title: Is it Round? Spectropolarimetry of the Type II-P Supernova 1999em

abstract:
  We present the first multi-epoch spectropolarimetry of a type II plateau
supernova (SN II-P), with optical observations of SN 1999em on days 7, 40, 49,
159, and 163 after discovery. These data are used to probe the geometry of the
electron-scattering atmosphere before, during, and after the plateau phase,
which ended roughly 90 days after discovery. Weak continuum polarization with
an unchanging polarization angle (theta ~ 160 deg) is detected at all epochs,
with p ~ 0.2% on day 7, p ~ 0.3% on days 40 and 49, and p ~ 0.5% in the final
observations. Distinct polarization modulations across strong line features are
present on days 40, 49, 159, and 163. Uncorrected for interstellar polarization
(which is believed to be quite small), polarization peaks are associated with
strong P Cygni absorption troughs and nearly complete depolarization is seen
across the H-alpha emission profile. The temporal evolution of the continuum
polarization and sharp changes across lines indicate polarization intrinsic to
SN 1999em. When modeled in terms of the oblate, electron-scattering atmospheres
of Hoeflich, the observed polarization implies anasphericity of at least 7%
during the period studied. The temporal polarization increase may indicate
greater asphericity deeper into the ejecta. We discuss the implications of
asphericity on the use of type II-P supernovae as primary extragalactic
distance indicators through the expanding photosphere method (EPM). If
asphericity produces directionally dependant flux and peculiar galaxy motions
are characterized by sigma_v_rec = 300 km/s, it is shown that the agreement
between previous EPM measurements of SNe II and distances to the host galaxies
predicted by a linear Hubble law restrict mean SN II asphericity to values less
than 30% (3-sigma) during the photospheric phase.


title:
Explaining the entropy excess in clusters and groups of galaxies without
  additional heating

abstract:
  The X-ray luminosity and temperature of clusters and groups of galaxies do
not scale in a self-similar manner. This has often been interpreted as a sign
that the intracluster medium has been substantially heated by non-gravitational
sources. In this paper, we propose a simple model which, instead, uses the
properties of galaxy formation to explain the observations. Drawing on
available observations, we show that there is evidence that the efficiency of
galaxy formation was higher in groups than in clusters. If confirmed, this
would deplete the low-entropy gas in groups, increase their central entropy and
decrease their X-ray luminosity. A simple, empirical, hydrostatic model appears
to match both the luminosity-temperature relation of clusters and properties of
their internal structure as well.


title:
A Deep Multicolor Survey. VII. Extremely Red Objects and Galaxy
  Formation

abstract:
  Extremely Red Objects (EROs) offer a window to the universe at z~1 analogous
to that provided by the Lyman Break galaxies at z=3. Passive evolution and
hierarchical galaxy formation models make very distinct predictions for the K
(2.2um) surface density of galaxies at z~1 and EROs are a powerful constraint
on these theories. I present a study of nine resolved EROs with R-K>5.3 and
K<18 mag found in the 185 arcmin^2 of the Deep Multicolor Survey with
near-infrared imaging. Photometric redshifts for these galaxies shows they all
lie at z=0.8-1.3. The relatively blue J-K colors of these galaxies suggest that
most are old ellipticals, rather than dusty starbursts. The surface density of
EROs in this survey (>0.05 arcmin^-2), which is a lower limit to the total z~1
galaxy surface density, is an order of magnitude below the prediction of
passive galaxy evolution, yet over a factor of two higher than the hierarchical
galaxy formation prediction for a flat, matter-dominated universe. A flat,
Lambda-dominated universe may bring the hierarchical galaxy formation model
into agreement with the observed ERO surface density.


title: Disks irradiated by beamed radiation from compact objects

abstract:
  We examine the reprocessing of X-ray radiation from compact objects by
accretion disks when the X-ray emission from the star is highly beamed. The
reprocessed flux for various degrees of beaming and inclinations of the beam
axis with respect to the disk is determined. We find that, in the case where
the beam is produced by a non-relativistic object, the intensity of the emitted
spectrum is highly suppressed if the beam is pointing away from the disk.
However, for beams produced by compact objects, general relativistic effects
cause only a small reduction in the reradiated flux even for very narrow beams
oriented perpendicularly to the disk. This is especially relevant in
constraining models for the anomalous X-ray pulsars, whose X-ray emission is
highly beamed. We further discuss other factors that can influence the emission
from disks around neutron stars.


title:
The supernova remnant RX J0852.0-4622: radio characteristics and
  implications for SNR statistics

abstract:
  We present new radio observations of the recently identified, young Galactic
supernova remnant (SNR) RX J0852.0-4622 (G266.2-01.2) made at 1.40 GHz with a
resolution of 14.9 arcmin. These results, along with other radio observations
from the literature, are used to derive the extent, morphology and radio
spectrum of the remnant. The possible age and distance to this remnant are
discussed, along with the consequences of its properties - especially its low
radio surface brightness - for statistical studies of Galactic SNRs. The
extended features identified by Combi et al. (1999) are considered, and we
conclude that these are probably unrelated to the new remnant. If RX
J0852.0-4622 is nearby, as is suggested by the available gamma-ray data, then
the range of intrinsic radio luminosities for SNRs of the same diameter may be
much larger than was previously thought.


title: Modelling Tools: Population and Evolutionary Synthesis

abstract:
  I review the basic concepts for the spectrophotometric and chemical evolution
of galaxies, contrast various approaches and discuss their respective
advantages and shortcomings, both for the interpretation of nearby and high
redshift galaxies. Focus is on recent attempts to include gas and dust into
galaxy evolution models and to account for the links among stars, gas and dust.
Chemically consistent models are described that try to cope with extended
stellar metallicity distributions observed in local galaxies and with subsolar
abundances in young galaxies.


title: The Physical Relation between Age and Metallicity in Galaxies

abstract:
  We present unified chemical and spectrophotometric evolutionary synthesis
models that allow to describe composite stellar populations in a chemically
consistent way. Keeping track of the ISM abundance at birth of each star and
using sets of input physics (stellar yields, tracks, spectra) for different
metallicities we account for the increasing initial metallicity of successive
stellar generations. For any galaxy type its Star Formation History determines
the physical relation between the ages and metallicities of its stars. As
compared to models using solar metallicity input physics only, differences are
significant, both for the ISM enrichment evolution and for the
spectrophotometric evolution, and they increase with lookback time. Results are
used to interprete Damped Ly$\alpha$ Absorbers. Knowledge of the chemical
evolution of the ISM allows to predict abundances of stars, star clusters, and
tidal dwarf galaxies that may form when spirals merge at any redshift.


title:
Probing the warm Inter-Galactic Medium through absorption against Gamma
  Ray Bursts X-ray afterglows

abstract:
  Gamma Ray Burst (GRB) afterglows close to their peak intensity are among the
brightest X-ray sources in the sky. Despite their fast power-law like decay,
when fluxes are integrated from minutes up to hours after the GRB event, the
corresponding number counts (logN-logF relation) far exceeds that of any other
high redshift (z>0.5) source, the flux of which is integrated over the same
time interval. We discuss how to use X-ray afterglows of GRBs as distant
beacons to probe the warm (10^5 K<T<10^7 K) intergalactic matter in filaments
and outskirts of clusters of galaxies by means of absorption features, the
``X-ray forest''. According to current cosmological scenarios this matter may
comprise 30-40% of the baryons in the Universe at z<1. Present-generation X-ray
spectrometers such as those on Chandra and XMM-Newton can detect it along most
GRBs' lines of sight, provided afterglows are observed fast enough (within
hours) after the burst. A dedicated medium-sized X-ray telescope (effective
area <=0.1 m^2) with pointing capabilities similar to that of Swift (minutes)
and high spectral resolution (E/DeltaE>=300) would be very well suited to
exploit the new diagnostic and study the physical conditions in the Universe at
the critical moment when structure is being formed.


title: Environmental Effects on Gas and Galaxy Evolution in Clusters

abstract:
  The cluster environment is the site of important transformations in galaxies
at a relatively recent cosmological epoch: the galactic morphological types and
star formation activity have evolved significantly during the last few Gyrs.
How is this related to the galactic gas content? The first part of this paper
briefly presents the optical observations of galaxies in distant clusters,
while the second part focuses on the link between the HI content and the star
formation activity, presenting the results of a multiwavelength study of the
cluster A2670 (z=0.08) where 42 galaxies have been detected in HI. We show the
star formation properties of the HI-normal and HI-deficient galaxies and
discuss their dependence on the location within the cluster. Finally, we
compare A2670 with clusters at intermediate redshift and with the Coma cluster.


title:
Construction of Cosmic String Induced Temperature Anisotropy Maps with
  CMBFAST and Statistical Analysis

abstract:
  We use the publicly available code CMBFAST as modified by L. Pogosian and T.
Vachaspati to simulate the effects of wiggly cosmic strings on the Cosmic
Microwave Background (CMB). Using the modified CMBFAST code which takes into
account vector modes and models wiggly cosmic strings by the one scale model,
we go beyond the angular power spectrum to construct CMB temperature maps with
resolution of a few degrees. The statistics of these maps are then studied
using conventional and recently proposed statistical tests optimized for the
detection of hidden temperature discontinuities induced by the
Gott-Kaiser-Stebbins effect. We show however, that these realistic maps can not
be distinguished in a statistically significant way from purely Gaussian maps
with identical power spectrum.


title:
X-Ray Flux Decrease of the Accretion-Powered Millisecond Pulsar SAX
  J1808.4-3658 in Quiescence Detected by ASCA

abstract:
  The accretion-powered millisecond X-ray pulsar, SAX J1808.4-3658, was
observed in quiescence with ASCA in September 1999. We detected a dim X-ray
source in the SIS data at the position consistent to SAX J1808.4-3658. The
source count rate was (1.1+-0.4)x10E-3 cts/s (0.5-5 keV) for a single SIS,
which corresponds to (3+-1)x10E-14 ergs/s/cmE2 if a power law energy spectrum
of photon index 2 with low-energy absorption corresponding to a hydrogen column
density of 1.3x10E21 cmE-2 is assumed. The statistical quality of the data was
insufficient to constrain the energy spectrum or to detect the 401 Hz coherent
pulsation. We compare the data with the BeppoSAX observation also made during
the quiescent state, and find that the X-ray flux measured by ASCA is at least
a factor of 4 smaller than that measured by BeppoSAX. We discuss the possible
X-ray emission mechanisms that could explain the flux change, including the
radio pulsar and the radio pulsar shock emission.


title: Reconstructing the inflationary power spectrum from CMBR data

abstract:
  The Cosmic Microwave Background Radiation (CMBR) holds information about
almost all the fundamental cosmological parameters, and by performing a
likelihood analysis of high precision CMBR fluctuation data, these parameters
can be inferred. However, this analysis relies on assumptions about the initial
power spectrum, which is usually taken to be a featureless power-law, P(k) ~
k^{n_s-1}. Many inflationary models predict power spectra with non-power law
features. We discuss the possibility for detecting such features by describing
the power spectrum as bins in k-space. This method for power spectrum
reconstruction is demonstrated in practise by performing likelihood
optimization on synthetic spectra, and the difficulties arising from
reconstructing smooth features using discontinuous bins are discussed in
detail.


title: The Impact of the NACRE Compilation on the Big Bang Nucleosynthesis

abstract:
  We update the Big Bang Nucleosynthesis (BBN) calculations on the basis of the
recent NACRE compilation of reaction rates. We estimate the uncertainties
related to the nuclear reaction rates on the abundances of D, 3He, 4He, 6Li,
7Li, 9Be, 10B and 11B of cosmological and astrophysical interest. We use
lithium as the main indicator of the baryon density of the Universe, rather
than deuterium.


title: Wide Field Imaging at 250 GHz

abstract:
  We summarize results from sensitive, wide-field imaging at 250 GHz using the
Max-Planck Bolometer Array at the IRAM 30m telescope, including source counts,
clustering, and redshift distribution.


title: HI Imaging of the Large Magellanic Cloud

abstract:
  We present results from the combined Australia Telescope Compact Array (ATCA)
aperture synthesis mosaic survey of HI emission in the Large Magellanic Cloud
with 64m Parkes single dish telescope observations.


title:
Absorption line systems on the line of sight from SN 1987A to SN 1993J
  and the intergalactic cloud in front of M81

abstract:
  We present an extended analysis of the high dispersion IUE spectra of SN
1993J in M81, based on the improved data in the IUE final archive. Eight
interstellar absorption components can be identified in the velocity range from
-200 km/s to +200 km/s. Column densities are determined for Fe II, Mg I, Mg II,
O I, S II, Si II, and Zn II. From the ion ratios, we estimate electron
densities and temperatures of the gas in these components. In addition, we
rederive column density profiles for the higher ionisation stages Al III, Si
IV, and C IV for the entire line of sight.
  Of special interest are the absorption components at positive velocities,
which are associated with the intergalactic medium (IGM) in the foreground of
M81. The medium has many gas components, as known from radio measurements,
probably released in dynamical interactions by galaxies in the M81 group. The
IUE spectra contain the only UV absorption information on such gas. We find
neutral and ionised gas absorption at the same velocity, having a metal content
similar to a galactic disk.
  We combine the spectra towards SN 1993J in M81 with those towards SN 1987A in
the LMC, the directions being essentially antipodes on the celestical sphere.
Comparing the total profile with QSO spectra, we conclude that most absorption
in QSO spectra occurs in diffuse clouds on those sight lines and is not similar
to absorption by galactic disk gas. However, one absorption component towards
SN 1993J is clearly very similar to some of the absorption components in QSO
spectra.


title: Parsec-Scale Blazar Monitoring: Proper Motions

abstract:
  We present proper motions obtained from a dual frequency, six-epoch, VLBA
polarization experiment monitoring a sample of 12 blazars. The observations
were made at 15 GHz and 22 GHz at bi-monthly intervals over 1996. Ten of the
eleven sources for which proper motion could be reliably determined are
superluminal. Only J2005+77 has no superluminal components. Three sources
(OJ287, J1224+21, and J1512-09) show motion faster than 10h^{-1}c, requiring
$\gamma_{pattern}$ of at least 10h^{-1}c (H_0 = 100h km/s/Mpc). We compare our
results to those in the literature and find motions outside the previously
observed range for four sources. While some jet components exhibit significant
non-radial motion, most motion is radial. In at least two sources there are
components moving radially at significantly different structural position
angles. In five of six sources (3C120, J1224+21, 3C273, 3C279, J1512-09, and
J1927+73) that have multiple components with measurable proper motion, the
innermost component is significantly slower than the others, suggesting that
acceleration occurs in the jet. In the motions of individual components we
observe at least one decelerating motion and two ``bending'' accelerations
which tend to align their motions with larger scale structure. We also discuss
in detail our procedures for obtaining robust kinematical results from
multi-frequency VLBI data spanning several epochs.


title: The Bar Pattern Speed in NGC 7079

abstract:
  We have used 2D Fabry-Perot absorption-line spectroscopy of the SB0 galaxy
NGC 7079 to measure its bar pattern speed, $\om$. As in all previous cases of
bar pattern speed measurements, we find a fast bar. We estimate that NGC 7079
has been undisturbed for at least the past Gyr or roughly 8 bar rotations, long
enough for the bar to have slowed down significantly through dynamical friction
if the disk is sub-maximal.


title: The Hamburg/RASS optical identification project

abstract:
  We use digitized Schmidt direct and prism plates taken for the northern
hemisphere Hamburg Quasar Survey (HQS) to obtain optical identifications for
all high galactic latitude X-ray sources in the ROSAT Bright Source Catalogue
(RASS-BSC) at |b|>=30 deg and DEC >= 0deg. In this part of the sky the RASS-BSC
contains about 5300 X-ray sources. Presently, identifications exist for about
4100 RASS-BSC sources in this galactic latitude range.


title: Radio observations of the 33.8 ms X-ray pulsar SAX J0635+0533

abstract:
  The hard X-ray source SAX J0635+0533 shows pulsations at a period of 33.8 ms
and is thought to be associated with a bright Be star. We here report on radio
observations towards this source with the VLA and Arecibo radiotelescopes. With
the VLA we do not detect any radio flux at the Be-star position, but one 4.7
mJy (at a radio frequency of 1.4 GHz) source lies just on the border of the
30'' X-ray error circle. Periodicity searches at 430 MHz performed with the
Arecibo telescope failed to detect any pulsation. We argue that the 4.7 mJy
source is not the radio counterpart of SAX J0635+0533. Most likely SAX
J0635+0533 is a rather ``non-standard'' Be-star/neutron-star X-ray binary
pulsar, probably with a relatively short orbital period. It could still be a
radio emitting pulsar but with an emission beam not pointing toward the Earth.


title: Probing Cosmology with the X-ray Forest

abstract:
  There is a growing consensus that in the present universe most baryons reside
in galaxy clusters and groups in the form of highly ionized gas at temperatures
of 10^6 ~ 10^8 K. The H-like and He-like ions of the heavy elements can produce
absorption features - the so-called ``X-ray Forest'' - in the X-ray spectrum of
a background quasar. We investigate the distribution of the X-ray absorption
lines produced by this gas under three different cosmological models: the
standard CDM with Omega_0=1, a flat model with Omega_0=0.3 and an open model
with with Omega_0=0.3. We give a semi- analytic calculation of the X-ray forest
distribution based on the Press- Schechter formalism, following Perna & Loeb
(1998). We choose three ions (O VIII, Si XIV and Fe XXV) and calculate the
distribution functions, the number of absorbers along the LOS to a distant
quasar vs. redshift and column density in a given ion. We find that significant
differences in the evolution of the distribution functions among the three
cosmological models. Using Monte Carlo simulations, we simulate the
distribution of X-ray absorption lines for 10,000 random LOS. We find there are
at least several O VIII lines with column density higher than 10^16 cm^-2.
Finally we explore the possibility of detecting the X-ray forest with current
and upcoming X-ray missions and we present an XMM RGS simulation of a
representative quasar X-ray spectrum.


title: Multiresolution Analysis of Substructure in Dark Matter Halos

abstract:
  Multiresolution analysis is applied to the problem of halo identification in
cosmological N-body simulations. The procedure makes use of a discrete wavelet
transform known as the algorithme a trous and segmentation analysis. It has the
ability to find subhalos in the dense regions of a parent halo and can discern
the multiple levels of substructure expected in the hierarchical clustering
scenario. As an illustration, a 500,000 particle dark matter halo is analyzed
and over 600 subhalos are found. Statistical properties of the subhalo
population are discussed.


title: Cosmic Defects and CMB anisotropy

abstract:
  Recent measurements of the cosmic microwave background (CMB) anisotropies by
BOOMERANG and MAXIMA collaborations have tightened the observational
constraints on theories of structure formation. They disagree with the
predictions of conventional topological defect models. Considering the fact
that topological defects are predicted by the majority of realistic particle
physics models, the exact nature of the constraints imposed by the recent data
on the population and the properties of the defects must be fully understood.
We show that the predictions of current cosmic string models can be brought
into a closer agreement with the observations by choosing a closed universe
with $\Omega=1.3$ and by including the effects of the small-scale structure and
radiation products of the strings. These alone, however, are not sufficient for
obtaining a good fit to the measured shape of the angular power spectrum. To
fit the data cosmic strings would either have to be correlated on large
(perhaps superhorizon) scales or would have to possess a higher degree of
coherence, i.e. be more ``time-correlated'.


title:
Chandra Observations of Cygnus A: Magnetic Field Strengths in the Hot
  Spots of a Radio Galaxy

abstract:
  We report X-ray observations of the powerful radio galaxy Cygnus A with the
Chandra X-ray Observatory. This letter focuses on the radio hot spots, all four
of which are detected in X-rays with a very similar morphology to their radio
structure. X-ray spectra have been obtained for the two brighter hot spots (A
and D). Both are well described by a power law with photon index \Gamma = 1.8
\pm 0.2 absorbed by the Galactic column in the direction of Cygnus A. Thermal
X-ray models require too high gas densities and may be ruled out. The images
and spectra strongly support synchrotron self-Compton models of the X-ray
emission, as proposed by Harris, Carilli & Perley on the basis of ROSAT imaging
observations. Such models indicate that the magnetic field in each of the
brighter hot spots is 1.5 \times 10^-4 gauss, with an uncertainty of a few tens
of percent. This value is close to the equipartition field strengths assuming
no protons are present. The possibility that the X-rays are synchrotron
radiation is briefly discussed, but not favored. We speculate that production
of the \gamma \sim 10^7 electrons necessary for X-ray synchrotron radiation
from hot spots is inhibited when the external gas density is high, as is the
case when the radio galaxy is within a cooling flow.


title: Gamma-Ray Bursts from Up-Scattered Self-Absorbed Synchrotron Emission

abstract:
  We calculate the synchrotron self-Compton emission from internal shocks
occurring in relativistic winds as a source of gamma-ray bursts, with allowance
for self-absorption. For plausible model parameters most pulses within a
Gamma-Ray Burst (GRB) are optically thick to synchrotron self-absorption at the
frequency at which most electrons radiate. Up-scattering of photon number
spectra harder than $\nu^0$ (such as the self-absorbed emission) yields inverse
Compton photon number spectra that are flat, therefore our model has the
potential of explaining the low-energy indices harder than $\nu^{-2/3}$ (the
optically thin synchrotron limit) that have been observed in some bursts. The
optical counterparts of the model bursts are sufficiently bright to be detected
by such experiments as LOTIS, unless the magnetic field is well below
equipartition.


title: Variability in LINERs

abstract:
  A small number of LINERs have been seen to display variable H-alpha emission
with a very broad, double-peaked profile. Recent observations with the Hubble
Space Telescope indicate that such emission may be a common attribute of
LINERs. The double-peaked or double-shouldered line profiles resemble those
found in a subset of broad-line radio galaxies. Several lines of argument
suggest that such features trace an outer thin accretion disk irradiated by an
inner ion torus, in accord with advection-dominated accretion flow (ADAF)
models. Variability monitoring of this broad H-alpha component thus may provide
a means of testing accretion physics on small scales within these sources.


title: The cosmic gamma-ray background in the MeV range

abstract:
  The $\gamma$-ray background from supernovae is calculated on the basis of the
reconstructed efficiency of supernova explosions from star formation at various
redshifts. The calculations presented here show how Type Ia SN rates compatible
with the results of optical supernova searches give a background emission in
the MeV range that can explain the extragalactic emission measured by COMPTEL
and SMM. Star formation histories reaching maximum values of 0.3-0.4
M$_{\odot}$ yr$^{-1}$ Mpc$^{-3}$ at z$\sim$ 1.5 (and/or possibly keeping that
value to higher z) give a $\gamma$-ray background compatible with observations
while they also predict the observed supernova rates per comoving volume. The
$\gamma$-ray background in the MeV range is mostly sensitive to the star
formation rate at z$\sim$ 1-2, but the activity in forming stars at even higher
z has an influence as well on the absolute level of the cosmic $\gamma$-ray
background: the time elapsed by the SNe Ia progenitors until they explode has a
broad distribution and the rates of SNe Ia at z$\sim$ 1.5-2 depend on the
formation frequencies of their progenitor stars at earlier epochs.
  The mutual consistency of predictions of optical rates and integrated
emission in the $\gamma$-ray domain place in a firm ground the Type Ia
supernova identification as the astrophysical source responsible for this
cosmic background


title:
The cosmic rate of supernovae and the range of stars ending as Type Ia
  SNe

abstract:
  The present cosmic rate of Type Ia supernovae (SNeIa) suggests that about 6%
of all stars in binary systems with primaries in the initial mass range $3-9\
M\sun$ end up as SNeIa. If that is confirmed, the unavoidable conclusion is
that SNeIa can only be explained by the single degenerate scenario. At most 1%
of stars in binary systems in the above range end up as CO + CO WD pairs, with
total mass equal to or larger than the Chandrasekhar mass. Given that the
number of mergers from pairs of CO + He WDs that reach the Chandrasekhar mass
is even lower, the conclusion strongly favors binaries containing just one CO
WD as the progenitors of SNeIa, since the SNeIa production efficiency (relative
to the instantaneous star formation rate) predicted for double degenerate (DD)
pairs lies more than $3\sigma$ below the observational data, and the DD
scenario can be rejected at more than 99% confidence level. Only if the SFR
measurements from $z\sim 0.1$ to $z\sim 0.5$ are being underestimated by a
factor of 6 while SNeIa rates are not, can we escape the above conclusion. We
evaluate the numbers and characteristics of double WD systems with different
chemical compositions (CO and He WDs) that should form and compare them with
the observations, in order to check our predictions. Our conclusions appear
robust after that test.


title:
Relation between blue/UV continuum shape and the ratio of radio to
  optical emission for B3-VLA quasars

abstract:
  The low frequency radio luminosity is believed to be an indicator of jet
power, while the optical/UV emission is probably from accretion discs in the
nuclei of steep-spectrum radio quasars. We present a correlation between the
ratio of radio to optical luminosities and the continuum spectral index in
blue/UV bands, which might indicate that the continuum shape in blue/UV bands
is related to the ratio of jet to accretion power. The results may imply that
the spectra and structure of accretion discs are probably affected by the
interactions between jets and discs.


title:
Kinematics of log N(HI)~17 [cm^-2], Metal-Rich Gas Extended Around
  Intermediate Redshift Galaxies

abstract:
  The kinematics of metal-enriched, low-ionization gas at large galactocentric
distances are compared to the host galaxy properties and are discussed in the
context of global galaxy evolution.


title:
Properties and evolution of disk galaxies in a hierarchical formation
  scenario

abstract:
  We highlight some results from disk galaxy evolution models conceived within
a cosmological context. When disk mergers and strong disk-halo feedback are
omitted, several properties and correlations of disk galaxies seem to be
related to initial conditions given by the CDM model, for example, the
intensive galaxy properties, the disk Hubble sequence, and the Tully-Fisher
relation in the infrared bands.


title: Multiphase Gas in Intermediate Redshift Galaxies

abstract:
  We present 40 quasar absorption line systems at intermediate redshifts (z~1),
with focus on one of the most kinematically complex known, as examples of how
the unique capabilities of space-based and ground-based facilities can be
combined to glean much broader insights into astrophysical systems.


title: Substructure and halo density profiles in a Warm Dark Matter scenario

abstract:
  High-resolution cosmological N-body simulations were performed in order to
study the substructure of Milky Way-like galactic halos and the density
profiles of halos in a warm dark matter scenario. The results favor this
scenario with respect to the cold dark matter one.


title:
ASCA Observations of the Twin Supernova Remnants in the Large Magellanic
  Cloud, DEM L316

abstract:
  We report results from an ASCA X-ray study of DEM L316, an emission nebula in
the Large Magellanic Cloud (LMC) consisting of two closely-spaced supernova
remnants (SNRs). The SIS image shows separate X-ray sources located at the
positions of the two radio- and optically-emitting SNR shells, 0547$-$69.7A and
0547$-$69.7B (hereafter, shell A and B). The individual X-ray spectrum of each
shell is well described by optically-thin thermal emission, although the
characteristics of the emission differ in important details between them. Shell
A exhibits strong iron L emission, which we attribute to the presence of
iron-rich ejecta leading to the suggestion that this SNR originates from a Type
Ia SN, an explosion of a moderate mass progenitor. Shell B, on the other hand,
has a chemical composition similar to that of the interstellar medium of the
LMC and so its X-ray emission is dominated by swept-up matter. The different
spectral features strongly disfavor the hypothesis that the two shells are due
to one supernova explosion into an interconnected bubble. We could not obtain
the evidence which positively supports the collision between two SNRs.


title: Light Curves of GRB Optical Flashes

abstract:
  The standard model of GRB afterglows assumes that relativistically expanding
material is decelerating due to interaction with the surrounding medium. The
afterglows are well described by the synchrotron radiation from a forward
shock, while the strong optical flash associated with GRB 990123 can be
attributed to the emission from a reverse shock. We give a detailed study on
the reverse shock emission. The full light curves are calculated for a long and
a short GRB cases. We discuss the lack of the prompt optical detections by
ROTSE for GRB 981121 and GRB 981223.


title: A Model of Void Formation

abstract:
  We introduce a simple model for the formation of voids. In this model the
underdensity of galaxies in voids is the product of two factors. The first
arises from a gravitational expansion of the negative density perturbation. The
second is due to biasing: galaxies are less likely to form in an underdense
region. One feature of the model is an upper cutoff in void sizes. We calculate
the volume filling factor of characteristic voids for different CDM models and
find that our formation model points to $\Lambda$CDM models as preferred models
of the power spectrum. A natural consequence of our model is that the
underdensity of the dark matter inside voids is smaller than the galaxy
underdensity.


title: Metal Abundances of Red Clump Stars in Open Clusters: I. NGC 6819

abstract:
  We present an analysis of high dispersion spectra (R~40000) of three red
clump stars in the old open cluster NGC 6819. The spectra were obtained with
SARG, the high dispersion spectrograph of the Telescopio Nazionale Galileo. The
spectra were analyzed using both equivalent widths measured with an automatic
procedure, and comparisons with synthetic spectra. NGC 6819 is found to be
slightly metal-rich ([Fe/H]= +0.09 +/-0.03, internal error); there are no
previous high resolution studies to compare with. Most element-to-element
abundance ratios are close to solar; we find a slight excess of Si, and a
significant Na overabundance. Our spectra can also be used to derive the
interstellar reddening towards the cluster, by comparing the observed colours
with those expected from line excitation: we derive E(B-V)=0.14 +/-0.04, in
agreement with the most recent estimate for this cluster.


title: The BeppoSAX observation of Mrk 766

abstract:
  The Narrow Line Seyfert 1 galaxy Mrk 766 has been observed by BeppoSAX on May
1997. The source was fairly variable, both in flux and spectrum, during the
observation. The variability is the largest around 2 keV, possibly due to
variations in the warm absorber properties. An oxygen line is clearly detected,
at least in the first part of the observation. An edge around 7.5 keV, coupled
with the lack of any detectable iron line, suggests either reprocessing of the
primary X-rays by a mildly ionized disc or absorption by a further, thicker and
more ionized material.


title:
The Chandra High Energy Transmission Grating Observation of an X-ray
  Ionization Cone in Markarian 3

abstract:
  We present a preliminary analysis of the first high-resolution X-ray spectrum
of a Seyfert 2 galaxy, Mkn 3, obtained with the High Energy Transmission
Grating Spectrometer onboard the Chandra X-ray Observatory. The high-energy
spectrum (lambda < 4 Ang) is dominated by reflection of the AGN continuum
radiation in a cold optically thick medium and contains bright K-alpha
fluorescent lines from iron and silicon, as well as weak, blended lines from
sulfur and magnesium. The soft X-ray emission (4 < lambda < 23 Ang) is
spatially extended along the [O III] ionization cone and shows discrete
signatures of emission following recombination and photoexcitation produced in
a warm photoionized region. The measured iron L line fluxes indicate that
emission from collisionally ionized plasma is almost completely negligible, and
does not contribute significantly to the total energy budget of the X-ray
emission. We find that significant fractions of the H- and He-like resonance
lines, as well as the observed iron L lines are produced through re-emission
from the warm absorbing medium observed in Seyfert 1 galaxies. Its X-ray
spectral properties are qualitatively consistent with those of a typical
Seyfert 1 galaxy viewed at a different orientation, and provide further
convincing evidence for the existence of an obscured Seyfert 1 nucleus in Mkn
3.


title:
Synchrotron Model for the Infrared, Optical and X-Ray Emission of the
  Crab Pulsar

abstract:
  We develop a model for the infrared, optical and soft X-ray emission of the
Crab pulsar in terms of anisotropic synchrotron emission by relativistic
particles in an outer gap scenario with a single energy distribution. It is
shown that such a distribution is naturally produced in an efficient pair
cascade and that the energy of the primary particles are limited by synchrotron
radiation. It is further shown that this synchrotron model is able to reproduce
the spectral shape between the infrared and soft X-rays and also the
corresponding luminosities. In particular, the long standing problem of the
rapid spectral decline towards infrared frequencies is understandable as
emission at very small pitch angles from low energy particles. Finally, we show
that the scaling of our synchrotron model explains the observed correlation
between the X-ray luminosity and the spin-down luminosity of the neutron star.


title: An empirical model for protostellar collapse

abstract:
  We propose a new analytic model for the initial conditions of protostellar
collapse in relatively isolated regions of star formation. The model is
non-magnetic, and is based on a Plummer-like radial density profile as its
initial condition. It fits: the observed density profiles of pre-stellar cores
and Class 0 protostars; recent observations in pre-stellar cores of roughly
constant contraction velocities over a wide range of radii; and the lifetimes
and accretion rates derived for Class 0 and Class I protostars. However, the
model is very simple, having in effect only 2 free parameters, and so should
provide a useful framework for interpreting observations of pre-stellar cores
and protostars, and for calculations of radiation transport and time-dependent
chemistry. As an example, we model the pre-stellar core L1544.


title: The Demise of the Classical BLR in the Luminous Quasar PG1416-129

abstract:
  New observations of the broad-line quasar PG1416-129 reveal a large decline
in its continuum luminosity over the past ten years. In response to the
continuum change the ``classical'' broad component of Hbeta has almost
completely disappeared (a x10 decrease in flux). In its place there remains a
redshifted/redward asymmetric very broad emission line component. The
significance of this change is multifold: (1) It confirms the existence of a
distinct redshifted Very Broad Line Region (VBLR) component that persists after
the demise of the broad component and that is frequently observed, along with
the broad component, in radio-loud sources. (2) The smaller (x2) intensity
change in the Hbeta very broad component supports the previously advanced idea
that the VBLR is physically distinct and likely to arise in an optically thin
region close to the central source. (3) The presence of a strong very broad
component in the radio-quiet quasar PG1416-129 reinforces the notion that such
``population B'' quasars share similar spectroscopic (and hence geometrical and
kinematical) properties to radio-loud sources. (4) AGN can show broad, very
broad, or both line components simultaneously, making statistical comparisons
of source profile widths difficult. (5) The interpretation, in reverberation
studies, of the presence or lack of correlated response in broad line wings
will be affected by this composite BLR/VBLR structure.


title:
Magnetic Deformation of Magnetars for the Giant Flares of the Soft
  Gamma-Ray Repeaters

abstract:
  We present one possible mechanism for the giant flares of the Soft Gamma-Ray
Repeaters (SGRs) within the framework of magnetar, i.e., superstrongly
magnetized neutron star model, motivated by the positive period increase
associated with the August 27 event from SGR 1900+14. From the second-order
perturbation analysis of the equilibrium of the magnetic polytrope, we find
that there exist different equilibrium states separated by the energy of the
giant flares and the shift in the moment of inertia to cause the period
increase. This suggests that, if we assume that the global reconfiguration of
the internal magnetic field of $H\simg 10^{16}$ G suddenly occurs, the positive
period increase $\Delta P_t/P_t \sim 10^{-4}$ as well as the energy $\simg
10^{44}$ ergs of the giant flares may be explained. The moment of inertia can
increase with a release of energy, because the star shape deformed by the
magnetic field can be prolate rather than oblate. In this mechanism, since the
oscillation of the neutron star will be excited, a pulsation of $\sim$ ms
period in the burst profile and an emission of the gravitational waves are
expected. The gravitational waves could be detected by the planned
interferometers such as LIGO, VIRGO and LCGT.


title:
Rapidly rotating strange stars for a new equation of state of strange
  quark matter

abstract:
  For a new equation of state of strange quark matter, we construct equilibrium
sequences of rapidly rotating strange stars in general relativity. The
sequences are the normal and supramassive evolutionary sequences of constant
rest mass. We also calculate equilibrium sequences for a constant value of
$\Omega$ corresponding to the most rapidly rotating pulsar PSR 1937 + 21. In
addition to this, we calculate the radius of the marginally stable orbit and
its dependence on $\Omega$, relevant for modeling of kilo-Hertz quasi-periodic
oscillations in X-ray binaries.


title: Doppler Tomography of Dwarf Nova IY UMa during Quiescence

abstract:
  Quiescent Doppler tomography of the newly discovered deeply-eclipsing SU UMa
system IY UMa reveals properties of the region where the accretion stream from
the donor impacts the edge of the disc. A very strong bright spot is produced
and the Keplerian disc emission in the impact region is disrupted or obscured.
The differing properties of Halpha, Hbeta and He I emission will allow physical
parameters of the converging flow region to be studied.


title: Star Formation in Viscous Galaxy Disks

abstract:
  The Lin and Pringle model (1987) of galactic disk formation postulates that
if star formation proceeds on the same timescale as the viscous redistribution
of mass and angular momentum in disk galaxies, then the stars attain an
exponential density profile. Their claim is that this result holds generally:
regardless of the disk galaxy's initial gas and dark matter distribution and
independent of the nature of the viscous processes acting in the disk. We
present new results from a set of 2D hydro-simulations which investigate their
analytic result.


title: Secular Evolution of the Galactic Disk

abstract:
  In the solar-neighbourhood, older stars have larger random velocities than
younger ones. It is argued that the increase in velocity dispersion with time
is predominantly a gradual process rather than one induced by discrete events
such as minor mergers. Ephemeral spiral arms seem to be the fundamental drivers
of disk heating, although scattering by giant molecular clouds plays an
important moderating role. In addition to heating the disk, spiral arms cause
stars' guiding centres to diffuse radially. The speed of this diffusion is
currently controversial.
  Data from the Hipparcos satellite has made it clear that the Galaxy is by no
means in a steady state. This development enormously increases the complexity
of the models required to account for the data. There are preliminary
indications that we see in the local phase-space distribution the dynamical
footprints of long-dissolved spiral waves.


title: SAURON Observations of Disks in Early-Type Galaxies

abstract:
  We briefly describe the SAURON project, aimed at determining the intrinsic
shape and internal dynamics of spheroids. We focus here on the ability of
SAURON to identify gaseous and stellar disks and to measure their morphology
and kinematics. We illustrate some of our results with complete maps of
NGC3377, NGC3623, and NGC4365.


title: Matter in Strong Magnetic Fields

abstract:
  The properties of matter are significantly modified by strong magnetic
fields, $B>>2.35\times 10^9$ Gauss ($1 G =10^{-4} Tesla$), as are typically
found on the surfaces of neutron stars. In such strong magnetic fields, the
Coulomb force on an electron acts as a small perturbation compared to the
magnetic force. The strong field condition can also be mimicked in laboratory
semiconductors. Because of the strong magnetic confinement of electrons
perpendicular to the field, atoms attain a much greater binding energy compared
to the zero-field case, and various other bound states become possible,
including molecular chains and three-dimensional condensed matter. This article
reviews the electronic structure of atoms, molecules and bulk matter, as well
as the thermodynamic properties of dense plasma, in strong magnetic fields,
$10^9G << B < 10^{16}G$. The focus is on the basic physical pictures and
approximate scaling relations, although various theoretical approaches and
numerical results are also discussed. For the neutron star surface composed of
light elements such as hydrogen or helium, the outermost layer constitutes a
nondegenerate, partially ionized Coulomb plasma if $B<<10^{14}G$, and may be in
the form of a condensed liquid if the magnetic field is stronger (and
temperature $<10^6$ K). For the iron surface, the outermost layer of the
neutron star can be in a gaseous or a condensed phase depending on the cohesive
property of the iron condensate.


title: A New Quadruple Gravitational Lens System: CLASS B0128+437

abstract:
  High resolution MERLIN observations of a newly-discovered four-image
gravitational lens system, B0128+437, are presented. The system was found after
a careful re-analysis of the entire CLASS dataset. The MERLIN observations
resolve four components in a characteristic quadruple-image configuration; the
maximum image separation is 542 mas and the total flux density is 48 mJy at 5
GHz. A best-fit lens model with a singular isothermal ellipsoid results in
large errors in the image positions. A significantly improved fit is obtained
after the addition of a shear component, suggesting that the lensing system is
more complex and may consist of multiple deflectors. The integrated radio
spectrum of the background source indicates that it is a GigaHertz-Peaked
Spectrum (GPS) source. It may therefore be possible to resolve structure within
the radio images with deep VLBI observations and thus better constrain the
lensing mass distribution.


title:
The Massive Stellar Population in a Nearby Massive Low Surface
  Brightness Galaxy

abstract:
  We have observed the closest known large, low surface brightness (LSB)
galaxy, UGC 2302, with HST using WFPC2 and the F555W and F814W filters. UGC
2302 is a typical large LSB galaxy, and thus represents a good choice for
detailed stellar population studies. Large LSBs represent an extreme star
formation environment, both locally within their disks, and on a larger scale,
often residing in underdense regions of the universe. Resolving the underlying
stellar component of such a galaxy can provide critical information on how
stars form and evolve in low metallicity, yet gas-rich environments. We resolve
for the first time the massive stars and tip of the red giant branch in such a
system.


title: Ultra-high energy cosmic rays: are they isotropic?

abstract:
  From the analysis of AGASA data above $4 \times 10^{19}$ eV, we show that the
ultra-high energy cosmic rays flux is neither purely isotropic, nor reflects
the expected anisotropy from a pure source distribution that maps large scale
structure in the local universe. The arrival distribution seems to be the
result of a mixture of fluxes (e.g., dark matter halo plus large scale
structure) or the superposition of a direct and a diffuse radiation field
components respectively. Another viable option is an arbitrary extragalactic
flux reprocessed by a magnetized galactic wind model as recently proposed in
the literature.


title:
Spectroscopically Peculiar Type Ia Supernovae and Implications for
  Progenitors

abstract:
  In a recent paper Li et al. (2000) reported that 36 percent of 45 Type Ia
supernovae (SNe Ia) discovered since 1997 in two volume-limited supernova
searches were spectroscopically peculiar, and they suggested that because this
peculiarity rate is higher than that reported for an earlier observational
sample by Branch et al. (1993), it is now more likely that SNe Ia are produced
by more than one kind of progenitor. In this paper I discuss and clarify the
differences between the results of Li et al. and Branch et al. and I suggest
that multiple progenitor systems are now less likely than they were before.


title: Baryonic Tully-Fisher Relations

abstract:
  I describe the disk mass-rotation velocity relation which underpins the
familiar luminosity-linewidth relation. Continuity of this relation favors
nearly maximal stellar mass-to-light ratios. This contradicts the low
mass-to-light ratios implied by the lack of surface brightness dependence in
the same relation.


title: The Accelerations of Stars Orbiting the Milky Way's Central Black Hole

abstract:
  Recent measurements, of the velocities of stars near the center of the Milky
Way have provided the strongest evidence for the presence of a supermassive
black hole in a galaxy, but the observational uncertainties poorly constrain
many of the properties of the black hole. Determining the accelerations of
stars in their orbits around the center provides much more precise information
about the position and mass of the black hole. Here we report measurements of
the accelerations for three stars located ~0.005 pc from the central radio
source Sgr A*; these accelerations are comparable to those experienced by the
Earth as it orbits the Sun. These data increase the inferred minimum mass
density in the central region of the Galaxy by an order of magnitude relative
to previous results and localized the dark mass to within 0.05 +- 0.04 arcsec
of the nominal position of Sgr A*. In addition, the orbital period of one of
the observed stars could be as short as 15 years, allowing us the opportunity
in the near future to observe an entire period.


title:
On the Physical Nature of the Magnetic-Field Freezing-in Effect in
  Collisionless Cosmic Plasmas

abstract:
  Attention is drawn to a fundamental difference between the physical
mechanisms responsible for the magnetic field freezing-in effect in spatially
isotropic (collisional) and strongly anisotropic (collisionless) plasmas. (The
first case is characteristic of internal regions of the Sun and other stars;
the second, for the solar corona, interplanetary and interstellar medium,
planetary ionospheres and magnetospheres, cometary tails.) It is shown that
particles of a collisionless plasma remain in the same field line during their
motion because of the properties of electrodynamic drift which stem from the
divergence-free character of the magnetic field and the equipotentiality of the
field lines (but not as a result of the appearance of induction currents,
compensating variations of the external magnetic flux through a closed contour,
as in the case of isotropic conductivity of the plasma).


title:
Monte Carlo simulations of star clusters - II. Tidally limited,
  multi-mass systems with stellar evolution

abstract:
  A revision of Stod\{'o}{\l}kiewicz's Monte Carlo code is used to simulate
evolution of large star clusters. A survey of the evolution of N-body systems
influenced by the tidal field of a parent galaxy and by stellar evolution is
presented. The results presented are in good agreement with theoretical
expectations and the results of other methods (Fokker-Planck, Monte Carlo and
N-body). The initial rapid mass loss, due to stellar evolution of the most
massive stars, causes expansion of the whole cluster and eventually leads to
the disruption of less bound systems ($W_0=3$). Models with larger $W_0$
survive this phase of evolution and then undergo core collapse and subsequent
post-collapse expansion, like isolated models. The expansion phase is
eventually reversed when tidal limitation becomes important. The results
presented are the first major step in the direction of simulating evolution of
real globular clusters by means of the Monte Carlo method.


title: A comparison of light and velocity variations in Semiregular variables

abstract:
  NIR velocity variations are compared with simultaneous visual light curves
for a sample of late-type semiregular variables (SRV). Precise radial velocity
measurements are also presented for the SRV V450 Aql. Our aim is to investigate
the nature of the irregular light changes found in these variables.
  Light and velocity variations are correlated in all stars of our sample.
Based on these results we discuss several possibilities to explain the observed
behavior. We find that pulsation is responsible for large amplitude variations.
In a recent paper Lebzelter (1999) invoked large convective cells to understand
observed velocity variations. This possibility is discussed with respect to the
observed correlation between light and velocity changes. In the light of these
results we investigate the origin of the semiregular variations.


title:
Radial arc statistics: A new powerful probe of the central density
  profile of galaxy clusters

abstract:
  We show that an expected number ratio of radial arcs (gravitationally lensed
images whose major axes lie in the radial direction of a cluster-lens
potential) to tangential arcs (gravitationally lensed images whose major axes
lie in the tangential direction) has strong dependence on the central density
profile of galaxy clusters and has little dependence on other parameters, e.g.
cluster temperature, background source galaxy redshift etc.. A comparison of
the expected number ratios with observed ratios provides a robust test to
constrain the central density profile of galaxy clusters. A tentative
comparison with the observational data shows that the central density profile
of galaxy clusters is r^{-1} - r^{-1.5}. This result indicates that the dark
matter is collisionless at least on cluster scale. Our result gives an upper
limit on a collision cross-section of self-interaction of dark matter
sigma_coll as sigma_coll/m < 0.1 cm^2/g where m is a dark matter particle mass.


title:
Structural Model of Molecular Cloud Complexes: Mass, Size, and External
  Pressure

abstract:
  We investigate the structure of the molecular cloud complexes (MCCs) as a
group of several giant molecular clouds (GMCs) in the Galaxy. Then, we find
that the mass-size relation which has been reported for the GMCs establishes
well even for the very large MCCs whose size is about 1 kpc. Since the
horizontal size of the MCCs is more than the thickness of the Galactic disk, we
can no longer consider the MCCs to be a sphere. Thus, we construct a structural
model of the MCCs, adopting a rectangular-solid geometry. As a result, our
model explains the observed mass-size relation of the MCCs very well. {}From
the estimated external pressure around the MCCs, we find that they are in a
rough pressure balance with the interstellar medium. Moreover, we find there is
observational deficiency of the MCCs with a large size and surface density.
Then, we suggest that the external pressure has a significant effect on the
structure and evolution of the MCCs. We also discuss the effect of H {\sc ii}
regions in the MCCs.


title:
FIRES at the VLT: Measuring the Rest-Frame V-Band Luminosity of Galaxies
  from z~3 to Now

abstract:
  We present early results from the Faint InfraRed Extragalactic Survey (FIRES)
at the VLT, the main goal of which is to study galaxy evolution in a deep,
K-band selected sample. With our NIR selection, we select galaxies based on
their rest-frame optical light at all redshifts z<3. Our seven band photometry,
coupled with an accurate and reliable photometric redshift technique, gives us
the ability to study galaxies at the same rest-frame wavelength across a large
range in redshift. We present here the rest-frame V-band luminosity of objects
in our sample as a function of redshift and demonstrate the importance of near
infrared data in measuring the correct photometric redshift and rest-frame
optical luminosity.


title: Non thermal emission from galaxy clusters: radio halos

abstract:
  The number of diffuse radio halos in clusters of galaxies has grown in recent
years, making it possible to derive statistical properties of these sources and
of the hosting clusters. We show that diffuse sources are associated with X-ray
luminous clusters which have undergone recent merger processes. The radio and
X-ray structures are often similar, and correlations are found between radio
and X-ray parameters. A model for the formation and maintenance of these
sources is suggested, including a first phase of relativistic particle
injection by past major merger events, starbust and AGN activity and a second
phase of reacceleration by the energy supplied from shocks and turbulence in a
recent merger event.


title:
A new scheme of radiation transfer in H II regions including transient
  heating of grains

abstract:
  A new scheme of radiation transfer for understanding infrared spectra of H II
regions, has been developed. This scheme considers non-equilibrium processes
(e. g. transient heating of the very small grains, VSG; and the polycyclic
aromatic hydrocarbon, PAH) also, in addition to the equilibrium thermal
emission from normal dust grains (BG). The spherically symmetric interstellar
dust cloud is segmented into a large number of "onion skin" shells in order to
implement the non-equilibrium processes. The scheme attempts to fit the
observed SED originating from the dust component, by exploring the following
parameters : (i) geometrical details of the dust cloud, (ii) PAH size and
abundance, (iii) composition of normal grains (BG), (iv) radial distribution of
all dust (BG, VSG & PAH).
  The scheme has been applied to a set of five compact H II regions (IRAS
18116- 1646, 18162-2048, 19442+2427, 22308+5812 & 18434-0242) whose spectra are
available with adequate spectral resolution. The best fit models and inferences
about the parameters for these sources are presented.


title: EVN Observations of GRS1915+105

abstract:
  We obtained EVN observations of the X-ray transient source GRS1915+105 in its
radio-loud state. In 2 images obtained before a major flare, the source is
resolved, showing two opposite asymmetric jets. This indicates that steady jets
exist also before a major flare, with an estimated velocity of 0.2-0.6c.


title: X-Ray Bursters A1742-294 and SLX1744-299/300 Near the Galactic Center

abstract:
  We present a study of two X-ray bursters in the Galactic Center field with
the ART-P telescope onboard GRANAT. During 1990-1992 approximately 100 X-ray
bursts were detected from the Galactic Center field and most of them were
identified with the two persistent sources, A1742-294 and SLX1744-299/300. The
burst recurrence times were found to be ~2.4 and ~4.6 hours, respectively,
which is significantly shorter them was previously thought. We calculated the
mean and maximum fluxes during the bursts and investigated their time profiles.
We found that the shape of A1742-294 bursts correlates with the burst peak
flux. The spectral analysis was carried out for the strongest burst, detected
from A1742-294 on Oct 18, 1990.


title:
The Luminosity Function of 80 Abell Clusters from the CRoNaRio
  catalogues

abstract:
  We present the composite luminosity function (hereafter LF) of galaxies for
80 Abell clusters studied in our survey of the Northern Hemisphere, using DPOSS
data in the framework of the CRoNaRio collaboration. Our determination of the
LF has been computed with very high accuracy thanks to the use of homogeneous
data both for the clusters and the control fields and to a local estimate of
the background, which takes into account the presence of large-scale structures
and of foreground clusters and groups.
  The global composite LF is quite flat down to M^+5 and it has a slope
alpha=-1.0 +/- 0.2 with minor variations from blue to red filters, and M^* =
-21.9,-22.0,-22.3 mag (H_0=50 km s^-1 Mpc^-1) in g, r and i filters,
respectively (errors are detailed in the text).
  We find a significant difference between rich and poor clusters supporting
the existence of an LF's dependence on the environment.


title: Parsec-scale properties of a complete sample of radio galaxies

abstract:
  We report the most important results on the parsec-scale properties of a
complete sample of radio galaxies carried out at radio frequencies with the
Global VLBI array and with the VLBA. Relativistic parsec-scale jets are common
both in FRI and FRII radio galaxies, and their orientation to the line of sight
is in agreement with the expectations from the unified schemes for radio loud
AGNs. Proper motion has been detected in a few FRI galaxies in the sample. FRI
and FRII radio galaxies exhibit very similar properties on the parsec-scale.
Finally a few radio sources in the sample show evidence of velocity structure
in the parsec-scale jet, i.e. a central spine with high Lorentz factor $\gamma$
and slower layers.


title: Radio cores in blazars

abstract:
  We present results and first epoch parsec-scale images from a monitoring
program on five $\gamma$--ray loud blazars selected on the basis of their total
flux density variability. We observed 0048$-$097, 0235+164, 0954+658,
1510$-$089 and 1749+096 with the Very Long Baseline Array simultaneously at 8.4
GHz and 22 GHz. Comparison between our high quality images and previous results
from the literature suggest that 0954+658 and 1510$-$089 are superluminal radio
sources, with a Lorentz factor $\gamma$ of the order of $\sim 2 - 3$.


title: Cosmic anti-friction and accelerated expansion

abstract:
  We explain an accelerated expansion of the present universe, suggested from
observations of supernovae of type Ia at high redshift, by introducing an
anti-frictional force that is self-consistently exerted on the particles of the
cosmic substratum. Cosmic anti-friction, which is intimately related to
``particle production'', is shown to give rise to an effective negative
pressure of the cosmic medium. While other explanations for an accelerated
expansion (cosmological constant, quintessence) introduce a component of dark
energy besides ``standard'' cold dark matter (CDM) we resort to a
phenomenological one-component model of CDM with internal self-interactions. We
demonstrate how the dynamics of the LambdaCDM model may be recovered as a
special case of cosmic anti-friction. We discuss the connection with
two-component models and obtain an attractor behavior for the ratio of the
energy densities of both components which provides a possible phenomenological
solution to the coincidence problem.


title:
The X-ray Properties of Low-Frequency Quasi-Periodic Oscillations from
  GRS 1915+105 up to 120 keV

abstract:
  We present a study of the properties of strong 0.8-3.0 Hz quasi-periodic
oscillations (QPOs) that occurred during 1997 RXTE observations of the
microquasar GRS 1915+105 in the low-hard state. The high count rates allow us
to track individual QPO peaks, and we exploit this to develop a QPO folding
technique. In contrast to previous QPO studies with RXTE, we emphasize the high
energy QPO properties and report the detection of a QPO in the 60-124 keV
energy band. Our technique allows us, for the first time, to measure the phase
of the QPO harmonics relative to the fundamental. Variation in this phase
difference leads to changes in the shape of the QPO profile with energy and
over time. The strength of the QPO fundamental increases up to 19 keV, but the
data do not suggest that the strength continues to increase above this energy.
In some cases, the QPO amplitudes in the 30-60 keV and 60-124 keV energy bands
are significantly less than in the 13-19 keV and 19-29 keV energy bands. We
also use our technique to measure the phase lag of the QPO fundamental and
harmonics. In the case where negative phase lags are detected for the
fundamental, positive phase lags are detected for the first harmonic.


title: Mean Field Dynamo Saturation: Toward Understanding Conflicting Results

abstract:
  Mean field dynamos may explain the origin of large scale magnetic fields of
galaxies, but controversy arises over the extent of dynamo quenching by the
growing field. Here we explain how apparently conflicting results may be
mutually consistent, by showing the role of magnetic helicity conservation and
boundary terms usually neglected. We estimate the associated magnetic energy
flowing out of the Galaxy but emphasize that the mechanism of field escape
needs to be addressed.


title:
STIS Echelle Observations of NGC 4151: Variable Ionization of the
  Intrinsic UV Absorbers

abstract:
  We present echelle observations of the intrinsic UV absorption lines in the
Seyfert galaxy NGC 4151, which were obtained with the Space Telescope Imaging
Spectrograph (STIS) on the Hubble Space Telescope on 1999 July 19. The UV
continuum flux at 1450 Angstroms decreased by factor of about four over the
previous two years and there was a corresponding dramatic increase in the
column densities of the low-ionization absorption lines (e.g., Si II, Fe II,
and Al II), presumably as a result of a decrease in the ionizing continuum. In
addition to the absorption lines seen in previous low states, we identify a
large number of Fe II absorption lines that arise from metastable levels as
high as 4.1 eV above the ground state, indicating high densities (> 10^6
cm^-3). We find that the transient absorption feature in the blue wing of the
broad C IV emission, seen in a Goddard High Resolution Spectrograph spectrum
and thought to be a high-velocity C~IV component, is actually a Si II
fine-structure absorption line at a radial velocity of -560 km/s (relative to
systemic). We also demonstrate that the ``satellite'' emission lines of C~IV
found in International Ultraviolet Explorer spectra are actually regions of
unabsorbed continuum plus broad emission that become prominent when the UV
continuum of NGC 4151 is in a low state.


title: The Black Hole-Host Galaxy Relation in Active Galactic Nuclei

abstract:
  The masses of the central black holes of Active Galactic Nuclei estimated by
the reverberation virial technique seem to be significantly smaller than
predicted from the black hole mass-bulge luminosity relation for massive black
holes detected by kinematic methods in less active and normal galaxies. We
reexamine the relation for updated data and suggest a few reasons that may
cause this discrepancy.


title: On the Stewart-Lyth Inverse Problem

abstract:
  In this paper the Stewart-Lyth inverse problem is rewritten using the
comoving scales as the basic parameter. It is shown that some information on
the inflaton potential can be obtained from observations taking into account
only the scalar power spectrum.


title:
WSRT and VLA Observations of the 6 cm and 2 cm lines of H2CO in the
  direction of W 58 C1(ON3) and W 58 C2

abstract:
  Absorption in the J{K-K+} = 2{11}-2{12} transition of formaldehyde at 2 cm
towards the ultracompact HII regions C1 and C2 of W 58 has been observed with
the VLA with an angular resolution of ~0.2'' and a velocity resolution of ~1
km/s. The high resolution continuum image of C1 (ON 3) shows a partial shell
which opens to the NE. Strong H2CO absorption is observed against W 58 C1. The
highest optical depth (tau > 2) occurs in the SW portion of C1 near the edge of
the shell, close to the continuum peak. The absorption is weaker towards the
nearby, more diffuse compact HII region C2, tau<~0.3. The H2CO velocity (-21.2
km/s) towards C1 is constant and agrees with the velocity of CO emission,
mainline OH masers, and the H76 alpha recombination line, but differs from the
velocity of the 1720 MHz OH maser emission (~-13 km/s). Observations of the
absorption in the J{K-K+} = 1{10}-1{11} transition of formaldehyde at 6 cm
towards W 58 C1 and C2 carried out earlier with the WSRT at lower resolution
(~4''x7'') show comparable optical depths and velocities to those observed at 2
cm. Based on the mean optical depth profiles at 6 cm and 2 cm, the volume
density of molecular hydrogen n(H2) and the formaldehyde column density N(H2CO)
were determined. The n(H2) is ~6E4 /cm**3 towards C1. N(H2CO) for C1 is ~8E14
/cm**2 while that towards C2 is ~8E13 /cm**2.


title:
The Dust Temperature of the "Dusty" Radio Galaxy MG 1019+0535: Evidence
  for an Outflow

abstract:
  Radio galaxies characteristically have strong Lya emission lines. However, a
few have Lya equivalent widths that are substantially weaker in relation to
other emission lines. One in particular was studied by Dey etal (1995), MG
1019+0535 (z=2.765). We report on our reduction of Infrared Space Observatory
(ISO}) data in the 160 micron-band for this galaxy. We also compile information
on two other high redshift active galaxies with weak Lya lines, the radio
galaxy TXS 0211-122, and the AGN-starburst galaxy F 10214+4724, to provide a
small weak-Lya line sample. IRAS plus ISO data show that F 10214+4724 has a
temperature 89 +/- 12 K. TXS 0211-122 was not detected in either the
submillimeter or microwave. Submillimeter measurements of MG 1019+0535 (Cimatti
etal 1998) were suggestive of a dust temperature in the range 35 K < T_d < 80
K. However our 2-sigma upper limit on the flux at 160 microns shows that T_d <~
32 K. An energy argument based on observations which constrain the total
optical extinction strongly suggests that the dust temperature must be even
lower; T_d <~ 20 K. We find the contrast between the high-temperature dust in
the active starburst galaxy and the low-temperature dust in the evolved, albeit
active galaxy, is consistent with an expanding cloud of dust. We find that the
temperature range can be reconciled if we are seeing MG 1019+0535 at a
post-starburst age of approx. 500-700 Myr, with the bulk of its dust cloud at a
galactocentric distance R_d >~ 300 kpc.


title: The Diverse Population of ULIRGs

abstract:
  We present results from an on-going Hubble Space Telescope (HST) survey of a
large sample of ULIRGs (Ultra-Luminous IR Galaxies). New ground-based
observations are now being used to complement the HST data and to assist in the
interpretation of these complex objects. A rich spectroscopic, morphological,
and dynamical diversity is found within the ULIRG population, nearly 100% of
which are merger and/or collision remnants. The consequences of this diversity
may apply to the interpretation of distant submm/FIR sources and their
subsequent evolution.


title:
The Normal Cluster Weak Lensing Survey: Mass Profiles and M/L Ratios of
  Eight Clusters at z=0.2

abstract:
  We present a survey of mass profiles and mass-to-light ratios of eight
typical galaxy clusters at a common redshift (z ~ 0.2). We use weak
gravitational lensing as a probe because it is unique in avoiding any
assumptions about the dynamical state of the clusters. To avoid bias toward the
rare and spectacular clusters that are easy targets for lensing work, we
selected an ensemble of much more common clusters with moderate X-ray
luminosity. Although the survey is still in progress, two conclusions are
emerging: (1) within a cluster, mass follows light very closely on the angular
scales that we can measure, $0.2-2h^{-1}$ Mpc, and (2) there is a significant
cluster-to-cluster scatter in mass-to-light (M/L) ratios despite uniformity of
observing, reduction, and analysis procedures. We also derive an estimate of
$\Omega_{matter}$ based on extrapolation from the mass properties of these
typical clusters. Finally, we discuss the discovery of other clusters in our
fields through their lensing signal.


title: Modelling CO emission from Mira's wind

abstract:
  We have modelled the circumstellar envelope of {\it o} Ceti (Mira) using new
observational constraints. These are obtained from photospheric light scattered
in near-IR vibrational-rotational lines of circumstellar CO molecules at 4.6
micron: absolute fluxes, the radial dependence of the scattered intensity, and
two line ratios. Further observational constraints are provided by ISO
observations of far-IR emission lines from highly excited rotational states of
the ground vibrational state of CO, and radio observations of lines from
rotational levels of low excitation of CO. A code based on the Monte-Carlo
technique is used to model the circumstellar line emission.
  We find that it is possible to model the radio and ISO fluxes, as well as the
highly asymmetric radio-line profiles, reasonably well with a spherically
symmetric and smooth stellar wind model. However, it is not possible to
reproduce the observed NIR line fluxes consistently with a `standard model' of
the stellar wind. This is probably due to incorrectly specified conditions of
the inner regions of the wind model, since the stellar flux needs to be larger
than what is obtained from the standard model at the point of scattering, i.e.,
the intermediate regions at approximately 100-400 stellar radii (2"-7") away
from the star. Thus, the optical depth in the vibrational-rotational lines from
the star to the point of scattering has to be decreased. This can be
accomplished in several ways. For instance, the gas close to the star (within
approximately 2") could be in such a form that light is able to pass through,
either due to the medium being clumpy or by the matter being in radial
structures (which, further out, developes into more smooth or shell-like
structures).


title: A Possible Evolutionary Connection between AGN and Starburst in LINERs

abstract:
  Our analysis on the two magnitude-limited samples of LINERs suggests a
correlation between $L_{\FIR}/L_{\B}$ or f(25\micron)/f(60\micron), and
Hubble-type index at $>$99.99% significance level. As $L_{\FIR}/L_{\B}$ and
f(25\micron)/f(60\micron) are considered as the indicators of star-formation
activity and AGN activity, respectively, our result suggests that LINERs with
higher AGN activity may have a lower star-formation contribution. The ones with
highest AGN activity and lowest star-formation contributions are ellipticals.
All well-studied LINER 1s belong to this group. On the other hand, LINERs with
higher star-formation activity present lower AGN contributions. We find all
well-studied LINER 2s in this parameter space. Most of LINERs having inner ring
structures belong to this group. Statistics with other indicators of
star-formation or AGN activity (nulear mass-to-light ratio at H band, and the
ratio of X-ray-to-UV power) provide further evidence for such a trend. We have
seen that along with the evolution of galaxies from late-type spirals to
early-type ones, and up to ellipticals, the intensity of AGN activity increases
with decreasing star-formation contributions, The above analyses may suggest a
possible connection between the host galaxies and nuclear activities, and it
might also indicate a possible evolutionary connection between AGN and
starburst in LINERs.


title: Geometrical estimators as a test of Gaussianity in the CMB

abstract:
  We investigate the power of geometrical estimators on detecting
non-Gaussianity in the cosmic microwave background. In particular the number,
eccentricity and Gaussian curvature of excursion sets above (and below) a
threshold are studied. We compare their different performance when applied to
non-Gaussian simulated maps of small patches of the sky, which take into
account the angular resolution and instrumental noise of the Planck satellite.
These non-Gaussian simulations are obtained as perturbations of a Gaussian
field in two different ways which introduce a small level of skewness or
kurtosis in the distribution. A comparison with a classical estimator, the
genus, is also shown. We find that the Gaussian curvature is the best of our
estimators in all the considered cases. Therefore we propose the use of this
quantity as a particularly useful test to look for non-Gaussianity in the CMB.


title:
ARCS, The Arcminute Radio Cluster-lens Search - I. Selection Criteria
  and Initial Results

abstract:
  We present the results of an unbiased radio search for gravitational lensing
events with image separations between 15 and 60 arcsec, which would be
associated with clusters of galaxies with masses >10^{13-14}M_{\sun}. A parent
population of 1023 extended radio sources stronger than 35 mJy with stellar
optical identifications was selected using the FIRST radio catalogue at 1.4 GHz
and the APM optical catalogue. The FIRST catalogue was then searched for
companions to the parent sources stronger than 7 mJy and with separation in the
range 15 to 60 arcsec. Higher resolution observations of the resulting 38 lens
candidates were made with the VLA at 1.4 GHz and 5 GHz, and with MERLIN at 5
GHz in order to test the lens hypothesis in each case. None of our targets was
found to be a gravitational lens system. These results provide the best current
constraint on the lensing rate for this angular scale, but improved
calculations of lensing rates from realistic simulations of the clustering of
matter on the relevant scales are required before cosmologically significant
constraints can be derived from this null result. We now have an efficient,
tested observational strategy with which it will be possible to make an
order-of-magnitude larger unbiased search in the near future.


title:
High column densities and low extinctions of gamma-ray bursts: Evidence
  for hypernovae and dust destruction

abstract:
  We analyze a complete sample of gamma-ray burst afterglows, and find X-ray
evidence for high column densities of gas around them. The column densities are
in the range 1e+22-1e+23/cm2, which is right around the average column density
of Galactic giant molecular clouds. We also estimate the cloud sizes to be
10-30 pc, implying masses greater than about 1e+5 solar masses. This strongly
suggests that gamma-ray bursts lie within star forming regions, and therefore
argues against neutron star mergers and for collapses of massive stars as their
sources. The optical extinctions, however, are 10-100 times smaller than
expected from the high column densities. This confirms theoretical findings
that the early hard radiation from gamma-ray bursts and their afterglows can
destroy the dust in their environment, thus carving a path for the afterglow
light out of the molecular cloud. Because of the self-created low extinction
and location in star-forming regions, we expect gamma-ray bursts to provide a
relatively unbiased sample of high-redshift star formation. Thus they may help
resolve what is the typical environment of high-redshift star formation.


title:
The mystery of cosmological vacuum energy density and the accelerated
  expansion of the universe

abstract:
  The principles of General Relativity allow for a non-vanishing cosmological
constant, which can possibly be interpreted at least partially in terms of
quantum-fluctuations of matter fields. Depending on sign and magnitude it can
cause accelerated or decelerated expansion at certain stages of cosmic
evolution. Recent observations in cosmology seem to indicate that we presently
live in an accelerated phase. We recall the history and fundamental issues
connected with the cosmological constant and then discuss present evidences for
a positive value, which causes the accelerated expansion.


title: High Energy Gamma Rays

abstract:
  This article reviews the present status of high energy gamma-ray astronomy at
energies above 30 MeV. Observations in the past decade using both space- and
ground-based experiments have been primarily responsible for giving a
tremendous boost to our knowledge of the high energy Universe. High energy
gamma-rays have been detected from a wide range of Galactic and extragalactic
astrophysical sources, such as gamma-ray bursters, pulsars, and active
galaxies. These observations have established high energy gamma-ray astronomy
as a vital and exciting field, that has a bright future. This review summarizes
the experimental techniques, observations and results obtained with recent
experiments, and concludes with a short description of future prospects.


title: The Mass Distribution in Low Surface Brightness Galaxies

abstract:
  The distribution of the stellar and gaseous components in low surface
brightness galaxies has been determined directly from optical and HI imaging.
The distribution of what might be the dominant mass component, the dark matter,
which is inferred from rotation curves, is far harder to determine. Although
the rotation curves themselves can be determined fairly accurately from HI
synthesis observations, and in particular from H$\alpha$ spectroscopy, the
uncertainty in the mass modeling leaves room for a wide range of possible dark
matter distributions, ranging from maximum stellar disks with shallow dark
halos to cuspy dark halos with little mass in stars.


title: Parsec-Scale Imaging of HI Absorption in 1946+708

abstract:
  In the last several years, a number of compact extragalactic radio sources
have been found to exhibit neutral hydrogen absorption at or near the systemic
velocities of their host galaxies. Models proposed to explain this phenomenon
involve a circumnuclear torus of gas and dust. The orientation of this
structure determines whether or not the central engine appears obscured.
Understanding the spatial distribution and kinematics of the HI detected toward
the central parsecs of these sources provides an important test of this model
and of unified schemes for AGN.
  We present results of Global VLBI Network observations of the redshifted 21
cm HI line toward the Compact Symmetric Object 1946+708 (z=0.101). This source
is of particular interest because it exhibits bi-directional motion measurable
on timescales of a few years. The resulting unique information about the
geometry of the continuum source greatly assists in the interpretation of the
HI distribution. We find significant structure in the gas on parsec scales. The
peak column density of the HI occurs near the center of activity of the source,
as does the highest velocity dispersion (FWHM ~ 350 to 400 km/s). The
distribution of gas in 1946+708 is strongly suggestive of a circumnuclear torus
of atomic material with one or more additional compact clumps of gas along the
line of sight to the approaching jet.


title: Polarization Limits in Compact Symmetric Objects

abstract:
  We present results of multifrequency polarimetric VLBA observations of 34
compact radio sources. The observations are part of a large survey undertaken
to identify CSOs Observed in the Northern Sky (COINS). Based on VLBI continuum
surveys of ~2000 compact radio sources, we have defined a sample of 52 CSOs and
CSO candidates. Positive identification of CSOs is contingent upon acquiring
multi-frequency observations in order to correctly identify the core of the
source, which is expected to have a strongly inverted spectrum. We also expect
CSOs to exhibit very little polarized flux. Despite the fact that synchrotron
emission is intrinsically highly polarized, less than 0.5% fractional
polarization is seen in low resolution studies of CSOs at frequencies up to 5
GHz. One possible explanation for the low observed linear polarization from
CSOs is that their radiation is depolarized as it passes through a magnetized
plasma associated with a circumnuclear torus. This interpretation is consistent
with the unified scheme of AGN, and also with the recent detections of
free-free and HI absorption in CSOs.
  Here we present limits on the polarized flux density at 8.4 GHz and ~1 mas
resolution for 21 CSOs and candidates in the COINS sample.


title: Global VLBI Observations of HI Absorption toward NGC 3894

abstract:
  One of the most important problems in the study of AGN is understanding the
detailed geometry, physics, and evolution of the central engines and their
environments. The leading models involve an accretion disk and torus around a
central black hole. Much of this torus should be comprised of atomic gas,
detectable in absorption toward the bright inner radio jets. In the last few
years, a number of compact symmetric radio sources have been found to exhibit
HI absorption, at or near the systemic velocity, toward the central parsecs.
Understanding the kinematics of the HI detected toward the central parsecs of
these sources will provide an important test of this model and of unified
schemes for AGN. We present results of Global VLBI Network observations at 1.4
GHz toward the active nucleus of the nearby elliptical galaxy NGC 3894 (a.k.a.
1146+596, z=0.01068). The center of activity in this source and the orientation
of the jets with respect to our line of sight have been determined using VLBI
studies of the proper motions of jet components. The 21 cm atomic hydrogen line
is seen in absorption slightly redshifted with respect to the systemic velocity
toward the core, jet, and counterjet of this source. The structure of the HI in
this source is complicated. We find several distinct components present along
the lines of sight to the approaching and receding jets, making interpretation
challenging.


title: Deep Near Infrared Photometry of New Galactic Globular Clusters

abstract:
  We present a preliminary report on the first deep infrared photometry of
2MASS GC01 and 2MASS GC02 (GC01 and GC02 hereafter) - new Galactic globular
cluster (GC) candidates, discovered by the 2MASS. They both appear to be
genuine disk GCs though highly obscured. The location of the two GCs suggests
that they are metal rich - [Fe/H]~-0.5. We estimated their distance and
reddening using the K_s-band brightness of the red giant branch (RGB) bump, and
J-K_s color of the RGB at M_K=-3 mag: D=3.1+/-0.5, 3.9+/-0.6 kpc, and
A_V=20.9+/-0.7, 17.2+/-1.2 mag, for GC01 and GC02 respectively. Variation in
the metal abundance can change our results within 30-35%.


title:
RXTE Investigation into Extended Hard X-ray Emission from Elliptical
  Galaxies

abstract:
  We present results of the first RXTE investigation of hard X-ray emission
from normal elliptical galaxies. Joint spectral analysis of RXTE PCA and ASCA
GIS data for NGC 4472 and NGC 4649 reveals the presence of about 5 10^-12 erg
cm^-2 s^-1 of 2-10 keV emission emanating from a region outside of the optical
galaxy, and of a spectral hardness intermediate between the galactic hot
interstellar gas and X-ray binary components. A large fraction of this emission
originates in the Virgo intracluster medium (ICM) and we present constraints on
the ICM temperature and metallicity in the vicinity of these two galaxies.
However, the diffuse flux is significantly greater than expected based on the
soft X-ray intensity measured with ROSAT, allowing for the possible presence of
an additional diffuse non-thermal component. We also derive new constraints on
the integrated X-ray binary emission from these two galaxies, and on the
presence of a nuclear flat-spectrum point source.


title: Irradiated Herbig-Haro Jets in the Orion Nebula and Near NGC 1333

abstract:
  We report the discovery of a dozen Herbig-Haro jets illuminated by the Lyman
continuum and/or softer far-ultraviolet radiation fields of nearby high mass
stars. Five irradiated outflows lie in the outer parts of the Orion Nebula and
seven lie near the reflection nebula NGC 1333 in the Perseus molecular cloud.
We propose that the UV radiation field has eroded residual material left over
from the formation of these young source stars. Many of the irradiated jets
exhibit unusual C-shaped bending. In the outskirts of the Orion Nebula, most
irradiated jets bend away from the core of the nebula. On the other hand, in
NGC 1333, the C-shaped jets bend back towards the cluster center. Jet bending
in the Orion Nebula may be dominated by either the outflow of material from the
nebular core or by the rocket effect pushing on the irradiated portion of a
mostly neutral jet beam. But in NGC 1333, jet bending may indicate that the
source stars have been ejected from the cluster core. Many irradiated jets are
asymmetric with one beam much brighter than the other. When fully
photo-ionized, irradiated jets may provide unique insights into the physical
conditions within outflows powered by young stars, permitting the determination
of the density and location of stellar ejecta even in the absence of shocks. We
present a model for the photo-ionization of these outflows by external
radiation fields and discuss possible mechanisms for producing the observed
asymmetries. We demonstrate that the UV radiation field may alter the amount of
cloud material entrained by the jet. We also report the discovery of some large
scale bow shocks which face the core of the Orion Nebula and which surround
visible young stars. These wind-wind collision fronts provide further evidence
for a large scale mass flow originating near the nebular core.


title: Starbursts and the Evolution of Gas-Rich Galaxies

abstract:
  Moderately luminous starbursts in the nearby universe often occur in disk
galaxies that are at most subject to mild external perturbations. An
investigation of this type of galaxy leads to a better understanding of
starburst triggering mechanisms and the resulting star formation processes, and
provides useful comparisons to more extreme starbursts seen at high redshifts.


title: Clustering in Highest Energy Cosmic Rays: Physics or Statistics?

abstract:
  Directional clustering can be expected in cosmic ray observations due to
purely statistical fluctuations for sources distributed randomly in the sky. We
develop an analytic approach to estimate the probability of random cluster
configurations, and use these results to study the strong potential of the
HiRes, Auger, Telescope Array and EUSO/OWL/AirWatch facilities for deciding
whether any observed clustering is most likely due to non-random sources.


title: X-ray Properties of Groups of Galaxies

abstract:
  ROSAT observations indicate that approximately half of all nearby groups of
galaxies contain spatially extended X-ray emission. The radial extent of the
X-ray emission is typically 50-500 kpc or approximately 10-50% of the virial
radius of the group. Diffuse X-ray emission is generally restricted to groups
that contain at least one early-type galaxy. X-ray spectroscopy suggests the
emission mechanism is most likely a combination of thermal bremsstrahlung and
line emission. This interpretation requires that the entire volume of groups be
filled with a hot, low-density gas known as the intragroup medium. Higher
temperature groups tend to follow the correlations found for rich clusters
between X-ray luminosity, temperature, and velocity dispersion. However, groups
with temperatures below approximately 1 keV appear to fall off the cluster L-T
relationship (and possibly the L-sigma and sigma-T cluster relationships,
although evidence for these latter departures is at the present time not very
strong.)


title:
Peculiar Extended X-ray Emission around the "Radio-Loud" Black Hole
  Candidate 1E1740.7-2942

abstract:
  We present the discovery of peculiar extended X-ray emission around
1E1740.7-2942, a black hole candidate that is known to produce prominent,
persistent radio jets. The data was obtained with the High-Energy Transmission
Grating Spectrometer (HETGS) aboard the Chandra X-ray Observatory. The
zeroth-order image reveals an elongated feature about 3" in length that is
roughly perpendicular to the radio lobes (or jets). The feature is roughly
symmetric about the point source. It is spatially resolved in the long
direction but not in the short direction.
  The position of 1E1740.7-2942 was determined with a statistical accuracy of
\~0.06" in the right ascension and ~0.04" in the declination, thanks to
Chandra's unprecedented spatial resolution. It is about 0.6" from the radio
position but the difference is well within the uncertainty in the absolute
aspect solutions of the observation. The dispersed HETGS spectra of
1E1740.7-2942 show evidence for the presence of weak, narrow emission lines,
although the statistics are quite limited. We discuss possible origins of the
extended emission and the implications of the emission lines.


title: A Comparison of Simulated and Analytic Major Merger Counts

abstract:
  We use large volume, high resolution, N-body simulations of 3 different
$\Lambda$CDM models, with different clustering strengths, to generate dark
matter halo merging histories. Over the reliable range of halo masses, roughly
galaxy groups to rich clusters of galaxies, we quantify the number density of
major mergers for two different time intervals and compare with analytic
predictions based on the extended Press-Schechter (1974) theory.


title: Deep near-infrared luminosity function of a cluster of galaxies at z=0.3

abstract:
  The deep near-infrared luminosity function of AC118, a cluster of galaxies at
z=0.3, is presented. AC118 is a bimodal cluster, as evidenced both by our
near-infrared images of lensed galaxies, by public X-ray Rosat images and by
the spatial distribution of bright galaxies. Taking advantage of the extension
and depth of our data, which sample an almost unexplored region in the depth
vs. observed area diagram, we derive the luminosity function (LF), down to the
dwarf regime (M*+5), computed in several cluster portions. The overall LF,
computed on a 2.66 Mpc2 areas (H_0=50 km/s/Mpc), has an intermediate slope
(alpha=-1.2). However, the LF parameters depend on the surveyed cluster region:
the central concentration has 2.6^{+5.1}_{-1.7} times more bright galaxies and
5.3^{+7.2}_{-2.3} times less dwarfs per typical galaxy than the outer region,
which includes galaxies at an average projected distance of ~580 kpc (errors
are quoted at the 99.9 % confidence level). The LF in the secondary AC118 clump
is intermediate between the central and outer one. In other words, the
near-infrared AC118 LF steepens going from high to low density regions. At an
average clustercentric distance of ~580 kpc, the AC118 LF is statistically
indistinguishable from the LF of field galaxies at similar redshift, thus
suggesting that the hostile cluster environment plays a minor role in shaping
the LF at large clustercentric distances, while it strongly affects the LF at
higher galaxy density.


title: UHECR Production and Curvature TeV Emission in Nearby, Dormant AGNs

abstract:
  The possibility that rapidly rotating supermassive black holes associated
with quasar remnants may provide sites for the acceleration of ultra-high
energy cosmic rays (UHECRs) is considered. It is shown that prodigious TeV
emission through curvature losses is an important consequence of this
mechanism. Given the measured UHECR flux, it is expected that nearby dormant
AGNs will be detectable by current Tev experiments. The implications for the
Sgr A* source are also briefly considered.


title: Excitation of H_2 and HD in shocks and PDRs

abstract:
  Photodissociation regions (PDRs) and shocks give rise to conspicuous emission
from rotationally and vibrationally excited molecular hydrogen. This line
emission has now been studied with ISO and from the ground in great detail. A
remarkable discovery has been that toward the Orion outflow and other
shock-excited regions, the H_2 level populations show a very high excitation
component. We suggest that these high-excitation populations may arise from
non-thermal pumping processes, such as H_2 formation and high-velocity
ion-molecule collision in partially dissociative shocks. In PDRs such as NGC
7023 however, formation pumping is always less important than fluorescent
pumping. We furthermore present two HD emission line detections toward Orion
Peak 1. This enables the first comparison of the H_2 and the HD excitation,
which surprisingly turn out to be identical.


title: Gravitational Lensing and Cluster of Galaxies

abstract:
  Multiple images, giant arcs, Einstein cross, fold, cusp, lip, caustics,
critical lines, sources, mapping, time delay, arclets, weak shear,
magnification bias, depletion, ellipticities, polarization, smearing,
convergence, kernel, mass reconstruction, sub-structure, dark halos, natural
telescope, amplification, distant galaxies, faintest sources ... This is a non
exhaustive list of favorite terms used when using gravitational lensing in
clusters of galaxies. I will introduce here lensing in clusters as a useful
tool in modern observational cosmology. I will give a summary of what we are
learning in terms of cluster mass distribution in the strong and weak regime,
and what information we will gain in terms of the cluster physics. I will
underline the benefit of using cluster-lenses as natural telescopes to probe
the distant Universe.


title: On the mystery of the cosmic vacuum energy density

abstract:
  After a short history of the $\Lambda$-term it is explained why the
(effective) cosmological constant is expected to obtain contributions from
short-distance physics, corresponding to an energy at least as large as the
Fermi scale. The actual tiny value of the cosmological constant by particle
physics standards represents, therefore, one of the deepest mysteries of
present-day fundamental physics. Recent proposals of an approach to the
cosmological constant problem which make use of (large) extra dimensions are
briefly discussed. Cosmological models with a dynamical $\Lambda$, which
attempt to avoid the disturbing cosmic coincidence problem, are also reviewed.


title:
The Durham/UKST Galaxy Redshift Survey - VII. Redshift-space distortions
  in the power spectrum

abstract:
  We investigate the effect of redshift-space distortions in the power spectrum
parallel and perpendicular to the observer's line of sight, P(k_par,k_perp),
using the optically selected Durham/UKST Galaxy Redshift Survey. On small,
non-linear scales anisotropy in the power-spectrum is dominated by the galaxy
velocity dispersion; the `Finger of God' effect. On larger, linear scales
coherent peculiar velocities due to the infall of galaxies into overdense
regions are the main cause of anisotropy. According to gravitational
instability theory these distortions depend only on the density and bias
parameters via beta. Geometrical distortions also occur if the wrong cosmology
is assumed, although these would be relatively small given the low redshift of
the survey. To quantify these effects, we assume the real-space power spectrum
of the APM Galaxy Survey, and fit a simple model for the redshift-space and
geometrical distortions. Assuming a flat Omega = 1 universe, we find values for
the one-dimensional pairwise velocity dispersion of sigma_p = 410 +- 170 km/s,
and beta = 0.38 +- 0.17. An open Omega = 0.3, and a flat Omega = 0.3, Lambda =
0.7 universe yield sigma_p = 420 km/s, beta = 0.40, and sigma_p = 440 km/s,
beta = 0.45 respectively, with comparable errors. These results are consistent
with estimates using the two-point galaxy correlation function, xi(sigma,pi),
and favour either a low-density universe with Omega ~ 0.3 if galaxies trace the
underlying mass distribution, or a bias factor of b ~ 2.5 if Omega = 1.