title:
The Nature of V359 Centauri Revealed: New Long-Period SU UMa-Type Dwarf
  Nova

abstract:
  We detected four outbursts of V359 Cen (possible nova discovered in 1939)
between 1999 and 2002. Time-resolved CCD photometry during two outbursts (1999
and 2002) revealed that V359 Cen is actually a long-period SU UMa-type dwarf
nova with a mean superhump period of 0.08092(1) d. We identified its supercycle
length as 307-397 d. This secure identification of the superhump period
precludes the previously supposed possibility that V359 Cen could be related to
a WZ Sge-type system with a long persistence of late superhumps. The outburst
characteristics of V359 Cen are, however, rather unusual in its low occurrence
of normal outbursts.


title: Chandra and XMM Observations of the ADC Source 0921-630

abstract:
  We analyze observations of the low mass X-ray binary 2S0921-63 obtained with
the gratings and CCDs on Chandra and XMM. This object is a high inclination
system showing evidence for an accretion disk corona (ADC). Such a corona has
the potential to constrain the properties of the heated accretion disk in this
system, and other LMXBs by extension. We find evidence for line emission which
is generally consistent with that found by previous experiments, although we
are able to detect more lines. For the first time in this source, we find that
the iron K line has multiple components. We set limits on the line widths and
velocity offsets, and we fit the spectra to photoionization models and discuss
the implications for accretion disk corona models. For the first time in any
ADC source we use these fits, together with density constraints based on the O
VII line ratio, in order to constrain the flux in the medium-ionization region
of the ADC. Under various assumptions about the source luminosity this
constrains the location of the emitting region. These estimates, together with
estimates for the emission measure, favor a scenario in which the intrinsic
luminosity of the source is comparable to what we observe.


title:
On the Minimum Energy Configuration of a Rotating Barotropic Fluid: A
  Response to Narayan & Pringle astro-ph/0208161

abstract: The authors respond to the commentary listed in the title.


title:
The Metallicity-Luminosity Relation, Effective Yields, and Metal Loss in
  Spiral and Irregular Galaxies

abstract:
  I present results on the correlation between galaxy mass, luminosity, and
metallicity for a sample of spiral and irregular galaxies having well-measured
abundance profiles, distances, and rotation speeds. Additional data for low
surface brightness galaxies from the literature are also included for
comparison. These data are combined to study the metallicity-luminosity and
metallicity-rotation speed correlations for spiral and irregular galaxies. The
metallicity luminosity correlation shows its familiar form for these galaxies,
a roughly uniform change in the average present-day O/H abundance of about a
factor 100 over 11 magnitudes in B luminosity. However, the O/H - V(rot)
relation shows a change in slope at a rotation speed of about 125 km/sec. At
faster V(rot), there appears to be no relation between average metallicity and
rotation speed. At lower V(rot), the metallicity correlates with rotation
speed. This change in behavior could be the result of increasing loss of metals
from the smaller galaxies in supernova-driven winds. This idea is tested by
looking at the variation in effective yield, derived from observed abundances
and gas fractions assuming closed box chemical evolution. The effective yields
derived for spiral and irregular galaxies increase by a factor of 10-20 from
V(rot) approximately 5 km/sec to V(rot) approximately 300 km/sec, asympotically
increasing to approximately constant y(eff) for V(rot) > 150 km/sec. The trend
suggests that galaxies with V(rot) < 100-150 km/sec may lose a large fraction
of their SN ejecta, while galaxies above this value tend to retain metals.


title:
Structure of Bright 2MASS Galaxies: 2D Fits to the Ks-band Surface
  Brightness Profiles

abstract:
  The unprecedented sky coverage and photometric uniformity of the Two Micron
All Sky Survey (2MASS) provides a rich resource for obtaining a detailed
understanding of the galaxies populating our local (z<0.1) Universe. A full
characterization of the physical structure of nearby galaxies is essential for
theoretical and observational studies of galaxy evolution and structure
formation. We have begun a quantified description of the internal structure and
morphology of 10,000 bright (10<Ks<11) 2MASS galaxies through multi-component
model fits to the 2D surface brightness profiles using GIM2D. From our initial
Monte Carlo tests on 77 galaxies drawn at random from the RC3, we find that the
model derived structural parameter errors due to sky uncertainies are typically
less than 10%.


title: Modulation of Ca II H & K Emission by Short-Period Planets

abstract:
  We have detected modulation of the Ca II H&K reversal structure in four out
of five 51 Peg-type stars whose planets have orbital periods between 3 and 4
days. We observe two effects in the K-core: (1) a broad 3-A variation at ~1%
level and (2) changes on a scale of 0.5 A (~1-3%) in each of the three reversal
features. The nightly variations are coherent in both H and K. From
differential radial velocities measured to better than 20 m/s, up-to-date
phases were extracted. The enhancements in the reversals tend to be greatest at
the sub-planetary points which may imply that there is a magnetic interaction
between the star's outer layers and the magnetosphere of the planet. These
high-S/N (500 per pixel in the continuum) and high-resolution (R = 110,000)
data are too few to confirm orbital synchronization.


title:
Pauli Paramagnetism of Neutron Star Matter and the Upper Limit for
  Neutron Star Magnetic Fields

abstract:
  A relativistic version of Pauli paramagnetism for $n-p-e$ system inside a
strongly magnetized neutron star has been developed. An analytical expressions
for the saturation value of magnetic field strength for each of these
constituents at which they are completely polarized have been obtained. From
the fully polarized configuration of electronic component, an upper limit for
neutron star magnetic field is predicted. It has been concluded that indeed,
magnetars, as stronly magnetized young neutron stars can not exist if the
constituents are electron, proton and neutron in $\beta$-equilibrium. An
alternative model has been proposed.


title: Cooling Properties of Cloudy Bag Strange Stars

abstract:
  As the chiral symmetry is widely recognized as an important driver of the
strong interaction dynamics, current strange stars models based on MIT bag
models do not obey such symmetry. We investigate properties of bare strange
stars using the Cloudy Bag Model, in which a pion cloud coupled to the
quark-confining bag is introduced such that chiral symmetry is conserved. We
find that in this model the decay of pions is a very efficient cooling way. In
fact it can carry out most the thermal energy in a few milliseconds and
directly convert them into 100MeV photons via pion decay. This may be a very
efficient $\gamma$-ray burst mechanism. Furthermore, the cooling behavior may
provide a possible way to distinguish a compact object between a neutron star,
MIT strange star and Cloudy Bag strange star in observations.


title: Chandra Observations of Neutron Stars -- An Overview

abstract:
  We present a brief review of Chandra observations of neutron stars, with a
concentration on neutron stars in supernova remnants. The early Chandra results
clearly demonstrate how critical the angular resolution has been in order to
separate the neutron star emission from the surrounding nebulosity.


title:
An inverse method to recover the star formation history and reddening
  properties of a galaxy from its spectrum. Application to NGC 7714

abstract:
  We develop a non-parametric inverse method to investigate the star formation
rate, the metallicity evolution and the reddening properties of galaxies based
on their spectral energy distributions (SEDs). This approach allows us to
clarify the level of information present in the data, depending on its
signal-to-noise ratio (S/N). When low resolution SEDs are available in the
ultraviolet, optical and near-IR wavelength ranges together, we conclude that
it is possible to constrain the star formation rate and the effective dust
optical depth simultaneously with a signal-to-noise ratio of 25. With excellent
signal-to-noise ratios, the age-metallicity relation can also be constrained.
We apply this method to the well-known nuclear starburst in the interacting
galaxy NGC 7714. We focus on deriving the SFR and the reddening law. We confirm
that classical extinction models cannot provide an acceptable simultaneous fit
of the SED and the lines. We also confirm that, with the adopted population
synthesis models and in addition to the current starburst, an episode of
enhanced star formation that started more than 200 Myr ago is required. As the
time elapsed since the last interaction with NGC 7715, based on dynamical
studies, is about 100 Myr, our result reinforces the suggestion that this
interaction might not have been the most important event in the life of NGC
7714.


title: The 2-10 keV emission properties of PSR B1937+21

abstract:
  We present the results of a BeppoSAX observation of the fastest pulsar known:
PSR B1937+21. The ~ 200 ks observation (78.5 (34) ks MECS (LECS) exposure
times) allowed us to investigate with high statistical significance both the
spectral properties and the pulse profile shape. The absorbed power law
spectral model gave a photon index of ~ 1.7 and N_H ~ 2.3 x 10^22 cm^-2. These
values explain both a) the ROSAT non-detection and b) the deviant estimate of a
photon index of ~ 0.8 obtained by ASCA. The pulse profile appears, for the
first time, clearly double peaked with the main component much stronger than
the other. The statistical significance is 10 sigma (main peak) and 5 sigma
(secondary peak). The 1.6-10 keV pulsed fraction is consistent with 100%; only
in the 1.6-4 keV band there is a ~ 2 sigma indication for a DC component. The
secondary peak is detected significantly only for energies above 3 / 4 keV. The
unabsorbed (2-10 keV) flux is F_2-10 = 3.7 x 10^-13 erg cm^-2 s^-1, implying a
luminosity of L_X = 4.6 x 10^31 Theta (d/3.6 kpc)^2 erg s^-1 and an X-ray
efficiency of eta = 4 x 10^-5 Theta, where Theta is the solid angle spanned by
the emission beam. These results are in agreement with those obtained by ASCA.


title: XMM-Newton EPIC observations of Her X-1

abstract:
  We present spin-resolved X-ray data of the neutron star binary Her X-1 taken
using the EPIC detectors on XMM-Newton. The data were taken at three distinct
epochs through the 35 day precession period. The energy dependent light curves
of this source vary significantly from epoch to epoch. It is known that the
relative phasing of the soft (<1 keV) and hard (>2 keV) X-rays varies. Here, we
find that the phase shift between the soft and hard bands during the main-on
state is considerably different from that observed in the past. Further, it
continues to change significantly during the other two observations. This
suggests that we are observing, for the first time, a it substantial and
continuous variation in the tilt of the disk, as it is expected if the
accretion disk is precessing in the system. Analysis of the spin resolved data
confirms that the equivalent width variation of the fluorescence Fe K line at
\~6.4 keV follows that of the soft X-ray emission in the main-on state, thus
suggesting a common origin for Fe K line and thermal component. The Fe K line
is considerably broader when the source is brightest.


title: Gamma-Ray Pulsars

abstract:
  Gamma-ray photons from young pulsars allow the deepest insight into the
properties and interactions of high-energy particles with magnetic and photon
fields in a pulsar magnetosphere. Measurements with the Compton Gamma-Ray
Observatory have led to the detection of nearly ten gamma-ray pulsars. Although
quite a variety of individual signatures is found for these pulsars, some
general characteristics can be summarized: (1) the gamma-ray lightcurves of
most high-energy pulsars show two major peaks with the pulsed emission covering
more than 50% of the rotation, i.e. a wide beam of emission; (2) the gamma-ray
spectra of pulsars are hard (power law index less than 2), often with a
luminosity maximum around 1 GeV. A spectral cutoff above several GeV is found;
(3) the spectra vary with rotational phase indicating different sites of
emission; and (4) the gamma-luminosity scales with the particle flux from the
open regions of the magnetosphere (Goldreich-Julian current).


title: Model atmospheres and SEDs of chemically peculiar stars

abstract:
  Procedure and results of computations of stellar model atmospheres and
spectral energy distributions are discussed. Model atmospheres of some
chemically peculiar stars are computed taking into account detailed information
about their abundances: -- R CrB-like stars of Teff $\sim$ 7000 K, -- Sakurai's
object (V4334 Sgr) of 4000 $<$ \Tef $<$ 7000 K -- Przybylski's star of Teff
$\sim$ 6500 K.
  We show that our self-consistent approach provides a unique possibility to
investigate the temporal changes of physical parameters of chemically peculiar
stars.
  Some problems of computation of model atmospheres of M and C-giants are also
considered.


title: A wind model for high energy pulses

abstract:
  A solution to the sigma problem - that of finding a mechanism capable of
converting Poynting energy flux to particle-borne energy flux in a pulsar wind
- was proposed several years ago by Coroniti and Michel who considered a
particular prescription for magnetic reconnection in a striped wind. This
prescription was later shown to be ineffective. In this paper, we discuss the
basic microphysics of the reconnection process and conclude that a more rapid
prescription is permissible. Assuming dissipation to set in at some distance
outside the light-cylinder, we compute the resulting radiation signature and
find that the synchrotron emission of heated particles appears periodic, in
general showing both a pulse and an interpulse. The predicted spacing of these
agrees well with observation in the case of the Crab and Vela pulsars. Using
parameters appropriate for the Crab pulsar - magnetization parameter at the
light cylinder sigma_L = 6 x 10^4, Lorentz factor Gamma=250 - reasonable
agreement is found with the observed total pulsed luminosity. This suggest that
the high-energy pulses from young pulsars originate not in the co-rotating
magnetosphere within the light cylinder (as in all other models) but from the
radially directed wind well outside it.


title:
Orbital dynamics of three-dimensional bars: III. Boxy/Peanut edge-on
  profiles

abstract:
  We present families, and sets of families, of periodic orbits that provide
building blocks for boxy and peanut (hereafter b/p) edge-on profiles. We find
cases where the b/p profile is confined to the central parts of the model and
cases where a major fraction of the bar participates in this morphology. A b/p
feature can be built either by 3D families associated with 3D bifurcations of
the x1 family, or, in some models, even by families related with the z-axis
orbits and existing over large energy intervals. The {\sf `X'} feature observed
inside the boxy bulges of several edge-on galaxies can be attributed to the
peaks of successive x1v1 orbits (Skokos et al. 2002a, hereafter paper I),
provided their stability allows it. However in general, the x1v1 family has to
overcome the obstacle of a S\ar\D\ar S transition in order to support the
structure of a b/p feature. Other families that can be the backbones of b/p
features are x1v4 and z3.1s. The morphology and the size of the boxy or
peanut-shaped structures we find in our models is determined by the presence
and stability of the families that support b/p features. The present study
favours the idea that the observed edge-on profiles are the imprints of
families of periodic orbits that can be found in appropriately chosen
Hamiltonian systems, describing the potential of the bar.


title: Vortex Configurations, Oscillations and Pinning in Neutron Star Crusts

abstract:
  The rotating neutron superfluid in the inner crust of a neutron star is
threaded by quantized vortex lines. The pinning force from lattice nuclei and
the Magnus force from neutron superfluid act onto a vortex line that has a
finite tension. The configuration of a vortex line in equilibrium comprises a
number of pinned straight lengths separated by unpinned kinks when the rotation
axis is slightly inclined to the major axis of a crystal lattice and the Magnus
force is not so strong. Energy of ~ 4 MeV is required to form a kink at
densities of ~ 3.4 x 10^13 g cm^-3. Magnus force makes the vortex line
parabolic on global scale. There exist two modes, rotational and helical
(Kelvin), for oscillations allowed on a vortex line. The vortex oscillations in
the pinned straight segments are possible only above a minimum frequency. We
find no unstable mode that grows with time. Hence, the vortex configurations
with kinks may be stable and yield the strongly pinned state. The essence of
our results may not be altered even when we consider the vortex behaviors in a
polycrystalline structure. Our studies suggest that pinning of a vortex line in
a polycrystalline structure would be still strong enough to explain the large
glitches.


title: What we can learn from observations of cooling neutron stars

abstract:
  A generic toy model of a cooling neutron star (NS) is used to analyze cooling
of NSs with nucleon and exotic composition of the cores. The model contains the
parameters which specify the levels of slow and enhanced neutrino emission as
well as the lower and upper densities of the layer where the slow emission
transforms into the enhanced one. The prospects to constrain these parameters
from the present and future observations of isolated middle-aged NSs are
discussed.


title: Thermal state of transiently accreting neutron stars

abstract:
  We study thermal states of transiently accreting neutron stars (with mean
accretion rates $\dot{M} \sim 10^{-14}-10^{-9}$ M$_\odot$ yr$^{-1}$) determined
by the deep crustal heating of accreted matter sinking into stellar interiors.
We formalize a direct correspondence of this problem to the problem of cooling
neutron stars. Using a simple toy model we analyze the most important factors
which affect the thermal states of accreting stars: a strong superfluidity in
the cores of low-mass stars and a fast neutrino emission (in nucleon,
pion-condensed, kaon-condensed, or quark phases of dense matter) in the cores
of high-mass stars. We briefly compare the results with the observations of
soft X-ray transients in quiescence. If the upper limit on the quiescent
thermal luminosity of the neutron star in SAX J1808.4-3658 (Campana et al.
2002) is associated with the deep crustal heating, it favors the model of
nucleon neutron-star cores with switched-on direct Urca process.


title:
Spectroscopic Analyses of the "Blue Hook" Stars in omega Centauri: A
  Test of the Late Hot Flasher Scenario

abstract:
  omega Cen contains the largest population of very hot horizontal branch (HB)
stars known in a globular cluster. Recent UV observations (Whitney et al. 1998;
D'Cruz et al. 2000) show a significant population of hot stars below the
zero-age horizontal branch (``blue hook'' stars), which cannot be explained by
canonical stellar evolution. Stars which suffer unusually large mass loss on
the red giant branch and thus experience the helium core flash while descending
the white dwarf cooling curve could populate this region. Theory predicts that
these ``late hot flashers'' should show higher temperatures than the hottest
canonical HB stars and should have helium- and carbon-rich atmospheres. We
obtained and analysed medium resolution spectra of a sample of blue hook stars
to derive their atmospheric parameters. The blue hook stars are indeed both
hotter (Teff > 35,000K) and more helium-rich than classical extreme HB stars.
In addition we find indications for a large enhancement of the carbon abundance
relative to the cluster abundance.


title: Correlations in the orientations of galaxy clusters

abstract:
  The relative orientation of clusters' major elongation axes and clusters'
angular momentum is studied using a large N-body simulation in a box of 500
Mpc/h base length for a standard LambdaCDM model. Employing the technique of
mark correlation functions, we successfully separated the correlations in the
orientation from the well known clustering signal traced by the two-point
correlation function. The correlations in the orientation are highly
significant for our sample of 3000 clusters. We found an alignment of
neighboring clusters, i.e. an enhanced probability of the major elongation axes
of neighboring cluster pairs to be in parallel with each other. At 10 Mpc/h
separation the amplitude of this signal is ~10% above the value expected from
random orientations, and it vanishes on scales larger than 15 Mpc/h. The
``filamentary'' alignment between clusters' major elongation axes and the lines
pointing towards neighboring clusters shows even stronger deviations from
random orientation, which can be detected out to scales of 100 Mpc/h, both in
2D and 3D analyses. Similarly, strong correlations of the angular momentum were
seen. Also a clear signal in the scalar correlation of the absolute value of
the angular momentum, the spin parameter and the mass was found. They extend up
to 50 Mpc/h and have an amplitude of 40%, 15%, and 10% above a random
distribution at 10 Mpc/h separation, respectively.


title: Inner vacuum gap formation and drifting subpulses in pulsars

abstract:
  The problem of formation of the inner vacuum gap in neutron stars with
${\bf\Omega}\cdot{\bf B}<0$ is considered. It is argued by means of the
condition $T_i/T_s>1$, where $T_i$ is the melting temperature of surface
$^{56}_{26}$Fe ions and $T_s$ is the actual temperature of the polar cap
surface, that the inner vacuum gap can form, provided that the actual surface
magnetic field is extremaly strong ($B_s\gtrsim 10^{13}$ G) and curved (${\cal
R}<10^6$ cm), irrespective of the value of dipolar component measured from the
pulsar spin down rate. The calculations are carried out for pulsars with
drifting subpulses and/or periodic intensity modulations, in which the
existence of the quasi steady vacuum gap discharging via ${\bf E}\times{\bf B}$
drifting sparks is almost unavoidable.


title:
Surface Brightness Profiles and Structural Parameters for 53 Rich
  Stellar Clusters in the Large Magellanic Cloud

abstract:
  We have compiled a pseudo-snapshot data set of two-colour observations from
the Hubble Space Telescope archive for a sample of 53 rich LMC clusters with
ages 10^6-10^10 yr. We present surface brightness profiles for the entire
sample, and derive structural parameters for each cluster, including core
radii, and luminosity and mass estimates. Because we expect the results
presented here to form the basis for several further projects, we describe in
detail the data reduction and surface brightness profile construction
processes, and compare our results with those of previous ground-based studies.
The surface brightness profiles show a large amount of detail, including
irregularities in the profiles of young clusters (such as bumps, dips, and
sharp shoulders), and evidence for both double clusters and post core-collapse
(PCC) clusters. In particular we find power-law profiles in the inner regions
of several candidate PCC clusters, with slopes of approximately -0.7, but
showing considerable variation. We estimate that 20 +/- 7 % of the old cluster
population of the LMC has entered PCC evolution, a similar fraction to that for
the Galactic globular cluster system. In addition, we examine the profile of
R136 in detail and show that it is probably not a PCC cluster. We also observe
a trend in core radius with age that has been discovered and discussed in
several previous publications by different authors. Our diagram has better
resolution however, and appears to show a bifurcation at several hundred Myr.
We argue that this observed relationship reflects true physical evolution in
LMC clusters, with some experiencing small scale core expansion due to mass
loss, and others large scale expansion due to some unidentified characteristic
or physical process.


title: A Substellar Mass Function for Alpha Per

abstract:
  We present a deep, wide-field optical survey of the young stellar cluster
Alpha Per, in which we have discovered a large population of candidate brown
dwarfs. Subsequent infrared photometric follow-up shows that the majority of
them are probable or possible members of the cluster, reaching to a minimum
mass of 0.035 Msun. We have used this list of members to derive the luminosity
and mass functions of the substellar population of the cluster
(alpha=0.59+-0.05) and compared its slope to the value measure for the
Pleiades. This comparison indicates that the two cluster mass functions are,
indeed, very similar.


title:
Coronal density diagnostics with Helium-like triplets: CHANDRA--LETGS
  observations of Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD
  Leo, YY Gem, and HR1099

abstract:
  We present an analysis of ten cool stars (Algol, Capella, Procyon, Eps Eri,
Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099) observed with the Low Energy
Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray
Observatory. This sample contains all cools stars observed with the LETGS
presently available to us with integration times sufficiently long to warrant a
meaningful spectral analysis. Our sample comprises inactive, moderately active,
and hyperactive stars and samples the bulk part of activity levels encountered
in coronal X-ray sources. We use the LETGS spectra to carry out density and
temperature diagnostics with an emphasis on the H-like and the He-like ions. We
find a correlation between line flux ratios of the Lyman-Alpha and He-like
resonance lines with the mean X-ray surface flux. We determine densities using
the He-like triplets. For active stars we find no significant deviations from
the low-density limit for the ions of Ne, Mg, and Si, while the measured line
ratios for the ions of C, N, and O do show evidence for departures from the
low-density limit in the active stars, but not in the inactive stars. Best
measurements can be made for the OVII triplet where we find significant
deviations from the low-density limit for the stars Algol, Procyon, YY Gem, Eps
Eri, and HR1099. We discuss the influence of radiation fields on the
interpretation of the He-like triplet line ratios in the low-Z ions, which is
relevant for Algol, and the influence of dielectronic satellite lines, which is
relevant for Procyon. For the active stars YY Gem, Eps Eri, and HR1099 the low
f/i ratios can unambiguously be attributed to high densties in the range 1--3
10^10 cm^-3 at OVII temperatures. We find our LETGS spectra to be an extremely
useful tool for plasma diagnostics of stellar coronae.


title: Effects of dust grains on early galaxy evolution

abstract:
  Stars form out of molecular gas and supply dust grains during their last
evolutionary stages; in turn hydrogen molecules (H2) are produced more
efficiently on dust grains. Therefore, dust can drastically accelerate H2
formation, leading to an enhancement of star formation activity. In order to
examine the first formation of stars and dust in galaxies, we model the
evolution of galaxies in the redshift range of 5<z<20. In particular, we focus
on the interplay between dust formation in Type II supernova ejecta and H2
production on dust grains. Such effect causes an enhancement of star formation
rate by an order of magnitude on a timescale (~3--5 galactic dynamical times)
shorter than the Hubble timescale. We also find that about half of the
radiative energy from stars is reprocessed by dust grains and is finally
radiated in the far infrared (FIR). Typical star formation rates and
luminosities (FIR, UV and metal-line luminosities) are calculated for a large
set of (M_vir, z_vir). Using these results and the Press-Schechter formalism,
we calculate galaxy number counts and integrated light from high-redshift (z>5)
galaxies in sub-millimetre and near-infrared bands. We find that: i) ALMA can
detect dust emission from several thousands of galaxies per square degree, and
ii) NGST can detect the stellar emission from 10^6 galaxies per square degree.
Further observational checks of our predictions include the integrated flux of
metal (oxygen and carbon) lines. We finally discuss possible color selection
strategies for high-redshift galaxy searches.


title: The Evolution of X-ray Clusters of Galaxies

abstract:
  Considerable progress has been made over the last decade in the study of the
evolutionary trends of the population of galaxy clusters in the Universe. In
this review we focus on observations in the X-ray band. X-ray surveys with the
ROSAT satellite, supplemented by follow-up studies with ASCA and Beppo-SAX,
have allowed an assessment of the evolution of the space density of clusters
out to z~1, and the evolution of the physical properties of the intra-cluster
medium out to z~0.5. With the advent of Chandra and Newton-XMM, and their
unprecedented sensitivity and angular resolution, these studies have been
extended beyond redshift unity and have revealed the complexity of the
thermodynamical structure of clusters. The properties of the intra-cluster gas
are significantly affected by non-gravitational processes including star
formation and Active Galactic Nucleus (AGN) activity. Convincing evidence has
emerged for modest evolution of both the bulk of the X-ray cluster population
and their thermodynamical properties since redshift unity. Such an
observational scenario is consistent with hierarchical models of structure
formation in a flat low density universe with Omega_m=0.3 and sigma_8=0.7-0.8
for the normalization of the power spectrum. Basic methodologies for
construction of X-ray-selected cluster samples are reviewed and implications of
cluster evolution for cosmological models are discussed.


title: Self-similar champagne flows in HII regions

abstract:
  (Abridged) We consider the expansion of an initially self-gravitating,
static, singular, isothermal cloud core. For t>0, the gas is ionized and heated
to a higher uniform temperature by the formation of a luminous, but massless,
star in its center. The approximation that the mass and gravity of the central
star is negligible for the subsequent motion of the HII region holds for
distances much greater than about 100 AU and for the massive cloud cores that
give rise to high-mass stars. If the initial ionization and heating is
approximated to occur instantaneously at t=0, then the subsequent flow (for r
>> 100 AU) caused by the resulting imbalance between self-gravity and thermal
pressure is self-similar. Because of the steep density profile, pressure
gradients produce a shock front that travels into the cloud, accelerating the
gas to supersonic velocities in what has been called the ``champagne phase.''
We then study the self-similar solutions of the expansion of HII regions
embedded in molecular clouds characterized by more general power-law density
distributions with exponent 3/2 < n < 3. In these cases, the shock velocity is
an increasing function of the exponent n, and diverges as n tends to 3. We show
that this happens because the model includes an origin, where the pressure
driving the shock diverges because the enclosed heated mass is infinite. Our
results imply that the continued photoevaporation of massive reservoirs of
neutral gas (e.g., surrounding disks and/or globules) nearby to the embedded
ionizing source is required in order to maintain over a significant timescale
the emission measure observed in champagne flows.


title: How to Test Stringy Dark Energy?

abstract:
  It is suggested, by using a covariant lagrangian formalism to estimate the
equation of state $w = p/\rho$, that stringy dark energy predicts $w < -1$, a
negative pressure larger in magnitude than that for a cosmological constant or
quintessence. This would lead to a later transition from decelerating to
accelerating cosmological expansion; $w = - 4/3$ is briefly considered as one
illustrative example.


title: On the orbital period of the cataclysmic variable V592 Herculis

abstract:
  We present a spectroscopic study of the long-recurrence-time dwarf nova V592
Herculis based on observations obtained during its August 1998 superoutburst.
  From the analysis of the radial velocities of the Halpha emission line we
find a most likely orbital period of 85.5 +- 0.4 minutes, but the 91.2 +- 0.6
minutes alias cannot be completely discarded. Both periods imply a very small
period excess and supports the brown-dwarf like nature of the secondary star.


title: Retro-MACHOs: Pi in the sky?

abstract:
  Shine a flashlight on a black hole, and one is greeted with the return of a
series of concentric rings of light. For a point source of light, and for
perfect alignment of the lens, source, and observer, the rings are of infinite
brightness (in the limit of geometric optics). In this manner, distant black
holes can be revealed through their reflection of light from the Sun. Such
retro-MACHO events involve photons leaving the Sun, making a Pi rotation about
the black hole, and then returning to be detected at the Earth. Our
calculations show that, although the light return is quite small, it may
nonetheless be detectable for stellar-mass black holes at the edge of our solar
system. For example, all (unobscured) black holes of mass M or greater will be
observable to a limiting magnitude m, at a distance given by: 0.02 pc x
\sqrt[3]{10^{(m-30)/2.5} (M/10 M_sun)^2}. Discovery of a Retro-MACHO offers a
way to directly image the presence of a black hole, and would be a stunning
confirmation of strong-field general relativity.


title: Analytic Cross Sections for Substructure Lensing

abstract:
  The magnifications of the images in a strong gravitational lens system are
sensitive to small mass clumps in the lens potential; this effect has been used
to infer the amount of substructure in galaxy dark matter halos. I study the
theory of substructure lensing to identify important general features, and to
compute analytic cross sections that will facilitate further theoretical
studies. I show that the problem of a clump anywhere along the line of sight to
a lens can be mapped onto an equivalent problem of a clump in a simple
convergence and shear field; clumps at arbitrary redshifts are therefore not
hard to handle in calculations. For clumps modeled as singular isothermal
spheres (SIS), I derive simple analytic estimates of the cross section for
magnification perturbations of a given strength. The results yield two
interesting conceptual points. First, lensed images with positive parity are
always made brighter by SIS clumps; images with negative parity can be
brightened but are much more likely to be dimmed. Second, the clumps need not
lie within the lens galaxy; they can be moved in redshift by several tenths and
still have a significant lensing effect. Isolated small halos are expected to
be common in hierarchical structure formation models, but it is not yet known
whether they are abundant enough compared with clumps inside lens galaxies to
affect the interpretation of substructure lensing.


title: Inventory of Black Hole Binaries

abstract:
  A small group of X-ray binaries currently provides the best evidence for the
existence of stellar-mass black holes. These objects are interacting binary
systems where the X-rays arise from accretion of material onto a compact object
(i.e. an object with a radius of less than a few hundred km). In some
favourable cases, optical studies of the companion star lead to dynamical mass
estimates for both components. In 17 cases, the mass of the compact object an
X-ray binary has been shown to exceed the maximum mass of a stable neutron star
(about 3 solar masses), which leads to the conclusion that these objects are
black holes. In this contribution I will review the basic properties of these
black hole binaries.


title:
Pseudo-Newtonian Potentials to Describe the Temporal Effects on
  Relativistic Accretion Disks around Rotating Black Holes and Neutron Stars

abstract:
  Two pseudo-Newtonian potentials, which approximate the angular and epicyclic
frequencies of the relativistic accretion disk around rotating (and counter
rotating) compact objects, are presented. One of them, the Logarithmically
Modified Potential, is a better approximation for the frequencies while the
other, the Second-order Expanded potential, also reproduces the specific energy
for circular orbits in close agreement with the General Relativistic values.
These potentials may be included in time dependent hydrodynamical simulations
to study the temporal behavior of such accretion disks.


title: Chemodynamical Modeling of Dwarf Galaxy Evolution

abstract:
  We present our recently developed 3-dimensional chemodynamical code for
galaxy evolution. It follows the evolution of all components of a galaxy such
as dark matter, stars, molecular clouds and diffuse interstellar matter (ISM).
Dark matter and stars are treated as collisionless $N$-body systems. The ISM is
numerically described by a smoothed particle hydrodynamics (SPH) approach for
the diffuse (hot) gas and a sticky particle scheme for the (cool) molecular
clouds. Additionally, the galactic components are coupled by several phase
transitions like star formation, stellar death or condensation and evaporation
processes within the ISM. As an example here we present the dynamical, chemical
and photometric evolution of a star forming dwarf galaxy with a total baryonic
mass of $2 \times 10^9 {\rm M}_\odot$.


title:
Carbon star populations in systems with different metallicities:
  statistics in Local Group galaxies

abstract:
  We present evolutionary population synthesis models for the study of the cool
and luminous intermediate age stellar populations in resolved galaxies with
particular emphasis on carbon star populations. We study the effects of the
star formation history, the age and the metallicity on the populations of
intermediate mass stars. In the case of instantaneous bursts, we confirm that
lower metallicity results in higher contribution of carbon stars to the total
star number, and in higher number ratios of carbon stars to late-type M stars.
Chemically consistent models are used to study the effect of the star formation
history on the relations between carbon star population properties and global
parameters of the parent galaxy (age, metallicity). Our models are able to
account, for the first time, for those correlations, as observed in the
galaxies of the Local Group. For stellar populations older than 1 Gyr, the
properties of carbon star populations are linked to the current metallicity in
a way that is quite independent of the star formation scenario. The number of
carbon stars to late-type M stars forms a metallicity sequence along which
stellar populations with very different star formation histories are found
(Abridged).


title: Calibration of White Dwarf cooling sequences: theoretical uncertainty

abstract:
  White Dwarf luminosities are powerful age indicators, whose calibration
should be based on reliable models. We discuss the uncertainty of some chemical
and physical parameters and their influence on the age estimated by means of
white dwarf cooling sequences. Models at the beginning of the white dwarf
sequence have been obtained on the base of progenitor evolutionary tracks
computed starting from the zero age horizontal branch and for a typical halo
chemical composition (Z=0.0001, Y=0.23). The uncertainties due to nuclear
reaction rates, convection, mass loss and initial chemical composition are
discussed. Then, various cooling sequences for a typical white dwarf mass
(M=0.6 Mo) have been calculated under different assumptions on some input
physics, namely: conductive opacity, contribution of the ion-electron
interaction to the free energy and microscopic diffusion. Finally we present
the evolution of white dwarfs having mass ranging between 0.5 and 0.9 Mo. Much
effort has been spent to extend the equation of state down to the low
temperature and high density regime. An analysis of the latest improvement in
the physics of white dwarf interiors is presented. We conclude that at the
faint end of the cooling sequence (log L/Lo=-5.5) the present overall
uncertainty on the age is of the order of 20%, which correspond to about 3 Gyr.
We suggest that this uncertainty could be substantially reduced by improving
our knowledge of the conductive opacity (especially in the partially degenerate
regime) and by fixing the internal stratification of C and O.


title:
Surface Brightness Profiles and Structural Parameters for 10 Rich
  Stellar Clusters in the Small Magellanic Cloud

abstract:
  As a follow up to our recent study of a large sample of LMC clusters
(astro-ph/0209031), we have conducted a similar study of the structures of ten
SMC clusters, using archival Hubble Space Telescope snapshot data. We present
surface brightness profiles for each cluster, and derive structural parameters,
including core radii and luminosity and mass estimates, using exactly the same
procedure as for the LMC sample. Because of the small sample size, the SMC
results are not as detailed as for the larger LMC sample. We do not observe any
post core-collapse clusters (although we did not expect to), and there is
little evidence for any double clusters in our sample. Nonetheless, despite the
small sample size, we show for the first time that the SMC clusters follow
almost exactly the trend in core radius with age observed for the LMC system,
including the apparent bifurcation at several hundred Myr. This further
strengthens our argument that this relationship represents true physical
evolution in these clusters, with some developing significantly expanded cores
due to an as yet unidentified physical process. Additional data, both
observational and from N-body simulations, is still required to clarify many
issues.


title:
Future Opportunities for Globular Cluster Astronomy at Ground Based
  Facilities

abstract:
  In spite of great progress over the last $\sim 10$ years, especially thanks
to HST, a number of exciting open problem still puzzle astronomers working on
globular clusters in our own and other galaxies. These problems range from
determining more accurate ages to assess whether massive black holes hide at
the center of some clusters, from identifying the physical origin of red giant
winds to assess whether there is an influence of cluster structure and dynamics
on the evolution of individual cluster stars, from demonstrating whether or not
some clusters possess a dark matter halo on their own to eventually understand
the formation of globular clusters in the context of galaxy formation, and
more. In this review, I briefly sketch how ground based telescopes and their
instrumentation can help solving these problems through the present decade,
2001-2010. A glimpse to the next decade is also given.


title: A deep UVBRI CCD photometric study of open clusters Tr 1 and Be 11

abstract:
  We present deep $UBVRI$ CCD photometry for the young open star clusters Tr 1
and Be 11. The CCD data for Be 11 is obtained for the first time. The sample
consists of $\sim$ 1500 stars reaching down to $V$ $\sim$ 21 mag. Analysis of
the radial distribution of stellar surface density indicates that radius values
for Tr 1 and Be 11 are 2.3 and 1.5 pc respectively. The interstellar extinction
across the face of the imaged clusters region seems to be non-uniform with a
mean value of $E(B-V)$ = 0.60$\pm$0.05 and 0.95$\pm$0.05 mag for Tr 1 and Be 11
respectively. A random positional variation of $E(B-V)$ is present in both the
clusters. In the cluster Be 11, the reason of random positional variation may
be apparent association of the HII region (S 213). The 2MASS $JHK$ data in
combination with the optical data in the cluster Be 11 yields $E(J-K)$ =
0.40$\pm$0.20 mag and $E(V-K)$ = 2.20$\pm$0.20 mag. Colour excess diagrams
indicate a normal interstellar extinction law in the direction of cluster Be
11. The distances of Tr 1 and Be 11 are estimated as 2.6$\pm$0.10 and
2.2$\pm$0.10 Kpc respectively, while the theoretical stellar evolutionary
isochrones fitted to the bright cluster members indicate that the cluster Tr 1
and Be 11 are 40$\pm$10 and 110$\pm$10 Myr old. The mass functions corrected
for both field star contamination and data incompleteness are derived for both
the clusters. The slopes $1.50\pm0.40$ and $1.22\pm0.24$ for Tr 1 and Be 11
respectively are in agreement with the Salpeter's value. Observed mass
segregations in both clusters may be due to the result of dynamical evolutions
or imprint of star formation processes or both.


title:
Kinematics of the Pencil Nebula (RCW 37) and its association with the
  young Vela supernova remnant RX J0852.0-4622

abstract:
  The association between the Pencil nebula (RCW 37, NGC 2736), the Vela X-ray
fragment D/D' and the recently discovered new X-ray supernova remnant (RX
J0852.0-4622) in Vela is investigated. Recently published Chandra images of
D/D' are compared with optical images of RCW 37 and confirm the close
association of the two objects. New optical line profiles of RCW 37 from an
extended slit position passing through this unusual optical nebula are
presented. They reveal a partial velocity ellipse with expansion velocities of
around 120 km/s. Various scenarios for the origin of the nebula are considered
and the evidence of a link with RX J0852.0-4622 is reviewed. A funnel of gas
similar to those in the Crab and DEM34a SNRs is not ruled out but a more
plausible explanation may be that a `wavy sheet' is responsible. We suggest
that RX J0852.0-4622 is located within the older larger Vela SNR and that some
of the X-ray gas from RX J0852.0-4622 has collided with the dense HI wall of
the older remnant. This gives rise to the morphology and velocity structure of
the optical emission and explains the unusual X-ray emission from this portion
of the supernova remnant. If our hypothesis is correct, a distance prediction
of 250 +/- 30 pc can be made, based on recent measurements of the distance to
the old Vela SNR. This is at the lower end of the range of distances quoted in
the literature would confirm unusual nature of this young nearby supernova
remnant.


title: Modeling the emission line sequence of H II galaxies

abstract:
  Using a sample of unprecedented size (about 400 objects) of H II galaxies in
which the oxygen abundances have been obtained using the temperature derived
from the [OIII] 4363/5007 line ratio, we confirm that the H II galaxies form a
very narrow sequence in many diagrams relating line ratios and Hbeta equivalent
width. We divide our sample in three metallicity bins, each of which is
compared with sequences of photoionization models for evolving starbursts with
corresponding metallicity. Our aim is to find under what conditions a
theoretical sequence can reproduce all the observed trends. Taking into account
the presence of an older, non-ionizing stellar population, for which
independent indications exist, we find that the simple model of an adiabatic
expanding bubble reproduces the observational diagrams very well if account is
taken of an aperture correction and the covering factor is assumed to decrease
with time exponentially with an e-folding time of 3 Myr. We find that the He II
4686 nebular line emission occurs too frequently and in too wide a range of
EW(Hbeta) to be attributable to either the hard radiation field from Wolf-Rayet
stars or the X-rays produced by the latest stellar generation. Assuming that
the He II 4686 line is due to photoionization by a hot plasma at a temperature
of 10^6 K, a total X-ray luminosity of 10^40 - 4x10^40 erg/s is required for at
least half of the sources. We find evidence for self-enrichment in nitrogen on
a time scale of several Myr, and argue for a possible self-enrichment in oxygen
as well.


title: Correlating galaxy morphologies and spectra in the 2dFGRS

abstract:
  The correlation between a galaxy's morphology and its observed optical
spectrum is investigated. As an example, 4000 galaxies from the 2dF Galaxy
Redshift Survey, which possess both good quality spectra and have visually
determined morphologies are analysed. Of particular use is the separation of
Early and Late type galaxies present in a redshift survey since these can then
be used in their respective redshift-independent distance estimators (Dn-sigma
and Tully-Fisher). It is determined that galaxies in this sample can be
relatively successfully separated into these two types by the use of various
statistical methods. These methods are briefly outlined in this paper and are
also compared to the default 2dFGRS spectral classification (eta). In addition
it is found that the 4000Ang break in the spectrum is the best discriminant in
determining its morphological type.


title: Highlights of Stellar Modeling with PHOENIX

abstract:
  We briefly describe the current version of the PHOENIX code. We then present
some illustrative results from the modeling of Type Ia and Type II supernovae,
hot stars, and irradiated giant planets. Good fits to observations can be
obtained, when account is taken for spherically symmetric, line-blanketed,
static or expanding atmospheres.


title: Radiative accelerations on Ne in the atmospheres of late B stars

abstract:
  Radiative accelerations on Ne are calculated for the atmospheres of main
sequence stars with 11000 < Teff < 15000 K, corresponding to the range of the
HgMn stars. The calculations take into account neon fine structure as well as
shadowing of neon lines using the entire Kurucz line list, bound-bound,
bound-free, and free-free opacity of H, He, and C as well as some NLTE effects.
NLTE effects modify the radiative acceleration by a factor of order 100 in the
outer atmosphere. The dependence of the radiative acelerations on the Ne
abundance, Teff, and gravity is studied. Radiative accelerations are well below
gravity in the entire range of Teff and it is predicted that in stable
atmospheres Ne should sink and be observed as underabundant. This agrees with
recent observations of low Ne abundances in HgMn stars.


title:
Solar Multi-Scale Convection and Rotation Gradients Studied in Shallow
  Spherical Shells

abstract:
  The differential rotation of the sun, as deduced from helioseismology,
exhibits a prominent radial shear layer near the top of the convection zone
wherein negative radial gradients of angular velocity are evident in the low-
and mid-latitude regions spanning the outer 5% of the solar radius.
Supergranulation and related scales of turbulent convection are likely to play
a significant role in the maintenance of such radial gradients, and may
influence dynamics on a global scale in ways that are not yet understood. To
investigate such dynamics, we have constructed a series of three-dimensional
numerical simulations of turbulent compressible convection within spherical
shells, dealing with shallow domains to make such modeling computationally
tractable. These simulations are the first models of solar convection in a
spherical geometry that can explicitly resolve both the largest dynamical
scales of the system (of order the solar radius) as well as smaller-scale
convective overturning motions comparable in size to solar supergranulation
(20--40 Mm). We find that convection within these simulations spans a large
range of horizontal scales, and that the radial angular velocity gradient in
these models is typically negative, especially in low- and mid-latitude
regions. Analyses of the angular momentum transport indicates that such
gradients are maintained by Reynolds stresses associated with the convection,
transporting angular momentum inward to balance the outward transport achieved
by viscous diffusion and large-scale flows in the meridional plane. We suggest
that similar mechanisms associated with smaller-scale convection in the sun may
contribute to the maintenance of the observed radial shear layer located
immediately below the solar photosphere.


title: The BTC40 Survey for Quasars at 4.8 < z < 6

abstract:
  The BTC40 Survey for high-redshift quasars is a multicolor search using
images obtained with the Big Throughput Camera (BTC) on the CTIO 4-m telescope
in V, I, and z filters to search for quasars at redshifts of 4.8 < z < 6. The
survey covers 40 sq. deg. in B, V, & I and 36 sq. deg. in z. Limiting
magnitudes (3 sigma) reach to V = 24.6, I = 22.9 and z = 22.9. We used the
(V-I) vs. (I-z) two-color diagram to select high-redshift quasar candidates
from the objects classified as point sources in the imaging data. Follow-up
spectroscopy with the AAT and CTIO 4-m telescopes of candidates having I < 21.5
has yielded two quasars with redshifts of z = 4.6 and z = 4.8 as well as four
emission line galaxies with z = 0.6. Fainter candidates have been identified
down to I = 22 for future spectroscopy on 8-m class telescopes.


title: Reionization of Hydrogen and Helium by Early Stars and Quasars

abstract:
  We compute the reionization histories of hydrogen and helium due to the
ionizing radiation fields produced by stars and quasars. For the quasars we use
a model based on halo-merger rates that reproduces all known properties of the
quasar luminosity function at high redshifts. The less constrained properties
of the ionizing radiation produced by stars are modeled with two free
parameters: (i) a transition redshift, z_tran, above which the stellar
population is dominated by massive, zero-metallicity stars and below which it
is dominated by a Scalo mass function; (ii) the product of the escape fraction
of stellar ionizing photons from their host galaxies and the star-formation
efficiency, f_esc f_*. We constrain the allowed range of these free parameters
at high redshifts based on the lack of the HI Gunn-Peterson trough at z<6 and
the upper limit on the total intergalactic optical depth for electron
scattering, tau_es<0.18, from recent cosmic microwave background (CMB)
experiments. We find that quasars ionize helium by a redshift z~4, but cannot
reionize hydrogen by themselves before z~6. A major fraction of the allowed
combinations of f_esc f_* and z_tran lead to an early peak in the ionized
fraction due to metal-free stars at high redshifts. This sometimes results in
two reionization epochs, namely an early HII or HeIII overlap phase followed by
recombination and a second overlap phase. Even if early overlap is not
achieved, the peak in the visibility function for scattering of the CMB often
coincides with the early ionization phase rather than with the actual
reionization epoch. Consequently, tau_es does not correspond directly to the
reionization redshift. We generically find values of tau_es>7%, that should be
detectable by the MAP satellite.


title:
Planetesimal disk evolution driven by planetesimal-planetesimal
  gravitational scattering

abstract:
  We investigate the process of an inhomogeneous planetesimal disk evolution
caused by the planetesimal-planetesimal gravitational scattering. We develop a
rather general approach based on the kinetic theory which self-consistently
describes the evolution in time and space of both the disk surface density and
its kinematic properties -- dispersions of eccentricity and inclination. The
gravitational scattering of planetesimals is assumed to be in the
dispersion-dominated regime which considerably simplifies analytical treatment.
The resultant equations are of advection-diffusion type. Distance dependent
scattering coefficients entering these equations are calculated analytically
under the assumption of two-body scattering in the leading order in Coulomb
logarithm. They are essentially nonlocal in nature. Our approach allows one to
explore the dynamics of nonuniform planetesimal disks with arbitrary mass and
random velocity distributions. It can also naturally include other physical
mechanisms which are important for the evolution of such disks -- gas drag,
migration, and so on.


title:
Planetesimal disk evolution driven by embryo-planetesimal gravitational
  scattering

abstract:
  The process of gravitational scattering of planetesimals by a massive
protoplanetary embryo is explored theoretically. We propose a method to
describe the evolution of the disk surface density, eccentricity, and
inclination caused by the embryo-planetesimal interaction. It relies on the
analytical treatment of the scattering in two extreme regimes of the
planetesimal epicyclic velocities: shear-dominated (dynamically ``cold'') and
dispersion-dominated (dynamically ``hot''). In the former, planetesimal
scattering can be treated as a deterministic process. In the latter, scattering
is mostly weak because of the large relative velocities of interacting bodies.
This allows one to use the Fokker-Planck approximation and the two-body
approximation to explore the disk evolution. We compare the results obtained by
this method with the outcomes of the direct numerical integrations of
planetesimal orbits and they agree quite well. In the intermediate velocity
regime an approximate treatment of the disk evolution is proposed based on
interpolation between the two extreme regimes. We also calculate the rate of
embryo's mass growth in an inhomogeneous planetesimal disk and demonstrate that
it is in agreement with both the simulations and earlier calculations. Finally
we discuss the question of the direction of the embryo-planetesimal interaction
in the dispersion-dominated regime and demonstrate that it is repulsive. This
means that the embryo always forms a gap in the disk around it, which is in
contrast with the results of other authors. The machinery developed here will
be applied to realistic protoplanetary systems in future papers.


title: The growth of planetary embryos: orderly, runaway, or oligarchic?

abstract:
  We consider the growth of a protoplanetary embryo embedded in a planetesimal
disk. We take into account the dynamical evolution of the disk caused by (1)
planetesimal-planetesimal interactions, which increase random motions and
smooth gradients in the disk, and (2) gravitational scattering of planetesimals
by the embryo, which tends to heat up the disk locally and repels planetesimals
away. The embryo's growth is self-consistently coupled to the planetesimal disk
dynamics. We demonstrate that details of the evolution depend on only two
dimensionless parameters incorporating all the physical characteristics of the
problem: the ratio of the physical radius to the Hill radius of any solid body
in the disk and the number of planetesimals inside the annulus of the disk with
width equal to the planetesimal Hill radius. The results of exploration in the
framework of our model of several situations typical for protosolar nebula can
be summarized as follows: initially, the planetesimal disk dynamics is not
affected by the presence of the embryo and the growth of the embryo's mass
proceeds very rapidly in the runaway regime. Later on, when the embryo starts
being dynamically important, its accretion slows down similar to the
``oligarchic'' growth picture. The scenario of orderly growth suggested by
Safronov (1972) is never realized in our calculations; scenario of runaway
growth suggested by Wetherill & Stewart (1989) is only realized for a limited
range in mass. Slow character of the planetesimal accretion on the oligarchic
stage of the embryo's accumulation leads to a considerable increase of the
protoplanetary formation timescale compared to that following from a simple
runaway accretion picture valid in the homogeneous planetesimal disks.


title:
Energy Spectra and Normalized Power Spectral Densities of X-Ray Nova GS
  2000+25

abstract:
  The X-ray energy spectra and Normalized Power Spectral Densities (NPSDs) of
an X-ray nova, GS 2000+25, were investigated. The X-ray energy spectra of the
source consist of two components: a hard component, which can be represented by
a power-law, and an ultra-soft component, represented by radiation from an
optically-thick accretion disk (the disk component). In a model in which the
power-law component is the Compton-scattered radiation, it is found that the
temperature of the incident blackbody radiation to the Compton cloud decrease
from 0.8 keV to 0.2 keV according to the decay of the intensity, which
coincides with that of the inner accretion disk. When the source changed from
the high-state to the low-state, both the photon index of the power-law
component (or Compton y-parameter) and the NPSD of the hard component
dramatically changed as did GS 1124-683. That is, the photon index changed from
2.2--2.6 to 1.7--1.8 and the absolute values of the NPSDs at 0.3 Hz of the hard
component in the low-state became about 10-times larger than those of the hard
component in the high-state. These X-ray properties were similar to those of
other black-hole candidates, such as Cyg X-1, GX 339-4, and LMC X-3.


title: On the Fate of Close-in Extrasolar Planets

abstract:
  It has been shown that there is a possible mass-period correlation for
extrasolar planets from the current observational data and this correlation is,
in fact, related to the absence of massive close-in planets, which are strongly
influenced by the tidal interaction with the central star. We confirm that the
model in P\"atzold & Rauer (2002) is a good approximation for the explanation
of the absence of massive close-in planets. We thus further determine the
minimum possible semimajor axis for these planets to be detected during their
lifetime and also study their migration time scale at different semimajor axes
by the calculations of tidal interaction. We conclude that the mass-period
correlation at the time when these planets were just formed was less tight than
it is now observed if these orbital migrations are taken into account.


title: SIMBOL-X, a new generation X-ray telescope for the 0.5-70 keV range

abstract:
  SIMBOL-X is a high energy "mini" satellite class mission that is proposed by
a French-Italian-English collaboration for a launch in 2009. SIMBOL-X is making
use of a classical X-ray mirror, of ~ 600 cm2 maximum effective area, with a 30
m focal length in order to cover energies up to several tens of keV. This focal
length will be achieved through the use of two spacecrafts in a formation
flying configuration. This will give to SIMBOL-X unprecedented spatial
resolution (20" HEW) and sensitivity in the hard X-ray range. By its coverage,
from 0.5 to 70 keV, and sensitivity, SIMBOL-X will be an excellent instrument
for the study of high energy processes in a large number of sources, as in
particular accreting black-holes, extragalactic jets and AGNs.


title: Cross-spectral analysis of the X-ray variability of Mrk 421

abstract:
  Using the cross-spectral method, we confirm the existence of the X-ray hard
lags discovered with cross-correlation function technique during a large flare
of Mrk 421 observed with BeppoSAX . For the 0.1--2 versus 2--10keV light
curves, both methods suggest sub-hour hard lags. In the time domain, the degree
of hard lag, i.e., the amplitude of the 3.2--10 keV photons lagging the lower
energy ones, tends to increase with the decreasing energy. In the Fourier
frequency domain, by investigating the cross-spectra of the 0.1--2/2--10 keV
and the 2--3.2/3.2--10 keV pairs of light curves, the flare also shows hard
lags at the lowest frequencies. However, with the present data, it is
impossible to constrain the dependence of the lags on frequencies even though
the detailed simulations demonstrate that the hard lags at the lowest
frequencies probed by the flare are not an artifact of sparse sampling, Poisson
and red noise. As a possible interpretation, the implication of the hard lags
is discussed in the context of the interplay between the (diffusive)
acceleration and synchrotron cooling of relativistic electrons responsible for
the observed X-ray emission. The energy-dependent hard lags are in agreement
with the expectation of an energy-dependent acceleration timescale. The
inferred magnetic field (B ~ 0.11 Gauss) is consistent with the value inferred
from the Spectral Energy Distributions of the source. Future investigations
with higher quality data that whether or not the time lags are
energy-/frequency-dependent will provide a new constraint on the current models
of the TeV blazars.


title: Hypernovae and their Nucleosynthesis

abstract:
  We review the characteristics of nucleosynthesis in 'Hypernovae', i.e.,
core-collapse supernovae with very large explosion energies ($ \gsim 10^{52} $
ergs). The hypernova yields show the following characteristics: 1) The mass
ratio between the complete and incomplete Si burning regions is larger in
hypernovae than normal supernovae. As a result, higher energy explosions tend
to produce larger [(Zn, Co, V)/Fe] and smaller [(Mn, Cr)/Fe], which could
explain the trend observed in very metal-poor stars. 2) Because of enhanced
$\alpha$-rich freezeout, $^{44}$Ca, $^{48}$Ti, and $^{64}$Zn are produced more
abundantly than in normal supernovae. The large [(Ti, Zn)/Fe] ratios observed
in very metal poor stars strongly suggest a significant contribution of
hypernovae. 3) Oxygen burning takes place in more extended regions in
hypernovae to synthesize a larger amount of Si, S, Ar, and Ca ("Si"), which
makes the "Si"/O ratio larger. The abundance pattern of the starburst galaxy
M82 may be attributed to hypernova explosions. We thus suggest that hypernovae
make important contribution to the early Galactic (and cosmic) chemical
evolution.


title: The low mas end of the young cluster IC2391

abstract:
  By collecting optical and infrared photometry, as well as medium resolution
spectroscopy, we have discovered a sample of low mass stars and brwon dwarfs in
the young cluster IC2391. Using the lithium depletion boundary near the
substellar limit, we have estimated the age of the cluster as ~50 Myr. We have
also estudied the H(alpha) emission in this sample.


title: The chemical evolution of the solar neighbourhood

abstract:
  Recent models of galactic chemical evolution account for updated evolutionary
models of massive stars (with special emphasis on stellar winds) and for the
effects of intermediate mass and massive binaries. The results are summarised.
We also present a critical discussion on possible effects of stellar rotation
on overall galactic chemical evolutionary simulations.


title:
The Massive Stellar Content in the Starburst NGC3049: A Test for
  Hot-Star Mode

abstract:
  We have obtained high-spatial resolution ultraviolet and optical STIS
spectroscopy and imaging of the metal-rich nuclear starburst in NGC3049. The
stellar continuum and the absorption line spectrum in the ultraviolet are used
to constrain the massive stellar population. The strong, blueshifted stellar
lines of CIV and SiIV detected in the UV spectra indicate a metal-rich,
compact, massive (1E6 Msol) cluster of age 3--4 Myr emitting the UV-optical
continuum. We find strong evidence against a depletion of massive stars in this
metal-rich cluster. The derived age and the upper mass-limit cut-off of the
initial mass function are also consistent with the detection of Wolf-Rayet (WR)
features at optical wavelengths. As a second independentconstraint on the
massive stellar content, the nebular emission-line spectrum is modeled with
photoionization codes using stellar spectra from evolutionary synthesis models.
However, the nebular lines are badly reproduced by 3--4 Myr instantaneous
bursts, as required by the UV line spectrum, when unblanketed WR and/or Kurucz
stellar atmospheres are used. The corresponding number of photons above 24 and
54 eV in the synthetic models is too high in comparison with values suggested
by the observed line ratios. Since the ionizing spectrum in this regime is
dominated by emission from WR stars, this discrepancy between observations and
models is most likely the result of incorrect assumptions about the WR stars.
Thus we conclude that the nebular spectrum of high-metallicity starbursts is
poorly reproduced by models for WR dominated populations. However, the new
model set of Smith et al. (2002) with blanketed WR and O atmospheres and
adjusted WR temperatures predicts a softer far-UV radiation field, providing a
better match to the data.


title: Microscopic study of neutrino trapping in hyperon stars

abstract:
  Employing the most recent parametrization of the baryon-baryon interaction of
the Nijmegen group, we investigate, in the framework of the
Brueckner--Bethe--Goldstone many-body theory at zero temperature, the influence
of neutrino trapping on the composition, equation of state, and structure of
neutron stars, relevant to describe the physical conditions of a neutron star
immediately after birth (protoneutron star). We find that the presence of
neutrinos changes significantly the composition of matter delaying the
appearance of hyperons and making the equation of state stiffer. We explore the
consequences of neutrino trapping on the early evolution of a neutron star and
on the nature of the final compact remnant left by the supernova explosion.


title: A Disk--Jet interaction model for the X--Ray Variability in Microquasars

abstract:
  We propose a simple dynamical model that may account for the observed
spectral and temporal properties of GRS 1915+105 and XTE J1550-5634. The model
is based on the assumption that a fraction of the radiation emitted by a hot
spot lying on the accreting disk is dynamically Comptonized by the relativistic
jet that typically accompanies the microquasar phenomenon. We show that
scattering by the jet produces a detectable modulation of the observed flux. In
particular, we found that the phase lag between hard and soft photons depends
on the radial position of the hot spot and, if the angle between the jet and
the line of sight is sufficiently large, the lags of the fundamental and its
harmonics may be either positive or negative.


title: I0-Jupiter system: A unique case of Moon-Planet interaction

abstract:
  Io and Jupiter constitute a moon-planet system that is unique in our solar
system. Io is the most volcanically active planetary body, while Jupiter is the
first among the planets in terms of size, mass, magnetic field strength, spin
rate, and volume of the magnetosphere. That Io is electrodynamically linked to
Jupiter is known for nearly four decades from the radio emissions. Io
influences Jupiter by supplying heavy ions to its magnetosphere, which
dominates its energetic and dynamics. Jupiter influences Io by tidally heating
its interior, which in turn drives the volcanic activity on Io. The role of Io
and Jupiter in their mutual interaction and the nature of their coupling were
first elaborated in greater detail by the two Voyagers flybys in 1979.
Subsequent exploration of this system by ground-based and Earth-satellite-borne
observatories and by the Galileo orbiter mission has improved our understanding
of the highly complex electrodynamical interaction between Io and Jupiter many
fold. A distinct feature of this interaction has been discovered in Jupiter's
atmosphere as a auroral-like bright emission spot along with a comet-like tail
in infrared (IR), ultraviolet (UV), and visible wavelengths at the foot of Io
flux tube (IFT). The HST and Galileo and Cassini imagining experiments have
observed emissions from the Io's atmosphere at UV and visible wavelengths,
which could be produced by energetic electrons in IFT. In this paper an
overview on these aspects of the Io-Jupiter system is presented, which by
virtue of its electrodynamical coupling, has implications for the extra-solar
planetary system and binary stars.


title:
On the electromagnetic field of a charged collapsing spherical shell in
  general relativity

abstract:
  A new exact solution of the Einstein-Maxwell equations for the gravitational
collapse of a shell of matter in an already formed black hole is given. Both
the shell and the black hole are endowed with electromagnetic structure and are
assumed spherically symmetric. Implications for current research are outlined.


title: Irreducible mass and energetics of an electromagnetic black hole

abstract:
  The mass-energy formula for a black hole endowed with electromagnetic
structure (EMBH) is clarified for the nonrotating case. The irreducible mass
$M_{\mathrm{irr}}$ is found to be independent of the electromagnetic field and
explicitly expressable as a function of the rest mass, the gravitational energy
and the kinetic energy of the collapsing matter at the horizon. The
electromagnetic energy is distributed throughout the entire region extending
from the horizon of the EMBH to infinity. We discuss two conceptually different
mechanisms of energy extraction occurring respectively in an EMBH with
electromagnetic fields smaller and larger than the critical field for vacuum
polarization. For a subcritical EMBH the energy extraction mechanism involves a
sequence of discrete elementary processes implying the decay of a particle into
two oppositely charged particles. For a supercritical EMBH an alternative
mechanism is at work involving an electron-positron plasma created by vacuum
polarization. The energetics of these mechanisms as well as the definition of
the spatial regions in which thay can occur are given. The physical
implementations of these ideas are outlined for ultrahigh energy cosmic rays
UHECR) and gamma ray bursts (GRBs).


title: How Sample Completeness Affects Gamma-Ray Burst Classification

abstract:
  Unsupervised pattern recognition algorithms support the existence of three
gamma-ray burst classes; Class I (long, large fluence bursts of intermediate
spectral hardness), Class II (short, small fluence, hard bursts), and Class III
(soft bursts of intermediate durations and fluences). The algorithms
surprisingly assign larger membership to Class III than to either of the other
two classes. A known systematic bias has been previously used to explain the
existence of Class III in terms of Class I; this bias allows the fluences and
durations of some bursts to be underestimated (Hakkila et al., ApJ 538, 165,
2000). We show that this bias primarily affects only the longest bursts and
cannot explain the bulk of the Class III properties. We resolve the question of
Class III existence by demonstrating how samples obtained using standard
trigger mechanisms fail to preserve the duration characteristics of small peak
flux bursts. Sample incompleteness is thus primarily responsible for the
existence of Class III. In order to avoid this incompleteness, we show how a
new dual timescale peak flux can be defined in terms of peak flux and fluence.
The dual timescale peak flux preserves the duration distribution of faint
bursts and correlates better with spectral hardness (and presumably redshift)
than either peak flux or fluence. The techniques presented here are generic and
have applicability to the studies of other transient events. The results also
indicate that pattern recognition algorithms are sensitive to sample
completeness; this can influence the study of large astronomical databases such
as those found in a Virtual Observatory.


title: Resolving the 47 Tucanae Distance Problem

abstract:
  Using a sample of 43 suitable local subdwarfs with newly acquired BVI
photometry, we apply our main sequence fitting method to the metal rich
Globular Cluster 47 Tucanae. Fitting in 2 colour planes, we find an apparent
distance modulus of (m-M)v = 13.37 (+0.10/-0.11), leading to a dereddened
distance modulus of (m-M)o = 13.25 (+0.06/-0.07). Consideration of the Red
Clump in the cluster produces a distance modulus fully consistent with this
result. The implied cluster age is 11 (+/-1.4) Gyr.


title:
Are Coronae of Magnetically Active Stars Heated by Flares? II. EUV and
  X-Ray Flare Statistics and the Differential Emission Measure Distribution

abstract:
  (Abridged) We investigate the EUV and X-ray flare rate distribution in
radiated energy of the late-type active star AD Leo using long EUVE and
BeppoSAX observations. We compare the observed light curves with light curves
synthesized from model flares that are distributed in energy according to a
power law with selectable index alpha (dN/dE ~ E^{-alpha}). Two methods are
applied, the first comparing flux distributions of the binned data, and the
second using the distributions of photon arrival time differences in the
unbinned data. We find acceptable alpha values between 2.0-2.5 for the EUVE DS
and the BeppoSAX LECS data. The BeppoSAX MECS data indicate a somewhat
shallower energy distribution than the LECS data, which is attributed to the
harder range of sensitivity of the MECS detector and the increasing peak
temperatures of flares with increasing total (radiative) energy. The results
suggest that flares can play an important role in the energy release of this
active corona. We discuss caveats related to time variability, total energy,
and multiple power-law distributions. Studying the limiting case of a corona
that is entirely heated by a population of flares, we derive an expression for
the time-averaged coronal differential emission measure distribution (DEM) that
can be used as a diagnostic for the flare energy distribution. The shape of the
analytical DEM agrees with previously published DEMs from observations of
active stars.


title:
The Low Velocity Wind from the Circumstellar Matter Around the B9V Star
  sigma Herculis

abstract:
  We have obtained FUSE spectra of sigma Her, a nearby binary system, with a
main sequence primary, that has a Vega-like infrared excess. We observe
absorption in the excited fine structure lines C II* at 1037 A, N II* at 1085
A, and N II** at 1086 A that are blueshifted by as much as ~30 km/sec with
respect to the star. Since these features are considerably narrower than the
stellar lines and broader than interstellar features, the C II and N II are
circumstellar. We suggest that there is a radiatively driven wind, arising from
the circumstellar matter, rather than accretion as occurs around beta Pic,
because of sigma Her's high luminosity. Assuming that the gas is liberated by
collisions between parent bodies at 20 AU, the approximate distance at which
blackbody grains are in radiative equilibrium with the star and at which 3-body
orbits become unstable, we infer dM/dt ~ 6 * 10^-12 M_{sun}/yr. This wind
depletes the minimum mass of parent bodies in less than the estimated age of
the system.


title:
Confirmation of SBS 1150+599A As An Extremely Metal-Poor Planetary
  Nebula

abstract:
  SBS 1150+599A is a blue stellar object at high galactic latitude discovered
in the Second Byurakan Survey. New high-resolution images of SBS 1150+599A are
presented, demonstrating that it is very likely to be an old planetary nebula
in the galactic halo, as suggested by Tovmassian et al (2001). An H-alpha image
taken with the WIYN 3.5-m telescope and its "tip/tilt" module reveals the
diameter of the nebula to be 9.2", comparable to that estimated from spectra by
Tovmassian et al. Lower limits to the central star temperature were derived
using the Zanstra hydrogen and helium methods to determine that the star's
effective temperature must be > 68,000K and that the nebula is optically thin.
New spectra from the MMT and FLWO telescopes are presented, revealing the
presence of strong [Ne V] lambda 3425, indicating that the central star
temperature must be > 100,000K. With the revised diameter, new central star
temperature, and an improved central star luminosity, we can constrain
photoionization models for the nebula significantly better than before. Because
the emission-line data set is sparse, the models are still not conclusive.
Nevertheless, we confirm that this nebula is an extremely metal-poor planetary
nebula, having a value for O/H that is less than 1/100 solar, and possibly as
low as 1/500 solar.


title: Imaging Spectroscopy for Extrasolar Planet Detection

abstract:
  Coronagraphic imaging in combination with moderate to high spectral
resolution may prove more effective in both detecting extrasolar planets and
characterizing them than a standard coronagraphic imaging approach. We envisage
an integral-field spectrograph coupled to a coronagraph to produce a 3D
datacube. For the idealised case where the spectrum of the star is well-known
and unchanging across the field, we discuss the utility of cross-correlation to
seek the extrasolar planet signal, and describe a mathematical approach to
completely eliminate stray light from the host star (although not its Poisson
noise). For the case where the PSF is dominated by diffraction and scattering
effects, and comprises a multitude of speckles within an Airy pattern typical
of a space-based observation, we turn the wavelength dependence of the PSF to
advantage and present a general way to eliminate the contribution from the star
while preserving both the flux and spectrum of the extrasolar planet. We call
this method `spectral deconvolution'. We illustrate the dramatic gains by
showing an idealized simulation that results in a 20-sigma detection of a
Jovian planet at 2 pc with a 2-m coronagraphic space telescope, even though the
planet's peak flux is only 1% that of the PSF wings of the host star. This
scales to detection of a terrestrial extrasolar planet at 2 pc with an 8-m
coronagraphic Terrestrial Planet Finder (TPF) in ~7 hr (or less with
appropriate spatial filtering). Data on the spectral characteristics of the
extrasolar planet and hence on its atmospheric constituents and possible
biomarkers are obtained naturally as part of this process.


title: Properties of Circum(sub)stellar Accretion Disks

abstract:
  We have completed a systematic survey for disks around young brown dwarfs and
very low mass stars. By choosing a well-defined sample and by obtaining
sensitive thermal IR observations, we can make an unbiased measurement of the
disk fraction around such low mass objects. We find that ~75% of our sample
show intrinsic IR excesses, indicative of circum(sub)stellar disks. We discuss
the physical properties of these disks and their relation to the much better
studied disks around solar-mass stars. The high incidence of disks around
substellar objects also raises the possibility of planetary systems around
brown dwarfs.


title: Solar Models: An Historical Overview

abstract:
  I summarize in four slides the 40 years of development of the standard solar
model that is used to predict solar neutrino fluxes and then describe the
current uncertainties in the predictions. I next dispel the misconception that
the p-p neutrino flux is determined by the solar luminosity and present a
related formula that gives, in terms of the p-p and 7Be neutrino fluxes, the
ratio of the rates of the two primary ways of terminating the p-p fusion chain.
I will also attempt to explain why it took so long, about three and a half
decades, to reach a consensus view that new physics is being learned from solar
neutrino experiments. Finally, I close with a personal confession.

categories: astro-ph hep-ph nucl-ex nucl-th physics.hist-ph


title:
Broad Absorption Line Quasars in the Early Data Release from the Sloan
  Digital Sky Survey

abstract:
  A new broad absorption line quasar (BAL) sample is derived from the first
data released by the Sloan Digital Sky Survey. With 116 objects, it is the
largest BAL sample yet assembled. Over the redshift range 1.8 < z < 3.8, the
crude fraction with broad absorption in the CIV line is roughly 15%. This
fraction may be subject to small selection-efficiency adjustments. There are
also hints of redshift-dependence in the BAL fraction. The sample is large
enough to permit the first estimate of the distribution of "balnicity index":
subject to certain arbitrary parameters in the definition of this quantity, it
is very broad, with (roughly) equal numbers of objects per logarithmic interval
of balnicity. BAL quasars are also found to be redder on average than non-BAL
quasars. The fraction of radio-loud BAL quasars is (weakly) consistent with the
fraction of radio-loud ordinary quasars.


title:
Completion of a SCUBA survey of Lynds dark clouds and implications for
  low-mass star formation

abstract:
  We have carried out a survey of optically-selected dark clouds using the
bolometer array SCUBA on the James Clerk Maxwell Telescope, at 850 microns
wavelength. The survey covers a total of 0.5 square degrees and is unbiased
with reference to cloud size, star formation activity, or the presence of
infrared emission. Several new protostars and starless cores have been
discovered; the protostars are confirmed through the detection of their
accompanying outflows in CO(2-1) emission. The survey is believed to be
complete for Class 0 and Class I protostars, and yields two important results
regarding the lifetimes of these phases. First, the ratio of Class 0 to Class
protostars in the sample is roughly unity, very different from the 1:10 ratio
that has previously been observed for the rho Ophiuchi star-forming region.
Assuming star formation to be a homogeneous process in the dark clouds, this
implies that the Class 0 lifetime is similar to the Class I phase, which from
infrared surveys has been established to be approximately 200,000 yr. It also
suggests there is no rapid initial accretion phase in Class 0 objects. A burst
of triggered star formation some 100,000 yr ago can explain the earlier results
for rho Ophiuchus. Second, the number of starless cores is approximately twice
that of the total number of protostars, indicating a starless core lifetime of
approximately 800,000 yr. These starless cores are therefore very short-lived,
surviving only two or three free-fall times. This result suggests that, on size
scales of 10,000 AU at least, the dynamical evolution of starless cores is
probably not controlled by magnetic processes.


title: FeH Absorption in the Near-Infrared Spectra of Late M and L Dwarfs

abstract:
  We present medium-resolution z-, J-, and H-band spectra of four late-type
dwarfs with spectral types ranging from M8 to L7.5. In an attempt to determine
the origin of numerous weak absorption features throughout their near-infrared
spectra, and motivated by the recent tentative identification of the E 4\Pi- A
^4\Pi system of FeH near 1.6 microns in umbral and cool star spectra, we have
compared the dwarf spectra to a laboratory FeH emission spectrum. We have
identified nearly 100 FeH absorption features in the z-, J-, and H-band spectra
of the dwarfs. In particular, we have identified 34 features which dominate the
appearance of the H-band spectra of the dwarfs and which appear in the
laboratory FeH spectrum. Finally, all of the features are either weaker or
absent in the spectrum of the L7.5 dwarf which is consistent with the weakening
of the known FeH bandheads in the spectra of the latest L dwarfs.


title:
ISO SWS Observations of H II Regions in NGC 6822 and I ZW 36: Sulfur
  Abundances and Temperature Fluctuations

abstract:
  We report ISO SWS infrared spectroscopy of the H II region Hubble V in NGC
6822 and the blue compact dwarf galaxy I Zw 36. Observations of Br alpha, [S
III] at 18.7 and 33.5 microns, and [S IV] at 10.5 microns are used to determine
ionic sulfur abundances in these H II regions. There is relatively good
agreement between our observations and predictions of S^+3 abundances based on
photoionization calculations, although there is an offset in the sense that the
models overpredict the S^+3 abundances. We emphasize a need for more
observations of this type in order to place nebular sulfur abundance
determinations on firmer ground. The S/O ratios derived using the ISO
observations in combination with optical data are consistent with values of
S/O, derived from optical measurements of other metal-poor galaxies.
  We present a new formalism for the simultaneous determination of the
temperature, temperature fluctuations, and abundances in a nebula, given a mix
of optical and infrared observed line ratios. The uncertainties in our ISO
measurements and the lack of observations of [S III] lambda 9532 or lambda 9069
do not allow an accurate determination of the amplitude of temperature
fluctuations for Hubble V and I Zw 36. Finally, using synthetic data, we
illustrate the diagnostic power and limitations of our new method.


title: Professional Astronomy without a Librarian

abstract:
  Virtually every ``serious'' place where professional astronomy is done has a
librarian, even if shared with the physics or math department. Since its
creation in 1994 of {\it Departamento de Astronom\'{\i}a} (DA) of Universidad
de Guanajuato (UG) it was neither provided with a librarian, nor with proper
space for its holdings, nor with a budget allowing institutional journal
subscriptions. I describe my experience of now five years as ``amateur''
librarian, and present information on other small astronomy institutions in
Mexico in a similar situation.


title:
Investigating a Possible Spectral Signature of the Wind-ISM Interaction
  Region of Alpha Tau

abstract:
  Ultraviolet spectra from the GHRS instrument on board the Hubble Space
Telescope reveal the presence of a mysterious absorption feature in the Mg II h
& k lines of the nearby (d=20.0 pc) K5 III star Alpha Tau. The narrow
absorption looks like an interstellar absorption feature but it is in the wrong
location based on our knowledge of the local ISM flow vector. Since the
absorption is close to the rest frame of the star, it has been interpreted as
being from the interaction region between Alpha Tau's massive, cool wind and
the interstellar medium, i.e., Alpha Tau's "astrosphere". We compute
hydrodynamic models of the Alpha Tau astrosphere in order to see if the models
can reproduce the Mg II absorption feature. These models do predict that
stellar wind material heated, decelerated, and compressed after passing through
a termination shock a few thousand AU from the star should produce a Mg II
absorption feature with about the right width at roughly the right velocity.
However, our first models underestimate the Mg II column density by an order of
magnitude. A much larger parameter search is necessary to see whether the
observed Mg II absorption can be reproduced by acceptable changes to the
adopted stellar wind and ISM properties.


title: X-ray spectroscopy of Eta Carinae with XMM-Newton

abstract:
  We present XMM-Newton observations of the luminous star Eta Carinae,
including a high resolution soft X-ray spectrum of the surrounding nebula
obtained with the Reflection Grating Spectrometer. The EPIC image of the field
around Eta Car shows many early-type stars and diffuse emission from hot,
shocked gas. The EPIC spectrum of the star is similar to that observed in
previous X-ray observations, and requires two temperature components. The RGS
spectrum of the surrounding nebula shows K-shell emission lines from hydrogen-
and helium-like nitrogen and neon and L-shell lines from iron, but little or no
emission from oxygen. The observed emission lines are not consistent with a
single temperature, but the range of temperatures observed is not large,
spanning ~0.15-0.6 keV. We obtain upper limits for oxygen line emission and
derive a lower limit of N/O > 9. This is consistent with previous abundance
determinations for the ejecta of Eta Car, and with theoretical models for the
evolution of massive, rotating stars.


title: Observations of quasar hosts with adaptive optics at Lick Observatory

abstract:
  We present near-infrared H-band observations of the hosts of three z~1
quasars from the Sloan Digital Sky Survey made with the adaptive optics system
at Lick Observatory. We derive a PSF for each quasar and model the host plus
quasar nucleus to obtain magnitudes and approximate scale sizes for the host
galaxies. We find our recovered host galaxies are similar to those found for
z~1 quasars observed with the Hubble Space Telescope. They also have, with one
interesting exception, black hole mass estimates from their bulge luminosities
which are consistent with those from emission-line widths. We thus demonstrate
that adaptive optics can be successfully used for the quantitative study of
quasar host galaxies, with the caveat that better PSF calibration will be
needed for studies of the hosts of significantly brighter or higher redshift
quasars with the Lick system.


title: Hard X-ray lightcurves of High Mass X-ray binaries

abstract:
  Using the 9 years of continuous data now available from the Burst And
Transient Source Experiment (BATSE) aboard CGRO, we have measured orbital
periods and produced folded lightcurves for 8 High Mass X-ray Binaries (HMXB).
Given the length of the datasets, our determinations are based on many more
binary orbits than previous investigations. Thus our source detections have
high statistical significance and we are able to follow long-term trends in
X-ray output. In particular we focus on two systems: A0538-668 and EXO2030+375
both HMXBs exhibiting Type I outbursts.


title: Milestones in the Observations of Cosmic Magnetic Fields

abstract:
  Magnetic fields are observed everywhere in the universe. In this review, we
concentrate on the observational aspects of the magnetic fields of Galactic and
extragalactic objects. Readers can follow the milestones in the observations of
cosmic magnetic fields obtained from the most important tracers of magnetic
fields, namely, the star-light polarization, the Zeeman effect, the rotation
measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio
polarization observations, as well as the newly implemented sub-mm and mm
polarization capabilities.
  (Another long paragraph is omitted due to the limited space here)


title: GeV Emission from TeV Blazars and Intergalactic Magnetic Fields

abstract:
  Several high-frequency peaked BL Lac objects such as Mrk 501 are strong TeV
emitters. However, a significant fraction of the TeV gamma rays emitted are
likely to be absorbed in interactions with the diffuse IR background, yielding
electron-positron pairs. Hence, the observed TeV spectrum must be steeper than
the intrinsic one. Using the recently derived intrinsic $\gamma$-ray spectrum
of Mrk 501 during its 1997 high state, we study the inverse-Compton scattering
of cosmic microwave photons by the resulting electron-positron pairs, which
implies the existence of a hitherto undiscovered GeV emission. The typical
duration of the GeV emission is determined by the flaring activity time and the
energy-dependent magnetic deflection time. We numerically calculate the
scattered photon spectrum for different intergalactic magnetic field (IGMF)
strengths, and find a spectral turnover and flare duration at GeV energies
which are dependent on the field strength. We also estimate the scattered
photon flux in the quiescent state of Mrk 501. The GeV flux levels predicted
are consistent with existing EGRET upper limits, and should be detectable above
the synchrotron -- self Compton (SSC) component with the {\em Gamma-Ray Large
Area Space Telescope} ({\em GLAST}) for IGMFs $\lesssim 10^{-16}$ G, as
expected in voids. Such detections would provide constraints on the strength of
weak IGMFs.


title:
ERO R1 in CL0939+4713 field - Evidence for an S0-like galaxy at z \sim
  1.5

abstract:
  We present further observations of the extremely red object ERO
J094258+4659.2, identified by \citet{iye00} as ERO R1 in their deep images of
the cluster A851. We estimate its redshift independently by eight-band
photometric redshift determination and cross-correlation of a new H-band
spectrum with the optical spectra of local E/S0 galaxies, and conclude that it
lies at $z \sim 1.5$. Although its colors are consistent both with an
elliptical galaxy and an S0 galaxy at that redshift, its elongated shape and
exponential luminosity profile suggest the presence of an evolved stellar disk
component. We rule out the possibility that these properties are strongly
influenced by gravitational lensing by the foreground cluster, and therefore
conclude that this object is more likely to be an S0-like galaxy, rather than a
lensed elliptical. The H-band spectrum does not show strong H$\alpha$ emission
and the star formation rate therefore appears to be very modest. The presence
of such a galaxy with an apparently relaxed disk of stars at this high redshift
provides a new and strong constraint on theoretical models which aim to explain
the formation and evolution of galaxies.


title: Constraining Evolution of Quintessence with CMB and SNIa Data

abstract:
  The equation of state of the hypothetical dark energy component, which
constitutes about two thirds of the critical density of the universe, may be
very different from that of a cosmological constant. Employing a
phenomenological model, we investigate semi-analytically the constraints
imposed on the scalar quintessence by supernovae observations, and by the
acoustic scale extracted from recent CMB data. We show that a universe with a
quintessence-dominated phase in the dark age is consistent with the current
observational constraints.


title: Numerical simulations of the intergalactic medium

abstract:
  The intergalactic medium at redshifts 2--6 can be studied observationally
through the absorption features it produces in the spectra of background
quasars. Most of the UV-absorption lines arise in mildly overdense regions,
which can be simulated reliably with current hydrodynamical simulations.
Comparison of observed and simulated spectra allows one to put contraints on
the model's parameters.


title: Globular Clusters in the Central Region of Nearby Galaxy Clusters

abstract:
  In this contribution, first results of deep VLT photometry (V,I) in the
central region of the Hydra I and Centaurus galaxy clusters are presented. In
both galaxy clusters, many star clusters have been identified down to the
turnover magnitude of the globular cluster luminosity function at V=26.0 mag.
They are distributed not only around the several early-type galaxies, but also
in the intra-cluster field, as far as 250 kpc from the cluster centers. Outside
the bulges of the central galaxies in Hydra I and Centaurus, the intra-cluster
globular cluster system is dominated by blue clusters whose spatial
distribution is similar to that of the (newly discovered) dwarf galaxies.