Astrophysics

astro-ph new abstracts, Thu, 24 Aug 00 04:00:12 GMT
0008351 — 0008375 received

astro-ph/0008351 [abs, src, ps, other] :

Title: EUV/X-ray Emission and the Thermal and Ionization Structure of B Star
Winds
Authors:
David H. Cohen,
Joseph P. Cassinelli,
Joseph J. MacFarlane,
Stanley P. Owocki
Comments: To appear in A.S.P. conf. ser. 204, Thermal and Ionization Structure
of Flows from Hot Stars: Observation and Theory, eds. Lamers and Sapar; paper
also available at this http URL

We discuss the EUV and X-ray properties of B stars, focusing on $epsilon$
CMa (B2 II) which is the only star with both emission lines and a photospheric
continuum detected with EUVE. We explore the modest effects of the photospheric
EUV continua on the wind, as well as the much stronger effects of the
short-wavelength EUV and soft X-ray emission lines. Attenuation of the EUV and
soft X-ray emission by the wind plays an important role, and leads to the
reprocessing of X-rays via He$^+$ ionization and the Bowen mechanism in the
wind. Finally, we explore some of the new diagnostics that will shortly become
available with the next generation of high spectral resolution X-ray
telescopes. All of this analysis is presented in the context of a two component
stellar wind–a dense component (clumps) that contains most of the mass but
fills a negligible fraction of the volume, and a rarefied component that fills
most of the volume but accounts for only a small fraction of the mass.
(97kb)

astro-ph/0008352 [abs, src, ps, other] :

Title: Cosmological Relativity: A New Theory of Cosmology
Authors:
S. Behar,
M. Carmeli

A general-relativistic theory of cosmology, the dynamical variables of which
are those of Hubble’s, namely distances and redshifts, is presented. The theory
describes the universe as having a three-phase evolution with a decelerating
expansion followed by a constant and an accelerating expansion, and it predicts
that the universe is now in the latter phase. The theory is actually a
generalization of Hubble’s law taking gravity into account by means of
Einstein’s theory of general relativity. The equations obtained for the
universe expansion are elegant and very simple. It is shown, assuming
Omega_0=0.24, that the time at which the universe goes over from a decelerating
to an accelerating expansion, i.e. the constant expansion phase, occurs at
0.03tau from the big bang, where tau is the Hubble time in vacuum. Also, at
that time the cosmic radiation temperature was 11K. Recent observations of
distant supernovae imply, in defiance of expectations, that the universe growth
is accelerating, contrary to what has always been assumed that the expansion is
slowing down due to gravity. Our theory confirms these recent experimental
results by showing that the universe now is definitely in a stage of
accelerating expansion.
(166kb)

astro-ph/0008353 [abs, src, ps, other] :

Title: Topology of the Galaxy Distribution in the Hubble Deep Fields
Authors:
Changbom Park,
J. Richard Gott III,
Y. J. Choi
Comments: 14 pages, 4 figures, submitted to ApJ

We have studied topology of the distribution of the high redshift galaxies
identified in the Hubble Deep Field (HDF) North and South. The two-dimensional
genus is measured from the projected distributions of the HDF galaxies at
angular scales from $3.8”$ to $ 6.1”$. We have also divided the samples into
three redshift slices with roughly equal number of galaxies using photometric
redshifts to see possible evolutionary effects on the topology.

The genus curve of the HDF North clearly indicates clustering of galaxies
over the Poisson distribution while the clustering is somewhat weaker in the
HDF South. This clustering is mainly due to the nearer galaxies in the samples.
We have also found that the genus curve of galaxies in the HDF is consistent
with the Gaussian random phase distribution with no significant redshift
dependence.
(212kb)

astro-ph/0008354 [abs, src, ps, other] :

Title: Radiation pressure instability as a variability mechanism in the
microquasar GRS 1915+105
Authors:
Agnieszka Janiuk,
Bozena Czerny,
Aneta Siemiginowska
Comments: 6 pages, 2 figures; accepted for publication in ApJ Letters

Physical mechanism responsible for high viscosity in accretion disks is still
under debate. Parameterization of the viscous stress as $alpha P$ proved to be
a successful representation of this mechanism in the outer parts of the disk,
explaining the dwarf novae and X-ray novae outbursts as due to ionization
instability. We show that this parameterization can be also adopted in the
innermost part of the disk where the adoption of the $alpha$-viscosity law
implies the presence of the instability in the radiation pressure dominated
region. We study the time evolution of such disks. We show that the
time-dependent behavior of GRS 1915+105 can be well reproduced if
$alpha$-viscosity disk model is calculated accurately (with proper numerical
coefficients in vertically averaged equations and with advection included), and
if the model is supplemented with (i) moderate corona dissipating 50% of energy
(ii) jet carrying luminosity-dependent fraction of energy. These necessary
modifications in the form of the presence of a corona and a jet are well
justified observationally. The model predicts outbursts at luminosity larger
than 0.16$dot M_{Edd}$, as required, correct outburst timescales and
amplitudes, including the effect of increasing outburst timescale with mean
luminosity. This result strongly suggests that the $alpha$-viscosity law is a
good description of the actual mechanism responsible for angular momentum
transfer also in the innermost, radiation pressure dominated part of the disk
around a black hole.
(22kb)

astro-ph/0008355 [abs, src, ps, other] :

Title: R-mode oscillations of rapidly rotating Newtonian stars – A new
numerical scheme and its application to the spin evolution of neutron stars
Authors:
Shigeyuki Karino (1),
Shin’ichirou Yoshida (2),
Shijun Yoshida (3),
Yoshiharu Eriguchi (1) ((1)Grad. School of Arts and Sciences, Univ. of Tokyo,(2)SISSA,(3)Tohoku Univ)
Comments: LaTeX 12 pages with 19 figures, to be published in PRD

We have developed a new numerical scheme to solve r-mode oscillations of {it
rapidly rotating polytropic stars} in Newtonian gravity. In this scheme, Euler
perturbations of the density, three components of the velocity are treated as
four unknown quantities together with the oscillation frequency. For the basic
equations of oscillations, the compatibility equations are used instead of the
linearized equations of motion.

By using this scheme, we have solved the classical r-mode oscillations of
rotational equilibrium sequences of polytropes with the polytropic indices $N =
0.5, 1.0$ and 1.5 for $m = 2, 3$ and 4 modes. Here $m$ is the rank of the
spherical harmonics $Y_l^m$. These results have been applied to investigate
evolution of uniformly rotating hot young neutron stars by considering the
effect of gravitational radiation and viscosity. We have found that the maximum
angular velocities of neutron stars are around 10-20% of the Keplerian angular
velocity irrespective of the softness of matter. This confirms the results
obtained from the analysis of r-modes with the slow rotation approximation
employed by many authors.
(37kb)

astro-ph/0008356 [abs, src, ps, other] :

Title: Thermal and Viscous Instability of Accretion Disc in AGN
Authors:
Agnieszka Janiuk,
Bozena Czerny
Comments: 5 pages, 3 figures; poster presented at Advanced Lectures on
Starburst AGN Connection, Mexico, June 2000

The standard accretion discs are known to be thermally and viscously unstable
over a certain range of temperatures. In the inner disc regions there may
develop radiation pressure driven instability, which is possibly related to the
rapid variability detected in AGNs in the UV range. In the outer disc develops
the ionization instability, similar to that in the cataclysmic variables, but
operating on much longer timescales. Due to this process the spectrum of the
accretion disc differs from that of a stationary one.
(11kb)

astro-ph/0008357 [abs, src, ps, other] :

Title: HI Recycling: Formation of Tidal Dwarf Galaxies
Authors:
Pierre-Alain Duc (1),
Elias Brinks (2) ((1)CNRS and CEA-Saclay, France (2)Guanajuato, Mexico)
Comments: 4 pages, 2 figures, to appear in ASP Conference Series, “Gas & Galaxy
Evolution” J.E. Hibbard, M.P. Rupen and J.H. van Gorkom, eds. also available
at: this http URL

Galactic collisions trigger a number of phenomena, such as transportation
inward of gas from distances of up to kiloparsecs from the center of a galaxy
to the nuclear region, fuelling a central starburst or nuclear activity. The
inverse process, the ejection of material into the intergalactic medium by
tidal forces, is another important aspect and can be studied especially well
through detailed HI observations of interacting systems which have shown that a
large fraction of the gaseous component of colliding galaxies can be expelled.
Part of this tidal debris might fall back, be dispersed throughout the
intergalactic medium or recondense to form a new generation of galaxies: the
so-called tidal dwarf galaxies. The latter are nearby examples of galaxies in
formation. The properties of these recycled objects are reviewed here and
different ways to identify them are reviewed.
(328kb)

astro-ph/0008358 [abs, src, ps, other] :

Title: Discovery of a new, third kHz QPO in 4U 1608-52, 4U 1728-34, and 4U
1636-53. Sidebands to the lower kHz QPO?
Authors:
Peter G. Jonker,
Mariano Mendez,
Michiel van der Klis
Comments: 11 pages, including 1 figure and 2 tables. Accepted for publication
in ApJL

We report the discovery of a third kilohertz quasi-periodic oscillation (kHz
QPO) in the power spectra of the low-mass X-ray binaries 4U 1608-52 (6.3
sigma), 4U 1728-34 (6.0 sigma), and 4U 1636-53 (3.7 sigma) which is present
simultaneously with the previously-known kHz QPO pair. The new kHz QPO is found
at a frequency that is 52.8+-0.9 Hz, 64+-2 Hz, 58.4+-1.9 Hz higher than the
frequency of the lower kHz QPO in 4U 1608-52, 4U 1728-34, and 4U 1636-53,
respectively. The difference between the frequency of the new kHz QPO and the
lower kHz QPO increased in 4U 1608-52 from 49.6+-1.4 Hz to 53.9+-0.5 Hz when
the frequency of the lower kHz QPO increased from 672 Hz to 806 Hz.
Simultaneously the difference between the frequency of the new kHz QPO and the
upper kHz QPO increased by ~60 Hz, suggesting that the new kHz QPO is unrelated
to the upper kHz QPO. In 4U 1636-53 a fourth, weaker, kHz QPO is simultaneously
detected (3 sigma) at the same frequency separation below the lower kHz QPO,
suggesting the new kHz QPOs are sidebands to the lower kHz QPO. We discuss the
nature of this new kHz QPO and its implications on the models for the kHz QPOs.
(33kb)

astro-ph/0008359 [abs, src, ps, other] :

Title: Gas Flow and Star Formation in the `Antennae’ Galaxies NGC 4038/9
Authors:
P. Englmaier,
D. Rigopoulou,
S. Mengel
Comments: To appear in proceedings of Gas and Galaxy Evolution, (VLA 20th
Anniversary Conference), ASP Conf. Series, ed. J. Hibbard, M. Rupen, & J. van
Gorkom. 2 pages, no figures, uses newpasp.sty

The prominent interacting galaxy pair NGC 4038/9 contains many active
star-forming regions and is continuously forming new star clusters. We present
a self-consistent n-body model for this system which includes an SPH gas
component. The model qualitatively explains the apparent concentration of gas
in the so-called overlap region between the two nuclei as a bridge of gas
connecting the two galaxies. Projected on the sky, the bridge appears as a
dense spot of gas. We discuss some implications for the evolution of
Ultra-luminous infrared galaxies.
(7kb)

astro-ph/0008360 [abs, src, ps, other] :

Title: Evolution of a Rotating Black Hole with a Magnetized Accretion Disk
Authors:
Hyun Kyu Lee,
Hui-Kyung Kim (Dep. of Physics, Hanyang University, Seoul)
Comments: 5 pages with 3 EPS figures, to appear in Journal of the Korean
Physical Society(JKPS) Vol. 36, No.3, pp. 188

The effect of an accretion disk on the Blandford-Znajek process and the
evolution of a black hole are discussed using a simplified system for the black
hole – accretion disk in which the accretion rate is supposed to be dominated
by the strong magnetic field on the disk. The evolutions of the mass and the
angular momentum of the black hole are formulated and discussed with numerical
calculations.
(48kb)

astro-ph/0008361 [abs, src, ps, other] :

Title: Study of the Temporal Behavior of 4U 1728-34 as a Function of its
Position in the Color-Color Diagram
Authors:
T. Di Salvo,
M. Méndez,
M. van der Klis,
E. Ford,
N. R. Robba
Comments: 27 pages, 9 figures, accepted by ApJ

We study the timing properties of the bursting atoll source 4U 1728-34 as a
function of its position in the X-ray color-color diagram. In the island part
of the color-color diagram (corresponding to the hardest energy spectra) the
power spectrum of 4U 1728-34 shows several features such as a band-limited
noise component present up to a few tens of Hz, a low frequency quasi-periodic
oscillation (LFQPO) at frequencies between 20 and 40 Hz, a peaked noise
component around 100 Hz, and one or two QPOs at kHz frequencies. In addition to
these, in the lower banana (corresponding to softer energy spectra) we also
find a very low frequency noise (VLFN) component below ~1 Hz. In the upper
banana (corresponding to the softest energy spectra) the power spectra are
dominated by the VLFN, with a peaked noise component around 20 Hz. We find that
the frequencies of the kHz QPOs are well correlated with the position in the
X-ray color-color diagram. For the frequency of the LFQPO and the break
frequency of the broad-band noise component the relation appears more complex.
These frequencies both increase when the frequency of the upper kHz QPO
increases from 400 to 900 Hz, but at this frequency a jump in the values of the
parameters occurs. We interpret this jump in terms of the gradual appearance of
a QPO at the position of the break at high inferred mass accretion rate, while
the previous LFQPO disappears. Simultaneously, another kind of noise appears
with a break frequency of ~7 Hz, similar to the NBO of Z sources. The 100 Hz
peaked noise does not seem to correlate with the position of the source in the
color-color diagram, but remains relatively constant in frequency. This
component may be similar to several 100 Hz QPOs observed in black hole
binaries.
(181kb)

astro-ph/0008362 [abs, src, ps, other] :

Title: ISO impact on stellar models and vice versa
Authors:
L. Decin (1),
C. Waelkens (1),
K. Eriksson (2),
B. Gustafsson (2)
B.Plez (3),
A.J. Sauval (4),
W. Van Assche (5),
B. Vandenbussche (1) ((1) Instituut voor Sterrenkunde, Leuven, Belgium, (2) Astronomiska Observatoriet, Uppsala, Sweden, (3) Universite de Montpellier II, Montpellier, France, (4) Observatoire Royal de Belgique, Bruxelles, Belgium, (5) Instituut voor Wiskunde, Leuven,Belgium)
Comments: 6 pages, 3 figures, to appear in `ISO beyond the peaks: The 2nd ISO
workshop on analytical spectroscopy’, held 2-4 February 2000, at VILSPA

We present a detailed spectroscopic study of a sample of bright, mostly cool,
stars observed with the Short-Wavelength Spectrometer (SWS) on board the
Infrared Space Observatory (ISO), which enables the accurate determination of
the stellar parameters of the cool giants, but also serves as a critical review
of the ISO-SWS calibration.
(105kb)

astro-ph/0008363 [abs, src, ps, other] :

Title: Testing the Correlation of Ultra-High Energy Cosmic Rays with High
Redshift Sources
Authors:
Guenter Sigl (1),
Diego Torres (2),
Luis Anchordoqui (3),
Gustavo Romero (2) ((1) CNRS, Institut d’Astrophysique de Paris, (2) Instituto Argentino de Radioastronomia, (3) Northeastern University, USA)
Comments: 4 latex pages, uses revtex, no figures

We study the correlation between compact radio quasars and ultra-high energy
cosmic rays using an updated list of air shower detections. We estimate the
level of positional correlation between both samples and the probability of
pure chance association through simulations of random sets of synthetic cosmic
ray events. We find that there are no reasons to claim for a physical
association and that some previous results appear to be an effect of the small
size of the sample used. This is also true when, instead of compact radio
quasars, 3EG gamma-ray blazars are considered. Consequently, unless somehow
severely deflected, it is unlikely that the high energy CR primaries are new
particles or particles with new interactions beyond the electroweak scale,
produced in high-redshift active galactic nuclei.
(8kb)

astro-ph/0008364 [abs, src, ps, other] :

Title: Particle and Astrophysics Aspects of Ultrahigh Energy Cosmic Rays
Authors:
Guenter Sigl (CNRS, Institut d’Astrophysique de Paris)
Comments: 55 latex pages, 13 postscript figures included, Lectures given at
Mexican School of Astrophysics (Guanajuato, August 1999) and at Summer School
on Astroparticle Physics and Cosmology (Trieste, Italy, June 2000)

The origin of cosmic rays is one of the major unresolved astrophysical
questions. In particular, the highest energy cosmic rays observed possess
macroscopic energies and their origin is likely to be associated with the most
energetic processes in the Universe. Their existence triggered a flurry of
theoretical explanations ranging from conventional shock acceleration to
particle physics beyond the Standard Model and processes taking place at the
earliest moments of our Universe. Furthermore, many new experimental activities
promise a strong increase of statistics at the highest energies and a
combination with gamma-ray and neutrino astrophysics will put strong
constraints on these theoretical models. Detailed Monte Carlo simulations
indicate that charged ultra-high energy cosmic rays can also be used as probes
of large scale magnetic fields whose origin may open another window into the
very early Universe. We give an overview over this quickly evolving reasearch
field.
(409kb)

astro-ph/0008365 [abs, src, ps, other] :

Title: Supernovae and the IGM
Authors:
James Binney (Oxford Univ)
Comments: 6 pages to appear in “Gas and Galaxy Evolution” ASP Conf. Ser.,
Hibbard, Rupen & van Gorkom eds

An energetic argument implies that a galaxy like the Milky Way is blowing a
powerful wind that carries away most of the heavy elements currently
synthesized and has impacted the IGM out to at least 180 kpc. Rich clusters of
galaxies appear to be closed systems in which most heavy elements are ejected
from galaxies. More supernovae are required than the yield of core-collapse SNe
from a Salpeter IMF. X-ray observations imply that the IGM in groups and
clusters as been strongly preheated. SNe probably cannot supply the required
energy, which must come from AGN.
(11kb)

astro-ph/0008366 [abs, src, ps, other] :

Title: Damped Lyman alpha systems at z=0.68 and z=1.15 towards HE 1122-1649 and
HE 0515-4414
Authors:
A. de la Varga (1),
D. Reimers (1),
D. Tytler (2),
T. Barlow (3),
S. Burles (4) ((1) Hamburger Sternwarte, Universit”at Hamburg, (2) Center for Astrophysics and Space Sciences, University of California, San Diego, (3) California Institute of Technology, (4) Department of Astronomy and Astrophysics, University of Chicago)
Comments: 35 pages, 8 figures, accepted for publication in A&A

Detailed analysis of the spectral lines from two low redshift damped Lyman
alpha absorbers (DLA) confirms that they are a heterogeneous population. Both
systems have low metal abundances of approximately 0.05 to 0.1 solar. The
abundance pattern of the DLA at z=1.15 towards HE 0515-4414 shows dust
depletion comparable to that found in our Galaxy, while the system at z=0.68
towards HE 1122-1649 shows abundance ratios resembling metal-poor halo stars
with no dust depletion, for a comparable HI column. Constraints for N/Fe and
N/Si also hint at z=0.68 DLA as a galaxy with recent star formation. The trend
of increasing CI/HI with decreasing z is discussed. Only weak absorption from
highly-ionized species associated with the DLA at moderate z have been detected
and it probably originates in regions distinct from the low ionization gas. The
low-ion profiles show very complex structures and are too large to be explained
by the rotation of a disk: the system at z=0.68 spans over approximately 300
km/s and the z=1.15 DLA presents substructure over more than 700 km/s, the
largest velocity extent found up to date for a DLA.
(185kb)

astro-ph/0008367 [abs, src, ps, other] :

Title: Superhumps in Low-Mass X-Ray Binaries
Authors:
Carole A. Haswell,
Andrew R. King,
James R. Murray,
Philip A. Charles
Comments: 6 pages, 1 encapsulated figure. Submitted to MNRAS; includes minor
revisions after referee’s comments

We propose a mechanism for the superhump modulations observed in optical
photometry of at least two black hole X-ray transients (SXTs). As in extreme
mass-ratio cataclysmic variables (CVs), superhumps are assumed to result from
the presence of the 3:1 orbital resonance in the accretion disc. This causes
the disc to become non-axisymmetric and precess. However the mechanism for
superhump luminosity variations in low mass X-ray binaries (LMXBs) must differ
from that in CVs, where it is attributed to a tidally-driven modulation of the
disc’s viscous dissipation, varying on the beat between the orbital and disc
precession period. By contrast in LMXBs, tidal dissipation in the outer
accretion disc is negligible: the optical emission is overwhelming dominated by
reprocessing of intercepted central X-rays. Thus a different origin for the
superhump modulation is required. Recent observations and numerical simulations
indicate that in an extreme mass-ratio system the disc area changes on the
superhump period. We deduce that the superhumps observed in SXTs arise from a
modulation of the reprocessed flux by the changing area. Therefore, unlike the
situation in CVs, where the superhump amplitude is inclination-independent,
superhumps should be best seen in low-inclination LMXBs, whereas an orbital
modulation from the heated face of the secondary star should be more prominent
at high inclinations. Modulation at the disc precession period (10s of days)
may indicate disc asymmetries such as warping. We comment on the orbital period
determinations of LMXBs, and the possibility and significance of possible
permanent superhump LMXBs.
(21kb)

astro-ph/0008368 [abs, src, ps, other] :

Title: Ionization, Magneto-rotational, and Gravitational Instabilities in Thin
Accretion Disks Around Supermassive Black Holes
Authors:
Kristen Menou (Princeton Univ.),
Eliot Quataert (IAS)
Comments: submitted to ApJ Letters

We consider the combined role of the thermal ionization, magneto-rotational
and gravitational instabilities in thin accretion disks around supermassive
black holes. We find that in the portions of the disk unstable to the
ionization instability, the gas remains well coupled to the magnetic field even
on the cold, neutral branch of the thermal limit cycle. This suggests that the
ionization instability is not a significant source of large amplitude
time-dependent accretion in AGN. We also argue that, for accretion rates
greater than 10^{-2} solar masses per year, the gravitationally unstable and
magneto-rotationally unstable regions of the accretion disk overlap; for lower
accretion rates they may not. Some low-luminosity AGN, e.g. NGC 4258, may thus
be in a transient phase in which mass is building up in a non-accreting
gravitationally and magneto-rotationally stable “dead zone.” We comment on
possible implications of these findings.
(19kb)

astro-ph/0008369 [abs, src, ps, other] :

Title: Signature neutrinos from ultrahigh-energy photons
Authors:
Alexander Kusenko
Comments: 3 pages, talk presented at ICHEP-2000, Osaka, Japan, July 27 – August
2, 2000

At high red shift, the temperature of cosmic microwave background is
sufficiently high for the ultrahigh-energy photons to pair-produce muons and
pions through interactions with the background photons. At the same time, the
radio background and magnetic fields are too weak to drain energy out of the
electromagnetic cascade before the muons and pions are produced. Decays of the
energetic muons and pions yield neutrinos with some distinctive spectral
properties that can be detected and can indicate the presence of
ultrahigh-energy photons at high red shift. The neutrino signature can help
identify the origin of cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff.
(12kb)

astro-ph/0008370 [abs, src, ps, other] :

Title: Dynamical Masses of T Tauri Stars and Calibration of PMS Evolution
Authors:
M. Simon,
A. Dutrey,
S. Guilloteau
Comments: 32 pages, 5 figures

We have used the high sensitivity and resolution of the IRAM interferometer
to produce sub-arcsecond 12CO 2-1 images of 9 protoplanetary disks surrounding
T Tauri stars in the Taurus-Auriga cloud (7 singles and 2 binaries). The images
demonstrate the disks are in Keplerian rotation around their central stars.
Using the least square fit method described in Guilloteau and Dutrey (1998), we
derive the disk properties, in particular its inclination angle and rotation
velocity, hence the dynamical mass. Since the disk mass is usually small, this
is a direct measurement of the stellar mass. Typically, we reach an internal
precision of 10% in the determinations of stellar mass. The over-all accuracy
is limited by the uncertainty in the distance to a specific star. In a distance
independent way, we compare the derived masses with theoretical tracks of
pre-main-sequence evolution. Combined with the mean distance to the Taurus
region (140 pc), for stars with mass close to 1 Msun, our results tend to favor
the tracks with cooler photospheres (higher masses for a given spectral type).
We find that in UZ Tau E the disk and the spectroscopic binary orbit appear to
have different inclinations.
(397kb)

astro-ph/0008371 [abs, src, ps, other] :

Title: Fragmentation of a Protostellar Core: The Case of CB230
Authors:
R. Launhardt (Caltech)
Comments: 4 pages, 3 figures; Proceedings of IAU Symposium No. 200 on The
Formation of Binary Stars

The Bok globule CB230 (L1177) contains an active, low-mass star-forming core
which is associated with a double NIR reflection nebula, a collimated bipolar
molecular outflow, and strong mm continuum emission. The morphology of the NIR
nebula suggests the presence of a deeply embedded, wide binary protostellar
system. High-angular resolution observations now reveal the presence of two
sub-cores, two distinct outflow centers, and an embedded accretion disk
associated with the western bipolar NIR nebula. In terms of separation and
specific angular momentum, the CB230 double protostar system probably results
from core fragmentation and can be placed at the upper end of the pre-main
sequence binary distribution.
(206kb)

astro-ph/0008372 [abs, src, ps, other] :

Title: Magnetic Extraction of Spin Energy from a Black Hole
Authors:
Julian H. Krolik
Comments: to appear in “Explosive Phenomena in Astrophysical Compact Objects,
Proceedings of the 1st KIAS Astrophysics Workshop”

Numerous variations have been proposed on the original suggestion by
Blandford and Znajek that magnetic fields could be used to extract rotational
energy from black holes. A new categorization of these variations is proposed
so that they may be considered in a systematic way. “Black hole spindown” is
defined more precisely, distinguishing decrease in the spin parameter a/M from
decreases in angular momentum a and rotational kinetic energy, M – M_i. Several
key physical questions are raised: Can the “stretched horizon” of a black hole
communicate with the outside world? Do accretion disks bring any net magnetic
flux to the black holes at their centers? Is the magnetic field adjacent to a
black hole force-free everywhere?
(16kb)

astro-ph/0008373 [abs, src, ps, other] :

Title: The mass function of NGC288
Authors:
A. Pasquali (ESO/ST-Ecf),
M.S. Brigas (ESO/ST-Ecf/Cagliari),
G. De Marchi (ESO/ESA/Stsci)
Comments: 6 pages, 6 figures, accepted for publication in Astronomy and
Astrophysics

We present NICMOS NIC3 observations of the Galactic globular cluster NGC 288,
taken South – East at 2.4 times the cluster’s half-light radius in the J and H
bands. We have detected the cluster main sequence down to J~25 and H~24. The
corresponding luminosity function covers the range 3<M_H<9 and peaks at
M_H~6.8. The theoretical tracks of Baraffe et al. (1997) at [Fe/H]=-1.3 give a
mass function which is best fitted by a log-normal distribution with
characteristic mass m_c=0.42 Msolar and a standard deviation sigma=0.35. This
result is fully consistent with the global mass function derived by Paresce &
De Marchi (2000) for a sample of 12 globular clusters with very different
dynamical histories, thus confirming that near the cluster’s half-light radius
the mass function appears “undistorted” by evaporation or tidal interactions
with the Galaxy and should then reflect the initial mass function.
(39kb)

astro-ph/0008374 [abs, src, ps, other] :

Title: SCUBA observations of Hawaii 167
Authors:
Geraint F. Lewis,
Scott C. Chapman
Comments: 4 pages, 1 figure, to appear in M.N.R.A.S. (pink pages)

We present the first submillimetre observations of the z=2.36 broad
absorption line system Hawaii 167. Our observations confirm the hypothesis that
Hawaii 167 contains a massive quantity of dust, the optical depth of which is
sufficient to completely extinguish our ultraviolet view of a central, buried
quasar. Hawaii~167’s submillimetre luminosity and associated dust mass are
similar to the ultraluminous class of infrared galaxies, supporting the
existence of an evolutionary link between these and the active galaxy
population. Hawaii 167 appears to be a young quasar which is emerging from its
dusty cocoon.
(18kb)

astro-ph/0008375 [abs, src, ps, other] :

Title: Sensitivity of the Radial Velocity Technique in Detecting Outer Planets
Authors:
J. A. Eisner,
S. R. Kulkarni
Comments: 31 pages (including 11 postscript figures). Submitted to ApJ

The technique of radial velocity (RV) has produced spectacular discoveries of
short-period Jovian mass objects around a fraction (5 to 10%) of nearby G
stars. Although we expect Jovian planets to be located in long-period orbits of
decades or longer (if our solar system is any guide), detecting such planets
with RV technique is difficult due to smaller velocity amplitudes and the
limited temporal baseline (5-10 yr) of current searches relative to the
expected orbital periods. In this paper, we develop an analytical understanding
of the sensitivity of RV technique in the regime where the the orbital period
is larger than the total baseline of the survey. Moreover, we focus on the
importance of the orbital phase in this “long-period” regime, and develop a
Least Squares detection technique based on the amplitude and phase of the
fitted signal.

To illustrate the benefits of this amplitude-phase analysis, we compare it to
existing techniques. Previous authors (e.g. Nelson & Angel 1998) have explored
the sensitivity of an amplitude-only analysis using Monte Carlo simulations.
Others have supplemented this by using the slope of the linear component of the
fitted sinusoid in addition (e.g. Walker et al. 1995; Cumming et al. 1999). In
this paper, we illustrate the benefits of Least Squares over periodogram
analysis, and demonstrate the superiority of an amplitude-phase technique over
previous analyses.
(113kb)

Cross-listings

gr-qc/0008056 [abs, src, ps, other] :

Title: The Topological Origin of Black Hole Entropy
Authors:
Zhong Chao Wu
Comments: 7 pages, received honorable mention from GRF2000

In gravitational thermodynamics, the origin of a black hole’s entropy is the
topology of its instanton or constrained instanton. We prove that the entropy
of an arbitrary nonrotating black hole is one quarter the sum of the products
of the Euler characteristics of its horizons with their respective areas. The
Gauss-Bonnet-like form of the action is not only crucial for the evaluation,
but also for the existence of the entropy. This result covers all previous
results on the entropy of a nonrotating black hole with a regular instanton.
The argument can be readily extended into the lower or higher dimensional
model. The problem of quantum creation of such a black hole is completely
resolved.
(6kb)

hep-th/0008177 [abs, src, ps, other] :

Title: Charged Brane-World Black Holes
Authors:
Andrew Chamblin,
Harvey S. Reall,
Hisa-aki Shinkai,
Tetsuya Shiromizu
Comments: 11 pages, RevTeX, 8 figures

We study charged brane-world black holes in the model of Randall and Sundrum
in which our universe is viewed as a domain wall in asymptotically anti-de
Sitter space. Such black holes can carry two types of “charge”, one arising
from the bulk Weyl tensor and one from a gauge field trapped on the wall. We
use a combination of analytical and numerical techniques to study how these
black holes behave in the bulk. It has been shown that a Reissner-Nordstrom
geometry is induced on the wall when only Weyl charge is present. However, we
show that such solutions exhibit pathological features in the bulk. For more
general charged black holes, our results suggest that the extent of the horizon
in the fifth dimension is usually less than for an uncharged black hole that
has the same mass or the same horizon radius on the wall.
(66kb)

hep-th/0008178 [abs, src, ps, other] :

Title: Superconducting Cosmic String with Propagating Torsion
Authors:
C.N. Ferreira (CBPF/DCP),
H.J. Mosquera-Cuesta (ICTP, CBPF/LAFEX),
L.C. Garcia de Andrade (UERJ)
Comments: 15 LaTeX pages, submmited to Phys. Lett. B

We show that it is possible to construct a consistent model describing a
current-carrying cosmic string endowed with torsion. The torsion contribution
to the gravitational force and geodesics of a test-particle moving around the
SCCS are analyzed. In particular, we point out two interesting astrophysical
phenomena in which the higher magnitude force we derived may play a critical
role: the dynamics of compact objects orbiting the torsioned SCCS and accretion
of matter onto it. The deficit angle associated to the SCCS can be obtained and
compared with data from the Cosmic Background Explorer (COBE) satellite. We
also derived a value for the torsion contribution to matter density
fluctuations in the early Universe.
(15kb)

Replacements

astro-ph/0003368 [abs, src, ps, other] :

Title: Angular Momentum Transport in Particle and Fluid Disks
Authors:
Eliot Quataert,
Eugene I. Chiang
Comments: 15 pages; final version accepted by ApJ; minor changes, some
clarification
Note: replaced with revised version Wed, 23 Aug 2000 17:16:53 GMT (14kb)

astro-ph/0004286 [abs, src, ps, other] :

Title: Constraining the Accretion Rate Onto Sagittarius A* Using Linear
Polarization
Authors:
Eliot Quataert,
Andrei Gruzinov (IAS)
Comments: final version accepted by ApJ; references added, somewhat shortened
Note: replaced with revised version Wed, 23 Aug 2000 17:28:50 GMT (13kb)

astro-ph/0006107 [abs, src, ps, other] :

Title: R-modes of neutron stars with a solid crust
Authors:
Shijun Yoshida,
Umin Lee
Comments: 10 pages, 3 figures, revised version accepted for publication in the
ApJ
Note: replaced with revised version Wed, 23 Aug 2000 05:51:32 GMT (37kb)

astro-ph/0007294 [abs, src, ps, other] :

Title: Accretion column disruption in GX 1+4
Authors:
D.K. Galloway
Comments: 10 pages, 2 figure, revised according to reviewer’s suggestions
following submission to ApJ Letters
Note: replaced with revised version Wed, 23 Aug 2000 14:16:46 GMT (51kb)

astro-ph/0007403 [abs, src, ps, other] :

Title: On the nature of cosmic rays above the Greisen–Zatsepin–Kuz’min cut
off
Authors:
L. A. Anchordoqui,
M. Kirasirova,
T. P. McCauley,
S. Reucroft,
J. D. Swain
Comments: References added
Note: replaced with revised version Wed, 23 Aug 2000 20:23:08 GMT (24kb)

astro-ph/0008092 [abs, src, ps, other] :

Title: Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3–4 Micron
Spectra
Authors:
Masatoshi Imanishi (NAO Japan, IfA),
C. C. Dudley (Naval Research Laboratory)
Comments: 29 pages, 2 figures, Accepted for publication in ApJ
Note: replaced with revised version Wed, 23 Aug 2000 03:28:03 GMT (109kb)

hep-th/0008102 [abs, src, ps, other] :

Title: Comments on Brane World Cosmology
Authors:
Luis Anchordoqui,
Kasper Olsen
Comments: References added
Note: replaced with revised version Wed, 23 Aug 2000 20:51:21 GMT (28kb) 
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