title:
Radio and X-Ray Detectability of Buoyant Radio Plasma Bubbles in
  Clusters of Galaxies

abstract:
  The Chandra X-ray Observatory is finding a surprisingly large number of
cavities in the X-ray emitting intracluster medium, produced by the release of
radio plasma from active galactic nuclei. In this Letter, we present simple
analytic formulae for the evolution of the X-ray deficit and for the radio
spectrum of a buoyantly rising bubble. The aim of this work is to provide a
theoretical framework for the planning and the analysis of X-ray and radio
observations of galaxy clusters. We show that the cluster volume tested for the
presence of cavities by X-ray observations is a strongly rising function of the
sensitivity.


title:
Submillimeter Evidence for the Coeval Growth of Massive Black Holes and
  Galaxy Bulges

abstract:
  The correlation, found in nearby galaxies, between black hole mass and
stellar bulge mass implies that the formation of these two components must be
related. Here we report submillimeter photometry of eight x--ray absorbed
active galactic nuclei which have luminosities and redshifts characteristic of
the sources that produce the bulk of the accretion luminosity in the universe.
The four sources with the highest redshifts are detected at 850 microns, with
flux densities between 5.9 and 10.1 milliJanskies, and hence are ultraluminous
infrared galaxies. Interpreting the submillimeter flux as emission from dust
heated by starbursts, these results suggest that the majority of stars in
spheroids were formed at the same time as their central black holes built up
most of their mass by accretion, accounting for the observed demography of
massive black holes in the local universe. The skewed rate of submillimeter
detection with redshift is consistent with a high redshift epoch of star
formation in radio quiet active galactic nuclei, similar to that seen in radio
galaxies.


title:
Implications of Cosmological Gamma-Ray Absorption - I.Evolution of the
  Metagalactic Radiation Field

abstract:
  Gamma-ray absorption due to gamma-gamma-pair creation on cosmological scales
depends on the line-of-sight integral of the evolving density of low-energy
photons in the Universe, i.e. on the history of the diffuse, isotropic
radiation field. Here we present and discuss a semi-empirical model for this
metagalactic radiation field based on stellar light produced and reprocessed in
evolving galaxies. With a minimum of parameters and assumptions, the
present-day background intensity is obtained from the far-IR to the ultraviolet
band. Predicted model intensities are independent of cosmological parameters,
since we require that the comoving emissivity, as a function of redshift,
agrees with observed values obtained from deep galaxy surveys. The far-infrared
background at present day prediced from optical galaxy surveys falls short in
explaining the observed one, and we show that this deficit can be removed by
taking into account (ultra)luminous infrared galaxies (ULIGs/LIGs) with a
seperate star formation rate. The accuracy and reliability of the model, out to
redshifts of 5, allow a realistic estimate of the attenuation length of
GeV-to-TeV gamma-rays and its uncertainty, which is the focus of a subsequent
paper.


title: R-modes in the ocean of a magnetic neutron star

abstract:
  We study the dynamics of r-modes in the ocean of a magnetic neutron star. We
modeled the star's ocean with a spherical rotating thin shell and assumed that
the magnetic field symmetry axis is not aligned to the shell's spin axis. In
the magnetohydrodynamic approximation, we calculate the frequency of $\ell=m$
r-modes in the shell of an incompressible fluid. Different r-modes with $\ell$
and $\ell\pm2$ are coupled by the {\it inclined} magnetic field. Kinematical
secular effects for the motion of a fluid element in the shell undergoing
$\ell=m=2$ r-mode are studied. The magnetic corrected drift velocity of a given
fluid element undergoing the $\ell=m$ r-mode oscillations is obtained. The
magnetic field increases the magnitude of the fluid drift produced by the
r-mode drift velocity, the high-$\ell$ modes in the ocean fluid will damp
faster than the low-$\ell$ ones.


title: Nonlinear Particle Acceleration in Relativistic Shocks

abstract:
  Monte Carlo techniques are used to model nonlinear particle acceleration in
parallel collisionless shocks of various speeds, including mildly relativistic
ones. When the acceleration is efficient, the backreaction of accelerated
particles modifies the shock structure and causes the compression ratio, r, to
increase above test-particle values. Modified shocks with Lorentz factors less
than about 3 can have compression ratios considerably greater than 3 and the
momentum distribution of energetic particles no longer follows a power law
relation. These results may be important for the interpretation of gamma-ray
bursts if mildly relativistic internal and/or afterglow shocks play an
important role accelerating particles that produce the observed radiation. For
shock Lorentz factors greater than about 10, r approaches 3 and the so-called
`universal' test-particle result of N(E) proportional to E^{-2.3} is obtained
for sufficiently energetic particles. In all cases, the absolute normalization
of the particle distribution follows directly from our model assumptions and is
explicitly determined.


title: Detection of superimposed periodic signals using wavelets

abstract:
  In this paper we present a wavelet based algorithm that is able to detect
superimposed periodic signals in data with low signal-noise ratio. In this
context, the results given by classical period determination methods highly
depend on the intrinsic characteristics of each periodic signal, like amplitude
or profile. It is then difficult to detect the different periods present in the
data set. The results given by the wavelet based method for period
determination we present here are independent of the characteristics of the
signals.


title:
High Resolution Spectroscopy of 14 Cooling-Flow Clusters of Galaxies
  Using the Reflection Grating Spectrometers on XMM-Newton

abstract:
  We present high resolution X-ray spectra of 14 cooling-flow X-ray clusters
and groups obtained with the Reflection Grating Spectrometers (RGS) on
XMM-Newton. The spectra exhibit line emission from a number of Fe L charge
states as well as O VIII, Mg XII, Ne X, Si XIV & XIII, N VII, and C VI. All
spectra show a deficit of soft X-ray lines predicted from the isobaric
multi-phase spectral model as compared with morphological mass deposition rates
from spatially-resolved spectroscopy with the European Photon Imaging Cameras
(EPIC). We present some weak detections of plasma several times cooler than the
ambient cluster temperatures. The results further suggest that either
morphological mass deposition rates systematically overestimate the actual
cooling rate or the emission measure of cooling-flows has a much steeper
distribution than that predicted by a simple isobaric multi-phase model. We
briefly discuss some modifications to the cooling-flow process.


title: X-ray line emission in Hercules X-1

abstract:
  We find line emission from the hydrogen- and/or helium-like ions of Ne, O, N
and C in the low and short-on states of Her X-1, using the XMM-Newton
Reflection Grating Spectrometer. The emission line velocity broadening is 200 <
sigma < 500 km/s. Plasma diagnostics with the Ne IX, O VII and N VI He-alpha
lines and the radiative recombination continua of O VII and N VII, indicate the
gas is heated by photoionization. We use spectral models to measure the element
abundance ratios N/O, C/O, and Ne/O, which quantify CNO processing in HZ Her.
Photoexcitation and high-density effects are not differentiated by the measured
He-alpha lines. We set limits on the location, temperature and density of the
line emission region. The narrow emission lines can be attributed to
reprocessing in either an accretion disk atmosphere and corona or on the X-ray
illuminated face of HZ Her. In the main-on state, the bright continuum only
allows the detection of interstellar absorption, plus O VII He-alpha emission
lines with sigma = 3200 +- 700 km/s and complex profiles. Other broad lines may
be present. The broad lines may originate in a region near the pulsar
magnetosphere. Fe L lines are not detected.


title: Constraints on nested bars - implications for gas inflow

abstract:
  A wide-spread belief that nested bars enhance gas inflow to the galactic
centre has recently been contradicted by dynamical models in which inner bars
seem to prohibit such inflow. Can the existing models of dynamically possible
double bars be modified to enable strong inflow in the secondary bar? I present
here simple dynamical arguments which imply that in general, double bars in
resonant coupling do not enhance gas inflow. However, stronger inflow with
straight shocks in the inner bar can occur if there is no resonant coupling of
the commonly assumed form between the bars.


title: Physical Sources of Scatter in the Tully-Fisher Relation

abstract:
  We analyze residuals from the Tully-Fisher relation for the emission-line
galaxies in the Nearby Field Galaxy Survey, a broadly representative survey
designed to fairly sample the variety of galaxy morphologies and environments
in the local universe. For spirals brighter than M_R^i=-18, we find strong
correlations between Tully-Fisher residuals and both B-R color and EW(Halpha).
The extremes of the correlations are populated by Sa galaxies, which show
consistently red colors, and spirals with morphological peculiarities, which
are often blue. If we apply an EW(Halpha)-dependent or B-R color-dependent
correction term to the Tully-Fisher relation, the scatter in the relation no
longer increases from R to B to U but instead drops to a nearly constant level
close to the scatter we expect from measurement errors. We argue that these
results probably reflect correlated offsets in luminosity and color as a
function of star formation history. Broadening the sample in morphology and
luminosity, we find that most non-spirals brighter than M_R^i=-18 follow the
same correlations as do spirals, albeit with greater scatter. However, the
color and EW(Halpha) correlations do not apply to galaxies fainter than
M_R^i=-18 or to emission-line S0 galaxies with anomalous gas kinematics. For
the dwarf galaxy population, the parameters controlling Tully-Fisher residuals
are instead related to the degree of recent disturbance: overluminous dwarfs
have higher rotation curve asymmetries, brighter U-band effective surface
brightnesses, and shorter gas consumption timescales than their underluminous
counterparts. As a result, sample selection strongly affects the measured
faint-end slope of the Tully-Fisher relation. Passively evolving, rotationally
supported galaxies display a break toward steeper slope at low luminosities.


title:
Collapse of a Rotating Supermassive Star to a Supermassive Black Hole:
  Post-Newtonian Simulations

abstract:
  We study the gravitational collapse of a rotating supermassive star (SMS) by
means of a (3+1) hydrodynamical simulation in a post-Newtonian (PN) approxi-
mation of general relativity. This problem is particularly challenging because
of the vast dynamical range in space which must be covered in the course of
col- lapse. We evolve a uniformly rotating SMS from the onset of radial
instability at R_{p}/M=411, where R_{p} is the proper polar radius of the star
and M is the total mass-energy, to the point at which the PN approximation
breaks down. We introduce a scale factor and a "comoving" coordinate to handle
the large varia- tion in radius during the collapse and focus on the central
core. Since T/W, the ratio of the rotational kinetic energy to the
gravitational binding energy, is nearly proportional to 1/R_{p} throughout the
collapse, the imploding star may ultimately exceed the critical value of T/W
for dynamical instability to bar-mode formation. However, for stars rotating
uniformly at the onset of col- lapse, we do not find any unstable growth of
bars prior to the termination of our simulation. We do find that the collapse
is likely to form a supermassive black hole (BH) coherently, with almost all of
the matter falling into the hole, leaving very little ejected matter to form a
disk. In the absence of nonaxi- symmetric bar formation, the collapse of a
uniformly rotating SMS does not lead to appreciable quasi-periodic
gravitational wave (GW) emission by the time our integrations terminate.
However, the coherent nature of the implosion suggests that rotating SMS
collapse will be a promising source of GW bursts. We also expect that,
following BH formation, long wavelength quasi-periodic waves will result from
quasi-normal ringing. These waves may be detectable by LISA.


title: Radial equation for an accretion flow driven by Poynting flux

abstract:
  Using a toy model of a two dimensional accretion disk, we discuss further the
radial equation of the accretion flow dominated by the Poynting flux. Assuming
the force-free condition is valid around the accretion disk, the relation
between the fluid angular velocity of the disk, $\Omega_D$, and the angular
velocity of the magnetic field lines, $\Omega_F$, is also discussed.


title:
Universal Lepton Asymmetry: New Constraints from the Cosmic Microwave
  Background and Primordial Nucleosynthesis

abstract:
  We study the primordial nucleosynthesis and cosmic age in the presence of a
net lepton asymmetry as well as baryon asymmetry. We explore a previously
unnoted region of the parameter space in which very large baryon densities $0.1
\le \Omega_b \le 1$ can be accommodated within the light-element constraints
from primordial nucleosynthesis. This parameter space consists of $\nu_\mu$ and
$\nu_\tau$ degeneracies with a small $\nu_e$ degeneracy. Constraints from
cosmic microwave background fluctuations are also discussed (orito00).


title: Modern optical astronomy: technology and impact of interferometry

abstract:
  The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.


title: The FIR/Radio correlation of high redshift galaxies in the HDF-N

abstract:
  The correlation between the far-infrared (FIR) and radio emission is well
established for nearby star forming galaxies. Many applications, in particular
the radio-to-submm spectral index redshift indicator, tacitly assume that the
relation holds well beyond our local neighbourhood, to systems located at
cosmological distances. In order to test this assumption I have constructed a
sample of 20 HDF-N galaxies, all with measured spectroscopic redshifts, and all
detected by both ISO and the WSRT at 15 micron and 1.4 GHz respectively. The
galaxies span a wide range of redshift with a median value of z ~ 0.7. The ISO
15 micron data were k-corrected and extrapolated to the FIR (60 and 100 micron)
by assuming a starburst (M82) spectral energy distribution (SED) for the entire
sample. An initial analysis of the data suggests that the correlation between
the FIR and the radio emission continues to apply at high redshift with no
obvious indication that it fails to apply beyond z ~ 1.3. The sample is
``contaminated'' by at least 1 distant (z=4.4), radio-loud AGN, VLA
J123642+621331. This source has recently been detected by the first deep field
VLBI observations of the HDF-N and is clearly identified as an outlier in the
FIR/radio correlation.


title:
The XMM Large Scale Structure Survey: Scientific Motivation and First
  Observations

abstract:
  Thanks to its unrivalled sensitivity and large field of view, XMM potentially
occupies a leading position as a survey instrument. We present cosmological
arguments in favour of a medium-sensitivity, large-scale structure survey with
XMM, using galaxy clusters as tracers of the cosmic network. We show how this
has motivated the definition of a concrete survey, the XMM Large-Scale
Structure Survey (XMM-LSS), which will cover 64 square degrees with a
sensitivity about 1000 times better than that of the ROSAT All-Sky Survey. We
present our predictions for cluster counts based on the Press-Schechter
formalism and detailed X-ray image simulations, and show how they agree with
the cluster statistics from recent ROSAT cluster surveys. We also present the
extensive multi-wavelength follow-up associated with XMM-LSS, as well as the
first observations from the programme.


title: Symbiotic stars on Asiago archive plates. II

abstract:
  The Asiago photographic archive has been searched for plates containing the
symbiotic stars Hen 2-468, QW Sge, LT Del, V407 Cyg, K 3-9, V335 Vul, FG Ser
and Draco C-1. A total of 635 plates imaging the program stars have been found
and the brightness estimated using the Henden & Munari (2000) UBVRI photometric
sequences. These historical data have allowed for the first time the
determination of the orbital periods of Hen 2-468 (774 days) and QW Sge (390.5
days), a significant improvement in the orbital period of LT Del (465.6 days)
and for V407 Cyg an evaluation of the Mira's pulsation period and complex
lightcurve shape in the red (R and I bands). Some previously unknown outbursts
have been discovered too. (Paper I: Munari et al. 2001, A&A 370, 503)


title:
Near-Infrared Adaptive Optics Spectroscopy of Binary Brown Dwarf HD
  130948B and C

abstract:
  We present near-infrared spectroscopy of low-mass companions in a nearby
triple system HD 130948 (Gliese 564, HR 5534). Adaptive optics on the Subaru
Telescope allowed spectroscopy of the individual components of the 0".13 binary
system. Based on a direct comparison with a series of template spectra, we
determined the spectral types of HD 130948B and C to be L4 +- 1. If we take the
young age of the primary star into account (0.3-0.8 Gyr), HD 130948B and C most
likely are a binary brown dwarf system.


title: On the outer boundary of the sunspot penumbra

abstract:
  Comparison of photographic observations and vector-magnetograph measurements
demonstrate, that the outer boundary of the sunspot penumbra --even in complex
sunspot groups-- closely follows the 0.075T isogauss line of the total value of
the magnetic field, corresponding approximately to the equipartition value in
the photosphere. Radio observations also show this feature. The thick penumbra
model with interchange convection (Jahn and Schmidt, 1994) gives the best
explanation of the penumbral structure.


title:
Imaging and Spatially Resolved Spectroscopy of AFGL 2688 in the Thermal
  Infrared Region

abstract:
  We present ground-based high-resolution (~0".3) imaging of AFGL 2688 at L'
(3.8 um) and M'(4.7um). A wealth of structure in the central region is revealed
due to less extinction in the thermal infrared. A clear border in the southern
lobe at L' corresponds to the edge of the heavily obscured region in visible,
indicating there is a dense material surrounding the central region. The images
also show a narrow dark lane oriented to 140 deg east of north with the normal
at 50 deg. The normal position angle is inconsistent with the optical polar
axis (PA = 15 deg), but is aligned to the high-velocity CO components found in
the radio wavelength observations. The central star remains invisible at L' and
M'. Several clumpy regions in the north lobe dominate in L' and M' luminosity.
In particular a pointlike source (peak A) at 0".5 northeast of the center of
the nebula exhibits the highest surface brightness with a very red spectral
energy distribution (SED). Based on the almost identical SED as adjacent
regions, we suggest that the pointlike source is not self-luminous, as was
proposed, but is a dense dusty blob reflecting thermal emission from the
central star.
  We also present spatially resolved slit spectroscopy of the bright dusty
blobs. An emission feature at 3.4 um as well as at 3.3 um is detected
everywhere within our field of view. There is no spatial variation in the
infrared emission feature (IEF) throughout the observed area (0".2-1".5, or
240-1800 AU from the central source). The constant flux ratio of the emission
feature relative to the continuum is consistent with the view that the blobs
are mostly reflecting the light from the central star in the 3 um region.


title:
A conspicuous tangential alignment of galaxies in a STIS Parallel Shear
  Survey field: A new dark-lens candidate ?

abstract:
  We report the serendipituous discovery of a conspicuous alignment of galaxies
in a field obtained through the STIS Parallel Shear Survey. This project
collects randomly distributed 50'' x 50'' fields to investigate the cosmic
shear effect on this scale. Analyzing the parallel observations having the
Seyfert galaxy NGC625 as primary target, we recognized over the whole field of
view a strong apparent tangential alignment of galaxy ellipticities towards the
image center. The field shows several arclet-like features typical for images
of massive galaxy clusters, but no obvious over-density of bright foreground
galaxies. We also find a multiple image candidate. On the basis of the possible
strong and weak lensing effect within the data, we discuss whether this could
be compatible with a massive halo with no clear optical counterpart.


title:
Ten Years of Nearby Galaxies Investigation with the Multi-Pupil
  Spectrograph of the 6m Telescope

abstract:
  We describe the history and results of our study of early-type disk galaxies
with the Multi-Pupil Spectrograph of the 6m telescope (MPFS). With the new data
we confirm the discovery of chemically distinct nuclei reported in 1992; now
such nuclei are found in two dozens galaxies. The structure of chemically
distinct features formed probably in secondary nuclear star-formation bursts
seems to be complex and closely related to an appearance of separate
circumnuclear disks. As by-product, we have also found inner polar gaseous
disks in 4 non-interacting, regular spiral galaxies; this phenomenon may be
related to bulge or bar triaxiality. Some preliminary statistical conclusions
on stellar population properties in the nuclei and in the bulges of nearby S0
galaxies are given.


title: DENIS Survey Data Probing Different Types of PNe

abstract:
  We present near-infrared photometry of a large sample of planetary nebulae
(PNe) and show that the IJK colours are a good tool to distinguish different
classes of PNe, like nebulae around symbiotic Miras or IR-[WC] PNe from genuine
PNe.


title: Nonradial Pulsations in Classical Pulsators

abstract:
  Recent analyses of photometric data on globular clusters and galaxies enabled
us to study more closely the long-periodic amplitude/phase modulation (Blazhko
effect) in classical variables. In the frequency spectra of these stars we see
either a doublet or an equally-spaced triplet with a very small frequency
separation close to the main component. None of the available theoretical
models are able to explain this behavior without invoking some form of
nonradial pulsation. In this review we describe the observational status of the
Blazhko variables, and discuss the limits of the applicability of the current
models to these stars.


title:
The energy distribution of atoms in the field of thermal blackbody
  radiation

abstract:
  Using the principle of detailed balance and the assumption on the absorption
cross-section consistent with available astrophysical data, we obtain the
energy distribution of atoms in the field of thermal blackbody radiation and
show that this distribution diverges from the Boltzmann law.


title:
A difference boosting neural network for automated star-galaxy
  classification

abstract:
  In this paper we describe the use of a new artificial neural network, called
the difference boosting neural network (DBNN), for automated classification
problems in astronomical data analysis. We illustrate the capabilities of the
network by applying it to star galaxy classification using recently released,
deep imaging data. We have compared our results with classification made by the
widely used Source Extractor (SExtractor) package. We show that while the
performance of the DBNN in star-galaxy classification is comparable to that of
SExtractor, it has the advantage of significantly higher speed and flexibility
during training as well as classification.


title: NGC 1866: a workbench for stellar evolution

abstract:
  The young LMC cluster NGC 1866 represents the ideal laboratory for testing
stellar evolutionary models: in particular, it can be used to discriminate
among classical stellar models, in which the extension of the convective
regions is fixed by the classical Schwarzschild criterion, from models with
overshooting, in which an ``extra-mixing'' is considered to take place beyond
the classical limit of the convective zone. Addressing this subject in a recent
work, Testa et al. (1999) reached the conclusion that the classical scheme for
the treatment of convection represents a good and sufficient approximation for
convective interiors. Using their own data, we repeat here the analysis. First
we revise the procedure followed by Testa et al. (1999) to correct the data for
completeness, second we calculate new stellar models with updated physical
input for both evolutionary schemes, finally we present many simulations of the
colour-magnitude diagrams and luminosity functions of the cluster using the
ratio of the integrated luminosity function of main sequence stars to the
number of giants as the normalization factor of the simulations. We also take
into account several possible physical agents that could alter the
color-magnitude diagram and the luminosity function: they are unresolved binary
stars, dispersion in the age, stochastic effects in the initial mass function.
Their effect is analyzed separately, with the conclusion that binary stars have
the largest impact. The main result of this study is that the convective
overshoot hypothesis (together with a suitable percentage of unresolved
binaries) is really needed to fully match the whole pattern of data. The main
drawback of the classical models is that they cannot reproduce the correct
ratio of main sequence to post-main sequence stars.


title: Variations of Alpha in Space and Time

abstract:
  We study inhomogeneous cosmological variations in the fine structure
'constant', $\alpha ,$ in Friedmann universes. Inhomogeneous motions of the
scalar field driving changes in $\alpha $ display spatial oscillations that
decrease in amplitude with increasing time. The inhomogeneous evolution quickly
approaches that found for exact Friedmann universes. We prove a theorem to show
that oscillations of $\alpha $ in time (or redshift) cannot occur in Friedmann
universes in the BSBM theories considered here.


title:
The Pairwise Velocity Distribution Function of Galaxies in the LCRS,
  2dF, and SDSS Redshift Surveys

abstract:
  A comparison of the galaxy pairwise velocity distribution functions
determined from the three largest publicly available galaxy redshift surveys is
presented. This is the first direct comparison of this function across these
surveys using an identical method. It is found that the two r-band selected
surveys, the LCRS (Las Campanas Redshift Survey) and the SDSS (Sloan Digital
Sky Survey), are in excellent agreement with 363 +/- 44 km/sec and 357 +/- 17
km/sec respectively. The b-band selected 2dF survey gives slightly lower
results with 331 +/- 19 km/sec. This difference is expected given the sampling
biases in the different surveys although it is not highly significant. These
results and analysis of subsets of data indicate that the method is stable to
singular features in each survey such as the prevalence of rich clusters. The
technique utilizes a Fourier-space deconvolution of the redshift-space
distortions in the correlation function in the sigma(rp)-pi basis, which has
been previously described. This method returns the entire distribution function
rather than just the second moment. In all cases the distribution function is
well-characterized by an exponential.


title:
Variations in the Bivariate Brightness Distribution with different
  galaxy types

abstract:
  We present Bivariate Brightness Distributions (BBDs) for four spectral types
discriminated by the 2dFGRS. We discuss the photometry and completeness of the
2dFGRS using a deep, wide-field CCD imaging survey. We find that there is a
strong luminosity-surface brightness correlation amongst galaxies with medium
to strong emission features, with gradient $\beta_{\mu}=0.25\pm0.05$ and width
$\sigma_{\mu}=0.56\pm0.01$. Strong absorption line galaxies, show a bimodal
distribution, with no correlation between luminosity and surface brightness.


title:
The 60-micron extragalactic background radiation intensity,
  dust-enshrouded AGNs and the assembly of groups and clusters of galaxies

abstract:
  Submillimetre observations reveal a cosmologically significant population of
high-redshift dust-enshrouded galaxies. The form of evolution inferred for this
population can be reconciled easily with COBE FIRAS and DIRBE measurements of
the cosmic background radiation (CBR) at wavelengths >100 microns. At shorter
wavelengths, however, the 60-micron CBR intensity reported by Finkbeiner et al.
is less easily accounted for. Lagache et al. have proposed that this excess CBR
emission is a warm Galactic component, and the detection of the highest-energy
gamma-rays from blazars limits the CBR intensity at these wavelengths, but here
we investigate sources of this excess CBR emission, assuming that it has a
genuine extragalactic origin. We propose and test three explanations, each
involving additional populations not readily detected in existing submm-wave
surveys. First, dust-enshrouded galaxies with hot dust temperatures, perhaps
dust-enshrouded, Compton-thick AGN as suggested by recent deep Chandra surveys.
Secondly, a population of relatively low-redshift dusty galaxies with SEDs more
typical of the existing submm-selected galaxies, which could plausibly be
associated with the assembly of groups and clusters of galaxies. Thirdly, a
population of low-luminosity, cool, quiescent spiral galaxies. Hot AGN and the
assembly of groups can account for the excess 60-micron background. There are
significant problems with the cluster assembly scenario, in which too many
bright IRAS sources are predicted. Spiral galaxies have the wrong SEDs to
account for the excess. Future wide-field far-IR surveys using SIRTF and
Herschel will sample representative volumes of the distant Universe, allowing
any hot population of dusty AGNs and forming groups to be detected.


title:
Globular Cluster Distances and Physical Properties from Double- and
  Fundamental Mode Variables

abstract:
  We briefly describe a method of obtaining relative intrinsic stellar
parameters, such as absolute magnitudes and colors from the light curves of
fundamental mode RR Lyrae (RRab) stars. Absolute stellar parameters of
double-mode variables (Cepheids and RR Lyrae stars) can be computed from their
periods and intrinsic colors combined with stellar atmosphere and pulsation
models. By using these two methods, one can determine, e.g., the distance of
any RRab star, assuming that accurate multicolor photometry is available. By
applying this and a related method for computing metallicity, we derive
distance, reddening and metallicity distribution for the RRab stars of omega
Cen.


title:
Dust depletion and abundance pattern in damped Lyman-alpha systems: a
  sample of Mn and Ti abundances at z<2.2

abstract:
  We analyse a sample of 24 damped Lyman-alpha (DLA)/moderate DLA systems at
0.3<z<2.2, all with measurement of the weak MnII absorption lines, to
investigate which elemental ratios could possibly be used as tracers of either
dust depletion or nucleosynthesis effects. We applied a component-by-component
analysis and show that the standard method which uses column densities
integrated over the whole absorption profiles could substantially underestimate
the abundance of rare elements relative to Fe. The apparent correlation we
found between [Mn/Fe] and [Zn/Fe] cannot be accounted for by any dust depletion
sequence: it implies either variations of the intrinsic Mn abundance relative
to Fe from -0.3 to +0.1 dex and/or a relation between depletion level and
metallicity. The correlation between [Mn/Fe] and metallicity strengthens the
assumption of intrinsic variations of [Mn/Fe] although some marginal
correlation between [Zn or Si/Fe] and [Zn/H] is present as well. The variations
of [Ti/Fe] vs. [Zn/Fe] cannot be fitted by a single dust depletion sequence
either. At high metallicity, [Fe/H]dc>~-0.5, the intrinsic (dust-corrected)
abundance pattern of Si, Ti, Cr and Mn in DLA absorbers closely follows the
trends observed in Galactic stars and these absorbers should thus have a
chemical evolution similar to that of our Galaxy. At lower metallicity, some
absorbers do follow the trends present in Galactic stars but a substantial
fraction of them have elemental ratios (in particular [Si/Fe]dc and [Mn/Fe]dc)
closer to the solar values than Galactic stars. This could be explained by a
larger contribution of type Ia supernovae to the chemical enrichment of these
DLA absorbers than in Galactic stars of similar metallicity. This metal-poor
DLA absorber population could trace HI-rich dwarf galaxies. (Abridged)


title: Probing CMB Non-Gaussianity Using Local Curvature

abstract:
  It is possible to classify pixels of a smoothed cosmic microwave background
(CMB) fluctuation map according to their local curvature in ``hill'', ``lake''
and ``saddle'' regions. In the Gaussian case, fractional areas occupied by
pixels of each kind can be computed analytically for families of excursion sets
as functions of threshold and moments of the fluctuation power spectrum. We
show how the shape of these functions can be used to constrain accurately the
level of non-Gaussianity in the data by applying these new statistics to an
hypothetical mixed model suggested by Bouchet et al. (2001). According to our
simple test, with only one 12.5x12.5 deg^2 map, Planck should be able to detect
with a high significance a non-Gaussian level as weak as 10% in temperature
standard deviation (rms) (5% in C_l), whereas a marginal detection would be
possible for MAP with a non-Gaussian level around 30% in temperature (15% in
C_l).


title:
Measuring Feedback Using the Intergalactic Medium State and Evolution
  Inferred from the Soft X-ray Background

abstract:
  We explore the intergalactic medium (IGM) as a potential source of the
unresolved soft X-ray background (XRB) and the feasibility to extract the IGM
state and evolution from XRB observations. We build two analytical models, the
continuum field model and the halo model, to calculate the IGM XRB mean flux,
angular auto correlation and cross correlation with galaxies. Our results
suggest that the IGM may contribute a significant fraction to the unresolved
soft XRB flux and correlations. We calibrated non-Gaussian errors estimated
against our $512^3$ moving mesh hydro simulation and estimate that the ROSAT
all sky survey plus Sloan galaxy photometric redshift survey would allow a
$\sim 10%$ accuracy in the IGM XRB-galaxy cross correlation power spectrum
measurement for $800<l<5000$ and a $\sim 20%$ accuracy in the redshift resolved
X-ray emissivity-galaxy cross correlation power spectrum measurement for
$z\lesssim 0.5$. At small scales, non-gravitational heating, e.g. feedback,
dominates over gravity and leaves unique signatures in the IGM XRB, which
allows a comparable accuracy in the measurement of the amount of
non-gravitational heating and the length scales where non-gravitational energy
balances gravity.


title:
The Potential of Differential Astrometric Interferometry from the High
  Antarctic Plateau

abstract:
  The low infrared background and high atmospheric transparency are the
principal advantages of Antarctic Plateau sites for astronomy. However, the
poor seeing (between one and three arcseconds) negates much of the sensitivity
improvements that the Antarctic atmosphere offers, compared to mid-latitude
sites such as Mauna Kea or Cerro Paranal. The seeing at mid-latitude sites,
though smaller in amplitude, is dominated by turbulence at altitudes of 10 to
20 km. Over the Antarctic plateau, virtually no high altitude turbulence is
present in the winter. The mean square error for an astrometric measurement
with a dual-beam, differential astrometric interferometer in the very narrow
angle regime is proportional to the integral of $h^2 C_N^2(h)$. Therefore,
sites at which the turbulence occurs only at low altitudes offer large gains in
astrometric precision. We show that a modest interferometer at the South Pole
can achieve 10 $\mu$as differential astrometry 300 times faster than a
comparable interferometer at a good mid-latitude site, in median conditions.
Science programs that would benefit from such an instrument include planet
detection and orbit determination and astrometric observation of stars
microlensed by dark matter candidates.


title:
The Spectrum and Variability of Circular Polarization in Sagittarius A*
  from 1.4 to 15 GHz

abstract:
  We report here multi-epoch, multi-frequency observations of the circular
polarization in Sagittarius A*, the compact radio source in the Galactic
Center. Data taken from the VLA archive indicate that the fractional circular
polarization at 4.8 GHz was -0.31% with an rms scatter of 0.13% from 1981 to
1998, in spite of a factor of 2 change in the total intensity. The sign
remained negative over the entire time range, indicating a stable magnetic
field polarity. In the Summer of 1999 we obtained 13 epochs of VLA A-array
observations at 1.4, 4.8, 8.4 and 15 GHz. In May, September and October of 1999
we obtained 11 epochs of Australia Telescope Compact Array observations at 4.8
and 8.5 GHz. In all three of the data sets, we find no evidence for linear
polarization greater than 0.1% in spite of strong circular polarization
detections. Both VLA and ATCA data sets support three conclusions regarding the
fractional circular polarization: the average spectrum is inverted with a
spectral index ~0.5 +/- 0.2; the degree of variability is roughly constant on
timescales of days to years; and, the degree of variability increases with
frequency. We also observed that the largest increase in fractional circular
polarization was coincident with the brightest flare in total intensity.
Significant variability in the total intensity and fractional circular
polarization on a timescale of 1 hour was observed during this flare,
indicating an upper limit to the size of 70 AU at 15 GHz. The fractional
circular polarization at 15 GHz reached -1.1% and the spectral index is
strongly inverted during this flare. We conclude that the spectrum has two
components that match the high and low frequency total intensity components.
(abridged)


title: On the Asymmetries of Extended X-ray Emission from Planetary Nebulae

abstract:
  Chandra X-ray Observatory (CXO) images have revealed that the X-ray emitting
regions of the molecule-rich young planetary nebulae (PNs) BD+30 3639 (BD+30)
and NGC 7027 are much more asymmetric than their optical nebulosities. To
evaluate the potential origins of these X-ray asymmetries, we analyze X-ray
images of BD+30, NGC 7027, and another planetary nebula resolved by CXO, NGC
6543, within specific energy bands. Image resolution has been optimized by
sub-pixel repositioning of individual X-ray events. The resulting
subarcsecond-resolution images reveal that the soft (E < 0.7 keV) X-ray
emission from BD+30 is more uniform than the harder emission, which is largely
confined to the eastern rim of the optical nebula. In contrast, soft X-rays
from NGC 7027 are highly localized and this PN is more axially symmetric in
harder emission. The broad-band X-ray morphologies of BD+30 and NGC 7027 are
highly anticorrelated with their distributions of visual extinction, as
determined from high-resolution, space- and ground-based optical and infrared
imaging. Hence, it is likely that the observed X-ray asymmetries of these
nebulae are due in large part to the effects of nonuniform intranebular
extinction. However, the energy-dependent X-ray structures in both nebulae and
in NGC 6543 -- which is by far the least dusty and molecule-rich of the three
PNs, and displays very uniform intranebular extinction -- suggests that other
mechanisms, such as the action of collimated outflows and heat conduction, are
also important in determining the detailed X-ray morphologies of young
planetary nebulae.


title:
The UCSD HIRES/KeckI Damped Lya Abundance Database III. An Empirical
  Study of Photoionization in the Damped Lya System Toward GB1759+7539

abstract:
  We investigate the ionization state of the damped Lya system at z=2.62 toward
GB1759+7539 through an analysis of ionic ratios sensitive to photoionization:
ArI/SII, FeIII/FeII, NII/NI, AlIII/AlII. Approximately half of the metals arise
in a mostly neutral velocity component with HI/H > 0.9, based on FeIII/FeII <
0.013. In contrast, the remaining half exhibits FeIII/FeII~0.3 indicative of a
partially ionized medium with HI/H~0.5. These conclusions are supported by the
observed NII/NI, AlIII/AlII, and ArI/SII ratios.
  We assess ionization corrections for the observed column densities through
photoionization models derived from the CLOUDY software package. In the neutral
gas, the ionization corrections are negligible except for ArI. However for the
partially ionized gas, element abundance ratios differ from the ionic ratios by
0.1-0.3 dex for (SiII, SII, NiII, AlII)/FeII ratios and more for (NI,
ArI)/FeII. Independent of the shape of the photoionizing spectrum and
assumptions on the number of ionization phases, these ionization corrections
have minimal impact (<0.1dex) on the total metallicity inferred for this damped
Lya system. Measurements on the relative elemental abundances of the partially
ionized gas, however, have a greater than ~0.15 dex uncertainty which hides the
effects of nucleosynthesis and dust depletion.
  We caution the reader that this damped system is unusual for a number of
reasons (e.g. a very low ArI/SII ratio) and we believe its ionization
properties are special but not unique. Nevertheless, it clearly shows the value
of examining photoionization diagnostics like FeIII/FeII in a larger sample of
systems.


title: Applications of Likelihood Analysis in Gamma-Ray Astrophysics

abstract:
  The field of gamma ray astronomy relies heavily on the statistical analysis
of data. Because of the paucity of data, and the often large errors associated
with detecting gamma rays, analysis and interpretation of the data require
sophisticated statistical techniques. Techniques for extending the currently
used maximum likelihood technique to more complicated data sets are presented.
Similarly presented are methods of calculating the distribution and behavior of
the maximum likelihood statistic used to measure source significance. A new
method for calculating source variability is also proposed, and used to examine
the sources found by the Energetic Gamma Ray Experiment Telescope (EGRET) on
board the Compton Gamma Ray Observatory (CGRO). The results show that the
Active Galactic Nuclei (AGN), pulsars, and unidentified sources have markedly
different variability, and that the unidentified sources fall into at least two
classes, differing in variability and spatial distribution. A class composed of
possible Supernova Remnant associations (SNR) is distinctly more variable than
the pulsars, but has a variability consistent with that of the other low
latitude unidentified sources. Finally, the results of the Fall 1997 GLAST
prototype beam test are presented. The results of the beam test are compared
with simulated results, and found to be in remarkably good agreement.


title: Past and future evolution of Sakurai's object

abstract:
  We present a stellar evolution model sequence of the past and future
evolution of the post-AGB born again star Sakurai's object (V4334 Sgr). In
order to match the short evolutionary time scale we have to assume that the
convective ingestion of hydrogen-rich envelope material into the He-flash
convection zone proceeds slower than predicted by the mixing length theory. For
the future we predict a swift second evolution through the central star region
before a second born-again evolution occurs.


title:
Fe-deficiency in H-deficient post-AGB stars due to n-capture
  nucleosynthesis

abstract:
  H-deficient post-AGB objects, e.g. PG1159 type star K1-16 and born-again AGB
star Sakurai's object, have been reported to be significantly iron-deficient.
We find that the iron deficiencies expected due to neutron-capture
nucleosynthesis during either the progenitor AGB evolution and/or the neutron
burst that occurs as a result of the rapid burning of protons during a post-AGB
He-flash are generally in line with observations.


title: Constrainting Cosmic Quintessence

abstract:
  A generic feature of cosmic quintessence models is the possibility of
significant energy density in the scalar field during the radiation dominated
epoch. This possibility is even greater if the quintessence field begins in a
kinetic-dominated regime, for example as might be generated at the end of
"quintessential inflation." As such, these models can be constrained by
primordial nucleosynthesis and the epoch of photon decoupling. Here, we analyze
both kinetic dominated and power-law quintessence fields (with and without a
supergravity correction). We quantify the allowed initial conditions and
effective-potential parameters. We also deduce constraints on the epoch of
matter creation at the end of quintessential inflation.


title: Measurements of the CMB: Current Status and Future Prospects

abstract:
  The study of the Cosmic Microwave Background (CMB) is a rapidly maturing
field. In remarkable advances in the past two years, experiments have begun to
probe the detailed structure of the CMB angular spectrum thereby providing
insight into the contents of the universe. We briefly review the BOOMERanG and
DASI results with an emphasis on what the data tell us with only minimal
cosmological assumptions. After a short discussion about a grand future for CMB
physics, key features of the MAP satellite, now in orbit, are described. We
also discuss how we anticipate MAP will advance the field beyond what we know
now.


title: The signature of high velocity gas in the spectra of NGC 4151

abstract:
  The multiwavelength emission spectrum and associated velocity field of the
Seyfert prototype NGC 4151 is modeled. HST data has impressively revealed the
existence of a large range of velocities (100 - 1500 \kms) dominating the
emitting clouds in the extended emission line region of the galaxy. Following
this observational result, a revision of the photoionization modeling approach
applied to NGC 4151 is presented. It is concluded that a mixture of radiation
dominated clouds and shock dominated clouds are required to explain the
multiwavelength line and continuum spectra of the galaxy.


title: Lithium and Halpha in stars and brown dwarfs of sigma Orionis

abstract:
  We present intermediate- and low-resolution optical spectra around Halpha and
LiI 6708 A for a sample of 25 low mass stars and 2 brown dwarfs with confirmed
membership in the pre-main sequence stellar sigma Orionis cluster. Our
observations are intended to investigate the age of the cluster. The spectral
types derived for our target sample are found to be in the range K6-M8.5, which
corresponds to a mass interval of roughly 1.2-0.02 Msun on the basis of
state-of-the-art evolutionary models. Radial velocities (except for one object)
are found to be consistent with membership in the Orion complex. All cluster
members show considerable Halpha emission and LiI in absorption, which is
typical of very young ages. We find that our pseudo-equivalent widths appear
rather dispersed (and intense in the case of Halpha) for objects cooler than
M3.5 spectral class, occurring at the approximate mass where low mass stars are
expected to become fully convective. The least massive brown dwarf in our
sample, SOri 45 (M8.5, ~0.02 Msun), displays variable Halpha emission and a
radial velocity that differs from the cluster mean velocity. Tentative
detection of forbidden lines in emission indicates that this brown dwarf may be
accreting mass from a surrounding disk. We also present recent computations of
LiI curves of growth for low gravities and for the temperature interval (about
4000-2600 K) of our sample. The comparison of our observations to these
computations allows us to infer that no lithium depletion has yet taken place
in sigma Orionis, and that the observed pseudo-equivalent widths are consistent
with a cluster initial lithium abundance close to the cosmic value. Hence, the
upper limit to the sigma Orionis cluster age can be set at 8 Myr, with a most
likely value around 2-4 Myr.


title:
Soft X-ray emission lines from photoionized accretion discs: constraints
  on their strength and width

abstract:
  We consider the properties of soft X-ray emission lines in the reprocessed
emission from a photoionized accretion disc. Observations of these lines will
be important in determining the ionization state and metallicity of the
innermost regions of active galaxies. Calculations of reflection from a
constant-density disc with an ionization parameter between 250 and 1000 erg
cm/s show that emission from O VIII Ly\alpha will dominate the soft X-ray
emission spectrum. There is also significant emission from C VI, N VII, O VII,
as well as Fe XVII--XIX. As the ionization parameter is increased these lines
become weaker and are broadened by Compton scattering. Significantly increasing
the O abundance primarily strengthens the O VII line, making it as large or
larger than the O VIII line. The nitrogen and carbon lines are quite weak with
equivalent widths (EWs) <30 eV, even with an increase in the N abundance. A
hydrostatic ionized disc model has a more realistic density structure and shows
a similar spectrum, but with the lines weaker and broader. This is a result of
the hot ionized skin at the surface of the disc. We apply these results to the
controversial claim of soft X-ray relativistic lines in the XMM-Newton spectrum
of MCG--6-30-15. We are unable to find a situation where O VIII has the
required EW without substantial emission from O VII. Furthermore, Compton
scattering results in the blue wing of the O VIII line to be much broader than
the << 10 eV drop observed in the data. We conclude that soft X-ray accretion
disc lines will, in general, be weak and broad features and are unlikely to
produce sharp edges in the data.


title: The Distribution of Atomic Hydrogen Around Two Irregular Galaxies

abstract:
  We present radio interferometric observations of two irregular galaxies that
were candidates for having unusually extended HI emission. The galaxies, UGC
199 and DDO 26, otherwise appeared to be normal, low-luminosity systems with
modest star-formation rates. To a detection limit of 2--3E19 /cm^2 at a
resolution of about 50", however, the HI around neither galaxy is unusually
extended compared to other irregulars. The HI around UGC 199 appears as a
regular, symmetric distribution with regular rotation and a maximum rotation
speed of about 80 km/s. By contrast, the HI around DDO 26 shows a concentration
into two blobs with an arm in the outer parts to the northwest and some
additional emission to the northwest of that. The kinematical major axis is
approximately 75 deg from the HI and optical morphological axis which is
unusual for Im galaxies. In addition the velocity field in the outer parts of
the galaxy is messy and the velocity profiles at the two HI peaks are broad. We
suggest that DDO 26 has been perturbed externally or may be two dwarfs in the
process of merging.


title: The XMM-Newton Bright Serendipitous Source Sample (XMM-Newton BSS)

abstract:
  The XMM-Newton Survey Science Center is constructing a large (~1000 sources)
and complete sample of bright serendipitous XMM-Newton sources at high galactic
latitude, so as to allow both the discovery of sources of high individual
interest as well as statistical population studies. The sample, known as ``The
XMM-Newton Bright Serendipitous Source Sample" (XMM-Newton BSS), has a flux
limit of ~10^(-13) cgs in the 0.5--4.5 keV energy band and will be fundamental
in complementing other medium and deep survey programs (having fluxes 10 to 100
times fainter) in order to: a) characterize the X-ray sky and its constituents,
b) understand the evolution of the population selected and c) define
statistical identification procedures to select rare and interesting
populations of X-ray sources (e.g. high z clusters of galaxies, BL Lacs, type 2
QSOs, etc..). We discuss here the scientific rationale and the details of the
project and we present some preliminary results.


title:
Chandra observations of the bursting X-ray transient SAX J1747.0-2853
  during low-level accretion activity

abstract:
  We present Chandra/ACIS observations of the bursting X-ray transient SAX
J1747.0-2853 performed on 18 July 2001. We detected a bright source at the
position of R.A = 17^h 47^m 02.60^s and Dec. = -28 52' 58.9'' (J2000.0; with a
1 sigma error of ~0.7 arcseconds), consistent with the BeppoSAX and ASCA
positions of SAX J1747.0-2853 and with the Ariel V position of the transient GX
+0.2,-0.2, which was active during the 1970's. The 0.5-10 keV luminosity of the
source during our observations was ~3 x 10^{35} erg/s (assuming a distance of 9
kpc) demonstrating that the source was in a low-level accretion state. We also
report on the long-term light curve of the source as observed with the all sky
monitor aboard the Rossi X-ray Timing Explorer. After the initial 1998
outburst, two more outbursts (in 2000 and 2001) were detected with peak
luminosities about two orders of magnitude larger than our Chandra luminosity.
Our Chandra observation falls in-between those two outbursts, making the
outburst history for SAX J1747.0-2853 complex. Those bright 2000 and 2001
outbursts combined with the likely extended period of low level activity
in-between those outbursts strongly suggest that the classification of SAX
J1747.0-2853 as a faint X-ray transient was premature. It might be possible
that the other faint X-ray transients also can exhibit bright, extended
outbursts which would eliminate the need for a separate sub-class of X-ray
transients. We discuss our results also in the context of the behavior of X-ray
binaries accreting at low levels with luminosities around 10^{35} erg/s, a
poorly studied accretion rate regime.


title: On the relationship between the Delta Scuti and Gamma Doradus pulsators

abstract:
  We searched for Delta Scuti-type pulsations amongst known and candidate Gamma
Doradus stars. We acquired 270 h of observations and monitored a total of 26
stars. One target, HD 209295, turned out to be a member of both classes of
pulsating star. We classify six of our targets as new bona fide Gamma Doradus
stars, nine more as good Gamma Doradus candidates, and three as ellipsoidal
variables. The remainder comprise one Delta Scuti star and five unexplained
variables.
  We revise the blue border of the Gamma Doradus phenomenon towards cooler
temperatures. This new blue edge extends from a temperature of about 7550 K on
the ZAMS to 7400 K one magnitude above it. Five bona fide Gamma Doradus stars
we observed are located inside the Delta Scuti instability strip, but none of
them exhibited observable Delta Scuti pulsations. We therefore suggest that
Gamma Doradus stars are less likely to be Delta Scuti pulsators compared to
other normal stars in the same region of the lower instability strip. In
addition, we show that there is a clear separation between the pulsation
constants Q of Delta Scuti and Gamma Doradus stars. The Gamma Doradus stars
known to date all have Q>0.23 d.


title: Photon-axion oscillations and Type Ia supernovae

abstract:
  We compute the probability of photon-axion oscillations in the presence of
both intergalactic magnetic fields and an electron plasma and investigate the
effect on Type Ia supernovae observations. The conversion probability is
calculated using a density matrix formalism by following light-paths through
simulated universes in a Monte-Carlo fashion. We find, that even though the
effect is highly frequency dependent, one needs to analyze relatively narrow
spectral features of high redshift objects in order to discern between the
dimming effect from oscillations and a cosmological constant, in contrast to
earlier claims that broad-band photometry is sufficient.


title:
Study of the Largest Multiwavelength Campaign of the Microquasar GRS
  1915+105

abstract:
  We present the results from a multiwavelength campaign of GRS 1915+105
performed from 2000 April 16 to 25. This is one of the largest coordinated set
of observations ever performed for this source, covering the wide energy band
in radio (13.3-0.3 cm), near-infrared (J-H-K), X-rays and Gamma-rays (from 1
keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the
"plateau" (or low/hard) state but sometimes showed soft X-ray oscillations:
before April 20.3, rapid, quasi-periodic (~= 45 min) flare-dip cycles were
observed. The radio flares observed on April 17 shows frequency- dependent peak
delay, consistent with an expansion of synchrotron-emitting region starting at
the transition from the hard-dip to the soft-flare states in X-rays. On the
other hand, infrared flares on April 20 appear to follow (or precede) the
beginning of X-ray oscillations with an inconstant time delay of ~= 5-30 min.
This implies that the infrared emitting region is located far from the black
hole by >~ 10E13 cm, while its size is <~ 10E12 cm constrained from the time
variability. We find a good correlation between the quasi-steady flux level in
the near-infrared band and in the X-ray band. From this we estimate that the
reprocessing of X-rays, probably occurring in the outer parts of the accretion
disk, accounts for about 20-30% of the observed K magnitude in the plateau
state. The OSSE spectrum in the 0.05-10 MeV band is represented by a single
power law with a photon index of 3.1 extending to ~1 MeV with no cutoff. The
power-law slope above ~30 keV is found to be very similar between different
states in spite of large flux variations in soft X-rays, implying that the
electron energy distribution is not affected by the change of the state in the
accretion disk.


title: The counterrotating core and the black hole mass of IC1459

abstract:
  The E3 giant elliptical galaxy IC1459 is the prototypical galaxy with a fast
counterrotating stellar core. We obtained one HST/STIS long-slit spectrum along
the major axis of this galaxy and CTIO spectra along five position angles. We
present self-consistent three-integral axisymmetric models of the stellar
kinematics, obtained with Schwarzschild's numerical orbit superposition method.
We study the dynamics of the kinematically decoupled core (KDC) in IC1459 and
we find it consists of stars that are well-separated from the rest of the
galaxy in phase space. The stars in the KDC counterrotate in a disk on orbits
that are close to circular. We estimate that the KDC mass is ~0.5% of the total
galaxy mass or ~3*10^9 Msun. We estimate the central black hole mass M_BH of
IC1459 independently from both its stellar and its gaseous kinematics. Some
complications probably explain why we find rather discrepant BH masses with the
different methods. The stellar kinematics suggest that M_BH = (2.6 +/-
1.1)*10^9 Msun (3 sigma error). The gas kinematics suggests that M_BH ~
3.5*10^8 Msun if the gas is assumed to rotate at the circular velocity in a
thin disk. If the observed velocity dispersion of the gas is assumed to be
gravitational, then M_BH could be as high as ~1.0*10^9 Msun. These different
estimates bracket the value M_BH = (1.1 +/- 0.3)*10^9 Msun predicted by the
M_BH-sigma relation. It will be an important goal for future studies to assess
the reliability of black hole mass determinations with either technique. This
is essential if one wants to interpret the correlation between the BH mass and
other global galaxy parameters (e.g. velocity dispersion) and in particular the
scatter in these correlations (believed to be only ~0.3 dex). [Abridged]


title:
Generation of galactic disc warps due to intergalactic accretion flows
  onto the disc

abstract:
  A new method is developed to calculate the amplitude of the galactic warps
generated by a torque due to external forces. This takes into account that the
warp is produced as a reorientation of the different rings which constitute the
disc in order to compensate the differential precession generated by the
external force, yielding a uniform asymptotic precession for all rings.
  Application of this method to gravitational tidal forces in the Milky Way due
to the Magellanic Clouds leads to a very low amplitude of the warp. If the
force were due to an extragalactic magnetic field, its intensity would have to
be very high, to generate the observed warps. An alternative hypothesis is
explored: the accretion of the intergalactic medium over the disk. A cup-shaped
distortion is expected, due to the transmission of the linear momentum; but,
this effect is small and the predominant effect turns out to be the
transmission of angular momentum, i.e. a torque giving an integral-sign shape
warp. The torque produced by a flow of velocity ~100 km/s and baryon density
\~10^{-25} kg/m^3 is enough to generate the observed warps and this mechanism
offers quite a plausible explanation. First, because this order of accretion
rate is inferred from other processes observed in the Galaxy, notably its
chemical evolution. The inferred rate of infall of matter, ~1 solar-mass/yr, to
the Galactic disc that this theory predicts agrees with the quantitative
predictions of this chemical evolution resolving key issues, notably the
G-dwarf problem. Second, because the required density of the intergalactic
medium is within the range of values compatible with observation. By this
mechanism, we can explain the warp phenomenon in terms of intergalactic
accretion flows onto the disk of the galaxy.


title: Fitting inverse power-law quintessence models using the SNAP satellite

abstract:
  We investigate the possibility of using the proposed SNAP satellite in
combination with low-z supernova searches to distinguish between different
inverse power-law quintessence models. If the true model is that of a
cosmological constant, we determine the prospects of ruling out the inverse
power-law potential. We show that SNAP combined with e.g. the SNfactory and an
independent measurement of the mass energy density to 17% accuracy can
distinguish between an inverse power-law potential and a cosmological constant
and put severe constraints on the power-law exponent.


title: Rapidly-rotating lithium-rich K giants: The new case of the giant PDS365

abstract:
  PDS365 is a newly detected rapidly rotating (vsin i = 20 km/s) single low
mass giant star which with HD233517 and HD219025 forms a remarkable ensemble of
single K giants with the unique properties of rapid rotation, very strong Li
lines, an asymmetrical Halpha profile, and a large far infrared excess. Their
vsin i values are between 18 and 23 km/s, and LTE Li abundances, log e(Li), are
between 2.9 and 3.9. Detailed analysis of PDS365 reveals it to be near one
solar mass giant with a value of 12C/13C approximately equal to 12. A clear
relation between high rotational velocities and very high Li abundances for K
giant stars is found only when asymmetrical Halpha profiles and large
far-infrared excesses are present. If we consider single K giants, we find that
among rapid (vsin i >= 8 km/s) rotators, a very large proportion (~ 50%) are
Li-rich giants. This proportion is in contrast with a very low proportion (~
2%) of Li-rich stars among the much more common slowly rotating K giants. This
striking difference is discussed in terms of proposed mechanisms for Li
enrichment.


title: The Composition of Cosmic Rays at the Knee

abstract:
  The observation of a small change in spectral slope, or 'knee' in the fluxes
of cosmic rays near energies 10^15 eV has caused much speculation since its
discovery over 40 years ago. The origin of this feature remains unknown. A
small workshop to review some modern experimental measurements of this region
was held at the Adler Planetarium in Chicago, USA in June 2000. This paper
summarizes the results presented at this workshop and the discussion of their
interpretation in the context of hadronic models of atmospheric airshowers.


title:
Double Starbursts Triggered by Mergers in Hierarchical Clustering
  Scenarios

abstract:
  We use cosmological SPH simulations to study the effects of mergers in the
star formation history of galactic objects in hierarchical clustering
scenarios. We find that during some merger events, gaseous discs can experience
two starbursts: the first one during the orbital decay phase, due to gas
inflows driven as the satellite approaches, and the second one, when the two
baryonic clumps collide. A trend for these first induced starbursts to be more
efficient at transforming the gas into stars is also found. We detect that
systems which do not experience early gas inflows have well-formed stellar
bulges and more concentrated potential wells, which seem to be responsible for
preventing further gas inward transport triggered by tidal forces. Our results
constitute the first proof that bulges can form as the product of collapse,
collisions and secular evolution in a cosmological framework, and they are
consistent with a rejuvenation of the stellar population in bulges at
intermediate z with, at least, 50% of the stars (in SCDM) being formed at high
z. (Abridged)


title: Two Subclasses of Proto-Planetary Nebulae: Model Calculations

abstract:
  We use detailed radiative transfer models to investigate the differences
between the Star-Obvious Low-level-Elongated proto-planetary nebulae (SOLE
PPNs) and DUst-Prominent Longitudinally-EXtended proto-planetary nebulae
(DUPLEX PPNs) which are two subclasses of PPNs suggested by Ueta, Meixner, &
Bobrowsky (2000). We select one SOLE PPN, HD 161796, and one DUPLEX PPN, IRAS
17150$-$3224, both of which are well studied and representative of their PPN
classes. Using an axisymmetric dust shell radiative transfer code, we model
these two sources in detail and constrain their mass-loss histories,
inclination angles and dust composition. The physical parameters derived for HD
161796 and IRAS 17150$-$3224 demonstrate that they are physically quite
different and that their observed differences cannot be attributed to
inclination angle effects. If these calculations reflect a more general truth
about SOLE vs. DUPLEX PPNs, then these two subclasses of PPNs are physically
distinct with the SOLE PPNs derived from low mass progenitors and DUPLEX PPNs
derived from high mass progenitors.


title: FUSE 900-1200A Spectroscopy of AM Her

abstract:
  Spectra of the magnetic white dwarf binary AM Her were obtained with the Far
Ultraviolet Spectroscopic Explorer (FUSE) during three consecutive spacecraft
orbits. These observations were split into 19 spectra of about 5 min duration
(0.025P binary phase) partially covering the binary orbit. We report the
phase-related changes in the far ultraviolet continuum light curve and the
emission lines, noting particularly the behavior of O VI. We discuss the fluxes
and velocities of the narrow and broad O VI emissions. We find the FUV light
curve has maximum amplitude at ~1000A, although at shorter wavelengths the
continuum may be strongly affected by overlapping Lyman lines. Weak, narrow
Lyman absorption lines are present. Their velocities don't appear to vary over
the observed orbital phases, and their mean value is consistent with the
systemic velocity.


title: Ice features in the mid-IR spectra of galactic nuclei

abstract:
  Mid infrared spectra provide a powerful probe of the conditions in dusty
galactic nuclei. They variously contain emission features associated with star
forming regions and absorptions by circumnuclear silicate dust plus ices in
cold molecular cloud material. Here we report the detection of 6-8um water ice
absorption in 18 galaxies observed by ISO. While the mid-IR spectra of some of
these galaxies show a strong resemblance to the heavily absorbed spectrum of
NGC 4418, other galaxies in this sample also show weak to strong PAH emission.
The 18 ice galaxies are part of a sample of 103 galaxies with good S/N mid-IR
ISO spectra. Based on our sample we find that ice is present in most of the
ULIRGs, whereas it is weak or absent in the large majority of Seyferts and
starburst galaxies. This result is consistent with the presence of larger
quantities of molecular material in ULIRGs as opposed to other galaxy types.
Like NGC 4418, several of our ice galaxy spectra show a maximum near 8um that
is not or only partly due to PAH emission. While this affects only a small part
of the galaxy population studied by ISO, it stresses the need for high S/N data
and refined diagnostic methods, to properly discriminate spectra dominated by
PAH emission and spectra dominated by heavy obscuration. The spectral variation
from PAH emission to absorbed continuum emission near 8um shows strong
similarities with Galactic star forming clouds. This leads us to believe that
our classification of ice galaxy spectra might reflect an evolutionary sequence
from strongly obscured beginnings of star formation (and AGN activity) to a
less enshrouded stage of advanced star formation (and AGN activity), as the
PAHs get stronger and the broad 8um feature weakens.


title:
Revised Coordinates and Proper Motions of the Stars in the Luyten
  Half-Second Catalogue

abstract:
  We present refined coordinates and proper motion data for the high proper
motion (HPM) stars in the Luyten Half-Second (LHS) catalogue. The positional
uncertainty in the original Luyten catalogue is typically >10" and is often
>30". We have used the digital scans of the Palomar Observatory Sky Survey
(POSS) I and POSS II plates to derive more accurate positions and proper
motions of the objects. Out of the 4470 candidates in the LHS catalogue, 4323
objects were manually re-identified in the POSS I and POSS II scans. A small
fraction of the stars were not found due to the lack of finder charts and
digitized POSS II scans. The uncertainties in the revised positions are
typically ~2", but can be as high as ~8" in a few cases; this is a large
improvement over the original data. Cross-correlation with the Tycho-2 and
Hipparcos catalogues yielded 819 candidates (with m_R < 12). For these brighter
sources, the position and proper motion data have been replaced with the more
accurate Tycho/Hipparcos data. In total, we have revised proper motion
measurements and coordinates for 4040 stars and revised coordinates for 4330
stars, which are presented here.


title:
Approaching Reionization: The Evolution of the Lyman Alpha Forest from
  Redshifts Four to Six

abstract:
  We analyze the Ly alpha forest properties of a sample of 15 high redshift
quasars lying between z = 4.42 and z = 5.75, using high signal-to-noise spectra
obtained with ESI on the Keck II 10 m telescope. The distribution of
transmissions in the Ly alpha region in this redshift range is shown to be
consistent with that found in lambda cold dark matter simulations with a
smoothly evolving ionization rate as a function of redshift. The extrapolation
of the ionizing flux to z = 6.05 lies a factor of two higher than a 2 sigma
upper limit placed by Cen & McDonald (2001) at this redshift, based on the
Becker et al. (2001) spectra of the z = 6.28 quasar SDSS 1030+0524. However,
the data are also consistent with models in which there is substantial
variation of the ionization parameter about the mean value, and in this case,
dark gaps such as those seen by Becker et al. become much more likely. We
conclude that further data are needed before we can be sure that we have seen
the epoch of reionization. We also summarize the damped Ly alpha systems seen
in these quasar lines of sight and measure their metallicities and kinematic
properties. We argue that the mean DLA metallicity has dropped substantially by
z = 5 compared with its value at z < 4.


title: The Epochs of Early-Type Galaxy Formation in Clusters and in the Field

abstract:
  We compute new population synthesis models of Lick absorption line indices
with variable alpha/Fe ratios and use them to derive average ages,
metallicities, and alpha/Fe element enhancements for a sample of 126 field and
cluster early-type galaxies. Calibrating the models on galactic globular
clusters, we show that any population synthesis model being based on stellar
libraries of the Milky Way is intrinsically biased towards super-solar alpha/Fe
ratios at metallicities below solar. We correct for this bias, so that the
models presented here reflect constant alpha/Fe ratios at all metallicities.
The use of such unbiased models is essential for studies of stellar systems
with sub-solar metallicities like (extragalactic) globular clusters or dwarf
galaxies.
  For the galaxy sample investigated here, we find a clear correlation between
alpha/Fe and velocity dispersion. Zero-point, slope, and scatter of this
correlation turn out to be independent of the environment. Additionally, the
alpha/Fe ratios and mean ages of elliptical galaxies are well correlated, i.e.
galaxies with high alpha/Fe ratios have also high average ages. This strongly
reinforces the view that the alpha/Fe element enhancement in ellipticals is
produced by short star formation timescales rather than by a flattening of the
initial mass function. The more massive the galaxy, the shorter is its star
formation timescale, and the higher is the redshift of the bulk of star
formation, independent of the environmental density. We show that this finding
is incompatible with the predictions from hierarchical galaxy formation models,
in which star formation is tightly linked to the assembly history of dark
matter halos.


title: Could SiC A+B grains have originated in a post-AGB thermal pulse?

abstract:
  The carbon and nitrogen isotopic ratios of pre-solar SiC grains of type A+B
suggest a proton-limited nucleosynthetic process as encountered, for instance,
during the very late thermal pulse of post-AGB stars. We study the nuclear
processes during this phase and find carbon and nitrogen isotopic ratios which
can reproduce those of A+B grains. These results are still preliminary because
they depend on uncertain factors such as the details of mixing during the
post-AGB thermal pulse, the rates of some nuclear reactions, and the
assumptions on mixing during the progenitor AGB phase.


title: Towards an Understanding of GRB Prompt Emission

abstract:
  We discuss the prompt emission of Gamma-Ray Bursts in different spectral
energy bands. First, we suggest that a three-part synchrotron emission model is
a good description of the ~20 keV - 1 MeV gamma-ray emission of GRBs. We show
that this model provides excellent fits to the data and naturally explains the
observed global correlations between spectral parameters. In particular, we
show there exists a negative correlation between between the peak of the nu-Fnu
spectrum, Ep, and the low energy photon index \alpha for bursts with -2/3 <
\alpha < 0, and suggest that this correlation is due to the mechanism
responsible for producing \alpha's above the value of -2/3 - namely, a
decreasing mean pitch angle of the electrons. We then discuss the physical
origin of the increasing number of GRBs that are observed to peak in the X-ray
energy band (~5-40 keV). Although either a cosmological (i.e. high redshift) or
intrinsic interpretation for the low values of Ep is viable at this point, the
data appear to suggest that intrinsic effects are playing the dominant role.
Finally, we briefly comment on the prompt GRB optical emission (~ eV) and very
high energy emission (>10 MeV), and how these spectral bands may be used to
place additional constraints on the physics of gamma-ray bursts.


title:
Chandra Observation of SNR G54.1+0.3 -- a Close Cousin of the Crab
  Nebula

abstract:
  We present a {\it Chandra} ACIS observation of SNR G54.1+0.3. This supernova
remnant is resolved into several distinct X-ray emitting components: a central
bright point-like source (CXOU J193030.13+185214.1), a surrounding ring,
bipolar elongations, plus low surface brightness diffuse emission. The spectra
of these components are all well described by power-law models; the spectral
index steepens with increasing distance from the point-like source. We find no
evidence for any thermal plasma emission that would correspond to shocked
interstellar medium or ejecta. The observed morphological and spectral
characteristics suggest that G54.1+0.3 is the closest ``cousin'' of the Crab
Nebula -- a pulsar wind nebula driven by a combination of equatorial and polar
outflows from the putative pulsar represented by the point-like X-ray source.


title: The Angular Expansion and Distance of the Planetary Nebula BD+30 3639

abstract:
  The WFPC2 camera aboard the HST was used to obtain images of the planetary
nebula BD+30 3639 at two epochs separated by 5.663 years. The expansion of the
nebula in the H-alpha and [N II] bands has been measured using several methods.
Detailed expansion maps for both emission lines were constructed from nearly
200 almost independent features. There is good agreement between the
(independent) H-alpha and [N II] proper motions. The central velocity split is
measured from the STIS echelle spectra of the C II] 2326A multiplet to be
+/-36.3 km/s at a position angle of 99 degrees. The angular displacement along
this slit position was measured to be 4.25 mas/yr at 2".47 from the center. We
constructed a tilted ellipsoidal shell model by fitting the radio brightness
variation of the 5 and 15 GHz VLA observations, and making use of the
ground-based echelle spectra from Bryce & Mellema (1999), to estimate distance.
Our model has an axial ratio of 1.56, is inclined to the line of sight by 9.7
degrees, and exhibits an expansion in the plane of the sky which is 2/3 that in
the radial direction, leading to a distance of 1.2 kpc. Not all the kinematic
data fits this simple model, so the distance must still be regarded as
uncertain. Based on the recent model atmosphere of Crowther et al. (2002), a
distance of 1.2 kpc implies a stellar luminosity of 4250 L_sun. The kinematic
age of the nebula varies somewhat from region to region; a good average value
is 800 years, while the expansion along the position of the echelle slit gives
about 600 years.


title: The 3 micron spectrum of R Doradus observed with the ISO-SWS

abstract:
  We have modeled the 2.6 - 3.7 um spectrum of the red semiregular variable R
Doradus observed with the Short-Wavelength Spectrometer on board the Infrared
Space Observatory. The wavelength resolution of the observations varies between
R = 2000 - 2500. We have calculated a synthetic spectrum using a hydrostatic
model photosphere in spherical geometry. The agreement between the synthetic
spectrum and the ISO observations is encouraging, especially in the wavelength
region of 2.8 - 3.7 um, suggesting that a hydrostatic model photosphere is
adequate for the calculation of synthetic spectra in the near infrared for this
moderately varying red giant star. However, an additional absorption component
is needed at 2.6- 2.8 um and this discrepancy is discussed. The spectral
signatures are dominated by water vapour in the stellar photosphere, but
several photospheric OH, CO, and SiO features are also present. The effective
temperature and surface gravity derived for R Dor, based on the 2.6 - 3.7 um
ISO spectrum and the modeling of it with a hydrostatic model photosphere, are
3000 +- 100 K and log g = 0 +- 1 (cgs), respectively. The spectral region
observed is found to be temperature sensitive. The effective temperature given
here is slightly higher than those reported in the literature. We also discuss
possible reasons for this.


title:
The Effect of Non Gaussian Errors on the Determination of Steeply
  Falling Spectra

abstract:
  The determination of a steeply falling energy spectrum from rare events with
non-gaussian measurement errors is a delicate matter. The final shape of the
spectrum may be severely distorted as a consequence of non-gaussian tails in
the energy resolution of the experiment. We illustrate this effect with the
recent experimental efforts to determine the ultra-high energy extreme of the
cosmic ray spectrum.


title: Dense Cores in Dark Clouds. XIV. N2H+(1-0) maps of dense cloud cores

abstract:
  We present results of an extensive mapping survey of N2H+(1-0) in about 60
low mass cloud cores already mapped in the NH3(1,1) inversion transition line.
The survey has been carried out at the FCRAO antenna with an angular resolution
about 1.5 times finer than the previous ammonia observations. Cores with stars
typically have map sizes about a factor of two smaller for N2H+ than for NH3,
indicating the presence of denser and more centrally concentrated gas compared
to starless cores. Significant correlations are found between NH3 and N2H+
column densities and excitation temperatures in starless cores, but not in
cores with stars, suggesting a different chemical evolution of the two species.
Velocity gradients range between 0.5 and 6 km/s/pc, similar to what has been
found with NH3 data. ``Local'' velocity gradients show significant variation in
both magnitude and direction, suggesting the presence of complexmotions not
interpretable as simple solid body rotation. Integrated intensity profiles of
starless cores present a ``central flattening'' and are consistent with a
spherically symmetric density law n ~ r^{-1.2} for r < ~0.03 pc and n ~ r^{-2}
at larger r. Cores with stars are better modelled with single density power
laws with n ~ r^{-2}. Line widths change across the core but we did not find a
general trend. The deviation in line width correlates with the mean line width,
suggesting that the line of sight contains ~ 10 coherence lengths. The
corresponding value of the coherence length, ~ 0.01 pc, is similar to the
expected cutoff wavelength for MHD waves. This similarity may account for the
increased ``coherence'' of line widths on small scales. Despite of the finer
angular resolution, the majority of N2H+ and NH3 maps show a similar ``simple''
structure, with single peaks and no elongation.


title: Radio Confusion on Cluster Sunyaev-Zel'dovich Effect

abstract:
  We examine the expected radio confusion on the thermal Sunyaev-Zel'dovich
(SZ) effect of galaxy clusters at 28.5 GHz and 90 GHz based on the cluster
radio luminosity function (CRLF) at 1.4 GHz. With the observationally
determined spectral index (${\alpha}$, where $S_{\rm\nu}\propto\nu^{-\alpha}$)
distribution, instead of a single average index $<\alpha>$, we convert the
cluster radio luminosity function at 1.4 GHz to the high frequency ones and
estimate the total radio flux in a cluster. At 28.5 GHz, radio confusion is up
to 10~100% for small clusters ($M\sim 2\times 10^{14}M_{\odot}$) below redshift
z=1, with more severe confusion for smaller and lower redshift clusters. By
contrast, at 90 GHz the confusion is less than 10% for small clusters even at
low redshifts.


title: The Anglo-Australian Observatory's 2dF Facility

abstract:
  The 2dF (Two-degree Field) facility at the prime focus of the
Anglo-Australian Telescope provides multiple object spectroscopy over a 2
degree field of view. Up to 400 target fibres can be independently positioned
by a complex robot. Two spectrographs provide spectra with resolutions of
between 500 and 2000, over wavelength ranges of 440nm and 110nm respectively.
The 2dF facility began routine observations in 1997.
  2dF was designed primarily for galaxy redshift surveys and has a number of
innovative features. The large corrector lens incorporates an atmospheric
dispersion compensator, essential for wide wavelength coverage with small
diameter fibres. The instrument has two full sets of fibres on separate field
plates, so that re-configuring can be done in parallel with observing. The
robot positioner places one fibre every 6 seconds, to a precision of 0.3 arcsec
(20micron) over the full field. All components of 2dF, including the
spectrographs, are mounted on a 5-m diameter telescope top-end ring for ease of
handling and to keep the optical fibres short in order to maximise UV
throughput . There is a pipeline data reduction system which allows each data
set to be fully analysed while the next field is being observed.
  In this paper we provide the historical background to the 2dF facility, the
design philosophy, a full technical description and a summary of the
performance of the instrument. We also briefly review its scientific
applications and possible future developments.


title:
Deep HST-WFPC2 photometry of NGC 288. II. The Main Sequence Luminosity
  Function

abstract:
  The Main Sequence Luminosity Function (LF) of the Galactic globular cluster
NGC 288 has been obtained using deep WFPC2 photometry. We have employed a new
method to correct for completeness and fully account for bin-to-bin migration
due to blending and/or observational scatter. The effect of the presence of
binary systems in the final LF is quantified and is found to be negligible.
There is a strong indication of the mass segregation of unevolved single stars
and clear signs of a depletion of low mass stars in NGC 288 with respect to
other clusters. The results are in good agreement with the prediction of
theoretical models of the dynamical evolution of NGC 288 that take into account
the extreme orbital properties of this cluster.


title:
Photometry of four binary subdwarf B stars and the nature of their
  unseen companion stars

abstract:
  We present lightcurves of four binary subdwarf B stars, Ton 245, Feige 11,
PG1432+159 and PG1017-086. We also present new spectroscopic data for
PG1017-086 from which we derive its orbital period, P=0.073d, and the mass
function, f_m = 0.0010 +/- 0.0002 solar masses. This is the shortest period for
an sdB binary measured to-date. The values of P and f_m for the other sdB
binaries have been published elsewhere. We are able to exclude the possibility
that the unseen companion stars to Ton 245, Feige 11 and PG1432+159 are
main-sequence stars or sub-giant stars from the absence of a sinusoidal signal
which would be caused by the irradiation of such a companion star, i.e., they
show no reflection effect. The unseen companion stars in these binaries are
likely to be white dwarf stars. By contrast, the reflection effect in
PG1017-086 is clearly seen. The lack of eclipses in this binary combined with
other data suggests that the companion is a low mass M-dwarf or, perhaps, a
brown dwarf.


title:
Spectroscopic Dating of Stellar Populations from Local Star Clusters to
  Distant Galaxies and the Age of the Universe

abstract:
  I summarize in terms of evolutionary population synthesis models our current
understanding of stellar populations in different environments, from star
clusters in nearby galaxies to distant galaxies in clusters or seen through
gravitational lenses. Constraints on the age of the stellar populations in
clusters and galaxies derived from comparing predicted and observed spectral
energy distributions are examined and contrasted with the maximum ages allowed
by cosmological models at the corresponding redshift.


title: Star Clusters as Type Ia Supernova Factories

abstract:
  We find a remarkably enhanced production rate in star clusters (relative to
the field) of very short period, massive double-white-dwarf stars and of
giant-white dwarf binaries. These results are based on N-body simulations
performed with the new GRAPE-6 special purpose hardware and are important in
identifying and characterizing the progenitors of type Ia supernovae. The high
incidence of very close double-white-dwarf systems is the result of dynamical
encounters between (mostly) primordial binaries and other cluster stars.
Orbital hardening rapidly drives these degenerate binaries to periods under ~10
hours. Gravitational radiation emission and mergers producing
supra-Chandrasekhar objects follow in less than a Hubble time. If most stars
are born in clusters then estimates of the double white dwarf merger rates in
galaxies (due to cluster dynamical interaction) must be increased more than
tenfold. A majority of the Roche lobe overflow giant-white dwarf binaries are
not primordial; they are produced in exchange reactions. Most cases resulted in
a common-envelope and formation of a double-white-dwarf binary rather than
Supersoft X-ray sources leading possibly to a type Ia supernova.


title: The Galactic Plane Observed by XMM-Newton

abstract:
  In A0-1 we proposed an ambitious long-term survey of selected regions of our
Galaxy (the XGPS survey) using the EPIC CCD cameras on XMM-Newton. The first
phase of the programme, which aims to survey a strip of the Galactic Plane in
the Scutum region, is currently underway. Here we report on the preliminary
results from the first 15 survey pointings. We show that the XGPS survey
strategy of fairly shallow (5-10 ks) exposures but wide-angle coverage is well
tuned to the goal of providing a large catalogue of predominantly Galactic
sources at relatively faint X-ray fluxes in the hard 2-6 keV band.


title:
Evidence for a Fast Decline in the Progenitor Population of Gamma Ray
  Bursts and the Nature of their Origin

abstract:
  We show that the source population of long gamma-ray bursts (GRBs) has
declined by at least a factor of 12 (at the 90% confidence level) since the
early stages of the Universe ($z \sim 2 - 3$). This result has been obtained
using the combined BATSE and \it Ulysses \rm GRB brightness distribution and
the detection of four GRBs with known redshifts brighter than 10$^{52}$ erg
s$^{-1}$ in the 50 - 300 keV range at their peak. The data indicate that the
decline of the GRB source population is as fast as, or even faster than, the
measured decline of the star formation rate. Models for the evolution of
neutron star binaries predict a significantly larger number of apparently
bright GRBs than observed. Thus our results give independent support to the
hypernova model, which naturally explains the fast decline in the progenitor
population.


title: OH-selected AGB and post-AGB objects I.Infrared and maser properties

abstract:
  Using 766 compact objects from a survey of the galactic Plane in the 1612-MHz
OH line, new light is cast on the infrared properties of evolved stars on the
TP-AGB and beyond. The usual mid-infrared selection criteria, based on IRAS
colours, largely fail to distinguish early post-AGB stages. A two-colour
diagram from narrower-band MSX flux densities, with bimodal distributions,
provides a better tool to do the latter. Four mutually consistent selection
criteria for OH-masing red PPNe are given, as well as two for early post-AGB
masers and one for all post--AGB masers, including the earliest ones. All these
criteria miss a group of blue, high-outflow post-AGB sources with 60-mum
excess; these will be discussed in detail in Paper II. The majority of post-AGB
sources show regular double-peaked spectra in the OH 1612-MHz line, with fairly
low outflow velocities, although the fractions of single peaks and irregular
spectra may vary with age and mass. The OH flux density shows a fairly regular
relation with the stellar flux and the envelope optical depth, with the maser
efficiency increasing with IRAS colour R21. The OH flux density is linearly
correlated with the 60-mum flux density.


title:
OH-selected AGB and post-AGB stellar objects II.Blue versus red
  evolution off the AGB

abstract:
  Using objects found in a systematic survey of the galactic Plane in the
1612-MHz OH line, we discuss in detail two ``sequences'' of post-AGB evolution,
a red and a blue. We argue that the red and the blue groups separate by initial
mass at 4Msun, based on evolutionary-sequence turn-off colours, spectral energy
distributions, outflow velocities and scaleheight. The higher-mass (blue)
objects may have earlier AGB termination. The lower-mass (red) objects undergo
very sudden reddening for IRAS colour R21\sim1.2; these sources must all
undergo a very similar process at AGB termination. The transition colour
corresponds to average initial masses of 1.7Msun. A combined IRAS-MSX colour
proves a very sensitive tool to distinguish lower-mass, early post-AGB objects
from sources still on the AGB and also to distinguish more evolved post-AGB
objects from star-forming regions. The high-mass blue objects are the likely
precursors of bipolar planetary nebulae, whereas the low-mass red objects will
evolve into elliptical planetary nebulae.


title: Studying Structure Formation with the Sloan Digital Sky Survey

abstract:
  I review recent SDSS results related to galaxies and large scale structure,
including: (1) discovery of coherent, unbound structures in the stellar halo,
(2) demonstration that Pal 5 has tidal tails and Draco doesn't, (3) precise
measurement of the galaxy luminosity function and its variation with surface
brightness, color, and morphology, (4) detailed examination of the Fundamental
Plane of 9000 early type galaxies, (5) measurement, via galaxy-galaxy lensing,
of the extended dark matter distributions around galaxies and their variation
with luminosity, morphology, and environment, (6) measurement of galaxy angular
clustering, spatial clustering and velocity dispersion as a function of
luminosity and color. I then discuss what we can hope to learn in the long run
from galaxy clustering in the SDSS and the 2dFGRS. Galaxy clustering depends on
the dark halo population and on the Halo Occupation Distribution (HOD), which
specifies the way that galaxies populate the halos. SPH simulations and
semi-analytic models make similar predictions for the probability P(N|M) that a
halo of virial mass M contains N galaxies of a specified type: a non-linear
mean occupation N_avg(M), sub-Poisson fluctuations about the mean in low mass
halos, and strong dependence of N_avg(M) on stellar population age. The
complementary sensitivity of different clustering statistics should make it
possible to determine the HOD empirically given an assumed cosmological model.
Furthermore, changes to the cosmological model change the halo population in
ways that would be difficult to mask by changing the HOD. Ultimately, we can
hope to have our cake and eat it too, obtaining strong guidance to the physics
of galaxy formation by deriving the HOD of different classes of galaxies, while
simultaneously carrying out precision tests of cosmological models.


title: Detection of the BL Lac Object H1426+428 at TeV Gamma Ray Energies

abstract:
  A very high energy (VHE) gamma-ray signal has been detected at the 5.4 sigma
level from H1426+428, an x-ray selected BL Lacertae object at a redshift of
0.129. The object was monitored from 1995 - 1998 with the Whipple 10m imaging
atmospheric Cherenkov telescope as part of a general blazar survey; the results
of these observations, although not statistically significant, were
consistently positive. X-ray observations of H1426+428 during 1999 with the
BeppoSAX instrument revealed that the peak of its synchrotron spectrum occurs
at > 100 keV, leading to the prediction of observable TeV emission from this
object. H1426+428 was monitored extensively at the Whipple Observatory during
the 1999, 2000, and 2001 observing seasons. The strongest TeV signals were
detected in 2000 and 2001. During 2001, an integral flux of 2.04 +/- 0.35
x10e-11 cm-2 s-1 above 280 GeV was recorded from H1426+428. The detection of
H1426+428 supports the idea that, as also seen in Markarian 501 and
1ES2344+514, BL Lacertae objects with extremely high synchrotron peak
frequencies produce gamma rays in the TeV range.


title:
Population synthesis of compact objects: neutron stars, strange (quark)
  stars and black holes

abstract:
  We compute and present the distribution in mass of single and binary neutron
stars, strange stars, and black holes. The calculations were performed using a
stellar population synthesis code. We follow evolution of massive single stars
as well as binaries with high mass primaries. The final product of the latter
evolution can be either a binary composed of a white dwarf and a compact object
(neutron star, black hole, strange star), two compact objects in a binary, or
two single stars if the system was disrupted. We find in binaries a population
of black holes which are more massive than single black holes which are a
product of either binary or single evolution. We also find that if quark stars
exist at all, their population can be as large as the population of black
holes.


title: The Baryon Density Through The (Cosmological) Ages

abstract:
  The light element abundances probe the baryon density of the universe within
a few minutes of the Big Bang. Of these relics from the earliest universe,
deuterium is the baryometer of choice. By comparing its primordial abundance
inferred from observations with that predicted by Big Bang Nucleosynthesis
(BBN), the early universe baryon density is derived. This is then compared to
independent estimates of the baryon density several hundred thousand years
after the Big Bang and at present, more than 10 billion years later. The
excellent agreement among these values represents an impressive confirmation of
the standard model of cosmology.