title: A Nearby Supernovae Search: Eros2

abstract:
  Type Ia supernovae (SNIa) have been used as approximate standard candles to
measure cosmological parameters such as the Hubble constant and the
deceleration parameter. These measurements rely on empirical correlations
between peak luminosities and other features that can be observed in the
supernovae spectra and their light curves. Such correlations deserve further
study since they have been established from small samples of nearby SNIa. Two
years ago, the EROS2 collaboration launched an automated search for supernovae
with the 1m Marly telescope operating at La Silla. In all, 57 SNe have been
discovered in this EROS2 search and spectra have been obtained for 26 of them.
We found that 75% were of type Ia and 25% of type II. Using this sample, a
preliminary SN explosion rate has been obtained. Our most recent observation
campaign took place in February and March 99. It was performed in the framework
of a large consortium led by the {\em Supernova Cosmology Project}. The aim of
this intensive campaign was to provide an independent set of high quality light
curves and spectra to study systematic effects in the measurement of
cosmological parameters. We will briefly describe our search procedure and
present the status of our ongoing analysis.


title:
A strong jet/cloud interaction in the Seyfert galaxy IC 5063: VLBI
  observations

abstract:
  We present 21-cm HI line and 13-cm continuum observations, obtained with the
Australian Long Baseline Array, of the Seyfert 2 galaxy IC 5063. This object
appears to be one of the best examples of Seyfert galaxies where shocks
produced by the radio plasma jet influence both the radio as well as the
near-infrared emission. The picture resulting from the new observations of IC
5063 confirms and completes the one derived from previous Australia Telescope
Compact Array (ATCA) lower resolution observations. A strong interaction
between the radio plasma ejected from the nucleus and a molecular cloud of the
ISM is occurring at the position of the western hot spot, about 0.6 kpc from
the active nucleus. Because of this interaction, the gas is swept up, forming,
around the radio lobe, a cocoon-like structure where the gas is moving at high
speed. Due to this, part of the molecular gas is dissociated and becomes
neutral or even ionised if the UV continuum produced by the shocks is hard and
powerful enough. The main component detected in the VLBI HI absorption profile
has a central velocity of 2786 km/s and is therefore blue-shifted 614 km/s with
respect to the systemic velocity. Its peak optical depth is 5.4 %. The
corresponding column density of the detected absorption, for a spin temperature
of 100 K, is N_HI ~ 2x10^21 atoms cm^-2. The HI absorption properties observed
in IC 5063 appear different from those observed in other Seyfert galaxies,
where the HI absorption detected is attributed to undisturbed foreground gas
associated with the large-scale galaxy disk.


title: Detection of deuterium Balmer lines in the Orion Nebula

abstract:
  The detection and first identification of the deuterium Balmer emission
lines, D-alpha and D-beta, in the core of the Orion Nebula is reported.
Observations were conducted at the 3.6m Canada-France-Hawaii Telescope, using
the Echelle spectrograph Gecko. These lines are very narrow and have identical
11 km/s velocity shifts with respect to H-alpha and H-beta. They are probably
excited by UV continuum fluorescence from the Lyman (DI) lines and arise from
the interface between the HII region and the molecular cloud.


title:
The Formation of Galaxies, the Formation of Old Globular Clusters and
  the Link with High-Redshift Objects

abstract:
  In this paper, we are exploring the properties of old, metal-poor globular
clusters in galaxies. We investigate whether their properties are related to
the properties of their host galaxies, and whether we can constrain their
formation. The main result is that the mean metallicities of old GC systems are
found to lie in a narrow range -1.7 < [Fe/H] < -1.1 (80 % of the population).
Moreover, no correlations are found between the mean metallicities and other
galaxy properties which implies a GC formation independent of the host
galaxies. Further, we try to identify the sites of old, metal-poor GC
formation, with any currently known high redshift objects. We find that the
metalicities of damped Ly$\alpha$ systems in the redshift range 1.6 < z < 4 are
consistent with our GC metalicities, which suggests that these high-density
neutral gas objects may be the progenitors of the old, metal-poor globular
clusters.


title:
Predicting the Properties of Binary Stellar Systems: The Evolution of
  Accreting Protobinary Systems

abstract:
  We investigate the formation of binary stellar systems. We consider a model
where a `seed' protobinary system forms, via fragmentation, within a collapsing
molecular cloud core and evolves to its final mass by accreting material from
an infalling gaseous envelope. This accretion alters the mass ratio and orbit
of the binary, and is largely responsible for forming the circumstellar and/or
circumbinary discs. Given this model for binary formation, we predict the
properties of binary systems and how they depend on the initial conditions
within the molecular cloud core. We predict that there should be a continuous
trend such that closer binaries are more likely to have equal mass components
and are more likely to have circumbinary discs than wider systems. Comparing
our results to observations, we find that the observed mass-ratio distributions
of binaries and the frequency of circumbinary discs as a function of separation
are most easily reproduced if the progenitor molecular cloud cores have radial
density profiles between uniform and 1/r (e.g. Gaussian) with near
uniform-rotation. This is in good agreement with the observed properties of
pre-stellar cores. Conversely, we find that the observed properties of binaries
cannot be reproduced if the cloud cores are in solid-body rotation and have
initial density profiles which are strongly centrally condensed. Finally, in
agreement with the radial-velocity searches for extra-solar planets, we find
that it is very difficult to form a brown dwarf companion to a solar-type star
with a separation < 10 AU, but that the frequency of brown dwarf companions
should increase with larger separations or lower mass primaries.


title:
Formation of the optical spectra of the coolest M- and L-dwarfs and
  lithium abundances in their atmospheres

abstract:
  Theoretical aspects of modeling of spectra of late M- and L-dwarfs are
discussed. We show, that the processes of formation of spectra of M- and
L-dwarfs are basically different. Instead of the case of M-dwarfs, atoms of Ti
and V should be depleted into grains in the atmospheres of L-dwarfs. Overall
shape of the L-dwarf spectra is governed by the K I + Na I resonance line wings
of the huge strength. To fit lithium lines observed in spectra of the coolest
dwarfs we used two additional suggestions: a) there are some EXTRA depletions
of molecular species absorbed in the optical spectra of L-dwarfs; b) there may
be (a few?) additional (``dusty''?) opacity sources in their atmospheres.
Problems of lithium line formation and the ``natural'' limitation of their use
for the ``lithium test'' for the case of L-dwarfs are considered.


title:
On radial gas flows, the Galactic Bar and chemical evolution in the
  Galactic Disc

abstract:
  We develop a numerical chemical model allowing for radial flows of gas, with
the aim to analyse the possible role of gas flows in the chemical evolution of
the Galactic Disc. The dynamical effects of the Galactic Bar on the radial gas
profile of the Disc are especially addressed.


title: E+A galaxies in the near-IR: Broad band photometry

abstract:
  (Abridged) We present near-IR photometry of a selected sample of southern
hemisphere E+A galaxies. The sample includes 50 galaxies from nearby and
distant clusters as well as E+A galaxies from the field. The photometry
includes J, H and Ks apparent magnitudes and colors. Observed colors are
obtained from the apparent total magnitudes and compared to spectrophotometric
models of galaxy evolution GISSEL96. There is an overall agreement between
integrated colors of models and observed ones, for both the E+A located in
clusters and in the field, at z~0.1. However, large differences are found
between colors predicted from models and those observed in E+A galaxies located
in more distant clusters. We investigate systematic properties of the E+A
sample as a function of their environment. Results seem to indicate that
cluster E+As (at low redshift) are bluer than field E+As at z~0.1. Even this
conclusion does not depend whether we use comoving or rest-frame colors, nor on
the models used to obtain rest-frame colors; the difference is not significant
enough, considering color dispersions between the samples. If differences are
real, they could imply different stellar content for the E+A galaxies located
in the field, compared to the cluster E+A.


title: UBVRI photometric comparison sequences for symbiotic stars

abstract:
  We present accurate UBVRI photometric comparison sequences around 20
symbiotic stars. The sequences extend over wide brightness and color ranges,
and are suited to cover quiescence as well as outburst phases. The sequences
are intended to assist both present time photometry as well as measurement of
photographic plates from historical archives. The types of variability
presented by symbiotic stars are reviewed. Individual notes on the known
photometric behaviour of the program stars are provided.


title: Spectral Analysis of the Lyman-Alpha Forest Using Wavelets

abstract:
  It is shown how wavelets may be used to analyse the absorption properties of
the Lya forest. The Discrete Wavelet Transform of a QSO spectrum is used to
decompose the light fluctuations that comprise the forest into orthogonal
wavelets. It is demonstrated that most of the signal is carried by the moderate
to lower frequency wavelets in high resolution spectra, and that a
statistically acceptable description of even high signal-to-noise spectra is
provided by only a fraction (10-30%) of the wavelets. The distributions of the
wavelet coefficients provide a statistical basis for discriminating between
different models of the Lya forest. The method is illustrated using the
measured spectrum of Q1937-1009. The procedure described is readily automated
and may be used to process both measured spectra and the large number of
spectra generated by numerical simulations, permitting a fair comparison
between the two.


title: Analysis of cosmic ray data

abstract:
  Reviews statistical methods for 1- and 2-dimensional analysis of cosmic ray
data including recent Bayesian analyses.


title:
Absence of "Ghost Images" Excludes Large Values of the Cosmological
  Constant

abstract:
  We used the 1.4 GHz NRAO NVSS survey to search for ghost images of radio
sources, expected in cosmologies with a positive cosmological constant and
positive space curvature. No statistically significant evidence for ghost
images was found, placing constraints on the values of L, the space curvature
or the duration of the radio-luminous phase of extragalactic radio sources.


title: Effect of Reionization on the Structure Formation in the Universe

abstract:
  I use simulations of cosmological reionization to quantify the effect of
photoionization on the gas fraction in low mass objects, in particular the
characteristic mass scale below which the gas fraction is reduced compared to
the universal value. I show that this characteristic scale can be up to an
order of magnitude lower than the linear theory Jeans mass, and that even if
one defines the Jeans mass at a higher overdensity, it does not track the
evolution of this characteristic suppression mass. Instead, the filtering mass,
which corresponds directly to the scale over which baryonic perturbations are
smoothed in linear perturbation theory, provides a remarkably good fit to the
characteristic mass scale. Thus, it appears that the effect of reionization on
structure formation in both the linear and nonlinear regimes is described by a
single characteristic scale, the filtering scale of baryonic perturbations. In
contrast to the Jeans mass, the filtering mass depends on the full thermal
history of the gas instead of the instantaneous value of the sound speed, so it
accounts for the finite time required for pressure to influence the gas
distribution in the expanding universe. In addition to the characteristic
suppression mass, I study the full shape of the probability distribution to
find an object with a given gas mass among all the objects with the same total
mass, and I show that the numerical results can be described by a simple
fitting formula that again depends only on the filtering mass. This simple
description of the probability distribution may be useful for semi-analytical
modeling of structure formation in the early universe.


title: Dynamical effects of a cosmological constant

abstract:
  The observational evidence for the existence of a non-zero cosmological
constant is getting stronger. It is therefore timely to address the question of
its eventual effect on the dynamics of galaxies, clusters and larger structures
in the Universe. We find, contrary to a recent claim, that the influence of the
cosmological constant has to be negligible for, e.g., the rotation curves of
galaxies. On larger scales, starting with large galaxy clusters, there are
potentially measurable effects from the repulsive addition to the Newtonian
gravitational force caused by the cosmological constant.


title: Can we predict the fate of the Universe?

abstract:
  We re-analyze the question of the use of cosmological observations to infer
the present state and future evolution of our patch of the universe. In
particular, we discuss under which conditions one might be able to infer that
our patch will enter an inflationary stage, as a prima facie interpretation of
the Type Ia supernovae and CMB data would suggest. We then establish a
`physical' criterion for the existence of inflation, to be contrasted with the
more `mathematical' one recently proposed by Starkman et al. \cite{STV}.


title:
Morphology and kinematics of Planetary Nebulae II. A Diabolo model for
  NGC 3132

abstract:
  We use a 3D photoionization modeling tool to study the morpho-kinematic
properties of the Planetary Nebula (PN) NGC 3132. We show that it is possible
to reproduce the low resolution observations (spectra and images) with an
ellipsoidal shell. However, high resolution observations, as those showing a
density variation along the nebula and the [O III]5007 velocity profiles,
definitively rule out this description. We show that a bipolar Diabolo shape
with a 40 degres rotation of the symmetry axis relative to the line of sight
successfully reproduces the observed images, as well as the high resolution
observations.


title:
Ultra-High-Energy Cosmic Ray Acceleration by Magnetic Reconnection in
  Newborn Accretion Induced Collapse Pulsars

abstract:
  We here investigate the possibility that the ultra-high energy cosmic ray
(UHECR) events observed above the GZK limit are mostly protons accelerated in
reconnection sites just above the magnetosphere of newborn millisecond pulsars
which are originated by accretion induced collapse (AIC). We show that
AIC-pulsars with surface magnetic fields $10^{12} G < B_{\star} \lesssim
10^{15}$ G and spin periods $1 ms \lesssim P_{\star} < 60 ms$, are able to
accelerate particles to energies $\geq 10^{20}$ eV. Because the expected rate
of AIC sources in our Galaxy is very small (\sim 10^{-5} yr^{-1}), the
corresponding contribution to the flux of UHECRs is neglegible, and the total
flux is given by the integrated contribution from AIC sources produced by the
distribution of galaxies located within the distance which is unaffected by the
GZK cutoff ($\sim 50$ Mpc). We find that the reconnection efficiency factor
needs to be $\xi \gtrsim 0.1$ in order to reproduce the observed flux of
UHECRs.


title: Inflation and Eternal Inflation

abstract:
  The basic workings of inflationary models are summarized, along with the
arguments that strongly suggest that our universe is the product of inflation.
The mechanisms that lead to eternal inflation in both new and chaotic models
are described. Although the infinity of pocket universes produced by eternal
inflation are unobservable, it is argued that eternal inflation has real
consequences in terms of the way that predictions are extracted from
theoretical models. The ambiguities in defining probabilities in eternally
inflating spacetimes are reviewed, with emphasis on the youngness paradox that
results from a synchronous gauge regularization technique. Vilenkin's proposal
for avoiding these problems is also discussed.


title: Structure of the Sagittarius dwarf galaxy at low Galactic latitudes

abstract:
  We report the detection of $\sim$ 1500 RR Lyrae of Bailey type ab located in
the Sagittarius dwarf galaxy (Sgr). These variables have been detected on two
ESO Schmidt fields centred on (l,b)=(3.1 deg,-7.1 deg) and (6.6 deg, -10.8
deg), covering an area of $\sim$50 square degree. We present a surface density
map of Sgr based on the spatial distribution of these RRab, allowing us to
trace its structure in a region that was still almost unexplored between b=-14
deg and b=-4 deg. We present the results of the fit of different models to the
density profile of Sgr. The best fit to the core of Sgr is an exponential with
a scale length of 4.1 deg along the major axis. When we look at the extension
of Sgr we find a break (significant at the $\sim2\sigma$ level) in the slope of
the surface density along the main axis of Sgr. The nearly flat (or at least
very slowly decreasing) profile in the outer region of Sgr shows that this
dwarf galaxy is probably extending even further out our fields.


title:
Ultra-High-Energy Cosmic Ray Acceleration by Magnetic Reconnection in
  Newborn Pulsars

abstract:
  We here investigate the possibility that the ultra-high energy cosmic ray
(UHECR) events observed above the GZK limit are mostly protons accelerated in
econnection sites just above the magnetosphere of newborn millisecond pulsars
which are originated by accretion induced collapse (AIC).


title:
Proper Motion of Water Masers Associated with IRAS 21391+5802: Bipolar
  Outflow and an AU-Scale Dusty Circumstellar Shell

abstract:
  We present VLBA observations of water maser emission associated with the
star-forming region IRAS 21391+5802, which is embedded in a bright rimmed
cometary globule in IC1396. The angular resolution of the maps is about 0.8
mas, corresponding to a spatial resolution of about 0.6 AU, at an estimated
distance of 750 pc. Proper motions are derived for 10 maser features identified
consistently over three epochs, which were separated by intervals of about one
month. The masers appear in four groups, which are aligned linearly on the sky,
roughly along a northeast-southwest direction, with a total separation of about
520 AU (about 0.7 arcseconds). The 3-D velocities of the masers have a maximum
value of about 42 km/s (about 9 AU/yr). The average error on the derived proper
motions is about 4 km/s. The overall pattern of proper motions is indicative of
a bipolar outflow. Proper motions of the masers in a central cluster, with a
projected extent of about 20 AU, show systematic deviations from a radial
outflow. However, we find no evidence of Keplerian rotation, as has been
claimed elsewhere. A nearly circular loop of masers lies near the middle of the
cluster. The radius of this loop is 1 AU and the line-of-sight velocities of
the masers in the loop are within 2 km/s of the systemic velocity of the
region. These masers presumably exist at the radial distance where significant
dust condensation occurs in the outflow emanating from the star.


title: Lyman-alpha Imaging of a Very Luminous z=2.3 Starburst Galaxy with WFPC2

abstract:
  We investigate a very luminous Lyman-alpha emitting galaxy, associated with a
z=2.3 damped absorption system in the spectrum of the QSO PHL 957. The galaxy
was observed with the HST WFPC2, through a narrow filter (F410M) corresponding
to rest-frame Lyman -alpha, for 41.2 ksec, with shorter exposures in F555W and
F814W. The galaxy is resolved into a close (0.35 arcsec) pair of two
components, CFgA and CFgB. The profile of CFgA is consistent with an
exponential disk, but CFgB is closer to a bulge galaxy. Fr om the observed
colours we estimate rest-frame Lyman-alpha equivalent widths of 151 Angstroms
for CFgA and 33 for CFgB. From the F814W and F555W magnitudes we estimate
rest-frame blue-band absolute magnitudes of -23.12 for CFgA and -23.24 for
CFgB, signi ficantly brighter than local galaxies of the same size. CFgA shows
a remarkable 3.9 magnitudes of surface brightness enhancement relative to local
spirals, and we speculate that this may be the result of a very luminous
starburst, triggered by the merger of the two components. The Lyman-alpha
emission could be from a brief phase early in the starburst in which most of
these photons can escape.
  We search for other z=2.3 galaxies with strong Lyman-alpha emission,
selecting these by a colour F410M-F555W<-0.2. Eight candidate sources, all
fainter than CFgA, are identified. One is a point-source and may be an AGN; the
others are irregular a nd of low surface brightness, appearing typical of Lyman
break galaxies, but with Lyman-alpha equivalent widths near 100 Angstroms.


title: Patterns of Super Star Cluster Formation in `Clumpy' Starburst Galaxies

abstract:
  We present preliminary results from a Hubble Space Telescope (HST) WFPC2
investigation of spatial and temporal distributions of star clusters in the
clumpy irregular galaxy NGC 7673 and the starburst spirals NGC 3310 and Haro 1.
We compare the spectral energy distributions of star clusters in the large
clumps in NGC 7673 to model calculations of stellar clusters of various ages.
We also propose that the presence of super star clusters in clumps seems to be
a feature of intense starbursts.


title: Characterizing the Peak in the CMB Angular Power Spectrum

abstract:
  A peak has been unambiguously detected in the cosmic microwave background
(CMB) angular spectrum. Here we characterize its properties with fits to
phenomenological models. We find that the TOCO and BOOM/NA data determine the
peak location to be in the range 175--243 and 151--259 respectively (both
ranges 95% confidence) and determine the peak amplitude to be between ~70 and
90 micro Kelvin. By combining all the data, we constrain the full-width at
half-maximum to be between 180 and 250 at 95% confidence. Such a peak is
consistent with inflation-inspired flat, cold dark matter plus cosmological
constant models of structure formation with adiabatic, nearly scale-invariant
initial conditions. It is inconsistent with open and defect models.


title: Adiabatic CDM Models and the Competition

abstract:
  The inflation-inspired flat, cold dark matter-dominated models of structure
formation with adiabatic, nearly scale-invariant initial conditions agree very
well with current CMB anisotropy data. The success of these models is
highlighted by the failure of alternatives; we argue that there are no longer
any viable competitors (with the exception of models with more complicated
matter content which are still flat and which still require inflation). CMB
data will soon be of sufficient quality that, if one {\it assumes} inflation,
one can detect a non-zero cosmological constant by combining a determination of
the peak location with Hubble constant measurements.


title: Is There a Detectable Vishniac Effect?

abstract:
  The dominant linear contribution to cosmic microwave background (CMB)
fluctuations at small angular scales (less than one arcsec) is a second-order
contribution known as the Vishniac or Ostriker-Vishniac effect. This effect is
caused by the scattering of CMB photons off free electrons after the universe
has been reionized, and is dominated by linear perturbations near the R_V =2
Mpc/(h Gamma/0.2) scale in the Cold Dark Matter cosmogony. As the reionization
of the universe requires that nonlinear objects exist on some scale, however,
one can compare the scale responsible for reionization to R_V and ask if a
linear treatment is even feasible in different scenarios of reionization. For
an Omega_0 = 1 cosmology normalized to cluster abundances, only about 65% of
the linear integral is valid if reionization is due to quasars in halos of mass
10^9 solar, while 75% of the integral is valid if reionization was caused by
stars in 10^6 solar mass halos. In lambda or open cosmologies, both the
redshift of reionization and z_V are pushed further back, but still only 75% to
85% of the linear integral is valid, independent of the ionization scenario. We
point out that all odd higher-order moments from Vishniac fluctuations are zero
while even moments are non-zero, regardless of the gaussianity of the density
perturbations. This provides a defining characteristic of the Vishniac effect
that differentiates it from other secondary perturbations and may be helpful in
separating them.


title: Beaming and Jets in GRBs

abstract:
  The origin of GRBs have been a mystery for almost 30 years. The afterglow
observed in the last few years enabled redshift determination for a handful of
bursts, and the cosmological origin is now firmly established. Though the
distance scale is settled, there still remains orders of magnitude uncertainty
in their rate and in the total energy that is released in the explosion due to
the possibility that the emission is not spherical but jet-like. Contrary to
the GRB itself, the afterglow can be measured up to months and even years after
the burst, and it can provide crucial information on the geometry of the
ejecta. We review the theory of afterglow from jets and discuss the evidence
that at least some of the bursts are not spherical. We discuss the prospects of
polarization measurements, and show that this is a powerful tool in
constraining the geometry of the explosion.


title: A spatially resolved plerionic X-ray nebula around PSR B0540-69

abstract:
  We present a high resolution Chandra X-ray observation of PSR B0540-69, the
Crab-like 50 msec pulsar in the Large Magellanic Cloud. We use phase-resolved
imaging to decompose the extended X-ray emission, as expected of a synchrotron
nebula, from the point-like emission of the pulsar. The image of the pulsed
X-ray emission shows a well-defined point-spread function of the observation,
while the resolved nebula has a morphology and size remarkably similar to the
Crab nebula, including evidence for a jet-like feature from PSR B0540-69. The
patchy outer shell, which most likely represents the expanding blast-wave of
the supernova, is reminiscent of that seen in radio. Based on morphology, size,
and energetics there can be little doubt that PSR B0540-69 is an analogous
system to the Crab but located in our neighboring galaxy.


title:
A Study of the Populations of X-ray Sources in the Small Magellanic
  Cloud with ASCA

abstract:
  The Advanced Satellite for Cosmology and Astrophysics (ASCA) has made
multiple observations of the Small Magellanic Cloud (SMC). X-ray mosaic images
in the soft (0.7--2.0 keV) and hard (2.0--7.0 keV) bands are separately
constructed, and the latter provides the first hard X-ray view of the SMC. We
extract 39 sources from the two-band images with a criterion of S/N>5, and
conduct timing and spectral analyses for all of these sources. Coherent
pulsations are detected from 12 X-ray sources; five of which are new
discoveries. Most of the 12 X-ray pulsars are found to exhibit long-term flux
variabilities, hence they are likely to be X-ray binary pulsars (XBPs). On the
other hand, we classify four supernova remnants (SNRs) as thermal SNRs, because
their spectra exhibit emission lines from highly ionized atoms. We find that
XBPs and thermal SNRs in the SMC can be clearly separated by their hardness
ratio (the ratio of the count rate between the hard and soft bands). Using this
empirical grouping, we find many XBP candidates in the SMC, although no
pulsations have yet been detected from these sources. Possible implications on
the star-formation history and evolution of the SMC are presented by a
comparison of the source populations in the SMC and our Galaxy.


title: The afterglows of gamma-ray bursts

abstract:
  Gamma-ray burst astronomy has undergone a revolution in the last three years,
spurred by the discovery of fading long-wavelength counterparts. We now know
that at least the long duration GRBs lie at cosmological distances with
estimated electromagnetic energy release of 10**51 -- 10**53 erg, making these
the brightest explosions in the Universe. In this article we review the current
observational state, beginning with the statistics of X-ray, optical, and radio
afterglow detections. We then discuss the insights these observations have
given to the progenitor population, the energetics of the GRB events, and the
physics of the afterglow emission. We focus particular attention on the
evidence linking GRBs to the explosion of massive stars. Throughout, we
identify remaining puzzles and uncertainties, and emphasize promising
observational tools for addressing them. The imminent launch of HETE-2 and the
increasingly sophisticated and coordinated ground-based and space-based
observations have primed this field for fantastic growth.


title: The hard X-ray properties of the Seyfert nucleus in NGC 1365

abstract:
  We present BeppoSAX observations of the Seyfert 1.8 galaxy NGC1365 in the
0.1--100 keV range. The source was 6 times brighter than during an ASCA
observation 3 years earlier. The 4--10 keV flux is highly variable during the
BeppoSAX observation, while the soft (0.1-4 keV) emission is constant within
the errors. Both a cold and a warm reflector and a cold absorber are required
to explain the observed spectrum. The comparison between ASCA and BeppoSAX
spectra strongly suggests that the circumnuclear material has a more complex
structure than a simple homogeneous torus, with quite different absorbing gas
columns along different lines of sight. A broad iron K_alpha line is also
present in the spectrum, with the peak energy significantly redshifted. This
can be explained by means of a relativistic disk line model. Alternatively, a
warm absorption Fe line system with N_H ~ 10^23 cm^(-2) could account for the
observed line profile.


title: Measuring the Nonlinear Biasing Function from a Galaxy Redshift Survey

abstract:
  We present a simple method for evaluating the nonlinear biasing function of
galaxies from a redshift survey. The nonlinear biasing is characterized by the
conditional mean of the galaxy density fluctuation given the underlying mass
density fluctuation, or by the associated parameters of mean biasing and
nonlinearity (following Dekel & Lahav 1999). Using the distribution of galaxies
in cosmological simulations, at smoothing of a few Mpc, we find that the mean
biasing can be recovered to a good accuracy from the cumulative distribution
functions (CDFs) of galaxies and mass, despite the biasing scatter. Then, using
a suite of simulations of different cosmological models, we demonstrate that
the matter CDF is robust compared to the difference between it and the galaxy
CDF, and can be approximated for our purpose by a cumulative log-normal
distribution of 1+\delta with a single parameter \sigma. Finally, we show how
the nonlinear biasing function can be obtained with adequate accuracy directly
from the observed galaxy CDF in redshift space. Thus, the biasing function can
be obtained from counts in cells once the rms mass fluctuation at the
appropriate scale is assumed a priori. The relative biasing function between
different galaxy types is measurable in a similar way. The main source of error
is sparse sampling, which requires that the mean galaxy separation be smaller
than the smoothing scale. Once applied to redshift surveys such as PSCz, 2dF,
SDSS, or DEEP, the biasing function can provide valuable constraints on galaxy
formation and structure evolution.


title:
Astrophysical Effects Related to Gravity-Induced Electric Polarization
  of Matter

abstract:
  The calculations in Thomas-Fermi approximation show that in a gravitational
field each cell of ultra dense matter inside celestial bodies obtains a very
small positive electric charge. A celestial body is electrically neutral as a
whole, because the negative electric charge exists at its surface. The positive
volume charge is very small, on the order of magnitude it equals to 10^{-18}e
per atom only. But it is sufficient to explain the occurrence of magnetic
fields of the celestial bodies and the existence of a discrete spectrum of
steady-state values of masses of planets, stars, and pulsars.


title: A wavelet analysis of QSO spectra

abstract:
  The temperature of the intergalactic medium (IGM) is an important factor in
determining the line-widths of the absorption lines in the Lyman-alpha forest.
We present a method to characterise the line-widths distribution using a
decomposition of a Lyman-alpha spectrum in terms of discrete wavelets. Such
wavelets form an orthogonal basis so the decomposition is unique. We
demonstrate using hydrodynamic simulations that the mean and dispersion of the
wavelet amplitudes is strongly correlated with both the temperature of the
absorbing gas and its dependence on the gas density. Since wavelets are also
localised in space, we are able to analyse the temperature distribution as a
function of position along the spectrum. We illustrate how this method could be
used to identify fluctuations in the IGM temperature which might result from
late reionization or local effects.


title: Radial Velocity Studies of Close Binary Stars.III

abstract:
  Radial velocity measurements and simple sine-curve fits to the orbital
velocity variations are presented for the third set of ten contact binary
systems: CN And, HV Aqr, AO Cam, YY CrB, FU Dra, RZ Dra, UX Eri, RT LMi, V753
Mon, OU Ser. All systems but two are contact, double-line spectroscopic
binaries with four of them (YY CrB, FU Dra, V753 Mon, OU Ser) being the recent
discoveries of the Hipparcos satellite project. The most interesting object is
V753 Mon with the mass-ratio closest to unity among all contact systems (q =
0.970 pm 0.003) and large total mass ((M1+M2)sin^3i = 2.93 pm 0.06). Several of
the studied systems are prime candidates for combined light and radial-velocity
synthesis solutions.


title:
The large scale distribution of warm ionized gas around nearby radio
  galaxies with jet-cloud interactions

abstract:
  Deep, narrow-band Halpha observations taken with the TAURUS Tunable Filter
(TTF) on the 4.2m WHT telescope are presented for two nearby radio galaxies
with strong jet-cloud interactions. Although the brightest emission line
components are closely aligned with the radio jets --- providing nearby
examples of the ``alignment effect'' most commonly observed in high redshift (z
> 0.5) radio galaxies --- lower surface brightness emission line structures are
detected at large distances (10's of kpc) from the radio jet axis. These latter
structures cannot be reconciled with anisotropic illumination of the ISM by
obscured quasar-like sources, since parts of the structures lay outside any
plausible quasar ionization cones. Rather, the distribution of the emission
lines around the fringes of the extended radio lobes suggests that the gas is
ionized either by direct interaction with the radio components, or by the
diffuse photoionizing radiation fields produced in the shocks generated in such
interactions. These observations serve to emphasise that the ionizing effects
of the radio components can extend far from the radio jet axes, and that deep
emission line imaging observations are required to reveal the true distribution
of warm gas in the host galaxies. We expect future deep imaging observations to
reveal similar structures perpendicular to the radio axes in the high-z radio
galaxies.


title: Finite-Correlation-Time Effects in the Kinematic Dynamo Problem

abstract:
  Most of the theoretical results on the kinematic amplification of small-scale
magnetic fluctuations by turbulence have been confined to the model of
white-noise-like advecting turbulent velocity field. In this work, the
statistics of the passive magnetic field in the diffusion-free regime are
considered for the case when the advecting flow is finite-time correlated. A
new method is developed that allows one to systematically construct the
correlation-time expansion for statistical characteristics of the field. The
expansion is valid provided the velocity correlation time is smaller than the
characteristic growth time of the magnetic fluctuations. This expansion is
carried out up to first order in the general case of a d-dimensional
arbitrarily compressible advecting flow. The growth rates for all moments of
the magnetic field are derived. The effect of the first-order corrections is to
reduce these growth rates. It is shown that introducing a finite correlation
time leads to the loss of the small-scale statistical universality, which was
present in the limit of the delta-correlated velocity field. Namely, the shape
of the velocity time-correlation profile and the large-scale spatial structure
of the flow become important. The latter is a new effect, that implies, in
particular, that the approximation of a locally-linear shear flow does not
fully capture the effect of nonvanishing correlation time. Physical
applications of this theory include the small-scale kinematic dynamo in the
interstellar medium and protogalactic plasmas.


title:
An eigenfunction method for particle acceleration at ultra-relativistic
  shocks

abstract:
  We adapt and modify the eigenfunction method of computing the power-law
spectrum of particles accelerated at a relativistic shock front via the
first-order Fermi process (Kirk, J.G., Schneider, P., Astrophysical Journal
315, 425 (1987)) to apply to shocks of arbitrarily high Lorentz factor. The
power-law index of accelerated particles undergoing isotropic small-angle
scattering at an ultrarelativistic, unmagnetized shock is found to be s=4.23
+/- 0.2 (where s=d\ln f/ d\ln p, with f the Lorentz-invariant phase-space
density and p the momentum), in agreement with the results of Monte-Carlo
simulations. We present results for shocks in plasmas with different equations
of state and for Lorentz factors ranging from 5 to infinity.


title: Formation of Molecular Gas in the debris of violent Galaxy Interactions

abstract:
  In many gravitational interactions between galaxies, gas and stars that have
been torn from either or both of the precursor galaxies can collect in 'tidal
tails'. Star formation begins anew in these regions to produce 'tidal dwarf
galaxies', giving insight into the process of galaxy formation through the
well-defined timescale of the interaction. But tracking the star formation
process has proved to be difficult: the tidal dwarf galaxies with young stars
showed no evidence of the molecular gas out of which new stars form. Here we
report the discovery of molecular gas (carbon monoxide emission) in two tidal
dwarf galaxies. In both cases, the molecular gas peaks at the same location as
the maximum in atomic-hydrogen density, unlike most gas-rich galaxies. We infer
from this that the molecular gas formed from the HI, rather than being torn in
molecular form from the interacting galaxies. Star formation in the tidal
dwarfs appears to mimic that process in normal spiral galaxies like our own.


title: What do $\gamma$-ray bursts look like?

abstract:
  There have been great and rapid progresses in the field of $\gamma$-ray
bursts (denoted as GRBs) since BeppoSAX and other telescopes discovered their
afterglows in 1997. Here, we will first give a brief review on the
observational facts of GRBs and direct understanding from these facts, which
lead to the standard fireball model. The dynamical evolution of the fireball is
discussed, especially a generic model is proposed to describe the whole
dynamical evolution of GRB remnant from highly radiative to adiabatic, and from
ultra-relativistic to non-relativistic phase. Then, Various deviations from the
standard model are discussed to give new information about GRBs and their
environment. In order to relax the energy crisis, the beaming effects and their
possible observational evidences are also discussed in GRB's radiations.


title:
Highly polarized structures in the near-nuclear regions of Cygnus A:
  intrinsic anisotropy within the cones?

abstract:
  We present near-IR imaging polarimetry observations of the nucleus of Cygnus
A, taken with the NICMOS camera of the HST at a wavelength of 2.0 microns.These
maps reveal a highly collimated region of polarized emission straddling the
nucleus and extending to a radius of 1.2 arcseconds. Remarkably, this feature
coincides with one, but only one, limb of the edge-brightened bicone structure
seen in the total intensity image. The high degree (P_k ~ 25%) and orientation
of the extended polarization feature are consistent with a scattering origin.
Most plausibly, the detection of polarization along only one limb of the bicone
is a consequence of intrinsic anisotropy of the near-IR continuum within the
radiation cones, with the direction of maximum intensity of the near-IR
radiation field significantly displaced from the direction of the radio axis.
The unresolved nuclear core source is also highly polarized (P_k > 28%), with a
position angle close to the perpendicular to the radio axis. Given that this
high degree of nuclear polarization can only be explained in terms of dichroic
extinction if the dichroic mechanism is unusually efficient in Cygnus A, it is
more likely that the nuclear polarization is due to the scattering of nuclear
light in an unresolved scattering region close to the AGN. In this case, the
flux of the core source in the K-band is dominated by scattered rather than
transmitted quasar light, and previous extinction estimates based on K-band
photometry of the core substantially underestimate the true nuclear extinction.


title: An Empirical Test and Calibration of H II Region Diagnostics

abstract:
  We present spectrophotometry in the 3600-9700 A region for a sample of 39 H
II regions in the Galaxy and Magellanic Clouds, for which independent
information is available on the spectral types and effective temperatures of
the ionizing stars. The spectra have been used to evaluate nebular diagnostics
of stellar temperature, metal abundance, and ionization parameter, and compare
the observed behavior of the line indices with predictions of nebular
photoionization models. We observe a strong degeneracy between forbidden-line
sequences produced by changes in stellar Teff and metal abundance, which
severely complicates the application of many forbidden-line diagnostics to
extragalactic H II regions. Our data confirm however that the Edmunds and Pagel
[O II]+[O III] abundance index and the Vilchez and Pagel `eta' index provide
more robust diagnostics of metal abundance and stellar effective temperature,
respectively. A comparison of the fractional helium ionization of the H II
regions with stellar temperature confirms the reliability of the spectral type
vs Teff calibration for the relevant temperature range Teff < 38000 K. We use
empirical relations between the nebular hardness indices and Teff to
reinvestigate the case for systematic variations in the stellar effective
temperatures and the upper IMFs of massive stars in extragalactic H II regions.
The data are consistent with a significant softening of the ionizing spectra
(consistent with cooler stellar temperatures) with increasing metal abundance,
especially for Z less than solar. However unresolved degeneracies between Z and
Teff still complicate the interpretation of this result.


title: Statistical properties of SGR 1806-20 bursts

abstract:
  We present statistics of SGR 1806-20 bursts, combining 290 events detected
with RXTE/PCA, 111 events detected with BATSE and 134 events detected with ICE.
We find that the fluence distribution of bursts observed with each instrument
are well described by power laws with indices 1.43, 1.76 and 1.67,
respectively. The distribution of time intervals between successive bursts from
SGR 1806-20 is described by a lognormal function with a peak at 103 s. There is
no correlation between the burst intensity and either the waiting times till
the next burst or the time elapsed since the previous burst. In all these
statistical properties, SGR 1806-20 bursts resemble a self-organized critical
system, similar to earthquakes and solar flares. Our results thus support the
hypothesis that the energy source for SGR bursts is crustquakes due to the
evolving, strong magnetic field of the neutron star, rather than any accretion
or nuclear power.


title: Stellar evolution and large extra dimensions

abstract:
  We discuss in detail the information on large extra dimensions which can be
derived in the framework of stellar evolution theory and observation. The main
effect of large extra dimensions arises from the production of the Kaluza-Klein
(KK) excitations of the graviton. The KK-graviton and matter interactions are
of gravitational strength, so the KK states never become thermalized and always
freely escape. In this paper we first pay attention to the sun. Production of
KK gravitons is incompatible with helioseismic constraints unless the 4+n
dimensional Planck mass M_s exceeds 300 Gev/c^2. Next we show that stellar
structures in their advanced phase of H burning evolution put much more severe
constraints, M_s > 3-4 TeV/c^2, improving on current laboratory lower limits.


title:
The Asiago-ESO/RASS QSO Survey. I.The Catalog and the Local QSO
  Luminosity Function

abstract:
  This paper presents the first results of a survey for bright quasars (V <
14.5 and R<15.4) covering the North Hemisphere at galactic latitudes |b|>30.
The photometric database is derived from the GSC and USNO catalogs. Quasars are
identified on the basis of their X-ray emission measured in the ROSAT All Sky
Survey. The surface density of quasars brighter than 15.5 mag turns out to be
$9 \pm 1 \cdot 10^{-3} deg^{-2}$, about 3 times higher than that estimated by
the PG survey. The quasar optical Luminosity Function (LF) at $0.04 < z \le
0.3$ is computed and shown to be consistent with a Luminosity Dependent
Luminosity Evolution of the type derived by La Franca and Cristiani (1997) in
the range $0.3 < z \le 2.2$. The predictions of semi-analytical models of
hierarchical structure formation agree remarkably well with the present
observations.


title: Extragalactic Results from the Infrared Space Observatory

abstract:
  More than a decade ago the IRAS satellite opened the realm of external
galaxies for studies in the 10 to 100 micron band and discovered emission from
tens of thousands of normal and active galaxies. With the 1995-1998 mission of
the Infrared Space Observatory the next major steps in extragalactic infrared
astronomy became possible: detailed imaging, spectroscopy and
spectro-photometry of many galaxies detected by IRAS, as well as deep surveys
in the mid- and far- IR. The spectroscopic data reveal a wealth of detail about
the nature of the energy source(s) and about the physical conditions in
galaxies. ISO's surveys for the first time explore the infrared emission of
distant, high-redshift galaxies. ISO's main theme in extragalactic astronomy is
the role of star formation in the activity and evolution of galaxies.


title: Cluster Selection and the Evolution of Brightest Cluster Galaxies

abstract:
  The K-band Hubble diagram of Brightest Cluster Galaxies (BCGs) is presented
for a large, X-ray selected cluster sample extending out to z = 0.8. The
controversy over the degree of BCG evolution is shown to be due to sample
selection, since the BCG luminosity depends upon the cluster environment.
Selecting only the most X-ray luminous clusters produces a BCG sample which
shows, under the assumption of an Einstein-de Sitter cosmology, significantly
less mass growth than that predicted by current semi-analytic galaxy formation
models, and significant evidence of any growth only if the dominant stellar
population of the BCGs formed relatively recently (z <= 2.6).


title: The Extreme Compact Starburst in MRK 273

abstract:
  Images of neutral Hydrogen 21cm absorption and radio continuum emission at
1.4 GHz from Mrk 273 were made using the Very Long Baseline Array and Very
Large Array. These images reveal a gas disk associated with the northern
nuclear region with a diameter of 0.5'' (370 pc), at an inclination angle of
53deg. The radio continuum emission is composed of a diffuse component plus a
number of compact sources. This morphology resembles those of nearby, lower
luminosity starburst galaxies. These images provide strong support for the
hypothesis that the luminosity of the northern source is dominated by an
extreme compact starburst. The HI 21cm absorption shows an east-west gradient
in velocity of 450 km/s across 0.3'' (220 pc), implying an enclosed mass of 2e9
M_solar, comparable to the molecular gas mass. The brightest of the compact
sources may indicate radio emission from an active nucleus (AGN), but this
source contributes only 3.8% to the total flux density of the northern nuclear
region. The HI 21cm absorption toward the southeast radio nucleus suggests
infall at 200 km/s on scales < 40 pc, and the southwest near IR nucleus is not
detected in high resolution radio continuum images.


title:
Eclipse maps of spiral shocks in the accretion disc of IP Pegasi in
  outburst

abstract:
  Eclipse lightcurves of the dwarf nova IP Peg during the November 1996
outburst are analysed with eclipse mapping techniques to constrain the location
and investigate the spatial structure of the spiral shocks observed in the
Doppler tomograms (Harlaftis et al. 1999). Eclipse maps in the blue continuum
and in the CIII+NIII 4650 emission line show two asymmetric arcs of \sim 90
degrees in azimuth and extending from intermediate to the outer disc regions (R
\simeq 0.2 - 0.6 R_{L1}, where R_{L1} is the distance from disc centre to the
inner Lagrangian point) which are interpreted as being the spiral shocks seen
in the Doppler tomograms. The HeII 4686 eclipse map also shows two asymmetric
arcs diluted by a central brightness source. The central source probably
corresponds to the low-velocity component seen in the Doppler tomogram and is
understood in terms of gas outflow in a wind emanating from the inner parts of
the disc. We estimate that the spirals contribute about 16 and 30 per cent of
the total line flux, respectively, for the HeII and CIII+NIII lines. Comparison
between the Doppler and eclipse maps reveal that the Keplerian velocities
derived from the radial position of the shocks are systematically larger than
those inferred from the Doppler tomography indicating that the gas in the
spiral shocks has sub-Keplerian velocities. We undertake simulations with the
aim to investigate the effect of artifacts on the image reconstruction of the
spiral structures.


title: Inflationary Models and Connections to Particle Physics

abstract:
  The basic workings of inflationary models are summarized, along with the
arguments that strongly suggest that our universe is the product of inflation.
The mechanisms that lead to eternal inflation in both new and chaotic models
are described. Although the infinity of pocket universes produced by eternal
inflation are unobservable, it is argued that eternal inflation has real
consequences in terms of the way that predictions are extracted from
theoretical models. The ambiguities in defining probabilities in eternally
inflating spacetimes are reviewed, with emphasis on the youngness paradox that
results from a synchronous gauge regularization technique. To clarify (but not
resolve) this ambiguity, a toy model of an eternally inflating universe is
introduced. Vilenkin's proposal for avoiding these problems is also discussed,
as is the question of whether it is meaningful to discuss probabilities for
unrepeatable measurements.


title:
Spatially-resolved spectra of the accretion disc of the novalike UU
  Aquarii

abstract:
  Time-resolved spectroscopy of the novalike variable UU Aquarii is analyzed
with eclipse mapping techniques to produce spatially resolved spectra of its
accretion disc and gas stream as a function of distance from disc centre in the
range 3600-6900 \AA. The spatially-resolved spectra show that the continuum
emission becomes progressively fainter and redder for increasing disc radius --
reflecting the radial temperature gradient -- and reveal that the HI and HeI
lines appear as deep, narrow absorption features in the inner disc regions
transitioning to emission with P Cygni profiles for intermediate and large disc
radii. The spectrum of the uneclipsed component has strong HI and HeI emission
lines plus a Balmer jump in emission and is explained as optically thin
emission from a vertically extended disc chromosphere + wind. Most of the line
emission probably arises from the wind. The spatially-resolved spectra also
suggest the existence of gas stream ``disk-skimming'' overflow in UU Aqr, which
can be seen down to R \simeq 0.2 R_{L1}. The comparison of our eclipse maps
with those of Baptista, Steiner & Horne (1996) suggests that the asymmetric
structure in the outer disc previously identified as the bright spot may be the
signature of an elliptical disc similar to those possibly present in SU UMa
stars during superoutbursts.


title: Constraining the Lifetime of Quasars from their Spatial Clustering

abstract:
  The lifetime t_Q of the luminous phase of quasars is constrained by current
observations to be between 10^6 and 10^8 years, but is otherwise unkown. We
model the quasar luminosity function in detail in the optical and X-ray bands
using the Press-Schechter formalism, and show that the expected clustering of
quasars depends strongly on their assumed lifetime. We quantify this
dependence, and find that existing measurements of the correlation length of
quasars are consistent with the range 10^6 < t_Q < 10^8 years. We then show
that future measurements of the power spectrum of quasars out to z=3, from the
2dF or Sloan Digital Sky Survey, can significantly improve this constraint, and
in principle allow a precise determination of t_Q. We estimate the systematic
errors introduced by uncertainties in the modeling of the quasar-halo
relationship, as well as by the possible existence of obscured quasars.


title:
Star Formation and Tidal Encounters with the Low Surface Brightness
  Galaxy UGC 12695 and Companions

abstract:
  We present VLA H I observations of the low surface brightness galaxy UGC
12695 and its two companions, UGC 12687 and a newly discovered dwarf galaxy
2333+1234. UGC 12695 shows solid body rotation but has a very lopsided
morphology of the H I disk, with the majority of the H I lying in the southern
arm of the galaxy. The H I column density distribution of this very blue, LSB
galaxy coincides in detail with its light distribution. Comparing the H I
column density of UGC 12695 with the empirical (but not well understood) value
of Sigma_c = 10E21 atoms/cm^2 found in, i.e., Skillman's 1986 paper shows the
star formation to be a local affair, occurring only in those regions where the
column density is above this star formation threshold. The low surface
brightness nature of this galaxy could thus be attributed to an insufficient
gas surface density, inhibiting star formation on a more global scale.
Significantly, though, the Toomre criterion places a much lower critical
density on the galaxy (+/-10E20 atoms/cm^2), which is shown by the galaxy's low
SFR to not be applicable.
  Within a projected distance of 300kpc/30kms of UGC 12695 lie two companion
galaxies - UGC 12687, a high surface brightness barred spiral galaxy, and
2333+1234, a dwarf galaxy discovered during this investigation. The close
proximity of the three galaxies, combined with UGC 12695's extremely blue color
and regions of localized starburst and UGC 12687's UV excess bring to mind
mutually induced star formation through tidal activity.


title: Strong, Variable Circular Polarization in PKS 1519-273

abstract:
  We report strong variability in the circular and linear polarization of the
intraday variable source PKS 1519-273. The circular polarization varies on a
timescale of hours to days at frequencies between 1.4 and 8.6 GHz, and is
strongly correlated with variations in the total intensity at 4.8 and 8.6 GHz.
We argue that the variability is due to interstellar scintillation of a highly
compact (15-35 \mu as) component of the source with -3.8\pm 0.4% circular
polarization at 4.8 GHz. We find that no simple model for the circular
polarization can account for both the high magnitude and the frequency
dependence in PKS 1519-273 at centimeter wavelengths.


title: A Theoretical Review of Axion

abstract:
  It is emphasized that the existence of a very light axion is consistent with
the strong CP invariance and cosmological and astrophysical constraints. The
attempt to embed the very light axion in superstring models is discussed.


title: Resonant inverse Compton scattering by secondary pulsar plasma

abstract:
  We consider resonant inverse Compton scattering of thermal photons by
secondary particles above the pulsar polar gap. The process appears to be an
essential energy loss mechanism for the particles. The distribution function of
the secondary plasma particles is found to be strongly affected by the
scattering. It becomes two-humped implying the development of two-stream
instability. The resonantly upscattered Compton photons are found to gain
energy of 1 - 10 MeV forming an additional component in the pulsar gamma-ray
spectrum. The corresponding gamma-ray flux is estimated as well.


title: ISO-SWS spectra of galaxies: continuum and features

abstract:
  We present an inventory of mid-infrared spectral features detected in high
resolution 2.4 to 45um ISO-SWS spectra of the galaxies M82, NGC253, Circinus,
NGC1068, and the 30Doradus region of the LMC. We discuss their identifications
and highlight possible relations between these features and the physical state
of the interstellar medium in galaxies. In the 5--13 um region, emission from
unidentified infrared bands (UIBs), usually ascribed to aromatic molecules, and
apparent silicate absorption dominate the spectrum. We demonstrate the danger
of overestimating the amount of silicate absorption by comparing the spectrum
of M82 to the (absorption free) spectrum of the reflection nebula NGC7023. No
strong silicate absorption is present in M82. The (very small grain) dust
continuum under the UIB emission in our starburst templates can be modeled by a
simple power law, starting at wavelengths between 8 and 9um. The spectra are
valuable templates for future mid-infrared missions. We smooth our data to
simulate low resolution spectra as obtained with ISOCAM-CVF, ISOPHOT-S, and in
the future with the low resolution mode of SIRTF-IRS, and use our high spectral
resolution information to highlight possible identification problems at low
resolving power that are caused by coincidences of lines and features.


title: Neutrino Pair Annihilation in the Gravitation of Gamma Ray Burst Sources

abstract:
  We study semianalytically the gravitational effects on neutrino pair
annihilation near the neutrinosphere and around the thin accretion disk. For
the disk case, we assume that the accretion disk is isothermal and that the
gravitational field is dominated by the Schwarzschild black hole. General
relativistic effects are studied only near the rotation axis. The energy
deposition rate is enhanced by the effect of orbital bending toward the center.
However, the effects of the redshift and gravitational trapping of the
deposited energy reduce the effective energy of the gamma ray bursts' source.
Although each effect is substantial, the effects partly cancel one another. As
a result, the gravitational effects do not substantially change the energy
deposition rate for either the spherical symmetric case or the disk case.


title: First VLT spectra of white dwarfs in a globular cluster

abstract:
  We present the first spectra obtained with the Very Large Telescope for white
dwarfs in a globular cluster. Estimates of atmospheric parameters are obtained
and compared to evolutionary tracks. We discuss possible implications for the
distance scale of globular clusters and white dwarf evolution and demonstrate
how white dwarfs might be used to establish an independent distance scale to
globular clusters.


title: Improving the Resolution of X-Ray Telescopes with Occulting Satellites

abstract:
  One of the challenges of X-ray astronomy is how to both collect large numbers
of photons yet attain high angular resolution. Because X-ray telescopes utilize
grazing optics, to collect more photons requires a larger acceptance angle
which in turn compromises the angular resolution. All X-ray telescopes thus
have angular resolution far poorer than their diffraction limit. Although
collecting more photons is a desirable goal, sometimes selective collecting
fewer photons may yield more information. Natural (such as lunar) occultations
have long been used to study sources on small angular scales. But natural
occulters are of limited utility because of their large angular velocities
relative to the telescope, and because of the serendipity of their transits. We
describe here how one can make use of an X-ray Big Occulting Steerable
Satellite (X-BOSS) to achieve very-high resolution of X-ray sources. An X-BOSS
could significantly improve the resolution of existing X-ray facilities such as
the Chandra telescope, or X-ray Multiple Mirror (XMM) satellite, and could
vastly improve the resolution of some future X-ray telescopes, particularly
Constellation X where sub-milliarcsecond resolution is possible for a wide
range of sources. Similar occulting satellites could also be deployed in
conjunction with planned space observatories for other wavebands.


title: The host galaxies of luminous radio-quiet quasars

abstract:
  We present the results of a deep K-band imaging study which reveals the host
galaxies around a sample of luminous radio-quiet quasars. The K-band images,
obtained at UKIRT, are of sufficient quality to allow accurate modelling of the
underlying host galaxy. Initially, the basic structure of the hosts is revealed
using a modified Clean deconvolution routine optimised for this analysis. 2 of
the 14 quasars are shown to have host galaxies with violently disturbed
morphologies which cannot be modelled by smooth elliptical profiles. For the
remainder of our sample, 2D models of the host and nuclear component are fitted
to the images using the chi-squared statistic to determine goodness of fit.
Host galaxies are detected around all of the quasars. The reliability of the
modelling is extensively tested, and we find the host luminosity to be well
constrained for 9 quasars. The derived average K-band absolute K-corrected host
galaxy magnitude for these luminous radio-quiet quasars is <M_K>=-25.15+/-0.04,
slightly more luminous than an L* galaxy. The spread of derived host galaxy
luminosities is small, although the spread of nuclear-to-host ratios is not.
These host luminosities are shown to be comparable to those derived from
samples of quasars of lower total luminosity and we conclude that there is no
correlation between host and nuclear luminosity for these quasars.
Nuclear-to-host ratios break the lower limit previously suggested from studies
of lower nuclear luminosity quasars and Seyfert galaxies. Morphologies are less
certain but, on the scales probed by these images, some hosts appear to be
dominated by spheroids but others appear to have disk-dominated profiles.


title: A local infrared perspective to deeper ISO surveys

abstract:
  We present new techniques to produce IRAS 12 micron samples of galaxies and
stars. We show that previous IRAS 12 micron samples are incompatible for
detailed comparison with ISO surveys and review their problems. We provide a
stellar infrared diagnostic diagram to distinguish galaxies from stars without
using longer wavelength IRAS colour criteria and produce complete 12 micron
samples of galaxies and stars. This new technique allows us to estimate the
contribution of non-dusty galaxies to the IRAS 12 micron counts and produce a
true local mid-infrared extragalactic sample compatible with ISO surveys. We
present our initial analysis and results.


title:
Chandra uncovers a hidden Low-Luminosity AGN in the radio galaxy Hydra~A
  (3C~218)

abstract:
  We report the detection with Chandra of a Low-Luminosity AGN (LLAGN) in the
Low Ionization Emission Line Region (LINER) hosted by Hydra A, a nearby
(z=0.0537) powerful FRI radio galaxy with complex radio and optical morphology.
In a 20 ks ACIS-S exposure during the calibration phase of the instrument, a
point source is detected at energies $\grtsim$ 2 keV at the position of the
compact radio core, embedded in diffuse thermal X-ray emission ($kT \sim 1$
keV) at softer energies. The spectrum of the point source is well fitted by a
heavily absorbed power law with intrinsic column density N$_H^{int} \sim 3
\times 10^{22}$ \nh and photon index $\Gamma \sim 1.7$. The intrinsic
(absorption-corrected) luminosity is $L_{2-10 keV} \sim 1.3 \times 10^{42}$
\lum. These results provide strong evidence that an obscured AGN is present in
the nuclear region of Hydra~A. We infer that the optical/UV emission of the AGN
is mostly hidden by the heavy intrinsic reddening. In order to balance the
photon budget of the nebula, we must either postulate that the ionizing
spectrum includes a UV bump or invoke and additional power source (shocks in
the cooling flow or interaction with the radio jets). Using an indirect
estimate of the black hole mass and the X-ray luminosity, we infer that the
accretion rate is low, suggesting that the accretion flow is advection
dominated. Finally, our results support current unification schemes for
radio-loud sources, in particular the presence of the putative molecular torus
in FR~Is. These observations underscore the power of the X-rays and of \chandra
in the quest for black holes.


title: Recent Advances in Binary Star Formation Using SPH

abstract:
  We review recent advances in the study of binary star formation that have
been made using the smoothed particle hydrodynamics (SPH) technique. We discuss
the importance of ensuring that the Jeans mass is always resolved during a
self-gravitating SPH calculation. Even obeying this criterion, we show that it
is now possible to perform calculations which follow the collapse of a
molecular cloud core all the way to stellar densities. These calculations
resolve 7 orders of magnitude in spatial extent and 17 orders of magnitude in
density contrast. Finally, we discuss the progress that has been made in
understanding the mass-ratio distributions of binary stellar systems by
studying the evolution of protobinary systems as they accrete gas from their
surrounding envelopes.


title:
Nuclear Matter and its Role in Supernovae, Neutron Stars and Compact
  Object Binary Mergers

abstract:
  The equation of state (EOS) of dense matter plays an important role in the
supernova phenomenon, the structure of neutron stars, and in the mergers of
compact objects (neutron stars and black holes). During the collapse phase of a
supernova, the EOS at subnuclear densities controls the collapse rate, the
amount of deleptonization and thus the size of the collapsing core and the
bounce density. Properties of nuclear matter that are especially crucial are
the symmetry energy and the nuclear specific heat. The nuclear
incompressibility, and the supernuclear EOS, play supporting roles. In a
similar way, although the maximum masses of neutron stars are entirely
dependent upon the supernuclear EOS, other important structural aspects are
more sensitive to the equation of state at nuclear densities. The radii,
moments of inertia, and the relative binding energies of neutron stars are, in
particular, sensitive to the behavior of the nuclear symmetry energy. The
dependence of the radius of a neutron star on its mass is shown to critically
influence the outcome of the compact merger of two neutron stars or a neutron
star with a small mass black hole. This latter topic is especially relevant to
this volume, since it stems from research prompted by the tutoring of David
Schramm a quarter century ago.


title:
Observed Smooth Energy is Anthropically Even More Likely As Quintessence
  Than As Cosmological Constant

abstract:
  For a universe presently dominated by static or dynamic vacuum energy,
cosmological constant (LCDM) or quintessence (QCDM), we calculate the
asymptotic collapsed mass fraction as function of the present ratio of vacuum
energy to clustered mass, \Omega_{Q0}/\Omega_{m0}. Identifying these collapsed
fractions as anthropic probabilities, we find the value \Omega_{Q0}/\Omega_{m0}
\sim 2 to be reasonably likely in LCDM, and very likely in QCDM.


title: Photometric catalog of nearby globular clusters (I)

abstract:
  We present the first part of the first large and homogeneous CCD
color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular
clusters (GGC) imaged in the V and I bands using only two telescopes (one for
each hemisphere). The observed clusters represent 75% of the known Galactic
globulars with (m-M)v<=16.15 mag, cover most of the globular cluster
metallicity range (-2.2 <= [Fe/H] <= -0.4), and span Galactocentric distances
from ~1.2 to ~18.5 kpc.
  In this paper, the CMDs for the 39 GGCs observed in the southern hemisphere
are presented. The remaining 13 northern hemisphere clusters of the catalog are
presented in a companion paper. For four clusters (NGC 4833, NGC 5986, NGC
6543, and NGC 6638) we present for the first time a CMD from CCD data. The
typical CMD spans from the 22nd V magnitude to the tip of the red giant branch.
Based on a large number of standard stars, the absolute photometric calibration
is reliable to the ~0.02 mag level in both filters.
  This catalog, because of its homogeneity, is expected to represent a useful
data base for the measurement of the main absolute and relative parameters
characterizing the CMD of GGCs.


title: On The Reddening in X-ray Absorbed Seyfert 1 Galaxies

abstract:
  There are several Seyfert galaxies for which there is a discrepancy between
the small column of neutral hydrogen deduced from X-ray observations and the
much greater column derived from the reddening of the optical/UV emission lines
and continuum. The standard paradigm has the dust within the highly ionized gas
which produces O~VII and O~VIII absorption edges (i.e., a ``dusty warm
absorber''). We present an alternative model in which the dust exists in a
component of gas in which hydrogen has been stripped, but which is at too low
an ionization state to possess significant columns of O~VII and O~VIII (i.e, a
``lukewarm absorber''). The lukewarm absorber is at sufficient radial distance
to encompass much of the narrow emission-line region, and thus accounts for the
narrow-line reddening, unlike the dusty warm absorber. We test the model by
using a combination of photoionization models and absorption edge fits to
analyze the combined ROSAT/ASCA dataset for the Seyfert 1.5 galaxy, NGC 3227.
We show that the data are well fit by a combination of the lukewarm absorber
and a more highly ionized component similar to that suggested in earlier
studies. We predict that the lukewarm absorber will produce strong UV
absorption lines of N V, C IV, Si IV and Mg II. Finally, these results
illustrate that singly ionized helium is an important, and often overlooked,
source of opacity in the soft X-ray band (100 - 500 eV).


title: Time Resolved GRB Spectroscopy

abstract:
  We present the main results of a study of time-resolved spectra of 43 intense
GRBs detected by BATSE. We considered the 4-parameter Band model and the
Optically Thin Synchrotron Shock model (OTSSM). We find that the large majority
of time-resolved spectra of GRBs are in remarkable agreement with the OTSSM.
However, about 15 % of initial GRB pulses show an apparent low-energy photon
suppression. This phenomenon indicates that complex radiative conditions
modifying optically thin emission may occur during the initial phases of some
GRBs.


title: The superbubble model for Li, Be and B production and Galactic evolution

abstract:
  We show that the available constraints relating to $^{6}$LiBeB Galactic
evolution can be accounted for by the so-called superbubble model, according to
which particles are efficiently accelerated inside superbubbles out of a
mixture of supernova ejecta and ambient interstellar medium. The corresponding
energy spectrum is required to be flat at low energy (in E^-1 below 500 MeV/n,
say), as expected from Bykov's acceleration mechanism. The only free parameter
is also found to have the value expected from standard SB dynamical evolution
models. Our model predicts a slope 1 (primary) and a slope 2 (secondary)
behaviour at respectively low and high metallicity, with all intermediate
slopes achieved in the transition region, between 10^-2 and 10^-1 Z_sol.


title:
ISO observations of the reflection nebula Ced 201: evolution of
  carbonaceous dust

abstract:
  We present spectrophotometric imaging mid-IR observations of the reflection
nebula Ced201. Ced201 is a part of a molecular cloud illuminated by a B9.5V
star moving through it at more than 12 km/s. The spectra of Ced201 give
evidence for transformation of very small carbonaceous grains into the carriers
of the Aromatic Infrared Bands (AIBs), due to the radiation field of the
illuminating star and/or to shock waves created by its motion. These very small
grains emit mainly very broad bands and a continuum. We suggest that they are
present everywhere in the interstellar medium but can only be detected in the
mid-IR under special circumstances such as those prevailing in this reflection
nebula. The efficiency of energy conversion of stellar light into mid-infrared
emission is 7.5% for both the very small grains and the AIB carriers, and the
fraction of interstellar carbon locked in these emitters is approximately 15%.


title:
A vestige low metallicity gas shell surrounding the radio galaxy
  0943-242 at z=2.92

abstract:
  Observations are presented showing the doublet CIV 1550 absorption lines
superimposed on the CIV emission in the radio galaxy 0943-242. Within the
errors, the redshift of the absorption system that has a column density of
N_CIV = 10^{14.5 +- 0.1} cm-2 coincides with that of the deep Ly-alpha
absorption trough observed by Rottgering et al. (1995). The gas seen in
absorption has a resolved spatial extent of at least 13 kpc (the size of the
extended emission line region). We first model the absorption and emission gas
as co-spatial components with the same metallicity and degree of excitation.
Using the information provided by the emission and absorption line ratios of
CIV and Ly-alpha, we find that the observed quantities are incompatible with
photoionization or collisional ionization of cloudlets with uniform properties.
We therefore reject the possibility that the absorption and emission phases are
co-spatial and favour the explanation that the absorption gas has low
metallicity and is located further away from the host galaxy (than the emission
line gas). The estimated low metallicity for the absorption gas in 0943-242 (Z
\~ 1% solar) and its proposed location -outer halo outside the radio cocoon-
suggest that its existence preceeds the observed AGN phase and is a vestige of
the initial starburst at the onset of formation of the parent galaxy.


title: Energy implications of temperature fluctuations in photoionized plasma

abstract:
  We quantify the energy radiated through all the collisionally excited lines
in a photoionized nebula which is permeated by temperature fluctuations. We
assume that these correspond to hot spots which are the results of an unknown
heating process distinct from the photoelectric heating. We consider all the
effects of using a higher mean temperature (as compared to the equilibrium
temperature) due to the fluctuations not only on each emission line but also on
the ionization state of the gas. If this yet unknown process was to radiate a
fixed amount of energy, we find that the fluctuations should correlate with
metallicity Z when it exceeds 0.7 solar. The excess energy radiated in the
lines as a result of the fluctuations is found to scale proportionally to their
amplitude t^2. When referred to the total energy absorbed through
photoionization, the excess energy is comparable in magnitude to t^2.


title: The porous atmosphere of eta Carinae

abstract:
  We analyze the wind generated by the great 20 year long super-Eddington
outburst of eta-Carinae. We show that using classical stellar atmospheres and
winds theory, it is impossible to construct a consistent wind model in which a
sufficiently small amount of mass, like the one observed, is shed. One expects
the super-Eddington luminosity to drive a thick wind with a mass loss rate
substantially higher than the observed one. The easiest way to resolve the
inconsistency is if we alleviate the implicit notion that atmospheres are
homogeneous. An inhomogeneous atmosphere, or "porous", allows more radiation to
escape while exerting a smaller average force. Consequently, such an atmosphere
yields a considerably lower mass loss rate for the same total luminosity.
Moreover, all the applications of the Eddington Luminosity as a strict
luminosity limit should be revised, or at least reanalyzed carefully.


title:
The Formation of the Hubble Sequence of Disk Galaxies: The Effects of
  Early Viscous Evolution

abstract:
  We investigate a model of disk galaxies whereby viscous evolution of the
gaseous disk drives material inwards to form a proto-bulge. We start from the
standard picture of disk formation through the settling of gas into a dark halo
potential well, with the disk initially coming into centrifugal equilibrium
with detailed conservation of angular momentum. We derive generic analytic
solutions for the disk-halo system after adiabatic compression of the dark
halo, with free choice of the input virialized dark halo density profile and of
the specific angular momentum distribution. We derive limits on the final
density profile of the halo in the central regions. Subsequent viscous
evolution of the disk is modelled by a variation of the specific angular
momentum distribution of the disk, providing analytic solutions to the final
disk structure. The assumption that the viscous evolution timescale and star
formation timescale are similar leads to predictions of the properties of the
stellar components. Focusing on small `exponential' bulges, ones that may be
formed through a disk instability, we investigate the relationship between the
assumed initial conditions, such as halo `formation', or assembly, redshift
$z_f$, spin parameter $\lambda$, baryonic fraction $F$, and final disk
properties such as global star formation timescale, gas fraction, and
bulge-to-disk ratio. We find that the present properties of disks, such as the
scale length, are compatible with a higher initial formation redshift if the
re-distribution by viscous evolution is included than if it is ignored. We also
quantify the dependence of final disk properties on the ratio $F/\lambda$, thus
including the possibility that the baryonic fraction varies from galaxy to
galaxy, as perhaps may be inferred from the observations.


title: Reionization and the abundance of galactic satellites

abstract:
  One of the main challenges facing standard hierarchical structure formation
models is that the predicted abundance of galactic subhalos with circular
velocities of 10-30 km/s is an order of magnitude higher than the number of
satellites actually observed within the Local Group. Using a simple model for
the formation and evolution of dark halos, based on the extended
Press-Schechter formalism and tested against N-body results, we show that the
theoretical predictions can be reconciled with observations if gas accretion in
low-mass halos is suppressed after the epoch of reionization. In this picture,
the observed dwarf satellites correspond to the small fraction of halos that
accreted substantial amounts of gas before reionization. The photoionization
mechanism naturally explains why the discrepancy between predicted halos and
observed satellites sets in at about 30 km/s, and for reasonable choices of the
reionization redshift (z_re = 5-12) the model can reproduce both the amplitude
and shape of the observed velocity function of galactic satellites. If this
explanation is correct, then typical bright galaxy halos contain many low-mass
dark matter subhalos. These might be detectable through their gravitational
lensing effects, through their influence on stellar disks, or as dwarf
satellites with very high mass-to-light ratios. This model also predicts a
diffuse stellar component produced by large numbers of tidally disrupted
dwarfs, perhaps sufficient to account for most of the Milky Way's stellar halo.


title: Correlated intense X-ray and TeV activity of Mrk~501 in 1998 June

abstract:
  We present exactly simultaneous X-ray and TeV monitoring with {\it RXTE} and
HEGRA of the TeV blazar Mrk 501 during 15 days in 1998 June. After an initial
period of very low flux at both wavelengths, the source underwent a remarkable
flare in the TeV and X-ray energy bands, lasting for about six days and with a
larger amplitude at TeV energies than in the X-ray band. At the peak of the TeV
flare, rapid TeV flux variability on sub-hour timescales is found. Large
spectral variations are observed at X-rays, with the 3--20 keV photon index of
a pure power law continuum flattening from $\Gamma=2.3$ to $\Gamma=1.8$ on a
timescale of 2--3 days. This implies that during the maximum of the TeV
activity, the synchrotron peak shifted to energies $\gtrsim 50$ keV, a behavior
similar to that observed during the longer-lasting, more intense flare in 1997
April. The TeV spectrum during the flare is described by a power law with
photon index $\Gamma=1.9$ and an exponential cutoff at $\sim$ 4 TeV; an
indication for spectral softening during the flare decay is observed in the TeV
hardness ratios. Our results generally support a scenario where the TeV photons
are emitted via inverse Compton scattering of ambient seed photons by the same
electron population responsible for the synchrotron X-rays. The simultaneous
spectral energy distributions (SEDs) can be fit with a one-zone
synchrotron-self Compton model assuming a substantial increase of the magnetic
field and the electron energy by a factor of 3 and 10, respectively.


title: Space VLBI Observations of 3C 279 at 1.6 and 5 GHz

abstract:
  We present the first VLBI Space Observatory Programme (VSOP) observations of
the gamma-ray blazar 3C 279 at 1.6 and 5 GHz. The combination of the VSOP and
VLBA-only images at these two frequencies maps the jet structure on scales from
1 to 100 mas. On small angular scales the structure is dominated by the quasar
core and the bright secondary component `C4' located 3 milliarcseconds from the
core (at this epoch). On larger angular scales the structure is dominated by a
jet extending to the southwest, which at the largest scale seen in these images
connects with the smallest scale structure seen in VLA images. We have
exploited two of the main strengths of VSOP: the ability to obtain
matched-resolution images to ground-based images at higher frequencies and the
ability to measure high brightness temperatures. A spectral index map was made
by combining the VSOP 1.6 GHz image with a matched-resolution VLBA-only image
at 5 GHz from our VSOP observation on the following day. The spectral index map
shows the core to have a highly inverted spectrum, with some areas having a
spectral index approaching the limiting value for synchrotron self-absorbed
radiation of 2.5. Gaussian model fits to the VSOP visibilities revealed high
brightness temperatures (>10^{12} K) that are difficult to measure with
ground-only arrays. An extensive error analysis was performed on the brightness
temperature measurements. Most components did not have measurable brightness
temperature upper limits, but lower limits were measured as high as 5x10^{12}
K. This lower limit is significantly above both the nominal inverse Compton and
equipartition brightness temperature limits. The derived Doppler factor,
Lorentz factor, and angle to the line-of-sight in the case of the equipartition
limit are at the upper end of the range of expected values for EGRET blazars.


title:
Properties of Gamma-Ray Burst Time Profiles Using Pulse Decomposition
  Analysis

abstract:
  The time profiles of many gamma-ray bursts consist of distinct pulses, which
offers the possibility of characterizing the temporal structure of these bursts
using a relatively small set of pulse shape parameters. This pulse
decomposition analysis has previously been performed on a small sample of
bright long bursts using binned data from BATSE, which comes in several data
types, and on a sample of short bursts using the BATSE Time-Tagged Event (TTE)
data type. We have developed an interactive pulse-fitting program using the
phenomenological pulse model of Norris, et al. and a maximum-likelihood fitting
routine. We have used this program to analyze the Time-to-Spill (TTS) data for
all bursts observed by BATSE up through trigger number 2000, in all energy
channels for which TTS data is available. We present statistical information on
the attributes of pulses comprising these bursts, including relations between
pulse characteristics in different energy channels and the evolution of pulse
characteristics through the course of a burst. We carry out simulations to
determine the biases that our procedures may introduce. We find that pulses
tend to have shorter rise times than decay times, and tend to be narrower and
peak earlier at higher energies. We also find that pulse brightness, pulse
width, and pulse hardness ratios do not evolve monotonically within bursts, but
that the ratios of pulse rise times to decay times tend to decrease with time
within bursts.


title:
Intrinsic and Cosmological Signatures in Gamma-Ray Burst Time Profiles:
  Time Dilation

abstract:
  The time profiles of many gamma-ray bursts consist of distinct pulses, which
offers the possibility of characterizing the temporal structure of these bursts
using a relatively small set of pulse shape parameters. We have used a pulse
decomposition procedure to analyze the Time-to-Spill (TTS) data for all bursts
observed by BATSE up through trigger number 2000, in all energy channels for
which TTS data is available. We obtain amplitude, rise and decay timescales, a
pulse shape parameter, and the fluences of individual pulses in all of the
bursts. We investigate the correlations between brightness measures (amplitude
and fluence) and timescale measures (pulse width and separation) which may
result from cosmological time dilation of bursts, or from intrinsic properties
of burst sources or from selection effects. The effects of selection biases are
evaluated through simulations. The correlations between these parameters among
pulses within individual bursts give a measure of the intrinsic effects while
the correlations among bursts could result both from intrinsic and cosmological
effects. We find that timescales tend to be shorter in bursts with higher peak
fluxes, as expected from cosmological time dilation effects, but also find that
there are non-cosmological effects contributing to this inverse correlation. We
find that timescales tend to be longer in bursts with higher total fluences,
contrary to what is expected from cosmological effects. We also find that peak
fluxes and total fluences of bursts are uncorrelated, indicating that they
cannot both be good distance indicators for bursts.


title: Changes in the long term intensity variations in Cyg X-2 and LMC X-3

abstract:
  We report the detection of changes in the long-term intensity variations in
two X-ray binaries, Cyg X-2 and LMC X-3. In this work, we have used the
long-term light curves obtained with the All-Sky Monitors (ASMs) of the Rossi
X-Ray Timing Explorer (RXTE), Ginga, Ariel 5, and Vela 5B and the scanning
modulation collimator of HEAO 1. It is found that in the light curves of both
the sources, obtained with these instruments at various times over the last 30
years, more than one periodic or quasi-periodic component is always present.
The multiple prominent peaks in the periodograms have frequencies unrelated to
each other. In Cyg X-2, RXTE-ASM data show strong peaks at 40.4 and 68.8 days,
and Ginga-ASM data show strong peaks at 53.7 and 61.3 days. Multiple peaks are
also observed in LMC X-3. The various strong peaks in the periodograms of LMC
X-3 appear at 104, 169, and 216 days (observed with RXTE-ASM) and 105, 214, and
328 days (observed with Ginga-ASM). The present results, when compared with the
earlier observations of periodicities in these two systems, demonstrate the
absence of any stable long period. The 78 day periodicity detected earlier in
Cyg X-2 was probably due to the short time base in the RXTE data that were
used, and the periodicity of 198 days in LMC X-3 was due to a relatively short
duration of observation with HEAO 1.


title:
Study of the Long Term Stability of two Anomalous X-ray Pulsars 4U
  0142+61 and 1E 1048.1-5937 with ASCA

abstract:
  We present new observations of two anomalous X-ray pulsars (AXP) 4U 0142+61
and 1E 1048.1-5937 made in 1998 with the ASCA. The energy spectra of these two
AXPs are found to consist of two components, a power-law and a blackbody
emission from the neutron star surface. These observations, when compared to
earlier ASCA observations in 1994 show remarkable stability in the intensity,
spectral shape and pulse profile. However, we find that the spin-down rate in
1E 1048.1-5937 is not constant. In this source, we have clearly identified
three epochs with spin-down rates different from each other and the average
value. This has very strong implications for the magnetar hypothesis of AXPs.
We also note that the spin-down rate and its variations in 1E 1048.1-5937 are
much larger than what can normally be produced by an accretion disk with very
low mass accretion rate corresponding to its low X-ray luminosity.


title:
Long-term photometry of the Wolf-Rayet stars WR 137, WR 140, WR 148, and
  WR 153

abstract:
  In 1991, a long term UBV-photometry campaign of four Wolf-Rayet stars was
started using the 60 cm telescope of the National Astronomical Observatory
Rozhen, Bulgaria. Here we report on our observational results and discuss the
light variations. The star WR 137 showed only random light variations, which
are probably due to dynamical wind instabilities but not to eclipses. WR 140
featured a dip in the light curve, the amplitude increasing towards shorter
wavelengths. The probable cause is electron and Rayleigh scattering when the
star was eclipsed by a dust envelope. In the case of WR 148 we found a period
of 4.3 days and significant scatter in the light curves. Additionally there
seems to be a long term variation with a period of 4 years. Our photometry of
WR 153 is consistent with the quadruple model for this star.


title: Snapshot coronagraphy with an interferometer in space

abstract:
  Diluted arrays of many optical apertures will be able to provide h
igh-resolution snapshot images if the beams are combined according to the
densified-pupil scheme. We show that the same principle can also provide
coronagraphic images, for detecting faint sources near a bright unresolved one.
Recent refinements of coronagraphic techniques, i.e. the use of a phase mask,
active apodization and dark-speckle analysis, are also applicable for enhanced
contrast. Implemented in the form of a proposed 50-500m Exo-Earth Discoverer
array in space, the principle can serve to detect Earth-like exo-planets in the
infra-red. It can also provide images of faint nebulosity near stars, active
galactic nuclei and quasars. Calculations indicate that exo-planets are
detectable amidst the zodiacal and exo-zodiacal emission faster than with a
Bracewell array of equivalent area, a consequence of the spatial selectivity in
the image.


title: A Near Infrared Polarized Bipolar Cone in the CIRCINUS Galaxy

abstract:
  We present near-infrared broad-band polarization images of the nuclear
regions of the Circinus galaxy in the J, H and K bands. For the first time the
south-eastern reflection cone is detected in polarized light, which is obscured
at optical wavelengths behind the galactic disk. This biconical structure is
clearly observed in J and H band polarized flux whilst in the K band a more
compact structure is detected. Total flux J-K and H-K colour maps reveal a
complex colour gradient toward the south-east direction (where the Circinus
galactic disk is nearer to us). We find enhanced extinction in an arc shaped
structure, at about 200pc from the nucleus, probably part of the star-formation
ring.
  We model the polarized flux images with the scattering and torus model of
Young etal, with the same basic input parameters as used by Alexander etal in
the spectropolarimetry modelling of Circinus. The best fit to the polarized
flux is achieved with a torus radius of ~16pc, and a visual extinction Av,
through the torus, to the near-infrared emission regions of >66 mags.


title: An X-ray and optical study of the cluster A33

abstract:
  We report the first detailed X-ray and optical observations of the
medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the
UH 2.2m and Keck II telescopes at Mauna Kea. The information deduced from X-ray
and optical imaging and spectroscopic data allowed us to identify the X-ray
source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint,
$F_{2-10 keV} \approx 2.4 \times 10^{-13} \ergscm2$, X-ray source
1SAXJ0027.2-1930, $\sim 2$ arcmin away from the optical position of the cluster
as given in the Abell catalogue, is identified with the central region of A33.
Based on six cluster galaxy redshifts, we determine the redshift of A33,
$z=0.2409$; this is lower than the value derived by Leir and Van Den Bergh
(1977). The source X-ray luminosity, $L_{2-10 keV} = 7.7 \times 10^{43} \ergs$,
and intracluster gas temperature, $T = 2.9$ keV, make this cluster interesting
for cosmological studies of the cluster $L_X-T$ relation at intermediate
redshifts. Two other X-ray sources in the A33 field are identified. An AGN at
z$=$0.2274, and an M-type star, whose emission are blended to form an extended
X-ray emission $\sim 4$ arcmin north of the A33 cluster. A third possibly
point-like X-ray source detected $\sim 3$ arcmin north-west of A33 lies close
to a spiral galaxy at z$=$0.2863 and to an elliptical galaxy at the same
redshift as the cluster.


title: Extended X-ray emission from FRIIs and RL quasars

abstract:
  We review the evidence that detectable fluxes of X-rays are produced by
inverse Compton scattering of nuclear photons with the relativistic electrons
in the radio lobes of strong FRII radio galaxies within the FRII-RL quasar
unification scheme. We report here on the possible detection of this effect in
two steep spectrum RL quasars. This may have important implications on the
physics and evolution of powerful radio galaxies.


title:
The Morphology, Color, and Gas Content of Low Surface Brightness
  Galaxies

abstract:
  Recent surveys have discovered hundreds of low surface brightness galaxies,
systems with central surface brightness fainter than 22.0 B mag arcsec^-2, in
the local universe. Plots of the surface brightness distribution - that is, the
space density of galaxies plotted against central surface brightness - show a
flat space density distribution from the canonical Freeman value of 21.65
through the current observational limit of 25.0 B mag arcsec^-2. It is
therefore extremely important to understand these diffuse systems if we wish to
understand galaxy formation and evolution as a whole. This talk is a review of
both the known properties of low surface brightness galaxies and of popular
theories describing the formation and evolution of these enigmatic systems.


title: A Single Circumbinary Disk in the HD 98800 Quadruple System

abstract:
  We present sub-arcsecond thermal infrared imaging of HD 98800, a young
quadruple system composed of a pair of low-mass spectroscopic binaries
separated by 0.8'' (38 AU), each with a K-dwarf primary. Images at wavelengths
ranging from 5 to 24.5 microns show unequivocally that the optically fainter
binary, HD 98800B, is the sole source of a comparatively large infrared excess
upon which a silicate emission feature is superposed. The excess is detected
only at wavelengths of 7.9 microns and longer, peaks at 25 microns, and has a
best-fit black-body temperature of 150 K, indicating that most of the dust lies
at distances greater than the orbital separation of the spectroscopic binary.
We estimate the radial extent of the dust with a disk model that approximates
radiation from the spectroscopic binary as a single source of equivalent
luminosity. Given the data, the most-likely values of disk properties in the
ranges considered are R_in = 5.0 +/- 2.5 AU, DeltaR = 13+/-8 AU, lambda_0 =
2(+4/-1.5) microns, gamma = 0+/-2.5, and sigma_total = 16+/-3 AU^2, where R_in
is the inner radius, DeltaR is the radial extent of the disk, lambda_0 is the
effective grain size, gamma is the radial power-law exponent of the optical
depth, tau, and sigma_total is the total cross-section of the grains. The range
of implied disk masses is 0.001--0.1 times that of the moon. These results show
that, for a wide range of possible disk properties, a circumbinary disk is far
more likely than a narrow ring.