title: SW Sextantis in an excited, low state

abstract:
  We present low-resolution spectrophotometric optical observations of the
eclipsing nova-like cataclysmic variable SW Sex, the prototype of the SW Sex
stars. We observed the system when it was in an unusual low state. The spectrum
is characterized by the presence of strong He II and C IV emission lines as
well as the normal single peaked Balmer emission lines. The radial temperature
profile of the disk follows the expected T ~R^3/4 only in the outer parts and
flattens off inside 0.5 times the white dwarf Roche lobe radius. The single
peaked emission lines originate in a region above the plane of the disk, at the
position of the hot spot.


title: Dust Migration and Morphology in Optically Thin Circumstellar Gas Disks

abstract:
  We analyze the dynamics of gas-dust coupling in the presence of stellar
radiation pressure in circumstellar gas disks, which are in a transitional
stage between the gas-dominated, optically thick, primordial nebulae, and the
dust-dominated, optically thin Vega-type disks. Dust undergo radial migration,
seeking a stable equilibrium orbit in corotation with gas. The migration of
dust gives rise to radial fractionation of dust and creates a variety of
possible observed disk morphologies, which we compute by considering the
equilibrium between the dust production and the dust-dust collisions removing
particles from their equilibrium orbits. Sand-sized and larger grains are
distributed throughout most of the gas disk, with concentration near the gas
pressure maximum in the inner disk. Smaller grains (typically in the range of
10 to 200 micron) concentrate in a prominent ring structure in the outer region
of the gas disk (presumably at radius 100 AU), where gas density is rapidly
declining with radius. The width and density, as well as density contrast of
the dust ring with respect to the inner dust disk depend on the distribution of
gas. Our results open the prospect for deducing the distribution of gas in
circumstellar disks by observing their dust. We have qualitatively compared our
models with two observed transitional disks around HR 4796A and HD 141569A.
Dust migration can result in observation of a ring or a bimodal radial dust
distribution, possibly very similar to the ones produced by gap-opening
planet(s) embedded in the disk, or shepherding it from inside or outside. We
conclude that a convincing planet detection via dust imaging should include
specific non-axisymmetric structure following from the dynamical simulations of
perturbed disks.


title: Presolar Grains from Novae

abstract:
  We report the discovery of five SiC grains and one graphite grain isolated
from the Murchison carbonaceous meteorite whose major-element isotopic
compositions indicate an origin in nova explosions. The grains are
characterized by low 12C/13C (4-9) and 14N/15N (5-20) ratios, large excesses in
30Si (30Si/28Si ratios range to 2.1 times solar) and high 26Al/27Al ratios.
These isotopic signatures are theoretically predicted for the ejecta from ONe
novae and cannot be matched by any other stellar sources. Previous studies of
presolar grains from primitive meteorites have shown that the vast majority
formed in red giant outflows and supernova ejecta. Although a classical nova
origin was suggested for a few presolar graphite grains on the basis of 22Ne
enrichments, this identification is somewhat ambiguous since it is based only
on one trace element. Our present study presents the first evidence for nova
grains on the basis of major element isotopic compositions of single grains. We
also present the results of nucleosynthetic calculations of classical nova
models and compare the predicted isotopic ratios with those of the grains. The
comparison points toward massive ONe novae if the ejecta are mixed with
material of close-to-solar composition.


title: The Capture of Particles by Chaotic Resonances During Orbital Migration

abstract:
  Because a chaotic zone can reduce the long timescale capture probabilities
and cause catastrophic events such as close encounters with a planet or star
during temporary capture, the dynamics of migrating planets is likely to be
strongly dependent on the widths of the resonance chaotic zones. Previous
theoretical work on the resonant capture of particles into mean-motion
resonances by orbital migration has been restricted to the study of integrable
models. By exploring toy drifting Hamiltonian models we illustrate how the
structure in phase space of a resonance can be used to generalize this
integrable capture theory to include the richer phenomenology of chaotic
resonances. We show that particles are temporarily captured into the chaotic
zone of a resonance with fixed shape for a time that is given by the width of
the chaotic zone divided by the resonance drift rate. Particles can be
permanently captured into a drifting chaotic resonance only if they are
captured into a growing integrable region. Therefore resonances containing wide
chaotic zones have lower permanent capture probabilities than those lacking
chaotic zones. We expect large deviations from the predictions of integrable
capture theories when the chaotic zone is large and the migration rate is
sufficiently long that many Lyapunov times pass while particles are temporarily
captured in the resonance. The 2:1 mean-motion resonance with Neptune in the
Kuiper Belt contains a chaotic zone, even when integrated on short timescales
such as a million years. Capture probabilities are lower than estimated
previously from drifting integrable models. This may offer an explanation for
low eccentricity Kuiper Belt objects between 45-47 AU which should have been
previously captured in the 2:1 resonance by Neptune's migration.


title: Demographics of Blazars

abstract:
  We discuss the preliminary results of an extensive effort to address the
fundamental, and yet un-answered, question that can be trivialized as: ``are
there more blue or red blazars?''. This problematic is tightly connected with
the much debated issue of the unified picture(s) of radio-loud AGNs, which in
turn revolves around the existence, and the properties of relativistic jets. We
address this question by comparing -- simultaneously -- the properties of the
collection of heterogeneously selected samples that are available now, with the
predictions of a set of plausible unifications scenarios. We show that it is
already possible to make significant progress even by using only the present
samples. The important role of selection effects is discussed. For instance we
show that the multiple flux selections typical of available surveys could
induce some of the correlations found in color-color diagrams. These latter
results should apply to any study of flux limited samples.


title: Halo enrichment by disrupted globular clusters

abstract:
  We study the evolution of the galactic globular cluster system to determine
its initial mass-function and the fraction of halo stars that could have come
from disrupted globular clusters. We study the cluster evolution under the
influence of two destruction mechanisms: Two-body relaxation and dynamical
friction. New results of N-body simulations are used for the lifetimes of
clusters dissolving under the influence of two-body relaxation.
  Two different mass-functions are studied: A gaussian initial distribution in
log(M_C) with mean mass and scatter similar to what one observes for the
galactic globular cluster system, and a power-law distribution resembling what
is seen for clusters in merging and interacting galaxies. We find that in the
inner parts of the galaxy, both distributions evolve in such a way that they
are consistent with the observations. In the outer parts, a gaussian initial
distribution gives the better fit. This might change however if elliptic orbits
are considered, or there are undiscovered low-mass clusters in the galactic
halo. In any case, only a small fraction of the stellar halo of the Milky Way
originated in globular clusters.


title: Accretion Disk Torqued by a Black Hole

abstract:
  If a Kerr black hole is connected to a disk rotating around it by a magnetic
field, the rotational energy of the Kerr black hole provides an energy source
for the radiation of the disk in addition to disk accretion. The black hole
exerts a torque on the disk, which transfers energy and angular momentum
between the black hole and the disk. If the black hole rotates faster than the
disk, energy and angular momentum are extracted from the black hole and
transfered to the disk. The energy deposited into the disk is eventually
radiated away by the disk, which will increase the efficiency of the disk. If
the black hole rotates slower than the disk, energy and angular momentum are
transfered from the disk to the black hole, which will lower the efficiency of
the disk. With suitable boundary conditions, quasi-steady state solutions are
obtained for a thin Keplerian disk magnetically coupled to a Kerr black hole.
By ``quasi-steady state'' we mean that any macroscopic quantity at a given
radius in the disk slowly changes with time: the integrated change within one
rotation period of the disk is much smaller than the quantity itself. We find
that, the torque produced by the magnetic coupling propagates only outward in
the disk, the total radiation flux of the disk is a superposition of the
radiation flux produced by the magnetic coupling and that produced by
accretion. Most interestingly, a disk magnetically coupled to a rapidly
rotating black hole can radiate without accretion. Such a disk has an infinite
efficiency. For a specific example that the magnetic field touches the disk at
the inner boundary, the radial radiation profile is very different from that of
a standard accretion disk: the emissivity index is significantly bigger, most
radiation comes from a region which is closer to the center of the disk.


title:
Indicator of Exo-Solar Planet(s) in the Circumstellar Disk Around Beta
  Pictoris

abstract:
  Our efficient numerical approach has been applied to modeling the asymmetric
circumstellar dust disk around Beta Pictoris as observed with the HST/STIS. We
present a new model on the origin of the warping of the Beta Pic disk. We
suggest that the observed warp is formed by the gravitational influence of a
planet with a mass of about 10 masses of Earth, at a distance of 70 AU, and a
small inclination ($\sim 2.5^\circ$) of the planetary orbit to the main dust
disk. Results of our modeling are compared with the STIS observations.


title: The Stellar Content and Distance of UGC 4483

abstract:
  We present HST/WFPC2 observations of UGC 4483, an irregular galaxy in the
M81/NGC 2403 complex. Stellar photometry was carried out with HSTphot, and is
complete to V ~ 26.0 and I ~ 24.7. We measure the red giant branch tip at I =
23.56 +/- 0.10 and calculated a distance modulus of (m-M)o = 27.53 +/- 0.12
(corresponding to a distance of 3.2 +/- 0.2 Mpc), placing UGC 4483 within the
NGC 2403 subgroup. We were able to measure properties of a previously-known
young star cluster in UGC 4483, finding integrated magnitudes of V = 18.66 +/-
0.21 and I = 18.54 +/- 0.10 for the stellar contribution (integrated light
minus Halpha and [OIII] contribution), corresponding to an age of ~10-15 Myr
and initial mass of ~10^4 Msun. This is consistent with the properties of the
cluster's brightest stars, which were resolved in the data for the first time.
Finally, a numerical analysis of the galaxy's stellar content yields a roughly
constant star formation rate of 1.3x10^-3 Msun/yr and mean metallicity of
[Fe/H] = -1.3 dex from 15 Gyr ago to the present.


title: Large scale dynamos with helicity loss through boundaries

abstract:
  Dynamo action is investigated in simulations of locally isotropic and
homogeneous turbulence in a slab between open boundaries. It is found that a
`pseudo-vacuum' boundary condition (where the field is vertical) leads to
strong helicity fluxes which significantly reduce the amplitude of the
resulting large scale field. On the other hand, if there is a conducting halo
outside the dynamo-active region the large scale field amplitude can reach
larger values, but the time scale after which this field is reached increases
linearly with the magnetic Reynolds number. In both cases most of the helicity
flux is found to occur on large scales. From the variety of models considered
we conclude that open boundaries tend to lower the saturation field strength
compared to the case with periodic boundaries. The rate at which this lower
saturation field strength is attained is roughly independent of the strength of
the turbulence and of the boundary conditions. For dynamos with less helicity,
however, significant field strengths could be reached in a shorter time.


title:
The Cyclotron Fundamental Exposed in the High-Field Magnetic Variable
  V884 Her

abstract:
  High-quality phase-resolved optical spectropolarimetry is presented for the
magnetic cataclysmic variable V884 Her. The overall circular polarization
during active accretion states is low and only slightly variable in the range
5000-8000A. However, the polarization is highly structured with wavelength,
showing very broad polarization humps, narrow features that are associated with
weak absorption lines in the total spectral flux, and sharp reversals across
each major emission line. The polarization reversals arise from Zeeman
splitting in the funnel gas in a longitudinal magnetic field B~30kG. The set of
narrow, polarized absorption features matches the Zeeman pattern of hydrogen
for a nearly uniform magnetic field of B=150MG, indicating that the features
are "halo" absorption lines formed in a relatively cool reversing layer above
the shock. With this identification, the broad polarization humps centered near
7150A and below 4000A are assigned to cyclotron emission from the fundamental
and first harmonic (n=2), respectively. V884 Her is only the second AM Her
system known with a field exceeding 100MG, and the first case in which the
cyclotron fundamental has been directly observed from a magnetic white dwarf.


title:
Deep BVR photometry of the Chandra Deep Field South from the COMBO-17
  survey

abstract:
  We report on deep multi-color imaging (R_5-sigma = 26) of the Chandra Deep
Field South, obtained with the Wide Field Imager (WFI) at the MPG/ESO 2.2 m
telescope on La Silla as part of the COMBO-17 survey. As a result we present a
catalog of 63501 objects in a field measuring 31.5' x 30' with astrometry and
BVR photometry. A sample of 37 variable objects is selected from two-epoch
photometry. We try to give interpretations based on color and variation
amplitude.


title:
Cosmological Parameters and Hyper-Parameters: The Hubble Constant from
  Boomerang and Maxima

abstract:
  We generalise the procedure for joint estimation of cosmological parameters
to allow freedom in the relative weights of various probes. This is done by
including in the joint Likelihood function a set of 'Hyper-Parameters', which
are dealt with using Bayesian considerations. The resulting algorithm is simple
to implement. We illustrate the method by estimating the Hubble constant H_0
from the recent Cosmic Microwave Background experiments Boomerang and Maxima.
For an assumed flat Lambda-CDM model with fixed parameters (n=1, Omega_m =
1-lambda = 0.3, Omega_b h^2 = 0.03, Qrms = 18 mu K) we solve for a single
parameter, H_0= 79 +- 4 km/sec/Mpc (95 % CL, random errors only), slightly
higher but still consistent with recent results from Cepheids. We discuss how
the 'Hyper-Parameters' approach can be generalised for a combination of cosmic
probes, and for other priors on the Hyper-Parameters.


title:
Intrinsic intraday variability in the gravitational lens system
  B0218+357

abstract:
  Radio monitoring of the gravitational lens system B0218+357 reveals it to be
a highly variable source with variations on timescales of a few days correlated
in both images. This shows that the variability is intrinsic to the background
lensed source and suggests that similar variations in other intraday variable
sources can also be intrinsic in origin.


title:
Axisymmetric Modes of Rotating Relativistic Stars in the Cowling
  Approximation

abstract:
  Axisymmetric pulsations of rotating neutron stars can be excited in several
scenarios, such as core-collapse, crust and core-quakes and binary mergers and
could become detectable either in gravitational waves or high-energy radiation.
Here, we present a comprehensive study of all low-order axisymmetric modes of
uniformly and rapidly rotating relativistic stars. Initial stationary
configurations are appropriately perturbed and are numerically evolved using an
axisymmetric, nonlinear relativistic hydrodynamics code, assuming
time-independence of the gravitational field (Cowling approximation). The
simulations are performed using a high-resolution shock-capturing
finite-difference scheme accurate enough to maintain the initial rotation law
for a large number of rotational periods, even for stars at the mass-shedding
limit. Through Fourier transforms of the time evolution of selected fluid
variables, we compute the frequencies of quasi-radial and non-radial modes with
spherical harmonic indices l=0,1,2 and 3, for a sequence of rotating stars from
the non-rotating limit to the mass-shedding limit. The frequencies of the
axisymmetric modes are affected significantly by rotation only when the
rotation rate exceeds about 50% of the maximum allowed. As expected, at large
rotation rates, apparent mode crossings between different modes appear. In
addition to the above modes, several axisymmetric inertial modes are also
excited in our numerical evolutions.


title: Cosmic Data Fusion

abstract:
  We compare and combine likelihood functions of the cosmological parameters
Omega_m, h and sigma_8 from the CMB, type Ia supernovae and from probes of
large scale structure. We include the recent results from the CMB experiments
BOOMERANG and MAXIMA-1. Our analysis assumes a flat LambdaCDM cosmology with a
scale-invariant adiabatic initial power spectrum. First we consider three data
sets that directly probe the mass in the Universe, without the need to relate
the galaxy distribution to the underlying mass via a `biasing' relation:
peculiar velocities, CMB and supernovae. We assume a baryonic fraction as
inferred from Big-Bang Nucleosynthesis and find that all three data sets agree
well, overlapping significantly at the 2-sigma level. This therefore justifies
a joint analysis, in which we find a joint best fit point and 95% confidence
limits of Omega_m=0.28 (0.17,0.39), h=0.74 (0.64,0.86), and sigma_8=1.17
(0.98,1.37). Secondly we extend our earlier work on combining CMB, supernovae,
cluster number counts, IRAS galaxy redshift survey data to include BOOMERANG
and MAXIMA-1 data and to allow a free Omega_b h^2. We find that, given our
assumption of a scale invariant initial power spectrum (n=1), we obtain the
robust result of Omega_b h^2= 0.031 +/- 0.03, which is dominated by the CMB
constraint.


title:
Rossby Wave Instability of Thin Accretion Disks - III. Nonlinear
  Simulations

abstract:
  (abridged) We study the nonlinear evolution of the Rossby wave instability in
thin disks using global 2D hydrodynamic simulations. The key questions we are
addressing in this paper are: (1) What happens when the instability becomes
nonlinear? Specifically, does it lead to vortex formation? (2) What is the
detailed behavior of a vortex? (3) Can the instability sustain itself and can
the vortex last a long time? Among various initial equilibria that we have
examined, we generally find that there are three stages of the disk evolution:
(1) The exponential growth of the initial small amplitude perturbations. This
is in excellent agreement with the linear theory; (2) The production of large
scale vortices and their interactions with the background flow, including
shocks. Significant accretion is observed due to these vortices. (3) The
coupling of Rossby waves/vortices with global spiral waves, which facilitates
further accretion throughout the whole disk. Even after more than 20
revolutions at the radius of vortices, we find that the disk maintains a state
that is populated with vortices, shocks, spiral waves/shocks, all of which
transport angular momentum outwards. We elucidate the physics at each stage and
show that there is an efficient outward angular momentum transport in stages
(2) and (3) over most parts of the disk, with an $\alpha$ in the range from
$10^{-4}$ to $10^{-2}$. We show why such vortices prove to be almost ideal
``units'' in transporting angular momentum outwards, namely by positively
correlating the radial and azimuthal velocity components. We find some special
cases in which entropy can remain the same while angular momentum is
transported. We conclude that Rossby wave/vortex instability is an efficient,
purely hydrodynamic mechanism for angular momentum transport in thin disks.


title:
Dynamics of embedded bars and the connection with AGN. I. ISAAC/VLT
  stellar kinematics

abstract:
  We present new stellar kinematical profiles of four galaxy hosts of active
galactic nuclei, using the CO bandhead around 2.3 micron with the ISAAC/VLT
spectrograph. We find that the nuclear bars or discs, embedded in large-scale
primary bars, have all a decoupled kinematics, in the sense that the maximum of
the rotational velocity occurs in the nuclear region. In three cases (NGC 1097,
NGC 1808 and NGC 5728), the velocity dispersion displays a significant drop at
the nucleus, a rarely observed phenomenon. We also detect kinematical
asymmetries (m=1 mode) along the nuclear bar major-axis of NGC 1808 and NGC
5728, dynamical counterparts of corresponding asymmetries in the surface
brightness. We have derived simple dynamical models in an attempt to fit the
kinematics of each galaxy and reconstruct the full velocity field. For all four
targets, the fits are good, and confirm the presence of the decoupled nuclear
components. These models cannot however reproduce the observed central drop in
the dispersion. We suggest that this drop is due to a transient cold nuclear
disc, fuelled by gas inflow along the bar, that has recently formed new stars.


title:
Diffuse Gas and LMXBs in the Chandra Observation of the S0 Galaxy NGC
  1553

abstract:
  We have spatially and spectrally resolved the sources of X-ray emission from
the X-ray faint S0 galaxy NGC 1553 using an observation from the Chandra X-ray
Observatory. The majority (70%) of the emission in the 0.3 - 10.0 keV band is
diffuse, and the remaining 30% is resolved into 49 discrete sources. Most of
the discrete sources associated with the galaxy appear to be low mass X-ray
binaries (LMXBs). The luminosity function of the LMXB sources is well-fit by a
broken power-law with a break luminosity comparable to the Eddington luminosity
for a 1.4 solar mass neutron star. It is likely that those sources with
luminosities above the break are accreting black holes and those below are
mostly neutron stars in binary systems. Spectra were extracted for the total
emission, diffuse emission, and sum of the resolved sources; the spectral fits
for all require a model including both a soft and hard component. The diffuse
emission is predominately soft while the emission from the sources is mostly
hard. Approximately 24% of the diffuse emission arises from unresolved LMXBs,
with the remainder resulting from thermal emission from hot gas. There is a
very bright source at the projected position of the nucleus of the galaxy. The
spectrum and luminosity derived from this central source are consistent with it
being an AGN; the galaxy also is a weak radio source. Finally, the diffuse
emission exhibits significant substructure with an intriguing spiral feature
passing through the center of the galaxy. The X-ray spectrum and surface
brightness of the spiral feature are consistent with adiabatic or shock
compression of ambient gas, but not with cooling. This feature may be due to
compression of the hot interstellar gas by radio lobes or jets associated with
the AGN.


title:
A Mid-Infrared Study of the Young Stellar Population in the NGC 2024
  Cluster

abstract:
  We present the results of the first broadband 10.8 um survey of the NGC 2024
cluster. The mid-infrared data were combined with our previously published JHKL
photometry in order to construct spectral energy distributions for all detected
sources. The main scientific goals were to investigate the nature of the young
stellar objects (YSOs) in the cluster, and to examine the efficiency of
detecting circumstellar disk sources from near-infrared JHKL color-color
diagrams. Out of 59 sources surveyed having K-band magnitudes K < 10.5, we
detected 35 (~59%) at 10 um. Combining these detections, and upper limits for
the non-detections, with existing JHKL data, we identify 1 Class I, 6 flat
spectrum, 28 Class II and 5 Class III sources. We find a circumstellar disk
fraction for NGC 2024 of ~85% +/- 15%, which confirms earlier published
suggestions that the majority, if not all, of the stars in NGC 2024 formed with
disks, and these disks still exist at the present time. In addition, all but
one of the disk sources identified in our survey lie in the infrared excess
region of the JHKL color-color diagram for the cluster. This demonstrates that
JHKL color-color diagrams are extremely efficient in identifying YSOs with
disks. Of the 14 sources with K - L colors suggestive of protostellar objects,
\~29% are protostellar in nature, while ~7% are true Class I YSOs. This may be
due to extinction producing very red K - L colors in Class II YSOs, thus making
them appear similar in color to protostars. This suggests caution must be
applied when estimating the sizes and lifetimes of protostellar populations
within star forming regions based on K - L colors alone. Finally, we calculate
the luminosities of the Class II YSOs in NGC 2024, rho Oph and Taurus and
discuss the results.


title: Cosmic Particle Acceleration: Basic Issues

abstract:
  Cosmic-rays are ubiquitous, but their origins are surprisingly difficult to
understand. A review is presented of some of the basic issues common to cosmic
particle accelerators and arguments leading to the likely importance of
diffusive shock acceleration as a general explanation. The basic theory of
diffusive shock acceleration is outlined, followed by a discussion of some of
the key issues that still prevent us from a full understanding of its outcomes.
Some recent insights are mentioned at the end that may help direct ultimate
resolution of our uncertainties.


title:
The Origin of the Magnetic Fields of the Universe: The Plasma
  Astrophysics of the Free Energy of the Universe

abstract:
  (abridged) The interpretation of Faraday rotation measure maps of AGNs within
galaxy clusters has revealed regions, $\sim 50-100$ kpc, that are populated
with large, $\sim 30 \mu$ G magnetic fields. The magnetic energy of these
coherent regions is $\sim 10^{59-60}$ ergs, and the total magnetic energy over
the whole cluster ($\sim 1$ Mpc across) is expected to be even larger. A
sequence of physical processes that are responsible for the production,
redistribution and dissipation of these magnetic fields is proposed. These
fields are associated with single AGNs within the cluster and therefore with
all galaxies during their AGN phase, simply because only the central
supermassive black holes ($\sim 10^8 M_{\odot}$) have an accessible energy,
$\sim 10^{61}$ ergs. We propose an $\alpha-\Omega$ dynamo process in an
accretion disk. The disk rotation naturally provides a large winding number,
$\sim 10^{11}$ turns, sufficient to make both large gain and large flux. The
helicity of the dynamo can be generated by the differential plume rotation
derived from star-disk collisions. This helicity generation process has been
demonstrated in the laboratory and the dynamo gain was simulated numerically. A
liquid sodium analog of the dynamo is being built. Speculations are that the
back reaction of the saturated dynamo will lead to the formation of a
force-free magnetic helix, which will carry the energy and flux of the dynamo
away from the accretion disk and redistribute the field within the clusters and
galaxy walls. The magnetic reconnection of a small fraction of this energy
logically is the source of the AGN luminosity, and the remainder of the field
energy should then dominate the free energy of the present-day universe.


title: [O II] as a tracer of current star formation

abstract:
  [O II] lambda 3727 Angstrom is often used as a tracer of star formation at
intermediate redshifts (z > 0.4), where Halpha is not easily observed. We use
the spectrophotometric data of the Nearby Field Galaxy Survey to investigate
the range and systematic variation in observed [O II]/Halpha emission line
ratio as a function of galaxy luminosity at low redshift. We find that the
observed [O II]/Halpha ratio varies by a factor of 7 at luminosities near M_B*.
The [O II]/Halpha ratio is inversely correlated with luminosity. The scatter in
the [O II]/Halpha ratio and the dependence of the ratio on luminosity are due
in equal parts to reddening and to the metallicity dependent excitation of the
ISM. The uncertainty in star formation rates derived from [O II] fluxes is
therefore large. If Halpha cannot be observed, high S/N Hbeta fluxes are much
preferable to [O II] fluxes for deriving star formation rates. We present
several purely empirical corrections for extinction.


title: Chandra studies of star forming regions

abstract:
  When observed with sufficiently high spatial resolution and sensitivity, star
formation regions are unusually complex X-ray sources. Low-mass protostars and
T Tauri stars, Herbig Ae/Be stars, OB and Wolf-Rayet stars are seen at levels
$28 \leq \log L_x \leq 34$ erg/s. High-amplitude variability from magnetic
reconnection flares are often present. From past star formation episodes,
supernova remnants and X-ray binary systems may dominate the emission on large
scales. Astrophysically, ionization of molecular material from yount stellar
X-rays which may have important consequences for circumstellar disk evolution,
bipolar flow ejection and star formation.
  We report here early results from Chandra X-ray Observatory studies of a wide
range of star forming regions using the ACIS camera. They include portions of
the nearby Ophiuchus and Perseus clouds, the Orion Nebula Cluster (ONC) and
elsewhere in the Orion giant molecular clouds, molecular clouds and star
clusters around the Galactic Center, the 30 Doradus region of the LMC, and the
prototype starburst galaxy M 82.


title:
AB Dor in '94: I. HST/GHRS Observations of the Quiescent Chromosphere of
  an Active Star

abstract:
  We analyze HST/GHRS spectra of AB Doradus, the prototypical ultra-rapidly
rotating K dwarf. We observed chromospheric (Mg II) and transition region (C
II, Si IV, C IV, and N V) lines periodically throughout the stellar rotation
period, and provide a low dispersion stellar atlas of 78 emission lines. The
quiescent line profiles of the chromospheric and transition region lines show
narrow cores superposed on very broad wings. The broad wings of the Mg II k & h
lines and of the transition region lines can be explained by emission from gas
co-rotating with the star and extending out to near the Keplerian co-rotation
radius (2.8 stellar radii). While this is not a unique solution, it is
consistent with previous studies of H-alpha emission that are naturally
explained by large co-rotating prominences. We find no evidence for rotational
modulation of the emission line fluxes. The density diagnostics suggest that
the transition region is formed at constant pressure, with an electron density
2-3 E12 /cm^3 at a temperature of 30,000 K. The electron pressure is about 100
times larger than that for the quiet Sun. The emission measure distribution
shows a minimum between log(T) = 5 and 5.5. The Mg II line exhibits three
interstellar absorption components along the 15 pc line of sight. We identify
the lowest velocity component with the G cloud, but the other components are
not identified with any interstellar clouds previously detected from other
lines of sight.


title:
Changes in the structure of the accretion disc of EX Draconis through
  the outburst cycle

abstract:
  (Abridged) We report on the analysis of high-speed photometry of the dwarf
nova EX Dra through its outburst cycle with eclipse mapping techniques. The
eclipse maps show evidence of the formation of a one-armed spiral structure in
the disc at the early stages of the outburst and reveal how the disc expands
during the rise until it fills most of the primary Roche lobe at maximum light.
The eclipse maps also suggest the presence of an inward and an outward-moving
heating wave during the rise and an inward-moving cooling wave in the decline.
Our results suggest a systematic deceleration of both the heating and the
cooling waves as they travel across the disc, in agreement with predictions of
the disc instability model. The analysis of the brightness temperature profiles
indicates that most of the disc appears to be in steady-state during quiescence
and at outburst maximum, but not during the intermediate stages. As a general
trend, the mass accretion rate in the outer regions is larger than in the inner
disc on the rising branch, while the opposite holds during the decline branch.
We estimate a mass accretion rate of Mdot= 10^{-8} Msun/yr at outburst maximum
and Mdot= 10^{-9.1} Msun/yr in quiescence. The brightness temperature profile
in quiescence also suggests that the viscosity parameter is high at this stage
which favours the mass-transfer instability model. The uneclipsed light has a
steady component, understood in terms of emission from the red secondary star,
and a variable component that is proportional to the out of eclipse flux and
corresponds to about 3 per cent of the total brightness of the system. The
variable component is interpreted as arising in a disc wind.


title: Exploration of Large Digital Sky Surveys

abstract:
  We review some of the scientific opportunities and technical challenges posed
by the exploration of the large digital sky surveys, in the context of a
Virtual Observatory (VO). The VO paradigm will profoundly change the way
observational astronomy is done. Clustering analysis techniques can be used to
discover samples of rare, unusual, or even previously unknown types of
astronomical objects and phenomena. Exploration of the previously poorly probed
portions of the observable parameter space are especially promising. We
illustrate some of the possible types of studies with examples drawn from
DPOSS; much more complex and interesting applications are forthcoming.
Development of the new tools needed for an efficient exploration of these vast
data sets requires a synergy between astronomy and information sciences, with
great potential returns for both fields.


title:
Maximum Particle Energies by Fermi Acceleration and the Origin of Cosmic
  Rays above the Knee

abstract:
  We derive the maximum accelerated particle energy from first-order and
second-order Fermi acceleration at nonrelativistic and relativistic shocks for
explosions taking place in a uniform surrounding medium. Second-order
stochastic processes in relativistic flows are shown to be capable of
accelerating cosmic rays to ultra-high energies. Cosmic rays above the knee of
the cosmic ray spectrum can be accelerated by the second-order Fermi mechanism
in relativistic flows, such as those occuring in gamma-ray bursts and unusual
supernovae like SN 1998bw.


title: Simulations of Incompressible MHD Turbulence

abstract:
  We simulate incompressible MHD turbulence in the presence of a strong
background magnetic field. Our major conclusions are: 1) MHD turbulence is most
conveniently described in terms of counter propagating shear Alfven and slow
waves. Shear Alfven waves control the cascade dynamics. Slow waves play a
passive role and adopt the spectrum set by the shear Alfven waves, as does a
passive scalar. 2) MHD turbulence is anisotropic with energy cascading more
rapidly along k_perp than along k_parallel, where k_perp and k_parallel refer
to wavevector components perpendicular and parallel to the local magnetic
field. Anisotropy increases with increasing k_perp. 3) MHD turbulence is
generically strong in the sense that the waves which comprise it suffer order
unity distortions on timescales comparable to their periods. Nevertheless,
turbulent fluctuations are small deep inside the inertial range compared to the
background field. 4) Decaying MHD turbulence is unstable to an increase of the
imbalance between the flux of waves propagating in opposite directions along
the magnetic field. 5) Items 1-4 lend support to the model of strong MHD
turbulence by Goldreich & Sridhar (GS). Results from our simulations are also
consistent with the GS prediction gamma=2/3. The sole notable discrepancy is
that 1D power law spectra, E(k_perp) ~ k_perp^{-alpha}, determined from our
simulations exhibit alpha ~ 3/2, whereas the GS model predicts alpha = 5/3.


title:
Consequences on variable Lambda-models from distant Type Ia supernovae
  and compact radio sources

abstract:
  We study the m-z relation for Type Ia supernovae data and the \theta-z
relation for the updated compact radio sources data in 4 variable \Lambda-
models: \Lambda \sim S^{-2}, \Lambda \sim H^2, \Lambda \sim \rho and \Lambda
\sim t^{-2}.
  It is found that all the models fit the data sets equally well and require
non-zero, positive values of \Lambda. The supernovae data favour an
accelerating expansion of the universe whereas the radio sources data imply
either sign of the deceleration parameter. The estimates of the density
parameter for the variable \Lambda-models are found higher than those for the
constant \Lambda-Friedmann model. It is also found that the Gurvits et al'
model (FRW model with \Lambda=0) is not the best-fitting model for the constant
\Lambda case. The best-fitting Friedmann model (with constant \Lambda) is found
to be a low density, vacuum-dominated accelerating universe. However, for
realistic values of the matter density parameter, the only interesting
solutions are (a) estimated from the supernovae data: the best-fit solutions
for the flat models (including the constant \Lambda case); (b) estimated from
the radio sources data: the global best-fit solutions for the models \Lambda
\sim H^2 and \Lambda \sim \rho, the best-fit solution for the flat model with
\Lambda=constant and the Gurvits et al' model.
  It is noted that, as in the case of recent CMB analyses, the data sets seem
to favour a spherical universe (k>0).


title:
Cluster AgeS Experiment: The Age and Distance of the Globular Cluster
  omega Centauri Determined from Observations of the Eclipsing Binary OGLEGC17

abstract:
  We use masses, radii, and luminosities of the detached eclipsing binary
OGLEGC17 derived from photometric and spectroscopic observations to calculate
the age and distance of the globular cluster omega Cen. Age versus turnoff mass
and age versus luminosity relations from Girardi et al. (2000) yield two
independent estimates of the age, 9.1<t<16.7 Gyr and 12.9<t<18.5 Gyr. The
distance and distance modulus derived by use of the infrared versus surface
brightness relation are d =5385+-300 pc and (m-M)_V=14.06+-0.11. Distances
derived from our infrared surface brightness versus color relation and the Teff
versus B-V color relation of Sekiguchi & Fukugita (2000) disagree by about 10
per cent. Major improvements in the accuracy in estimated age and distance can
be made with better measurements of the masses of the components of OGLEGC17.


title: Testing Hydrodynamic Models of LMC X-4 with UV and X-ray Spectra

abstract:
  We compare the predictions of hydrodynamic models of the LMC X-4 X-ray binary
system with observations of UV P Cygni lines with the GHRS and STIS
spectrographs on the Hubble Space Telescope. The hydrodynamic model determines
density and velocity fields of the stellar wind, wind-compressed disk,
accretion stream, Keplerian accretion disk, and accretion disk wind. We use a
Monte Carlo code to determine the UV P Cygni line profiles by simulating the
radiative transfer of UV photons that originate on the star and are scattered
in the wind. The qualitative orbital variation predicted is similar to that
observed, although the model fails to reproduce the strong orbital asymmetry
(the observed absorption is strongest for phi>0.5). The model predicts a
mid-eclipse X-ray spectrum, due almost entirely to Compton scattering, with a
factor 4 less flux than observed with ASCA. We discuss how the model may need
to be altered to explain the spectral variability of the system.


title: Present Status of Diffusive Shock Acceleration

abstract:
  Diffusive shock acceleration (DSA) is now widely accepted as the model to
explain the production of cosmic rays (CRs) in a wide range of astrophysical
environments. Despite initial successes of the theory in explaining the
energetics and the spectrum of CRs accelerated by supernova remnants, there
still remain some unresolved issues such as particle injection out of the
thermal plasma at shocks, CR diffusion due to the self-generated MHD waves and
yet-to-be-detected gamma-ray emission due to the ionic CRs. Recent technical
advancements to resolve these issues are reviewed.


title: A Free Boundary Problem in the Theory of the Stars

abstract:
  We investigate numerically models of the static spherically symmetric
boson-fermion stars in the scalar-tensor theory of gravity with massive dilaton
field. The proper mathematical model of such stars is interpreted as a
nonlinear two-parametric eigenvalue problem with unknown internal boundary. To
solve this problem the Continuous Analogue of Newton Method is used.


title: Error estimation for the MAP experiment

abstract:
  We report here the first full sky component separation and CMB power spectrum
estimation using a Wiener filtering technique on simulated data from the
upcoming MAP experiment, set to launch in early 2001. The simulations included
contributions from the three dominant astrophysical components expected in the
five MAP spectral bands, namely CMB radiation, Galactic dust, and synchrotron
emission. We assumed a simple homogeneous and isotropic white noise model and
performed our analysis up to a spherical harmonic multipole lmax=512 on the
fraction of the sky defined by b>20 degrees. We find that the reconstruction
errors are reasonably well fitted by a Gaussian with an rms of 24 $\mu $K, but
with significant deviations in the tails. Our results further support the
predictions on the resulting CMB power spectrum of a previous estimate by
Bouchet and Gispert (1999), which entailed a number of assumptions this work
removes.


title:
Semi analytic approach to understanding the distribution of neutral
  hydrogen in the universe: Comparison of simulations with observations

abstract:
  Following Bi & Davidsen (1997), we perform one dimensional semi analytic
simulations along the lines of sight to model the intergalactic medium (IGM).
Since this procedure is computationally efficient in probing the parameter
space -- and reasonably accurate -- we use it to recover the values of various
parameters related to the IGM (for a fixed background cosmology) by comparing
the model predictions with different observations. For the currently favoured
LCDM model (\Omega_m=0.4, \Omega_{\Lambda}=0.6 and h=0.65), we obtain, using
statistics obtained from the transmitted flux, constraints on (i) the
combination f=(\Omega_B h^2)^2/J_{-12}, where \Omega_B is the baryonic density
parameter and J_{-12} is the total photoionisation rate in units of 10^{-12}
s^{-1}, (ii) temperature T_0 corresponding to the mean density and (iii) the
slope \gamma of the effective equation of state of the IGM at a mean redshift z
\simeq 2.5. We find that 0.8 <(T_0/10^4 K)< 2.5 and 1.3<\gamma<2.3. while the
constraint obtained on f is 0.020^2<f<0.032^2. A reliable lower bound on
J_{-12} can be used to put a lower bound on \Omega_B h^2, which can be compared
with similar constraints obtained from Big Bang Nucleosynthesis (BBN) and CMBR
studies. We find that if J_{-12}>1.2, the lower bound on \Omega_B h^2 is in
violation of the BBN value.


title: Clustered vs. Isolated Star Formation

abstract:
  I argue that star formation is controlled by supersonic turbulence, drawing
for support on a number of 3D hydrodynamical and MHD simulations as well as
theoretical arguments. Clustered star formation appears to be a natural result
of a lack of turbulent support, while isolated star formation is a signpost of
global turbulent support.


title: Starburst Clusters in Galactic Nuclei

abstract:
  Galactic nuclei often harbor a disproportionately large amount of star
formation activity with respect to their surrounding disks. Not coincidentally,
the density of molecular material in galactic nuclei is often also much greater
than that in disks (Table 1 in Kennicutt 1998). The interplay between rich
populations of young stars and dense molecular environments is evident in our
own Galactic center, which hosts over 10% of Galactic star formation activity
within only $<$0.1% of the volume of the Galactic disk. Data obtained with the
VLA and HST reveal a variety of star forming sites in the Galactic Center,
including a substantial population of stars that are formed in very dense and
massive clusters, while other stars are formed in somewhat sparsely populated
associations of massive stars. Indeed, three of the stellar clusters are the
most massive and densest in the Galaxy. In this paper, we discuss the Galactic
center environment and its compact young star clusters, and compare them to
their counterparts in star forming galactic nuclei, concluding that dense
molecular environments and large velocity dispersions combine to alter star
formation activity in both cases, particularly as regards massive young
clusters.


title:
Deep-Imaging Observations of a Candidate of an Absorbed QSO at z=0.653,
  AX J131831+3341

abstract:
  The results of deep-imaging observations of a candidate of an absorbed QSO at
z=0.653, AX J131831+3341, are presented. AX J131831+3341 was found during the
course of optical follow-up observations of the ASCA Large Sky Survey, and has
an X-ray luminosity of 10^{45} erg s^{-1} (2-10keV), which corresponds to those
of QSOs. Its optical spectrum shows no significant broad H_beta emission line,
suggesting that the object is an absorbed QSO. Deep R and V band images reveal
the presence of a point-like nucleus and an asymmetric extended component. The
nuclear component has a blue color, and the optical magnitude is much fainter
than that expected from the observed X-ray flux for typical type-1 AGNs. These
photometric properties and the presence of broad MgII 2800A emission can be
explained simultaneously if the observed nuclear light is dominated by
scattered nuclear light, though there is a possibility that the nuclear
component is a slightly absorbed nucleus if its intrinsic X-ray to optical flux
ratio is the largest among X-ray selected AGNs. The size of the extended
component, which is thought to be the host galaxy of the QSO, is larger than
those of normal disk galaxies at z=0-0.75, and the absolute magnitude is
similar to those of the brightest host galaxies of QSOs at redshifts smaller
than 0.5. The V-R and R-I colors of the component are consistent with a 1
Gyr-old stellar population model without absorption.


title: An Extremely Red Nucleus in an Absorbed QSO at z=0.65

abstract:
  The results of K-band-imaging observations of a candidate of an absorbed QSO
at z=0.653, AX J131831+3341, are presented. The B-K color of the object is 4.85
mag, which is much redder than optically-selected QSOs. The K-band image shows
nuclear and extended components, the same as in the optical V-, R-, and I-band
images. The nuclear component (I-K = 4.29 mag) is much redder than the
power-law models with energy indices of 0 to -1.0, which well reproduce the V-R
and R-I optical colors of the nuclear component. A heavily absorbed (A_V = 3
mag) nucleus may emerge in the K-band, while optical light may originate from
scattered nuclear light. The I-K color of the extended component is 2.2 mag,
which is consistent with the post-starburst nature of the host galaxy, which is
also suggested from the V-R and R-I colors of the extended component.


title:
The 0.1-200 keV spectrum of the blazar PKS 2005-489 during an active
  state

abstract:
  The bright BL Lac object PKS 2005-489 was observed by BeppoSAX on November
1-2, 1998, following an active X-ray state detected by RossiXTE. The source,
detected between 0.1 and 200 keV, was in a very high state with a continuum
well fitted by a steepening spectrum due to synchrotron emission only. Our
X-ray spectrum is the flattest ever observed for this source. The different
X-ray spectral slopes and fluxes, as measured by various satellites, are
consistent with relatively little changes of the peak frequency of the
synchrotron emission, always located below 10^{17} Hz. We discuss these results
in the framework of synchrotron self-Compton models. We found that for the
BeppoSAX observation, the synchrotron peak frequency is between 10^{15} and
2.5x10^{16} Hz, depending on the model assumptions.


title: Constraining Dark Matter candidates from structure formation

abstract:
  We show that collisional damping of adiabatic primordial fluctuations yields
constraints on the possible range of mass and interaction rates of Dark Matter
particles. Our analysis relies on a general classification of Dark Matter
candidates, that we establish independently of any specific particle theory or
model. From a relation between the collisional damping scale and the Dark
Matter interaction rate, we find that Dark Matter candidates must have
cross-sections at decoupling smaller than $ 10^{-33} \frac{m_{dm}}{1 MeV} cm^2$
with photons and $10^{-37} \frac{m_{dm}}{1 MeV} cm^2$ with neutrinos, to
explain the observed primordial structures of $10^9$ Solar mass. These damping
constraints are particularly relevant for Warm Dark Matter candidates. They
also leave open less known regions of parameter space corresponding to
particles having rather high interaction rates with other species than
neutrinos and photons.


title:
Galactic chemical abundance evolution in the solar neighborhood up to
  the Iron peak

abstract:
  We have developed a detailed standard chemical evolution model to study the
evolution of all the chemical elements up to the iron peak in the solar
vicinity. We consider that the Galaxy was formed through two episodes of
exponentially decreasing infall, out of extragalactic gas. In a first infall
episode, with a duration of $\sim$ 1 Gyr, the halo and the thick disk were
assembled out of primordial gas, while the thin disk formed in a second episode
of infall of slightly enriched extragalactic gas, with much longer timescale.
The model nicely reproduces the main observational constraints of the solar
neighborhood, and the calculated elemental abundances at the time of the solar
birth are in excellent agreement with the solar abundances. By the inclusion of
metallicity dependent yields for the whole range of stellar masses we follow
the evolution of 76 isotopes of all the chemical elements between hydrogen and
zinc. Those results are confronted with a large and recent body of
observational data, and we discuss in detail the implications for stellar
nucleosynthesis.


title: An X-ray and Near-IR spectroscopic analysis of the ULIRG IRAS 05189-2524

abstract:
  We present new, quasi-simultaneous hard X-ray and near-IR spectra of the
ultraluminous infrared galaxy IRAS 05189-2524, and discuss them together with
archival and literature data. The 1.9 Seyfert nucleus is Compton-thin. The
near-IR broad lines are seen in transmission, similarly to the X rays, and the
medium along the line of sight has an Av/Nh ratio definitely lower than
Galactic. The increase in obscuration observed at the latter epoch has (Delta
Av)/(Delta Nh) also less than Galactic, supporting a correlation between the
properties of the obscuring matter and its proximity to the center. The
measured Av is compatible with the broad component of Halpha being seen in
transmission, as opposed to scattering, so that most of the observed
polarization must be due to dichroism. The bolometric luminosity of the AGN,
deduced from the X-ray and line luminosities, falls definitely short of
accounting for the IR luminosity of the galaxy, consistent with its coolish
infrared color.


title:
Star Formation in Clusters: Subclustering, Cloud Fragmentation and the
  Origin of the Stellar IMF

abstract:
  We review recent high spatial resolution millimeter continuum and spectral
line observations of (proto-)cluster regions. These observations reveal that
the mass distribution of prestellar cores is consistent with the initial mass
function for field stars suggesting that the IMF is connected to the molecular
clouds structure or the cloud fragmentation processes, rather than the details
of the star formation mechanism. We discuss the evidence for at-birth
subclustering independently obtained for two separate protoclusters. The
presence of subclustering within coherent subclumps suggests that the
fragmentation process is hierarchical and that young stellar clusters are
assembled by independent substructures. The local (proto-)stellar density and
star formation efficiency within the subclusters are much higher than the
average values for the entire star forming cloud. Unfortunately, current
observations are sparse and limited to the nearest star forming regions, for
spatial resolution and sensitivity considerations, the future millimeter wave
arrays, especially ALMA, will allow to expand considerably the sample of
observed regions.


title: 3EG J2016+3657: Confirming an EGRET Blazar Behind the Galactic Plane

abstract:
  We recently identified the blazar-like radio source G74.87+1.22 (B2013+370)
as the counterpart of the high-energy gamma-ray source 3EG J2016+3657 in the
Galactic plane. However, since most blazar identifications of EGRET sources are
only probabilistic in quality even at high Galactic latitude, and since there
also exists a population of unidentified Galactic EGRET sources, we sought to
obtain additional evidence to support our assertion that 3EG J2016+3657 is a
blazar. These new observations consist of a complete set of classifications for
the 14 brightest ROSAT X-ray sources in the error circle, of which B2013+370
remains the most likely source of the gamma-rays. We also obtained further
optical photometry of B2013+370 itself which shows that it is variable,
providing additional evidence of its blazar nature. Interestingly, this field
contains, in addition to the blazar, the plerionic supernova remnant CTB 87,
which is too distant to be the EGRET source, and three newly discovered
cataclysmic variables, all five of these X-ray sources falling within 16' of
each other. This illustrates the daunting problem of obtaining complete
identifications of EGRET sources in the Galactic plane.


title: Are Silicon Nanoparticles an Interstellar Dust Component?

abstract:
  Silicon nanoparticles (SNPs) have been proposed as the source of the observed
"extended red emission" (ERE) from interstellar dust. We calculate the thermal
emission expected from such particles in a reflection nebula such as NGC 2023,
and in the diffuse interstellar medium (ISM). Pure neutral Si SNPs would emit
at 16.4 micron (um), while Si/SiO2 SNPs (both neutral and charged) produce a
feature at 20 um. Observational upper limits on the 16.4 um and 20 um features
in NGC 2023 impose upper limits of < 1.5 ppm in pure Si SNPs, and or < 0.2 ppm
in Si/SiO2 SNPs. The observed ERE intensity from NGC 2023 then gives a lower
bound on the required photoluminescence efficiency eta. For foreground
extinction A(0.68um) = 1.2, we find eta > 5% for Si SNPs, or eta > 24% for
Si/SiO2 SNPs in NGC 2023. Measurement of the R band extinction toward the
ERE-emitting region could strengthen these lower limits. The ERE emissivity of
the diffuse ISM appears to require > 42% (> 33%) of solar Si abundance in
Si/SiO2 (Si) SNPs. We predict IR emission spectra and show that DIRBE
photometry appears to rule out such high abundances of free-flying SNPs in the
diffuse ISM. If the ERE is due to SNPs, they must be either in clusters or
attached to larger grains. Future observations by SIRTF will be even more
sensitive to the presence of free-flying SNPs.


title: Probing the dark energy: methods and strategies

abstract:
  The presence of dark energy in the Universe is inferred directly from the
accelerated expansion of the Universe, and indirectly, from measurements of
cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3
of the critical density, is very smoothly distributed, and has large negative
pressure. Its nature is very much unknown. Most of its discernible consequences
follow from its effect on evolution of the expansion rate of the Universe,
which in turn affects the growth of density perturbations and the age of the
Universe, and can be probed by the classical kinematic cosmological tests.
Absent a compelling theoretical model (or even a class of models), we describe
the dark energy by an effective equation-of-state w=p_X/\rho_X which is allowed
to vary with time. We describe and compare different approaches for determining
w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies
and clusters, and CMB anisotropy, focusing particular attention on the use of a
sample of several thousand type Ia supernova with redshifts z\lesssim 1.7, as
might be gathered by the proposed SNAP satellite. Among other things, we derive
optimal strategies for constraining cosmological parameters using type Ia
supernovae. While in the near term CMB anisotropy will provide the first
measurements of w, supernovae and number counts appear to have the most
potential to probe dark energy.


title:
Nonlinear Stochastic Biasing of Peaks and Halos: Scale-Dependence,
  Time-Evolution, and Redshift-Space Distortion from Cosmological N-body
  Simulations

abstract:
  We quantify the degree of nonlinearity and stochasticity of the clustering of
biased objects, using cosmological N-body simulations. Adopting the peaks and
the halos as representative biasing models, we focus on the two-point
correlation of the biased objects, dark matter and their cross-correlation.
Especially, we take account of the effect of redshift-space distortion and
attempt to clarify the scale-dependence and the time-dependence by analyzing
the biasing factor and the cross-correlation factor. On small scales,
stochasticity and nonlinearity become appreciable and strongly
object-dependent, especially in redshift space due to the pair-wise velocity
dispersion of the biased objects. Nevertheless, an approximation of
deterministic linear biasing $\delta_{\rm obj}\simeq b_{\rm obj} \delta_{\rm
mass}$ works reasonably well even in the quasi-linear regime $r > 10 h^{-1}$
Mpc, and linear redshift-space distortion explains the clustering amplitudes in
redshift space in this regime.


title: Wolf-Rayet stars and GRB connection

abstract:
  Observed properties of GRBs, WR stars and their CO-cores in the end of
evolution are analyzed. A possible bimodality of the observed GRB energy
distribution ($10^{48}$ erg for GRB9809425; $3\times 10^{51}\div 2\times
10^{54}$ erg for others) is in accord with the bimodal mass distribution of
relativistic objects ($M_{NS}=(1.35\pm 0.15) M_\odot$; $M_{BH}=(4\div 15)
M_\odot$). The peculiarity of SN1998bw can be related to the rotation of the
collapsing CO-core. The expected galactic collapse rate of CO-cores of most
compact WR stars of type WO is $\sim 10^{-5}$ per year, only by one and a half
order of magnitude higher than the GRB rate. The allowance for a gamma-ray
beaming or random outcome of the CO-core collapse due to some instabilities
brings this rate in accordance GRB rate. We argue that WR stars (most probably,
of type WO) can be considered as progenitors of cosmic gamma-ray bursts. Two
types of GRBs are predicted in correspondence with the bimodal mass
distribution of the relativistic objects. Three types of optical afterglows
should appear depending on which CO-core is collapsing: of a single WR star, of
a WR star in a WR+O or a hypothetic WR+(A-M) binary system. We briefly discuss
a model of GRB as a transient phenomenon occurring at early stages of galactic
evolution ($z>1$), when very massive ($M>100 M_\odot$) low-metallicity stars
could form. WR-galaxies can be most probable candidates for GRB host galaxies.


title: Applications of Indirect Imaging techniques in X-ray binaries

abstract:
  A review is given on aspects of indirect imaging techniques in X-ray binaries
which are used as diagnostics tools for probing the X-ray dominated accretion
disc physics. These techniques utilize observed properties such as the emission
line profile variability, the time delays between simultaneous optical/X-ray
light curves curves, the light curves of eclipsing systems and the pulsed
emission from the compact object in order to reconstruct the accretion disc's
line emissivity (Doppler tomography), the irradiated disc and heated secondary
(echo mapping), the outer disc structure (modified eclipse mapping) and the
accreting regions onto the compact object, respectively.


title:
Application of random walk theory to the first order Fermi acceleration
  in shock waves

abstract:
  We formulate the first order Fermi acceleration in parallel shock waves in
terms of the random walk theory. The formulation is applicable to any value of
the shock speed and the particle speed, in particular to the acceleration in
relativistic shocks, as long as large angle scattering is suitable for the
scattering process of particles. We first show that the trajectory of a
particle suffering from large angle scattering can be treated as a random walk
in a moving medium with an absorbing boundary (e.g., the shock front). We
derive an integral equation to determine the density of scattering points of
the random walk, and by solving it approximately we obtain approximate
solutions of the probability density of pitch angle at and the return
probability after the shock crossing in analytical form. These approximate
solutions include corrections of several non-diffusive effects to the
conventional diffusion approximation and we show that they agree well with the
Monte Carlo results for isotropic scattering model for any shock speed and
particle speed. Finally, we give an analytical expression of the spectral index
of accelerated particles in parallel shocks valid for arbitrary shock speed.


title:
Spectral Signature of Wind Generation From The Post-Shock Region in
  GRS1915+105 Accretion Disk

abstract:
  Accretion and outflows are common in systems which include black holes.
Especially important is the case of the well known micro-quasar GRS1915+105 in
our own galaxy, where super-luminal outflows are detected. We present a few
observation which are suggestive of an outflow which is generated very close to
the black hole, within a few tens of Schwarzschild radii. In the presence of
mass loss (e.g., an outflowing wind), the electron density of matter within the
centrifugal pressure supported region (which generates hard X-rays) goes down
and it is easier to cool these electrons by soft photons coming from the
Keplerian disk. If, on the other hand, the post-shock region gains mass from
outside, the spectra would be harder. These properties of spectral `softening'
of the low state and `hardening' of the high state have been detected in
several days of RXTE data of GRS1915+105 which we present here.


title: Oscillations During Thermonuclear X-ray Bursts

abstract:
  High amplitude, nearly coherent X-ray brightness oscillations during
thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer
(RXTE) in early 1996. Spectral and timing evidence strongly supports the
conclusion that these oscillations are caused by rotational modulation of the
burst emission and that they reveal the spin frequency of neutron stars in low
mass X-ray binaries, a long sought goal of X-ray astronomy. Studies carried out
over the past year have led to the discovery of burst oscillations in four new
sources, bringing to ten the number with confirmed burst oscillations. I review
the status of our knowledge of these oscillations and indicate how they can be
used to probe the physics of neutron stars. For a few burst oscillation sources
it has been proposed that the strongest and most ubiquitous frequency is
actually the first overtone of the spin frequency and hence that two nearly
antipodal hot spots are present on the neutron star. This inference has
important implications for both the physics of thermonuclear burning as well as
the mass - radius relation for neutron stars, so its confirmation is crucial. I
discuss recent attempts to confirm this hypothesis for 4U 1636-53, the source
for which a signal at the putative fundamental (290 Hz) has been claimed.


title: Ages and Metallicities of Fornax Dwarf Ellipticals

abstract:
  Narrow band photometry is presented on 27 dwarf ellipticals in the Fornax
cluster. Calibrated with Galactic globular cluster data and spectrophotometric
population models, the colors indicated that dwarf ellipticals have a mean
[Fe/H] of -1.00+/-0.28 ranging from -1.6 to -0.4. The mean age of dwarf
ellipticals, also determined photometrically, is estimated at 10+/-1 Gyrs
compared to 13 Gyrs for bright Fornax ellipticals. Comparison of our
metallicity color and Mg_2 indices demonstrates that the [Mg/Fe] ratio is lower
in dwarf ellipticals than their more massive cousins, which is consistent with
a longer duration of initial star formation to explain their younger ages.
There is a increase in dwarf metallicity with distance from the Fornax cluster
center where core galaxies are, on average, 0.5 dex more metal-poor than halo
dwarfs. In addition, we find the halo dwarfs are younger in mean age compared
to core dwarfs. One possible explanation is that the intracluster medium ram
pressure strips the gas from dwarf ellipticals halting star formation (old age)
and stopping enrichment (low metallicity) as they enter the core.


title: The halo model and numerical simulations

abstract:
  Recently there has been a lot of attention focussed on a virialized
halo-based approach to understanding the properties of the matter and galaxy
power spectrum. A key ingredient in this model is the number and distribution
of galaxies within dark matter halos as a function of mass. This quantity has
been predicted from semi-analytic modeling and from fits to observational data.
Here we present predictions for the occupation number and spatial distribution
of sub-halos based on a high-resolution hydrodynamical simulation including
cooling, star-formation and feedback.


title: A Non-Triggered Burst Supplement to the BATSE Gamma-Ray Burst Catalogs

abstract:
  The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray
Observatory detected gamma-ray bursts (GRBs) with a real-time burst detection
(or "trigger") system running onboard the spacecraft. Under some circumstances,
however, a GRB may not have activated the onboard burst trigger. For example,
the burst may have been too faint to exceed the onboard detection threshold, or
it may have occurred while the onboard burst trigger was disabled for technical
reasons. This paper describes a catalog of 873 "non-triggered" GRBs that were
detected in a search of the archival continuous data from BATSE, recorded
between 1991 December 9.0 and 1997 December 17.0. For each burst, the catalog
gives an estimated source direction, duration, peak flux, and fluence. Similar
data are presented for 50 additional bursts of unknown origin that were
detected in the 25--50 keV range; these events may represent the low-energy
"tail" of the GRB spectral distribution. This catalog increases the number of
GRBs detected with BATSE by 48% during the time period covered by the search.


title: Circumstellar Nebulae in Young Supernova Remnants

abstract:
  Supernovae descendent from massive stars explode in media that have been
modified by their progenitors' mass loss and UV radiation. The supernova ejecta
will first interact with the circumstellar material shed by the progenitors at
late evolutionary stages, and then interact with the interstellar material.
Circumstellar nebulae in supernova remnants can be diagnosed by their small
expansion velocities and high [N II]/H$\alpha$ ratios. The presence of
circumstellar nebulae appears ubiquitous among known young supernova remnants.
These nebulae can be compared to those around evolved massive stars to assess
the nature of their supernova progenitors. Three types of archeological
artifacts of supernova progenitors have been observed in supernovae and/or
young supernova remnants: (1) deathbed ejecta, (2) circumstellar nebulae, and
(3) interstellar bubbles. Examples of these three types are given.


title: Jets and Outflows From Advective Accretion Disks

abstract:
  Jets and outflows must be produced directly from accretion disks and inflows,
especially when the central gravitating objects are compact, such as neutron
stars and black holes, and themselves are {\it not} mass losing. Here, we
review the formation of jets from advective inflows. We show that the
centrifugal pressure supported boundary layer (CENBOL) of the black holes may
play crucial role in producing outflows. CENBOL is not present in Keplerian
disks. Thus energetic jet formation is directly connected to sub-Keplerian
flows close to compact objects.


title: Jets, Disks and Spectral States of Black Holes

abstract:
  We show that outflow rates in jets directly depend on the spectral states of
black holes. In particular, in soft states, when the Comptonized electrons are
cold, outflow rate is close to zero. In hard states, outflow could be steady,
but the rate may be very small -- only a few percent of the inflow. In the
intermediate states, on the other hand, the outflow rate is the highest --
roughly thirty percent of the inflow. In this case, piled up matter below the
sonic surface of the outflow could become optically thick and radiative
processes could periodically cool the outflow and produce very interesting
effects including transitions between burst (high-count or On) and quiescence
(low-count or Off) states such as those observed in GRS 1915+105.


title: Classification of Light curves of the Black Hole Candidate GRS1915+105

abstract:
  The black hole candidate GRS 1915+105 exhibits a rich variety of variability.
Assuming that the earlier paradigm of black hole accretion which includes a
shock is applicable for this system as well, one can classify these
variabilities into four classes. We present light curves of these classes and
discuss the basis of our classification.


title: Advective Flow Paradigm And Microquasar GRS1915+105

abstract:
  Advective accretion disks and winds are the most self-consistent solutions
today. We describe this paradigm briefly and show how it attempts to explain
some of the interesting observations of the galactic microquasar GRS1915+105.


title: Understanding Galactic Black Hole Candidate GRS 1915+105

abstract:
  We interpret observed features of the black hole candidate GRS1915+105 in the
light of the advective flow paradigm. The light curve of this black hole is
seen to be of four classes, Soft, Hard, Semi-Soft and Intermediate. Each class
can display more than one type of light curve making altogether twelve or more
types of light curves. In each type, the mode of accretion may be one or more
of three types: which we identify as HW (hard state with winds), CC (Compton
cooling) and EA (enhanced accretion) respectively. Apart from these three
states there are two more fundamental states in a black hole accretion which
are soft and hard states. We also find that winds and outflows could soften
spectra in hard states and the enhanced accretion could harden the soft states.
These are observed in the spectra of GRS 1915+105. Generally, we find that
advective flow paradigm can satisfactorily explain all the features of the
enigmatic black hole GRS 1915+105.


title:
Fundamental States of Accretion/Jet Configuration and the Black Hole
  Candidate GRS1915+105

abstract:
  Advective disk paradigm of black hole accretion includes self-consistent
formation of shocks and outflows from post-shock region. We apply this paradigm
to understand rich variation of the light curve of the black hole candidate
GRS1915+105. We propose that out of five possible {\it fundamental states} the
black hole candidate GRS1915+105 moves around among three of them creating all
possible observed light curves.


title:
On the source of QPO of the black hole candidate GRS1915+105: some new
  observations and their interpretation

abstract:
  A few classes of the light curve of the black hole candidate GRS 1915+105
have been analyzed in detail. We discover that unlike the previous findings,
QPOs occasionally occur even in the so-called `On' or softer states. Such
findings may require a revision of the accretion/wind scenario of the black
hole candidates. We conjecture that considerable winds which is produced in
`Off' states, cool down due to Comptonization, and falls back to the disk and
creating an excess accretion rate to produce the so-called `On' state. After
the drainage of the excess matter, the disk goes back to the `Off' state. Our
findings strengthen the shock oscillation model for QPOs.


title:
Relation of Light Curve Behaviour with Accretion Rates in Black Hole
  Candidate GRS1915+105

abstract:
  We report some properties of the light curves of GRS 1915+105 and present
their interpretation using the variation of net accretion rate.


title:
Effect of an Accretion Disk on the Gravitational Wave Signal from an
  Inspiralling Binary

abstract:
  Since black holes can only accrete sub-Keplerian matter, a companion black
hole orbiting on a circular and instantaneously Keplerian orbit around a
central, massive black hole in a galactic Centre will loss angular momentum and
energy to the accreting matter. This loss could be a significant fraction of
the loss due to gravitational wave (GW) emission. The corresponding GW signal
would be modified. We discuss this effects in the light of the modern accretion
disk theory.


title: State-or-the-art Accretion and Wind Solutions Around Black Holes

abstract:
  We report all possible basic solutions of an advective disk model and use
them to explain major observations from black hole candidates.


title: Bulk Motion Comptonization - a sure sign of Black Holes

abstract:
  Bulk motion Comptonization utilizes properties of both matter and radiation
close to the horizon of a black hole. Computation with these considerations
produce hard tails of energy spectral slope $\sim 1.5-1.7$. These are the most
direct evidence of the horizon of a black hole. We argue that even in presence
of winds and outflows this property is not likely to change as winds are
negligible in soft states.


title: Future High Energy Neutrino Telescopes

abstract:
  This talk summarizes the main physics goals and basic methods of telescopes
for high energy neutrinos. It reviews the present status of deep underwater
telescopes and sketches the ICECUBE project as an example for a cube kilometer
detector. It is suggested to develop techniques for radio and acoustic
detection hand in hand with big optical arrays. These large arrays should be
complemented by medium-size detectors in the Megaton range.


title:
Generation and Acceleration of Jets from Effective Boundary Layer around
  Black Hole

abstract:
  We propose the processes of generation and radiative acceleration of jets
from the centrifugal pressure dominated boundary layer around a black hole.


title: On Radiative Acceleration of Jets and Outflows from Advective Disks

abstract:
  Jets and outflows are known to form out of advective accretion flows around
black holes. Hard photons from the centrifugal barrier directly hit the
electrons and deposit momentum on them. For optically thick flows such
deposition is not efficient, but for optically thin flows matter could be
accelerated to relativistic speed. In fact, even bound matter could be made
free through successive deposition. We discuss these possibilities.


title: Java-Applet For Radio Spectra Analysis

abstract:
  New services for Clusters of Galaxies Database created in the Astronomical
Institute of SPbU have been constructed. The detailed description of database
and its content is available at http://www.astro.spbu.ru/CLUSTERS/. The
information contained in the database can be used for solution of the specific
astronomical problems. One of these problems is the researches of radio
emission spectra of clusters' objects. The researches can give help in solution
of the problems of origin and evolution of extragalactic radio sources. Spectra
of radio galaxies contain important information about radio power in the
processes responsible for their activity. This report presents the software for
the database that provides work with radio spectra of extragalactic sources.
This client-application has been released as the Java-applet and thus provides
a Web based interface that is supported on many operating systems. The
facilities of the applet such as approximations of spectra measurement points
and calculation of spectral parameters are illustrated in the report. Also we
demonstrate new version of the application that realized on Java2 and gave
access to additional functions such as printing.


title:
Optical and X-ray clusters as tracers of the supercluster-void network.
  I Superclusters of Abell and X-ray clusters

abstract:
  We study the distribution of X-ray selected clusters of galaxies with respect
to superclusters determined by Abell clusters of galaxies and show that the
distribution of X-ray clusters follows the supercluster-void network determined
by Abell clusters. We find that in this network X-ray clusters are more
strongly clustered than other clusters. Poor, non-Abell X-ray clusters follow
the supercluster-void network as well: these clusters are embedded in
superclusters determined by rich clusters and populate filaments between them.
We present a new catalog of superclusters of Abell clusters out to a redshift
of z_{lim}=0.13, a catalog of X-ray clusters located in superclusters
determined by Abell clusters, and a list of additional superclusters of X-ray
clusters.


title:
Optical and X-ray clusters as tracers of the supercluster-void network.
  II The spatial correlation function

abstract:
  We study the space distribution of Abell and X-ray selected clusters of
galaxies from the ROSAT Bright Source Catalog, and determine correlation
functions for both cluster samples. On small scales the correlation functions
depend on the cluster environment: clusters in rich superclusters have a larger
correlation length and amplitude than all clusters. On large scales correlation
functions depend on the distribution of superclusters. On these scales
correlation functions for both X-ray and Abell clusters are oscillating with a
period of ~115 h^{-1} Mpc. This property shows the presence of a dominating
scale in the distribution of rich superclusters.


title:
Optical and X-ray clusters as tracers of the supercluster-void network.
  III Distribution of Abell and APM clusters

abstract:
  We present a comparison of Abell and APM clusters of galaxies as tracers of
the large scale structure of the Universe. We investigate selection functions
of both cluster catalogs. We show that the supercluster-void network can be
traced with both cluster samples; the network has a well-defined period of ~120
h^{-1} Mpc. We calculate the correlation function and the power spectrum for
Abell and APM cluster samples. The APM cluster sample with measured redshifts
covers a small volume which contains only a few very rich superclusters that
surround one void and have exceptionally large mutual separations. Due to this
property the maximum of the power spectrum of APM clusters with measured
velocities is shifted to larger scales than the corresponding feature in the
power spectrum of Abell clusters. We conclude that the APM sample is not
representative for the large-scale structure as a whole due to the small space
coverage. We present a catalog of superclusters of galaxies, based on APM
clusters up to a redshift z_{lim}=0.13.


title:
Further Evidence for Cosmological Evolution of the Fine Structure
  Constant

abstract:
  We describe the results of a search for time variability of the fine
structure constant, alpha, using absorption systems in the spectra of distant
quasars. Three large optical datasets and two 21cm/mm absorption systems
provide four independent samples, spanning 23% to 87% of the age of the
universe. Each sample yields a smaller alpha in the past and the optical sample
shows a 4-sigma deviation: da/a = -0.72 +/- 0.18 x 10^{-5} over the redshift
range 0.5 < z < 3.5. We find no systematic effects which can explain our
results. The only potentially significant systematic effects push da/a towards
positive values, i.e. our results would become more significant were we to
correct for them.

categories: astro-ph gr-qc hep-ph hep-th physics.atom-ph


title:
Innermost stable circular orbits around rotating compact quark stars and
  QPOs

abstract:
  It has been suggested that observations of quasi periodic oscillations (QPOs)
in the X-ray fluxes from low mass X-ray binaries can be used to constrain the
mass of the compact object and the equation of state of its matter. A specific
suggestion that the kHz QPO frequency saturates at the maximum orbital
frequency has been widely considered. We examine rotating compact stars
described by a new model of strange quark matter (Dey et al. 1998). We
calculate the maximum orbital frequencies for both normal and supramassive
strange stars described by the Dey model, and present these frequencies for
sequences of equilibrium models with constant baryon mass. The maximum orbital
frequencies for these compact objects are always higher than the kHz QPO
frequencies observed to date.


title:
Protoneutron stars and constraints on maximum and minimum mass of
  neutron stars

abstract:
  Constraints on minimum and maximum mass of ordinary neutron stars are imposed
by the consideration of their early evolution (protoneutron star stage).
Calculations are performed for a realistic standard model of hot, dense matter
(Lattimer & Swesty 1991) valid for both supranuclear and subnuclear densities.
Various assumptions concerning protoneutron star interior (large trapped lepton
number, no trapped lepton number, isentropic, isothermal) are taken into
account.


title:
The change in the inclination angle of the non-eclipsing binary SS
  Lacertae: future eclipses

abstract:
  Eclipses in the 14.4-day period double-lined binary SS Lac were observed
photographically and visually early in the 20th century, but stopped some 50 or
60 years ago. This has been explained by the presence of a distant third star
in the system, which has now been detected spectroscopically with a period of
679 days. The plane of the orbit of the binary is changing relative to the line
of sight in response to perturbations from this third object. A recent analysis
by Milone et al. (M00) of all photometric material available for the system,
including a re-measurement of original Harvard plates, has confirmed earlier
reports of changes in the depth of the eclipses as a function of time, which
are due to the third star. In this paper we discuss our detailed analysis of
the eclipse amplitude measurements, and extract from them information on the
change in the inclination angle of the binary over the last century. Our use of
a much improved ephemeris for the system by Torres & Stefanik was found to be
crucial, and prompted us to re-determine all the amplitudes from the historical
data at our disposal, including the Harvard material used by M00.
Systematically lower measurements on the branches of the minima were properly
accounted for, and we made use of both a linear approximation to the time
variation of the inclination angle and a more realistic model based on the
theory of three-body interactions ("regression of the nodes" effect). The nodal
cycle is found to be about 600 yr, within which TWO eclipse "seasons" occur,
each lasting about 100 yr. The non-eclipsing status of the system is expected
to continue until the beginning of the 23rd century.


title: Protoneutron stars and neutron stars

abstract:
  We find constraints on minimum and maximum mass of ordinary neutron stars
imposed by their early evolution (protoneutron star stage). We calculate models
of protoneutron stars using a realistic standard equation of state of hot,
dense matter valid for both supranuclear and subnuclear densities. Results for
different values of the nuclear incompressibility are presented.


title: Relativistic models of kHz QPOs

abstract:
  After reviewing the general-relativistic ``gap'' model of accretion, I
discuss its relation to the high frequency quasi-periodic oscillations observed
in low-mass X-ray binaries. The ``300'' Hz frequency seen in some X-ray bursts
may be a relativistic signature of keplerian rotation of the neutron star.


title:
Diffusion and the occurrence of hydrogen shell flashes in helium white
  dwarf stars

abstract:
  We investigate the effects of element diffusion on the structure and
evolution of low-mass helium white dwarfs (WD). Attention is focused on the
occurrence of hydrogen shell flashes induced by diffusion processes during
cooling phases. Initial models from 0.406 to 0.161 solar masses are constructed
by applying mass loss rates at different stages of the RGB evolution of a solar
model. The multicomponent flow equations describing gravitational settling, and
chemical and thermal diffusion are solved and the diffusion calculations are
coupled to an evolutionary code. In addition, the same sequences are computed
but neglecting diffusion. We find that element diffusion strongly affects the
structure and cooling history of helium WD. In particular, diffusion induces
the occurrence of hydrogen shell flashes in models with masses ranging from
0.18 to 0.41 solar masses, which is in sharp contrast from the situation when
diffusion is neglected. In connection with the further evolution, these
diffusion-induced flashes lead to much thinner hydrogen envelopes, preventing
stable nuclear burning from being an appreciable energy source at advanced
stages of evolution. This implies much shorter cooling ages than in the case
when diffusion is neglected. These new WD models are discussed in light of
recent observational data of some millisecond pulsar systems with WD
companions. We find that age discrepancies between the predictions of standard
evolutionary models and such observations appear to be the result of ignoring
element diffusion in such models. Indeed, such discrepancies vanish when
account is made of diffusion.


title: The Formation of Star Clusters

abstract:
  The ability of HST to resolve objects ten times smaller than possible from
the ground has rejuvenated the study of young star clusters. A recurrent
morphological theme found in nearby resolved sytems is the observation of young
(typically 1 - 10 Myr), massive (10**3 - 10**4 M_sun), compact (rho ~ 10**5
M_sun/pc**3) clusters which have evacuated the gas and dust from a spherical
region around themselves. New stars are being triggered into formation along
the edges of the envelopes, with pillars (similar to the Eagle Nebula) of
molecular gas streaming away from the the regions of star formation. The
prototype for these objects is 30 Doradus. Another major theme has been the
discovery of large numbers of young (typically 1 - 500 Myr), massive (10**3 -
10**7 M_sun), compact star clusters in merging, starbursting, and even some
barred and spiral galaxies. The brightest of these clusters have all the
attributes expected of protoglobular clusters, hence allowing us to study the
formation of globular clusters in the local universe rather than trying to
ascertain how they formed ~14 Gyr ago. The prototype is the Antennae Galaxy.


title: Low-mass quark stars as Maclaurin spheroids

abstract:
  We show that in the limit of low masses (M<0.1M solar), the orbital and
rotational frequencies in exact relativistic numerical models of rotating,
axially symmetric, quark stars coincide with those for Maclaurin spheroids. In
particular, when the eccentricity of the spheroid exceeds a critical value
(e>0.83458318), circular orbits in the equatorial plane are unstable for a
range of orbital radii outside the stellar surface. The orbital frequency in
the marginally stable orbit, and all other orbits, around Maclaurin spheroids
goes to zero in the limit e=1. Maximum orbital frequencies in accreting
Galactic X-ray sources may be a poor indication of the source mass.


title: Neutron stars and strong-field effects of general relativity

abstract:
  The basic observed properties of neutron stars are reviewed. I suggest that
neutron stars in low-mass X-ray binaries are the best of all known sites for
testing strong-field effects of general relativity.


title: Characteristics of Astronomy-Related Organizations

abstract:
  Geographical distributions, ages and sizes of astronomy-related organizations
have been investigated from comprehensive and up-to-date samples extracted from
the master files for StarGuides/StarWorlds. Results for professional
institutions, associations, planetariums, and public observatories are
commented, as well as specific distributions for astronomy-related publishers
and commercial-software producers.
  The highly uneven general pattern displayed by geographical distributions is
still very much the same as it was at the beginning of the XXth century, even
if the densities are higher -- another illustration of the well-known
socio-economic effect of self-reinforcement. Other geographical peculiarities
(local concentrations, national cultures and policies, electronic astronomy,
..) are discussed in the paper, as well as the uneasy separation between
amateur and professional astronomers in associations.
  Some events had a clear impact on the rate of foundation of astronomy-related
organizations, such as World Wars I and II, the beginning of space exploration,
the landing of man on the Moon, the end of the Cold War, spectacular comets,
and so on. However, as detailed in the paper, not all of them affected in the
same way Western Europe and North America, nor the various types of
organizations.
  The size of the vast majority of astronomy-related organizations is
relatively small, with again some differences between Western Europe and North
America.


title: Polarized Microwave Radiation from Dust

abstract:
  Observations of cosmic microwave background in the range 10-90 GHz have
revealed an anomalous foreground component well correlated with 12 \mum, 60
\mum and 100 \mum emission from interstellar dust. As the recent
cross-correlation analysis of WHAM H\alpha maps with the Tenerife 10 and 15 GHz
maps supports an earlier conclusion that the emission does not arise from
free-free radiation, the interstellar dust origin of it is left as the only
suspect. Two competing models of this emission exist. The more favored at the
moment is the spinning dust model, the other is the model that uses grains with
strong magnetic response. In the spinning dust model the emission arises from
rapid rotation of ultrasmall grains that have dipole moments, while in the
other model magnetic grains emit due to thermal vibrations of magnetic dipoles.
Both models predict the emission to be partially polarized and this emission
can seriously interfere with the CMB polarization measurements. We discuss
observational signatures that can be used to distinguish and eventually filter
out the polarized component of the microwave dust radiation.


title:
Population clustering as a signal for deconfinement in accreting compact
  stars

abstract:
  We study the evolution of the rotation frequency for accreting compact stars.
The discontinuous change of the moment of inertia of a rapidly rotating star
due to the possible quark core appearance entails a characteristic change in
the spin evolution. Numerical solutions have been performed using a model
equation of state describing the deconfinement phase transition. Trajectories
of spin evolution are discussed in the angular velocity - baryon number plane
(phase diagram) for different accretion scenarios defined by the initial values
of mass and magnetic field of the star, as well as mass accretion rate and
magnetic field decay time. We observe a characteristic increase in the waiting
time when a configuration enters the quark core regime. Overclustering of the
population of Z sources of LMXBs in the phase diagram is suggested as a direct
measurement of the critical line for the deconfinement phase transition since
it is related to the behaviour of the moment of inertia of the compact star.


title: HI observations of luminous infrared galaxy mergers

abstract:
  A total of 19 luminous infrared galaxy mergers, with L_IR~2 10^11 L_sun for
H_0=75 km/s/Mpc, have been observed in the HI line at Nancay and four of them
were observed at Arecibo as well. Of these 19, ten had not been observed
before. Six were clearly detected, one of which for the first time. The
objective was to statistically sample the \HI gas mass in luminous infrared
mergers along a starburst merger sequence where the molecular CO gas content is
already known.


title: The Bell Laboratories (13)CO Survey: Longitude-Velocity Maps

abstract:
  A survey is presented of the Galactic plane in the J=1-0 transition of
(13)CO. About 73,000 spectra were obtained with the 7 m telescope at Bell
Laboratories over a ten-year period. The coverage of survey is (l, b) = (-5 to
117, -1 to +1), or 244 square degrees, with a grid spacing of 3' for |b| < 0.5,
and a grid spacing of 6' for |b| > 0.5. The data presented here have been
resampled onto a 3' grid. For 0.68 km/s channels, the rms noise level of the
survey is 0.1 K on the $T_R^*$ scale. The raw data have been transformed into
FITS format, and all the reduction processes, such as correcting for emission
in the reference positions, baseline removal and interpolation were conducted
within IRAF using the FCRAO task package and additional programs. The reduced
data are presented here in the form of longitude-velocity color maps at each
latitude. These data allow identification and classification of molecular
clouds with masses in excess of ~ 1,000 solar masses throughout the first
quadrant of the Galaxy. Spiral structure is manifested by the locations of the
largest and brightest molecular clouds.


title: The Lyman-Alpha Forest at 1.5 < z < 4

abstract:
  Using high resolution (R ~ 45000), high S/N (20-50) VLT/UVES observations
covering the Lyman-alpha forest at 1.5 < z < 2.4 combined with similar
observations at z > 2.4 from the literature, we have presented the redshift
evolution of the Lyman-alpha forest at 1.5 < z < 4. We applied two parallel
analyses: the tradiational Voigt profile fitting and a statistical measure of
the flux. The general conclusions from both analyses are in good agreement. In
general, the properties of the Lyman-alpha forest at 1.5 < z < 2.4, such as the
different density distribution function, the correlation strengths and the mean
neutral hydrogen opacity, evolve as expected extrapolating from at z > 2.4.
These results suggest the main drive of the redshift evolution of the forest at
1.5 < z < 4 is the Hubble expansion. When combined with the HST observations
from the QSO key project at z < 1.7, a flattening of the line number density
evolution does seem to occur at z ~ 1.2. The result suggests that the ionizing
UV background might not evolve as strongly as a QSO-dominated background,
indicating a contribution to the UV background from galaxies at z < 2. The
lower cut-off Doppler paramter at the fixed column denisty log N = 13.5 shows a
slight increase as z decreases, with a possible local maximum at z ~ 2.9. The
slope of the lower cut-off Doppler parameter is not well-defined with z.
However, it is flatter at z < 3.1 than at z ~ 3.75.


title: Ultra Efficient Internal Shocks

abstract:
  Gamma-ray bursts are believed to originate from internal shocks which arise
in an irregular relativistic wind. The process has been thought to be
inefficient, converting only a few percent of the kinetic energy into
gamma-rays. We define ultra efficient internal shocks as those in which the
fraction of emitted energy is larger than the fraction of energy given to the
radiating electrons at each collision.
  We show that such a scenario is possible and even plausible. In our model,
colliding shells which do not emit all their internal energy are reflected from
each other and it causes subsequent collisions, allowing more energy to be
emitted. As an example, we obtain about 60% overall efficiency even if the
fraction of energy that goes to electrons is $\epsilon_e=0.1$ provided that the
shells' Lorentz factor varies between 10 and $10^4$.
  The numerical temporal profile reflects well the activity of the source which
ejects the shells, though numerous collisions take place in this model.


title: Supernova, Hypernova and Gamma Ray Bursts

abstract:
  Recent observations suggest that gamma ray bursts (GRBs) and their afterglows
are produced by highly relativistic jets emitted in core collapse supernova
explosions (SNe). The result of the event, probably, is not just a compact
object plus a spherical ejecta: within days, a fraction of the parent star
falls back to produce a thick accretion disk around the compact object.
Instabilities in the disk induce sudden collapses with ejection of highly
relativistic ``cannonballs'' of plasma, similar to those ejected by
microquasars. The jet of cannonballs exit the supernova shell/ejecta reheated
by their collision with it, emitting highly forward-collimated radiation which
is Doppler shifted to $\gamma$-ray energy. Each cannonball corresponds to an
individual pulse in a GRB. They decelerate by sweeping up the ionised
interstellar matter in front of them, part of which is accelerated to
cosmic-ray energies and emits synchrotron radiation: the afterglow. The
Cannonball Model cannot predict the timing sequence of these pulses, but it
fares very well in describing the total energy, energy spectrum, and
time-dependence of the individual $\gamma$-ray pulses and afterglows. It also
predicts that GRB pulses are accompanied by detectable short pulses of TeV
neutrinos and sub TeV $\gamma$-rays, that are much more energetic and begin and
peak a little earlier.