Astrophysics astro-ph new abstracts 4 September 2000
Astrophysics
astro-ph new abstracts, Mon, 4 Sep 00 04:00:12 GMT
0009001 — 0009027 received
astro-ph/0009001 [abs, src, ps, other] :
Title: The Origin of a Chemically Enriched lya Absorption System at z=0.167
Authors:
Hsiao-Wen Chen,
Jason X. Prochaska (Carnegie Observatories)
Comments: 18 pages, 1 figure. Accepted for publication in the ApJ Letters
We present the first detailed analysis of the chemical abundances, ionization
state, and origin of a partial Lyman limit system (N(hI) ~ 10^{16} cmjj) at
low redshift (z=0.167 towards PKS0405-1219). Two galaxies at ~ 70 h^{-1} kpc
projected distance to the QSO have been identified at the absorber redshift. We
analyze an echelle spectrum of the QSO obtained with the Space Telescope
Imaging Spectrograph and find that this absorption system exhibits associated
lines produced by C^+, N^+, O^0, Si^+, Si^{++}, Si^{+3}, Fe^+, and Fe^{++}, and
most interestingly, O^{+5} and N^{+4}. The results of our analysis show that
the partial Lyman limit system traced by various ions is likely to be embedded
in a collisionally ionized ovi gas of larger spatial extent. Furthermore, the
partial Lyman limit system appears to have a metallicity of {em at least} 1/10
solar and most likely solar or super solar despite the fact that no luminous
galaxies are seen within a projected distance
ho = 60 h^{-1} kpc to the QSO.
Finally, adopting the temperature estimated for the hot gas T ~ 2.5 imes 10^5
K and assuming a simple isothermal halo, we estimate that the galaxy or galaxy
group that supports the extended gas may have a total mass ~ 1.5 imes 10^{12}
M_odot and a gas number density apl 3 imes 10^{-5} cm^{-3}.
(37kb)
astro-ph/0009002 [abs, src, ps, other] :
Title: Magnification relations in gravitational lensing via multidimensional
residue integrals
Authors:
Neal Dalal,
Jeffrey M. Rabin
Comments: 16 pages, uses revtex4, submitted to Journal of Mathematical Physics
We investigate the so-called magnification relations of gravitational lensing
models. We show that multidimensional residue integrals provide a simple
explanation for the existence of these relations, and an effective method of
computation. We illustrate the method with several examples, thereby deriving
new magnification relations for galaxy lens models and microlensing (point mass
lensing).
(60kb)
astro-ph/0009003 [abs, src, ps, other] :
Title: Non-Thermal Production of WIMPs and the Sub-Galactic Structure of the
Universe
Authors:
W.B. Lin,
D.H. Huang,
X. Zhang,
R. Brandenberger
Comments: 6 pages, 2 figures
There is increasing evidence that conventional cold dark matter (CDM) models
lead to conflicts between observations and numerical simulations of dark matter
halos on sub-galactic scales. Spergel and Steinhardt showed that if the CDM is
strongly self-interacting, then the conflicts disappear. However, the
assumption of strong self-interaction would rule out the favored candidates for
CDM, namely weakly interacting massive particles (WIMPs), such as the
neutralino. In this paper we propose a mechanism of non-thermal production of
WIMPs and study its implications on the power spectrum. We find that the
non-vanishing velocity of the WIMPs suppresses the power spectrum on small
scales compared to what it obtained in the conventional CDM model. Our results
show that, in this context, WIMPs as candidates for dark matter can work well
both on large scales and on sub-galactic scales.
(34kb)
astro-ph/0009004 [abs, src, ps, other] :
Title: Three-Dimensional Magnetohydrodynamical Accretion Flows into Black Holes
Authors:
Mami Machida (1),
Ryoji Matsumoto (1)
and Shin Mineshige (2) ((1) Chiba University, (2) Kyoto University)
Comments: 4pages, 2 figures. Submitted to PASJ Letters
Outflows and convective motions in accretion flows have been intensively
discussed recently in the context of advection-dominated accretion flow (ADAF)
based on two-dimensional (2D) and three-dimensional (3D) hydrodynamical
simulations. We, however, point that without proper treatments of the disk
magnetic fields, a major source of viscosity, one can never derive general,
firm conclusions concerning the occurrence of outflows and convection. We
analyzed the 3D MHD numerical simulation data of magnetized accretion flows
initially threaded by weak toroidal magnetic fields, finding large-scale
convective motions dominating near the black hole. In contrast, outflows occur
only temporarily and are not very significant in our simulations. If there grow
strong vertical fields somehow, however, formation of bi-polar jets is
inevitable. It is claimed that radiation could be dominant at the outermost
zones of the convective disks because of outward energy flow by convection,
however, this is no longer the case in convective MHD flows, since accretion
energy can be released via magnetic reconnection in the inner parts. Such
reconnection leads to sporadic flare events, thus producing substantial
variability in out-going radiation.
(24kb)
astro-ph/0009005 [abs, src, ps, other] :
Title: On the variation of the Initial Mass Function
Authors:
Pavel Kroupa (Heidelberg)
Comments: MNRAS, in press; 34 pages, 14 figures (figs.1 and 14 in colour)
(shortened) In this contribution an average or Galactic-field IMF is defined,
stressing that there is evidence for a change in the power-law index at only
two masses: near 0.5 Msun and 0.08 Msun. Using this supposed universal IMF, the
uncertainty inherent to any observational estimate of the IMF is investigated,
by studying the scatter introduced by Poisson noise and the dynamical evolution
of star clusters. It is found that this apparent scatter reproduces quite well
the observed scatter in power-law index determinations, thus defining the
fundamental limit within which any true variation becomes undetectable.
Determinations of the power-law indices alpha are subject to systematic errors
arising mostly from unresolved binaries. The systematic bias is quantified
here, with the result that the single-star IMFs for young star-clusters are
systematically steeper by d_alpha=0.5 between 0.1 and 1 Msun than the
Galactic-field IMF, which is populated by, on average, about 5 Gyr old stars.
The MFs in globular clusters appear to be, on average, systematically flatter
than the Galactic-field IMF, and the recent detection of ancient white-dwarf
candidates in the Galactic halo and absence of associated low-mass stars
suggests a radically different IMF for this ancient population. Star-formation
in higher-metallicity environments thus appears to produce relatively more
low-mass stars.
(119kb)
astro-ph/0009006 [abs, src, ps, other] :
Title: Constraining cosmological parameters with the clustering properties of
galaxy clusters in optical and X-ray bands
Authors:
Lauro Moscardini,
Sabino Matarrese,
H.J. Mo
Comments: 13 pages, Latex using MN style. Submitted to MNRAS
(abridged) We use a theoretical model to predict the clustering properties of
galaxy clusters. Our technique accounts for past light-cone effects on the
observed clustering and follows the non-linear evolution of the dark matter
correlation function and cluster bias factor. A linear treatment of
redshift-space distortions is also included. We perform a maximum-likelihood
analysis by comparing the theoretical predictions to a set of observational
data, both in the optical (APM catalogue) and X-ray band (RASS1, BCS, XBACs,
REFLEX). In the framework of CDM models, we compute the constraints on
cosmological parameters. Our results show that X-ray data are more powerful
than optical ones, allowing smaller regions in the parameter space. We find
that the clustering properties of clusters are almost independent of the matter
density parameter and of the presence of a cosmological constant, while they
appear to be strongly dependent on the shape parameter. Using the X-ray data
only, we obtain Gamma~0.1 and 0.4<sigma_8<0.9 for the Einstein-de Sitter model,
while 0.14<Gamma<0.22 and 0.6<sigma_8<1.1 for open and flat models with
Omega_0m=0.3. Finally, we use our model to make predictions on the correlation
length of galaxy clusters expected in future surveys. In particular, we show
the results for an optical catalogue with characteristics similar to the EIS
project and for two different X-rays samples, including a very deep catalogue
with the characteristics of the XMM/LSS survey. We find that clusters at high
redshifts are expected to have larger correlation length than local ones.
(139kb)
astro-ph/0009007 [abs, src, ps, other] :
Title: Temperature and Heavy Element Abundance Profiles of Cool Clusters of
Galaxies from ASCA
Authors:
A. Finoguenov (AIP),
M. Arnaud (CEA Saclay),
L.P. David (CfA)
Comments: 14 pages, ApJ submitted
We perform a spatially resolved X-ray spectroscopic study of a set of 18
relaxed clusters of galaxies with gas temperatures below 4 keV. Spectral
analysis was done using ASCA/SIS data with spatial information required for the
modeling taken from ROSAT/PSPC or Einstein/IPC observations. We derive the
temperature profiles using single-temperature fits and also correct for the
presence of cold gas at cluster centers. For all of the clusters in the sample
we derive Si and Fe abundance profiles, and for a few of the clusters we also
derive Ne and S abundance profiles. We present a comparison of the elemental
abundances derived at similar overdensities as well as element mass-to-light
ratios. We conclude that the preferential accretion of low entropy, low
abundance gas into the potentials of groups and cold clusters can explain most
of the observed trends in metallicity. In addition, we discuss the importance
of energy input from SNe II on cluster scaling relations and on the relation
between the observed scatter in the retainment of SN Ia products with
differences between the epoch of cluster formation.
(302kb)
astro-ph/0009008 [abs, src, ps, other] :
Title: A study of the core of the Shapley Concentration: V. The A3528 complex:
a young merger event?
Authors:
S.Bardelli,
E.Zucca,
A.Baldi
Comments: 15 pages (MN LaTeX style) with 7 encapsulated figures; MNRAS in press
We present the results of a redshift survey of galaxies in the A3528 complex,
a chain of interacting clusters in the core of the Shapley Concentration. This
complex is characterized in the X-ray band by two pairs of roughly similar
interacting clumps: one pair has been resolved as two optical Abell clusters
(A3530 and A3532), while the two components of the other pair are both
associated to A3528. The optical data show that the distance between the
centers of A3530 and A3532 is smaller than their Abell radii, an indication of
the existence at least of tidal interactions, and that the contours of galaxies
in A3528 appear to be elongated in the North-South direction, pointing towards
the A3530-A3532 pair.
From our survey we obtained ~600 new radial velocity determinations: using
this sample, we studied the dynamics of the four Abell clusters in this region
(A3528, A3530, A3532 and A3535) and derived their mean velocities and velocity
dispersions. Moreover we performed a substructure analysis, both bi-dimensional
and three-dimensional, of the whole complex.
All the characteristics of this structure seem to point toward a merging
scenario in an early stage, whose effects on the galaxy population and on the
cluster dynamics are not yet evident, contrary to what happens in the nearby
A3558 complex, where the merging events are in a rather advanced stage and were
already able to induce modifications in the galaxy population.
(192kb)
astro-ph/0009009 [abs, src, ps, other] :
Title: Broad-band diffuse gamma ray emission of the Galactic Disk
Authors:
F.A. Aharonian,
A.M. Atoyan
Comments: 17 pages, 7 figures, Astronomy and Astrophysics, accepted for
publication
The contributions of different radiation mechanisms to the diffuse gamma-ray
emission of the galactic disk are studied in a broad energy region from X-rays
to very high energy gamma rays.
(66kb)
astro-ph/0009010 [abs, src, ps, other] :
Title: Halpha emitting galaxies and the cosmic star formation rate at z = 2.2
Authors:
Alan F.M. Moorwood,
Paul P. van der Werf,
Jean Gabriel Cuby,
Tino Oliva
Comments: 11 pages including 9 postscript figures. To appear in A&A
About 10 candidate Halpha emitting galaxies at z = 2.2 have been detected in
a 2.1 um narrow band imaging survey covering an area of 100 sq. arcmin
including the WFPC2 and STIS fields in the Hubble Deep Field South. Six of
these have subsequently been confirmed spectroscopically using ISAAC at the ESO
VLT. Star formation rates of the individual galaxies derived from their Halpha
fluxes are 20-35 Msolar/yr, without any correction for extinction, whereas SFRs
derived from their rest frame UV continuum fluxes are up to a factor of 4 lower
– consistent with lower extinction to Halpha. Velocity dispersions are
typically ~ 100km/s and one galaxy, observed under the most favorable
conditions, shows a rotation curve with a terminal velocity ~ 140 km/s at ~
3kpc radius which is within the range observed for nearby spiral galaxies.
These thus appear to be relatively massive systems at high redshift. Comparison
with the HST NICMOS grism Halpha survey of Yan et al. (1999) reveals little or
no evolution in the Halpha luminosity function between z ~ 1.3 and 2.2. The
inferred star formation rate density of 0.12 Msolar/Mpc^3/yr at z = 2.2 is also
equal to that at z ~ 3-4.5 derived by Steidel et al.(1999) from extinction
corrected UV continuum fluxes.
(476kb)
astro-ph/0009011 [abs, src, ps, other] :
Title: Compact High Velocity Clouds
Authors:
Robert Braun
Comments: 8 pages, 2 figures, to appear in ASP Conf. Ser. “Gax and Galaxy
Evolution”, Eds. Hibbard, Rupen and Van Gorkom
We summarize the observed properties of the CHVC population, which provide
strong evidence for source distances in the range 200-1000 kpc. At these
distances, the population corresponds to strongly dark-matter dominated
sub-dwarf galaxies still accreting onto the more massive Local Group systems.
Recent searches for faint associated stellar populations have revealed
red-giant candidates for which follow-up spectroscopy is scheduled. A sensitive
HI survey for CHVC counterparts in the NGC 628 galaxy group has allowed
tentative detection of 40 candidates, for which confirming observations have
been approved. Many open issues should be resolved by observational programs
within the coming years.
(36kb)
astro-ph/0009012 [abs, src, ps, other] :
Title: Selection effects in high-redshift submillimeter surveys and pointed
observations
Authors:
Andrew W. Blain (Cambridge)
Comments: 8 pages, UMass/INAOE conference proceedings on Deep Millimeter
Surveys, in press
The results of the first generation of submillimeter-wave surveys have been
published. The opening of this new window on the distant Universe has added
considerably to our understanding of the galaxy formation process, by revealing
a numerous population of very luminous distant galaxies. Most would have been
very difficult to identify using other methods. The potential importance of
selection effects, especially those connected with the spectral energy
distributions of the detected galaxies, for the interpretation of the results
are highlighted.
(31kb)
astro-ph/0009013 [abs, src, ps, other] :
Title: Wide band observations of the new X-ray burster SAX J1747.0-2853 during
the March 1998 outburst
Authors:
L. Natalucci (1),
A. Bazzano (1),
M. Cocchi (1),
P. Ubertini (1),
J. Heise (2),
E. Kuulkers (2),
J.J.M. in ‘t Zand (2) ((1) Istituto di Astrofisica Spaziale/CNR, Roma, Italy, (2) Space Research Organization Netherlands, Utrecht, Netherlands)
Comments: 11 pages, 3 figures, accepted for publication in ApJ Letters
We report on our discovery and follow-up observations of the X-ray source SAX
J1747.0-2853 detected in outburst on 1998, March 10 with the BeppoSAX Wide
Field Cameras in the energy range 2-28 keV. The source is located about half
degree off the Galactic Nucleus. A total of 14 type-I X-ray bursts were
detected in Spring 1998, thus identifying the object as a likely low-mass X-ray
binary harboring a weakly magnetized neutron star. Evidence for photospheric
radius expansion is present in at least one of the observed bursts, leading to
an estimate of the source distance of about 9 kpc. We performed a follow-up
target of opportunity observation with the BeppoSAX Narrow Field Instruments on
March 23 for a total elapsed time of 72 ks. The source persistent luminosity
was 2.6×10^36 erg/s in the 2-10 keV energy range. The wide band spectral data
(1-200 keV) are consistent with a remarkable hard X-ray spectrum detected up to
150 keV, highly absorbed at low energies (Nh of the order of 10^23 cm^-2) and
with clear evidence for an absorption edge near 7 keV. A soft thermal component
is also observed, which can be described by single temperature blackbody
emission at about 0.6 keV.
(38kb)
astro-ph/0009014 [abs, src, ps, other] :
Title: HST/STIS Imaging of the Host Galaxy of GRB980425/SN1998bw
Authors:
J. U. Fynbo (1),
S. Holland (2),
M. I. Andersen (3),
B. Thomsen (2),
J. Hjorth (1),
G. Bjornsson (4),
A. O. Jaunsen (5),
P. Natarajan (6,7),
N. Tanvir (8) ((1)University of Copenhagen, (2) University of Aarhus, (3) University of Oulu, (4) University of Iceland, (5) Univsersity of Oslo, (6) Cambridge University, (7) Yale University, (8) University of Hertfordshire)
Comments: 12 pages, 2 figures, AASTeX v5.02 accepted for publication in ApJ
Letters
We present HST/STIS observations of ESO 184-G82, the host galaxy of the
gamma-ray burst GRB 980425 associated with the peculiar Type Ic supernova
SN1998bw. ESO 184-G82 is found to be an actively star forming SBc sub-luminous
galaxy. We detect an object consistent with being a point source within the
astrometric uncertainty of 0.018 arcseconds of the position of the supernova.
The object is located inside a star-forming region and is at least one
magnitude brighter than expected for the supernova based on a simple
radioactive decay model. This implies either a significant flattening of the
light curve or a contribution from an underlying star cluster.
(233kb)
astro-ph/0009015 [abs, src, ps, other] :
Title: 3D simulations of shear instabilities in magnetized flows
Authors:
M. Brüggen (MPA),
W. Hillebrandt (MPA)
Comments: submitted to MNRAS, figures in colour and higher quality at
this http URL
We present results of three-dimensional (3D) simulations of the
magnetohydrodynamic Kelvin-Helmholtz instability in a stratified shear layer.
The magnetic field is taken to be uniform and parallel to the shear flow. We
describe the evolution of the fluid flow and the magnetic field for a range of
initial conditions. In particular, we investigate how the mixing rate of the
fluid depends on the Richardson number and the magnetic field strength. It was
found that the magnetic field can enhance as well as suppress mixing. Moreover,
we have performed two-dimensional (2D) simulations and discuss some interesting
differences between the 2D and 3D results.
(218kb)
astro-ph/0009016 [abs, src, ps, other] :
Title: Redshift space bias and beta from the halo model
Authors:
Uros Seljak (Princeton University)
Comments: 6 pages, 2 figires, submitted to MNRAS
We analyze scale dependence of redshift space bias $b$ and $eta equiv
Omega_m^{0.6}/b$ in the context of the halo model. We show that linear bias is
a good approximation only on large scales, for $k<0.1h$Mpc$^{-1}$. On
intermediate scales the virial motions of the galaxies cause a suppression of
the power spectrum relative to the linear one, which differs from the same
effect in dark matter. This suppression can potentially mimic the effect of
massive neutrinos and the degeneracy can only be broken if the power spectrum
is measured for $k ll 0.1h$Mpc$^{-1}$. Different methods to determine $eta$
converge for $k<0.1h$Mpc$^{-1}$, but give drastically different results on
smaller scales, which explains some of the trends observed in the real data. We
also asses the level of stochasticity by calculating the cross-correlation
coefficient between the reconstructed velocity field divergence and the
galaxies and show that the two fields decorrelate for $k>0.1h$Mpc$^{-1}$. Most
problematic are galaxies predominantly found in groups and clusters, such as
red or elliptical galaxies, where we find poor convergence to a constant bias
or $eta$ even on large scales.
(19kb)
astro-ph/0009017 [abs, src, ps, other] :
Title: The strength and width of Fe Kalpha lines in Seyferts and their
correlations with the X-ray slope
Authors:
Piotr Lubinski (Heavy Ion Laboratory, Warsaw University, Warsaw, Poland),
Andrzej A. Zdziarski (N. Copernicus Astronomical Center, Warsaw, Poland)
Comments: 6 pages, 4 figures, LaTeX 2.09 MNRAS style, submitted to MNRAS
(Letters)
We study the properties of Fe K lines of a large sample of Seyfert 1s
observed by ASCA. When fitted by a power law and a Gaussian line, the average
line width is 0.22+-0.03 keV and the equivalent width is 0.13+-0.01 keV, i.e.,
the typical lines are relatively weak and narrow. We then obtain the average
line profile of all our spectra, and find it to consist of a narrow core and
blue and red wings, with the red wing being much weaker than those of, e.g.,
MCG-6-30-15 or NGC 3516. We also obtain 3 average spectra of Seyfert grouped
according to the increasing power-law slope, and find the equivalent width of
the core to be ~50 eV in all 3 cases. This narrow line probaly originates in a
large-scale torus. In addition, the spectra show broad components well fitted
by lines from a disc with strong relativistic effects. The equivalent width of
the broad line correlates with the slope, increasing from ~70 eV for the
hardest spectrum to ~120 eV for the softest one. The inner disc radius
decreases correspondingly from ~40 to ~10 gravitational radii, and the disc
inclination is ~45 degrees for all 3 average spectra. The obtained correlation
between the slope and the strength of the broad line is found to be consistent
with the previously-found correlation of the slope and Compton reflection, thus
demonstrating that there is no discrepancy between those 2 kinds of
reprocessing features.
(48kb)
astro-ph/0009018 [abs, src, ps, other] :
Title: The ISM of Low Surface Brightness Galaxies
Authors:
L. D. Matthews (NRAO),
Kenneth Wood (CfA),
Yu Gao (IPAC)
Comments: 4 pages; requires newpasp.sty; to appear in “Gas and Galaxy
Evolution”, a conference held in Socorro, NM, May 2000, ASP Conference
Series, ed. J. E. Hibbard et al., in press
Using Monte Carlo radiative transfer techniques, we model the dust content of
the edge-on low surface brightness (LSB) galaxy UGC 7321 and explore the
effects of dust on its disk color gradients. Dust alone cannot explain the
large radial disk color gradients observed in this galaxy and we find that a
significant fraction (~50%) of the dust in UGC 7321 appears to be contained in
a clumped medium, indicating that at least some LSB galaxies can support a
modest multi-phase ISM structure. In addition, we report some of the first
direct detections of molecular gas (CO) in LSB galaxies.
(92kb)
astro-ph/0009019 [abs, src, ps, other] :
Title: Stellar models and Hyades: the Hipparcos test
Authors:
V. Castellani (1 and 2),
S. Degl’Innocenti (1 and 2),
P. G. Prada Moroni (3 and 4) ((1) Dipartimento di Fisica, Universit`a di Pisa, Italy, (2) INFN Sezione di Pisa, Italy, (3) Dipartimento di Fisica, Universit`a di Genova, Italy, (4) INFN Sezione di Genova, Italy)
Comments: 5 pages, 8 figures, MNRAS accepted
We compare theoretical stellar models for Main Sequence (MS) stars with the
Hipparcos database for the Hyades cluster to give a warning against the
uncritical use of available theoretical scenarios and to show how formal MS
fittings can be fortuitous if not fictitious. Moreover, we find that none of
the current theoretical scenarios appears able to account for an observed
mismatch between theoretical predictions and observations of the coolest Hyades
MS stars. Finally, we show that current theoretical models probably give too
faint He burning luminosities unlike the case of less massive He burning
models, with degenerate progenitors, which have been suggested to suffer the
opposite discrepancy.
(100kb)
astro-ph/0009020 [abs, src, ps, other] :
Title: The Case Against Cosmology
Authors:
M. J. Disney
Comments: 9 pages, no figures
Journal-ref: GReGr (2000) 32 1125
It is argued that some of the recent claims for cosmology are grossly
overblown. Cosmology rests on a very small database: it suffers from many
fundamental difficulties as a science (if it is a science at all) whilst
observations of distant phenomena are difficult to make and harder to
interpret. It is suggested that cosmological inferences should be tentatively
made and sceptically received.
(9kb)
astro-ph/0009021 [abs, src, ps, other] :
Title: A detailed two-dimensional stellar population study of M32
Authors:
C. del Burgo (IAC, IAP),
R. F. Peletier (Nottingham),
A. Vazdekis (Durham),
S. Arribas (IAC),
E.Mediavilla (IAC)
Comments: accepted in MNRAS
We present Two-Dimensional Spectroscopy of the 9×12 arcsec^2 central region
of M32 obtained with the 2D_FIS fibre spectrograph installed at the William
Herschel Telescope. From these spectra line strength maps have been
reconstructed for about 20 absorption lines, mostly belonging to the Lick
system. We find good agreement with long-slit line strength profiles in the
literature. In contrast with previous studies, indices were azimuthally
averaged along continuum isophotes of M32. A remarkable result is that no
gradients are presented in the spectral indices. So, we have fitted the mean
values of each spectral index and central colours to the models of Vazdekis et
al. (1996) and Worthey (1994), finding that an intermediate age (~4 Gyr) and
metallicity similar to solar (Z=0.02) are the best fitted values for the
innermost region of M32.
(175kb)
astro-ph/0009022 [abs, src, ps, other] :
Title: Viscosity Mechanisms in Accretion Disks
Authors:
Kristen Menou (Princeton Univ.)
Comments: 7 pages, 2 figures, accepted for publication in Science
Journal-ref: Science 288, 2022 (2000)
The self-sustained turbulence which develops in magnetized accretion disks is
suppressed in the weakly-ionized, quiescent disks of close binary stars.
Because accretion still proceeds during quiescence, another viscosity mechanism
operates in these systems. An anticorrelation of the recurrence times of SU UMa
dwarf novae with their mass ratio supports spiral waves or shock-waves tidally
induced by the companion star as the main process responsible for accretion in
the quiescent disks. Other weakly-ionized gaseous disks in systems lacking a
massive companion have to rely on yet another transport mechanism or they could
be essentially passive.
(26kb)
astro-ph/0009023 [abs, src, ps, other] :
Title: Imaging the secondary stars in cataclysmic variables
Authors:
V. S. Dhillon,
C. A. Watson (University of Sheffield)
Comments: 25 pages, 15 figures, to appear in the Proceedings of the
Astro-tomography Workshop, Brussels, July 2000, eds. H. Boffin, D. Steeghs,
Springer-Verlag Lecture Notes in Physics. A version with higher quality
figures, is available at
this http URL
The secondary, Roche-lobe filling stars in cataclysmic variables (CVs) are
key to our understanding of the origin, evolution and behaviour of this class
of interacting binary. We review the basic properties of the secondary stars in
CVs and the observational and analysis methods required to detect them. We then
describe the various astro-tomographic techniques which can be used to map the
surface intensity distribution of the secondary star, culminating in a detailed
explanation of Roche tomography. We conclude with a summary of the most
important results obtained to date and future prospects.
(526kb)
astro-ph/0009024 [abs, src, ps, other] :
Title: A Submillimeter Selected Quasar in the Field of Abell 478
Authors:
K.K. Knudsen,
P.P. van der Werf,
W. Jaffe (Leiden Observatory)
Comments: 4 pages, 3 figures, in “Deep Millimeter Surveys: Implications for
Galaxy Formation and Evolution”, ed. J. Lowenthal and D. Hughes, World
Scientific Publishers
We report the discovery of a z=2.83 quasar in the field of the cooling flow
galaxy cluster Abell 478. This quasar was first detected in a submm survey of
star forming galaxies at high redshifts, as the brightest source. We discuss
the optical spectrum and far-IR spectral energy distribution (SED) of this
object.
(213kb)
astro-ph/0009025 [abs, src, ps, other] :
Title: VLT spectroscopy of GRB 990510 and GRB 990712; probing the faint and
bright end of the GRB host galaxy population
Authors:
P.M. Vreeswijk,
A. Fruchter,
L. Kaper,
E. Rol,
T.J. Galama,
J. van Paradijs,
C. Kouveliotou,
R.A.M.J. Wijers,
E. Pian,
E. Palazzi,
N. Masetti,
F. Frontera,
S. Savaglio,
K. Reinsch,
F.V. Hessman,
K. Beuermann,
H. Nicklas,
E.P.J. van den Heuvel
Comments: 9 pages; accepted for publication in the Astrophysical Journal
We present time-resolved optical spectroscopy of the afterglows of the
gamma-ray bursts GRB 990510 and GRB 990712. Through the identification of
several absorption lines in the first epoch GRB 990510 spectrum, we determine
the redshift for this burst at z >= 1.619. No clear emission lines are
detected. The strength of the MgI feature is indicative of a dense environment,
most likely the host galaxy of GRB 990510. Although the host is extremely faint
(V >~ 28), the GRB afterglow allows us to probe its interstellar medium and –
in principle – to measure its metallicity. The optical spectrum of GRB 990712
(whose host galaxy is the brightest of the known GRB hosts at cosmological
redshifts), shows clear features both in emission and absorption, at a redshift
of z = 0.4331 +/- 0.0004. On the basis of several line emission diagnostic
diagrams, we conclude that the host galaxy of GRB 990712 is most likely an HII
galaxy. We derive a unreddened [OII] star formation rate of 2.7 +/- 0.8
Msun/yr. Correcting for the measured extinction intrinsic to the host galaxy
(A(V) = gpm{3.4}{2.4}{1.7}), this value increases to gpm{35}{178}{25}
Msun/yr. The [OII] equivalent width, compared to that of field galaxies at z <=
1, also suggests that the host of GRB 990712 is vigorously forming stars. We
employ the oxygen and Hbeta emission-line intensities to estimate the global
oxygen abundance for the host of GRB 990712: log(O/H) = -3.7 +- 0.4, which is
slightly below the lowest metallicity one finds in nearby spiral galaxies. For
both GRBs we study the time evolution of the absorption lines, whose equivalent
width might be expected to change with time if the burst resides in a dense
compact medium. We find no evidence for a significant change in the MgII width.
(40kb)
astro-ph/0009026 [abs, src, ps, other] :
Title: A Deep, Wide-Field H-alpha Survey of Nearby Clusters of Galaxies
Authors:
Shoko Sakai (UCLA),
Robert Kennicutt (Steward),
Chris Moss (Liverpool)
Comments: 2 pages, 1 figure. To appear in ASP Conference Series, “Galaxy Disks
and Disk Galaxies”, J.G. Funes S.J. and E.M. Corsini, eds
We present a progress report on an ongoing H-alpha imaging survey of nearby
clusters of galaxies. Four clusters have been surveyed to date: A1367, A1656,
A347 and A569. A preliminary comparison of H-alpha luminosity functions
obtained from our imaging survey with those from the prism survey reveals a
significant level of incompleteness in the latter. This in turn is due to a
combination of insensitivity to low-luminosity emission-line galaxies and to
brighter galaxies with weak extended H-alpha emission. The survey has also
revealed a unique population of clustered dwarf emission-line objects which may
be the results of recent tidal encounters between larger gas-rich galaxies.
(10kb)
astro-ph/0009027 [abs, src, ps, other] :
Title: SN 1997bs in M66: Another Extragalactic Eta Carinae Analog?
Authors:
S.D. Van Dyk,
C.Y. Peng,
J.Y. King,
A.V. Filippenko,
R.R. Treffers,
W.D. Li,
M.W. Richmond
Comments: 15 pages, 8 figures, to appear in the PASP (2000 Dec issue)
We report on SN 1997bs in NGC 3627 (M66), the first supernova discovered by
the Lick Observatory Supernova Search using the 0.75-m Katzman Automatic
Imaging Telescope (KAIT). Based on its early-time optical spectrum, SN 1997bs
was classified as Type IIn. However, from the BVRI light curves obtained by
KAIT early in the supernova’s evolution, and F555W and F814W light curves
obtained from Hubble Space Telescope archival WFPC2 images at late times, we
question the identification of SN 1997bs as a bona fide supernova. We believe
that it is more likely a super-outburst of a very massive luminous blue
variable star, analogous to Eta Carinae, and similar to SN 1961V in NGC 1058
(Filippenko et al. 1995 [AJ, 110, 2261]) and SN 1954J (“Variable 12”) in NGC
2403 (Humphreys & Davidson 1994 [PASP, 106, 1025]). The progenitor may have
survived the outburst, since the SN is seen in early 1998 at m_F555W=23.4,
about 0.5 mag fainter than the progenitor identified by Van Dyk et al. (1999,
[AJ, 118, 2331]) in a pre-discovery image. Based on analysis of its environment
in the Hubble Space Telescope images, the progenitor was not in an H II region
or association of massive stars. The recent discovery of additional objects
with properties similar to those of SN 1997bs suggests that the heterogeneous
class of Type IIn supernovae consists in part of “impostors.”
(156kb)
Cross-listings
hep-ph/0008328 [abs, src, ps, other] :
Title: Inflationary preheating and primordial black holes
Authors:
Bruce A. Bassett (Portsmouth),
Shinji Tsujikawa (Waseda)
Comments: 6 pages, 5 figures
Preheating after inflation may over-produce primordial black holes (PBH’s) in
many regions of parameter space. As an example we study two-field models with a
massless self-interacting inflaton, taking into account second order field and
metric backreaction effects as spatial averages. We find that a complex quilt
of parameter regions above the Gaussian PBH over-production threshold emerges
due to the enhancement of curvature perturbations on all scales. It should be
possible to constrain realistic models of inflation through PBH over-production
although many issues, such as rescattering and non-Gaussianity, remain unsolved
or unexplored.
(296kb)
Replacements
astro-ph/9912301 [abs, src, ps, other] :
Title: Cold ideal equation of state for strongly magnetized neutron-star
matter: effects on muon production and pion condensationn
Authors:
In-Saeng Suh,
G. J. Mathews (Univ. of Notre Dame)
Comments: 10 pages included 9 figures, ApJ in press
Note: replaced with revised version Fri, 1 Sep 2000 20:47:02 GMT (232kb)
astro-ph/0005576 [abs, src, ps, other] :
Title: On the photodissociation of H2 by the first stars
Authors:
Simon C.O. Glover (IfA, Edinburgh),
Peter W.J.L. Brand (IfA, Edinburgh)
Comments: 13 pages, 10 figures. Minor revisions to match version accepted by
MNRAS
Note: replaced with revised version Fri, 1 Sep 2000 13:10:01 GMT (141kb)
astro-ph/0008208 [abs, src, ps, other] :
Title: Emergence of power-law correlation in 1-dimensional self-gravitating
system
Authors:
Hiroko Koyama,
Tetsuro Konishi
Comments: 9 pages, 7 figures
Subj-class: Astrophysics; Chaotic Dynamics
Note: replaced with revised version Fri, 1 Sep 2000 05:13:48 GMT (546kb)
astro-ph/0008472 [abs, src, ps, other] :
Title: ASTRO-F – The next generation of mid-infrared surveys
Authors:
Pearson C.,
Matsuhara H.,
Watarai H.,
Matsumoto T. (Institute of Space and Astronautical Sciences, Japan),
Onaka T. (University of Tokyo)
Comments: 18 pages, 17 figures, submitted to MNRAS
Note: replaced with revised version Fri, 1 Sep 2000 01:25:23 GMT (629kb)
hep-ph/0003089 [abs, src, ps, other] :
Title: Inflation in Models with Large Extra Dimensions Driven by a Bulk Scalar
Field
Authors:
R. N. Mohapatra,
A. Pérez-Lorenzana,
C. A. de S. Pires
Comments: 6 pages, LaTeX file, no figures. Minor changes. Final version to
appear in Phys. Rev D
Note: replaced with revised version Fri, 1 Sep 2000 20:48:27 GMT (12kb)
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