title: The non-stellar infrared continuum of Seyfert galaxies

abstract:
  JHKL'M (1-5 micron) imaging of a sample of Seyfert (Sy) 2 galaxies is
presented. We confirm that the 1-2.2 micron nuclear continuum of some Sy 2s is
dominated by stellar emission, whereas the continuum emission at longer
wavelengths (3-5 micron) is almost entirely non-stellar in origin. The IR
non-stellar spectral energy distributions (SED) (up to 15 micron) of Sy
galaxies show a variety of shapes, and they are well reproduced with the
tapered disk models of Efstathiou & Rowan-Robinson (1995). We have used two
models, one including an optically thin cone component and a coneless model.
Although our modelling of the SEDs does not allow us to favor either model to
account for all the observed SEDs, we find that the viewing angle towards the
central source is well constrained by both models. We have also investigated
non-stellar color-color diagrams. The colors of the Sy galaxies with viewing
angles theta < 30 degree are better reproduced with the cone model. These
diagrams provide a good means to separate Sy 2s with moderate obscuration (A_V
< 20 mag, from hard X-ray observations) from those with high obscuration. The
ground-based 4.8 micron and ISO 9.6 micron luminosities are well correlated
with the hard X-ray luminosities of Sy 1s and 2s. These continuum emissions
appear as a good indicator of the AGN luminosity, at least in the cases of hard
X-ray Compton-thin Sy galaxies. We finally stress the finding that some Compton
thick galaxies show bright non-stellar emission at 5 micron. This suggests that
the near-IR emission in Sys is produced in an extended component illuminated by
the central source, that is more visible from all viewing angles. We discuss
possible implications of mid-IR surveys for the search of counterparts of
highly obscured hard X-ray sources. (Abridged)


title:
Fluctuations in galaxy counts: a new test for homogeneity versus
  fractality

abstract:
  Fractal properties are usually characterized by means of various statistical
tools which deal with spatial average quantities. Here we focus on the
determination of fluctuations around the average counts and we develop a test
for the study of galaxy distribution both in redshift and magnitude space.
Fluctuations in the counts of galaxies, in a fractal distribution, are of the
same order of the average number at all scales as a function of redshift and
magnitude. We point out that the study of these kind of fluctuations can be a
powerful test to understand the nature of galaxy clustering at very large
scales.


title: Destruction of protoplanetary disks in the Orion Nebula Cluster

abstract:
  We use numerical N-body simulations of the Orion Nebula Cluster (ONC) to
investigate the destruction of protoplanetary disks by close stellar encounters
and UV radiation from massive stars. The simulations model a cluster of 4000
stars, and we consider separately cases in which the disks have fixed radii of
100 AU and 10 AU. In the former case, depending on a star's position and orbit
in the cluster over 10^7 years, UV photoevaporation removes at least 0.01 Msol
from its disk, and can remove up to 1 Msol. We find no dynamical models of the
ONC consistent with the suggestion of Storzer and Hollenbach that the observed
distribution and abundance of proplyds could be explained by a population of
stars on radial orbits which spend relatively little time near Theta 1C Ori
(the most massive star in the ONC). Instead the observations require either
massive disks (e.g. a typical initial disk mass of 0.4 Msol) or a very recent
birth for Theta 1C Ori. When we consider the photoevaporation of the inner 10
AU of disks in the ONC, we find that planet formation would be hardly affected.
Outside that region, planets would be prevented from forming in about half the
systems, unless either the initial disk masses were very high or they formed in
less than ~ 2 Myr and Theta 1C Ori has only very recently appeared. We also
present statistics on the distribution of minimum stellar encounter
separations. This peaks at 1000 AU, with less than 10% of stars having had an
encounter closer than 100 AU after 10^7 years. We conclude that stellar
encounters are unlikely to play a significant role in destroying protoplanetary
disks. In the absence of any disruption mechanism other than those considered
here, we would thus predict planetary systems like our own to be common amongst
stars forming in ONC-like environments.


title:
The BMW (Brera-Multiscale-Wavelet) Catalogue of Serendipitous X-ray
  Sources

abstract:
  In collaboration with the Observatories of Palermo and Rome and the SAX-SDC
we are constructing a multi-site interactive archive system featuring specific
analysis tools. In this context we developed a detection algorithm based on the
Wavelet Transform (WT) and performed a systematic analysis of all ROSAT-HRI
public data (~3100 observations +1000 to come). The WT is specifically suitable
to detect and characterize extended sources while properly detecting point
sources in very crowded fields. Moreover, the good angular resolution of HRI
images allows the source extension and position to be accurately determined.
This effort has produced the BMW (Brera Multiscale Wavelet) catalogue, with
more than 19,000 sources detected at the 4.2 sigma level. For each source
detection we have information on the X-ray flux and extension, allowing for
instance to select complete samples of extended X-ray sources such as candidate
clusters of galaxies or SNR's. Here we present an overview of first results
from several undergoing projects which make use of the BMW catalogue.


title: X-ray variability in a complete sample of Soft X-ray selected AGN

abstract:
  We present ROSAT All-Sky Survey and ROSAT pointed observations (PSPC and HRI)
of a complete sample of 113 bright soft X-ray AGN selected from the ROSAT
Bright Source Catalog. We compare these observations in order to search for
extreme cases of flux and spectral X-ray variability - X-ray transient AGN.
Three definite transients and one transient candidate are found.
  The other sources show amplitude variations typically by factors of 2-3 on
timescales of years. We found that the variability strength on timescales of
days is a function of the steepness of the X-ray spectrum: steeper X-ray
objects show stronger variability than flat X-ray spectrum sources. We also
present new HRI measurements of our extreme X-ray transients IC 3599 and
WPVS007. We discuss possible models to explain the X-ray transience and the
variabilities observed in the non-transient sources.


title:
Formation of the Planetary Sequence in a Highly Flattened Disk of
  Frequently Colliding Planetesimals

abstract:
  The kinetic theory is used to study the evolution of the self-gravitating
disk of planetesimals. The effects of frequent collisions between planetesimals
are taken into account by using a Krook integral in the Boltzmann kinetic
equation. It is shown that as a result of an aperiodic collision-dissipative
instability of small gravity disturbances the disk is subdivided into numerous
dense fragments. These can eventually condense into the planetary sequence.


title: The Core-Wing Anomaly of Cool Ap Stars: Abnormal Balmer Profiles

abstract:
  Paper by Cowley et al. The Core-Wing Anomaly Etc. The profiles of H$\alpha$
in a number of cool Ap stars are anomalous. Broad wings, indicative of
temperatures in the range 7000-8000K end abruptly in narrow cores. The widths
of these cores are compatible with those of dwarfs with temperatures of 6000K
or lower. This profile has been known for Przybylski's star, but it is seen in
other cool Ap's. The H$\beta$ profile in several of these stars shows a similar
core-wing anomaly (CWA). In Przybylski's star, the CWA is probably present at
higher Balmer members. We are unable to account for these profiles within the
context of LTE and normal dwarf atmospheres. We conclude that the atmospheres
of these stars are not ``normal.'' This is contrary to a notion that has long
been held.


title: X-ray emission in the direction of the SNR G318.2+0.1

abstract:
  We report the discovery of three X-ray sources within the radio shell
G318.2+0.1, one of which may be extended. Two of the sources were detected
during the \sax Galactic Plane Survey and one was found in archival \ros data.
The fainter \sax source is coincident with an ultra-compact galactic H {\sc ii}
region, and we discuss the possibility that it can be a flaring young stellar
object, while the other \sax source has no obvious counterpart. The PSPC source
is consistent with emission from a foreground star. The hard spectrum of the
brighter \sax source is consistent with a non-thermal origin, although a
thermal nature cannot be formally excluded. If this source is associated with
G318.2+0.1, then its hard spectrum suggests that it may be site of non-thermal
electron acceleration.


title:
Proper motion of very low mass stars and brown dwarfs in the Pleiades
  cluster

abstract:
  We report proper motion measurements for 25 very-low mass (VLM) star and
brown dwarf (BD) candidates of the Pleiades cluster previously identified by
Bouvier et al. (1998). Proper motions are measured with an accuracy of 9
mas/yr, compared to an expected tangential motion of about 50 mas/yr for
Pleiades members. Of the 25 candidates, 15 have a membership probability of 95%
or more and 7 are rejected as being field dwarfs. The 3 remaining candidates
exhibit independent evidence for membership (lithium absorption or long-term
proper motion). From the firm identification of Pleiades VLM and BD members,
the cluster's substellar mass function is revised to dN/dM \propto M^{-0.5} in
the mass range from 0.04 to 0.3 M_solar.


title:
The ROSAT-ESO Flux-Limited X-Ray (REFLEX) Galaxy Cluster Survey III: The
  Power Spectrum

abstract:
  We present a measure of the power spectrum on scales from 15 to 800 Mpc/h
using the ROSAT-ESO Flux-Limited X-Ray(REFLEX) galaxy cluster catalogue. The
REFLEX survey provides a sample of the 452 X-ray brightest southern clusters of
galaxies with the nominal flux limit S=3.0 10^{-12}erg/s/cm2 for the ROSAT
energy band (0.1-2.4)keV. Several tests are performed showing no significant
incompletenesses of the REFLEX clusters with X-ray luminosities brighter than
10^{43}erg/s up to scales of about 800 Mpc/h. They also indicate that cosmic
variance might be more important than previous studies suggest. We regard this
as a warning not to draw general cosmological conclusions from cluster samples
with a size smaller than REFLEX. Power spectra, P(k), of comoving cluster
number densities are estimated for flux- and volume-limited subsamples. The
most important result is the detection of a broad maximum within the comoving
wavenumber range 0.022<k<0.030 h/Mpc. The data suggest an increase of the power
spectral amplitude with X-ray luminosity. Compared to optically selected
cluster samples the REFLEX P(k)is flatter for wavenumbers k<0.05 h/Mpc thus
shifting the maximum of P(k) to larger scales. The smooth maximum is not
consistent with the narrow peak detected at k=0.05 h/Mpc using the Abell/ACO
richness $\ge 0$ data. In the range 0.02<k<0.4 h/Mpc general agreement is found
between the slope of the REFLEX P(k) and those obtained with optically selected
galaxies. A semi-analytic description of the biased nonlinear power spectrum in
redshift space gives the best agreement for low-density Cold Dark Matter models
with or without a cosmological constant.


title: Heating the Quiet Corona by Nanoflares: Evidence and Problems

abstract:
  The content of coronal material in the quiet Sun is not constant as soft
X-ray and high-temperature EUV line observations have shown. New material,
probably heated and evaporated from the chromosphere is occasionally injected
even in the faintest parts above the magnetic network cell interiors. Assuming
that the smaller events follow the pattern of the well observed larger ones, we
estimate the total energy input. Various recent analyses are compared and
discussed. The results using similar EUV data from EIT/SOHO and TRACE basically
agree on the power-law exponent when the same method is used. The most serious
deviations are in the number of nanoflares per energy unit and time unit. It
can be explained only partially by different thresholds for flare detection.


title: BeppoSAX confirmation of beamed afterglow emission from GRB990510

abstract:
  We compare the prompt X-ray (2-10 keV) emission of GRB990510 measured by the
BeppoSAX Wide Field Cameras (WFC) during the burst to the X-ray afterglow
detected by the BeppoSAX Narrow Field Instruments. A single power-law model for
the afterglow, f(t) ~ t^{-1.42}, is ruled out. Provided the initial time of the
afterglow is assumed to coincide with the last short pulse in the X-ray prompt
event (i.e., 72 seconds after the GRB trigger time), the X-ray emission from
\~80 to 10^5 seconds after the GRB trigger is well described by an external
shock expanding in a decelerating jet, in which synchrotron radiation takes
place. This model, represented by a double power-law of indices alpha_1 ~ 1 and
alpha_2 ~ 2 before and after a jet collimation break time of ~0.5 days after
GRB, respectively, is consistent with the second and third upper limits
measured by the WFC, but not with the first. This may be related to
inhomogeneities in the circumburst medium. Our finding indicates that the
temporal behavior of the GRB990510 X-ray afterglow is similar to that at
optical wavelengths, and thus strengthens the interpretation of the
multiwavelength afterglow as synchrotron emission in a jet with decreasing
Lorentz factor. GRB990510 is thus the only burst in which evidence of a
spreading jet has been found in X-rays.


title:
On the use of a heterogeneous MIMD-SIMD platform to simulate the
  dynamics of globular clusters with a central massive object

abstract:
  The dynamics of a large stellar (globular) cluster containing N=128,000 stars
has been simulated by a direct summation (O(N$^2$)) method by using a
heterogeneous platform. Preliminary simulations have been carried out on model
systems with and without the presence, in their center of mass, of a black hole
whose mass has been varied from 0.02 to 0.1 times the total mass of the
cluster. These simulations followed the evolution of the globular cluster in
order to describe its dynamics over an interval of time sufficiently large
respect to the internal crossing time. Computations have demonstrated that the
platform heterogeneity, allowing a very efficient use of the computational
resources, can be considered a key feature for sustaining large computational
loads. Our results show that the massive object in the center of the cluster
alters the surrounding star distribution very quickly; the following evolution
is much slower as it occurs via two-body collisional relaxation.


title: Lost and Found: The Damped Lyman Alpha Absorbers in the QSO OI 363

abstract:
  The galaxy giving rise to the damped Ly$\alpha$ absorbing system in the QSO
OI 363 with z=0.221 has been found. A galaxy which is probably associated with
the second DLA in this same QSO at z=0.0912 has also been found. Neither galaxy
is very luminous, and neither galaxy shows signs of extensive current star
formation, a massive disk or lots of gas. The impact parameters for each of the
two galaxies with respect to the QSO are reasonable. If most DLA absorbers
arise in such low luminosity galaxies, it will be difficult to pick out the
correct galaxy giving rise to DLA systems at high redshift within the large
projected areal density on the sky of faint galaxies around distant QSOs.


title:
Optical Surface Photometry of a Sample of Disk Galaxies. II Structural
  Components

abstract:
  This work presents the structural decomposition of a sample of 11 disk
galaxies, which span a range of different morphological types. The U, B, V, R,
and I photometric information given in Paper I (color and color-index images
and luminosity, ellipticity, and position-angle profiles) has been used to
decide what types of components form the galaxies before carrying out the
decomposition. We find and model such components as bulges, disks, bars, lenses
and rings.


title: Chandra--ASCA--RXTE observations of the micro-quasar GRS 1915+105

abstract:
  A Chandra AO1 30ks HETGS observation of the X-ray transient micro-quasar GRS
1915+105 reveals absorption edges and faint line emission over the HETG energy
range. We find from a preliminary analysis evidence for prominent neutral K
edges associated with iron, silicon, magnesium, and tentatively sulphur. The
column densities assuming solar abundances are consistent with ~ few x $10^{22}
cm^{-2}$ in excess of the Galactic value, and may point to surrounding cold
material associated with GRS 1915+105. Neutral Fe K$\alpha$ emission, and
ionized absorption from Fe XXV and Fe XXVI are resolved. We limit our
discussion to the Chandra results.


title: The inverse cascade in turbulent dynamos

abstract:
  The emergence of a large scale magnetic field from randomly forced isotropic
strongly helical flows is discussed in terms of the inverse cascade of magnetic
helicity and the alpha-effect. In simulations of such flows the maximum field
strength exceeds the equipartition field strength for large scale separation.
However, helicity conservation controls the speed at which this final state is
reached. In the presence of open boundaries magnetic helicity fluxes out of the
domain are possible. This reduces the timescales of the field growth, but it
also tends to reduce the maximum attainable field strength.


title: Direct N-body Modelling of Stellar Populations: Blue Stragglers in M67

abstract:
  We present a state-of-the-art N-body code which includes a detailed treatment
of stellar and binary evolution as well as the cluster dynamics. This code is
ideal for investigating all aspects relating to the evolution of star clusters
and their stellar populations. It is applicable to open and globular clusters
of any age. We use the N-body code to model the blue straggler population of
the old open cluster M67. Preliminary calculations with our binary population
synthesis code show that binary evolution alone cannot explain the observed
numbers or properties of the blue stragglers. On the other hand, our N-body
model of M67 generates the required number of blue stragglers and provides
formation paths for all the various types found in M67. This demonstrates the
effectiveness of the cluster environment in modifying the nature of the stars
it contains and highlights the importance of combining dynamics with stellar
evolution. We also perform a series of N = 10000 simulations in order to
quantify the rate of escape of stars from a cluster subject to the Galactic
tidal field.


title:
Eccentric Nuclear Disks with Self Gravity: Predictions for the Double
  Nucleus of M31

abstract:
  We present a method for constructing models of weakly self-gravitating,
finite dispersion eccentric stellar disks around central black holes. The disk
is stationary in a frame rotating at a constant precession speed. The stars
populate quasiperiodic orbits whose parents are numerically integrated periodic
orbits in the total potential. We approximate the quasiperiodic orbits by
distributions of Kepler orbits dispersed in eccentricity and orientation, using
an approximate phase space distribution function written in terms of the Kepler
integrals of motion. We show an example of a model with properties similar to
those of the double nucleus of M31. The properties of our models are primarily
determined by the behavior of the periodic orbits. Self-gravity in the disk
causes these orbits to assume a characteristic radial eccentricity profile,
which gives rise to distinctive multi-peaked line-of-sight velocity
distributions (LOSVDs) along lines of sight near the black hole. The
multi-peaked features should be observable in M31 at the resolution of STIS.
These features provide the best means of identifying an eccentric nuclear disk
in M31, and can be used to constrain the disk properties and black hole mass.


title: A Search for CO in the Local Group Dwarf Irregular Galaxy WLM

abstract:
  We present 12CO J = 1-0 and J = 2-1 observations of the low metallicity (12 +
log(O/H) = 7.74) Local Group dwarf irregular galaxy WLM made with the 15 m SEST
and 14 m FCRAO telescopes. Despite the presence a number of HII regions, we
find no CO emission. We obtain low upper limits on the integrated intensity
(I(CO) >= 0.18 K km/s for CO (1-0)). The non-detection is consistent with the
result of Taylor, Kobulnicky and Skillman (1998), that dwarf galaxies below a
metallicity of ~ 7.9 are not detected in CO emission. WLM shows that this trend
continues for low metallicity galaxies even as their metallicities approach
7.9. These results are consistent with the models of the metal poor ISM by
Norman and Spaans (1997). By comparing our CO data with observations of star
formation in WLM, we find evidence for a high CO to H$_2$ conversion factor.


title: Gas motions in the plane of the spiral galaxy NGC 3631

abstract:
  The velocity field of the nearly face-on galaxy NGC 3631, derived from
observations in the H alpha line and the HI radio line, is analysed to study
perturbations related to the spiral structure of the galaxy. We confirm our
previous conclusion that the line-of-sight velocity field gives evidence of the
wave nature of the observed two-armed spiral structure. Fourier analysis of the
observed velocity field is used to determine the location of corotation of the
spiral structure of this galaxy, and the radius of corotation R_c is found to
be about 42 arcsec, or 3.2 kpc. The vector velocity field of the gas in the
plane of the disc is restored, and taking into account that we previously
investigated vertical motions, we now have a full 3D gaseous velocity field of
the galaxy. We show clear evidence of the existence of two anticyclonic and
four cyclonic vortices near corotation in a frame of reference rotating with
the spiral pattern. The centres of the anticyclones lie between the observed
spiral arms. The cyclones lie close to the observed spirals, but their centres
are shifted from the maxima in brightness.


title:
The Effect of Formation Redshifts on the Cluster Mass-Temperature
  Relation

abstract:
  I employ an ensemble of hydrodynamical simulations and the XSPEC MEKAL
emission model to reproduce observable spectral and flux-weighted temperatures
for 24 clusters. Each cluster is imaged at 16 points in its history, which
allows the investigation of evolutionary effects on the mass-temperature
relation. In the zero redshift scaling relations, I find no evidence for a
relationship between cluster temperature and formation epoch for those clusters
which acquired 75% of their final mass since a redshift of 0.6. This result
holds for both observable and intrinsic intracluster medium temperatures, and
implies that halo formation epochs are not an important variable in analysis of
observable cluster temperature functions.


title:
Precession of Magnetically Driven Warped Disks and Low-Frequency QPOs in
  Low-Mass X-Ray Binaries

abstract:
  An accretion disk around a rotating magnetized star is subjected to magnetic
torques which induce disk warping and precession. These torques arise from
interactions between the stellar field and the induced surface currents on the
disk. Applying these new effects to weakly magnetized ($B\sim 10^7-10^9$G)
neutron stars in low-mass X-ray binaries, we study the global hydrodynamical
warping/precession modes of the disk under the combined influences of
relativistic frame dragging, classical precession due to the oblateness of the
neutron star, and the magnetic torques. Under quite general conditions, the
magnetic warping torque can overcome the ``Bardeen-Petterson'' viscous damping
and makes the modes grow. The modes are confined to the inner region of the
disk, and have frequencies close to the sum of the Lense-Thirring frequency,
the classical precession frequency, and the magnetically driven precession
frequency evaluated at the inner disk radius $r_{in}$. As $\dot M$ increases,
the mode frequency is reduced relative to the total precession frequency at
$r_{in}$ since the mode is less concentrated around $r_{in}$ due to the
increasing viscous stress associated with the large $\dot M$. Because of this,
and because the magnetically driven precession is retrograde and depends
strongly on $\dot M$, the mode frequency can have a non-monotonic dependence on
$\dot M$. This may account for several observed features of low-frequency
(10--60 Hz) quasi-periodic oscillations (LFQPOs) in low-mass X-ray binaries
which are otherwise difficult to explain, such as the flattening/turnover in
the LFQPO frequency--$\dot M$ correlation or in the LFQPO frequency--kHz QPO
frequency correlation (e.g., as seen clearly in GX 17+2).


title: The Stanford Cluster Search for Distant Galaxy Clusters

abstract:
  We describe the scientific motivation behind, and the methodology of, the
Stanford Cluster Search (StaCS), a program to compile a catalog of optically
selected clusters of galaxies at intermediate and high (0.3 < z < 1) redshifts.
The clusters are identified using an matched filter algorithm applied to deep
CCD images covering approximately 60 square degrees of sky. These images are
obtained from several data archives, principally that of the Berkeley Supernova
Cosmology Project of Perlmutter et al. Potential clusters are confirmed with
spectroscopic observations at the 9.2 m Hobby-Eberly Telescope. Follow-up
observations at optical, sub-mm, and X-ray wavelengths are planned in order to
estimate cluster masses. Our long-term scientific goal is to measure the
cluster number density as a function of mass and redshift, which is sensitive
to the cosmological density parameter, and the amplitude of density
fluctuations on cluster scales. Our short-term goals are the detection of
high-redshift cluster candidates over a broad mass range and the measurement of
evolution in cluster scaling relations. The combined data set will contain
clusters ranging over an order of magnitude in mass, and allow constraints on
these parameters accurate to ~10%. We present our first spectroscopically
confirmed cluster candidates and describe how to access them electronically.


title: How to measure CMB polarization power spectra without losing information

abstract:
  We present a method for measuring CMB polarization power spectra given
incomplete sky coverage and test it with simulated examples such as Boomerang
2001 and MAP. By augmenting the quadratic estimator method with an additional
step, we find that the E and B power spectra can be effectively disentangled on
angular scales substantially smaller than the width of the sky patch in the
narrowest direction. We find that the basic quadratic and maximum-likelihood
methods display a unneccesary sensitivity to systematic errors when T-E
cross-correlation is involved, and show how this problem can be eliminated at
negligible cost in increased error bars. We also test numerically the widely
used approximation that sample variance scales inversely with sky coverage, and
find it to be an excellent approximation on scales substantially smaller than
the sky patch.


title: The Starburst-AGN Connection

abstract:
  The issue of a starburst-AGN connection in local and distant galaxies is
relevant for understanding galaxy formation and evolution, the star formation
and metal enrichment history of the universe, the origin of the extragalactic
background at low and high energies, and the origin of nuclear activity in
galaxies. Here I review some of the observational evidence recently brought
forward in favor of a connection between the starburst and AGN phenomena. I
conclude by raising a number of questions concerning the exact nature of this
connection.


title: Neutrino Emission from Neutron Stars

abstract:
  We review the main neutrino emission mechanisms in neutron star crusts and
cores. Among them are the well-known reactions such as the electron-positron
annihilation, plasmon decay, neutrino bremsstrahlung of electrons colliding
with atomic nuclei in the crust, as well as the Urca processes and neutrino
bremsstrahlung in nucleon-nucleon collisions in the core. We emphasize recent
theoretical achievements, for instance, band structure effects in neutrino
emission due to scattering of electrons in Coulomb crystals of atomic nuclei.
We consider the standard composition of matter (neutrons, protons, electrons,
muons, hyperons) in the core, and also the case of exotic constituents such as
the pion or kaon condensates and quark matter. We discuss the reduction of the
neutrino emissivities by nucleon superfluidity, as well as the specific
neutrino emission produced by Cooper pairing of the superfluid particles. We
also analyze the effects of strong magnetic fields on some reactions, such as
the direct Urca process and the neutrino synchrotron emission of electrons. The
results are presented in the form convenient for practical use. We illustrate
the effects of various neutrino reactions on the cooling of neutron stars. In
particular, the neutrino emission in the crust is critical in setting the
initial thermal relaxation between the core and the crust. Finally, we discuss
the prospects of exploring the properties of supernuclear matter by confronting
cooling simulations with observations of the thermal radiation from isolated
neutron stars.


title: Jet directions in Seyfert galaxies: Radio continuum imaging data

abstract:
  We present the results of VLA A-array 8.46 GHz continuum imaging of 55
Seyfert galaxies (19 Seyfert 1's and 36 Seyfert 2's). These galaxies are part
of a larger sample of 88 Seyfert galaxies, selected from mostly isotropic
properties, the flux at 60 mum and warm infrared 25 mum to 60 mum colors. These
images are used to study the structure of the radio continuum emission of these
galaxies and their position angles, in the case of extended sources. These
data, combined with information from broad-band B and I observations, have been
used to study the orientation of radio jets relative to the plane of their host
galaxies (Kinney et al. 2000).


title: Blazars in Low-Luminosity and Radio-Weak AGN?

abstract:
  Typical blazars seem to be associated with FR I and FR II radio galaxies and
radio-loud quasars. However, what happens at lower powers? Do blazars exist in
low-luminosity AGN or do they exist in radio-quiet AGN? A recent detection of
superluminal motion in a supposedly radio-quiet Seyfert raises the question
whether beaming can play an important role in some of these objects as well.
Moreover, VLBI observations of nearby low-luminosity AGN reveal compact
flat-spectrum radio cores very similar to those in bright radio-loud blazars.
Furthermore, with the detection of X-ray emission from the least luminous AGN
we can study, Sgr A* in the Galactic Center, this source now seems to be
dominated entirely by non-thermal emission -- like in BL Lacs. The same may be
true for some X-ray binaries in the Low/Hard-state. Inclusion of low-power
radio jets into the overall picture of AGN provides some clues for what type of
accretion is important, what the power, radiative efficiency and matter-content
of jets is, and what mechanism could be responsible for making jets radio-loud.
We specifically discuss whether proton-proton collisions in a hot accretion
flow could provide the switch for the radio-dichotomy.


title: Spectra and power of blazar jets

abstract:
  The spectra of blazars form a sequence which can be parametrized in term of
their observed bolometric luminosity. At the most powerful extreme of the
sequence we find objects whose jet power can rival the power extracted by
accretion, while at the low power end of the sequence we find TeV and TeV
candidate blazars, whose spectral properties can give information on the
particle acceleration mechanism and can help to measure the IR background. Most
of the emission of blazars is produced at a distance of few hundreds
Schwarzschild radii from the center, and must be a small fraction of the
kinetic power carried by the jet itself: most of the jet energy must be
transported outwards, to power the extended radio structures. The radiation
produced by jets can be the result of internal shocks between shells of plasma
with different bulk Lorentz factors. This mechanism, thought to be at the
origin of the gamma-rays observed in gamma-ray bursts, can work even better in
blazars, explaining the observed main characteristics of these objects. Chandra
very recently discovered large scale X-ray jets both in blazars and in
radio-galaxies, which can be explained by enhanced Compton emission with
respect to a pure synchrotron self Compton model. In fact, besides the local
synchrotron emission, the radiation coming from the sub-pc jet core and the
cosmic background radiation can provide seed photons for the scattering
process, enahancing the large scale jet X-ray emission in radio-galaxies and
blazars, respectively.


title: The Nuclei of Nearby Radio-Loud Ellipticals

abstract:
  We have observed a complete sample of 21 nearby (D < 70h^{-1} Mpc) Fanaroff &
Riley Type I galaxies with HST/WFPC2 and detected dust disks and lanes in 19 of
them. The radio jets are roughly perpendicular to the dust which is used to
constrain the Doppler boosting factors of the radio jet and cores. The VLBA
core flux correlates with the central Halpha+[NII] flux which might indicate
that the VLBA core is dominated by an isotropic component. Twelve galaxies show
nuclear optical sources. We discuss various possible origins for this emission.


title: A multi-frequency study of the radio galaxy NGC326

abstract:
  We present preliminary results of a multi-frequency study of the inversion
symmetric radio galaxy NGC326 based on VLA observations at 1.4, 1.6, 4.8, 8.5,
and 14.9 GHz. These data allow us to investigate in detail the morphological,
spectral and polarization properties of this peculiar object at different
levels of spatial resolution.


title:
Potential Sources of Gravitational Wave Emission and Laser Beam
  Interferometers

abstract:
  The properties of potential gravitational wave sources like neutron stars,
black holes and binary systems are reviewed, as well as the different
contributions (stochastic and continuous) to the gravitational wave background.
The detectability of these sources by the present generation of laser beam
interferometers, which will be fully operational around 2002, is also
considered.


title: Chandra Grating Spectroscopy of the Seyfert Galaxy Ton S180

abstract:
  This paper presents results from spectral observations of Ton S180 using
Chandra and ASCA. The data confirm the presence of the soft excess but the
Chandra LETG spectrum reveals it to be broad and smooth, rather than resolved
into individual emission lines. This excess may represent either a primary or
reprocessed continuum component or a blend of broad lines from an ionized
accretion disk. The occurrence of a similar feature in five other NLSy1s leads
us to conclude that this soft X-ray component may be a characteristic of
sources accreting at a very high rate. The X-ray spectrum shows no evidence for
absorption lines, indicating that if gas exists in the line-of-sight then it is
in a very high ionization-state or has an extremely broad velocity
distribution. The new ASCA data confirm that the narrow component of the Fe
Kalpha line peaks close to a rest-energy of 7 keV, indicating the presence of a
significant amount of highly-ionized material in the nuclear environs.


title: Mapping the Dynamics of the Quasar 3C 48

abstract:
  The archetypical, nearby (z=0.37) quasar 3C 48 is an unusual CSS radio source
with excess far-IR emission, whose one-sided radio jet is aligned with the
extended ionized emission and a putative second nucleus. Because of its high
AGN luminosity and proximity, 3C 48 is a good candidate to search for kinematic
signatures of the radio jet-gas coupling and/or of a recent interaction. The
radio morphology and our ground-based integral field spectroscopy suggest that
the jet is interacting with its immediate environment. Using STIS aboard HST in
several slit positions within the central 1", we map the kinematics and
physical conditions of the extended emission line gas and their relations to
near-nuclear star forming regions found in existing HST images.


title: A radio and optical study of Molonglo radio sources

abstract:
  We present multi-wavelength radio observations with the Very Large Array and
narrow- and broad-band optical observations with the 2.5m telescope at the Las
Campanas Observatory, of a well-defined sample of high-luminosity
Fanaroff-Riley class II radio galaxies and quasars, selected from the Molonglo
Reference Catalogue 1-Jy sample. These observations were carried out as part of
a programme to investigate the effects of orientation and environment on some
of the observed properties of these sources. We examine the dependence of the
Liu-Pooley relationship, which shows that radio lobes with flatter radio
spectra are less depolarized, on size, identification and redshift, and show
that it is significantly stronger for smaller sources, with the strength of the
relationship being similar for both radio galaxies and quasars. In addition to
Doppler effects, there appears to be intrinsic differences between the lobes on
opposite sides. We discuss the asymmetry in brightness and location of the
hotspots, and present estimates of the ages and velocities from matched
resolution observations at L- and C-bands. The narrow- and broad-band optical
images of some of these sources were made to study their environments and
correlate with the symmetry parameters. Extended emission-line region is seen
in a quasar and in four of the objects, possible companion galaxies are seen
close to the radio axis.


title:
Theoretical predictions for the cold part of the colliding wind
  interaction zone

abstract:
  We present 2D and 3D hydrodynamical simulations of the colliding wind
interaction zone in WR+O binaries. It is shown that 3D effects can basically
explain certain observed, orbit dependent flux variations. Possible connections
between the interior structure of the interaction zone and dust formation are
outlined and its stability is re-investigated.


title: Theoretical considerations on colliding clumped winds

abstract:
  First attempts are made to derive astrophysical implications of the collision
of clumped stellar winds from order of magnitude estimates and preliminary
numerical simulations. Compared to colliding smooth winds, we find that the
most significant differences occur in widely separated systems like WR 140.
Clumped winds de-stabilize the wind-wind interaction zone of such systems.
Highly compressed, cold knots of WR-wind material can form. Hydrogen rich
material is likely to be mixed into these knots by the excited turbulence. Such
knots, therefore, are good candidates to form dust. We briefly discuss to what
degree our results can be applied to other systems and look at different
possibilities for the origin and nature of the inhomogeneities in hot star
winds.


title:
Systematic Errors in the Estimation of Black Hole Masses by
  Reverberation Mapping

abstract:
  The mass of the central black hole in many active galactic nuclei has been
estimated on the basis of the assumption that the dynamics of the broad
emission line gas are dominated by the gravity of the black hole. The most
commonly-employed method is to estimate a characteristic size-scale $r_*$ from
reverberation mapping experiments and combine it with a characteristic velocity
$v_*$ taken from the line profiles; the inferred mass is then estimated by $r_*
v_*^2/G$. We critically discuss the evidence supporting the assumption of
gravitational dynamics and find that the arguments are still inconclusive. We
then explore the range of possible systematic error if the assumption of
gravitational dynamics is granted. Inclination relative to a flattened system
may cause a systematic underestimate of the central mass by a factor $\sim
(h/r)^2$, where $h/r$ is the aspect ratio of the flattening. The coupled
effects of a broad radial emissivity distribution, an unknown angular radiation
pattern of line emission, and sub-optimal sampling in the reverberation
experiment can cause additional systematic errors as large as a factor of 3 or
more in either direction.


title:
Helium contamination from the progenitor stars of planetary nebulae: The
  He/H radial gradient and the Delta Y/Delta Z enrichment ratio

abstract:
  In this work, two aspects of the chemical evolution of 4He in the Galaxy are
considered on the basis of a sample of disk planetary nebulae (PN). First, an
application of corrections owing to the contamination of 4He from the evolution
of the progenitor stars shows that the He/H abundance by number of atoms is
reduced by 0.012 to 0.015 in average, leading to an essentially flat He/H
radial distribution. Second, a determination of the helium to heavy element
enrichment ratio using the same corrections leads to values in the range 2.8 <
Delta Y/Delta Z < 3.6 for Yp = 0.23 and 2.0 < Delta Y/Delta Z < 2.8 for Yp =
0.24, in good agreement with recent independent determinations and theoretical
models.


title: Evolution of a Neutron Star From its Birth to Old Age

abstract:
  The main stages in the evolution of a neutron star, from its birth as a
proto-neutron star, to its old age as a cold, catalyzed configuration, are
described. A proto-neutron star is formed in the aftermath of a successful
supernova explosion and its evolution is dominated by neutrino diffusion. Its
neutrino signal is a valuable diagnostic of its internal structure and
composition. During its transformation from a hot, lepton-rich to a cold,
catalyzed remnant, the possibility exists that it can collapse into a black
hole, which abruptly terminates neutrino emissions. The essential microphysics,
reviewed herein, that controls its evolution are the equation of state of dense
matter and its associated neutrino opacities. Several simulations of the
proto-neutron star evolution, involving different assumptions about the
composition of dense matter, are described. After its evolution into a nearly
isothermal neutron star a hundred or so years after its birth, it may be
observable through its thermal emission in X-rays during its life in the next
million years. Its surface temperature will depend upon the rapidity of
neutrino emission processes in its core, which depends on the composition of
dense matter and whether or not its constituents exhibit superfluidity and
superconductivity. Observations of thermal emission offer the best hope of a
determination of the radius of a neutron star. The implications for the
underlying dense matter equation of state of an accurate radius determination
are explored.


title:
Dynamical variations of the differential rotation in the solar
  convection zone

abstract:
  Recent analyses of helioseismological observations seem to suggest the
presence of two new phenomena connected with the dynamics of the solar
convective zone. Firstly, there are present torsional oscillations with periods
of about 11 years, which penetrate significantly into the solar convection zone
and secondly, oscillatory regimes exist near the base of the convection which
are markedly different from those observed near the top, having either
significantly reduced periods or being non-periodic.
  Recently spatiotemporal fragmentation/bifurcation has been proposed as a
possible dynamical mechanism to account for such observed multi-mode behaviours
in different parts of the solar convection zone. Evidence for this scenario was
produced in the context of an axisymmetric mean field dynamo model operating in
a spherical shell, with a semi-open outer boundary condition and a zero order
angular velocity obtained by the inversion of the MDI data, in which the only
nonlinearity was the action of the Lorentz force of the dynamo generated
magnetic field on the solar angular velocity.
  Here we make a detailed study of the robustness of this model with respect to
plausible changes to its main ingredients, including changes to the alpha and
eta profiles as well as the inclusion of a nonlinear alpha quenching. We find
that spatiotemporal fragmentation is present in this model for different
choices of the rotation data and as the details of the model are varied. Taken
together, these results give strong support to the idea that spatiotemporal
fragmentation is likely to occur in general dynamo settings.


title:
Chemical equilibrium and stable stratification of a multi-component
  fluid: thermodynamics and application to neutron stars

abstract:
  A general thermodynamic argument shows that multi-component matter in full
chemical equilibrium, with uniform entropy per baryon, is generally stably
stratified. This is particularly relevant for neutron stars, in which the
effects of entropy are negligible compared to those of the equilibrium
composition gradient established by weak interactions. It can therefore be
asserted that, regardless of the uncertainties in the equation of state of
dense matter, neutron stars are stably stratified. This has important,
previously discussed consequences for their oscillation modes, magnetic field
evolution, and internal angular momentum transport.

categories: astro-ph gr-qc physics.ao-ph physics.flu-dyn


title: Quintessence and the Separation of CMB Peaks

abstract:
  We propose that it should be possible to use the CMB to discriminate between
dark energy models with different equations of state, including distinguishing
a cosmological constant from many models of quintessence. The separation of
peaks in the CMB anisotropies can be parametrised by three quantities: the
amount of quintessence today, the amount at last scattering, and the averaged
equation of state of quintessence. In particular, we show that the CMB peaks
can be used to measure the amount of dark energy present before last
scattering.


title:
A Search for the Damped Ly-alpha Absorber at z=1.86 toward QSO 1244+3443
  with NICMOS

abstract:
  We have carried out a high-resolution imaging search for the galaxy
associated with the damped Lyman-alpha (DLA) absorber at z=1.859 toward the
z_{em}=2.48 quasar QSO 1244+3443, using the HST and the NICMOS. Images were
obtained in the broad filter F160W and the narrow filter F187N with camera 2 on
NICMOS with the goal of detecting the rest-frame optical continuum and the
H-alpha line emission from the DLA. After PSF subtraction, two weak features
are seen at projected separations of 0.16-0.24" from the quasar. Parts of these
features may be associated with the DLA absorber, although we cannot completely
rule out that they could be artifacts of the point spread function (PSF). If
associated with the DLA, the objects would be ~1-2 h_{70}^{-1} kpc in size with
integrated flux densities of 2.5 and 3.3 mu Jy in the F160W filter, implying
luminosities at lambda_{central}=5600 A in the DLA rest frame of 4.4-5.9 x
10^{9} h_{70}^{-2} L_{solar} at z=1.86, for q0=0.5. However, no significant
H-alpha line emission is seen from these objects, suggesting low star formation
rates (SFRs). Our 3 sigma upper limit on the SFR in the DLA is 1.3 h_{70}^{-2}
M_{solar}/yr for q0 = 0.5 (2.4 h_{70}^{-2} M_{solar} yr^{-1} for q0 = 0.1).
This together with our earlier result for LBQS 1210+1731 mark a significant
improvement over previous constraints on the star formation rates of DLAs. A
combination of low SFR and some dust extinction is likely to be responsible for
the lack of H-alpha emission. Alternatively, the objects, may be associated
with the quasar host galaxy. In any case, our observations suggest that the DLA
is not a large bright proto-disk, but a compact object or a low-surface
brightness galaxy. If the two features are PSF artifacts then the constraints
on DLA properties are even more severe.


title: Constraining Isocurvature Perturbations with CMB Polarization

abstract:
  The role of cosmic microwave background (CMB) polarisation data in
constraining the presence of primordial isocurvature modes is examined. While
the MAP satellite mission will be unable to simultaneously constrain
isocurvature modes and cosmological parameters, the PLANCK mission will be able
to set strong limits on the presence of isocurvature modes if it makes a
precise measurement of the CMB polarisation sky. We find that if we allow for
the possible presence of isocurvature modes, the recently obtained BOOMERANG
measurement of the curvature of the universe fails. However, a comparably
sensitive polarisation measurement on the same angular scales will permit a
determination of the curvature of the universe without the prior assumption of
adiabaticity.


title:
Ultraviolet and Optical Observations of OB Associations and Field Stars
  in the Southwest Region of the Large Magellanic Cloud

abstract:
  Using photometry from the Ultraviolet Imaging Telescope (UIT) and photometry
and spectroscopy from three ground-based optical datasets we have analyzed the
stellar content of OB associations and field areas in and around the regions N
79, N 81, N 83, and N 94 in the LMC. We compare data for the OB association
Lucke-Hodge 2 (LH 2) to determine how strongly the initial mass function (IMF)
may depend on different photometric reductions and calibrations. We also
correct for the background contribution of field stars, showing the importance
of correcting for field star contamination in determinations of the IMF of star
formation regions. It is possible that even in the case of an universal IMF,
the variability of the density of background stars could be the dominant factor
creating the differences between calculated IMFs for OB associations.
  We have also combined the UIT data with the Magellanic Cloud Photometric
Survey to study the distribution of the candidate O-type stars in the field. We
find a significant fraction, roughly half, of the candidate O-type stars are
found in field regions, far from any obvious OB associations. These stars are
greater than 2 arcmin (30 pc) from the boundaries of existing OB associations
in the region, which is a distance greater than most O-type stars with typical
dispersion velocities will travel in their lifetimes. The origin of these
massive field stars (either as runaways, members of low-density star-forming
regions, or examples of isolated massive star formation) will have to be
determined by further observations and analysis.


title: Difference Image Analysis of the OGLE-II Bulge Data. I. The Method

abstract:
  I present an implementation of the difference image photometry based on the
Alard & Lupton optimal PSF matching algorithm. The most important feature
distinguishing this method from the ones using Fourier divisions is that
equations are solved in real space and the knowledge of each PSF is not
required for determination of the convolution kernel. I evaluate the method and
software on 380 GB of OGLE-II bulge microlensing data obtained in 1997--1999
observing seasons. The error distribution is Gaussian to better than 99% with
the amplitude only 17% above the photon noise limit for faint stars. Over the
entire range of the observed magnitudes the resulting scatter is improved by a
factor of 2--3 compared to DoPhot photometry, currently a standard tool in
microlensing searches. For testing purposes the photometry of ~4600 candidate
variable stars and sample difference image data are provided for BUL_SC1 field.
In the candidate selection process, very few assumptions have been made about
the specific types of flux variations, which makes this data set well suited
for general variability studies, including the development of the
classification schemes.


title:
Optical Gravitational Lensing Experiment. OGLE 2000-BUL-43: A
  Spectacular Ongoing Parallax Microlensing Event. Difference Image Analysis

abstract:
  We present the photometry and theoretical models for a Galactic bulge
microlensing event OGLE-2000-BUL-43. The event is very bright with I=13.54 mag,
and has a very long time scale, t_E=156 days. The long time scale and its light
curve deviation from the standard shape strongly suggest that it may be
affected by the parallax effect. We show that OGLE-2000-BUL-43 is the first
discovered microlensing event, in which the parallax distortion is observed
over a period of 2 years. Difference Image Analysis (DIA) using the PSF
matching algorithm of Alard & Lupton enabled photometry accurate to 0.5%. All
photometry obtained with DIA is available electronically. Our analysis
indicates that the viewing condition from a location near Jupiter will be
optimal and can lead to magnifications ~ 50 around January 31, 2001. These
features offer a great promise for resolving the source (a K giant) and
breaking the degeneracy between the lens parameters including the mass of the
lens, if the event is observed with the imaging camera on the Cassini space
probe.


title: Observations of YSO Circumstellar Discs

abstract:
  We present the results of short baseline interferometry observations at
submillimetre wavelengths, using a two-element interferometer comprising the
JCMT and CSO, of circumstellar discs around young YSOs. We model data for the
Class 0 protostar IRAS03282 and the Class I protostar L1709B with discs and
compare them with previously published results. We find evidence for the ratio
of the disc mass to envelope mass to increase as the objects evolve.


title: First Results from the SPICES Survey

abstract:
  We present first results from SPICES, the Spectroscopic, Photometric,
Infrared-Chosen Extragalactic Survey. SPICES is comprised of four ~30 square
arcminute high Galactic latitude fields with deep BRIzJK imaging reaching
depths of ~25th magnitude (AB) in the optical and ~23rd magnitude (AB) in the
near-infrared. To date we have 626 spectroscopic redshifts for
infrared-selected SPICES sources with K<20 (Vega). The project is poised to
address galaxy formation and evolution to redshift z~2. We discuss initial
results from the survey, including the surface density of extremely red objects
and the fraction of infrared sources at z>1. One of the SPICES fields has been
the target of a deep 190 ksec Chandra exposure; we discuss initial results from
analysis of that data set. Finally, we briefly discuss a successful campaign to
identify high-redshift sources in the SPICES fields.


title: On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium

abstract:
  The abundance of both amorphous and crystalline silicates in very small
grains is limited by the fact that the 10 micron silicate emission feature is
not detected in the diffuse ISM. On the basis of the observed IR emission
spectrum for the diffuse ISM, the observed ultraviolet extinction curve, and
the 10 micron silicate absorption profile, we obtain upper limits on the
abundances of ultrasmall (a < 15 Angstrom) amorphous and crystalline silicate
grains.
  Contrary to previous work, as much as ~20% of interstellar Si could be in a <
15 Angstrom silicate grains without violating observational constraints. Not
more than ~5% of the Si can be in crystalline silicates (of any size).


title:
Magnetic field effects on the thermonuclear combustion front of
  Chandrasekhar mass white dwarfs

abstract:
  The explosion of a type Ia supernova starts in a white dwarf as a laminar
deflagration at the center of the star and soon several hydrodynamic
instabilities, in particular, the Rayleigh-Taylor instability, begin to act. A
cellular stationary combustion and a turbulent combustion regime are rapidly
achieved by the flame and maintained up to the end of the so-called flamelet
regime when the transition to detonation is believed to occur. The burning
velocity at these regimes is well described by the fractal model of combustion.
Using a semi-analytic approach, we describe the effect of magnetic fields on
the fractalization of the front considering a white dwarf with a nearly dipolar
magnetic field. We find an intrinsic asymmetry on the velocity field that may
be maintained up to the free expansion phase of the remnant. Considering the
strongest values inferred for a white dwarf's magnetic fields with strengths up
to $10^{8}-10^{9}$ G at the surface and assuming that the field near the centre
is roughly 10 times greater, asymmetries in the velocity field higher than
$10-20 %$ are produced between the magnetic polar and the equatorial axis of
the remnant which may be related to the asymmetries found from recent
spectropolarimetric observations of very young SN Ia remnants. Dependence of
the asymmetry with white dwarf composition is also analyzed.

categories: astro-ph physics.comp-ph physics.plasm-ph quant-ph


title: Global Constraints On Key Cosmological Parameters

abstract:
  Data from Type Ia supernovae, along with X-ray cluster estimates of the
universal baryon fraction and Big Bang Nucleosynthesis (BBN) determinations of
the baryon-to-photon ratio, are used to provide estimates of several global
cosmological parameters at epochs near zero redshift. We show that our estimate
of the present baryon density is in remarkably good agreement with that
inferred from BBN at high redshift, provided the primordial abundance of
deuterium is relatively low and the Universe is flat. We also compare these
estimates to the baryon density at z = 1100 as inferred from the CMB angular
power spectrum.


title: Deep HST Imaging of IC 1613. I. Variable Stars and Distance

abstract:
  We present WFPC2 VI photometry of a field in the halo of IC 1613, finding 13
RR Lyraes and 11 Cepheids. Our photometry of the red giant branch tip and red
clump is used to derive distances to IC 1613, which are consistent with each
other and with distances based on the variable stars. We compare these values
with similarly-measured distances for the Magellanic Clouds, and are able to
measure metallicity dependencies of the RR Lyrae and Cepheid distances by
requiring consistent relative distance measurements from the four techniques.
For metallicities of [Fe/H] = -1.3 (RR Lyraes) and -1.0 (Cepheids), we find a
relatively steep slope of 0.34 +/- 0.20 magnitudes per dex for the RR Lyraes
and a shallow slope of -0.07 +/- 0.16 mag/dex for the Cepheids, both values
within the range of theoretical and empirical results in the literature. We
find that a dependence of the red clump absolute magnitude on age, in addition
to metallicity, is required to produce self-consistent relative distances
between IC 1613 and the Magellanic Clouds. Adopting such a red clump
calibration and self-consistent calibrations for the other three distance
indicators, we find that the distances to all three objects are in excellent
agreement. Our best distance modulus to IC 1613 is mu_0 = 24.31 +/- 0.06,
corresponding to a distance of 730 +/- 20 kpc. This distance produces an RR
Lyrae absolute magnitude of MV = 0.61 +/- 0.08.


title:
A Preliminary Detection of Arcminute Scale Cosmic Microwave Background
  Anisotropy with the BIMA Array

abstract:
  We have used the Berkeley-Illinois-Maryland-Association (BIMA) array
outfitted with sensitive cm-wave receivers to expand our search for arcminute
scale anisotropy of the Cosmic Microwave Background (CMB). The interferometer
was placed in a compact configuration toobtain high brightness sensitivity on
arcminute scales over its 6.6' FWHM field of view. The sensitivity of this
experiment to flat band power peaks at a multipole of l=5530 which corresponds
to an angular scale of ~2'. We present the analysis of a total of 470 hours of
on-source integration time on eleven independent fields which were selected
based on their low IR contrast and lack of bright radio sources. Applying a
Bayesian analysis to the visibility data, we find CMB anisotropy flat band
power Q_flat = 6.1(+2.8/-4.8) microKelvin at 68% confidence. The confidence of
a non- zero signal is 76% and we find an upper limit of Q_flat < 12.4
microKelvin at 95% confidence. We have supplemented our BIMA observations with
concurrent observations at 4.8 GHz with the VLA to search for and remove point
sources. We find the point sources make an insignificant contribution to the
observed anisotropy.


title:
Linking the Metallicity Distribution of Galactic Halo Stars to the
  Enrichment History of the Universe

abstract:
  We compare the metallicity distribution of Galactic Halo stars with 3D
realizations of hierarchical galaxy formation. Outflows from dwarf galaxies
enrich the intergalactic medium inhomogeneously, at a rate depending on the
local galaxy density. Consequently, the first stars created in small
early-forming galaxies are less metal-rich that the first stars formed in more
massive galaxies which typically form later. As most halo stars are likely to
originate in accreted dwarfs, while disk stars formed out of outflow-enriched
gas, this scenario naturally generates a ``metallicity floor'' for old disk
stars, which we find to be roughly coincident with the higher end of our
predicted metallicity distribution of halo stars, in agreement with
observations. The broad and centrally peaked distribution of halo star
metallicities is well reproduced in our models, with a natural dispersion
depending on the exact accretion history. Our modeling includes the important
``baryonic stripping'' effect of early outflows, which brush away the tenuously
held gas in neighboring pre-virialized density perturbations. This stripping
process does not significantly modify the predicted shape of the halo star
metal distribution but inhibits star-formation and hence the number of accreted
stars, helping to reproduce the observed total Galactic halo luminosity and
also the lack of low-luminosity local dwarf galaxies relative to N-body
predictions.


title:
Position-Space Description of the Cosmic Microwave Background and Its
  Temperature Correlation Function

abstract:
  We suggest that the cosmic microwave background (CMB) temperature correlation
function C(theta) as a function of angle provides a direct connection between
experimental data and the fundamental cosmological quantities. The evolution of
inhomogeneities in the prerecombination universe is studied using their Green's
functions in position space. We find that a primordial adiabatic point
perturbation propagates as a sharp-edged spherical acoustic wave. Density
singularities at its wavefronts create a feature in the CMB correlation
function distinguished by a dip at theta ~ 1.2 deg. Characteristics of the
feature are sensitive to the values of cosmological parameters, in particular
to the total and the baryon densities.


title: Discovery of Five Binary Radio Pulsars

abstract:
  We report on five binary pulsars discovered in the Parkes multibeam Galactic
plane survey. All of the pulsars are old, with characteristic ages 1-11 Gyr,
and have relatively small inferred magnetic fields, 5-90e8 G. The orbital
periods range from 1.3 to 15 days. As a group these objects differ from the
usual low-mass binary pulsars (LMBPs): their spin periods of 9-88 ms are
relatively long; their companion masses, 0.2-1.1 Msun, are, in at least some
cases, suggestive of CO or more massive white dwarfs; and some of the orbital
eccentricities, 1e-5 < e < 0.002, are unexpectedly large. We argue that these
observed characteristics reflect binary evolution that is significantly
different from that of LMBPs. We also note that intermediate-mass binary
pulsars apparently have a smaller scale-height than LMBPs.


title: The black hole mass vs bulge mass relationship in spiral galaxies

abstract:
  We describe an on-going HST program aimed at determining the relationship
between the nuclear black hole mass and bulge mass in spiral galaxies. We have
selected a volume limited sample of 54 nearby spiral galaxies for which we
already have ground based emission line rotation curves, CCD surface photometry
and radio maps. We are now obtaining HST/STIS longslit observations of each of
the galaxies in the sample in order to determine the nuclear Halpha rotation
curve at high (~0.1") spatial resolution. We will use these data to measure the
unresolved dark mass concentration at the nucleus of each object. Here we show
the first results from observations of objects in the sample.


title: Growth of Galactic Bulges by Mergers: I. Dense Satellites

abstract:
  Andredakis, Peletier & Balcells (1995) fit Sersic's law $\mu(r) \sim r^{1/n}$
to the bulges of the Balcells & Peletier (1994) galaxy sample, and infer that
$n$ drops with morphological type T from $n \approx$ 4--6 for S0 to $n=1$
(exponential) for Sc's. We use collisionless N body simulations to test the
assumption that initially the surface brightness profiles of all bulges were
exponential, and that the steepening of the profiles toward the early-types is
due to satellite accretion. The results are positive. After the accretion of a
satellite, bulge-disk fits show that the bulge grows and that the bulge profile
index $n$ increases proportional to the satellite mass. For a satellite as
massive as the bulge, $n$ rises from 1 to 4. We present kinematic diagnostics
on the remnants and disk thickening. The latter suggests that the bulge growth
must have occurred before the last formation of a thin disk in the galaxy. The
thick disks created by the merger are reminiscent of thick disks seen in
early-type edge-on galaxies.
  The efficiency of the process suggests that present day bulges of late-type
spirals showing exponential profiles cannot have grown significantly by
collisionless mergers.


title: Chaotic Inflation with Variable Space Dimensions

abstract:
  Assuming the space dimension is not constant but decreases during the
expansion of the Universe, we study chaotic inflation with the potential $m^2
\phi^2/2$. We write down field equations in the slow-roll approximation and
define slow -roll parameters by assuming the space dimension to be a dynamical
parameter. The dynamical character of the space dimension shifts the initial
and final value of the inflaton field to larger values, producing delayed
chaotic inflation. We obtain an upper limit for the space dimension at the
Planck length. This result is in agreement with previous works on the effective
time variation of the Newtonian gravitational constant in a model Universe with
variable space dimensions. We present some cosmological consequences and
calculate observable quantities including the spectral indices, their
scale-dependence, and the mass of the inflaton field.


title:
The Hamburg/SAO Survey for Emission--Line Galaxies. IV. The Fourth List
  of 119 Galaxies

abstract:
  We present the fourth list with results of the Hamburg/SAO Survey for
Emission-Line Galaxies (HSS hereafter, SAO - Special Astrophysical Observatory,
Russia). The list is a result of the follow-up spectroscopy conducted with the
6m SAO RAS telescope in 1998, 1999 and 2000. The data of this snap-shot
spectroscopy survey confirmed 127 emission-line objects out of 176 observed
candidates and allowed their quantitative spectral classification. We could
classify 76 emission-line objects as BCG/HII galaxies or probable BCGs, 8 - as
QSOs, 2 - as Seyfert galaxies, 2 - as super-associations in a subluminous
spiral and an irregular galaxy, and 37 as low-excitation objects - either
starburst nuclei (SBN), or dwarf amorphous nuclei starburst galaxies (DANS). We
could not classify 2 ELGs. Furthermore, for 5 galaxies we did not detect any
significant emission lines. For 91 emission-line galaxies, the redshifts and/or
line intensities are determined for the first time. Of the remaining 28
previously known ELGs we give either improved data on the line intensities or
some independent measurements. The candidates were taken from three different
samples selected by different criteria. Among our first priority candidates we
achieved a detection rate of emission-line objects (ELGs + QSOs) of 68%, among
which 51% are BCGs. Observations of a random selected sample among our second
priority candidates showed that only ~10% are BCGs. We found that the confirmed
BCGs have usually a blue colour ((B-R) < 1.0) and a non-stellar appearance in
the APM database. Our third sample is comprised of second priority candidates
fulfilling these criteria derived from the APM. Follow-up spectroscopy of a
small subsample indicates that the expected detection rate for BCGs is ~40%.


title: Parsec-Scale Jets and Tori in Seyfert Galaxies

abstract:
  What causes the dichotomy between very powerful and very weak radio emission
from AGNs? Perhaps the engines are the same but the jets get disrupted by dense
ISM in radio-quiet objects, or else the engines are intrinsically different
with jet power scaling with, say, black hole spin. To distinguish, one can look
for interaction between the jets and the NLR and measure the jet speed close to
the core using VLBI, before environmental effects become important. We find
that in radio-quiet AGN, the jets appear slower and have a greater tendency to
bend, and that one-sidedness and flat-spectrum cores are probably due to
obscuration.


title: Positional correlation between low-latitude gamma-ray sources and SNRs

abstract:
  We present the results of a spatial correlation analysis between unidentified
gamma-ray sources in the 3EG catalog and candidates to supernova remnants. This
work extends a previous study made by Romero, Benaglia & Torres (1999). We also
consider the gamma-ray emission variability and the spectral index for the
sources with positional coincidence.


title: Dark Matter and Large Scale Structure

abstract:
  A review of the study of dark matter and large scale structure of the
Universe at Tartu Observatory is given. Tartu astronomers have participated in
this development, starting from Ernst "Opik and Grigori Kuzmin, and continuing
with the present generation of astronomers. Our goal was to understand better
the structure, origin and evolution of the Universe.


title: Structure of the X-ray Emission from the Jet of 3C 273

abstract:
  We present images from five observations of the quasar 3C 273 with the
Chandra X-ray Observatory. The jet has at least four distinct features which
are not resolved in previous observations. The first knot in the jet (A1) is
very bright in X-rays. Its X-ray spectrum is well fitted with a power law with
alpha = 0.60 +/- 0.05. Combining this measurement with lower frequency data
shows that a pure synchrotron model can fit the spectrum of this knot from
1.647 GHz to 5 keV (over nine decades in energy) with alpha = 0.76 +/- 0.02,
similar to the X-ray spectral slope. Thus, we place a lower limit on the total
power radiated by this knot of 1.5e43 erg/s; substantially more power may be
emitted in the hard X-ray and gamma-ray bands.
  Knot A2 is also detected and is somewhat blended with knot B1. Synchrotron
emission may also explain the X-ray emission but a spectral bend is required
near the optical band. For knots A1 and B1, the X-ray flux dominates the
emitted energy. For the remaining optical knots (C through H), localized X-ray
enhancements that might correspond to the optical features are not clearly
resolved. The position angle of the jet ridge line follows the optical shape
with distinct, aperiodic excursions of +/-1 deg from a median value of
-138.0deg. Finally, we find X-ray emission from the ``inner jet'' between 5 and
10" from the core.


title:
MACHO 96-LMC-2: Lensing of a Binary Source in the LMC and Constraints on
  the Lensing Object

abstract:
  We present photometry and analysis of the microlensing alert MACHO 96-LMC-2.
The ~3% photometry provided by the Global Microlensing Alert Network follow--up
effort reveals a periodic modulation in the lightcurve. We attribute this to
binarity of the lensed source. Microlensing fits to a rotating binary source
magnified by a single lens converge on two minima, separated by delta chi^2 ~
1. The most significant fit X1 predicts a primary which contributes ~100% of
the light, a dark secondary, and an orbital period (T) of 9.2 days. The second
fit X2 yields a binary source with two stars of roughly equal mass and
luminosity, and T = 21.2 days.
  The lensed object appears to lie on the upper LMC main sequence. We estimate
the mass of the primary component of the binary system, M ~2 M_sun. For the
preferred model X1, we explore the range of dark companions by assuming 0.1
M_sun and 1.4 M_sun objects in models X1a and X1b, respectively. We find lens
velocities projected to the LMC in these models of v^hat_X1a = 18.3 +/- 3.1
km/s and v^hat_X1b = 188 +/- 32 k/ms. In both these cases, a likelihood
analysis suggests an LMC lens is preferred over a Galactic halo lens, although
only marginally so in model X1b. We also find v^hat_X2 = 39.6 +/- 6.1 k/ms,
where the likelihood for the lens location is strongly dominated by the LMC
disk. In all cases, the lens mass is consistent with that of an M-dwarf. The
LMC self-lensing rate contributed by 96-LMC-2 is consistent with model
self-lensing rates. (Abridged)


title: Chandra Observations of M31 and their Implications for its ISM

abstract:
  We have been regularly observing the bulge and inner disk of M31 for nearly 1
year, using both the HRC-I and ACIS-I instruments on the Chandra X-Ray
Observatory. We present results from our program that are of interest to the
study of the ISM in M31. In particular, we find that the unresolved emission
within 3' of the center of M31 has a distinctly softer spectrum than that of
most of the resolved x-ray sources in the region. Preliminary spectral analysis
of bright point sources in the bulge shows no evidence (within the poor
statistics) for soft spectral components, but does reveal significant
extra-galactic x-ray extinction (NH~1E21). We find no new x-ray counterparts to
supernova remnants to date.


title:
The 2dF Galaxy Redshift Survey: The Number and Luminosity Density of
  Galaxies

abstract:
  We present the bivariate brightness distribution (BBD) for the 2dF Galaxy
Redshift Survey (2dFGRS) based on a preliminary subsample of 45,000 galaxies.
The BBD is an extension of the galaxy luminosity function incorporating surface
brightness information. It allows the measurement of the local luminosity
density, j_B, and the galaxy luminosity and surface brightness distributions
while accounting for surface brightness selection biases. The recovered 2dFGRS
BBD shows a strong surface brightness-luminosity relation (M_B~2.4\mu_e). The
luminosity-density is dominated by normal galaxies and the luminosity-density
peak lies away from the selection boundaries implying that the 2dFGRS is
complete and that luminous low surface brightness galaxies are rare. The final
value we derive for the local luminosity-density, inclusive of surface
brightness corrections, is: j_B=2.49+/-0.20x10^8 h L_solar Mpc^-3.
Representative Schechter function parameters are: M*=-19.75+/-0.05,
phi*=2.02+/-0.02x10^-2 and alpha=-1.09+/-0.03. Extending the conventional
methodology to incorporate surface brightness selection effects has resulted in
an increase in the luminosity-density of 37%.


title: Diffuse Cluster-wide Radio Halos

abstract:
  We will discuss the properties and origins of halos and relics including
estimates of the cluster magnetic fields, and present results for a few
recently discovered halos and relics. The electrons in the suprathermal high
energy tail of the thermal gas distribution are likely to provide the seed
particles for acceleration through mergers and turbulences to relativistic
energies. These relativistic particles are then responsible for the synchrotron
emission of the halos.


title:
The Evolution of Ellipticals, Spirals and Irregulars: Overcoming
  Selection Bias

abstract:
  The Hubble Deep Fields represent our best opportunity for probing galaxy
evolution over a substantive look-back time. However as with any dataset the
HDFs are prone to selection biases. These biases are extremely severe beyond z
\~1.25 such that a meaningful interpretation of generic galaxy evolution is not
possible. We can however extract well defined volume-limited samples at z < 1.
The data are entirely consistent with passive/null-evolution for ellipticals,
spirals and irregulars however this concluion is tempered by small number
statistics. Alas stringent constraints on galaxy evolution await an order of
magnitude increase in the number of HDFs.


title: DENIS-P J104814.7-395606.1: An M9 dwarfs at about 4 pc

abstract:
  We present the discovery of a previously unknown member of the immediate
solar neighbourhood, DENIS-P J104814.7-395606.1 (hereafter DENIS 1048-39),
identified while mining the DENIS database for new nearby stars. A HIRES
echelle spectrum obtained with the 10-m Keck telescope shows that it is an M9
dwarf. DENIS 1048-39 has a very bright apparent magnitude (I=12.67) for its
spectral type and colour (I-J=3.07), and is therefore very nearby. If it is
single its distance is only 4.1 +- 0.6pc, ranking it as between our twelfth and
fortyth closest neighbour. It is also the closest star or brown dwarf with a
spectral type later than M7V. Its proper motion was determined through
comparison of Sky atlas Schmidt plates, scanned by the MAMA microdensitometer,
with the DENIS images. At 1.53"/yr it further attests the closeness of DENIS
1048-39, and hence its dwarf status. These characteristics make it an obvious
target for further detailed studies.


title: Weak lensing study of low mass galaxy groups: implications for Omega_m

abstract:
  We report on the first measurement of the average mass and mass-to-light
ratio of galaxy groups by analysing the weak lensing signal induced by these
systems. The groups, which have velocity dispersions of 50-400 km/s, have been
selected from the Canadian Network for Observational Cosmology Field Galaxy
Redshift Survey (CNOC2). This survey allows the identification of a large
number of groups with redshifts ranging from z=0.12-0.55, ideal for a weak
lensing analysis of their mass distribution. For our analysis we use a sample
of 50 groups which are selected on the basis of a careful dynamical analysis of
group candidates. We detect a signal at the 99% confidence limit. The best fit
singular isothermal sphere model yields an Einstein radius of 0.72+-0.29". This
corresponds to a velocity dispersion of 274^{+48}_{-59} km/s (using photometric
redshift distributions for the source galaxies), which is in good agreement
with the dynamical estimate. Under the assumption that the light traces the
mass, we find an average mass-to-light ratio of 191+-83 h Msun/Lsun in the
restframe B band. Unlike dynamical estimates, this result is insensitive to
problems associated with determining group membership. After correction of the
observed mass-to-light ratio for luminosity evolution to z=0, we find 254+-110
h Msun/Lsun, lower than what is found for rich clusters. We use the observed
mass-to-light ratio to estimate the matter density of the universe, for which
we find Omega_m=0.19+-0.10 (Omega_Lambda=0), in good agreement with other
recent estimates. For a closed universe, we obtain Omega_m=0.13+-0.07.


title: The nuclear cusp slopes of dwarf elliptical galaxies

abstract:
  We derive the light profiles for a sample of 25 dwarf elliptical galaxies
observed by us with HST/WFPC2 in F555W and F814W. These profiles are fitted
with Nuker, R^1/4, exponential, and Sersic laws, and are also used to derive
the nuclear cusp slopes gamma. We discuss the correlation of nuclear cusp slope
with galactic luminosity, presence of a nucleus, and type of light profile. The
results are compared to those found in the literature for elliptical galaxies
and the bulges of spiral galaxies. We find that as a class the nuclear regions
of dwarf ellipticals are very similar to those of the exponential bulges of
spiral galaxies, and have nuclear cusp slopes shallower than those of bulges
that were well fitted by a de Vaucouleurs R^1/4 profile with the same
luminosity. For the 14 nucleated galaxies in our sample this conclusion is less
certain than for the 11 non-nucleated objects since it relies on an
extrapolation of galaxy light under the nucleus. In terms of their light
profiles and nuclear properties, most spheroidal stellar systems can be broadly
divided into two subclasses: the exponential shallow cusp objects and the
R^1/4, steep cusp objects. Membership of a class does not appear to correlate
with the presence of a massive stellar disk.


title: Warm molecular gas in nearby galaxies. Mapping of the CO(3-2) emission

abstract:
  Using the Heinrich-Hertz-Telescope on Mt. Graham, Arizona, we have observed
several nearby galaxies in the CO(3-2) line. The CO(3-2) emission traces - in
contrast to lower rotational transitions - a warmer and denser component of the
molecular gas.
  We find that this emission is spatially extended in the target galaxies. The
excitation conditions seem to vary with the location of the gas within the
galaxy, and also with the overall properties of the target objects. However, a
clear correlation between the CO(3-2) emission and other quantities, such as
Hubble type or IR luminosity, is not present.


title:
A New Formation Channel for Double Neutron Stars Without Recycling:
  Implications for Gravitational Wave Detection

abstract:
  We report on a new evolutionary path leading to the formation of close double
neutron stars (NS), with the unique characteristic that none of the two NS ever
had the chance to be recycled by accretion. The existence of this channel stems
from the evolution of helium-rich stars (cores of massive NS progenitors),
which has been neglected in most previous studies of double compact object
formation. We find that these non-recycled NS-NS binaries are formed from bare
carbon-oxygen cores in tight orbits, with formation rates comparable to or
maybe even higher than those of recycled NS-NS binaries. On the other hand,
their detection probability as binary pulsars is greatly reduced (by about
1000) relative to recycled pulsars, because of their short lifetimes. We
conclude that, in the context of gravitational-wave detection of NS-NS inspiral
events, this new type of binaries calls for an increase of the rate estimates
derived from the observed NS-NS with recycled pulsars, typically by factors of
1.5-3 or even higher.


title:
STIS Ultraviolet Spectral Evidence for Outflows in Extreme Narrow-Line
  Seyfert 1 Galaxies

abstract:
  (abridged) I present and discuss the results of HST STIS observations of IRAS
13224-3809 and 1H 0707-495, two narrow-line Seyfert 1 (NLS1) galaxies. We
discovered that high-ionization UV emission lines are much broader and strongly
blueshifted compared with the low-ionization and intermediate-ionization lines,
which are relatively narrow and centered at the rest wavelength. We interpret
this as evidence that the high-ionization lines come from a wind, while the
low-ionization lines are emitted from the accretion disk or low-velocity base
of the wind. The optically thick disk blocks our view of the receding wind. We
also found that not all NLS1s display strongly blueshifted emission lines, and
the degree of asymmetry is inversely correlated with the equivalent width and
correlated with the SiIII] to CIII] ratio, a density indicator. It may also be
significant that these NLS1s display the extreme in the X-ray properties: they
have the strongest X-ray soft-excess components and the highest-amplitude,
flaring variability. We postulate that this combination of properties are all
related to a high value of L/M_BH, even among NLS1s. The high-ionization and
low-ionization lines are nearly completely kinematically separated, a fact that
allows us to study the conditions in the disk and wind separately.(...)


title: A Hierarchical Triple Star System in M4

abstract:
  The radio millisecond pulsar PSR B1620-26 is part of an extraordinary triple
star system in the globular cluster M4. The inner companion to the neutron star
is thought to be a white dwarf of mass m1 ~0.3 Msun in an orbit of period ~0.5
year. The nature and orbital characteristics of the second, more distant
companion, have remained a mystery for many years. A theoretical analysis of
the latest available radio pulsar timing data is presented here, allowing us to
determine approximately the mass and orbital parameters of the second
companion. Remarkably, the current best-fit parameters correspond to a second
companion of **planetary mass**, with m2 ~0.007 Msun, in an orbit of
eccentricity e2 ~0.45 and with a large semimajor axis a2 ~60 AU. The short
dynamical lifetime of this very wide triple in M4 suggests that large numbers
of such planets must be present in globular clusters. We also address the
question of the anomalously high eccentricity of the inner binary pulsar. While
this eccentricity could have been induced during the same dynamical interaction
that created the triple, we find that it could also naturally arise from
long-term secular perturbation effects in the triple, combining the general
relativistic precession of the inner orbit with the Newtonian gravitational
perturbation by the outer planet.


title:
Discovery of a very X-ray luminous galaxy cluster at z=0.89 in the WARPS
  survey

abstract:
  We report the discovery of the galaxy cluster ClJ1226.9+3332 in the Wide
Angle ROSAT Pointed Survey (WARPS). At z=0.888 and L_X=1.1e45 erg/s (0.5-2.0
keV, h_0=0.5) ClJ1226.9+3332 is the most distant X-ray luminous cluster
currently known. The mere existence of this system represents a huge problem
for Omega_0=1 world models.
  At the modest (off-axis) resolution of the ROSAT PSPC observation in which
the system was detected, ClJ1226.9+3332 appears relaxed; an off-axis HRI
observation confirms this impression and rules out significant contamination
from point sources. However, in moderately deep optical images (R and I band)
the cluster exhibits signs of substructure in its apparent galaxy distribution.
A first crude estimate of the velocity dispersion of the cluster galaxies based
on six redshifts yields a high value of 1650 km/s, indicative of a very massive
cluster and/or the presence of substructure along the line of sight. While a
more accurate assessment of the dynamical state of this system requires much
better data at both optical and X-ray wavelengths, the high mass of the cluster
has already been unambiguously confirmed by a very strong detection of the
Sunyaev-Zel'dovich effect in its direction (Joy et al. 2001).
  Using ClJ1226.9+3332 and ClJ0152.7-1357 (z=0.835), the second-most distant
X-ray luminous cluster currently known and also a WARPS discovery, we obtain a
first estimate of the cluster X-ray luminosity function at 0.8<z<1.4 and
L_X>5e44 erg/s. Using the best currently available data, we find the comoving
space density of very distant, massive clusters to be in excellent agreement
with the value measured locally (z<0.3), and conclude that negative evolution
is not required at these luminosities out to z~1. (truncated)


title: Gaseous Disks of Spiral Galaxies: Arms and Rings

abstract:
  An improved linear stability theory of small-amplitude oscillations of a
self-gravitating, infinitesimally thin gaseous disk of spiral galaxies has been
developed. It was shown that in the differentially rotating disks for
nonaxisymmetric perturbations Toomre's modified hydrodynamical simulations to
test the validity of the modified local criterion.


title: Supercomputer Simulations of Disk Galaxies

abstract:
  The time evolution of models for an isolated disk of highly flattened
galaxies of stars is investigated by direct integration of the Newtonian
equations of motion of N=30,000 identical stars over a time span of many
galactic rotations. Certain astronomical implications of the simulations to
actual disk-shaped (i.e. rapidly rotating) galaxies are explored as well.


title: Self-Interacting Cold Dark Matter Halos

abstract:
  The evolution of halos consisting of weakly self-interacting dark matter
particles is summarized. The halos initially contain a central density cusp as
predicted by cosmological models. Weak self-interaction leads to the formation
of an isothermal, low-density core which is in agreement with published data on
the rotation curves of dwarf galaxies. However, subsequently, core collapse
leads to an even steeper central density cusp. In order to explain the observed
dark matter rotation curves by weak interaction, the cross section must be in a
narrow range around sigma/mp= 0.1 cm*cm/g.


title: Radial gradients and metallicities in the galactic disk

abstract:
  Radial O/H abundance gradients derived from HII regions, hot stars and
planetary nebulae are combined with [Fe/H] gradients from open cluster stars in
order to derive an independent [O/Fe] x [Fe/H] relation for the galactic disk.
A comparison of the obtained relation with recent observational data and
theoretical models suggests that the [O/Fe] ratio is not higher than [O/Fe] ~
0.4, at least within the metallicity range of the considered samples.


title: Modeling of C stars with core/mantle grains: Amorphous carbon + SiC

abstract:
  A set of 45 dust envelopes of carbon stars has been modeled. Among them, 34
were selected according to their dust envelope class (as suggested by Sloan,
Little-Marenin & Price, 1998) and 11 are extreme carbon stars. The models were
performed using a code that describes the radiative transfer in dust envelopes
considering core/mantle grains composed by an alpha-SiC core and an amorphous
carbon (A.C.) mantle. In addition, we have also computed models with a code
that considers two kinds of grains - alpha-SiC and A.C. - simultaneously.
Core-mantle grains seem to fit dust envelopes of evolved carbon stars, while
two homogeneous grains are more able to reproduce thinner dust envelopes. Our
results suggest that there exists an evolution of dust grains in the carbon
star sequence. In the beginning of the sequence, grains are mainly composed of
SiC and amorphous carbon; with dust envelope evolution, carbon grains are
coated in SiC. This phenomena could perhaps explain the small quantity of SiC
grains observed in the interstellar medium. However, in this work we consider
only alpha-SiC grains, and the inclusion of beta-SiC grains can perhaps change
some of there results.


title:
Chemical yields from low- and intermediate-mass stars: model predictions
  and basic observational constraints

abstract:
  In this work we analyse the role of low- and intermediate-mass stars in
contributing to the chemical enrichment of the interstellar medium. First we
present new sets of stellar yields basing on the results of updated
evolutionary calculations, which extend from the ZAMS up to the end of the AGB
phase (Girardi et al. 2000; Marigo et al. 1999a). These new yields, that
present a significant dependence on metallicity, are then compared to those of
other available sets (Renzini & Voli 1981; van de Hoek & Groenewegen 1997). The
resulting differences are explained in terms of different model assumptions --
i.e. treatment of convective boundaries, mass loss, dredge-up, hot-bottom
burning --, and further discussed on the basis of important empirical
constraints which should be reproduced by theory -- i.e. the initial-final mass
relation, white dwarf mass distribution, carbon star luminosity function, and
chemical abundances of planetary nebulae. We show that present models are able
to reproduce such constraints in a satisfactory way.


title:
Confirmation of the existence of coherent orientations of quasar
  polarization vectors on cosmological scales

abstract:
  In order to verify the existence of coherent orientations of quasars
polarization vectors on very large scales, we have obtained new polarization
measurements for a sample of quasars located in a given region of the
three-dimensional Universe where the range of polarization position angles was
predicted in advance. For this new sample, the hypothesis of uniform
distribution of polarization position angles may be rejected at the 1.8%
significance level on the basis of a simple binomial test. This result provides
an independent confirmation of the existence of alignments of quasar
polarization vectors on very large scales. In total, out of 29 polarized
quasars located in this region of the sky, 25 have their polarization vectors
coherently oriented. This alignment occurs at redshifts 1-2 suggesting the
presence of correlations in objects or fields on Gpc scales. More global
statistical tests applied to the whole sample of polarized quasars distributed
all over the sky confirm that polarization vectors are coherently oriented in a
few groups of 20-30 quasars. Some constraints on the phenomenon are also
derived. Considering more particularly the quasars in the selected region of
the sky, we found that their polarization vectors are roughly parallel to the
plane of the Local Supercluster. But the polarization vectors of objects along
the same line of sight at lower redshifts are not accordingly aligned. We also
found that the known correlations between quasar intrinsic properties and
polarization are not destroyed by the alignment effect. Several possible
mechanisms are discussed, but the interpretation of this orientation effect
remains puzzling.


title:
Astronomical x-ray polarimetry based on photoelectric effect with
  microgap detectors

abstract:
  The polarisation of x-ray photons can be determined by measuring the
direction of emission of a K-shell photoelectron. Effective exploitation of
this effect below 10 keV would allow development of a highly sensitive x-ray
polarimeter dedicated in particular to x-ray astronomy observations. Only with
the advent of finely segmented gas detectors was it possible to detect
polarisation sensitivity based on the photoelectric effect in this energy
range. Simulation and measurements at 5.4 and 8.04 keV with a microgap gas
counter, using both a polarised and an unpolarised x-ray source, showed that
the photoelectron track in a neon-based gas mixture retains the memory of the
polarisation of the incoming photons. Possible experiments aimed at
galactic/extragalactic sources and solar flares are considered and their
sensitivity to these sources is calculated.


title: Fractal Structure in Galactic Star Fields

abstract:
  The fractal structure of star formation on large scales in disk galaxies is
studied using the size distribution function of stellar aggregates in kpc-scale
star fields. Achival HST images of 10 galaxies are Gaussian smoothed to define
the aggregates, and a count of these aggregates versus smoothing scale gives
the fractal dimension. Fractal and Poisson models confirm the procedure. The
fractal dimension of star formation in all of the galaxies is ~2.3. This is the
same as the fractal dimension of interstellar gas in the Milky Way and nearby
galaxies, suggesting that star formation is a passive tracer of gas structure
defined by self-gravity and turbulence. Dense clusters like the Pleiades form
at the bottom of the hierarchy of structures, where the protostellar gas is
densest. If most stars form in such clusters, then the fractal arises from the
spatial distribution of their positions, giving dispersed star fields from
continuous cluster disruption. Dense clusters should have an upper mass limit
that increases with pressure, from ~1000 Msun in regions like the Solar
neighborhood to one million Msun in starbursts.


title: Surveys and the Blazar Parameter Space

abstract:
  The rareness of blazars, combined with the previous history of relatively
shallow, single-band surveys, has dramatically colored our perception of these
objects. Despite a quarter-century of research, it is not at all clear whether
current samples can be combined to give us a relatively unbiased view of blazar
properties, or whether they present a view so heavily affected by biases
inherent in single-band surveys that a synthesis is impossible. We will use the
coverage of X-ray/radio flux space for existing surveys to assess their biases.
Only new, deeper blazar surveys approach the level needed in depth and coverage
of parameter space to give us a less biased view of blazars. These surveys have
drastically increased our knowledge of blazars' properties. We will
specifically review the discovery of ``blue'' blazars, objects with broad
emission lines but broadband spectral characteristics similar to HBL BL Lac
objects.


title: tau Boo b: Not so bright, but just as heavy

abstract:
  We present new results derived from high-resolution optical spectra of the
tau Boo system, secured in March-May 2000. The results do not show the same
feature reported by Cameron et al (1999) as a candidate reflected-light
signature from the planet. Together with earlier results from the 1998 and 1999
seasons, the new data yield a 99.9 percent upper limit on the opposition
planet/star flux ratio epsilon<3.5E-5 between 387.4 and 586.3 nm, a factor 3
deeper than the upper limit of Charbonneau et al (1999). For an assumed planet
radius Rp= 1.2 RJup, the upper limit on the mean geometric albedo is p < 0.22,
40 percent that of Jupiter. We find new evidence that the star's rotation is
synchronised with the planet's orbital motion. Using a Monte Carlo analysis we
infer that the planet's mass must lie in the range 5.5 to 10 times the mass of
Jupiter.


title: A Far-Ultraviolet Spectroscopic Survey of the Globular Cluster 47 Tuc

abstract:
  We present preliminary results from a FUV spectroscopic and photometric
survey of the globular cluster 47 Tuc. Our main goal is to either confirm or
rule out the existence of a large population of CVs in the core of this
cluster.
  We have so far identified approximately 425 FUV sources, most of which are
probably hot, young WDs. However, we have also found approximately 30 FUV
sources whose position in a FUV-optical color-magnitude diagram makes them
strong CV candidates. If most or all of these objects are eventually confirmed
as CVs, the large CV population predicted by tidal capture theory has finally
been found.
  Our data has also allowed us to resolve the long-standing puzzle surrounding
AKO 9, a UV-bright and highly variable 1.1 day binary system in 47 Tuc. AKO 9
is the brightest FUV source in our data and presents a blue FUV spectrum with
strong CIV and HeII emission lines. Its spectrum is similar to that of the
long-period, DN-type field CV GK Per. Based on this similarity and other
evidence, we suggest that AKO 9 is a long-period CV in which mass-transfer is
driven by the nuclear evolution of a sub-giant donor star.


title: The microarcsecond quasar J1819+3845

abstract:
  We present new WSRT observations of the micro-arcsecond quasar J1819+3845.
All short term variations are attributed to interstellar scintillation of a
source which is at most 30 micro-arcseconds in diameter. The timescale of the
modulations changes over the year, which we interpret as due to a peculiar
velocity of the scattering medium. The scintillation behaviour can be used to
determine sub-structure in the source.