title:
Understanding the nature of FRII optical nuclei: a new diagnostic plane
  for radio galaxies

abstract:
  We extend our study of the nuclei of 3CR FR II radio galaxies through HST
optical images up to z=0.3. In the majority of them an unresolved nucleus
(central compact core, CCC) is found. We analyze their position in the plane
formed by the radio and optical nuclear luminosities in relation to their
optical spectral properties. The broad-lined objects (BLO) have the brightest
nuclei: they are present only at optical luminosities nu L_nu > 4 X 10^42 erg
s^-1 which we suggest might represent a threshold in the radiative efficiency
combined to a small range of black hole masses. About 40 % of the high and low
excitation galaxies (HEG and LEG) show CCC which resemble those previously
detected in FR I galaxies, in apparent contrast to the unification model. The
equivalent width of the [OIII] emission line (with respect to the nuclear
luminosity) reveals the nature of these nuclei, indicating that the nuclei of
HEG are obscured to our line of sight and only scattered radiation is observed.
This implies that the population of FR II is composed by objects with different
nuclear properties, and only a fraction of them can be unified with quasars.


title: The Next Generation Sky Survey and the Quest for Cooler Brown Dwarfs

abstract:
  The Next Generation Sky Survey (NGSS) is a proposed NASA MIDEX mission to map
the entire sky in four infrared bandpasses - 3.5, 4.7, 12, and 23 um. The
seven-month mission will use a 50-cm telescope and four-channel imager to
survey the sky from a circular orbit above the Earth. Expected sensitivities
will be half a million times that of COBE/DIRBE at 3.5 and 4.7 um and a
thousand times that of IRAS at 12 and 23 um. NGSS will be particularly
sensitive to brown dwarfs cooler than those presently known. Deep absorption in
the methane fundamental band at 3.3 um and a predicted 5-um overluminosity will
produce uniquely red 3.5-to-4.7 um colors for such objects. For a limiting
volume of 25 pc, NGSS will completely inventory the Solar Neighborhood for
brown dwarfs as cool as Gl 229B. At 10 pc, the census will be complete to 500
K. Assuming a field mass function with alpha = 1, there could be one or more
brown dwarfs warmer than 150 K lying closer to the Sun than Proxima Centauri
and detectable primarily at NGSS wavelengths. NGSS will enable estimates of the
brown dwarf mass and luminosity functions to very cool temperatures and will
provide both astrometric references and science targets for NGST.


title: Impact of AGNs on the Surrounding Medium

abstract:
  The time- and ensemble-averaged mechanical energy outputs of radio galaxies
may be large enough to offset much of the cooling inferred from X-ray
observations of galaxy clusters. But does this heating actually counterbalance
the cooling, diminishing cooling flows or quenching them altogether? I will
argue that energy injection by radio galaxies may be important even in clusters
where no active source is present, due to the likely intermittency of the jets.
If the energy injected by radio galaxies percolates through the intracluster
medium without excessive mixing, it could stabilize the atomic cooling
responsible for X-ray emission.


title: The Relative Ages of the Globular Cluster Subpopulations in M87

abstract:
  Relative ages for the globular cluster (GC) subpopulations in the Virgo giant
elliptical galaxy M87 (NGC 4486) have been determined from Stroemgren
photometry obtained with WFPC2 on board HST. Using a variety of population
synthesis models, and assuming the GC mass at the turnover of the luminosity
function is the same for both subpopulations, differential ages have been
determined from the observed magnitudes at the turnover of the globular cluster
luminosity function and from the mean color of each subpopulation. We measure
an age difference between the two subpopulations of 0.2 +/- 1.5 (systematic)
+/- 2 (random) Gyr, in the sense that the blue GCs are formally older. Thus, to
within our measurement errors, the two subpopulations are found to be coeval.
Combined with previous spectroscopic age determinations for M87 GCs, our
results favor a picture in which the GCs associated with this galaxy are formed
at high redshift, and within a period of a few Gyr.


title: Clouds and Clearings in the Atmospheres of the L and T Dwarfs

abstract:
  A sophisticated approach to condensate opacity is required to properly model
the atmospheres of L and T dwarfs. Here we review different models for the
treatment of condensates in brown dwarf atmospheres. We conclude that models
which include both particle sedimentation and upwards transport of condensate
(both gas and particles) provide the best fit for the L dwarf colors. While a
globally uniform cloud model fits the L dwarf data, it turns to the blue in J-K
too slowly to fit the T dwarfs. Models which include local clearings in the
global cloud deck, similar to Jupiter's prominent five-micron hot spots, better
reproduce the available photometric data and also account for the observed
resurgence of FeH absorption in early type T dwarfs.


title: The distribution of mass ratios in compact object binaries

abstract:
  Using the StarTrack population synthesis code we compute the distribution of
masses of merging compact object (black hole or neutron star) binaries. The
shape of the mass distribution is sensitive to some of the parameters governing
the stellar binary evolution. We discuss the possibility of constraining
stellar evolution models using mass measurements obtained from the detection of
compact object inspiral with the upcoming gravitational-wave observatories.


title:
Keck-Nirspec Infrared OH Lines: Oxygen Abundances in Metal-Poor Stars
  Down to [Fe/H] = -2.9

abstract:
  Infrared OH lines at 1.5 - 1.7 um in the H band were obtained with the
NIRSPEC high-resolution spectrograph at the 10m Keck Telescope for a sample of
seven metal-poor stars. Detailed analyses have been carried out, based on
optical high-resolution data obtained with the FEROS spectrograph at ESO.
Stellar parameters were derived by adopting infrared flux method effective
temperatures, trigonometric and/or evolutionary gravities and metallicities
from FeII lines. We obtain that the sample stars with metallicities [Fe/H] <
-2.2 show a mean oxygen abundance [O/Fe] ~ 0.54, for a solar oxygen abundance
of epsilon(O) = 8.87, or [O/Fe] ~ 0.64 if epsilon(O) = 8.77 is assumed.


title: Metallicity Evolution of Damped Lyman-Alpha Galaxies

abstract:
  We have reanalyzed the existing data on Zinc abundances in damped Ly-alpha
(DLA) absorbers to investigate whether their mean metallicity evolves with
time. Most models of cosmic chemical evolution predict that the mass- weighted
mean interstellar metallicity of galaxies should rise with time from a low
value ~ 1/30 solar at z ~ 3 to a nearly solar value at z ~ 0. However, several
previous analyses have suggested that there is little or no evolution in the
global metallicity of DLAs. We have used a variety of statistical techniques to
quantify the global metallicity-redshift relation and its uncertainties, taking
into account both measurement and sampling errors. Three new features of our
analysis are: (a) an unbinned N(H I)-weighted nonlinear chi-square fit to an
exponential relation; (b) survival analysis to treat the large number of limits
in the existing data; and (c) a comparison of the data with several models of
cosmic chemical evolution based on an unbinned N(H I)-weighted chi-square. We
find that a wider range of evolutionary rates is allowed by the present data
than claimed in previous studies. The slope of the exponential fit to the N(H
I)-weighted mean Zn metallicity vs. redshift relation is -0.20 plus minus 0.11
counting limits as detections and -0.27 plus minus 0.12 counting limits as
zeros. Similar results are also obtained if the data are binned in redshift,
and if survival analysis is used. These slopes are marginally consistent with
no evolution, but are also consistent with the rates predicted by several
models of cosmic chemical evolution. Finally, we outline some future
measurements necessary to improve the statistics of the global
metallicity-redshift relation.


title: Evolution of Star Forming and Active Galaxies in Nearby Clusters

abstract:
  (Abridged) We have used optical spectroscopy to investigate the radio-
selected active galaxy populations in a sample of 20 nearby Abell clusters. The
spectra were used to characterize the galaxies as AGN or galaxies forming stars
at rates comparable to or greater than the Milky Way. A significant population
of star forming galaxies with large amounts of nuclear dust extinction were
revealed. This extinction eliminates bluer emission lines such as [OII],
meaning their star formation could easily be overlooked in studies which focus
on such features. Around 20% of cluster star forming galaxies have such
spectra, and their radial distribution suggests they are the consequence of
some cluster environmental effect. We note that galaxies of this type may be
identified using their 4000-Angstrom break strengths. We also find that
discrepancies in reported radio luminosity functions for AGN are likely the
result of classification differences. There exists a large population of
cluster galaxies whose radio fluxes, FIR fluxes, and optical magnitudes suggest
their radio emission may be powered by stars, yet their spectra lack emission
lines. Understanding the nature of these galaxies is critical to assessing the
importance of AGN in the radio luminosity function at low luminosities.


title: Old elliptical galaxies at z=1.5 and the Kormendy relation

abstract:
  Deep spectroscopy of the two mJy radio galaxies LBDS 53W069 and 53W091 has
previously shown them to have old (>3 Gyr) stellar populations at z=1.5. Here
we present the results of HST observations of these galaxies. 53W069 has an
r^1/4 profile in both the F814W & F110W data with an effective radius of 0.30
arcsec (2.7 kpc). The restframe U-B colour gradient requires a stellar
population of super-solar (3Z_sun) metallicity that formed on a very short
timescale at high redshift (z>5). 53W091 has a regular r^1/4 profile in F110W
with an effective radius of 0.32 arcsec (2.9 kpc). The F814W profile is more
extended and is consistent with a blue exponential disk that contributes 20% of
the flux within r_e. The restframe U-B colour gradient is significantly larger
than that observed in field ellipticals at z<1, implying a stellar population
of mixed metallicity (1-3Z_sun) that formed in a high-redshift rapid burst.
  We have compared these two LBDS radio galaxies with the Kormendy relation of
ten 3CR radio galaxies at z=0.8. The LBDS galaxies follow the same relation as
the more radio-luminous 3CR galaxies, assuming passive evolution of their
stellar populations, although they are smaller than the 3CR galaxies whose mean
effective radius is 12 kpc. Their sizes and radio luminosities are consistent
with scaling relations applied to the 3CR galaxies, in which both radio power
and effective radius scale with galaxy mass. Compared with a sample of z=0.4
cluster ellipticals, 53W069 & 53W091 lie well within the scatter of the
Kormendy relation. We conclude that the hosts of these mJy radio sources at
z=1.5 are passively-evolving elliptical galaxies that will evolve into ordinary
L* ellipticals by the present day. (Abridged)


title:
Stable clustering, the halo model and nonlinear cosmological power
  spectra

abstract:
  We present the results of a large library of cosmological N-body simulations,
using power-law initial spectra. The nonlinear evolution of the matter power
spectra is compared with the predictions of existing analytic scaling formulae
based on the work of Hamilton et al. The scaling approach has assumed that
highly nonlinear structures obey `stable clustering' and are frozen in proper
coordinates. Our results show that, when transformed under the self-similarity
scaling, the scale-free spectra define a nonlinear locus that is clearly
shallower than would be required under stable clustering. Furthermore, the
small-scale nonlinear power increases as both the power-spectrum index n and
the density parameter Omega decrease, and this evolution is not well accounted
for by the previous scaling formulae. This breakdown of stable clustering can
be understood as resulting from the modification of dark-matter haloes by
continuing mergers. These effects are naturally included in the analytic `halo
model' for nonlinear structure; using this approach we are able to fit both our
scale-free results and also our previous CDM data. This approach is more
accurate than the commonly-used Peacock--Dodds formula and should be applicable
to more general power spectra. Code to evaluate nonlinear power spectra using
this method is available from
http://as1.chem.nottingham.ac.uk/~res/software.html Following publication, we
will make the power-law simulation data available through the Virgo website
http://www.mpa-garching.mpg.de/Virgo


title: Instabilities in two-fluid magnetized media with inter-component drift

abstract:
  We analyse the stability of a magnetized medium consisting of a neutral fluid
and a fluid of charged particles, coupled to each other through a drag force
and exposed to differential body forces (for example, as the result of
radiation forces on one phase). We consider a uniform equilibrium and simple
model input physics, but do not arbitrarily restrict the relative orientations
of the magnetic field, slip velocity and wave vector of the disturbance. We
find several instabilities and classify these in terms of wave resonances. We
briefly apply our results to the structure of SiO maser regions appearing in
the winds from late-type stars.


title: SCUBA observations of the host galaxies of four dark gamma-ray bursts

abstract:
  We present the results of a search for submillimetre-luminous host galaxies
of optically dark gamma-ray bursts (GRBs) using the Submillimetre Common-User
Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). We made
photometry measurements of the 850-micron flux at the location of four `dark
bursts', which are those with no detected optical afterglow despite rapid deep
searches, and which may therefore be within galaxies containing substantial
amounts of dust. We were unable to detect any individual source significantly.
Our results are consistent with predictions for the host galaxy population as a
whole, rather than for a subset of dusty hosts. This indicates that optically
dark GRBs are not especially associated with very submillimetre-luminous
galaxies and so cannot be used as reliable indicators of dust-enshrouded
massive star-formation activity. Further observations are required to establish
the relationship between the wider GRB host galaxy population and SCUBA
galaxies.


title: Model Atmosphere Analysis of Two Very Cool White Dwarfs

abstract:
  A detailed analysis of the very cool white dwarfs SDSS 1337+00 and LHS 3250
is presented. Model atmosphere calculations with improved collision-induced
absorptions by molecular hydrogen indicate that a pure hydrogen composition can
be ruled out, and that the strong infrared absorption observed in these cool
stars is better explained in terms of collisions of H2 with neutral helium. It
is shown that even though the overall shape of the observed energy
distributions can be reproduced reasonably well with helium-rich models, the
peak of the energy distribution near 6000 A is always predicted too narrow. The
extreme helium-rich composition inferred for both objects is discussed in the
broader context of the extremely cool white dwarfs reported in various surveys.


title: The long-term effect of radio sources on the ICM

abstract:
  We have performed 3D hydrodynamical simulations of FR-II radio sources in
beta-profile cooling-flow clusters. The effects of cooling of the cluster gas
were incorporated into a modified version of the ZEUS-MP code. The simulations
followed not only the active phase of the radio source, but also the long term
behaviour for up to 2 Gyr after the jets of the radio source were switched off.
We find as expected that the radio source has a significant effect on the
cooling flow while it is active, however we also find that the effects of the
radio source on the cluster are long-lived. A buoyancy driven convective flow
is established as the remnants of the radio source rise through the cluster
dragging material from the cluster core. Although the central Mpc of the
cluster reverts to having a cooling flow, this asymmetric convective flow is
able to remove the cool gas accumulating at the cluster core and indeed there
is a net outflow persisting for timescales of about an order of magnitude
longer than the time for which the source is active or longer. The convective
flow may also provide a mechanism to enhance the metallicity of the cluster gas
at large cluster radii.


title: What Happened to the NGC 6251 Counterjet?

abstract:
  We have used the VLBA to produce a high dynamic range image of the nucleus of
NGC 6251 at 1.6 GHz and snapshot images at 5.0, 8.4, and 15.3 GHz to search for
emission from a parsec-scale counterjet. Previous VLBI images at 1.6 GHz have
set a lower limit for the jet/counterjet brightness ratio near the core at
about 80:1, which is larger than expected given the evidence that the radio
axis is fairly close to the plane of the sky. A possible explanation is that
the inner few pc of the counterjet is hidden by free-free absorption by ionized
gas associated with an accretion disk or torus. This would be consistent with
the nearly edge-on appearance of the arcsecond-scale dust disk seen in the
center of NGC 6251 by HST. We detect counterjet emission close to the core at
1.6 GHz, but not at the higher frequencies. Given that the optical depth of
free-free absorption falls off more rapidly with increasing frequency than the
optically thin synchrotron emission from a typical radio jet, this result
implies that the absence of a detectable parsec-scale counterjet at high
frequencies is not due to free-free absorption unless the density of ionized
gas is extremely high and we have misidentified the core at 1.6 GHz. The most
likely alternative is a large jet/counterjet brightness ratio caused by
relativistic beaming, which in turn requires the inner radio axis to be closer
to our line of sight than the orientation of the HST dust disk would suggest.


title:
XENON: a 1 tonne Liquid Xenon Experiment for a Sensitive Dark Matter
  Search

abstract:
  XENON is a novel liquid xenon experiment concept for a sensitive dark matter
search using a 1-tonne active target, distributed in an array of ten
independent time projection chambers. The design relies on the simultaneous
detection of ionization and scintillation signals in liquid xenon, with the
goal of extracting as much information as possible on an event-by-event basis,
while maintaining most of the target active. XENON is expected to have
effective and redundant background identification and discrimination power,
higher than 99.5%, and to achieve a very low threshold, on the order of 4 keV
visible recoil energy.
  Based on this expectation and the 1-tonne mass of active xenon, we project a
sensitivity of 0.0001 events/kg/day, after 3 yr operation in an appropriate
underground location. The XENON experiment has been recently proposed to the
National Science Foundation (NSF) for an initial development phase leading to
the development of the 100 kg unit module.


title:
Non-thermal emission from extragalactic radio sources: a high resolution
  broad band (radio to X-rays) approach

abstract:
  In the framework of the study of extragalactic radio sources, we will focus
on the importance of the spatial resolution at different wavelengths, and of
the combination of observations at different frequency bands. In particular, a
substantial step forward in this field is now provided by the new generation
X-ray telescopes which are able to image radio sources in between 0.1--10 keV
with a spatial resolution comparable with that of the radio telescopes (VLA)
and of the optical telescopes. After a brief description of some basic aspects
of acceleration mechanisms and of the radiative processes at work in the
extragalactic radio sources, we will focus on a number of recent radio, optical
and X-ray observations with arcsec resolution, and discuss the deriving
constraints on the physics of these sources.


title: 2MASS Data Mining and the M, L, and T Dwarf Archives

abstract:
  Studies of brown dwarfs as a distinct galactic population have been largely
pioneered by dedicated, vast-area surveys at deep optical and near-infrared
wavebands. The Two Micron All Sky Survey has, because of its full-sky coverage
and depth, been the most successful at providing new targets for further study.
The author briefly reviews some of the ways in which 2MASS data have been used
by brown dwarf researchers. One of the by-products -- namely the 2MASS Team's
follow-up spectroscopy of brown dwarf candidates -- is potentially valuable as
a scientific resource itself and is also being released to the public.


title: Improved constraints on supersymmetric dark matter from muon g-2

abstract:
  The new measurement of the anomalous magnetic moment of the muon by the
Brookhaven AGS experiment 821 again shows a discrepancy with the Standard Model
value. We investigate the consequences of these new data for neutralino dark
matter, updating and extending our previous work [E. A. Baltz and P. Gondolo,
Phys. Rev. Lett. 86, 5004 (2001)]. The measurement excludes the Standard Model
value at 2.6sigma confidence. Taking the discrepancy as a sign of
supersymmetry, we find that the lightest superpartner must be relatively light
and it must have a relatively high elastic scattering cross section with
nucleons, which brings it almost within reach of proposed direct dark matter
searches. The SUSY signal from neutrino telescopes correlates fairly well with
the elastic scattering cross section. The rate of cosmic ray antideuterons
tends to be large in the allowed models, but the constraint has little effect
on the rate of gamma ray lines. We stress that being more conservative may
eliminate the discrepancy, but it does not eliminate the possibility of high
astrophysical detection rates.


title: Tracing Black Hole Mergers Through Radio Lobe Morphology

abstract:
  Binary supermassive black holes are produced by galactic mergers as the black
holes from the two galaxies fall to the center of the merged system and form a
bound pair. The two black holes will eventually coalesce in an enormous burst
of gravitational radiation. Here we show that the orientation of a black hole's
spin axis would change dramatically even in a minor merger, leading to a sudden
flip in the direction of any associated jet. We identify the winged or X-type
radio sources with galaxies in which this has occurred. The implied coalescence
rate is similar to the overall galaxy merger rate, suggesting that the
prospects are good for observing gravitational waves from coalescing
supermassive black holes.


title:
Importance of Cluster Structural Evolution in Using X-ray and SZE Galaxy
  Cluster Surveys to Study Dark Energy

abstract:
  We examine the prospects for measuring the dark energy equation of state
parameter w within the context of the still uncertain redshift evolution of
galaxy cluster structure. We show that for a particular X-ray survey (SZE
survey) the constraints on w degrade by roughly a factor of 3 (factor of 2)
when one accounts for the possibility of non--standard cluster evolution. With
followup measurements of a cosmology independent, mass--like quantity it is
possible to measure cluster evolution, improving constraints on cosmological
parameters (like w Omega_M). We examine scenarios where 1%, 10% and 100% of
detected clusters are followed up, showing that even a modest followup program
can enhance the final cosmological constraints. For the case of followup
measurements on 1% of the cluster sample with an uncertainty of 30% on
individual cluster mass--like quantities, constraints on w are improved by a
factor of 2 to 3. For the best case scenario of a zero curvature universe,
these particular X-ray and SZE surveys can deliver uncertainties on w of ~4% to
6%.


title: Lyman-alpha absorption around nearby galaxies

abstract:
  We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption lines
in the outer regions of eight nearby galaxies using background QSOs and AGN as
probes. Lya lines are detected within a few hundred km/s of the systemic
velocity of the galaxy in all cases. We conclude that a background
line-of-sight which passes within 26-200 h-1 kpc of a foreground galaxy is
likely to intercept low column density neutral hydrogen with log N(HI) >~ 13.0.
The ubiquity of detections implies a covering factor of ~ 100% for low N(HI)
gas around galaxies within 200 h-1 kpc. We discuss the difficulty in trying to
associate individual absorption components with the selected galaxies and their
neighbors, but show that by degrading our STIS data to lower resolutions, we
are able to reproduce the anti-correlation of Lya equivalent width and impact
parameter found at higher redshift. We also show that the equivalent width and
column density of Lya complexes (when individual components are summed over ~
1000 km/s) correlate well with a simple estimate of the volume density of
galaxies brighter than M(B) = -17.5 at the same redshift as a Lya complex. We
do not reject the hypothesis that the selected galaxies are directly
responsible for the observed Lya lines, but our analysis indicates that
absorption by clumpy intragroup gas is an equally likely explanation. (Abriged)


title: Stellar Halo Parameters from 4588 Subdwarfs

abstract:
  Using a reduced proper motion discriminator, I obtain a sample of 4588
subdwarfs from the Revised NLTT Catalog of Salim & Gould. The ample statistics
and low contamination permit much more precise determinations of halo
parameters than has previously been possible. The stellar halo is not moving
with respect to the Local Standard of Rest (LSR) in either the vertical or
radial direction, up to uncertainties of 2 km/s. This indicates that either the
LSR is on a circular orbit or the Sun happens to lie very close to an extremum
of the LSR's elliptical orbit. Similarly, tentative detections of vertical
proper motion of Sgr A* relative to the LSR are either incorrect or they
reflect real physical motion of the central black hole relative to the Galactic
potential. The correlation coefficients of the halo velocity ellipsoid, which
would reflect any possible misalignment between its principal axes and the
cardinal directions of the Galaxy, vanish to within 2%. The halo subdwarf
luminosity function peaks at M_V ~ 10.5 with a full width half maximum of about
2.5 mag.


title:
Cosmological Implications of the BIMA 30 Ghz Sunyaev-Zel'dovich Effect
  Galaxy Cluster Survey

abstract:
  We explore the cosmological implications of 7 deep survey fields observed at
the Berkeley-Illinois-Maryland Association (BIMA) Array with 30 GHz receivers.
These observations probe the Cosmic Microwave Background anisotropy on scales
corresponding to l=5500, and an earlier analysis of these data detected no
galaxy clusters. We use numerical cluster simulations and mock observations to
characterize the cluster detection efficiency for each of the BIMA fields. With
these detection efficiencies we derive constraints on the cosmological
parmaters OmegaM and sigma8, ruling out those models which overproduce galaxy
clusters. Using only these seven BIMA fields, we calculate a 2sigma upper limit
of sigma8 < 1.00OmegaM**(-0.43OmegaM-0.22) for flat models with 0.1<OmegaM<1.
When the power spectrum of density fluctuations is COBE normalized, we find
OmegaM < 0.63 at 95% confidence level for flat models. This constraint includes
our estimate of the large uncertainties in the SZE flux-virial mass
relationship as well as published uncertainties in the Hubble parameter, the
COBE power spectrum normalization and the primordial power spectrum index. In
addition, we account for the effects of sample variance. Thus, we conclude that
the non-detections are to be expected in a low OmegaM universe, given the
sensitivity and solid angle of the deepest SZE survey to date.


title: Search for Point Sources of High Energy Neutrinos with AMANDA

abstract:
  This paper describes the search for astronomical sources of high-energy
neutrinos using the AMANDA-B10 detector, an array of 302 photomultiplier tubes,
used for the detection of Cherenkov light from upward traveling
neutrino-induced muons, buried deep in ice at the South Pole. The absolute
pointing accuracy and angular resolution were studied by using coincident
events between the AMANDA detector and two independent telescopes on the
surface, the GASP air Cherenkov telescope and the SPASE extensive air shower
array. Using data collected from April to October of 1997 (130.1 days of
livetime), a general survey of the northern hemisphere revealed no
statistically significant excess of events from any direction. The sensitivity
for a flux of muon neutrinos is based on the effective detection area for
through-going muons. Averaged over the Northern sky, the effective detection
area exceeds 10,000 m^2 for E_{mu} ~ 10 TeV. Neutrinos generated in the
atmosphere by cosmic ray interactions were used to verify the predicted
performance of the detector. For a source with a differential energy spectrum
proportional to E_{nu}^{-2} and declination larger than +40 degrees, we obtain
E^2(dN_{nu}/dE) <= 10^{-6}GeVcm^{-2}s^{-1} for an energy threshold of 10 GeV.


title: Radiative Heat Conduction and the Magnetorotational Instability

abstract:
  A photon or neutrino gas--semi-contained by a baryonic species through
scattering--comprises a rather peculiar MHD fluid where the magnetic field is
truly frozen only to the co-moving volume associated with the mass density.
Although radiative diffusion precludes an adiabatic treatment of compressive
perturbations, we show that the energy equation may be cast in
"quasi-adiabatic" form for exponentially growing non-propagating wave modes.
Defining a generalized quasi-adiabatic index leads to a relatively
straightforward dispersion relation for non-axisymmetric magnetorotational
modes in the horizontal regime when an accretion disk has comparable stress
contributions from diffusive and non-diffusive particle species. This analysis
is generally applicable to optically thick, neutrino-cooled disks since the
pressure contributions from photons, pairs and neutrinos, all have the same
temperature dependence whereas only the neutrino component has radiative heat
conduction properties on the time and length scales of the instability. We
discuss the energy deposition process and the temporal and spatial properties
of the ensuing turbulent disk structure on the basis of the derived dispersion
relation.


title: Discovery of GRB 020405 and its Late Red Bump

abstract:
  We present the discovery of GRB 020405 made with the Inter-Planetary Network
(IPN). With a duration of 60 s, the burst appears to be a typical long duration
event. We observed the 75-square acrminute IPN error region with the Mount
Stromlo Observatory's 50-inch robotic telescope and discovered a transient
source which subsequently decayed and was also associated with a variable radio
source. We identify this source as the afterglow of GRB 020405. Subsequent
observations by other groups found varying polarized flux and established a
redshift of 0.690 to the host galaxy. Motivated by the low redshift we
triggered observations with WFPC2 on-board the Hubble Space Telescope (HST).
Modeling the early ground-based data with a jet model, we find a clear red
excess over the decaying optical lightcurves that is present between day 10 and
day 141 (the last HST epoch). This `bump' has the spectral and temporal
features expected of an underlying supernova (SN). In particular, the red color
of the putative SN is similar to that of the SN associated with GRB 011121, at
late time. Restricting the sample of GRBs to those with z<0.7, a total of five
bursts, red bumps at late times are found in GRB 970228, GRB 011121, and GRB
020405. It is possible that the simplest idea, namely that all long duration
GRBs have underlying SNe with a modest dispersion in their properties
(especially peak luminosity), is sufficient to explain the non detections.


title: The FUSE survey of OVI absorption in and near the Galaxy

abstract:
  We present FUSE observations of OVI absorption in a sample of 100
extragalactic targets and 2 distant halo stars. We describe the details of the
calibration, alignment in velocity, continuum fitting, and manner in which
contaminants were removed (Galactic H2, absorption intrinsic to the background
target and intergalactic Ly-beta lines). We searched for OVI absorption in the
velocity range -1200 to 1200 km/s. With a few exceptions, we only find OVI
between -400 and 400 km/s; the exceptions may be intergalactic OVI. We discuss
the separation of the observed OVI absorption into components associated with
the Galactic halo and components at high-velocity, which are probably located
in the neighborhood of the Galaxy. We describe the measurements of equivalent
width and column density, and we analyze the different contributions to the
errors. We conclude that low-velocity Galactic OVI absorption occurs along all
sightlines - the few non-detections only occur in noisy spectra. We further
show that high-velocity OVI is very common, having equivalent width >65 mAA in
50% of the sightlines and >30 mAA in 70% of the high-quality sightlines. The
high-velocity OVI absorption has velocities relative to the LSR of
+/-(100--330) km/s; there is no correlation between velocity and absorption
strength. We present 50 km/s wide OVI channel maps. These show evidence for the
imprint of Galactic rotation. They also highlight two known HI high-velocity
clouds (complex~C and the Magellanic Stream). The channel maps further show
that OVI at velocities <-200 km/s occurs along all sightlines in the region
l=20-150, b<-30, while OVI at velocities >200 km/s occurs along all sightlines
in the region l=180-300, b>20 (abbreviated).


title:
Comparing WIMP Interaction Rate Detectors with Annual Modulation
  Detectors

abstract:
  We compare the sensitivity of WIMP detection via direct separation of
possible signal vs. background to WIMP detection via detection of an annual
modulation, in which signal and background cannot be separated on an
event-by-event basis. In order to determine how the constraints from the two
different types of experiments might be combined an adequate incorporation of
uncertainties due to galactic halo models must be made. This issue is
particularly timely in light of recent direct detection limits from Edelweiss
and CDMS, which we now demonstrate cannot be made consistent with a recent
claimed DAMA annual modulation observation, even by including halo
uncertainties. On the other hand, we demonstrate that a combination of these
two techniques, in the event of any positive direct detection signal, could
ultimately allow significant constraints on anisotropic halo models even
without directional sensitivity in these detectors.


title:
Modeling the Spectral Signatures of Accretion Disk Winds: A New Monte
  Carlo Approach

abstract:
  Bipolar outflows are present in many disk-accreting astrophysical systems. In
disk-accreting cataclysmic variables (CVs), these outflows are responsible for
most of the strong features in the ultraviolet spectra of these systems.
However, there have been few attempts to model these features quantitatively.
Here, we describe a new, hybrid Monte Carlo/Sobolev code, which allows us to
synthesize the complete spectrum of a disk-dominated, mass-losing CV.
  The line profiles we calculate for C IV resemble those calculated by previous
workers when an identical geometry is assumed. However, our synthetic spectra
exhibit not only the well-known resonance lines of O VI, N V, Si IV and C IV,
but, with an appropriate choice of mass-loss rate and wind geometry, also many
lines originating from excited lower states. Many of these lines have already
been seen in the far ultraviolet spectra of CVs obtained with HUT, FUSE, and
HST. In order to illustrate the degree to which we are currently able to
reproduce observed spectra, we finally present a preliminary fit to the Hopkins
Ultraviolet Telescope spectrum of the dwarf nova Z Cam in outburst.


title:
The Far Ultraviolet Spectroscopic picture of the Missing Baryons in the
  Local Group

abstract:
  The number of detected baryons in the low-redshift Universe (z < 1) is far
small er than the corresponding number of baryons observed at higher redshift.
According to hydrodynamical simulations for the formation of structure in the
Universe, up to 2/3 of the 'missing baryons' may have escaped identification so
far, due to their high temperature and low density. One of the few ways to
detect this matter is to look for its UV absorption signature on the light from
background sources. Here we show that the amplitude of the average velocity
vector of 'high velocity' OVI absorbers detected in a UV survey of AGN
decreases significantly in moving from the Local Standard of Rest, to the
Galactic Standard of Rest and Local Group frames. At least 82 % of these
absorbers are not associated with any 'high velocity' HI complex (HV-HI) in our
Galaxy, and so are strongly implicated as being due to primordial Warm-Hot
Intergalactic Medium (WHIM) pervading an extended Galactic Corona or our Local
Group. We estimate that the total baryonic mass contained in this medium is as
large as ~ 1e12 solar masses, similar to the combined mass of the two most
massive virialized constituents of the Local Group (the Andromeda and the Milky
Way galaxies), and of the order of the mass required to dynamically stabilize
the Local Group.


title: X-Ray Synchrotron Emitting Fe-Rich Ejecta in SNR RCW 86

abstract:
  Supernova remnants may exhibit both thermal and nonthermal X-ray emission. We
present Chandra observations of RCW 86. Striking differences in the morphology
of X-rays below 1 keV and above 2 keV point to a different physical origin.
Hard X-ray emission is correlated fairly well with the edges of regions of
radio emission, suggesting that these are the locations of shock waves at which
both short-lived X-ray emitting electrons, and longer-lived radio-emitting
electrons, are accelerated. Soft X-rays are spatially well-correlated with
optical emission from nonradiative shocks, which are almost certainly portions
of the outer blast wave. These soft X-rays are well fit with simple thermal
plane-shock models. Harder X-rays show Fe K alpha emission and are well
described with a similar soft thermal component, but a much stronger
synchrotron continuum dominating above 2 keV, and a strong Fe K alpha line.
Quantitative analysis of this line and the surrounding continuum shows that it
cannot be produced by thermal emission from a cosmic-abundance plasma; the
ionization time is too short, as shown both by the low centroid energy (6.4
keV) and the absence of oxygen lines below 1 keV. Instead, a model of a plane
shock into Fe-rich ejecta, with a synchrotron continuum, provides a natural
explanation. This requires that reverse shocks into ejecta be accelerating
electrons to energies of order 50 TeV. We show that maximum energies of this
order can be produced by radiation-limited diffusive shock acceleration at the
reverse shocks.


title: Parallaxes of Brown Dwarfs at USNO

abstract:
  Trigonometric parallaxes have been measured by Dahn et al. (2002) for 28 cool
dwarfs and brown dwarfs, including 17 L dwarfs and three T dwarfs. Broadband
CCD and near-IR photometry (VRIz*JHK) have been obtained for these objects and
for 24 additional late-type dwarfs. These data have been supplemented with
astrometry and photometry from the literature, including parallaxes for the
brighter companions of ten L and two T dwarfs. The absolute magnitudes and
colors are reviewed here. The I-J color and the spectral type are both good
predictors of absolute magnitude for late-M and L dwarfs. M_J becomes
monotonically fainter with I-J color and with spectral type through late-L
dwarfs, then brightens for early-T dwarfs. In contrast, the J-K color
correlates poorly with absolute magnitude for L dwarfs. Using several other
parameters from the literature (Li detection, H-alpha emission strength,
projected rotation velocity, and tangential velocity), we fail to uncover any
measurable parameter that correlates with the anomalous J-K color.


title: Braneworld Tensor Anisotropies in the CMB

abstract:
  Cosmic microwave background (CMB) observations provide in principle a
high-precision test of models which are motivated by M theory. We set out the
framework of a program to compute the tensor anisotropies in the CMB that are
generated in braneworld models. In the simplest approximation, we show the
braneworld imprint as a correction to the power spectra for standard
temperature and polarization anisotropies.


title:
Modelling of intermediate-age stellar populations: III Effects of
  dust-shells around AGB stars

abstract:
  In this paper,we present single stellar population models of intermediate age
stellar populations where dust-enshrouded AGB stars are introduced. The
formation of carbon stars is also accounted for, and is taken to be a function
of both initial mass and metallicity. The effect of the dusty envelopes around
AGB stars on the optical/near-infrared spectral energy distribution were
introduced using semi-emipirical models where the mass-loss and the
photospheric chemistry determine the spectral properties of a star along the
AGB sequence. The spectral dichotomy between O-rich stars and C-rich stars is
taken into account in the modelling. We have investigated the AGB sequence
morphology in he near-infrared CMD as a function of time and metallicity. We
show that this diaggram is characterized by three morphological features,
occupied by optically bright O-rich stars, optically bright C-rich stars, and
dust-enshrouded O-rich and C-rich stars respectively. Our models are able to
reproduce the distribution of the three AGB subtype stellar populations in
colour-colour diagrams. Effects of dusty envelopes on the luminosity function
are also investigated (Abriged).


title: An Unexpectedly High AGN Fraction in Red Cluster Galaxies

abstract:
  As part of a program to study the evolution of active galactic nuclei (AGN)
in clusters of galaxies, we present our results for Abell 2104. A deep Chandra
observation of this massive, z = 0.154 cluster reveals a significant X-ray
point source excess over the expectations of blank fields, including eight
X-ray counterparts with R<20 mag. Our spectroscopy shows that all six X-ray
sources associated with red counterparts are cluster members and their X-ray
properties are consistent with all of them being AGN. Only one of the six has
the emission lines characteristic of optically selected AGN; the remaining five
would not have been classified as AGN based on their optical spectra. This
suggests the existence of a large population of obscured, or at least optically
unremarkable, AGN in clusters of galaxies. These six sources correspond to a
lower limit of ~5% of the AGN fraction in cluster galaxies with R<20 mag
(rest-frame M_V = -19.5 mag) and is comparable to the blue galaxy fraction in
the cluster. Such an obscured AGN population in clusters of galaxies has many
implications for cluster galaxy evolution, the hidden growth of their central,
supermassive black holes, estimates of the star formation rate at infrared and
radio wavelengths, and the observed variance in the hard X-ray background.


title: Molecular Gas and Star Formation in Bars of Nearby Spiral Galaxies

abstract:
  We compare the distribution of molecular gas and star formation activity in
the bar region of six spirals (NGC 2903, NGC 3627, NGC 4321, NGC 5457, NGC
6946, & IC 342) from the BIMA Survey of Nearby Galaxies (SONG). The molecular
gas, traced using the CO (J=1--0) emission line, is brightest along the leading
edge of the stellar bar in the bar dust lanes. The star formation activity,
traced using the Halpha emission line, is offset towards the leading side of
the CO emission. A cross-correlation analysis shows that a) the HII regions are
offset 0--800 pc on the leading side of the CO emission, b) the largest offsets
are found in the strongest bars, and c) there is a wide range in offsets in a
single bar with no systematic pattern as a function of the galacto-centric
radius. The CO-Halpha offset constrains how stars may form depending on the gas
flow. We examine possible star formation scenarios in context of the two main
classes of bar gas flow simulations, the N-body/sticky particle and
hydrodynamic models. Though both model gas flows are generally consistent with
the observed offsets, we suggest the inclusion of a two- or multi-phase medium
to improve the agreement between models and observation.


title:
Chemical Composition of the Carbon-rich, Extremely Metal-Poor Star CS
  29498--043: A New Class of Extremely Metal-Poor Stars with Excesses of
  Magnesium and Silicon

abstract:
  We analyze a high-resolution, high signal-to-noise spectrum of the
carbon-rich, extremely metal-poor star CS29498-043, obtained with the Subaru
Telescope High Dispersion Spectrograph. We find its iron abundance is extremely
low ([Fe/H] = -3.7), placing it among the few stars known with [Fe/H] < -3.5,
while Mg and Si are significantly overabundant ([Mg/Fe] = +1.8, and [Si/Fe] =
+1.1) compared with stars of similar metallicity without carbon excess.
Overabundances of N and Al were also found. These characteristics are similar
to the carbon-rich, extremely metal-poor star CS22949-037. Though the sample is
small, our discovery of CS29498-043 suggests the existence of a class of
extremely metal-poor stars with large excesses of C, N, Mg, and Si.


title:
A Subaru/HDS study of Lead (Pb) abundances in eight
  s-process-element-rich, metal-poor stars

abstract:
  We report the abundances of neutron-capture elements in eight carbon-rich,
metal-poor (-2.7=<[Fe/H]=<-1.9) stars observed with the Subaru Telescope High
Dispersion Spectrograph. The derived abundance patterns indicate that the
neutron-capture elements in these objects primarily originated from s-process
nucleosynthesis, although the [Ba/Eu] abundance ratios in some objects are
lower than that of the solar-system s-process component. The present analysis
has yielded the Pb abundances for seven objects, as well as an upper limit for
one object, from use of the Pb I 4057A and 3683A lines. The values of [Pb/Ba]
in these objects cover a wide range, between -0.3 and +1.2. Theoretical studies
of s-process nucleosynthesis at low metallicity are required to explain this
large dispersion of the [Pb/Ba] values. Variations in radial velocity have been
found for two of the eight objects, suggesting that, at least in these
instances, the observed excess of s-process elements is due to the transfer of
material across a binary system including an AGB star. Comparisons with
predictions of AGB nucleosynthesis models are discussed.


title:
Radio ejection in the evolution of X-ray binaries: the bridge between
  low mass X-ray binaries and millisecond pulsars

abstract:
  We present a scenario for the spin-up and evolution of binary millisecond
pulsars. This can explain the observational properties of the recently
discovered binary millisecond pulsar PSR J1740-5340, with orbital period 32.5
hrs, in the Globular Cluster NGC 6397. The optical counterpart of this system
is a star as luminous as the cluster turnoff stars, but with a lower Teff (a
larger radius) which we model with a star of initial mass compatible with the
masses evolving in the cluster (~0.85 Msun). This star has suffered Roche lobe
overflow while evolving off the main sequence, spinning up the neutron star to
the present period of 3.65 ms. There are evidences that at present, Roche lobe
overflow is still going on. Indeed Roche lobe deformation of the mass losing
component is necessary to be compatible with the optical light curve. The
presence of matter around the system is also consistent with the long lasting
irregular radio eclipses seen in the system. We propose that this system is
presently in a phase of `radio-ejection' mass loss. The radio-ejection phase
can be initiated only if the system is subject to intermittency in the mass
transfer during the spin-up phase. In fact, when the system is detached the
pulsar radio emission is not quenched, and may be able to prevent further mass
accretion due to the action of the pulsar pressure at the inner Lagrangian
point.


title: GMRT radio observations of microquasar GRS 1915+105

abstract:
  We have observed microquasar GRS 1915+105 at 1.28 GHz for 8 days from June 18
to July 1, 2001 using Giant Metrewave Radio Telescope (GMRT). We have seen
several isolated radio baby flares of varying intensity and duration. We have
also observed broad composite flares with rise and decay times of few hours on
June 28-29, 2001 few days prior to when source went to the ``plateau radio
state'' on 3rd July, 2001. These broad radio flares consist of several
overlapping baby radio flares. The source was in the low-hard X-ray state
during this period. We compare these results with 15 GHz radio data from the
Ryle telescope.


title: Statistics of Neutral Regions During Hydrogen Re-Ionization

abstract:
  We present predictions for two statistical measures of the hydrogen
reionization process at high redshift. The first statistic is the number of
neutral segments identified in spectra of high redshift QSOs as a function of
their length. The second is the cross-correlation of neutral regions with
possible sources of ionizing radiation. These independent probes are sensitive
to the topology of the ionized regions. If reionization proceeded from high to
low density regions then the cross-correlation will be negative, while if voids
were ionized first then we expect a positive correlation and a relatively small
number of long neutral segments. We test the sensitivity of these statistics
for reionization by stars in high redshift galaxies. The flux of ionizing
radiation emitted from stars is estimated by identifying galaxies in an N-body
simulation using a semi-analytic galaxy formation model. The spatial
distribution of ionized gas is traced in various models for the propagation of
the ionization fronts. A model with ionization proceeding from high to low
density regions is consistent with the observations of Becker et al. (2001),
while models in which ionization begins in the lowest density regions appear to
be inconsistent with the present data.


title: White Dwarf Seismology and the ^{12}C(alpha,gamma)^{16}O Rate

abstract:
  Recent determinations of the internal composition and structure of two
helium-atmosphere variable white dwarf stars, GD 358 and CBS 114, have led to
conflicting implied rates for the ^{12}C(alpha,gamma)^{16}O reaction. If we
assume that both stars were formed through single-star evolution, then the
initial analyses of their pulsation frequencies must have differed in some
systematic way. I present improved fits to the two sets of pulsation data,
helping to resolve the tension between the initial results.


title: The Stability Analysis of the HD 82943 and HD 37124 Planetary Systems

abstract:
  We carry out numerical simulations to explore the dynamical evolution of the
HD 82943 and HD 37124 planetary systems,which both have two Jupiter-like
planets. By simulating various planetary configurations in the neighborhood of
the fitting orbits, we find three mechanisms to maintain the stability of these
systems: For HD 82943,we find that the 2:1 mean motion resonance can act as the
first mechanism for all the stable orbits. The second mechanism is the
alignment of the periastron of the two planets of HD 82943 system. In the
paper,we show one case is simultaneously maintained by the two mechanisms.
Additionally,we also use the corresponding analytical models successfully to
explain the different numerical results for the system. The third mechanism is
the Kozai resonance which takes place in the mutual highly orbits of HD 37124.
In the simulations,we discover that the argument of periastron $\omega$ of the
inner planet librates about $90^{\circ}$ or $270^{\circ}$ for the whole time
span. The Kozai mechanism can explain the stable configuration of large
eccentricity of the inner planet.


title: Relations Between Environments of Quasars and Galaxy Formation

abstract:
  We investigate the environments of quasars such as number distribution of
galaxies using a semi-analytic model which includes both galaxy and quasar
formations based on the hierarchical clustering scenario. We assume that a
supermassive black hole is fueled by accretion of cold gas and that it is a
source of quasar activity during a major merger of the quasar host galaxy with
another galaxy. This major merger causes spheroid formation of the host galaxy.
Our model can reproduce not only general form of the galaxy luminosity
functions in the local Universe but also the observed relation between a
supermassive black hole mass and a spheroid luminosity, the present black hole
mass function and the quasar luminosity functions at different redshifts. Using
this model, we predict the mean number of quasars per halo, bias parameter of
quasars and the probability distribution of the number of galaxies around
quasars. In our model, analysis of the mean number of quasars per halo shows
that the spatial distribution of galaxies is different from that of quasars.
Furthermore, we found from calculation of the probability distribution of
galaxy numbers that at $0.2 \lesssim z \lesssim 0.5$, most quasars are likely
to reside in galaxy groups. On the other hand, at $1 \lesssim z \lesssim 2$
most quasars seem to reside in more varied environments than at a lower
redshift; quasars reside in environments ranging from small groups of galaxies
to clusters of galaxies. Comparing these predictions with observations in
future will enable us to constrain our quasar formation model.


title: Cosmic Microwave Background Temperature at Galaxy Clusters

abstract:
  We have deduced the cosmic microwave background (CMB) temperature in the Coma
cluster (A1656, $z=0.0231$), and in A2163 ($z=0.203$) from spectral
measurements of the Sunyaev-Zel'dovich (SZ) effect over four passbands at radio
and microwave frequencies. The resulting temperatures at these redshifts are
$T_{Coma} = 2.789^{+0.080}_{-0.065}$ K and $T_{A2163} =
3.377^{+0.101}_{-0.102}$ K, respectively. These values confirm the expected
relation $T(z)=T_{0}(1+z)$, where $T_{0}= 2.725 \pm 0.002$ K is the value
measured by the COBE/FIRAS experiment. Alternative scaling relations that are
conjectured in non-standard cosmologies can be constrained by the data; for
example, if $T(z) = T_{0}(1+z)^{1-a}$ or $T(z)=T_{0}[1+(1+d)z]$, then
$a=-0.16^{+0.34}_{-0.32}$ and $d = 0.17 \pm 0.36$ (at 95% confidence). We
briefly discuss future prospects for more precise SZ measurements of $T(z)$ at
higher redshifts.


title: Neutron star/supernova remnant associations: the view from Tbilisi

abstract:
  We propose a new approach for studying the neutron star/supernova remnant
associations, based on the idea that the supernova remnants (SNRs) can be
products of an off-centered supernova (SN) explosion in a preexisting bubble
created by the wind of a moving massive star. A cavity SN explosion of a moving
star results in a considerable offset of the neutron star (NS) birth-place from
the geometrical center of the SNR. Therefore: a) the high transverse velocities
inferred for a number of NSs through their association with SNRs can be
reduced; b) the proper motion vector of a NS should not necessarily point away
from the geometrical center of the associated SNR. Taking into account these
two facts allow us to enlarge the circle of possible NS/SNR associations, and
could significantly affect the results of previous studies of associations. The
possibilities of our approach are illustrated with some examples. We also show
that the concept of an off-centered cavity SN explosion could be used to
explain the peculiar structures of a number of SNRs and for searches for
stellar remnants possibly associated with them.


title: Youn open clusters in the Carina region

abstract:
  We present results of a new investigation (Carraro et al. 2002) aimed at
clarifying the mutual relationship between the most prominent young open
clusters close to eta Carinae, namely Trumpler 16, Trumpler 14 and Collinder
232.


title: Point X-ray sources in the SNR G 315.4-2.30 (MSH 14-63, RCW 86)

abstract:
  We report the results of a search for a point X-ray source (stellar remnant)
in the southwest protrusion of the supernova remnant G 315.4-2.30 (MSH 14-63,
RCW 86) using the archival data of the Chandra X-ray Observatory. The search
was motivated by a hypothesis that G 315.4-2.30 is the result of an
off-centered cavity supernova explosion of a moving massive star, which ended
its evolution just near the edge of the main-sequence wind-driven bubble. This
hypothesis implies that the southwest protrusion in G 315.4-2.30 is the
remainder of a pre-existing bow shock-like structure created by the interaction
of the supernova progenitor's wind with the interstellar medium and that the
actual location of the supernova blast center is near the center of this
hemispherical structure. We have discovered two point X-ray sources in the
"proper" place. One of the sources has an optical counterpart with the
photographic magnitude $13.38\pm0.40$, while the spectrum of the source can be
fitted with an optically thin plasma model. We interpret this source as a
foreground active star of late spectral type. The second source has no optical
counterpart to a limiting magnitude $\sim 21$. The spectrum of this source can
be fitted almost equally well with several simple models (power law: photon
index $=1.87$; two-temperature blackbody: $kT_1 =0.11$ keV, $R_1 =2.34 $ km and
$kT_2 =0.71$ keV, $R_2 =0.06$ km; blackbody plus power law: $kT =0.07$ keV,
photon index $=2.3$). We interpret this source as a candidate stellar remnant
(neutron star), while the photon index and non-thermal luminosity of the source
(almost the same as those of the Vela pulsar and the recently discovered pulsar
PSR J 0205+6449 in the supernova remnant 3C 58) suggest that it can be a young
"ordinary" pulsar.


title: Mapping Initial Hydrostatic Models in Godunov Codes

abstract:
  We look in detail at the process of mapping an astrophysical initial model
from a stellar evolution code onto the computational grid of an explicit,
Godunov type code while maintaining hydrostatic equilibrium. This mapping
process is common in astrophysical simulations, when it is necessary to follow
short-timescale dynamics after a period of long timescale buildup. We look at
the effects of spatial resolution, boundary conditions, the treatment of the
gravitational source terms in the hydrodynamics solver, and the initialization
process itself. We conclude with a summary detailing the mapping process that
yields the lowest ambient velocities in the mapped model.


title:
Early acceleration and adiabatic matter perturbations in a class of
  dilatonic dark-energy models

abstract:
  We estimate the growth of matter perturbations in a class of recently
proposed dark-energy models based on the (loop-corrected) gravi-dilaton string
effective action, and characterized by a global attractor epoch in which
dark-matter and dark-energy density scale with the same effective equation of
state. Unlike most dark-energy models, we find that the accelerated phase might
start even at redshifts as high as z~5 (thus relaxing the coincidence problem),
while still producing at present an acceptable level of matter fluctuations. We
also show that such an early acceleration is not in conflict with the recently
discovered supernova SN1997ff at z~1.7 . The comparison of the predicted value
of sigma_{8} with the observational data provides interesting constraints on
the fundamental parameters of the given model of dilaton-dark matter
interactions.


title: Warm-hot intergalactic baryons revealed

abstract:
  Several popular cosmological models predict that most of the baryonic mass in
the local universe is located in filamentary and sheet-like structures
associated with galaxy overdensities. This gas is expected to be
gravitationally heated to ~10^6 K and therefore emitting in the soft X-rays. We
have detected diffuse soft X-ray structures in a high Galactic latitude ROSAT
field after point source subtraction and correction for Galactic absorption.
These diffuse structures have an X-ray energy distribution that is much softer
than expected from clusters, groups or unresolved emission from AGNs, but are
consistent with that expected from a diffuse warm intergalactic medium. To
discriminate between a Galactic or extragalactic nature of the diffuse gas we
have correlated the soft X--map with multiband optical images in this field. We
have found a significant overdensity of galaxies in correspondence with the
strongest diffuse X-ray structure. The photometric redshift distribution of the
galaxies over the X-ray peak has an excess over field galaxies at z~0.45. This
result strongly suggests that the diffuse X-ray flux is due to extragalactic
emission by warm gas associated with an overdense galaxy region at z~0.45.


title: Supernova-Remnant Origin of Cosmic Rays?

abstract:
  It is thought that Galactic cosmic ray (CR) nuclei are gradually accelerated
to high energies (up to ~300 TeV/nucleon, where 1TeV=10^12eV) in the expanding
shock-waves connected with the remnants of powerful supernova explosions.
However, this conjecture has eluded direct observational confirmation^1,2 since
it was first proposed in 1953 (ref. 3). Enomoto et al.^4 claim to have finally
found definitive evidence that corroborates this model, proposing that the
very-high-energy, TeV-range, gamma-rays from the supernova remnant (SNR) RX
J1713.7-3946 are due to the interactions of energetic nuclei in this region.
Here we argue that their claim is not supported by the existing multiwavelength
spectrum of this source. The search for the origin(s) of Galactic cosmic ray
nuclei may be closing in on the long-suspected supernova-remnant sources, but
it is not yet over.


title: Monte Carlo Study of Supernova Neutrino Spectra Formation

abstract:
  The neutrino flux and spectra formation in a supernova core is studied by
using a Monte Carlo code. The dominant opacity contribution for nu_mu and
nu_tau is elastic scattering on nucleons. In addition we switch on or off a
variety of processes which allow for the exchange of energy or the creation and
destruction of neutrino pairs, notably nucleon bremsstrahlung, the e^+ e^- pair
annihilation process and nu_e-bar nu_e -> nu_{mu,tau} nu_{mu,tau}-bar, recoil
and weak magnetism in elastic nucleon scattering, elastic scattering on
electrons and positrons and elastic scattering on electron neutrinos and
anti-neutrinos. The least important processes are neutrino-neutrino scattering
and e^+ e^- annihilation. The formation of the spectra and fluxes of nu_mu is
dominated by the nucleonic processes, i.e. bremsstrahlung and elastic
scattering with recoil, but also nu_e nu_e-bar annihilation and nu_mu e^\pm
scattering contribute significantly. When all processes are included, the
spectral shape of the emitted neutrino flux is always ``pinched,'' i.e. the
width of the spectrum is smaller than that of a thermal spectrum with the same
average energy. In all of our cases we find that the average nu_mu-bar energy
exceeds the average nu_e-bar energy by only a small amount, 10% being a typical
number. Weak magnetism effects cause the opacity of nu_mu to differ slightly
from that of nu_mu-bar, translating into differences of the luminosities and
average energies of a few percent. Depending on the density, temperature, and
composition profile, the flavor-dependent luminosities L_{nu_e}$, L_{nu_e-bar},
and L_{nu_mu} can mutually differ from each other by up to a factor of two in
either direction.


title:
Exploring physics of rotation powered pulsars with sub-10 GeV imaging
  atmospheric Cherenkov telescopes

abstract:
  We discuss the potential of future sub-10 GeV threshold imaging atmospheric
Cherenkov telescope arrays for exploring the physics of rotation powered
pulsars and their interactions with the ambient medium through relativistic
winds and termination shocks.


title: From Precision Cosmology to Accurate Cosmology

abstract:
  This is the dawning of the age of precision cosmology, when all the important
parameters will be established to one significant figure or better, within the
cosmological model. In the age of accurate cosmology the model, which nowadays
includes general relativity theory and the CDM model for structure formation,
will be checked tightly enough to be established as a convincing approximation
to reality. I comment on how we might make the transition. We already have some
serious tests of gravity physics on the length and time scales of cosmology.
The evidence for consistency with general relativity theory is still rough, but
impressive, considering the enormous extrapolation from the empirical basis,
and these probes of gravity physics will be considerably improved by work in
progress on the cosmological tests. The CDM model has some impressive
observational successes too, and some challenges, not least of which is that
the model is based on a wonderfully optimistic view of the simplicity of
physics in the dark sector. I present as a cautionary example a model for dark
matter and dark energy that biases interpretations of cosmological observations
that assume the CDM model. In short, cosmology has become an empirically rich
subject with a well-motivated standard model, but it needs work to be
established as generally accurate.


title:
Addendum to Astro-ph/0207612: Reflection Symmetry of Cusps in
  Gravitational Lensing

abstract:
  A contour plot of positive iso-J curves is shown for a gravitational binary
lens epsilon_2 = 0.1883 and ell = 0.687. The caustic curve is made of 4-cusped
central caustic (so-called "stealth bomber") on the lens axis and two
triangular caustics off the lens axis. The cusps of the trioids are all
negative cusps. The positive image magnification contours outside the positive
cusps on the lens axis are elongated along the symmetry axis. It is in contrast
with figure 4 of astro-ph/0206162 (Gaudi and Petters) where the contours appear
to contract along the symmetry axis. We apologize if our citation of their
figure 4 without the caution played any role of causing confusion with readers.


title: Violence in the Hearts of Galaxies - Aberration or Adolescence?

abstract:
  Violent activity in the nuclei of galaxies has long been considered a
curiosity in its own right; manifestations of this phenomenon include distant
quasars in the early Universe and comparatively nearby Seyfert galaxies, both
thought to be powered by the release of gravitational potential energy as
material from the host galaxy accretes onto a central supermassive black hole
(SMBH). Traditionally, the broader study of the formation, structure and
evolution of galaxies has largely excluded active galactic nuclei. Recently
however, this situation has changed dramatically, both observationally and
theoretically, with the realisation that the growth and influence of the SMBH,
the origin and development of galaxies and nuclear activity at different epochs
in the Universe may be intimately related. I review the intriguing evidence for
causal links between supermassive black holes, nuclear activity and the
formation and evolution of galaxies, and describe opportunities for testing
these relationships using the next generation of earth-bound and space-borne
astronomical facilities. (Abridged)


title:
Detection of CO emission 12 CO J=1->0 and 12 CO J=2->1 from the Luminous
  Blue Variable Star AG Carinae: circumstellar envelope or disk?

abstract:
  We present the first detection of 12 CO J=2->1 and 12 CO J=1->0 emission from
the LBV AG Carinae. AG Carinae resides in a region which is very rich in
molecular gas with complex motions. We find evidence of a slow outflow of
molecular gas, expanding at ~ 7 km/s. This emission appears spatially
unresolved. We argue that it is spatially localised, rather than extended, and
possibly associated with the immediate circumstellar region of AG Carinae. Does
it originate from a circumstellar envelope, similar to carbon stars, or from a
circumstellar disk? The option of the circumstellar disk is preferable because
it is consistent with additional independent indications for the existence of
wind asymmetries in close proximity to the central star, found from
spectropolarimetry and analysis of the UV and optical line profiles, and it
provides the conditions of density and shielding necessary for the survival of
the CO molecules in proximity to such a hot star (Teff ~ 14000 K - 20000 K). In
the assumption that the CO emission originated when AG Carinae was in an
evolved state, we derive a lower limit to the mass of molecular gas of 2.8
solar masses. This is smaller, but still comparable with the mass of ionized
gas present in the circumstellar environment (4.2 solar masses), with the
implication that the molecular gas fraction can contribute significantly to the
overall mass lost from the central star in its post main sequence evolution.


title:
The phase-space structure of cold dark-matter halos: Insights into the
  Galactic halo

abstract:
  We study the formation of the Milky Way's halo in a $\Lambda$CDM cosmology by
scaling down a high resolution simulation of the formation of a cluster of
galaxies. We determine how much phase-space substructure is left over from the
objects that merge to build up the present galaxy. We study the debris streams
originating from such objects and find that their evolution can be explained
simply in terms of the conservation of phase-space density. Analysing the mass
growth history of our halo we find that its inner regions have been in place
for more than 10 Gyr, but that the growth of the halo as a whole is more
gradual, in agreement with other high resolution simulations of dark-matter
halos. Recent accretion contributes to the inner 10 kpc of the halo only at the
10$^{-4}$ level. Finally we determine the number of dark-matter streams as a
function of distance from the centre of the halo. In the equivalent of the
``Solar vicinity'', we find that the dark-matter is smoothly distributed in
space, and that the velocity ellipsoid is formed by hundreds of thousands of
streams, most of which have velocity dispersions of the order of 1 km/s or
less.


title: Using All-Sky Surveys to Find Planetary Transits

abstract:
  Transits of bright stars offer a unique opportunity to study detailed
properties of extrasolar planets that cannot be determined through
radial-velocity observations. We propose a new technique to find such systems
using all-sky small-aperture transit surveys. We derive a general formula for
the number of stars that can be probed for such systems as a function of the
characteristics of the star, the planet, and the survey. We use this formula to
derive the optimal telescope design for finding transits of bright stars: a 5
cm ``telescope'' with a 4k x 4k camera.


title: Quasar Lensing

abstract:
  Massive structures, such as galaxies, act as strong gravitational lenses on
background sources. When the background source is a quasar, several lensed
images are seen, as magnified or de-magnified versions of the same object. The
detailed study of the image configuration and the measurement of
``time-delays'' between the images yield estimates of the Hubble parameter H_0.
We describe in a simple way the phenomenon of strong lensing and review recent
progress made in the field, including microlensing by stars in the main lensing
galaxy.


title: The Spectrum of the Mass Donor Star in SS 433

abstract:
  We present results from a short series of blue, moderate resolution spectra
of the microquasar binary, SS 433. The observations were made at a time
optimized to find the spectrum of the donor star, i.e., when the donor was in
the foreground and well above the plane of the obscuring disk. In addition to
the well-known stationary and jet emission lines, we find evidence of a weak
absorption spectrum that resembles that of an A-type evolved star. These lines
display radial velocity shifts opposite to those associated with the disk
surrounding the compact star, and they appear strongest when the disk is
maximally eclipsed. All these properties suggest that these absorption lines
form in the atmosphere of the hitherto unseen mass donor star in SS 433. The
radial velocity shifts observed are consistent with a mass ratio M_X / M_O =
0.57 +/- 0.11 and masses of M_O = (19 +/- 7) M_sun and M_X = (11 +/- 5) M_sun.
These results indicate that the system consists of an evolved, massive donor
and a black hole mass gainer.


title: Early Structure Formation and the Epoch of First Light

abstract:
  In popular cold dark matter cosmological scenarios, stars may have first
appeared in significant numbers around a redshift of 10 or so, as the gas
within protogalactic halos with virial temperatures in excess of 20,000 K
(corresponding to masses comparable to those of present--day dwarf ellipticals)
cooled rapidly due to atomic processes and fragmented. It is this `second
generation' of subgalactic stellar systems, aided perhaps by an early
population of accreting black holes in their nuclei, which may have generated
the ultraviolet radiation and mechanical energy that ended the cosmic ``dark
ages'' and reheated and reionized most of the hydrogen in the cosmos by a
redshift of 6. The detailed history of the universe during and soon after these
crucial formative stages depends on the power--spectrum of density fluctuations
on small scales and on a complex network of poorly understood `feedback'
mechanisms, and is one of the missing link in galaxy formation and evolution
studies. The astrophysics of the epoch of first light is recorded in the
thermal state, ionization degree, and chemical composition of the intergalactic
medium, the main repository of baryons at high redshifts.


title: Imbalanced Weak MHD Turbulence

abstract:
  MHD turbulence consists of waves that propagate along magnetic fieldlines, in
both directions. When two oppositely directed waves collide, they distort each
other, without changing their respective energies. In weak MHD turbulence, a
given wave suffers many collisions before cascading. "Imbalance" means that
more energy is going in one direction than the other. In general, MHD
turbulence is imbalanced. A number of complications arise for the imbalanced
cascade that are unimportant for the balanced one.
  We solve weak MHD turbulence that is imbalanced. Of crucial importance is
that the energies going in both directions are forced to equalize at the
dissipation scale. We call this the "pinning" of the energy spectra. It affects
the entire inertial range.
  Weak MHD turbulence is particularly interesting because perturbation theory
is applicable. Hence it can be described with a simple kinetic equation.
Galtier et al. (2000) derived this kinetic equation. We present a simpler, more
physical derivation, based on the picture of colliding wavepackets. In the
process, we clarify the role of the zero-frequency mode. We also explain why
Goldreich & Sridhar claimed that perturbation theory is inapplicable, and why
this claim is wrong. (Our "weak" is equivalent to Goldreich & Sridhar's
"intermediate.")
  We perform numerical simulations of the kinetic equation to verify our
claims. We construct simplified model equations that illustrate the main
effects. Finally, we show that a large magnetic Prandtl number does not have a
significant effect, and that hyperviscosity leads to a pronounced bottleneck
effect.


title:
Horizontal-Branch Morphology and the Photometric Evolution of Old
  Stellar Populations

abstract:
  Theoretical integrated broad-band colors ranging from far-UV to near-IR have
been computed for old stellar systems from our evolutionary population
synthesis code. These models take into account, for the first time, the
detailed systematic variation of horizontal-branch (HB) morphology with age and
metallicity. Our models show that some temperature-sensitive color indices are
significantly affected by the presence of `blue HB stars'. Our models are
calibrated in the B-V, V-I, C-T1, and M-T1 vs. [Fe/H] planes, using
low-reddened Galactic globular clusters (GCs) [E(B-V) < 0.2] and the relative
age difference between the older inner halo Galactic GCs and younger outer halo
counterparts is well reproduced. Several empirical linear color-metallicity
transformation relations are assessed with our models and it is noted that they
may not be safely used to estimate metallicity if there are sizable age
differences amongst GCs within and between galaxies. It is anticipated that the
detailed population models presented here coupled with further precise
spectrophotometric observations of globular cluster systems in external
galaxies from the large ground-based telescopes and space UV facilities will
enable us to accurately estimate their ages and metallicities. (abridged)


title: Domination of black hole accretion in brane cosmology

abstract:
  We consider the evolution of primordial black holes formed during the high
energy phase of the braneworld scenario. We show that the effect of accretion
from the surrounding radiation bath is dominant compared to evaporation for
such black holes. This feature lasts till the onset of matter (or black hole)
domination of the total energy density which could occur either in the high
energy phase or later. We find that the black hole evaporation times could be
significantly large even for black holes with small initial mass to survive
till several cosmologically interesting eras.


title:
Flat Spectrum X-ray Emission from the Direction of a Molecular Cloud
  Associated with SNR RX J1713.7-3946

abstract:
  We report on the discovery of a hard X-ray source with ASCA from a molecular
cloud in the vicinity of the SNR RX J1713.7-3946. The energy spectrum (1--10
keV) shows a flat continuum which is described by a power-law with photon index
1.0 +-0.4. We argue that this unusually flat spectrum can be best interpreted
in terms of characteristic bremsstrahlung emission from the
ionization-loss-flattened distribution of either sub-relativistic protons or
mildly-relativistic electrons. The strong shock of the SNR RX J1713.7-3946,
which presumably interacts with the molecular cloud, as evidenced by
observations of CO-lines, seems to be a natural site of acceleration of such
sub- or mildly-relativistic nonthermal particles. However, the observed X-ray
luminosity of 1.7 10^35 erg/s (for 6 kpc distance) requires that a huge kinetic
energy of about 10^50 erg be released in the form of nonthermal particles to
illuminate the cloud. The shock-acceleration at RX J1713.7-3946 can barely
satisfy this energetic requirement, unless (i) the source is located much
closer than 6 kpc and/or (ii) the mechanical energy of the explosion
essentially exceeds 10^51 erg. Another possibility would be that an essential
part of the "lost" energy is somehow converted to plasma waves, which return
this energy to nonthermal particles through their turbulent reacceleration on
plasma waves. Irrespective of mechanisms responsible for production of
high-energy particles, the flat X-ray emission seems to be a signature of a new
striking energetic phenomenon in molecular clouds.


title:
Weak Gravitational Lensing by a Sample of X-ray Luminous Clusters of
  Galaxies -- III. Serendipitous Weak Lensing Detections of Dark and Luminous
  Mass Concentrations

abstract:
  In the course of a weak gravitational lensing survey of 39 clusters of
galaxies,covering a total sky area of ~1 square degree, we have serendipitously
discovered mass concentrations in the fields of A1705 and A1722 which are most
probably not associated with the main cluster target. By combining weak lensing
information with two-color galaxy photometry in fields centered on our sample
clusters, we identify a new cluster candidate at z~0.5 in the field of A1705.
This cluster candidate also displays strong lensing in the form of a giant
luminous arc. The new mass concentration in the field of A1722 also seems to be
associated with an optically luminous cluster of galaxies at z~0.5, but in this
case there is some evidence for additional structures along the line of sight
that may contribute to the lensing signal. A third cluster, A959, has a dark
sub-clump which shows interesting morphological evidence in the mass map for
being associated with the main cluster. This is the first case where there is
any significant evidence for a physical association between a dark sub-clump
(discovered from weak lensing) and a normal cluster. Analysis of archival X-ray
data shows that the three new mass concentrations are not firmly detected in
X-rays and that they are X-ray underluminous.


title:
3D modeling of 1612 MHz OH masers: Monte Carlo modeling of the maser
  shells and the amplified stellar image

abstract:
  We present the first results of our 3D Monte Carlo maser radiative transfer
code, used to model the 1612 MHz OH maser shell and the amplification of
emission from the stellar radio-photosphere.


title:
Magnetic Fields in the envelopes of late-type stars: Circular
  Polarization of H2O Masers

abstract:
  We present the first circular polarization measurements of circumstellar
water masers around a sample of late-type stars. These observations are used to
obtain the magnetic field strength in the water maser region with both an LTE
and non-LTE analysis. We find fields from a few hundred milliGauss up to a few
Gauss, indicating a solar-type r^(-2) dependence of the magnetic field on the
distance. No linear polarization is detected to less than 1%.


title: Mass Segregation in Star Clusters: Analytic Estimation of the Timescale

abstract:
  Mass segregation in a star cluster is studied in an analytical manner. We
consider a two-component cluster, which consists of two types of stars with
different masses. Plummer's model is used for the initial condition. We trace
the overall behaviors of the probability distribution functions of the two
components and obtain the timescale of mass segregation as a simple function of
the cluster parameters. The result is used to discuss the origin of a black
hole with mass of > 1000 M(sun) found in the starburst galaxy M82.


title:
A Sample of Ultra Steep Spectrum Sources Selected from the Westerbork In
  the Southern Hemisphere (WISH) survey

abstract:
  The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the
southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a
limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the
observations, the survey has a much lower resolution in declination than in
right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS
shows that the positional accuracy is less constrained in declination than in
right ascension, but there is no significant systematic error. We present a
source list containing 73570 sources.
  We correlate this WISH catalogue with the NVSS to construct a sample of faint
Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies
with large optical telescopes in the southern hemisphere. This sample is aimed
at increasing the number of known high redshift radio galaxies to allow
detailed follow-up studies of these massive galaxies and their environments in
the early Universe.


title: The primordial density perturbation in the curvaton scenario

abstract:
  We analyse the primordial density perturbation when it is generated by a
`curvaton' field different from the inflaton. In some cases this perturbation
may have large isocurvature components, fully correlated or anti-correlated
with the adiabatic component. It may also have a significant non-Gaussian
component. All of these effects are calculated in a form which will enable
direct comparison with current and forthcoming observational data.


title:
Using Cepheids to determine the galactic abundance gradient. III.First
  results for the outer disc

abstract:
  As a continuation of our previous work, which concerned the radial abundance
distribution in the galactic disc over the distances 4-10 kpc this paper
presents the first results on the metallicicty in the outer disc (RG > 10 kpc).
Based on high-resolution spectra obtained for 19 distant Cepheids we sampled
galactocentric distances from 10 to 12 kpc. Combined with the results of our
previous work on the inner and middle parts of the galactic disc, the present
data enable one to study the structure of the radial abundance distribution
over a large baseline. In particular, we find indications of a discontinuity in
the radial abundance distribution for iron as well as a number of the other
elements. The discontinuity is seen at a galactocentric distance RG = 10 kpc.
This finding supports the results reported earlier by Twarog et al. (1997).


title: Population effects on the red giant clump absolute magnitude: The K-band

abstract:
  We present a detailed analysis of the behaviour of the Red Clump K-band
absolute magnitude (M(K,RC)) in simple and composite stellar populations, in
light of its use as standard candle for distance determinations. The advantage
of using M(K,RC), following recent empirical calibrations of its value for the
solar neighbourhood, arises from its very low sensitivity to the extinction by
interstellar dust. We provide data and equations which allow the determination
of the K-band population correction Delta(M(K,RC)) (difference between the Red
Clump brightness in the solar neighbourhood and in the population under
scrutiny) for any generic stellar population. These data complement the results
presented in Girardi & Salaris(2001) for the V- and I-band. We show how data
from galactic open clusters consistently support our predicted Delta(M(V,RC)),
Delta(M(I,RC)) and Delta(M(K,RC)) values.
  Multiband VIK population corrections for various galaxy systems are provided.
They can be used in conjunction with the method devised by Alves et al.(2002),
in order to derive simultaneously reddening and distance from the use of VIK
observations of Red Clump stars. We have positively tested this technique on
the Galactic globular cluster 47Tuc, for which both an empirical parallax-based
main sequence fitting distance and reddening estimates exist. We have also
studied the case of using only V and I photometry, recovering consistent
results for both reddening and distance. Application of this method to an
OGLE-II field, and the results by Alves et al.(2002), confirm a LMC distance
modulus of about 18.50, in agreement with the HST extragalactic distance scale
zero-point. (abridged)


title:
Radiation driven atmospheres of O-type stars: constraints on the
  mass-luminosity relation of central stars of planetary nebulae

abstract:
  Recent advances in the modelling of stellar winds driven by radiation
pressure make it possible to fit many wind-sensitive features in the UV spectra
of hot stars, opening the way for a hydrodynamically consistent determination
of stellar radii, masses, and luminosities from the UV spectrum alone. It is
thus no longer necessary to assume a theoretical mass-luminosity relation. As
the method has been shown to work for massive O-stars, we are now able to test
predictions from the post-AGB evolutionary calculations quantitatively for the
first time. Here we present the first rather surprising consequences of using
the new generation of model atmospheres for the analysis of a sample of central
stars of planetary nebulae.


title: The host galaxies of type Ia supernovae at z=0.6

abstract:
  We examine the host galaxies of high redshift type Ia supernovae (SNe Ia)
using archival I and R band data from the Hubble Space Telescope. The SNe Ia
host galaxies show a wide variety of morphologies, including undisturbed
ellipticals, spirals and disturbed systems. SNe Ia are also found over a wide
range of projected distances from the host galaxy centres, ranging from 3kpc to
30kpc. For a sample of 22 SNe Ia at <z> = 0.6, 70% are found in spiral galaxies
and 30% are found in elliptical systems, similar to the proportions observed
locally. Including additional previously published data, we find no significant
difference in the average light-curve-shape-corrected peak B band magnitudes
for high-z SNe Ia between spirals and ellipticals. These results are consistent
with predictions based on the locally-derived understanding of SNe Ia physics
and the influence of progenitor mass and metallicity. We also construct colour
maps for two host galaxies and find that both show a non-uniform colour
structure with typical variations of rest-frame B-V~0.5. This is most plausibly
attributed to the presence of, and variation in dust extinction in these
galaxies. Moreover, we find no evidence that the SNe Ia are preferentially
found in outer regions (>10kpc) of the host galaxies where extinction would be
low. This suggests that the range of host galaxy extinctions of SNe Ia at z~0.6
should be comparable to those of local SNe Ia. Although observational bias
cannot be completely ruled out, this appears to be in conflict with the finding
of low extinction for SNe Ia found in the high-z supernova search studies.


title: The mass and temperature functions in a moving barrier model

abstract:
  In this paper, I use the extension of the excursion set model of Sheth &
Tormen (2002) and the barrier shape obtained in Del Popolo & Gambera (1998) to
calculate the unconditional halo mass function, and the conditional mass
function in several cosmological models. I show that the barrier obtained in
Del Popolo & Gambera (1998), which takes account of tidal interaction between
proto-haloes, is a better description of the mass functions than the spherical
collapse and is in good agreement with numerical simulations (Tozzi & Governato
1998, and Governato et al. 1999). The results are also in good agreement with
those obtained by Sheth & Tormen (2002), only slight differences are observed
expecially at the low mass end. I moreover calculate, and compare with
simulations, the temperature function obtained by means of the mass functions
previously calculated and also using an improved version of the M-T relation,
which accounts for the fact that massive clusters accrete matter
quasi-continuously, and finally taking account of the tidal interaction with
neighboring clusters. Even in this case the discrepancy between the
Press-Schecter predictions and simulations is considerably reduced.


title: A Test of Newton's Law of Gravity in the Weak Acceleration Regime

abstract:
  A pilot experiment suitable to test Newton's law of gravity down to the
regime of acceleration typical of galaxies has been carried out in Omega
Centauri. Stars in the extreme periphery of this globular cluster are used as
test particles immersed in such weak gravitational field. The stellar velocity
dispersion is found to remain constant at large radii, rather than decrease
monotonically, starting at acceleration a=10e-7 cm/s2. This is comparable to
the acceleration at which the effect of dark matter becomes relevant in
galaxies. Explanations for this result within Newtonian dynamics exist (e.g.
cluster evaporation, tidal effects, presence of dark matter) but require fine
tuning of the relevant parameters in order to make the dispersion profile flat.
An interesting alternative is that this result, together with a similar one for
Palomar 13 and the anomalous behavior of spacecrafts outside the solar system,
suggests a breakdown of Newton's law in the weak acceleration regime.


title: Near-Infrared Coronal Lines in Narrow-Line Seyfert 1 Galaxies

abstract:
  We report spectroscopic observations in the wavelength region 0.8-2.4 microns
aimed at detecting near-infrared coronal lines in a sample of 5 narrow-line and
1 broad-line Seyfert 1 galaxies. Our measurements show that [SiVI] 1.963mu,
[SIX] 1.252mu and [SVIII] 0.991mu are present in most of the objects and are
useful tracers of nuclear activity. Line ratios between coronal and low
ionization forbidden lines are larger in narrow-line Seyfert 1 galaxies. A
positive correlation between FHWM and ionization potential of the forbidden
lines is observed. Some coronal lines have widths similar to that of lines
emitted in the broad line region (BLR), indicating that part of their flux
originates in gas close to the outer portions of the BLR. Most coronal lines
are blueshifted relative to the systemic velocity of the galaxy and this shift
increases with the increase in line width. Assymetries towards the blue are
observed in the profiles of high-ionization Fe lines, suggesting that the
emitting gas is related to winds or outflows, most probably originating in
material that is being evaporated from the torus. This scenario is supported by
models that combine the effects of shock ionization and photoionization by a
central continuum source in the gas clouds. The agreement between the coronal
line emission predicted by the models and the observations is satisfactory; the
models reproduced the whole range of coronal line intensities observed. We also
report the detection of [FeXIII] 1.074,1.079mu in three of our objects and the
first detection of [PII] 1.188mu and [NiII] 1.191mu in a Seyfert 1 galaxy, ARK
564. Using the ratio [PII]/[FeII] we deduced that most Fe present in the outer
NLR of ARK 564 is locked up in grains, and the influence of shocks is
negligible.


title: Weak Lensing

abstract: Weak lensing review at the first-year graduate student level.


title:
Steps Toward Determination of the Size and Structure of the Broad-Line
  Region in Active Galactic Nuclei. XVI. A Thirteen-Year Study of Spectral
  Variability in NGC 5548

abstract:
  We present the final installment of an intensive 13-year study of variations
of the optical continuum and broad H-beta emission line in the Seyfert 1 galaxy
NGC 5548. The data base consists of 1530 optical continuum measurements and
1248 H-beta measurements. The H-beta variations follow the continuum variations
closely, with a typical time delay of about 20 days. However, a year-by-year
analysis shows that the magnitude of emission-line time delay is correlated
with the mean continuum flux. We argue that the data are consistent with the
simple model prediction that the size of the broad-line region is proportional
to the square root of the ionizing luminosity. Moreover, the apparently linear
nature of the correlation between the H-beta response time and the nonstellar
optical continuum arises as a consequence of the changing shape of the
continuum as it varies, specifically with the optical (5100 A) continuum
luminosity proportional to the ultraviolet (1350 A) continuum luminosity to the
0.56 power.


title: PKS 1510-089: A Head-On View of a Relativistic Jet

abstract:
  The gamma-ray blazar PKS 1510-089 has a highly superluminal milli-arcsecond
jet at a position angle (PA) of -28 degrees and an arcsecond jet with an
initial PA of 155 degrees. With a PA difference of 177 degrees between the
arcsecond and milli-arcsecond jets, PKS 1510-089 is perhaps the most highly
misaligned radio jet ever observed and serves as a graphic example of
projection effects in a highly beamed relativistic jet. Here we present the
results of observations designed to bridge the gap between the milli-arcsecond
and arcsecond scales. We find that a previously detected ``counter-feature'' to
the arcsecond jet is directly fed by the milli-arcsecond jet. This feature is
located 0.3" from the core, corresponding to a de-projected distance of 30
kiloparsecs. The feature appears to be dominated by shocked emission and has an
almost perfectly ordered magnetic field along its outside edge. We conclude
that it is most likely a shocked bend, viewed end-on, where the jet crosses our
line of sight to form the southern arcsecond jet. While the bend appears to be
nearly 180 degrees when viewed in projection, we estimate the intrinsic bending
angle to be between 12 and 24 degrees. The cause of the bend is uncertain;
however, we favor a scenario where the jet is bent after it departs the galaxy,
either by ram pressure due to winds in the intracluster medium or simply by the
density gradient in the transition to the intergalactic medium.


title: The Structure and Energetics of Active Galactic Nuclei

abstract:
  The black-hole/accretion-disk paradigm for active galactic nuclei (AGNs) is
now reasonably secure, but there are still important unresolved issues, some of
which will require the capabilities of an 8 to 10-m class UV/optical
space-based telescope. Imaging spectroscopy with a diffraction-limited large
telescope will be required to measure AGN black-hole masses from stellar
dynamics for direct comparison with reverberation mapping-based masses. High
spectral resolution in the UV is required to determine the mass and kinetic
energy of the outflows observed in the absorption spectra of AGNs and to
understand the energetics of the accretion process. As with ground-based
astronomy, however, effective use of a large UV/optical space telescope
requires complementary smaller facility instruments; a meter-class UV
spectroscopic telescope, for example, can fit into a Medium Explorer budget.


title:
The X-ray afterglows of gamma-ray bursts GRB 001025A and GRB 010220
  observed with XMM-Newton

abstract:
  The X-ray afterglows of GRB 001025A and GRB 010220 were detected by
XMM-Newton with an average 0.2--10.0 keV flux of 4.4 and 3.3x10^{-14} erg
cm^{-2} s^{-1} respectively; the afterglow of GRB 001025A is observed to decay.
Afterglows at other wavelengths were not detected for either burst. A set of
broadened soft X-ray emission lines are detected in the afterglow of GRB
001025A, at 5.0 sigma significance above a Galactic-absorbed power-law
continuum. The spectra of both afterglows are significantly better fit by a
variable abundance thermal plasma model than by an absorbed power-law and are
consistent with the observations of GRB 011211, indicating that thermal
emission from light elements may be common in the early X-ray afterglows of
GRBs.


title: Fast Infrared Sub-Flares From GRS 1915+105

abstract:
  We report the discovery of fast (~ 100 sec) 2.2 micron flares from the
microquasar GRS 1915+105, which are superimposed on longer (~ 30 min), brighter
flares corresponding to episodes of jet formation. The number and strength of
the sub-flares in each bright flare varies, and does not seem to correlate in
any obvious way with the underlying light curve or with changes in the X-ray
emission. However, the fact that these sub-flares only occur in tandem with the
larger flares indicates that they might be related to the jet ejection process.