title: The Origin of Subdwarf B Star (I): the Formation Channels

abstract:
  Subdwarf B (sdB) stars (and related sdO/sdOB stars) are believed to be helium
core-burning objects with very thin hydrogen-rich envelopes. In recent years it
has become increasingly clear from observational surveys that a large fraction
of these objects are members of binary systems. To better understand their
formation, we here present the results of a detailed investigation of the three
main binary evolution channels that can lead to the formation of sdB stars: the
common envelope (CE) ejection channel, the stable Roche lobe overflow (RLOF)
channel and the double helium white dwarfs (WDs) merger channel. We obtained
the conditions for the formation of sdB stars from each of these channels using
detailed stellar and binary evolution calculations where we modelled the
detailed evolution of sdB stars and carried out simplified binary population
synthesis simulations. The observed period distribution of sdB stars in compact
binaries strongly constrains the CE ejection parameters. We also present the
distribution of sdB stars in the $T_{\rm eff}$ - $\log g$ diagram, the
Hertzsprung-Russell diagram and the distribution of mass functions.


title:
Statistical Mechanics of gravitating systems in static and cosmological
  backgrounds

abstract:
  This pedagogical review addresses several issues related to statistical
description of gravitating systems in both static and expanding backgrounds,
focusing on the latter. After briefly reviewing the results for the static
background, I describe the key issues and recent progress in the context of
gravitational clustering of collision-less particles in an expanding universe.
The questions addressed include: (a) How does the power injected into the
system at a given wave number spread to smaller and larger scales? (b) How does
the power spectrum of density fluctuations behave asymptotically at late times?
(c) What are the universal characteristics of gravitational clustering that are
independent of the initial conditions and manifest at the late time evolution
of the system? The review is intended for non cosmologists and will be of
interest to people working in fluid mechanics, non linear dynamics and
condensed matter physics.


title:
Molecular Beam Dumps as Tracers of Hadronic Cosmic Ray Sources: the Case
  of SNR IC443

abstract:
  The gamma-ray & neutrino visibility of cosmic ray (CR) accelerators will be
dramatically increased by the presence of molecular material abutting such
sites due to the increased probability of pion production -- and, in the case
of neutral pions, subsequent gamma-decay. This was recognized by Pinkau,
Montmerle, and Black & Fazio, and others in the 1970's. In an effort to examine
the long-standing -- but unproven -- conjecture that galactic supernova
remnants (SNRs) are indeed the sites of nucleonic CR acceleration to <~300TeV/n
we have carried out a 3-way coincidence search between the SNRs in Green's
(2001) catalog, the GeV range unidentified sources from the third EGRET catalog
(Hartman et al.,1999), and molecular clouds, at low Galactic latitudes (|b|<~5
deg). In order to be quantitative regarding the distribution and amount of the
ambient molecular masses we have extracted the CO(J=1->0) mm wavelength data
from the compilation of Dame, Hartmann & Thaddeus (2001), at the best estimates
of the various SNR distances. We outline the overall correlative study and
examine the interesting case of SNR IC443, a likely accelerator of CR nuclei.


title:
The r-process in the neutrino winds of core-collapse supernovae and U-Th
  cosmochronology

abstract:
  The discovery of the second highly $r$-process-enhanced, extremely metal-poor
star, CS 31082-001 ([Fe/H] $= -2.9$) has provided a powerful new tool for age
determination, by virtue of the detection and measurement of the radioactive
species uranium and thorium. One of the serious limitations of this approach,
however, is that predictions of the production ratio of U and Th have not been
made in the context of a realistic astrophysical model of the $r$-process. We
have endeavored to produce such a model, based on the ``neutrino winds'' that
are expected to arise from the nascent neutron star of a core-collapse
supernova. The mass-integrated $r$-process yields, obtained by assuming a
simple time evolution of the neutrino luminosity, are compared to the available
spectroscopic elemental abundance data of CS 31082-001. As a result, the
``age'' of this star is determined to be $14.1 \pm 2.5$ Gyr, in excellent
agreement with lower limits on the age of the universe estimated by other
dating techniques, as well as with other stellar radioactive age estimates.
Future measurements of Pt and Pb in this star, as well as expansion of searches
for additional $r$-process-enhanced, metal-poor stars (especially those in
which both U and Th are measurable), are of special importance to constrain the
current astrophysical models for the $r$-process.


title: New Measurements of Orbital Period Change in Cygnus X-3

abstract:
  A nonlinear nature of the binary ephemeris of Cygnus X-3 indicates either a
change in the orbital period or an apsidal motion of the orbit. We have made
extended observations of Cygnus X-3 with the Pointed Proportional Counters
(PPCs) of the Indian X-ray Astronomy Experiment (IXAE) during 1999 July 3-13
and October 11-14. Using the data from these observations and the archival data
from ROSAT, ASCA, BeppoSAX and RXTE, we have extended the data base for this
source. Adding these new arrival time measurements to the published results, we
make a comparison between the various possibilities, (a) orbital decay due to
mass loss from the system, (b) mass transfer between the stars, and (c) apsidal
motion of the orbit due to gravitational interaction between the two
components. Orbital decay due to mass loss from the companion star seems to be
the most probable scenario.


title:
An ISO--SWS survey of molecular hydrogen in Starburst and Seyfert
  Galaxies

abstract:
  We present results from a survey of molecular hydrogen emission from a sample
of Starburst and Seyfert galaxies carried out with the Infrared Space
Observatory (ISO). Pure rotational H_2 emission has been detected in a number
of extragalactic objects and a variety of environments. A number of transitions
from S(7) to S(0) are detected in both Starbursts and Seyferts. Using
excitation diagrams we derive temperatures and masses of the ``warm'' molecular
hydrogen. We find that the temperature of the ``warm'' gas is similar in
Starbursts and Seyferts (those Seyferts for which we have firm detections of
the S(0) line) with a value of around T~150 K. This ``warm'' gas accounts for
as much as 10% of the total galactic mass (as probed by CO molecular
observations) in Starbursts. The fraction of ``warm'' gas is overall higher in
Seyferts, ranging between 2--35%. We then investigate the origin of the warm
H_2 emission. Comparison with published theoretical models and Galactic
templates implies that although emission from photodissociation regions (PDR)
alone could explain the emission from Starbursts and Seyferts, most likely a
combination of PDR, shock emission and gas heated by X-rays (mostly for the
Seyferts) is responsible for H_2 excitation in extragalactic environments.
Finally, we find that although PAH and H_2 line emission correlate well in
Starbursts and the large scale emission in AGN, H_2 emission is much stronger
compared to PAH emission in cases where a ``pure'' AGN dominates the energy
output.


title:
Spectral Energy Distributions of starburst galaxies in the 900-1200 A
  range

abstract:
  We present the 970-1175 A spectral energy distributions (SEDs) of 12
starburst galaxies observed with the Far Ultraviolet Spectroscopic Explorer
FUSE. We take benefit of the high spectral resolution of FUSE to estimate a
continuum as much as possible unaffected by the interstellar lines. The
continuum is rather flat with, in few cases, a decrease at lambda <~1050 A, the
amplitude of which being correlated with various indicators of the dust
extinction. The far-UV SEDs are compared with synthetic population models. The
galaxies with almost no extinction have a SED consistent with an on-going star
formation over some Myrs. We derive a mean dust attenuation law in the
wavelength range 965-1140 A by comparing the SED of obscured galaxies to an
empirical dust-free SED. The extinction is nearly constant longward of 1040 A
but rises at shorter wavelengths. We compare our results with other studies of
the extinction for galaxies and stars in this wavelength range.


title: Rotational Periods of very Young Brown Dwarfs in ChaI

abstract:
  A photometric monitoring campaign of brown dwarfs in the ChaI star forming
region in the i and R band revealed significant periodic variations of the
three M6.5-M7 type brown dwarf candidates ChaHa2, 3 and 6 (Joergens et al.
2002). These are the first rotational periods for very young (1-5 Myr) brown
dwarfs and among the first rotational periods for brown dwarfs at all. The
relatively long periods of 2.2 to 3.4 days as well as vsini values (Joergens &
Guenther 2001) indicate that our targets are moderately fast rotators in
contrast to very rapidly rotating old brown dwarfs. The periods for the ChaI
brown dwarf candidates provide valuable data points in an as yet, in terms of
rotational characteristic, almost unexplored region of the age-mass diagram. A
comparison with rotational properties of older brown dwarfs indicates that most
of the acceleration during the contraction phase takes place within the first
30 Myr or less of the lifetime of a brown dwarf. We have also determined
periods for the two M5-M5.5 type very low-mass stars B34 and CHXR78C.


title:
Primordial pairing and binding of superheavy charge particles in the
  early Universe

abstract:
  Primordial superheavy particles, considered as the source of Ultra High
Energy Cosmic Rays (UHECR) and produced in local processes in the early
Universe, should bear some strictly or approximately conserved charge to be
sufficiently stable to survive to the present time. Charge conservation makes
them to be produced in pairs, and the estimated separation of particle and
antiparticle in such pair is shown to be in some cases much smaller than the
average separation determined by the averaged number density of considered
particles. If the new U(1) charge is the source of a long range field similar
to electromagnetic field, the particle and antiparticle, possessing that
charge, can form primordial bound system with annihilation timescale, which can
satisfy the conditions, assumed for this type of UHECR sources. These
conditions severely constrain the possible properties of considered particles.


title:
Properties of the PCygni wind found using the Self Absorption Curve
  method

abstract:
  We have used the optical lines of N II and Fe III to study the wind of the
luminous blue variable P Cyg. This was performed by applying a version of the
Self Absorption Curve (SAC) method, involving few assumptions, to lines whose
flux can be measured. A rather surprising result was obtained; the lines of
more excited multiplets without blue shifted absorption components appear to be
optically thick, while the lines of the most excited multiplets may show some
indications of being optically thicker than the lines of less excited ones.
Explanations of such effects are discussed, including possible inhomogeneities
in the wind.


title:
Extragalactic Globular Clusters in the Near Infrared I: A comparison
  between M87 and NGC 4478

abstract:
  We compare optical and near infrared colours of globular clusters in M87, the
central giant elliptical in Virgo, and NGC 4478, an intermediate luminosity
galaxy in Virgo, close in projection to M87. Combining V and I photometry
obtained with the WFPC2 on HST and Ks photometry obtained with the NIRC on Keck
1, we find the broad range in colour and previously detected bi-modality in
M87. We confirm that NGC 4478 only hosts a blue sub-population of globular
clusters and now show that these clusters' V-I and V-K colours are very similar
to those of the halo globular clusters in Milky Way and M31. Most likely, a
metal-rich sub-population never formed around this galaxy (rather than having
formed and been destroyed later), probably because its metal-rich gas was
stripped during its passage through the centre of the Virgo cluster.
  The V-I, V-K colours are close to the predicted colours from SSP models for
old populations. However, M87 hosts a few red clusters that are best explained
by intermediate ages (a few Gyr). Generally, there is evidence that the red,
metal-rich sub-population has a complex colour structure and is itself composed
of clusters spanning a large metallicity and, potentially, age range. This
contrasts with the blue, metal-poor population which appears very homogeneous
in all galaxies observed so far.


title: On the formation of inner vacuum gaps in radio pulsars

abstract:
  The problem of formation of the Ruderman-Sutherland type inner vacuum gap in
neutron stars with ${\bf\Omega}\cdot{\bf B}<0$ is considered. It is argued by
means of the condition $T_i/T_s>1$ (where $T_i$ is the critical temperature
above which $^{56}_{26}$Fe ions will not be bound at the surface and $T_s$ is
the actual temperature of the polar cap surface heated by the back-flow of
relativistic electrons) that the inner vacuum gap can form, provided that the
actual surface magnetic field is extremaly strong ($B_s\gtrsim 10^{13}$ G) and
curved (${\cal R}<10^6$ cm), irrespective of the value of dipolar component
measured from the pulsar spin down rate. Calculations are carried out for
pulsars with drifting subpulses and/or periodic intensity modulations, in which
the existence of the quasi steady vacuum gap discharging via ${\bf E}\times{\bf
B}$ drifting sparks is almost unavoidable. Using different pair-production
mechanisms and different estimates of the cohesive energies of surface iron
ions, we show that it is easier to form the vacuum gap controlled by the
resonant inverse Compton scaterring seed photons than by the curvature
radiation seed photons.


title:
Non-radial oscillation modes as a probe of density discontinuities in
  neutron stars

abstract:
  A phase transition occurring in the inner core of a neutron star could be
associated to a density discontinuity that would affect the frequency spectrum
of the non-radial oscillation modes in two ways. Firstly, it would produce a
softening of the equation of state, leading to more compact equilibrium
configurations and changing the frequency of the fundamental and pressure modes
of the neutron star. Secondly, a new non-zero frequency g-- mode would appear,
associated to each discontinuity. These discontinuity g--modes have typical
frequencies larger than those of g--modes previously studied in the literature
(thermal, core g-- modes, or g--modes due to chemical inhomogeneities in the
outer layers), and smaller than that of the fundamental mode; therefore they
should be distinguishable from the other modes of non radial oscillation. In
this paper we investigate how high density discontinuities change the frequency
spectrum of the non-radial oscillations, in the framework of the general
relativistic theory of stellar perturbations. Our purpose is to understand
whether a gravitational signal, emitted at the frequencies of the quasi normal
modes, may give some clear information on the equation of state of the neutron
star and, in particular, on the parameters that characterize the density
discontinuity. We discuss some astrophysical processes that may be associated
to the excitation of these modes, and estimate how much gravitational energy
should the modes convey to produce a signal detectable by high frequency
gravitational detectors.


title: Abundance analysis of two late A-type stars HD 32115 and HD 37594

abstract:
  We have performed abundance analysis of two slowly rotating, late A-type
stars, HD 32115 (HR 1613) and HD 37594 (HR 1940), based on obtained echelle
spectra covering the spectral range 4000-9850 AAngstrom. These spectra allowed
us to identify an extensive line list for 31 chemical elements, the most
complete to date for A-type stars. Two approaches to abundance analysis were
used, namely a ``manual'' (interactive) and a semi-automatic procedure for
comparison of synthetic and observed spectra and equivalent widths. For some
elements non-LTE (NLTE) calculations were carried out and the corresponding
corrections have been applied. The abundance pattern of HD 32115 was found to
be very close to the solar abundance pattern, and thus may be used as an
abundance standard for chemical composition studies in middle and late A stars.
Further, its H-alpha line profile shows no core-to-wing anomaly like that found
for cool Ap stars and therefore also may be used as a standard in comparative
studies of the atmospheric structures of cool, slowly rotating Ap stars. HD
37594 shows a metal deficiency at the level of -0.3 dex for most elements and
triangle-like cores of spectral lines. This star most probably belongs to the
Delta Scuti group.


title:
Faint Stars in the Ursa Minor Dwarf Spheroidal Galaxy: Implications for
  the Low-Mass Stellar Initial Mass Function at High Redshift

abstract:
  The stellar initial mass function at high redshift is an important defining
property of the first stellar systems to form and may also play a role in
various dark matter problems. We here determine the faint stellar luminosity
function in an apparently dark-matter-dominated external galaxy in which the
stars formed at high redshift. The Ursa Minor dwarf spheroidal galaxy is a
system with a particularly simple stellar population - all of the stars being
old and metal-poor - similar to that of a classical halo globular cluster. A
direct comparison of the faint luminosity functions of the UMi Sph and of
similar metallicity, old globular clusters is equivalent to a comparison of the
initial mass functions and is presented here, based on deep HST WFPC2 and STIS
imaging data. We find that these luminosity functions are indistinguishable,
down to a luminosity corresponding to 0.3 solar masses. Our results show that
the low-mass stellar IMF for stars that formed at very high redshift is
apparently invariant across environments as diverse as those of an extremely
low-surface-brightness, dark-matter-dominated dwarf galaxy and a
dark-matter-free, high-density globular cluster within the Milky Way.


title:
Discovery of an accreted stellar system within the globular cluster
  omega Centauri

abstract:
  Recent wide-field photometric surveys (Lee et al.; Pancino et al.) have shown
the existence of a previously unknown metal-rich ([Fe/H] -0.6) stellar
population in the galactic globular cluster omega Centauri. The discovery of
this new component, which comprises only a small percentage (~5%) of the entire
cluster population, has added a new piece to the already puzzling picture of
the star formation and chemical evolution of this stellar system. In this
Letter we show that stars belonging to the newly discovered metal-rich
population have a coherent bulk motion with respect to the other cluster stars,
thus demonstrating that they formed in an independent self-gravitating stellar
system. This is the first clear-cut evidence that extreme metal-rich stars were
part of a small stellar system (a satellite of omega Centauri?) that has been
accreted by the main body of the cluster. In this case, we are witnessing an in
vivo example of hierarchical merging on the sub-galactic scale.


title: Two-Dimensional Topology of the Sloan Digital Sky Survey

abstract:
  We present the topology of a volume-limited sample of 11,884 galaxies,
selected from an apparent-magnitude limited sample of over 100,000 galaxies
observed as part of the Sloan Digital Sky Survey (SDSS). The data currently
cover three main regions on the sky: one in the Galactic north and one in the
south, both at zero degrees declination, and one area in the north at higher
declination. Each of these areas covers a wide range of survey longitude but a
narrow range of survey latitude, allowing the two dimensional genus to be
measured.
  The genus curves of the SDSS sub-samples are similar, after appropriately
normalizing these measurements for the different areas. We sum the genus curves
from the three areas to obtain the total genus curve of the SDSS. The total
curve has a shape similar to the genus curve derived from mock catalogs drawn
from the Hubble Volume Lambda CDM simulation and is similar to that of a
Gaussian random field. Likewise, comparison with the genus of the 2dFGRS, after
normalization for the difference in area, reveals remarkable similarity in the
topology of these samples.
  We test for the effects of galaxy type segregation by splitting the SDSS data
into thirds, based on the u^*- r^* colors of the galaxies, and measure the
genus of the reddest and bluest sub-samples. This red/blue split in u^*- r^* is
essentially a split by morphology (Strateva et al. 2001). We find that the
genus curve for the reddest galaxies exhibits a ``meatball'' shift of the
topology -- reflecting the concentration of red galaxies in high density
regions -- compared to the bluest galaxies and the full sample, in agreement
with predictions from simulations.


title:
Extragalactic Globular Clusters in the Near-Infrared II. The Globular
  Clusters Systems of NGC 3115 and NGC 4365

abstract:
  We combine near-infrared photometry obtained with the VLT/ISAAC instrument
and archival HST/WFPC2 optical images to determine VIK magnitudes and colours
of globular clusters in two early-type galaxies, NGC 3115 and NGC 4365. The
combination of near-IR and optical photometry provides a way to lift the
age-metallicity degeneracy. For NGC 3115, the globular cluster colours reveal
two major sub-populations, consistent with previous studies. By comparing the
V-I, V-K colours of the NGC 3115 globular clusters with SSP models, we find
that the colour difference between the two >10 Gyr old major sub-populations is
primarily due to a difference in metallicity. We find \Delta[Fe/H] = 1.0 +/-
0.3 dex and the blue and red globular cluster sub-populations being coeval
within 3 Gyr. In contrast to the NGC 3115 globular clusters, the globular
cluster system in NGC 4365 exhibits a more complex age and metallicity
structure. We find a significant population of intermediate-age very metal-rich
globular clusters along with an old population of both metal-rich and
metal-poor clusters. Specifically, we observe a large population of globular
clusters with V-K and V-I colours, for which all current SSP models give ages
and metallicities in the range ~2-8 Gyr and ~0.5-3 Z_solar, respectively. After
10 Gyr of passive evolution, the intermediate-age globular clusters in NGC 4365
will have colours which are consistent with the very metal-rich population of
globular clusters in giant elliptical galaxies, such as M87. Our results for
both globular cluster systems are consistent with previous age and metallicity
studies of the diffuse galactic light. In addition to the major globular
cluster populations in NGC 3115 and NGC 4365 we report on the detection of
objects with extremely red colours.


title:
Chandra Observations of Unresolved X-ray Sources around two Clusters of
  Galaxies

abstract:
  We have searched for unresolved X-ray sources in the vicinity of two rich
clusters of galaxies: Abell 1995 (A1995) and MS 0451.6-0305 (MS0451), using the
Chandra X-ray observatory. We detected significantly more unresolved sources
around A1995 than expected based on the number of X-ray sources to the same
flux limit detected in deep \CHANDRA observations of blank fields. Previous
studies have also found excess X-ray sources in the vicinity of several nearby
clusters of galaxies using \ROSAT$ $, and recently in more distant ($z ~ 0.5$)
clusters (RXJ0030 and 3C295) using Chandra. In contrast, we detect only 14
unresolved X-ray sources near MS0451, which is consistent with the number
expected from a cluster-free background. We determine the luminosity functions
of the extra sources under the assumption that they are at the distance of
their respective clusters. The characteristic luminosity of the extra sources
around A1995 must be an order of magnitude fainter than that of the extra
sources around RXJ0030 and 3C295. The apparent lack of extra sources around
MS0451 is consistent with its greater distance and the same characteristic
luminosity as the A1995 sources. Hardness ratios suggest that, on average, the
extra sources in A1995 may have harder spectra than those of RXJ0030 and 3C295.
These results indicate that different classes of objects may dominate in
different clusters, perhaps depending on the formation history and/or dynamical
state of the accompanying cluster.


title:
Modeling the Energy Dependent Pulse Profiles of the Accreting
  Millisecond Pulsar SAX J1808.4-3658

abstract:
  The pulse profiles of the accreting X-ray millisecond pulsar SAX J1808.4-3658
at different energies are studied. The two main emission component, a black
body and a power-law tail, clearly identified in the time-averaged spectrum, do
not vary in phase. We show that the observed variability can be easily
explained if the emission patterns of the black body and the Comptonized
radiation are different: a "knife" and a "fan"-like, respectively. We suggest
that Comptonization in a hot slab (radiative shock) of Thomson optical depth
\~0.3 at the surface of the neutron star may be responsible for the emission.
We construct a detailed model of the X-ray production accounting for the
Doppler boosting, relativistic aberration and gravitational light bending. The
model reproduces well the pulse profiles at different energies simultaneously,
corresponding phase lags, as well as the time-averaged spectrum. By fitting the
observed pulse profiles we obtain constraints on the neutron star radius
(R=7.5+-1.0 km), the inclination of the system i>60 deg, and the angle between
the magnetic dipole and the rotational axis delta=20deg+-5deg.


title:
Mid-infrared observations of the ultraluminous galaxies IRAS14348-1447,
  IRAS19254-7245, and IRAS23128-5919

abstract:
  We present a study of the three ultraluminous infrared galaxies
IRAS14348-1447, IRAS19254-7245, and IRAS23128-5919, based on mid-infrared (MIR)
spectro-imaging (5-18microns) observations performed with ISOCAM. We find that
the MIR emission from each system, which consists of a pair of interacting late
type galaxies, is principally confined to the nuclear regions with diameters of
1-2kpc and can account for more than 95% of their IRAS 12micron flux. In each
interacting system, the galaxy hosting an active galactic nucleus (AGN)
dominates the total spectrum and shows stronger dust continuum (12-16microns)
relative to the Unidentified Infrared Band (UIB) emission (6-9microns),
suggestive of its enhanced radiation field. The MIR dominant galaxy also
exhibits elevated 15micron/Halpha and 15micron/K ratios which trace the high
extinction due to the large quantities of molecular gas and dust present in its
central regions. Using only diagnostics based on our mid-infrared spectra, we
can establish that the Seyfert galaxy IRAS19254-7245 exhibits MIR spectral
features of an AGN while the MIR spectrum of the Seyfert (or LINER) member of
IRAS23128-5919 is characteristic of dust emission principally heated by star
forming regions.


title:
HETE-2 Localization and Observations of the Short, Hard Gamma-Ray Burst
  GRB020531

abstract:
  The {\it HETE-2} (hereafter \HETE) French Gamma Telescope (FREGATE) and the
Wide-field X-ray Monitor (WXM) instruments detected a short ($t_{50} = 360$
msec in the FREGATE 85-300 keV energy band), hard gamma-ray burst (GRB) that
occurred at 1578.72 SOD (00:26:18.72 UT) on 31 May 2002. The WXM flight
localization software produced a valid location in spacecraft (relative)
coordinates. However, since no on-board real-time star camera aspect was
available, an absolute localization could not be disseminated. A preliminary
localization was reported as a GCN Position Notice at 01:54:22 UT, 88 min after
the burst. Further ground analysis produced a refined localization, which can
be expressed as a 90% confidence rectangle that is 67 arcminutes in RA and 43
arcminutes in Dec (90% confidence region), centered at RA = +15$^{\rm h}$
14$^{\rm m}$ 45$^{\rm s}$, Dec = -19$^\circ$ 21\arcmin 35\arcsec (J2000). An
IPN localization of the burst was disseminated 18 hours after the GRB (Hurley
et al. 2002b). A refined IPN localization was disseminated $\approx$ 5 days
after the burst. This hexagonal-shaped localization error region is centered on
RA = 15$^{\rm h}$ 15$^{\rm m}$ 03.57$^{\rm s}$, -19$^\circ$ 24\arcmin
51.00\arcsec (J2000), and has an area of $\approx$ 22 square arcminutes (99.7%
confidence region). The prompt localization of this short, hard GRB by \HETE
and the anti-Sun pointing of the \HETE instruments, coupled with the refinement
of the localization by the IPN, has made possible rapid follow-up observations
of the burst at radio, optical, and X-ray wavelengths.


title: Type Ia Supernovae and High Velocity White Dwarfs

abstract:
  I examine the hypothesis that many of the high velocity white dwarfs observed
by Oppenheimer et al. (2001) are the remnants of donor stars from binaries that
produced type Ia supernovae via the `single degenerate' channel. If this
channel is a significant contributor to the Galactic SN Ia supernova rate, then
the local density of such remnants with V>100 km/s could be as high as 2.e-4
per cubic parsec, comparable to the densities found by Oppenheimer et al. This
white dwarf population differs from others in that it is composed exclusively
of single stars.


title:
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies:
  I. A Keck/HST Study of Six Virgo Cluster Dwarfs

abstract:
  Keck/ESI spectroscopy is presented for six Virgo Cluster dwarf elliptical
(dE) galaxies. The mean line-of-sight velocity and velocity dispersion are
resolved as a function of radius along the major axis of each galaxy, nearly
doubling the total number of dEs with spatially-resolved stellar kinematics.
None of the observed objects shows evidence of strong rotation: upper limits on
v_rot/sigma are well below those expected for rotationally-flattened objects.
Such limits place strong constraints on dE galaxy formation models. Although
these galaxies continue the trend of low rotation velocities observed in Local
Group dEs, they are in contrast to recent observations of large rotation
velocities in slightly brighter cluster dEs. Using WFPC2 surface photometry and
spherically-symmetric dynamical models, we determine global mass-to-light
ratios 3 < M/L_V < 6. These ratios are comparable to those expected for an
intermediate-age stellar population and are broadly consistent with the (V-I)
colors of the galaxies. This implies that these dEs do not have a significant
dark matter component inside an effective radius. Central black holes more
massive than 10^7 M_sun can be ruled out. For the 5 nucleated dEs in our
sample, we determine kinematic and photometric properties for the central
nucleus separately from the underlying host dE galaxy. These nuclei are as
bright or brighter than the most luminous Galactic globular clusters and lie
near the region of Fundamental Plane space occupied by globular clusters. In
this space, the Virgo dE galaxies lie in the same general region as Local Group
and other nearby dEs, although non-rotating dEs appear to have a slightly
higher mean mass and mass-to-light ratio than their rotating counterparts.


title: A Physical Model for the Luminosity Function of High-Redshift Quasars

abstract:
  We provide a simple theoretical model for the quasar luminosity function at
high redshifts that naturally reproduces the statistical properties of the
luminous SDSS quasar sample at redshifts z~4.3 and z>5.7. Our model is based on
the assumptions that quasar emission is triggered by galaxy mergers, and that
the black hole mass is proportional to a power-law in the circular velocity v
of the host galactic halo. We assume that quasars shine at their Eddington
luminosity over a time proportional to the mass ratio between the small and
final galaxies in the merger. This simple model fits the quasar luminosity
function at z~2-3, reproduces the normalization and logarithmic slope (beta
-2.58) at z~4.3, explains the space density of bright SDSS quasars at z~6.0,
reproduces the black hole - halo mass relation for dormant black holes in the
local universe, and matches the estimated duty cycle of quasar activity (~10^7
years) in Lyman-break galaxies at z~3. Based on the derived luminosity function
we predict the resulting gravitational lensing rates for high redshift quasars.
The lens fractions in the SDSS samples are predicted to be ~2% at z~4.3 and
~10% at z>5.7. Interestingly, the limiting quasar luminosity in our best-fit
relation of L proportional to v^5/G, scales as the binding energy of the host
galaxy divided by its dynamical time, implying that feedback is the mechanism
that regulates black hole growth in galactic potential wells.


title: The Angular Trispectra of CMB Temperature and Polarization

abstract:
  We develop the formalism necessary to study four-point functions of the
cosmic microwave background (CMB) temperature and polarization fields. We
determine the general form of CMB trispectra, with the constraints imposed by
the assumption of statistical isotropy of the CMB fields, and derive
expressions for their estimators, as well as their Gaussian noise properties.
We apply these techniques to initial non-Gaussianity of a form motivated by
inflationary models. Due to the large number of four-point configurations, the
sensitivity of the trispectra to initial non-Gaussianity approaches that of the
temperature bispectrum at high multipole moment. These trispectra techniques
will also be useful in the study of secondary anisotropies induced for example
by the gravitational lensing of the CMB by the large scale structure of the
universe.


title:
New grids of ATLAS9 atmospheres I: Influence of convection treatments on
  model structure and on observable quantities

abstract:
  We present several new sets of grids of model stellar atmospheres computed
with modified versions of the ATLAS9 code. Each individual set consists of
several grids of models with different metallicities ranging from [M/H] = -2.0
to +1.0 dex. The grids range from 4000 to 10000 K in T_eff and from 2.0 to 5.0
dex in logg. The individual sets differ from each other and from previous ones
essentially in the physics used for the treatment of the convective energy
transport, in the higher vertical resolution of the atmospheres and in a finer
grid in the (T_eff, logg) plane. These improvements enable the computation of
derivatives of color indices accurate enough for pulsation mode identification.
In addition, we show that the chosen vertical resolution is necessary and
sufficient for the purpose of stellar interior modelling. To explain the
physical differences between the model grids we provide a description of the
currently available modifications of ATLAS9 according to their treatment of
convection. Our critical analysis of the dependence of the atmospheric
structure and observable quantities on convection treatment, vertical
resolution and metallicity reveals that spectroscopic and photometric
observations are best represented when using an inefficient convection
treatment. This conclusion holds whatever convection formulation investigated
here is used, i.e. MLT(alpha=0.5), CM and CGM are equivalent. We also find that
changing the convection treatment can lead to a change in the effective
temperature estimated from Stroemgren color indices from 200 to 400 K.


title:
Properties of Low Surface Brightness Galaxies and Normal Spirals in the
  Near-IR

abstract:
  (Abridged) We present results for J and Ks near-IR imaging data on a large
sample of 88 galaxies drawn from the catalogue of Impey et al. (1996). The
near-IR data unveils many features of LSBGs not seen before in the optical.
First, a high fraction of the observed LSBGs are very luminous in the near-IR,
indicating that they have a well developed old stellar population, and that
older LSBGs are more frequent in the universe than data from optical bands
suggested. Second, the near-IR morphologies are often quite different than seen
in the optical. Third, we find significant trends between the near-IR
morphologies of the galaxies and their ratio of HI mass to near-IR luminosity.
Fourth, we find no trend in disk surface brightness with absolute magnitude,
but significant correlations when the bulge surface brightness is used.
Finally, we find that the formation of a bulge requires a galaxy to have a
total baryonic mass above ~ 10**10 Msun. A wide variety of other correlations
are explored for the sample. The strongest of our correlations are with the
ratio of HI mass to total baryonic mass, MHI/Mbaryonic, which tracks the
evolutionary state of the galaxies as they convert gas into stars, and which
ranges from 0.05 up to nearly 1 for the galaxies in our sample. We see also
trends between MHI/Mbaryonic and central surface density, suggesting that
increased star formation efficiency with increasing gas surface density
strongly drives the conversion of gas into stars.


title: An analysis of gamma-ray burst spectral break models

abstract:
  Typical gamma-ray burst spectra are characterized by a spectral break, Ep,
which for bright BATSE bursts is found to be narrowly clustered around 300 keV.
Recently identified X-ray flashes, which may account for a significant portion
of the whole GRB population, seem to extend the Ep distribution to a broader
range below 40 keV. Positive correlations among Ep and some other observed
parameters have been noticed. On the other hand, within the cosmological
fireball model, the issues concerning the dominant energy ingredient of the
fireball as well as the location of the GRB emission site are still unsettled,
leading to several variants of the fireball model. Here we analyze these models
within a unified framework, and critically reexamine the Ep predictions in the
various model variants. Attention is focused on the predictions of the
narrowness of the Ep distribution in different models, and the correlations
among Ep and some other measurable observables. These model properties may be
tested against the current and upcoming GRB data, through which the nature of
the fireball as well as the mechanism and site of the GRB emission will be
identified. In view of the current data, various models are appraised through a
simple Monte-Carlo simulation, and a tentative discussion about the possible
nature of X-ray flashes is presented.


title: New CrH Opacities for the Study of L and Brown Dwarf Atmospheres

abstract:
  In this paper, we calculate new line lists and opacities for the 12 bands of
the A$^6\Sigma^{+}$ -- X$^6\Sigma^{+}$ transitions of the CrH molecule.
Identified in objects of the new L dwarf spectroscopic class (many of which are
brown dwarfs), as well as in sunspots, the CrH molecule plays an important role
in the diagnosis of low-temperature atmospheres. As a tentative first
application of these opacities, we employ our new theoretical CrH data in an
atmospheres code to obtain a CrH/H$_2$ number ratio for the skin of the L5
dwarf 2MASSI J1507038-151648 of $\sim 2-4\times 10^{-9}$, in rough agreement
with chemical equilibrium expectations. Since in previous compilations the
oscillator strength was off by more than an order of magnitude, this agreement
represents a modest advance. However, in order to determine the CrH abundance
in an L dwarf atmosphere, silicate clouds need to be incorporated into the
model, and cloud modeling is still in a primitive stage of development.
Nevertheless, one important step in L dwarf modeling is a reliable CrH opacity
and this is what we have here attempted to provide.


title: Chandra X-ray Observations of the Spiral Galaxy M81

abstract:
  A Chandra X-Ray Observatory ACIS-S imaging observation is used to study the
population of X-ray sources in the nearby Sab galaxy M81 (NGC 3031). A total of
177 sources are detected with 124 located within the D25 isophote to a limiting
X-ray luminosity of 3e36 ergs/cm2/s. Source positions, count rates,
luminosities in the 0.3-8.0 keV band, limiting optical magnitudes, and
potential counterpart identifications are tabulated. Spectral and timing
analysis of the 36 brightest sources are reported including the low-luminosity
active galactic nucleus, SN 1993J, and the Einstein-discovered ultra-luminous
X-ray source X6.


title:
The Effect of Merger Boosts on the Luminosity, Temperature, and Inferred
  Mass Functions of Clusters of Galaxies

abstract:
  In the standard Cold Dark Matter model of structure formation, massive
clusters form via the merger of smaller clusters. N-body/hydrodynamical
simulations of merging galaxy clusters have shown that mergers can temporarily
boost the X-ray luminosity and temperature of the merged cluster above the
equilibrium values for the merged system. The cumulative effect of these
"merger boosts" will affect the observed X-ray luminosity functions (XLFs) and
temperature functions (TFs) of clusters. Merger boosts may bias the values of
sigma_8 and Omega_0 inferred from cluster XLFs and TFs if virial equilibrium is
assumed. We use a semi-analytic technique to estimate the effect of merger
boosts on the X-ray luminosity and temperature functions. The boosts from
individual mergers are derived from N-body/hydrodynamical simulations of
mergers. The statistics of the merger histories of clusters are determined from
extended Press-Schechter (PS) merger trees. We find that merger boosts can
increase the apparent number of hot, luminous clusters. For example, in a
Universe with Omega_0 = 0.3 and Omega_Lambda = 0.7 at a redshift of z=1, the
number of clusters with temperatures T > 10 keV is increased by a factor of
9.5, and the number of clusters with luminosities L_X > 5x10^44 h^-2 erg/s is
increased by a factor of 8.9. We have used our merger-boosted TFs and XLFs to
derive the cosmological structure parameters sigma_8 and Omega_0 by fitting
Press-Schechter equilibrium relations to local (z=0) and distant (either z=0.5
or z=1) cluster samples. Merger boosts cause sigma_8 to be overestimated by
about 20%. The matter density parameter Omega_0 may be underestimated by about
20%, although this result is less clear.


title: Gravitational Microlensing Near Caustics II: Cusps

abstract:
  We present a rigorous, detailed study of the generic, quantitative properties
of gravitational microlensing near cusp catastrophes. We derive explicit
formulas for the total magnification and centroid of the images created for
sources outside, on, and inside the cusped caustic. We obtain results on how
the image magnifications scale with respect to separation from the cusped
caustic for arbitrary source positions. Along the axis of symmetry of the cusp,
the total magnification $\mu$ scales as $\mu \propto u^{-1}$, where $u$ is the
distance of the source from the cusp, whereas perpendicular to this axis, $\mu
\propto u^{-2/3}$. When the source passes through a point $\bu_0$ on a fold arc
abutting the cusp, the image centroid has a jump discontinuity; we present a
formula for the size of the jump in terms of the local derivatives of the lens
potential. The total magnifications for a small extended source located both
on, and perpendicular to, the axis of symmetry are also derived, for both
uniform and limb darkened surface brightness profiles. We find that the
difference in magnification between a finite and point source is $< 5%$ for
separations of $> 2.5$ source radii from the cusp point, while the effect of
limb-darkening is $< 1%$ in the same range. Our predictions for the astrometric
and photometric behavior of both pointlike and finite sources passing near a
cusp are illustrated and verified using numerical simulations of the
cusp-crossing Galactic binary-lens event MACHO-1997-BUL-28. We discuss several
possible applications of our results to Galactic binary lenses and quasar
microlensing.


title: An FeLoBAL Binary Quasar

abstract:
  In an ongoing infrared imaging survey of quasars at Keck Observatory, we have
discovered that the z=1.285 quasar SDSS J233646.2-010732.6 comprises two point
sources with a separation of 1.67". Resolved spectra show that one component is
a standard quasar with a blue continuum and broad emission lines; the other is
a broad absorption line (BAL) quasar, specifically, a BAL QSO with prominent
absorption from MgII and metastable FeII, making it a member of the ``FeLoBAL''
class. The number of known FeLoBALs has recently grown dramatically from a
single example to more than a dozen, including a gravitationally lensed example
and the binary member presented here, suggesting that this formerly rare object
may be fairly common. Additionally, the presence of this BAL quasar in a
relatively small separation binary adds to the growing evidence that the BAL
phenomenon is not due to viewing a normal quasar at a specific orientation, but
rather that it is an evolutionary phase in the life of many, if not all,
quasars, and is particularly associated with conditions found in interacting
systems.


title: BL Lac Objects in the Synchrotron Proton Blazar Model

abstract:
  We calculate the spectral energy distribution (SED) of electromagnetic
radiation and the spectrum of high energy neutrinos from BL Lac objects in the
context of the Synchrotron Proton Blazar Model. In this model, the high energy
hump of the SED is due to accelerated protons, while most of the low energy
hump is due to synchrotron radiation by co-accelerated electrons. To accelerate
protons to sufficiently high energies to produce the high energy hump, rather
high magnetic fields are required. Assuming reasonable emission region volumes
and Doppler factors, we then find that in low-frequency peaked BL Lacs (LBLs),
which have higher luminosities than high-frequency peaked BL Lacs (HBLs), there
is a significant contribution to the high frequency hump of the SED from pion
photoproduction and subsequent cascading, including synchrotron radiation by
muons. In contrast, in HBLs we find that the high frequency hump of the SED is
dominated by proton synchrotron radiation. We are able to model the SED of
typical LBLs and HBLs, and to model the famous 1997 flare of Markarian 501. We
also calculate the expected neutrino output of typical BL Lac objects, and
estimate the diffuse neutrino intensity due to all BL Lacs. Because pion
photoproduction is inefficient in HBLs, as protons lose energy predominantly by
synchrotron radiation, the contribution of LBLs dominates the diffuse neutrino
intensity. We suggest that nearby LBLs may well be observable with future
high-sensitivity TeV gamma-ray telescopes.


title: The Star Cluster System of the NGC 7673 Starburst

abstract:
  We investigate the star cluster system in the starburst galaxy NGC 7673 using
archival Hubble Space Telescope WFPC2 broad-band images. For the first time we
are able to examine the internal structures of the prominent optical clumps in
this galaxy. The clumps are composed of young stars, 16-33 % of which are in
bright star clusters. We identify 268 star cluster candidates in both the F555W
and F814W images, and 50 clusters with the F255W filter. These data allow us to
estimate ages and masses using color-magnitude and two-color diagrams for our
sample. We find a population of young, < 6 Myr clusters located throughout the
galaxy with concentrations in the clumps. Star cluster mass estimates are 5-50
x 10^4 M_solar for the brightest objects. The starburst remains active in
physically well-separated regions, indicating a widespread starburst trigger.
We discuss clump lifetimes, their implications for the future evolution of NGC
7673, and possible relationships to high redshift starbursts.


title: How fast could a proto-pulsar rotate?

abstract:
  According to two estimated relations between the initial period and the
dynamo-generated magnetic dipole field of pulsars, we calculate the statistical
distributions of pulsar initial periods. It is found that proto-pulsars are
very likely to have rotation periods between 20 and 30 ms, and that most of the
pulsars rotate initially at a period < 60 ms.


title:
Chemical Evolution of the Circumstellar Envelopes of Carbon-rich
  Post-AGB objects

abstract:
  We have observed with the 30-m IRAM telescope, the CSO telescope and the
ISOsatellite (Infrared Space Observatory) the rotational lines of CO at
millimeter, submillimeter and far infrared wavelengths in the direction of
C-rich stellar objects at different stages of evolution : CRL 2688 (a very
young Proto-Planetary Nebula), CRL 618 (a Proto-Planetary Nebula), and NGC 7027
(a young Planetary Nebula). Several changes in the longwave emission of CO and
other molecules are discussed here in relation with the degree of evolution of
the objects. In the early stages, represented by CRL 2688, the longwave
emission is dominated by CO lines. In the intermediate stage, CRL 618, very
fast outflows are present which, together with the strong UV field from the
central star, dissociate CO. The released atomic oxygen is seen via its atomic
lines, and allows the formation of new O-bearing species, such as water and OH.
The abundance of HNC is enhanced with respect to HCN as a result of the
chemical processes occurring in the photo-dissociation region (PDR). At this
stage, CO lines and [OI] lines are the dominant coolants, while the cooling
effect of [CII] is rising. At the Planetary Nebula stage, NGC 7027, large parts
of the old CO AGB material have been reprocessed. The spectrum is then
dominated by atomic and ionic lines. New species such as CH+ appear. Water has
probably been reprocessed in OH.


title:
The K20 survey. III. Photometric and spectroscopic properties of the
  sample

abstract:
  The K20 survey is an ESO VLT optical and near-infrared spectroscopic survey
aimed at obtaining spectral information and redshifts of a complete sample of
about 550 objects to K_s\leq20.0 over two independent fields with a total area
of 52 arcmin^2. In this paper we discuss the scientific motivation of such a
survey, we describe the photometric and spectroscopic properties of the sample,
and we release the $K_s$-band photometric catalog. Extensive simulations showed
that the sample is photometrically highly complete to K_s=20. The observed
galaxy counts and the R-K_s color distribution are consistent with literature
results. We observed spectroscopically 94% of the sample, reaching a
spectroscopic redshift identification completeness of 92% to K_s\leq20.0 for
the observed targets, and of 87% for the whole sample (i.e. counting also the
unobserved targets). Deep spectroscopy was complemented with multi-band deep
imaging in order to derive tested and reliable photometric redshifts for the
galaxies lacking spectroscopic redshifts. The results show a very good
agreement between the spectroscopic and the photometric redshifts with
<z_{spe}-z_{phot}>=0.01 and with a dispersion of \sigma_{\Delta z}=0.09. Using
both the spectroscopic and the photometric redshifts, we reached an overall
redshift completeness of about 98%. The size of the sample, the redshift
completeness, the availability of high quality photometric redshifts and
multicolor spectral energy distributions make the K20 survey database one of
the most complete samples available to date for constraining the currently
competing scenarios of galaxy formation and for a variety of other galaxy
evolution studies.


title: Resolved and unresolved populations: statistics and synthesis models

abstract:
  In this contribution, I present the 90% confidence limits on the diagnostic
diagrams of EW(WR bump) and L(WR bump)/L(Hb) ratio vs. EW(Hb) resulting from
evolutionary synthesis models that include the statistical dispersion due to
finite stellar populations in real star forming regions.


title: Multiple X-ray reflection from ionized slabs

abstract:
  Multiple reflection of X-rays may be important when an accretion disc and its
hot corona have a complicated geometry, or if returning radiation due to
gravitational light bending is important, or in emission from a funnel such as
proposed in some gamma-ray burst models. We simulate the effects of multiple
reflection by modifying the boundary condition for an X-ray illuminated slab.
Multiple reflection makes the soft X-ray spectrum steeper (softer) and
strengthens broad emission and absorption features, especially the K-shell
features of iron. This may be important in explaining the spectra of sources
such as the Narrow-Line Seyfert 1 galaxy 1H0707-495.


title:
Magnetic Alignment Process : A New Mechanism for Extracting Energy from
  Rotating Black Holes

abstract:
  As a complementary or companion process to the Blandford-Znajek mechanism for
the rotational energy extraction from a Kerr black hole to serve as a viable
model for the central engine of quasar, AGN and even GRB, the magnetic
alignment process is proposed. In contrast to the environment assumed in the
Blandford-Znajek mechanism in which the rotating hole's spin axis and the
asymptotic direction of the magnetic field are aligned, this new process
operates when they are generally misaligned which obviously is the more natural
situation likely to happen. The time scales over which these two processes take
place and the total radiated powers released at the horizon by them have been
estimated and found to be nearly comparable. This may imply that in a random,
non-axisymmetric configuration, the magnetic alignment process would operate
first during which some of the hole's rotational energy is released and upon
completion of the alignment, the Blandford-Znajek mechanism may follow and the
rest of the hole's rotational energy, if any left, would be further released.


title:
Mass loss rates of a sample of irregular and semiregular M-type
  AGB-variables

abstract:
  We have determined mass loss rates and gas expansion velocities for a sample
of 69 M-type irregular (IRV; 22 objects) and semiregular (SRV; 47 objects)
AGB-variables using a radiative transfer code to model their circumstellar CO
radio line emission. We believe that this sample is representative for the mass
losing stars of this type. The (molecular hydrogen) mass loss rate distribution
has a median value of 2.0E-7 solar masses per year. M-type IRVs and SRVs with a
mass loss rate in excess of 5E-7 solar masses per year must be very rare, and
among these mass losing stars the number of sources with mass loss rates below
a few 10E-8 solar masses per year must be small. We find no significant
difference between the IRVs and the SRVs in terms of their mass loss
characteristics. Among the SRVs the mass loss rate shows no dependence on the
period. Likewise the mass loss rate shows no correlation with the stellar
temperature. The gas expansion velocity distribution has a median of 7.0 km/s.
The mass loss rate and the gas expansion velocity correlate well, a result in
line with theoretical predictions for an optically thin, dust-driven wind. In
general, the model produces line profiles which acceptably fit the observed
ones.
  We have compared the results of this M-star sample with a similar C-star
sample analysed in the same way. The mass loss rate characteristics are very
similar for the two samples. On the contrary, the gas expansion velocity
distributions are clearly different. In particular, the number of low-velocity
sources is much higher in the M-star sample. We found no example of the sharply
double-peaked CO line profile, which is evidence of a large, detached CO-shell,
among the M-stars. About 10% of the C-stars show this phenomenon.


title: Big Bang Nucleosynthesis with Gaussian Inhomogeneous Neutrino Degeneracy

abstract:
  We consider the effect of inhomogeneous neutrino degeneracy on Big Bang
nucleosynthesis for the case where the distribution of neutrino chemical
potentials is given by a Gaussian. The chemical potential fluctuations are
taken to be isocurvature, so that only inhomogeneities in the electron chemical
potential are relevant. Then the final element abundances are a function only
of the baryon-photon ratio $\eta$, the effective number of additional neutrinos
$\Delta N_\nu$, the mean electron neutrino degeneracy parameter $\bar \xi$, and
the rms fluctuation of the degeneracy parameter, $\sigma_\xi$. We find that for
fixed $\eta$, $\Delta N_\nu$, and $\bar \xi$, the abundances of helium-4,
deuterium, and lithium-7 are, in general, increasing functions of $\sigma_\xi$.
Hence, the effect of adding a Gaussian distribution for the electron neutrino
degeneracy parameter is to decrease the allowed range for $\eta$. We show that
this result can be generalized to a wide variety of distributions for $\xi$.


title: LMXBs may be important LIGO sources after all

abstract:
  Andersson et al. and Bildsten proposed that the spin of accreting neutron
stars is limited by removal of angular momentum by gravitational radiation
which increases dramatically with the spin frequency of the star. Both Bildsten
and Andersson et al. argued that the r-modes of the neutron star for
sufficiently quickly rotating and hot neutron stars will grow due to the
emission of gravitational radiation, thereby accounting for a time varying
quadrupole component to the neutron star's mass distribution. However, Levin
later argued that the equilibrium between spin-up due to accretion and
spin-down due to gravitational radiation is unstable, because the growth rate
of the r-modes and consequently the rate of gravitational wave emission is an
increasing function of the core temperature of the star. The system executes a
limit cycle, spinning up for several million years and spinning down in less
than a year. However, the duration of the spin-down portion of the limit cycle
depends sensitively on the amplitude at which the nonlinear coupling between
different r-modes becomes important. As the duration of the spin-down portion
increases the fraction of accreting neutron stars which may be emitting
gravitational radiation increases while the peak flux in gravitational
radiation decreases. Depending on the distribution of quickly rotating neutron
stars in the Galaxy and beyond, the number of gravitational emitters detectable
with LIGO may be large.


title:
HST/STIS Spectroscopy of the Optical Outflow from DG Tau: Indications
  for Rotation in the Initial Jet Channel

abstract:
  We have carried out a kinematical, high angular resolution (~ 0".1) study of
the jet from DG Tau within 0."5 from the source (or 110 AU along this flow). We
analysed line profiles extracted from a set of seven spectra taken with STIS on
board the Hubble Space Telescope, with the slits parallel to the jet axis but
displaced transversely every 0".07. For the flow of moderate velocity (-70
km/s), we have found systematic differences in the radial velocities of lines
emitted on alternate sides of the jet axis. The results are corrected for the
effects due to uneven illumination of the slit. The relative Doppler shifts
range from 5 to 20 km/s. If this is interpreted as rotation, the flow is then
rotating clockwise looking from the jet towards the source and the derived
toroidal velocities are in the range 6 - 15 km/s. Using recent estimates of the
mass loss rate, one obtains for the considered velocity regime, an angular
momentum flux of ~ 3.8x10E-5 M_sun/yr AU km/s. Our findings may constitute the
first detection of rotation in the initial channel of a jet flow. The derived
values appear to be consistent with the predictions of popular
magneto-centrifugal jet-launching models, although we cannot exclude transverse
outflow asymmetries other than rotation.


title:
Detecting dark matter substructure spectroscopically in strong
  gravitational lenses

abstract:
  The Cold Dark Matter (CDM) model for galaxy formation predicts that a
significant fraction of mass in the dark matter haloes that surround L L*
galaxies is bound in substructures of mass 1E4-1E7Msun. The number of
observable baryonic substructures (such as dwarf galaxies and globular
clusters) falls short of these predictions by at least an order of magnitude.
We present a method for searching for substructure in the haloes of
gravitational lenses that produce multiple images of QSOs, such as 4-image
Einstein Cross lenses. Current methods based on broadband flux ratios cannot
cleanly distinguish between substructure, differential extinction, microlensing
and, most importantly, ambiguities in the host lens model. These difficulties
may be overcome by utilizing the prediction that when substructure is present,
the magnification will be a function of source size. QSO broad line and narrow
line emission regions are approximately ~1pc and >100pc in size, respectively.
When narrow line region (NLR) features are used as a normalisation, the
relative intensity and equivalent width of broad line region (BLR) features
will respectively reflect substructure-lensing and microlensing effects.
Spectroscopic observations of just a few image pairs would probably be able to
cleanly extract the desired substructure signature and distinguish it from
microlensing. In the rest-optical, the Hbeta/[OIII] region is ideal, since the
narrow wavelength range also largely eliminates differential reddening
problems. Simulations of Q2237+030 are done as an example to determine the
level of substructure that is detectable in this way, and possible systematic
difficulties are discussed. This is an ideal experiment to be carried out with
near-infrared integral field unit spectrographs on 8-m class telescopes.


title:
Planetary Nebulae as Standard Candles. XII. Connecting the Population I
  and Population II Distance Scales

abstract:
  We report the results of [OIII] lambda 5007 surveys for planetary nebulae
(PNe) in NGC 2403, 3115, 3351, 3627, 4258, and 5866. Using on-band/off-band
[OIII] and H-alpha images, we identify samples of PNe in these galaxies and
derive distances using the planetary nebula luminosity function (PNLF). We then
combine these measurements with previous data to compare the PNLF, Cepheid, and
surface brightness fluctuation (SBF) distance scales. We use a sample of 13
galaxies to show that the absolute magnitude of the PNLF cutoff is fainter in
small, low-metallicity systems, but the trend is well modelled theoretically.
When this dependence is removed, the scatter between the Cepheid and PNLF
distances becomes consistent with the internal errors of the methods and
independent of any obvious galaxy parameter. We then use the data to
recalibrate the zero point of the PNLF distance scale. We use a sample of 28
galaxies to show that the scatter between the PNLF and SBF distance
measurements agrees with that predicted from the techniques' internal errors,
and that no systematic trend exists between the distance residuals and stellar
population. However, we find the PNLF and SBF methods have a significant scale
offset: Cepheid-calibrated PNLF distances are, on average, ~0.3 mag smaller
than Cepheid-calibrated SBF distances. We discuss the possible causes of this
offset, and suggest that internal extinction in the bulges of the SBF
calibration galaxies is the principle cause of the discrepancy. If this is
correct, the SBF-based Hubble Constant must be increased by ~7%. We use our
distance to NGC 4258 to argue that the short distance scale to the LMC is
correct, and that the global Hubble Constant inferred from the HST Key Project
should be increased by 8 +/- 3% to H_0 = 78 +/- 7 km/s/Mpc. (abridged)


title: On the Double Planet System Around HD 83443

abstract:
  The Geneva group has reported two Saturn-mass planets orbiting HD 83443 (K0V)
with periods of 2.98 and 29.8 d. The two planets have raised interest in their
dynamics because of the possible 10:1 orbital resonance and the strong
gravitational interactions. We report precise Doppler measurements of HD 83443
obtained with the Keck/HIRES and the AAT/UCLES spectrometers. These
measurements strongly confirm the inner planet with period of 2.985 d, with
orbital parameters in very good agreement with those of the Geneva group.
However these Doppler measurements show no evidence of the outer planet, at
thresholds of 1/4 (3 m/s) of the reported velocity amplitude of 13.8 m/s. Thus,
the existence of the outer planet is in question. Indeed, the current Doppler
measurements reveal no evidence of any second planet with periods less than a
year.


title:
The Friedmann integrals and physical vacuum in the framework of
  macroscopic extra dimensions

abstract:
  The structure and origin of the Friedmann integrals are analyzed within the
framework of large extra dimensions proposed by Arkani-Hamed et all. (1998). It
is demonstrated that the integrals might emerge from extra-dimension physics
and reveal its signature. In the case of two extra dimensions, the integrals
are expressed via the product $M_* R$ of the only fundamental energy $M_*$ and
the size $R $ of the extra dimensions. The cosmic vacuum density turns out to
be $\sim R^4$, in this case. The effective cut-off in the spectrum of the
quantum zero-point oscillations at the frequency $\omega_V \sim 1/R$ is assumed
to be associated with the epoch when the Hubble radius becomes larger than $R$.
This occurs at temperatures $ \sim M_*$ in the first three picoseconds of the
cosmic expansion.


title: Seismic tests for solar models with tachocline mixing

abstract:
  We have computed accurate 1-D solar models including both a macroscopic
mixing process in the solar tachocline as well as up-to-date microscopic
physical ingredients. Using sound speed and density profiles inferred through
primary inversion of the solar oscillation frequencies coupled with the
equation of thermal equilibrium, we have extracted the temperature and hydrogen
abundance profiles. These inferred quantities place strong constraints on our
theoretical models in terms of the extent and strength of our macroscopic
mixing, on the photospheric heavy elements abundance, on the nuclear reaction
rates such as $S_{11}$ and $S_{34}$ and on the efficiency of the microscopic
diffusion. We find a good overall agreement between the seismic Sun and our
models if we introduce a macroscopic mixing in the tachocline and allow for
variation within their uncertainties of the main physical ingredients. From our
study we deduce that the solar hydrogen abundance at the solar age is $X_{\rm
inv}=0.732\pm 0.001$ and that based on the $^9$Be photospheric depletion, the
maximum extent of mixing in the tachocline is 5% of the solar radius. The
nuclear reaction rate for the fundamental $pp$ reaction is found to be
$S_{11}(0)=4.06\pm 0.07$ $10^{-25}$ MeV barns, i.e., 1.5% higher than the
present theoretical determination. The predicted solar neutrino fluxes are
discussed in the light of the new SNO/SuperKamiokande results.


title:
High-Resolution X-ray Spectroscopy of Hercules X-1 with the XMM-Newton
  RGS: CNO Element Abundance Measurements and Density Diagnostics of a
  Photoionized Plasma

abstract:
  We analyze the high-resolution X-ray spectrum of Hercules X-1, an
intermediate-mass X-ray binary, which was observed with the XMM-Newton
Reflection Grating Spectrometer. We measure the elemental abundance ratios by
use of spectral models, and we detect material processed through the CNO-cycle.
The CNO abundances, and in particular the ratio N/O > 4.0 times solar, provide
stringent constraints on the evolution of the binary system. The low and
short-on flux states of Her X-1 exhibit narrow line emission from C VI, N VI, N
VII, O VII, O VIII, Ne IX, and Ne X ions. The spectra show signatures of
photoionization. We measure the electron temperature, quantify photoexcitation
in the He alpha lines, and set limits on the location and density of the gas.
The recombination lines may originate in the accretion disk atmosphere and
corona, or on the X-ray illuminated face of the mass donor (HZ Her). The
spectral variation over the course of the 35 d period provides additional
evidence for the precession of the disk. During the main-on state, the narrow
line emission is absent, but we detect excesses of emission at ~10--15 A, and
also near the O VII intercombination line wavelength.


title:
Analysis of two-point statistics of cosmic shear: I. Estimators and
  covariances

abstract:
  We derive in this paper expressions for the covariance matrix of the cosmic
shear two-point correlation functions which are readily applied to any survey
geometry. Furthermore, we consider the more special case of a simple survey
geometry which allows us to obtain approximations for the covariance matrix in
terms of integrals which are readily evaluated numerically. These results are
then used to study the covariance of the aperture mass dispersion which has
been employed earlier in quantitative cosmic shear analyses. We show that the
aperture mass dispersion, measured at two different angular scales, quickly
decorrelates with the ratio of the scales. Inverting the relation between the
shear two-point correlation functions and the power spectrum of the underlying
projected matter distribution, we construct estimators for the power spectrum
and for the band powers, and show that they yields accurate approximations; in
particular, the correlation between band powers at different wave numbers is
quite weak. The covariance matrix of the shear correlation function is then
used to investigate the expected accuracy of cosmological parameter estimates
from cosmic shear surveys. Depending on the use of prior information, e.g. from
CMB measurements, cosmic shear can yield very accurate determinations of
several cosmological parameters, in particular the normalization $\sigma_8$ of
the power spectrum of the matter distribution, the matter density parameter
$\Omega_{\rm m}$, and the shape parameter $\Gamma$.


title: The Radio Evolution of the Ordinary Type Ic SN 2002ap

abstract:
  We report the discovery and monitoring of radio emission from the Type Ic SN
2002ap ranging in frequency from 1.43 to 22.5 GHz, and in time from 4 to 50
days after the SN explosion. As in most other radio SNe, the radio spectrum of
SN 2002ap shows evidence for absorption at low frequencies, usually attributed
to synchrotron self-absorption or free-free absorption. While it is difficult
to discriminate between these two processes based on a goodness-of-fit, the
unabsorbed emission in the free-free model requires an unreasonably large
ejecta energy. Therefore, on physical grounds we favor the synchrotron
self-absorption (SSA) model. In the SSA framework, at about day 2, the shock
speed is approximately 0.3c, the energy in relativistic electrons and magnetic
fields is approximately 1.5e45 erg and the inferred progenitor mass loss rate
is approximately 5e-7 solar masses per year (assuming a 1,000 km/sec wind).
These properties are consistent with a model in which the outer, high velocity
supernova ejecta interact with the progenitor wind. The amount of relativistic
ejecta in this model is small, so that the presence of broad lines in the
spectrum of a Type Ib/c supernova, as observed in SN 2002ap, is not a reliable
indicator of a connection to relativistic ejecta and hence gamma-ray emission.


title:
Dwarf Nova-like Outburst of Short Period Intermediate Polar HT
  Camelopardalis

abstract:
  We report the first time-series observations of the short outburst of the
proposed intermediate polar HT Cam (=RX J0757.0+6306). On 2001 December 29, we
detected the object was undergoing a bright outburst at the magnitude of
$m_{vis}=12.2$. Following this detection, we started international joint
observations through VSNET. The light curve showed a gradual decline for the
first 0.5 d. Following this short plateau phase, the rate of decline
dramatically increased to more than 4 mag d$^{-1}$. Within 1.5 d from the
outburst detection, the object almost declined to the quiescent level. During
the rapidly declining phase, long-term modulations with a period of 86 min and
strong pulses with a period of 8.6 min were observed. We concluded that 86 min
and 8.6 min are the orbital period and the spin period of HT Cam, respectively.
By the detection of the spin period, we confirmed the IP classification of HT
Cam. However, its outburst behavior rather resembles that of dwarf novae.
  The discrepancy between the declining rates of the total flux and the pulse
flux strongly suggests that the disk instabilities were taking place during the
outburst.


title: Towards Proper Motions in the Local Group

abstract:
  Key and still largely missing parameters for measuring the mass content and
distribution of the Local Group are the proper motion vectors of its member
galaxies. The problem when trying to derive the gravitational potential of the
Local Group is that usually only radial velocities are known, and hence
statistical approaches have to be used. The expected proper motions for
galaxies within the Local Group, ranging from 20 to 100 $\mu$as/yr, are
detectable with VLBI using the phase-referencing technique. We present
phase-referencing observations of bright masers in IC~10 and M33 with respect
to background quasars. We observed the H$_2$O masers in IC10 three times over a
period of two months to check the accuracy of the relative positions. The
relative positions were obtained by modeling the interferometer phase data for
the maser sources referenced to the background quasars. The model allowed for a
relative position shift for the source and a single vertical atmospheric delay
error in the correlator model for each antenna. The rms of the relative
positions for the three observations is only 0.01 mas, which is approximately
the expected position error due to thermal noise. Also, we present a method to
measure the geometric distance to M33. This will allow re-calibration of the
extragalactic distance scale based on Cepheids. The method is to measure the
relative proper motions of two H$_2$O maser sources on opposite sides of M33.
The measured angular rotation rate, coupled with other measurements of the
inclination and rotation speed of the galaxy, yields a direct distance
measurement.


title: The white dwarf cooling sequence in the old open cluster NGC 188

abstract:
  We develop the white dwarf luminosity function (LF) of the old open cluster
NGC 188 in order to determine a lower limit to the age of the cluster by using
the faint end of the cooling sequence.
  To produce an extensive sequence of the cooling white dwarfs we imaged four
contiguous HST-WFPC2 fields in the center of the cluster in the F555W and F814W
filters. After imposing selection criteria on the detected objects we found a
white dwarf cooling sequence (down to V ~26.5) including 28 candidate white
dwarfs in the cluster. The exposures are not deep enough to reach the end of
this sequence, but the results of our analysis allow us to establish a lower
limit to the age of the cluster independently of the isochrone fit to the
cluster turnoff.
  The most ancient white dwarfs found are ~4 Gyr old, an age that is set solely
by the photometric limit of our data. Classical methods provide an estimate of
\~7 Gyr (Sarajedini et al., 1999).


title:
XMM-Newton Reflection Grating Spectrometer Observations of the
  Prototypical Starburst Galaxy M82

abstract:
  We present results from XMM-Newton Reflection Grating Spectrometer
observations of the prototypical starburst galaxy M82. These high resolution
spectra represent the best X-ray spectra to date of a starburst galaxy. A
complex array of lines from species over a wide range of temperatures is seen,
the most prominent being due to Lyman-alpha emission from abundant low Z
elements such as N, O, Ne, Mg and Si. Emission lines from Helium-like charge
states of the same elements are also seen in emission, as are strong lines from
the entire Fe-L series. Further, the OVII line complex is resolved and is seen
to be consistent with gas in collisional ionization equilibrium. Spectral
fitting indicates emission from a large mass of gas with a differential
emission measure over a range of temperatures (from 0.2 keV to 1.6 keV, peaking
at 0.7 keV), and evidence for super-solar abundances of several elements is
indicated. Spatial analysis of the data indicates that low energy emission is
more extended to the south and east of the nucleus than to the north and west.
Higher energy emission is far more centrally concentrated.


title: Black Hole Blackbodies

abstract:
  Many black-hole sources emit a substantial fraction of their luminosities in
blackbody-like spectral components. It is usual to assume that these are
produced in regions at least comparable in size to the hole's Schwarzschild
radius, so that a measure of the emitting area provides an estimate of the
black hole mass M. However there is then no guarantee that the source
luminosity (if isotropic) obeys the Eddington limit corresponding to M. We show
that the apparent blackbody luminosity L_sph and temperature T must obey the
inequality L_sph < 2.3 10^44 (T/100 eV)^-4 erg s^-1 for this to hold. Sources
violating this limit include ultrasoft AGN and some of the ultraluminous X-ray
sources (ULXs) observed in nearby galaxies. We discuss the possible
consequences of this result, which imply either super-Eddington or anisotropic
emission in both cases. We suggest that the ultrasoft AGN are the AGN analogues
of the ULXs.


title:
Properties of the close binary and circumbinary torus of the Red
  Rectangle

abstract:
  New diffraction-limited speckle images of the Red Rectangle in the wavelength
range 2.1--3.3 microns with angular resolutions of 44--68 mas and previous
speckle images at 0.7--2.2 microns revealed well-resolved bright bipolar
outflow lobes and long X-shaped spikes originating deep inside the outflow
cavities. This set of high-resolution images stimulated us to reanalyze all
infrared observations of the Red Rectangle using our two-dimensional radiative
transfer code. The new detailed modeling, together with estimates of the
interstellar extinction in the direction of the Red Rectangle enabled us to
more accurately determine one of the key parameters, the distance D=710 pc with
model uncertainties of 70 pc, which is twice as far as the commonly used
estimate of 330 pc. The central binary is surrounded by a compact, massive
(M=1.2 Msun), very dense dusty torus with hydrogen densities reaching
n_H=2.5x10^12 cm^-3 (dust-to-gas mass ratio rho_d/rho~0.01). The bright
component of the spectroscopic binary HD 44179 is a post-AGB star with mass
M*=0.57 Msun, luminosity L*=6000 Lsun, and effective temperature T*=7750 K.
Based on the orbital elements of the binary, we identify its invisible
component with a helium white dwarf with Mwd~0.35 Msun, Lwd~100 Lsun, and
Twd~6x10^4 K. The hot white dwarf ionizes the low-density bipolar outflow
cavities inside the dense torus, producing a small HII region observed at radio
wavelengths. We propose an evolutionary scenario for the formation of the Red
Rectangle nebula, in which the binary initially had 2.3 and 1.9 Msun components
at a separation of 130 Rsun. The nebula was formed in the ejection of a common
envelope after Roche lobe overflow by the present post-AGB star.


title: On the Nature of X-ray Variability in Ark 564

abstract:
  We use data from a recent long ASCA observation of the Narrow Line Seyfert 1
Ark 564 to investigate in detail its timing properties. We show that a thorough
analysis of the time series, employing techniques not generally applied to AGN
light curves, can provide useful information to characterize the engines of
these powerful sources.We searched for signs of non-stationarity in the data,
but did not find strong evidences for it. We find that the process causing the
variability is very likely nonlinear, suggesting that variability models based
on many active regions, as the shot noise model, may not be applicable to Ark
564. The complex light curve can be viewed, for a limited range of time scales,
as a fractal object with non-trivial fractal dimension and statistical
self-similarity. Finally, using a nonlinear statistic based on the scaling
index as a tool to discriminate time series, we demonstrate that the high and
low count rate states, which are indistinguishable on the basis of their
autocorrelation, structure and probability density functions, are intrinsically
different, with the high state characterized by higher complexity.


title:
A QSO survey via optical variability and zero proper motion in the M92
  field.III. Narrow emission line galaxies

abstract:
  We study a sample of 23 narrow-emission line galaxies (NELGs) which were
selected by their strong variability as QSO candidates in the framework of a
variability-and-proper motion QSO survey on digitised Schmidt plates. In
previous work, we have shown that variability is an efficient method to find
AGNs. The variability properties of the NELGs are however significantly
different from those of the QSOs. The main aim of this paper is to clarify the
nature of this variability and to estimate the fraction of AGN-dominated NELGs
in this sample. New photometric and spectroscopic observations are presented,
along with revised data from the photographic photometry. The originally
measured high variability indices could not be confirmed. The diagnostic
line-ratios of the NELG spectra are consistent with HII region-like spectra. No
AGN could be proved, yet we cannot rule out the existence of faint
low-luminosity AGNs masked by HII regions from intense star formation.


title:
Star Formation in Bright Rimmed Clouds. I. Millimeter and Submillimeter
  Molecular Line Surveys

abstract:
  We present the results of the first detailed millimeter and submillimeter
molecular line survey of bright rimmed clouds, observed at FCRAO in the CO
(J=1-0), C18O (J=1-0), HCO+ (J=1-0), H13CO+ (J=1-0), and N2H+ (J=1-0)
transitions, and at the HHT in the CO (J=2-1), HCO+ (J=3-2), HCO+ (J=4-3),
H13CO+ (J=3-2), and H13CO+ (J=4-3) molecular line transitions. The source list
is composed of a selection of bright rimmed clouds from the catalog of such
objects compiled by Sugitani et al. (1991). We also present observations of
three Bok globules done for comparison with the bright rimmed clouds. We find
that the appearance of the millimeter CO and HCO+ emission is dominated by the
morphology of the shock front in the bright rimmed clouds. The HCO+ (J=1-0)
emission tends to trace the swept up gas ridge and overdense regions which may
be triggered to collapse as a result of sequential star formation. Five of the
seven bright rimmed clouds we observe seem to have an outflow, however only one
shows the spectral line blue-asymmetric signature that is indicative of infall,
in the optically thick HCO+ emission. We also present evidence that in bright
rimmed clouds the nearby shock front may heat the core from outside-in thereby
washing out the normally observed line infall signatures seen in isolated star
forming regions. We find that the derived core masses of these bright rimmed
clouds are similar to other low and intermediate mass star forming regions.


title:
Kinematics of Diffuse Ionized Gas Halos: A Ballistic Model of Halo
  Rotation

abstract:
  To better understand diffuse ionized gas kinematics and halo rotation in
spiral galaxies, we have developed a model in which clouds are ejected from the
disk and follow ballistic trajectories through the halo. The behavior of clouds
in this model has been investigated thoroughly through a parameter space search
and a study of individual cloud orbits. Synthetic velocity profiles have been
generated in z (height above the plane) from the models for the purpose of
comparing with velocity centroid data from previously obtained long-slit
spectra of the edge-on spirals NGC 891 (one slit) and NGC 5775 (two slits). In
each case, a purely ballistic model is insufficient in explaining observed DIG
kinematics. In the case of NGC 891, the observed vertical velocity gradient is
not as steep as predicted by the model, possibly suggesting a source of
coupling between disk and halo rotation or an outwardly directed pressure
gradient. The ballistic model more successfully explains DIG kinematics
observed in NGC 5775; however, it cannot explain the observed trend of high-z
gas velocities nearly reaching the systemic velocity. Such behavior can be
attributed to either an inwardly directed pressure gradient or a possible tidal
interaction with its companion, NGC 5774. In addition, the ballistic model
predicts that clouds move radially outward as they cycle through the halo. The
mass and energy fluxes estimated from the model suggest this radially outward
gas migration leads to a redistribution of material that may significantly
affect the evolution of the ISM.


title: Fine Tuning in Quintessence Models with Exponential Potentials

abstract:
  We explore regions of parameter space in a simple exponential model of the
form $V = V_0 e^{- \lambda \frac{Q}{M_p}}$ that are allowed by observational
constraints. We find that the level of fine tuning in these models is not
different from more sophisticated models of dark energy. We study a transient
regime where the parameter $\lambda$ has to be less than $\sqrt{3}$ and the
fixed point $\Omega_Q = 1$ has not been reached. All values of the parameter
$\lambda$ that lead to this transient regime are permitted. We also point out
that this model can accelerate the universe today even for $\lambda >
\sqrt{2}$, leading to a halt of the present acceleration of the universe in the
future thus avoiding the horizon problem. We conclude that this model can not
be discarded by current observations.


title:
Discovery of absorption features in the X-ray spectrum of an isolated
  neutron star

abstract:
  We observed 1E 1207.4--5209, a neutron star in the center of the supernova
remnant PKS 1209--51/52, with the ACIS detector aboard the Chandra X-ray
observatory and detected two absorption features in the source spectrum. The
features are centered near 0.7 keV and 1.4 keV, their equivalent widths are
about 0.1 keV. We discuss various possible interpretations of the absorption
features and exclude some of them. A likely interpretation is that the features
are associated with atomic transitions of once-ionized helium in the neutron
star atmosphere with a strong magnetic field. The first clear detection of
absorption features in the spectrum of an isolated neutron star provides an
opportunity to measure the mass-to-radius ratio and constrain the equation of
state of the superdense matter.


title:
Turbulent Convection Under the Influence of Rotation: Sustaining a
  Strong Differential Rotation

abstract:
  The intense turbulence present in the solar convection zone is a major
challenge to both theory and simulation as one tries to understand the origins
of the striking differential rotation profile with radius and latitude that has
been revealed by helioseismology. The differential rotation must be an
essential element in the operation of the solar magnetic dynamo and its cycles
of activity, yet there are many aspects of the interplay between convection,
rotation and magnetic fields that are still unclear. We have here carried out a
series of 3--D numerical simulations of turbulent convection within deep
spherical shells using our anelastic spherical harmonic (ASH) code on massively
parallel supercomputers. These studies of the global dynamics of the solar
convection zone concentrate on how the differential rotation and meridional
circulation are established. We have analyzed the transport of angular momentum
in establishing such differential rotation, and clarified the roles played by
Reynolds stresses and the meridional circulation in this process. We have found
that the Reynolds stresses are crucial in transporting angular momentum toward
the equator. The effects of baroclinicity (thermal wind) have been found to
have a modest role in the resulting mean zonal flows. The simulations have
produced differential rotation profiles within the bulk of the convection zone
that make reasonable contact with ones inferred from helioseismic inversions,
namely possessing a fast equator, an angular velocity difference of about 30%
from equator to pole, and some constancy along radial lines at mid-latitudes.


title:
Parkes HI observations of galaxies behind the southern Milky Way. - I.
  The Hydra/Antlia region (l : 266 to 296 deg)

abstract:
  As part of our program to map the large-scale distribution of galaxies behind
the Milky Way, we used the Parkes 210 ft (64 m) radio telescope for pointed HI
observations of a sample of low surface-brightness (due to heavy obscuration)
spiral galaxies selected from the deep optical Zone of Avoidance (ZOA) galaxy
catalog in the Hydra/Antlia region (Kraan-Korteweg 2000a). Searching a
simultaneous velocity range of either 300 to 5500 km/s or 300 to 10500 km/s to
an rms level of typically 2 - 4 mJy resulted in detections in 61 of the 139
pointings, leading to a total of 66 detections (an additional detection was
made in a reference position, and two other pointings revealed two and four
independent signals respectively). Except for 2 strong HI emitters identified
in the shallow Zone of Avoidance HI survey (Henning et al. 2000), all HI
detections are new. An analysis of the properties of the observed and detected
galaxies prove that pointed HI observations of highly obscured galaxies allow
the tracing of a population of nearby, intrinsically large and bright spiral
galaxies that otherwise would not be recovered. The new data identified a
previously unrecognized nearby group at l=287.5, b=-9.5, V=1700 km/s, the
continuation of the Hydra/Antlia filament on the opposite side of the Galactic
plane, and helped to delimit a distinct void in the ZOA centered at 2000 km/s.


title:
WHAM Observations of H-alpha from High-Velocity Clouds: Are They
  Galactic or Extragalactic?

abstract:
  It has been suggested that high velocity clouds may be distributed throughout
the Local Group and are therefore not in general associated with the Milky Way
galaxy. With the aim of testing this hypothesis, we have made observations in
the H-alpha line of high velocity clouds selected as the most likely candidates
for being at larger than average distances. We have found H-alpha emission from
4 out of 5 of the observed clouds, suggesting that the clouds under study are
being illuminated by a Lyman continuum flux greater than that of the
metagalactic ionizing radiation. Therefore, it appears likely that these clouds
are in the Galactic halo and not distributed throughout the Local Group.


title: An Upper Limit to the Age of the Galactic Bar

abstract:
  Using data from the Two Micron All-Sky Survey (2MASS), we identify a
population of infrared carbon (IR C) stars with J-K >= 2 in the Milky Way.
These stars are shown to trace the stellar bar previously identified in IR and
optical surveys. The properties of C stars strongly suggest that they are of
intermediate age. We conclude that the bar is likely to have formed more
recently than 3 Gyr ago, and must be younger than 6 Gyr. Implications and
further tests of this conclusion are briefly discussed.


title:
Physical structure of the protoplanetary nebula CRL618. I. Optical
  long-slit spectroscopy and imaging

abstract:
  In this paper (paper I) we present optical long-slit spectroscopy and imaging
of the protoplanetary nebula CRL618. The optical lobes of CRL618 consist of
shock-excited gas, which emits many recombination and forbidden lines, and
dust, which scatters light from the innermost regions. From the analysis of the
scattered Halpha emission, we derive a nebular inclination of i=24+-6 deg. The
spectrum of the innermost part of the east lobe (visible as a bright, compact
nebulosity close to the star in the Halpha HST image) is remarkably different
from that of the shocked lobes but similar to that of the inner HII region,
suggesting that this region represents the outermost parts of the latter. We
find a non-linear radial variation of the gas velocity along the lobes.
  The largest projected LSR velocities (~80 km/s) are measured at the tips of
the lobes, where the direct images show the presence of compact bow-shaped
structures. The velocity of the shocks in CRL618 is in the range ~75-200 km/s,
as derived from diagnostic line ratios and line profiles. We report a
brightening (weakening) of [OIII]5007AA ([OI]6300AA) over the last ~10 years
that may indicate a recent increase in the speed of the exciting shocks. From
the analysis of the spatial variation of the nebular extinction, we find a
large density contrast between the material inside the lobes and beyond them:
the optical lobes seem to be `cavities' excavated in the AGB envelope by
interaction with a more tenuous post-AGB wind. The electron density, with a
mean value n_e~5E3-1E4 cm-3, shows significant fluctuations but no systematic
decrease along the lobes, in agreement with most line emission arising in a
thin shell of shocked material (the lobe walls) rather than in the post-AGB
wind filling the interior of the lobes. (...)


title:
Detection of an optical transient following the 13 March 2000 short/hard
  gamma-ray burst

abstract:
  We imaged the error box of a gamma-ray burst of the short (0.5 s), hard type
(GRB 000313), with the BOOTES-1 experiment in southern Spain, starting 4 min
after the gamma-ray event, in the I-band. A bright optical transient (OT
000313) with I = 9.4 +/- 0.1 was found in the BOOTES-1 image, close to the
error box (3-sigma) provided by BATSE. Late time VRIK'-band deep observations
failed to reveal an underlying host galaxy. If the OT 000313 is related to the
short, hard GRB 000313, this would be the first optical counterpart ever found
for this kind of events (all counterparts to date have been found for bursts of
the long, soft type). The fact that only prompt optical emission has been
detected (but no afterglow emission at all, as supported by theoretical models)
might explain why no optical counterparts have ever been found for short, hard
GRBs.This fact suggests that most short bursts might occur in a low-density
medium and favours the models that relate them to binary mergers in very
low-density enviroments.


title:
Discovery of an edge-on dust disk around the [WC10] central star
  CPD-568032

abstract:
  We present Hubble Space Telescope ultraviolet and optical STIS spectroscopy
of the [WCL] planetary nebula central star CPD-568032, obtained during its
latest lightcurve minimum. The UV spectrum shows the central star's continuum
light distribution to be split into two bright peaks separated by 0.10 arcsec.
We interpret this finding as due to an edge-on disk or torus structure that
obscures direct light from the star, which is seen primarily via its light
scattered from the disk's rims or lobes. CPD-568032 is an archetype of dual
dust chemistry [WCL] planetary nebulae, which exhibit strong infrared emission
features from both carbon-rich and oxygen-rich materials, and for which the
presence of a disk harboring the O-rich grains had been suggested. Our direct
observation of an edge-on occulting dust structure around CPD-568032 provides
strong support for such a model and for binary interactions being responsible
for the correlation between the dual dust chemistry phenomenon in planetary
nebulae and the presence of a hydrogen-deficient [WCL] Wolf-Rayet central star.


title: The Role of a Hot Gas Environment on the Evolution of Galaxies

abstract:
  Most spiral galaxies are found in galaxy groups with low velocity
dispersions; most E/S0 galaxies are found in galaxy groups with relatively high
velocity dispersions. The mass of the hot gas we can observe in the E/S0 groups
via their thermal X-ray emission is, on average, as much as the baryonic mass
of the galaxies in these groups. By comparison, galaxy clusters have as much or
more hot gas than stellar mass. Hot gas in S-rich groups, however, is of low
enough temperature for its X-ray emission to suffer heavy absorption due to
Galactic HI and related observational effects, and hence is hard to detect. We
postulate that such lower temperature hot gas does exist in low velocity
dispersion, S-rich groups, and explore the consequences of this assumption. For
a wide range of metallicity and density, hot gas in S-rich groups can cool in
far less than a Hubble time. If such gas exists and can cool, especially when
interacting with HI in existing galaxies, then it can help link together a
number of disparate observations, both Galactic and extragalactic, that are
otherwise difficult to understand.


title:
Gamma-Ray Burst Spectra and Light Curves as Signatures of a
  Relativistically Expanding Plasma

abstract:
  Several patterns have been discovered in how some spectral characteristics
change during the decaying phase of long (> few s.) GRB pulses. We compare
these observed signatures with those expected from a relativistically expanding
shell. Within the internal shock model and assuming a short cooling time, we
show that the angular dependence in arrival time can explain the general
characteristics of long GRB pulses. This includes the pulse shape, with a fast
rise and a slower decay, ~ (1+t/tau)^2, and the spectral evolution, which can
be described by the hardness-intensity correlation (HIC), with the intensity
being proportional to the square of the hardness. A variation of the relevant
time scales involved (the angular spreading and the dynamic) can explain the
broad, observed dispersion of the HIC index. Reasonable estimates of physical
parameters lead to situations where the HIC relation deviates from a pure power
law; features that are indeed present in the observations. Depending on the
relative values of the rise and decay times of the intrinsic light curve, the
spectral/temporal behavior, as seen by an observer, will produce hard-to-soft
or tracking pulses. The observed spectrum is a superposition of many intrinsic
spectra arriving from different parts of the shell with varying spectral
shifts. Therefore, it will be broader than the emitted spectrum and its
spectral parameters could have complex relations with the intrinsic ones.
Furthermore, we show that the softening of the low-energy power-law index, that
has been observed in some pulses, can be explained by geometric effects and
does not need to be an intrinsic behavior.


title: The dwarf galaxy population of the Virgo Cluster

abstract:
  I review the status of knowledge about the dwarf galaxies in the Virgo
Cluster (VC) concentrating on work published after 1995. I explain the present
ideas about the nature and history of the dwarf elliptical galaxies and
emphasize the major increments in understanding achieved in the study of the
dwarf irregular population. Special attention is given to the samples of
late-type dwarf galaxies in the VC studied at the Wise Observatory(BCDs and
dIs), and to a comparison of their properties.