title: The Structural Evolution of Substructure

abstract:
  We investigate the evolution of substructure in cold dark matter halos using
N-body simulations of tidal stripping of substructure halos (subhalos) within a
static host potential. We find that halos modeled following the Navarro, Frenk
& White (NFW) mass profile lose mass continuously due to tides from the massive
host, leading to the total disruption of satellite halos with small tidal
radii. The structure of stripped NFW halos depends mainly on the fraction of
mass lost, and can be expressed in terms of a simple correction to the original
NFW profile. We apply these results to substructure in the Milky Way, and
conclude that the dark matter halos surrounding its dwarf spheroidal (dSph)
satellites have circular velocity curves that peak well beyond the luminous
radius at velocities significantly higher than expected from the stellar
velocity dispersion. Our modeling suggests that the true tidal radii of dSphs
lie well beyond the putative tidal cutoff observed in the surface brightness
profile, suggesting that the latter are not really tidal in origin but rather
features in the light profile of limited dynamical relevance. For Draco, in
particular, our modeling implies that its tidal radius is much larger than
derived by Irwin & Hatzidimitriou (1995), lending support to the interpretation
of recent Sloan survey data by Odenkirchen et al. (2001). Similarly, our model
suggests that Carina's halo has a peak circular velocity of ~55 km/s, which may
help explain how this small galaxy has managed to retain enough gas to undergo
several bursts of star formation. Our results imply a close correspondence
between the most massive subhalos expected in a CDM universe and the known
satellites of the Milky Way, and suggest that only subhalos with peak circular
velocities below 35 km/s lack readily detectable luminous counterparts.


title:
X-ray Properties of LINERs and Low-luminosity Seyfert Galaxies Observed
  with ASCA. I. Observations and Results

abstract:
  This paper presents a comprehensive study of the X-ray properties of
low-ionization nuclear emission-line regions (LINERs) and low-luminosity
Seyfert galaxies based on observations obtained with ASCA. We analyzed data of
53 observations of 21 LINERs and 17 low-luminosity Seyferts. X-ray emission has
been detected in all but one object. The X-ray luminosities in the 2-10 keV
band range from 4e39 ergs/s to 5e41 ergs/s, which are 1-3 orders of magnitude
smaller than in classical Seyfert galaxies. The X-ray spectra of most objects
are well described by a canonical model which consists of (1) a soft component
from a thermal plasma with kT<1 keV and (2) a hard component represented by a
power law with a photon index~1.8 or thermal bremsstrahlung emission with kT~10
keV. Several objects do not require the soft thermal component, and their
continua are well fitted by a single power-law model. Some objects show heavy
absorption with column densities in excess of 1e23 cm^-2. We detect in several
objects Fe K line emission with equivalent widths ranging from 50 eV to 2 keV.
Variability on timescales less than a day is uncommon in our sample. By
comparing multiple observations made with ASCA or with published observations
from other satellites, we show that at least eight objects are variable on
timescales of a week to several years. We find that the morphologies of many
objects, both in the soft and hard bands, are consistent with being pointlike
relative to the telescope PSF; a few are clearly extended in either or both
energy bands.


title:
Effect of a wide binary companion to the lens on the astrometric
  behavior of gravitational microlensing events

abstract:
  In this paper, we investigate the effect of a wide binary companion of the
lens on the astrometric behavior of Galactic gravitational microlensing events
and compare it to the effect on the photometric behavior. We find that the wide
binary companion of the lens can affect the centroid motion of images
substantially even if the corresponding light curve appears to be the one of a
standard single point-mass lens event. The relatively significant effect of the
wide binary lens on the astrometric lensing behavior, on one side, calls for
careful consideration of the lens binarity in analyzing the future astrometric
lensing data. On the other side, larger astrometric effect of the companion
makes astrometric lensing an efficient method to detect binary lenses over a
broad range of separations.


title: Dark Matter and the Voids

abstract:
  It is now, generally, believed that the presence of some form of dark matter
is essential to explain the flat rotation curves of galaxies, and anomalous
large velocities of galaxies in the clusters and superclusters. This dark
matter turns out to be too elusive and, so far, there is no direct evidence for
such matter although there is a large variety of candidates proposed by
theoretical models. One would expect that the existence of vast amount of dark
matter would lead to the formation of some dark galaxies or clusters which
could be seen by gravitational lensing events.This could serve as a direct
evidence for dark matter. However, so far, there is no conclusive lensing event
pertaining to that.
  In spite of absence of any direct evidence, there is a consensus among
physicists in favour of some form of non-baryonic dark matter. In this paper,
we take a different viewpoint and would like to view dark matter as an emergent
phenomenon - very much like many such phenomena known in condensed matter
systems.
  We propose here a novel mechanism involving Voids, which can, in principle
give rise to a difference between the gravitational and the inertial mass, and
thereby, create effects similar to the dark matter.


title: Numerical simulations of the cosmic star formation history

abstract:
  The cosmic star formation history in Cold Dark Matter dominated cosmological
scenarios is studied by means of hydrodynamical numerical simulations. In
particular, we explore a low density model with a Lambda-term and two high
density models with different power spectra, all of them being spatially flat.
Our simulations employ a fully nonlinear N-body and Eulerian hydrodynamics
algorithm with a model for star formation and supernovae feedback that depends
on two phenomenological parameters determined in agreement with previous
papers. We find a nearly constant star formation rate beyond z=1, and we
discuss which facts may determine the decrease in the SFR from z=1 to the
present epoch. The Lambda-term cosmology with realistic parameters for star
formation and feedback best reproduces the observed star formation history.


title:
The radio colour-colour diagram of Van der Laan bubbles - an application
  to SS433

abstract:
  A radio "colour-colour" diagram is defined in order to determine the
evolutionary state of synchrotron-emitting plasma bubbles that are ejected
during outbursts in microquasars. We establish the colour-colour diagram for
the plasmons of SS433 observed on 18 April 1998 using VLBI observations. We
show that the radio plasmons are not consistent with a simple expanding sphere
of plasmon. This may indicate that in-situ particle acceleration is taking
place away from the central engine.


title:
IRAS 05358+3543: Multiple outflows at the earliest stages of massive
  star formation

abstract:
  We present a high-angular-resolution molecular line and millimeter continuum
study of the massive star formation site IRAS 05358+3543. The most remarkable
feature is a highly collimated (collimation factor ~10) and massive (>10 M_sun)
bipolar outflow of 1 pc length, which is part of a quadrupolar outflow system.
The three observed molecular outflows forming the IRAS 05358+3543 outflow
system resemble, in structure and collimation, those typical of low-mass
star-forming regions. They might therefore, just like low-mass outflows, be
explained by shock entrainment models of jets. We estimate a mass accretion
rate of 10^{-4) M_sun/yr, sufficient to overcome the radiative pressure of the
central object and to build up a massive star, lending further support to the
hypothesis that massive star formation occurs similarly to low-mass star
formation, only with higher accretion rates and energetics.


title: Tensor Correlations and Pions in Dense Nuclear Matter

abstract:
  The study of tensor correlations and pions in dense matter in astronomical
contexts has recently acquired renewed importance for a number of reasons. One
is the discovery by Akmal, and Pandharipande (Phys. Rev. C56 2261 (1997)) of a
striking increase in tensor correlations in cold matter at densities not far
above that of isospin-symmetric nuclear matter at saturation. A second is that,
according to a calculation by Mayle and Wilson, softening of the equation of
state by the appearance of thermal pions can play an important role. A third is
that the strength of tensor correlations is a crucial ingredient in calculating
rates of neutrino emission and scattering, which are needed in calculations of
stellar collapse and of the cooling of neutron stars. We describe some recent
results for the response of nuclear matter when tensor interactions are taken
into account, and indicate some unresolved issues.


title:
The Detection of Pure Dark Matter Objects with Bent Multiply Imaged
  Radio Jets

abstract:
  When a gravitational lens produces two or more images of a quasar's radio jet
the images can be compared to reveal the presence of small structures along one
or more of the lines of sight. If mass is distributed smoothly on scales of <~
10^7 Msun independent bends in the jet images on milli-arcsecond scales will
not be produced. All three of the well collimated multiply imaged radio jets
that have been mapped on milli-arcsecond scales show some evidence of
independent bends in their images. Using existing data we model the lens system
B1152+199 and show that it likely contains a substructure of mass ~10^5 - 10^7
h^-1 Msun or a velocity dispersion of ~ 10 km/s. An alternative explanation is
that an intrinsic bend in the jet is undetected in one image and magnified in
the other. This explanation is disfavored and future observations could remove
any ambiguity that remains. The probability of a radio jet being bent by small
scale structure both inside and outside of the host lens is then investigate.
The known populations of dwarf galaxies and globular clusters are far too small
to make this probability acceptable. A previously unknown population of massive
dark objects is needed. The standard Cold Dark Matter (CDM) model might be able
to account for the observations if small mass halos are sufficiently compact.
In other cosmological models where small scale structure is suppressed, such as
standard Warm Dark Matter (WDM), the observed bent jets would be very unlikely
to occur.


title:
The scaling relations of early--type galaxies in clusters I. Surface
  photometry in seven nearby clusters

abstract:
  This is the first paper of a series investigating the scaling relations of
early-type galaxies in clusters. Here we illustrate the multi-band imagery and
the image reduction and calibration procedures relative to the whole sample of
22 clusters at 0.05 < z < 0.25. We also present the detailed surface photometry
of 312 early-type galaxies in 7 clusters in the first redshift bin,
z~0.025-0.075. We give for each galaxy the complete set of luminosity and
geometrical profiles, and and a number of global, photometric and morphological
parameters. They have been evaluated taking into account the effects of seeing.
Internal consistency checks and comparisons with data in the literature confirm
the quality of our analysis. These data, together with the spectroscopic ones
presented in the second paper of the series, will provide the local calibration
of the scaling relations.


title: Inter-galactic Shock Acceleration and the Cosmic Gamma-ray Background

abstract:
  We investigate numerically the contribution to the cosmic gamma-ray
background from cosmic-rays ions and electrons accelerated at intergalactic
shocks associated with cosmological structure formation. We show that the
kinetic energy of accretion flows in the low-red-shift inter-galactic medium is
thermalized primarily through moderately strong shocks, which allow for an
efficient conversion of shock ram pressure into cosmic-ray pressure.
Cosmic-rays accelerated at these shocks produce a diffuse gamma-ray flux which
is dominated by inverse Compton emission from electrons scattering off cosmic
microwave background photons. Decay of neutral pi-mesons generated in p-p
inelastic collisions of the ionic cosmic-ray component with the thermal gas
contribute about 30% of the computed emission. Based on experimental upper
limits on the photon flux above 100 MeV from nearby clusters we constrain the
efficiency of conversion of shock ram pressure into relativistic CR electrons
to < 1%. Thus, we find that cosmic-rays of cosmological origin can generate an
overall significant fraction of order 20% and no more than 30% of the measured
gamma-ray background.


title: Searches for the Shell Swept up by the Stellar Wind from Cyg OB2

abstract:
  We investigated the kinematics of ionized gas in an extended (20 degrees by
15 degrees) region containing the X-ray Superbubble in Cygnus with the aim of
finding the shell swept up by a strong wind from Cyg OB2. H-alpha observations
were carried out with high angular and spectral resolutions using a Fabry-Perot
interferometer attached to the 125-cm telescope at the Crimean Observatory of
the Sternberg Astronomical Institute. We detected high-velocity gas motions,
which could result from the expansion of the hypothetical shell at a velocity
of 25-50 km/s. Given the number of OB stars increased by Knoedlseder (2000) by
an order of magnitude, Cyg OB2 is shown to possess a wind that is strong enough
[Lw ~= (1-2)x10^39 erg/s] to produce a shell comparable in size to the X-ray
Superbubble and to a giant system of optical filaments. Based on our
measurements and on X-ray and infrared observations, we discuss possible
observational manifestations of the shell swept up by the wind.


title:
Extended Near-Infrared Emission from Candidate Protostars in the
  Taurus-Auriga Molecular Cloud

abstract:
  We describe near-IR imaging data for a sample of 23 class I sources in the
Taurus-Auriga dark clouds. Combining our data with previous photometry, we
detect brightness variations of 0.1-0.5 mag in many sources. The near-IR
morphologies are consistent with mm continuum measurements. Most (60%) of the
sample are true protostars; the rest may be objects in transition between class
I and class II, T Tauri stars with edge-on disks, or heavily reddened T Tauri
stars.


title: A photoionization model of the compact HII region G29.96-0.02

abstract:
  We present a detailed photoionization model of G29.96-0.02 (hereafter
G29.96), one of the brightest Galactic Ultra Compact HII (UCHII) regions in the
Galaxy. This source has been observed extensively at radio and infrared
wavelengths. The most recent data include a complete ISO (SWS and LWS)
spectrum, which displays a remarkable richness in atomic fine-structure lines.
The number of observables is twice as much as the number available in previous
studies. In addition, most atomic species are now observed in two ionization
stages. The radio and infrared data on G29.96 are best reproduced using a
nebular model with two density components: a diffuse (n_e~680cm-3) extended (~1
pc) component surrounding a compact (~0.1 pc) dense (n_e~57000cm-3) core. The
properties of the ionizing star were derived using state-of-the-art stellar
atmosphere models. CoStar models yield an effective temperature of
\~30^{+2}_{-1} kK whereas more recent non-LTE line blanketed atmospheres with
stellar winds indicate somewhat higher values, Teff~32--38 kK. This range in
Teff is compatible with all observational constraints, including near-infrared
photometry and bolometric luminosity. The range 33-36 kK is also compatible
with the spectral type O5-O8 determined by Watson and Hanson (97) when recent
downward revisions of the effective temperature scale of O stars are taken into
account. The age of the ionizing star of G29.96 is found to be a few 10^6 yr,
much older than the expected lifetime of UCHII regions. Accurate gas phase
abundances are derived with the most robust results being Ne/S=7.5 and N/O=0.43
(1.3 and 3.5 times the solar values, respectively).


title: Loop Corrections to Scalar Quintessence Potentials

abstract:
  The stability of scalar quintessence potentials under quantum fluctuations is
investigated for both uncoupled models and models with a coupling to fermions.
We find that uncoupled models are usually stable in the late universe. However,
the coupling to fermions is severely restricted. We check whether a graviton
induced fermion-quintessence coupling is compatible with this restriction.


title: On the nature of X-ray Bright Optically Normal galaxies

abstract:
  Multiwavelength observations of the hard X-ray selected sources by Chandra
and XMM-Newton surveys have significantly improved our knowledge of the objects
responsible of the hard X-ray background. A surprising finding is the discovery
of a population of optically dull, X-ray bright galaxies emerging at 2-10 keV
fluxes of the order of 10^{-14} erg cm^{-2} s^{-1}. We present preliminary
results of multiwavelength observations of a few objects serendipitously
discovered in the field of XMM-Newton and Chandra observations and intensively
studied at longer wavelengths.


title:
H_3^{++}$ molecular ion in a strong magnetic field: triangular
  configuration

abstract:
  The existence of the molecular ion $H_3^{++}$ in a magnetic field in a
triangular configuration is revised. Variational method with an optimization of
the form of the vector potential (gauge fixing) is used. It is shown that in
the range of magnetic fields $10^8 < B < 10^{11} G$ the system $(pppe)$, with
protons forming an equilateral triangle perpendicular to magnetic line, has a
well-pronounced minimum in the total energy. This configuration is unstable
towards decays $H{-atom} + p + p$ and $H_2^+ + p$. Triangular configuration of
$H_3^{++}$ complements $H_3^{++}$ in the linear configuration which exists for
$B \gtrsim 10^{10} G$.


title:
Soft X-ray Spectroscopy of NGC 1068 with XMM-Newton RGS and Chandra
  LETGS

abstract:
  We present high-resolution soft-X-ray spectra of the prototypical Seyfert 2
galaxy, NGC 1068, taken with XMM-Newton RGS and Chandra LETGS. Its rich
emission-line spectrum is dominated by recombination in a warm plasma (bright,
narrow radiative recombination continua provide the ``smoking gun''), which is
photoionized by the inferred nuclear power-law continuum. Radiative decay
following photoexcitation of resonant transitions is also significant. A
self-consistent model of an irradiated cone of gas is capable of reproducing
the hydrogenic/heliumlike ionic line series in detail. The radial ionic column
densities we infer are consistent with absorption measurements (the warm
absorber) in Seyfert 1 galaxies. This strongly suggests that the emission
spectrum we observe from NGC 1068 emanates from its warm absorber. The observed
extent of the ionization-cone/warm absorber in NGC 1068 of about 300 pc implies
that a large fraction of the gas associated with generic warm absorbers may
typically exist on the hundreds-of-parsec scale rather than much closer to the
nucleus (e.g., less than a parsec). Spatially-resolved spectroscopy using the
LETGS of two distinct emission regions yields two noticeably different spectra.
We show that these differences are solely due to differing radial column
densities. A fairly flat distribution in ionization parameter is necessary to
explain the inferred radial ionic column densities of all spectra. This must
primarily be due to a broad density distribution at each radius, spanning
roughly 0.1-100 cm$^{-3}$. (Abridged)


title:
Redshift-distance Survey of Early-type Galaxies: the ENEARc Cluster
  Sample

abstract:
  This paper presents data on the ENEARc subsample of the larger ENEAR survey
of the nearby early-type galaxies. The ENEARc galaxies belong to clusters and
were specifically chosen to be used for the construction of a D_n-sigma
template. The ENEARc sample includes new measurements of spectroscopic and
photometric parameters (redshift, velocity dispersion, line index Mg_2, and the
angular diameter d_n) as well as data from the literature. New spectroscopic
data are given for 229 cluster early-type galaxies and new photometry is
presented for 348 objects. Repeat and overlap observations with external data
sets are used to construct a final merged catalog consisting of 640 early-type
galaxies in 28 clusters. Objective criteria, based on catalogs of groups of
galaxies derived from complete redshift surveys of the nearby universe, are
used to assign galaxies to clusters. In a companion paper these data are used
to construct the template D_n-sigma distance relation for early-type galaxies
which has been used to estimate galaxy distances and derive peculiar velocities
for the ENEAR all-sky sample.


title: Redshift-distance Survey of Early-type Galaxies: The D_n-sigma Relation

abstract:
  In this paper R-band photometric and velocity dispersion measurements for a
sample of 452 elliptical and S0 galaxies in 28 clusters are used to construct a
template D_n-sigma relation. This template relation is constructed by combining
the data from the 28 clusters, under the assumption that galaxies in different
clusters have similar properties. The photometric and spectroscopic data used
consist of new as well as published measurements, converted to a common system,
as presented in a accompanying paper. The resulting direct relation, corrected
for incompleteness bias, is log{D_n} =1.203 log{sigma} + 1.406; the zero-point
has been defined by requiring distant clusters to be at rest relative to the
CMB. This zero-point is consistent with the value obtained by using the
distance to Virgo as determined by the Cepheid period-luminosity relation. This
new D_n-sigma relation leads to a peculiar velocity of -72 (\pm 189) km/s for
the Coma cluster. The scatter in the distance relation corresponds to a
distance error of about 20%, comparable to the values obtained for the
Fundamental Plane relation. Correlations between the scatter and residuals of
the D_n-sigma relation with other parameters that characterize the cluster
and/or the galaxy stellar population are also analyzed. The direct and inverse
relations presented here have been used in recent studies of the peculiar
velocity field mapped by the ENEAR all-sky sample.


title: Variation of Molecular Cloud Properties across the Spiral Arm in M 51

abstract:
  We present the results of high-resolution 13CO(1-0) mapping observations with
the NRO 45m telescope of the area toward the southern bright arm region of M51,
including the galactic center. The obtained map shows the central depression of
the the circumnuclear ring and the spiral arm structure.The arm-to-interarm
ratio of the 13CO(1-0) integrated intensity is 2-4. We also have found a
feature different from that found in the 12CO results. The 12CO/13CO ratio
spatially varies, and shows high values (~20) for the interarm and the central
region, but low values(~10) for the arm. These indicate that there is a denser
gas in the spiral arm than in the interarm. The distribution of the 13CO shows
a better correspondence with that of the H\alpha emission than with the 12CO in
the disk region, except for the central region. We found that the 13CO emission
is located on the downstream side of the 12CO arm, namely there is an offset
between the 12CO and the 13CO as well as the H\alpha emission. This suggests
that there is a time delay between the accumulation of gas caused by the
density wave and dense gas formation, accordingly star formation. This time
delay is estimated to be ~10^7 yr based on the assumption of galactic rotation
derived by the rotation curve and the pattern speed of M51. It is similar to
the growth timescale of a gravitational instability in the spiral arm of M51,
suggesting that the gravitational instability plays an important role for dense
gas formation.


title: The XMM-Newton SSC Survey of the Galactic Plane

abstract:
  The XMM-Newton Survey Science Center is currently conducting an optical
identification programme of serendipitous EPIC sources at low galactic
latitudes. The aim of this study is to quantify the various populations
contributing to the overall X-ray emission of the Galaxy and elaborate
identification rules that can be later applied to the bulk of the low galactic
latitude EPIC detections. We report here on preliminary results from an optical
campaign performed in two very low b XMM-Newton fields and discuss the
contributions of the various X-ray populations. This paper is presented on
behalf of the Survey Science Center and of the AXIS collaboration.


title: The Magnetohydrodynamics of Convection-Dominated Accretion Flows

abstract:
  Radiatively inefficient accretion flows onto black holes are unstable due to
both an outwardly decreasing entropy (`convection') and an outwardly decreasing
rotation rate (the `magnetorotational instability'; MRI). Using a linear
magnetohydrodynamic stability analysis, we show that long-wavelength modes are
primarily destabilized by the entropy gradient and that such `convective' modes
transport angular momentum inwards. Moreover, the stability criteria for the
convective modes are the standard Hoiland criteria of hydrodynamics. By
contrast, shorter wavelength modes are primarily destabilized by magnetic
tension and differential rotation. These `MRI' modes transport angular momentum
outwards. The convection-dominated accretion flow (CDAF) model, which has been
proposed for radiatively inefficient accretion onto a black hole, posits that
inward angular momentum transport and outward energy transport by
long-wavelength convective fluctuations are crucial for determining the
structure of the accretion flow. Our analysis suggests that the CDAF model is
applicable to a magnetohydrodynamic accretion flow provided the magnetic field
saturates at a sufficiently sub-equipartition value (plasma beta >> 1), so that
long-wavelength convective fluctuations can fit inside the accretion disk.
Numerical magnetohydrodynamic simulations are required to determine whether
such a sub-equipartition field is in fact obtained.


title: Hydrodynamic Simulations for the Nuclear Morphology of NGC 4314

abstract:
  We performed SPH simulations to study the nuclear morphology of a barred
galaxy NGC 4314. We have constructed the mass models based on the results of a
profile decomposition into disk, bulge, and bar components. Our models have
three different nuclear structures according to the assumption about the
nuclear bar: no nuclear bar, a synchronous nuclear bar and a fast nuclear bar.
Our SPH simulations show that the morphology of the nuclear region of NGC 4314
which is characterized by an elongated ring/spiral of newly formed stars and
HII regions, aligned nearly parallel to the primary bar can be understood in
terms of the secular evolution driven by the non-axisymmetric potential. The
slightly elongated and aligned nuclear ring of NGC 4314 can be formed by the
strong barred potential and the moderate central concentration of the bulge
mass with and without a nuclear bar. However, the nuclear spiral pattern can
not be developed without a nuclear bar. The nuclear bar of NGC 4314 seems to
rotate faster than the primary bar since the nuclear morphology induced by the
synchronous nuclear bar is much different from the observed one.


title:
{BOAO Photometric Survey of Galactic Open Clusters. II. Physical
  Parameters of 12 Open Clusters

abstract:
  We have initiated a long-term project, the BOAO photometric survey of open
clusters, to enlarge our understanding of galactic structure using UBVI CCD
photometry of open clusters which have been little studied before. This is the
second paper of the project in which we present the photometry of 12 open
clusters. We have determined the cluster parameters by fitting the Padova
isochrones to the color-magnitude diagrams of the clusters. All the clusters
except for Be 0 and NGC 1348 are found to be intermediate-age to old (0.2 - 4.0
Gyrs) open clusters with a mean metallicity of [Fe/H] = 0.0.


title: Young Populations in the Nuclei of Barred Galaxies

abstract:
  We have conducted a $UBVRI$ and $H_{\alpha}$ CCD photometry of 5 barred
galaxies, NGC 2523, NGC 2950, NGC 3412, NGC 3945 and NGC 5383, along with SPH
simulations, in order to understand the origin of young stellar populations in
the nuclei of barred galaxies. The $H_{\alpha}$ emissions which are thought to
be emitted by young stellar populations are either absent or strongly
concentrated on the nuclei of early type galaxies (NGC 2950, NGC 3412, NGC
3945), while they are observed in the nuclei and circumnuclear regions of
intermediate type galaxies with strong bars (NGC 2523, NGC 5383). SPH
simulations of realistic mass models for these galaxies show that some disk
material can be driven into the nuclear regions by strong bar potentials. This
implies that the young stellar populations in the circumnuclear regions of
barred galaxies can be formed out of such gas. The existence of the nuclear
dust lanes is an indication of an on-going gas inflow and extremely young
stellar populations in these galaxies, because the nuclear dust lanes such as
those in NGC 5383 are not long-lasting features according to our simulations.


title: Super-Eddington Fluxes from Thin Accretion Disks?

abstract:
  Radiation pressure-dominated accretion disks are predicted to exhibit strong
density inhomogeneities on scales much smaller than the disk scale height, due
to the nonlinear development of photon bubble instability. Radiation would
escape from such a "leaky" disk at a rate higher than that predicted by
standard accretion disk theory. The disk scale height is then smaller than that
of a similar disk without small-scale inhomogeneities, and the disk can remain
geometrically thin even as the flux approaches and exceeds the Eddington limit.
An idealized one-zone model for disks with radiation-driven inhomogeneities
suggests that the escaping flux could exceed L_E by a factor of up to ~10-100,
depending on the mass of the central object. Such luminous disks would develop
strong mass loss, but the resulting decrease in accretion rate would not
necessarily prevent the luminosity from exceeding L_E. We suggest that the
observed "ultraluminous X-ray sources" are actually thin, super-Eddington
accretion disks orbiting stellar-mass black holes, and need not indicate the
existence of a class of intermediate-mass black holes.


title: Heat conduction in X-ray clusters: Spitzer over 3

abstract:
  Effective heat conduction in a random variable magnetic field should be equal
to one third of the Spitzer's value. Recent observations indicate that this
heat conduction is sufficient to account for the bremsstrahlung in cooling
X-ray clusters.


title:
Stellar Contents and Globular Cluster Candidates in the Sculptor Group
  Galaxy NGC 300

abstract:
  We present UBVI CCD photometry of the stellar contents and globular
cluster(GC) candidates in the spiral galaxy NGC 300 in the Sculptor group.
Color-magnitude diagrams for 18 OB associations having more than 30 member
stars are presented. The slope of the initial mass function for the bright
stars in NGC 300 is estimated to be Gamma = -2.6 +/- 0.3. Assuming the distance
to NGC 300 of (m-M)_0 = 26.53 +/- 0.07, the mean absolute magnitude of three
brightest blue stars is obtained to be <M_V^{BSG}(3)> = -8.95 mag. We have
performed search for GCs in NGC 300 and have found 17 GC candidates in this
galaxy. Some characteristics of these GC candidates are discussed.


title:
Maximum mass and radius of strange stars in the linear approximation of
  the EOS

abstract:
  The Chandrasekhar limit for strange stars described by a linear equation of
state (describing quark matter with density-dependent quark masses) is
evaluated. The maximum mass and radius of the star depend on the fundamental
constants and on the energy density of the quark matter at zero pressure. By
comparing the expression for the mass of the star with the limiting mass
formula for a relativistic degenerate stellar configuration one can obtain an
estimate of the mass of the strange quark.


title:
The REM Telescope: Detecting the Near Infra-Red Counterparts of
  Gamma-Ray Bursts and the Prompt Behaviour of Their Optical Continuum

abstract:
  Observations of the prompt afterglow of Gamma Ray Burst events are
unanimously considered of paramount importance for GRB science and related
cosmology. Such observations at NIR wavelengths are even more promising
allowing one to monitor high-z Ly-alpha absorbed bursts as well as events
occurring in dusty star-forming regions. In these pages we present REM (Rapid
Eye Mount), a fully robotized fast slewing telescope equipped with a high
throughput NIR (Z', J, H, K') camera dedicated to detecting the prompt IR
afterglow. REM can discover objects at extremely high red-shift and trigger
large telescopes to observe them. The REM telescope will simultaneously feed
ROSS (REM Optical Slitless spectrograph) via a dichroic. ROSS will intensively
monitor the prompt optical continuum of GRB afterglows. The synergy between
REM-IR cam and ROSS makes REM a powerful observing tool for any kind of fast
transient phenomena.


title:
X-ray Sources and Star Formation Activity in the Sgr B2 Cloud Observed
  with Chandra

abstract:
  We report the X-ray population study in the giant molecular cloud Sagittarius
B2 (SgrB2). More than a dozen of X-ray cloud members (and candidates) are
discovered with Chandra. Two bright X-ray sources are located near Sgr B2 Main,
the most copious complex of the ultra compact HII sources. The X-ray spectra
are fitted with a thin thermal plasma model of 5-10 keV temperature. The
intrinsic luminosity after correcting the absorption of 5 x 10^23 H/cm^2 is
about 10^33 erg/s. Although these two X-ray sources are attributable to young
stellar objects (YSOs) in the same HII complex, they are in sharp contrast; one
at the center of the HII complex exhibits strong K-shell transition lines of
iron, while the other near the east has only weak lines. The other HII
complexes, SgrB2 North and South, also show hard and highly absorbed X-ray
emissions due possibly to the star formation activity. The composite X-ray
spectrum of the other cloud member X-ray sources is fitted with a thin thermal
plasma of about 10-keV temperature with the hydrogen column density (N_H) of
1.3 x 10^23 H/cm^2, and the individual X-ray luminosity of a few times of
10^31-32$ erg/s. These are likely to be a single or cluster of YSO(s), but
neither radio nor infrared counterpart is found. An alternative scenario of
isolated white dwarfs powered by the Bondi-Hoyle accretion from the dense cloud
gas is also discussed. The X-ray spectra exhibit an additional 6.4-keV line of
neutral or low-ionization irons, which indicates that the environment gas is
concentrated near at the sources.


title:
Asymptotic Giant Branch evolution at varying surface C/O ratio: effects
  of changes in molecular opacities

abstract:
  We investigate the effects of molecular opacities on the evolution of TP-AGB
stars that experience the third dredge-up, i.e. with surface abundances of
carbon and oxygen varying with time. To this aim, a routine is constructed to
derive the molecular concentrations through dissociation equilibrium
calculations, and estimate the opacities due to H2, H2O, OH, C2, CN, and CO for
any given density, temperature, and chemical composition of the gas. Then,
synthetic TP-AGB models with dredge-up are calculated by either 1) adopting the
newly developed routine, or 2) interpolating between fixed opacity tables for
solar chemical composition, which is the usual prescription in AGB evolution
calculations. The comparison between the two cases shows that the change in the
dominant opacity sources, as the C/O ratio grows from below to above unity,
crucially affects the evolution of the effective temperature, i.e. causing a
notable cooling of the carbon-rich models (with C/O>1). From the comparison
with observational data, it turns out that TP-AGB models with variable
molecular opacities are able to reproduce the observed range of effective
temperatures, mass-loss rates, and wind expansion velocities of C-type giants
in the solar neighbourhood, otherwise failed if assuming fixed molecular
opacities for solar-scaled mixtures. Finally, we mention other important
evolutionary and observational effects that result from the adoption of the
variable opacities, such as: i) significant shortening of the C-star phase due
to the earlier onset of the super-wind; ii) consequent reduction of the carbon
yields; iii) reproduction of the observed range of near-infrared colours of
C-stars.


title:
EROS/MACHO Gravitational Microlensing Events Toward LMC in Evans Halo
  Model

abstract:
  After a decade of gravitational microlensing experiments, 13 to 17 events by
MACHO (depending on quality) and two events by EROS have been detected. All of
those have been observed in the direction of Large Magellanic Cloud. We use
Evans spherically symmetric halo model to study the rate of microlensing
events. The expected number of events in this model obtain by using EROS and
MACHO observational efficiencies. We compare our numbers with the observed
events to obtain the fraction of halo that is made by compact objects. It is
shown that results derived from two experiments are in good agreement with each
other and MACHOs, comprise only a fraction (depending on the model) of Milky
Way halo. The results are also compatible with the White Dwarfs population
studies in the Hubble Deep Field.


title: Nuclear Stellar Disks in Spiral Galaxies

abstract:
  We report evidence for nuclear stellar disks in 3 early-type spirals, namely
NGC 1425, NGC 3898 and NGC 4698, revealed by WFPC2/F606W images out of a sample
of 38 spiral galaxies, selected from the Hubble Space Telescope Data Archive.
Adopting the photometric method introduced by Scorza & Bender we derived their
central surface brightness and scalelength by assuming them to be
infinitesimally thin exponential disks. No nuclear disk was found in barred
galaxies or galaxies of Hubble type later than Sb. The external origin of the
disk in NGC 4698 is strongly suggested by its orthogonal geometrical decoupling
with respect to the host galaxy.


title:
A new concept and a preliminary design for a high resolution (HR) and
  very-high resolution (VHR) spectrograph for the LBT

abstract:
  A way to fully exploit the large collecting area of modern 8-10m class
telescopes is high resolution spectroscopy. Many astrophysical problems from
planetary science to cosmology benefit from spectroscopic observations at the
highest resolution currently achievable and would benefit from even higher
resolutions. Indeed in the era of 8-10m class telescopes no longer the
telescope collecting area but the size of the beam - which is related to the
maximum size in which reflection gratings are manufactured - is what mainly
limits the resolution. A resolution-slit product Rphi ~ 40,000 is the maximum
currently provided by a beam of 20 cm illuminating the largest grating mosaics.
We present a conceptual design for a spectrograph with Rphi ~ 80,000, i.e.
twice as large as that of existing instruments. Examples of the possible
exploitation of such a high Rphi value, including spectropolarimetry and very
high resolution (R ~ 300,000), are discussed in detail. The new concept is
illustrated through the specific case of a high resolution spectropolarimeter
for the Large Binocular Telescope.


title: Radiation from the Relativistic Jet: a Role of the Shear Boundary Layer

abstract:
  Recent radio and optical large scale jets' observations suggest a
two-component jet morphology, consisting of a fast central spine surrounded
with a boundary layer with a velocity shear. We study radiation of electrons
accelerated at such boundary layers as an option for standard approaches
involving internal shocks in jets. The acceleration process in the boundary
layer yields in a natural way a two component electron distribution: a
power-law continuum with a bump at the energy, where energy gains equal
radiation losses, followed by a cut-off. For such distributions we derive the
observed spectra of synchrotron and inverse-Compton radiation, including
comptonization of synchrotron and CMB photons. Under simple assumptions of
energy equipartition between the relativistic particles and the magnetic field,
the relativistic jet velocity at large scales and a turbulent character of the
shear layer, the considered radiation can substantially contribute to the jet
radiative output. In the considered conditions the synchrotron emission is
characterized by a spectral index of the radio-to-optical continuum being
approximately constant along the jet. A characteristic feature of the obtained
broad-band synchrotron spectrum is an excess at X-ray frequencies, similar to
the one observed in some objects by Chandra. As compared to the uniform jet
models, the velocity shear across the radiating boundary region leads to
decrease and frequency dependence of the observed jet-counterjet radio
brightness asymmetry. We conclude that a careful investigation of the
observational data looking for the derived effects can allow to evaluate the
role of the boundary layer acceleration processes and/or impose constraints for
the physical parameters of such layers in large scale jets.


title: Optical and infrared observations of the supernova SN 1999el

abstract:
  Optical and near-infrared light curves of the Type IIn supernova 1999el in
NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is
covered from the first observation obtained a few days before maximum light.
Spectroscopic observations are also discussed. Using as a distance calibrator
the Type Ia SN 2000E, which occurred some months later in the same galaxy, and
fitting a blackbody law to the photometric data we obtain a maximum bolometric
luminosity for SN 1999el of $\sim 10^{44}$ erg s$^{-1}$. In general, the
photometric properties of SN 1999el are very similar to those of SN 1998S, a
bright and well studied Type IIn SN, showing a fast decline in all observed
bands similar to those of Type II-L SNe. The differences with SN 1998S are
analyzed and ascribed to the differences in a pre-existing circumstellar
envelope in which dust was already present at the moment of the SN outburst. We
infer that light echoes may play a possibly significant role in affecting the
observed properties of the light curves, although improved theoretical models
are needed to account for the data. We conclude that mass loss in the
progenitor RG stars is episodic and occurs in an asymmetric way. This implies
that collapsing massive stars appear as normal Type II SN if this occurs far
from major mass loss episodes, whereas they appear as Type IIn SNe if a large
mass loss episode is in progress.


title: Observations of Disk Galaxy Evolution

abstract:
  The morphologies of disk galaxies begin to deviate systematically from those
of nearby galaxies at surprisingly low redshifts, possibly as low as z=0.3.
This corresponds to a time ~3.5 Gyr in the past, which is only one quarter of
the present age of the Universe. Beyond z = 0.5 (a look-back time of 5 Gyr) the
effects of evolution on spiral structure are rather obvious: spiral arms are
less well-developed and more chaotic, and barred spiral galaxies seem rarer. By
z=1, around 30% of the galaxy population is sufficiently peculiar that
classification on Hubble's traditional tuning fork system is meaningless. On
the other hand, the co-moving space density and the sizes of luminous disks
have not changed significantly since z=1. Tully-Fisher measurements indicate
that the dynamical state and luminosities of large disk systems are also
consistent with passive evolution out to a redshift of unity. We conclude that
the general appearance of luminous disk galaxies has continuously changed with
cosmic epoch, but their overall numbers have been conserved since z=1, and the
bulk of the stars in these systems probably formed at z>1.


title:
RXJ0806.3+1527: a double degenerate binary with the shortest known
  orbital period (321s)

abstract:
  We carried out optical observations of the field of the X-ray pulsator
RXJ0806.3+1527. A blue V=21.1 star was found to be the only object consistent
with the X-ray position. VLT FORS spectra revealed a blue continuum with no
intrinsic absorption lines. Broad (v~1500 km/s), low equivalent width (about
-1/-6A) emission lines from the HeII Pickering series were clearly detected. B,
V and R time-resolved photometry revealed the presence of about 15% pulsations
at the 321s X-ray period, confirming the identification. These findings,
together with the period stability and absence of any additional modulation in
the 1min-5hr period range, argue in favour of the orbital interpretation of the
321s pulsations. The most likely scenario is thus that RXJ0806.3+1527 is a
double degenerate system of the AM CVn class. This would make RXJ0806.3+1527
the shortest orbital period binary currently known and one of the best
candidates for gravitational wave detection.


title:
Identifying Gamma-Ray Burst Remnants Through Positron Annihilation
  Radiation

abstract:
  We model the annihilation of relic positrons produced in a gamma-ray burst
(GRB) after its afterglow has faded. We find that the annihilation signal from
at least one GRB remnant in the Milky Way galaxy should be observable with
future space missions such as INTEGRAL and EXIST, provided that the gas
surrounding the GRB source has the typical density of the interstellar medium,
< 1 cm^-3. Three fortunate circumstances conspire to make the signal
observable. First, unlike positrons in a standard supernova, the GRB positrons
initially travel at a relativistic speed and remain ahead of any
non-relativistic ejecta until the ejecta become rarefied and the annihilation
time becomes long. Second, the GRB remnant remains sufficiently hot (T > 5 x
10^5 K) for a strong annihilation line to form without significant smearing by
three-photon decay of positronium. Third, the annihilation signal persists over
a time longer than the average period between GRB events in the Milky Way
galaxy.


title: Star Cluster Simulations Including Stellar Evolution

abstract:
  The past few years have seen dramatic improvements in the scope and realism
of star cluster simulations. Accurate treatments of stellar evolution, coupled
with robust descriptions of all phases of binary evolution, have been
incorporated self-consistently into several dynamical codes, allowing for the
first time detailed study of the interplay between stellar dynamics and stellar
physics. The coupling between evolution, dynamics, and the observational
appearance of the cluster is particularly strong in young systems and those
containing large numbers of primordial binary systems, and important inroads
have been made in these areas, particularly in N-body simulations. I discuss
some technical aspects of the current generation of N-body integrators, and
describe some recent results obtained using these codes.


title: Spectroscopic Deprojection-Analysis of 3C 129

abstract:
  We report on spectroscopic imaging observations of the nearby (z=0.022)
galaxy cluster 3C 129 performed with the ACIS detector on board of the Chandra
X-ray observatory. Applying a deprojection analysis which fully takes into
account the spatially resolved X-ray energy spectra we investigate the radial
variation of temperature and particle density of the Intracluster Medium (ICM).
While earlier data indicated a weak cooling flow and a cool cluster core, the
Chandra data suggests that the core is hotter than the rest of the cluster: at
the center we infer (7.9+4.4-2.4) keV while the mean temperature of all the
other ICM shells is (5.1+-0.3) keV (all errors on 90% confidence level). Based
on the radial entropy profile we discuss the evidence for shock heating of the
ICM at the cluster center. We discuss the possibility to use imaging
spectroscopy data of more regular clusters to extract maps of the gravitational
dark matter potential.


title: Black Hole Demographics

abstract:
  The purpose of this contribution is to review the current status of black
hole demographics in light of recent advances in the study of high redshift
QSOs (section 2), local AGNs (section 3) and local quiescent galaxies (section
4). I will then outline the prospects for future progress (section 5), and
discuss what I believe will be the challenges for the years to come [ABRIDGED].


title: After Acoustic Peaks: What's Next in CMB?

abstract:
  The advent of high signal-to-noise cosmic microwave background (CMB)
anisotropy experiments has allowed detailed studies on the power spectrum of
temperature fluctuations. The existence of acoustic oscillations in the
anisotropy power spectrum is now established with the detection of the first
two, and possibly the third, peaks. Beyond the acoustic peak structure, we
consider cosmological and astrophysical information that can be extracted by
pushing anisotropy observations to fine angular scales with higher resolution
instruments. At small scales, a variety of contributions allow the use of CMB
photons as a probe of the large scale structure: we outline possible studies
related to understanding detailed physical properties such as the distribution
of dark matter, baryons and pressure, and ways to measure the peculiar,
transverse and rotational velocities of virialized halos such as galaxy
clusters. Beyond the temperature, we consider several useful aspects of the CMB
polarization and comment on an ultimate goal for future CMB experiments
involving the direct detection of inflationary gravity-waves through their
distinct signature in the curl-type polarization.


title: Diffuse X-ray emission from the planetary nebula NGC 7009

abstract:
  XMM-Newton EPIC observations of the planetary nebula (PN) NGC 7009, the
Saturn Nebula, have detected extended X-ray emission in its central cavity. The
diffuse X-ray emission must originate in the shocked fast stellar wind. The
spectra show that the temperature of the hot gas is 1.8*10^6 K. The rms density
derived from the volume emission measure is a few tens H-atom/cm^3. The hot gas
does not appear over-pressurized with respect to the nebular shell. NGC 7009
represents an evolutionary stage at which the influence of the hot gas in the
PN interior starts to decline due to the diminishing strength of the fast
stellar wind and the expansion of the central cavity.


title:
The Structure and Variability of Sagittarius A*: Zooming in to the
  Supermassive Black Hole at the Galactic Center

abstract:
  The Galactic center provides a unique astrophysical laboratory for us to
study various astrophysical processes. In this paper, we review and outline the
latest results from observations of Sgr~A$^*$ in terms of source structure and
variations in flux density. Sgr~A$^*$ phenomenon represents a typical case of
low radiative efficiency accretion flow surrounding a supermassive black hole
in low luminosity AGNs. Many pending astrophysical problems found from
observations of Sgr A$^*$ have challenged the existing astrophysical theories.
Current theoretical models of Sgr A$^*$ are also reviewed.


title: The evolution of galaxy mass in hierarchical models

abstract:
  Advances in extragalactic astronomy have prompted the development of
increasingly realistic models which aim to describe the formation and evolution
of galaxies. We review the philosophy behind one such technique, called
semi-analytic modelling, and explain the relation between this approach and
direct simulations of gas dynamics. Finally, we present model predictions for
the evolution of the stellar mass of galaxies in a universe in which structure
formation is hierarchical.


title: The physical conditions within dense cold clouds in cooling flows II

abstract:
  This is a progress report on our numerical simulations of conditions in the
cold cores of cooling flow condensations. The physical conditions in any
non-equilibrium plasma are the result of a host of microphysical processes,
many involving reactions that are research areas in themselves. We review the
dominant physical processes in our previously published simulations, to clarify
those issues that have caused confusion in the literature. We show that
conditions in the core of an X-ray illuminated cloud are very different from
those found in molecular clouds, largely because carbon remains substantially
atomic and provides powerful cooling through its far infrared lines. We show
how the results of the Opacity Project have had a major impact on our
predictions, largely because photoionization cross sections of atoms and first
ions are now calculated to be far larger than previously estimated. Finally we
show that the predicted conditions are strongly affected by such complexities
as microturbulence or the presence of small amounts of dust. Large masses of
cold dense gas, in addition to the warmer molecular gas detected recently,
could be present in cooling flows.


title: RX J0806+15: the shortest period binary?

abstract:
  The X-ray source RX J0806+15 was discovered using ROSAT, and shows an X-ray
light curve with a prominent modulation on a period of 321.5 sec. We present
optical observations in which we report the detection of its optical
counterpart. We find an optical period consistent with the X-ray period. We do
not find convincing evidence for a second period in the data: this implies the
321.5 sec period is the orbital period. As such it would be the shortest period
stellar binary system yet known. We discuss the nature of this system. We
conclude that an isolated neutron star and an intermediate polar interpretation
is unlikely and that a double degenerate interpretation is the most likely.


title: The Environments of Soft Gamma-Ray Repeaters: A Brief & Biased Review

abstract:
  I review some recent developments in our understanding of the environments of
soft gamma-ray repeaters. I pay particular attention to the apparent
association betwwen SGR 1900+14 and SGR 1806-20 and embedded clusters of stars.


title: Globular Clusters at High Redshift

abstract:
  Globular clusters will be present at high redshifts, near the very beginning
of the galaxy formation process. Stellar evolution ensures that they will be
much more luminous than today. We show that the redshift distribution at
nano-Jansky levels should be very broad, extending up to the redshift of
formation. A bracketing range of choices for the redshift of formation,
spectral energy evolution models and population density evolution, leads to the
conclusion that the sky densities should be around 10^7 per square degree at
1nJy (m_AB=31.4 mag) in bands around 4 microns. Such high sky densities begin
to present a confusion problem at these wavelengths to diffraction limited 6m
class telescopes. These star-like, low metallicity, clusters will be a
significant foreground population for ``first light'' object searches. On the
other hand they are an exceptionally interesting ``second light'' population in
their own right. Depending on the details of galaxy assembly, the clusters will
have a noticeable cross-correlation with galaxies on scales of about 20 arcsec,
or less, depending on the details of the buildup of galaxy assembly after
globular cluster formation. High redshift globular clusters will be an
accessible, direct, probe of the earliest stages of the formation of galaxies
and the buildup of metals in the universe.


title:
Why the Bradley aberration cannot be used to measure absolute speeds. A
  comment

abstract:
  In a recent article in this journal [G. Sardin, Measure of the absolute speed
through the Bradley aberration of light beams on a three-axis frame, Europhys.
Lett. 53 (2001) 310], Sardin proposed to use the Bradley aberration of light
for the construction of a speedometer capable of measuring absolute speeds. The
purpose of this comment is to show that the device would not work.


title:
Smoothed Particle Hydrodynamics with particle splitting, applied to
  self-gravitating collapse

abstract:
  We describe and demonstrate a method for increasing the resolution locally in
a Smoothed Particle Hydrodynamic (SPH) simulation, by splitting particles. We
show that in simulations of self-gravitating collapse (of the sort which are
presumed to occur in star formation) the method is stable, and affords great
savings in computer time and memory. When applied to the standard Boss &
Bodenheimer test -- which has been shown to depend critically on fulfilment of
the Jeans Condition -- the results are comparable both with those obtained
using Adaptive Mesh Refinement, and with those obtained using a standard
high-resolution SPH simulation, but they are achieved with considerably less
computational resource. Further development and testing is required before the
method can safely be applied to more general flows.


title:
QED and the High Polarization of the Thermal Radiation from Neutron
  Stars

abstract:
  The thermal emission of strongly magnetized neutron-star atmospheres is
thought to be highly polarized. However, because of the different orientations
of the magnetic field over the surface of the neutron star (NS), it is commonly
assumed that the net observed polarization will be significantly reduced as the
polarization from different regions will cancel each other. We show that the
birefringence of the magnetized QED vacuum decouples the polarization modes in
the magnetosphere; therefore, the direction of the polarization follows the
direction of the magnetic field up to a large distance from the stellar
surface. At this distance, the rays that leave the surface and are destined for
our detectors pass through only a small solid angle; consequently, the
polarization direction of the emission originating in different regions will
tend to align together. The net observed polarization of the thermal radiation
of NSs should therefore be very large. Measurement of this polarization will be
the first direct evidence of the birefringence of the magnetized vacuum due to
QED and a direct probe of behavior of the vacuum at magnetic fields of order of
and above the critical QED field of 4.4 x 10 13 G. The large observable
polarization will also help us learn more about the atmospheric properties of
NSs.


title: The extreme Type I planetary nebula M2-52

abstract:
  High-resolution spectrophotometric data of the central zone of the Br-type
planetary nebula M2-52 are presented. The nebula has a rich spectrum, with high
and low excitation lines. The chemical composition derived from the spectra
shows that He and N are very enhanced in M2-52. Thus, this object can be
classified as an extreme Peimbert's Type I PN. The chemical composition of the
ionized gas is: He/H =0.165 +/- 0.010, O/H = (2.6 +/- 0.5)E-04, N/O = 2.3 +/-
0.3, Ne/O = 0.37 +/-0.10, Ar/O = (9.2 +/- 2.0)E-03 and S/O > 2.0 E-03. The
expansion velocity of the nebula is, on average, about 20 +/- 2 km/s, but the
low ionization species (N+ and S+) seem to show systematically slightly lower
expansion velocities (18 km/s) than O(++) and He+ which have v(exp) = 20 km/s
while H+ and He(++) present v(exp) = 22 km/s. This behavior could indicate that
the outer zones of the ionized gas are being decelerated by the molecular ring
located around the central star.


title: Long baseline interferometric observations of Cepheids

abstract:
  We present observations of the galactic cepheids eta Aql and zeta Gem. Our
observations are able to resolve the diameter changes associated with
pulsation. This allows us to determine the distance to the Cepheids independent
of photometric observations. We determine a distance to eta Aql of 320 +/- 32
pc, and a distance to zeta Gem of 362 +/- 38 pc. These observations allow us to
calibrate surface brightness relations for use in extra-galactic distance
determination. They also provide a measurement of the mean diameter of these
Cepheids, which is useful in constructing structural models of this class of
star.


title: Weak Gravitational Lensing by Dark Clusters

abstract:
  We calculate the abundance of dark-matter concentrations that are
sufficiently overdense to produce a detectable weak-gravitational-lensing
signal. Most of these overdensities are virialized halos containing
identifiable X-ray and/or optical clusters. However, a significant fraction are
nonvirialized overdensities still in the process of gravitational
collapse--these should produce significantly weaker or no X-ray emission. Our
predicted abundance of such dark clusters are consistent with the abundance
implied by the Erben et al. (2000) detection of a dark lens. Weak lensing by
these nonvirialized objects will need to be considered when determining
cosmological parameters with the lens abundance in future weak-lensing surveys.
Such weak lenses should also help shed light on the process of cluster
formation.


title: Photometric Abundances for G-Dwarfs: A Cautionary Tale

abstract:
  Analysis of cluster and field star uvby data demonstrates the existence of a
previously undetected discrepancy in a widely used photometric metallicity
calibration for G dwarfs. The discrepancy is systematic and strongly
color-dependent, reducing the estimated [Fe/H] for stars above [Fe/H] ~ -0.2 by
between +0.1 and +0.4 dex, and creating a deficit of metal-rich stars among
dwarfs of mid-G and later spectral type. The source of the problem, triggered
for stars with b-y greater than about 0.47, appears to be an enhanced
metallicity dependence for the c1 index that increases as temperature declines.
The link between c1, normally a surface gravity indicator, and metallicity
produces two secondary effects. The deficit in the photometric abundance for a
cool dwarf is partially compensated by some degree of evolution off the main
sequence and cool dwarfs with metallicities significantly above the Hyades are
found to have c1 indices that classify them as giants. The potential impact of
the problem on stellar population studies is discussed.


title:
The Origin of Hot Subluminous Horizontal-Branch Stars in Omega Centauri
  and NGC 2808

abstract:
  Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch
(EHB) are found in the UV color-magnitude diagrams of omega Cen and NGC 2808.
Such stars are unexplained by canonical HB theory. In order to explore the
origin of these subluminous stars, we evolved a set of low-mass stars from the
main sequence through the helium-core flash to the HB for a wide range in the
mass loss along the red-giant branch (RGB). Stars with the largest mass loss
evolve off the RGB to high effective temperatures before igniting helium in
their cores. Our results indicate that the subluminous EHB stars, as well as
the gap within the EHB of NGC 2808, can be explained if these stars undergo a
late helium-core flash on the white-dwarf cooling curve. Under these conditions
the flash convection will penetrate into the stellar envelope, thereby mixing
most, if not all, of the envelope hydrogen into the hot helium- burning
interior. This phenomenon is analogous to the "born-again" scenario for
producing hydrogen-deficient stars during a very late helium-shell flash.
"Flash mixing" greatly enhances the envelope helium and carbon abundances and,
as a result, leads to an abrupt increase in the HB effective temperature. We
argue that the EHB gap in NGC 2808 is caused by this theoretically predicted
dichotomy in the HB morphology. Using new helium- and carbon-rich stellar
atmospheres, we show that the flash-mixed stars have the same reduced UV flux
as the subluminous EHB stars. Moreover, we demonstrate that models without
flash mixing lie, at most, ~0.1 mag below the EHB and hence fail to explain the
observations. Flash mixing may also provide a new evolutionary channel for
producing the high gravity, He-rich sdO and sdB stars.


title: Modes of Accretion in X-ray Sources

abstract:
  Three classical modes of accretion are briefly discussed: wind-fed,
spherical, and disk. The three modes are illustrated with the mass transfer
onto black holes in high-mass X-ray binaries. Then a new regime of mini-disk
accretion is described and it is argued that observed wind-fed X-ray sources
are likely to accrete in this regime. Switching from one accretion mode to
another can cause the observed spectral state transitio ns.


title: The Reddest Quasars II. A gravitationally-lensed FeLoBAL quasar

abstract:
  We report the discovery of a z=2.65 low-ionization iron broad absorption line
quasar, FIRST J100424.9+122922, which is gravitationally-lensed by a galaxy at
z~0.95. The object was discovered as part of a program to find very red quasars
by matching the FIRST radio survey with the 2-MASS near-infrared survey.
J100424.9+122922 is the second lensed system to be found in this program,
suggesting that many gravitational lenses are probably missed from conventional
optical quasar surveys. We have made a simple lens model and a rough estimate
of the reddening in the immediate environment of the quasar which suggests that
the quasar is intrinsically very luminous and is accreting at close to the
Eddington limit of its ~10^9 M_sun black hole. The lensing galaxy has a small
amount of dust which is responsible for some excess reddening observed in the
fainter image of the quasar, but is otherwise a fairly typical massive
elliptical galaxy. We model the selection effects working against the detection
of red quasars in both lensed and unlensed samples. We show that these
selection effects are very effective at removing even lightly-reddened high
redshift quasars from magnitude-limited samples, whether they are lensed or
not. This suggests that the red quasar population in general could be very
large, and in particular the class of iron broad absorption line quasars of
which J100424.9+122922 is a member may be much larger than their rarity in
magnitude-limited samples would suggest.


title: Dynamics of HCGs

abstract:
  It is shown that compact groups of galaxies (HCGs, ShCGS) are stable
formations, in which principal member galaxies together with faint galaxies in
their environment rotate in elongated orbits around the common gravitational
center of the group. Hence, the multitude of puzzles related to CGs: the very
existence of CGs, absence of strong radio sources, absence of strong signs of
interaction and merging, the fact that elliptical members (the best candidates
for ongoing merging) are not more frequently first-ranked than spirals, etc.,
are solved. The number of such groups, may be much higher in the near Universe,
since only those of them, the elongation of which is oriented close to the line
of sight, or bright members of which happen to be close to each other during
regular rotation, are detected as the so-called compact groups.


title:
The nonlinear development of the thermal instability in the atomic ISM
  and its interaction with random fluctuations

abstract:
  (Abridged) We discuss the nonlinear development of the isobaric mode of
thermal instability (TI) in the context of the atomic interstellar medium
(ISM), in order to assess the ability of TI to establish a well-segregated
multi-phase structure in the turbulent ISM. The key parameter is the ratio of
the cooling time to the dynamical crossing time $\eta$. The isobaric density
perturbations of sizes $\gtrsim 15$ pc in media with mean density $\sim 1$
cm$^{-3}$ develop inflow motions with Mach number larger than 0.5 and a shock
that propagates outwards from the condensation and brings the surrounding
medium out of thermal equilibrium. The time for the dynamical transient state
to subside ranges from 4 to 30 Myr for initial density perturbations of 20% and
sizes 3 to 75 pc. By the time the condensations have formed, a substantial
fraction of the mass is still traversing the unstable range and, therefore,
clouds formed by TI should be bounded by accreting gas traversing the unstable
range, rather than by sharp transitions to the stable warm phase. In the
presence of random velocity forcing the condensation process can be suppressed
for arbitrarily long times if the forcing causes a moderate rms Mach number
($\gtrsim 0.3$) and extends to small enough scales that $\eta>1$. We suggest
that these mechanisms may be at the origin of the relatively large amounts of
gas mass in the unstable regime. We remark that in the (stable) warm diffuse
medium, $\eta>1$ for velocity perturbations of scales up to several pc. The
flow's response to them is thus nearly adiabatic, and relatively weakly
compressible, consistent with observations that suggest a nearly Kolmogorov
power spectrum in this medium.


title:
Optically faint counterparts to the ISO-FIRBACK 170 micron population:
  the discovery of cold, luminous galaxies at high redshift

abstract:
  We present Keck spectroscopy and UKIRT near-IR imaging observations of two
170micron-selected sources from the ISO-FIRBACK survey which have faint
counterparts in the optical, and r-K~5. Both sources were expected to lie at
z>1 based on their far-infrared, submillimeter and radio fluxes, assuming a
similar spectral energy distribution to the local ultra-luminous infrared
galaxy (ULIRG) Arp220. However, our spectroscopy indicates that the redshifts
of these galaxies are z<1: z=0.91 for FN1-64 and z=0.45 for FN1-40. While the
bolometric luminosities of both galaxies are similar to Arp220, it appears that
the dust emission in these systems has a characteristic temperature of 30K much
cooler than the ~50K seen in Arp220. Neither optical spectrum shows evidence of
AGN activity. If these galaxies are characteristic of the optically faint
FIRBACK population, then evolutionary models of the far-infrared background
must include a substantial population of cold, luminous galaxies. These
galaxies provide an important intermediate comparison between the local
luminous IR galaxies, and the high redshift submillimeter-selected galaxies,
for which there is very little information available.


title: Quark-diquark equation of state and compact star structure

abstract:
  (abridged) We construct quark-diquark equations of state using the quark mass
density-dependent formalism. A region inside a $2-D$ parameter space in which
this matter is absolutely stable is identified. Motivated by the reported
compactness of some neutron star candidates we present stellar sequences and
show that the quark-diquark EOSs allow a very compact structure, even in the
cases in which the diquark itself is not bound.


title: Chandra deep X-ray observation on the Galactic plane

abstract:
  Using the Chandra ACIS-I instruments, we have carried out the deepest X-ray
observation on a typical Galactic plane region at l 28.5 deg, where no discrete
X-ray sources have been known previously. We have detected, as well as strong
diffuse emission, 275 new point X-ray sources (4 sigma confidence) within two
partially overlapping fields (~250 arcmin^2 in total) down to ~3 x 10^{-15} erg
s^{-1} cm^{-2} (2 -- 10 keV) or ~ 7 x 10^{-16} erg s^{-1} cm^{-2} (0.5 -- 2
keV). We have studied spectral distribution of these point sources, and found
that very soft sources detected only below ~ 3 keV are more numerous than hard
sources detected only above ~ 3 keV. Only small number of sources are detected
both in the soft and hard bands. Surface density of the hard sources is almost
consistent with that at high Galactic regions, thus most of the hard sources
are considered to be Active Galactic Nuclei seen through the milky way. On the
other hand, some of the bright hard X-ray sources which show extremely flat
spectra and iron line or edge features are considered to be Galactic,
presumably quiescent dwarf novae. The soft sources show thermal spectra and
small interstellar hydrogen column densities, and some of them exhibit X-ray
flares. Therefore, most of the soft sources are probably X-ray active nearby
late type stars.


title:
Massive star formation in 100,000 years from turbulent and pressurized
  molecular clouds

abstract:
  Massive stars (with mass m_* > 8 solar masses) are fundamental to the
evolution of galaxies, because they produce heavy elements, inject energy into
the interstellar medium, and possibly regulate the star formation rate. The
individual star formation time, t_*f, determines the accretion rate of the
star; the value of the former quantity is currently uncertain by many orders of
magnitude, leading to other astrophysical questions. For example, the variation
of t_*f with stellar mass dictates whether massive stars can form
simultaneously with low-mass stars in clusters. Here we show that t_*f is
determined by conditions in the star's natal cloud, and is typically ~10^5 yr.
The corresponding mass accretion rate depends on the pressure within the cloud
- which we relate to the gas surface density - and on both the instantaneous
and final stellar masses. Characteristic accretion rates are sufficient to
overcome radiation pressure from ~100 solar mass protostars, while
simultaneously driving intense bipolar gas outflows. The weak dependence of
t_*f on the final mass of the star allows high- and low-mass star formation to
occur nearly simultaneously in clusters.


title: The Formation of Massive Stars and Star Clusters

abstract:
  We model the formation of high-mass stars, specifying the accretion rate in
terms of the instantaneous and final mass of the star, the ambient pressure of
the star-forming region and the form of polytropic pressure support of the
pre-stellar gas core. The high pressures typical of Galactic regions of massive
star formation allow a 100 solar mass star to form in ~10^5 years with a final
accretion rate ~10^-3 solar masses per year. By modeling protostellar evolution
we predict the properties of several nearby massive protostars. We model
cluster formation by applying this theory to many stars. We use the observed
intensity of outflows from protoclusters to estimate the star formation rate,
finding that clusters take at least several free-fall times to form; for a
cluster similar to the Orion Nebula Cluster, we predict a formation timescale
of ~1x10^6 years.


title:
Nonthermal Electrons at High Mach Number Shocks: Electron Shock Surfing
  Acceleration

abstract:
  We study the suprathermal electron acceleration mechanism in a perpendicular
magnetosonic shock wave in a high Mach number regime by using a
particle-in-cell simulation. We find that shock surfing/surftron acceleration
producing the suprathermal electrons occurs in the shock transition region
where a series of large amplitude electrostatic solitary waves (ESWs) are
excited by Buneman instability under the interaction between the reflected ions
and the incoming electrons. It is shown that the electrons are likely to be
trapped by ESWs, and during the trapping phase they can be effectively
accelerated by the shock motional/convection electric field. We discuss that
suprathermal electrons can be accelerated up to $m_i c^2 (v_0/c)$, where $m_i
c^2$ is the ion rest mass energy and $v_0$ is the shock upstream flow velocity.
Furthermore, some of these suprathermal electrons may be effectively trapped
for infinitely long time when Alfv\'en Mach number $M_A$ exceeds several 10,
and they are accelerated up to the shock potential energy determined by the
global shock size.


title: An inverse method to interpret colour-magnitude diagrams

abstract:
  An inverse method is developed to determine the star formation history, the
age-metallicity relation, and the IMF slope from a colour-magnitude diagram.
  The method is applied to the Hipparcos HR diagram. We found that the thin
disk of our Galaxy shows a peak of stellar formation 1.6 Gyr ago. The stars
close to the Sun have a solar metallicity and a mean IMF index equal to 3.2.
However, the model and the evolutionary tracks do not correctly reproduce the
horizontal giant branch.


title: New results from AMS cosmic ray measurements

abstract:
  The Alpha Magnetic Spectrometer (AMS) is a detector designed to search for
antimatter in the cosmic rays. The physics results from the test flight in June
1998 are analyzed and published. This paper reviews the results in the five
published papers of the AMS collaboration, updates the current understanding of
two puzzles, albedo $e^+/e^-$ and albedo $^3$He, and disscusses the influence
of albedo particles.


title: The simplest curvaton model

abstract:
  We analyze the simplest possible realization of the curvaton scenario, where
a nearly scale-invariant spectrum of adiabatic perturbations is generated by
conversion of an isocurvature perturbation generated during inflation, rather
than the usual inflationary mechanism. We explicitly evaluate all the
constraints on the model, under both the assumptions of prompt and delayed
reheating, and outline the viable parameter space.


title: Galactic Models and White Dwarf Populations

abstract:
  We make use of a previous well tested Galactic model, but describing the
observational behavior of the various stellar components in terms of suitable
assumptions on their evolutionary status. In this way we are able to predict
the expected distribution of Galactic White Dwarfs (WDs), with results which
appear in {\em rather good} agreement with recent estimates of the local WD
luminosity function. The predicted occurrence of WDs in deep observations of
selected galactic fields is presented, discussing the role played by WDs in
star counts. The effects on the theoretical predictions of different White
Dwarfs evolutionary models, ages, initial mass functions and relations between
progenitor mass and WD mass are also discussed.


title: HD 304373, the second case of 1O/2O double-mode Cepheid in the Galaxy

abstract:
  We report on the discovery of the second case of a galactic Cepheid,
ASAS112843-5925.7=HD 304373, pulsating in the the first (1O) and second (2O)
radial overtones. The ratio between the periods (0.8058), the short value of
the 1O period (0.922405 d) and the shape of the 1O light curve makes HD 304373
very similar to the 1O/2O Cepheids in the Magellanic Clouds. The implications
of a so close similarity between a galactic 1O/2O pulsator and LMC ones are
discussed in terms of importance of the metallicity effects.


title: In-flight verification of the FREGATE spectral response

abstract:
  We present the first results of the in-flight validation of the spectral
response of the FREGATE X/gamma detectors on-board the HETE-2 satellite. This
validation uses the Crab pulsar and nebula as reference spectra.


title: FREGATE observation of a strong burst from SGR1900+14

abstract:
  After a long period of quiescence, the soft gamma repeater SGR1900+14 was
suddenly reactivated on April 2001. On July 2, 2001, a bright flare emitted by
this source triggerred the WXM and FREGATE instruments onboard the HETE-2
satellite. Unlike typical short (0.1 s) and spiky SGRs recurrent bursts, this
event features a 4.1 s long main peak, with a sharp rise (50 ms) and a slower
cutoff (250 ms). This main peak is followed by a 2 sec decreasing tail. We
found no evidence of any precursor or any extended `afterglow' tail to this
burst. We present the preliminary spectral fits of the total emission of this
flare as observed by the FREGATE instrument between 7 and 150 keV. The best fit
is obtained with a model consisting of two blackbody components of temperatures
4.15 keV and 10.4 keV. A thermal bremsstrahlung can not be fitted to this
spectrum. We compare these features and the burst energetics with the other
strong or giant flares from SGR1900+14.


title: The origin of the strings in the outer regions of Eta Carinae

abstract:
  The narrow optical filaments (`strings' or `spikes') emerging from the
Homunculus of Eta Carinae are modelled as resulting from the passage of
ballistic `bullets' of material through the dense circumstellar environment. In
this explanation, the string is the decelerating flow of ablated gas from the
bullet. An archive HST image and new forbidden line profiles of the most
distinct of the strings are presented and discussed in terms of this simple
model.


title: Observational constraints on growth of massive black holes

abstract:
  We study the observational constraints on the growth of massive black holes
(BHs) in galactic nuclei. We use the velocity dispersions of early-type
galaxies obtained by the SDSS and the relation between BH mass and velocity
dispersion to estimate the local BH mass density to be 2.5x10^5 Msun/Mpc^3. We
also use the QSO luminosity function from the 2dF Redshift Survey to estimate
the BH mass density accreted during optically bright QSO phases. The local BH
mass density is consistent with the density accreted during optically bright
QSO phases if QSOs have an efficiency 0.1. By studying the continuity equation
for the BH mass distribution, including the effect of BH mergers, we find
relations between the local BH mass function and the QSO luminosity function.
If the BH mass is assumed to be conserved during BH mergers, comparison of the
predicted relations with the observations suggests that luminous QSOs
(L_{bol}>10^{46} erg/s) have a high efficiency (e.g. 0.2), and the growth of
high-mass BHs (>10^8 Msun) comes mainly from accretion during optically bright
QSO phases, or that luminous QSOs have a super-Eddington luminosity. If
luminous QSOs are not accreting with super-Eddington luminosities and the
growth of low-mass BHs also occurs mainly during optically bright QSO phases,
less luminous QSOs must accrete with a low efficiency <0.1; alternatively, they
may accrete with high efficiency, but a significant fraction should be
obscured. We estimate that the mean lifetime of luminous QSOs is (3-13)x10^7
yr, which is comparable to the Salpeter time. We also investigate the case in
which total BH mass decreases during BH mergers due to gravitational radiation,
and the observations again suggest that BHs in most luminous QSOs are Kerr BHs
accreting with an efficiency >0.1.


title:
On The Origin Of HI In Galaxies: The Sizes and Masses of HI
  Photodissociation Regions

abstract:
  Young stars in the disks of galaxies produce HI from their parent H2 clouds
by photodissociation. This paper describes the observational evidence for and
the morphology of such HI. Simple estimates of the amount of dissociated gas
lead to the startling conclusion that much, and perhaps even all, of the HI in
galaxy disks can be produced in this way.


title:
Spectrum and Duration of Delayed MeV-GeV Emission of Gamma-Ray Bursts in
  Cosmic Background Radiation Fields

abstract:
  We generally analyze prompt high-energy emission above a few hundreds of GeV
due to synchrotron self-Compton scattering in internal shocks. However, such
photons cannot be detected because they may collide with cosmic infrared
background photons, leading to electron/positron pair production.
Inverse-Compton scattering of the resulting electron/positron pairs off cosmic
microwave background photons will produce delayed MeV-GeV emission, which may
be much stronger than a typical high-energy afterglow in the external shock
model. We expand on the Cheng & Cheng model by deriving the emission spectrum
and duration in the standard fireball shock model. A typical duration of the
emission is ~ 10^3 seconds, and the time-integrated scattered photon spectrum
is nu^{-(p+6)/4}, where p is the index of the electron energy distribution
behind internal shocks. This is slightly harder than the synchrotron photon
spectrum, nu^{-(p+2)/2}. The lower energy property of the scattered photon
spectrum is dependent on the spectral energy distribution of the cosmic
infrared background radiation. Therefore, future observations on such delayed
MeV-GeV emission and the higher-energy spectral cutoff by the Gamma-Ray Large
Area Space Telescope (GLAST) would provide a probe of the cosmic infrared
background radiation.


title: Supernova Hosts for Gamma-Ray Burst Jets: Dynamical Constraints

abstract:
  I constrain a possible supernova origin for gamma-ray bursts by modeling the
dynamical interaction between a relativistic jet and a stellar envelope
surrounding it. The delay in observer's time introduced by the jet traversing
the envelope should not be long compared to the duration of gamma-ray emission;
also, the jet should not be swallowed by a spherical explosion it powers. The
only stellar progenitors that comfortably satisfy these constraints, if one
assumes that jets move ballistically within their host stars, are compact
carbon-oxygen or helium post-Wolf-Rayet stars (type Ic or Ib supernovae); type
II supernovae are ruled out. Notably, very massive stars do not appear capable
of producing the observed bursts at any redshift unless the stellar envelope is
stripped prior to collapse. The presence of a dense stellar wind places an
upper limit on the Lorentz factor of the jet in the internal shock model;
however, this constraint may be evaded if the wind is swept forward by a photon
precursor. Shock breakout and cocoon blowout are considered individually;
neither presents a likely source of precursors for cosmological GRBs.
  These envelope constraints could conceivably be circumvented if jets are
laterally pressure-confined while traversing the outer stellar envelope. If so,
jets responsible for observed GRBs must either have been launched from a region
several hundred kilometers wide, or have mixed with envelope material as they
travel. A phase of pressure confinement and mixing would imprint correlations
among jets that may explain observed GRB variability-luminosity and
lag-luminosity correlations.


title: Fine-structure diagnostics of neutral carbon toward HE 0515-4414

abstract:
  New high-resolution high signal-to-noise spectra of the $z=1.15$ damped Lyman
$\alpha$ (DLA) system toward the quasi-stellar object HE 0515-4414 reveal
absorption lines of the multiplets 2 and 3 in \ion{C}{i}. The resonance lines
are seen in two components with total column densities of $\log N=13.79\pm0.01$
and $\log N=13.36\pm0.01$, respectively. The comparision of theoretical
calculations of the relative fine-structure population with the ratios of the
observed column densities suggests that the \ion{C}{i} absorbing medium is
either very dense or exposed to very intense UV radiation. The upper limit on
the local UV energy density is 100 times the galactic UV energy density, while
the upper limit on the \ion{H}{i} number density is 110 cm$^{-3}$. The
excitation temperatures of the ground state fine-structure levels of $T=15.7$
and $T=11.1$ K, respectively, are consistent with the temperature-redshift
relation predicted by the standard Friedmann cosmology. The cosmic microwave
background radiation (CMBR) is only a minor source of the observed
fine-structure excitation.


title:
Power-law correlation and discreteness in cosmological N-body
  simulations

abstract:
  We analyse with simple real-space statistics the Virgo consortium's
cosmological N-body simulations. Significant clustering rapidly develops well
below the initial mean interparticle separation \Lambda_i, where the
gravitational force on a particle is dominated by that with its nearest
neighbours. A power-law behaviour in the two point correlation function
emerges, which in the subsequent evolution is continuously amplified and
shifted to larger scales, in a roughly self-similar manner. We conclude that
the density fluctuations at the smallest scales due to the particle-like nature
of the distribution being evolved are thus essential in the development of
these correlations, and not solely, as usually supposed, the very small
continuous (fluid-like) fluctuations at scales larger than \Lambda_i >.


title: Neutrino Emission from Goldstone Modes in Dense Quark Matter

abstract:
  We calculate neutrino emissivities from the decay and scattering of Goldstone
bosons in the color-flavor-locked (CFL) phase of quarks at high baryon density.
Interactions in the CFL phase are described by an effective low-energy theory.
For temperatures in the tens of keV range, relevant to the long-term cooling of
neutron stars, the emissivities involving Goldstone bosons dominate over those
involving quarks, because gaps in the CFL phase are $\sim 100$ MeV while the
masses of Goldstone modes are on the order of 10 MeV. For the same reason, the
specific heat of the CFL phase is also dominated by the Goldstone modes.
Notwithstanding this, both the emissivity and the specific heat from the
massive modes remain rather small, because of their extremely small number
densities. The values of the emissivity and the specific heat imply that the
timescale for the cooling of the CFL core in isolation is $\sim 10^{26}$ y,
which makes the CFL phase invisible as the exterior layers of normal matter
surrounding the core will continue to cool through significantly more rapid
processes. If the CFL phase appears during the evolution of a proto-neutron
star, neutrino interactions with Goldstone bosons are expected to be
significantly more important since temperatures are high enough ($\sim 20-40$
MeV) to admit large number densities of Goldstone modes.


title:
On the Lack of Type I X-ray Bursts in Black Hole X-ray Binaries:
  Evidence for the Event Horizon?

abstract:
  Type I X-ray bursts are very common in neutron star X-ray binaries, but no
Type I burst has been seen in the dozen or so binaries in which the accreting
compact star is too massive to be a neutron star and therefore is identified as
a black hole candidate. We have carried out a global linear stability analysis
of the accumulating fuel on the surface of a compact star to identify the
conditions under which thermonuclear bursts are triggered. Our analysis, which
improves on previous calculations, reproduces the gross observational trends of
bursts in neutron star systems. It further shows that, if black hole candidates
have surfaces, they would very likely exhibit instabilities similar to those
that lead to Type I bursts on neutron stars. The lack of bursts in black hole
candidates is thus significant, and indicates that these objects have event
horizons. We discuss possible caveats to this conclusion.


title: A Global Jet/Circulation Model for Young Stars

abstract:
  Powerful, highly collimated jets, surrounded by bipolar molecular outflows,
are commonly observed near Young Stellar Objects (YSOs). In the usual
theoretical picture of star formation, a jet is ejected from a magnetized
accretion disk, with a molecular outflow being driven either by the jet or by a
wider wind coming from the disk. Here, we propose an alternative global model
for the flows surrounding YSOs. In addition to a central accretion-ejection
engine driving the jet, the molecular outflow is powered by the infalling
matter and follows a circulation pattern around the central object without
necessarily being entrained by a jet. It is shown that the model produces a
heated pressure-driven outflow with magneto-centrifugal acceleration and
collimation. We report solutions for the three different parts of this
self-similar model, i.e. the jet, the infalling envelope and the circulating
matter that eventually forms the molecular outflow. This new picture of the
accretion/outflow phase provides a possible explanation for several observed
properties of YSO outflows. The most relevant ones are the presence of high
mass molecular outflows around massive protostars, and a realistic fraction
(typically 0.1) of the accretion flow that goes into the jet.


title: A Redshift z = 6.56 Galaxy Behind the Cluster Abell 370

abstract:
  We report the discovery of a redshift z=6.56 galaxy lying behind the cluster
Abell 370. The object HCM 6A was found in a narrowband imaging survey using a
118 Angstrom bandpass filter centered at 9152 Ang in the LRIS camera on the 10
m Keck II Telescope. Candidate Lyman alpha emitters were identified by the
equivalent width of the emission and the absence of lower wavelength flux in
ultradeep broadband images. HCM6A is the first galaxy to be confirmed at
redshift z>6, and has W_lambda(observed)=190 Angstroms, flux = 2.7 x 10^-17 erg
cm^-2 s^-1. Spectra obtained with LRIS confirm the emission line and the
continuum break across the line, and show an asymmetric line profile with steep
fall-off on the blue side. Deep Subaru near-infrared CISCO images in J, H and
K' which extend the sampled continuum to longer wavelengths give a consistent
estimate of the continuum flux density in these line-free regions of 2.6+/-0.7
x 10^-30 erg cm^-2 s^-1 Hz^-1. The line width and strength, asymmetric profile,
and very deep spectral break are only consistent with the interpretation of the
line as a redshifted Lyman alpha feature. From the detailed lensing model of
this cluster, we estimate a lensing amplification of 4.5 for this galaxy, which
is located slightly over an arcminute from the center of the cluster, for an
unlensed flux of 6.5 x 10^-18 erg cm^-2 s^-1. The presence of such a galaxy
suggests that the reionizing epoch is beyond z=6.6.


title: Infrared Surveys for AGN

abstract:
  From the earliest extragalactic infrared studies AGN have shown themselves to
be strong infrared sources and IR surveys have revealed new populations of AGN.
I briefly review current motivations for AGN surveys in the infrared and
results from previous IR surveys. The Luminous Infrared Galaxies, which in some
cases house dust-enshrouded AGN, submillimeter surveys, and recent studies of
the cosmic x-ray and infrared backgrounds suggest that there is a population of
highly-obscured AGN at high redshift. ISO Surveys have begun to resolve the
infrared background and may have detected this obscured AGN population. New
infrared surveys, particularly the SIRTF Wide-area Infrared Extragalactic
Legacy Survey (SWIRE), will detect this population and provide a platform for
understanding the evolution of AGN, Starbursts and passively evolving galaxies
in the context of large-scale structure and environment.


title: The Velocity Distribution of the Nearest Interstellar Gas

abstract:
  The bulk flow velocity for the cluster of interstellar cloudlets within about
30 pc of the Sun is determined from optical and ultraviolet absorption line
data, after omitting from the sample stars with circumstellar disks or variable
emission lines and the active variable HR 1099. Ninety-six velocity components
towards the remaining 60 stars yield a streaming velocity through the local
standard of rest of -17.0+/-4.6 km/s, with an upstream direction of l=2.3 deg,
b=-5.2 deg (using Hipparcos values for the solar apex motion). The velocity
dispersion of the interstellar matter (ISM) within 30 pc is consistent with
that of nearby diffuse clouds, but present statistics are inadequate to
distinguish between a Gaussian or exponential distribution about the bulk flow
velocity. The upstream direction of the bulk flow vector suggests an origin
associated with the Loop I supernova remnant. Groupings of component velocities
by region are seen, indicating regional departures from the bulk flow velocity
or possibly separate clouds. The absorption components from the cloudlet
feeding ISM into the solar system form one of the regional features. The
nominal gradient between the velocities of upstream and downstream gas may be
an artifact of the Sun's location near the edge of the local cloud complex. The
Sun may emerge from the surrounding gas-patch within several thousand years.


title: Acceptable Inverse Power Law Potential Quintessence with n=18/7

abstract:
  We present a particle physics quintessence model which agrees well with
existing cosmological data, including the position of the acoustic peaks. This
model has an inverse power law potential (IPL) with $n=18/7\sim 2.57$ and it
gives $\weff=-0.75$, an acoustic scale $l_A=307$ and a density contrast
$\s8=0.95$.
  Models with $n>1$ have been said to be disfavored by the analysis of the
acoustic peaks. However, the results are not correct. The main reason is that
the tracker approximation has been used in deriving the IPL constrains and for
$n<5$ the scalar field has not reached its tracker value by present day.
  The model can be derived from particle physics, using Affleck-Dine-Seiberg
"ADS" superpotential, for a non-abelian gauge group with $N_c=8, N_f=1$. The
advantage of having $N_f=1$ is that there is only one degree of freedom below
the condensation scale given by the condensate (quintessence)
  $\phi^2=<Q\tilde Q>$ field. The condensation scale is at $1 GeV$ a very
interesting scale since it connects the quintessence "Q" with the standard
model "SM" scale. The similarity in energy scales between $Q$ and $SM$ scale
gives an "explanation" to the coincidence problem. The fact that only recently
the universe is accelerating is a natural consequence of the Q scale and the
evolution of $\phi$.


title: A best fit evolution scenario for the SCUBA galaxies

abstract:
  We explore the evolution of the SCUBA sub-mm galaxy population using Monte
Carlo simulations to generate synthetic sub-mm/radio color magnitude diagrams.
To represent the local distribution of observed dust properties, we use a local
far-infrared luminosity function derived from the IRAS 1.2 Jy catalog,
bivariate in FIR luminosity and 60micron/100micron color. We assume a peak
luminosity evolution scenario and a fixed cosmology, to fit a single parameter
model to the existing sub-mm/radio data. Our best fitting model has a peak in
the luminosity evolution at z=2.6.


title: Photometric Calibrations for the SIRTF Infrared Spectrograph

abstract:
  The SIRTF InfraRed Spectrograph (IRS) is faced with many of the same
calibration challenges that were experienced in the ISO SWS calibration
program, owing to similar wavelength coverage and overlapping spectral
resolutions of the two instruments. Although the IRS is up to ~300 times more
sensitive and without moving parts, imposing unique calibration challenges on
their own, an overlap in photometric sensitivities of the high-resolution
modules with the SWS grating sections allows lessons, resources, and certain
techniques from the SWS calibration programs to be exploited. We explain where
these apply in an overview of the IRS photometric calibration planning.