title:
The evolution of main sequence star + white dwarf binary systems towards
  Type~Ia supernovae

abstract:
  Close binaries consisting of a main sequence star and a white dwarf are
considered as candidates for Type~Ia supernova progenitors. We present
selfconsistent calculations of the time dependence of the structure of the main
sequence star, the mass transfer rate, and the orbit by means of a binary
stellar evolution program. In contrast to results based on simple estimates of
the mass transfer rate in systems of the considered type, our results allow for
the possibility that even systems with rather small initial white dwarf masses
(~ 0.7 M_sun) may produce Type Ia supernovae. We present results for two
different metallicities, Z=0.02 and Z=0.001. We find that for systems with the
lower metallicity, the mass transfer rates are on average five times larger
than in comparable system at solar metallicity. This leads to a systematic
shift of the supernova Ia progenitor population. Firstly, while for Z=0.02
donor star initial masses in supernova progenitor systems are restricted to the
range 1.6...2.3 M_sun, they are in the interval 1.4...1.8 M_sun at low Z.
Secondly, the initial white dwarf masses need, on average, to be larger by 0.2
M_sun at low Z in order to obtain a Chandrasekhar mass white dwarf. This
metallicity dependences may be responsible for a drop of the Type Ia supernova
rate for low metallicity, and may introduce a Z-dependence in the properties of
supernovae. We also estimate the X-ray luminosities of the computed systems,
and investigate their donor star and orbital properties.


title: A Wide-Field CCD Survey for Centaurs and Kuiper Belt Objects

abstract:
  A modified Baker-Nunn camera was used to conduct a wide-field survey of 1428
square degrees of sky near the ecliptic in search of bright Kuiper Belt objects
and Centaurs. This area is an order of magnitude larger than any previously
published CCD survey for Centaurs and Kuiper Belt Objects. No new objects
brighter than red magnitude m=18.8 and moving at a rate 1"/hr to 20"/hr were
discovered, although one previously discovered Centaur 1997 CU26 Chariklo was
serendipitously detected. The parameters of the survey were characterized using
both visual and automated techniques. From this survey the empirical projected
surface density of Centaurs was found to be SigmaCentaur(m<18.8)=7.8(+16.0
-6.6)x10^-4 per square degree and we found a projected surface density 3sigma
upper confidence limit for Kuiper Belt objects of SigmaKBO(m< 18.8)<4.1x10^-3
per square degree. We discuss the current state of the cumulative luminosity
functions of both Centaurs and Kuiper Belt objects. Through a Monte Carlo
simulation we show that the size distribution of Centaurs is consistent with a
q=4 differential power law, similar to the size distribution of the parent
Kuiper Belt Objects. The Centaur population is of order 10^7 (radius > 1 km)
assuming a geometric albedo of 0.04. About 100 Centaurs are larger than 50 km
in radius, of which only 4 are presently known. The current total mass of the
Centaurs is 10^-4 Earth Masses. No dust clouds were detected resulting from
Kuiper Belt object collisions, placing a 3sigma upper limit <600 collisionally
produced clouds of m<18.8 per year.


title: Looking for a varying $\alpha$ in the Cosmic Microwave Background

abstract:
  We perform a likelihood analysis of the recently released BOOMERanG and
MAXIMA data, allowing for the possibility of a time-varying fine-structure
constant. We find that in general this data prefers a value of $\alpha$ that
was smaller in the past (which is in agreement with measurements of $\alpha$
from quasar observations). However, there are some interesting degeneracies in
the problem which imply that strong statements about $\alpha$ can not be made
using this method until independent accurate determinations of $\Omega_b h^2$
and $H_0$ are available.
  We also show that a preferred lower value of $\alpha$ comes mainly from the
data points around the first Doppler peak, whereas the main effect of the
high-$\ell$ data points is to increase the preferred value for $\Omega_b h^2$
(while also tightening the constraints on $\Omega_0$ and $H_0$). We comment on
some implications of our results.


title: Powerful jets from black hole X-ray binaries in Low/Hard X-ray states

abstract:
  Four persistent (Cygnus X-1, GX 339-4, GRS 1758-258 and 1E 1740.7-2942) and
three transient (GS 2023+38, GRO J0422+32 and GS 1354-64) black hole X-ray
binary systems have been extensively observed at radio wavelengths during
extended periods in the Low/Hard X-ray state, which is characterised in X-rays
by a hard power-law spectrum and strong variability. All seven systems show a
persistent flat or inverted (in the sense that spectral index alpha >= 0) radio
spectrum in this state, markedly different from the optically thin radio
spectra exhibited by most X-ray transients within days of outburst.
Furthermore, in none of the systems is a high-frequency cut-off to this
spectral component detected, and there is evidence that it extends to
near-infrared or optical regimes. Luminous persistent hard X-ray states in the
black hole system GRS 1915+105 produce a comparable spectrum. This spectral
component is considered to arise in synchrotron emission from a conical,
partially self-absorbed jet, of the same genre as those originally considered
for Active Galactic Nuclei. Whatever the physical origin of the Low/Hard X-ray
states, these self-similar outflows are an ever-present feature. The power in
the jet component is likely to be a significant (> 5%) and approximately fixed
fraction of the total accretion luminosity. The correlation between hard X-ray
and synchrotron emission in all the sources implies that the jets are
intimately related to the Comptonisation process, and do not have very large
bulk Lorentz factors, unless the hard X-ray emission is also beamed by the same
factor.


title: The Impact of Adaptive Optics on Star Formation Research

abstract:
  In this paper, we discuss the benefits of ground-based, adaptive optics (AO)
aided observations for star formation research. After outlining the general
advantages, we present results obtained during the ALFA science demonstration
programme in 1999. These results underline the absolute necessity of AO
assistance for almost any kind of observations regarding star formation
regions.


title:
The complete S5 polar cap sample: en route to phase-delay global
  astrometry

abstract:
  We report on the present status of our S5 polar cap phase-connected
astrometry program. We observe 13 radio sources in the northernmost 20deg of
the sky at the wavelengths of 3.6cm and 2cm, and we plan to extend the program
to 0.7cm. We phase-connect jointly all our data successfully. We image the
radio sources and some of them show morphological changes, in which astrometric
registration is needed to determine the kinematics of the source components. We
aim at unprecedented astrometric accuracy and at a check of the jet standard
model at the 5-10 microarcsec/yr level.


title: Mapping the peculiar binary GP Com

abstract:
  We present high resolution spectra of the AM CVn helium binary GP Com at two
different wavelength ranges. The spectra show the same flaring behaviour
observed in previous UV and optical data. We find that the central spike
contributes to the flare spectra indicating that its origin is probably the
compact object. We also detect that the central spike moves with orbital phase
following an S-wave pattern. The radial velocity semiamplitude of the S-wave is
\~10 km/s which indicates its origin is near the centre of mass of the system,
which in this case lies very close to the white dwarf. The Stark effect seems
to affect significantly the central spike of some of the lines suggesting that
it forms in a high electron density region. This again favours the idea that
the central spike originates in the white dwarf. We present Doppler maps
obtained for the emission lines which show three clear emission regions.


title: Massive warm dark matter

abstract:
  Many independent high resolution simulations have indicated that the standard
collisionless cold dark matter model does not reproduce the structure of
observed present day galaxies well. Several possible solutions in the form of
modifications to the physics of the dark matter particles have been proposed.
One of the most promising is warm dark matter (WDM), particles with significant
thermal motion in the early universe. It is usually assumed that such particles
are relativistically decoupled particles with a mass of approximately 1 keV.
However, here we have investigated the possibility that much more massive
particles with highly non-thermal spectra could make up warm dark matter.
Several possible production mechanisms are reviewed and the only one found to
be viable is that the WDM is produced by the non-relativistic decay of some
massive species in the early universe. Such very massive warm dark matter could
possibly be detected in direct detection experiments, as opposed to standard
thermal warm dark matter.


title: On the coupling between different species during recombination

abstract:
  Measurements of fluctuations in the Cosmic Microwave Background Radiation
(CMBR) is one of the most promising methods for measuring the fundamental
cosmological parameters. However, in order to infer parameters from precision
measurements it is necessary to calculate the theoretical fluctuation spectrum
to at least the measurement accuracy. Standard treatments assume that
electrons, ions and neutral hydrogen are very tightly coupled during the entire
recombination history, and that the baryon-photon plasma can be treated as a
two-fluid system consisting of baryons and photons interacting via Thomson
scattering. We investigate the validity of this approximation by explicitly
writing down and solving the full set of Boltzmann equations for electrons,
ions, neutral hydrogen and photons. The main correction to the standard
treatment is from including Rayleigh scattering between photons and neutral
hydrogen, a change of less than 0.1% in the CMBR power spectrum. Our conclusion
is thus that the standard treatment of the baryon-photon system is a very good
approximation, better than any possible measurement accuracy.


title: The survival of subhaloes in galaxies and galaxy clusters

abstract:
  This paper discusses physical and numerical disruption processes acting on
subhaloes in galaxy haloes and in galaxy cluster haloes, and compare the
effects of these processes on the subhalo abundance within both types of
haloes. N-body simulations with a resolution high enough not to suffer from
overmerging (subhalo disruption due to numerical processes) show a high
abundance of subhaloes in both galaxies and in galaxy clusters. However,
observations seem to show a high subhalo abundance in galaxy clusters only.
Thus, it appears that too many subhaloes survive in simulated galaxy haloes.
There are five main causes for this apparent galaxy subhalo problem. The most
radical one is a change to a cosmology in which structure formation is not
hierarchical below the galaxy halo mass scale. If this is unacceptable, four
causes remain, of which the most important one appears to be that dynamical
friction is not properly simulated yet, not even for the highest resolution
simulations to date, resulting in an 'undermerging' problem. The other causes
are (numerical) overmerging, differences in the timing of halo formation and
merging in hierarchical structure formation, and significant differences is
mass-to-light ratios. The net effect of these four causes is that galaxies have
a relatively low abundance of subhaloes, i.e. dwarfs, while at the same time a
large number of field dwarf galaxies can exist which are dark enough to be
missed observationally.


title:
Density, Velocity, and Magnetic Field Structure in Turbulent Molecular
  Cloud Models

abstract:
  We use 3D numerical MHD simulations to follow the evolution of cold,
turbulent, gaseous systems with parameters representing GMC conditions. We
study three cloud simulations with varying mean magnetic fields, but identical
initial velocity fields. We show that turbulent energy is reduced by a factor
two after 0.4-0.8 flow crossing times (2-4 Myr), and that the magnetically
supercritical cloud models collapse after ~6 Myr, while the subcritical cloud
does not collapse. We compare density, velocity, and magnetic field structure
in three sets of snapshots with matched Mach numbers. The volume and column
densities are both log-normally distributed, with mean volume density a factor
3-6 times the unperturbed value, but mean column density only a factor 1.1-1.4
times the unperturbed value. We use a binning algorithm to investigate the
dependence of kinetic quantities on spatial scale for regions of column density
contrast (ROCs). The average velocity dispersion for the ROCs is only weakly
correlated with scale, similar to the mean size-linewidth relation for clumps
within GMCs. ROCs are often superpositions of spatially unconnected regions
that cannot easily be separated using velocity information; the same difficulty
may affect observed GMC clumps. We analyze magnetic field structure, and show
that in the high density regime, total magnetic field strengths increase with
density with logarithmic slope 1/3 -2/3. Mean line-of-sight magnetic field
strengths vary widely across a projected cloud, and do not correlate with
column density. We compute simulated interstellar polarization maps at varying
orientations, and determine that the Chandrasekhar-Fermi formula multiplied by
a factor ~0.5 yields a good estimate of the plane-of sky magnetic field
strength provided the dispersion in polarization angles is < 25 degrees.


title:
Long-term optical and X-ray observations of the old novae DI Lacertae
  and V841 Ophiuchi

abstract:
  We present an analysis of ground-based optical photometry and spectroscopy,
and Rossi X-ray Timing Explorer X-ray observations of the old novae DI Lacertae
and V841 Ophiuchi. Our optical photometry data (obtained with the automated
photometry telescope RoboScope) comprise an almost decade-long light curve for
each star, while the contemporaneous spectroscopy and X-ray observations
repeatedly sampled each nova during separate intervals of ~45-55 d in length.
The long-term optical light curves of both novae reveal quasiperiodic
variability on typical time scales of ~30-50 d with amplitudes of dV ~ 0.4-0.8
mag. V841 Oph also displays a long-term, sinusoidal modulation of its optical
light on a time scale of 3.5-5 yr. The optical spectra of these novae display
quite different characteristics from each other, with DI Lac showing narrow
Balmer emission cores situated in broad absorption troughs while V841 Oph
exhibits strong single-peaked Balmer, He I and He II emission lines. We find
little change between spectra obtained during different optical brightness
states. The X-ray count rates for both novae were very low (< ~1.5 ct/s) and
there was no reliable correlation between X-ray and optical brightness. The
combined X-ray spectrum of DI Lac is best fit by a bremsstrahlung emission
model (with kT ~ 4 keV and N_H < 1.8x10^22 cm^-3); the X-ray spectrum of V841
Oph is too weak to allow model fitting. We discuss the possible origin of
variability in these old novae in terms of magnetic activity on the secondary
star, dwarf nova type disk instabilities, and the ``hibernation'' scenario for
cataclysmic variable stars.


title: High redshift CO line emission: perspectives

abstract:
  Although about a dozen high redshift (z larger than 2) starburst galaxies
have been recently detected in the CO lines, spectroscopic detections of
molecular gas of very young galaxies are still very difficult. The CO lines are
usually optically thick, which limits greatly the increase of emission with
redshift, as observed for the dust continuum. However the future instruments
(LMT, ALMA, etc..) will allow large progress in this domain, and perspectives
are discussed. Computations are based on a simple extrapolation of what is
known of starbursting galaxies at lower redshift.


title: An unresolved X-ray source inside the supernova remnant RCW 86

abstract:
  We report on the discovery of an unresolved X-ray source inside the supernova
remnant G315.4-2.3 (RCW 86). The source is located 7' to the Southwest of the
geometrical centre and may be close to the actual explosion centre of the
supernova, which makes this a candidate for the stellar remnant associated with
RCW 86. However, the presence of a possible optical counterpart with $V \sim
14$ at 3" from the X-ray position and evidence for long term variability means
that the source is probably an active star. A better X-ray position and better
X-ray spectroscopy along with an identification of the optical source are
needed to exclude the X-ray source as a neutron star candidate.


title:
Kinematics of the Parsec-Scale Relativistic Jet in Quasar 3C 279: 1991 -
  1997

abstract:
  We present results of long-term high-frequency VLBI monitoring of the
relativistic jet in 3C279, consisting of 18 epochs at 22 GHz from 1991 to 1997
and 10 epochs at 43 GHz from 1995 to 1997. Three major results of this study
are: apparent speeds measured for six superluminal components range from 4.8 to
7.5 c (H_{0}=70 km s^{-1} Mpc^{-1}, q_{0}=0.1), variations in the total radio
flux are due primarily to changes in the VLBI core flux, and the uniform-sphere
brightness temperature of the VLBI core is about 1 x 10^{13} K at 22 GHz after
1995, one of the highest direct estimates of a brightness temperature. If the
variability brightness temperature measured for 3C279 by Lahteenmaki & Valtaoja
is an actual value and not a lower limit, then the rest-frame brightness
temperature of 3C279 is quite high and limited by inverse Compton effects
rather than equipartition. The parsec-scale morphology of 3C279 consists of a
bright, compact VLBI core, a jet component (C4) that moved from about 2 mas to
about 3.5 mas from the core during the course of our monitoring, and an inner
jet that extends from the core to a stationary component, C5, at about 1 mas
from the core. Components in the inner jet are relatively short-lived, and fade
by the time they reach about 1 mas from the core. The components have different
speeds and position angles from each other, but these differences do not match
the differences predicted by the precession model of Abraham & Carrara.
Although VLBI components were born about six months prior to each of the two
observed gamma-ray high states, the sparseness of the gamma-ray data prevents a
statistical analysis of possible correlations.


title: Low-luminosity AGN and Normal Galaxies

abstract:
  Low-luminosity AGN (with X-ray luminosity < 1e42 ergs/s) far outnumber
ordinary AGN, and are therefore perhaps more relevant to our understanding of
AGN phenomena and the relationship between AGN and host galaxies. Many normal
galaxies harbor LINER and starburst nuclei, which, together with LLAGN, are a
class of ``low-activity'' galaxies that have a number of surprisingly similar
X-ray characteristics, despite their heterogenous optical classification. This
strongly supports the hypothesis of an AGN-starburst connection. Further, X-ray
observations of normal galaxies without starburst or AGN-like activity in their
nuclei offer opportunities to study populations of X-ray binaries, HII regions,
and warm or hot ISM under different conditions than is often the case in the
Milky Way. The results of recent X-ray observations of these types of galaxies
are reviewed, and what we hope to learn about both nearby and high redshift
galaxies of each type from observations with forthcoming and planned satellites
is discussed.


title: Embedded Star Clusters: The ISO View

abstract:
  We summarize the main results of a mid-IR photometric survey with ISO for a
few nearby embedded clusters. The sensitivity and spatial resolution of ISOCAM
provided a wonderful tool for studies of the youngest stellar clusters, which
are still deeply embedded in their parent molecular clouds. Mid-IR photometry
is found to be extremely efficient in finding all the young stellar objects
(YSOs) with IR excesses, i.e. mainly T Tauri stars surrounded by circumstellar
disks and also some Class I sources. The spatial distribution of these sources
is highly clustered and even sub-clustered, with a tendency of stronger
concentration for the younger regions. The improved samples of IR-excess YSOs
appear complete down to 0.03 L_sun for the most nearby clusters. This gives
constraints on the mass functions well into the brown dwarf domain. The first
results show that the mass functions of these clusters are identical to the
field star IMF derived by Kroupa et al. (1993) with a flattening of the mass
function at M_star ~ 0.5 M_sun.


title: Snapshot Identification of Gamma Ray Burst Optical Afterglows

abstract:
  Gamma ray burst afterglows can be identified in single epoch observations
using three or more optical filters. This method relies on color measurements
to distinguish the power law spectrum of an afterglow from the curved spectra
of stars. Observations in a fourth filter will further distinguish between
afterglows and most galaxies up to redshifts z ~ 1. Many afterglows can also be
identified with fewer filters using ultraviolet excess, infrared excess, or
Lyman break techniques. By allowing faster identification of gamma ray burst
afterglows, these color methods will increase the fraction of bursts for which
optical spectroscopy and other narrow-field observations can be obtained.
Because quasar colors can match those of afterglows, the maximum error box size
where an unambiguous identification can be expected is set by the flux limit of
the afterglow search and the quasar number-flux relation. For currently typical
error boxes (10 -- 100 square arcminutes), little contamination is expected at
magnitudes R < 21.5 +- 0.5. Archival data demonstrates that the afterglow of
GRB 000301C could have been identified using this method. In addition to
finding gamma ray burst counterparts, this method will have applications in
``orphan afterglow'' searches used to constrain gamma ray burst collimation.


title: A Probabilistic Quantification of Galaxy Cluster Membership

abstract:
  Clusters of galaxies are important laboratories for understanding both galaxy
evolution and constraining cosmological quantities. Any analysis of clusters,
however, is best done when one can reliably determine which galaxies are
members of the cluster. While this would ideally be done spectroscopically, the
difficulty in acquiring a complete sample of spectroscopic redshifts becomes
rather daunting, especially at high redshift where the background contamination
becomes increasingly larger. Traditionally, an alternative approach of applying
a statistical background correction has been utilized, which, while useful in a
global sense, does not provide information for specific galaxies. In this
paper, we develop a more robust technique which uses photometrically estimated
redshifts to determine cluster membership. This technique can either be used as
an improvement over the commonly used statistical correction method or it can
be used to determine cluster candidates on an individual galaxy basis. By
tuning the parameters of our algorithm, we can selectively maximize our
completeness or, alternatively, minimize our contamination. Furthermore, our
technique provides a statistical quantification of both our resulting
completeness and contamination from foreground and background galaxies.


title:
Three-Dimensional Modeling of the Deflagration Stage of a Type Ia
  Supernova Explosion

abstract:
  The paper describes a physical model and numerical algorithm for modeling
Type Ia supernova (SNIa) explosions in three dimensions and presents first
results of modeling a deflagration explosion in a nonrotating,
Chandrasekhar-mass carbon-oxygen (CO) white dwarf. Simulations show that the
turbulent flame speed grows exponentially, reaches approximately 30% of the
speed of sound, and then declines as the large-scale turbulence is frozen by
expansion. The freezing of turbulent motions appears to be a crucial physical
mechanism regulating the rate of deflagration in SNIa. The energy of the
explosion is comparable to that of a typical SNIa. However, the presence of the
outer layer of unburned CO and the formation of intermediate mass elements and
pockets of unburned CO near the center pose problems for the modeling of SNIa
spectra. Delayed detonation is a way to alleviate these problems and to produce
consistent spectra.


title:
Spherically symmetric model atmospheres for low mass pre-Main Sequence
  stars with effective temperatures between 2000 and 6800 K

abstract:
  We present a grid of spherically symmetric model atmospheres for young pre-MS
stars. This grid spans the parameter range $2000\K \leq \Teff \leq 6800\K$ and
$2.0 \leq \logg \leq 3.5$ for $M=0.1\Msun$, appropriate for low mass stars and
brown dwarfs. A major improvement is the replacement of TiO and \water line
lists with the newer line list calculated by the NASA-AMES group, for TiO
(about 175 million lines of 5 isotopes) and for \water (about 350 million lines
in 2 isotopes). We provide the model structures, spectra and broad-band colors
in standard filters in electronic form.


title: TiO and H$_2$O absorption lines in cool stellar atmospheres

abstract:
  We compare the structures of model atmospheres and synthetic spectra
calculated using different line lists for TiO and water vapor. We discuss the
effects of different line list combinations on the model strutures and spectra
for both dwarf and giant stars. It is shown that recent improvements result in
significantly improved spectra, in particular in the optical where TiO bands
are important. The water vapor dominated near-IR region remains problematic as
the current water line lists do not yet completely reproduce the shapes of the
observed spectra. We find that the AMES TiO list provides more opacity in most
bands and that the new, smaller oscillator strengths lead to systematically
cooler temperatures for early type M dwarfs than previous models. These effects
combine and will help to siginificantly improve the fits of models to
observations in the optical as well as result in improved synthetic photometry
of M stars. We show that the Davis 1986 \fel-values for the $\delta$ and $\phi$
bands of TiO best reproduce the observed (V-I) color indices.


title: Stars and Planetary Nebulae in the Galactic Bulge

abstract:
  We compare the populations of Red Giant stars and Planetary Nebulae in the
Galactic Bulge, in the light of recent determinations of their abundances
patterns. We find both populations to be compatible. From the planetary
nebulae, we find evidences that the Bulge did not form stars recently. The
whole abundances pattern remains however puzzling, some elements favoring a
quick evolution of the Galactic Bulge (Mg and Ti), and others a much slower one
(He, O, Si, S, Ar and Ca).


title:
Chandra X-ray Observations of Pictor A: High Energy Cosmic Rays in a
  Radio Galaxy?

abstract:
  We report X-ray observations of the nearby, powerful radio galaxy Pictor A
with the Chandra Observatory and optical and near uv observations of its
western radio hot spot with the Hubble Space Telescope. X-ray emission is
detected from the nucleus, a 1.9 arcmin (110 kpc) long jet to the west of the
nucleus, the western radio hot spot some 4.2 arcmin (240 kpc) from the nucleus,
and the eastern radio lobe. The morphology of the western hot spot is
remarkably similar to that seen at radio and optical wavelengths, where the
emission is known to be synchrotron radiation. The X-ray spectrum of the hot
spot is well described by an absorbed power law with photon index \Gamma = 2.07
(+/- 0.11). The X-ray jet coincides with a weak radio jet and is laterally
extended by \simeq 2.0 arcsec (1.9 kpc). The observed jet is up to \simeq 15
times brighter in X-rays than any counter jet, a difference ascribed to
relativistic boosting as the western radio lobe is probably the closer. The
jet's spectrum is well modelled by an absorbed power law with \Gamma = 1.94
(+0.43/-0.49) and poorly fitted by a Raymond-Smith thermal plasma model.
  (Abstract truncated).


title:
Stellar Populations in the Phoenix Dwarf (dIrr/dSph) Galaxy as Observed
  by HST/WFPC2

abstract:
  We present HST/WFPC2 photometry of the central regions of the Phoenix dwarf.
Accurate photometry allows us to: 1) confirm the existence of the horizontal
branch previously detected by ground-based observations, and use it to
determine a distance to Phoenix, 2) clearly detect the existence of multiple
ages in the stellar population of Phoenix, 3) determine a mean metallicity of
the old red giant branch stars in Phoenix, and suggest that Phoenix has evolved
chemically over its lifetime, 4) extract a rough star formation history for the
central regions which suggests that Phoenix has been forming stars roughly
continuously over its entire lifetime.


title: Secondary CMB Anisotropies from Cosmological Reionization

abstract:
  We use numerical simulation of cosmological reionization to calculate the
secondary CMB anisotropies in a representative flat low density cosmological
model. We show that the kinetic Sunyaev-Zel'dovich effect (scattering off of
moving electrons in the ionized intergalactic medium) is dominated by the
nonlinear hydrodynamic and gravitational evolution of the density and velocity
fields, rather than the detailed distribution of the ionization fraction
(``patchy reionization'') on all angular scales. Combining our results with the
recent calculation of secondary CMB anisotropies by Springel et al., we are
able to accurately predict the power spectrum of the kinetic SZ effect on
almost all angular scales.


title: The Principal Axis of the Virgo Cluster

abstract:
  Using accurate distances to individual Virgo cluster galaxies obtained by the
method of Surface Brightness Fluctuations, we show that Virgo's brightest
ellipticals have a remarkably collinear arrangement in three dimensions. This
axis, which is inclined by 10 to 15 degrees from the line of sight, can be
traced to even larger scales where it appears to join a filamentary bridge of
galaxies connecting Virgo to the rich cluster Abell 1367. The orientations of
individual Virgo ellipticals also show some tendency to be aligned with the
cluster axis, as does the jet of the supergiant elliptical M87. These results
suggest that the formation of the Virgo cluster, and its brightest member
galaxies, have been driven by infall of material along the Virgo-A1367
filament.


title:
Physical Diagnostics from a Narrow Fe-Kalpha Emission Line Detected by
  Chandra in the Seyfert 1 Galaxy NGC 5548

abstract:
  We report the detection of a narrow Fe-K emission line in the Seyfert 1
galaxy NGC 5548 with the Chandra High-Energy Transmission Gratings. In the
galaxy frame we measure a center energy of 6.40 \pm 0.03 keV, a FWHM of 4515
(+3525,-2645) km/s, and an equivalent width of 133 (+62,-54) eV. The line
energy is consistent with an origin in cold, neutral matter, but ionization
states up to ~Fe XVIII are not ruled out. Assuming Keplerian motion, the
velocity width is consistent with the line being produced in the outer
optical/UV broad-line region (BLR) at about a light-month from the central
X-ray source. We cannot rule out some contribution to the Fe-K line from a
putative, parsec-scale obscuring torus. The continuum intensity during the
Chandra observation was a factor ~2 less than typical historical levels. If the
X-ray continuum was > than a factor 2 higher in the recent past before the
Chandra observation and the narrow Fe-K line intensity had not yet responded,
then the predicted line equivalent width and intensity for an origin in the BLR
is within the 90% measurement errors. Retroactive spectral fitting of archival
ASCA data shows evidence that the narrow Fe-K has a variable intensity. It will
be important to measure the non-disk component of the Fe-K line in other AGN to
obtain a more complete understanding of the total Fe-K line emission.
Measurement of the narrow-line parameters provides powerful diagnostics of
conditions beyond the accretion disk and is necessary to properly deconvolve
the broad, relativistic Fe-K line.


title: ASTRO-F - The next generation of mid-infrared surveys

abstract:
  We present basic observational strategies for ASTRO-F (also known as the
Imaging Infra Red Surveyor (IRIS)) to be launched in 2004 by the Japanese
Institute of Space and Astronautical Science (ISAS). We examine 2 survey
scenarios, a deep ~1sq.deg. survey reaching sensitivities an order of magnitude
below than the deepest surveys performed by ISO in the mid-IR, and a shallow
\~18sq.deg mid-infrared (7-25um in 6 bands) covering an area greater than the
entire area covered by all ISO mid-IR surveys. Using 2 cosmological models the
number of galaxies predicted for each survey is calculated. The first model
uses an enhancement of the pure luminosity evolution model of Pearson &
Rowan-Robinson while the new models incorporate a strongly evolving ULIG
component. For the deep survey, between 20,000-30,000 galaxies should be
detected in the shortest wavebands and ~5000 in the longest (25um) band. The
shallow survey would be expected to detect of the order of 100,000 - 150,000
sources.


title: Neutrino-electron processes in a strongly magnetized thermal plasma

abstract:
  We present a new method of calculating the rate of neutrino-electron
interactions in a strong magnetic field based on finite temperature field
theory. Using this method, in which the effect of the magnetic field on the
electron states is taken into account exactly, we calculate the rates of all of
the lowest order neutrino-electron interactions in a plasma. As an example of
the use of this technique, we explicitly calculate the rate at which neutrinos
and antineutrinos annihilate in a highly magnetized plasma, and compare that to
the rate in an unmagnetized plasma. The most important channel for energy
deposition is the gyromagnetic absorption of a neutrino-antineutrino pair on an
electron or positron in the plasma ($\nu\bar{\nu} e^\pm\leftrightarrow e^\pm$).
Our results show that the rate of annihilation increases with the magnetic
field strength once it reaches a certain critical value, which is dependent on
the incident neutrino energies and the ambient temperature of the plasma. It is
also shown that the annihilation rates are strongly dependent on the angle
between the incident particles and the direction of the magnetic field. If
sufficiently strong fields exist in the regions surrounding the core of a type
II supernovae or in the central engines of gamma ray bursts, these processes
will lead to more efficient plasma heating mechanism than in an unmagnetized
medium, and moreover, one which is intrinsically anisotropic.


title: A cannonball model of gamma-ray bursts: superluminal signatures

abstract:
  Recent observations suggest that the long-duration gamma ray bursts (GRBs)
and their afterglows are produced by highly relativistic jets emitted in
supernova explosions. We propose that the result of the event is not just a
compact object plus the ejecta: within a day, a fraction of the parent star
falls back to produce a thick accretion disk. The subsequent accretion
generates jets and constitutes the GRB ``engine'', as in the observed ejection
of relativistic ``cannonballs'' of plasma by microquasars and active galactic
nuclei. The GRB is produced as the jetted cannonballs exit the supernova shell
reheated by the collision, re-emitting their own radiation and boosting the
light of the shell. They decelerate by sweeping up interstellar matter, which
is accelerated to cosmic-ray energies and emits synchrotron radiation: the
afterglow. We emphasize here a smoking-gun signature of this model of GRBs: the
superluminal motion of the afterglow, that can be searched for ---the sooner
the better--- in the particular case of GRB 980425.


title: A toroidal black hole for the AGN phenomenon

abstract:
  A new approach to the study of the AGN phenomenon is proposed, in which the
nucleus activity is related to the metric of the inner massive black hole. The
possibility of a Toroidal Black Hole (TBH), in contrast to the usual Spherical
Black Hole (SBH), is discussed as a powerful tool in understanding AGN related
phenomena, such as the energetics, the production of jets and the acceleration
of particles, the shape of the magnetic field and the lifetime of nucleus
activity.


title:
A modification of the Monte Carlo method for simulation of radiative
  transfer in molecular clouds

abstract:
  We propose a method of simulation that is based on the averaging of formal
solutions of the transfer equation by taking the integral by the Monte Carlo
method. This method is used to compute two models, which correspond to the
limiting cases of hot gas and cold background radiation and of hot background
radiation and cold gas, for E-methanol emission from a compact homogeneous
spherical region. We analyse model level populations by using rotational
diagrams in the limiting cases mentioned above. Model optical depths of the
lines with frequencies below 300 GHz up to J=11 inclusive are given.


title:
Can a Very Low-Luminosity and Cold White Dwarf be a Self-gravitating
  Bose Condensed System

abstract:
  An entirely new model for the structure as well as for the cooling mechanism
of white dwarfs has been proposed. We have argued that the massive part of the
constituents of white dwarfs- the positively charged ions are boson and under
the extreme physical condition (density and temperature) at the interior, it is
possible to have condensation of charged bose gas. We have tried to establish
that a cold white dwarf is a self gravitating charged bose condensed system.


title: Box- and peanut-shaped bulges: II. NIR observations

abstract:
  We have observed 60 edge-on galaxies in the NIR in order to study the stellar
distribution in galaxies with box/peanut-shaped bulges. The much smaller amount
of dust extinction at these wavelengths allows us to identify in almost all
target galaxies with box/peanut-shaped bulges an additional thin, central
component in cuts parallel to the major axis. This structure can be identified
with a bar. The length of this structure scaled by the length of the bulge
correlates with the morphologically classified shape of the bulge. This newly
established correlation is therefore mainly interpreted as the projection of
the bar at different aspect angles. Galaxies with peanut bulges have a bar seen
nearly edge-on and the ratio of bar length to thickness, 14 +/- 4, can be
directly measured for the first time. In addition, the correlation of the
boxiness of bulges with the bar strength indicates that the bar characteristic
could partly explain differences in the bulge shape. Furthermore, a new size
relation between the box/peanut structure and the central bulge is found. Our
observations are discussed in comparison to a N-body simulation for barred
galaxies (Pfenniger & Friedli 1991). We conclude that the inner region of
barred disk galaxies are build up by three distinct components: the spheroidal
bulge, a thin bar, and a b/p structure most likely representing the thick part
of the bar.


title: On the occurrence of dwarf nova outbursts in post novae

abstract:
  We show that irradiation of the accretion disc by the white dwarf limits the
occurrence of dwarf nova outbursts in post nova accretion discs. After the nova
explosion, the white dwarf has to cool for up to ~100 yr - depending on the
orbital period (i.e., disc size) and the temperature of the white dwarf after
the nova-eruption - before the disc can begin producing dwarf nova outbursts.
During this time the inner disc is maintained in a hot, ionised state. Using
these calculations, we interpret the long-term photometric variability of the
post nova V446 Her (Nova Her 1960) which shows today regular dwarf nova
outbursts. As the white dwarf in V446 Her continues to cool over the next
\~10-20 yr, we predict an increase in the amplitude of outbursts and a decrease
of the outburst frequency, because the decreasing irradiation of the accretion
disc should allow an increasing annular extent of the accretion disc to
participate in limit cycle oscillations.


title: Modelling 20 years of synchrotron flaring in the jet of 3C 273

abstract:
  We present a phenomenological jet model which is able to reproduce well the
observed variations of the submillimetre-to-radio emission of the bright quasar
3C 273 during the last 20 years. It is a generalization of the original shock
model of Marscher & Gear (1985), which is now able to describe an accelerating
or decelerating shock wave, in a curved, non-conical and non-adiabatic jet. The
model defines the properties of a synchrotron outburst which is expected to be
emitted by the jet material in a small region just behind the shock front. By a
proper parameterization of the average outburst's evolution and of the
peculiarities of individual outbursts, we are able to decompose simultaneously
thirteen long-term light-curves of 3C 273 in a series of seventeen distinct
outbursts. It is the first time that a model is so closely confronted to the
long-term multi-wavelength variability properties of a quasar. The ability of
the model to reproduce the very different shapes of the submillimetre-to-radio
light curves of 3C 273 gives strong support to the shock model of Marscher &
Gear (1985). Indirectly, it also reinforces the idea that the outbursts seen in
the light-curves are physically linked to the distinct features observed to
move along the jet with apparently superluminal velocities.


title:
Gravitational Wave Astronomy: in Anticipation of First Sources to be
  Detected

abstract:
  The first generation of long-baseline laser interferometric detectors of
gravitational waves will start collecting data in 2001-2003. We carefully
analyse their planned performance and compare it with the expected strengths of
astrophysical sources. The scientific importance of the anticipated discovery
of various gravitatinal wave signals and the reliability of theoretical
predictions are taken into account in our analysis. We try to be conservative
both in evaluating the theoretical uncertainties about a source and the
prospects of its detection. After having considered many possible sources, we
place our emphasis on (1) inspiraling binaries consisting of stellar mass black
holes and (2) relic gravitational waves. We draw the conclusion that
inspiraling binary black holes are likely to be detected first by the initial
ground-based interferometers. We estimate that the initial interferometers will
see 2-3 events per year from black hole binaries with component masses
10-15M_\odot, with a signal-to-noise ratio of around 2-3, in each of a network
of detectors consisting of GEO, VIRGO and the two LIGOs. It appears that other
possible sources, including coalescing neutron stars, are unlikely to be
detected by the initial instruments. We also argue that relic gravitational
waves may be discovered by the space-based interferometers in the frequency
interval 2x10^{-3}-10^{-2} Hz, at the signal-to-noise ratio level around 3.


title: Blue Quasars and Blazar Unification Schemes

abstract:
  Blue quasars (BQs) are sources with strong broad emission lines and flat hard
X-ray spectra, properties that resemble classical flat spectrum radio quasars
(FSRQs), and high peak frequencies and steep soft X-ray spectra, properties
that resemble intermediate or high peak frequency BL Lacertae objects(IBLs and
HBLs respectively).
  BQs challenge our understanding of blazar properties in terms of a luminosity
sequence, which makes their incorporation into current blazar unification
schemes problematic. In this work we show that this situation can be remedied
if, in addition to the intrinsic luminosity, the orientation of the blazar jet
is explicitly considered. We show, using published data, that the recently
studied BQs are relatively misaligned blazars, and we examine the predicted
aligned population. We examine both possible cases, sources with pure
synchrotron spectra and sources with an optical--UV thermal contribution, for
both constant velocity and accelerating jets. We show that the aligned sources
are similar to FSRQs, and we suggest ways to distinguish between constant
velocity and accelerating flows. We point out that IBLs are more aligned and
less powerful than BQs and we address the very different emission line
properties of these sources which display similar spectral energy
distributions.


title: Cluster galaxies: contribution to the arc statistics

abstract:
  We present the results of a set of numerical simulations aiming at evaluating
the effects of cluster galaxies on the arc statistics. At this goal we use nine
different galaxy clusters obtained from N-body simulations. We mimic the
presence of a population of galaxies inside each cluster, trying to reproduce
the observed luminosity function and the spatial distribution. We compare the
statistical distributions of the properties of the gravitational arcs produced
by our clusters with and without galaxies. We find that the cluster galaxies do
not introduce perturbations strong enough to significantly change the number of
arcs and the distributions of the properties of long arcs.


title:
Prospects for future far-infrared/submillimeter studies of the
  high-redshift Universe

abstract:
  Observations made using COBE, SCUBA, ISO and MAMBO have provided a reasonable
working knowledge of both the intensity of the submm and far-infrared
background radiation and the source counts of luminous high-redshift dusty
galaxies. However, because there are uncertainties in the background intensity
determinations, the samples of detected galaxies are small, and most
importantly, their redshift distributions are very incomplete, details of the
evolution of dusty galaxies remain unresolved. The next steps forward in the
field will be the launches of SIRTF and ASTRO-F, the commissioning of SOFIA and
new, more capable ground-based mm/submm-wave cameras - BOLOCAM, SHARC-II and
SCUBA-II - the use of ultra-long duration balloon experiments, such as BLAST,
the construction of ALMA and the arrival of FIRST, and ultimately the advent of
space-borne far-infrared interferometers, such as SPECS. There are also
exciting prospects for direct mm/submm-wave CO-line redshift surveys using
wide-band spectrographs. Using these new facilities, the number of
high-redshift dusty galaxies known will be increased dramatically. Spectroscopy
using SIRTF, SOFIA and FIRST will probe the astrophysical processes within
these sources in detail, hopefully addressing the open question of the fraction
of the counts and background radiation that is generated by the formation of
high-mass stars and by active galactic nuclei (AGNs). The spatial and spectral
structure of distant dusty galaxies will finally be resolved in detail using
ALMA and SPECS.


title: Isolated neutron stars discovered by ROSAT

abstract:
  ROSAT has discovered a new group of isolated neutron stars characterized by
soft black-body like spectra (kT ~ 50-120 eV), apparent absence of radio
emission and no association with supernovae remnants. So far only six such
sources are known. A small fraction of these stars exhibit X-ray pulsations
with relatively long periods of the order of 10 sec. Two very different
mechanisms may be envisaged to explain their properties. The neutron stars may
be old and re-heated by accretion from the ISM in which case their population
properties could provide information on past stellar formation and secular
magnetic field decay. Alternatively, this group may at least partly be made of
relatively young cooling neutron stars possibly descendant from magnetars. We
review the last observational results and show how they can shed light on the
evolutionary path of these new objects within the whole class of isolated
neutron stars.


title:
Multiwaveband studies of the hard ROSAT SMC transient 1WGA J0053.8-7226:
  a new X-ray pulsar

abstract:
  We report on two optical candidates for the counterpart to an X-ray source in
the SMC, 1WGA J0053.8-7226, identified as a serendipitous X-ray source from the
ROSAT PSPC archive, and also observed by the Einstein IPC. Its X-ray
properties, namely the hard X-ray spectrum, flux variability and column density
indicate a hard, transient source, with a luminosity of 3.8 x 10E35 ergs/sec.
XTE and ASCA observations have confirmed the source to be an X-ray pulsar, with
a 46 s spin period. Our optical observations reveal two possible candidates
within the error circle. Both exhibit strong H alpha and weaker H beta
emission. The optical colours indicate that both objects are Be-type stars. The
Be nature of the stars implies that the counterpart is most likely a Be/X-ray
binary system. Subsequent IR photometry JHK of one of the objects shows the
source varies by at least 0.5 mag, while the (J-K) measured nearly
simultaneously with the UBVRI and spectroscopic observations indicate an
IR-excess of approximately 0.3 magnitudes.


title:
Diffraction-limited near-IR imaging at Keck reveals asymmetric,
  time-variable nebula around carbon star CIT 6

abstract:
  We present multi-epoch, diffraction-limited images of the nebula around the
carbon star CIT 6 at 2.2 microns and 3.1 microns from aperture masking on the
Keck-I telescope. The near-IR nebula is resolved into two main components, an
elongated, bright feature showing time-variable asymmetry and a fainter
component about 60 milliarcseconds away with a cooler color temperature. These
images were precisely registered (~35 milliarcseconds) with respect to recent
visible images from the Hubble Space Telescope (Trammell et al. 2000), which
showed a bipolar structure in scattered light. The dominant near-IR feature is
associated with the northern lobe of this scattering nebula, and the
multi-wavelength dataset can be understood in terms of a bipolar dust shell
around CIT 6. Variability of the near-IR morphology is qualitatively consistent
with previously observed changes in red polarization, caused by varying
illumination geometry due to non-uniform dust production. The blue emission
morphology and polarization properties can not be explained by the above model
alone, but require the presence of a wide binary companion in the vicinity of
the southern polar lobe. The physical mechanisms responsible for the breaking
of spherical symmetry around extreme carbon stars, such as CIT 6 and IRC+10216,
remain uncertain.


title: Raman-Scattering Wings of H alpha in Symbiotic Stars

abstract:
  Nussbaumer et al. (1989) proposed that broad H$\alpha$ wings can be formed
through Raman scattering of Ly$\beta$ photons, and in this Letter we argue that
the H$\alpha$ wings prevalently seen in symbiotic stars may be indeed formed in
this way. Assuming a flat incident UV radiation around Ly$\beta$, we generate
template wing profiles around H$\alpha$ that are formed through Raman
scattering in a plane-parallel H~I region. We perform profile fitting analyses
to show that the template wing profiles are in excellent agreement with the
observed ones that are provided by van Winckel et al. (1993) and Ivison et al.
(1994). The wing flux is determined by the scattering H~I column density and
the incident Ly$\beta$ flux strength and profile. From our profile analysis it
is proposed that the Raman scattering component may be identified with the
neutral envelope with a column density ranging $10^{18-20} {\rm cm^{-2}}$ that
surrounds the binary system. We briefly discuss alternative candidates for the
wing formation mechanism and observational implications of Raman scattering in
symbiotic stars and in other astronomical objects including planetary nebulae,
post AGB stars and active galactic nuclei.


title:
The Theory of Steady State Super-Eddington Winds and its Application to
  Novae

abstract:
  We present a model for steady state winds of systems with super-Eddington
luminosities. These radiatively driven winds are expected to be optically thick
and clumpy as they arise from an instability driven porous atmosphere. The
model is then applied to derive the mass loss observed in bright classical
novae. The main results are:
  1) A general relation between the mass loss rate and the total luminosity in
super-Eddington systems.
  2) A quantitative agreement between the observed luminosity evolution which
is used to predict both the mass loss and temperature evolution, and their
observations.
  3) An agreement between the predicted average integrated mass loss of novae
as a function of WD mass and its observations.
  4) A natural explanation for the `transition phase' of novae.
  5) Agreement with eta Carinae which was used to double check the theory. The
prediction for the mass shed in the star's great eruption agrees with
observations to within the measurement error.


title: How many young star clusters exist in the Galactic center?

abstract:
  We study the evolution and observability of young compact star clusters
within about 200pc of the Galactic center. Calculations are performed using
direct N-body integration on the GRAPE-4, including the effects of both stellar
and binary evolution and the external influence of the Galaxy. The results of
these detailed calculations are used to calibrate a simplified model applicable
over a wider range of cluster initial conditions. We find that clusters within
200 pc from the Galactic center dissolve within about 70 Myr. However, their
projected densities drop below the background density in the direction of the
Galactic center within 20 Myr, effectively making these clusters undetectable
after that time. Clusters farther from the Galactic center but at the same
projected distance are more strongly affected by this selection effect, and may
go undetected for their entire lifetimes. Based on these findings, we conclude
that the region within 200 pc of the Galactic center could easily harbor some
50 clusters with properties similar to those of the Arches or the Quintuplet
systems.


title: Cosmic Rays and the Structure of Space-Time

abstract:
  Even a fundamental symmetry like Lorentz Invariance is an experimental fact
and must be experimentally verified. We show that the study of the interactions
of Cosmic Rays with universal diffuse background radiation can provide very
stringent tests of this symmetry. The interactions we consider are the ones
characterized by well defined energy thresholds whose energy position can be
predicted on the basis of Special Relativity. We argue that the experimental
verification of these thresholds can address the physics of supra-Planckian
scales.


title: Far-Ultraviolet Spectra of AGN: First Results from FUSE

abstract:
  Composite spectra derived from HST observations of moderate redshift (z~1)
quasars show that the peak of the spectral energy distribution is at ~1000 A,
and that the ionizing continuum falls off smoothly to shorter wavelengths as
$f_\nu \sim \nu^{-1.8}$. HUT and FUSE observations of nearby AGN (e.g., 3C 273)
show similar results. FUSE spectra reveal a wealth of detail in the 912-1200 A
spectral range, including multi-component intrinsic absorption in the O VI
doublet and Lyb, and surprisingly strong narrow-line emission from O VI
1032,1038. Monitoring observations of AGN below 1200 A are feasible, and such
experiments could help to unravel the structure of intrinsic absorbers in AGN
as well as the highest ionization portions of the broad-line region.


title:
How young are early-type cluster galaxies ? Quantifying the young
  stellar component in a rich cluster at z=0.41

abstract:
  We present a new method of quantifying the mass fraction of young stars in
galaxies by analyzing near-ultraviolet (NUV)-optical colors. We focus our
attention on early-type cluster galaxies, whose star formation history is at
present undetermined. Rest-frame NUV (F300W) and optical (F702W) images of
cluster Abell 851 (z=0.41) using HST/WFPC2 allow us to determine a NUV-optical
color-magnitude relation, whose slope is incompatible with a monolithic
scenario for star formation at high redshift. A degeneracy between a young
stellar component and its fractional mass contribution to the galaxy is found,
and a photometric analysis comparing the data with the predictions for a simple
two-stage star formation history is presented. The analysis shows that some of
the early-type galaxies may have fractions higher than 10% of the total mass
content in stars formed at z~0.5. An increased scatter is found in the
color-magnitude relation at the faint end, resulting in a significant fraction
of faint blue early-type systems. This would imply that less massive galaxies
undergo more recent episodes of star formation, and this can be explained in
terms of a positive correlation between star formation efficiency and
luminosity.


title: Neutrinos and the Supernova Origin of the Elements

abstract:
  Intense fluxes of neutrinos are emitted by the hot neutron star produced in a
supernova. The electron neutrino and antineutrino capture reactions on neutrons
and protons, respectively, provide heating to drive a wind from the hot neutron
star. The same reactions also determine the neutron-richness of the wind
material. Nucleosynthesis via rapid neutron capture, the r-process, may occur
in the wind material as it expands away from the neutron star. The
neutron-richness of the wind material, and hence, the r-process nucleosynthesis
therein, are sensitive to mixing between the muon (or tauon)
neutrino/antineutrino and the electron (or sterile) neutrino/antineutrino.
Indirect arguments and direct tests for the supernova origin of the r-process
elements are discussed with a goal to establish supernova r-process
nucleosynthesis as an important probe for neutrino mixing.


title:
What Is The BBN Prediction for the Baryon Density and How Reliable Is
  It?

abstract:
  Together, the standard theory of big-bang nucleosynthesis (BBN) and the
primeval deuterium abundance now very precisely peg the baryon density. Based
upon our analysis of the deuterium data and the theoretical uncertainties
associated with the BBN predictions, we determine Omega_B h^2 = 0.020\pm 0.002
(95% C.L.), with the uncertainty from the measured deuterium abundance about
twice that from the predicted abundance. We discuss critically the reliability
of the BBN baryon density, and in light of possible systematic uncertainties
also derive a very conservative range. We conclude that within the standard
cosmology and standard theory of BBN a baryon density Omega_B h^2=0.032 (the
central value implied by recent CMB anisotropy measurements) simply cannot be
accommodated.


title: A moving cold front in the intergalactic medium of A3667

abstract:
  We present results from a Chandra observation of the central region of the
galaxy cluster A3667, with emphasis on the prominent sharp X-ray brightness
edge spanning 0.5 Mpc near the cluster core. Our temperature map shows
large-scale nonuniformities characteristic of the ongoing merger, in agreement
with earlier ASCA results. The brightness edge turns out to be a boundary of a
large cool gas cloud moving through the hot ambient gas, very similar to the
"cold fronts" discovered by Chandra in A2142. The higher quality of the A3667
data allows the direct determination of the cloud velocity. At the leading edge
of the cloud, the gas density abruptly increases by a factor of 3.9+-0.8, while
the temperature decreases by a factor of 1.9+-0.2 (from 7.7 keV to 4.1 keV).
The ratio of the gas pressures inside and outside the front shows that the
cloud moves through the ambient gas at near-sonic velocity, M=1+-0.2 or
v=1400+-300 km/s. In front of the cloud, we observe the compression of the
ambient gas with an amplitude expected for such a velocity. A smaller surface
brightness discontinuity is observed further ahead, ~350 kpc in front of the
cloud. We suggest that it corresponds to a weak bow shock, implying that the
cloud velocity may be slightly supersonic. Given all the evidence, the cold
front appears to delineate the remnant of a cool subcluster that recently has
merged with A3667. The cold front is remarkably sharp. The upper limit on its
width, 3.5 arcsec or 5 kpc, is several times smaller than the Coulomb mean free
path. This is a direct observation of suppression of the transport processes in
the intergalactic medium, most likely by magnetic fields.


title: Dynamics of Black-Hole Nuclei

abstract:
  Space-based observations are beginning to yield detailed information about
the stellar kinematics at the very centers of galaxies, within the sphere of
gravitational influence of the black hole. The structure and dynamics of these
regions is probably determined in part by the infall and coalescence of black
holes during galaxy mergers. A goal of N-body simulations is to reproduce the
kinematics near the black holes as well as the relations that exist between the
nuclear and global properties of galaxies. However, the problem is
computationally difficult due to the wide range of length and time scales, and
no single N-body code can efficiently follow the evolution from kiloparsec to
sub-parsec scales. We review existing N-body work on this problem and present
the first, fully self-consistent merger simulations of galaxies containing
dense stellar cusps and black holes.


title:
Scattering of energetic particles by anisotropic magnetohydrodynamic
  turbulence with a Goldreich-Sridhar power spectrum

abstract:
  Scattering rates for a Goldreich-Sridhar (GS) spectrum of anisotropic,
incompressible, magnetohydrodynamic turbulence are calculated in the
quasilinear approximation. Because the small-scale fluctuations are constrained
to have wave vectors nearly perpendicular to the background magnetic field,
scattering is too weak to provide either the mean free paths commonly used in
Galactic cosmic-ray propagation models or the mean free paths required for
acceleration of cosmic rays at quasi-parallel shocks. Where strong pitch-angle
scattering occurs, it is due to fluctuations not described by the GS spectrum,
such as fluctuations generated by streaming cosmic rays.


title:
Chandra estimate of the magnetic field strength near the cold front in
  A3667

abstract:
  We use the Chandra observation of the cold front in the intracluster gas of
A3667 to estimate the magnetic field strength near the front. The front is seen
in the Chandra data as a sharp discontinuity in the gas density which
delineates a large body of dense cool gas moving with the near-sonic velocity
through the less dense, hotter gas. Without a magnetic field, the front should
be quickly disturbed by the Kelvin-Helmholtz instability arising from
tangential motion of gas layers. However, Chandra image shows that the front is
stable within a +-30deg sector in the direction of the cloud motion, beyond
which it gradually disappears. We suggest that the Kelvin-Helmholtz instability
within the +-30deg sector is suppressed by surface tension of the magnetic
field whose field lines are parallel to the front. The required field strength
is B ~ 10 muG. Magnetic field near the front is expected to be stronger and
have very different structure compared to the bulk of the intergalactic medium,
because the field lines are stretched by the tangential gas motions. Such a
magnetic configuration, once formed, would effectively stop the plasma
diffusion and heat conduction across the front, and may inhibit gas mixing
during the subcluster merger. We note that even the increased magnetic field
near the front contributes only 10-20% to the total gas pressure, and therefore
magnetic pressure is unimportant for hydrostatic cluster mass estimates.


title:
omega Centauri - a former nucleus of a dissolved dwarf galaxy? New
  evidence from Stroemgren photometry

abstract:
  CCD vby Stroemgren photometry of a statistically complete sample of red
giants and stars in the main sequence turn-off region in omega Centauri has
been used to analyse the apparently complex star formation history of this
cluster. From the location of stars in the (b-y),m_1 diagram metallicities have
been determined. These have been used to estimate ages of different
sub-populations in the color-magnitude diagram. The metal-poor population
around -1.7 dex is the oldest population found. More metal-rich stars between
[Fe/H]=-1.5 and -1.0 dex tend to be 1-3 Gyr younger. These stars are more
concentrated towards the center than the metal-poor ones. The most-metal rich
stars (-0.7 dex) might be up to 6 Gyr younger than the oldest population. They
are asymmetrically distributed around the center with an excess of stars
towards the South. We argue that the Stroemgren metallicity in terms of element
abundances has another meaning than in other globular clusters. From a
comparison with spectroscopic element abundances, we find the best correlation
with the sum C+N. The high Stroemgren metallicities, if interpreted by strong
CN-bands, result from progressively higher N and perhaps C abundances in
comparison to iron. We see an enrichment already among the metal-poor
population, which is difficult to explain by self-enrichment alone. An
attractive speculation is that omega Cen was the nucleus of a dwarf galaxy. We
propose a scenario in which omega Cen experienced mass inflow over a long
period of time, until the gas content of its host galaxy was so low that star
formation in omega Cen stopped, or alternatively the gas was stripped off
during its infall in the Milky Way potential. A mass inflow occuringcn a clumpy
and discontinuous manner could explain several of our findings.


title:
The Effects of Rotation on the Evolution of Rising Omega-loops in a
  Stratified Model Convection Zone

abstract:
  We present three-dimensional MHD simulations of buoyant magnetic flux tubes
that rise through a stratified model convection zone in the presence of solar
rotation. The equations of MHD are solved in the anelastic approximation, and
the results are used to determine the effects of solar rotation on the dynamic
evolution an Omega-loop. We find that the Coriolis force significantly
suppresses the degree of fragmentation at the apex of the loop during its
ascent toward the photosphere. If the initial axial field strength of the tube
is reduced, then, in the absence of forces due to convective motions, the
degree of apex fragmentation is also reduced. We show that the Coriolis force
slows the rise of the tube, and induces a retrograde flow in both the
magnetized and unmagnetized plasma of an emerging active region.
Observationally, we predict that this flow will appear to originate at the
leading polarity, and will terminate at the trailing polarity.


title: Effects of weak lensing on the topology of CMB maps

abstract:
  We investigate the non-Gaussian signatures in Cosmic Microwave Background
(CMB) maps induced by the intervening large-scale structure through weak
lensing. In order to measure the deviation from the Gaussian behavior of the
intrinsic temperature anisotropies, we use a family of three morphological
descriptors, the so-called Minkowski functionals. We show analytically how
these quantities depend on the temperature threshold, and compare the results
to numerical experiments including the instrumental effects of Planck.
Minkowski functionals can directly measure the statistical properties of the
displacement field and hence provide useful constraints on large-scale
structure formation in the past.


title: Warm Absorbing Gas in Cooling Flows

abstract:
  We summarize the discovery of oxygen absorption and warm (10^5-10^6 K) gas in
cooling flows. Special attention is given to new results for M87 for which we
find the strongest evidence to date for ionized oxygen absorption in these
systems. We briefly discuss implications for observations of cooling flows with
Chandra and XMM.


title: Galaxy Halo Masses from Galaxy-Galaxy Lensing

abstract:
  We present measurements of the extended dark halo profiles of bright early
type galaxies at redshifts 0.1 to 0.9 obtained via galaxy-galaxy lensing
analysis of images taken at the CFHT using the UH8K CCD mosaic camera. Six half
degree fields were observed for a total of 2 hours each in I and V, resulting
in catalogs containing ~20 000 galaxies per field. We used V-I color and I
magnitude to select bright early type galaxies as the lens galaxies, yielding a
sample of massive lenses with fairly well determined redshifts and absolute
magnitudes M ~ M_* \pm 1. We paired these with faint galaxies lying at angular
distances 20" to 60", corresponding to physical radii of 26 to 77 kpc (z = 0.1)
and 105 to 315 kpc (z = 0.9), and computed the mean tangential shear of the
faint galaxies. The shear falls off with radius roughly as expected for flat
rotation curve halos. The shear values were weighted in proportion to the
square root of the luminosity of the lens galaxy. Our results give a value for
the average mean rotation velocity of an L_* galaxy halo at r~50-200 kpc of v_*
= 238^{+27}_{-30} km per sec for a flat lambda (Omega_m0 = 0.3, Omega_l0 = 0.7)
cosmology (v_* = 269^{+34}_{-39} km per sec for Einstein-de Sitter), and with
little evidence for evolution with redshift. We compare to halo masses measured
by other groups/techniques. We find a mass-to-light ratio of ~121\pm28h(r/100
kpc) and these halos constitute Omega ~0.04 \pm 0.01(r/100 kpc) of closure
density. (abridged)


title:
Complex Spectral Variability from Intensive Multi-wavelength Monitoring
  of Mrk421 in 1998

abstract:
  We conducted a multi-frequency campaign for the TeV blazar Mrk~421 in 1998
April. The campaign started from a pronounced high amplitude flare recorded by
SAX and Whipple; ASCA observation started three days later. In the X-ray data,
we detected multiple flares, occuring on time scales of about one day. ASCA
data clearly reveal spectral variability. The comparison of the data from ASCA,
EUVE and RXTE indicates that the variability amplitudes in the low energy
synchrotron component are larger at higher photon energies. In TeV Gamma-rays,
large intra-day variations -- which were correlated with the X-ray flux -- were
observed when results from three Cherenkov telescopes are combined. The RMS
variability of TeV Gamma--rays was similar to that observed in hard X-rays,
above 10 keV. The X-ray light curve reveals flares which are almost symmetric
for most of cases, implying the dominant time scale is the light crossing time
through the emitting region. The structure function analysis based on the
continuous X-ray light curve of seven days indicates that the characteristic
time scale is ~0.5 day. The analysis of ASCA light curves in various energy
bands appears to show both soft (positive) and hard (negative) lags. These may
not be real, as systematic effects could also produce these lags, which are all
much smaller than an orbit. If the lags of both signs are real, these imply
that the particle acceleration and X-ray cooling time scales are similar.


title:
Very Large Telescope Observations of the peculiar globular cluster
  NGC6712. Discovery of a UV, H-alpha excess star in the core

abstract:
  We present results from multi-band observations in the central region of the
cluster NGC6712 with the ESO-Very Large Telescope. Using high resolution images
we have identified three UV-excess stars. In particular two of them are within
the cluster core, a few arcsec apart: the first object is star "S" which
previous studies identified as the best candidate to the optical counterpart to
the luminous X-ray source detected in this cluster. The other UV object shows
clearcut H-alpha emission and, for this reason, is an additional promising
interacting binary candidate (a quiescent LMXB or a CV). The presence of two
unrelated interacting binary systems a few arcsec apart in the core of this
low-density cluster is somewhat surprising and supports the hypothesis that the
(internal) dynamical history of the cluster and/or the (external) interaction
with the Galaxy might play a fundamental role in the formation of these
peculiar objects.


title:
Hierarchical clustering and formation of power-law correlation in
  1-dimensional self-gravitating system

abstract:
  The process of formation of fractal structure in one-dimensional
self-gravitating system is examined numerically. It is clarified that
structures created in small spatial scale grow up to larger scale through
clustering of clusters, and form power-law correlation.


title: The compact core-jet region of the superluminal quasar 3C216

abstract:
  Space very long baseline interferometry (VLBI) observations of the quasar
3C216 with the VLBI Space Observatory Programme (VSOP) reveal that the parsec
scale structure of the source can be well described by compact jet models
developed for interpreting the core region of radio-loud active galactic nuclei
(AGN). The measured brightness temperature of T_(b) = 7.9*10^{11} K is
comparable to the inverse Compton limit, from which we determine a lower limit
of delta ~ 3.17 for the Doppler-boosting factor. The apparent transvers
velocity of the superluminal component is beta_(app) = (3.0+-0.2) h^{-1}
asuming a constant velocity, but deceleration of the jet material cannot be
excluded from our data. A combination of the above values indicates that the
viewing angle of the core-jet to the line-of-sight is less than 18.4 degrees,
and the jet Lorentz-factor exceeds 3.16. The observed small size of the source
is probably caused by both interaction with the interstellar medium, and a
projection effect.


title: WSRT Observations of the Hubble Deep Field Region

abstract:
  We present deep WSRT 1.4 GHz observations of the Hubble Deep Field region. At
the 5 sigma level, the WSRT clearly detects 85 regions of radio emission in a
10' x 10' field centred on the HDF. Eight of these regions fall within the HDF
itself, four of these are sources that have not previously been detected at 1.4
GHz, although two of these are VLA detections at 8.5GHz. The two new radio
sources detected by the WSRT are identified with relatively bright (I<21m)
moderate redshift spiral and irregular type galaxies. In the full field, the
WSRT detects 22 regions of emission that were not previously detected by the
VLA at 1.4GHz. At least two of these are associated with nearby, extended
star-forming galaxies.


title: Electromagnetic Radiation and Motion of Real Particle

abstract:
  Relativistically covariant equation of motion for real dust particle under
the action of electromagnetic radiation is derived. The particle is neutral in
charge. Equation of motion is expressed in terms of particle's optical
properties, standardly used in optics for stationary particles.


title: Changing Molecular Gas Properties in the Bar and Canter of NGC7479

abstract:
  We present sensitive interferometric 12CO, 13CO and HCN observations of the
barred spiral galaxy NGC7479, known to be one of the few barred galaxies with a
continuous gas-filled bar. We focus on the investigation and interpretation of
12CO/13CO line intensity ratios, which is facilitated by having more than 90%
of the flux in our interferometer maps. The global (9kpc by 2.5kpc) value of
the 12CO/13CO ratio is high at 20 - 40. On smaller scales (~ 750 pc), the ratio
is found to vary dramatically, reaching values > 30 in large parts of the bar,
but dropping to values ~ 5, typical for galactic disks, at a 13CO condensation
in the southern part of the bar. We interpret these changes in terms of the
relative importance of the contribution of a diffuse molecular component,
characterized by unbound gas that has a moderate optical depth in the 12CO(1 -
0) transition. This component dominates the 12CO along the bar and is also
likely to play an important role in the center of NGC7479. In the center, the
12CO and the HCN intensity peaks coincide, while the 13CO peak is slightly
offset. This can be explained in terms of high gas temperature and density at
the 12CO peak position. Along the bar, the relation between the distribution of
12CO, 13CO, dust lanes and velocity gradient is complex. A southern 13CO
condensation is found offset from the 12CO ridge that generally coincides with
the most prominent dust lanes. It is possible that strong 13CO detections along
the bar indicate quiescent conditions, downstream from the major bar shock.
Still, these condensations are found close to high velocity gradients. In the
central region, the velocity gradient is traced much more closely by 13CO than
by 12CO.


title: Numerical hydrodynamics: SPH vs. AMR

abstract:
  The advantages and disadvantages of two approaches to astrophysical
hydrodynamics, Smoothed Particle Hydrodynamics and Adaptive Mesh Refinement,
are briefly discussed together with some current problems of computational
hydrodynamics.


title:
Near-infrared imaging of the host galaxies of intermediate redshift
  steep spectrum radio quasars

abstract:
  We present the results of near-infrared H-band (1.65 microns) imaging of 19
steep spectrum radio quasars (SSRQ) in the redshift range 0.5 < z < 1.0. This
sample of SSRQs is matched with our previously studied complete sample of 20
flat spectrum radio quasars (FSRQ) with respect to redshift and optical and
radio luminosity. We are able to clearly detect the host galaxy in 10 (53 %)
SSRQs and marginally in 6 (32 %) others, while the host remains unresolved in 3
(16 %) SSRQs. The galaxies hosting the SSRQs are large (average bulge
scale-length R(e) = 9.0+-1.7 kpc) and luminous (average M(H) = -27.2+-1.1).
They are, therefore, about 2 mag more luminous than the typical galaxy
luminosity L* (M*(H) = -25.0+-0.2), and about 1 mag more luminous than the
brightest cluster galaxies (M(H) = -26.3+-0.3). The SSRQ hosts appear to have
similar luminosity to those of the FSRQ hosts (M(H) = -27), and they fall
between the luminosities of lower redshift (M(H) = -26) and higher redshift
(M(H) = -29) radio-loud quasars. The average nucleus-to-galaxy luminosity ratio
of SSRQs (LN/LG = 3.8+-3.2) is much smaller than that found for the FSRQs
(LN/LG = 21+-11), in good agreement with the current unified models. We confirm
for the most luminous SSRQs the trend noted for the FSRQs between the host and
nuclear luminosity. This trend supports the suggestion based on studies of
lower redshift AGN, that there is a minimum host galaxy luminosity which
increases linearly with the quasar luminosity. Finally, FSRQs seem to reside in
richer environments than SSRQs, as evidenced by a larger number of close
companion galaxies.


title: Tidally-induced angular momentum transport in disks

abstract:
  We discuss the transport of angular momentum induced by tidal effects in a
disk surrounding a star in a pre-main sequence binary system. We consider the
effect of both density and bending waves. Although tidal effects are important
for truncating protostellar disks and for determining their size, it is
unlikely that tidally-induced angular momentum transport plays a dominant role
in the evolution of protostellar disks. Where the disk is magnetized, transport
of angular momentum is probably governed by MHD turbulence. In a non
self-gravitating laminar disk, the amount of transport provided by tidal waves
is probably too small to account for the lifetime of protostellar disks. In
addition, tidal effects tend to be localized in the disk outer regions.


title:
The Global-Normal Disk Oscillations and the Persistent Low Frequency QPO
  in X-ray Binaries

abstract:
  We suggest that persistent low-frequency quasi-periodic oscillations (QPOs)
detected in X-ray, ultraviolet, optical energy ranges the black hole (BH)
sources XTE J1118+480, GRO J1655-40 LMC X-1 at ~ 0.1 Hz, and QPOs in HZ Her/Her
X-1 at ~ 0.05 Hz and in Neutron Star (NS) binaries 4U 1323-62, 4U 1746-31 and
EXO 0748-76 at ~ 1 Hz are caused by the global disk oscillations in the
direction normal to the disk (normal mode). We argue that these disk
oscillations are a result of the gravitational interaction between the central
compact object and the disk. A small displacement of the disk from the
equatorial plane results in a linear gravitational restoring force opposite to
this displacement. Our analysis shows that the frequency of this mode is a
function of the mass of the central object and it also depends on the inner and
outer radii of the disk which in turn are related to the rotation period of the
binary system. We derive an analytical formula for the frequency of the normal
disk mode and show that these frequencies can be related to the persistent
lower QPO frequencies observed in the NS and BH sources. We offer a new
independent approach to the black hole mass determination by interpreting this
low QPO frequency as the global disk oscillation frequency. The implementation
of this method combined with the independent method which uses the X-ray energy
spectra (Shrader & Titarchuk 1999) results in stringent constraints for the
black hole masses.


title: Asteroseismology for the Masses

abstract:
  For many years, astronomers interested in white dwarf stars have promised
that the study of these relatively simple compact objects would ultimately lead
to useful information about the physics under extreme conditions of temperature
and pressure. We are finally ready to make good on that promise. Using the
observational techniques of the Whole Earth Telescope developed over the past
decade, and a new analytical method only recently made feasible by the
availability of fast inexpensive computers, we demonstrate that meaningful
constraints can now be made on the rates of important nuclear fusion reactions
which cannot presently be measured in the laboratory.


title:
Chandra measurements of the distribution of mass in the luminous lensing
  cluster Abell 2390

abstract:
  We present spatially-resolved X-ray spectroscopy of the luminous lensing
cluster Abell 2390, using observations made with the Chandra observatory. The
temperature of the X-ray gas is shown to rise with increasing radius within the
central ~200 kpc of the cluster, and then remain approximately isothermal, with
kT =11.5^{+1.5}_{-1.6} keV, out to the limits of the observations at r~1.0 Mpc.
The total mass profile determined from the Chandra data has a form in good
agreement with the predictions from numerical simulations. Using the
parameterization of Navarro, Frenk & White (1997), we measure a scale radius
r_s~0.9 Mpc and a concentration parameter c~4. The best-fit X-ray mass model is
in good agreement with independent gravitational lensing results and optical
measurements of the galaxy velocity dispersion in the cluster. The X-ray
gas-to-total-mass ratio rises with increasing radius with f_gas = 21 \pm 10 per
cent at r=0.9 Mpc. The azimuthally-averaged 0.3-7.0 keV surface brightness
profile exhibits a small core radius and a clear `break' at r~500 kpc, where
the slope changes from S_X \approxpropto r^{-1.5} to S_X \approxpropto
r^{-3.6}. The data for the central region of the cluster indicate the presence
of a cooling flow with a mass deposition rate of 200-300 solar masses per year
and an age of 2-3 Gyr.


title:
Particle reacceleration in Coma cluster: radio properties and hard X-ray
  emission

abstract:
  The radio spectral index map of the Coma halo shows a progressive steepening
of the spectral index with increasing radius. Such a steepening cannot be
simply justified by models involving continuous injection of fresh particles in
the Coma halo or by models involving diffusion of fresh electrons from the
central regions. We propose a {\it two phase} model in which the relativistic
electrons injected in the Coma cluster by some processes (starbursts, AGNs,
shocks, turbulence) during a {\it first phase} in the past are systematically
reaccelerated during a {\it second phase} for a relatively long time ($\sim$ 1
Gyr) up to the present time. We show that for reacceleration time scales of
$\sim 0.1$ Gyr this hypothesis can well account for the radio properties of
Coma C. For the same range of parameters which explain Coma C we have
calculated the expected fluxes from the inverse Compton scattering of the CMB
photons finding that the hard X-ray tail discovered by BeppoSAX may be
accounted for by the stronger reacceleration allowed by the model. The
possibility of extending the main model assumptions and findings to the case of
the other radio haloes is also discussed, the basic predictions being
consistent with the observations.


title: Massive star populations and the IMF in metal-rich starbursts

abstract:
  We present new spectroscopic observations of Mkn 309, a starburst galaxy with
one of the largest WR populations known. A highly super solar metallicity is
derived. Using additional objects we analyse a sample of five metal-rich WR
galaxies with the main goal of constraining the basic properties of the massive
star populations (IMF slope, M_up) and the star formation history (age, burst
duration) of these objects by quantitative comparisons with evolutionary
synthesis models. The following main results are obtained: 1) The observations
are well explained by extended bursts of star formation or a superposition of
several bursts. Ages and burst durations are estimated. This naturally explains
both the observed WR populations (including WN and WC stars) and the presence
of red supergiants. 2) The fitted SEDs indicate that the stellar light suffers
from a smaller extinction than that of the gas, confirming independent earlier
findings. 3) All the considered observational constraints are compatible with a
Salpeter IMF extending to masses >~ 40 Msun. Adopting a conservative approach
we derive a LOWER LIMIT of Mup >~ 30 Msun for the Salpeter IMF. From more
realistic assumptions on the metallicity and SF history we favour a lower limit
Mup >~ 30-40 Msun, which is also in agreement with Hbeta equivalent width
measurements of metal-rich HII regions in spiral galaxies indicating an upper
mass cut-off of at least ~ 35 - 50 Msun. Steep IMF slopes (alpha >~ 3.3) are
very unlikely. (abridged/modified abstract)


title:
Infrared Observations of AR Ursae Majoris: Modeling the Ellipsoidal
  Variations

abstract:
  We have obtained time-series infrared photometry for the highly magnetic
cataclysmic variable AR UMa. Our J and K' band observations occurred during a
low state and they show a distinctive double-humped structure. Using detailed
models for the expected ellipsoidal variations in the infrared due to the
non-spherical secondary star, we find that the most likely value for the system
inclination is 70 degrees. We also model low state V band photometry and find
that its observed double-humped structure is not caused by ellipsoidal
variations, as they have been ascribed to, but are due to beamed cyclotron
radiation. We use this result to estimate the magnetic field strength of the
active southern accretion region (B <= 190 MG) and its magnetic longitude (330
degrees).


title: Assessing the state of galaxy formation

abstract:
  We present the results of a survey of nearby, quiescent, non-peculiar,
extremely isolated galaxies to search for the gaseous remnants of galaxy
formation. Such remnants are predicted to persist around galaxies into the
present day by galaxy formation models. We find low-mass HI companions around 7
of 34 galaxies surveyed. In addition we find 5 galaxies with lopsided HI
distributions. The implications for galaxy formation and the nature of high
velocity clouds are discussed.


title: Variable Iron K-alpha Lines in Seyfert 1 Galaxies

abstract:
  We find that variability of the iron K-alpha line is common in Seyfert 1
galaxies. Using data from the ASCA archive for objects that have been observed
more than once during the mission, we study the time-averaged spectra from
individual observations, thereby probing variability on timescales that range
from days to years. Since the statistics of the data do not warrant searches
for line variability in terms of a complex physical model, we use a a simple
Gaussian to model the gross shape of the line, and then use the centroid
energy, intensity and equivalent width as robust indicators of changes in the
line profile. We find that ~70% of Seyfert 1s (ten out of fifteen) show
variability in at least one of these parameters: the centroid energy,
intensity, and equivalent width vary in six, four, and eight sources
respectively. Due to the low S/N, limited sampling and time averaging, we
consider these results to represent lower limits to the rate of incidence of
variability. In most cases changes in the line do not appear to track changes
in the continuum. In particular, we find no evidence for variability of the
line intensity in NGC 4151, suggesting an origin in a region larger than the
putative accretion disk, where most of the iron line has been thought to
originate. Mkn 279 is investigated on short timescales. The time-averaged
effective line energy is 6.5 keV in the galaxy rest frame. As the continuum
flux increases by 20% in a few hours, the Fe K line responds with the effective
line energy increasing by 0.22 keV (~10,500 km s^-1). Problems with the ASCA
and Rosat calibration that affect simultaneous spectral fits are discussed in
an appendix.


title: Pulsar Astronomy: the HST Contribution

abstract:
  HST observations have contributed significantly to our knowledge on the
behaviour of Isolated Neutron Stars (INSs) as optical emitters. First, HST has
been instrumental both to discover new optical counterparts (PSR B1055-52, PSR
B1929+10, PSR B0950+08) and to confirm proposed identifications (PSR B0656+14).
Second, HST multicolor photometry provided useful information to characterize
the optical emission mechanism(s) at work in middle-aged INSs like PSR B0656+14
and Geminga. Last, but not least, the superior angular resolution of the HST
allowed both to perform a very accurate morphological study of the plerionic
environments of young pulsars (e.g. the Crab and PSR B0540-69) and to perform
very accurate astrometric measurements yielding proper motions (Crab, Vela,
Geminga, PSR B0656+14) and parallaxes (Geminga).


title: Kinematic Evidence of Minor Mergers in Normal Sa Galaxies

abstract:
  A detailed study of nearby, morphologically normal Sa galaxies reveals that
about half show some spectrocopic evidence for kinematically distinct
components despite their undisturbed optical appearance. In eight of nine
objects mapped in the 21 cm HI line, the HI distribution extends far outside
the optical disk and warps of the HI disk are complex. The multiwavelength
evidence can be interpreted in terms of the kinematic "memory" of past minor
mergers in objects that otherwise exhibit no morphological signs of
interaction.


title: Comparison of UHECR spectra from necklaces and vortons

abstract:
  Cosmic rays of energy higher than 10^19 eV may be explained by topological
defects produced in the early stages of universe. Two suitable alternatives
are: necklaces formed by magnetic monopoles connected by strings, and vortons
which are loops stabilized by superconducting currents. The former are
uniformly distributed in the universe, may account for cosmic rays above the
ankle, suffer a transient GZK cutoff with a subsequent recovery and isotropy of
observations is expected. The latter are concentrated in the galactic halo,
require an additional extragalactic contribution between the ankle and the GZK
cutoff, beyond which give a harder component and predict anisotropy related to
mass concentration.


title:
Discovery of nearly coherent oscillations with a frequency of ~567 Hz
  during type-I X-ray bursts of the X-ray transient and eclipsing binary X
  1658-298

abstract:
  We report the discovery of nearly coherent oscillations with a frequency of
567 Hz during type-I X-ray bursts from the X-ray transient and eclipsing binary
X 1658-298. If these oscillations are directly related to the neutron star
rotation then the spin period of the neutron star in X 1658-298 is 1.8 ms. The
oscillations can be present during the rise or decay phase of the bursts.
Oscillations during the decay phase of the bursts show an increase in the
frequency of 0.5 to 1 Hz. However, in one particular burst the oscillations
reappear at the end of the decay phase at about 571.5 Hz. This represents an
increase in oscillation frequency of about 5 Hz which is the largest frequency
change seen so far in a burst oscillation. It is unclear if such a large change
can be accommodated by present models used to explain the frequency evolution
of the oscillations. The oscillations at 571.5 Hz are unusually soft compared
to the oscillations found at 567 Hz. We also observed several bursts during
which the oscillations are detected at much lower significance or not at all.
Most of these bursts happen during periods of X-ray dipping behavior,
suggesting that the X-ray dipping might decrease the amplitude of the
oscillations (although several complications exist with this simple picture).
We discuss our discovery in the framework of the neutron star spin
interpretation.


title: The Origin of a Chemically Enriched lya Absorption System at z=0.167

abstract:
  We present the first detailed analysis of the chemical abundances, ionization
state, and origin of a partial Lyman limit system (N(\hI) ~ 10^{16} \cmjj) at
low redshift (z=0.167 towards PKS0405-1219). Two galaxies at ~ 70 h^{-1} kpc
projected distance to the QSO have been identified at the absorber redshift. We
analyze an echelle spectrum of the QSO obtained with the Space Telescope
Imaging Spectrograph and find that this absorption system exhibits associated
lines produced by C^+, N^+, O^0, Si^+, Si^{++}, Si^{+3}, Fe^+, and Fe^{++}, and
most interestingly, O^{+5} and N^{+4}. The results of our analysis show that
the partial Lyman limit system traced by various ions is likely to be embedded
in a collisionally ionized \ovi gas of larger spatial extent. Furthermore, the
partial Lyman limit system appears to have a metallicity of {\em at least} 1/10
solar and most likely solar or super solar despite the fact that no luminous
galaxies are seen within a projected distance \rho = 60 h^{-1} kpc to the QSO.
Finally, adopting the temperature estimated for the hot gas T ~ 2.5\times 10^5
K and assuming a simple isothermal halo, we estimate that the galaxy or galaxy
group that supports the extended gas may have a total mass ~ 1.5\times 10^{12}
M_\odot and a gas number density \apl 3\times 10^{-5} cm^{-3}.


title:
Magnification relations in gravitational lensing via multidimensional
  residue integrals

abstract:
  We investigate the so-called magnification relations of gravitational lensing
models. We show that multidimensional residue integrals provide a simple
explanation for the existence of these relations, and an effective method of
computation. We illustrate the method with several examples, thereby deriving
new magnification relations for galaxy lens models and microlensing (point mass
lensing).


title:
Non-Thermal Production of WIMPs and the Sub-Galactic Structure of the
  Universe

abstract:
  There is increasing evidence that conventional cold dark matter (CDM) models
lead to conflicts between observations and numerical simulations of dark matter
halos on sub-galactic scales. Spergel and Steinhardt showed that if the CDM is
strongly self-interacting, then the conflicts disappear. However, the
assumption of strong self-interaction would rule out the favored candidates for
CDM, namely weakly interacting massive particles (WIMPs), such as the
neutralino. In this paper we propose a mechanism of non-thermal production of
WIMPs and study its implications on the power spectrum. We find that the
non-vanishing velocity of the WIMPs suppresses the power spectrum on small
scales compared to what it obtained in the conventional CDM model. Our results
show that, in this context, WIMPs as candidates for dark matter can work well
both on large scales and on sub-galactic scales.


title: Three-Dimensional Magnetohydrodynamical Accretion Flows into Black Holes

abstract:
  Outflows and convective motions in accretion flows have been intensively
discussed recently in the context of advection-dominated accretion flow (ADAF)
based on two-dimensional (2D) and three-dimensional (3D) hydrodynamical
simulations. We, however, point that without proper treatments of the disk
magnetic fields, a major source of viscosity, one can never derive general,
firm conclusions concerning the occurrence of outflows and convection. We
analyzed the 3D MHD numerical simulation data of magnetized accretion flows
initially threaded by weak toroidal magnetic fields, finding large-scale
convective motions dominating near the black hole. In contrast, outflows occur
only temporarily and are not very significant in our simulations. If there grow
strong vertical fields somehow, however, formation of bi-polar jets is
inevitable. It is claimed that radiation could be dominant at the outermost
zones of the convective disks because of outward energy flow by convection,
however, this is no longer the case in convective MHD flows, since accretion
energy can be released via magnetic reconnection in the inner parts. Such
reconnection leads to sporadic flare events, thus producing substantial
variability in out-going radiation.


title: On the variation of the Initial Mass Function

abstract:
  (shortened) In this contribution an average or Galactic-field IMF is defined,
stressing that there is evidence for a change in the power-law index at only
two masses: near 0.5 Msun and 0.08 Msun. Using this supposed universal IMF, the
uncertainty inherent to any observational estimate of the IMF is investigated,
by studying the scatter introduced by Poisson noise and the dynamical evolution
of star clusters. It is found that this apparent scatter reproduces quite well
the observed scatter in power-law index determinations, thus defining the
fundamental limit within which any true variation becomes undetectable.
Determinations of the power-law indices alpha are subject to systematic errors
arising mostly from unresolved binaries. The systematic bias is quantified
here, with the result that the single-star IMFs for young star-clusters are
systematically steeper by d_alpha=0.5 between 0.1 and 1 Msun than the
Galactic-field IMF, which is populated by, on average, about 5 Gyr old stars.
The MFs in globular clusters appear to be, on average, systematically flatter
than the Galactic-field IMF, and the recent detection of ancient white-dwarf
candidates in the Galactic halo and absence of associated low-mass stars
suggests a radically different IMF for this ancient population. Star-formation
in higher-metallicity environments thus appears to produce relatively more
low-mass stars.