title: Detection of Nuclear X-ray Sources in Nearby Galaxies with Chandra

abstract:
  We report preliminary results from an arcsecond-resolution X-ray survey of
nearby galaxies using ACIS on board Chandra. The total sample consists of 41
low-luminosity AGNs, including Seyferts, LINERs, and LINER/H II transition
objects. In the initial subsample of 24 objects observed thus far, we detect in
62% of the objects a compact, pointlike source astrometrically coincident with
either the optical or radio position of the nucleus. The high detection rate
strongly suggests that the majority of the objects do contain weakly active,
AGN-like cores, presumably powered by central massive black holes. The 2-10 keV
luminosities of the nuclear sources range from 10^38 to 10^41 erg/s, with a
median value of 2x10^38 erg/s. Our detection limit corresponds to 8x10^37 erg/s
for the typical sample distance of 12 Mpc; this limit is two orders of
magnitude fainter than the weakest sources of this kind previously studied
using ASCA or BeppoSAX. The new data extend toward lower luminosities the known
linear correlation between hard X-ray and H-alpha luminosity for broad-line
AGNs. Many narrow-line objects do contain X-ray cores, consistent with either
weak AGNs or X-ray binary systems, but they have X-ray luminosities a factor of
10 below the L_X-L(Halpha) relation of the broad-line sources. Their
distributions of photon energies show no indication of exceptionally high
absorption. The optical line emission in these nuclei is likely powered, at
least in part, by stellar processes.


title:
The Central Regions of Early-Type Galaxies Hosting Active Galactic
  Nuclei as Viewed with HST/NICMOS

abstract:
  We present preliminary results from surface photometry of a sample of
early-type galaxies observed with NICMOS on board HST in the F160W (H-band)
filter. Dust is found to occur mostly in galaxies which possess unresolved
nuclei, and in a few cases the presence of dust causes the isophotes to appear
boxy. We performed a 2-D modeling of the host galaxy light distribution using
the empirical Nuker function, which proves to be an adequate representation of
the surface-brightness profile for most early-type galaxies. The accurate
modeling of the bulge light allows us to obtain the magnitude of the unresolved
central source without contamination from the underlying stellar population.
Our classification of early-type galaxies into core-type and power-law galaxies
agrees with the results from previous work based on HST optical images, with
core profiles occurring in luminous galaxies and power-law profiles occurring
in low-luminosity galaxies with disky isophotes. We do not find a clear
dichotomy in the distribution of inner slopes. Unresolved nuclear point sources
are evident in about one-third of the sample galaxies, with H magnitudes in the
range 13.5 to 17.3. Most of the type 1 Seyfert and LINER nuclei (83%) reveal a
distinct point source, while the detection rate is much less for type 2 nuclei
(35%). The occurrence of point sources appears to be independent of whether the
underlying galaxy has core-type profile or power-law profile.


title:
Radio Continuum Survey of an Optically-Selected Sample of Nearby Seyfert
  Galaxies

abstract:
  We have used the Very Large Array (VLA) to conduct a survey for radio
continuum emission in the sample of 52 Seyfert nuclei selected from the optical
spectroscopic galaxy catalog of Ho, Filippenko, and Sargent. This Seyfert
sample is the most complete and least biased available, and, as such, it will
be useful for a variety of statistical analyses. Here we present the
observations, measurements, and an atlas of radio maps.
  The observations were made at 6 cm in the B-array and at 20 cm in the
A-array, yielding matched angular resolutions of approximately 1". We detected
44 objects (85%) at 6 cm and 37 objects (71%) at 20 cm above a 3-sigma
threshold of 0.12 mJy/beam. The sources have a wide range of radio powers
(10^{18}-10^{25} W/Hz), spectral indices (+0.5 to -1 between 20 and 6 cm), and
linear sizes (from a few tens pc to 15 kpc). The morphology of the radio
emission is predominantly that of a compact core, either unresolved or slightly
resolved, occasionally accompanied by elongated, jet-like features. Linearly
polarized emission was detected at 6 cm in 12 sources, 9 of which were also
detected at 20 cm.


title: Binaries and Globular Cluster Dynamics

abstract:
  We summarize the results of recent theoretical work on the dynamical
evolution of globular clusters containing primordial binaries. Even a very
small initial binary fraction (e.g., 10%) can play a key role in supporting a
cluster against gravothermal collapse for many relaxation times. Inelastic
encounters between binaries and single stars or other binaries provide a very
significant energy source for the cluster. These dynamical interactions also
lead to the production of large numbers of exotic systems such as ultracompact
X-ray binaries, recycled radio pulsars, double degenerate systems, and blue
stragglers. Our work is based on a new parallel supercomputer code implementing
Henon's Monte Carlo method for simulating the dynamical evolution of dense
stellar systems in the Fokker-Planck approximation. This new code allows us to
calculate very accurately the evolution of a cluster containing a realistic
number of stars (N ~ 10^5 - 10^6) in typically a few hours to a few days of
computing time. The discrete, star-by-star representation of the cluster in the
simulation makes it possible to treat naturally a number of important
processes, including single and binary star evolution, all dynamical
interactions of single stars and binaries, and tidal interactions with the
Galaxy.


title:
The evolutionary time scale of Sakurai's object: A test of convection
  theory?

abstract:
  Sakurai's object (V4334 Sgr) is a born again AGB star following a very late
thermal pulse. So far no stellar evolution models have been able to explain the
extremely fast evolution of this star, which has taken it from the pre-white
dwarf stage to its current appearance as a giant within only a few years. A
very high stellar mass can be ruled out as the cause of the fast evolution.
Instead the evolution time scale is reproduced in stellar models by making the
assumption that the efficiency for element mixing in the He-flash convection
zone during the very late thermal pulse is smaller than predicted by the
mixing-length theory. As a result the main energy generation from fast proton
capture occurs closer to the surface and the expansion to the giant state is
accelerated to a few years. Assuming a mass of V4334 Sgr of 0.604Msun -- which
is consistent with a distance of 4kpc -- a reduction of the mixing length
theory mixing efficiency by a factor of ~ 100 is required to match its
evolutionary time scale. This value decreases if V4334 Sgr has a smaller mass
and accordingly a smaller distance. However, the effect does not disappear for
the smallest possible masses. These findings may present a semi-empirical
constraint on the element mixing in convective zones of the stellar interior.


title: Modeling the evolution of Sakurai's object

abstract:
  Sakurai's object is a born again AGB star of the very late thermal pulse
flavor. In this contribution I will discuss new models of stellar evolution and
nucleosynthesis models of this phase. Two most intriguing properties of
Sakurai's objects have so far not been understood theoretically: the peculiar
chemical appearance, in particular the high lithium abundance and the short
time scale of only a few years on which the transition from the dwarf
configuration into the born again giant appearance has occurred. A new
nucleosynthesis mode of hot hydrogen-deficient He3 burning can explain the
extraordinary lithium abundance. During the thermal pulse He3 is ingested from
the envelope together with the protons into the hot He-flash convection zone.
The first network calculations show that due to the large C12 abundance protons
are rather captured by carbon than destroy newly formed Be7 and ultimately Li7.
Moreover, the short evolution time scale has been reproduced by making the
assumption that the convective efficiency for element mixing is smaller by two
to three orders of magnitude than predicted by the mixing-length theory. As a
result the main energy generation from fast convective proton capture will
occur at a larger mass coordinate, closer to the surface and the expansion to
the giant state is accelerated to a few years in agreement with Sakurai's
behavior. This result may represent an independent empirical constraint on the
poorly known efficiency of element mixing in convective zones of the stellar
interior.


title: Stellar evolution and nucleosynthesis of Post-AGB Stars

abstract:
  I discuss recent new models of post-Asymptotic Giant Branch stellar
evolution. These models aim to clarify the evolutionary origin and status of a
variety of hydrogen-deficient post-AGB stars such as central stars of planetary
nebulae of Wolf-Rayet spectral type, PG1159 stars or Sakurai's object. Starting
with AGB models with overshoot such stars can evolve through one of four
distinct channels. Each of these channels has typical abundance patterns
depending on the relative timing of the departure from the AGB and the
occurrence of the last thermal pulse. I discuss the responsible mechanisms and
observational counterparts.


title:
Zodiacal Infrared Foreground Prediction for Space Based Infrared
  Interferometer Missions

abstract:
  The zodiacal foreground for a highly sensitive space infrared interferometer
is predicted for various observing locations. For the predictions we use a
model that was derived from measurements of the Cosmic Background Explorer
(COBE). We find that at a wavelength of $10{\rm \mu m}$ 96% of the sky is
darker than $1{MJy}{\rm sr}^{-1}$ for observations in the ecliptic plane at
$5{\rm AU}$, and 83% is darker than $0.1{\rm MJy}{\rm sr}^{-1}$. At $1{\rm
AU}$, however, always more than 50% of the sky are brighter than $1{\rm
MJy}{\rm sr}^{-1}$, even if the observations are made from $30^\circ$ or
$60^\circ$ of latitude above the ecliptic plane, at 10 or $20{\rm \mu m}$.
Thus, according to the employed model, the foreground reduction by increasing
the heliocentric distance of the observing location is more effective than by
increasing the latitude.


title: G-band Spectral Synthesis in Solar Magnetic Concentrations

abstract:
  Narrow band imaging in the G-band is commonly used to trace the small
magnetic field concentrations of the Sun, although the mechanism that makes
them bright has remained unclear. We carry out LTE syntheses of the G-band in
an assorted set of semi-empirical model magnetic concentrations. The syntheses
include all CH lines as well as the main atomic lines within the band-pass. The
model atmospheres produce bright G-band spectra having many properties in
common with the observed G-band bright points. In particular, the contrast
referred to the quiet Sun is about twice the contrast in continuum wavelengths.
The agreement with observations does not depend on the specificities of the
model atmosphere, rather it holds from single fluxtubes to MIcro-Structured
Magnetic Atmospheres. However, the agreement requires that the real G-band
bright points are not spatially resolved, even in the best observations. Since
the predicted G-band intensities exceed by far the observed values, we foresee
a notable increase of contrast of the G-band images upon improvement of the
angular resolution. According to the LTE modeling, the G-band spectrum emerges
from the deep photosphere that produces the continuum. Our syntheses also
predict solar magnetic concentrations showing up in continuum images but not in
the G-band . Finally, we have examined the importance of the CH
photo-dissociation in setting the amount of G-band absorption. It turns out to
play a minor role.


title: Relativistic large scale jets and minimum power requirements

abstract:
  The recent discovery, by the Chandra satellite, that jets of blazars are
strong X-ray emitters at large scales (0.1-1 Mpc) bears support to the
hypothesis that (also) on these scales the emitting plasma is moving at highly
relativistic speeds. In this case in fact the emission via inverse Compton
scattering off cosmic background photons is enhanced and the resulting
predicted X-ray spectrum well accounts for the otherwise puzzling observations.
Here we point out another reason to favor relativistic large scale jets, based
on a minimum power argument: by estimating the Poynting flux and bulk kinetic
powers corresponding to, at least, the relativistic particles and magnetic
field responsible for the emission, one can derive the value of the bulk
Lorentz factor for which the total power is minimized. It is found that both
the inner and extended parts of the jet of PKS 0637-752 satisfy such condition.


title: Lengths of the First days of the Universe

abstract:
  The early stage of the Universe is discussed and the time lengths of its
first days are given. If we denote the Hubble time in the zero-gravity limit by
T (approximately 12.16 billion years), and T(n) denotes the length of the n-th
day, then we have the very simple relation T(n)=T/(2n-1). Hence we obtain for
the first days the following lenghts of time: T(1)=T, T(2)=T/3, T(3)=T/5, etc.


title: Cusped Mass Models Of Gravitational Lenses

abstract:
  Recent observations of galaxy luminosity profiles and dark matter simulations
find luminosity and mass distributions characterized by central cusps rather
than finite core radii. We introduce and implement a set of cusped ellipsoidal
lens models which include limits similar to the Jaffe, Hernquist, \eta and NFW
models and apply them to the gravitational lenses APM 08279+5255 and B
1933+503. A successful model of APM 08279+5255 with its central, odd image
requires a very shallow cusp, $\gamma \ltorder 0.4$ where $\rho \propto
r^{-\gamma}$ as $r\to 0$, which is similar to a core rather than the favored $1
\ltorder \gamma \ltorder 2$ cusps. B~1933+503, by contrast, is well modeled
with a steep density cusp, $1.6 \ltorder \gamma \ltorder 2.0$.


title: Magnetic Fields of Neutron Stars: an Overview

abstract:
  Observations indicate that magnetic fields on neutron stars span at least the
range $10^{8-15}$ G, corresponding to a range of magnetic fluxes similar to
that found in white dwarfs and main sequence stars. The observational evidence
is discussed, as well as the possible origin of the field, and the associated
phenomenology (``classical'', millisecond, and binary pulsars, ``magnetars'',
etc.). Particular attention is given to physical processes potentially leading
to magnetic field evolution.


title: New results on the temporal structure of GRBs

abstract:
  We analyze the temporal structure of long ((T_{90}>2sec)) and short
((T_{90}<2sec)) BATSE bursts. We find that: (i) In many short bursts (\delta
t_{min}/T\ll 1) (where (\delta t_{min}) is the shortest pulse). This indicates
that short bursts arise, like long ones, in internal shocks. (ii) In long
bursts there is an excess of long intervals between pulses (relative to a
lognormal distribution). This excess can be explained by the existence of
\emph{quiescent times}, long periods with no signal above the background that
arise, most likely, from periods with no source activity. The lognormal
distribution of the intervals (excluding the \emph{quiescent times}) is similar
and correlated with the distribution of the pulses width, in agreement with the
predictions of the internal shock model.


title: Ground-Based Coronagraphy with High Order Adaptive Optics

abstract:
  We summarize the theory of coronagraphic optics, and identify a dimensionless
fine-tuning parameter, F, which we use to describe the Lyot stop size in the
natural units of the coronagraphic optical train and the observing wavelength.
We then present simulations of coronagraphs matched to adaptive optics (AO)
systems on the Calypso 1.2m, Palomar Hale 5m and Gemini 8m telescopes under
various atmospheric conditions, and identify useful parameter ranges for AO
coronagraphy on these telescopes. Our simulations employ a tapered, high-pass
filter in spatial frequency space to mimic the action of adaptive wavefront
correction. We test the validity of this representation of AO correction by
comparing our simulations with recent K-band data from the 241-channel Palomar
Hale AO system and its dedicated PHARO science camera in coronagraphic mode.


title:
ROSAT-HRI detection of the Class I protostar YLW16A in the rho Ophiuchi
  dark cloud

abstract:
  I analyze unpublished or partially published archival ROSAT data of the rho
Ophiuchi dark cloud. This set of seven overlapping ROSAT HRI pointings,
composed of eight ~one-hour exposures, detects mainly the X-ray brightest T
Tauri stars of this star-forming region. Only two HRI sources are new X-ray
sources, and their optical counterparts are proposed as new Weak T Tauri star
candidates. Meanwhile the ROSAT HRI caught during just one exposure a weak
X-ray source (maximum likelihood=10; SNR=4.1\sigma for Gaussian statistics)
among a group of three embedded young stellar objects including two Class I
protostars. Previous ROSAT PSPC, ASCA GIS observations, and as I argue here one
Einstein IPC observation, have already detected an X-ray source in this area,
but this higher angular resolution data show clearly that X-rays are emitted by
the Class I protostar YLW16A. This is the second Class I protostar detected by
the ROSAT HRI in this dark cloud. The determination of the intrinsic X-ray
luminosity of this event, L_X[0.1-2.4 keV]=(9.4-450)*1E30 erg/s, critically
depends on the source absorption estimate. Improvements will be obtained only
by the direct determination of this parameter from fitting of Chandra and
XMM-Newton spectra.


title:
New Results from the X-ray and Optical Survey of the Chandra Deep Field
  South: The 300ks Exposure

abstract:
  We present results from 300 ks of X-ray observations of the Chandra Deep
Field South. The field of the four combined exposures is now 0.1035 deg^2 and
we reach a flux limit of 10^{-16} erg s^{-1} cm^{-2} in the 0.5-2 keV soft band
and 10^{-15} erg s^{-1} cm^{-2} in the 2-10 keV hard band, thus a factor 2
fainter than the previous 120 ks exposure. The total catalogue is composed of
197 sources including 22 sources detected only in the hard band, 51 only in the
soft band, and 124 detected in both bands. We have now the optical spectra for
86 optical counterparts. We compute the total contribution to the X-ray
background in the 2-10 keV band, which now amounts to (1.45\pm 0.15)*10^{-11}
erg cm^{-2} s^{-1} deg^{-2} (after the inclusion of the ASCA sources to account
for the bright end) to a flux limit of 10^{-15} erg s^{-1} cm^{-2}. This
corresponds to 60-90% of the unresolved hard X-ray background (XRB), given the
uncertainties on its actual value.[ABRIDGED]


title: Supernova Explosions and Neutron Star Formation

abstract:
  The current picture of the collapse and explosion of massive stars and the
formation of neutron stars is reviewed. According to the favored scenario,
however by no means proven and undisputed, neutrinos deposit the energy of the
explosion in the stellar medium which surrounds the nascent neutron star.
Observations, in particular of Supernova~1987A, suggest that mixing processes
play an important role in the expanding star, and multi-dimensional simulations
show that these are linked to convective instabilities in the immediate
vicinity of the neutron star. Convectively enhanced energy transport inside the
neutron star can have important consequences for the neutrino emission and thus
the neutrino-heating mechanism. This also holds for a suppression of the
neutrino interactions at nuclear densities. Multi-dimensional hydrodynamics,
general relativity, and a better understanding of the neutrino interactions in
neutron star matter may be crucial to resolve the problem that state-of-the-art
spherical models do not yield explosions even with a very accurate treatment of
neutrino transport by solving the Boltzmann equation.


title:
Evidence for Prolonged Main Sequence Stellar Evolution of F Stars in
  close binaries

abstract:
  Binary F stars exhibit large brightness anomaly, which is defined here as the
difference between the absolute magnitude from the uvby photometry and the
actual absolute magnitude of the star. We have found that the anomaly inversely
correlates with the binary components separation. There is evidence that the
correlation reflects actual population differences between close and wide
binary pairs, in which case it indicates that the anomaly is somehow associated
with the interaction of binary's components. The anomaly has also been found to
correlate with both kinematics and metallicity. The sense of the correlations
implies that the anomaly increases as the star evolves, suggesting a peculiar
evolution of a primary F star in a tight binary pair. This conclusion has
further been supported by the study of the age-velocity relation (AVR) of F
stars that are cataloged in the HIPPARCOS as single. Among these stars, those
with brightness anomaly were previously shown to be most likely unidentified
close binaries. We have found that the AVR of these binary candidates is
different from that of the ``truly single'' F stars. The discrepancy between
the two AVRs indicates that the putative binaries are, on average, older than
similar normal single F stars at the same effective temperature and luminosity,
which is consistent with the inferred peculiar evolution in close binaries. It
appears that this peculiarity is caused by the impact of the components
interaction in a tight pair on stellar evolution, which results in the
prolonged main sequence lifetime of the primary F star.


title: Large-Scale Structure, Theory and Statistics

abstract:
  I review the standard paradigm for understanding the formation and evolution
of cosmic structure, based on the gravitational instability of dark matter, but
many variations on this basic theme are viable. Despite the great progress that
has undoubtedly been made, steps are difficult because of uncertainties in the
cosmological parameters, in the modelling of relevant physical processes
involved in galaxy formation, and perhaps most fundamentally in the
relationship between galaxies and the underlying distribution of matter. For
the foreseeable future, therefore, this field will be led by observational
developments allowing model parameters to be tuned and, hopefully, particular
scenarios falsified. In these lectures I focus on two ingredients in this class
of models: (i) the role of galaxy bias in interpreting clustering data; and
(ii) the statistical properties of the initial fluctuations. In the later case,
I discuss some ideas as to how the standard assumption - that the primordial
density fluctuations constitute a Gaussian random field - can be tested using
measurements galaxy clustering and the cosmic microwave background.


title:
Possible Detection of Baryonic Fluctuations in the Large-Scale Structure
  Power Spectrum

abstract:
  We present a joint analysis of the power spectra of density fluctuations from
three independent cosmological redshift surveys; the PSCz galaxy catalog, the
APM galaxy cluster catalog and the Abell/ACO cluster catalog. Over the range
0.03 <= k <= 0.15 h/Mpc,the amplitudes of these three power spectra are related
through a simple linear biasing model with b = 1.5 and b = 3.6 for Abell/ACO
versus APM and Abell/ACO versus the PSCz respectively. Furthermore, the shape
of these power spectra are remarkably similar despite the fact that they are
comprised of significantly different objects (individual galaxies through to
rich clusters). Individually, each of these surveys show visible evidence for
``valleys'' in their power spectra. We use a newly developed statistical
technique called the False Discovery Rate, to show that these ``valleys'' are
statistically significant. One favored cosmological explanation for such
features in the power spectrum is the presence of a non-negligible baryon
fraction (Omega_b/Omega_m) in the Universe which causes acoustic oscillations
in the transfer function of adiabatic inflationary models. We have performed a
maximum-likelihood marginalization over four important cosmological parameters
of this model (Omega_m, Omega_b, n_s, H_o). We use a prior on H_0 = 69(+/-15),
and find Omega_mh^2 = 0.12(+0.03/-0.02), Omega_bh^2 =0.029(+0.011/-0.015), n_s
= 1.08^(+0.17/-0.20) (2 sigma confidence limits) which are fully consistent
with the favored values of these cosmological parameters from the recent Cosmic
Microwave Background (CMB) experiments. This agreement strongly suggests that
we have detected baryonic oscillations in the power spectrum of matter at a
level expected from a Cold Dark Matter model normalized to fit these CMB
measurements.


title: The Formation of Brown Dwarfs as Ejected Stellar Embryos

abstract:
  We conjecture that brown dwarfs are substellar objects because they have been
ejected from small newborn multiple systems which have decayed in dynamical
interactions. In this view, brown dwarfs are stellar embryos for which the star
formation process was aborted before the hydrostatic cores could build up
enough mass to eventually start hydrogen burning. The disintegration of a small
multiple system is a stochastic process, which can be described only in terms
of the half-life of the decay. A stellar embryo competes with its siblings in
order to accrete infalling matter, and the one that grows slowest is most
likely to be ejected. With better luck, a brown dwarf would therefore have
become a normal star. This interpretation of brown dwarfs readily explains the
rarity of brown dwarfs as companions to normal stars (aka the ``brown dwarf
desert''), the absence of wide brown dwarf binaries, and the flattening of the
low mass end of the initial mass function. Possible observational tests of this
scenario include statistics of brown dwarfs near Class 0 sources, and the
kinematics of brown dwarfs in star forming regions while they still retain a
kinematic signature of their expulsion. Because the ejection process limits the
amount of gas brought along in a disk, it is predicted that substellar
equivalents to the classical T Tauri stars should be very rare.


title: Cosmic Radio Jets

abstract:
  Extragalactic radio sources, including quasars, are now typically understood
as being produced by a pair of nearly symmetric, oppositely directed
relativistic jets. While some these sources span megaparsecs, and are thus the
largest physically connected structures in the universe, emitting regions
identified as jets have now been found on all scales down to fractions of a
parsec, and jets appear to be a common element of most (maybe all) types of
active galactic nuclei (AGN). We first summarize key observations of different
classes of cosmic radio jets, and describe how they may be connected.
Theoretical models for the launching and propagation of extragalactic jets are
briefly described. All of these models assume a magnetized plasma, which
typically amounts to only a small fraction of the accreted gas, is ejected from
the vicinity of a supermassive black hole. The extreme complexity of the
relevant physics has demanded numerical simulations to examine non-linear
effects on the stability of propagating jets, and some recent results from
these efforts are summarized.


title:
New Insights from HST Studies of Globular Cluster Systems I: Colors,
  Distances and Specific Frequencies of 28 Elliptical Galaxies

abstract:
  We present an analysis of the globular cluster systems of 28 elliptical
galaxies using archival WFPC2 images in the V and I-bands. The V-I color
distributions of at least 50% of the galaxies appear to be bimodal {\it at the
present level of photometric accuracy}. We argue that this is indicative of
multiple epochs of cluster formation early in the history of these galaxies,
possibly due to mergers. We also present the first evidence of bimodality in
low luminosity galaxies and discuss its implication on formation scenarios. The
mean color of the 28 cluster systems studied by us is V-I = 1.04$\pm$0.04
(0.01) mag corresponding to a mean metallicity of Fe/H = -1.0$\pm$0.19 (0.04).
We find that the turnover magnitudes of the globular cluster luminosity
functions (GCLF) of our sample are in excellent agreement with the distance
measurements using other methods and conclude that the accuracy of the GCLF is
at least as good as the surface brightness fluctuation method. The absolute
magnitude of the turnover luminosity of the GCLF is M$_V^0$ = -7.41 (0.03) in V
and M$_I^0$ = -8.46 (0.03) in I. The mean local specific frequency of our
sample of elliptical galaxies within the WFPC2 field-of-view is 2.4$\pm$1.8
(0.4), considerably higher than the 1.0$\pm$0.6 (0.1) derived for a comparable
sample of S0s in a similar analysis. It shows no obvious correlation with
metallicity, host galaxy mass or membership in a galaxy cluster. The median
size of clusters in all galaxies appears to be remarkably constant at $\sim$2.4
pc. We suggest that in the future it might be possible to use the sizes of
clusters in the inner regions of galaxies as a simple geometrical distance
indicator.


title: Quark Stars as inner engines for Gamma Ray Bursts?

abstract:
  A model for Gamma ray bursts inner engine based on quark stars (speculated to
exist in nature) is presented. We describe how and why these objects might
constitute new candidates for GRB inner engines. At the heart of the model is
the onset of exotic phases of quark matter at the surface of such stars, in
particular the 2-flavor color superconductivity. A novel feature of such a
phase is the generation of particles which are unstable to photon decay
providing a natural mechanism for a fireball generation; an approach which is
fundamentally different from models where the fireball is generated during
collapse or conversion of neutron star to quark star processes. The model is
capable of reproducing crucial features of Gamma ray bursts, such as the
episodic activity of the engine (multiple and random shell emission) and the
two distinct categories of the bursts (two regimes are isolated in the model
with \sim 2 s and \sim 81 s burst total duration).


title: Center of Light Curves for Whitney Fold and Cusp

abstract:
  The generic, qualitative, local behavior of center-of-light curves near folds
and cusps are studied. The results apply to any finite number of lens planes.


title:
General Relativistic Simulations of Stellar Core Collapse and Postbounce
  Evolution with Boltzmann Neutrino Transport

abstract:
  We present self-consistent general relativistic simulations of stellar core
collapse, bounce, and postbounce evolution for 13, 15, and 20 solar mass
progenitors in spherical symmetry. Our simulations implement three-flavor
Boltzmann neutrino transport and standard nuclear physics. The results are
compared to our corresponding simulations with Newtonian hydrodynamics and
O(v/c) Boltzmann transport.


title: Cold Molecular Gas, PDRs, and the Origin of HI in Galaxies

abstract:
  In the currently-accepted model for star formation out of the interstellar
gas in galaxies, the basic construction material is assumed to be large clouds
of atomic hydrogen (HI). These clouds are thought to form higher-density
complexes of gas and dust, and turn molecular (H2). Stars then form out of this
molecular gas.
  In this paper arguments are advanced for a contrary view, in which the basic
construction material is cold molecular gas out of which the stars form
directly. HI appears in the region when the leftover H2 is illuminated with UV
photons from nearby young stars. The physics of photodissociation regions
provides a natural and quantitative explanation for the appearance of HI
envelopes around the clouds, and for CO(1-0) emission from the higher-density
parts of their surfaces. In this picture, much of the HI in a galaxy is a
product of the star formation process, not a precursor to it.


title: The First Observations of the Second Brightest Quasar

abstract:
  We report the discovery of a new bright quasar PHL 1811 as part of a followup
program to identify bright quasars in the FIRST radio survey. With B=13.9,
R=13.9, and z=0.192, this quasar is now the second brightest quasar (in
apparent magnitude) known beyond z=0.1. Optically classified as a Narrow-line
Seyfert 1 galaxy (NLS1), PHL 1811 is unusual for an object in this class in
that it was not detected in X-rays in the ROSAT All Sky survey or in any
previous X-ray survey. A follow-up BeppoSAX observation confirms that it is
deficient in X-rays compared with other quasars, but poor signal to noise
prevents a definitive characterization of the X-ray spectrum. We consider three
alternative hypotheses to explain why PHL 1811 is a weak X-ray source: 1.) it
is a BALQSO and suffers X-ray absorption; 2.) like several other luminous
NLS1s, it exhibits high amplitude X-ray variability, and has been observed only
when it is in an X-ray quiescent state; 3.) it is intrinsically weak because it
simply lacks an X-ray emitting region.


title:
An Adaptive Optics Survey for Companions to Stars with Extra-Solar
  Planets

abstract:
  We have undertaken an adaptive optics (AO) imaging survey of extrasolar
planetary systems and stars showing interesting radial velocity trends from
high precision radial velocity searches. AO increases the resolution and
dynamic range of an image, substantially improving the detectability of faint
close companions. This survey is sensitive to objects less luminous than the
bottom of the main sequence at separations as close as 1 arcsec. We have
detected stellar companions to the planet bearing stars HD 114762 and Tau Boo.
We have also detected a companion to the non-planet bearing star 16 Cyg A.


title: Evidence For and Against Collimation of Gamma Ray Bursts

abstract:
  The degree to which gamma ray bursts are collimated is now the dominant
uncertainty in their energy requirements and event rates. In this review I
begin with the reasons for studying GRB collimation, then discuss existing
tests for collimation and their applications to date, and finally outline some
possible future tests. The most important conclusions are that (1) mean
collimation angles much tighter than 1 degree appear ruled out; (2) the
collimation angle appears to vary from burst to burst (like most other GRB
properties). Some alternative explanations of apparent collimation signatures
remain, but it should be possible to distinguish them from true collimation
with future data sets and may be possible already. New satellites, improved
followup observations, and new tests for collimation all promise continued
rapid progress in coming years.


title: Weak Lensing Measurements of 42 SDSS/RASS Galaxy Clusters

abstract:
  We present a lensing study of 42 galaxy clusters imaged in Sloan Digital Sky
Survey (SDSS) commissioning data. Cluster candidates are selected optically
from SDSS imaging data and confirmed for this study by matching to X-ray
sources found independently in the ROSAT all sky survey (RASS). Five color SDSS
photometry is used to make accurate photometric redshift estimates that are
used to rescale and combine the lensing measurements. The mean shear from these
clusters is detected to 2 h-1 Mpc at the 7-sigma level, corresponding to a mass
within that radius of 4.2 +/- 0.6 x 10^14 h-1 M_sun. The shear profile is well
fit by a power law with index -0.9 +/- 0.3, consistent with that of an
isothermal density profile. This paper demonstrates our ability to measure
ensemble cluster masses from SDSS imaging data.


title:
Distributions of secondary muons at sea level from cosmic gamma rays
  below 10 TeV

abstract:
  The FLUKA Monte Carlo program is used to predict the distributions of the
muons which originate from primary cosmic gamma rays and reach sea level. The
main result is the angular distribution of muons produced by vertical gamma
rays which is necessary to predict the inherent angular resolution of any
instrument utilizing muons to infer properties of gamma ray primaries.
Furthermore, various physical effects are discussed which affect these
distributions in differing proportions.


title: The Radio and Gamma-Ray Luminosities of Blazars

abstract:
  Based on the $\gamma$-ray data of blazars in the third EGRET catalog and
radio data at 5 GHz, we studied the correlation between the radio and
$\gamma$-ray luminosities using two statistical methods. The first method was
the partial correlation analysis method, which indicates that there exist
correlations between the radio and $\gamma$-ray luminosities in both high and
low states as well as in the average case.
  The second method involved a comparison of expected $\gamma$-ray luminosity
distribution with the observed data using the Kolmogorov--
  Smirnov (KS) test. In the second method, we assumed that there is a
correlation between the radio and $\gamma$-ray luminosities and that the
$\gamma$-ray luminosity function is proportional to the radio luminosity
function. The KS test indicates that the expected gamma-ray luminosity
distributions are consistent with the observed data in a reasonable parameter
range. Finally, we used different $\gamma$-ray luminosity functions to estimate
the possible 'observed'
  $\gamma$-ray luminosity distributions by GLAST.


title:
Raman Scattered He II Line in the Planetary Nebula M2-9 and the
  Symbiotic Stars RR Telescopii and He 2-106

abstract:
  In this Letter, we report the detection of an emission feature around 6545
\AA in the spectra of the bipolar planetary nebula M2-9 and the symbiotic stars
RR Telescopii and He 2-106 and propose to identify it as the He II Raman
scattered feature. This feature was predicted by Nussbaumer, Schmid & Vogel
(1989), who suggested that it is formed through Raman scattering by atomic
hydrogen of He II $n=6\to n=2$ photons with slightly shorter wavelength than
that of Ly$\beta$. The scattering cross section $\sim 10^{-20}{\rm cm^2}$ for
this process implies the existence of a neutral hydrogen component with a
column density $N_{HI}\sim 10^{20}{\rm cm^{-2}}$ around the He II emission
regions in these objects, which are believed to be associated with the mass
loss process in the late stage of stellar evolution. Brief discussions on the
astrophysical implications of Raman scattering in these objects are presented.


title: The Departure of Eta Carinae from Axisymmetry and the Binary Hypothesis

abstract:
  I argue that the large scale departure from axisymmetry of the Eta Carinae
nebula can be explained by the binary stars model of Eta Carinae. The companion
diverts the wind blown by the primary star, by accreting from the wind and
possibly by blowing its own collimated fast wind (CFW). The effect of these
processes depends on the orbital separation, hence on the orbital phase of the
eccentric orbit. The variation of the mass outflow from the binary system with
the orbital phase leads to a large-scale departure from axisymmetry along the
equatorial plane, as is observed in Eta Car. I further speculated that such a
companion may have accreted a large fraction of the mass that was expelled in
the Great Eruption of 1850 and the Lesser Eruption of 1890. The accretion
process was likely to form an accretion disk, with the formation of a CFW, or
jets, on the two sides of the accretion disk. The CFW may have played a crucial
role in the formation of the two lobes.


title: The Peculiar Type Ia Supernova 1999by: Spectroscopy at Early Epochs

abstract:
  We present medium resolution (lambda/Delta lambda = 2500) optical
spectroscopy of SN 1999by in NGC 2841 made around its light maximum. The depth
ratio of the two Si II features at 5800 AA and 6150 AA being R(SiII) approx.
0.63 at maximum indicates that this SN belongs to the peculiar, sub-luminous
SNe Ia. Radial velocities inferred from the minimum of the 6150 AA trough
reveal a steeper decline of the velocity curve than expected for ``normal'' SNe
Ia, consistent with the behavior of published VRI light curves. A revised
absolute magnitude of SN 1999by and distance to its host galaxy NGC 2841 is
estimated based on the Multi-Color Light Curve Shape (MLCS) method, resulting
in M_V(max)=-18.06+/- 0.1 mag and d = 17.1+/-1.2 Mpc, respectively. An
approximative linear dependence of the luminosity parameter Delta on R(SiII) is
presented.


title:
The CH out-of-plane bending modes of PAH molecules in astrophysical
  environments

abstract:
  We present 10-15 micron spectra of a sample of H II regions, YSOs and evolved
stars that show strong unidentified infrared emission features, obtained with
the ISO/SWS spectrograph on-board ISO. These spectra reveal a plethora of
emission features with bands at 11.0, 11.2, 12.0, 12.7, 13.5 and 14.2 micron.
These features are observed to vary considerably in relative strength to
each-other from source to source. In particular, the 10-15 micron spectra of
the evolved stars are dominated by the 11.2 micron band while for H II regions
the 12.7 is typically as strong as the 11.2 micron band. Analysing the ISO data
we find a good correlation between the 11.2 micron band and the 3.3 micron
band, and between the 12.7 micron and the 6.2 micron band. There is also a
correlation between the ratio of the UIR bands to the total dust emission and
the 12.7 over 11.2 micron ratio. Bands in the 10-15 micron spectral region are
due to CH out-of-plane (OOP) bending modes of polycyclic aromatic hydrocarbons
(PAHs). We summarise existing laboratory data and theoretical quantum chemical
calculations of these modes for neutral and cationic PAHs. Due to mode
coupling, the exact peak position of these bands depends on the number of
adjacent CH groups and hence the observed interstellar 10-15 micron spectra can
be used to determine the molecular structure of the interstellar PAHs emitting
in the different regions. We conclude that evolved stars predominantly inject
compact ~100-200 C-atom PAHs into the ISM where they are subsequently
processed, resulting in more open and uneven PAH structures.


title: Submillimeter CO emission from shock-heated gas in the L1157 outflow

abstract:
  We present the CO J=6-5, 4-3, and 3-2 spectra from the blueshifted gas of the
outflow driven by the low-mass class 0 protostar in the L1157 dark cloud.
Strong submillimeter CO emission lines with T_mb > 30 K have been detected at
63" (~0.13 pc) south from the protostar. It is remarkable that the blue wings
in the submillimeter lines are stronger by a factor of 3-4 than that of the CO
J=1-0 emission line. The CO line ratios suggest that the blueshifted lobe of
this outflow consists of moderately dense gas of n(H_2) = (1-3)x10^4 cm^-3
heated to T_kin = 50-170 K.It is also suggested that the kinetic temperature of
the outflowing gas increases from ~80 K near the protostar to ~170 K at the
shocked region in the lobe center, toward which the largest velocity dispersion
of the CO emission is observed. A remarkable correlation between the kinetic
temperature and velocity dispersion of the CO emission along the lobe provides
us with direct evidence that the molecular gas at the head of the jet-driven
bow shock is indeed heated kinematically. The lower temperature of ~80 K
measured at the other shocked region near the end of the lobe is explained if
this shock is in a later evolutionary stage, in which the gas has been cooled
mainly through radiation of the CO rotational lines.


title: The Stellar Content of Obscured Galactic Giant H II Regions III.: W31

abstract:
  We present near infrared (J, H, and K) photometry and moderate resolution
(lambda/Deltalambda = 3000) K-band spectroscopy of the embedded stellar cluster
in the giant H II region W31. Four of the brightest five cluster members are
early O--type stars based on their spectra. We derive a spectro--photometric
distance for W31 of 3.4 +/- 0.3 kpc using these new spectral types and infrared
photometry. The brightest cluster source at K is a red object which lies in the
region of the J - H vs. H - K color--color plot inhabited by stars with excess
emission in the K-band. This point source has an H plus K-band spectrum which
shows no photospheric features, which we interpret as being the result of
veiling by local dust emission. Strong Brackett series emission and permitted
FeII emission are detected in this source; the latter feature is suggestive of
a dense inflow or outflow. The near infrared position of this red source is
consistent with the position of a 5 GHz thermal radio source seen in previous
high angular resolution VLA images. We also identify several other K-band
sources containing excess emission with compact radio sources. These objects
may represent stars in the W31 cluster still embedded in their birth cocoons.


title: Light Curves from an Expanding Relativistic Jet

abstract:
  We perform fully relativistic hydrodynamic simulations of the deceleration
and lateral expansion of a relativistic jet as it expands into an ambient
medium. The hydrodynamic calculations use a 2D adaptive mesh refinement (AMR)
code, which provides adequate resolution of the thin shell of matter behind the
shock. We find that the sideways propagation is different than predicted by
simple analytic models. The physical conditions at the sides of the jet are
found to be significantly different than at the front of the jet, and most of
the emission occurs within the initial opening angle of the jet. The light
curves, as seen by observers at different viewing angles with respect to the
jet axis, are then calculated assuming synchrotron emission. For an observer
along the jet axis, we find a sharp achromatic `jet break' in the light curve
at frequencies above the typical synchrotron frequency, at $t_{jet}\approx
5.8(E_{52}/n_1)^{1/3}(\theta_0/0.2)^{8/3}$ days, while the temporal decay index
$\alpha$ ($F_{\nu}\propto t^{\alpha}$) after the break is steeper than $-p$
($\alpha=-2.85$ for $p=2.5$). At larger viewing angles $t_{jet}$ increases and
the jet break becomes smoother.


title:
The Ursa Major Cluster of Galaxies. III. Optical observations of dwarf
  galaxies and the luminosity function down to M_R=-11

abstract:
  Results are presented of a deep optical survey of the Ursa Major Cluster, a
spiral-rich cluster of galaxies at a distance of 18.6 Mpc which contains about
30% of the light but only 5% of the mass of the nearby Virgo Cluster. Fields
around known cluster members and a pattern of blind fields along the major and
minor axes of the cluster were studied with mosaic CCD cameras on the
Canada-France-Hawaii Telescope. The dynamical crossing time for the Ursa Major
Cluster is only slightly less than a Hubble time. Most galaxies in the local
Universe exist in similar moderate density environments. The Ursa Major Cluster
is therefore a good place to study the statistical properties of dwarf galaxies
since this structure is at an evolutionary stage representative of typical
environments yet has enough galaxies that reasonable counting statistics can be
accumulated. The main observational results of our survey are: (i) The galaxy
luminosity function is flat, with a logarithmic slope alpha = -1.1 for -17 <
M_R < -11, from a power-law fit. The error in alpha is likely to be less than
0.2 and is dominated by systematic errors, primarily associatedd with
uncertainties in assigning membership to specific galaxies. This faint end
slope is quite different to what was seen in the Virgo Cluster where
alpha=-2.26. (ii) Dwarf galaxies are as frequently found to be blue dwarf
irregulars as red dwarf spheroidals in the blind cluster fields. The density of
red dwarfs is significantly higher in the fields around luminous members than
in the blind fields. The most important result is the failure to detect many
dwarfs. If the steep luminosity function claimed for the Virgo Cluster were
valid for Ursa Major then in our blind fields we should have found about 1000
galaxies with -17 < M_R <-11 where we have found two dozen.


title: The Galaxy and Mass N-Point Correlation Functions: a Blast from the Past

abstract:
  Correlation functions and related statistics have been favorite measures of
the distributions of extragalactic objects ever since people started analyzing
the clustering of the galaxies in the 1930s. I review the evolving reasons for
this choice, and comment on some of the present issues in the application and
interpretation of these statistics, with particular attention to the question
of how closely galaxies trace mass.


title:
Chandra X-ray Observations of the Quadruply Lensed Quasar RX
  J0911.4+0551

abstract:
  We present results from X-ray observations of the quadruply lensed quasar RX
J0911.4+0551 using data obtained with the Advanced CCD Imaging Spectrometer
(ACIS) on board the Chandra X-ray Observatory. The 29 ks observation detects a
total of ~404 X-ray photons (0.3 to 7.0 keV) from the four images of the lensed
quasar. Deconvolution of the aspect corrected data resolves all four lensed
images, with relative positions in good agreement with optical measurements.
When compared to contemporaneous optical data, one of the lensed images
(component A3) is dimmer by a factor of ~6 in X-rays with respect to the 2
brighter images (components A1 and A2). Spectral fitting for the combined
images shows significant intrinsic absorption in the soft (0.2 to 2.4 keV)
energy band, consistent with the mini-BAL nature of this quasar, while a
comparison with ROSAT PSPC observations from 1990 shows a drop of ~6.5 in the
total soft bandpass flux. The observations also detect ~157 X-ray photons
arising from extended emission of the nearby cluster (peaked ~42" SW of
RXJ0911.4+0551) responsible for the large external shear present in the system.
The Chandra observation reveals the cluster emission to be complex and
non-spherical, and yields a cluster temperature of kT = 2.3^{+1.8}_{-0.8} keV
and a 2.0 to 10 keV cluster luminosity within a 1 Mpc radius of L_X =
7.6_{-0.2}^{+0.6} x 10^{43} ergs/s (error bars denote 90% confidence limits).
Our mass estimate of the cluster within its virial radius is 2.3^{+1.8}_{-0.7}
x 10^{14} solar, and is a factor of 2 smaller than, although consistent with,
previous mass estimates based on the observed cluster velocity dispersion.


title:
Surveying the Sky with the Arcminute MicroKelvin Imager: Expected
  Constraints on Galaxy Cluster Evolution and Cosmology

abstract:
  We discuss prospects for cluster detection via the Sunyaev-Zel'dovich (SZ)
effect in a blank field survey with the proposed interferometer array, the
Arcminute MicroKelvin Imager (AMI). Clusters of galaxies selected in the SZ
effect probe cosmology and structure formation with little observational bias,
because the effect directly measures integrated gas pressure, and does so
independently of cluster redshift. We use hydrodynamical simulations in
combination with the Press-Schechter expression to simulate SZ cluster sky
maps. These are used with simulations of the observation process to gauge the
expected SZ cluster counts. Even with a very conservative choice of parameters
we find that AMI will discover at least several tens of clusters every year
with total mass down to 10^14 solar masses; the numbers depends on factors such
as the mean matter density, the density fluctuation power spectrum and cluster
gas evolution. The AMI survey itself can distinguish between these to some
degree, and parameter degeneracies are largely eliminated given optical and
X-ray follow-up of these clusters; this will also permit direct investigation
of cluster physics and what drives the evolution.


title: An Auger test of the Cen A model of highest energy cosmic rays

abstract:
  If, as recently proposed by Farrar and Piran, Cen A is the source of cosmic
rays detected above the Greisen-Zatsepin-Kuz'min cutoff, neutrons are $\approx
140$ more probable than protons to be observed along its line of sight. This is
because the proton flux is rendered nearly isotropic by ${\cal O}(\mu$G)
intergalactic magnetic fields. With the anticipated aperture of the Southern
Auger Observatory, one may expect on the order of 2 neutron events/year above
$10^{20}$ eV in the line of sight of Cen A.


title: Modeling the Low State Spectrum of the X-Ray Nova XTE J1118+480

abstract:
  Based on recent multiwavelength observations of the new X-ray nova XTE
J1118+480, we can place strong constraints on the geometry of the accretion
flow in which a low/hard state spectrum, characteristic of an accreting black
hole binary, is produced. We argue that the absence of any soft blackbody-like
component in the X-ray band implies the existence of an extended hot
optically-thin region, with the optically-thick cool disk truncated at some
radius R_{tr} > 55 R_{Schw}. We show that such a model can indeed reproduce the
main features of the observed spectrum: the relatively high optical to X-ray
ratio, the sharp downturn in the far UV band and the hard X-ray spectrum. The
absence of the disk blackbody component also underscores the requirement that
the seed photons for thermal Comptonization be produced locally in the hot
flow, e.g. via synchrotron radiation. We attribute the observed spectral break
at 2 keV to absorption in a warm, partially ionized gas.


title: A Black Hole in the Superluminal source SAX J1819.3-2525 (V4641 Sgr)

abstract:
  (shortened) Spectroscopic observations of the fast X-ray transient and
superluminal jet source SAX J1819.3-2525 (V4641 Sgr) reveal a best fitting
period of P_spect=2.81678 +/- 0.00056 days and a semiamplitude of K_2=211.0 +/-
3.1 km/sec. The optical mass function is f(M)=2.74 +/- 0.12 solar masses. We
find a photometric period of P_photo=2.81730 +/- 0.00001 days using a light
curve measured from photographic plates. The folded light curve resembles an
ellipsoidal light curve with two maxima of roughly equal height and two minima
of unequal depth per orbital cycle. The secondary star is a late B-type star
which has evolved off the main sequence. Using a moderate resolution spectrum
(R=7000) we measure T_eff=10500 +/- 200K, log(g)=3.5 +/- 0.1, and
V_rot*sin(i)=123 +/- 4 km/sec (1 sigma errors). Assuming synchronous rotation,
our measured value of the projected rotational velocity implies a mass ratio of
Q=M_1/M_2=1.50 +/- 0.08 (1sigma). The lack of X-ray eclipses implies an upper
limit to the inclination of i<70.7 deg. On the other hand, the large amplitude
of the folded light curve (about 0.5 mag) implies a large inclination (i>60
deg). Using the above mass function, mass ratio, and inclination range, the
mass of the compact object is in the range 8.73 < M_1 < 11.70 solar masses and
the mass of the secondary star is in the range 5.49 < M_2 < 8.14 solar masses
(90% confidence). The mass of the compact object is well above the maximum mass
of a stable neutron star and we conclude that V4641 Sgr contains a black hole.


title: H0 from an orientation-unbiased sample of SZ and X-ray clusters

abstract:
  We have observed the Sunyaev-Zel'dovich effect in a sample of five
moderate-redshift clusters with the Ryle Telescope, and used them in
conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure
the Hubble constant. This sample was chosen with a strict X-ray flux limit
using both the BCS and NORAS cluster catalogues to be well above the
surface-brightness limit of the ROSAT All-Sky Survey, and hence to be unbiased
with respect to the orientation of the cluster. This controls the major
potential systematic effect in the SZ/X-ray method of measureing H0. Taking the
weighted geometric mean of the results and including the main sources of random
error, namely the noise in the SZ measurement, the uncertainty in the X-ray
temperatures and the unknown ellipticity of the clusters, we find H0 = 59 +8/-7
km/s/Mpc assuming a standard CDM model with Omega_M = 1.0, Omega_Lambda = 0.0,
or H0 = 65 +8/-7 km/s/Mpc if Omega_M = 0.3, Omega_Lambda = 0.7.


title: Constraints on inflation from CMB and Lyman-alpha forest

abstract:
  We constrain the spectrum of primordial curvature perturbations by using
recent Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) data.
Specifically, we consider CMB data from the COBE, Boomerang and Maxima
experiments, the real space galaxy power spectrum from the IRAS PSCz survey,
and the linear matter power spectrum inferred from Ly-alpha forest spectra. We
study the case of single field slow roll inflationary models, and we extract
bounds on the scalar spectral index, n, the tensor to scalar ratio, r, and the
running of the scalar spectral index, dlnk, for various combinations of the
observational data. We find that CMB data, when combined with data from
Lyman-alpha forest, place strong constraints on the inflationary parameters.
Specifically, we obtain n \approx 0.9, r < 0.3 and dlnk \approx 0, indicating
that single field hybrid models are ruled out.


title: Polarization Insights for Active Galactic Nuclei

abstract:
  Optical spectropolarimetry and broadband polarimetry in other wavebands has
been a key to understanding many diverse aspects of AGN. In some cases
polarization is due to synchrotron radiation, and in other cases it's due to
scattering. Recognition of relativistically beamed optical synchrotron emission
by polarization was vital for understanding blazars (BL Lacs and Optically
Violently Variable quasars), both physically and geometrically. Radio
polarimetry of quiescent AGN is equally important, again for both purposes.
Scattering polarization was central to the Unified Model for Seyferts, Radio
Galaxies and (high ionization) Ultraluminous Infrared Galaxies. It provides a
periscope for viewing AGN from other directions. Finally, if we could
understand its message, polarization would also provide major insights
regarding the nature of the AGN "Featureless Continuum" and Broad (emission)
Line Region. I point out that high ionization ULIRGs have all the exact right
properties to be called Quasar 2s. Mid-IR observations generally don't
penetrate to the nucleus, greatly reducing their ability to diagnose the energy
source. In particular, LINER ULIRGs aren't necessarily starburst-dominated, as
has been claimed.


title: Clusters in the Precision Cosmology Era

abstract:
  Over the coming decade, the observational samples available for studies of
cluster abundance evolution will increase from tens to hundreds, or possibly to
thousands, of clusters. Here we assess the power of future surveys to determine
cosmological parameters. We quantify the statistical differences among
cosmologies, including the effects of the cosmic equation of state parameter w,
in mock cluster catalogs simulating a 12 sq. deg Sunyaev-Zeldovich Effect
survey and a deep 10^4 sq. deg X-ray survey. The constraints from clusters are
complementary to those from studies of high-redshift Supernovae (SNe), CMB
anisotropies, or counts of high-redshift galaxies. Our results indicate that a
statistical uncertainty of a few percent on both Omega_m and w can be reached
when cluster surveys are used in combination with any of these other datasets.


title: Warm Dark Matter, Small Scale Crisis, and the High Redshift Universe

abstract:
  Warm Dark Matter (WDM) models have recently been resurrected to resolve
apparent conflicts of Cold Dark Matter (DM) models with observations. Endowing
the DM particles with non-negligible velocities causes free-streaming, which
suppresses the primordial power spectrum on small scales. The choice of a
root-mean-square velocity dispersion v(rms) = 0.05 km/s at redshift z=0
(corresponding to a particle mass of 1 keV if the WDM particles are fermions
decoupling while relativistic) helps alleviate most, but probably not all, of
the small-scale problems faced by CDM. An important side-effect of the particle
velocities is the severe decrease in the number of collapsed halos at high
redshift. This is caused both by the loss of small-scale power, and by the
delay in the collapse of the smallest individual halos (with masses near the
effective Jeans mass of the DM). The presence of early halos is required in
order (1) to host either early quasars or galaxies that can reionize the
universe by redshift z=5.8, and (2) to allow the growth of the supermassive
black hole believed to power the recently discovered quasar SDSS 1044-1215 at
this redshift. We quantify these constraints using a modified Press-Schechter
formalism, and find v(rms) < 0.04 km/s (or m_X > 1 keV). If future observations
uncover massive black holes at z > 10, or reveal that reionization occurred at
z > 10, this could conclusively rule out WDM models as the solution to the
small-scale crisis of the CDM paradigm.


title:
Complete and Simultaneous Spectral Observations of the Black-Hole X-ray
  Nova XTE J1118+480

abstract:
  The X-ray nova XTE J1118+480 suffers minimal extinction (b = 62 degrees) and
therefore represents an outstanding opportunity for multiwavelength studies.
Hynes et al. (2000) conducted the first such study, which was centered on 2000
April 8 using UKIRT, EUVE, HST and RXTE. On 2000 April 18, the Chandra X-ray
Observatory obtained data coincident with a second set of observations using
all of these same observatories. A 30 ks grating observation using Chandra
yielded a spectrum with high resolution and sensitivity covering the range
0.24-7 keV. Our near-simultaneous observations cover approximately 80% of the
electromagnetic spectrum from the infrared to hard X-rays. The UV/X-ray
spectrum of XTE J1118+480 consists of two principal components. The first of
these is an approximately 24 eV thermal component which is due to an accretion
disk with a large inner disk radius: > 35 Schwarzschild radii. The second is a
quasi power-law component that was recorded with complete spectral coverage
from 0.4-160 keV. A model for this two-component spectrum is presented in a
companion paper by Esin et al. (2001).


title:
Merging Timescales and Merger Rates of Star Clusters in Dense Star
  Cluster Complexes

abstract:
  Interacting galaxies like the famous Antennae (NGC 4038/4039) or Stephan's
Quintet (HCG 92) show considerable star forming activity in their tidal arms.
High resolution images (e.g. from HST-observations) indicate that these regions
consist of up to hundreds of massive stellar clusters or tidal dwarf galaxies
(TDG). In this paper we want to investigate the future fate of these clusters
of massive star clusters (in this work called super-clusters). We simulate
compact super-clusters in the tidal field of a host-galaxy and investigate the
influence of orbital and internal parameters on the rate and timescale of the
merging process. We show that it is possible that such configurations merge and
build a dwarf galaxy, which could be an important mechanism of how long-lived
dwarf satellite galaxies form. A detailed study of the merger object will
appear in a follow-up paper.


title:
The local power spectrum and correlation hierarchy of the cosmic mass
  field

abstract:
  We analyze the power spectrum of a QSO's Ly_alpha transmitted flux in the
discrete wavelet transform (DWT) representation. Although the mean DWT power
spectrum is consistent with its counterpart in Fourier representation, the
spatial distribution of the local power varies greatly, i.e. the local DWT
power spectra show remarkably spiky structures on small scales. To measure
these spiky features, we introduce the quantities, roughness, of the local
power spectrum, and the correlation between spikes on different scales. We then
test the predictions made by the correlation hierarchy model on the roughness
and the scale-scale correlations of the local power spectrum. Using the
Ly_alpha transmitted flux of the QSO HS1700, we find that the underlying cosmic
mass field of the transmitted flux at redshift around z ~ 2.2 can be described
by the hierarchical clustering model on physical scales from 2.5 h^{-1} Mpc to
few tens h^{-1} kpc in an Einstein-de Sitter universe. However, the non-linear
features of the clustering show differences on different scale ranges; 1. On
physical scales larger than ~ 1.3 h^{-1} Mpc, the field is almost Gaussian. 2.
On scales 1.3 h^{-1} Mpc - 0.3 h^{-1} Mpc, the field is consistent with the
correlation hierarchy with a constant value for the coefficient Q_4. 3. On
scales less than 300 h^{-1} kpc, the field is no longer Gaussian, but
essentially intermittent. In this case, the field can still be fitted by the
correlation hierarchy, but the coefficient, Q_4, should be scale-dependent.
These three points are strongly supported by the following result: the scale
dependencies of Q_4 given by two statistically independent measures, i.e. Q_4^R
by the roughness and Q_4^C by scale-scale correlation, are the same in the
entire scale range considered.


title: Optical observations of BL Lacertae from 1997 to 1999

abstract:
  We present the optical (V, R, and I) photometry for BL Lacertae, which was
observed from 1997 through 1999, with the 1.56-m telescope at the Shanghai
astronomical observatory (SHAO). After the 1997 outburst, it dimmed to a low
state and then brightened again. During the period JD 2450701 to JD 2450701.5,
variations of 0.40mag, 0.27mag, and 0.21mag over a time scale of 100 minutes
were found for V, R, and I bands, suggesting that the variations were
decreasing with wavelength.
  The correlation between V, R, and I is also analyzed using the
  DCF (Discrete Correlation Function) method. This shows that the variability
in the V, R, and I bands are correlated with no time delay longer than 0.2 day.


title:
A survey of hard spectrum ROSAT sources 2: optical identification of
  hard sources

abstract:
  We have surveyed 188 ROSAT PSPC fields for X-ray sources with hard spectra
(alpha<0.5); such sources must be major contributors to the X-ray background at
faint fluxes. In this paper we present optical identifications for 62 of these
sources: 28 AGN which show broad lines in their optical spectra (BLAGN), 13
narrow emission line galaxies (NELGs), 5 galaxies with no visible emission
lines, 8 clusters and 8 Galactic stars. The BLAGN, NELGs and galaxies have
similar distributions of X-ray flux and spectra. Their ROSAT spectra are
consistent with their being AGN obscured by columns of 20.5<log(NH/cm^2)<23.
The hard spectrum BLAGN have a distribution of X-ray to optical ratios which is
similar to that found for AGN from soft X-ray surveys (1<alpha_OX<2). However,
a relatively large proportion (15%) of the BLAGN, NELGs and galaxies are radio
loud. This could be because the radio jets in these objects produce
intrinsically hard X-ray emission, or if their hardness is due to absorption,
it could be because radio loud objects are more X-ray luminous than radio quiet
objects. The 8 hard sources identified as clusters of galaxies are the
brightest, and softest group of sources and hence clusters are unlikely to be
an important component of the hard, faint population. We propose that BLAGN are
likely to constitute a significant fraction of the faint, hard, 0.5 - 2 keV
population and could be important to reproducing the shape of the X-ray
background, because they are the most numerous type of object in our sample
(comprising almost half the identified sources), and because all our high
redshift (z>1) identified hard sources have broad lines.


title: The 2dF QSO Redshift Survey - 10K@2K!

abstract:
  With ~10000 QSO redshifts, the 2dF QSO Redshift Survey (2QZ) is already the
biggest individual QSO survey. The aim for the survey is to have ~25000 QSO
redshifts, providing an order of magnitude increase in QSO clustering
statistics. We first describe the observational parameters of the 2dF QSO
survey. We then describe several highlights of the survey so far; we present
new estimates of the QSO luminosity function and the QSO correlation function.
We also present the first estimate of the QSO power spectrum from the 2QZ
catalogue, probing the form of the fluctuation power-spectrum out to the
\~1000h-1Mpc scales only previously probed by COBE. We find a power spectrum
which is steeper than the prediction of standard CDM and more consistent with
the prediction of Lambda-CDM. The best-fit value for the power spectrum shape
parameter for a range of cosmologies is Gamma=0.1+-0.1. Finally, we discuss how
the complete QSO survey will be able to constrain the value of Omega_Lambda by
combining results from the evolution of QSO clustering and from a geometric
test of clustering isotropy.


title: Magnetohydrodynamic turbulence in warped accretion discs

abstract:
  Warped, precessing accretion discs appear in a range of astrophysical
systems, for instance the X-ray binary Her X-1 and in the active nucleus of
NGC4258. In a warped accretion disc there are horizontal pressure gradients
that drive an epicyclic motion. We have studied the interaction of this
epicyclic motion with the magnetohydrodynamic turbulence in numerical
simulations. We find that the turbulent stress acting on the epicyclic motion
is comparable in size to the stress that drives the accretion, however an
important ingredient in the damping of the epicyclic motion is its parametric
decay into inertial waves.


title:
The Host Galaxy and Optical Light Curve of the Gamma-Ray Burst GRB
  980703

abstract:
  We present deep HST/STIS and ground-based photometry of the host galaxy of
the gamma-ray burst GRB 980703 taken 17, 551, 710, and 716 days after the
burst. We find that the host is a blue, slightly over-luminous galaxy with
V_gal = 23.00 +/- 0.10, (V-R)_gal = 0.43 +/- 0.13, and a centre that is
approximately 0.2 mag bluer than the outer regions of the galaxy. The galaxy
has a star-formation rate of 8-13 M_sun/yr, assuming no extinction in the host.
We find that the galaxy is best fit by a Sersic R^(1/n) profile with n ~= 1.0
and a half-light radius of 0.13 arcsec (= 0.72/h_100 proper kpc). This
corresponds to an exponential disk with a scale radius of 0.22 arcsec (=
1.21/h_100 proper kpc). Subtracting a fit with elliptical isophotes leaves
large residuals, which suggests that the host galaxy has a somewhat irregular
morphology, but we are unable to connect the location of GRB 980703 with any
special features in the host. The host galaxy appears to be a typical example
of a compact star forming galaxy similar to those found in the Hubble Deep
Field North. The R-band light curve of the optical afterglow associated with
this gamma-ray burst is consistent with a single power-law decay having a slope
of alpha = -1.37 +/- 0.14. Due to the bright underlying host galaxy the late
time properties of the light-curve are very poorly constrained. The decay of
the optical light curve is consistent with a contribution from an underlying
Type Ic supernova like SN1998bw, or a dust echo, but such contributions cannot
be securely established.


title: Stellar populations in the nuclear regions of nearby radiogalaxies

abstract:
  We present optical spectra of the nuclei of seven luminous (P(178MHz) >
10**25 W Hz**(-1) Sr**(-1)) nearby (z<0.08) radiogalaxies, which mostly
correspond to the FR II class. In two cases, Hydra A and 3C 285, the Balmer and
4000A break indices constrain the spectral types and luminosity classes of the
stars involved, revealing that the blue spectra are dominated by blue
supergiant and/or giant stars. The ages derived for the last burst of star
formation in Hydra A are between 7 and 40 Myr, and in 3C 285 about 10 Myr. The
rest of the narrow-line radiogalaxies (four) have 4000A break and metallic
indices consistent with those of elliptical galaxies. The only broad-line
radiogalaxy in our sample, 3C 382, has a strong featureless blue continuum and
broad emission lines that dilute the underlying blue stellar spectra. We are
able to detect the Ca II triplet in absorption in the seven objects, with good
quality data for only four of them. The strengths of the absorptions are
similar to those found in normal elliptical galaxies, but these values are both
consistent with single stellar populations of ages as derived from the Balmer
absorption and break strengths, and, also, with mixed young+old populations.


title:
The evolution of core and surface magnetic field in isolated neutron
  stars

abstract:
  We apply the model of flux expulsion from the superfluid and superconductive
core of a neutron star, developed by Konenkov & Geppert (2000), both to neutron
star models based on different equations of state and to different initial
magnetic field structures. When initially the core and the surface magnetic
field are of the same order of magnitude, the rate of flux expulsion from the
core is almost independent of the equation of state, and the evolution of the
surface field decouples from the core field evolution with increasing
stiffness. When the surface field is initially much stronger than the core
field, the magnetic and rotational evolution resembles to those of a neutron
star with a purely crustal field configuration; the only difference is the
occurence of a residual field. In case of an initially submerged field
significant differences from the standard evolution occur only during the early
period of neutron star's life, until the field has been rediffused to the
surface. The reminder of the episode of submergence is a correlation of the
residual field strength with the submergence depth of the initial field. We
discuss the effect of the rediffusion of the magnetic field on to the
difference between the real and the active age of young pulsars and on their
braking indices. Finally, we estimate the shear stresses built up by the moving
fluxoids at the crust--core interface and show that preferentially in neutron
stars with a soft equation of state these stresses may cause crust cracking.


title:
Magnetic Stresses at the Inner Edges of Accretion Disks Around Black
  Holes

abstract:
  For the past twenty-five years, nearly all analyses of accretion disk
dynamics have assumed that stress inside the disk is locally proportional to
pressure (the "alpha-model") and that this stress goes to zero at the
marginally stable orbit. Recently, it has been demonstrated that MHD turbulence
accounts for the bulk of internal disk stress. In contradiction with the
traditional view, the stress from this MHD turbulence does not diminish near
the marginally stable orbit, and the ratio of magnetic stress to pressure rises
sharply there. Examples of the consequences include: an increase in accretion
efficiency that may also be time- and circumstance-dependent; a decrease in the
rate of black hole spin-up by accretion; and generation of disk luminosity
fluctuations. Preliminary results from numerical simulations lend support to
analytic estimates of these effects.


title:
Observational evidence for mass ejection during soft X-ray dips in
  GRS1915+105

abstract:
  We investigate the connection between the X-ray and radio properties of the
Galactic microquasar GRS1915+105, by analyzing the X-ray data observed with
RXTE, during the presence of a huge radio flare (~450 mJy). The X-ray
lightcurve shows two dips of ~100 second duration. Detailed time resolved
spectral analysis shows the existence of three spectral components: a
multicolor disk-blackbody, a Comptonized component due to hot plasma and a
power-law. We find that the Comptonized component is very weak during the dip.
This is further confirmed by the PHA ratio of the raw data and ratio of the
lightcurves in different energy bands. These results, combined with the fact
that the 0.5 -- 10 Hz QPO disappears during the dip and that the Comptonized
component is responsible for the QPO lead to the conclusion that during the
dips the matter emitting Comptonized spectrum is ejected away. This establishes
a direct connection between the X-ray and radio properties of the source.


title: The Abundance Distribution in the Extrasolar-Planet Host Star HD19994

abstract:
  Abundances of 22 elements have been determined from a high-resolution, high
signal-to-noise spectrum of HD19994, a star recently announced as harboring an
extrasolar planet. A detailed spectroscopic analysis of this stars finds it to
have a mass of 1.2+/-0.1Msun. HD19994 is found to be slightly enriched in
"metals" relative to the Sun 9[Fe/H]=+0.09+/-0.05 and an average of all metals
of [m/H]=+0.13), as are most stars known with extrasolar planets. In a search
for possible signatures of accretion of metal-rich gas onto the parent stars
(using HD19994 and published abundances for other stars), it is found that a
small subset of stars with planets exhibit a trend of increasing [X/H] with
increasing condensation temperature for a given element X. This trend may point
to the accretion of chemically fractionated solid material into the outer
(thin) convection zones of these solar-type stars. It is also found that this
small group of stars exhibiting an accretion signature all have large planets
orbiting much closer than is found, in general, for stars with planets not
showing this peculiar abundance trend, suggesting a physical link between
accretion and orbital separation. In addition, the stars showing evidence of
fractionated accretion are, on average, of larger mass (1.2Msun) than stars not
showing measurable evidence of accretion (1.0Msun).


title: First Results from the 2dF QSO redshift survey

abstract:
  We present some initial results from the 2dF QSO redshift survey. The aim of
the survey is to produce an optically-selected catalogue of 25000 QSOs over the
redshift range 0<z<3 using the 2-degree field at the Anglo-Australian
Telescope.


title: Infrared and Millimetric Study of the Young Outflow Cepheus E

abstract:
  The Cepheus E outflow has been studied in the mid and far infrared using the
ISO CAM and LWS instruments, and at millimetric wavelengths using OVRO. In the
near and mid-IR, its morphology is similar to that expected for a jet driven
outflow, where the leading bow shocks entrain and accelerate the surrounding
molecular gas. As expected, fine structure atomic/ionic emission lines arise
from the bow shocks, at both the Mach Disk and the stagnation tip, where
J-shocks are dominant. The H2, H2O and CO molecular emission could arise
further `downstream' at the bow shock wings where the shocks (v = 8-35 km/s)
are oblique and more likely to be C-type. The 13CO emission arises from
entrained molecular gas and a compact high velocity emission is observed,
together with an extended low velocity component that almost coincides
spatially with the H2 near-IR emission. The millimetric continuum emission
shows two sources. We identify one of them with IRAS 23011+6126, postulating is
the driver of the Cepheus E outflow; the other, also an embedded source, is
likely to be driving one of other outflows observed in the region.


title: IC 10: More evidence that it is a blue compact dwarf

abstract:
  We present optical spectroscopy of H {\sc ii} regions in the Local Group
galaxy IC 10 and $UBVR$ photometry of foreground stars in three fields towards
this galaxy. From these data, we find that the foreground reddening due to the
Milky Way is $E(B-V)=0.77\pm 0.07 \mathrm{mag}$. We find that IC 10 contains
considerable internal dust, which qualitatively explains the variety of
reddening values found by studies of its different stellar populations. Based
upon our foreground reddening, IC 10 has intrinsic photometric properties like
those of a blue compact dwarf galaxy, and not those of a dwarf irregular. This
result is consistent with much evidence that IC 10 is in the throes of a
starburst that began at least $10 \mathrm{Myr}$ ago. We also report the
discovery of a new WR star in the H {\sc ii} region HL111c.


title:
Interpreting the Cosmic Infrared Background: Constraints on the
  Evolution of the Dust Enshrouded Star Formation Rate

abstract:
  We present a detailed interpretation of the spectrum of the cosmic infrared
background longwards of 5 microns and of galaxy counts from various surveys at
mid-infrared, far-infrared and submillimeter wavelengths by evolving the
mid-infrared local luminosity function with redshift. We find that all
evolutionary models that fit the counts require a flattening at z~0.8 to avoid
overproducing the CIRB. About 80% of the 140 micron CIRB is produced at 0 < z <
1.5 while only about 30% of the 850 micron background is produced within the
same redshift range. The nature of the evolution is translated into a measure
of the dust enshrouded star formation rate density as a function of redshift
and compared with estimates from optical/near-infrared surveys. We find that
the dust obscured star formation rate density appears to peak at z=0.8+/-0.1,
much sooner than previously thought, with a value of 0.25+/-0.12 M_sun/yr and
remains almost constant up to z~2. At least 70% of this star formation takes
place in luminous infrared galaxies with L_IR > 10^11 L_sun. The long
wavelength observations that constrain our evolutionary models do not strongly
trace the evolution at z > 2 and a drop off in the dust enshrouded star
formation rate is consistent with both the CIRB spectrum and the number counts.
However, a comparison with the infrared luminosity function derived from
extinction corrected optical/UV observations of the Lyman-break galaxy (LBG)
population at z~3 suggests that the flat comoving star formation rate seen
between redshifts 0.8 and 2, extends up to a redshift of z~4.


title:
Likelihood analysis of the CfA2+SSRS2 and of the Las Campanas redshift
  surveys

abstract:
  We present the results from the correlation analysis of two galactic redshift
surveys, the extended CfA2+SSRS2 and the slice centered on $\delta=-12^{\circ}$
of Las Campanas. Furthermore, we evaluate the likelihood confidence regions for
the CDM model and for the fractal model parameters. Our results indicate that,
although the CDM model is in good agreement with the data, the fractal
description cannot be ruled out, because of its intrinsic high variance.


title: Hubble's Nobel Prize

abstract:
  Astronomy is not in the list of natural sciences aimed at by the Nobel
awards. In spite of that, there were, throughout the 1930s until the early
1950s, effective moves by important scientists to distinguish Hubble with the
Prize. A short report on these attempts is made as well as speculation on what
would be the citation for the prize in view of the broad range of Hubble's
scientific achievements. Within this context, the opportunity is also taken for
publicizing the Crafoord Prize which does consider astronomy.


title:
Face-on SS433 stars as a possible new type of extragalactic X-ray
  sources

abstract:
  The SS433 objects is a well-known source of relativistic jets, which are
formed in supercritical accretion disk. It is very probable that the disk has
polar channels and their radiation is collimated (the photocones). The face-on
SS433 object can appear as beamed ultra-bright (and highly variable) X-ray
source, L_x = 10^39 - 10^42 erg/s. We discuss properties of these hypothetical
objects and their frequency expected in galaxies. We describe a search for such
objects using the ROSAT ASS Bright Source Catalog and Faint Source Catalog
(99528 point-like sources) and the RC3 catalog (16741 spiral and irregular
galaxies). Among in total 418 positive correlations in all types of galaxies we
find that in S and Irr galaxies 142 sources are unknown as AGNs. We isolated by
visual inspection 37 clear non-nuclear, 43 probably non-nuclear and 35 probably
nuclear sources. The last two classes certainly contain many unknown AGNs. The
sources of the 1-st class have X-ray luminosities mainly 10^39 - 3 10^41 erg/s.
Their observed frequency is about 4% - 5% per S/Irr galaxy, what is in
agreement with expected frequency of face-on SS433 stars. The only way to
recognize such stars is their expected violent variability in X-rays.


title:
ESO Imaging Survey. Deep Public Survey: Multi-Color Optical Data for the
  Chandra Deep Field South

abstract:
  This paper presents multi-passband optical data obtained from observations of
the Chandra Deep Field South (CDF-S), located at alpha ~ 3h 32m, delta ~ -27d
48m. The observations were conducted at the ESO/MPG 2.2m telescope at La Silla
using the 8kx8k Wide-Field Imager (WFI). This data set, taken over a period of
one year, represents the first field to be completed by the ongoing Deep Public
Survey (DPS) being carried out by the ESO Imaging Survey (EIS) project. This
paper describes the optical observations, the techniques employed for
un-supervised pipeline processing and the general characteristics of the final
data set. The paper includes data taken in six different filters U'UBVRI. The
data cover an area of about 0.25 square degrees reaching 5 sigma limiting
magnitudes of U'_AB=26.0, U_AB=25.7, B_AB=26.4$, V_AB=25.4, R_AB=25.5 and I_AB=
24.7 mag, as measured within a 2xFWHM aperture. The optical data covers the
area of ~ 0.1


title: A Mapping Survey of the 12CO and 13CO Emission in Galaxies

abstract:
  We present spectra of the extended 12CO and 13CO J=1-0 emission along the
major axes of 17 nearby galaxies. Spatial variations in the ratio of CO and
13CO integrated intensities, R, are found in nearly every galaxy observed.
There is an overall variation in R of 20-40% from the inner 2 kpc to the disk.
Roughly a third of the survey galaxies have such gradients in R detected above
the 2-sigma confidence level. Though some galaxies show a lower central value
of R, on average R inside 2 kpc is 10-30% higher than R outside of 2 kpc.
  An increase in the CO/13CO intensity ratio from disk to nucleus may imply
that the conversion factor between CO intensity and H2 column density, X, is
lower in galactic nuclei. Also variations in physical conditions, most notably
the gas kinetic temperature, affect both R and X. Abundance variations probably
do not cause the gradient in R, though we do not rule out a decrease in
effective cloud column densities in galactic nuclei possibly caused by
destructive starburst superwinds. A modest rise in temperature (less than a
factor of 2 or 3) from outside a 2 kpc radius towards the nucleus can easily
account for the observed gradient. These results support previous work implying
that X is lower in the center of the Milky Way and probably most galactic
nuclei. Therefore calculating H2 masses using the standard Galactic X-factor,
especially within the central few kpc of galaxies, overestimates the true mass
by factors of a few. The standard X-factor still appears to be appropriate for
galactic disks.


title:
Extensive Air Shower Simulations with CORSIKA and the Influence of
  High-Energy Hadronic Interaction Models

abstract:
  When high-energy cosmic rays (gamma's, protons, or heavy nuclei) impinge onto
the Earth's atmosphere, they interact at high altitude with the air nuclei as
targets. By repeated interaction of the secondaries an `extensive air shower'
(EAS) is generated with huge particle numbers in the maximum of the shower
development. Such cascades are quantitatively simulated by the Monte Carlo
computer program CORSIKA. The most important uncertainties in simulations arise
from modeling of high-energy hadronic interactions: a) The inelastic hadron-air
cross sections. b) The energies occurring in EAS may extend far above the
energies available in man-made accelerators, and when extrapolating towards
higher energies one has to rely on theoretical guidelines. c) In collider
experiments which are used to adjust the interaction models the very forward
particles are not accessible, but just those particles carry most of the
hadronic energy, and in the EAS development they transport a large energy
fraction down into the atmosphere. CORSIKA is coupled alternatively with 6
high-energy hadronic interaction codes (DPMJET, HDPM, neXus, QGSJET, SIBYLL,
VENUS). The influence of those interaction models on observables of simulated
EAS is discussed.


title: QSO host galaxy star formation history from multicolour data

abstract:
  We investigate multicolour imaging data of a complete sample of low redshift
(z<0.2) QSO host galaxies. The sample was imaged in four optical (BVRi) and
three near-infrared bands (JHKs), and in addition spectroscopic data is
available for a majority of the objects.
  We extract host luminosities for all bands by means of two-dimensional
modeling of galaxy and nucleus. Optical and optical-to-NIR colours agree well
with the average colours of inactive early type galaxies. The six independent
colours are used to fit population synthesis models. We assess the presence of
young populations in the hosts for which evidence shows to be very weak.


title: Supernova constraints on spatial variations of the vacuum energy density

abstract:
  We consider a very simple toy model for a spatially varying `cosmological
constant', where we are inside a spherical bubble (with a given set of
cosmological parameters) that is surrounded by a larger region where these
parameters are different. This model includes essential features of more
realistic scenarios with a minimum number of parameters. We calculate the
luminosity distance in the presence of spatial variations of the vacuum energy
density using linear perturbation theory and discuss the use of type Ia
supernovae to impose constraints on this type of models. We find that presently
available observations are only constraining at very low redshifts, but also
provide independent confirmation that the high red-shift supernovae data does
prefer a relatively large positive cosmological constant.


title:
Magellanic Clouds Planetary Nebulae: an updated view on stellar
  evolution and populations

abstract:
  Planetary Nebulae (PNs) in the Magellanic Clouds are studied to understand
stellar populations and evolution of low- and intermediate-mass stars in
different chemical environments. Using HST observations from our LMC and SMC PN
morphological survey and from the HST Data Archive, we look at the relations
between PN morphology and their evolution and populations. In this paper we
show some of our recent results on these relations, in an historical context.


title: Properties of the circumnuclear medium in Active Galactic Nuclei

abstract:
  We propose a classification scheme for the circumnuclear medium of AGNs based
on their location in the A_V - N_H plane (related to dust absorption and gas
absorption, respectively). We present evidence that the A_V/N_H ratio is often
lower than the Galactic value. This is shown by the broad line ratios of a
sample of intermediate Seyferts, and by the optical/X-ray ratio of line
selected (as opposed to color selected) AGNs. We point out the implications for
the physical properties of the absorber. A complete classification would
require a third axis, related to the density of the absorber and/or its
distance from the AGN.


title:
The Cosmic Infrared Background at 1.25 microns and 2.2 microns using
  DIRBE and 2MASS: a contribution not due to galaxies ?

abstract:
  Using the 2MASS 2nd Incremental Data Release and the Zodiacal-Subtracted
Mission Average maps of COBE/DIRBE, we estimate the cosmic background in the J
(1.25 micron) and K (2.2 microns) bands using selected areas representing 550
square degrees of sky. We find a J background of 22.9 \pm 7.0 kJy/sr (54.0 \pm
16.8 nW/m2/sr) and a K background of 20.4 \pm 4.9 kJy/sr (27.8 \pm 6.7
nW/m2/sr). This large scale study shows that the main uncertainty comes from
the residual zodiacal emission. The cosmic background we obtain is
significantly higher than integrated galaxy counts (3.6 \pm 0.8 kJy/sr and 5.3
\pm 1.2 kJy/sr for J and K, respectively), suggesting either an increase of the
galaxy luminosity function for magnitudes fainter than 30 or the existence of
another contribution to the cosmic background from primeval stars, black holes,
or relic particle decay.


title:
First results from the Isaac Newton Telescope Wide Angle Survey: The z>5
  quasar survey

abstract:
  We report the first results of an observational program designed to determine
the luminosity density of high redshift quasars (z > 5 quasars) using deep
multi-colour CCD data. We report the discovery and spectra of 3 i < 21.5 high
redshift (z > 4.4) quasars, including one with z > 5. At z=5.17, this is the
fourth highest redshift quasar currently published. Using these preliminary
results we derive an estimate of the M \rm_B < - 25.0 (M \rm_{AB1450} < - 24.5)
quasar space density in the redshift range 4.8 < z < 5.8 of 3.6 \pm2.5\times
10^{-8} \Mpc ^{-3} . When completed the survey will provide a firm constraint
on the contribution to the ionizing UV background in the redshift range 4.5 -
5.5 from quasars by determining the faint end slope of the quasar luminosity
function. The survey uses imaging data taken with the 2.5m Isaac Newton
Telescope as part of the Public Isaac Newton Group Wide Field Survey (WFS).
This initial sample of objects is taken from two fields of effective area $\sim
12.5deg ^2$ from the final $\sim 100deg ^2$.


title:
The spin-down problem in the white dwarf of AE Aquarii: numerical study
  of a turn-over scenario

abstract:
  The white dwarf in AE Aqr is observed to spin down at a steady time rate ~
5.64*10^{-14} s s^{-1}, while at the same time its UV and X-ray accretion
luminosities remain almost unchanged. This is a contradiction, however, since
the classicaly estimated spin-down power ~ -10^{34} erg s^{-1} exceeds the
accretion luminosity of the primary by a factor ~ 10^2 and, as a dominating
power, should lead either to observable luminosity changes or to other
detectable effects. This so-called "spin-down problem" can be relaxed under the
assumption that the primary is now in a phase of rapidly decreasing its
differential rotation under constant angular momentum, undergoing a
nonaxisymmetric transition (i.e., turning over its magnetic symmetry axis with
respect to its angular momentum axis and eventually becoming a perpendicular
rotator) from a "differential rotation state" (DRS) to a "rigid rotation state"
(RRS) on a relatively short "nonaxisymmetric DRS-to-RRS transition timescale".
If so, then the estimated spin-down power ~ -3*10^{32} erg s^{-1} becomes
comparable to the observed luminosities and the spin-down problem is
drastically simplified. We present a detailed numerical study of such a
"turn-over scenario", which study mainly points out the fact that an observed
large spin-down time rate does not always imply a large spin-down power.


title: The Redshift of the Optical Transient Associated with GRB 010222

abstract:
  The gamma-ray burst (GRB) 010222 is the brightest GRB detected to date by the
BeppoSAX satellite. Prompt identification of the associated optical transient
(OT) allowed for spectroscopy with the Tillinghast 1.5m telescope at F. L.
Whipple Observatory while the source was still relatively bright (R ~ 18.6
mag), within five hours of the burst. The OT shows a blue continuum with many
superimposed absorption features corresponding to metal lines at z = 1.477,
1.157, and possibly also at 0.928. The redshift of GRB 010222 is therefore
unambiguously placed at z >= 1.477. The high number of Mg II absorbers and
especially the large equivalent widths of the Mg II, Mg I, and Fe II absorption
lines in the z = 1.477 system further argue either for a very small impact
parameter or that the z = 1.477 system is the GRB host galaxy itself. The
spectral index of the OT is relatively steep, beta = 0.89 +/- 0.03, and this
cannot be caused by dust with a standard Galactic extinction law in the z =
1.477 absorption system. This spectroscopic identification of the redshift of
GRB 010222 shows that prompt and well-coordinated followup of bright GRBs can
be successful even with telescopes of modest aperture.


title: Bumpy Power Spectra and Galaxy Clusters

abstract:
  The evolution of the abundance of galaxy clusters is not a reliable measure
of Omega if there are features on scales of a few Mpc in the primordial power
spectrum. Conversely, if we know the cosmological model parameters from other
measurements, the cluster abundance evolution permits us to probe features in
the power spectrum that are in the nonlinear regime at the present epoch, and
hence difficult to discern directly from current epoch measurements.
  We have investigated the influence of an artificially introduced Gaussian
feature on an otherwise unperturbed SCDM power spectrum. Using these modified
spectra as an input to cosmological N-body simulations, we are able to show
that in terms of the cluster abundance evolution, a SCDM model displays
characteristics similar to an OCDM model. However, strong modifications would
also be visible at a redshift z=0 in the dark matter power spectrum whereas
minor alterations to the usual SCDM spectrum are washed away by non-linear
evolution effects. We therefore conclude that features with characteristics
such as discussed here might not be detectable using observations of the galaxy
power spectrum, the local cluster abundance or the large-scale velocity field
as measured by the velocity distribution of galaxy clusters. The only quantity
that shows a pronounced difference at the present epoch between our models
under investigation is the halo-halo correlation function which appears to be
strongly biased with respect to an unmodified SCDM model. This is due to a lack
of power on certain scales which subsequently modifies the relative amplitude
of high-and low-k waves. Apart from observations of the evolution of cluster
abundance, measurements of the Lyman-alpha forest at high redshift could put
constraints on possible features in the power spectrum, too.


title: A Simple Model for r-Process Scatter and Halo Evolution

abstract:
  Recent observations of heavy elements produced by rapid neutron capture
(r-process) in the halo have shown a striking and unexpected behavior: within a
single star, the relative abundances of r-process elements heavier than Eu are
the same as the same as those of solar system matter, while across stars with
similar metallicity Fe/H, the r/Fe ratio varies over two orders of magnitude.
In this paper we present a simple analytic model which describes a star's
abundances in terms of its ``ancestry,'' i.e., the number of nucleosynthesis
events (e.g., supernova explosions) which contributed to the star's
composition. This model leads to a very simple analytic expression for the
abundance scatter versus Fe/H, which is in good agreement with the data and
with more sophisticated numerical models. We investigate two classes of
scenarios for r-process nucleosynthesis, one in which r-process synthesis
events occur in only \sim 4% of supernovae but iron synthesis is ubiquitous,
and one in which iron nucleosynthesis occurs in only about 9% of supernovae.
(the Wasserburg- Qian model). We find that the predictions in these scenarios
are similar for [Fe/H] \ga -2.5, but that these models can be readily
distinguished observationally by measuring the dispersion in r/Fe at [Fe/H] \la
-3.