course of 5 hours, we observed 6 faint infrared (IR) flares with peak amplitudes of $\sim 0.3-0.6 $ mJy and durations of $\sim 500-600 $ seconds. These flares are associated with X-ray soft-dip/soft-flare cycles, as opposed to the brighter IR flares associated with X-ray hard-dip/soft-flare cycles seen in August 1997 by Eikenberry et al. (1998). Interestingly, the IR flares begin {\it before} the X-ray oscillations, implying an ``outside-in'' origin of the IR/X-ray cycle. We also show that the quasi-steady IR excess in August 1997 is due to the pile-up of similar faint flares. We discuss the implications of this flaring behavior for understanding jet formation in microquasars.

2009-10-31

astro-ph/0001473

Oleg V. Verkhodanov

H.Andernach (1), O.V.Verkhodanov (2), N.V.Verkhodanova (2), ((1) Depto. de Astronomia, Univ. Guanajuato, Guanajuato, Mexico; (2) Special astrophysical observatory, Russia)

Radio-optical identification of very-steep spectrum radio sources from the UTR-2 catalogue

7 pages, 5 figures. This was the poster as presented on IAU Symp 199. The short (final) version was submitted the Symp. Proceedings

astro-ph

We used radio source catalogues accessible from the CATS database (http://cats.sao.ru) to establish radio continuum spectra for decametric radio sources in the UTR-2 catalogue (Braude et al., 1978--1994). From these, we select a sample of 23 sources with ultra steep radio spectra (\alpha<=-1.2, S ~ \nu^{\alpha}) and present accurate positions and sizes from FIRST and NVSS. The search for optical counterparts from the APM (object) and DSS (image) databases, as well as infrared and X-ray identifications of these UTR sources are in progress.

2007-05-23

astro-ph/0001474

Vangioni-Flam Elisabeth

Elisabeth Vangioni-Flam and Michel Casse

LiBeB Production and Associated Astrophysical Sites

10 pages, no figure, to be published in "Tle light Elements and their Evolution", IAU Symp. 198 (Natal Conf.), ASP Conf. Series, 2000

astro-ph

The various modes of spallative LiBeB production are summarized, and classified according to their dependence or independence on the abundance of medium heavy elements (CNO) illustrated by that of oxygen in the interstellar medium. The predictions of the models are confronted to the available observational correlations (Be, B vs O). Clearly, a primary mechanism should lead to a slope one in the lg(Be/H) vs [O/H] plot and a secondary mechanism to a slope two. Due to the ambiguity of the O data, another criterion, based on energetics, can help us to select an adequate model. A purely secondary origin in the very early Galaxy is much more energy demanding than a primary one. Indeed, magnesium seems to be a possible surrogate of oxygen and iron since i) it is spectroscopically more easy to cope with and ii) its nucleosynthetic yield is independent of the mass cut and does not depend on metallicity.

2007-05-23

astro-ph/0001475

Timo Ekholm

T. Ekholm, P. Lanoix, P. Teerikorpi, P. Fouque and G. Paturel

Investigations of the Local Supercluster Velocity Field III. Tracing the backside infall with distance moduli from the direct Tully-Fisher relation

13 pages, 9 figures. Accepted to A&A. Typeset with the A&A Latex package

astro-ph

We have extended the discussion of Paper II (Ekholm et al. 1999) to cover also the backside of the Local Supercluster (LSC) by using 96 galaxies within Theta<30 deg from the adopted centre of LSC and with distance moduli from the direct B-band Tully-Fisher relation. In order to minimize the influence of the Malmquist bias we required log V_max>2.1 and sigma_{B_T}<0.2 mag. We found out that if R_Virgo<20 Mpc this sample fails to follow the expected dynamical pattern from the Tolman-Bondi (TB) model. When we compared our results with the Virgo core galaxies given by Federspiel et al. (1998) we were able to constrain the distance to Virgo: R_Virgo=20-24 Mpc. When analyzing the TB-behaviour of the sample as seen from the origin of the metric as well as that with distances from the extragalactic Cepheid PL-relation we found additional support to the estimate R_Virgo=21 Mpc given in Paper II. Using a two-component mass-model we found a Virgo mass estimate M_Virgo= (1.5-2)M_virial, where M_virial=9.375.10^14M_sun for R_Virgo=21 Mpc. This estimate agrees with the conclusion in Paper I (Teerikorpi et al. 1992). Our results indicate that the density distribution of luminous matter is shallower than that of the total gravitating matter when q_0<=0.5. The preferred exponent in the density power law, alpha\approx2.5, agrees with recent theoretical work on the universal density profile of dark matter clustering in an Einstein-deSitter universe (Tittley & Couchman 1999).

2007-05-23

astro-ph/0001476

Martino Romaniello

Nino Panagia, Martino Romaniello, Salvatore Scuderi and Robert P. Kirshner

Young Stellar Populations Around SN1987A

31 pages, 12 figures. Accepted for publication in the Astrophysical Journal. Please contact [email protected] for the full color version of the figures. Minor typos fixed, suffix of Figure 7b changed from ps to gif

Astrophys.J.539:197-208,2000

10.1086/309212

astro-ph

We present the results of a study of the stellar population in a region of 30 pc radius around SN1987A, based on an analysis of multi-band HST-WFPC2 images. The effective temperature, radius and, possibly, reddening of each star were determined for 21,955 stars by fitting the measured broad band magnitudes to the ones calculated with model atmospheres. In addition, we have identified all stars with Halpha equivalent widths in excess of 8 A, amounting to a total of 492 stars. An inspection to the HR diagram reveals the presence of several generations of young stars, with ages between 1 and 150 Myrs, superposed on a much older field population (0.6-6 Gyrs). A substantial fraction of young stars have ages around 12 Myrs which is the stellar generation coeval to SN 1987A progenitor. The youngest stars in the field appear to be strong-line T Tauri stars. This constitute the first positive detection of low mass (about 1-2 Mo) Pre Main Sequence (PMS) stars outside the Milky Way. Their positions in the HR diagram appear to require that star formation in the LMC occurs with accretion rates about 10 times higher than in the Milky Way, i.e. ~10^{-4} Mo/yr. SN1987A appears to belong to a loose, young cluster 12+/-2 Myrs old, in which the slope of the present mass function is almost identical to Salpeter's for masses above 3 Mo, but becomes much flatter for lower masses. On a large scale, we find that the spatial distribution of massive stars and low-mass PMS stars are conclusively different. This results casts doubts on the validity of an IMF concept on a small scale (say, less than 10 pc). A preliminary analysis, done for the whole field as a single entity, shows that the IMF slope for the young population present over the entire region is steeper than Gamma ~ -1.7.

2008-11-26

astro-ph/0001477

Duncan Forbes

Duncan A. Forbes, Karen L. Masters (University of Birmingham), Dante Minniti (P. Universidad Catolica) and Pauline Barmby (Harvard)

The Elliptical Galaxy formerly known as the Local Group: Merging the Globular Cluster Systems

22 pages, Latex, 4 figures, 5 tables, submitted to A & A

astro-ph

Prompted by a new catalogue of M31 globular clusters, we have collected together individual metallicity values for globular clusters in the Local Group. Although we briefly describe the globular cluster systems of the individual Local Group galaxies, the main thrust of our paper is to examine the collective properties. In this way we are simulating the dissipationless merger of the Local Group, into presumably an elliptical galaxy. Such a merger is dominated by the Milky Way and M31, which appear to be fairly typical examples of globular cluster systems of spiral galaxies. The Local Group `Elliptical' has about 700 +/- 125 globular clusters, with a luminosity function resembling the `universal' one. The metallicity distribution has peaks at [Fe/H] ~ -1.55 and -0.64 with a metal-poor to metal-rich ratio of 2.5:1. The specific frequency of the Local Group Elliptical is initially about 1 but rises to about 3, when the young stellar populations fade and the galaxy resembles an old elliptical. The metallicity distribution and stellar population corrected specific frequency are similar to that of some known early type galaxies. Based on our results, we briefly speculate on the origin of globular cluster systems in galaxies.

2007-05-23

astro-ph/0001478

Ignazio Bombaci

Ignazio Bombaci and Bhaskar Datta

Conversion of neutron stars to strange stars as the central engine of gamma-ray bursts

ApJ, 530, 2000 February 20, Lxxx (in press)

Astrophys.J. 530 (2000) L69

10.1086/312497

astro-ph hep-ph nucl-th

We study the conversion of a neutron star to a strange star as a possible energy source for gamma-ray bursts. We use different recent models for the equation of state of neutron star matter and strange quark matter. We show that the total amount of energy liberated in the conversion is in the range of (1-4) 10^{53} ergs (one order of magnitude larger than previous estimates) and is in agreement with the energy required to power gamma-ray burst sources at cosmological distances.

2009-10-31

astro-ph/0001479

Igor V. Igumenshchev

Marek A. Abramowicz, Jean-Pierre Lasota, Igor V. Igumenshchev

On the absence of winds in ADAFs

7 pages, submitted to MNRAS on June 2, 1999, (positive) referee's report received on Oct 21, re-submitted on Dec 10

astro-ph

We show that recently published assertions that advection dominated accretion flows (ADAFs) require the presence of strong winds are unfounded because they assume that low radiative efficiency in flows accreting at low rates onto black holes implies vanishing radial energy and angular momentum fluxes through the flow (which is also formulated in terms of the `Bernoulli function' being positive). This, however, is a property only of self-similar solutions which are an inadequate representation of global accretion flows. We recall general properties of accretion flows onto black holes and show that such, necessarily transonic, flows may have either positive or negative Bernoulli function depending on the flow viscosity. Flows with low viscosities (alpha<0.1 in the alpha-viscosity model) have a negative Bernoulli function. Without exception, all 2-D and 1-D numerical models of low viscosity flows constructed to date experience no significant outflows. At high viscosities the presence of outflows depends on the assumed viscosity, the equation of state and on the outer boundary condition. The positive sign of the Bernoulli function invoked in this context is irrelevant to the presence of outflows. As an illustration, we recall 2-D numerical models with moderate viscosity that have positive values of the Bernoulli function and experience no outflows. ADAFs, therefore, do not differ from this point of view from thin Keplerian discs: they may have, but they do not have to have strong winds.

2007-05-23

astro-ph/0001480

Eric C. Ford

Steve van Straaten, Eric C. Ford, Michiel van der Klis, Mariano Mendez (U Amsterdam), and Philip Kaaret (CfA)

Relations Between Timing Features and Colors in the X-Ray Binary 4U 0614+09

ApJ, refereed

10.1086/309351

astro-ph

We study the correlations between timing and X-ray spectral properties in the low mass X-ray binary 4U 0614+09 using a large (265-ks) data set obtained with the Rossi X-ray Timing Explorer. We find strong quasi-periodic oscillations (QPOs) of the X-ray flux, like the kilohertz QPOs in many other X-ray binaries with accreting neutron stars, with frequencies ranging from 1329 Hz down to 418 Hz and, perhaps, as low as 153 Hz. We report the highest frequency QPO yet from any low mass X-ray binary at 1329+-4 Hz, which has implications for neutron star structure. This QPO has a 3.5-sigma single-trial significance, for an estimated 40 trials the significance is 2.4-sigma. Besides the kilohertz QPOs, the Fourier power spectra show four additional components: high frequency noise (HFN), described by a broken power-law with a break frequency between 0.7 and 45 Hz, very low frequency noise (VLFN), which is fitted as a power-law below 1 Hz, and two broad Lorentzians with centroid frequencies varying from 6 to 38 Hz and 97 to 158 Hz, respectively. We find strong correlations between the frequencies of the kilohertz QPOs, the frequency of the 6 to 38 Hz broad Lorentzian, the break frequency of the HFN, the strength of both the HFN and the VLFN and the position of the source in the hard X-ray color vs. intensity diagram. The frequency of the 97 to 158 Hz Lorentzian does not correlate with these parameters. We also find that the relation between power density and break frequency of the HFN is similar to that established for black hole candidates in the low state. We suggest that the changing mass accretion rate is responsible for the correlated changes in all these parameters.

2009-10-31

astro-ph/0001481

Stefano Liberati

Stefano Liberati (SISSA, INFN; Trieste), Bruce A. Bassett (University of Oxford, Portsmouth University), Carmen Molina-Paris (Los Alamos), Matt Visser (Washington University in Saint Louis)

Chi-Variable-Speed-of-Light Cosmologies

4 pages, use esprc2.sty. Talk given at the 3rd Meeting on Constrained Dynamics and Quantum Gravity (QG 99), Villasimius, Sardinia, Italy, 14-18 Sep 1999

Nucl.Phys.Proc.Suppl. 88 (2000) 259-262

10.1016/S0920-5632(00)00780-5

astro-ph

Variable-Speed-of-Light (VSL) cosmologies are currently attracting much interest as a possible alternative to cosmological inflation. We discuss the fundamental geometrodynamic aspects of VSL cosmologies, and provide several alternative implementations. These implementations provide a large class of VSL cosmologies that pass the zeroth-order consistency tests of being compatible with both classical Einstein gravity and low-energy particle physics. While they solve the ``kinematic'' puzzles as well as inflation does, VSL cosmologies typically do not solve the flatness problem since in their purest form no violation of the strong energy condition occurs. Nevertheless, these models are easy to unify with inflation.

2009-10-31

astro-ph/0001482

John Boger

J. Boger (Brookhaven National Laboratory), R. L. Hahn (Brookhaven National Laboratory), J. B. Cumming (Brookhaven National Laboratory)

Do statistically significant correlations exist between the Homestake solar neutrino data and sunspots?

17 pages, 5 figures, AasTeX

Astrophys.J. 537 (2000) 1080-1085

10.1086/309069

BNL-66906

astro-ph

It has been suggested by various authors that a significant anticorrelation exists between the Homestake solar neutrino data and the sunspot cycle. Some of these claims rest on smoothing the data by taking running averages, a method that has recently undergone criticism. We demonstrate that no significant anticorrelation can be found in the Homestake, data, or in standard 2- and 4-point averages of that data. However, when 3-, 5-, and 7-point running averages are taken, an anticorrelation seems to emerge whose significance grows as the number of points in the average increases. Our analysis indicates that the apparently high significance of these anticorrelations is an artifact of the failure to consider the loss of independence introduced in the running average process. When this is considered, the significance is reduced to that of the unaveraged data. Furthermore, when evaluated via parametric subsampling, no statistically significant anticorrelation is found. We conclude that the Homestake data can not be used to substantiate any claim of an anticorrelation with the sunspot cycle.

2009-10-31

astro-ph/0001483

Nikos Prantzos

Nikos Prantzos (Institut d'Astrophysique de Paris)

The role of Star Formation in the evolution of spiral galaxies

10 pages, 14 figures (ESLAB LaTex style). Invited paper to appear in Proc. of 33d ESLAB Symp. "Star formation from the small to the large scale" (F. Favata, A. Kaas and A. Wilson eds., ESA SP-445, 2000)

astro-ph

Spiral galaxies offer a unique opportunity to study the role of star formation in galaxy evolution and to test various theoretical star formation schemes. I review some recent relevant work on the evolution of spiral galaxies. Detailed models are used for the chemical and spectrophotometric evolution, with metallicity dependent stellar yields, tracks and spectra. The models are ``calibrated'' on the Milky Way disk and generalised to other spirals with some simple scaling relations, obtained in the framework of Cold Dark Matter models for galaxy formation. The results compare favourably to the main observables of present day spirals, provided a crucial assumption is made: massive disks form their stars earlier than low mass ones. It is not clear whether this picture is compatible with currently popular hierarchical models of galaxy evolution. The resulting abundance gradients are found to be anticorrelated to the disk scalelength, support radially dependent star formation efficiencies and point to a kind of ``homologuous evolution'' for spirals.

2007-05-23

astro-ph/0001484

Mark L. McConnell

M. L. McConnell, J. M. Ryan, W. Collmar, V. Schoenfelder, H. Steinle, A. W. Strong, H. Bloemen, W. Hermsen, L. Kuiper, K. Bennett, B. F. Phlips, and J. C. Ling

A High Sensitivity Measurement of the MeV Gamma-Ray Spectrum of Cygnus X-1

28 pages, 6 figures, accepted for publication in ApJ. Considerably revised from original submission

10.1086/317128

astro-ph

The Compton Gamma-Ray Observatory (CGRO) has observed the Cygnus region on several occasions since its launch in 1991. The data collected by the COMPTEL experiment on CGRO represent the most sensitive observations to date of Cygnus X-1 in the 0.75-30 MeV range. A spectrum accumulated by COMPTEL over 10 weeks of observation time shows significant evidence for emission extending out to several MeV. We have combined these data with contemporaneous data from both BATSE and OSSE to produce a broad-band gamma-ray spectrum, corresponding to the low X-ray state of Cygnus X-1, extending from 50 keV up to approximately 5 MeV. Although there is no evidence for any broad line-like emissions in the MeV region, these data further confirm the presence of a hard tail at energies above several hundred keV. In particular, the spectrum at MeV energies can be described as a power-law with a photon spectral index of $\alpha$ = -3.2, with no evidence for a cutoff at high energies. For the 200 keV to 5 MeV spectrum, we provide a quantitative description of the underlying electron spectrum, in the context of a hybrid thermal/non-thermal model for the emission. The electron spectrum can be described by a thermal Maxwellian with a temperature of $kT_e$ = 86 keV and a non-thermal power-law component with a spectral index of $p_e$ = 4.5. The spectral data presented here should provide a useful basis for further theoretical modeling.

2009-10-31

astro-ph/0001485

Mark L. McConnell

M. L. McConnell, K. Bennett, H. Bloemen, W. Collmar, W. Hermsen, L. Kuiper, B. Phlips, J. M. Ryan, V. Schoenfelder, H. Steinle, and A.W. Strong

The Spectral Variability of Cygnus X-1 at MeV Energies

5 pages, 4 figures, to be published in AIP Conf. Proc., "The Fifth Compton Symposium"

10.1063/1.1303185

astro-ph

In previous work, we have used data from the first three years of the CGRO mission to assemble a broad-band $\gamma$-ray spectrum of the galactic black hole candidate Cygnus X-1. Contemporaneous data from the COMPTEL, OSSE and BATSE experiments on CGRO were selected on the basis of the hard X-ray flux (45--140 keV) as measured by BATSE. This provided a spectrum of Cygnus X-1 in its canonical low X-ray state (as measured at energies below 10 keV), covering the energy range from 50 keV to 5 MeV. Here we report on a comparison of this spectrum to a COMPTEL-OSSE spectrum collected during a high X-ray state of Cygnus X-1 (May, 1996). These data provide evidence for significant spectral variability at energies above 1 MeV. In particular, whereas the hard X-ray flux {\it decreases} during the high X-ray state, the flux at energies above 1 MeV {\it increases}, resulting in a significantly harder high energy spectrum. This behavior is consistent with the general picture of galactic black hole candidates having two distinct spectral forms at soft $\gamma$-ray energies. These data extend this picture, for the first time, to energies above 1 MeV.

2009-10-31

astro-ph/0001486

Ralf Launhardt

R. Launhardt (1), A.I. Sargent (1), H. Zinnecker (2) ((1) Caltech (2) AIP Potsdam)

Search for Binary Protostars

4 pages, 2 figures, ALMA conference proceedings

astro-ph

In an effort to shed more light on the formation process of binary stars, we have started a program to study multiplicity among nearby low- and intermediate-mass protostars using the OVRO Millimeter Array. Here, we describe the project and present the first results on the protostellar core in the Bok globule CB230 (L1177). At 10 arcsec resolution, the molecular core is resolved into two components separated by 5000 AU. The morphology and kinematics of the double core suggest that it formed from a single cloud core due to rotational fragmentation.

2007-05-23

astro-ph/0001487

William Raphael Hix

W. Raphael Hix, Michael S. Smith, Anthony Mezzacappa, Sumner Starrfield, Donald L. Smith

The Impact of Nuclear Reaction Rate Uncertainties on Evolutionary Studies of the Nova Outburst

4 pages, 3 figures. to appear in "Cosmic Explosions", proceeding of the 10th Annual October Astrophysics Conference in Maryland (ed. S.S. Holt and W. W. Zhang)

10.1063/1.1291740

astro-ph

The observable consequences of a nova outburst depend sensitively on the details of the thermonuclear runaway which initiates the outburst. One of the more important sources of uncertainty is the nuclear reaction data used as input for the evolutionary calculations. A recent paper by Starrfield, Truran, Wiescher, & Sparks (1998) has demonstrated that changes in the reaction rate library used within a nova simulation have significant effects, not just on the production of individual isotopes (which can change by an order of magnitude), but on global observables such as the peak luminosity and the amount of mass ejected. We present preliminary results of systematic analyses of the impact of reaction rate uncertainties on nova nucleosynthesis.

2009-10-31

astro-ph/0001488

Eric J. Hooper

Belinda J. Wilkes (1), Eric J. Hooper (1), Kim K. McLeod (2), Martin S. Elvis (1), David H. Hughes (3), Chris D. Impey (4), Joanna K. Kuraszkiewicz (1), Carol S. Lonsdale (5), Matt A. Malkan (6), Jonathan C. McDowell (1) ((1) Harvard-Smithsonian CfA, (2) Wellesley College, (3) INAOE, (4) Steward Observatory, (5) IPAC, (6) UCLA)

Infrared Properties of High Redshift and X-ray Selected AGN Samples

8 pages, 3 figures (2 color), to be published in the Springer Lecture Notes of Physics Series as part of the proceedings for "ISO Surveys of a Dusty Universe," a workshop held at Ringberg Castle, Germany, November 8 - 12, 1999. Requires latex style files for this series: cl2emult.cls, cropmark.sty, lnp.sty, sprmindx.sty, subeqnar.sty (included with submission)

astro-ph

The NASA/ISO Key Project on active galactic nuclei (AGN) seeks to better understand the broad-band spectral energy distributions (SEDs) of these sources from radio to X-rays, with particular emphasis on infrared properties. The ISO sample includes a wide variety of AGN types and spans a large redshift range. Two subsamples are considered herein: 8 high-redshift (1 < z < 4.7) quasars; and 22 hard X-ray selected sources. The X-ray selected AGN show a wide range of IR continuum shapes, extending to cooler colors than the optical/radio sample of Elvis et al. (1994). Where a far-IR turnover is clearly observed, the slopes are < 2.5 in all but one case so that non-thermal emission remains a possibility. The highest redshift quasars show extremely strong, hot IR continua requiring ~ 100 solar masses of 500 - 1000 Kelvin dust with ~ 100 times weaker optical emission. Possible explanations for these unusual properties include: reflection of the optical light from material above/below a torus; strong obscuration of the optical continuum; or an intrinsic deficit of optical emission.

2007-05-23

astro-ph/0001489

Cheongho Han

Cheongho Han & Seong-Hong Park (Chungbuk National University, Korea)

Colour Change Measurements of Gravitational Microlensing Events by Using the Difference Image Analysis Method

total 8 pages, including 4 figures and no table, MNRAS, in press

Mon.Not.Roy.Astron.Soc. 320 (2001) 41

10.1046/j.1365-8711.2001.03926.x

astro-ph

Detecting colour changes of a gravitational microlensing event induced by the limb-darkened extended source effect is important to obtain useful information both about the lens and source star. However, precise measurements of the colour changes are hampered by blending, which also causes colour changes of the event. In this paper, we show that although the colour change measured from the subtracted image by using the recently developed photometric method of the ``difference image analysis'' (DIA) differs from the colour change measured by using the conventional method based on the extraction of the individual source stars' point spread functions, the curve of the colour changes (colour curve) constructed by using the DIA method enables one to obtain the same information about the lens and source star, but with significantly reduced uncertainties due to the absence of blending. We investigate the patterns of the DIA colour curves for both single lens and binary lens events by constructing colour change maps.

2009-10-31

astro-ph/0001490

Cheongho Han

Cheongho Han (Chungbuk National University), Ho-Il Kim (Korea Astronomy Observatory), Kyungae Chang (Chongju Univeristy), Seong-Hong Park (Chungbuk National University)

Detection of Stellar Spots from the Observations of Caustic-Crossing Binary-Lens Gravitational Microlensing Events

11 pages, 2 figures

Mon.Not.Roy.Astron.Soc. 316 (2000) 665

10.1046/j.1365-8711.2000.03534.x

CNU-A&SS-07/99

astro-ph

Recently, Heyrovsk\'y & Sasselov (1999) investigated the sensitivity of {\it single-lens} gravitational microlensing event light curves to small spots and found that during source transit events spots can cause deviations in amplification larger than 2%, and thus be detectable. In this paper, we explore the feasibility of spot detection from the observations of {\it caustic-crossing binary-lens} microlensing events instead of single-lens events. For this we investigate the sensitivity of binary-lens event light curves to spots and compare it to that of single-lens events. From this investigation, we find that during caustic crossings the fractional amplification deviations of microlensing light curves from those of spotless source events are equivalent to the deviations of single-lens events, implying that spots can also be detected with a similar photometric precision to that required for spot detection by observing single-lens events. We discuss the relative advantages of observing caustic-crossing binary-lens events over the observations of single-lens events in detecting stellar spots.

2009-10-31

astro-ph/0001491

Cheongho Han

Cheongho Han (Chungbuk National University)

Better Astrometric Deblending of Gravitional Microlensing Events by Using the Difference Image Analysis Method

12 pages, 3 figures

CNU-A&SS-11/99

astro-ph

Due to the choice of very dense star fields for a higher event rate, the current microlensing searches suffer from large uncertainties caused by blending effect. To measure light variations of microlensing events free from the effect of blending, a newly developed method of Differential Image Analysis (DIA) was proposed for microlensing searches. However, even with the light variation curve obtained by using the DIA method, dramatic reduction of the uncertainty in the determined Einstein time scale is not expected due to the difficulty in determining the baseline flux of a source star. However, we show in this paper that if the blending effect is investigated by detecting the shift of a source star image centroid, the DIA method will allow one to detect the blending effect with a significantly enhanced efficiency compared the efficiency of the current method based on PSF photometry (PSF method). This is because for a given event the centroid shift measurable by using the DIA method, $\delta\theta_{\rm c,DIA}$, is {\it always} larger than the centroid shift measurable by using the PSF method, $\delta\theta_{\rm c,PSF}$. We find that the ratio $\delta\theta_{\rm c,DIA}/\delta\theta_{\rm c,DIA}$ rapidly increases with increasing fraction of blended light. In addition, for events affected by the same fraction of blended light, the ratio $\delta\theta_{\rm c,DIA}/ \delta \theta_{\rm c,DIA}$ is larger for the event with a lower amplification. Therefore, centroid shift measurements by using the DIA method will be an efficient method to detect the blending effect especially of highly blended events, for which the uncertainties in the determined Einstein time scale are large, as well as of low amplification events, for which the current method is highly inefficient.

2007-05-23

astro-ph/0001492

Heather Morrison

Heather L. Morrison, Mario Mateo, Edward W. Olszewski, Paul Harding, R.C. Dohm-Palmer, Kenneth C. Freeman, John E. Norris and Miwa Morita

Mapping the Galactic Halo I. The `Spaghetti' Survey

55 pages, 22 figures, to appear in the Astronomical Journal

Astron.J.119:2254-2273,2000

10.1086/301357

astro-ph

We describe a major survey of the Milky Way halo designed to test for kinematic substructure caused by destruction of accreted satellites. We use the Washington photometric system to identify halo stars efficiently for spectroscopic followup. Tracers include halo giants (detectable out to more than 100 kpc), blue horizontal branch stars, halo stars near the main sequence turnoff, and the ``blue metal-poor stars'' of Preston et al (1994). We demonstrate the success of our survey by showing spectra of stars we have identified in all these categories, including giants as distant as 75 kpc. We discuss the problem of identifying the most distant halo giants. In particular, extremely metal-poor halo K dwarfs are present in approximately equal numbers to the distant giants for V fainter than 18, and we show that our method will distinguish reliably between these two groups of metal-poor stars. We plan to survey 100 square degrees at high galactic latitude, and expect to increase the numbers of known halo giants, BHB stars and turnoff stars by more than an order of magnitude. In addition to the strong test that this large sample will provide for the question `was the Milky Way halo accreted from satellite galaxies?', we will improve the accuracy of mass measurements of the Milky Way beyond 50 kpc via the kinematics of the many distant giants and BHB stars we will find. We show that one of our first datasets constrains the halo density law over galactocentric radii of 5-20 kpc and z heights of 2-15 kpc. The data support a flattened power-law halo with b/a of 0.6 and exponent -3.0. More complex models with a varying axial ratio may be needed with a larger dataset.

2008-11-26

astro-ph/0001493

Uros Seljak

Uros Seljak (Princeton University)

Analytic model for galaxy and dark matter clustering

16 pages, 7 figures, submitted to Phys. Rev. D

Mon.Not.Roy.Astron.Soc. 318 (2000) 203

10.1046/j.1365-8711.2000.03715.x

astro-ph

We investigate an analytic model to compute nonlinear power spectrum of dark matter, galaxies and their cross-correlation. The model is based on Press-Schechter halos, which cluster and have realistic dark matter profiles. The total power spectrum is a sum of two contributions, one from correlations betwen the halos and one from correlations within the same halo. We show that such a model can give dark matter power spectra which match well with the results of N-body simulations, provided that concentration parameter decreases with the halo mass. Galaxy power spectrum differs from dark matter power spectrum because pair weighted number of galaxies increases less rapidly than the halo mass, as predicted by theoretical models and observed in clusters. In this case the resulting power spectrum becomes a power law with the slope closed to the observed. Such a model also predicts a later onset of nonlinear clustering compared to the dark matter, which is needed to reconcile the CDM models with the data. Generic prediction of this model is that bias is scale dependent and nonmonotonic. For red or elliptical galaxies bias in power spectrum may be scale dependent even on very large scales. Our predictions for galaxy-dark matter correlations, which can be observed through the galaxy-galaxy lensing, show that these cannot be interpreted simply as an average halo profile of a typical galaxy, because different halo masses dominate at different scales and because larger halos host more than one galaxy. We discuss the prospects of using cross-correlations in combination with galaxy clustering to determine the dark matter power spectrum (ABRIDGED).

2016-08-30

astro-ph/0001494

Li-Xin Li

Li-Xin Li (Princeton University)

Electromagnetic Energy for a Charged Kerr Black Hole in a Uniform Magnetic Field

9 pages, 1 figure

Phys.Rev. D61 (2000) 084033

10.1103/PhysRevD.61.084033

POPe-820

astro-ph

With the Komar mass formula we calculate the electromagnetic energy for a charged Kerr black hole in a uniform magnetic field. We find that the total electromagnetic energy takes the minimum when the Kerr black hole possesses a non-zero net charge $Q = 2\xi B_0 J_H$ where $B_0$ is the strength of the magnetic field, $J_H$ is the angular momentum of the black hole, $\xi$ is a dimensionless parameter determined by the spin of the black hole.

2009-10-31

astro-ph/0001495

Ann I. Zabludoff

Ann I. Zabludoff (Steward Obs./University of Arizona), John S. Mulchaey (Carnegie Obs.)

The Properties of Poor Groups of Galaxies: III. The Galaxy Luminosity Function

36 pages, AASLaTeX with 8 figures. Table 1 also available at http://atropos.as.arizona.edu/aiz/papers/all_grp_lf_ascii.dat.final . To appear in ApJ

10.1086/309191

astro-ph

We obtain R-band photometry for galaxies in six nearby poor groups for which we have spectroscopic data, including 328 new galaxy velocities. For the five groups with luminous X-ray halos, the composite group galaxy luminosity function (GLF) is fit adequately by a Schechter function with Mstar = -21.6 +/- 0.4 + 5log h and alpha = -1.3 +/- 0.1. We also find that (1) the ratio of dwarfs to giants is significantly larger for the five groups with luminous X-ray halos than for the one marginally X-ray detected group, (2) the composite GLF for the luminous X-ray groups is consistent in shape with that for rich clusters, (3) the composite group GLF rises more steeply at the faint end than that of the field, (4) the shape difference between the field and composite group GLF's results mostly from the population of non-emission line galaxies, whose dwarf-to-giant ratio is larger in the denser group environment than in the field, and (5) the non-emission line dwarfs are more concentrated about the group center than the non-emission line giants. This last result indicates that the dwarfs and giants occupy different orbits (i.e., have not mixed completely) and suggests that the populations formed at a different times. Our results show that the shape of the GLF varies with environment and that this variation is due primarily to an increase in the dwarf-to-giant ratio of quiescent galaxies in higher density regions, at least up to the densities characteristic of X-ray luminous poor groups. This behavior suggests that, in some environments, dwarfs are more biased than giants with respect to dark matter. This trend conflicts with the prediction of standard biased galaxy formation models. (Abridged)

2009-10-31

astro-ph/0001496

Roger Blandford

Roger Blandford, Gabriela Surpi (Caltech) and Tomislav Kundic (Renaissance Technologies)

Modeling Galaxy Lenses

Latex 10 pages 4 figures. To appear in ``Gravitational Lensing: Recent Progress and Future Goals'' Editors: Tereasa G. Brainerd and Christopher S. Kochanek

astro-ph

In order to use a gravitational lens to measure the Hubble constant accurately, it is necessary to derive a reliable model of the lens surface potential. If the analysis is restricted to the locations and magnifications of point images, the derived Hubble constant depends upon the class of mass models used to fit the data. However, when there is extended emission from an Einstein ring, it may be possible to derive a potential from the observed surface brightness in a model-independent manner. This procedure is illustrated with reference to B1608+656. The multi-band images are de-reddened, de-convolved and de-contaminated so that the luminous matter and the surface brightness contours in the Einstein ring are both faithfully mapped. This intensity distribution can then be used to reconstruct the potential. Progress in implementing this program is reported. The observed incidence of multiple-imaged galaxies on the Hubble Deep Fields is an order of magnitude smaller than naively predicted on the basis of radio lens surveys, like CLASS, but consistent with the rate computed using surface photometry of candidate lens galaxies assuming standard mass to light ratios. In order to resolve this paradox, it is suggested that most galaxy lenses are located in compact groups.

2007-05-23

astro-ph/0001497

Ray Stathakis

R. A. Stathakis, B. J. Boyle, D. H. Jones, M. S. Bessell, T. J. Galama, Lisa M. Germany, M. Hartley, D. M. James, C. Kouveliotou, I. J. Lewis, Q. A. Parker, K. S. Russell, E. M. Sadler, C. G. Tinney, J. van Paradijs and P. M. Vreeswijk

Spectral Evolution of the Peculiar Ic Supernova 1998bw

8 pages, 6 figures

10.1046/j.1365-8711.2000.03373.x

astro-ph

SN 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supenovae and probably the first supernova associated with a gamma-ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the AAT, UKST and the SSO 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 days after V_band maximum in comparison to well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from the observations of classical Ic SNe, we find that the evolution from the photospheric to the nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10% - 50% higher than other SNe and on day 94 emission lines are 45% broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope.

2009-10-31

astro-ph/0001498

Roger Blandford

R. D. Blandford (Caltech)

Current Issues

To appear in Cosmic Explosions: Proc. 10th Maryland Conference on Astrophysics. Ed. S. Holt and W. Zhang AIP

10.1063/1.1291693

astro-ph

Cosmic explosions are observed in many astrophysical environments. They range in scale from hydromagnetic instabilities in the terrestrial magnetotail and solar ``nanoflares'' to cosmological gamma ray bursts, supernovae and the protracted intervals of nuclear activity that produce the giant quasars and radio galaxies. There are many parallels in the analyses of the explosion sites that are highlighted at this workshop, specifically stellar coronae, accretion disks, supernovae and compact objects. In this introductory talk, some general issues are discussed and some more specific questions relating to the individual sites are raised.

2009-10-31

astro-ph/0001499

Roger Blandford

R. D. Blandford (Caltech)

Quasar Jets and their Fields

Latex. 17pages Proc Discusison Meeting on Magnetic Activity in Stars, Discs and Quasars. Ed. D. Lynden-Bell, E. R. Priest and N. O. Weiss. To appear in Phil. Trans. Roy. Soc. A

Phil.Trans.A.Math.Phys.Eng.Sci.358:811,2000

10.1098/rsta.2000.0560

astro-ph

Observations of jets from quasars and other types of accreting black hole are briefly summarized. The importance of beaming and $\gamma$-ray observations for understanding the origin of these jets is emphasised. It is argued that both the power source and the collimation are likely to be magnetic in origin, although the details remain controversial. Ultrarelativistic jets may be formed by the spinning hole and collimated by a hydromagnetic disc wind. Progress in understanding jets has been handicapped by our inadequate knowledge of how magnetic field really behaves under cosmic conditions. Fortunately, significant insights are coming from solar observations, numerical simulation and laboratory plasma experiments. Some possible, evolutionary ramifications are briefly discussed and it is suggested that it is the mass of the black hole relative to that of the galaxy which determines the eventual galaxy morphology.

2010-04-23

astro-ph/0001500

C. R. Keeton

C. R. Keeton (Arizona), E. E. Falco (CfA), C. D. Impey (Arizona), C. S. Kochanek, J. Lehar, B. A. McLeod (CfA), H.-W. Rix (MPIA), J. A. Munoz (CfA), C. Y. Peng (Arizona)

The Host Galaxy of the Lensed Quasar Q 0957+561

Submitted to ApJ; 33 pages with 3 embedded figures, plus 6 GIF figures; full paper with all figures embedded available at http://cfa-www.harvard.edu/glensdata/papers.html

10.1086/309517

astro-ph

Infrared images of the Q 0957+561 gravitational lens obtained with the Hubble Space Telescope show two large (\sim 5 arcsec) lensed images of the z_s=1.41 quasar host galaxy. Parts of the host galaxy are doubly-imaged like the quasar, while other parts are quadruply-imaged. The distortions of the host galaxy offer the best probe yet of the global structure of the lensing potential, which is essential for determining the Hubble constant from the measured time delay. The distortions are inconsistent with the predictions of previously published lens models, which invalidates those models and their implications for H_0. New models show that the distortions finally break the long-standing degeneracy between the shape of the lens galaxy and the tidal shear contributed by the cluster containing the lens galaxy. The shape of the lens galaxy's mass distribution must be remarkably similar to the shape of its luminosity distribution, and most models that produce reasonable values for the Hubble constant roughly match the observed ellipticity gradient and isophote twist of the lens galaxy. Also, the cluster must be non-spherical and produce a relatively small tidal shear. Although there are still degeneracies in the lens models that lead to a 25% uncertainty in the derived value of the Hubble constant, there are also strong prospects for new observations to further improve the constraints and reduce the uncertainties.

2009-10-31