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astro-ph/0001201

F. Nicastro

F. Nicastro (1,2,3), L. Piro (1), A. De Rosa (1), M. Feroci (1), P. Grandi (1), F. Fiore (3), M. Elvis (2), F. Haardt (4), J. Kaastra (5), A. Malizia (6), L. Maraschi(7), G. Matt(8), G. C. Perola(8), P. O. Petrucci (7) ((1) IAS-CNR, Roma, Italy, (2) CfA, Cambridge, MA, USA, (3) Oss. Astr. di Roma, Monteporzio-Catone, Italy, (4) Uni. di Milano, Milano, Italy, (5) SRON, Utrecht, The Netherlands, (6) BeppoSAX-SDC, Rome, Italy, (7) Oss. Astr. di Brera, Milano, Italy, (8) Uni. degli Studi Roma-Tre, Roma, Italy)

A Long Observation of NGC 5548 by BeppoSAX: the High Energy Cut-off, Intrinsic Spectral Variability and a Truly Warm Absorber

23 pages, 8 figures. Accepted for publication in The Astrophysical Journal

10.1086/308950

astro-ph

NGC 5548 was observed by BeppoSAX in a single long (8 day) observation from 0.2 to 200 keV. We find (1) the spectral variation of the source is produced by a change of the intrinsic power law slope; (2) a high energy cut-off at $E_c= 115^{+39}_{-27}$ keV with a hint of change of $E_c$ with flux; (3) OVII and OVIII absorption K edges, and a possible blended OVII-OVIII K$\alpha,\beta$ emission feature at $0.54^{+0.07}_{-0.06}$ keV, inconsistent with a purely photoionized gas in equilibrium. We propose that the temperature of the absorbing and emitting gas is $\sim 10^6$ K so that both collisional ionization and photoionization contribute.

2009-10-31

astro-ph/0001202

Pavel Kroupa

Pavel Kroupa

Stellar-Dynamics of Young Star Clusters

8 pages, to appear in Massive Stellar Clusters, eds: A. Lancon, C. Boily, PASP Conf.Series, revised version is slightly shorter and contains additional references

astro-ph

The stellar-dynamical evolution of bound star clusters during the first few Myr is dominated by binary-binary and binary-star interactions, the rapid sinking of the most massive stars to the centre of the clusters and mass loss from evolving stars. The consequences of these processes for the binary and stellar population in clusters, and for the star clusters as a whole, are studied by following the evolution over 150 Myr of a library of compact cluster models containing up to 10^4 stars.

2007-05-23

astro-ph/0001203

Hameury

Kristen Menou, Jean-Marie Hameury, Jean-Pierre Lasota and Ramesh Narayan

Disc instability models for X-ray transients: evidence for evaporation and low alpha-viscosity ?

14 pages, 8 figures; accepted for publication in MNRAS

10.1046/j.1365-8711.2000.03357.x

astro-ph

We construct time-dependent models of accretion discs around black holes and neutron stars. We investigate the effect of evaporating the disc inner regions during quiescence on the predictions of the Disc Instability Model (DIM) for these systems. We do not include irradiation of the disc in the models. Removing the inner, most unstable parts of the accretion disc increases the predicted recurrence times. However, DIMs with values of the viscosity parameter alpha_hot ~ 0.1 and alpha_cold ~ 0.02 (typical of applications of the DIM to standard dwarf nova outbursts) fail to reproduce the long recurrence times of SXTs (unless we resort to fine-tuning of the parameters) independent of the evaporation strength. We show that models with evaporation and a smaller value of alpha_cold (~ 0.005) do reproduce the long recurrence times and the accretion rates at the level of the Eddington rate observed in outburst. The large difference between the values of alpha_hot and alpha_cold, if confirmed when disc irradiation is included, suggests that several viscosity mechanisms operate in these accretion discs. For some choices of parameters our models predict reflares during the decline from outburst. They are a physical property of the model and result from a heating front forming in the wake of an initial cooling front and subsequent, multiple front reflections. The reflares disappear in low-alpha models where front reflection can not occur.

2009-10-31

astro-ph/0001204

Werner Collmar

W. Collmar, O. Reimer, K. Bennett, H. Bloemen, W. Hermsen, G.G. Lichti, J. Ryan, V. Schoenfelder, H. Steinle, O.R. Williams, M. Boettcher

A large high-energy gamma-ray flare from the blazar 3C 273

9 pages including 7 figures, accepted for publication in A&A

astro-ph

The Compton Gamma-Ray Observatory (CGRO) experiments EGRET and COMPTEL observed the Virgo sky region continuously for 7 weeks between December 10, 1996 and January 28, 1997. The prominent quasar 3C~273 was found to be the brightest source in gamma-rays and was significantly detected by EGRET and COMPTEL. The EGRET experiment observed a time-variable flux at energies above 100 MeV, which reached in a 2-week flaring period (December 30, 1996 to January 14, 1997) its highest flux level observed during the CGRO-era. COMPTEL, however, does not observe obvious time variability at energies below ~30 MeV contemporaneous to EGRET. In particular, no flare was observed, indicating that this outburst is solely a high-energy (>100 MeV) phenomenon. The energy spectrum between 3 MeV and 10 GeV is well represented by a simple power-law model. Below 3 MeV a spectral turnover is indicated. Performing spectral analysis for different time periods, we found evidence for a spectral hardening during the flaring period, which is consistent with the flare occurring mainly at the higher energies and with its absence at COMPTEL energies of a few MeV. This may be interpreted as an indication that the emission in the EGRET energy range is dominated by a different radiation mechanism than the MeV emission. We argue that the most likely mechanism for the high-energy flare is inverse-Compton scattering of reprocessed accretion-disk radiation.

2007-05-23

astro-ph/0001205

Krzysztof T. Chyzy

K. T. Chyzy, R. Beck, S. Kohle, U. Klein and M. Urbanik

Regular magnetic fields in the dwarf irregular galaxy NGC 4449

10 pages, 7 figures, accepted for publication in A&A, ps-file with the full paper at: http://www.oa.uj.edu.pl/~chris/publ/9419.ps.gz

astro-ph

We present a high-resolution VLA study of the total power and polarized radio continuum emission at 8.46 and 4.86 GHz of the irregular galaxy NGC 4449, known for its weak rotation and non-systematic gas motions. We found strong galaxy-scale regular magnetic fields, which is surprising because of a lack of ordered rotation required for the dynamo action. The strength of the regular field reaches 8 $\mu$G and that of the total field 14 $\mu$G, comparable to that of the total magnetic field strength in radio-bright spirals. The magnetic vectors in NGC 4449 form radial ``fans'' in the central region and fragments of a spiral pattern in the galaxy's outskirts. These structures are associated with large regions of systematic Faraday rotation, implying genuine galaxy-scale magnetic fields rather than random ones compressed and stretched by gas flows. The observed pattern of polarization B-vectors is similar to dynamo-type fields in normal spirals. Nonstandard, fast dynamo concepts are required to explain the observed field strengths, though it is unknown what kind of magnetic field geometry can be produced in slowly and chaotically rotating objects. The so far neglected role of magnetic fields for the dynamics and star formation in dwarf irregulars also needs to be revised.

2007-05-23

astro-ph/0001206

Claudia Winge

Claudia Winge (1), Thaisa Storchi-Bergmann (1), Martin J. Ward (2) and Andrew S. Wilson (3) ((1) IF-UFRGS, Brazil, (2) Univ. of Leicester, U.K., (3) Univ. of Maryland and STScI, U.S.A.)

Extended Gas in Seyfert Galaxies: Near-Infrared Observations of 15 Active Nuclei

19 pages (LaTeX, mn.sty), 27 Postscript figures embedded. Accepted for publication in the Monthly Notices of the R.A.S

Mon.Not.Roy.Astron.Soc. 316 (2000) 1

10.1046/j.1365-8711.2000.03614.x

astro-ph

Results from an analysis of low resolution (R~250) near-IR long-slit spectra covering simultaneously the I, J, H, and K bands, for a sample of 15 Seyfert galaxies and the N5253 starburst nucleus, are presented. The Seyfert galaxies were selected as presenting `linear' or cone-like high excitation emission line in the optical, most probably due to the collimation of the central source's radiation by a dusty molecular torus. Our goal was to look for signatures of this torus, and to investigate the gaseous distribution, excitation and reddening. The IR emission lines are spatially extended in most cases, and we have used the [FeII]/Pa(beta) ratio as a measure of the gaseous excitation in Mrk573, N1386, and N7582. Values for this ratio between 1.5 and 6 are found, suggesting excitation of [FeII] by X-rays or shock waves in some regions. Nuclear Pa(beta) in N1365, and possibly nuclear Br(gama) in Mrk573, are broad. From analysis of the spatial distribution of the continuum (J-H) and (H-K) colours derived from our spectra, we find redder colours for the nucleus than the nearby bulge in most of the Seyfert 2s observed. Comparison with models including emission from dust and stars shows that hot (T~1000 K) dust emission dominates the nuclear continuum in N1365, N2110, N3281, N7582, and ESO362-G18. In N1386, N5643, and N5728 the main contributor is the underlying stellar population, combined with some foreground reddening and/or cool dust emission. In a few cases, the (J-H) colours on opposite sides of the nucleus differ by 0.3-0.8 mag, an effect that we interpret as partly due to differences in the local stellar population, and possibly extinction gradients.

2009-10-31

astro-ph/0001207

Patrick Valageas

P. Valageas, J. Silk, R. Schaeffer

The redshift evolution of bias and baryonic matter distribution

13 pages, final version published in A&A

Astron.Astrophys. 366 (2001) 363

10.1051/0004-6361:20000351

astro-ph

We study the distribution of baryonic and luminous matter within the framework of a hierarchical scenario. Using an analytical model for structure formation which has already been checked against observations for galaxies, Lyman-$\alpha$ clouds, clusters and reionization processes, we present its predictions for the bias of these objects. We describe its dependence on the luminosity (for galaxies or quasars) or the column density (for Lyman-$\alpha$ absorbers) of the considered objects. We also study its redshift evolution, which can exhibit an intricate behaviour. These astrophysical objects do not trace the dark matter density field, the Lyman-$\alpha$ forest clouds being undercorrelated and the bright galaxies overcorrelated, while the intermediate class of Lyman-limit systems is seen to sample the matter field quite well. We also present the distribution of baryonic matter over these various objects. We show that light does not trace baryonic mass, since bright galaxies which contain most of the stars only form a small fraction of the mass associated with virialized and cooled halos. We consider two cosmologies: a critical density universe and an open universe. In both cases, our results agree with observations and show that hierarchical scenarios provide a good model for structure formation and can describe a wide range of objects which spans at least the seven orders of magnitude in mass for which data exist. More detailed observations, in particular of the clustering evolution of galaxies, will constrain the astrophysical models involved.

2016-08-30

astro-ph/0001208

Sarbani Basu

S. Basu, S. Turck-Chieze, G. Berthomieu, A. S. Brun, T. Corbard, J. Christensen-Dalsgaard, J. Provost, S. Thiery, A. H. Gabriel, P. Boumier

Structure of the solar core: Effect of asymmetry of peak profiles

To appear in ApJ

Astrophys.J.535:1078-1084,2000

10.1086/308875

astro-ph

Recent studies have established that peaks in solar oscillation power spectra are not Lorentzian in shape, but have a distinct asymmetry. Fitting a symmetric Lorentzian profile to the peaks therefore produces a shift in frequency of the modes. Accurate determination of low-frequency modes is essential to infer the structure of the solar core by inversion of the mode frequencies. In this paper we investigate how the changes in frequencies of low-degree modes obtained by fitting symmetric and asymmetric peak profiles change the inferred properties of the solar core. We use data obtained by the Global Oscillations at Low Frequencies (GOLF) project on board the SoHO spacecraft. Two different solar models and inversion procedures are used to invert the data to determine the sound speed in the solar core. We find that for a given set of modes no significant difference in the inferred sound-speed results from taking asymmetry into account when fitting the low-degree modes.

2008-11-26

astro-ph/0001209

Tim Roberts

T.P. Roberts and R.S. Warwick (University of Leicester)

A ROSAT HRI survey of bright nearby galaxies

20 pages, 7 figures, accepted for publication in MNRAS. Also available from http://www.star.le.ac.uk/~tro/papers/xhfs.ps

Mon.Not.Roy.Astron.Soc. 315 (2000) 98

10.1046/j.1365-8711.2000.03384.x

astro-ph

We use the extensive public archive of ROSAT High Resolution Imager (HRI) observations to carry out a statistical investigation of the X-ray properties of nearby galaxies. Specifically we focus on the sample of 486 bright (B_T < 12.5) northern galaxies studied by Ho, Filippenko and Sargent (HFS) in the context of their exploration of the optical spectroscopic properties of nearby galactic nuclei. Over 20% of HFS galaxies are encompassed in ROSAT HRI fields of reasonable (> 10ks) exposure. The X-ray sources detected within the optical extent of each galaxy are categorised as either nuclear or non-nuclear depending on whether the source is positioned within or outside of a 25 arcsecond radius circle centred on the optical nucleus. A nuclear X-ray source is detected in over 70% of the galaxies harbouring either a Seyfert or LINER nucleus compared to a detection rate of only ~40% in less active systems. The correlation of the H alpha luminosity with nuclear X-ray luminosity previously observed in QSOs and bright Seyfert 1 galaxies appears to extend down into the regime of ultra-low luminosity (L(x)~10^38 - 10^40 erg/s) active galactic nuclei (AGN). The inferred accretion rates for this sample of low-luminosity AGN are significantly sub-Eddington. In total 142 non-nuclear sources were detected. In combination with published data for M31 this leads to a luminosity distribution (normalised to an optical blue luminosity of L(B) = 10^10 L(solar)) for the discrete X-ray source population in spiral galaxies of the form dN/dL38 = 1.0 +/- 0.2 L38^-1.8, where L38 is the X-ray luminosity in units of 10^38 erg/s. The implied L(x)/L(B) ratio is ~1.1 x 10^39 erg/s/(10^10 L(solar)). The nature of the substantial number of ``super-luminous'' non-nuclear objects detected in the survey is discussed.

2009-10-31

astro-ph/0001210

Harald Kuntschner

Harald Kuntschner (University of Durham, UK)

The stellar populations of early-type galaxies in the Fornax cluster

25 pages. Accepted for publication in MNRAS

Astrophys.Space Sci. 276 (2001) 885-891

10.1023/A:1017525223856

astro-ph

We have measured central line strengths for a magnitude-limited sample of early-type galaxies in the Fornax cluster, comprising 11 elliptical (E) and 11 lenticular (S0) galaxies, more luminous than MB=-17. When compared with single-burst stellar population models we find that the centres of Fornax ellipticals follow a locus of fixed age and have metallicities varying roughly from half solar to two times solar. The centres of (lower luminosity) lenticular galaxies, however, exhibit a substantial spread to younger luminosity-weighted ages indicating a more extended star formation history. Galaxies with old stellar populations show tight scaling relations between metal-line indices and the central velocity dispersion. Remarkably also the Fe-lines are well correlated with sigma. Our detailed analysis of the stellar populations suggests that these scaling relations are driven mostly by metallicity. Galaxies with a young stellar component do generally deviate from the main relation. In particular the lower luminosity S0s show a large spread. Furthermore we find that elliptical galaxies and the bulge of one bright S0 are overabundant in magnesium, where the most luminous galaxies show the strongest overabundances. The stellar populations of young and faint S0s are consistent with solar abundance ratios or a weak Mg underabundance. (abriged)

2009-10-31

astro-ph/0001211

Jean-Pierre Lasota

A.A. Esin (Caltech), J.-P. Lasota (IAP) and R.I. Hynes (Southampton)

The 1996 outburst of GRO J1655-40: disc irradiation and enhanced mass transfer

Astronomy and Astrophysics - in press

astro-ph

We show that the 1996 outburst of the X-ray binary transient system GRO J1655-40 can be explained by the standard dwarf-nova type disc instability, followed by an episode of enhanced mass transfer from the secondary if the mass transfer rate in GRO J1655-40 is within a factor < 10 of the stability limit. We argue that irradiation of the secondary during the onset of the outburst driven by the thermal instability in the outer disc can increase the mass transfer rate above the minimum value required for stable accretion. This will then produce the period of near-constant X-ray emission seen in this system. This scenario can also explain the observed anti-correlation between the optical and X-ray fluxes. It is generally accepted that optical emission in low-mass X-ray binaries is produced by irradiation of the outer disc by X-rays. There is also strong circumstantial evidence that in order for the outer disc to see the irradiating flux, it must be warped. Depending on the warp propagation mechanism, either a burst of mass from the secondary or viscous decay are likely to decrease the degree of warping, thereby causing the decrease in the observed optical flux while the X-ray flux remains constant or even increases, exactly as observed in GRO J1655-40. Finally, the decrease of the disc warping and, therefore, irradiation will cause the disc to become unstable once again, terminating the outburst.

2007-05-23

astro-ph/0001212

Dr Pierre Maxted

P. F. L. Maxted (1), T. R. Marsh (1), C. K. J. Moran (1) and Z. Han (2) ((1) University of Southampton, (2) Yunnan Observatory, China)

The triple degenerate star WD1704+481

5 pages, 4 figures

MNRAS 314, 334, 2000

10.1046/j.1365-8711.2000.03343.x

astro-ph

WD1704+481 is a visual binary in which both components are white dwarfs. We present spectra of the H-alpha line of both stars which show that one component (WD1704+481.2 = Sanduleak B = GR 577) is a close binary with two white dwarf components. Thus, WD1704+481 is the first known triple degenerate star. From radial velocity measurements of the close binary we find an orbital period of 0.1448d, a mass ratio, q=Mbright/Mfaint of q=0.70+-0.03 and a difference in the gravitational redshifts of 11.5+-2.3km/s. The masses of the close pair of white dwarfs predicted by the mass ratio and gravitational redshift difference combined with theoretical cooling curves are 0.39+-0.05 solar mass and 0.56+-0.07 solar masses. WD1704+481 is therefore also likely to be the first example of a double degenerate in which the less massive white dwarf is composed of helium and the other white dwarf is composed of carbon and oxygen.

2009-10-31

astro-ph/0001213

Alexander Vilenkin

V. Berezinsky, B. Hnatyk, and A. Vilenkin

Superconducting cosmic strings as gamma ray burst engines

version submitted to PRL on 6 March 2000 (unpublished)

astro-ph gr-qc hep-ph hep-th

Cusps of superconducting strings can serve as GRB engines. A powerful beamed pulse of electromagnetic radiation from a cusp produces a jet of accelerated particles, whose propagation is terminated by the shock responsible for GRB. A single free parameter, the string scale of symmetry breaking $\eta \sim 10^{14} GeV$, together with reasonable assumptions about the magnitude of cosmic magnetic fields and the fraction of volume that they occupy, explains the GRB rate, duration and fluence, as well as the observed ranges of these quantities. The wiggles on the string can drive the short-time structures of GRB. This model predicts that GRBs are accompanied by strong bursts of gravitational radiation which should be detectable by LIGO, VIRGO and LISA detectors.

2007-05-23

astro-ph/0001214

Mario van den Ancker

M.E. van den Ancker, P.R. Wesselius and A.G.G.M. Tielens

ISO Spectroscopy of Young Intermediate-Mass Stars in the BD+40 4124 Group

17 pages, 12 figures, accepted for publication in Astronomy & Astrophysics

astro-ph

We present the results of ISO SWS and LWS grating scans towards the three brightest members of the BD+40 4124 group in the infrared: BD+40 4124 (B2Ve), LkHalpha 224 (A7e) and the embedded source LkHalpha 225. Emission from the pure rotational lines of H_2, from ro-vibrational transitions of CO, from PAHs, from H I recombination lines and from the infrared fine structure lines of [Fe II], [Si II], [S I], [O I], [O III] and [C II] was detected. These emission lines arise in the combination of a low-density (approx 10^2 cm^-3) H II region with a clumpy PDR in the case of BD+40 4124. The lower transitions of the infrared H I lines observed in BD+40 4124 are optically thick; most likely they arise in either a dense wind or a circumstellar disk. This same region is also responsible for the optical H I lines and the radio continuum emission. In the lines of sight towards LkHalpha 224 and LkHalpha 225, the observed emission lines arise in a non-dissociative shock produced by a slow (approx 20 km/s) outflow arising from LkHalpha 225. Toward LkHalpha 225 we also observe a dissociative shock, presumably located closer to the outflow source than the non-dissociative shock. In the line of sight towards LkHalpha 225 we observed absorption features due to solid water ice and amorphous silicates, and due to gas-phase H_2O, CO and CO_2. No solid CO_2 was detected towards LkHalpha 225, making this the first line of sight where the bulk of the CO_2 is in the gas-phase.

2007-05-23

astro-ph/0001215

Juan Carlos Lopez Vieyra

J. C. Lopez V

H_3^(2+) molecular ion in a strong magnetic field: a triangular configuration

8 pages, 3 figures, RevTex; typos corrected and some stylistic changes made

icn-unam 00-01

astro-ph

The bound state in the system of three protons and an electron (pppe) under a homogeneous strong magnetic field where the protons are situated in the vertices of an equilateral triangle perpendicular to the magnetic field lines is found. It is shown that for magnetic fields B = 10^11 - 4.414x10^13 G the potential energy curves as a function of the internuclear distance R have an explicit minimum. For all magnetic fields studied, the binding energy of the triangular configuration is less than the binding energy of the linear parallel configuration (A. Turbiner et al. JETP Lett. 69, p. 844). In the contrary to the linear case, the binding energy decreases with a magnetic field growth, while the equilibrium internuclear distance slowly increases.

2007-05-23

astro-ph/0001216

Yuri Mishurov

J.R.D.Lepine (Instituto Astronomico e Geofisico da USP, Brazil), Yu.N.Mishurov, S.Yu.Dedikov (Rostov State University, Russia)

A New Model for the Spiral Structure of the Galaxy. Superposition of 2+4-armed patterns

17 pages, 9 figures, Latex, uses aas2pp4.sty

10.1086/318225

astro-ph

We investigate the possibility of describing the spiral pattern of the Milky Way in terms of a model of superposition 2- and 4-armed wave harmonics (the simplest description, besides pure modes). Two complementary methods are used: a study of stellar kinematics, and direct tracing of positions of spiral arms. In the first method, the parameters of the galactic rotation curve and the free parameters of the spiral density waves were obtained from Cepheid kinematics, under different assumptions. To turn visible the structure corresponding to these models, we computed the evolution of an ensemble of N-particles, simulating the ISM clouds, in the perturbed galactic gravitational field. In the second method, we present a new analysis of the longitude-velocity (l-v) diagram of the sample of galactic HII regions, converting positions of spiral arms in the galactic plane into locii of these arms in the l-v diagram. Both methods indicate that the ``self-sustained'' model, in which the 2-armed and 4-armed mode have different pitch angles (6 arcdeg and 12 arcdeg, respectively) is a good description of the disk structure. An important conclusion is that the Sun happens to be practically at the corotation circle. As an additional result of our study, we propose an independent test for localization of the corotation circle in a spiral galaxy: a gap in the radial distribution of interstellar gas has to be observed in the corotation region.

2009-10-31

astro-ph/0001217

Dmitriy Bizyaev

D. V. Bizyaev (Sternberg Astronomical Institute)

Comparison of Star Formation Rate estimations from $H_{\alpha}$, FIR and radio data

7 pages including 3 PostScript figures. To be published in "The Evolution of galaxies on Cosmological timescales", Ap. & Space Science, Proceedings of the meeting held at Puerto de la Cruz (Spain) on November 30-December 5, 1998

10.1023/A:1017540132516

astro-ph

We used three indicators of massive star formation: $H_{\alpha}$, FIR and non-thermal radio luminosities, to compare estimations of Star Formation Rate (SFR) for the sample of 34 spiral galaxies. To adjust SFR values, obtained from different indicators, we considered the slope $\alpha$ and/or upper mass limit $M_{up}$ of Initial Mass Function (IMF) as free parameters. The best agreement between these indicators reaches for $M_{up} \approx 60 - 100 ~M_{\odot}$ and $\alpha \approx -3.1 $ in the high mass end of IMF ($M > 10 ~M_{\odot}$). Parallel with SFR we also estimated FIR excess $X_{FIR}$ defined as a fraction of the observed FIR which is not related to young massive stars directly. $X_{FIR}$ is found to be well correlated with types of spiral galaxies and their colors (B-V): the redder a galaxy the higher is its FIR excess. We conclude that for any parameters of IMF the observed FIR flux of early type spiral galaxies needs the additional source of energy but the massive star radiation.

2009-10-31

astro-ph/0001218

Kunihito Ioka

Kunihito Ioka and Keisuke Taniguchi

Gravitational waves from inspiralling compact binaries with magnetic dipole moments

15 pages, no figures, accepted for publication in ApJ

10.1086/309004

KUNS-1593, YITP-99-49

astro-ph gr-qc

We investigate the effects of the magnetic dipole-dipole coupling and the electromagnetic radiation on the frequency evolution of gravitational waves from inspiralling binary neutron stars with magnetic dipole moments. This study is motivated by the discovery of the superstrongly magnetized neutron stars, i.e., magnetar. We derive the contributions of the magnetic fields to the accumulated cycles in gravitational waves as $N_{mag} \sim 6 \times 10^{-3} (H/10^{16}{\rm G})^{2}$, where $H$ denotes the strength of the polar magnetic fields of each neutron star in the binary system. It is found that the effects of the magnetic fields will be negligible for the detection and the parameter estimation of gravitational waves, if the upper limit for magnetic fields of neutron stars are less than $\sim 10^{16}$G, which is the maximum magnetic field observed in the soft gamma repeaters and the anomalous X-ray pulsars up to date. We also discuss the implications of electromagnetic radiation from the inspiralling binary neutron stars for the precursory X-ray emission prior to the gamma ray burst observed by the Ginga satellite.

2009-10-31

astro-ph/0001219

Vladimir Avila-Reese

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

Disc galaxy evolution models in a hierarchical formation scenario: structure and dynamics

Accepted for publication in MNRAS. 19 pages including 11 figures. Replaced with revised version, some references added

Mon.Not.Roy.Astron.Soc.315:457,2000

10.1046/j.1365-8711.2000.03338.x

astro-ph

We predict the structure and dynamics of disc galaxies using galaxy evolution models within a hierarchical formation scenario The halo mass aggregation histories, for a Lambda CDM model, were generated and used to calculate the virialization of dark matter (DM) haloes. A diversity of halo density profiles were obtained, the most typical one being close to the NFW profile. We modeled the formation of discs in centrifugal equilibrium within the evolving DM haloes using gas accretion rates proportional to the halo mass aggregation rates, and assuming detailed angular momentum conservation. We calculated the gravitational interactions between halo and disc, and the hydrodynamics, star formation, and evolution of the galaxy discs. We found that the slope and zero-point of the infrared Tully-Fisher relations (TFR) may be explained as a direct consequence of the cosmological initial conditions. This relation is almost independent of the assumed disc mass fraction. The rms scatter of the TFR originates mainly from the scatter in the DM halo structure and, to a minor extension, from the dispersion of the primordial spin parameter. The scatter obtained does not disagree with the observational estimates. Our models allow us to understand why the residuals of the TFR do not correlate significantly with disc size or surface brightness (SB), and why low and high SB galaxies have the same TFR. The correlations between gas fraction and SB, and between scale length and V_max agree with those observed. The discs present nearly exponential SB distributions. The shape of the rotation curves changes with the SB and is nearly flat for most cases. The rotation curve decompositions show a dominance of DM down to very small radii. The introduction of shallow cores in the DM halo attenuates this difficulty.

2008-11-26

astro-ph/0001220

Takuji Tsujimoto

Takuji Tsujimoto, Toshikazu Shigeyama, Yuzuru Yoshii

Probing the Site for r-Process Nucleosyntheis with Abundances of Barium and Magnesium in Extremely Metal-Poor Stars

6 pages including 3 figures, to appear in ApJ Letters

10.1086/312514

astro-ph

We suggest that if the astrophysical site for r-process nucleosynthesis in the early Galaxy is confined to a narrow mass range of Type II supernova (SN II) progenitors, with a lower mass limit of Mms = 20 Msun, a unique feature in the observed distribution of [Ba/Mg] vs.[Mg/H] for extremely metal-poor stars can be adequately reproduced. We associate this feature, a bifurcation of the observed elemental ratios into two branches in the Mg abundance interval -2.7 < [Mg/H] < -2.3, with two distinct processes. The first branch, which we call the ``y''-branch, is associated with the production of Ba and Mg from individual massive supernovae. We conclude that SNe II with Mms = 20 Msun are the dominant source of r-process nucleosynthesis in the early Galaxy. An SN-induced chemical evolution model with this Mms-dependent Ba yield creates the y-branch, reflecting the different nucleosynthesis yields of [Ba/Mg] for each SN II with Mms > 20 Msun. The second branch, which we call the ``i''-branch, is associated with the elemental abundance ratios of stars which were formed in the dense shells of the interstellar medium swept up by SNe II with Mms < 20 Msun that do not synthesize r-process elements, and applies to stars with observed Mg abundances in the range [Mg/H] < -2.7. The Ba abundances in these stars reflect those of the interstellar gas at the (later) time of their formation. The existence of a [Ba/Mg] i-branch strongly suggests that SNe II which are associated with stars of progenitor mass Mms < 20 Msun are infertile sources for the production of r-process elements. We predict the existence of this i-branch for other r-process elements, such as europium (Eu), to the extent that their production site is in common with Ba.

2009-10-31

astro-ph/0001221

Vladimir Anguelov Anguelov

V. Anguelov and H. Vankov (INRNE, Sofia, Bulgaria)

Electromagnetic showers in a strong magnetic field

11 pages, 9 eps figures, LaTex2e, Iopart.cls, Iopart12.clo, Iopams.sty

J.Phys.G25:1755,1999

10.1088/0954-3899/25/8/317

astro-ph

We present the results concerning the main shower characteristics in a strong magnetic field obtained through shower simulation. The processes of magnetic bremsstrahlung and pair production were taken into account for values of the parameter $\chi \gg 1$. We compare our simulation results with a recently developed cascade theory in a strong magnetic field.

2016-08-30

astro-ph/0001222

John D. Larwood

P. Kalas, J. Larwood, and B.A. Smith, and A. Schultz

Rings in the Planetesimal Disk of Beta Pic

Accepted by ApJ Letters. LaTeX, 13 pages, 4 figures, full PostScript file available from http://www.maths.qmw.ac.uk/~jdl/

10.1086/312494

astro-ph

The nearby main sequence star Beta Pictoris is surrounded by an edge-on disk of dust produced by the collisional erosion of larger planetesimals. Here we report the discovery of substructure within the northeast extension of the disk midplane that may represent an asymmetric ring system around Beta Pic. We present a dynamical model showing that a close stellar flyby with a quiescient disk of planetesimals can create such rings, along with previously unexplained disk asymmetries. Thus we infer that Beta Pic's planetesimal disk was highly disrupted by a stellar encounter in the last hundred thousand years.

2009-10-31

astro-ph/0001223

Diego Saez

J.V. Arnau and D. Saez

Deconvolving the Beam in Small Angular Scale CMB Experiments

33 pages, 5 figures, to appear in New Astronomy

10.1016/S1384-1076(00)00019-1

astro-ph

This paper is concerned with experiments which measure CMB anisotropies on small angular scales. A certain coverage, a beam structure and a level of uncorrelated noise define each experiment. We focus our atention on the reversion of the beam average. In each experiment, we look for the best pixelization for reversion, namely, for the pixelization that -after reversion- leads to good maps containing right spectra for the most wide range of angular scales. Squared pixels having different sizes "smaller" than the beam radius are considered. For a given size, the following question arises: How well can we assign a temperature to each pixel? Various mathematical methods are used to show that, in practice, this assignation -beam reversion or deconvolution- only leads to right spectra for pixel sizes greater than a certain lower limit close to the half of the beam radius. This limit is estimated for negligible and relevant levels of noise and also for spherically symmetric and asymmetric beams. After this general study, we focus our attention on two feasible detectors (which have been proposed to be on board of PLANCK satellite). For each of them, we estimate the size of the most appropriate pixelization compatible with beam reversion, difraction, observational strategy et cetera and, then, we answer the following question: Which is the part of the angular power spectrum which can be extracted from appropriately pixelized maps after deconvolution?

2009-10-31

astro-ph/0001224

Didier Pelat

J. Moultaka, D. Pelat

Error analysis for stellar population synthesis as an inverse problem

11 pages, LaTeX, 4 figures, 1 table. M.N.R.A.S.(2000) in press

10.1046/j.1365-8711.2000.03394.x

astro-ph

Stellar population synthesis can be approached as an inverse problem. The physical information is extracted from the observations through an inverse model. The process requires the transformation of the observational errors into model errors. A description is given for the error analysis to obtain objectively the errors in the model. Finding a solution for overdetermined and under-determined case was the purpose of two preceding papers. This new one completes the problem of stellar populations synthesis by means of a data base, by providing practical formul\ae defining the set of acceptable solutions. All solutions within this set are compatible, at a given confidence level, with the observations.

2009-10-31

astro-ph/0001225

Doerte Mehlert

D. Mehlert (1), S. Seitz (2), R.P. Saglia (2), T.L. Hoffmann (2), I. Appenzeller (1), R. Bender (2), U, Hopp (2), R.-P. Kudritzki (2) A.W.A. Pauldrach (2) ((1) Landessternwarte Heidelberg, (2) Universitaetssternwarte Muenchen)

Spectra of High Redshift Galaxies using a Cluster as a Gravitational Telescope

7 pages, including 6 eps-files, Latex, uses lamuphys.sty, to appear in the proceedings of the Ringberg workshop " Galaxies in the Young Universe, II." held in August 1999 (eds. H. Hippelein, Springer)

astro-ph

Using the Focal Reducer Spectrograph (FORS) at the Very Large Telescope (VLT) during the FORS commissioning time in December 1998 we took long slit spectra of the gravitational arc visible on images of the galaxy cluster 1E 0657 (z = 0.296). This cluster is one of the hottest (massive) cluster known so far and hence perfectly acts as a gravitational telescope magnifying the flux of background sources up to a factor of 17. Here we present the spectra of the gravitational arc (z = 3.23) and 4 additional high redshift objects (z=2.35 to 3.09), that also fall on the slit by chance coincidence. We briefly discuss the stellar contents of these galaxies and show first models of the observed spectra. Furthermore we point out the effectivity of using FORS in combination with available gravitational telescopes.

2007-05-23

astro-ph/0001226

Dr Paul A. Crowther

Paul A. Crowther (University College London)

Wind properties of Wolf-Rayet stars at low metallicity: Sk41 (SMC)

9 pages, 6 figures, accepted for A&A (main journal)

astro-ph

The stellar properties of Sk41 (AB4, WN5h), the only known single Wolf-Rayet star in the SMC, are derived from ultraviolet (IUE), optical (AAT) and near-IR (NTT) spectroscopy. Contrary to expectations, the stellar properties of Sk41 are typical of equivalent WN stars in the Galaxy and LMC, with T=42kK, log(L/Lo)=5.7, v_inf=1300 km/s, Mdot/sqrt(f)=3x10^-5 Mo/yr and H/He=2 by number, where f is the volume filling factor. The stellar luminosity of Sk41 is 50% below the minimum value predicted by single star evolutionary models at the metallicity of the SMC. Emission line luminosities of HeII 4686A and CIV 5801-12A in SMC WR stars are not systematically lower than their Galactic and LMC counterparts. From 43 late-type and 59 early-type WN stars, log L(HeII)=36.0 erg/s and 35.8 erg/s respectively, while log L(CIV)=36.5 erg/s from 25 early-type WC stars. This new calibration has application in deriving WR populations in young starburst galaxies. Synthetic WN models are calculated with identical parameters except that metal abundances are varied. Following the Smith et al. WN classification scheme, CNO equilibrium models reveal that earlier spectral types are predicted at lower metallicity, i.e. WN3--4 at 0.04 Z(solar) versus WN6 at 1.0 Z(solar). This provides an explanation for the trend towards earlier WN spectral types at low metallicity.

2007-05-23

astro-ph/0001227

Tariq Shahbaz

T. Shahbaz (Oxford), P. Groot (Amsterdam), S.N. Phillips (Oxford), J. Casares (IAC), P.A. Charles (Oxford), J. van Paradijs (Amsterdam)

Irradiation of the secondary star in X-ray Nova Scorpii 1994 (=GRO J1655--40)

5 pages, 2 figures, accepted by MNRAS

10.1046/j.1365-8711.2000.03341.x

astro-ph

We have obtained intermediate resolution optical spectra of the black-hole candidate Nova Sco 1994 in June 1996, when the source was in an X-ray/optical active state (R~15.05). We measure the radial velocity curve of the secondary star and obtain a semi-amplitude of 279+/-10 km/s; a value which is 30 per cent larger than the value obtained when the source is in quiescence. Our large value for K_2 is consistent with 60 +9,-7 per cent of the secondary star's surface being heated; compared to 35 per cent, which is what one would expect if only the inner face of the secondary star were irradiated. Effects such as irradiation-induced flows on the secondary star may be important in explaining the observed large value for K_2.

2009-10-31

astro-ph/0001228

Dr Paul A. Crowther

Luc Dessart (UCL), Paul A. Crowther (UCL), D. John Hillier (Pittsburgh) Allan J. Willis (UCL), Patrick W. Morris (Amsterdam), Karel A. van der Hucht (Utrecht)

Quantitative analysis of WC stars: Constraints on neon abundances from ISO/SWS spectroscopy

16 pages,7 figures accepted for MNRAS

Mon.Not.Roy.Astron.Soc. 315 (2000) 407

10.1046/j.1365-8711.2000.03399.x

astro-ph

Neon abundances are derived in four Galactic WC stars -- gamma Vel (WR11, WC8+O7.5III), HD156385 (WR90, WC7), HD192103 (WR135, WC8), and WR146 (WC5+O8) - using mid-infrared fine structure lines obtained with ISO/SWS. Stellar parameters for each star are derived using a non-LTE model atmospheric code (Hillier & Miller 1998) together with ultraviolet (IUE), optical (INT, AAT) and infrared (UKIRT, ISO) spectroscopy. In the case of gamma Vel, we adopt results from De Marco et al. (2000), who followed an identical approach. ISO/SWS datasets reveal the [NeIII] 15.5um line in each of our targets, while [NeII] 12.8um, [SIV] 10.5um and [SIII] 18.7um are observed solely in gamma Vel. Using a method updated from Barlow et al. (1988) to account for clumped winds, we derive Ne/He=3-4x10^-3 by number, plus S/He=6x10^-5 for gamma Vel. Neon is highly enriched, such that Ne/S in gamma Vel is eight times higher than cosmic values. However, observed Ne/He ratios are a factor of two times lower than predictions of current evolutionary models of massive stars. An imprecise mass-loss and distance were responsible for the much greater discrepancy in neon content identified by Barlow et al. Our sample of WC5--8 stars span a narrow range in T* (=55--71kK), with no trend towards higher temperature at earlier spectral type, supporting earlier results for a larger sample by Koesterke & Hamann (1995). Stellar luminosities range from 100,000 to 500,000 Lo, while 10^-5.1 < Mdot/(Mo/yr) < 10^-4.5, adopting clumped winds, in which volume filling factors are 10%. In all cases, wind performance numbers are less than 10, significantly lower than recent estimates. Carbon abundances span 0.08 < C/He < 0.25 by number, while oxygen abundances remain poorly constrained.

2009-10-31

astro-ph/0001229

Donald Terndrup

J. R. Stauffer (1), R. D. Jeffries (2), E. L. Martin (3), and D. M. Terndrup (4) ((1) Center for Astrophysics, (2) Department of Physics, Keele University, (3) Planetary Sciences Division, Caltech, (4) Department of Astronomy, Ohio State University)

Ages, Distances, and the Initial Mass Functions of Stellar Clusters

13 pages, including 3 embedded figures (4 EPS files). To appear in "11th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun," ed. R. J. Garcia Lopez, R. Rebolo, and M. R. Zapatero Osorio

astro-ph

We provide a review of the current status of several topics on the ages, distances, and mass functions of open clusters, with a particular emphasis on illuminating the areas of uncertainty. Hipparcos has obtained parallaxes for nearby open clusters that have expected accuracies much better than has been previously achievable. By using the lithium depletion boundary method and isochrone fitting based on much improved new theoretical evolutionary models for low mass stars, it is arguable that we will soon have have much better age scales for clusters and star-forming regions. With improved optical and near-IR cameras, we are just now beginning to extend the mass function of open clusters like the Pleiades into the regime below the hydrogen burning mass limit. Meanwhile, observations in star-forming regions are in principle capable of identifying objects down to of order 10 Jupiter masses.

2007-05-23

astro-ph/0001230

Sean G. Ryan

Sean G. Ryan

7Li in Metal-Poor Stars: The Spread of the Li Plateau

Proc. IAU Symp. 198, "The Light Elements and Their Evolution", L. da Silva, R. de Medeiros, & M. Spite (eds), ASP Conf. Ser. xxx (2000). 10 pages including 5 figures

astro-ph

A highly homogeneous study of 23 halo field dwarf stars has achieved a Li abundance accuracy of 0.033 dex per star. The work shows that the intrinsic spread of the Li abundances of these stars at a given metallicity is <0.02 dex, and consistent with zero. That is, the Spite Li plateau for halo field dwarfs is incredibly thin. The thinness rules out depletion by more than 0.1 dex by a rotational-induced extra-mixing mechanism. Despite the thinness of the plateau, an increase of Li with [Fe/H] is seen, interpreted as evidence of Galactic chemical evolution (GCE) of Li, primarily due to Galactic cosmic ray (GCR) spallation reactions in the era of halo formation. The rate of Li evolution is concordant with: (1) observations of spallative 6Li in halo dwarfs; (2) GCE models; and (3) data on Li in higher metallicity halo stars. New data have also revealed four new ultra-Li-deficient halo dwarfs, doubling the number known. Based on their propensity to cluster at the halo main sequence turnoff and also to exist redward of the turnoff, we hypothesise that they are the products of binary mergers that ultimately will become blue stragglers. We explain their low Li abundances by normal pre-main-sequence (and possibly main-sequence) destruction in the low mass stars prior to their merging. If this explanation is correct, then such stars need no longer be considered an embarrassment to the existence of negligible Li destruction in the majority of field halo dwarfs.

2007-05-23

astro-ph/0001231

Sergio Molinari

Sergio Molinari, Jan Brand, Riccardo Cesaroni, Francesco Palla

A search for precursors of Ultracompact HII Regions in a sample of luminous IRAS sources. III: Circumstellar Dust Properties

14 pages, 6 figures, to be published on Astronomy and Astrophysics

astro-ph

The James Clerk Maxwell Telescope has been used to obtain submillimeter and millimeter continuum photometry of a sample of 30 IRAS sources previously studied in molecular lines and centimeter radio continuum. All the sources have IRAS colours typical of very young stellar objects (YSOs) and are associated with dense gas. In spite of their high luminosities (L>10000 solar units), only ten of these sources are also associated with a radio counterpart. In 17 cases we could identify a clear peak of millimeter emission associated with the IRAS source, while in 9 sources the millimeter emission was extended or faint and a clear peak could not be identified; upper limits were found in 4 cases only. Using simple greybody fitting model to the observed SED, we derive global properties of the circumstellar dust. The dust temperature varies from 24 K to 45 K, while the exponent of the dust emissivity vs frequency power-law spans a range 1.56<beta<2.38, characteristic of silicate dust; total circumstellar masses range up to more than 500 solar masses. We find that for sources with comparable luminosities, the total column densities derived from the dust masses do not distinguish between sources with and without radio counterpart. We interpret this result as an indication that dust does not play a dominant role in inhibiting the formation of the HII region. We examine several scenarios for their origin in terms of newborn ZAMS stars and although most of these fail to explain the observations, we cannot exclude that these sources are young stars already on the ZAMS with modest residual accretion that quenches the expansion of the HII region. Finally, we consider the possibility that the IRAS sources are high-mass pre-ZAMS (or pre-H-burning) objects deriving most of the emitted luminosity from accretion.

2007-05-23

astro-ph/0001232

Romano Corradi

Romano L.M. Corradi (Instituto de Astrofisica de Canarias, La Laguna, Tenerife, Spain)

Morphology vs. physical properties: some comments and questions

9 pages, to appear in ``Asymmetrical Planetary Nebulae II: from Origins to Microstructures,'' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N. Soker, & S.A. Rappaport, eds

astro-ph

Some of the correlations between morphological and other physical properties of planetary nebulae (PNe) are reviewed. In particular, the finding that bipolar (b) PNe have more massive progenitors than the other morphological classes is discussed in detail. Earlier results are confirmed; including all the various sources of uncertainty, the Galactic distribution of objects indicate that b PNe are formed by stars with initial masses >1.3 solar masses, while elliptical (e) PNe by progenitors with masses <1.3 solar masses. Recent results for the chemical abundances of b and e PNe and their orientation within the Galaxy are also presented. Finally, the key role in the discussion of the formation of b PNe played by detached binary systems such as symbiotic stars is briefly discussed.

2007-05-23

astro-ph/0001233

Stuart D. Wick

Stuart D. Wick, Thomas W. Kephart, Thomas J. Weiler, and Peter L. Biermann

Signatures for a Cosmic Flux of Magnetic Monopoles

33 pages, 5 figures, revtex, to appear in Astro. Part. Phys

Astropart.Phys. 18 (2003) 663-687

10.1016/S0927-6505(02)00200-1

preprint VAND-TH-99-12

astro-ph hep-ex hep-ph

Any early universe phase transition occurring after inflation has the potential to populate the universe with relic magnetic monopoles. Observations of galactic magnetic fields, as well as observations matched with models for extragalactic magnetic fields, lead to the conclusion that monopoles of mass $\lsim 10^{15}$ GeV are accelerated in these fields to relativistic velocities. We explore the possible signatures of a cosmic flux of relativistic monopoles impinging on the earth. The electromagnetically-induced signatures of monopoles are reliable. The hadronically-induced signatures are highly model-dependent. Among our findings are (i) the electromagnetic energy losses of monopoles continuously initiate a protracted shower of small intensity; (ii) monopoles may traverse the earth's diameter, making them a probe of the earth's interior structure; (iii) in addition to the direct monopole Cherenkov signal presently employed, a very attractive search strategy for monopoles is detection of their radio-Cherenkov signal produced by the coherent charge-excess in the $e^+-e^-$ shower - in fact, Cherenkov-detectors have the potential to discover a monopole flux (or limit it) several orders of magnitude below the theoretical Parker limit of $10^{-15}/\rm{cm}^2$/s/sr; (iv) it is conceivable (but not compelling) that bound states of colored monopoles may be the primary particles initiating the air showers observed above the GZK cutoff.

2009-10-31

astro-ph/0001234

Romano Corradi

R.L.M. Corradi (1), M. Livio (2), H.E. Schwarz (3) & U. Munari (4) ((1) Instituto de Astrofisica de Canarias, Spain (2) Space Telescope Science Institute, USA (3) Nordic Optical Telescope, Spain (4) Osservatorio Astronomico di Padova, Italy)

Symbiotic Miras can do it

4 pages, to appear in ``Asymmetrical Planetary Nebulae II: from Origins to Microstructures,'' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N. Soker, & S.A. Rappaport, eds

astro-ph

Symbiotic Miras give a nice practical demonstration of the formation of bipolar and highly aspherical nebulae as a consequence of interaction in detached binaries. We believe that these binary systems are among the most promising candidates for the progenitors of bipolar planetary nebulae. We present a list of the optically extended nebulae known to date around symbiotic Miras, and illustrate their properties using recent HST and ESO-NTT [NII] images of He 2-104 and He 2-147.

2007-05-23

astro-ph/0001235

Sean G. Ryan

Sean G. Ryan

Abundances in Very Metal-Poor Stars

Proc. 35th Liege International Astrophysics Colloquium, Liege, 1999 "The Galactic Halo: From Globular Clusters to Field Stars" A. Noels, P. Magain, D. Caro, E. Jehin, G. Parmentier, & A. Thoul (eds) 16 pages including 7 figures

astro-ph

Metal-poor stars provide information on the characteristics and chemical evolution of the halo population of the Galaxy, the first epoch of star formation and Galaxy formation (not just locally but with relevance to high-redshift objects), and big bang nucleosynthesis. This review looks at recent developments in this subject.

2007-05-23

astro-ph/0001236

Joe McCauley

J. L. McCauley

The Galaxy Distribution: Homogeneous, Fractal, or Neither

Fractals 6 (1998) 109-119

astro-ph

From the standpoint of theoretical physics we can treat Newtonian cosmology as a problem in nonlinear dynamics. The attempt to average the density, in search of a method of making contact between theory and observation, is replaced by the more systematic idea of coarsegraining. I also explain in this context why two previous attempts at the construction of hierarchical models of the universe are not useful in data analysis. The main ideas behind two older competing data analyses purporting to show evidence from galaxy statistics for either a homogeneous and isotropic universe in one case, and for a mono-fractal universe in the other, are presented and discussed. I also present the method and results of a newer data analysis that shows that visible matter provides no evidence that would allow us to claim that the cosmological principle holds, or that the universe is fractal (or multifractal). In other words, observational data provides us with no evidence that the universe is either homogeneous and isotropic, or monofractal.

2007-05-23

astro-ph/0001237

David B. Cline

David B. Cline

A Novel Supernova Detector

4 pages containing 5 figures, 4 tables; workshop on Next Generation Nucleon Decay and Neutrino Detectors, NNN99 (SUNY at Stony Brook, NY, Sept. 23-25, 1999), and to be published by the American institute of Physics

AIP Conf.Proc.533:124-127,2000

10.1063/1.1361733

UCLA APH-0122-12/99

astro-ph

We discuss the prospects for detecting nu_{mu,tau} and nu_{tau}neutrinos from Type II supernovas using the novel detector at the Supernova Burst Observatory (SNBO) or OMNIS that is being designed for an underground laboratory in the USA. This detector would collect ~2000 flavor selected events from a Galactic supernova and could probe neutrino mass down to a few eV, as well as the dynamics of the supernova process. We believe this is essential to further our understanding of the neutrino section of elementary particle physics.

2009-09-28

astro-ph/0001238

Lilia Bassino

L. P. Bassino (1), S. Waldhausen (1), R. E. Martinez (1) ((1) Universidad Nacional de La Plata, Argentina)

CCD photometry in the region of NGC 6994: the remains of an old open cluster

10 pages including 11 figures and 1 table. Accepted for publication in Astronomy & Astrophysics

astro-ph

We present the results of BV(RI)_KC CCD photometry down to V=21 mag in the region of NGC 6994. To our knowledge, no photometry has previously been reported for this object and we find evidences that it is a poor and sparse old open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the 3 arcmin originally assigned to it. We obtain a color excess E(B-V) = 0.07 +/- 0.02 mag by means of the BVI_(C) technique. Based on the theoretical isochrones from VandenBergh (1985) that are in better agreement with our data, we estimate for this cluster a distance from the Sun of 620 pc (Vo-Mv = 9 +/- 0.25 mag) and an age lying within the range of 2 - 3 Gyr, adopting solar metallicity. Thus, the corresponding cluster's Galactocentric distance is 8.1 kpc and is placed at about 350 pc below the Galactic plane. According to this results, NGC 6994 belongs to the old open cluster population located in the outer disk and at large distances from the Galactic plane, and must have suffered significant individual dynamical evolution, resulting in mass segregation and evaporation of low mass stars.

2007-05-23

astro-ph/0001239

Demosthenes Kazanas

Andrew J. Berkley, Demosthenes Kazanas and Jonathan Ozik

Modeling the X-ray - UV Correlations in NGC 7469

16 pages, 13 figures, ApJ in press

10.1086/308880

astro-ph

We model the correlated X-ray - UV observations of NGC 7469, for which well sampled data in both these bands have been obtained recently in a multiwavelength monitoring campaign. To this end we derive the transfer function in wavelength \ls and time lag \t, for reprocessing hard (X-ray) photons from a point source to softer ones (UV-optical) by an infinite plane (representing a cool, thin accretion disk) located at a given distance below the X-ray source, under the assumption that the X-ray flux is absorbed and emitted locally by the disk as a black body of temperature appropriate to the incident flux. Using the observed X-ray light curve as input we have computed the expected continuum UV emission as a function of time at several wavelengths (\l \l 1315 \AA, \l \l 6962 \AA, \l \l 15000 \AA, \l \l 30000 \AA) assuming that the X-ray source is located one \sc radius above the disk plane, with the mass of the black hole $M$ and the latitude angle $\theta$ of the observer relative to the disk plane as free parameters. We have searched the parameter space of black hole masses and observer azimuthal angles but we were unable to reproduce UV light curves which would resemble, even remotely, those observed. We also explored whether particular combinations of the values of these parameters could lead to light curves whose statistical properties (i.e. the autocorrelation and cross correlation functions) would match those corresponding to the observed UV light curve at \l \l 1315 \AA. Even though we considered black hole masses as large as $10^9$ M$_{\odot}$ no such match was possible. Our results indicate that some of the fundamental assumptions of this model will have to be modified to obtain even approximate agreement between the observed and model X-ray - UV light curves.

2009-10-31

astro-ph/0001240

Munshi Dipak

Dipak Munshi (MPA)

Probing The Gravity Induced Bias with Weak Lensing: Test of Analytical results Against Simulations

17 pages including 8 figures and 1 table, MNRAS, submitted

Mon.Not.Roy.Astron.Soc.318:145,2000

10.1046/j.1365-8711.2000.03707.x

astro-ph

Future weak lensing surveys will directly probe the density fluctuation in the universe. Recent studies have shown how the statistics of the weak lensing convergence field is related to the statistics of collapsed objects. Extending earlier analytical results on the probability distribution function of the convergence field we show that the bias associated with the convergence field can directly be related to the bias associated with the statistics of underlying over-dense objects. This will provide us a direct method to study the gravity induced bias in galaxy clustering. Based on our analytical results which use the hierarchical {\em ansatz} for non-linear clustering, we study how such a bias depends on the smoothing angle and the source red-shift. We compare our analytical results against ray tracing experiments through N-body simulations of four different realistic cosmological scenarios and found a very good match. Our study shows that the bias in the convergence map strongly depends on the background geometry and hence can help us in distinguishing different cosmological models in addition to improving our understanding of the gravity induced bias in galaxy clustering.

2008-11-26

astro-ph/0001241

Mark Dragovan

Mark Dragovan

Low Mass Density Wide Field Far-IR/Submillimeter Telescope Systems

4 pages, 3 figures

astro-ph

Fundamentally new technology is described for constructing low areal mass density (1kg/m^2), high precision (< 10micron RMS) reflectors scalable to large apertures (10 to 20 meters) for use as the primary element of a telescope system. A large reduction in mass is achieved by minimizing the mass of the reflective surface using a high reflectivity metallic membrane. A wide field diffraction limited telescope system can be constructed using the primary reflector in conjunction with secondary and tertiary optics.

2009-09-25

astro-ph/0001242

Demosthenes Kazanas

Demosthenes Kazanas

Models of the Time Variability of BHC: Light Curves, PSD, Lags

to appear in "The Neutron Star - Black Hole Connection", proceedings of NATO Advanced Study Institute, 7 - 18 June 1999, Elounda, Crete, Greece

astro-ph

We present a model for the aperiodic variablity of accreting Black Hole Candidates (BHC) along with model light curves. According to the model this variability is the combined outcome of random (Poisson) injection of soft photons near the center of an extended {\sl inhomogeneous} distribution of hot electrons (similar to those advocated by the ADAF or ADIOS flows) and the stochastic nature of Compton scattering which converts these soft photons into the observed high energy radiation. Thus, the timing properties (PSD, lags, coherence) of the BHC light curves reflect, to a large extent, the properties of the scattering medium (which in this approximation acts as a combination of a {\sl linear} amplifier/filter) and they can be used to probe its structure, most notably the density profile of the scattering medium. The model accounts well for the observed PSDs and lags and also the reduction in the RMS variability and the increase in the characteristic PSD frequencies with increasing source luminosity. The electron density profiles obtained to date are consistent mainly with those of ADIOS but also with pure ADAF flows.

2007-05-23

astro-ph/0001243

David B. Cline

David B. Cline

A WIMP Detector with Two-Phase Liquid Xenon

3 pages with 4 figures; for Proceedings, Sixth Int'l Wksp. On Topics in Astroparticle and Underground Physics, TAUP99 (College de France, Paris, Sept. 6-10, 1999), to be published in Nucl. Phys. B(PS)

Nucl.Phys.Proc.Suppl. 87 (2000) 114-116

10.1016/S0920-5632(00)00649-6

UCLA APH-0123-12/99

astro-ph

We describe the liquid-xenon dark-matter detector program of the UCLA-Torino team. A two-phase detector, ZEPLIN II, for the Boulby Mine is a good match for the current search for WIMP dark matter.

2009-10-31

astro-ph/0001244

Kristy K. Dyer

K.K. Dyer, S.P. Reynolds, K.J. Borkowski

New Models for X-Ray Synchrotron Radiation from the Remnant of Supernova 1006 AD

10 pages, 2 figures. to appear in "Cosmic Explosions", proceeding of the 10th Annual October Astrophysics Conference (ed. S.S. Holt and W. W. Zhang) LaTex aipproc.sty

10.1063/1.1291700

astro-ph

Galactic cosmic rays up to energies of around 10^15 eV are assumed to originate in supernova remnants (SNRs). The shock wave of a young SNR like SN 1006 AD can accelerate electrons to energies greater than 1 TeV, where they can produce synchrotron radiation in the X-ray band. A new model (SRESC) designed to model synchrotron X-rays from Type Ia supernovae can constrain values for the magnetic-field strength and electron scattering properties, with implications for the acceleration of the unseen ions which dominate the cosmic-ray energetics. New observations by ASCA, ROSAT, and RXTE have provided enormously improved data, which now extend to higher X-ray energies. These data allow much firmer constraints. We will describe model fits to these new data on SN 1006 AD, emphasizing the physical constraints that can be placed on SNRs and on the cosmic-ray acceleration process.

2009-10-31

astro-ph/0001245

Bennett Link

Bennett Link (1,2), Richard I. Epstein (2) and James M. Lattimer (3) ((1) Montana State University, (2) Los Alamos National Laboratory, (3) State University of New York, Stony Brook)

Probing the Neutron Star Interior with Glitches

Invited talk at the Pacific Rim Conference on Stellar Astrophysics, Hong Kong, Aug. 1999. 9 pages, 5 figures

10.1007/978-94-010-0878-5_14

astro-ph

With the aim of constraining the structural properties of neutron stars and the equation of state of dense matter, we study sudden spin-ups, glitches, occurring in the Vela pulsar and in six other pulsars. We present evidence that glitches represent a self-regulating instability for which the star prepares over a waiting time. The angular momentum requirements of glitches in Vela indicate that at least 1.4% of the star's moment of inertia drives these events. If glitches originate in the liquid of the inner crust, Vela's `radiation radius' $R_\infty$ must exceed ~12 km for a mass of 1.4 solar masses. The isolated neutron star RX J18563-3754 is a promising candidate for a definitive radius measurement, and offers to further our understanding of dense matter and the origin of glitches.

2016-01-27

astro-ph/0001246

Sanjay K. Ghosh

Shibaji Banerjee, Sanjay K. Ghosh and Sibaji Raha

The Chandrasekhar limit for quark stars

LateX file

J.Phys. G26 (2000) L1-L4

10.1088/0954-3899/26/1/101

astro-ph

The Chandrasekhar limit for quark stars is evaluated from simple energy balance relations, as proposed by Landau for white dwarfs or neutron stars. It has been found that the limit for quark stars depends on, in addition to the fundamental constants, the Bag constant.

2009-10-31

astro-ph/0001247

Martin White

Martin White and Rupert A.C. Croft

Suppressing Linear Power on Dwarf Galaxy Halo Scales

9 pages, 9 figures

Astrophys.J.539:497,2000

10.1086/309273

astro-ph

Recently is has been suggested that the dearth of small halos around the Milky Way arises due to a modification of the primordial power spectrum of fluctuations from inflation. Such modifications would be expected to alter the formation of structure from bottom-up to top-down on scales near where the short-scale power has been suppressed. Using cosmological simulations we study the effects of such a modification of the initial power spectrum. While the halo multiplicity function depends primarily on the linear theory power spectrum, most other probes of power are more sensitive to the non-linear power spectrum. Collapse of large-scale structures as they go non-linear regenerates a ``tail'' in the power spectrum, masking small-scale modifications to the primordial power spectrum except at very high-z. Even the small-scale (k>2h/Mpc) clustering of the Ly-alpha forest is affected by this process, so that CDM models with sufficient power suppression to reduce the number of 10^10 Msun halos by a factor of about 5 give similar Ly-alpha forest power spectrum results. We conclude that other observations that depend more directly on the number density of collapsed objects, such as the number of damped Ly-alpha systems, or the redshift of reionization may provide the most sensitive tests of these models.

2009-08-18

astro-ph/0001248

Nicholas B. Suntzeff

Nicholas B. Suntzeff (Cerro Tololo Inter-American Observatory)

The Observations of Type Ia Supernovae

10 pages, aipproc LaTeX, two eps figures, to be published in "Cosmic Explosions! The Proceedings of the Tenth Maryland Conference on Astrophysics," eds, Steven S. Holt and William W. Zhang, AIP

10.1063/1.1291696

astro-ph

The past ten years have seen a tremendous increase in the number of Type Ia supernovae discovered and in the quality of the basic data presented. The cosmological results based on distances to Type Ia events have been spectacular, leading to statistically accurate values of the Hubble constant, Omega_M, and Omega_Lambda. However, in spite of the recent advances, a number of mysteries continue to remain in our understanding of these events. In this short review, I will concentrate on unresolved problems and curious correlations in the data on Type Ia SNe, whose resolution may lead to a deeper understanding of the physical mechanism of the Type Ia supernova explosions.

2009-10-31

astro-ph/0001249

Jin Koda

Jin Koda, Yoshiaki Sofue (IoA, U.Tokyo), Keiichi Wada (NAO, Japan)

A Unified Scaling Law in Spiral Galaxies

Accepted for publication in ApJ Letters. 6 pages including 2 figures

10.1086/312509

astro-ph

We investigate the origin of a unified scaling relation in spiral galaxies. Observed spiral galaxies are spread on a plane in the three-dimensionallogarithmic space of luminosity L, radius R and rotation velocity V. The plane is expressed as $L \propto (V R)^{\alpha}$ in I-passband, where $\alpha$ is a constant. On the plane, observed galaxies are distributed in an elongated region which looks like the shape of a surfboard. The well-known scaling relations, L-V (Tully-Fisher relation), V-R (also the Tully-Fisher relation) and R-L (Freeman's law), can be understood as oblique projections of the surfboard-like plane into 2-D spaces. This unified interpretation of the known scaling relations should be a clue to understand the physical origin of all the relations consistently. Furthermore, this interpretation can also explain why previous studies could not find any correlation between TF residuals and radius. In order to clarify the origin of this plane, we simulate formation and evolution of spiral galaxies with the N-body/SPH method, including cooling, star formation and stellar feedback. Initial conditions are set to isolated 14 spheres with two free parameters, such as mass and angular momentum. The CDM (h=0.5, $\Omega_0=1$) cosmology is considered as a test case. The simulations provide the following two conclusions: (a) The slope of the plane is well reproduced but the zero-point is not. This zero-point discrepancy could be solved in a low density ($\Omega_0<1$) and high expansion (h>0.5) cosmology. (b) The surfboard-shaped plane can be explained by the control of galactic mass and angular momentum.

2009-10-31

astro-ph/0001250

F. P. Israel

F.P. Israel (Sterrewacht Leiden)

Extragalactic H2 and its variable relation to CO

4 pages, 2 figures, in: "H2 in Space", Cambridge University Press, ed. F. Combes and G. Pineau des Forets

astro-ph

A steep metallicity dependence of the CO-to-H2 conversion factor X of the form log X = 12.2 - 2.5 log[O]/[H], based on a sample of 20 (extra)galactic determinations, is presented and discussed. The apparently less steep dependence found from millimeter interferometer observations is explained within the context of photon-dominated regions.

2007-05-23

astro-ph/0001251

Chamula Marian

V. Skalsky

A problem of hypothetical emerging of cosmic background radiation photons on horizon in the standard model of universe

3 pages

Skalsky, V. & Sukenik, M.: Radiation of the cosmic background, Astrophysics and Space Science (ISSN 0004-640X), vol. 187, No 1, pp. 155-158, 01/1992

astro-ph

The present temperature of cosmic background radiation and the present number density of photons of cosmic background radiation in the observed expansive and isotropic relativistic Universe is in the standard model of universe explained by the assumption of emergence of the photons of cosmic background radiation on the horizon (of the most remote visibility). However, the physical analysis shows unambiguously that this assumption contradicts the special theory of relativity and the quantum mechanics.

2008-12-19

astro-ph/0001252

Vladimir Anguelov Anguelov

V. Anguelov (1), S. Petrov (1), L. Gurdev (2), J. Kourtev (2) ((1)INRNE, Sofia, Bulgaria, (2)IE, Sofia, Bulgaria)

On the numerical analysis of triplet pair production cross-sections and the mean energy of produced particles for modelling electron-photon cascade in a soft photon field

18 pages, 8 figures, 2 tables, LaTex2e, Iopart.cls, Iopart12.clo, Iopams.sty

J.Phys. G25 (1999) 1733

10.1088/0954-3899/25/8/315

astro-ph hep-ph

The double and single differential cross-sections with respect to positron and electron energies as well as the total cross-section of triplet production in the laboratory frame are calculated numerically in order to develop a Monte Carlo code for modelling electron-photon cascades in a soft photon field. To avoid numerical integration irregularities of the integrands, which are inherent to problems of this type, we have used suitable substitutions in combination with a modern powerful program code Mathematica allowing one to achieve reliable higher-precission results. The results obtained for the total cross-section closely agree with others estimated analytically or by a different numerical approach. The results for the double and single differential cross-sections turn out to be somewhat different from some reported recently. The mean energy of the produced particles, as a function of the characteristic collisional parameter (the electron rest frame photon energy), is calculated and approximated by an analytical expression that revises other known approximations over a wide range of values of the argument. The primary-electron energy loss rate due to triplet pair production is shown to prevail over the inverse Compton scattering loss rate at several ($\sim$2) orders of magnitude higher interaction energy than that predicted formerly.

2009-10-31

astro-ph/0001253

Donatella Romano

Donatella Romano (1) and Francesca Matteucci (2, 1) ((1) SISSA/ISAS, Italy, (2) Dipartimento di Astronomia, Univ. di Trieste, Italy)

The influence of nova nucleosynthesis on the chemical evolution of the Galaxy

8 pages, latex, 3 figures. To appear in "The Chemical Evolution of the Milky Way: Stars versus Clusters", eds. F. Giovannelli and F. Matteucci (Kluwer: Dordrecht)

10.1007/978-94-010-0938-6_54

astro-ph

We adopt up-to-date yields of 7Li, 13C, 15N from classical novae and use a well tested model for the chemical evolution of the Milky Way in order to predict the temporal evolution of these elemental species in the solar neighborhood. In spite of major uncertainties due to our lack of knowledge of metallicity effects on the final products of explosive nucleosynthesis in nova outbursts, we find a satisfactory agreement between theoretical predictions and observations for 7Li and 13C. On the contrary, 15N turns out to be overproduced by about an order of magnitude.

2016-01-27

astro-ph/0001254

Paola Andreani (1,2) Andrea Cimatti (3), Laurent Loinard (4), Huub Roettgering (5) ((1) Osservatorio Astronomico, Padova, Italy, (2) MPI f. Extr. Phys. Garching, Germany, (3) Osservatorio Astrofisico di Arcetri, Italy, (4) IRAM, Grenoble, France, (5) Sterrenwacht, Leiden, The Netherlands)

Co Detection of the Extremely Red Galaxy HR10

5 pages, A&A Letter, in press

Astron.Astrophys.354:L 1,2000

astro-ph

CO J = 5 - 4 and J = 2 - 1 emission lines were detected towards the extremely red galaxy (ERG) HR10 (J164502+4626.4) at z=1.44. The CO intensities imply a molecular gas mass M(H2) of 1.6 x 10^{11} h^{-2}_50 solar masses, and, combined with the intensity of the dust continuum, a gas-to-dust mass ratio around 200-400 (assuming galactic values for the conversion factors). The peak of the CO lines are at the same redshift as the [O II]3727 line, but blue- shifted by 430 km s^{-1} from the Halpha line. These CO detections confirm the previous results that HR10 is a highly obscured object with a large thermal far-infrared luminosity and a high star-formation rate. The overall properties of HR10 (CO detection, L_FIR to L'_CO ratio, and FIR to radio flux ratio) clearly favour the hypothesis that its extreme characteristics are related to star-formation processes rather than to a hidden AGN.

2011-05-23

astro-ph/0001255

Daniel Cormier

D. Cormier and R. Holman

Metric Perturbations and Inflationary Phase Transitions

4 pages, 3 figures, COSMO-99 Proceedings

10.1142/9789812792129_0027

astro-ph

We study the out of equilibrium dynamics of inflationary phase transitions and compute the resulting spectrum of metric perturbations relevant to observation. We show that simple single field models of inflation may produce an adiabatic perturbation spectrum with a blue spectral tilt and that the precise spectrum depends on initial conditions at the outset of inflation.

2016-11-03

astro-ph/0001256

Venturi Tiziana

T. Venturi (1), S. Bardelli (2), R. Morganti (1), R. W. Hunstead (3) ((1) IRA-CNR, Bologna, Italy, (2) Osservatorio Astronomico, Bologna, Italy, (3) School of Physics, University of Sydney, Australia)

Radio Properties of the Shapley Concentration. III. Merging Clusters in the A3558 Complex

18 pages, 14 figures. Accepted for publication on MNRAS

10.1046/j.1365-8711.2000.03403.x

BAP-01-2000-01-IRA

astro-ph

We present the results of a 22 cm radio survey carried out with the A3558 complex, a chain formed by the merging ACO clusters A3556-A3558-A3562 and thetwo groups SC1327-312 and SC1323-313, located in the central region of the complex, a chain formed by the merging ACO clusters A3556-A3558-A3562 and the two groups SC1327-312 and SC1323-313, located in the central region of the Shapley Concentration. The purpose of our survey is to study the effects of cluster mergers on the statistical properties of radio galaxies and to investigate the connection between mergers and the presence of radio halos and relic sources. We found that the radio source counts in the A3558 complex are consistent with the background source counts. Furthermore, we found that no correlation exists between the local density and the radio source power, and that steep spectrum radio galaxies are not segregated in denser optical regions. The radio luminosity function for elliptical and S0 galaxies is significantly lower than that for cluster type galaxies and for those not selected to be in clusters at radio powers logP(1.4) > 22.5, implying that the probability of a galaxy becoming a radio source above this power limit is lower in the Shapley Concentration compared with any other environment. The detection of a head-tail source in the centre of A3562, coupled with careful inspection of the 20 cm NRAO VLA Sky Survey (NVSS) and of 36 cm MOST observations, allowed us to spot two extended sources in the region between A3562 and SC1329-313, i.e. a candidate radio halo at the centre of A3562, and low brightness extended emission around a 14.96 magnitude Shapley galaxy.

2009-10-31

astro-ph/0001257

Silvio Giordano

S. Giordano, E. Antonucci, G. Noci, M. Romoli, J.L. Kohl

Identification of the Coronal Sources of the Fast Solar Wind

14 pages, 4 figures, 3 tables, Accepted by ApJ Letters

10.1086/312525

astro-ph

The present spectroscopic study of the ultraviolet coronal emission in a polar hole, detected on April 6-9, 1996 with the Ultraviolet Coronagraph Spectrometer aboard the SOHO spacecraft, identifies the inter-plume lanes and background coronal hole regions as the channels where the fast solar wind is preferentially accelerated. In inter-plume lanes, at heliocentric distance 1.7 \rsun, the corona expands at a rate between 105 km/s and 150 km/s, that is, much faster than in plumes where the outflow velocity is between 0 km/s and 65 km/s. The wind velocity is inferred from the Doppler dimming of the O VI $\lambda\lambda$ 1032, 1037 \AA lines, within a range of values, whose lower and upper limit corresponds to anisotropic and isotropic velocity distribution of the oxygen coronal ions, respectively.

2009-10-31

astro-ph/0001258

Roberto Aloisio

R. Aloisio (Univ. Aq and INFN-LNGS), P. Blasi (FNAL), P.L. Ghia (CNR and INFN Turin), A.F. Grillo (INFN-LNGS)

Probing The Structure of Space-Time with Cosmic Rays

20 pages, 3 tables, no figures. Version to appear in Phys. Rev. D. A few changes in the presentation. Conclusions unchanged. Some references added

Phys.Rev. D62 (2000) 053010

10.1103/PhysRevD.62.053010

FERMILAB-Pub-00/011-A

astro-ph gr-qc hep-ph

The study of the interactions of Cosmic Rays (CR's) with universal diffuse background radiation can provide very stringent tests of the validity of Special Relativity. The interactions we consider are the ones characterized by well defined energy thresholds whose energy position can be predicted on the basis of Special Relativity. We argue that the experimental confirmation of the existence of these thresholds can in principle put very stringent limits on the scale where Special Relativity and/or continuity of space-time may possibly break down.

2009-10-31

astro-ph/0001259

Pavel Kroupa

Michael Fellhauer (ARI), Pavel Kroupa (MPIA/ITA)

Could merged star-clusters build up a small galaxy?

6 pages, to appear in Massive Stellar Clusters, eds: A. Lancon, C. Boily, ASP Conf.Series, revised version has improved formatting

astro-ph

We investigate the behaviour of a cluster of young massive star clusters (hereafter super-cluster) in the tidal field of a host galaxy with a high-resolution particle-mesh code, Superbox. Specifically we want to establish if and how such super star-clusters merge and carry out a detailed study of the resulting merger-object. This merger-object shows either the properties of a compact spherical object or the elongated (`fluffy') shape of dSph-galaxies depending on the initial concentration of the super-cluster.

2007-05-23

astro-ph/0001260

Michael Pierce

Michael J. Pierce (Indiana Univ.) and Robert C. Berrington (Indiana Univ.)

Evidence for Stellar Streaming in the Cores of Elliptical Galaxies: A Kinematic Signature of Mergers?

Latex, 5 pages, 2 figures

10.1086/312532

astro-ph

We present evidence for non-Gaussian velocity fields within the cores of luminous elliptical galaxies. This evidence is based upon high signal-to-noise, medium-resolution spectroscopy of the cores of early-type members of the Virgo and Coma clusters obtained with the WIYN 3.5-m telescope. The Virgo data were acquired using an integral-field unit (DensePak) allowing the velocity field to be sampled over a variety of spatial scales. The Coma data were obtained through single, 2-arcsec diameter fibers. The cross-correlation profiles of luminous ellipticals show considerable structure, often having several features with amplitudes as high as 10% that of the cross-correlation peak itself. This structure is most obvious within a radius of 1.5 arcsec (at Virgo), or < 100 pc, and is nearly undetectable when the data are binned over R < 15 arcsec, or < 1 kpc. Similar features are found in the single-fiber spectra of the luminous ellipticals in the Coma Cluster suggesting they are ubiquitous to giant ellipticals. Interesting, only the most luminous elliptical galaxies show this phenomena; the central regions of lower luminosity ellipticals have regular, Gaussian-like profiles. We interpret this kinematic structure as ``stellar streaming'' and suggest that this phenomena could be a relic signature of the merger history of luminous elliptical galaxies.

2009-10-31

astro-ph/0001261

David B. Cline

David B. Cline

Search for Relic Neutrinos and Supernova Bursts

12 pages with 11 figures, 5 tables; for Proceedings of VIII Int'l Wksp. on Neutrino Telescopes (Venice, Italy, Feb. 23-26, 1999

UCLA APH-0118-5/99

astro-ph

We describe the current situation concerning methods to search for relic neutrinos from the Big Bang and from all past supernovae (SNs). The most promising method for Big Bang neutrinos is by the interaction of ultra-high- energy (UHE) neutrinos. For supernova neutrinos, both Super Kamiokande- and ICARUS-type detectors will be important to study both nubar_{e} and nu_{e} fluxes. We also discuss a dedicated supernova burst observatory (OMNIS) being planned for three sites in the world. We also describe the possible analysis of the supernova type-II (SNII) neutrinos, including flavor mixing, that might be carried out in the future.

2007-05-23

astro-ph/0001262

Gunnar Paesold

Gunnar Paesold and Arnold O. Benz

Electron Firehose instability and acceleration of electrons in solar flares

6 pages, 7 figures

Astronomy & Astrophysics 1999, 351, 741-746

astro-ph

An electron distribution with a temperature anisotropy T_par/T_perp > 1 can lead to the Electron Firehose instability (Here par and perp denote directions relative to the background magnetic field B_0). Since possible particle acceleration mechanisms in solar flares exhibit a preference of energizing particles in parallel direction, such an anisotropy is expected during the impulsive phase of a flare. The properties of the excited waves and the thresholds for instability are investigated by using linearized kinetic theory. These thresholds were connected to the pre-flare plasma parameters by assuming an acceleration model acting exclusively in parallel direction. For usually assumed pre-flare plasma conditions the electrons become unstable during the acceleration process and lefthand circularly polarized waves with frequencies of about the proton gyrofrequency are excited at parallel propagation. Indications have been found, that the largest growth rates occur at oblique propagation and the according frequencies lie well above the proton gyrofrequency.

2007-05-23

astro-ph/0001263

Stefanie Komossa

Stefanie Komossa (MPE Garching)

Warm Absorbers in Active Galactic Nuclei

10 pages incl. 9 figures, needs agnsymp.cls; to appear in `ASCA/ROSAT Workshop on AGN and the X-ray Background' (Tokyo, Nov. 1-3, 1999), T. Takahashi and H. Inoue (eds). Preprint and related papers also available at http://www.xray.mpe.mpg.de/~skomossa/

astro-ph

We first provide a review of the properties of warm absorbers concentrating on what we have learned from ROSAT and ASCA. This includes dusty and dust-free warm absorbers, non-X-ray emission and absorption features of warm absorbers, and the possible warm absorber interpretation of the peculiar 1.1 keV features. We then discuss facets of warm absorbers by a more detailed investigation of individual objects: In a first part, we discuss several candidates for dusty warm absorbers. In a second part, we review and extend our earlier study of a possible relation between warm absorber and CLR in NGC 4051, and confirm that both components are of different origin (the observed coronal lines are underpredicted by the models, the warm absorber is too highly ionized). We then suggest that a potential overprediction of these lines in more lowly ionized absorbers can be avoided if these warm absorbers are dusty. In a third part, we present first results of an analysis of a deep ROSAT PSPC observation of the quasar MR2251-178, the first one discovered to host a warm absorber. Finally, we summarize our scrutiny under which conditions a warm absorber could account for the dramatic spectral variability of the Narrow-line Seyfert 1 galaxy RXJ0134-4258.

2007-05-23

astro-ph/0001264

Stefanie Komossa

Stefanie Komossa (MPE Garching)

The giant X-ray outbursts from nearby, non-active galaxies: tidal disruption flares ?

6 pages incl. 2 figures, needs agnsymp.cls; to appear in `ASCA/ROSAT Workshop on AGN and the X-ray Background' (Tokyo, Nov. 1-3, 1999), T. Takahashi and H. Inoue (eds). Typo in equation (1) corrected. Preprint and related papers also available at http://www.xray.mpe.mpg.de/~skomossa/

astro-ph

One efficient method to probe the direct vicinity of SMBHs in nearby galaxies is to make use of the detection of flares from tidally disrupted stars (e.g., Lidskii & Ozernoi 1979, Rees 1988). The first few excellent candidates for the occurrence of this process in non-active galaxies have emerged recently. Here, we present a review of these observations, compare with variability in AGN, and discuss theoretical implications. We concentrate on the cases of NGC 5905 and RXJ1242-1119, and report results from a systematic search for further X-ray flares from a sample of >100 nearby galaxies.

2007-05-23

astro-ph/0001265

Hector Cuevas

D.Proust (1), H. Cuevas (2), H.V. Capelato (3), L. Sodre Jr. (2), B. Tome Lehodey (3), O. Le Fevre (4) and A. Mazure (4). ((1) DAEC, CNRS, Observatoire de Paris-Meudon, France, (2) Departamento de Astronomia IAG/USP, Brazil, (3) Divisao de Astrofisica INPE/MCT, Brazil, (4) Laboratoire d'Astronomie Spatiale, France)

Dynamics of the X-ray clusters Abell 222, Abell 223 and Abell 520

Accepted for publication in A&A. 12 pages, 15 eps figures

astro-ph

We present the results of a dynamical analysis of three rich, X-ray luminous galaxy clusters, Abell 222, Abell 223 and Abell 520, that are at intermediate redshifts. Our study is based on radial velocities for 71 cluster members, respectively 30 for A222, 20 for A223 and 21 for A520, measured from spectra obtained at the Canada-France-Hawaii Telescope, the European Southern Observatory, and the Pic du Midi Observatory, and supplemented with radial velocities from the literature. A222 galaxies have slightly higher velocities than those of A223, with bi-weighted mean velocity of V_{bi} = 64242 +/- 194 km/s for A222, and of V_{bi} = 63197 +/- 266 km/s for A223. The velocity dispersions of the two clusters are about the same: sigma_{bi} = 1013 +/- 150 km/s and sigma_{bi} = 1058 +/- 160 km/s for A222 and A223, respectively. For A520 we obtain V_{bi} = 60127 +/- 284 km/s with sigma_{bi} = 1250 +/- 189 km/s. We also give mass and mass-luminosities ratio estimates for each cluster separately. We argue that these clusters are presently undergoing strong dynamical evolution and that A222 and A223 will probably merge in the future. We have applied a Principal Component Analysis to a sample of 51 CFHT spectra to produce a spectral classification for these galaxies. This classification has allowed us to show that the morphological and kinematical segregations were already established in these intermediate redshift clusters.

2007-05-23

astro-ph/0001266

Ivo Saviane

Ivo Saviane (1), Alfred Rosenberg (2 and 3), Giampaolo Piotto (1) Antonio Aparicio (4) ((1) Universita' di Padova, Italy (2) TNG, Padova, Italy, (3) Osservatorio Astronomico di Padova, Italy, (4) Instituto de Astrofisica de Canarias, Tenerife, Spain)

The red giant branches of Galactic globular clusters in the [(V-I)o,Mv] plane: metallicity indices and morphology

14 pages, 11 PS figures, accepted for publication in Astronomy & Astrophysics, main journal

astro-ph

The purpose of this study is to carry out a thorough investigation of the changes in morphology of the red giant branch (RGB) of Galactic globular clusters (GGC) as a function of metallicity, in the V,I bands. To this aim, two key points are developed in the course of the analysis. (a) Using our photometric V,I database for Galactic globular clusters (the largest homogeneous data sample to date; Rosenberg et al. 1999) we measure a complete set of metallicity indices, based on the morphology and position of the red-giant branch. In particular, we provide here the first calibration of the S, DV_(1.1) and DV_(1.4) indices in the (V-I,V) plane. We show that our indices are internally consistent, and we calibrate each index in terms of metallicity, both on the Zinn & West (1984) and the Carretta & Gratton (1997) scales. Our new calibrations of the (V-I)o,g, DV_(1.2), (V-I)_(-3.0) and (V-I)_(-3.5) indices are consistent with existing relations. (b) Using a grid of selected RGB fiducial points, we define a function in the {(V-I)o,Mi,[Fe/H]} space which is able to reproduce the whole set of GGC giant branches in terms of a single parameter (the metallicity). As a first test, we show that the function is able to predict the correct trend of our observed indices with metallicity. The usage of this function will improve the current determinations of metallicity and distances within the Local Group, since it allows to easily map [(V-I)o,Mi] coordinates into {[Fe/H],Mi} ones. To this aim the ``synthetic'' RGB distribution is generated both for the currently used Lee et al. (1990) distance scale, and for the most recent results on the RR Lyr distance scale.

2007-05-23

astro-ph/0001267

James G. Bartlett

James G. Bartlett

Sunyaev-Zel'dovich Surveys: Analytic treatment of cluster detection

16 pages, submitted to Astronomy and Astrophysics

astro-ph

Thanks to advances in detector technology and observing techniques, true Sunyaev-Zel'dovich (SZ) surveys will soon become a reality. This opens up a new window into the Universe, in many ways analogous to the X-ray band and inherently well-adapted to reaching high redshifts. I discuss the nature, abundance and redshift distributions of objects detectable in ground-based searches with state-of-the-art technology. An advantage of the SZ approach is that the total SZ flux density depends only on the thermal energy of the intracluster gas and not on its spatial or temperature structure, in contrast to the X-ray luminosity. Because ground-based surveys will be characterized by arcminute angular resolution, they will resolve a large fraction of the cluster population. I quantify the resulting consequences for the cluster selection function; these include less efficient cluster detection compared to idealized point sources and corresponding steeper integrated source counts. This implies, contrary to expectations based on a point source approximation, that deep surveys are better than wide ones in terms of maximizing the number of detected objects. At a given flux density sensitivity and angular resolution, searches at millimeter wavelengths (bolometers) are more efficient than centimeter searches (radio), due to the form of the SZ spectrum. Possible ground-based surveys could discover up to $\sim 100$ clusters per square degree at a wavelength of 2 mm and $\sim 10$/sq. deg. at 1 cm, modeling clusters as a simple self-similar population.

2007-05-23

astro-ph/0001268

Rob Thacker

R. J. Thacker, H. M. P. Couchman

High Resolution Simulation of Galaxy Formation with Feedback

Submitted to ApJ Letters

astro-ph

We present results from a Smoothed Particle Hydrodynamic (SPH) simulation of galaxy formation that exceeds the minimum resolution requirement suggested by Steinmetz & Muller (1993) of 3*10^4 SPH particles per galaxy. Using the multiple mass technique an effective resolution of a little over one billion particles is attained within a 48 Mpc cube. We find that even with an SPH mass resolution of 1.5*10^6 solar masses and a plausible feedback algorithm, the cooling catastrophe continues to be a problem for Einstein-de Sitter CDM cosmologies. Increasing resolution also appears to exacerbate the core-halo angular momentum transport problem.

2007-05-23

astro-ph/0001269

Maxim Markevitch

M. Markevitch, T. J. Ponman, P. E. J. Nulsen, M. W. Bautz, D. J. Burke, L. P. David, D. Davis, R. H. Donnelly, W. R. Forman, C. Jones, J. Kaastra, E. Kellogg, D.-W. Kim, J. Kolodziejczak, P. Mazzotta, A. Pagliaro, S. Patel, L. VanSpeybroeck, A. Vikhlinin, J. Vrtilek, M. Wise, P. Zhao

Chandra Observation of Abell 2142: Survival of Dense Subcluster Cores in a Merger

Latex, 9 pages, 5 figures (including color), uses emulateapj.sty. Submitted to ApJ

Astrophys.J. 541 (2000) 542

10.1086/309470

astro-ph

We use Chandra data to map the gas temperature in the central region of the merging cluster A2142. The cluster is markedly nonisothermal; it appears that the central cooling flow has been disturbed but not destroyed by a merger. The X-ray image exhibits two sharp, bow-shaped, shock-like surface brightness edges or gas density discontinuities. However, temperature and pressure profiles across these edges indicate that these are not shock fronts. The pressure is reasonably continuous across these edges, while the entropy jumps in the opposite sense to that in a shock (i.e. the denser side of the edge has lower temperature, and hence lower entropy). Most plausibly, these edges delineate the dense subcluster cores that have survived a merger and ram pressure stripping by the surrounding shock-heated gas.

2009-10-31

astro-ph/0001270

Thomas Matheson

Thomas Matheson, Alexei V. Filippenko, Ryan Chornock, Douglas C. Leonard, and Weidong Li (Department of Astronomy, UC Berkeley)

Helium Emission in the Type Ic SN 1999cq

17 pages (AASTeX V5.0), 4 figures, accepted for publication in the Astronomical Journal

10.1086/301352

astro-ph

We present the first unambiguous detection of helium emission lines in spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full width at half maximum ~ 2000 km/s, and the distinct absence of any other intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic 1999cq are interacting with dense circumstellar material composed of almost pure helium. This strengthens the argument that the progenitors of SNe Ic are core-collapse events in stars that have lost both their hydrogen and helium envelopes, either through a dense wind or mass-transfer to a companion. In this way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that helped firmly establish a physical connection between Type Ib and Type II supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid rise followed by a quick decline. SN 1999cq is also found to exhibit a high level of emission at blue wavelengths (< 5500 A), likely resulting from either an unusually large amount of iron and iron-group element emission or uncharacteristically low reddening compared with other SNe Ic.

2009-10-31

astro-ph/0001271

Zoltan Haiman

Zoltan Haiman (Princeton University, Fermilab)

Probing the Cosmic Dark Age in X-rays

10 pages, Invited talk at "X-ray Astronomy 1999", Bologna, Italy, September 1999

10.1063/1.1434627

astro-ph

Empirical studies of the first generation of stars and quasars will likely become feasible within the next decade in several different wavelength bands. Microwave anisotropy experiments, such as MAP or Planck, will set constraints on the ionization history of the intergalactic medium due to these sources. In the infrared, the Next Generation Space Telescope (NGST) will be able to directly detect sub-galactic objects at redshifts z>10. In the optical, data from the Hubble Deep Field already places a constraint on the abundance of high-redshift quasars. However, the epoch of the first quasars might be first probed in X-ray bands, by instruments such as the Chandra X-ray Observatory (CXO) and the X-ray Multi-mirror Mission (XMM). In a 500 Ksec integration, CXO reaches a sensitivity of 2x10-16 erg/s cm^2. Based on simple hierarchical CDM models, we find that at this flux threshold approx. 100 quasars might be detectable from redshifts z>5, and approx. 1 quasar at z=10, in each 17x17 arcmin field. Measurement of the power spectrum of the unresolved soft X-ray background will further constrain models of faint, high-redshift quasars.

2017-02-08

astro-ph/0001272

Kim Griest

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

The MACHO Project: Microlensing Results from 5.7 Years of LMC Observations

53 pages, Latex with 12 postscript figures, submitted to ApJ

Astrophys.J. 542 (2000) 281-307

10.1086/309512

astro-ph

We report on our search for microlensing towards the Large Magellanic Cloud (LMC). Analysis of 5.7 years of photometry on 11.9 million stars in the LMC reveals 13 - 17 microlensing events. This is significantly more than the $\sim$ 2 to 4 events expected from lensing by known stellar populations. The timescales ($\that$) of the events range from 34 to 230 days. We estimate the microlensing optical depth towards the LMC from events with $2 < \that < 400$ days to be 1.2 ^{+0.4}_ {-0.3} \ten{-7}$, with an additional 20% to 30% of systematic error. The spatial distribution of events is mildly inconsistent with LMC/LMC disk self-lensing, but is consistent with an extended lens distribution such as a Milky Way or LMC halo. Interpreted in the context of a Galactic dark matter halo, consisting partially of compact objects, a maximum likelihood analysis gives a MACHO halo fraction of 20% for a typical halo model with a 95% confidence interval of 8% to 50%. A 100% MACHO halo is ruled out at the 95% C.L. for all except our most extreme halo model. Interpreted as a Galactic halo population, the most likely MACHO mass is between $ 0.15 \msun$ and $ 0.9 \msun$, depending on the halo model, and the total mass in MACHOs out to 50 kpc is found to be 9+4-3 10^{10} msun, independent of the halo model. These results are marginally consistent with our previous results, but are lower by about a factor of two. Besides a larger data set, this work also includes an improved efficiency determination, improved likelihood analysis, and more thorough testing of systematic errors, especially with respect to the treatment of potential backgrounds to microlensing, such as supernovae in galaxies behind the LMC. [Abridged]

2009-10-31

astro-ph/0001273

Watanabe Gentaro

Gentaro Watanabe, Kei Iida, Katsuhiko Sato (U. of Tokyo)

Thermodynamic properties of nuclear "pasta" in neutron star crusts

37 pages and 10 postscript figures. Nuclear Physics A (accepted)

Nucl.Phys. A676 (2000) 455-473; Erratum-ibid. A726 (2003) 357-365

10.1016/S0375-9474(00)00197-4

UTAP-361, RESCUE-3/00

astro-ph nucl-th

Equilibrium phase diagrams for neutron star matter at subnuclear densities are obtained at zero temperature. Spherical, rod-like and slab-like nuclei as well as spherical and rod-like nuclear bubbles are taken into account by using a compressible liquid-drop model. This model is designed to incorporate uncertainties in the nuclear surface tension and in the proton chemical potential in a gas of dripped neutrons. The resultant phase diagrams show that for typical values of these quantities, the phases with rod-like nuclei and with slab-like nuclei occur in the form of Coulomb lattice at densities below a point where the system becomes uniform. Thermal fluctuations leading to displacements of such nuclei from their equilibrium positions are considered through explicit evaluations of their elastic constants; these fluctuations can be effective at destroying the layered lattice of slab-like nuclei in the temperature region typical of matter in the neutron star crust.

2009-10-31

astro-ph/0001274

Nestor Sanchez

Nestor Sanchez and Neyda Anez

Neutrino decay and the thermochemical equilibrium of the interstellar medium

5 pages, 4 figures, accepted for A&A (main journal)

Astron.Astrophys.354:1123,2000

astro-ph

We calculate the thermochemical equilibrium of the diffuse interstellar medium, including ionization by a photon flux F_{nu} from neutrino decay. The main heating mechanism considered is photoelectrons from grains and PAHs. For the studied range of F_{nu} values, there always exists two regions of stability (a warm and a cold phase) that can coexist in equilibrium if the thermal interstellar pressure is between a maximum value P_{max} and a minimum value P_{min}. High F_{nu} values (~10^4-10^5 cm^{-2} s^{-1}) can be consistent with observed interstellar pressures only if more efficient sources are heating the gas. It is shown that a neutrino flux increase (due, for example, to an increase in the supernova explosion rate) may stimulate the condensation of cold gas by decreasing P_{max} below the interstellar pressure value.

2011-05-23

astro-ph/0001275

Ray Jayawardhana

Ray Jayawardhana (CfA), Wayne S. Holland, Jane S. Greaves (JAC, Hawaii), William R. F. Dent (ROE), Geoffrey W. Marcy (UC Berkeley), Lee W. Hartmann, Giovanni G. Fazio (CfA)

Dust in the 55 Cancri planetary system

8 pages and 2 figures, to appear in the Astrophysical Journal

10.1086/308942

astro-ph

The presence of debris disks around $\sim$ 1-Gyr-old main sequence stars suggests that an appreciable amount of dust may persist even in mature planetary systems. Here we report the detection of dust emission from 55 Cancri, a star with one, or possibly two, planetary companions detected through radial velocity measurements. Our observations at 850$\mu$m and 450$\mu$m imply a dust mass of 0.0008-0.005 Earth masses, somewhat higher than that in the the Kuiper Belt of our solar system. The estimated temperature of the dust grains and a simple model fit both indicate a central disk hole of at least 10 AU in radius. Thus, the region where the planets are detected is likely to be significantly depleted of dust. Our results suggest that far-infrared and sub-millimeter observations are powerful tools for probing the outer regions of extrasolar planetary systems.

2009-10-31

astro-ph/0001276

Rob Thacker

R. J. Thacker, H. M. P. Couchman

Implementing Feedback in Simulations of Galaxy Formation: A Survey of Methods

Submitted to ApJ. 25 pages emulateapj style. Full resolution figures available from first author

Astrophys.J.545:728-752,2000

10.1086/317828

astro-ph

We present a detailed investigation of different approaches to modeling feedback in simulations of galaxy formation. Gas-dynamic forces are evaluated using Smoothed Particle Hydrodynamics (SPH) while star formation and supernova feedback are included using a three parameter model which determines the star formation rate normalization, feedback energy and lifetime of feedback regions. The star formation rate is calculated using a Lagrangian Schmidt Law for all gas particles which satisfy temperature, density and convergent flow criteria. Feedback is incorporated as thermal heating of the ISM. We compare the effects of distributing this energy over the smoothing scale or depositing it on a single particle. Radiative losses are prevented from heated particles by adjusting the density used in radiative cooling. We test the models on the formation of galaxies from cosmological initial conditions and also on isolated Milky Way and dwarf galaxies. Extremely violent feedback is necessary to produce a gas disk with angular momentum remotely close to that of observed disk galaxies. This is a result of the extreme central concentration of the dark halos in the sCDM model, and the pervasiveness of the core-halo angular momentum transport mechanism. We emphasize that the disks formed in hierarchical simulations are partially a numerical artifact produced by the minimum mass scale of the simulation acting as a highly efficient `support' mechanism. Disk formation is strongly affected by the treatment of dense regions in SPH, which along with the difficulty of representing the hierarchical formation process, means that realistic simulations of galaxy formation require far higher resolution than currently used.

2010-11-04

astro-ph/0001277

Rob Swaters

R.A. Swaters, B.F. Madore, M. Trewhella

High Resolution Rotation Curves of Low Surface Brightness Galaxies

Accepted for publication in ApJ Letters

10.1086/312540

astro-ph

High resolution Halpha rotation curves are presented for five low surface brightness galaxies. These Halpha rotation curves have shapes different from those previously derived from HI observations, probably because of the higher spatial resolution of the Halpha observations. The Halpha rotation curves rise more steeply in the inner parts than the HI rotation curves and reach a flat part beyond about two disk scale lengths. With radii expressed in optical disk scale lengths, the rotation curves of the low surface brightness galaxies presented here and those of HSB galaxies have almost identical shapes. Mass modeling shows that the contribution of the stellar component to the rotation curves may be scaled to explain most of the inner parts of the rotation curves, albeit with high stellar mass-to-light ratios. On the other hand, well fitting mass models can also be obtained with lower contributions of the stellar disk. These observations suggest that the luminous mass density and the total mass density are coupled in the inner parts of these galaxies.

2009-10-31

astro-ph/0001278

Marcella Contini

M. Contini (1), S.M. Viegas (2) ((1) School of Physics and Astronomy, Tel Aviv University, (2) Instituto Astronomico e Geofisico, USP)

The optical-ultraviolet continuum of Seyfert 2 galaxies

26 pages, LaTeX (including 5 Tables) + 17 PostScript figures. To appear in "The Astrophysical Journal"

10.1086/308886

astro-ph

This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting the single galaxies in the sample of Heckman et al. (1995) with composite models (shock+ photoionization from the active center), we show that five main components characterize the SED of the continuum. Shocks play an important role since they produce a high temperature zone where soft X-rays are emitted. We show that in the optical-UV range, the slope of the NLR emission reproduces the observed values, and may be the main component of the featureless continuum. The presence of star forming regions cannot be excluded in the circumnuclear region of various Seyfert galaxies. An attempt is made to find their fingerprints in the observed AGN spectra. Finally, it is demonstrated that multi-cloud models are necessary to interpret the spectra of single objects, even in the global investigation of a sample of galaxies.

2009-10-31

astro-ph/0001279

Hans J. Haubold

H.J. Haubold (UN, Austria) and A.M. Mathai (McGill University, C anada)

The Fractional Kinetic Equation and Thermonuclear Functions

14 pages, LaTeX

Astrophys.Space Sci. 273 (2000) 53-63

astro-ph

The paper discusses the solution of a simple kinetic equation of the type used for the computation of the change of the chemical composition in stars like the Sun. Starting from the standard form of the kinetic equation it is generalized to a fractional kinetic equation and its solutions in terms of H-functions are obtained. The role of thermonuclear functions, which are also represented in terms of G- and H-functions, in such a fractional kinetic equation is emphasized. Results contained in this paper are related to recent investigations of possible astrophysical solutions of the solar neutrino problem.

2016-08-30

astro-ph/0001280

Hans J. Haubold

M.A. Chaudhry (King Fahd University, Saudi Arabia), H.J. Haubold (UN, Austria), and A.M. Mathai (McGill University, Canada)

Analytical Study of Thermonuclear Reaction Probability Integrals

12 pages, LaTeX

Astrophys.Space Sci. 273 (2000) 43-52

astro-ph

An analytic study of the reaction probability integrals corresponding to the various forms of the slowly varying cross-section factor $S(E)$ is attempted. Exact expressions for reaction probability integrals are expressed in terms of the extended gamma functions.

2007-05-23

astro-ph/0001281

Soker Noam

Noam Soker (Univ. of Haifa)

Solar-Like Cycle in Asymptotic Giant Branch Stars

10 pages, submitted to ApJ

10.1086/309326

astro-ph

I propose that the mechanism behind the formation of concentric semi-periodic shells found in several planetary nebulae (PNs) and proto-PNs, and around one asymptotic giant branch (AGB) star, is a solar-like magnetic activity cycle in the progenitor AGB stars. The time intervals between consecutive ejection events is about 200-1,000 years, which is assumed to be the cycle period (the full magnetic cycle can be twice as long, as is the 22-year period in the sun). The magnetic field has no dynamical effects; it regulates the mass loss rate by the formation of magnetic cool spots. The enhanced magnetic activity at the cycle maximum results in more magnetic cool spots, which facilitate the formation of dust, hence increasing the mass loss rate. The strong magnetic activity implies that the AGB star is spun up by a companion, via a tidal or common envelope interaction. The strong interaction with a stellar companion explains the observations that the concentric semi-periodic shells are found mainly in bipolar PNs.

2009-10-31

astro-ph/0001282

Shay Zucker

Shay Zucker and Tsevi Mazeh (Tel-Aviv University, Tel-Aviv, Israel)

Analysis of The Hipparcos Measurements of HD10697 - A Mass Determination of a Brown-Dwarf Secondary

6 pages, 2 figures, LaTex, aastex, accepted for publication by ApJ Letters

Astrophys.J. 531 (2000) L67-L69

10.1086/312523

astro-ph

HD10697 is a nearby main-sequence star around which a planet candidate has recently been discovered by means of radial-velocity measurements (Vogt et al. 1999, submitted to ApJ). The stellar orbit has a period of about three years, the secondary minimum mass is 6.35 Jupiter masses and the minimum semi-major axis is 0.36 milli-arc-sec (mas). Using the Hipparcos data of HD10697 together with the spectroscopic elements of Vogt et al. (1999) we found a semi-major axis of 2.1 +/- 0.7 mas, implying a mass of 38 +/- 13 Jupiter masses for the unseen companion. We therefore suggest that the secondary of HD10697 is probably a brown dwarf, orbiting around its parent star at a distance of 2 AU.

2007-05-23

astro-ph/0001283

Mordehai Milgrom

Mordehai Milgrom and Vladimir V. Usov (Weizmann Institute)

Induction of supernova-like explosions by gamma-ray bursts in close binary systems

Latex, 10 pages, to be published in ApJL

10.1086/312545

astro-ph

We propose that a gamma-ray burst in one member of a binary may induce a supernova-like explosion of a close, white-dwarf companion. Such an explosion might be brought about in rather light companions, which cannot undergo the standard accretion-induced explosion. This would give some GRB-associated supernova an appearance rather unlike that of the typical Type I. GRB 980425, if indeed associated with SN 1998bw, is too weak to have produced it through our proposed mechanism.

2009-10-31

astro-ph/0001284

Tsevi Mazeh

T. Mazeh, D. Naef, G. Torres, D. W. Latham, M. Mayor, J.-L. Beuzit, T. M. Brown, L. Buchhave, M. Burnet, B. W. Carney, D. Charbonneau, G. A. Drukier, J. B. Laird, F. Pepe, C. Perrier, D. Queloz, N. C. Santos, J.-P. Sivan, S. Udry and S. Zucker

The Spectroscopic Orbit of the Planetary Companion Transiting HD209458

11 pages, 1 figure, 2 tables, LaTex, aastex, accepted for publication by ApJ Letters

10.1086/312558

astro-ph

We report a spectroscopic orbit with period P = 3.52433 +/- 0.00027 days for the planetary companion that transits the solar-type star HD209458. For the metallicity, mass, and radius of the star we derive [Fe/H] = 0.00 +/- 0.02, M = 1.1 +/- 0.1 solar masses, and R = 1.3 +/- 0.1 solar radii. This is based on a new analysis of the iron lines in our HIRES template spectrum, and also on the absolute magnitude and color of the star, and uses isochrones from four different sets of stellar evolution models. Using these values for the stellar parameters we reanalyze the transit data and derive an orbital inclination of i = 85.2 +/- 1.4 degrees. For the planet we derive a mass of Mp = 0.69 +/- 0.05 Jupiter masses, a radius of Rp = 1.54 +/- 0.18 Jupiter radii, and a density of 0.23 +/- 0.08 grams per cubic cm.

2009-10-31

astro-ph/0001285

Richard G. McMahon

Richard G. McMahon (Institute of Astronomy, Cambridge, UK), N.A. Walton(Isaac Newton Group, LaPalma, Spain) M.J. Irwin(Institute of Astronomy, Cambridge, UK), J.R. Lewis(Institute of Astronomy, Cambridge, UK), P.S. Bunclark(Institute of Astronomy, Cambridge, UK), D.H.P. Jones(Institute of Astronomy, Cambridge, UK), R.G. Sharp(Institute of Astronomy, Cambridge, UK)

The INT Wide Field Imaging Survey(WFS)

11 pages, 2 figures, Latex(requires elsart.cls). To appear in New Astronomy Reviews (see http://www.ast.cam.ac.uk/~wfcsur for further details)

10.1016/S1387-6473(00)00137-8

astro-ph

The 2.5m Isaac Newton Telescope(INT) is currently being used to carry out a major multi-colour, multi-epoch, CCD based wide field survey over an area of 100 square degrees. The survey parameters have been chosen to maximise scientific return over a wide range of scientific areas and to complement other surveys being carried out elsewhere. Unique aspects of the survey is that it concentrates on regions of sky that are easily accessible from telescopes in both Northern and Southern terrestrial hemispheres and that it the first public survey to use filters similar to that being used by the Sloan Digital Sky Survey. A major aim of the the INT Wide Field Survey program is to bridge the gap between the all-sky photographic 2 and 3 band surveys such as the Palomar and UK Schmidt sky surveys and the ultra-deep keyhole surveys such as the Hubble Deep Field.

2009-10-31

astro-ph/0001286

Roger Coziol

S. Considere, R. Coziol, T. Contini, E. Davoust

Starbursts in barred spiral galaxies IV: On young bars and the formation of abundance gradients

14 pages, 12 figures, accepted in Astronomy & Astrophysics

astro-ph

The oxygen (O/H) and N/O abundance ratios along the bar of 16 barred spiral starburst galaxies are determined using long-slit spectroscopy. The abundance gradients and the spatial distribution of the ionized gas along the bar are used to understand the role of bars in starburst galaxies. The oxygen abundance gradients are steeper than in normal barred galaxies, while the intersects are low. This excludes the possibility that these are chemically evolved galaxies rejuvenated by the effect of a bar. The nitrogen-to-oxygen abundance gradients are flatter than the oxygen ones. But N/O intersects are high, which rules out the possibility that a large quantity of gas was recently funneled by a bar toward the center of a young galaxy. Bars, therefore, cannot be at the origin of the bursts in the nuclei of our sample galaxies. The oxygen and N/O abundance gradients are generally stronger in the bar than in the disk and are linked together by a linear relation. This can be fully explained in terms of star formation history: the gradients build up from the inside out, becoming stronger as the oxygen and N/O abundances increase in the bulge while staying low in the disk. In many of the sample galaxies, star formation occurs at one or both ends of the bar. The low level of chemical enrichment in these regions suggests that they recently experienced bar-triggered star formation: this is the only visible effect of bars. Our analysis shows that bars probably appeared very recently (a few 10^7 years) in the starburst galaxies, which are relatively "young" galaxies still in the process of formation.(Abridged)

2007-05-23

astro-ph/0001287

Roger Coziol

R. Coziol, S. Considere, E. Davoust, T. Contini

The formation of bars and disks in Markarian starburst galaxies

7 pages, 4 figures, accepted for publication in Astronomy & Astrophysics

astro-ph

We have proposed in a companion paper (Considere et al. 2000) that bars appeared recently in massive starburst nucleus galaxies. We now test this hypothesis on an extended sample of barred and unbarred Markarian starburst galaxies, using several samples of normal galaxies as control samples. In support of this hypothesis, we show that the proportion of barred galaxies is much lower in Markarian starburst galaxies than in normal galaxies. In addition to this deficiency of bars, we find that Markarian starburst galaxies have smaller disks than normal galaxies, and that the disks of unbarred starburst galaxies are smaller, on average, than barred ones. Finally, we show that the Markarian starburst galaxies do not seem to follow the local Tully--Fisher relation. Various alternatives are examined to explain the deficiency of bars and the small disk dimensions in Markarian starburst galaxies. One possibility, which is in agreement with the young bar hypothesis, is that the formation of disks happens after the formation of bulges and that bars appear only later, when enough gas has been accreted in the disk.

2007-05-23

astro-ph/0001288

Yipeng Jing

Y.P. Jing (NAO, Tokyo) and Yasushi Suto (RESCEU, Tokyo)

Dark Matter Halos Simulated with Million Particles

talk at the 4th RESCUE International Symposium on Birth and Evolution of the Universe, in press; 4 pages with 2 figures included

astro-ph

We report a series of high-resolution N-body simulations designed to examine the internal physical properties of dark matter halos. A total of fifteen halos, each represented by $\sim 1$ million particles within the virial radius, have been simulated covering the mass range of $2\times10^{12}\sim 5\times10^{14} h^{-1}{\rm M_\odot}$. As the first application of these simulations, we have examined the density profiles of the halos. We found a clear systematic correlation between the halo mass and the slope of the density profile at one percent of the virial radius, in addition to the variations of the slope among halos of the similar mass. More specifically, the slope is $\sim - 1.5$, -1.3, and -1.1 for galaxy, group, and cluster mass halos, respectively. Thus we conclude that the dark matter density profiles, especially in the inner region, are not universal.

2009-09-25

astro-ph/0001289

Masayuki Akiyama

M.Akiyama, K.Ohta, T.Yamada, N.Kashikawa, M.Yagi, W.Kawasaki, M.Sakano, T.Tsuru, Y.Ueda, T.Takahashi, I.Lehmann, G.Hasinger, W.Voges

Optical Identification of the ASCA Large Sky Survey

Accepted for publication in ApJ. 57 pages with 13 figures, 9 JPG plates, 5 additional PS tables. Original EPS plates (gzipped format ~1Mbyte/plate) and TeX tables are available from ftp://ftp.kusastro.kyoto-u.ac.jp/pub/akiyama/0001289/

10.1086/308606

Dept. of Astronomy, Kyoto Univ. ASPR-00-7

astro-ph

We present results of optical identification of the X-ray sources detected in the ASCA Large Sky Survey. Optical spectroscopic observations were done for 34 X-ray sources which were detected with the SIS in the 2-7 keV band above 3.5 sigma. The sources are identified with 30 AGNs, 2 clusters of galaxies, and 1 galactic star. Only 1 source is still unidentified. The flux limit of the sample corresponds to 1 x 10^{-13} erg s^{-1} cm^{-2} in the 2-10 keV band. Based on the sample, the paper discusses optical and X-ray spectral properties of the AGNs, contribution of the sources to the Cosmic X-ray Background, and redshift and luminosity distributions of the AGNs. An interesting result is that the redshift distribution of the AGNs suggests a deficiency of high-redshift (0.5 < z < 2) and luminous (Lx(2-10 keV) > 10^{44} erg s^{-1}) absorbed narrow-line AGNs (so called type 2 QSOs).

2009-10-31

astro-ph/0001290

Dmitriy Bizyaev

D.Bizyaev, A.Zasov (Sternberg Astronomical Institute) and S.Kajsin (Special Astrophysical Observatory of RAS)

Combined color indexes and photometric structure of galaxies NGC 834 and NGC 1134

3 pages, 4 embedded figures, LaTeX2e, using the EslabStyle.cls file, presented as a poster in the 33rd ESLAB Symp. "Star formation from the small to the large scale", Noordwijk, The Netherlands, 2-5 November 1999, (F. Favata, A.A. Kaas & A. Wilson eds, ESA SP-445)

Astron.Lett. 27 (2001) 217-227

10.1134/1.1358378

astro-ph

We present the results of BVRI photometry of two galaxies with active star formation: NGC 834 and NGC 1134. Combined color index Q_{BVI} was used to investigate the photometrical structure of the galaxies. Index Q_{BVI} is not affected by internal extinction and is sensitive to the presence of blue stars. Ring-like region with active star formation at 15" from the center reveals itself in the Q_{BVI} map of NGC 834. Three-arm spiral structure is well-seen on the Q_{BVI} map of NGC 1134. We propose to use the combined indexes Q_{BVI} and similarly defined indices as a tracers of Star Formation activity and structure of dusty galaxies.

2009-10-31

astro-ph/0001291

Stefanie Phleps

S. Phleps (1), K. Meisenheimer (1), B. Fuchs (2), C. Wolf (1) ((1) Max-Planck-Institut fuer Astronomie, Heidelberg, (2) Astronomisches Recheninstitut, Heidelberg)

CADIS deep star counts: Galactic structure and the stellar luminosity function

11 pages, 14 figures, accepted for publication by A&A

astro-ph

In this paper we present the first results of deep star counts carried out within the Calar Alto Deep Imaging Survey, CADIS (Meisenheimer 1998). Although CADIS was designed as an extragalactic survey, it also attempts to identify the stars in the fields in order to avoid confusion with quasars and compact galaxies. We have identified a sample of about 300 faint stars 15.5< R < 23), which are well suited to study the structure of the Galaxy. The stars lie in two fields, hereafter 16h and 9h field, respectively. The stars have been separated from galaxies by a classification scheme based on photometric spectra and morphological criteria. Distances were derived by photometric parallaxes. We are able to find stars up to distances of approximately 25 kpc above the Galactic plane. The vertical density distribution of the stars shows the contribution of the thin disk, the stellar halo and the ``thick disk'' of the Galaxy. We give quantitative descriptions of the components in terms of exponential disks and a de Vaucouleurs spheroid. For the disk stars we derive the luminosity function. It is equal within the errors to the local luminosity function and continues to rise out to at least M_V = 13. Implications for the mass function are briefly discussed.

2007-05-23

astro-ph/0001292

Pedro Pina Avelino

P. P. Avelino, C. J. A. P. Martins and G. Rocha

VSL theories and the Doppler peak

10 pages, references added, minor changes to match accepted version

Phys. Lett. B483 (2000) 210

10.1016/S0370-2693(00)00567-0

astro-ph

We discuss constraints on so-called `varying speed of light theories' coming from the physics of the early universe. Specifically, we consider the position of the first acoustic peak of the CMB angular power spectrum, showing that the recent determination of its position by various CMB experiments, in particular BOOMERanG/NA, can be used to constrain the value of the speed of light $c$ after the epoch of last scattering. Specifically, we find that for a flat universe and a standard density of baryonic matter a variation in $c$ of up to 4% is consistent with the current observations. The position of the Doppler peak is fairly sensitive to changes in $c$, and future observations should dramatically improve this bound. On the other hand, we also find that the maximum baryonic density allowed in VSL theories is about $\Omega_B h^2\sim 0.06\Omega_0$. We comment on the significance of these results.

2009-10-31

astro-ph/0001293

Sarbani Basu

H. M. Antia, Sarbani Basu, J. Pintar, B. Pohl

Solar cycle variation in solar f-mode frequencies and radius

To appear in Solar Physics

Solar Phys. 192 (2000) 459

10.1023/A:1005204800696

astro-ph

Using data from the Global Oscillation Network Group (GONG) covering the period from 1995 to 1998, we study the change with solar activity in solar f-mode frequencies. The results are compared with similar changes detected from the Michelson Doppler Imager (MDI) data. We find variations in f-mode frequencies which are correlated with solar activity indices. If these changes are due to variation in solar radius then the implications are that the solar radius decreases by about 5 km from minimum to maximum activity.

2015-06-24

astro-ph/0001294

Sarbani Basu

Sarbani Basu and H. M. Antia

Solar cycle variations of large scale flows in the Sun

To appear in Solar Physics

Solar Phys. 192 (2000) 469

10.1023/A:1005256817534

astro-ph

Using data from the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory (SOHO), we study the large-scale velocity fields in the outer part of the solar convection zone using the ring diagram technique. We use observations from four different times to study possible temporal variations in flow velocity. We find definite changes in both the zonal and meridional components of the flows. The amplitude of the zonal flow appears to increase with solar activity and the flow pattern also shifts towards lower latitude with time.

2015-06-24

astro-ph/0001295

Jarrod Hurley

J.R. Hurley, O.R. Pols, C.A. Tout

Comprehensive analytic formulae for stellar evolution as a function of mass and metallicity

29 pages, 20 figures, submitted for publication in MNRAS

Mon.Not.Roy.Astron.Soc.315:543,2000

10.1046/j.1365-8711.2000.03426.x

astro-ph

We present analytic formulae that approximate the evolution of stars for a wide range of mass and metallicity. Stellar luminosity, radius and core mass are given as a function of age, M and Z, for all phases from the zero-age main-sequence up to, and including, the remnant stages. For the most part we find continuous formulae accurate to within 5% of detailed models. These formulae are useful for purposes such as population synthesis that require very rapid but accurate evaluation of stellar properties, and in particular for use in combination with N-body codes. We describe a mass loss prescription that can be used with these formulae and investigate the resulting stellar remnant distribution.

2011-05-05

astro-ph/0001296

Paul P. van der Werf

Paul P. van der Werf

H2 emission as a diagnostic of physical processes in starforming galaxies

invited review, to appear in Molecular Hydrogen in Space, eds. F. Combes and G. Pineau des Forets, Cambridge University Press. 8 pages with 3 embedded postscript figures; uses cupconf.sty

astro-ph

Observations and interpretation of extragalactic rotational and rovibrational H2 emission are reviewed. Direct observations of H2 lines do not trace bulk H2 mass, but excitation rate. As such, the H2 lines are unique diagnostics, if the excitation mechanism can be determined, which generally requires high-quality spectroscopy and suitable additional data. The diagnostic power of the H2 lines is illustrated by two cases studies: H2 purely rotational line emission from the disk of the nearby spiral galaxy NGC891 and high resolution imaging and spectroscopy of H2 vibrational line emision from the luminous merger NGC6240.

2007-05-23

astro-ph/0001297

Miguel A. de Avillez

Miguel A. de Avillez

Are HVCs Produced in Galactic Fountains?

9 pages, 3 figures; contribution to the proceedings of "Astrophysical Dynamics" (Evora, April 1999; in honour of Franz D. Kahn), D. Berry, D. Breitschwerdt, A. da Costa, J. Dyson (eds); to appear in Ap&SS

Astrophys.Space Sci. 272 (2000) 23-30

10.1023/A:1002616817343

astro-ph

Three-dimensional simulations of the disk-halo interaction show the formation of a thick HI and HII gas disk with different scale heights. The thick HI disk prevents the disk gas from expanding freely upwards, unless some highly energetic event such as chimneys occurs, whereas the thick HII disk acts as a disk-halo interaction region from where the hot ionized gas flows freely into the halo. The upflowing gas reaches the maximum height at $z\sim 9.3\pm 1$ kpc becoming thermally unstable due to radiative losses, and condenses into HI clouds. Because the major fraction of the gas is gravitationally bound to the Galaxy, the cold gas returns to the disk. The descending clouds will have at some height high velocities. In a period of 200 Myr of fountain evolution, some 10 percent of the total number of clouds are HVCs.

2009-10-31

astro-ph/0001298

Daniel C. Homan

D. C. Homan and J. F. C. Wardle (Brandeis University, Waltham MA, USA)

Direct Distance Measurements to Superluminal Radio Sources

18 pages, 8 figures, to be published in The Astrophysical Journal

10.1086/308884

astro-ph

We present a new technique for directly measuring the distances to superluminal radio sources. By comparing the observed proper motions of components in a parsec scale radio jet to their measured Doppler factors, we can deduce the distance to the radio source independent of the standard rungs in the cosmological distance ladder. This technique requires that the jet angle to the line of sight and the ratio of pattern to flow velocities are sufficiently constrained. We evaluate a number of possibilities for constraining these parameters and demonstrate the technique on a well defined component in the parsec scale jet of the quasar 3C279 (z = 0.536). We find an angular size distance to 3C279 of greater than 1.8 (+0.5,-0.3) n^{1/8} Gpc, where n is the ratio of the energy density in the magnetic field to the energy density in the radiating particles in that jet component. For an Einstein-de Sitter Universe, this measurement would constrain the Hubble constant to be H < 65 n^{-1/8} km/s/Mpc at the two sigma level. Similar measurements on higher redshift sources may help discriminate between cosmological models.

2009-10-31

astro-ph/0001299

Shai Kaspi

Shai Kaspi, W. N. Brandt and Donald P. Schneider (Pennsylvania State University)

The X-ray Properties of z>4 Quasars

7 pages, 4 figures included, LaTeX emulateapj.sty, accepted for publication in the Astronomical Journal

10.1086/301362

astro-ph

We report on a search for X-ray emission from quasars with redshifts greater than four using the ROSAT public database. Our search has doubled the number of z>4 quasars detected in X-rays from 6 to 12. Most of those known prior to this work were radio-loud and X-ray selected sources; our study increases the number of X-ray detected, optically selected z>4 quasars from one to seven. We present their basic X-ray properties and compare these to those of lower redshift quasars. We do not find any evidence for strong broad-band spectral differences between optically selected z>4 quasars and those at lower redshifts.

2009-10-31

astro-ph/0001300

Titus J. Galama

T.J. Galama (1) and A.G. De Bruyn (2,3)((1) Caltech, (2) Kapteyn Astronomical Institute, (3) NFRA)

The Unique Potential of SKA Radio Observations of Gamma-Ray Bursts

8 pages, 2 figures, to appear in Perspectives in Radio Astronomy: Scientific Imperatives at cm and m Wavelengths (Dwingeloo: NFRA), Edited by: M.P. van Haarlem & J.M. van der Hulst

astro-ph

Radio observations with the Square Kilometer Array (SKA) provide the agility, sensitivity, and spectral coverage to trace the evolution of the size, shape and spectra of gamma-ray burst (GRB) remnants from the earliest moments on. In the first hours to days after the burst a major, and unique tool, will be provided through the study of dynamically evolving radio spectra, caused by diffractive and refractive scintillation in the local ISM. Simultaneous observations from optically thin to optically thick frequencies will provide strong constraints on any model for the GRB remnant. SKA will also allow for extremely rapid (within minutes, if not seconds) follow-up observations by electronic steering of the array. SKA observations have the sensitivity to detect GRB afterglows out to redshifts of 10 or greater. They therefore allow studies of the high redshift universe, and measure the massive star formation (and massive star death rate!) history of the universe, unbiased by optical obscuration. Wide field surveys may detect thousands of GRBs within a few days of observing (depending on the amount of collimation, the width of the GRB luminosity function, the number of GRBs like GRB 980425/SN 1998bw). There would be new ones, but many more would be old, fading afterglows, allowing the determination of the multi-variate GRB-optical-radio luminosity function of GRBs. This should elucidate the relation of the `faint' ones, like GRB 980425, to the luminous ones like GRB 970508. Such surveys will also tell us whether GRB fireballs (and which ones) are collimated into jets.

2007-05-23