title:
The Population of Weak MgII Absorbers. II The Properties of Single-Cloud
  Systems

abstract:
  We present an investigation of MgII absorbers characterized as single-cloud
weak systems at z~1. We measured column densities and Doppler parameters for
MgII and FeII in 15 systems found in HIRES/Keck spectra at 6.6 km/s. Using
these quantities and CIV, Lyman alpha and Lyman limit absorption observed with
FOS/HST (resolution ~230 km/s) we applied photoionization models to each system
to constrain metallicities, densities, ionization conditions, and sizes.
  We find that: (1) Single-cloud weak systems are optically thin in neutral
hydrogen and may have their origins in a population of objects distinct from
the optically thick strong MgII absorbers, which are associated with bright
galaxies. (2) Weak systems account for somewhere between 25% to 100% of the z <
1 Lyman alpha forest clouds in the range 15.8<log N(HI)<16.8 cm^-2. (3) At
least seven of 15 systems have two or more ionization phases of gas (multiphase
medium). (4) We identify a subset of weak MgII absorber that we term
``iron-rich''. These clouds are not alpha-group enhanced and are constrained to
have sizes of ~10 pc. At that size, to produce the observed redshift path
density, they would need to outnumber L* galaxies by approximately six orders
of magnitude.
  We discuss these results and the implications that the iron-rich systems
require enrichment from Type Ia supernovae. Further, we address how star
clusters or supernova remnants in dwarf galaxies might give rise to absorbers
with the inferred properties. This would imply far larger numbers of such
objects than are presently known, even locally. We compare the weak systems to
the weak kinematic subsystems in strong MgII absorbers and to Galactic high
velocity clouds. (abridged)


title:
Optical Identification of Multiple Faint X-ray Sources in the Globular
  Cluster NGC 6752: Evidence for Numerous Cataclysmic Variables

abstract:
  We report on the Chandra ACIS-S3 imaging observation of the globular cluster
NGC 6752. We detect 6 X-ray sources within the 10.5" core radius and 13 more
within the 115" half-mass radius down to a limiting luminosity of Lx approx
10^{30} erg/s for cluster sources. We reanalyze archival data from the Hubble
Space Telescope and the Australia Telescope Compact Array and make 12 optical
identifications and one radio identification. Based on X-ray and optical
properties of the identifications, we find 10 likely cataclysmic variables
(CVs), 1-3 likely RS CVn or BY Dra systems, and 1 or 2 possible background
objects. Of the 7 sources for which no optical identifications were made, we
expect that ~2-4 are background objects and that the rest are either CVs or
some or all of the five millisecond pulsars whose radio positions are not yet
accurately known. These and other Chandra results on globular clusters indicate
that the dozens of CVs per cluster expected by theoretical arguments are being
found. The findings to date also suggest that the ratio of CVs to other types
of X-ray sources is remarkably similar in clusters of very different structural
parameters.


title:
The Eventual Quintessential Big Collapse of the Closed Universe with the
  Present Accelerative Phase

abstract:
  Whether our universe with present day acceleration can eventually collapse is
very interesting problem. We are also interesting in such problems, whether the
universe is closed? Why it is so flat? How long to expend a period for a cycle
of the universe? In this paper a simple ``slow-fast'' type of the quintessence
potential is designed for the closed universe to realize the present
acceleration of our universe and its eventual big collapse. A detail numerical
simulation of the universe evolution demonstrates that it divides the seven
stages, a very rich story. It is unexpected that the quintessential kinetic
energy is dominated in the shrink stage of the universe with very rapid
velocity of the energy increasing. A complete analytic analysis is given for
each stage. Some very interesting new problems brought by this collapse are
discussed. Therefore our model avoids naturally the future event horizon
problem of the present accelerative expanding universe and maybe realize the
infinite cycles of the universe, which supplies a mechanism to use naturally
the anthropic principle. This paper shows that the understanding on the essence
of the cosmological constant should contain a richer content.


title: A Pilot Study of the Tully-Fisher Relation in Cl0024+1654 at z=0.4

abstract:
  We present the first determination of the Tully-Fisher relation (TFR) for a
distant galaxy cluster. We have measured internal kinematics of seven members
of Cl0024+1654 from spatially resolved emission observed in 2D Keck (LRIS)
spectra. Measurements of disk structural parameters were made from HST (WFPC2)
images. While we do not find evidence for a change in the slope or zeropoint of
the cluster TFR, we do find that there was more scatter in the past. We intend
to expand this study with kinematic measurements from fifteen more Cl0024
members.


title: A Deep Keck Spectral Survey of Cl0024+1654 at z=0.4

abstract:
  We have undertaken a Keck spectral survey of galaxies to R~24 near the
central region of Cl0024+1654 at z=0.4. The spectral resolution and slits have
been selected to yield kinematics such as the velocity dispersions of
early-type systems and rotation curves of disks. The spectra also provide a
suite of lines that yield star formation, age, and metallicity information.


title:
On the Variety of the Spectral and Temporal Behaviors of Long Gamma-Ray
  Burst Pulses

abstract:
  We find and study a variety of the spectral-temporal behavior during the
decay phase of long and bright GRB pulses. Even though only a small fraction of
observed bursts exhibit such pulses, these are of interest to study as they
reflect individual emission episodes during the burst. We have previously found
that for about half of these decays, the instantaneous photon flux ~ 1/time,
which is a consequence of the validity of both a power-law hardness-intensity
correlation (HIC) and an exponential hardness-fluence correlation (HFC). Here,
we study a complete sample of 25 BATSE pulses (having a peak flux in 1 s
resolution of > 5 photons/s/cm^2 and a S/N of 30 in at least 8 time bins) and,
specifically, search for other types of decay behaviors. First, we find that a
power law gives a better description of the pulse decays than a stretched
exponential, the most commonly assumed pulse shape so far. Then we find that
about half of the decays behave approximately as 1/time, and the other half
approximately as 1/time^3. For a few of the latter decays, the two
correlations, the HIC and the HFC, are constrained and found to be consistent
with the light curve behavior. For these cases, the HIC is still a power law
while the HFC is described by a generalized function. Finally, we briefly
discuss our results in a physical context.


title: Spiral waves in accretion discs

abstract:
  In the first part of this article, we review the observational evidence for
spirals in the accretion discs of cataclysmic variables. It is shown that with
the increasing amount of data available, spirals appear to be an omnipresent
feature of accretion discs in outburst. Spirals seem to live until decline that
is, for several tens of orbital periods. We then study the formation of spiral
shocks from a theoretical side, using the results of various numerical
simulations. We make a comparison between observations and theory and briefly
discuss the implications of the presence of spirals in the discs of cataclysmic
variables.


title: High resolution simulations of star formation

abstract:
  In order to study the capabilities of SPH in self-gravitating hydrodynamical
problems, we have performed a series of three-dimensional numerical simulations
of the collapse of a rotating homogeneous cloud, varying the number of
particles and the artificial viscosity prescription.


title: Direct Monte Carlo simulations of accretion discs

abstract:
  We apply the Direct Simulation Monte Carlo (DSMC) method, developed
originally to calculate rarefied gas dynamical problems, to study the gas flow
in an accretion disc in a close binary system. The method involves viscosity
and thermal conduction automatically, and can thus simulate turbulent viscosity
(alpha viscosity).


title: Application of the DSMC method to astrophysical flows

abstract:
  The Direct Simulation Monte Carlo (DSMC) method, developed originally to
calculate rarefied gas dynamical problems, is applied to continuous flow
including shocks assuming that the Knudsen number is sufficiently small. In
particular, we study the formation of spiral shocks in the accretion disc of a
close binary system. The method involves viscosity and thermal conduction
automatically, and can thus simulate turbulent viscosity.


title: L1521E: A Starless Core in the Early Evolutionary Stage ?

abstract:
  We have studied the physical and chemical properties of a quiescent starless
core L1521E with various molecular lines. It is found that there exists a
compact dense core traced by the H^13CO^+, HN^13C, CCS, and HC_3N lines; their
distributions have a single peak at the same position. The core radius is as
small as 0.031 pc, whereas the H_2 density at the peak position is as high as
(1.3-5.6)times10^5 cm^-3. Although the density is high enough to excite the
inversion transitions of NH_3, these lines are found to be very faint in
L1521E. The distributions of NH_3 and CCS seem to be different from those of
well-studied starless cores, L1498 and L1544, where the distribution of CCS
shows a shell-like structure while that of NH_3 is concentrated at the center
of the core. Abundances of carbon-chain molecules are higher in L1521E than the
other dark cloud cores, and especially those of sulfur-bearing molecules C_nS
are comparable to the cyanopolyyne peak of TMC-1. Our results suggest that
L1521E would be in a very early stage of physical and chemical evolution.


title: Spiral waves in accretion discs - theory

abstract:
  Spirals shocks have been widely studied in the context of galactic dynamics
and protostellar discs. They may however also play an important role in some
classes of close binary stars, and more particularly in cataclysmic variables.
In this paper, we review the physics of spirals waves in accretion discs,
present the results of numerical simulations and consider whether theory can be
reconcilied with observations.


title: The prompt gamma-ray emission of novae

abstract:
  Classical novae are potential gamma-ray emitters, because of the
disintegration of some radioactive nuclei synthesized during the explosion.
Some short-lived isotopes (such as 13N and 18F), as well as the medium-lived
22Na, decay emitting positrons, which annihilate with electrons and thus are
responsible for the prompt emission of gamma-rays from novae. This emission
consists of a 511 keV line plus a continuum between 20 and 511 keV, and is
released before the maximum in visual luminosity, i.e., before the discovery of
the nova. The main characteristics of this prompt emission, together with the
related uncertainties (both of nuclear and hydrodynamical origin, with a
particular emphasis on the influence of the envelope properties) and prospects
for detectability are analyzed in this paper.


title:
Quasi-Periodic Oscillation in Seyfert galaxies: Significance levels. The
  Case of Mrk 766

abstract:
  We discuss methods to compute significance levels for the existence of
quasi-periodic oscillations (QPOs) in Active Galactic Nuclei (AGN) which take
the red-noise character of the X-ray lightcurves of these objects into account.
Applying epoch folding and periodogram analysis to the XMM-Newton observation
of the Seyfert galaxy Mrk 766, a possible QPO at a timescale of 4200s has been
reported. Our computation of the significance of this QPO, however, shows that
the 4200s peak is not significant at the 95% level. We conclude that the 4200s
feature is an artifact of the red-noise process and not the result of a
physical process within the Active Galactic Nuclei.


title: Flux-loss of buoyant ropes interacting with convective flows

abstract:
  We present 3-d numerical magneto-hydrodynamic simulations of a buoyant,
twisted magnetic flux rope embedded in a stratified, solar-like model
convection zone. The flux rope is given an initial twist such that it neither
kinks nor fragments during its ascent. Moreover, its magnetic energy content
with respect to convection is chosen so that the flux rope retains its basic
geometry while being deflected from a purely vertical ascent by convective
flows. The simulations show that magnetic flux is advected away from the core
of the flux rope as it interacts with the convection. The results thus support
the idea that the amount of toroidal flux stored at or near the bottom of the
solar convection zone may currently be underestimated.


title:
IR Com: Deeply Eclipsing Dwarf Nova Below the Period Gap -- A Twin of HT
  Cas?

abstract:
  We observed an X-ray selected, deeply eclipsing cataclysmic variable IR Com
(=S 10932). We detected an outburst occurring on 1996 January 1. The light
curve of the outburst closely resembled that of a normal outburst of an SU
UMa-type dwarf nova, rather than that of an intermediate polar. Time-resolved
photometry during outburst showed that eclipses became systematically deeper
and narrower as the outburst faded. Full-orbit light curves in quiescence
showed little evidence of orbital humps or asymmetry of eclipses. In addition
to the presence of high--low transitions in quiescence, the overall behavior of
outbursts and characteristics of the eclipse profiles suggest that IR Com can
be best understood as a twin of HT Cas, a famous eclipsing SU UMa-type dwarf
nova with a number of peculiarities.


title: HV Virginis and WZ Sge-Type Dwarf Novae

abstract:
  A dwarf nova HV Vir was observed photometrically for eight nights during the
outburst in 1992 April - May. The star showed two distinct types of periodic
variation: (1) 82.20-min (0.05708 d) double-humped variation with decaying
amplitudes during the early stage of the outburst, and (2) 83.80-min (0.05820
d) superhumps in later stages. We attributed the former to "early superhumps",
which are only seen in the earliest stage of WZ Sge-type outbursts. The
superhump period and evolution of the superhumps, together with general
characteristics of the light curve, make HV Vir a typical WZ Sge-type dwarf
nova. HV Vir also showed a large increase of the superhump period during the
superoutburst. Upon the recognition of the WZ Sge-type nature of an object
previously considered as a nova, we present a comprehensive list of candidates
for WZ Sge-type dwarf novae, and related systems.


title: A simulation of solar convection at supergranulation scale

abstract:
  We present here numerical simulations of surface solar convection which cover
a box of 30$\times30\times$3.2 Mm$^3$ with a resolution of
315$\times315\times$82, which is used to investigate the dynamics of scales
larger than granulation. No structure resembling supergranulation is present;
possibly higher Reynolds numbers (i.e. higher numerical resolution), or
magnetic fields, or greater depth are necessary. The results also show
interesting aspects of granular dynamics which are briefly presented, like
extensive p-mode ridges in the k-$\omega$ diagram and a ringlike distribution
of horizontal vorticity around granules. At large scales, the horizontal
velocity is much larger than the vertical velocity and the vertical motion is
dominated by p-mode oscillations.


title:
Lower limits on the maximum orbital frequency around rotating strange
  stars

abstract:
  Observations of kHz quasi-periodic oscillations (QPOs) in the X-ray fluxes of
low-mass X-ray binaries (LMXBs) have been used in attempts to constrain the
external metric of the compact members of these binaries, as well as their
masses and the equation of state of matter at supranuclear denisties. We
compute the maximum orbital frequency of stable circular motion around
uniformly rotating strange stars described by the MIT bag model. The
calculations are performed for both normal and supramassive constant baryon
mass sequences of strange stars rotating at all possible rates. We find the
lower limits on the maximum orbital frequency and discuss them for a range of
masses and for all rotational frequencies allowed in the model considered. We
show that for slowly and moderately rotating strange stars the maximum value of
orbital frequency can be a good indicator of the mass of the compact object.
However, for rapidly rotating strange stars the same value of orbital frequency
in the innermost stable circular orbit is obtained for stars with masses
ranging from that of a planetoid to about three solar masses. At sufficiently
high rotation rates of the strange star, the rotational period alone constrains
the stellar mass to a surprisingly narrow range.


title: Cosmic shear from STIS pure parallels - II. Analysis

abstract:
  We report on the marginal detection of cosmic shear on sub-arcmin scales with
archive data from the STIS camera on board HST. For the measurement 121 galaxy
fields with a field of view of 51'' x 51'' are used to obtain an rms cosmic
shear of ~ 4% with 1.5sigma significance. This value is consistent with
groundbased results obtained by other groups on larger scales, and with
theoretical predictions for a standard LambdaCDM cosmology. To show the
suitability of STIS for weak shear measurements we carefully investigated the
stability of the PSF. We demonstrate that small temporal changes do not affect
the cosmic shear measurement by more than ~ 10%. We also discuss the influence
of various weighting and selection schemes for the galaxy ellipticities.


title: Quintessence-the Dark Energy in the Universe?

abstract:
  Quintessence - the energy density of a slowly evolving scalar field - may
constitute a dynamical form of the homogeneous dark energy in the universe. We
review the basic idea and indicate observational tests which may distinguish
quintessence from a cosmological constant.


title: Physics near a black-hole horizon

abstract:
  I discuss several general-relativistic effects that are likely to be of
interest in the astrophysics of black holes and neutron stars


title:
Infrared to millimetre photometry of ultra-luminous IR galaxies: new
  evidence favouring a 3-stage dust model

abstract:
  Infrared to millimetre spectral energy distributions have been obtained for
41 bright ultra-luminous infrared galaxies. The observations were carried out
with ISOPHOT between 10 and 200 micron and supplemented for 16 sources with
SCUBA at 450 and 850 micron and with SEST at 1.3 mm. In addition, seven sources
were observed at 1.2 and 2.2 $\mu$m with the 2.2 m telescope on Calar Alto.
These new SEDs represent the most complete set of infrared photometric
templates obtained so far on ULIRGs in the local universe.


title: Acoustic modes in spheroidal cavities

abstract:
  Oscillation modes of rapidly rotating stars have not yet been calculated with
precision, rotational effects being generally approximated by perturbation
methods. We are developing a numerical method able to account for the
deformation of the star by the centrifugal force and, as a first step, we
determined the acoustic modes of a uniform density spheroid and studied how the
spheroid flatness affects these modes.


title: Possible detection of hard X-ray afterglows of short gamma-ray bursts

abstract:
  We report the discovery of a transient and fading hard X-ray emission in the
BATSE lightcurves of a sample of short gamma-ray bursts. We have summed each of
the four channel BATSE light curves of 76 short bursts to uncover the average
overall temporal and spectral evolution of a possible transient signal
following the prompt flux. We found an excess emission peaking ~30 s after the
prompt one, detectable for ~100 s. The soft power-law spectrum and the
time-evolution of this transient signal suggest that it is produced by the
deceleration of a relativistic expanding source, as predicted by the afterglow
model.


title: The intracluster iron distribution around 4C+55.16

abstract:
  We report on the metal distribution in the intracluster medium around the
radio galaxy 4C+55.16 (z=0.24) observed with the Chandra X-ray Observatory. The
radial metallicity profile shows a dramatic change at 10 arcsec (~50 kpc) in
radius from half solar to twice solar at inner radii. Also found was a
plume-like feature located at ~3 arcsec to the south-west of the centre of the
galaxy, which is mostly accounted for by a strong enhancement of iron L
emission. The X-ray spectrum of the plume is characterized by the metal
abundance pattern of Type Ia supernovae (SNeIa), i.e., large ratios of Fe to
alpha-elements, with the iron metallicity being unusually high at 7.9(+24/-5.0)
solar (90 per cent error). How the plume has been formed is not entirely clear.
The inhomogeneous iron distribution suggested in this cluster provides
important clues to understanding the metal enrichment process of the cluster
medium.


title: HS 0705+6700: a new eclipsing sdB binary

abstract:
  We report the discovery of an eclipsing binary - HS 0705+6700 - being an sdB
star with a faint companion. From its light curve the orbital period of 8263.87
s, the mass ratio of the system q = 0.28, the inclination of 84.4 deg and other
system parameters are derived. The companion does not contribute to the optical
light of the system except through a strong reflection effect. The
semi-amplitude of the radial velocity curve K1 = 85.8 km/s and a mass function
of f(m) = 0.00626 Msun are determined. A spectroscopic analysis of the blue
spectra results in Teff = 28800K, log g = 5.40, and log n(He)/n(H) = -2.68.
These characteristics are typical for sdB stars, as is its mass of 0.48 Msun.
According to its mass (0.13 Msun) and radius (0.19 Rsun), the companion is an M
dwarf. The primary is in a core helium burning phase of evolution, and the
system must have gone through a common envelope stage when the primary was near
the tip of the red giant branch.


title: The Interstellar Medium around the Supernova Remnant G320.4-1.2

abstract:
  Using the Australia Telescope Compact Array, we have carried out a survey of
the HI emission in the direction of the ``barrel-shaped'' supernova remnant
(SNR) G320.4-1.2 (MSH 15-52) and its associated young pulsar B1509-58. The
angular resolution of the data is 4.0x2.7 arcmin, and the rms noise of the
order of 30 mJy/beam (~0.5 K). The HI observations indicate that the N-NW radio
limb has encountered a dense HI filament (density ~12 cm^-3) at the same LSR
velocity than that of the SNR (V_LSR ~ -68 km/s). This HI concentration would
be responsible for the flattened shape of the NW lobe of G320.4-1.2, and for
the formation of the radio/optical/X-ray nebula RCW 89. The emission associated
with the bright knots in the interior of RCW 89 can be explained as arising
from the interaction between the collimated relativistic outflow from the
pulsar and the denser part of this HI filament (density ~15 cm^-3). The S-SE
half of the SNR, on the other hand, seems to have rapidly expanded across a
lower density enviroment (density ~0.4 cm^-3). The HI data also reveal an
unusual HI feature aligned with a collimated outflow generated by the pulsar,
suggestive of association with the SNR. The anomalous kinematical velocity of
this feature (V_LSR ~ 15 km/s), however, is difficult to explain.


title:
On black hole masses, radio-loudness and bulge luminosities of Seyfert
  galaxies

abstract:
  We estimated black hole masses for 9 Seyfert 1 and 13 Seyfert 2 galaxies in
the Palomar and CfA bright Seyfert samples using the tight correlation between
black hole mass and bulge velocity dispersion. Combining other 13 Seyfert 1s
and 2 Seyfert 2s in these samples but with black hole masses measured recently
by reverberation mapping and stellar/gas dynamics, we studied the correlations
of black hole masses with radio loudness and bulge luminosities for a sample of
37 Seyfert galaxies. We found that if radio-loudness is measured using the
optical and radio luminosities of the nuclear components, the black hole masses
of radio-loud Seyfert 1s tend to increase with the radio-loudness. The black
hole masses of all Seyfert galaxies increase with the radio power, but Seyfert
galaxies have larger radio powers than nearby galaxies with the same black hole
masses. In addition, the correlation between black hole masses and bulge V-band
luminosities for Seyfert galaxies is consistent with that found for quasars and
normal galaxies. The combined sample of 37 Seyfert galaxies, 15 quasars and 30
normal galaxies suggests a possible universal nonlinear relation between black
hole and bulge masses, $M(BH) \propto M(bulge)^{1.74\pm0.14}$, which is
slightly steeper than that found recently by Laor (2001) for a smaller sample.
This nonlinear relation is supported by a larger sample including 65 Seyfert
galaxies. The different M(BH)/M(bulge) ratio for galaxies with different bulge
luminosities or different black hole masses may be explained by this relation.
These results are consistent with some theoretical implications and are
important for understanding the nature of radio emissions and the formation and
evolution of supermassive black holes and galaxies.


title: Galaxy Spectral Types and Their Applications in the 2dFGRS

abstract:
  The 2dF Galaxy Redshift Survey (2dFGRS) has already measured over 200,000
redshifts of nearby (median redshift z~0.1) galaxies. This is the single
largest set of galaxy spectra ever collected. It allows us to subdivide the
survey into subsets according to the galaxy intrinsic properties. We outline
here a method (based on Principal Component Analysis) for spectrally
classifying these galaxies in a robust and independent manner. In so doing we
develop a continuous measure of spectral type, eta, which reflects the actual
distribution of spectra in the observed galaxy population. We demonstrate the
usefulness of this classification by estimating luminosity functions and
clustering per spectral type.


title:
Archeops: a large sky coverage millimeter experiment for mapping Cosmic
  Microwave Background anisotropies

abstract:
  We present Archeops, a balloon-borne bolometer experiment designed to map a
large part of the sky at millimeter and submillimeter wavelengths. The main
scientific goal is to study the Cosmic Microwave Background anisotropies on all
scales, in order to properly derive the cosmological parameters of the
Universe. We present the sky coverage map of the first scientific flight.


title:
Discovery of new embedded Herbig-Haro objects in the rho Ophiuchi dark
  cloud

abstract:
  We report here the discovery of a 30"-chain of embedded Herbig-Haro (HH)
objects in the rho Ophiuchi dark cloud. These HH objects were first detected
during a deep K_S-band observation (completeness magnitude for point source~19)
made with NTT/SOFI. We confirm their nature with follow-up observations made
with H_2 v=1-0 S(1) narrow-band filter. We argue that they belong to two
different jets emanating from two Class I protostars: the main component of the
recently resolved subarcsecond radio binary YLW15 (also called IRS43), and
IRS54. We propose also to identify the [S II] knot HH224NW1 (Gomez et al 1998)
as emanating from a counterjet of YLW15. The alignment between these HH objects
and the thermal jet candidate found in YLW15 by Girart et al. (2000) implies
that this jet is not precessing at least on timescale ~(2-4)x1E4 yr.


title:
The population of galaxies in the forming cluster around the radio
  galaxy MRC 1138-262 at z=2.2

abstract:
  We have recently discovered a forming cluster around the radio galaxy MRC
1138-262 at redshift 2.2. Besides the population of Ly alpha emitting galaxies
that have been confirmed spectroscopically, we have detected many candidate H
alpha emitters that seem to have a different spatial distribution from the
other galaxies: they are more clustered towards the center of the cluster and
seem to be distributed along the same direction as the radio source. We present
here the characteristics of the Ly alpha and H alpha emitters and study the
nature of these populations.


title:
Plasma Diagnostics in High-Resolution X-ray Spectra of Magnetic
  Cataclysmic Variables

abstract:
  Using the Chandra HETG spectrum of EX Hya as an example, we discuss some of
the plasma diagnostics available in high-resolution X-ray spectra of magnetic
cataclysmic variables. Specifically, for conditions appropriate to collisional
ionization equilibrium plasmas, we discuss the temperature dependence of the H-
to He-like line intensity ratios and the density and photoexcitation dependence
of the He-like R line ratios and the Fe XVII I(17.10 A)/I(17.05 A) line ratio.
We show that the plasma temperature in EX Hya spans the range from ~ 0.5 to ~
10 keV and that the plasma density n > 2E14 cm^{-3}, orders of magnitude
greater than that observed in the Sun or other late-type stars.


title:
Prospects for Detecting Supersymmetric Dark Matter at Post-LEP Benchmark
  Points

abstract:
  A new set of supersymmetric benchmark scenarios has recently been proposed in
the context of the constrained MSSM (CMSSM) with universal soft
supersymmetry-breaking masses, taking into account the constraints from LEP, $b
\to s \gamma$ and $g_\mu - 2$. These points have previously been used to
discuss the physics reaches of different accelerators. In this paper, we
discuss the prospects for discovering supersymmetric dark matter in these
scenarios. We consider direct detection through spin-independent and
spin-dependent nuclear scattering, as well as indirect detection through relic
annihilations to neutrinos, photons, and positrons. We find that several of the
benchmark scenarios offer good prospects for direct detection via
spin-independent nuclear scattering and indirect detection via muons produced
by neutrinos from relic annihilations inside the Sun, and some models offer
good prospects for detecting photons from relic annihilations in the galactic
centre.


title:
Predictions for the Counts of Faint, High-Redshift Galaxies in the
  Mid-Infrared

abstract:
  Deep mid-infrared (MIR) observations could reveal a population of faint,
high-redshift (z>3) dusty starburst galaxies that are the progenitors of
present-day spheroids or bulges, and are beyond the reach of current
instruments. We utilize a semi-analytic galaxy formation scheme to find an
extreme model for the MIR galaxy counts, designed to maximize the number of
detectable sources down to a flux level of a few nJy. The model incorporates
the formation of heavily dust-enshrouded stellar populations at high redshift,
and is consistent with existing observations, including faint counts at 1.6um
in the NICMOS Hubble Deep Field, and the upper limit on the extragalactic MIR
background from TeV gamma rays. Our models predict upto 0.5 galaxies/sq.arcsec
at the threshold of 100 nJy at 6um, with a comparable or larger surface density
at longer MIR wavelengths. We conclude that a significant new population of
high-redshift galaxies could be detected by the Space Infrared Telescope
Facility (SIRTF) and Next Generation Space Telescope (NGST). Such a population
would constitute background noise for the Terrestrial Planet Finder (TPF), and
could necessitate repeat observations: every {\it TPF} resolution element have
a 10 percent chance of being contaminated by a background galaxy.


title: Chandra detection of the radio and optical double hot spot of 3C 351

abstract:
  In this letter we report a Chandra X-ray detection of the double northern hot
spot of the radio quasar 3C 351. The hot spot has also been observed in the
optical with the Hubble Space Telescope (R-band) and with the 3.5m. Telescopio
Nazionale Galileo (B-band). The radio-to-optical and X-ray spectra are
interpreted as the results of the synchrotron and synchrotron-self-Compton
(SSC) mechanisms, respectively, with hot-spot magnetic field strengths ~3 times
smaller than the equipartition values. In the framework of shock acceleration
theory, we show that the requirement for such a relatively small field strength
is in agreement with the fitted synchrotron spectral models and with the sizes
of the hot spots. Finally, we show that the combination of a lower magnetic
field strength with the high frequencies of the synchrotron cut-off in the
fitted synchrotron spectra provides strong evidence for electron acceleration
in the hot spots.


title: Multi-Phase Gas Dynamics in a Weak Barred Potential

abstract:
  The structure of the interstellar medium in the central kpc region of a
galaxy with a weak bar-like potential is investigated taking into account
realistic cooling and heating processes and the self-gravity of the gas. Using
high resolution hydrodynamical simulations, it is revealed that the resonant
structures (e.g. smooth spiral shocks and a nuclear ring) are very different
from those seen in past numerical models where simple models of the ISM, i.e.
non-self-gravitating, isothermal gas were assumed. We find that the pc-scale
filaments and clumps form large scale spirals, which resemble those seen in
real galaxies. The fine structures are different between the arms and in the
nuclear region. The next generation millimeter interferometer (ALMA) may reveal
the fine structures of the cold gas in nearby galaxies. We also find a large
scale anisotropy in the gas temperature, which is caused due to non-circular
velocity field of the gas.The damped orbit model based on the epicyclic
approximation explains the distribution of the hot (> 10^4 K) and cold (< 100
K) gases appearing alternately around the galactic center. Because of the
temperature anisotropy, cold gases observed by molecular lines do not
necessarily represent the real gas distribution in galaxies. Position-Velocity
diagrams depend strongly on the viewing angles. As a result, the rotational
velocity inferred from the PV maps could be two times larger or smaller than
the true circular velocity.


title: Stratified disks are locally stable

abstract:
  Notwithstanding recent claims by Richard et al., there is no linear
hydrodynamic instability of axisymmetrically stable disks in the local limit.
We prove this by means of an exact stability analysis of an unbounded
incompressible flow having constant stratification and constant shear.


title:
Computational AstroStatistics: Fast and Efficient Tools for Analysing
  Huge Astronomical Data Sources

abstract:
  I present here a review of past and present multi-disciplinary research of
the Pittsburgh Computational AstroStatistics (PiCA) group. This group is
dedicated to developing fast and efficient statistical algorithms for analysing
huge astronomical data sources. I begin with a short review of
multi-resolutional kd-trees which are the building blocks for many of our
algorithms. For example, quick range queries and fast n-point correlation
functions. I will present new results from the use of Mixture Models (Connolly
et al. 2000) in density estimation of multi-color data from the Sloan Digital
Sky Survey (SDSS). Specifically, the selection of quasars and the automated
identification of X-ray sources. I will also present a brief overview of the
False Discovery Rate (FDR) procedure (Miller et al. 2001a) and show how it has
been used in the detection of ``Baryon Wiggles'' in the local galaxy power
spectrum and source identification in radio data. Finally, I will look forward
to new research on an automated Bayes Network anomaly detector and the possible
use of the Locally Linear Embedding algorithm (LLE; Roweis & Saul 2000) for
spectral classification of SDSS spectra.


title: Large-Scale Structure Studies with Clusters of Galaxies

abstract:
  I present here a review of Large-Scale Structure (LSS) studies using clusters
of galaxies. First, I re-evaluate the `pros' and `cons' of using clusters for
such studies, especially in this era of large galaxy redshift surveys.
Secondly, I provide an historical review of the Cluster Correlation Function
and show that the latest measurements of xi_cc from Abell and X-ray catalogs
are in excellent agreement. Thirdly, I review the latest measurements of the
power spectrum of clusters which provide strong constraints on the cosmological
parameters e.g. Omega_m and models of structure formation. Moreover, I
highlight the recent discovery of ``Baryon Wiggles'' in the local cluster p(k)
which is in perfect agreement with the recent CMB data. Lastly, I examine
recent advances in the measurement of the X-ray Cluster Luminosity Function and
emphasize the importance of accurately determining the selection function of
future cluster surveys.


title: The Epoch of Galaxy Formation

abstract:
  I present a biased review of when the epoch of formation of galaxies (both
disks and ellipticals) maybe took place. I base my arguments in simple (mostly)
analytic models that have been recently developed to reproduce most of the
observed photometric, chemical and dynamical properties of galaxies both at low
and high redshift.


title: Simulations of Galaxy Clusters observed by Chandra

abstract:
  A software package able to simulate imaging observations of galaxy clusters
by the Chandra X-ray telescope is here presented. We start from high resolution
N-body hydrodynamical simulations of galaxy clusters and assign to each gas
particle a spectrum of emissivity, after assuming the MeKaL model. We then
construct spatial images of the source differential flux which are used to
create lists of incoming X-ray photons, preserving information on photon
direction and energy. The photon lists are passed on to the Chandra simulator
(MARX) to produce the final observation events. Background events are added to
complete the simulation. Data analysis is currently in progress and simulated
observations by other telescopes will become available in the future.


title:
The Kramers-Heisenberg Formula and the Gunn-Peterson Trough from the
  First Objects in the Universe

abstract:
  Recent cosmological observations indicate that the reionized universe may
have started at around z=6, where a significant suppression around Ly alpha has
been observed from the neutral intergalactic medium. The associated neutral
hydrogen column density is expected to exceed 10^{21}cm^{-2}},where it is very
important to use the accurate scattering cross section known as the
Kramers-Heisenberg formula that is obtained from the fully quantum mechanical
time-dependent second order perturbation theory. We present the
Kramers-Heisenberg formula and compare it with the formula introduced in a
heuristic way by Peebles (1993) treating the hydrogen atom as a two-level atom,
from which we find a devitaion by a factor of two in the red wing region far
from the line center. Adopting simple cosmological models, we compute the
Gunn-Peterson optical depths and the trough profiles. Our results are compared
with the works performed by Madau & Rees (2000), who adopted the cross section
introduced by Peebles. We find deviations up to 5 per cent in the Gunn-Peterson
transmission coefficient for an accelerated expanding universe in the red
off-resonance wing part with the rest wavelength Delta_lambda~10{AA}.


title:
The Frequency of Active and Quiescent Galaxies with Companions:
  Implications for the Feeding of the Nucleus

abstract:
  We analyze the idea that nuclear activity, either AGN or star formation, can
be triggered by interactions, studying the percentage of active, HII and
quiescent galaxies with companions. Our sample was selected from the Palomar
survey, and avoids selection biases faced by previous studies. The comparison
between the local galaxy density distributions showed that in most cases there
is no statistically significant difference among galaxies of different activity
types. The comparison of the percentage of galaxies with nearby companions
showed that there is a higher percentage of LINERs, transition, and absorption
line galaxies with companions than Seyferts and HII galaxies. However, we find
that when we consider only galaxies of similar morphological types (ellipticals
or spirals), there is no difference in the percentage of galaxies with
companions among different activity types, indicating that the former result
was due to the morphology-density effect. Also, only small differences are
found when we consider galaxies with similar Halpha luminosities. The
comparison between HII galaxies of different Halpha luminosities shows that
there is a significantly higher percentage of galaxies with companions among
the higher luminosity HII galaxies, indicating that interactions increase the
amount of circumnuclear star formation, in agreement with previous results. The
fact that we find that galaxies of different activity types have the same
percentage of companions, suggests that interactions between galaxies is not a
necessary condition to trigger the nuclear activity in AGNs. We compare our
results with previous ones and discuss their implications. (abridged)


title:
On Radio Quiescence of Anomalous X-ray Pulsars and Soft Gamma-Ray
  Repeaters

abstract:
  In the hot environments of the anomalous X-ray pulsars and the soft gamma-ray
repeaters, as indicated by their luminous, pulsed, quiescent X-ray emission,
$\gamma$-rays generated from the inner gaps may have shorter attenuation
lengths via two photon pair production than via magnetic photon splitting. The
AXP/SGR environments may not be pairless, even if photon splitting could
completely suppress one photon pair production in super-strong magnetic fields,
as conjectured by Baring & Harding. Two-photon pair production more likely
occurs near the threshold, which tends to generate low energy pairs that are
not energetic enough to power radio emission in the observed bands. However,
emission in longer wavelengths may not be prohibited in principle if these
objects are indeed magnetars. The so-called ``photon splitting deathlines'' are
still valid for high magnetic field pulsars which are much dimmer in X-rays, if
$\gamma$-rays with both polarization modes split.


title: The effect of atmospheric attenuation on inclined cosmic ray air showers

abstract:
  The increasing cosmic ray statistics collected by present experiments and the
future prospects with new large arrays demand accurate calculations of the
extensive air shower parameters. The energy of the primary particle is
estimated by ground arrays fitting a lateral distribution function (LDF) to the
particle densities at a given observing level. However, the lack of appropriate
parameterization for these distributions, able to reproduce the data collected
from all arrival directions, makes it difficult the experimental analysis.
Starting from analytical LDF for vertical showers we study the atmospheric
depth dependence of the shower parameters, which is necessary to obtain the
corresponding particle density distributions for inclined showers. In our
approach both geometrical and atmospheric attenuation effects producing a
lateral asymmetry in non-vertical showers are included. The resulting electron
and muon LDF fit very well the Monte Carlo simulated data at all zenith angles.


title: The temperature structure of dusty planetary nebulae

abstract:
  We have analyzed the effects of photoelectric heating by dust grains in
photoionization models of planetary nebulae. We have shown that this process is
particularly important if planetary nebulae contain a population of small
grains. The presence of such grains would solve a number of problems that have
found no satisfactory solution so far: i) the thermal energy deficit in some
objects inferred from tailored photoionization modelling; ii) the large
negative temperature gradients inferred directly from spatially resolved
observations and indirectly from integrated spectra in some planetary nebulae;
iii) the fact that the temperatures derived from the Balmer jump are smaller
than those derived from [O III] 4363/5007; iv) the fact that the observed
intensities of [O I] 6300 are often larger than predicted by photoionization
models. In presence of moderate density inhomogeneities, such as inferred from
high resolution images of planetary nebulae, photoelectric heating would boost
the temperature of the tenuous component, which would then better confine the
clumps. The temperature structure of such dusty and filamentary nebulae would
solve the long standing problem of temperature fluctuations posed by Peimbert
(1967, ApJ, 150, 825).


title:
Quasi-self-similar evolution of the two-point correlation function:
  strongly nonlinear regime in Omega_0 < 1 universes

abstract:
  The well-known self-similar solution for the two-point correlation function
of the density field is valid only in an Einstein-de Sitter universe. We
attempt to extend the solution for non-Einstein-de Sitter universes. For this
purpose we introduce an idea of quasi-self-similar evolution; this approach is
based on the assumption that the evolution of the two-point correlation is a
succession of stages of evolution, each of which spans a short enough period to
be considered approximately self-similar. In addition we assume that clustering
is stable on scales where a physically motivated `virialization condition' is
satisfied. These assumptions lead to a definite prediction for the behavior of
the two-point correlation function in the strongly nonlinear regime. We show
that the prediction agrees well with N-body simulations in non-Einstein-de
Sitter cases, and discuss some remaining problems.


title: Large-Amplitude 2.65-d Oscillation in the VY Scl-Type star V425 Cas

abstract:
  From long-term photometry of a VY Scl-type star, V425 Cas, between 1998 and
2000, we discovered a short-term, large-amplitude (up to 1.5 mag) variations.
The variation was well represented by a single period of 2.65 d. The large
amplitude and the profile of the folded light curve suggest that the dwarf
nova-type disk instability is responsible for this variation. The shortness of
the period is unprecedented in hydrogen-rich cataclysmic variables. Given the
recent emerging evidence that the irradiation from white dwarfs in VY Scl-type
systems affect their light behavior, we propose a possibility that this unique
variation in V425 Cas can be explained by the combination of the dwarf
nova-type disk instability and irradiation. Similar short-period "outbursts"
have been known in X-ray transients (V518 Per), and helium cataclysmic
variables (CR Boo and V803 Cen). We discuss the possibility that these
phenomena have a common origin to the unique variation in V425 Cas.


title: 1998 Superoutburst of the Large-Amplitude SU UMa-Type Dwarf Nova WX Ceti

abstract:
  We observed the 1998 November superoutburst of WX Cet, a dwarf nova
originally proposed as a WZ Sge-like system. The observation established that
WX Cet is an SU UMa-type dwarf nova with a mean superhump period of 0.05949(1)
d, which is 2.1% longer than the reported orbital period. The lack of early
superhumps at the earliest stage of the superoutburst, the rapid development of
usual superhumps, and the possible rapid decay of late superhumps seem to
support that WX Cet is a fairly normal large-amplitude SU UMa-type dwarf nova,
rather than a WZ Sge-type dwarf nova with a number of peculiarities. However, a
period increase of superhumps at a rate dot(P)/P = (+8.5+/-1.0) x 10^-5 was
observed, which is one of the largest dot(P)/P ever observed in SU UMa-type
dwarf novae. A linear decline of light, with a rate of 0.10 mag/d, was observed
in the post-superoutburst stage. This may be an exemplification of the decay of
the viscosity in the accretion disk after the termination of a superoutburst,
mechanism of which is proposed to explain a variety of post-superoutburst
phenomena in some SU UMa-type dwarf novae.


title: Frequency dependence of pulsar radiation patterns

abstract:
  We report on new results from simultaneous, dual frequency, single pulse
observation of PSR B0329+54 using the Giant Metrewave Radio Telescope. We find
that the longitude separation of subpulses at two different frequencies (238
and 612 MHz) is less than that for the corresponding components in the average
profile. A similar behaviour has been noticed before in a number of pulsars. We
argue that subpulses are emitted within narrow flux tubes of the dipolar field
lines and that the mean pulsar beam has a conal structure. In such a model the
longitudes of profile components are determined by the intersection of the line
of sight trajectory with subpulse-associated emission beams. Thus, we show that
the difference in the frequency dependence of subpulse and profile component
longitudes is a natural property of the conal model of pulsar emission beam. We
support our conclusions by numerical modelling of pulsar emission, using the
known parameters for this pulsar, which produce results that agree very well
with our dual frequency observations.


title: The evolution of the cluster environments of radio sources at z<1.8

abstract:
  An analysis of the cluster environments around distant radio galaxies is
presented, in particular the results from new NTT deep optical-IR imaging of
the fields of radio sources at z ~ 1.6. A net overdensity of K-band galaxies is
found, together with a sharp peak in the angular cross-correlation amplitude,
centred on the radio galaxies. This excess clustering is associated
predominantly with red galaxies, with colours consistent with being old
ellipticals at the radio source redshift. A large excess of such red galaxies
is seen, particularly within 100 kpc of the radio source. These comprise
amongst the most distant red sequences of cluster ellipticals yet discovered,
that is, the highest redshift `normal' clusters.


title:
Stellar Populations in Star Clusters: The Role Played by Stochastic
  Effects

abstract:
  In this paper I combine the results of a set of population synthesis models
with simple Montecarlo simulations of stochastic effects in the number of stars
occupying sparsely populated stellar evolutionary phases, to show that the
scatter observed in the magnitudes and colors of LMC and NGC 7252 star clusters
can be understood in the framework of current stellar evolution theory, without
the need to introduce ad-hoc corrections (e.g. artificially increasing the
number of AGB stars).


title:
Galaxy Clusters in Hubble Volume Simulations: Cosmological Constraints
  from Sky Survey Populations

abstract:
  We use giga-particle N-body simulations to study galaxy cluster populations
in Hubble Volumes of LCDM (Omega_m=0.3, Omega_Lambda=0.7) and tCDM (Omega_m=1)
world models. Mapping past light-cones of locations in the computational space,
we create mock sky surveys of dark matter structure to z~1.4 over 10,000 sq deg
and to z~0.5 over two full spheres. Calibrating the Jenkins mass function at
z=0 with samples of ~1.5 million clusters, we show that the fit describes the
sky survey counts to <~20% acccuracy over all redshifts for systems larger than
poor groups (M>5e13 Msun/h). Fitting the observed local temperature function
determines the ratio beta of specific thermal energies in dark matter and
intracluster gas. We derive a scaling with power spectrum normalization beta
\propto sigma8^{5/3}, and measure a 4% error on sigma8 arising from cosmic
variance in temperature-limited cluster samples. Considering distant clusters,
the LCDM model matches EMSS and RDCS X-ray-selected survey observations under
economical assumptions for intracluster gas evolution. Using transformations of
mass-limited cluster samples that mimic sigma8 variation, we explore SZ search
expectations for a 10 sq deg survey complete above 10^{14} Msun/h. Cluster
counts are shown to be extremely sensitive to sigma8 uncertainty while redshift
statistics, such as the sample median, are much more stable. For LCDM, the
characteristic temperature at fixed sky surface density is a weak function of
redshift, implying an abundance of hot clusters at z>1. Assuming constant beta,
four kT>8 keV clusters lie at z>2 and 40 kT>5 keV clusters lie at z>3 on the
whole sky. Detection of Coma-sized clusters at z>1 violate LCDM at 95%
confidence if their surface density exceeds 0.003 per sq deg, or 120 on the
whole sky.


title:
The shape of the Red Giant Branch Bump as a diagnostic of partial mixing
  processes in low-mass stars

abstract:
  We suggest to use the shape of the Red Giant Branch (RGB) Bump in metal-rich
globular clusters as a diagnostic of partial mixing processes between the base
of the convective envelope and the H-burning shell. The Bump located along the
differential luminosity function of cluster RGB stars is a key observable to
constrain the H-profile inside these structures. In fact, standard evolutionary
models that account for complete mixing in the convective unstable layers and
radiative equilibrium in the innermost regions do predict that the first
dredge-up lefts over a very sharp H-discontinuity at the bottom of the
convective region. Interestingly enough we found that both atomic diffusion and
a moderate convective overshooting at the base of the convective region
marginally affects the shape of the RGB Bump in the differential Luminosity
Function (LF). As a consequence, we performed several numerical experiments to
estimate whether plausible assumptions concerning the smoothing of the
H-discontinuity, due to the possible occurrence of extra-mixing below the
convective boundary, affects the shape of the RGB Bump. We found that the
difference between the shape of RGB Bump predicted by standard and by smoothed
models can be detected if the H-discontinuity is smoothed over an envelope
region whose thickness is equal or larger than 0.5 pressure scale heights.
Finally, we briefly discuss the comparison between theoretical predictions and
empirical data in metal-rich, reddening free Galactic Globular Clusters (GGCs)
to constrain the sharpness of the H-profile inside RGB stars.


title:
Turbulence, turbulent mixing, and gravitational structure formation in
  the early Universe

abstract:
  Turbulence and turbulent mixing of temperature powered the big bang formation
of the universe at Planck length, time, and temperature scales. Planck-Kerr
inertial-vortex forces balanced Planck gravitational forces to produce Planck
(particle-pair) gas, Planck-gas turbulence and space-time-energy. Inflation at
the strong force temperature fossilized the turbulence. Gluon-neutrino-photon
bulk viscous forces exceeded gravitational and inertial-vortex forces of the
baryonic (ordinary) matter during the radiation dominated hot plasma epoch, and
large diffusive velocities of the weakly interacting nonbaryonic dark matter
(possibly neutrinos) prevented gravitational structure formation of this
material, contrary to the 1902 Jeans acoustic criterion and "cold dark matter"
models. The first plasma structures were proto-galaxy-super-cluster fragments
and voids triggered by turbulent-viscous-gravitational masses matching the
horizon mass at time 10^12 s. The last plasma structures formed were
proto-galaxies. At the 10^13 s plasma-gas transition, the proto-galaxies
fragmented to form proto-globular-star-cluster clumps of earth-mass
primordial-fog-particles (PFPs) that now comprise the baryonic dark matter.
Observational evidence of PFPs is provided by young globular star clusters
formed when galaxies merge, thousands of cometary knots seen around dying
stars, and the rapid twinkling of lensed quasar images.


title: The puzzle of the polar structure in NGC 4650A

abstract:
  This work presents new surface photometry and two-dimensional modeling of the
light distribution of the Polar Ring Galaxy NGC 4650A, based on near-infrared
(NIR) observations and high resolution optical imaging acquired during the
Hubble Heritage program. The NIR and optical integrated colors of the S0 and
the polar ring, and their scale parameters, are compared with those for
standard galaxy morphological types. The polar structure appears to be a disk
of a very young age, while the colors and light distribution of the host galaxy
do not resemble that of a typical early-type system. We compare these
observational results with the predictions from different formation scenarios
for polar ring galaxies. The peculiarities of the central S0 galaxy, the polar
disk structure and stellar population ages suggest that the polar ring galaxy
NGC 4650A may be the result of a dissipative merger event, rather than of an
accretion process.


title: Ab initio simulations of accretion disc boundary layers

abstract:
  I discuss the results of simplified three dimensional magnetohydrodynamic
simulations of the boundary layer between a disc and a non-rotating,
unmagnetized star. Strong magnetic fields, possibly approaching equipartition
with the thermal energy, occur in the boundary layer due to the shearing of
disc-generated fields. The mean boundary layer magnetic field, which is highly
variable on an orbital timescale, is estimated to exceed 50 kG for a CV with an
accretion rate of 10^(-9) solar masses per year. However, these fields do not
drive efficient angular momentum transport within the boundary layer. As a
consequence the radial velocity in the boundary layer is low, and the density
high.


title: Radio Properties of FIRST Radio Sources at 1 mJy

abstract:
  This paper presents a detailed analysis of the radio properties for the
sample of faint radio sources introduced in Magliocchetti et al. (2000). The
sample comprises mainly intrinsically low-power sources whose majority ($\simgt
70$ per cent) is made of FR I radio galaxies. These objects show some degree
(at 1$\sigma$ confidence level) of luminosity evolution, which is also needed
to correctly reproduce the total number and shape of the counts distribution at
1.4 GHz. Analysis of the de-evolved local radio luminosity function shows a
good agreement between data and model predictions for this class of sources.
Particular care has been devoted to the issue of 'lined' galaxies (i.e. objects
presenting in their spectra a continuum typical of early-type galaxies plus
emission lines of different nature), which appear as an intermediate class of
sources between AGN-dominated and starburst galaxies. Different evolutionary
behaviours are seen between the two sub-populations of lined and non-lined
low-power radio galaxies, the first class indicating a tendency for the radio
luminosity to decrease with look-back time, the second one showing positive
evolution. We note that different evolutionary properties also seem to
characterize BL Lacs selected in different bands, so that one might envisage an
association between lined FR I and the sub-class of BL Lacs selected in the
X-ray band.


title: Multifrequency Study of The Radio Galaxy NGC326

abstract:
  We present the results of a multi-frequency study of the inversion symmetric
radio galaxy NGC326 based on Very Large Array observations at 1.4, 1.6, 4.8,
8.5 and 14.9 GHz. The morphological, spectral and polarization properties of
this peculiar object are studied at different levels of spatial resolutions.
The interpretation of the data will be discussed in forthcoming papers.


title: Braking and bouncing

abstract:
  I discuss the case for an efficient orbital braking mechanism in CVs, and the
effect of nova outbursts on the observed range of mass transfer rates. I review
the continuing problem that models have in interpreting the short-period
cut-off of the CV period distribution.


title: Cluster cores as observed with Chandra

abstract:
  We review recent results from Chandra observations of the X-ray bright cores
of clusters of galaxies. We discuss the detection of ``cold fronts'' and their
implication for thermal conduction, the interaction of cooling flow and radio
source in the Perseus cluster and the dynamical state of the central region of
A1795. The radial distribution of metals in A1795 and the azimuthal variation
in metallicity in 4C+55.16 are presented.


title: The apsidal motion in close binary stars

abstract:
  It is usually accepted to consider an apsidal motion in binary stars as a
direct confirmation that a substance inside stars is not uniformly distributed.
It is shown in this paper that the apsidal motion in binary systems observation
data is in a good agreement with an existence of uniform plasma cores inside
stars if they consist of hydrogen-deuterium-helium mixture.


title:
Modelling the Spectral Signatures of Accretion Disk Winds in Cataclysmic
  Variables

abstract:
  Bipolar outflows are known to be present in many disk-accreting astrophysical
systems. In disk-dominated cataclysmic variables, these outflows are
responsible for most of the features in UV and FUV spectra. However, there have
been very few attempts to model the features that appear in the spectra of
disk-accreting cataclysmic variables quantitatively. The modelling that has
been attempted has been concentrated almost entirely on explaining the shape of
C IV.
  Here we describe a new hybrid Monte Carlo/Sobolev code that allows a
synthesis of the complete UV spectrum of a disk-dominated cataclysmic variable.
A large range of azimuthally-symmetric wind geometries can be modelled. Changes
in line shape in eclipsing systems can also be studied. Features in the
synthesized spectra include not only well-known resonance lines of O VI, NV, Si
IV, and C IV, but, with an appropriate choice of mass loss rate and wind
geometry, many of the lines originating from excited lower states that are
observed in HUT, FUSE, and ORFEUS spectra. The line profiles of C IV resemble
those calculated by previous workers, when an identical geometry is assumed. We
compare the synthesized spectra to HUT spectrum of Z Cam, showing that in this
case a reasonably good ``fit'' to the spectrum can be obtained.


title:
Deep HST Imaging of Sextans A I. The Spatially Resolved Recent Star
  Formation History

abstract:
  We have measured stellar photometry from deep Cycle 7 Hubble Space
Telescope/WFPC2 imaging of the dwarf irregular galaxy Sextans A. The imaging
was taken in three filters: F555W ($V$; 8 orbits), F814W ($I$; 16 orbits), and
F656N (H$\alpha$; 1 orbit). Combining these data with Cycle 5 WFPC2
observations provides nearly complete coverage of the optically visible portion
of the galaxy. The Cycle 7 observations are nearly 2 magnitudes more sensitive
than the Cycle 5 observations, which provides unambiguous separation of the
faint blue helium burning stars (BHeB stars) from contaminant populations. The
depth of the photometry allows us to compare recent star formation histories
recovered from both the main sequence (MS) stars and the BHeB stars for the
last 300 Myr. The excellent agreement between these independent star formation
rate (SFR) calculations is a resounding confirmation for the legitimacy of
using the BHeB stars to calculate the recent SFR. Using the BHeB stars we have
calculated the global star formation history over the past 700 Myr. The history
calculated from the Cycle 7 data is remarkably identical to that calculated
from the Cycle 5 data, implying that both halves of the galaxy formed stars in
concert. We have also calculated the spatially resolved star formation history,
combining the fields from the Cycle 5 and Cycle 7 data. Our interpretation of
the pattern of star formation is that it is an orderly stochastic process.


title:
Analysis of the First Disk-Resolved Images of Ceres from Ultraviolet
  Observations with the Hubble Space Telescope

abstract:
  We present HST Faint Object Camera observations of the asteroid 1 Ceres at
near-, mid-, and far-UV wavelengths (lambda = 3636, 2795, and 1621 A,
respectively) obtained on 1995 June 25. The disk of Ceres is well-resolved for
the first time, at a scale of ~50km. We report the detection of a large, ~250km
diameter surface feature for which we propose the name ``Piazzi''; however it
is presently uncertain if this feature is due to a crater, albedo variegation,
or other effect. From limb fits to the images, we obtain semi-major and
semi-minor axes of R_1=484.8+/-5.1km and R_2=466.4+/-5.9km, respectively, for
the illumination-corrected projected ellipsoid. Although albedo features are
seen, they do not allow for a definitive determination of the rotation or pole
positions of Ceres, particularly because of the sparse sampling (two epochs) of
the 9 hour rotation period. From full-disk integrated albedo measurements, we
find that Ceres has a red spectral slope from the mid- to near-UV, and a
significant blue slope shortward of the mid-UV. In spite of the presence of
Piazzi, we detect no significant global differences in the integrated albedo as
a function of rotational phase for the two epochs of data we obtained. From
Minnaert surface fits to the near- and mid-UV images, we find an unusually
large Minnaert parameter of k~0.9, suggesting a more Lambertian than lunar-like
surface.


title:
Detecting Clusters of Galaxies in the Sloan Digital Sky Survey I : Monte
  Carlo Comparison of Cluster Detection Algorithms

abstract:
  We present a comparison of three cluster finding algorithms from imaging data
using Monte Carlo simulations of clusters embedded in a 25 deg^2 region of
Sloan Digital Sky Survey (SDSS) imaging data: the Matched Filter (MF; Postman
et al. 1996), the Adaptive Matched Filter (AMF; Kepner et al. 1999) and a
color-magnitude filtered Voronoi Tessellation Technique (VTT). Among the two
matched filters, we find that the MF is more efficient in detecting faint
clusters, whereas the AMF evaluates the redshifts and richnesses more
accurately, therefore suggesting a hybrid method (HMF) that combines the two.
The HMF outperforms the VTT when using a background that is uniform, but it is
more sensitive to the presence of a non-uniform galaxy background than is the
VTT; this is due to the assumption of a uniform background in the HMF model. We
thus find that for the detection thresholds we determine to be appropriate for
the SDSS data, the performance of both algorithms are similar; we present the
selection function for each method evaluated with these thresholds as a
function of redshift and richness. For simulated clusters generated with a
Schechter luminosity function (M_r^* = -21.5 and alpha = -1.1) both algorithms
are complete for Abell richness >= 1 clusters up to z ~ 0.4 for a sample
magnitude limited to r = 21. While the cluster parameter evaluation shows a
mild correlation with the local background density, the detection efficiency is
not significantly affected by the background fluctuations, unlike previous
shallower surveys.


title: High spectral resolution time-resolved optical spectroscopy of V893 Sco

abstract:
  We present high resolution time-resolved optical spectra of the high
inclination short orbital period dwarf nova V893 Sco. We performed spectral
analysis through radial velocity measurements, Doppler mapping, and ratioed
Doppler maps. Our results indicate that V893 Sco's accretion disk is dissimilar
to WZ Sge's accretion disk, and does not fit any of the current accretion disk
models. We derive the system parameters M1 and i, and present evidence for V893
Sco as a very young cataclysmic variable and an ER UMa star. We advance the
hypothesis that all ER UMa stars may be newly formed cataclysmic variables.


title:
X-ray and UV Variability in the Core of M15: the nature of
  X2127+119/AC211

abstract:
  The prototypical post-core-collapse globular cluster M15 provides an ideal
environment for the formation of exotic binaries, it being already known to
contain a luminous LMXB (X2127+119, optically identified with the 17.1 hour
eclipsing binary AC211) and six millisecond pulsars in the core. However, the
X-ray properties of X2127+119 are strange in that it appears to be a high
inclination accretion disc corona source (ADC) from which we only see scattered
X-radiation, and yet it has produced extremely luminous type I X-ray bursts,
which may or may not have come from AC211. We have therefore examined the
5-year RXTE/ASM light curve of this object in order to search for long-term
modulations which might shed light on this unusual behaviour, and which led to
our discovery of further X-ray bursts. Furthermore we have used archival HST UV
images of the M15 core to search for other variable objects which might
indicate the presence of a second LMXB. From these we have found one highly
variable (> 5 mag) object which we interpret as a dwarf nova.


title:
A FUSE Survey of Interstellar Molecular Hydrogen in the Small and Large
  Magellanic Clouds

abstract:
  We describe a moderate-resolution FUSE survey of H2 along 70 sight lines to
the Small and Large Magellanic Clouds, using hot stars as background sources.
FUSE spectra of 67% of observed Magellanic Cloud sources (52% of LMC and 92% of
SMC) exhibit absorption lines from the H2 Lyman and Werner bands between 912
and 1120 A. Our survey is sensitive to N(H2) >= 10^14 cm^-2; the highest column
densities are log N(H2) = 19.9 in the LMC and 20.6 in the SMC. We find reduced
H2 abundances in the Magellanic Clouds relative to the Milky Way, with average
molecular fractions <f_H2> = 0.010 (+0.005, -0.002) for the SMC and <f_H2> =
0.012 (+0.006, -0.003) for the LMC, compared with <f_H2> = 0.095 for the
Galactic disk over a similar range of reddening. The dominant uncertainty in
this measurement results from the systematic differences between 21 cm radio
emission and Lya in pencil-beam sight lines as measures of N(HI). These results
imply that the diffuse H2 masses of the LMC and SMC are 8 x 10^6 Msun and 2 x
10^6 Msun, respectively, 2% and 0.5% of the H I masses derived from 21 cm
emission measurements. The LMC and SMC abundance patterns can be reproduced in
ensembles of model clouds with a reduced H2 formation rate coefficient, R ~ 3 x
10^-18 cm^3 s^-1, and incident radiation fields ranging from 10 - 100 times the
Galactic mean value. We find that these high-radiation, low-formation-rate
models can also explain the enhanced N(4)/N(2) and N(5)/N(3) rotational
excitation ratios in the Clouds. We use H2 column densities in low rotational
states (J = 0 and 1) to derive a mean kinetic and/or rotational temperature
<T_01> = 82 +/- 21 K for clouds with N(H2) >= 10^16 cm^-2, similar to Galactic
gas. We discuss the implications of this work for theories of star formation in
low-metallicity environments. [Abstract abridged]


title:
Evolution of binaries producing Type Ia supernovae, luminous supersoft
  X-ray sources, and recurrent novae

abstract:
  We have been proposing two evolutionary paths to Type Ia supernovae (SNe Ia),
which are called the supersoft X-ray source (SSS) channel and the symbiotic
channel, depending on the orbital separation just prior to an SN Ia explosion.
The essential difference of our treatment is inclusion of strong, optically
thick winds on mass-accreting white dwarfs (WDs) in binary evolutions when the
mass accretion rate on to WDs exceeds a critical rate of ~ 1 x 10^{-6} Mo/yr.
Once optically thick winds blow from the WD, the binary can avoid forming a
common envelope in some cases. So that the WDs are able to grow up to the
Chandrasekhar mass and explode as an SN Ia, showing SSS or recurrent nova
phenomena in the way to SNe Ia. Thus, the accretion wind process of WDs can
open new channels to SNe Ia. We have modeled the LMC supersoft source RX
J0513.9-6951 as an example of the systems in the accretion wind phase. Further
inclusions of two other elementary processes make the channels much wider;
these are the case BB mass transfer in the SSS channel and the strong orbital
shrinkage during the superwind phase of the primary star in the symbiotic
channel. As a result, the estimated birth rate of SNe Ia via these two channels
becomes compatible with the observation in our Galaxy. Interestingly, the U Sco
and T CrB subclasses of recurrent novae can be naturally understood as a part
of evolutionary stages in these two SSS and symbiotic channels to SNe Ia,
respectively. Thus we have a unified picture of binary evolutions to SNe Ia,
luminous SSS, and recurrent novae.


title:
Revised analysis of the supersoft X-ray phase, helium enrichment, and
  turn-off time in the 2000 outburst of the recurrent nova CI Aquilae

abstract:
  The recurrent nova CI Aquilae entered the final decline phase a bit before
May of 2001, showing the slowest evolution among the recurrent novae. Based on
the optically thick wind mass-loss theory of the thermonuclear runaway model,
we have estimated the turn-off time of the CI Aql 2000 outburst in March of
2001, after a supersoft X-ray source (SSS) phase lasts 150 days from December
of 2000 until May of 2001. Fitting our theoretical light curves with both the
1917 and 2000 outbursts, we also obtained the WD mass to be M_{WD}= 1.2 \pm
0.05 M_\sun, helium enrichment of ejecta, He/H ~ 0.5 by number, the mass of the
hydrogen-rich envelope on the WD of \Delta M ~ 6 x 10^{-6} M_\sun at the
optical maximum, which is indicating an average mass accretion rate of \dot
M_{acc} ~ 0.8 x 10^{-7} M_\sun yr^{-1} during the quiescent phase between the
1917 and 2000 outbursts.


title:
V2487 Ophiuchi: A strong candidate for a recurrent nova and a progenitor
  of Type Ia supernova

abstract:
  The light curve of the 1998 outburst of V2487 Ophiuchi (Nova Oph 1998) shows
a very rapid decline (t_3 ~ 9 day) and a mid-plateau phase from 10 to 30 days
after the optical maximum, which are characteristics common to the U Sco
subclass of the recurrent novae. We have numerically reproduced light curves of
the 1998 outburst based on a thermonuclear runaway model with optically thick
winds. The results show that the mass of the white dwarf (WD) is as massive as
1.35 \pm 0.01 M_\sun; the envelope mass of the WD at the optical maximum is ~ 6
x 10^{-6} M_\sun; the hydrogen content of the WD envelope is as low as X ~ 0.1
by mass weight. The mass transfer rate in quiescence is roughly estimated to be
\~ 1.5 x 10^{-7} M_\sun yr^{-1} and, therefore, that the recurrence period of
nova outbursts is about 40 yr. Since the WD mass may be now growing at a rate
of ~ 2 x 10^{-8} M_\sun yr^{-1}, V2487 Oph is a strong candidate for a
progenitor of a Type Ia supernova.


title: Analysis of thermally-induced effects in Planck Low Frequency Instrument

abstract:
  The Planck mission will provide full-sky maps of the Cosmic Microwave
Background with unprecedented angular resolution (~ 10') and sensitivity (DT /
T = 10^-6). This requires cryogenically cooled, high sensitivity detectors as
well as an extremely accurate control of systematic errors, which must be kept
at micro-K level. In this work we focus on systematic effects arising from
thermal instabilities in the Low Frequency Instrument operating in the 30-100
GHz range. Our results show that it is of crucial importance to assure "in
hardware" a high degree of stability. In addition, we provide an estimate of
the level at which it is possible to reduce the contamination level in the
observed maps by proper analysis of the Time Ordered Data.


title: Rapid optical spectroscopy of X-ray binaries with Keck II

abstract:
  The large collecting area of 4+ metre class telescopes allows atronomers to
observe bright objects on faster timescales than previously possible. In order
to exploit this capability, we designed a novel read-out mode for use on the
10-m Keck-II telescope on Mauna Kea, Hawaii. This took the form of a continuous
read-out mode, enabling us to obtain a target spectrum between 3500 and 8500
\AA, with a dispersion of ~2.5 \AA/pix, every *70 milliseconds*. I present
results from 5 nights of observations of Interacting Binaries, using this novel
data acquisition system in July 1998. During the run we obtained more than 1.2
million optical spectra, many of which were simultaneous with pointed RXTE
observations. This fast spectroscopic capability has allowed us to explore
regimes previously only accessible with broadband instruments. I will
concentrate on results from the coordinated Keck/RXTE observations, which have
revealed interesting correlated variability on timescales from seconds to days.
I will also show the results of a spectroscopic-timing analysis of QPOs in
Hercules X-1, which shows evidence for the decay of individual blobs of
material orbiting the neutron star.


title: Stellar and circumstellar evolution of long period variable stars

abstract:
  In a first paper, HIPPARCOS astrometric and kinematic data were used to
calibrate both infrared K and IRAS luminosities at the same time as kinematic
parameters of Long Period Variable stars (LPVs). Individual estimated absolute
magnitudes and a probabilistic assignation to galactic populations were deduced
from these calibrations for each LPV of our sample. Here we propose a scenario
of simultaneous stellar and circumstellar evolution according to the galactic
populations. The transitory states of S and Tc stars allow us to confirm the
location of the first dredge-up at $M_{bol}=-3.5$. There is also evidence
suggesting that a previous enrichment in s-elements from a more evolved
companion may accelerate the evolution along the AGB. The possible evolution to
OH LPVs is included in this scenario, and any of these stars may have a mass at
the limit of the capability for a C enrichment up to C/O > 1.
  A list of bright massive LPVs with peculiar envelope and luminosity
properties is proposed as Hot Bottom Burning candidates. The He-shell flash
star, R Cen, is found to be exceptionally bright and could become, before
leaving the AGB, a C-rich LPV brighter than the usual luminosity limit of
carbon stars.


title:
The XMM-Newton Serendipitous Survey. II. First results from the AXIS
  high galactic latitude medium sensitivity survey

abstract:
  We present the first results on the identifications of a medium sensitivity
survey (X-ray flux limit 2E-14 erg/cm2/s in the 0.5-4.5 keV band) at high
galactic latitude (|b|>20 deg) carried out with the XMM-Newton X-ray
observatory within the AXIS observing programme. This study is being conducted
as part of the XMM-Newton Survey Science Centre activities towards the
identification of the sources in the X-ray serendipitous sky survey. The sample
contains 29 X-ray sources in a solid angle of 0.26deg2 (source density 113 +/-
21 sources/deg2), out of which 27 (93%) have been identified. The majority of
the sources are broad-line AGN (19), followed by narrow emission line X-ray
emitting galaxies (6, all of which turn out to be AGN), 1 nearby non-emission
line galaxy (NGC 4291) and 1 active coronal star. Among the identified sources
we find 2 broad-absorption line QSOs (z~1.8 and z~1.9), which constitute ~10%
of the AGN population at this flux level, similar to optically selected
samples. Identifications of a further 10 X-ray sources fainter than our survey
limit are also presented.


title: The stability of axisymmetric Taylor-Couette flow in hydromagnetics

abstract:
  The linear marginal instability of an axisymmetric MHD Taylor-Couette flow of
infinite vertical extension is considered. The dependence of the flow stability
on magnetic Prandtl number, Pm, and gap-width between rotating cylinders is
investigated. There is an unstability for flows with resting outer cylinder
even without a magnetic field. Nevertheless, there are solutions with smaller
critical Reynolds numbers for certain (weak) magnetic fields. These solutions,
however, exist for not too small Pm or large enough gap. For hydrodynamically
stable flow, we found that a magnetic field amplitude always exsits where the
critical Reynolds number is minimal. In all calculated cases the minimal
critical Reynolds numbers are running with 1/Pm for small Pm and the critical
Reynolds numbers exceed value of 10^6 for Pm of sodium (10^{-5}) or gallium
(10^{-6}).


title:
Astrometry with Hubble Space Telescope: A Parallax of the Fundamental
  Distance Calibrator RR Lyrae

abstract:
  We present an absolute parallax and relative proper motion for the
fundamental distance scale calibrator, RR Lyr. We obtain these with astrometric
data from FGS 3, a white-light interferometer on HST. We find $\pi_{abs} = 3.82
\pm 0.2$ mas. Spectral classifications and VRIJHKT$_2$M and DDO51 photometry of
the astrometric reference frame surrounding RR Lyr indicate that field
extinction is low along this line of sight. We estimate <A_V>=0.07\pm0.03 for
these reference stars. The extinction suffered by RR Lyr becomes one of the
dominant contributors to the uncertainty in its absolute magnitude. Adopting
the average field absorption, <A_V>=0.07 \pm 0.03, we obtain M_V^{RR} = 0.61
^{-0.11}_{+0.10}. This provides a distance modulus for the LMC, m-M = 18.38 -
18.53^{-0.11}_{+0.10} with the average extinction-corrected magnitude of RR Lyr
variables in the LMC, <V(RR)>, remaining a significant uncertainty. We compare
this result to more than 80 other determinations of the distance modulus of the
LMC.


title:
Local Axisymmetric Simulations of Magneto-Rotational Instability in
  Radiation-Dominated Accretion Disks

abstract:
  We perform numerical simulations of magneto-rotational instability in a local
patch of accretion disk in which radiation pressure exceeds gas pressure. Such
conditions may occur in the central regions of disks surrounding compact
objects in active galactic nuclei and Galactic X-ray sources. We assume
axisymmetry, and neglect vertical stratification. The growth rates of the
instability on initially uniform magnetic fields are consistent with the linear
analysis of Blaes & Socrates 2001. As is the case when radiation effects are
neglected, the non-linear development of the instability leads to transitory
turbulence when the initial magnetic field has no net vertical flux. During the
turbulent phase, angular momentum is transported outwards. The Maxwell stress
is a few times the Reynolds stress, and their sum is about four times the mean
pressure in the vertical component of the magnetic field. For magnetic pressure
exceeding gas pressure, turbulent fluctuations in the field produce density
contrasts about equal to the ratio of magnetic to gas pressure. These are many
times larger than in the corresponding gas pressure dominated situation, and
may have profound implications for the steady-state vertical structure of
radiation-dominated disks. Diffusion of radiation from compressed regions damps
turbulent motions, converting kinetic energy into photon energy.


title:
L Dwarfs Found in Sloan Digital Sky Survey Commissioning Data II.
  Hobby-Eberly Telescope Observations

abstract:
  Low dispersion optical spectra have been obtained with the Hobby-Eberly
Telescope of 22 very red objects found in early imaging data from the Sloan
Digital Sky Survey. The objects are assigned spectral types on the 2MASS system
(Kirkpatrick et al. 1999) and are found to range from late M to late L. The
red- and near-infrared colors from SDSS and 2MASS correlate closely with each
other, and most of the colors are closely related to spectral type in this
range; the exception is the (i^* - z^*) color, which appears to be independent
of spectral type between about M7 and L4. The spectra suggest that this
independence is due to the disappearance of the TiO and VO absorption in the
i-band for later spectral types; to the presence of strong Na I and K I
absorption in the i-band; and to the gradual disappearance of the 8400 Angstrom
absorption of TiO and FeH in the z-band.


title: Dynamical Modeling of the Stellar Nucleus of M31

abstract:
  We present stellar dynamical models of the lopsided, double-peaked nucleus of
M31, derived from Hubble Space Telescope (HST) photometry. A Schwarzscild-type
method, in conjunction with Richardson-Lucy deconvolution, was employed to
construct steadily rotating, hot, stellar disks. The stars orbit a massive dark
object, on prograde and retrograde quasi-periodic loop orbits. Our results
support Tremaine's eccentric disk model, extended to include a more massive
disk, non zero pattern speed ($\Omega$), and different viewing angle. Most of
the disk mass populated prograde orbits, with $\simeq 3.4%$ on retrograde
orbits. The best fits to photometric and kinematic maps were disks with
$\Omega\approx 16\kmspc $. We speculate on the origins of the lopsidedness,
invoking recent work on the linear overstability of nearly Keplerian disks,
that possess even a small amount of a counter-rotating component. Accretion of
material-no more massive than a globular cluster-onto a preexisting stellar
disk, will account for the mass in our retrograde orbits, and could have
stimulated the lopsidedness seen in the nucleus of M31.


title: Automated Galaxy Morphology: A Fourier Approach

abstract:
  We use automated surface photometry and pattern classification techniques to
morphologically classify galaxies. The two-dimensional light distribution of a
galaxy is reconstructed using Fourier series fits to azimuthal profiles
computed in concentric elliptical annuli centered on the galaxy. Both the phase
and amplitude of each Fourier component have been studied as a function of
radial bin number for a large collection of galaxy images using principal
component analysis. We find that up to 90 percent of the variance in many of
these Fourier profiles may be characterized in as few as 3 principal components
and their use substantially reduces the dimensionality of the classification
problem. We use supervised learning methods in the form of artificial neural
networks to train galaxy classifiers that detect morphological bars at the
85-90 percent confidence level and can identify the Hubble type with a 1-sigma
scatter of 1.5 steps on the 16-step stage axis of the revised Hubble system.
Finally, we systematically characterize the adverse effects of decreasing
resolution and S/N on the quality of morphological information predicted by
these classifiers.


title:
Evidence for a Galactic Origin of Very Short Gamma Ray Bursts and
  Primordial Black Hole Sources

abstract:
  We systematically study the shortest time duration gamma ray bursts and find
unique features that are best interpreted as sources of a galactic origin.
There is a significant angular asymmetry and the V/Vmax distribution provides
evidence for a homogenous or Euclidean source distribution. We eview the
arguments that primordial black hole evaporation can give such GRBs. The rate
of events is consistent with a PBH origin if we assume on enhanced local
density, as are the other distributions. We suggest further tests of this
hypothesis.


title:
Timing and Spectral Properties of X-ray Emission from the Converging
  Flows onto Black hole: Monte-Carlo Simulations

abstract:
  We demonstrate that a X-ray spectrum of a converging inflow (CI) onto a black
hole is the sum of a thermal (disk) component and the convolution of some
fraction of this component with the Comptonization spread (Green's) function.
The latter component is seen as an extended power law at energies much higher
than the characteristic energy of the soft photons. We show that the high
energy photon production (source function) in the CI atmosphere is distributed
with the characteristic maximum at about the photon bending radius, 1.5r_S,
independently of the seed (soft) photon distribution. We show that high
frequency oscillations of the soft photon source in this region lead to the
oscillations of the high energy part of the spectrum but not of the thermal
component. The high frequency oscillations of the inner region are not
significant in the thermal component of the spectrum. We further demonstrate
that Doppler and recoil effects (which are responsible for the formation of the
CI spectrum) are related to the hard (positive) and soft (negative) time lags
between the soft and hard photon energy channels respectively.


title:
On the Role of Massive Stars in the Support and Destruction of Giant
  Molecular Clouds

abstract:
  We argue that massive stars are the dominant sources of energy for the
turbulent motions within giant molecular clouds, and that the primary agent of
feedback is the expansion of H II regions within the cloud volume. This
conclusion is suggested by the low efficiency of star formation and
corroborated by dynamical models of H II regions. We evaluate the turbulent
energy input rate in clouds more massive than one third of a million solar
masses, for which gravity does not significantly affect the expansion of H II
regions. Such clouds achieve a balance between the decay of turbulent energy
and its regeneration in H II regions; summed over clouds, the implied ionizing
luminosity and star formation rate are roughly consistent with the Galactic
total. H II regions also photoevaporate their clouds: we derive cloud
destruction times somewhat shorter than those estimated by Williams and McKee.
The upper mass limit for molecular clouds in the Milky Way may derive from the
fact that larger clouds would destroy themselves in less than one crossing
time. The conditions within starburst galaxies do not permit giant molecular
clouds to be supported or destroyed by H II regions. This should lead to rapid
cloud collapse and the efficient formation of massive star clusters, explaining
some aspects of the starburst phenomenon.


title: Molecular Hydrogen in High-Velocity Clouds

abstract:
  We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of
interstellar molecular hydrogen (H_2) in two Galactic high-velocity clouds
(HVCs). Molecular hydrogen absorption is detected in the Magellanic Stream
(abundance ~0.3 solar) toward the Seyfert galaxy Fairall 9 in the lowest three
rotational states (J=0-2) at v(LSR)=+190 km/s, yielding a total H_2 column
density of log N(H_2)=16.40(+0.26)(-0.53). In contrast, no H_2 absorption is
seen in the high-velocity cloud Complex C (abundance ~0.1 solar) toward the
quasar PG 1259+593 (log N(H_2)<13.96 at v(LSR)=-130 km/s) although both HVCs
have similar HI column densities on the order of log N(HI)~20. Weak H_2
absorption is detected in the Intermediate-Velocity Arch (IV Arch; abundance
\~1.0 solar) toward PG 1259+593 (log N(H_2)=14.10(+0.21)(-0.44) at v(LSR)=-55
km/s and log N(HI)=19.5). It thus appears that metal- and dust-poor halo clouds
like Complex C are not able to form and maintain widely distributed H_2,
whereas metal and dust-rich halo clouds like the IV Arch can maintain H_2 even
at low HI column densities.


title: Lyman Alpha Emitters at Redshift z=5.7

abstract:
  Lyman alpha galaxies at high redshifts offer a powerful probe of both the
formation of galaxies and the reionization of the intergalactic medium. Lyman
alpha line emission is an efficient tool for identifying young galaxies at high
redshift, because it is strong in systems with young stars and little or no
dust-- properties expected in galaxies undergoing their first burst of
star-formation. Lyman alpha galaxies also provide a robust test of the
reionization epoch that is independent of Gunn-Peterson trough observations in
quasar spectra and is better able to distinguish line center optical depths
tau=5 from tau=10^5. This is because neutral gas scatters Lyman alpha photons,
dramatically ``blurring'' images of Lyman alpha galaxies embedded in a neutral
intergalactic medium and rendering them undetectable.
  We present a photometrically selected sample of z=5.7 Lyman alpha emitters
derived from the Large Area Lyman Alpha survey. The presence of these
low-luminosity Lyman alpha sources at z=5.7 immediately implies that the
reionization redshift was > 5.7. Comparing these objects to our earlier z=4.5
sample, we find that the number of z=5.7 emitters at fixed line luminosity
marginally exceeds the no-evolution expectation, but falls well short of
published model predictions. The equivalent width distribution is similar at
the two redshifts. The large equivalent widths of the Lyman alpha line indicate
young galaxies undergoing their first star formation.


title:
Spiral Galaxies with HST/NICMOS. I. Nuclear Morphologies, Color Maps and
  Distinct Nuclei

abstract:
  This is the first of two papers where we present the analysis of an HST
NICMOS-Cam2 near-infared (NIR) snapshot survey in the F160W (H) filter for a
sample of 78 spiral galaxies selected from the UGC and ESOLV catalogs. For 69
of these objects we provide nuclear color information derived by combining the
H data either with additional NICMOS F110W (J) images or with V WFPC2/HST data.
Here we present the NIR images and the optical-NIR color maps. We focus our
attention on the properties of the photometrically-distinct `nuclei' which are
found embedded in most of the galaxies, and provide measurements of their
half-light radii and magnitudes in the H (and when available, in the J) band.
We find that: (i) In the NIR, the nuclei embedded in the bright early- to
intermediate-type galaxies span a much larger range in brightness than the
nuclei which are typically found embedded in bulgeless late-type disks; (ii)
Nuclei are found in both non-barred and barred hosts, in large-scale ($\gta$ 1
kpc) as well as in nuclear (up to a few 100pc) bars; (iii) There is a
significant increase in half-light radius with increasing luminosity of the
nucleus in the early/intermediate types; (iv) The nuclei of
early/intermediate-type spirals cover a large range of optical-NIR colors, from
$V-H\approx$ -0.5 to 3. Some nuclei are bluer and others redder than the
surrounding galaxy, indicating the presence of activity or reddening by dust in
many of these systems; (v) Some early/intermediate nuclei are elongated and/or
slightly offset from the isophotal center of the host galaxy. On average,
however, these nuclei appear as centered, star-cluster-like structures similar
to those which are found in the late-type disks. [abridged]


title:
Spiral Galaxies with HST/NICMOS. II. Isophotal Fits and Nuclear Cusp
  Slopes

abstract:
  We present surface brightness profiles for 56 of the 78 spiral galaxies
observed in the HST/{\tt NICMOS/Camera-2} F160W snapshot survey introduced in
Carollo et al. (2001; paper I), as well as surface brightness profiles for 23
objects out of the 41 that were also observed in the F110W filter. We fit these
surface brightness profiles with the Nuker law of Lauer et al. (1995), and use
the smooth analytical descriptions of the data to compute the average nuclear
stellar cusp slopes $<\gamma>$ in the 0.1$''-0.5''$ radial range. Our main
result is the startling similarity between the nuclear stellar cusp slopes
$<\gamma>$ in the near-infared compared to those derived in the visual
passband. This similarity has several implications: (1.) There are typically
little or no optical-NIR {\it global} color gradients, and thus no global
stellar population variations, inside $\sim 50$-100 pc from the nucleus in
nearby spirals. (2.) The large observed range of the strength of the nuclear
stellar cusps seen in the HST optical study of spiral galaxies reflects a
physical difference between galaxies, and is not an artifact caused by nuclear
dust and/or recent star formation. (3.) The dichotomy between $R^{1/4}$ bulges,
with steep nuclear stellar cusps $<\gamma > \sim 1$, and exponential bulges,
with shallow nuclear stellar cusps $<\gamma > < 0.3$, is also not an artifact
of the effects of dust or recent star formation. (4) A surrounding massive disk
appears to have no effect on the rise of the stellar density distribution
within the innermost hundred pc of the


title: Discovery of Molecular Gas in the Outflow and Tidal Arms around M82

abstract:
  We present the first fully sampled map of 12CO (1-0) emission from M82
covering the entire galaxy. Our map contains a 12 x 15 kpc^2 area. We find that
extraplanar CO emission, previously reported at short distances above the
galactic plane, extends to heights of up to 6 kpc above the disk. Some of this
emission is associated with tidal arms seen in HI, implying either that M82
contained substantial amounts of molecular gas in the outer disk, or that
molecular gas formed after the tidal features. CO emission along the direction
of the outflow extends to distances of 3 kpc above and below the disk. At this
distance, the line is shifted in velocity about 100 km/s, and has the same
sense as the galactic outflow from the central starburst. This implies that
molecular gas may be entrained into the outflow.


title: New X-ray Clusters in the EMSS II: Optical Properties

abstract:
  We present optical images for 9 new clusters of galaxies we have found in a
reanalysis of the Einstein IPC images comprising the Extended Medium
Sensitivity Survey (EMSS). Based on the presence of a red sequence of galaxies
in a color-magnitude (CM) diagram, a redshift is estimated for each cluster.
Galaxy overdensities (cluster richnesses) are measured in each field using the
B_gc statistic which allows their plausible identification with the X-ray
emission. The nature of our X-ray detection algorithm suggests that most of
these clusters have low X-ray surface brightness (LSB) compared to the
previously known EMSS clusters. We compare the optical and X-ray observations
of these clusters with the well-studied Canadian Network for Observational
Cosmology (CNOC) subsample of the EMSS, and conclude that the new clusters
exhibit a similar range of optical richnesses, X-ray luminosities, and,
somewhat surprisingly, galaxy populations as the predominantly rich, relaxed
EMSS/CNOC clusters.


title: Topological Defects in Cosmology

abstract:
  Topological defects are ubiquitous in condensed-matter physics but only
hypothetical in the early universe. In spite of this, even an indirect evidence
for one of these cosmic objects would revolutionize our vision of the cosmos.
We give here an introduction to the subject of cosmic topological defects and
their possible observable signatures. Beginning with a review of the basics of
general defect formation and evolution, we then focus on mainly two topics in
some detail: conducting strings and vorton formation, and some specific
imprints in the cosmic microwave background radiation from simulated cosmic
strings.