title: On ionisation effects and abundance ratios in damped Lyman-alpha systems

abstract:
  The similarity between observed velocity structures of Al III and singly
ionised species in damped Lyman-alpha systems (DLAs) suggests the presence of
ionised gas in the regions where most metal absorption lines are formed.
  To explore the possible implications of ionisation effects we construct a
simplified two-region model for DLAs consisting of an ionisation bounded region
with an internal radiation field and a neutral region with a lower metal
content. Within this framework we find that ionisation effects are important.
If taken into account, the element abundance ratios in DLAs are quite
consistent with those observed in Milky Way stars and in metal-poor H II
regions in blue compact dwarf galaxies. In particular we cannot exclude the
same primary N origin in both DLAs and metal-poor galaxies. From our models no
dust depletion of heavy elements needs to be invoked; little depletion is
however not excluded.


title: Aberration of Light and Motion of Real Particle

abstract:
  Correct and complete (to terms of $\vec{v} / c$ -- $\vec{v}$ is particle's
velocity, $c$ is the speed of light) derivation of equation of motion for real
dust particle under the action of electromagnetic radiation is derived. The
effect of aberration of light is used. Equation of motion is expressed in terms
of particle's optical properties, standardly used in optics for stationary
particles.


title: Solar Radiation and Asteroidal Motion

abstract:
  Effects of solar wind and solar electromagnetic radiation on motion of
asteroids are discussed. The results complete the statements presented in
Vokrouhlick\'{y} and Milani (2000). As for the effect of electromagnetic
radiation, the complete equation of motion is presented to the first order in
$v/c$ -- the shape of asteroid (spherical body is explicitly presented) and
surface distribution of albedo should be taken into account. Optical quantities
must be calculated in proper frame of reference.


title:
X-Rays from the Nearby Solitary Millisecond Pulsar PSR J0030+0451 - the
  Final ROSAT Observations

abstract:
  We report on X-ray observations of the solitary 4.8 ms pulsar PSR J0030+0451.
The pulsar was one of the last targets observed in DEC-98 by the ROSAT PSPC.
X-ray pulses are detected on a $4.5\sigma$ level and make the source the
$11^{th}$ millisecond pulsar detected in the X-ray domain. The pulsed fraction
is found to be $69\pm18%$. The X-ray pulse profile is characterized by two
narrow peaks which match the gross pulse profile observed at 1.4 GHz. Assuming
a Crab-like spectrum the X-ray flux is in the range $f_x= 2-3\times 10^{-13}$
erg s$^{-1}$ cm$^{-2} $ ($0.1-2.4$ keV), implying an X-ray efficiency of
$L_x/\dot{E}\sim 0.5-5 \times 10^{-3} (d/0.23 {kpc})^2$.


title:
Morphological Number Counts and Redshift Distributions to I = 25 from
  the Hubble Deep Fields: Constraints on Cosmological Models from Early Type
  Galaxies

abstract:
  We combine magnitude and photometric redshift data on galaxies in the Hubble
Deep Fields with morphological classifications in order to separate out the
distributions for early type galaxies. The updated morphological galaxy number
counts down to I = 25 and the corresponding redshift distributions are used as
joint constraints on cosmological models, in particular on the values of the
density parameter Omega_{0} and normalised cosmological constant Lambda_{0}.
  We find that an Einstein - de Sitter universe with simple passive evolution
gives an excellent fit to the counts and redshift data at all magnitudes. An
open, low Omega_{0}, model with no net evolution (and conservation of the
number of ellipticals), which fits the counts equally well, is somewhat less
successful, predicting slightly lower mean redshifts and, more significantly,
the lack of a high--z tail. A number conserving model with a dominant
contribution from Lambda_{0}, on the other hand, is far less successful,
predicting a much narrower distribution than seen. More complex models are
obviously possible, but we conclude that if large scale transmutation between
types does {\it not} occur, then the lambda-dominated models provide a very
poor fit to the current data.


title: HI in Early-Type Galaxies

abstract:
  We briefly discuss the main differences between the HI properties of luminous
and low-luminosity early-type galaxies. In luminous early-type galaxies the HI
is often irregularly distributed, but in a few cases regular HI disks, of low
surface density, are seen. In low-luminosity galaxies, the HI is more often in
a disk with high central surface densities. This suggests a different evolution
of the gas in these two groups of galaxies.


title: Antikaon condensation and the metastability of protoneutron stars

abstract:
  We investigate the condensation of $\bar K^0$ meson along with $K^-$
condensation in the neutrino trapped matter with and without hyperons.
Calculations are performed in the relativistic mean field models in which both
the baryon-baryon and (anti)kaon-baryon interactions are mediated by meson
exchange. In the neutrino trapped matter relevant to protoneutron stars, the
critical density of $K^-$ condensation is shifted considerably to higher
density whereas that of $\bar K^0$ condensation is shifted slightly to higher
density with respect to that of the neutrino free case. The onset of $K^-$
condensation always occurs earlier than that of $\bar K^0$ condensation. A
significant region of maximum mass protoneutron stars is found to contain $\bar
K^0$ condensate for larger values of the antikaon potential. With the
appearance of $\bar K^0$ condensation, there is a region of symmetric nuclear
matter in the inner core of a protoneutron star. It is found that the maximum
mass of a protoneutron star containing $K^-$ and $\bar K^0$ condensate is
greater than that of the corresponding neutron star. We revisit the implication
of this scenario in the context of the metastability of protoneutron stars and
their evolution to low mass black holes.


title: Asphericity of galaxy clusters and Sunyaev-Zel'dovich effect

abstract:
  In this paper we investigate the Sunyaev-Zel'dovich (SZ) effect and the X-ray
surface brightness for clusters of galaxies with a non-spherical mass
distribution. In particular, we consider the influence of the shape and the
finite extension of a cluster as well as of a polytropic thermal profile on the
Compton parameter, the X-ray surface brightness and on the determination of the
Hubble constant. We find that the the non-inclusion of such effects can induce
errors up to 30 per cent in the various parameters and in particular on the
Hubble constant value, when compared with results obtained under the
isothermal, infinitely extended and spherical shape assumptions.


title: The HI halo of NGC 2403

abstract:
  Deep VLA HI observations of the nearby spiral galaxy NGC 2403 reveal the
presence of an extended HI halo that shows slower rotation and a general inflow
(about 15-25 km\s) towards the center of the galaxy.


title: Parsec-scale structures of radio galaxies in the 2-Jy sample

abstract:
  In this paper we present the results of VLBI observations of six radio
galaxies belonging to the 2-Jy sample. The selected objects are 3C17, PKS
0620-52, PKS 0625-35, PKS 1318-43, PKS 1333-33 and 3C317. The first is a high
power radio galaxy and the remainder are low power objects. Our observations
were carried out with a set of different arrays and frequencies, and cover a
range of resolutions from a few mas to a few tens of mas. Parsec-scale images
are presented and discussed in the light of unification for radio loud
galaxies. Estimates for the intrinsic plasma speed in these objects in the
proximity of the parsec-scale core and tehir orientation to the line of sight
are in agreement with the predictions from unified models and their optical and
X-ray properties.


title:
Multiband optical polarimetry of the BL Lac object PKS 2155--304.
  Intranight and long term variability

abstract:
  The polarized and total flux of the BL Lac object PKS 2155-304 were monitored
intensively and simultaneously in the optical UBVRI bands with the Turin
photopolarimeter at the CASLEO 2.15 m telescope during 4 campaigns in June,
August, November 1998 and August 1999. The effective observation time amounted
to ~47 hours. PKS 2155-304 showed a linear polarization percentage (P) usually
ranging between 3% and 7% and a polarization position angle (PA) mainly between
70 and 120 deg. The highest temporal resolution of our observations, 15
minutes, is unprecedented for polarimetric monitoring of this source, and has
allowed us to detect amplitude variations of the linear polarization percentage
from 6 to 7.5% in time scales of hours. In some nights the polarization
percentage seems to increase toward shorter wavelengths, however the polarized
spectrum does not vary significantly with time. The most remarkable variability
event occurred on 1998 June 18, when the degree of linear polarization
decreased by more than a factor 2 in one day in all bands, while the PA rotated
by 90 deg. This is consistent with the presence of two emission components, of
different polarization degree and position angle. Intranight variability of P
and PA can be interpreted with small amplitude physical or geometrical changes
within the jet. Measurements of the circular polarization over time intervals
of days set upper limits of 0.2%. Simultaneous photometry taken with the Turin
Photopolarimeter and with a CCD camera at Cordoba Astronomical Observatory did
not show light variations correlated with those of the linearly polarized flux.


title:
2MASS Observations of the Perseus, Orion A, Orion B, and Monoceros R2
  Molecular Clouds

abstract:
  We use the 2MASS Second Incremental Release Point Source Catalog to
investigate the spatial distribution of young stars in the Perseus, Orion A,
Orion B, and MonR2 molecular clouds. After subtracting a semi-empirical model
of the field star contamination from the observed star counts, stellar surface
density maps are used to identify compact clusters and any stellar population
found more uniformly distributed over the molecular cloud. Each cloud contains
between 2 to 7 clusters, with at least half of the cluster population found in
a single, rich cluster. In addition, a distributed stellar population is
inferred in the Orion A and MonR2 molecular clouds within the uncertainties of
the field star subtraction with a surface density between 0.013 - 0.083
arcmin**-2. The fraction of the total stellar population contained in clusters
for the nominal extinction model ranges from ~50-100% if the distributed
population is relatively young (< 10 Myr), to ~25%-70% if it is relatively old
(~100 Myr). The relatively high fraction of stars contained in clusters
regardless of the age of the distributed population, in conjunction with the
young ages generally inferred for embedded clusters in nearby molecular clouds,
indicates that a substantial fraction of the total stellar population in these
regions has formed within the past few million years in dense clusters. This
suggests that either the star formation rate in each these clouds has recently
peaked if one assumes clouds have ages > 10 Myr, or molecular clouds are
younger than typically thought if one assumes that the star formation rate has
been approximately constant in time.


title: The HI halos of spiral galaxies

abstract:
  The results of observational studies on the vertical HI density distribution
and kinematics of the disks of spiral galaxies are reported and discussed.
Attention is drawn to the presence of HI emission, unknown before and here
referred to as the `beard', which has anomalous structure and kinematics,
different from the known cold HI disk. This component is extended and probably
located in the halo region, it is rotating more slowly than the disk and shows
radial inward motion. Its nature and origin -galactic fountain or infall of
primordial gas?- are still a puzzle.


title:
Cooling of Hybrid Neutron Stars and Hypothetical Self-bound Objects with
  Superconducting Quark Cores

abstract:
  We study the consequences of superconducting quark cores (with
color-flavor-locked phase as representative example) for evolution of
temperature profiles and the cooling curves in quark-hadron hybrid stars and in
hypothetical self-bounded objects having no a hadron shell (quark core neutron
stars). The quark gaps are varied from 0 to $\Delta_q =50$ MeV. For hybrid
stars we find time scales of $1\div5$, $5\div10$ and $50\div100$ years for the
formation of a quasistationary temperature distribution in the cases $\Delta_q
=0$, 0.1 MeV and $\gsim$ 1 MeV, respectively. These time scales are governed by
the heat transport within quark cores for large diquark gaps ($\Delta \gsim$ 1
MeV) and within the hadron shell for small diquark gaps ($\Delta \lsim 0.1$
MeV). For quark core neutron stars we find a time scale $\simeq 300$ years for
the formation of a quasistationary temperature distribution in the case $\Delta
\gsim$ 10 MeV and a very short one for $\Delta \lsim$ 1 MeV. If hot young
compact objects will be observed they can be interpreted as manifestation of
large gap color superconductivity. Depending on the size of the pairing gaps,
the compact star takes different paths in the ${lg}T_s $ vs. ${lg} t$ diagram
where $T_s$ is the surface temperature. Compared to the corresponding hadronic
model which well fits existing data the model for the hybrid neutron star (with
a large diquark gap) shows too fast cooling. The same conclusion can be drawn
for the corresponding self-bound objects.


title: High-Redshift Galaxies: The Far-Infrared and Sub-Millimeter View

abstract:
  Observations at long wavelengths, in the wide interval from a few to 1000
micron, are essential to study diffuse media in galaxies, including all kinds
of atomic, ionic and molecular gases and dust grains. Hence they are
particularly suited to investigate the early phases in galaxy evolution, when a
very rich ISM is present in the forming systems.
  During the last few years a variety of observational campaigns in the
far-IR/sub-mm, exploiting both ground-based and space instrumentation, have
started to provide results of relevant cosmological impact. Most crucial among
these have been the discovery of an intense diffuse background in the
far-IR/sub-mm of extragalactic origin, and the deep explorations from space in
the far-IR and with large millimetric telescopes on ground. These results
challenge those obtained from optical-UV observations, by revealing luminous to
very luminous phases in galaxy evolution at substantial redshifts, likely
corresponding to violent events of star-formation in massive systems. This is
bringing to significant refinements of the present schemes of galaxy formation,
as far as the history of baryon transformations is concerned.


title: The Magnetic Field Geometry in M82 and Cen A

abstract:
  Imaging polarimetry at 1.65 and 2.2 $\mu $m is presented for the classic
starburst galaxy M82 and the advanced merger system Cen A. Polarimetry at near
IR wavelengths allows the magnetic field geometry in galaxies to be probed much
deeper into dusty regions than optical polarimetry. In M82, the magnetic field
throughout the nucleus has a polar geometry, presumably due to the massive
vertical flow that is a result of the intense star formation there. Fully two
thirds of the line of sight dust through to the center of M82 contains a
vertical magnetic field. In Cen A, the prominent dust lane shows a normal
planar field geometry. There is no indication of significant disturbance in the
field geometry in the dust lane and the polarization strength is near normal
for the amount of extinction. Either the magnetic field geometry was well
maintained during the merger, or it reestablished itself very easily.


title:
Discovery of An Extremely Metal--Poor Galaxy: Optical Spectroscopy of
  UGCA 292

abstract:
  The results of optical spectroscopy of two HII regions in UGCA 292 (CVn I
dwA) are presented. UGCA 292 is a nearby (D=3.1 Mpc) gas-rich dwarf irregular
galaxy (M_H/L_B ~ 6.9) which was first discovered in a blind HI survey. The
derived oxygen abundance is the third lowest of known star-forming galaxies [12
+ log(O/H) = 7.30 +/- 0.05], making UGCA 292 one of the nearest metal-poor
galaxies known. The derived N/O ratio is similar to that found in other low
metallicity galaxies [log(N/O) = -1.47 +/- 0.10], and is indicative of a
primary origin for nitrogen. The derived oxygen abundance is consistent with
closed-box chemical evolution for this low mass galaxy. The observed blue
colors, high gas mass fraction, and low metallicity suggest that UGCA 292 is
relatively unevolved. The possibility that future blind HI surveys may yield
similar low metallicity galaxies is discussed.


title: VLBA Observations Of A Sample Of Nearby FR I Radio Galaxies

abstract:
  We observed 17 nearby low luminosity FR I radio galaxies using the NRAO Very
Long Baseline Array (VLBA) at 1.67 GHz, as part of a multi-wavelength study of
a complete sample of 21 sources selected by radio flux density from the Uppsala
General Catalogue of Galaxies. We detected radio emission from all 17 galaxies.
At a FWHM resolution of ~ 10x4 mas, five galaxies show only an unresolved radio
core, ten galaxies show core-jet structures, and two galaxies show twin-jet
structures. Comparing these VLBA images with images previously obtained with
the NRAO VLA, we find that all detected VLBA jets are well-aligned on parsec
scales with the VLA jets on kilo parsec scales, and that the jet to counter-jet
surface brightness ratios, or the sidedness, decreases systematically with
increasing distance along the jet. We attribute the sidedness to the Doppler
boosting effect and its decline to the deceleration of the jets. We show that a
distribution of Lorentz factor centered near Gamma = 5 can reproduce our VLBA
detection statistics for core, core-jet and twin-jet sources. We also note that
the luminosity per unit length, L_j, of the VLBA jets drops quickly with
distance, r, along the jet, approximately as L_j being proportional to
r^(-2.0). We discuss three different mechanisms to explain this jet fading: (1)
the decrease of Doppler boosting due to jet deceleration, (2) synchrotron
losses, and (3) expansion losses in constant velocity but adiabatically
spreading jets. Mechanisms (1) and (2) are inconsistent with the observations,
while mechanism (3) is consistent with the observations provided the magnetic
field lines in the jets are aligned perpendicular to the jet axis. This implies
that the deceleration of the jets required by the Unified Scheme does not occur
on the tens of parsec scales, but must occur on larger scales.


title: Photon Consumption in Minihalos during Cosmological Reionization

abstract:
  At the earliest epochs of structure formation in cold dark matter (CDM)
cosmologies, the smallest nonlinear objects are the numerous small halos that
condense with virial temperatures below 10,000 K. Such ``minihalos'' are not
yet resolved in large-scale three-dimensional cosmological simulations. Here we
employ a semi-analytic method, combined with three-dimensional simulations of
individual minihalos, to examine their importance during cosmological
reionization. We show that, depending on when reionization takes place, they
potentially play an important role as sinks of ionizing radiation. If
reionization occurs at sufficiently high redshifts (z_r > 20), the
intergalactic medium is heated to 10,000 K and most minihalos never form. On
the other hand, if z_r < 20, a significant fraction (>10 percent) of all
baryons have already collapsed into minihalos, and are subsequently removed
from the halos by photoevaporation as the ionizing background flux builds up.
We show that this process can require a significant budget of ionizing photons;
exceeding the production by a straightforward extrapolation back in time of
known quasar and galaxy populations by a factor of up to 10 and 3,
respectively.


title: Probing High-Redshift Disks with Damped Lyman Alpha Systems

abstract:
  Evidence is presented that the damped Lyman alpha absorption systems are the
high-redshift (z > 3) progenitors of galaxy disks. I discuss kinematic evidence
that the damped Lyman Alpha systems are rotating disks. I also discuss
implications of the lack of metal-poor damped Lyman alpha systems with line
width Delta v > 100 {\kms}. I then present new evidence stemming from
correlations between element-abundance ratios and [Fe/H], which connects damped
systems to the thick stellar disk of the Galaxy. I discuss the connections
between damped Lyman alpha systems and Lyman break galaxies, and how [CII] 158
micron emission from damped Lyman alpha systems discriminates among competing
theories of galaxy formation. ~


title: Inflation and the dwarf galaxy problem

abstract:
  Cosmological N-body simulations with scale-invariant initial perturbations
show too many virialized objects of dwarf-galaxy masses in a typical galactic
halo in contradiction to observation and stability of galactic discs. We
present a model of double hybrid inflation which predicts density fluctuations
with a small-scale cutoff to account for the absence of these objects in
observations.


title:
High Speed Interconnects and Parallel Software Libraries: Enabling
  Technologies for the NVO

abstract:
  The NVOs core data mining and archive federation activities are heavily
dependent on the underlying data pipeline software necessary to translate the
raw data into scientifically relevant source detections. The data pipeline
software dictates: the raw data storage and retrieval mechanisms, the meaning
and format of the fields in the source catalogs, and the ability of the NVO
users to re-analyze raw data for their own purposes. Increasing the performance
of the core data pipeline software so that it can address the needs of current
and future high data rate surveys is an important activity that should be
addressed in concert with the development of the NVO.


title: Defect models of cosmic structure in light of the new CMB data

abstract:
  Defect models of cosmic structure formation have faced a number of difficult
challenges over recent years. Yet interestingly, new CMB data does not show
strong evidence for secondary oscillations in the anisotropy power. Here I
review the current standing of the cosmic defect models of structure formation
in light of the current data.


title:
Dynamical Constraints on the Formation of NGC 4472 and Its Globular
  Clusters

abstract:
  We present new radial velocities for 87 globular clusters around the
elliptical galaxy NGC 4472, and combine these with our previously published
data to create a data set of velocities for 144 globular clusters around NGC
4472. We utilize this data set to analyze the kinematics of the NGC 4472
globular cluster system. The new data confirms our previous discovery that the
metal-poor clusters have significantly higher velocity dispersion than the
metal-rich clusters in NGC 4472. We also find very little or no rotation in the
more spatially concentrated metal-rich population, with a resulting upper limit
for this population of (v/sigma)_{proj} < 0.34 at a 99% confidence level. The
very small angular momentum in the metal-rich population requires efficient
angular momentum transport during the formation of this population which is
spatially concentrated and chemically enriched. Such angular momentum transfer
can be provided by galaxy mergers, but has not been achieved in other extant
models of elliptical galaxy formation that include dark matter halos. We also
calculate the velocity dispersion as a function of radius, and show that it is
consistent with roughly isotropic orbits for the clusters and the mass
distribution of NGC 4472 inferred from X-ray observations of the hot gas around
the galaxy.


title: Adiabatic and entropy perturbations from inflation

abstract:
  We study adiabatic (curvature) and entropy (isocurvature) perturbations
produced during a period of cosmological inflation that is driven by multiple
scalar fields with an arbitrary interaction potential. A local rotation in
field space is performed to separate out the adiabatic and entropy modes. The
resulting field equations show explicitly how on large scales entropy
perturbations can source adiabatic perturbations if the background solution
follows a curved trajectory in field space, and how adiabatic perturbations
cannot source entropy perturbations in the long-wavelength limit. It is the
effective mass of the entropy field that determines the amplitude of entropy
perturbations during inflation. We present two applications of the equations.
First, we show why one in general expects the adiabatic and entropy
perturbations to be correlated at the end of inflation, and calculate the
cross-correlation in the context of a double inflation model with two
non-interacting fields. Second, we consider two-field preheating after
inflation, examining conditions under which entropy perturbations can alter the
large-scale curvature perturbation and showing how our new formalism has
advantages in numerical stability when the background solution follows a
non-trivial trajectory in field space.


title:
The kinematics of 3:1-merger remnants and the formation of
  low-luminosity elliptical galaxies

abstract:
  We test the formation of low-luminosity elliptical galaxies through
collisionless mergers of unequal-mass disk galaxies. The kinematic properties
of a small survey of simulated merger end-products with initial disk mass
ratios of 3:1 is compared to a sample of seven low-luminosity galaxies observed
by Rix et al. that were chosen photometrically to be "ellipticals". In this
paper, we go beyond a comparison in terms of global properties (using one
number to characterize a model or a galaxy e.g. <a4>, ellipticity at some fixed
radius or central velocity dispersion) and examine the detailed kinematics as
function of galactocentric distance. The merger remnants are ``observed''
through a slit along the major and minor axis, using a pixel binning and slit
width similar to the one used during the spectroscopic observations. We compare
the rotational support (v/sigma) of the merger remnants, the normalized
rotation on the minor axis and the major axis Gauss-Hermite moments h3, to that
of the observed galaxies. The N-body remnants are very flattened when viewed
edge-on (<epsilon> = 0.6) and should be inclined before making a fair
comparison with the Rix et al. data set (which has <epsilon> = 0.3). When the
merger remnants are appropriately inclined, their v/sigma profiles rise slower
than the observed ones. Note that even when the remnants are viewed edge-on,
the v/sigma profiles do not match the observations. The detailed comparison of
the observations with purely collisionless 3:1-merger remnants suggests that
this kind of dissipationless merger is not likely to be the dominant formation
channel for low-luminosity elliptical galaxies. (abridged)


title: Differential O and Si Abundances in M33 Early B Supergiants

abstract:
  We present non-LTE analyses of four M33 early B-supergiant stars and five
Galactic counterparts. This is the first time that B supergiants beyond the
Magellanic Clouds are analyzed by means of detailed Non-LTE techniques. Stellar
temperatures, gravities, microturbulences and Si abundances are derived for all
objects using the Si ionization equilibrium and the Balmer line wings. O
abundances are then also derived. Important approximations made during the
calculations are described, and their influence on the results is analyzed. It
is found that these approximations have no significant effect on the results at
any microturbulence. We find that a strict differential analysis is needed to
detect abundance differences. Thus we compare results line by line in M33 and
Galactic stars of stellar parameters as similar as possible. Three of the four
M33 stars turned out to be O deficient as compared to their Galactic
counterparts, and only one, close to the center of M33 (M33 1054) is found to
be moderately O enriched. From these differential analyses we find that our
data are compatible with a radial O gradient in M33 as that derived from HII
region data: we obtain -0.19+/-0.13 or -0.20+/-0.07 dex/kpc, depending on
whether B133 is included or not. Our data are also consistent with other
possibilities such as a steep increase of the O abundance in the inner region
(at projected distances less than 9 arcmin from the center of M33), followed by
a flat O abundance profile towards the outer parts of M33. Si shows the same
pattern, and it is shown that Si and O correlate well, as expected for
alpha-elements, supporting then the high value of the O abundance gradient in
M33 as compared to the Milky Way and other nearby spiral galaxies.


title:
Variability of Southern T Tauri Stars I: The Continuum and the H$\beta$
  Inverse PCygni Profile of GQ LUPI

abstract:
  We present time series spectrophotometric observations of GQ Lupi, a typical
representative of the YY Ori subgroup of T Tauri stars that show conspicuous
inverse PCygni profiles. The data set consists of 32 exposures taken over 5 and
8 consecutive nights of May and July 1998, respectively, and covers the
spectral range of 3100 \AA~ $< \lambda < 5100 $ \AA. The region redward and
next to the Balmer jump varies significantly on a night-to-night basis and the
amplitude of such variability decreases sharply at $\lambda >$ 4600 \AA. The
Balmer continuum slope indicates that the spectral energy distribution is
governed by a gas of temperature greater than that of the stellar photosphere.
We find an anticorrelation between the veiling and the observed Balmer jump.
The time series of the redward absorption component behaves similarly to the
veiling time series. We model the emitting region by a gas of uniform
temperature and density. The models indicate that the gas densities and the
respective temperatures are strongly anticorrelated. In addition, the model
time series show that the increase in the gas density is mirrored by an
increase of the projected emitting area (filling factor). Large/small gas
densities and filling factors are characterized by high/low observed veiling.
As the accretion rate fades from night-to-night, the observed veiling
decreases, as does the gas density and the total projected emitting area.


title: Power spectrum of the polarized diffuse Galactic radio emission

abstract:
  We have analyzed the available polarization surveys of the Galactic emission
to estimate to what extent it may be a serious hindrance to forthcoming
experiments aimed at detecting the polarized component of Cosmic Microwave
Background (CMB) anisotropies. Regions were identified for which independent
data consistently indicate that depolarization must be small. The power
spectrum of the polarized emission, in terms of antenna temperature, was found
to be described by $C_{\ell}\simeq (1.2\pm 0.8)\cdot 10^{-9}\cdot (\ell /
450)^{-1.8\pm 0.3}\cdot (\nu/ 2.4{\rm GHz})^{-5.8}$ K$^{2}$, from arcminute to
degree scales. Data on larger angular scales ($\ell\le 100$) indicate a steeper
slope $\sim \ell^{-3}$. We conclude that polarized Galactic emission is
unlikely to be a serious limitation to CMB polarization measurements at the
highest frequencies of the MAP and {\sc Planck}/LFI instruments, at least for
$\ell\ge 50$ and standard cosmological models. The weak correlation between
polarization and total power and the low polarization degree of radio emission
close to the Galactic plane, found also in low-depolarization regions, is
interpreted as due to large contributions to the observed intensity from
unpolarized sources, primarily strong HII regions, concentrated on the Galactic
plane. Thus estimates of the power spectrum of total intensity at low Galactic
latitudes are not representative of the spatial distribution of Galactic
emission far from the plane. Both total power and polarized emissions show
highly significant deviations from a Gaussian distribution.


title: Scales of the Extra Dimensions and their Gravitational Wave Backgrounds

abstract:
  Circumstances are described in which symmetry breaking during the formation
of our three-dimensional brane within a higher-dimensional space in the early
universe excites mesoscopic classical radion or brane-displacement degrees of
freedom and produces a detectable stochastic background of gravitational
radiation. The spectrum of the background is related to the unification energy
scale and the the sizes and numbers of large extra dimensions. It is shown that
properties of the background observable by gravitational-wave observatories at
frequencies $f\approx 10^{-4}$ Hz to $10^3$ Hz contain information about
unification on energy scales from 1 to $10^{10}$ TeV, gravity propagating
through extra-dimension sizes from 1 mm to $10^{-18}$mm, and the dynamical
history and stabilization of from one to seven extra dimensions.


title:
The Formation of Broad Line Clouds in the Accretion Shocks of Active
  Galactic Nuclei

abstract:
  Recent work on the gas dynamics in the Galactic Center has improved our
understanding of the accretion processes in galactic nuclei, particularly with
regard to properties such as the specific angular momentum distribution,
density, and temperature of the inflowing plasma. This information can be
valuable in trying to determine the origin of the Broad Line Region (BLR) in
Active Galactic Nuclei (AGNs). In this paper, we explore various scenarios for
the cloud formation based on the underlying principle that the source of plasma
is ultimately that portion of the gas trapped by the central black hole from
the interstellar medium. Based on what we know about the Galactic Center, it is
likely that in highly dynamic environments such as this, the supply of matter
is due mostly to stellar winds from the central cluster. Winds accreting onto a
central black hole are subjected to several disturbances capable of producing
shocks, including a Bondi-Hoyle flow, stellar wind-wind collisions, and
turbulence. Shocked gas is initially compressed and heated out of thermal
equilibrium with the ambient radiation field; a cooling instability sets in as
the gas is cooled via inverse-Compton and bremsstrahlung processes. If the
cooling time is less than the dynamical flow time through the shock region, the
gas may clump to form the clouds responsible for broad line emission seen in
many AGN spectra. Clouds produced by this process display the correct range of
densities and velocity fields seen in broad emission lines. Very importantly,
the cloud distribution agrees with the results of reverberation studies, in
which it is seen that the central line peak responds slower to continuum
changes than the line wings.


title: Far Ultraviolet Imagery of the Edge-On Spiral Galaxy NGC 4631

abstract:
  Far ultraviolet FUV imagery of the edge-on, Sc/SBd galaxy, NGC 4631 reveals
very strong FUV emission, resulting from active star formation, uniformly
distributed along the galactic mid- plane. Multi-band imagery, HI and HII
position-velocity curves and extinction considerations all imply that the
emission is from the outer edges of the visible galaxy. The overall FUV
morphology of this edge-on disk system is remarkably similar to those of the
so-called "chain galaxies" evident at high redshift, thus suggesting a similar
interpretation for at least some of those distant objects. FUV, U, B and V
magnitudes, measured for 48 star forming regions, along with corresponding
H-alpha and H-beta measurements are used to construct diagnostic color-color
diagrams. Although there are significant exceptions, most of the star forming
regions are less massive and older than 30 Doradus. Comparison with the
expectations from two star formation models yields ages of 2.7 to 10 Myr for
the instantaneous burst (IB) model and star formation cut-off ages of 0 to 9
Myr for the continuous star formation (CSF) model. Interpreted in terms of the
IB model the photometry implies a total created mass in the 48 star forming
regions of 25 million solar-masses. When viewed as resulting from constant star
formation the photometry implies a star formation rate of 0.33 solar-masses/yr.
These results are compared to those derived from FIR and radio observations.
Corrections for FUV emission reprocessed by interstellar grains are estimated.


title: Constrained Superconducting Membranes

abstract:
  We present a geometrical canonical description for superconducting membranes.
We consider a general action which includes a general class of superconducting
extended objects (strings and domain walls). The description is inspired in the
ADM framework of general relativity but, instead of the standard canonical
variables a different kind of phase space is considered.
  The Poisson algebra of the constraints and the counting of degrees of freedom
is performed. The new description is illustrated considering a superconducting
domain wall on a curved background spacetime.


title: Chiral Superconducting Membranes

abstract:
  We develop the dynamics of the chiral superconducting membranes (with null
current) in an alternative geometric approach either making a Lagrangian
description and a Hamiltonian point of view. Besides of this, we show the
equivalence of the resulting descriptions to the one known Dirac-Nambu-Goto
(DNG) case. Integrability for chiral string model is obtained using a proposed
light-cone gauge. In a similar way, domain walls are integrated by means of a
simple ansatz. We compare the results with recently works appeared in the
literature.


title:
VLT-detection of two edge-on Circumstellar Disks in the rho Oph dark
  cloud

abstract:
  Observations of the rho Ophiuchi star forming region with VLT ANTU and ISAAC
under 0.35" seeing conditions reveal two bipolar reflection nebulosities
intersected by central dust lanes. The sources (OphE-MM3 and CRBR 2422.8-3423)
can be identified as spatially resolved circumstellar disks viewed close to
edge-on, similar to edge-on disk sources discovered previously in the Taurus
and Orion star forming regions. Millimeter continuum fluxes yield disk masses
of the order of 0.01 Mo, i.e. about the mass deemed necessary for the minimum
solar nebula. Follow-up spectroscopic observations with SUBARU and CISCO show
that both disk sources exhibit featureless continua in the K-band. No accretion
or outflow signatures were detected. The slightly less edge-on orientation of
the disk around CRBR 2422.8-3423 compared to HH 30 leads to a dramatic
difference in the flux seen in the ISOCAM 4.5 mu to 12 mu bands. The
observations confirm theoretical predictions on the effect of disk geometry and
inclination angle on the spectral energy distribution of young stellar objects
with circumstellar disks.


title: Modeling gas and stellar kinematics in disc galaxies

abstract:
  We present V-band surface photometry and major-axis kinematics of stars and
ionized gas of three early-type spiral galaxies, namely NGC 772, NGC 3898 and
NGC 7782. For each galaxy we built a self-consistent Jeans model for the
stellar kinematics, adopting the light distribution of bulge and disc derived
by means of a two-dimensional parametric photometric decomposition. This
allowed us to investigate the presence of non-circular gas motions, and derive
the mass distribution of luminous and dark matter in these objects. We found
that the observed gas rotation corresponds to the circular velocity except for
the innermost region (|r|<8") of NGC 3898. This behaviour is quite common,
although not ubiquitous, in the few bulge-dominated galaxies, for which
dynamical modeling allows the comparison between the gas velocity and the
circular speed.


title:
The brighter side of sub-mm source counts: a SCUBA scan-map of the
  Hubble Deep Field

abstract:
  We present an 11 X 11 arcminute map centred on the Hubble Deep Field taken at
850 microns with the SCUBA camera on the JCMT. The map has an average one-sigma
sensitivity to point sources of about 2.3 mJy and thus probes the brighter end
of the sub-mm source counts. We find 7 sources with a flux greater than 9 mJy
(roughly 4 sigma), and therefore estimate N(>9 mJy)= 208 (+90/-72) per degree.
This result is consistent with work from other groups, but improves the
statistics at the bright end, and is suggestive of a steepening of the counts.


title:
A New Connection between Central Engine Weak Physics and the Dynamics of
  Gamma-Ray Burst Fireballs

abstract:
  We demonstrate a qualitatively new aspect of the dynamics of Gamma-Ray Burst
(GRB) fireballs: the development of a substantial dispersion in the proton
component in fireballs in which neutron decoupling occurs and is sufficiently
pronounced. This effect depends sensitively on the neutron to proton ratio in
the fireball, becoming more dramatic with increasing neutron excess. Simple
physical arguments and transport calculations indicate that the dispersion in
Lorentz factor of the protons can be of order the final mean Lorentz factor of
the fireball. We show how plasma instabilities could play an important role in
the evolution of the fireball and how they might ultimately govern the
development of such a velocity dispersion in the proton component. The role of
these instabilities in setting/diminishing a proton Lorentz factor dispersion
represents a new and potentially important venue for the study of plasma
instabilities. Significant dispersion in the proton velocities translates into
fewer protons attaining the highest Lorentz factors. This is tantamount to a
reduction in the total energy required to attain a given Lorentz factor for the
highest energy protons. As well, a proton component dispersion can have
consequences for the electromagnetic and neutrino signature of GRBs.


title: Scattering and Polarization Properties of the Non-Spherical Particles

abstract:
  The albedo and dichroic polarization of spheroidal particles are studied. For
the description of the phase function two asymmetry parameters $g_{||}$ and
$g_{\bot}$ characterizing the anisotropy in forward/backward and left/right
directions are introduced and calculated. The consideration is based on the
solution to the light scattering problem by the Separation of Variables Method
(Voshchinnikov and Farafonov, 1993).


title: Modelling of Polarization Properties of Cometary Dust Grains

abstract:
  Observational data for dusty comets are summarized and systemized.
  The dependence of the linear polarization on various parameters (the phase
angle, wavelength, etc.) is analyzed. An ensemble of aligned spheroidal
particles having various sizes and chemical compositions is used to fit the
linear and circular polarization observed for the comet Halley.


title:
Profiles and Polarization Properties of Emission Lines from Relativistic
  Disks

abstract:
  We examined the profiles and polarization properties of emission lines
originating from the extremely relativistic region of Kepler disks.
  Because the emission region is more localized to the inner part, e.g., a few
times the black hole radius, the profiles, and polarization properties are
remarkably modified. The black hole spin significantly affects the properties
through the inner edge. This observation, in spite of the technical
difficulties, provides an important diagnostic of the relativistic region.


title: Optical Spectroscopy Of The X-Ray Transient XTE J1118+480 In Outburst

abstract:
  We report on optical spectroscopic observations of the X-ray Transient XTE
J1118+480 covering the period from April 7, 2000 to July 4, 2000. The spectrum
is characterized by weak, broad, double-peaked Balmer and He lines on top of a
blue continuum of slope p ~ 1/3, as expected for an optically-thick accretion
disk. The weak Bowen blend seen in our spectra may indicate a low intrinsic
metallicity for the source. The presence of a partial S-wave pattern in the
HeII lambda-4686 line appears consistent with the reported photometric orbital
period Porb = 4.1 hr for XTE J1118+480. By using a combination of Doppler
mapping and various theoretical arguments, we constrain plausible orbital
parameters for the system: a mass ratio 0.02 <~ q <~ 0.1, an inclination i >~
70 deg for a neutron star primary, or 30 deg <~ i <~ 50 deg for a black hole
primary with a mass between 4 and 10 Msun. CaII absorption features observed at
very high resolution constrain the interstellar hydrogen absorption column
log[N_HI (cm^{-2})] ~ 20.45 +/- 0.2 and the identification of three absorbing
clouds indicate a distance to the source <~ 1 kpc, assuming the line-of-sight
to XTE J1118+480 has average high-latitude properties. These results are
discussed in the context of previous multiwavelength observations of this
unusual system.


title: The Temperature of Nonspherical Circumstellar Dust Grains

abstract:
  The temperatures of prolate and oblate spheroidal dust grains in the
envelopes of stars of various spectral types are calculated. Homogeneous
particles with aspect ratios {\small $a/b \le 10$} composed of amorphous
carbon, iron, dirty ice, various silicates, and other materials are considered.
The temperatures of spherical and spheroidal particles were found to vary
similarly with particle size, distance to the star, and stellar temperature.
The temperature ratio {\small $T_{\rm d}({\rm spheroid})/T_{\rm d}({\rm
sphere}) $} depends most strongly on the grain chemical composition and shape.
Spheroidal grains are generally colder than spherical particles of the same
volume; only iron spheroids can be slightly hotter than iron spheres. At
{\small $a/b \approx 2$}, the temperature differences do not exceed 10 %. If
{\small $a/b \ga 4$}, the temperatures can differ by 30-40 %. For a fixed dust
mass in the medium, the fluxes at wavelengths {\small $\lambda \ga 100 \mkm$}
are higher if the grains are nonspherical, which gives over estimated dust
masses from millimeter observations. The effect of grain shape should also be
taken into account when modeling Galactic-dust emission properties, which are
calculated when searching for fluctuations of the cosmic microwave background
radiation in its Wien wing.


title: Structure formation in anisotropic Einstein-Cartan cosmologies

abstract:
  Density linear perturbations in Einstein-Cartan two fluid cosmologies where
the outer model is an isotropic Friedmann solution with closed model while the
inner model is a flat anisotropic Einstein-Cartan (EC) cosmology with shear are
computed by taking into consideration superhorizon situations.This situation is
in agreement with the present isotropy of the Cosmic Background Radiation where
the anisotropic EC model evolves into an isotropic general relativistic
model.Galaxy formation is discussed based on this model.Another type of two
fluid is considered where the inner solution is a pressureless Kasner type
solution while the outer solution is a de Sitter solution with spin and
torsion.


title:
Probing Early Structure Formation with Far-Infrared Background
  Correlations

abstract:
  The large-scale structure of high-redshift galaxies produces correlated
anisotropy in the far-infrared background (FIRB). In regions of the sky where
the thermal emission from Galactic dust is well below average, these
high-redshift correlations may be the most significant source of angular
fluctuation power over a wide range of angular scales, from about 7' to about 3
degrees, and frequencies, from about 400 to about 1000 GHz. The strength of
this signal should allow detailed studies of the statistics of the FIRB
fluctuations, including the shape of the angular power spectrum at a given
frequency and the degree of coherence between FIRB maps at different
frequencies. The FIRB correlations depend upon and hence constrain the
redshift-dependent spectral energy distributions, number counts, and clustering
bias of the galaxies and active nuclei that contribute to the background. We
quantify the accuracy to which Planck and a newly proposed balloon-borne
mission EDGE could constrain models of the high-redshift universe through the
measurement of FIRB fluctuations. We conclude that the average bias of
high-redshift galaxies could be measured to an accuracy of less than
approximately 1% or, for example, separated into 4 redshift bins with about 10%
accuracy.


title: Sub-mm counterparts to Lyman-break galaxies

abstract:
  We summarize the main results from our SCUBA survey of Lyman-break galaxies
(LBGs) at z~3. Analysis of our sample of LBGs reveals a mean flux of
S850=0.6$\pm$0.2 mJy, while simple models of emission based on the UV
properties predict a mean flux about twice as large. Known populations of LBGs
are expected to contribute flux to the weak sub-mm source portion of the far-IR
background, but are not likely to comprise the bright source (S850>5 mJy) end
of the SCUBA-detected source count. The detection of the LBG, Westphal-MM8, at
1.9 mJy suggests that deeper observations of individual LBGs in our sample
could uncover detections at similar levels, consistent with our UV-based
predictions. By the same token, many sub-mm selected sources with S850<2 mJy
could be LBGs. The data are also consistent with the FarIR/$\beta$ relation
holding at z=3.


title: Number Count of Peaks in the CMB Map

abstract:
  We investigate the dependence of cosmological parameters on the number count
of peaks (local maxima and minima) in the cosmic microwave background (CMB)
sky. The peak statistics contains the whole information of acoustic
oscillations in the angular power spectrum $C_l$ over $l$-space and thus it can
place complementary constraints on the cosmological parameters to those
obtained from measurements of $C_l$. Based on the instrumental specifications
of Planck, we find that the number count of peaks can provide new constraints
on the combination of the matter density $\Omega_{\rm m}$ and the Hubble
parameter $h$ approximately scaled as $\Omega_{\rm m} h^{-4.9}$ for a flat
$\Lambda$CDM model with $\Omega_{m}=0.3$ and $h=0.7$. Therefore, we suggest
that combining it with the constraints from $C_l$ scaled as $\Omega_{m}h^{3.8}$
(or commonly $\Omega_{\rm m}h^2$) can potentially determine $\Omega_{\rm m}$ or
equivalently solve the cosmic degeneracy by the CMB data alone.


title: The Canada-UK Deep Submillimetre Survey: The Survey of the 14-hour field

abstract:
  We have used SCUBA to survey an area of 50 square arcmin, detecting 19
sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We have
used Monte-Carlo simulations to assess the effect of source confusion and noise
on the SCUBA fluxes and positions, finding that the fluxes of sources in the
SCUBA surveys are significantly biased upwards and that the fraction of the 850
micron background that has been resolved by SCUBA has been overestimated. The
radio/submillmetre flux ratios imply that the dust in these galaxies is being
heated by young stars rather than AGN. We have used simple evolution models
based on our parallel SCUBA survey of the local universe to address the major
questions about the SCUBA sources: (1) what fraction of the star formation at
high redshift is hidden by dust? (2) Does the submillimetre luminosity density
reach a maximum at some redshift? (3) If the SCUBA sources are
proto-ellipticals, when exactly did ellipticals form? However, we show that the
observations are not yet good enough for definitive answers to these questions.
There are, for example, acceptable models in which 10 times as much
high-redshift star formation is hidden by dust as is seen at optical
wavelengths, but also acceptable ones in which the amount of hidden star
formation is less than that seen optically. There are acceptable models in
which very little star formation occurred before a redshift of three (as might
be expected in models of hierarchical galaxy formation), but also ones in which
30% of the stars have formed by this redshift. The key to answering these
questions are measurements of the dust temperatures and redshifts of the SCUBA
sources.


title: The So-Called "Bar" in the Large Magellanic Cloud

abstract:
  The off-centered "bar" of the Large Magellanic Cloud (LMC) is commonly
assumed, for simplicity's sake, to lie in the same plane as the LMC disk.
Relaxing this assumption to the extent allowed by the observations, we can
drastically change our interpretation of the microlensing events towards the
LMC. We propose that the off-centered ``bar'' in the Large Magellanic Cloud is
a foreground object slightly misaligned with, and offset from, the plane of the
LMC disk. The small displacement and misalignment are consequences of recent
tidal interactions with the Small Magellanic Cloud and the Galaxy. This
proposal, though radical, is consistent with the kinematics of the LMC and
near-infrared star count maps from the DENIS and 2MASS surveys. It does not
violate any of the observational limits on the depth and structure of the LMC
-- in particular, the reported 25 to 50 degree inclination range of the LMC and
the east-west gradient of distance moduli of standard candles. Contributions to
LMC microlensing come from the mutual lensing of stars in the disk and the
``bar'', as well as self-lensing of the disk and the ``bar''. The microlensing
optical depth of such configurations from self-lensing alone is comparable to
the observed microlensing signal reported by the EROS and MACHO groups.
Possible observations are suggested to discriminate between our misaligned,
offset ``bar'' model and the conventional picture of an off-centered, planar
bar.


title:
Chemical abundances and winds of massive stars in M31: a B-type
  supergiant and a WC star in OB10

abstract:
  We present high quality spectroscopic data for two massive stars in the OB10
association of M31, OB10-64 (B0Ia) and OB10-WR1 (WC6). Medium resolution
spectra of both stars were obtained using the ISIS spectrograph on the William
Hershel Telescope. This is supplemented with HST-STIS UV spectroscopy and KeckI
HIRES data for OB10-64. A non-LTE model atmosphere and abundance analysis for
OB10-64 is presented indicating that this star has similar photospheric CNO, Mg
and Si abundances as solar neighbourhood massive stars. A wind analysis of this
early B-type supergiant reveals a mass-loss rate of M_dot=1.6x10^-6
M_solar/yr,and v_infty=1650 km/s. The corresponding wind momentum is in good
agreement with the wind momentum -- luminosity relationship found for Galactic
early B supergiants. Observations of OB10W-R1 are analysed using a non-LTE,
line-blanketed code, to reveal approximate stellar parameters of log L/L_solar
\~ 5.7, T~75 kK, v_infty ~ 3000 km/s, M_dot ~ 10^-4.3 M_solar/yr, adopting a
clumped wind with a filling factor of 10%. Quantitative comparisons are made
with the Galactic WC6 star HD92809 (WR23) revealing that OB10-WR1 is 0.4 dex
more luminous, though it has a much lower C/He ratio (~0.1 versus 0.3 for
HD92809). Our study represents the first detailed, chemical model atmosphere
analysis for either a B-type supergiant or a WR star in Andromeda, and shows
the potential of how such studies can provide new information on the chemical
evolution of galaxies and the evolution of massive stars in the local Universe.


title: Chemical abundances in the inner 5 kpc of the Galactic disk

abstract:
  High-resolution, high signal-to-noise spectral data are presented for four
young B-type stars lying towards the Galactic Centre. Determination of their
atmospheric parameters from their absorption line profiles, and uvby
photometric measurement of the continua indicate that they are massive objects
lying slightly out of the plane, and were probably born in the disk between
2.5-5 kpc from the Centre. We have carried out a detailed absolute and
differential line-by-line abundance analyses of the four stars compared to two
stars with very similar atmospheric parameters in the solar neighbourhood. The
stars appear to be rich in all the well sampled chemical elements (C, N, Si,
Mg, S, Al), except for oxygen. Oxygen abundances derived in the atmospheres of
these four stars are very similar to that in the solar neighbourhood. If the
photospheric composition of these young stars is reflective of the gaseous ISM
in the inner Galaxy, then the values derived for the enhanced metals are in
excellent agreement with the extrapolation of the Galactic abundance gradients
previously derived by Rolleston et al. (2000) and others. However, the data for
oxygen suggests that the inner Galaxy may not be richer than normal in this
element, and the physical reasons for such a scenario are unclear.


title:
Photometric redshifts and selection of high redshift galaxies in the NTT
  and Hubble Deep Fields

abstract:
  We present and compare in this paper new photometric redshift catalogs of the
galaxies in three public fields: the NTT Deep Field, the HDF-N and the HDF-S.
Photometric redshifts have been obtained for thewhole sample, by adopting a
$\chi^2$ minimization technique on a spectral library drawn from the Bruzual
and Charlot synthesis models, with the addition of dust and intergalactic
absorption. The accuracy, determined from 125 galaxies with known spectroscopic
redshifts, is $\sigma_z\sim 0.08 (0.3)$ in the redshift intervals $z=0-1.5
(1.5-3.5)$. The global redshift distribution of I-selected galaxies shows a
distinct peak at intermediate redshifts, z~0.6 at I_{AB}<26 and z~0.8 at
I_{AB}<27.5 followed by a tail extending to z~6. We also present for the first
time the redshift distribution of the total IR-selected sample to faint limits
($Ks \leq 21$ and $J\leq22$). It is found that the number density of galaxies
at 1.25<z<1.5 is ~ 0.1 /arcmin^22 at J<=21 and ~1./arcmin^2} at J<22, and drops
to 0.3/arcmin^2 (at J<22) at 1.5<z<2. The HDFs data sets are used to compare
the different results from color selection criteria and photometric redshifts
in detecting galaxies in the redshift range 3.5<z<4.5 Photometric redshifts
predict a number of high z candidates in both the HDF-N and HDF-S that is
nearly 2 times larger than color selection criteria, and it is shown that this
is primarily due to the inclusion of dusty models that were discarded in the
original color selection criteria by Madau et al 1998. In several cases, the
selection of these objects is made possible by the constraints from the IR
bands. Finally, it is shown that galactic M stars may mimic z>5 candidates in
the HDF filter set and that the 4 brightest candidates at $z>5$ in the HDF-S
are indeed most likely M stars. (ABRIDGED)


title:
Spectral analysis of multi mode pulsating sdB stars II. Feige 48, KPD
  2109+4401 and PG 1219+534

abstract:
  Three members of the new class of pulsating sdB stars (sdBV or EC 14026
stars) are analysed from Keck HIRES spectra using line blanketed NLTE and LTE
model atmospheres. Atmospheric parameters (Teff, log g, He/H), metal abundances
and rotational velocities are determined. As is typical for sdB stars, all
programme stars are found to be helium deficient, with a He abundance ranging
from 1/80 solar for Feige 48 to 1/3 solar for PG 1219+534, probably due to
diffusion. Most metals are also depleted. The abundances of C, O, Ne, Mg, Al
and Si in the high gravity programme stars KPD 2109+4401 and PG 1219+534 are
considerably lower than in the lower gravity stars Feige 48 and PG 1605+072
which could be explained by an equilibrium between gravitational settling and
radiative levitation. Surprisingly iron is solar to within error limits in all
programme stars irrespective of their gravity, confirming predictions from
diffusion calculations. The metal lines are very sharp and allow the
microturbulent velocity to be constrained to be lower than 5km/s (KPD2109+4401,
PG 1219+534). Also the projected rotational velocities have to be very low
(vrot sini<10km/s). For Feige 48 the limits are even tighter (vmicro<=3km/s,
vrot sini<=5km/s).


title: Broad band spectrum of Cygnus X-1 in two spectral states with BeppoSAX

abstract:
  We report on the 0.5--200 keV spectral properties of Cyg X-1 observed at
different epochs with the Narrow Field Instruments of the BeppoSAX satellite.
The source was in its soft state during the first observation of 1996 June. In
the second observation of 1996 September, the source had parameters
characteristic to its hard state. A soft X-ray excess, a broad Fe K$\alpha$
line and Compton reflection are clearly detected in both states. The soft-state
broad-band continuum is well modeled by a disk blackbody (accounting for the
soft excess) and Compton upscattering of the disk photons by a hybrid,
thermal/non-thermal, plasma, probably forming a corona above the disk (also
giving rise to the Compton-reflection component). In the hard state, the
primary hard X-ray spectrum can be well modeled by Compton upscattering of a
weak blackbody emission by a thermal plasma at a temperature of $\sim 60$ keV.
The soft excess is then explained by thermal Comptonization of the same
blackbody emission by another hot plasma cloud characterized by a low value of
its Compton parameter. Finally, we find the characteristic ratio of the
bolometric flux in the soft state to that in the hard state to be about 3. This
value is much more compatible with theories of state transitions than the
previously reported (and likely underestimated) value of 1.5.


title: Maximum Disk Mass Models for Spiral Galaxies

abstract:
  We present axisymmetric maximum disk mass models for a sample of 74 spiral
galaxies taken from the southern sky Fabry-Perot Tully-Fisher survey (Schommer
et al. 1993). The sample contains galaxies spanning a large range of
morphologies and having rotation widths from 180 km/sec to 680 km/secs. For
each galaxy we have an I-band image and a 2-d H_alpha velocity field. The
distribution of mass is modeled as a sum of disk and bulge components with
distinct, constant mass-to-light ratios. No dark matter halo is included in the
fits. The models reproduce the overall structure of the rotation curves in the
majority of galaxies, providing good fits to galaxies which exhibit pronounced
structural differences in their surface brightness profiles. 75% of galaxies
for which the rotation curve is measured to R_23.5 or beyond are well fit by a
mass-traces-light model for the entire region within R_23.5. The models for
about 20% of the galaxies do not fit well; the failure of most of these models
is traced directly to non-axisymmetric structures, primarily bars but also
strong spiral arms. The median I-band M/L of the disk plus bulge is 2.4+/-0.9
h_75 in solar units, consistent with normal stellar populations. These results
require either that the mass of dark matter within the optical disk of spiral
galaxies is small, or that its distribution is very precisely coupled to the
distribution of luminous matter.


title: The Kuiper Belt and Olbers Paradox

abstract:
  We investigate the constraints that Olbers Paradox, applied to the Zodiacal
Background as measured from space, sets on outer solar system objects. If
extended to very faint limits, R = 40--50 mag, the steep optical luminosity
function (LF) of Kuiper Belt objects (KBOs) at R less than 26 mag implies an
infinitely bright night sky. Small KBOs with radii of 1 mm to 1 km must have a
size distribution n(r) proportional to r^{-a}, with a = 3.5 or smaller to
satisfy the known limits on the sky-surface brightness at optical and
far-infrared wavelengths. Improved limits on the measured KBO surface
brightness can yield direct estimates of the albedo, temperature, and size
distribution for small KBOs in the outer solar system.


title: Groups and clusters detection on DPOSS catalogs

abstract:
  We discuss the implementation and validation of a procedure aimed to detect
groups and clusters of galaxies in DPOSS catalogs.


title: On the Hardness-Intensity Correlation in Gamma-Ray Burst Pulses

abstract:
  We study the hardness-intensity correlation (HIC) in gamma-ray bursts (GRBs).
In particular, we analyze the decay phase of pulse structures in their light
curves. The study comprises a sample of 82 long pulses selected from 66 long
bursts observed by BATSE on the Compton Gamma-Ray Observatory. We find that at
least 57% of these pulses have HICs that can be well described by a power law.
The distribution of the power law indices, obtained by modeling the HIC of
pulses from different bursts, is broad with a mean of 1.9 and a standard
deviation of 0.7. We also compare indices among pulses from the same bursts and
find that their distribution is significantly narrower. The probability of a
random coincidence is shown to be very small. In most cases, the indices are
equal to within the uncertainties. This is particularly relevant when comparing
the external versus the internal shock models. In our analysis, we also use a
new method for studying the HIC, in which the intensity is represented by the
peak value of the E F_E spectrum. This new method gives stronger correlations
and is useful in the study of various aspects of the HIC. In particular, it
produces a better agreement between indices of different pulses within the same
burst. Also, we find that some pulses exhibit a "track jump" in their HICs, in
which the correlation jumps between two power laws with the same index. We
discuss the possibility that the "track jump" is caused by strongly overlapping
pulses. Based on our findings, the constancy of the index is proposed to be
used as a tool for pulse identification in overlapping pulses.


title:
Inhomogeneous Chemical Evolution of the Galactic Halo: Abundance of
  r-process Elements

abstract:
  We present a stochastic model based on the Monte Carlo technique to study the
inhomogeneous chemical evolution of the Galactic halo. In particular, we
consider the local enrichment and subsequent mixing of the interstellar gas
resulting from bursts of star formation, following explicitly the fragmentation
and coalescence of interstellar gas clouds. The model takes into account the
mixing of halo gas through cloud-cloud collisions and the delayed mixing of
supernova ejecta into the interstellar medium. The consequences of the infall
of halo gas onto the Galactic disk are also discussed. The mass spectrum of
clouds, the age-metallicity relation, and the G-dwarf distribution are
investigated at different times. We analyze in detail the predictions of our
model for the abundance of elements like Eu, Ba, and Sr in the Galactic halo,
following their production by $r$-process nucleosynthesis for different
assumptions on the supernova mass range. Finally, we compare our results with
spectroscopic data for the chemical composition of metal-poor halo stars.


title: Peculiar velocities of galaxies and clusters

abstract:
  We present a simple model for the shape of the distribution function of
galaxy peculiar velocities. We show how both nonlinear and linear theory terms
combine to produce a distribution which has an approximately Gaussian core with
exponential wings. The model is easily extended to study how the statistic
depends on the type of particle used to trace the velocity field (dark matter
particles, dark matter haloes, galaxies), and on the density of the environment
in which the test particles are. Comparisons with simulations suggest that our
model is accurate. We also show that the evolution of the peculiar velocities
depends on the local, rather than the global density. Since clusters populate
denser regions on average, using cluster velocities with the linear theory
scaling may lead to an overestimate of the global value of Omega. Conversely,
using linear theory with the global value of Omega to scale cluster velocities
from the initial to the present time results in an underestimate of their true
velocities. In general, however, the directions of motions of haloes are rather
well described by linear theory. Our results help to simplify models of
redshift-space distortions considerably.


title: Linear and nonlinear contributions to pairwise peculiar velocities

abstract:
  We write the correlation function of dark matter particles, xi(r), as the sum
of two terms - one which accounts for nonlinear evolution, and dominates on
small scales, and another which is essentially the term from linear theory, and
dominates on large scales. We use models of the number and spatial distribution
of haloes and halo density profiles to describe the nonlinear term and its
evolution. The result provides a good description of the evolution of xi(r) in
simulations. We then use this decomposition to provide simple and accurate
models of how the single particle velocity dispersion evolves with time, and
how the first and second moments of the pairwise velocity distribution depend
on scale. The key idea is to use the simple physics of linear theory on large
scales, the simple physics of the virial theorem on small scales, and our model
for the correlation function to tell us how to weight the two types of
contributions (linear and nonlinear) to the pairwise velocity statistics. When
incorporated into the streaming model, our results will allow a simple accurate
description of redshift-space distortions over the entire range of linear to
highly nonlinear regimes.


title:
Steady-state conduction-driven temperature profile in clusters of
  galaxies

abstract:
  The temperature profile (TP) of the intracluster medium (ICM) is of primeval
importance for deriving the dynamical parameters of the largest equilibrium
systems known in the universe, in particular their total mass profile.
Analytical models of the ICM often assume that the ICM is isothermal or
parametrize the TP with a polytropic index. This parameter is ajusted to
observations, but has in fact poor physical meaning for values other than 1 or
5/3, when considering monoatomic gases. In this article, I present a
theoretical model of a relaxed cluster where the TP is instead structured by
electronic thermal conduction. Neglecting cooling and heating terms, the
stationnary energy conservation equation reduces to a 2nd order differential
equation, whose resolution requires two boundary conditions, taken here as the
inner radius and the ratio between inner and outer temperature. Once these two
constants are chosen, the TP has a fixed analytical expression, which
reproduces nicely the observed ``universal'' TP obtained by Markevitch et al.
(1998) from ASCA data. Using observed X-ray surface brightnesses for two hot
clusters with spatially resolved TP, the local polytropic index and the hot gas
fraction profile are predicted and compare very well with ASCA observations
(Markevitch et al 1999). Moreover, the total density profile derived from
observed X-ray surface brightness, hydrostatic equilibrium and the
conduction-driven TP is very well fit by three analytical profiles found to
describe the structure of galactic or cluster halos in numerical simulations of
collisionless matter (Hernquist, 1991; Navarro et al. 1995, 1997; Burkert
1995). (abriged)


title: Eccentric orbits and QPOs in neutron star X-ray binaries

abstract:
  We investigate the suggestion that the frequencies of the kilohertz and other
QPOs in the emission from neutron stars in low-mass X-ray binaries are
generated by geodesic motion of gas clumps around the star. First we assume,
following previous work, that the dominant frequencies produced by such motions
are the azimuthal frequency \nuk, the apsidal precession frequency \nuap, and
the first overtone of the nodal precession frequency \nunp. We investigate
whether geodesics can be found for which these frequencies agree with the
observed frequencies. Correcting calculational errors made when the geodesic
precession hypothesis was first proposed, we find that \nuk and \nuap disagree
qualitatively with the frequencies of the kilohertz QPOs for infinitesimally or
even moderately eccentric geodesics. These frequencies are similar to the
frequencies of the kilohertz QPOs only for highly eccentric geodesics, with
apastron to periastron ratios \sim3--4; for these geodesics, 2\nunp differs
qualitatively from the frequencies of the low-frequency QPOs. Next we
investigate whether these frequencies would be the dominant frequencies
produced by orbiting clumps. We find that they are not and that the dominant
frequencies are instead harmonics and sidebands of the radial epicyclic
frequency \nur. Finally, we show that gas dynamical constraints restrict the
radii of orbiting clumps to be \ll 10^{-3} of the stellar radius; the
fractional modulation that could be produced by clumps is therefore \ll
10^{-6}. We conclude that there are significant difficulties in interpreting
the kilohertz and low-frequency QPOs as consequences of geodesic motion of gas
clumps.


title: Intermediate Velocity Clouds - Distances, Infall and Shadowing

abstract:
  We present the current distance estimates to 11 intermediate velocity clouds
(IVCs) which are part of the David Dunlap Observatory Intermediate Velocity
Cloud (DDO IVC) Distance Project (Clarke et al. 1999). We briefly discuss
constraints these place on infall models and show the potential of IVCs to
constrain the radial distribution of hot gas in the Galaxy through shadowing of
the soft X-ray background.


title: The core-jet structure of the JVAS gravitational lens B1030+074

abstract:
  We present results from VLBA+Effelsberg 1.7 GHz, VLBA 8.4 GHz and VLBA 15 GHz
observations of the JVAS gravitational lens system B1030+074. The
VLBA+Effelsberg 1.7 GHz data with 3 mas resolution reveal a detailed 60 mas jet
structure in the strong A component of the lens system and maybe a first hint
of the corresponding jet structure in the faint component B. As we go to the
higher resolution 8.4 GHz and 15 GHz data we can see more of the inner
structure of the A core, which is resolved, while the B core still remains
unresolved.


title: Where are the absorbers towards Q2302+029?

abstract:
  We present images and spectroscopy of objects close to the sightline of
Q2302+029 in order to search for galaxies responsible for the remarkable z=0.7
high-ionization absorption line system found by Jannuzi et al (1996). This
system shows `normal' narrow OVI, NV, and CIV lines superimposed on broader
(3,000-5,000 km/s wide), unsaturated absorption troughs some 56,000 km/s away
from the QSO emission redshift (z=1.052). Despite reaching sensitivities
sufficient to detect 1/10 L* galaxies in the optical and 1/20 L* in the
infra-red, we are unable to detect any obvious bright galaxies which might be
responsible for the absorption beyond ~ 6 h-1 kpc of the sightline. This
supports the hypotheses that the absorption is either intrinsic to the QSO, or
arises in intracluster gas. Adopting either explanation is problematic: in the
first case, `associated' absorption at such high ejection velocities is hard to
understand, and challenges the conventional discrimination between intrinsic
and intervening absorbers; in the second case, the gas must reside in a ~ 40
h-1 Mpc long filament aligned along the line of sight in order to reproduce the
broad absorption. Spectroscopy of objects beyond the immediate vicinity of the
QSO sightline reveals a galaxy cluster at z=0.59, which coincides with strong
Lya and more narrow high ionization lines in the quasar spectrum. Here too, the
lack of galaxies at distances comparable to those found for, e.g.,
Lya-absorbing galaxies, suggests that the absorption may arise from
intracluster gas unassociated with any individual galaxies.


title: A Moderate Cluster Cooling Flow Model

abstract:
  We propose that the outer portions of cooling flows (CFs) in clusters of
galaxies are frequently disrupted by radio jets, and that their effective ages
are much shorter than the cluster ages. The inner regions, where the gas
density is higher, are more difficult to disrupt, and may continue to harbor
CFs even after disruption events. The main assumption of the proposed scenario
is that, on a time scale of about 2-4 times 10^9 years the cD galaxies in CF
clusters undergo powerful bursts of AGN activity that produce strong radio
jets. The jets excite shock waves moving at several thousands km/sec and heat
the CF region, hence terminating it in the outer regions. The total accreted
mass due to the CF is an order of magnitude lower than the mass accreted
according to the "standard" CF model (which assumes an undisturbed CF for a
time equal to the age of the cluster). The scenario, therefore, brings to
agreement the observations that a large fraction of clusters harbor CFs, that
strong optical and radio activity are present only in the very inner regions of
CFs, and the lack of a satisfactory reservoir of the expected (in the standard
CF model) large mass that has been cooling over the life of the cluster.


title: Deuterium-burning in substellar objects

abstract:
  We consider the depletion of primordial deuterium in the interior of
substellar objects as a function of mass, age and absolute magnitude in several
photometric passbands. We characterize potential spectroscopic signatures of
deuterium in the lines of deuterated water HDO. These results will serve as a
useful, independent diagnostic to characterize the mass and/or the age of young
substellar objects, and to provide an independent age determination of very
young clusters. These results can serve to identify objects at the
deuterium-burning limit and to confront the theoretical prediction that
D-burning is a necessary condition to form star-like objects.


title: Compact steep-spectrum sources from the S4 sample

abstract:
  We present the results of 5-GHz observations with the VLA A-array of a sample
of candidate Compact Steep Spectrum sources (CSSs) selected from the S4 survey.
We also estimate the symmetry parameters of high-luminosity CSSs selected from
different samples of radio sources, and compare these with the larger sources
of similar luminosity to understand their evolution and the consistency of the
CSSs with the unified scheme for radio galaxies and quasars. The majority of
CSSs are likely to be young sources advancing outwards through a dense
asymmetric environment. The radio properties of CSSs are found to be consistent
with the unified scheme, in which the axes of the quasars are observed close to
the line of sight, while radio galaxies are observed close to the plane of the
sky.


title: Dust Formation in Primordial Type II Supernovae

abstract:
  We have investigated the formation of dust in the ejecta of Type II
supernovae (SNe), mostly of primordial composition, to answer the question of
where are the first solid particles formed in the universe. However, we have
also considered non-zero progenitor's metallicity values up to Z=Zsun. The
calculations are based on standard nucleation theory and the scheme has been
first tested on the well studied case of SN1987A, yielding results that are in
agreement with the available data. We find that: i) the first dust grains are
predominantly made of silicates, amorphous carbon (AC), magnetite, and
corundum; ii) the largest grains are the AC ones, with sizes around 300 A,
whereas other grain types have smaller radii, around 10-20 A. The grain size
distribution depends somewhat on the thermodynamics of the ejecta expansion and
variations in the results by a factor ~ 2 might occur within reasonable
estimates of the relevant parameters. Also, and for the same reason, the grain
size distribution, is essentially unaffected by metallicity changes. The
predictions on the amount of dust formed are very robust: for Z=0, we find that
SNe with masses in the range (12-35) Msun produce about 0.08 Msun < M_dust <
0.3 Msun of dust/SN. The above range increases by roughly 3 times as the
metallicity is increased to solar values. We discuss the implications and the
cosmological consequences of the results.


title:
Analysis of isoplanatic high resolution stellar fields by Starfinder
  code

abstract:
  We describe a new code for the deep analysis of stellar fields, designed for
Adaptive Optics Nyquist-sampled images with high and low Strehl ratio. The
Point Spread Function is extracted directly from the image frame, to take into
account the actual structure of the instrumental response and the atmospheric
effects. The code is written in IDL language and organized in the form of a
self-contained widget-based application, provided with a series of tools for
data visualization and analysis. A description of the method and some
applications to AO data are presented.


title: NGC 4340: Double Bar + Fossil Nuclear Ring

abstract:
  NGC 4340 is a double-barred SB0 galaxy in the Virgo cluster (Wozniak et al.
1995). Here, we present evidence that this galaxy also posseses a luminous
stellar nuclear ring of relatively old stars with little or no gas. The ring
lies just outside the inner bar, at the probable inner inner Lindblad resonance
(IILR) of the outer bar. Careful inspection of the isophotes and unsharp masks
shows that the two bars are slightly misaligned, which suggests they may be
independently rotating.


title: The Lithium Depletion Boundary as a Clock and Thermometer

abstract:
  We take a critical look at the lithium depletion boundary (LDB) technique
that has recently been used to derive the ages of open clusters. We identify
the sources of experimental and systematic error and show that the probable
errors are larger by approximately a factor two than presently claimed in the
literature. We then use the Pleiades LDB age and photometry in combination with
evolutionary models to define empirical colour-T_eff relations that can be
applied to younger clusters. We find that these relationships DO NOT produce
model isochrones that match the younger cluster data. We propose that this is
due either to systematic problems in the evolutionary models or an age
(gravity) sensitivity in the colour-T_eff relation which is not present in
published atmospheric models.


title:
The distance to the Fornax dwarf galaxy using red clump stars, and the
  discrepancy between red clump and tip of the red giant branch distances

abstract:
  I determine a distance to the Fornax dwarf galaxy using stars in the red
clump and at the tip of the red giant branch. They are in very good agreement,
with $\mu_0 = 20.66 mag$. Comparing the magnitudes of the tip of the red giant
branch and of the red clump in Fornax, Carina and the Magellanic Clouds, I
propose a possible solution to the problem of the discrepancy between these two
types of distance measurements.


title:
Near-infrared imaging of the host galaxies of three radio-loud quasars
  at z = 1.5

abstract:
  We present high spatial resolution near-infrared H-band (1.65 microns)
images, taken with ISAAC on UT1 of ESO VLT, of three radio-loud quasars at z =
1.5, as a pilot study for imaging of a larger sample of radio-loud and
radio-quiet quasars in the redshift range 1 < z < 2. We are able to clearly
detect the host galaxy in two quasars (PKS 0000-177 and PKS 0348-120) and
marginally in the third (PKS 0402-362). The host galaxies appear compact
(average bulge scale-length R(e) = 4 kpc) and luminous (average M(H) =
-27.6+-0.1). They are 2.5 mag more luminous than the typical galaxy luminosity
(M*(H) = -25.0+-0.2), and are comparable to the hosts of low redshift
radio-loud quasars (M(H) = -26), taking into account passive stellar evolution.
Their luminosities are also similar to those of high redshift radio galaxies.
All three quasars have at least one close companion galaxy at a projected
distance < 50 kpc from the quasar, assuming they are at the same redshift.


title: Chemical analysis of 8 recently discovered extra-solar planet host stars

abstract:
  We present the chemical analysis of a new set of stars known to harbor low
mass companions, namely HD 1237, HD 52265, HD 82943, HD 83443, HD 169830, and
HD 202206. In addition, we have also analyzed HD 13445 and HD 7528}, already
studied elsewhere. The abundances of C and alpha-elements O, S, Si, Ca and Ti
are presented and discussed in the context of the metallicity distribution of
the stars with extra-solar planets. We compare the metallicity distribution of
stars with planets with the same distribution of field dwarfs. The results
further confirm that stars with planets are over-abundant in [Fe/H].


title:
The Composite Broad Band Spectrum of Cir X-1 at the Periastron: a
  Peculiar Z-source

abstract:
  We report on the spectral analysis of the peculiar source Cir X-1 observed by
the BeppoSAX satellite when the X-ray source was near the periastron. A flare
lasting $\sim 6 \times 10^3$ s is present at the beginning of the observation.
The luminosity during the persistent emission is $1 \times 10^{38}$ erg
s$^{-1}$, while during the flare is $2 \times 10^{38}$ erg s$^{-1}$. We
produced broad band (0.1-100 keV) energy spectra during the flare and the
persistent emission. At low energies the continuum is well fitted by a model
consisting of Comptonization of soft photons, with a temperature of $\sim 0.4$
keV, by electrons at a temperature of $\sim 1$ keV. Out of the flare a
power-law component, with photon index $\sim 3$, is dominant at energies higher
than 10 keV. This component contributes to $\sim 4%$ of the total luminosity.
During the flare its addition is not statistically significant. An absorption
edge at $\sim 8.4$ keV, with optical depth $\sim 1$, corresponding to the
K-edge of Fe XXIII-XXV, and an iron emission line at 6.7 keV are also present.
The iron line energy is in agreement with the ionization level of the
absorption edge. The hydrogen column deduced from the absorption edge is $\sim
10^{24}$ cm$^{-2}$, two order of magnitude larger than the absorption measured
in this source. We calculated the radius of the region originating the
comptonized seed photons, $R_W \sim 150$ km.
  We propose a scenario where $R_W$ is the inner disk radius, a highly ionized
torus surrounds the accretion disk and a magnetosphere is large up to $R_W$.
The absorption edge and the emission line could originate in the photoionized
torus, while the comptonized component originates in an inner region of the
disk.


title:
Rayleigh-Taylor stability of a strong vertical magnetic field at the
  Galactic center confined by a disk threaded with horizontal magnetic field

abstract:
  Observations of narrow radio-emitting filaments near the Galactic center have
been interpreted in previous studies as evidence of a pervasive vertical (i.e.
perpendicular to the Galactic plane) milliGauss magnetic field in the central
150 pc of the Galaxy. A simple cylindrically symmetric model for the
equilibrium in this central region is proposed in which horizontal (i.e.
parallel to the Galactic plane) magnetic fields embedded in an annular band of
partially ionized molecular material of radius 150 pc are wrapped around
vertical magnetic fields threading low-density hot plasma. The central vertical
magnetic field, which has a pressure that significantly exceeds the thermal
pressure of the medium, is confined by the weight of the molecular material.
The stability of this equilibrium is studied indirectly by analyzing a
uniformly rotating cylinder of infinite extent along the z axis in cylindrical
coordinates (r,theta,z), with low-density plasma and an axial magnetic field at
r< 150 pc, high-density plasma and an azimuthal field at r> 150 pc, and a
gravitational acceleration g* proportional to r directed in the negative-r-hat
direction. The density profile and gravity tend to destabilize the plasma, but
the plasma tends to be stabilized by rotation and magnetic tension--since the
interface between the high and low-density plasmas can not be perturbed without
bending either the horizontal or vertical field. It is shown analytically that
when beta= 8(pi)p/B^2 is small and the dense plasma is supported against
gravity primarily by rotation, the necessary and sufficient condition for
stability to k_z=0 modes is |g| < (2|Omega| a), where g = g* - Omega^2 r is the
effective gravity, Omega is the uniform angular velocity, and "a" is the sound
speed in the dense plasma.


title: Gravitational Stirring in Planetary Debris Disks

abstract:
  We describe gravitational stirring models of planetary debris disks using a
new multi-annulus planetesimal evolution code. The current code includes
gravitational stirring and dynamical friction; future studies will include
coagulation, fragmentation, Poynting-Robertson drag, and other physical
processes. We use the results of our calculations to investigate the physical
conditions required for small bodies in a planetesimal disk to reach the
shattering velocity and begin a collisional cascade. Our results demonstrate
that disks composed primarily of bodies with a single size will not undergo a
collisional cascade which produces small dust grains at 30-150 AU on timescales
of 1 Gyr or smaller. Disks with a size distribution of bodies reach conditions
necessary for a collisional cascade in 10 Myr to 1 Gyr if the disk is at least
as massive as a minimum mass solar nebula and if the disk contains objects with
radii of 500 km or larger. The estimated 500 Myr survival time for these disks
is close to the median age of roughly 400 Myr derived for nearby stars with
dusty disks.


title:
Formation and Evolution of E and S0 Galaxies from HST and Keck Studies
  of z~0.3-1 Clusters

abstract:
  We have witnessed a dramatic increase over the last five years in results on
distant galaxies, in large part because of the high resolution imaging
capability of HST, and the multiobject spectroscopic capability of the Keck
telescopes. Our program to obtain wide-field, multi-color WFPC2 mosaics with
HST of intermediate redshift clusters, and spectroscopic membership and high
S/N spectroscopy with LRIS on Keck, has provided new insights into the nature
of elliptical and S0 galaxies in the cluster environment over a wide range of
densities. In particular, most ellipticals, and a significant fraction of the
S0 population, have large luminosity-weighted ages, suggesting that their
stellar populations were formed at redshifts beyond z~2, though the existence
of substantial numbers of major mergers in MS 1054-03 at z=0.83 suggests that
final assembly of such galaxies may not have occurred until much later for a
significant fraction of early-type galaxies.


title: Galaxies at High Redshift

abstract:
  Within just the last few years, we have advanced from knowing only a few
galaxies at z>2 to having redshifts for nearly 1000 z~2-5 objects. The majority
of this sample has been detected through the photometric ``drop-out'' technique
used so successfully by Steidel and his collaborators. In addition, a handful
of objects have already been detected at z>5, and we may already have a few
objects at z>6! These data, plus that at z<2 have resulted in a
characterization of the star formation history of the universe, commonly known
as the ``Madau plot'', which gives SFR per comoving volume vs redshift from the
present day at z=0 to z~5. Recently, we have realized that dust has
significantly affected our SFR estimates for the objects that have been
detected in the optical, and have developed approaches to correct for that
extinction. We now also have increasingly good evidence that a substantial
fraction (>50%?) of the high redshift star formation occurs in dust-enshrouded
starbursts that were detected at 850 micron with a submm bolometer SCUBA on the
JCMT telescope. These objects will typically be too faint to detect and measure
redshifts in the optical, though those that can have already provided valuable
constraints. The highest redshift objects at z~5 and beyond are intriguing
sources, but test even the limits of Keck and of HST. The detailed study of
such sources may well only be practical for gravitationally-lensed objects,
where the high magnification allows for a much more detailed study of the
proto-galaxy's structure, until even larger space-based (NGST) and ground-based
(30-m plus) telescopes are developed.


title: Black Hole Mass, Velocity Dispersion and the Radio Source in AGN

abstract:
  The recent discovery of a correlation between nuclear black hole mass, M_bh,
and the stellar velocity dispersion (Gebhardt et al. 2000, Ferrarese and
Merritt 2000), in elliptical galaxies and spiral bulges, has raised the
question whether such a relationship exists for AGN. Estimates of M_bh for many
AGN, made using reverberation mapping techniques, allow exploration of the
relationship between black hole mass, the host galaxy and the energetics of
nuclear emission. However, since only a few AGN have both M_bh and velocity
dispersion measurements, we use the [OIII] 5007 emission line widths on the
assumption that for most AGN the forbidden line kinematics are dominated by
virial motion in the host galaxy bulge. We find that a relation does exist
between M_bh and [OIII] line width for AGN which is similar to the one found by
Gebhardt et al. 2000, although with more scatter as expected if secondary
influences on the gas kinematics are also present. Our conclusion is that both
active and inactive galaxies follow the same relationship between black hole
mass and bulge gravitational potential. We find no compelling evidence for
systematic differences in the mass estimates from reverberation mapping and
stellar dynamics. We also find that for radio quiet AGN the radio power and
black hole mass are highly correlated linking emission on scales of kiloparsecs
with the nuclear energy source.


title:
The Effect of the Mass Accretion Rate on the Burst Oscillations in 4U
  1728-34

abstract:
  We present a comprehensive study of the properties of nearly coherent
brightness oscillations (NCOs) in a large sample of type-I X-ray bursts
observed from low mass X-ray binary 4U 1728-34. We have analyzed ~545ks of data
of this source obtained with the Rossi X-ray Timing Explorer over a 3 year span
from 1996-1999. The data contain 38 bursts, 16 of which show NCOs. We find no
NCOs present when the inferred mass accretion rate of the system is lowest.
Furthermore, we define a measure of the strength of the oscillations and find
that this strength increases with increasing mass accretion rate. This
correlation is particularly evident within bursts detected only a few weeks
apart, and becomes less clear for bursts separated in time by several months to
years. The correlation we find for 4U 1728-34 between the NCOs and the inferred
accretion rate of the system is similar to that found for KS 1731-260 by Muno
et al. (2000), where the NCOs are only present at relatively high mass
accretion rates. However, unlike the case for KS 1731-260, we find an
anti-correlation in the bursts of 4U 1728-34 between the existence of episodes
of photospheric radius expansion and the inferred mass accretion rate of the
system. Moreover, we distinguish between NCOs present in the rise and in the
decay phase of the burst and find that the bursts with NCOs only in the decay
phase occur at intermediate accretion rates, while those with NCOs in both the
rise and the decay phases are concentrated at high inferred mass accretion
rates. We discuss these results in the context of the theory of thermonuclear
bursts and propose intrinsic differences in the neutron stars in KS 1731-260
and 4U 1728-34 as the origin of the different behaviors.


title: The Local Ly-alpha Forest: HI in Nearby Intergalactic Space

abstract:
  Detecting HI using redshifted Ly-alpha absorption lines is 1e6 times more
sensitive than using the 21cm emission line. We review recent discoveries of HI
Ly-alpha absorbers made with the Hubble Space Telescope (HST) which have
allowed us a first glimpse at gas in local intergalactic space between us and
the ``Great Wall''. Despite its mere 2.4m aperture, HST can detect absorbers
with column densities as low as those found using Keck at high-z (log
N(HI)=12.5 1/cm**2). New results that will be discussed include: the evolution
of absorbers with redshift, the location of absorbers relative to galaxies
(including the two-point correlation function for absorbers), the metallicity
of absorbers far from galaxies, and the discovery of hot 1e5-1e6 K
(shock-heated?) absorbers. The unique ability of VLA HI observations in
discovering the nearest galaxies to these absorbers is stressed.


title: Analysis of resonances in grand design spiral galaxies

abstract:
  We have searched for corotations (CR) in three Southern grand design spiral
galaxies: NGC 1365, NGC 1566 and NGC 2997. We have also introduced a method of
quantifying errors in the phase diagram used to detect CR. We established the
m=2 pattern CR at 12.1 kpc, 9.4 kpc and 7 kpc, for NGC 1365, NGC 1566 and NGC
2997, respectively. By using published rotation curves, we could determine
spiral pattern angular speeds of 25.0 km/sec/kpc, 12.2 km/sec/kpc and 17.6
km/sec/kpc, respectively. A three armed component has been detected in NGC
2997, with the CR placed at 8.7 kpc with a pattern angular speed
Omega_{CR_3}=12.7 km/sec/kpc. An m=1 component was detected in NGC 1566. We
warily locate the CR at 7.1 kpc, with a pattern angular speed Omega_{CR}
approx. 16.6 km/sec/kpc. This pattern does not present ILR. Ages have been
determined by studying the radial density profile of the m=2 Fourier components
in g (newly formed stars) and i (perturbing SDW supported by the disk of old
stars), aided by the global aspect of the real spiral pattern in comparison
with numerical simulations. The pattern is approx. 1200 Myr old in NGC 1365,
approx. 800 Myr old in NGC 1566 and younger than 80 Myr in NGC 2997.


title: On Black Hole Masses and Radio Loudness in AGN

abstract:
  The distribution of radio to optical fluxes in AGN is bimodal. The physical
origin for this bimodality is not understood. In this Letter I describe
observational evidence, based on the Boroson & Green PG quasar sample, that the
radio loudness bimodality is strongly related to the black hole mass (M_BH).
Nearly all PG quasars with M_BH>10^9M_sun are radio loud, while quasars with
M_BH<3x10^8M_sun are practically all radio quiet. This result is consistent
with the dependence of quasar host galaxy morphology on radio loudness. There
is no simple physical explanation for this result, but it may provide a clue on
how jets are formed near massive black holes. The radio loudness--black hole
mass relationship suggests that the properties of various types of AGN may be
largely set by three basic parameters, M_BH, L/L_Eddington, and inclination
angle.