title: Polaris: astrometric orbit, position, and proper motion

abstract:
  We derive the astrometric orbit of the photo-center of the close pair alpha
UMi AP (=alpha UMi Aa) of the Polaris multiple stellar system. The orbit is
based on the spectroscopic orbit of the Cepheid alpha UMi A (orbital period of
AP: 29.59 years), and on the difference Delta mu between the
quasi-instantaneously measured HIPPARCOS proper motion of Polaris and the
long-term-averaged proper motion given by the FK5. There remains an ambiguity
in the inclination i of the orbit, since Delta mu cannot distinguish between a
prograde orbit (i=50.1 deg) and a retrograde one (i=130.2 deg). Available
photographic observations of Polaris favour strongly the retrograde orbit. For
the semi-major axis of the photo-center of AP we find about 29 milliarcsec
(mas). For the component P, we estimate a mass of 1.5 solar masses and a
magnitude difference with respect to the Cepheid of 6.5 mag. The present
separation between A and P should be about 160 mas. We obtain the proper motion
of the center-of-mass of alpha UMi AP with a mean error of about 0.45 mas/year.
Using the derived astrometric orbit, we find the position of the center-of-mass
at the epoch 1991.31 with an accuracy of about 3.0 mas. Our ephemerides for the
orbital correction, required for going from the position of the center-of-mass
to the instantaneous position of the photo-center of AP at an arbitrary epoch,
have a typical uncertainty of 5 mas. For epochs which differ from the HIPPARCOS
epoch by more than a few years, a prediction for the actual position of Polaris
based on our results should be significantly more accurate than using the
HIPPARCOS data in a linear prediction, since the HIPPARCOS proper motion
contains the instantaneous orbital motion of about 4.9 mas/year = 3.1 km/s.
Finally we derive the galactic space motion of Polaris.


title:
Abundances of light elements in metal-poor stars. III. Data analysis and
  results

abstract:
  We present the analysis of an extensive set of new and literature high
quality data concerning Fe, C, N, O, Na, and Mg, exploiting the Teff scale
determined in Gratton et al. (1996), and the non-LTE abundance corrections
computed in Gratton et al. (1999). Results obtained with various abundance
indices are discussed and compared. Our non-LTE analysis yields the same O
abundances from both permitted and forbidden lines for stars with Teff>4600 K,
in agreement with King (1993), but not with other studies using a lower
Teff-scale for subdwarfs. However we obtain slightly smaller O abundances for
the most luminous metal poor field stars than for fainter stars of similar
metallicities, an effect attributed to inadequacies of the adopted model
atmospheres (Kurucz 1992, with overshooting) for cool stars. We find a nearly
constant O overundance in metal poor stars ([Fe/H]<-0.8), at a mean value of
0.46+-0.02 dex (sigma=0.12, 32 stars), with only a gentle slope with [Fe/H] (~
-0.1); this result is different from the steeper slope recently obtained using
OH band in the near UV. If only 'bonafide' unmixed stars are considered, C
abundances scale with Fe ones (i.e. [C/Fe]~ 0) down to [Fe/H]~ -2.5. Due to our
adoption of a different Teff-scale, we do not confirm the slight C excess in
the most metal poor disk dwarfs (-0.8<[Fe/H]<-0.4) found in previous studies.
Na abundances scale as Fe ones in the high metallicity regime, while metal-poor
stars present a Na underabundance. None of the field stars analyzed belong to
the group of O-poor and Na-rich stars observed in globular clusters. Na is
deficient with respect to Mg in halo and thick disk stars; within these
populations, Na deficiency may be a slow function of [Mg/H]. Solar [Na/Mg]
ratios are obtained for thin disk stars.


title: Non-LTE Effects in Berylium Abundances

abstract:
  In this work we analyze the beryllium-iron chemical diagram from the point of
view of non-LTE effects. Be abundances were re-calculated by considering
non-LTE corrections in ionization equilibrium (logg) and Fe abundances
([Fe/H]). These corrections seem do not affect the linear relation between
Be-Fe for metal-poor stars already found in the literature for LTE derived
abundances.


title:
The structure and evolution of weakly self-interacting cold dark matter
  halos

abstract:
  The evolution of halos consisting of weakly self-interacting dark matter
particles is investigated using a new numerical Monte-Carlo N-body method. The
halos initially contain kinematically cold, dense 1/r-power-law cores. For
interaction cross sections (sigma/mp) >= 10-100 cm**2/g weak self-interaction
leads to the formation of isothermal, constant density cores within a Hubble
time as a result of heat transfer into the cold inner regions. This core
structure is in good agreement with the observations of dark matter rotation
curves in dwarf galaxies. The isothermal core radii and core densities are a
function of the halo scale radii and scale masses which depend on the
cosmological model. Adopting the currently popular LCDM model, the predicted
core radii and core densities are on good agreement with the observations. For
large interaction cross sections, massive dark halos with scale radii rs >=
14000 cm**2/g/(sigma/mp) kpc could experience core collapse during their
lifetime, leading to cores with singular isothermal density profiles.


title:
Signatures of Planets in the Observable Structure of Circumstellar
  Debris Disks

abstract:
  Recent advances in astronomical instrumentation mean that we are now able to
image the thermal emission from the disks of dust around main sequence stars
that may be the fossil remnants of planetary formation. These observations
imply that the distribution of dust in the debris disks is neither smooth nor
symmetrical; e.g., mid-infrared images of the disk of dust around the young A0V
star HR 4796A show two lobes of emission, one of which may be ~5% brighter than
the other. The observed structure of the debris disk in the solar system, i.e.,
the zodiacal cloud, also contains asymmetries: it has an offset center of
symmetry, it is warped, and there is an asymmetric ring of dust co-orbiting
with the Earth. Since the zodiacal cloud's asymmetries have been shown to be
signatures of the gravitational perturbations of the solar system's planets, it
is hoped that it may be possible to indirectly detect extrasolar planetary
systems by their signatures in debris disk observations. This dissertation uses
the physical processes that affect the evolution of debris material in the
solar system to create a generalized model for the evolution of circumstellar
debris material. It then shows how planetary perturbations affect that
evolution, thereby causing the signatures of planets seen in the structure of
the zodiacal cloud. This model can be used to provide a quantitative
interpretation of debris disk observations, and the necessary modeling
techniques are demonstrated by their application to observations of the HR 4796
disk. As well as determining the large scale structure of the HR 4796 disk, the
modeling shows how a small body (>10 Earth mass) in the HR 4796 system that is
on an orbit with an eccentricity larger than 0.02 could be the cause of the
observed brightness asymmetry.


title:
Kinetic theory of cosmic ray and gamma-ray production in supernova
  remnants expanding into wind bubbles

abstract:
  Abbreviated Abstract: A kinetic model of particle acceleration in supernova
remnants (SNRs) is extended to study the cosmic ray (CR) and associated high
energy gamma-ray production during SN shock propagation through the
inhomogeneous circumstellar medium of a progenitor star that emits a strong
wind. The wind forms a low-density bubble surrounded by a swept-up shell of
interstellar matter. Gamma rays are produced as a result of decay of pions
which in turn are the result of collisions of CRs with nuclei of the thermal
plasma. The time evolution of the SNRs is followed numerically, taking into
account the nonlinear backreaction of the accelerated CRs. Examples typical for
SN type Ib and SN type II explosions are considered. Apart from the
confirmation of the known fact that acceleration is extremely rapid and that
the upper momentum cutoff is reached almost immediately after the explosion due
to the high wind magnetic field, it is also shown that the CRs are accelerated
with high efficiency. The CR energy spectrum, ultimately produced in the SNRs,
has a power law form with index = 2.0 to 2.1 in a wide energy range up to a
maximum energy which is about 10^14 eV if the CR diffusion coefficient is as
small as the Bohm limiting value. However, the expected pi^0-decay gamma-ray
flux is considerably lower than in the case of a uniform interstellar medium; a
relatively high gamma-ray luminosity in the TeV band, detectable at distances
of several kpc, is only expected in the case of a relatively dense ISM with a
number density above 10/cc.


title:
Expected Number and Flux Distribution of Gamma-Ray-Burst Afterglows with
  High Redshifts

abstract:
  If Gamma-Ray-Bursts (GRBs) occur at high redshifts, then their bright
afterglow emission can be used to probe the ionization and metal enrichment
histories of the intervening intergalactic medium during the epoch of
reionization. In contrast to other sources, such as galaxies or quasars, which
fade rapidly with increasing redshift, the observed infrared flux from a GRB
afterglow at a fixed observed age is only a weak function of its redshift. This
results from a combination of the spectral slope of GRB afterglows and the
time-stretching of their evolution in the observer's frame. Assuming that the
GRB rate is proportional to the star formation rate and that the characteristic
energy output of GRBs is ~10^{52} ergs, we predict that there are always ~15
GRBs from redshifts z>5 across the sky which are brighter than ~100 nJy at an
observed wavelength of ~2 \mu m. The infrared spectrum of these sources could
be taken with the future Next Generation Space Telescope, as a follow-up on
their early X-ray localization with the Swift satellite.


title: Primordial Adiabatic Fluctuations from Cosmic Defects

abstract:
  We point out that in the context of ``two-metric'' theories of gravity there
is the possibility that cosmic defects will produce a spectrum of primordial
adiabatic density perturbations. This will happen when the speed characterising
the defect-producing scalar field is much larger than the speed characterising
gravity and all standard model particles. This model will exactly mimic the
standard predictions of inflationary models, with the exception of a small
non-Gaussian signal which could be detected by future experiments. We briefly
discuss defect evolution in these scenarios and analyze their cosmological
consequences.


title:
Superluminal Caustic is Just a Common Misconception: A Comment on
  astro-ph/0001199 by Zheng Zheng and Andrew Gould

abstract:
  When angular objects in lensing are considered as linear objects, interesting
phenomena start happening. Tachyonic caustics are one example. We review that
the intrinsic variables of the lens equation are angular variables. We argue
that the "fast glance effect" of a caustic curve that is far away from lenses
does not share the physical bearing of the well-known (apparent) superluminal
motion. There is no dbout that it would be a useful exercise to study the null
geodesics in the metric of, say, a rapidly rotating black hole binary.
Lienard-Wiechert potentials ($A_\mu$) satisfy Maxwell's equations in Minkowski
space. Authors' claim that swapping eQ and GM makes the time component ($A_0$)
of the Lienard-Wiechert potentials into "the gravitational analog" that governs
the behavior of the null geodesics near a relativistic binary system seems to
be unfounded.


title: Comptonization, reflection and noise in black hole binaries

abstract:
  Based on the analysis of a large sample of RXTE/PCA observations of several
black hole binaries in the low spectral state we show that a correlation exists
between the spectral parameters and characteristic noise frequency. In
particular, the amplitude of reflection increases and the slope of Comptonized
radiation steepens as the noise frequency increases. We consider possible
implications of these results on the accretion flow models and discuss a
possible observational test aimed to discriminate between different geometries
of the accretion flow.


title: A Lens Mapping Algorithm for Weak Lensing

abstract:
  We develop an algorithm for the reconstruction of the two-dimensional mass
distribution of a gravitational lens from the observable distortion of
background galaxies. From the measured reduced shear, the lens mapping is
obtained, from which a mass distribution is derived. This is unlike other
methods where the convergence ("kappa") is directly obtained. We show that this
method works best for sub-critical lenses, but can be applied to a critical
lens away from the critical lines. For finite fields the usual mass-sheet
degeneracy is shown to exist in this method as well. We show that the algorithm
reproduces the mass distribution within acceptable limits when applied to
simulated noisy data.


title:
Research and Education in Basic Space Science: The Approach Pursued in
  the UN/ESA Workshops

abstract:
  Since 1990, the United Nations in cooperation with the European Space Agency
is holding annually a workshop on basic space science for the benefit of the
worldwide development of astronomy. These workshops have been held in countries
of Asia and the Pacific (India, Sri Lanka), Latin America and the Caribbean
(Costa Rica, Colombia, Honduras), Africa (Nigeria), Western Asia (Egypt,
Jordan), and Europe (Germany, France). Additional to the scientific benefits of
the workshops and the strengthening of international cooperation, the workshops
lead to the establishment of astronomical telescope facilities in Colombia,
Egypt, Honduras, Jordan, Morocco, Paraguay, Peru, Philippines, Sri Lanka, and
Uruguay. The annual UN/ESA Workshops continue to pursue an agenda to network
these astronomical telescope facilities through similar research and education
programmes. Teaching material and hands-on astrophysics material has been
developed for the operation of such astronomical telescope facilities in an
university environment.


title:
The Optical Gravitational Lensing Experiment. Catalog of Microlensing
  Events in the Galactic Bulge

abstract:
  We present the Catalog of microlensing events detected toward the Galactic
bulge in three observing seasons, 1997--1999, during the OGLE-II microlensing
survey. The search for microlensing events was performed using a database of
about 4*10^9 photometric measurements of about 20.5 million stars from the
Galactic bulge. The Catalog comprises 214 cases of microlensing events found in
the fields covering about 11 square degrees on the sky and distributed in
different parts of the Galactic bulge. The sample includes 20 binary
microlensing events, 14 of them are caustic crossing. In one case a double star
is likely lensed.
  We present distribution of the basic parameters of microlensing events and
show preliminary rate of microlensing in different regions of the Galactic
bulge. The latter reveals clear dependence on the Galactic coordinates. The
dependence on 'l' indicates that the majority of lenses toward the Galactic
bulge are located in the Galactic bar. Models of the Galactic bar seem to
reasonably predict the observed spatial distribution of microlensing events in
the Galactic bulge.
  All data presented in the Catalog and photometry of all events are available
from the OGLE Internet archive.


title: On the Perturbations of Viscous Rotating Newtonian Fluids

abstract:
  The perturbations of weakly-viscous, barotropic, non-self-gravitating,
Newtonian rotating fluids are analyzed via a single partial differential
equation. The results are then used to find an expression for the
viscosity-induced normal-mode complex eigenfrequency shift, with respect to the
case of adiabatic perturbations. However, the effects of viscosity are assumed
to have been incorporated in the unperturbed (equilibrium) model. This paper is
an extension of the normal-mode formalism developed by Ipser & Lindblom for
adiabatic pulsations of purely-rotating perfect fluids. The formulas derived
are readily applicable to the perturbations of thin and thick accretion disks.
We provide explicit expressions for thin disks, employing results from previous
relativistic analyses of adiabatic normal modes of oscillation. In this case,
we find that viscosity causes the fundamental p- and g- modes to grow while the
fundamental c-mode could have either sign of the damping rate.


title: Shellflow. I. The Convergence of the Velocity Field at 6000 km/s

abstract:
  We present the first results from the Shellflow program, an all-sky
Tully-Fisher (TF) peculiar velocity survey of 276 Sb-Sc galaxies with redshifts
between 4500 and 7000 km/s. Shellflow was designed to minimize systematic
errors between observing runs and between telescopes, thereby removing the
possibility of a spurious bulk flow caused by data inhomogeneity. A fit to the
data yields a bulk flow amplitude V_bulk = 70{+100}{-70} km/s (1 sigma error)
with respect to the Cosmic Microwave Background, i.e., consistent with being at
rest. At the 95% confidence level, the flow amplitude is < 300 km/s. Our
results are insensitive to which Galactic extinction maps we use, and to the
parameterization of the TF relation. The larger bulk motion found in analyses
of the Mark III peculiar velocity catalog are thus likely to be due to
non-uniformities between the subsamples making up Mark III. The absence of bulk
flow is consistent with the study of Giovanelli and collaborators and flow
field predictions from the observed distribution of IRAS galaxies.


title:
The Composition and Distribution of Dust Along the Line of Sight Towards
  the Galactic Center

abstract:
  We discuss the composition of dust and ice along the line of sight to the
Galactic Center (GC) based on analysis of mid-infrared spectra (2.4-13 micron)
from the Short Wavelength Spectrometer on the Infrared Space Observatory (ISO).
We have analyzed dust absorption features arising in the molecular cloud
material and the diffuse interstellar medium along the lines of sight toward
Sagittarius A* and the Quintuplet sources, GCS3 and GCS4. It is evident from
the depth of the 3.0 micron H2O and the 4.27 micron CO2 ice features that there
is more molecular cloud material along the line of sight toward Sgr A* than
GCS3 and 4. In fact, Sgr A* has a rich infrared ice spectrum with evidence for
the presence of solid CH4, NH3, and possibly HCOOH.
  Hydrocarbon dust in the diffuse interstellar medium along the line of sight
to the GC is characterized by absorption features centered at 3.4, 6.85, and
7.25 micron. Ground-based studies have identified the 3.4 micron feature with
aliphatic hydrocarbons, and ISO has given us the first meaningful observations
of the corresponding modes at longer wavelengths. The integrated strengths of
these three features suggest that hydrogenated amorphous carbon is their
carrier. We attribute an absorption feature centered at 3.28 micron in the GCS3
spectrum to the C-H stretch in aromatic hydrocarbons. This feature is not
detected, and its C-C stretch counterpart appears to be weaker, in the SgrA*
spectrum. One of the key questions which now arises is whether aromatics are a
widespread component of the diffuse interstellar medium, analogous to aliphatic
hydrocarbons.


title: Simulating the effects of intergalactic grey dust

abstract:
  Using a high-resolution cosmological hydrodynamic simulation, we present a
method to constrain extinction due to intergalactic grey dust based on the
observed magnitudes of distant Type IA supernovae. We apply several simple
prescriptions to relate the intergalactic dust density to the gas density in
the simulation, thereby obtaining dust extinctions that may be directly
compared to the observed distribution of supernova magnitudes. Our analysis is
sensitive to the spatial distribution of grey dust, but is not dependent on its
intrinsic properties such as its opacity or grain size. We present an
application of our technique to the supernova data of Perlmutter et al., who
find that their high redshift sample is ~0.2 magnitudes fainter than the
expectation for a non-accelerating, low-density universe. We find that for grey
dust to be responsible, it must be distributed quite smoothly, e.g., tracing
intergalactic gas. More realistic dust distributions, such as dust tracing the
metal density, are inconsistent with observations at the 1.5-2 sigma level.
Upcoming observations and improved modelling of the dust distribution should
lead to stronger constraints on intergalactic grey dust extinction.


title:
Photographic photometries and astrophysical parameters of the open
  clusters NGC1750 and NGC1758

abstract:
  Photographic photometries of 789 stars in the region of the open clusters
NGC1750 and NGC1758 are derived from a set of 8 photometric plates. According
to the astronomical data including proper motions, positions and membership
probabilities of individual stars, several astrophysical parameters for these
two clusters are determined, such as HR diagrams, ages, distances, luminosity
functions, masses and kinematics, etc. It is found that the distances are
  ($525\pm 48$pc) and ($794\pm 73$pc) with ages of $1.5\times10^8$yr and
$6.3\times10^8$yr for
  NGC1750 and NGC1758 respectively. Both clusters show no significant mass
segregation effects because of their relatively young ages. The analysis of the
proper motions imply that their velocity distributions are isotropy.


title:
The HI shell G132.6-0.7-25.3: A Supernova Remnant or an Old Wind-Blown
  Bubble?

abstract:
  Data from the Canadian Galactic Plane Survey reveal an abundance of HI shells
and arcs in the disk of our galaxy. While their shape is suggestive of stellar
winds or supernovae influence, very few of these structures have been examined
in detail thus far. A fine example is an HI shell in the outer Galaxy with no
continuum counterpart discovered in the survey's pilot project. Its size and
kinematics suggest that it was created by the winds of a single late-type O
star which has since evolved off the main sequence or by a supernova explosion.
A B1 Ia star at the centre of the shell, in projection, is a possible candidate
for energy source if the shell is assumed to be wind-blown. The shell's shape
implies a surprisingly small scale height of less than about 30 pc for the
surrounding gas if the elongation is due to evolution in a density gradient.


title: Evolution of Lyman Break Galaxies Beyond Redshift Four

abstract:
  The formation rate of luminous galaxies seems to be roughly constant from z~2
to z~4 from the recent observations of Lyman break galaxies (LBGs) (Steidel et
al 1999). The abundance of luminous quasars, on the other hand, appears to drop
off by a factor of more than twenty from z~2 to z~5 (Warren, Hewett, & Osmer
1994; Schmidt, Schneider, & Gunn 1995). The difference in evolution between
these two classes of objects in the overlapping, observed redshift range,
z=2-4, can be explained naturally, if we assume that quasar activity is
triggered by mergers of luminous LBGs and one quasar lifetime is ~10^{7-8} yrs.
If this merger scenario holds at higher redshift, for the evolutions of these
two classes of objects to be consistent at z>4, the formation rate of luminous
LBGs is expected to drop off at least as rapidly as exp(-(z-4)^{6/5}) at z>4.


title:
Eccentric discs in binaries with intermediate mass ratios: Superhumps in
  the VY Sculptoris stars

abstract:
  We investigate the role of the eccentric disc resonance in systems with mass
ratios q greater than 1/4, and demonstrate the effects that changes in the mass
flux from the secondary star have upon the disc radius and structure. The
addition of material with low specific angular momentum to its outer edge
restricts a disc radially. Should the mass flux from the secondary be reduced,
it is possible for the disc in a system with mass ratio as large as 1/3 to
expand to the 3:1 eccentric inner Lindblad resonance and for superhumps to be
excited.


title:
Dust lanes, thick absorbers, and the unification model for Seyfert
  galaxies

abstract:
  A modification of the popular unification model for Seyfert galaxies is
proposed, which takes into account recent observational findings on the
statistical properties of both type 1 and type 2 Seyferts. In the proposed
scenario, Compton-thick Seyfert 2 galaxies are those sources observed through
compact, thick matter (the `torus'), while Compton-thin/intermediate Seyfert
galaxies are obscured by dust lanes at larger distances.


title: The Impact of Rotation on Cluster Dynamics

abstract:
  The evolution of rotating, isolated clusters of stars up to core-collapse is
investigated with n-body numerical codes. The simulations start off from
axisymmetric generalisations of King profiles, with added global angular
momentum. In this contribution I report on results obtained for two sets of
single-mass cluster simulations. These confirm the more rapid evolution of even
mildly-rotating clusters. A model is presented with rotational energy
comparable to omega-Centauri's; it reaches core-collapse in less than half the
time required for non-rotating model clusters.


title:
Erratum: Excitation Mechanism of Near-Infrared [Fe II] Emission in
  Seyfert and Starburst Galaxies (ApJ, 528, 186 [2000])

abstract:
  In the paper "Excitation Mechanism of Near-Infrared [Fe II] Emission in
Seyfert and Starburst Galaxies" by Hideaki Mouri, Kimiaki Kawara, and Yoshiaki
Taniguchi (ApJ, 528, 186 [2000]), the two panels of Figure 6 were printed into
different sizes, as the result of an error in the printing process. The correct
version of Figure 6 appears here.


title: Neutrino Afterglows and Progenitors of Gamma-Ray Bursts

abstract:
  Currently popular models for progenitors of gamma-ray bursts (GRBs) are the
mergers of compact objects and the explosions of massive stars. These two cases
have distinctive environments for GRBs: compact object mergers occur in the
interstellar medium (ISM) and the explosions of massive stars occur in the
preburst stellar wind. We here discuss neutrino afterglows from reverse shocks
as a result of the interaction of relativistic fireballs with their surrounding
wind matter. After comparing with the analytical result of Waxman & Bahcall
(2000) for the homogeneous ISM case, we find that the differential spectrum of
neutrinos with energy from $\sim 3\times 10^{15}$ to $\sim 3\times 10^{17}$ eV
in the wind case is softer by one power of the energy than in the ISM case.
Furthermore, the expected flux of upward moving muons produced by neutrino
interactions below a detector on the surface of the Earth in the wind case is
$\sim 5$ events per year per km$^2$, which is about one order of magnitude
larger than in the ISM case. In addition, these properties are independent of
whether the fireballs are isotropic or beamed. Therefore, neutrino afterglows,
if detected, may provide a way of distinguishing between GRB progenitor models
based on the differential spectra of neutrinos and their event rates in a
detector.


title: Constraints to the SSC model for Mkn 501

abstract:
  We fit the SEDs of the TeV blazar Mkn 501 adopting the homogeneous
Synchrotron-Self Compton model to simultaneous X-ray and TeV spectra recently
become available. We present detailed model spectra calculated with the above
constraints and taking into account the absorption of TeV photons by the IR
background. We found that the curved TeV spectra can be naturally reproduced
even without IRB absorption. Taking IRB absorption into account changes the
required parameter values only slightly.


title: Searching for cluster substructure using APM and ROSAT data

abstract:
  We present a detailed study of the morphological features of 22 rich galaxy
clusters. Our sample is constructed from a cross-correlation of optical
(Abell+APM) data with X-ray (0.1 - 2.4) keV ROSAT pointed observations. We
systematically compare cluster images and morphological parameters in an
attempt to reliably identify possible substructure in both optical and the
X-ray images. To this end, we compute various moments of the optical and X-ray
surface-brightness distribution such as the ellipticities, center-of-mass
shifts and ellipsoidal orientations. We assess the significance of our results
using Monte Carlo simulations. We find significant correlations between the
optical and X-ray morphological parameters, indicating that in both parts of
the spectrum it is possible to identify correctly the dynamical state of a
cluster. Most of our clusters (17/22) have a good 1-to-1 correspondence between
the optical and the X-ray images and about 10 appear to have strong indications
of substructure. This corresponds to a minimum percentage of order 45 per cent
which is in very good accordance with other similar analyses. Finally, 5 out of
22 systems seem to have distinct subclumps in the optical which are not
verified in the X-ray images, and thus are suspect of being due to optical
projection effects. These results will serve as a useful guide in interpreting
subsequent analyses of large optical cluster catalogues.


title:
Rapid fading of optical afterglows as evidence for beaming in gamma-ray
  bursts

abstract:
  Based on the refined dynamical model proposed by us earlier for beamed
$\gamma$-ray burst ejecta, we carry out detailed numerical procedure to study
those $\gamma$-ray bursts with rapidly fading afterglows (i.e., $\sim t^{-2}$).
It is found that optical afterglows from GRB 970228, 980326, 980519, 990123,
990510 and 991208 can be satisfactorily fitted if the $\gamma$-ray burst ejecta
are highly collimated, with a universal initial half opening angle $\theta_0
\sim 0.1$. The obvious light curve break observed in GRB 990123 is due to the
relativistic-Newtonian transition of the beamed ejecta, and the rapidly fading
optical afterglows come from synchrotron emissions during the mildly
relativistic and non-relativistic phases. We strongly suggest that the rapid
fading of afterglows currently observed in some $\gamma$-ray bursts is evidence
for beaming in these cases.


title: Quantum Perturbative Approach to Discrete Redshift

abstract:
  On the largest scales there is evidence of discrete structure, examples of
this are superclusters and voids and also by redshift taking discrete values.
In this paper it is proposed that discrete redshift can be explained by using
the spherical harmonic integer l; this occurs both in the metric or density
perturbations and also in the solution of wave equations in Robertson-Walker
spacetime. It is argued that the near conservation of energy implies that l
varies regularly for wave equations in Robertson-Walker spacetime, whereas for
density perturbations l cannot vary regularly. Once this is assumed then
perhaps the observed value of discrete redshift provides the only observational
or experimental data that directly requires an explanation using both
gravitational and quantum theory. In principle a model using this data could
predict the scale factor R (or equivalently the deceleration parameter q).
Solutions of the Klein-Gordon equation in Robertson-Walker spacetimes are used
to devise models which have redshift taking discrete values, but they predict a
microscopic value for R. A model in which the stress of the Klein-Gordon
equation induces a metrical perturbation of Robertson-Walker spacetime is
devised. Calculations based upon this model predict that the Universe is closed
with $2q_0-1=10^{-4}$.


title: The robust detection of stars on CCD images

abstract:
  Two parameters are developed to analyze the CCD images from ground-based
and/or space telescopes. The first parameter, deduced from the intensity
profile of the object sharp, is useful to resolve stars and hot pixels. The
second parameter shape distinguishes the stars from the background cosmic-ray
events using geometric characteristics defined by its shapes. The parameters
are applied to a simulated OMC/INTEGRAL image and a HST image.


title:
Constraining the Radio-Submm Redshift Indicator using data from the
  SCUBA Local Universe Galaxy Survey

abstract:
  Many of the faint submm sources uncovered by deep SCUBA surveys still remain
unidentified at most, if not all other wavelengths. The most successful method
so far of obtaining accurate positions and hence allowing more secure
identifications has been to use centimetre wavelength imaging with the VLA.
This has led to a tempting approach for obtaining redshift estimates for this
population (Carilli & Yun 1999,2000), which relies on the tight FIR-radio
relationship and takes advantage of the steep spectral slope in the submm. In
this paper we use the submm data from the SCUBA Local Universe Galaxy Survey
(SLUGS) to estimate the usefulness of, and the uncertainties in, the
radio-submm redshift estimator. We investigate the dependencies of the
submm-radio spectral index on various galaxy properties and find that there is
no significant trend with dust temperature or 850 micron luminosity. The ratio
of 850 micron/1.4 GHz flux was found to decrease with increasing radio and FIR
luminosity, and we propose that this is due to a component of the dust not
associated with recent star formation but which is instead heated to 15-20 K by
the general interstellar radiation field.


title:
Weak gravitational lensing in different cosmologies, using an algorithm
  for shear in three dimensions

abstract:
  We present the results of weak gravitational lensing statistics in four
different cosmological $N$-body simulations. The data has been generated using
an algorithm for the three-dimensional shear, which makes use of a variable
softening facility for the $N$-body particle masses, and enables a physical
interpretation for the large-scale structure to be made. Working in
three-dimensions also allows the correct use of the appropriate angular
diameter distances. Our results are presented on the basis of the filled beam
approximation in view of the variable particle softening scheme in our
algorithm. The importance of the smoothness of matter in the universe for the
weak lensing results is discussed in some detail. The low density cosmology
with a cosmological constant appears to give the broadest distributions for all
the statistics computed for sources at high redshifts. In particular, the range
in magnification values for this cosmology has implications for the
determination of the cosmological parameters from high-redshift Type Ia
Supernov\ae. The possibility of determining the density parameter from the
non-Gaussianity in the probability distribution for the convergence is
discussed.


title:
Resolved Spectroscopy of the Narrow-Line Region in NGC 1068: Kinematics
  of the Ionized Gas

abstract:
  We have determined the radial velocities of the [O III] emitting gas in the
inner narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068, along a slit
at position angle of 202 degrees, from STIS observations at a spatial
resolution of 0.1 arcsec and a spectral resolving power of approximately 1000.
We use these data to investigate the kinematics of the NLR within 6 arcsec (430
pc) of the nucleus. The emission-line knots show evidence for radial
acceleration, to a projected angular distance of 1.7 arcsec in most cases,
followed by deceleration that approaches the systemic velocity at a projected
distance of about 4 arcsec. We find that a simple kinematic model of biconical
radial outflow can match the general trend of observed radial velocities. In
this model, the emitting material is evacuated along the bicone axis, and the
axis is inclined 5 degrees out of the plane of the sky. The acceleration of the
emission-line clouds provides support for dynamical models that invoke
radiation and/or wind pressure. We suggest that the deceleration of the clouds
is due to their collision with a patchy and anistropically distributed ambient
medium.


title: C32, A Young Star Cluster in IC 1613

abstract:
  The Local Group irregular galaxy IC 1613 has remained an enigma for many
years because of its apparent lack of star clusters. We report the successful
search for clusters among several of the candidate objects identified many
years ago on photographic plates. We have used a single HST WFPC2 pointing and
a series of images obtained with the WIYN telescope under exceptional seeing
conditions, examining a total of 23 of the previously published candidates. All
but six of these objects were found to be either asterisms or background
galaxies. Five of the six remaining candidates possibly are small, sparse
clusters and the sixth, C32, is an obvious cluster. It is a compact, young
object, with an age of less than 10 million years and a total absolute
magnitude of M_V = -5.78+/-0.16 within a radius of 13 pc.


title:
ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur
  and HD 163296

abstract:
  Using both the Short- and Long-wavelength Spectrometers on board the Infrared
Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae
systems AB Aur and HD 163296. In addition, we obtained ground-based N band
images of HD 163296. Our results can be summarized as follows: (1) The main
dust components in AB Aur are amorphous silicates, iron oxide and PAHs; (2) The
circumstellar dust in HD 163296 consists of amorphous silicates, iron oxide,
water ice and a small fraction of crystalline silicates; (3) The infrared
fluxes of HD 163296 are dominated by solid state features; (4) The colour
temperature of the underlying continuum is much cooler in HD 163296 than in AB
Aur, pointing to the existence of a population of very large (mm sized) dust
grains in HD 163296; (5) The composition and degree of crystallization of
circumstellar dust are poorly correlated with the age of the central star. The
processes of crystallization and grain growth are also not necessarily coupled.
This means that either the evolution of circumstellar dust in protoplanetary
disks happens very rapidly (within a few Myr), or that this evolution is
governed by factors other than stellar mass and age.


title:
Winds from accretion disks driven by the radiation and
  magnetocentrifugal force

abstract:
  We study the 2-D, time-dependent hydrodynamics of radiation-driven winds from
luminous accretion disks threaded by a strong, large-scale, ordered magnetic
field. The radiation force is due to spectral lines and is calculated using a
generalized multidimensional formulation of the Sobolev approximation. The
effects of the magnetic field are approximated by adding a force that emulates
a magnetocentrifugal force. Our approach allows us to calculate disk winds when
the magnetic field controls the flow geometry, forces the flow to corotate with
the disk, or both. In particular, we calculate models where the lines of the
poloidal component of the field are straight and inclined to the disk at a
fixed angle. Our numerical calculations show that flows which corotate with the
disk have a larger mass loss rate than their counterparts which conserve
specific angular momentum. The difference in the mass loss rate between these
two types of winds can be several orders of magnitude for low disk luminosities
but vanishes for high disk luminosities. Winds which corotate with the disk
have much higher velocities than angular momentum conserving winds. Fixing the
wind geometry stabilizes winds which are unsteady when the geometry is derived
self-consistently. The inclination angle between the poloidal velocity and the
normal to the disk midplane is important. Non-zero inclination angles allow the
magnetocentrifugal force to increase the mass loss rate for low luminosities,
and increase the wind velocity for all luminosities. Our calculations also show
that the radiation force can launch winds from magnetized disks. The line force
can be essential in producing MHD winds from disks where the thermal energy is
too low to launch winds or where the field lines make an angle of < 30^o with
respect to the normal to the disk.


title: Physics in Ultra-strong Magnetic Fields

abstract:
  In magnetic fields stronger than B_Q = 4.4 X 10^13 Gauss, an electron's
Landau excitation energy exceeds its rest energy. I review the physics of this
strange regime and some of its implications for the crusts and magneto- spheres
of neutron stars. In particular, I describe how ultra-strong fields
  >> render the vacuum birefringent and capable of distorting and magnifying
images ("magnetic lensing");
  >> change the self-energy of electrons: as B increases they are first
slightly lighter than $m_e$, then slightly heavier;
  >> cause photons to rapidly split and merge with each other;
  >> distort atoms into long, thin cylinders and molecules into strong,
polymer-like chains;
  >> enhance the pair density in thermal pair-photon gases; >> strongly
suppress photon-electron scattering, and >> drive the vacuum itself unstable,
at extremely large B.
  In a concluding section, I discuss recent observations of the spindown
histories of soft gamma repeaters and anomalous X-ray pulsars. The magnetar
model gives a promising framework for understanding these data.


title:
Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy
  Concentration at z=1.31

abstract:
  We have discovered a concentration of extremely red objects (EROs; R-K>6) in
the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly
overabundant compared to the field ERO surface density. The optical/near-IR
colors of the EROs and numerous other red galaxies in this field are consistent
with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies
show regular morphologies, most of them being disky or diffuse and without any
obvious evidence for interactions. Ground-based IR images show similar
morphologies, indicating any dust reddening in these objects is spatially
uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four
of the red galaxies lie at <z>=1.31, and a fifth lies in the foreground at
z=1.20. Of the <z>=1.31 galaxies, one is a reddened AGN while the remaining
three have rest-frame UV absorption-line spectra characteristic of old (few
Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55.
Including the MgII absorber seen in the QSO spectrum, we find five galaxies at
<z>=1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we
have discovered a coherent structure of old galaxies at high-redshift, possibly
associated with a massive galaxy cluster.


title:
Heliospheric, Astrospheric, and Insterstellar Lyman-alpha Absorption
  Toward 36 Oph

abstract:
  We use high-resolution UV spectra taken by the Space Telescope Imaging
Spectrograph instrument on board the Hubble Space Telescope to study the 5.5 pc
line of sight to the K0 V star 36 Oph A. The one interstellar component
detected for this line of sight has a velocity inconsistent with the local
interstellar cloud (LIC) flow vector, but consistent with the flow vector of
the so-called G cloud, a very nearby warm cloud in the Galactic Center
direction. From our data, we measure the following values for the interstellar
temperature, nonthermal velocity, H I column density, and D/H value:
T=5900+/-500 K, xi=2.2+/-0.2$ km/s, log N(H)=17.85+/-0.15, and
D/H=(1.5+/-0.5)e-5. The temperature of the G cloud is somewhat lower than that
of the LIC, and Mg and Fe depletions are also lower, but the D/H value appears
to be the same. Based on upper limits for the LIC absorption, we estimate the
distance to the edge of the LIC to be d(edge)<0.19 pc, which the Sun will reach
in t(edge)<7400 yrs. The H I Lyman-alpha absorption line has properties
inconsistent with those of the other absorption lines, indicating the presence
of one or more absorption components not seen in the other lines. We present
evidence that hot neutral hydrogen local to both the Sun and the star is
responsible for the excess Lyman-alpha absorption. This hot H I is created by
the interaction between the ISM and the winds of the Sun and 36 Oph A. The
observed line of sight lies only 12 degrees from the upwind direction of the
LIC flow vector, where hydrodynamic models of the heliosphere suggest that
heliospheric H I absorption should be particularly prominent.


title:
NICMOS Imaging of a Damped Lyman-alpha Absorber at z=1.89 toward LBQS
  1210+1731 : Constraints on Size and Star Formation Rate

abstract:
  We report results of a high-resolution imaging search (in rest frame
H-$\alpha$ and optical continuum) for the galaxy associated with the damped
Lyman-$\alpha$ (DLA) absorber at $z=1.892$ toward the $z_{em}=2.543$ quasar
LBQS 1210+1731, using HST/NICMOS. After PSF subtraction, a feature is seen in
both the broad-band and narrow-band images, at a projected separation of
0.25$\arcsec$ from the quasar. If associated with the DLA, the object would be
$\approx 2-3$ $h_{70}^{-1}$ kpc in size with a flux of $9.8 \pm 2.4$ $\mu$Jy in
the F160W filter, implying a luminosity at $\lambda_{central}=5500$ {\AA} in
the rest frame of $1.5 \times 10^{10}$ $h_{70}^{-2}$ L$_{\odot}$ at $z=1.89$,
for $q_{0}=0.5$. However, no significant H-$\alpha$ emission is seen,
suggesting a low star formation rate (SFR) (3 $\sigma$ upper limit of 4.0
$h_{70}^{-2}$ M$_{\odot}$ yr$^{-1}$), or very high dust obscuration.
Alternatively, the object may be associated with the host galaxy of the quasar.
H-band images obtained with the NICMOS camera 2 coronagraph show a much fainter
structure $\approx 4-5$ $h_{70}^{-1}$ kpc in size and containing four knots of
continuum emission, located 0.7$\arcsec$ away from the quasar. We have probed
regions far closer to the quasar sight-line than in most previous studies of
high-redshift intervening DLAs. The two objects we report mark the closest
detected high-redshift DLA candidates yet to any quasar sight line. If the
features in our images are associated with the DLA, they suggest faint,
compact, somewhat clumpy objects rather than large, well-formed proto-galactic
disks or spheroids.


title:
The Lx-T, Lx-sigma and sigma-T relations for groups and clusters of
  galaxies

abstract:
  While in the hierarchical model of structure formation, groups of galaxies
are believed to be the scaled-down version of clusters of galaxies, a
similarity breaking in the fundamental laws may occur on the group scale,
reflecting a transition between galaxy-dominated and intracluster medium
dominated properties. In this paper, we present an extensive study of the
relations between the X-ray luminosity (Lx), the temperature (T) of hot diffuse
gas and the velocity dispersion (sigma) of galaxies for groups and clusters of
galaxies, based on the largest sample of 66 groups and 274 clusters drawn from
literature. Our best fit Lx-T and Lx-sigma relations for groups read Lx propto
T^(5.57+-1.79) propto sigma^(2.35+-0.21), which deviates remarkably from those
for clusters: Lx propto T^(2.79+-0.08) propto sigma^(5.30+-0.21). The
significance of these correlations have been justified by both the
co-consistency test and the Kendall's tau statistics. We have thus confirmed
the existence of similarity breaking in the Lx-T and Lx-sigma relations between
groups and clusters as claimed in previous work, although the best fit sigma-T
relations remain roughly the same in both systems: sigma propto T^0.64.
Alternatively, the significant disagreement between the observationally fitted
Lx-T and Lx-sigma relations for groups and those expected from a perfect
hydrostatic equilibrium hypothesis indicates that the X-ray emission of
individual galaxies and the non-gravitational heating must play a potentially
important role in the dynamical evolution of groups. Therefore, reasonable
caution should be exercised in the cosmological applications of the dynamical
properties of groups.


title: Optically dim counterparts of hard X-ray selected AGNs

abstract:
  We present near-IR photometry and imaging observations of a small sample of
sources identified in the BeppoSAX 5-10 keV survey (HELLAS) which resolves ~
20-30% of the X-ray background at these energies. The near-IR data are combined
with optical spectra and photometry. Only 40% of the sources in our sample have
the blue, power law continuum typical of color-selected QSOs. The remaining 60%
are dominated by a galactic component which, on the basis of the continuum
colors and shape, have ages ranging from 10^9 to 10^10 years. The images show
that the blue QSOs are pointlike at our angular resolution, while all the other
sources are extended, consistent with their spectral appearance and low
redshift. Since down to R=20 only about two thirds of the HELLAS sources have a
counterpart, the preliminary HELLAS census comprises in roughly equal parts: i)
blue QSOs (mostly at high redshifts); ii) optically dim, galaxy-dominated
active nuclei (mostly at modest redshifts); and iii) empty fields (possibly
highly absorbed QSOs at high redshifts).


title: Observing high-redshift Supernovae in lensed galaxies

abstract:
  Supernovae in distant galaxies that are gravitationally lensed by foreground
galaxy clusters make excellent cosmological candles for measuring quantities
like the density of the Universe in its various components and the Hubble
constant. Distant supernovae will be more easily detectable since foreground
cluster lenses would magnify such supernovae by up to 3-4 magnitudes. We show
that in the case of the lens cluster Abell 2218, the detectability of
high-redshift supernovae is significantly enhanced due to the lensing effects
of the cluster. Since lensed supernovae will remain point images even when
their host galaxies are stretched into arcs, the signal-to-noise ratio for
their observation will be further enhanced, typically by an order of magnitude.
We recommend monitoring well-modelled clusters with several known arclets for
the detection of cosmologically useful SNe around z=1 and beyond.


title:
What Damped Ly-alpha Systems Tell Us About the Radial Distribution of
  Cold Gas at High Redshift

abstract:
  We investigate the properties of damped Lyman-alpha systems (DLAS) in
semi-analytic models, focusing on whether the models can reproduce the
kinematic properties of low-ionization metal lines described by Prochaska &
Wolfe (1997b, 1998). We explore a variety of approaches for modelling the
radial distribution of the cold neutral gas associated with the galaxies in our
models, and find that our results are very sensitive to this ingredient. If we
use an approach based on Fall & Efstathiou (1980), in which the sizes of the
discs are determined by conservation of angular momentum, we find that the
majority of the DLAS correspond to a single galactic disc. These models
generically fail to reproduce the observed distribution of velocity widths. In
alternative models in which the gas discs are considerably more extended, a
significant fraction of DLAS arise from lines of sight intersecting multiple
gas discs in a common halo. These models produce kinematics that fit the
observational data, and also seem to agree well with the results of recent
hydrodynamical simulations. Thus we conclude that Cold Dark Matter based models
of galaxy formation can be reconciled with the kinematic data, but only at the
expense of the standard assumption that DLAS are produced by rotationally
supported gas discs whose sizes are determined by conservation of angular
momentum. We suggest that the distribution of cold gas at high redshift may be
dominated by another process, such as tidal streaming due to mergers.


title: Spark Model for Pulsar Radiation Modulation Patterns

abstract:
  A non-stationary polar gap model first proposed by Ruderman & Sutherland
(1975) is modified and applied to spark-associated pulsar emission at radio
wave-lengths. It is argued that under physical and geometrical conditions
prevailing above pulsar polar cap, highly non-stationary spark discharges do
not occur at random positions. Instead, sparks should tend to operate in well
determined preferred regions. At any instant the polar cap is populated as
densely as possible with a number of two-dimensional sparks with a
characteristic dimension as well as a typical distance between adjacent sparks
being about the polar gap height. Our model differs, however, markedly from its
original 'hollow cone' version. The key feature is the quasi-central spark
driven by pair production process and anchored to the local pole of a
sunspot-like surface magnetic field. This fixed spark prevents the motion of
other sparks towards the pole, restricting it to slow circumferential drift
across the planes of field lines converging at the local pole. We argue that
the polar spark constitutes the core pulsar emission, and that the annular
rings of drifting sparks contribute to conal components of the pulsar beam. We
found that the number of nested cones in the beam of typical pulsar should not
excced three; a number also found by Mitra & Deshpande (1999) using a
completely different analysis.


title:
Tully-Fisher Relation and its Implications for Halo Density Profile and
  Self-interacting Dark Matter

abstract:
  We show that the Tully-Fisher relation observed for spiral galaxies can be
explained in the current scenario of galaxy formation without invoking subtle
assumptions, provided that galactic-sized dark haloes have shallow, core-like
central profiles, with a core radius proportional to halo circular velocity. In
such a system, both disk and halo contribute significantly to the maximum
rotation of the disk, and the interaction between the disk and halo components
acts to reduce the scatter in the Tully-Fisher relation. With model parameters
chosen in plausible ranges, the model can well accommodate the zero-point,
slope, scatter of the observed Tully-Fisher relation, as well as the large
range of disk sizes. The model predicts that LSB disks obey a Tully-Fisher
relation similar to that of normal disks, if disk mass-to-light ratio is
properly taken into account. The halo profile required by the Tully-Fisher
relation is as shallow as that required by the rotation curves of faint disks,
but much shallower than that predicted by conventional CDM models. Our results
cannot be explained by some of the recent proposals for resolving the conflict
between conventional CDM models and the rotation-curve shapes of faint
galaxies. If dark matter self-interaction (either scattering or annihilation)
is responsible for the shallow profile, the observed Tully-Fisher relation
requires the interaction cross section \sigma_X to satisfy
<\sigma_{X}|v|>/m_{X}~10^{-16} cm^3/s/GeV.


title: Optical Counterparts to Damped Lyman Alpha Systems

abstract:
  Previously we have shown (Maller et al, 1998) that the kinematics of Damped
Lyman Alpha Systems (DLAS) as measured by Prochaska and Wolfe (1998) can be
reproduced in a multiple disk model (MDM) if the gaseous disks are of
sufficient radial extent. Here we discuss this model's predictions for the
relationship between DLAS and Lyman break galaxies (LBGs), which we here take
to be objects at z~3 brighter than R=25.5. We expect that future observations
of the correlations between DLAS and LBGs will provide a new data set able to
discriminate between different theoretical models of the DLAS. Djorgovski
(1997) has already detected a few optical counterparts and more studies are
underway.


title:
Discovering Ultra High Energy Neutrinos by Horizontal and Upward tau
  Air-Showers: Evidences in Terrestrial Gamma Flashes?

abstract:
  Ultra high energy neutrinos UHE neutrino Tau, anti-neutrino Tau,
anti-neutrino electron at PeVs, and higher energy may induce tau air-showers
whose detectability is million to billion times amplified by their secondaries.
We considered UHE nu_{tau}- N and UHE bar\nu_{e}- e interactions beyond
mountains as a source of such horizontal amplified Tau air-showers. We also
consider vertical upward UHE nu_{tau}-N interaction on Earth crust leading to
UHE Tau airshowers {UPTAUS} or at the horizont edges {HORTAUS} and their
beaming toward high mountains gamma, X, Cherenkov detectors on mountains. We
show their detectability. We notice that such rare upward Tau air-shower,
UPTAUS and HORTAUS, may hit even nearby airlines, ballons, satellite and flash
them by short diluted gamma-burst at the edge of Gamma Ray Observatory (GRO)
detection threshold. We suggest the identification of these events with recent
discovered (BATSE) Terrestrial Gamma Flashes and we claim their probable UHE
Tau by UHE nu_\tau origin. From these data approximated UHE nu_tau flux and
Delta m_{nu_mu \nu_tau} lower bound are derived. Known X-gamma-{TeV} active
galactic and extragalactic sources have been identified in most TGF arrival
directions. Maximal EGRET activity in galactic Center overlap with maximal TGF
flux. The UHECR AGASA an-isotropy at 10^{18} eV shows also possible
correlations with TGF events. The unique UHECR triplet in AGASA clustering,
pointing toward BL Lac 1ES0806+524, finds, within its error box, a
corresponding TGF event, BATSE (Trigger 2444). Finally a partial TGF Galactic
signature, combined with above correlations suggests an astrophysical tau
origin of TGF events.


title:
Damped Ly-alpha Systems in Semi-Analytic Models: Sensitivity to
  dynamics, disk properties, and cosmology

abstract:
  Previously we have shown that it is possible to account for the kinematic
properties of damped Lyman alpha systems (DLAS) in the context of semi-analytic
models. In these models, hierarchical structure formation is approximated by
constructing a merger tree for each dark matter halo. A natural consequence is
that every virialized halo may contain not only a central galaxy, but also a
number of satellite galaxies as determined by its merging history. Thus the
kinematics of the DLAS arise from the combined effects of the internal rotation
of gas disks and the motions between gas disks within a common halo. Here we
investigate the sensitivity of this model to some of the assumptions made
previously, including the modeling of satellite dynamics, the scale height of
the gas, and the cosmology.


title: AGB evolution with overshoot: hot bottom burning and dredge up

abstract:
  We calculated models of massive AGB stars with a self-consistent coupling of
time-dependent mixing and nuclear burning for 30 isotopes and 74 reactions.
Overshoot with an exponentially declining velocity field was considered and
applied during all stages of evolution and in all convective regions. Very
efficient 3rd dredge-up was found even overcompensating the growth of the
hydrogen-exhausted core after a few thermal pulses. Hot bottom burning occurs
for M>4Msol within the sequences with overshoot. Carbon star formation in these
more massive AGB stars is delayed or even prevented by hot bottom burning
despite the very efficient dredge-up. With the simultaneous treatment of mixing
and burning the formation of Li-rich AGB stars due to the Cameron-Fowler
mechanism was followed. For a 6Msol model the maximum Li abundance was found to
be epsilon(Li7)=4.4.


title: ISO-SWS Observations of OMC-1: H_2 and Fine Structure Lines

abstract:
  Using the Short-Wavelength-Spectrometer on the Infrared Space Observatory
(ISO), we obtained near- and mid-infrared spectra toward the brightest H_2
emission peak of the Orion OMC-1 outflow. A wealth of emission and absorption
features were detected, dominated by 56 H_2 ro-vibrational and pure rotational
lines reaching from H_2 0-0 S(1) to 0-0 S(25). The spectra also show a number
of H I recombination lines, atomic and ionic fine structure lines, and
molecular lines of CO and H_2O. Between 6 and 12 mu the emission is dominated
by PAH features. The H_2 level column density distribution shows no signs of
fluorescent excitation or a deviation from an ortho-to-para ratio of three. It
shows an excitation temperature which increases from about 600 K for the lowest
rotational and vibrational levels to about 3200 K at level energies E(v,J)/k >
14 000 K. No single steady state shock model can reproduce the observed H_2
excitation. The higher energy H_2 levels may be excited either thermally in
non-dissociative J-shocks, through non-thermal collisions between fast ions and
molecules with H_2 in C-shocks, or they are pumped by newly formed H_2
molecules. The highest rotational levels may be populated by yet another
mechanism, such as the gas phase formation of H_2 through H^-.


title:
Non-uniform reionization by galaxies and its effect on the cosmic
  microwave backgroun

abstract:
  We present predictions for the reionization of the intergalactic medium by
stars in high-redshift galaxies. We calculate ionizing luminosities of
galaxies, including the effects of absorption by interstellar gas and dust on
the escape fraction, in order to calculate the filling factor of ionized
hydrogen in the IGM. For a $\Lambda{\rm CDM}$ cosmology and a physical
calculation of the escape fraction, we find that the hydrogen in the IGM will
be reionized at redshift z=6.1 if the IGM has uniform density, but only by
z=4.5 if the IGM is clumped. We combine our model with an N-body simulation of
the distribution of dark matter in the universe in order to calculate the
secondary temperature anisotropies induced in the cosmic microwave background
(CMB) by scattering off free electrons. The models predict a spectrum of
secondary anisotropies covering a broad range of angular scales, with
fractional temperature fluctuations $\sim 10^{-7}-10^{-6}$ on arcminute scales.
The amplitude depends somewhat on the geometry of reionization, with models in
which the regions of highest gas density are reionized first giving larger CMB
fluctuations than the case where galaxies ionize surrounding spherical regions,
and models where low density regions reionize first giving the smallest
fluctuations. Measurement of these anisotropies can therefore put important
constraints on the reionization process, in particular, the redshift evolution
of the filling factor, and should be a primary objective of a next generation
submillimeter telescope such as the Atacama Large Millimeter Array. (abrdiged)


title: The spark-associated soliton model for pulsar radio emission

abstract:
  We propose a new, self-consistent theory of coherent pulsar radio emission
based on the non-stationary sparking model of Ruderman & Sutherland (1975),
modified by Gil & Sendyk (2000) in the accompanying Paper I. According to these
authors, the polar cap is populated as densely as possible by a number of
sparks with a characteristic perpendicular dimension D approximately equal to
the polar gap height scale h, separated from each other also by about h. Each
spark reappears in approximately the same place on the polar cap for a time
scale much longer than its life-time and delivers to the open magnetosphere a
sequence of electron-positron clouds which flow orderly along a flux tube of
dipolar magnetic field lines. The overlapping of particles with different
momenta from consecutive clouds leads to effective two-stream instability,
which triggers electrostatic Langmuir waves at the altitudes of about 50
stellar radii. The electrostatic oscillations are modulationally unstable and
their nonlinear evolution results in formation of ``bunch-like'' charged
solitons. A characteristic soliton length along magnetic field lines is about
30 cm, so they are capable of emitting coherent curvature radiation at radio
wavelengths. The net soliton charge is about 10^21 fundamental charges,
contained within a volume of about 10^14 cm^3. For a typical pulsar, there are
about 10^5 solitons associated with each of about 25 sparks operating on the
polar cap at any instant. One soliton moving relativisticaly along dipolar
field lines with a Lorentz factor of the order of 100 generates a power of
about 10^21 erg/s by means of curvature radiation. Then the total power of a
typical radio pulsar can be estimated as being about 10^(27-28) erg/s.


title: The Apparent and Intrinsic Shape of the APM Galaxy Clusters

abstract:
  We estimate the distribution of intrinsic shapes of APM galaxy clusters from
the distribution of their apparent shapes. We measure the projected cluster
ellipticities using two alternative methods. The first method is based on
moments of the discrete galaxy distribution while the second is based on
moments of the smoothed galaxy distribution. We study the performance of both
methods using Monte Carlo cluster simulations covering the range of APM cluster
distances and including a random distribution of background galaxies. We find
that the first method suffers from severe systematic biases, whereas the second
is more reliable. After excluding clusters dominated by substructure and
quantifying the systematic biases in our estimated shape parameters, we recover
a corrected distribution of projected ellipticities. We use the non-parametric
kernel method to estimate the smooth apparent ellipticity distribution, and
numerically invert a set of integral equations to recover the corresponding
distribution of intrinsic ellipticities under the assumption that the clusters
are either oblate or prolate spheroids. The prolate spheroidal model fits the
APM cluster data best.


title: The hard X-ray emission of luminous infrared galaxies

abstract:
  We present a study of the hard X-ray properties of a sample that includes all
the Luminous Infrared Galaxies (LIGs, L_IR > 10^11 L_sun) observed in the 2-10
keV energy band (new and archival data). We find that a significant fraction of
the sources optically classified as AGNs do not show any indication of nuclear
activity in the X rays, thus suggesting heavy absorption along our line of
sight. The absence of strong emission in the 20-200 keV band in a subsample of
LIGs observed with BeppoSAX suggests that in many cases these sources are
completely Compton thick (N_H > 10^25 cm^(-2)). From a comparison between the
infrared and the X-ray emission we deduce that the mid-IR emission is absorbed
by a lower column density than the X-ray emission or, alternatively, that the
dust-to-gas ratio is lower than Galactic. We describe a simple model that
reproduces the IR-X correlation by means of mixed AGN and starburst
contributions and we compare the predictions of this model with the
observational data at X-ray and optical wavelengths. Finally, we discuss the
biases that affect the currently available samples of LIGs and briefly analyze
a small unbiased sample, finding that at least 50% of the sources host a (weak)
AGN.


title:
Identification of a nearby stellar association in the Hipparcos catalog:
  implications for recent, local star formation

abstract:
  The TW Hydrae Association (~55 pc from Earth) is the nearest known region of
recent star formation. Based primarily on the Hipparcos catalog, we have now
identified a group of 9 or 10 co-moving star systems at a common distance (~45
pc) from Earth that appear to comprise another, somewhat older, association
(``the Tucanae Association''). Together with ages and motions recently
determined for some nearby field stars, the existence of the Tucanae and TW
Hydrae Associations suggests that the Sun is now close to a region that was the
site of substantial star formation only 10-40 million years ago. The TW Hydrae
Association represents a final chapter in the local star formation history.


title: Event categories in the EDELWEISS WIMP search experiment

abstract:
  Four categories of events have been identified in the EDELWEISS-I dark matter
experiment using germanium cryogenic detectors measuring simultaneously charge
and heat signals. These categories of events are interpreted as electron and
nuclear interactions occurring in the volume of the detector, and electron and
nuclear interactions occurring close to the surface of the detectors(10-20 mu-m
of the surface). We discuss the hypothesis that low energy surface nuclear
recoils,which seem to have been unnoticed by previous WIMP searches, may
provide an interpretation of the anomalous events recorded by the UKDMC and
Saclay NaI experiments. The present analysis points to the necessity of taking
into account surface nuclear and electron recoil interactions for a reliable
estimate of background rejection factors.


title: Some Aspects of Inverse Compton Emission from 3K Background Photons

abstract:
  We review the history and a few features of IC/3K emission. We discuss
observing strategies, the physical parameters which can be derived directly or
indirectly from successful detections, and the disparities between magnetic
field strength estimates found by different methods.


title: A Comparison of the Extra Nuclear X-ray and Radio Features in M87

abstract:
  ROSAT High Resolution Imager (HRI) data from eight observations have been
co-added to obtain an effective exposure of 230 ksec. We have identified a
number of features and regions with excess X-ray brightness over that from a
circularly symmetric model of the well known hot gas component. A prominent
`spur' extends 4' from the vicinity of knot A towards the south-west. The
brightness to the south and east of this spur is significantly higher than that
to the north and west. Excess brightness is also found to the East of the
nucleus, with a local maximum centered on the eastern radio lobe 3' from the
core.
  There are two well known relationships between radio and x-ray emission for
radio galaxies in clusters: coincidence of emissions because the X-rays come
from inverse Compton or synchrotron processes; and anti-coincidence caused by
exclusion of hot gas from radio entities. We present a radio/X-ray comparison
to determine if either of these relationships can be isolated in M87. The
greatest obstacle we face is the unknown projection which affects both bands.


title:
Delta Scuti stars in stellar systems: on the variability of HD 220392
  and HD 220391

abstract:
  HD 220392 (HR 8895), the brightest member of the visual double star CCDM
23239-5349, is a new short-period variable bright star, probably of the Delta
Scuti type. The period analysis performed on the complete set of definitive
Geneva photometry as well as on the data obtained at the ESO 0.5m telescope
shows two periodicities of about 4.7 and 5.5 cycles per day (cpd) with
amplitudes of 0.014 and 0.011 mag respectively. A similar period search on the
(smaller) dataset obtained for the 1 mag fainter B-component, HD 220391,
however shows no periodicity with an amplitude significantly above the noise
level of the data (about 0.006 mag). This difference in variability behaviour
is discussed from the consideration that both stars form a common origin pair
and are located in the Delta Scuti instability strip.


title: Pulsation in two Herbig Ae stars: HD 35929 and V351 Ori

abstract:
  New photometric observations of seven intermediate mass pre-main sequence
delta Scuti candidates are presented. The periods and pulsation modes are
derived for two of these stars, namely HD 35929 and V351 Ori. The comparison
between observations and nonlinear pulsational models allows us to provide some
initial constraints on their mass and evolutionary state. As an illustration we
discuss the use of periods to identify the mode of pulsation in these two stars
and to have an independent estimate of their distances.


title: An Australia telescope survey for CMB anisotropies

abstract:
  We have surveyed six distinct `empty fields' using the Australia Telescope
Compact Array in an ultra-compact configuration with the aim of imaging, with a
high brightness sensitivity, any arcmin-scale brightness-temperature
anisotropies in the background radio sky. The six well-separated regions were
observed at a frequency of 8.7 GHz and the survey regions were limited by the
ATCA primary beams which have a full width at half maximum of 6 arcmin at this
frequency; all fields were observed with a resolution of 2 arcmin and an rms
thermal noise of 24 microJy/beam. After subtracting foreground confusion
detected in higher resolution images of the fields, residual fluctuations in
Stokes I images are consistent with the expectations from thermal noise and
weaker (unidentified) foreground sources; the Stokes Q and U images are
consistent with expectations from thermal noise.
  Within the sensitivity of our observations, we have no reason to believe that
there are any Sunyaev-Zeldovich holes in the microwave sky surveyed. Assuming
Gaussian-form CMB anisotropy with a `flat' spectrum, we derive 95 per cent
confidence upper limits of Q_flat < 10--11 microK in polarized intensity and
Q_flat < 25 microK in total intensity. The ATCA filter function peaks at l=4700
and has half maximum values at l=3350 and 6050.


title:
The Fraction of High Redshift Galaxies in Deep Infrared Selected Field
  Galaxy Samples

abstract:
  Recent results on the incidence of red galaxies in a > 100 square arcminute
field galaxy survey to K=20 and a K=22 survey of the Hubble Deep Field are
presented. We argue that a simple photometric redshift indicator, based on J-K
color and supported by spectroscopic results obtained with Keck, gives a
reliable lower limit of ~25% for the fraction of z>1 galaxies in the 100 square
arcminute survey. This fraction is substantially higher than found in previous
smaller samples, and is at least as consistent with predictions for pure
luminosity evolution as with those for hierarchical models. The same technique
yields a very low fraction for the HDF, which appears to be unusually
underabundant in red galaxies.


title:
Revealing the Photodissociation Region: Hubble Space Telescope/NICMOS
  Imaging of NGC 7027

abstract:
  We report results from a Hubble Space Telescope (HST) and Near-Infrared
Camera and Multiobject Spectrometer (NICMOS) program to study the distribution
of hot neutral (molecular hydrogen) and ionized circumstellar material in the
young planetary nebulae NGC 7027. HST/NICMOS provided very high spatial
resolution imaging in line and continuum emission, and the stability and large
dynamic range needed for investigating detailed structures in the circumstellar
material. We present dramatic new images of NGC 7027 that have led to a new
understanding of the structure in this important planetary nebula. The central
star is clearly revealed, providing near-infrared fluxes that are used to
directly determine the stellar temperature very accurately (T = 198,000 K). It
is found that the photodissociation layer as revealed by near-infrared
molecular hydrogen emission is very thin, and is biconical in shape. The
interface region is structured and filamentary, suggesting the existence of
hydrodynamic instabilities. We discuss evidence for the presence of one or more
highly collimated, off-axis jets that might be present in NGC 7027. The
evolutionary future of NGC 7027 is discussed.


title:
Properties of Radio-Selected Broad Absorption-Line Quasars from the
  FIRST Survey

abstract:
  In a spectroscopic follow-up to the VLA FIRST survey, the FIRST Bright Quasar
Survey (FBQS) has found 29 radio-selected broad absorption line (BAL) quasars.
This sample provides the first opportunity to study the properties of
radio-selected BAL quasars. Contrary to most previous studies, we establish
that a significant population of radio-loud BAL quasars exists. Radio-selected
BAL quasars display compact radio morphologies and possess both steep and flat
radio spectra. Quasars with low-ionization BALs have a color distribution
redder than that of the FBQS sample as a whole. The frequency of BAL quasars in
the FBQS is significantly greater, perhaps by as much as a factor of two, than
that inferred from optically selected samples. The frequency of BAL quasars
appears to have a complex dependence on radio-loudness. The properties of this
sample appear inconsistent with simple unified models in which BAL quasars
constitute a subset of quasars seen edge-on.


title:
Exclusion Limits on the WIMP-Nucleon Cross-Section from the Cryogenic
  Dark Matter Search

abstract:
  The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search
for WIMPs via their elastic-scattering interactions with nuclei while
discriminating against interactions of background particles. CDMS data give
limits on the spin-independent WIMP-nucleon elastic-scattering cross-section
that exclude unexplored parameter space above 10 GeV c^{-2} WIMP mass and, at >
84% CL, the entire 3$\sigma$ allowed region for the WIMP signal reported by the
DAMA experiment.


title: Stability of Relativistic Blast Waves

abstract:
  A spherical blast wave with relativistic velocity can be described by a
similarity solution, that is used for theoretical models of gamma-ray bursts.
We consider the linear stability of such a relativistic blast wave propagating
into a medium with density gradient. The perturbation can also be expressed by
a self-similar form. We show that the shock front is unstable in general, and
we evaluate the growth rate.


title: The dynamical evolution of the dust shell of IRC+10216

abstract:
  We present high-resolution J-, H-, and K-band observations of the carbon star
IRC+10216. The images were reconstructed from 6 m telescope speckle
interferograms using the bispectrum speckle interferometry method. The H and K
images consist of several compact components within a 0.2" radius and a fainter
asymmetric nebula. The brightest four components are denoted with A to D in the
order of decreasing brightness. A comparison of our images gives - almost like
a movie of five frames - insight to the dynamical evolution of the inner
nebula. For instance, the separation of the two brightest components A and B
increased by almost 40% from 191 mas in 1995 to 265 mas in 1998. At the same
time, component B is fading and the components C and D become brighter. The
X-shaped bipolar structure of the nebula implies an asymmetric mass-loss
suggesting that IRC+10216 is very advanced in its AGB evolution, shortly before
turning into a protoplanetary nebula. The cometary shape of component A
suggests that the core of A is not the central star, but the southern lobe of a
bipolar structure. The position of the central star is probably at or near the
position of component B.


title:
A deep search for the optical counterpart to the anomalous X-ray pulsar
  1E 2259+58.6

abstract:
  We present Keck R and I band images of the field of the anomalous X-ray
pulsar 1E 2259+58.6. We derive an improved X-ray position from archival ROSAT
HRI observations by correcting for systematic (boresight) errors. Within the
corresponding error circle, no object is found on the Keck images, down to
limiting magnitudes R = 25.7 and I = 24.3. We discuss the constraints imposed
by these limits, and conclude that it is unlikely that 1E 2259+58.6 is powered
by accretion from a disk, irrespective of whether it is in a binary or not,
unless the binary is extremely compact.


title: Prospects of Variable Star Research by Future Space Missions

abstract:
  ESA and NASA are studying projects having a tremendous return on variable
star research. Other national space agencies are also studying or developing
projects of smaller costs but with impressive returns. The projects range from
global Galactic surveys like the ESA mission GAIA which will give photometric
time series for about 1 billion stars, to detailed pulsation modes studies like
the CNES mission COROT which could reach a photometric precision lower than 1
ppm. The presentation will emphasize the future astrometric, asteroseismologic
and planet detection missions.


title: Some statistical properties of spiral galaxies

abstract:
  This paper presents some statistical correlations of 72 northern spiral
galaxies. The results show that early-type spirals that are brighter, and
thicker, and the axis ratios ($H_{z}/H_r$) of the disk tend to be smaller along
the Hubble sequence. We also find that $H_{z}/H_r$ correlates strongly with the
galaxy's color, and early-type spirals have larger values of $H_{z}/H_r$. The
inclinations obtained by fitting the pattern of a spiral structure with a
logarithmic spiral form are nearly the same as those obtained by using the
formulas of Aaronson et al. (1980). Finally, the mean measured pitch angles for
the different Hubble sequences in the Third Catalogue of Bright Galaxies by de
Vaucouleurs et al. (1991) are derived.


title: Dependence of Spiral Galaxy Distribution on Viewing Angle in RC3

abstract:
  The normalized inclination distributions are presented for the spiral
galaxies in RC3. The results show that, except for the bin of
$81^{\circ}$-$90^{\circ}$, in which the apparent minor isophotal diameters that
are used to obtain the inclinations, are affected by the central bulges, the
distributions for Sa, Sab, Scd and Sd are well consistent with the Monte-Carlo
simulation of random inclinations within 3-$\sigma$, and Sb and Sbc almost, but
Sc is different. One reason for the difference between the real distribution
and the Monte-Carlo simulation of Sc may be that some quite inclined spirals,
the arms of which are inherently loosely wound on the galactic plane and should
be classified to Sc galaxies, have been incorrectly classified to the earlier
ones, because the tightness of spiral arms which is one of the criteria of the
Hubble classification in RC3 is different between on the galactic plane and on
the tangent plane of the celestial sphere. Our result also implies that there
might exist biases in the luminosity functions of individual Hubble types if
spiral galaxies are only classified visually.


title:
Non-equilibrium H2 ortho-to-para ratio in two molecular clouds of the
  Galactic Center

abstract:
  We present ISO observations of the S(0), S(1), S(2), and S(3) rotational
lines of molecular hydrogen from two molecular clouds near the Galactic Center
(GC). We have also measured continuum dust emission at infrared wavelengths
with ISO and the rotational radio lines J=1-0 of 13CO and C18O and J=2-1 of
C18O with the IRAM-30m telescope. Using the dust continuum spectra and the CO
lines we derive a total visual extinction of 15-20 magnitudes toward these GC
clouds. After correcting the H2 data for extinction, the gas temperatures are
\~250 K and the column densities of warm gas are ~2e21 cm-2. This is the first
direct measure of the H2 column densities of the warm component; with this, we
estimate an NH3 abundance in the warm gas of ~ 2e-7. The column density of warm
gas is, at least, a factor of 100 larger than the corresponding column
densities derived from the warm dust. The observed ortho-to-para ratio (OTPR)
is ~ 1, clearly below the local thermodynamical equilibrium (LTE) OTPR for gas
at 250 K of ~3. Low velocity shocks (~ 10 km/s) are the most likely explanation
for the column densities of warm gas and dust and the non-LTE H2 OTPR.


title: Resonant scattering of X-rays by the warm intergalactic medium

abstract:
  For the low density filamentary and sheet-like structures in the warm ($\sim
10^4$ to $\sim 10^6$ K) IGM predicted by numerical simulations the resonant
line scattering of X-ray background (XRB) photons by He and H-like ions of
heavy elements can exceed the ``local'' thermal emission by a factor of a few
or more. Due to the conservative nature of scattering this resonantly scattered
radiation can only be identified if a significant fraction of the XRB is
resolved and removed. While the combined spectrum of the resolved sources will
contain X-ray absorption features, the residual background will contain
corresponding emission features with the same intensity. At the relevant
densities and temperatures the lines of He and H-like oxygen at 0.57 and 0.65
keV are most promising. These lines (which have a typical width of $\sim$ 1-2
eV) may contain up to 50% of the total 0.5-1 keV emission of the filament. For
a nearby ($z \la 0.1$) filament with a Thomson optical depth of $10^{-4}$ XMM
should detect about 200 photons in the OVII line during a $10^5$ s exposure if
the metallicity of the gas is as large as observed in galaxy clusters. On
average up to a few percent of the soft XRB could be resonantly scattered by
this phase of the IGM and resonantly scattered photons should account for a
significant fraction of the truly diffuse background at low energies. Close to
bright X-ray sources like galaxy clusters or AGN the flux of scattered
radiation will be further enhanced. Off-line blazars are the most promising
illuminating sources. The scattered emission from AGN may also constrain the
duration of the active phase of these objects.


title:
Delta Scuti Stars in Stellar Systems: the interest of HD 220392 and HD
  220391

abstract:
  The very wide double star CCDM 23239-5349 is an interesting study case of a
pulsating star within a common origin pair or wide binary. Both stars are
located in the Delta Scuti instability strip. Based on data obtained at La
Silla (Chile), at the Swiss 0.7m and the ESO 0.5m telescopes, we found two
periodicities of about 4.7 and 5.5 cycles per day (cpd) with amplitudes of
0.014 and 0.011 mag, respectively, for HD 220392, the brightest member of the
system. The most dominant periodicity was also detected in the Hipparcos Epoch
Photometry data. A similar period search on the (smaller) dataset obtained for
the 1 mag fainter B-component, HD 220391, however shows no periodic behaviour
with an amplitude significantly above the noise level of the data (about 0.006
mag).


title:
Precise Measurement of Cosmic-Ray Proton and Helium Spectra with the
  BESS Spectrometer

abstract:
  We report cosmic-ray proton and helium spectra in energy ranges of 1 to 120
GeV and 1 to 54 GeV/nucleon, respectively, measured by a balloon flight of the
BESS spectrometer in 1998. The magnetic-rigidity of the cosmic-rays was
reliably determined by highly precise measurement of the circular track in a
uniform solenoidal magnetic field of 1 Tesla. Those spectra were determined
within overall uncertainties of +-5 % for protons and +- 10 % for helium nuclei
including statistical and systematic errors.


title: Simple dynamical models of the Sagittarius dwarf galaxy

abstract:
  We present two simple dynamical models for Sagittarius based on N-body
simulations of the progressive disruption of a satellite galaxy orbiting for
12.5 Gyr within a realistic Galactic potential. In both models the satellite
initially has observable properties similar to those of current outlying
dwarfs; in one case it is purely stellar while in the other it is embedded in
an extended massive halo. The purely stellar progenitor is a King model with a
total velocity dispersion of 18.9 km/s, a core radius of 0.44 kpc and a tidal
radius of 3 kpc. The initial stellar distribution in the other case follows a
King profile with the same core radius, a slightly larger total velocity
dispersion and similar extent. Both these models are consistent with all
published data on the current Sagittarius system, they match not only the
observed properties of the main body of Sagittarius, but also those reported
for unbound debris at larger distances.


title: The Polytropic Equation of State of Interstellar Gas Clouds

abstract:
  Models are presented for the polytropic equation of state of
self-gravitating, quiescent interstellar gas clouds. A detailed analysis,
including chemistry, thermal balance, and radiative transfer, is performed for
the physical state of the gas as a function of density, metallicity, velocity
field, and background radiation field. It is found that the stiffness of the
equation of state strongly depends on all these physical parameters, and the
adiabatic index varies between 0.2-1.4. The implications for star formation, in
particular at high redshift and in starburst galaxies, and the initial stellar
mass function are discussed.


title:
The Spatial Distribution of Atomic Carbon Emission in the Giant
  Molecular Cloud NGC 604-2

abstract:
  We have mapped a giant molecular cloud in the giant HII region NGC 604 in M33
in the 492 GHz ^3P_1 -- ^3P_0 transition of neutral atomic carbon using the
James Clerk Maxwell Telescope. We find the distribution of the [CI] emission to
be asymmetric with respect to the CO J=1--0 emission, with the peak of the [CI]
emission offset towards the direction of the center of the HII region. In
addition, the line ratio I_{[CI]}/I_{CO} is highest (~ 0.2) facing the HII
region and lowest (< 0.1) away from it. These asymmetries indicate an edge-on
morphology where the [CI] emission is strongest on the side of the cloud facing
the center of the HII region, and not detected at all on the opposite side This
suggests that the sources of the incident flux creating C from the dissociation
of CO are the massive stars of the HII region. The lowest line ratios are
similar to what is observed in Galactic molecular clouds, while the highest are
similar to starburst galaxies and other regions of intense star formation. The
column density ratio, N(C)/N(H_2) is a few times 10^{-6}, in general agreement
with models of photodissociation regions.


title: Search for molecular gas in HVCs through HCO+ absorption

abstract:
  High-Velocity Clouds (HVCs) have radial velocities that cannot be explained
by the global Galactic rotation; their distances remain mostly unknown, and
their true nature and origin are still a mystery. Some of them could be of
galactic origin, or belong to tidal streams drawn by the Milky-Way/ Magellanic
Clouds interaction, or could even be intergalactic clouds infalling onto the
Local Group. In the latter hypothesis, they play a major role in the
hierarchical formation scenario of the Milky-Way and are connected to the
Lyman-limit absorption systems. In any case, the determination of their
physical state (density, temperature, internal structure, abundances,
excitation) will help to discriminate between current theories on their origin
and nature. A recent UV measurement (Richter et al 1999) has discovered for the
first time in a HVC the molecular phase that was previously searched for,
without success, through CO emission. Previous non detections could be due
either to metallicity problems, or insufficient excitation (because of low
density). Low-excitation molecular gas may, however, be detectable though
absorption. Here we report on a sensitive search for HCO+(1-0) absorption lines
in front of 27 quasars, already known to be strong millimetric continuum
sources. Except for one tentative case, no detection was obtained in most HVCs,
although HCO+(1-0) was clearly detected towards galactic low-velocity clouds.
We discuss the implications of this result.


title: Modification of AGB wind in a binary system

abstract:
  We explore one of plausible causes of asymmetry in the wind of an AGB star -
the presence of a binary companion. We have developed a simple method for
estimating the intrinsic non-sphericity of the outflow in that case. Assuming
the Roche model, local stellar parameters (T_eff, g) are calculated, and then a
formula for the local mass loss rate is applied. As a by-product a relation
between the ratio of stellar radius to the Roche lobe radius and the overall
wind enhancement is obtained.


title: Post-Glitch RXTE-PCA Observations of the Vela Pulsar

abstract:
  We report the results of analysis of observations of the Vela Pulsar by PCA
on RXTE. Our data consists of two parts. The first part contains observations
at 1, 4, and 9 days after the glitch in 1996 and has 27000 sec. total exposure
time. The second part of observations were performed three months after this
glitch and have a total exposure time of 93000 sec. We found pulsations in both
sets. The observed spectrum is a power-law with no apparent change in flux or
count rate. The theoretical expectations of increase in flux due to internal
heating after a glitch are smaller than the uncertainty of the observations.


title:
Fundamental parameters of Galactic luminous OB stars V. The effect of
  microturbulence

abstract:
  We study the effect of microturbulence in the line formation calculations of
H and He lines, in the parameter range typical for O and early B stars. We are
specially interested in its effect on the determination of stellar parameters:
effective temperature, surface gravity and specially on the He abundance. We
find that only HeI lines and HeII 4686 are sensibly affected by
microturbulence, and that models with lower gravities, the ones suitable for
supergiants, are more sensitive to it. We analyze five stars using
microturbulence velocities of 0 and 15 km/s. The parameters obtained for 15
km/s differ from the ones at 0 km/s within the limits of the standard error box
of our analysis. The quality of the line fits only improves for HeI 4471, but
not to the extent of completely solving the so-called dilution effect.
Therefore our conclusion is that microturbulence is affecting the derivation of
stellar parameters, but its effect is comparable to the adopted uncertainties.
Thus it can reduce moderate He overabundances and solve line fit quality
differences, but it cannot explain by itself large He overabundances in O
stars.


title: Present and Near-Future Reflected Light Searches for Close-In Planets

abstract:
  Close-in extrasolar giant planets may be directly detectable by their
reflected light, due to the proximity of the planet to the illuminating star.
The spectrum of the system will contain a reflected light component that varies
in amplitude and Doppler shift as the planet orbits the star. Intensive
searches for this effect have been carried out for only one extrasolar planet
system, tau Boo. There exist several other attractive targets, including the
transiting planet system HD 209458.


title:
A New Complete Sample of Sub-millijansky Radio Sources: An Optical and
  Near-Infrared Study

abstract:
  The Very Large Array (VLA) has been used in C-configuration to map an area
\~0.3 square degrees at 1.4 GHz with 5sigma sensitivities of 0.305, 0.325,
0.380 and 0.450 mJy/beam over four equal subareas. Radio properties are
presented for 62 detected sources. Deep optical imaging to Gunn r~25 mag using
the Hale 5-m telescope covering ~0.21 square degrees is reported for a subset
of 43 sources. This optical follow-up is much deeper than that of existing
larger area radio surveys of similar radio sensitivity. Archival J, H and
K-band photometry from the Two-Micron All Sky Survey (2MASS) is also presented.
Using a robust likelihood-ratio technique, we optically identified 26 radio
sources with probabilities >80%. Nine are uncertain/ambiguous detections and
eight are empty fields. Comparisons with a stellar synthesis model that
includes radio emission and dust reddening suggests that the
near-infrared--to--optical emission in a small, bright sub-sample is reddened
by `optically-thin' dust with absorption A_V ~ 2-2.5 mag, regardless of
morphological type. This is consistent with other, more direct determinations
of absorption. The radio--to--optical(--near-infrared) flux ratios of
early-type galaxies require significant contamination in the radio by an active
galactic nucleus (AGN), consistent with the current paradigm. Using our simple
modeling approach, we also discuss a potential diagnostic for selecting
Ultraluminous Infrared Galaxies (ULIGS) to z~1.6 from microJansky radio
surveys.


title: Hot Stars and Cool Clouds: The Photodissociation Region M16

abstract:
  We present high-resolution spectroscopy and images of a photodissociation
region (PDR) in M16 obtained during commissioning of NIRSPEC on the Keck II
telescope. PDRs play a significant role in regulating star formation, and M16
offers the opportunity to examine the physical processes of a PDR in detail. We
simultaneously observe both the molecular and ionized phases of the PDR and
resolve the spatial and kinematic differences between them. The most prominent
regions of the PDR are viewed edge-on. Fluorescent emission from nearby stars
is the primary excitation source, although collisions also preferentially
populate the lowest vibrational levels of H2. Variations in density-sensitive
emission line ratios demonstrate that the molecular cloud is clumpy, with an
average density n = 3x10^5 cm^(-3). We measure the kinetic temperature of the
molecular region directly and find T_H2 = 930 K. The observed density,
temperature, and UV flux imply a photoelectric heating efficiency of 4%. In the
ionized region, n_i=5x10^3 cm^(-3) and T_HII = 9500 K. In the brightest regions
of the PDR, the recombination line widths include a non-thermal component,
which we attribute to viewing geometry.


title: Neutrino astronomy with the MACRO detector

abstract:
  High energy gamma ray astronomy is now a well established field and several
sources have been discovered in the region from a few GeV up to several TeV. If
sources involving hadronic processes exist, the production of photons would be
accompanied by neutrinos too. Other possible neutrino sources could be related
to the annihilation of WIMPs at the center of galaxies with black holes.
  We present the results of a search for point-like sources using 1100
upward-going muons produced by neutrino interactions in the rock below and
inside the MACRO detector in the underground Gran Sasso Laboratory. These data
show no evidence for a possible neutrino point-like source or for possible
correlations between gamma ray bursts and neutrinos. They have been used to set
flux upper limits for candidate point-like sources which are in the range
10^-14-10^-15 cm-2 s-1.


title: The stellar content of brightest cluster galaxies

abstract:
  We present near-infrared K-band spectroscopy of 21 elliptical or cD Brightest
Cluster Galaxies (BCGs), for which we have measured the strength of the 2.293
micron CO stellar absorption feature. We find that the strength of this feature
is remarkably uniform among these galaxies, with a smaller scatter in
equivalent width than for the normal elliptical population in the field or
clusters. The scatter for BCGs is 0.156 nm, compared with 0.240 nm for Coma
cluster ellipticals, 0.337 nm for ellipticals from a variety of other clusters,
and 0.422 nm for field ellipticals. We interpret this homogeneity as being due
to a greater age, or more uniform history, of star formation in BCGs than in
other ellipticals; only a small fraction of the scatter can be due to
metallicity variations, even in the BCGs. Notwithstanding the small scatter,
correlations are found between CO strength and various galaxy properties,
including R-band absolute magnitude, which could improve the precision of these
galaxies as distance indicators in measurements of cosmological parameters and
velocity flows.