title:
The Old Halo metallicity gradient: the trace of a self-enrichment
  process

abstract:
  Based on a model of globular cluster self-enrichment published in a previous
paper, we present an explanation for the metallicity gradient observed
throughout the galactic Old Halo. Our self-enrichment model is based on the
ability of globular cluster progenitor clouds to retain the ejecta of a first
generation of Type II Supernovae. The key point is that this ability depends on
the pressure exerted on the progenitor cloud by the surrounding protogalactic
medium and therefore on the location of the cloud in the protoGalaxy. Since
there is no significant (if any) metallicity gradient in the whole halo, we
also present a review in favour of a galactic halo partly build via accretions
and mergers of satellite systems. Some of them bear their own globular clusters
and therefore ``contaminate'' the system of globular clusters formed ``in
situ'', namely within the original potential well of the Galaxy. Therefore, the
comparison between our self-enrichment model and the observational data should
be limited to the genuine galactic globular clusters, the so-called Old Halo
group.


title: The Faint Sky Variability Survey I: An Overview

abstract:
  The Faint Sky Variability Survey is aimed at finding variable objects in the
brightness range between 17th and 25th magnitude on timescales between tens of
minutes and years with photometric precisions ranging from 3 millimagnitudes
for the brightest to 0.2 magnitudes for the faintest objects. An area of at
least 50 square degrees, located at mid-galactic latitudes, will be covered
using the Wide Field Camera on the 2.5m Isaac Newton Telescope on La Palma. The
survey started in November 1998 as part of the INT Wide Field Survey program.
Here we describe the main goals of the Faint Sky Variability Survey, the
methods used in extracting the relevant information and the future prospects of
the survey.


title: The Faint Sky Variability Survey II: Initial Results

abstract:
  We discuss the first results from the Faint Sky Variability Survey (Groot et
al. 2000). The data consist of V-band light curves, BVI colours, astrometry,
and morphology information on several hundred thousand point and extended
sources in the magnitude range V=17-25. We discuss the first 30 survey fields
covering an area of 8.4 square degrees towards moderate and high galactic
latitudes. We analyse the quality of and discuss our differential photometry
light curves. We employ statistical methods to select variable objects and
present example variable light curves. The distribution of the colours and
magnitudes of point sources in the survey is discussed and compared to galactic
star count models. Finally, we discuss our search for trans-Neptunian objects
in the FSVS fields observed towards ecliptic opposition.


title:
Differences between the Two Anomalous X-Ray Pulsars: Variations in the
  Spin Down Rate of 1E 1048.1-5937 and An Extended Interval of Quiet Spin Down
  in 1E 2259+586

abstract:
  We analysed the RXTE archival data of 1E 1048.1-5937 covering a time span of
more than one year. The spin down rate of this source decreases by 30 percent
during the observation. We could not resolve the X-ray flux variations because
of contamination by Eta Carinae. We find that the level of pulse frequency
fluctuations of 1E 1048.1-5937 is consistent with typical noise levels of
accretion powered pulsars. Recent RXTE observations of 1E 2259+586 have shown a
constant spin down with a very low upper limit on timing noise. We used the
RXTE archival X-ray observations of 1E 2259+586 to show that the intrinsic
X-ray luminosity times series is also stable, with an rms fractional variation
of less than 15 percent. The source could have been in a quiet phase of
accretion with a constant X-ray luminosity and spin down rate.


title: Discovery of the Orbit of the Transient X ray Pulsar SAX J2103.5+4545

abstract:
  Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we carried out
pulse timing analysis of the transient X-ray pulsar SAX J2103.5+4545. An
outburst was detected by All Sky Monitor (ASM) October 25 1999 and reached a
peak X-ray brightness of 27 mCrab October 28. Between November 19 and December
27, the RXTE/PCA carried out pointed observations which provided us with pulse
arrival times. These yield an eccentric orbit (e= 0.4 \pm 0.2) with an orbital
period of 12.68 \pm 0.25 days and light travel time across the projected
semimajor axis of 72 \pm 6 sec. The pulse period was measured to be 358.62171
\pm 0.00088 s and the spin-up rate (2.50 \pm 0.15) \times 10^{-13} Hz s^{-1}.
The ASM data for the February to September 1997 outburst in which BeppoSAX
discovered SAX J2103.5+4545 (Hulleman, in't Zand and Heise 1998) are modulated
at time scales close to the orbital period. Folded light curves of the 1997 ASM
data and the 1999 PCA data are similar and show that the intensity increases at
periastron passages.


title:
The beryllium abundance in the very metal-poor halo star G 64-12 from
  VLT/UVES observations

abstract:
  We report on a new spectroscopic analysis of the very metal deficient star G
64-12 ([Fe/H]=-3.3), aimed at determining, for the first time, its Be content.
The spectra were observed during the Science Verification of UVES, the ESO VLT
Ultraviolet and Visible Echelle Spectrograph. The high resolution (~48,000) and
high S/N (~130 per pixel) achieved at the wavelengths of the BeII resonance
doublet allowed an accurate determination of its abundance: log N(Be/H) =
-13.10 +/- 0.15 dex. The Be abundance is significantly higher than expected
from previous measurements of Be in stars of similar metallicity (3D and NLTE
corrections acting to make a slightly higher value than an LTE analysis). When
compared to iron, the high [Be/Fe] ratio thus found may suggest a flattening in
the beryllium evolutionary trend at the lowest metallicity end or the presence
of dispersion at early epochs of galactic evolution.


title: Polarization measurements of Vega-like stars

abstract:
  Optical linear polarization measurements are presented for about 30 Vega-like
stars. These are then compared with the polarization observed for normal field
stars. A significant fraction of the Vega-like stars are found to show
polarization much in excess of that expected to be due to interstellar matter
along the line of sight to the star. The excess polarization must be intrinsic
to the star, caused by circumstellar scattering material that is distributed in
a flattened disk. A correlation between infrared excess and optical
polarization is found for the Vega-like stars.


title: Young radio-loud AGN: A new sample at low redshift

abstract:
  We report on the investigation of a complete sample of young radio-loud AGN
at z<0.25, selected using the new comprehensive radio surveys and the optical
APM/POSS-I catalog. This new sample will provide a unique opportunity for
statistical studies of the early evolution of radio-loud AGN, free of
cosmological evolution effects. In particular, their local luminosity function,
linear-size and dynamical age distributions, may strongly constrain possible
evolution scenarios. In addition, this new sample is well suited for
statistical studies of other important properties, like their X-ray and
infrared emissions, optical cluster environments, and neutral hydrogen in
absorption towards the compact radio sources.


title:
Cosmological parameters from observational data on the large scale
  structure of the Universe

abstract:
  The observational data on the large scale structure (LSS) of the Universe are
used to determine cosmological parameters within the class of adiabatic
inflationary models. We show that a mixed dark matter model with cosmological
constant ($\Lambda$MDM model) and parameters $\Omega_m=0.37^{+0.25}_{-0.15}$,
$\Omega_{\Lambda}=0.69^{+0.15}_{-0.20}$, $\Omega_{\nu}=0.03^{+0.07}_{-0.03}$,
$N_{\nu}=1$, $\Omega_b=0.037^{+0.033}_{-0.018}$, $n_s=1.02^{+0.09}_{-0.10}$,
$h=0.71^{+0.22}_{-0.19}$, $b_{cl}=2.4^{+0.7}_{-0.7}$ (1$\sigma$ confidence
limits) matches observational data on LSS, the nucleosynthesis constraint,
direct measurements of the Hubble constant, the high redshift supernova type Ia
results and the recent measurements of the location and amplitude of the first
acoustic peak in the CMB anisotropy power spectrum. The best model is $\Lambda$
dominated (65% of the total energy density) and has slightly positive
curvature, $\Omega=1.06$. The clustered matter consists in 8% massive
neutrinos, 10% baryons and 82% cold dark matter (CDM). It is shown that the LSS
observations together with the Boomerang (+MAXIMA-1) data on the first acoustic
peak rule out zero-$\Lambda$ models at more than $2\sigma$ confidence level.


title: High-latitude molecular clouds and near-by OB associations

abstract:
  The Galactic distribution of the high-latitude molecular clouds is
considered. It is suggested that the majority of these clouds are clustered in
two large shells around the two closest OB associations, Per OB3/Cas-Tau and
Sco OB2. The most prominent shell of high-latitude clouds is centred around the
Per OB3/ Cas-Tau association which is also at the centre of the Gould's Belt.
However, the Per OB3/Cas-Tau group of high-latitude clouds appears as an
elliptical shell at nearly right angles to the plane of the Gould's Belt. Its
kinematic age (~10 Myr) is much smaller than the expansion age (~35 Myr) of the
ring of intertellar matter associated with the Gould's Belt. It is suggested
that while, as is generally understood, the larger expanding ring of gas
associated with the Gould's Belt was created by stellar winds and supernova
explosions of the more massive OB stars of the Per OB3/Cas-Tau association ~35
Myr ago, the Per OB3 shell of high-latitude clouds was formed from the
back-falling gas as it was swept up by a more recent supernova explosion of an
early B type star in Per OB3 ~10 Myr ago. More distant OB associations also
produce similar shells of clouds at large heights from the Galactic plane
having relatively smaller angular sizes due to their greater distances. These
can be seen as higher latitude extensions of cloud complexes at lower Galactic
latitudes as, for example, in the case of Vela OB2.


title:
Composition of active galactic nuclei jets: pair-plasma dominance in the
  3C 345 and 3C 279 jets

abstract:
  We investigate whether the parsec-scale jets of quasars 3C 345 and 3C 279 are
dominated by a normal (proton-electron) plasma or a pair (electron-positron)
plasma. We first present a new method to compute the kinetic luminosity of a
conical jet by using the core size observed at a single very long baseline
interferometry frequency. The deduced kinetic luminosity gives electron
densities of individual radio-emitting components as a function of the
composition. We next constrain the electron density independently by using the
theory of synchrotron self-absorption. Comparing the two densities, we can
discriminate the composition. We then apply this procedure to the five
components in the 3C 345 jet and find that they are pair-plasma dominated at 14
epochs out of the total 19 epochs at which the turnover frequencies are
reported, provided that the bulk Lorentz factor is less than 15 throughout the
jet. We also investigate the composition of the 3C 279 jet and demonstrate that
its two components are likely pair-plasma dominated at all the four epochs,
provided that their Doppler factors are less than 10, which are consistent with
observations. The conclusions do not depend on the lower cutoff energy of
radiating particles.


title:
Reverberation Measurements of Quasars and the Size-Mass-Luminosity
  Relations in Active Galactic Nuclei

abstract:
  A 7.5 years spectrophotometric monitoring program of 28 Palomar-Green quasars
to determine the size of their broad emission line region (BLR) is reviewed. We
find both the continuum and the emission line fluxes of all quasars to vary
during this period. Seventeen objects has adequate sampling for reverberation
mapping and in all of them we find the Balmer line variations to lag those of
the continuum by ~100 days. This study increases the available luminosity range
for studying the size-mass-luminosity relations in active galactic nuclei
(AGNs) by two orders of magnitude and doubles the number of objects suitable
for such studies. Combining our results with data available for Seyfert 1
galaxies, we find the BLR size to scale with the rest-frame 5100 A luminosity
as L^{0.70 +/- 0.03}. This result is different from previous studies, and
suggests that the effective ionization parameter in AGNs may be a decreasing
function of luminosity. We are also able to constrain, subject to the
assumption that gravity dominates the motions of the BLR gas, the scaling
relation between the mass of the central black hole and the AGN's luminosity.
We find that the central mass scales with the 5100 A luminosity as
M\proptoL^{0.5 +/- 0.1}.
  A program to monitor 11 high-luminosity quasars is presented here for the
first time. Preliminary results from this program indicate continuum variation
of order of 0.1 mag in all objects. We illustrate the importance and
feasibility of monitoring those objects spectrophotometrically. When this
program will be completed reverberation mapping studies will cover the entire
AGNs luminosity range from 10^{41} to 10^{48} ergs/s.


title:
OB Associations, Open Clusters, and the Luminosity Calibration of the
  Nearer Stars

abstract:
  In the context of the luminosity calibration of the nearer stars I discuss
the Hipparcos results on distances to nearby OB associations and open clusters.
The shortcomings and assumptions in the analyses used to derive these results
are pointed out and for the open clusters a comparison is made with results
obtained from main sequence fitting. I conclude that given the considerable
uncertainties in the latter technique there is no convincing evidence that the
Hipparcos based distances to open clusters beyond the Hyades should not be
trusted.


title:
Can differences in the nickel abundance in Chandrasekhar mass models
  explain the relation between brightness and decline rate of normal Type Ia
  Supernovae?

abstract:
  The use of Type Ia supernovae as distance indicators relies on the
determination of their brightness. This is not constant, but it can be
calibrated using an observed relation between the brightness and the properties
of the optical light curve (decline rate, width, shape), which indicates that
brighter SNe have broader, slower light curves. However, the physical basis for
this relation is not yet fully understood. Among possible causes are different
masses of the progenitor white dwarfs or different opacities in
Chandrasekhar-mass explosions. We parametrise the Chandrasekhar-mass models
presented by Iwamoto et al (1999), which synthesize different amounts of Ni,
and compute bolometric light curves and spectra at various epochs. Since
opacity in SNe Ia is due mostly to spectral lines, it should depend on the mass
of Fe-peak elements synthesized in the explosion, and on the temperature in the
ejecta. Bolometric light curves computed using these prescriptions for the
optical opacity reproduce the relation between brightness and decline rate.
Furthermore, when spectra are calculated, the change in colour between maximum
and two weeks later allows the observed relation between M_B(Max) and
Dm_{15}(B) to be reproduced quite nicely. Spectra computed at various epochs
compare well with corresponding spectra of spectroscopically normal SNeIa
selected to cover a similar range of Dm_{15}(B) values.


title: Acceleration of the Universe

abstract:
  The cosmological model best capable of fitting current observational data
features two separate epochs during which the Universe is accelerating. During
the earliest stages of the Universe, such acceleration is known as cosmological
inflation, believed to explain the global properties of the Universe and the
origin of structure. Observations of the present state of the Universe strongly
suggest that its density is currently dominated by dark energy with properties
equivalent or similar to a cosmological constant. In these lecture notes, I
provide an introductory account of both topics, including the possibility that
the two epochs may share the same physical description, and give an overview of
the current status.


title: Constraints on Inflation

abstract:
  A short introduction to structure formation is given, followed by a
discussion of the possible characteristics of the initial perturbations
assuming a generic inflationary origin. Observational data related to
large-scale structure and the cosmic microwave background radiation is then
used in an attempt to constrain the characteristics of such perturbations.
Future directions are also explored.
  The possibility of direct detection of a stochastic gravitational wave
background produced during an inflationary phase in the early Universe is
briefly discussed, as well as the available evidence regarding the present
value of the total energy density in the Universe.


title: VLBI imaging of the gravitational lens MGJ0414+0534

abstract:
  We observed the quadruple gravitationally lensed image of MGJ0414+0534 on 23
November 1997 with a global VLBI array at 8.4 GHz. We report wide-field imaging
results of its four components at submilliarcsecond resolution, displaying
complex core-like and jet-like extended structures. A simple model combining a
singular isothermal ellipsoid to represent the main lens galaxy, external
shear, and a singular isothermal sphere to represent an additional, nearby
object accounts well for the core positions and flux densities of the VLBI
images. This model predicts delays between the different lensed images of
several weeks.


title: The bright 175um knots of the Andromeda Galaxy

abstract:
  Discrete far-infrared (FIR) sources of M31 are identified in the ISO 175um
map and characterized via their FIR colours, luminosities and masses. With a
mean size of 800pc, they probably represent several clouds in chance projection
or giant cloud complexes. The 175um data point provides crucial information in
addition to the IRAS 60 and 100um data: At least two modified Planck curves
with temperatures of about 40K and 15-21K are necessary to fit the SEDs of the
knots. We distinguish between three types of knots - cold, medium, warm - in
order to recognize trends. Comparisons with radio and optical tracers show that
- statistically - the cold knots can be identified well with CO and HI radio
sources and thus might represent mainly molecular cloud complexes. The warm
knots coincide with known HII regions and supernova remnants. The medium knots
might contain a balanced mixture of molecular clouds and HII regions. The cold
knots have a considerable luminosity and their discovery raises the question of
hidden star formation. Though the optically dark dust lanes in M31 generally
match the FIR ring, surprisingly we do not find a convincing coincidence of our
knots with individual dark clouds which might therefore show mainly foreground
dust features. The ratio of FIR luminosity to dust mass, L/M, is used to
measure the energy content of the dust. The knots have a clear L/M excess over
the rest of M31, providing evidence that they are powered by star formation in
addition to the interstellar radiation field. The L/M ratio of the warm knots
is comparable to that of Galactic HII regions like M42 or NGC2024, while that
of the cold knots still reaches values like in the average Orion complex. Thus
both the warm and the cold knots are interpreted as containing large cloud
complexes with considerable ongoing star formation.


title: Properties of galaxy halos in Clusters and Voids

abstract:
  We use the results of a high resolution N-body simulation to investigate the
role of the environment on the formation and evolution of galaxy-sized halos.
Starting from a set of constrained initial conditions, we have produced a final
configuration hosting a double cluster in one octant and a large void extending
over two octants of the simulation box. We present results for two statistics:
the relationship between 1-D velocity dispersion and mass and the probability
distribution of the spin parameter $P(\lambda)$. The \svm relationship is well
reproduced by the Truncated Isothermal Sphere (TIS) model introduced by Shapiro
et al. (1999), although the slope is different from the original prediction. A
series of \svm relationships for different values of the anisotropy parameter
$\beta$, obtained using the theoretical predictions by Lokas and Mamon (2001)
for NFW density profiles are found to be only marginally consistent with the
data. Using some properties of the equilibrium TIS models, we construct
subsamples of {\em fiducial} equilibrium TIS halos from each of the three
subregions, and we study their properties. For these halos, we do find an
environmental dependence of their properties, in particular of the spin
parameter distribution $P(\lambda)$. We study in more detail the TIS model, and
we find new relationships between the truncation radius and other structural
parameters. No gravitationally bound halo is found having a radius larger than
the critical value for gravithermal instability for TIS halos (\rt $\ge 34.2
r_{0}$, where $r_{0}$ is the core radius of the TIS solution). We do however
find a dependence of this relationship on the environment, like for the
$P(\lambda)$ statistics. These facts hint at a possible r\^{o}le of tidal
fields at determining the statistical properties of halos.


title:
HST/NICMOS2 coronagraphic observations of the circumstellar environment
  of three old PMS stars: HD 100546, SAO 206462 and MWC 480

abstract:
  The close environment of four old Pre-Main Sequence stars has been observed
thanks to the coronagraphic mode of the HST/NICMOS2 camera at lambda=1.6
micron. In the course of this program, the detection of a circumstellar annulus
around HD 141569 has already been presented in Augereau et al.(1999b). In this
paper, we report the detection of an elliptical structure around the Herbig Be
star HD 100546 extending from the very close edge of the coronagraphic mask
(~50 AU) to 350-380 AU (3.5-3.8 arcsec) from the star. The axis ratio gives a
disk inclination of 51+/-3 degrees to the line-of-sight and a position angle of
161+/-5 degrees, measured east of north. At 50 AU, the disk has a surface
brightness between 10.5 and 11 mag/arcsec^2, then follows a -2.92+/-0.04 radial
power law up to 250-270 AU and finally falls as r^{-5.5+/-0.2}. The inferred
optical thickness suggests that the disk is at least marginally optically thick
inside 80 AU and optically thin further out. Combined with anisotropic
scattering properties, this could explain the shape of a brightness asymmetry
observed along the minor axis of the disk. This asymmetry needs to be
confirmed. The circumstellar disks around SAO 206462 and MWC 480 are not
resolved, leading to constraints on the dust distribution. A tight binary
system separated by only 0.32+/-0.04 arcsec is nevertheless detected in the
close vicinity of SAO 206462.


title: Astrophysical Quantities of Cepheid Variables Measured with the NPOI

abstract:
  We present mean angular diameters for two cepheid variables, alpha Ursae
Minoris and zeta Geminorum, determined with the Navy Prototype Optical
Interferometer (NPOI). We present linear radii for these cepheids and two
additional cepheids, delta Cephei and eta Aquilae, previously observed at the
NPOI. We find the limb-darkened angular diameter of alpha Ursae Minoris and of
zeta Geminorum to be 3.28 +/- 0.02 and 1.55 +/- 0.09 milliarcseconds
respectively. Using trigonometric parallaxes, we find the linear radii of alpha
Ursae Minoris, zeta Geminorum, delta Cephei and eta Aquilae to be 46 (+/- 3),
60 (+25, -14), 45 (+8, -6), and 69 (+28, -15) Solar radii respectively. We
compare the pulsation periods and linear radii of this sample of cepheids,
which range in period from three to 11 days, to theoretical and empirical
period-radius and period-radius-mass relations found in the literature. We find
that the observed diameter of alpha Ursae Minoris is in excellent agreement
with the predicted diameter as determined from both surface brightness
techniques and theory only if alpha Ursae Minoris is a first overtone pulsator.


title: Accretion disc coronae as magnetic reservoirs

abstract:
  Most astrophysical sources powered by accretion onto a black hole, either of
stellar mass or supermassive, when observed with hard X-rays show signs of a
hot Comptonizing component in the flow, the so-called corona, with observed
temperatures and optical depths lying in a narrow range (0.1 < \tau < 1 and
1x10^9 K < T < 3x10^9 K). Here we argue that these facts constitute strong
supporting evidence for a magnetically-dominated corona. We show that the
inferred thermal energy content of the corona, in all black hole systems, is
far too low to explain their observed hard X-ray luminosities, unless either
the size of the corona is at least of the order of 10^3 Schwarzschild radii, or
the corona itself is in fact a reservoir, where the energy is mainly stored in
the form of a magnetic field generated by a sheared rotator (probably the
accretion disc). We briefly outline the main reasons why the former possibility
is to be discarded, and the latter preferred.


title: Measurement of intrinsic alignments in galaxy ellipticities

abstract:
  We measure the alignment of galaxy ellipticities in the local universe over a
range of scales using digitized photographic data from the SuperCOSMOS Sky
Survey. We find for a magnitude cut of b_J < 20.5, corresponding to a median
galaxy redshift of z = 0.1, and 2x10^6 galaxies, that the galaxy ellipticities
exhibit a non-zero correlation over a range of scales between 1 and 100
arcminutes. In particular, we measure the variance of mean galaxy
ellipticities, sg^2(theta), in square angular cells on the sky as a function of
cell size and find it lies in the range, 2 x 10^{-4} > sg^2(theta) > 1 x
10^{-5} for cell side lengths between 15 < theta < 100 arcminutes. Considering
the low median redshift of the galaxies in the sample and hence the relatively
low effective cross-section for lensing of these galaxies by the large-scale
structure of the Universe, we propose that we have detected an intrinsic
alignment of galaxy ellipticities. We compare our results to recent analytical
and numerical predictions made for the intrinsic galaxy alignment and find good
agreement. We discuss the importance of these results for measuring cosmic
shear from upcoming shallow surveys (e.g. Sloan Digital Sky Survey) and we
outline how these measurements could possibly be used to constrain models of
galaxy formation and/or measure the mass distribution in the local universe.


title:
An Empirically Based Model for Predicting Infrared Luminosity Functions,
  Deep Infrared Galaxy Counts and the Diffuse Infrared Background

abstract:
  We predict luminosity functions and number counts for extragalactic infrared
sources at various wavelengths using the framework of our empirically based
model. Comparisons of our galaxy count results with existing data indicate that
either galaxy luminosity evolution is not much stronger than Q=3.1, where L is
proportional to (1+z)^{Q}, or that this evolution does not continue beyond a
redshift of 2. However, a derivation of the far infrared background from
COBE-DIRBE data suggests a stronger evolution for far infrared emission with Q
> 4 in the redshift range beteen 0 and 1. We discuss several interpretations of
these results and also discuss how future observations can reconcile this
apparent conflict. We also make predictions of the redshift distributions of
extragalactic infrared sources at selected flux levels which can be tested by
planned detectors. Finally, we predict the fluxes at which various future
surveys will become confusion limited.


title: Emission from Bow Shocks of Beamed Gamma-Ray Bursts

abstract:
  Beamed gamma-ray burst (GRB) sources produce a bow shock in their gaseous
environment. The emitted flux from this bow shock may dominate over the direct
emission from the jet for lines of sight which are outside the angular radius
of the jet emission, theta. The event rate for these lines of sight is
increased by a factor of 260*(theta/5_degrees)^{-2}. For typical GRB
parameters, we find that the bow shock emission from a jet with half-angle of
about 5 degrees is visible out to tens of Mpc in the radio and hundreds of Mpc
in the X-rays. If GRBs are linked to supernovae, studies of peculiar supernovae
in the local universe should reveal this non-thermal bow shock emission for
weeks to months following the explosion.


title: Non-LTE Modeling of Nova Cygni 1992

abstract:
  We present a grid of nova models that have an extremely large number of
species treated in non-LTE, and apply it to the analysis of an extensive time
series of ultraviolet spectroscopic data for Nova Cygni 1992. We use
ultraviolet colors to derive the time development of the effective temperature
of the expanding atmosphere during the fireball phase and the first ten days of
the optically thick wind phase. We find that the nova has a pure optically
thick wind spectrum until about 10 days after the explosion. During this
interval, we find that synthetic spectra based on our derived temperature
sequence agree very well with the observed spectra. We find that a sequence of
hydrogen deficient models provides an equally good fit providing the model
effective temperature is shifted upwards by ~1000 K. We find that high
resolution UV spectra of the optically thick wind phase are fit moderately well
by the models. We find that a high resolution spectrum of the fireball phase is
better fit by a model with a steep density gradient, similar to that of a
supernova, than by a nova model.


title: X-ray iron line variability: constraints on the inner accretion disk

abstract:
  After reviewing the basic physics of X-ray reflection in AGN, we present
three case studies which illustrate the current state of X-ray reflection
studies. For the low-luminosity AGN NGC4258, we find that the iron line is much
narrower than is typically found in higher luminosity AGN. We argue that this
is evidence for either a truncated cold accretion disk (possibly due to a
transition to an advection dominate accretion flow at r ~ 100GM/c^2) or a large
r ~ 100GM/c^2 X-ray emitting corona surrounding the accretion disk. We also
present results for the higher luminosity Seyfert nuclei in NGC5548 and
MCG-6-30-15. In both of these sources, RXTE shows that the iron line equivalent
width decreases with increasing luminosity. Furthermore, the iron line
equivalent width is found to be anticorrelated with the relative strength of
the reflection continuum, contrary to all simple reflection models. It is
proposed that continuum-flux correlated changes in the ionization of the
accretion disk surface can explain this spectral variability. Finally, we
address the issue of X-ray iron line reverberation in the light of these
complicating factors.


title:
A Compact Population of Red Giants in the Blue Compact Dwarf Galaxy UGCA
  290

abstract:
  We present HST/WFPC2 single-star photometry for the blue dwarf galaxy UGCA
290, whose morphology is intermediate between classic iE Blue Compact Dwarfs
and blue dwarfs which exhibit no red background sheet of older stars. The
color-magnitude diagram of this galaxy in V and I, extending over six
magnitudes, is remarkably similar to that of the star-forming region in the iE
Blue Compact Dwarf VII Zw 403. There is no evidence for gaps in its
star-formation history over the last billion years, and the color of its red
giant branch indicates a very metal-poor stellar population. From the magnitude
of the tip of the red giant branch, we derive a distance of 6.7 Mpc, more than
twice the distance estimated from the brightest blue supergiants.


title:
Abundance Patterns in the Draco, Sextans and Ursa Minor Dwarf Spheroidal
  Galaxies

abstract:
  The Keck I telescope has been used to obtain HIRES spectra for red giants
belonging to the Draco, Sextans and Ursa Minor dwarf spheroidal (dSph)
galaxies. An analysis of these spectra is presented, along with abundance
ratios for more than 20 elements. The resulting database of element abundances
for 17 stars is the most extensive yet assembled for stars in dSph
environments. Our main findings are summarized as follows: (1) There is
unambiguous evidence for a large internal spread in metallicity in all three
galaxies: our program stars span a range of [Fe/H] = 1.53, 1.40 and 0.73 dex in
Draco, Sextans and Ursa Minor, respectively. (2) The abundance patterns among
the dSph stars are remarkably uniform, suggesting that all three galaxies have
similar nucleosynthetic histories. (3) A comparison of the measured abundance
ratios for our sample of dSph stars with published values for Galactic halo and
disk field stars suggests that the dSph galaxies have 0.02 < [alpha/Fe] < 0.13
dex, whereas the halo field star sample has [alpha/Fe] ~ 0.28 dex over the same
range in metallicity. (4) The most metal-rich dSph stars in our sample have
[Y/Fe] abundances which are significantly lower than those measured for halo
field stars of similar metallicity, while the measured [Ba/Eu] ratios for the
dSph stars suggest that the early chemical evolution of these galaxies was
dominated by the r-process. Taken together, these results suggest that the
Galactic halo is unlikely to have assembled, in its entirety, through the
disruption of dwarf galaxies similar to the low-luminosity dSphs studied here.
(ABRIDGED).


title: Light Element Nucleosynthesis

abstract:
  An introductory review of the early evolution of the Universe relevant to the
primordial synthesis of the light nuclides deuterium, helium-3, helium-4 and
lithium-7. The predictions of the element abundances in the "standard", hot,
big bang cosmological model (SBBN) are described. After descriptions of the
evolution of the primordial abundances from "there and then" to "here and now",
the SBBN predictions are compared to current observational data. The
implications for the standard model and for physics beyond the standard model
are discussed.


title: UV Spectropolarimetry of Narrow-line Radio Galaxies

abstract:
  We present the results of UV spectropolarimetry (2000 - 3000A) and far-UV
spectroscopy (1500 - 2000A) of two low-redshift narrow-line radio galaxies
(NLRGs) taken with the Faint Object Spectrograph onboard the Hubble Space
Telescope (HST). Spectropolarimetry of several NLRGs has shown that, by the
presence of broad permitted lines in polarized flux spectrum, they have hidden
quasars seen through scattered light. Imaging polarimetry has shown that NLRGs
including our targets often have large scattering regions of a few kpc to >~10
kpc scale. This has posed a problem about the nature of the scatterers in these
radio galaxies. Their polarized continuum has the spectral index similar to or
no bluer than that of quasars, which favors electrons as the dominant
scattering particles. The large scattering region size, however, favors dust
scattering, because of its higher scattering efficiency compared to electrons.
In this paper, we investigate the polarized flux spectrum over a wide
wavelength range, combining our UV data with previous optical/infrared
polarimetry data. We infer that the scattering would be often caused by opaque
dust clouds in the NLRGs and this would be a part of the reason for the
apparently grey scattering. In the high-redshift radio galaxies, these opaque
clouds could be the proto-galactic subunits inferred to be seen in the HST
images. However, we still cannot rule out the possibility of electron
scattering, which could imply the existence of a large gas mass surrounding
these radio galaxies.


title: Weak lensing mass reconstruction of MS1008.1-1224

abstract:
  We present an in-depth weak lensing analysis of the cluster MS1008 based on
deep multicolor imaging obtained during the Science Verification of FORS1 at
the VLT. The image quality (half arcsec seeing) and depth of the VLT images
allow the shear signal to be mapped with high signal-to-noise and to be traced
out to 1.2 h_50^-1 Mpc, near the edge of the 6'.8x6'.8 field of view. Using
BVRI color information, as well as 81 redshifts in the field from the CNOC
survey, background galaxies can be effectively separated from cluster and
foreground objects. PSF distorsions are found to be moderate across the FORS
images and thus easily removed. Due to the small statistical errors in the mass
reconstruction, this dataset provides a testing ground where several systematic
effects (e.g. mass-sheet degeneracy, redshift distribution of the background
sources, cluster galaxy contamination) can be quantified. Several methods are
used to remove the mass-sheet degeneracy which is found to dominate the
systematic error budget. We measure a lower limit to the mass of 2.6 10^14
h_50^-1 M_sun within 1 h_50^-1 Mpc and a ``total'' mass of 5.3 10^14 h_50^-1
M_sun by fitting a softened isothermal sphere. The availability of the CNOC
redshift data and X-ray observations on this cluster allow a comparison of
different determinations of the mass radial profile. We find the lensing and
X-ray measurements in excellent agreement, while the mass derived from the
virial analysis is marginally (1-2 sigma) in agreement at radii where both
methods are reliable.


title: Dynamical friction of bodies orbiting in a gaseous sphere

abstract:
  The dynamical friction experienced by a body moving in a gaseous medium is
different from the friction in the case of a collisionless stellar system. Here
we consider the orbital evolution of a gravitational perturber inside a gaseous
sphere using three-dimensional simulations, ignoring however self-gravity. The
results are analysed in terms of a `local' formula with the associated Coulomb
logarithm taken as a free parameter. For forced circular orbits, the asymptotic
value of the component of the drag force in the direction of the velocity is a
slowly varying function of the Mach number in the range 1.0-1.6. The dynamical
friction timescale for free decay orbits is typically only half as long as in
the case of a collisionless background, which is in agreement with E.C.
Ostriker's recent analytic result. The orbital decay rate is rather insensitive
to the past history of the perturber. It is shown that, similar to the case of
stellar systems, orbits are not subject to any significant circularization.
However, the dynamical friction timescales are found to increase with
increasing orbital eccentricity for the Plummer model, whilst no strong
dependence on the initial eccentricity is found for the isothermal sphere.


title: Microlensing of Quasars

abstract:
  There are two possible causes of variability in gravitationally lensed
quasars: intrinsic fluctuations of the quasar and ``microlensing'' by compact
objects along the line of sight. If disentangled from each other,
microlens-induced variability can be used to study two cosmological issues of
great interest: the size and brightness profile of quasars on one hand, and the
distribution of compact (dark) matter along the line of sight on the other.
Here we present a summary of recent observational evidence for quasar
microlensing as well as of theoretical progress in the field. Particular
emphasis is given to the questions which microlensing can address regarding the
search for dark matter, both in the halos of lensing galaxies and in a
cosmologically distributed form. A discussion of desired observations and
required theoretical studies is presented as a conclusion/outlook.


title: Period changes in omega Centauri RR Lyrae stars

abstract:
  A century of observations of omega Centauri allows us to accurately follow
the period changes of a large sample of variable stars. Although the period
changes are composed of monotone and irregular changes, period increases
dominate in most of the RRab stars. The typical period increase rates are of
the same order of magnitude as model calculations predict for the evolved,
redward phase of horizontal branch evolution. For the 44 well observed RRab
stars which show monotonic period changes, a mean rate of 0.15 d/Myr has been
found. The period changes of the first overtone RRc type stars show a much more
complex, irregular behavior.


title: Simulations of Merging Clusters of Galaxies

abstract:
  Numerical simulations of cluster mergers reveal many characteristics of the
merging process: shock structure and strength, observational signatures of the
dynamical state, effects on the mass determination, turbulence and the
evolution of the X-ray luminosity and the magnetic field. In this article I
review the results obtained from various simulations over the last years.


title: A NICMOS imaging study of high-z quasar host galaxies

abstract:
  We present the first results from a major Hubble Space Telescope program
designed to investigate the cosmological evolution of quasar host galaxies from
z~2 to the present day. Here we describe J and H-band NICMOS imaging of two
quasar samples at redshifts of 0.9 and 1.9 respectively. Each sample contains
equal numbers of radio-loud and radio-quiet quasars, selected to lie within the
same narrow range of optical absolute magnitude (-24 > M_V > -25). Filter and
target selection were designed to ensure that at each redshift the images
sample the same part of the object's rest-frame spectrum, avoiding potential
contamination by [OIII]lambda5007 and H-alpha emission lines. At z=1 the hosts
of both radio-loud and radio-quiet quasars lie on the same Kormendy relation
described by 3CR radio galaxies at comparable redshift. There is some evidence
for a gap of ~1 mag between the host luminosities of RLQs and RQQs, a
difference that cannot be due to emission-line contamination given the design
of our study. However, within current uncertainties, simple passive stellar
evolution is sufficient to link these galaxies with the elliptical hosts of
low-redshift quasars of comparable nuclear output, implying that the hosts are
virtually fully assembled by z=1. At z=2 the luminosity gap appears to have
widened further to ~1.5 mag. Thus while the hosts of radio-loud quasars remain
consistent with a formation epoch of z>3, allowing for passive evolution
implies that the hosts of radio-quiet quasars are ~2-4 times less massive at
z=2 than at low z.


title: Cosmic Shear and Clusters of Galaxies

abstract:
  The first detections of cosmic shear signal reported recently by 4
independent groups cover angular scales between one and 10 arcmin. On those
scales, the cosmic shear is a signature of non-linear perturbations, like
groups and clusters of galaxies. We present the results obtained by our team on
CFHT and on the VLT and discuss its impact for the analysis of cluster
abundances and cosmology


title: Dust in active nuclei. I. Evidence for "anomalous" properties

abstract:
  We present observational evidences that dust in the circumnuclear region of
AGNs has different properties than in the Galactic diffuse interstellar medium.
By comparing the reddening of optical and infrared broad lines and the X-ray
absorbing column density we find that the E(B-V)/N_H ratio is nearly always
lower than Galactic by a factor ranging from ~3 up to ~100. Other observational
results indicate that the Av/N_H ratio is significantly lower than Galactic in
various classes of AGNs including intermediate type 1.8-1.9 Seyferts, hard
X-ray selected and radio selected quasars, broad absorption line QSOs and grism
selected QSOs. The lack of prominent absorption features at 9.7um (silicates)
and at 2175A (carbon dip) in the spectra of Seyfert 2s and of reddened Seyfert
1s, respectively, add further evidence for dust in the circumnuclear region of
AGNs being different from Galactic.
  These observational results indicate that the dust composition in the
circumnuclear region of AGNs could be dominated by large grains, which make the
extinction curve flatter, featureless and are responsible for the reduction of
the E(B-V)/N_H and Av/N_H ratios.
  Regardless of the physical origin of these phenomena, the reduced dust
absorption with respect to what expected from the gaseous column density should
warn about a mismatch between the optical and the X-ray classification of the
active galactic nuclei in terms of their obscuration.


title: Observations of a Series of Six Recent Glitches in the Crab Pulsar

abstract:
  From 1995 to 1999, daily monitoring of the radio emission from the Crab
pulsar at the Green Bank and Jodrell Bank observatories revealed a series of
six sudden rotational spinups or glitches, doubling the number of glitches
observed for this pulsar since 1969. With these observations, the range of time
intervals between significant Crab glitches has widened considerably,
indicating that the occurrence of Crab glitches may be more random than
previously thought. The new glitch amplitudes ($\Delta\nu/\nu$) span an order
of magnitude from 2e-9 to 3e-8. Except in one case, which we suggest may
represent an ``aftershock'' event, the frequency jumps display an exponential
recovery with a timescale of $\sim$3 days for the smaller glitches and $\sim$10
days for the largest (1996) glitch. In the largest event, a portion of the
spinup was resolved in time, as was previously reported for the 1989 glitch. A
pronounced change in frequency derivative also occurs after each glitch and is
correlated with the size of the initial frequency jump, although for some of
the smaller glitches this appears to be a temporary effect. We discuss the
properties of the ensemble of observed Crab glitches and compare them with the
properties of Vela glitches, highlighting those differences which must be
explained by evolutionary models.


title:
Time-Resolved HST Spectroscopy of Four Eclipsing Magnetic Cataclysmic
  Variables

abstract:
  Time-resolved HST UV eclipse spectrophotometry is presented for the magnetic
CVs V1309 Ori, MN Hya, V2301 Oph, and V1432 Aql. Separation of the light curves
into wavebands allows the multiple emission components to be distinguished.
Photospheric hot spots are detected in V1309 Ori and V2301 Oph. The emission-
line spectra of V1309 Ori and MN Hya are unusual, with the strength of N V 1240
and N IV 1718 suggesting an overabundance of nitrogen. Three epochs of
observation of the asynchronous V1432 Aql cover ~1/3 of a 50-day lap cycle
between the white dwarf spin and binary orbit. The light curves vary from epoch
to epoch and as a function of waveband. The dereddened UV spectrum is extremely
bright and the spectral energy distribution coupled with the duration of
eclipse ingress indicate that the dominant source of energy is a hot
(T~35,000K) white dwarf. Undiminished line emission through eclipse indicates
that the eclipse is caused by the accretion stream, not the secondary star. The
hot white dwarf, combined with its current asynchronous nature and rapid
timescale for relocking, suggests that V1432 Aql underwent a nova eruption in
the past 75-150 yr. The reversed sense of asynchronism, with the primary star
currently spinning up toward synchronism, is not necessarily at odds with this
scenario, if the rotation of the magnetic white dwarf can couple to the ejecta
during the wind phase of the eruption.


title: Advances in s-process models

abstract:
  Within the framework of the current models for the slow neutron capture (s)
process in Asymptotic Giant Branch (AGB) stars we explore the uncertainties
introduced by the assumptions made on stellar modeling. On the basis of star
models constructed with three different evolutionary codes we generate detailed
neutron-capture nucleosynthesis post-processing models. The main difference
among the codes is that one of them includes an overshooting mechanism. As a
result, the neutron fluxes are stronger both during the interpulse periods and
within thermal pulses. The efficiency of the C13 source is also studied and we
find that a linear relationship exists between the initial C12 in the
intershell and the maximum number of neutrons produced.


title: SiO Emission in the Multi-Lobe Outflow associated with IRAS 16293-2422

abstract:
  We have mapped the thermal emission line of SiO (v = 0; J = 2-1) associated
with the quadrupolar molecular outflow driven by the very cold far-infrared
source IRAS 16293-2422. The SiO emission is significantly enhanced in the
northeastern red lobe and at the position ~50" east of the IRAS source. Strong
SiO emission observed at ~50" east of the IRAS source presents evidence for a
dynamical interaction between a part of the eastern blue lobe and the dense
ambient gas condensation, however, such an interaction is unlikely to be
responsible for producing the quadrupolar morphology. The SiO emission in the
northeastern red lobe shows the spatial and velocity structure similar to those
of the CO outflow, suggesting that the SiO emission comes from the molecular
outflow in the northeastern red lobe itself. The observed velocity structure is
reproduced by a simple spatio-kinematic model of bow shock with a shock
velocity of 19-24 km/s inclined by 30-45 deg from the plane of the sky. This
implies that the northeastern red lobe is independent of the eastern blue lobe
and that the quadrupolar structure is due to two separate bipolar outflows.
  The SiO emission observed in the western red lobe has a broad pedestal shape
with low intensity. Unlike the SiO emission in the northeastern red lobe, the
spatial extent of the SiO emission in the western red lobe is restricted to its
central region. The spatial and velocity structures and the line profiles
suggest that three different types of the SiO emission are observed in this
outflow; the SiO emission arises from the interface between the outflowing gas
and the dense ambient gas clump, the SiO emission coming from the outflow lobe
itself, and the broad SiO emission with low intensity observed at the central
region of the outflow lobe.


title: Parameter information from nonlinear cosmological fields

abstract:
  We develop a general formalism for analysing parameter information from
non-Gaussian cosmic fields. The method can be adapted to include the nonlinear
effects in galaxy redshift surveys, weak lensing surveys and cosmic velocity
field surveys as part of parameter estimation. It can also be used as a test of
non-Gaussianity of the Cosmic Microwave Background. Generalising Maximum
Likelihood analysis to second-order, we calculate the nonlinear Fisher
Information matrix and likelihood surfaces in parameter space. To this order we
find that the information content is always increased by including
nonlinearity. Our methods are applied to a realistic model of a galaxy redshift
survey, including nonlinear evolution, galaxy bias, shot-noise and
redshift-space distortions to second-order. We find that including
nonlinearities allows all of the degeneracies between parameters to be lifted.
Marginalised parameter uncertainties of a few percent will then be obtainable
using forthcoming galaxy redshift surveys.


title: TeV Gamma-Ray Absorption and the Intergalactic Infrared Background

abstract:
  In this paper, I will take a synoptic approach to determining the
intergalactic infrared radiation field (IIRF). This approach draws on both the
multi-TeV gamma-ray observations and the infrared background observations and
relates them via the semi-empirical modelling method of Malkan and Stecker. I
discuss the evidence for an intergalactic infrared background obtained by an
analysis of the HEGRA observations of the high energy gamma-ray spectrum of Mrk
501 and from constraints from Mrk 421 deduced from the Whipple air Cherenkov
telescope results. I will show that this evidence is in accord with the
predictions made by Malkan and Stecker for the intergalactic infrared spectral
energy distribution produced by galaxies. The Malkan-Stecker predictions are
also in excellent agreement with mid- and far infrared galaxy counts. However,
there may be potential problems relating these predictions with the results of
the analysis of COBE-DIRBE far infrared data. The gamma-ray and COBE-DIRBE
observations may also need to be reconciled. I will discuss possible ways to
resolve this situation including a partial nullification of the $\gamma$-ray
absorption process which can hypothetically occur if Lorentz invariance is
broken.


title: Astrophysics of the Soft Gamma Repeaters and Anomalous X-Ray Pulsars

abstract:
  I summarize the recent advances in our understanding of the Soft Gamma
Repeaters: in particular their spin behavior, persistent emission and
hyper-Eddington outbursts. The giant flares on 5 March 1979 and 27 August 1998
provide compelling physical evidence for magnetic fields stronger than 10
B_{QED} = 4.4 x 10^{14} G, consistent with the rapid spindown detected in two
of these sources. The persistent X-ray emission and variable spindown of the
6-12 s Anomalous X-ray Pulsars are compared and contrasted with those of the
SGRs, and the case made for a close connection between the two types of
sources. Their collective properties point to the existence of {\it magnetars}:
neutron stars in which a decaying magnetic field (rather than accretion or
rotation) is the dominant source of energy for radiative and particle
emissions. Observational tests of the magnetar model are outlined, along with
current ideas about the trigger of SGR outbursts, new evidence for the trapped
fireball model, and the influence of QED processes on X-ray spectra and
lightcurves. A critical examination is made of coherent radio emission from
bursting strong-field neutron stars. I conclude with an overview of the genetic
connection between neutron star magnetism and the violent fluid motions in a
collapsing supernova core.


title:
Detections of SiO and H$_2$O Masers in the Bipolar Nebula IRAS
  19312+1950

abstract:
  We report on the detection of SiO and water masers toward a newly found
bipolar nebula, IRAS 19312+1950. This object exhibits extreme red IRAS color
log (F25/F12)=0.5 and log (F60/F25)=0.7 and a nebulosity having a size of about
30" extended to the South-West in the 2MASS near-infrared image. Toward this
object, we have detected emission from the H2O 6(1,6)-5(2,3) transition, the
SiO J=1-0, v=1 and 2, and J=2-1, v=1 transitions, and the SO 2(2)--1(1) and
H13CN J=1-0 transitions. The thermal lines of SO and H13CN are shifted by about
12 km/s in radial velocity with respect to the maser lines, indicating that
thermal emission comes from the background molecular cloud. However, the SiO
J=2-1, v=2 spectrum shows another component of SiO emission separated by 26
km/s from the main component, that might be formed in a rotating or expanding
shell.


title:
Long-Term Variability of the Low-Luminosity Active Galactic Nucleus of
  M81

abstract:
  Long-term X-ray variability of the low-luminosity active galactic nucleus of
M81 was studied, using 16 ASCA observations spanning 5.5 years. The object
exhibits a factor three variation over the 5.5 years. The source intensity was
relatively constant within each observation which lasted typically for one day,
but intra-day variability by 30% was detected on the 15th observation. The
power-spectral density (PSD) was estimated in ``forward'' manner, over a
frequency range of 10^(-8.2)--10^(-4.3) Hz (period range of 1/4 day-5.5 years),
by utilizing structure function and extensive Monte-Carlo simulations in order
to overcome the very sparse and uneven data samplings. When the PSD is assumed
to be white below a "break frequency" f_b and falls off as proptional to
f^(-alpha) above f_b, where "f" is frequency and alpha is a positive parameter,
the M81 light curve is well described with 1/f_b > 800 days and alpha = 1.4 +-
0.2.


title: The luminosity calibration of the uvby-$\beta$ photometry

abstract:
  The ESA HIPPARCOS satellite has provided astrometry of unprecedented
accuracy, allowing to reassess, improve and refine the pre-HIPPARCOS luminosity
calibrations. We review the "classical" absolute magnitude calibrations with
the Stroemgren-Crawford intermediate-band photometric system. A small zero
point correction of about 2-4% seems necessary, as well as to refine the
dependences on metallicity and projected rotational velocity. The need of a
rigorous statistical treatment of the extremely precise HIPPARCOS to derive
definite dependences of the luminosity on physical stellar parameters is
emphasized.


title:
A Method to Search for Local Sources of Short Duration Bursts of
  Superhigh Energy Gamma Rays

abstract:
  A method of a search for local sources of superhigh energy gamma rays is
described in the paper.It is shown that the method is more effective then the
usually used method extracting excess from total intensity if gamma ray burst
durations are short.Using the suggested method,the information detected with
the Baksan installation ``Carpet'' during 1992-1996 years was analyzed.An
excess of event numbers was found at the confidence level of 6.5$\sigma$ in the
direction to Mrk 501.


title: Nucleosynthesis in massive stars revisited

abstract:
  We have performed the first calculations to follow the evolution of all
stable nuclei and their radioactive progenitors in a finely-zoned stellar model
computed from the onset of central hydrogen burning through explosion as a Type
II supernova. Calculations were done for 15, 20, and 25 solar masses Pop I
stars using the most recently available set of experimental and theoretical
nuclear data, revised opacity tables, and taking into account mass loss due to
stellar winds. Here results are presented for one 15 solar masses model.


title: Self-broadening in Balmer line wing formation in stellar atmospheres

abstract:
  Details of a theory of self-broadening of hydrogen lines are presented. The
main features of the new theory are that the dispersive-inductive components of
the interaction (van der Waals forces) have been included, and the resonance
components have been computed by perturbation theory without the use of the
multipole expansion. The theory is applied to lower Balmer lines and the
theoretical and observational impact of the new broadening theory is examined.
It is shown that this theory leads to considerable differences in the predicted
line profiles in cool stars when compared with previous theories which include
only resonance interactions. In particular, the effect is found to be very
important in metal poor stars. The theory provides a natural explanation for
the behaviour of effective temperatures derived from Balmer lines by others
using a theory which includes only resonance broadening. When applied to Balmer
lines in the solar spectrum the theory predicts an improved agreement between
observed and computed profiles for models which also match limb darkening
curves and rules out a model which does not. However significant discrepancies
still remain which could be due to inadequacies in our theory or the
atmospheric model or both.


title: Buoyant radio plasma in clusters of galaxies

abstract:
  Radio galaxies are known to inflate lobes of hot relativistic plasmas into
the intergalactic medium. Here we present hydrodynamical and
magnetohydrodynamical simulations of these hot plasma bubbles in FRII objects.
We focus on the later stages of their evolution after the jet has died down and
after the bow shock that surrounded the lobes at earlier stages has vanished.
We investigate the evolution of the plasma bubbles as they become subject to
Rayleigh-Taylor instabilities. From our simulations we calculate the radio and
X-ray emissivities of the bubbles and discuss their appearance in observations.
Finally, we investigate the influence of large-scale magnetic fields on the
evolution of the bubbles. The issues of re-acceleration and diffusion of
relativistic particles are briefly discussed.


title: Cosmological Origin of the Lowest Metallicity Halo Stars

abstract:
  We explore the predictions of the standard hierarchical clustering scenario
of galaxy formation, regarding the numbers and metallicities of PopIII stars
likely to be found within our Galaxy today. By PopIII we shall be referring to
stars formed at large redshift ($z>4$), with low metallicities
($[Z/Z_{\odot}]<-2.5$) and in small systems (total mass $\simlt$ $2\times
10^{8} M_{\odot}$) that are extremely sensitive to stellar feedback, and which
through a prescribed merging history (Lacey & Cole 1993) end up becoming part
of the Milky Way today. An analytic, extended Press-Schechter formalism is used
to get the mass functions of halos which will host PopIII stars at a given
redshift, and which will end up in Milky Way sized systems today. Each of these
is modeled as a mini galaxy, with a detailed treatment of the dark halo
structure, angular momentum distribution, final gas temperature and disk
instabilities, all of which determine the fraction of the baryons which are
subject to star formation. Use of new primordial metallicity stellar
evolutionary models allows us to trace the history of the stars formed, give
accurate estimates of their expected numbers today, and their location in
$L/L_{\odot}$ vs. $T/K$ HR diagrams. A first comparison with observational data
suggests that the IMF of the first stars was increasingly high mass weighted
towards high redshifts, levelling off at $z\simgt 9$ at a characteristic
stellar mass scale $m_s=10-15 M_\odot$.


title:
The European Large Area ISO Survey IV: the preliminary 90 micron
  luminosity function

abstract:
  We present the luminosity function of 90um selected galaxies from the
European Large Area ISO Survey (ELAIS), extending to z=0.3. Their luminosities
are in the range 10^9 < h_65^-2 L/Lsun < 10^12, i.e. non-ultraluminous. From
our sample of 37 reliably detected galaxies in the ELAIS S1 region from the
Efstathiou et al. (2000) S_90 >= 100mJy database, we found optical, 15um or
1.4GHz identifications for 24 (65%). We have obtained 2dF and UK Schmidt FLAIR
spectroscopy of 89% of IDs to rigid multivariate flux limits. We construct a
luminosity function assuming (a) our spectroscopic subset is an unbiased sparse
sample, and (b) there are no galaxies which would not be represented in our
spectroscopic sample at {\it any} redshift. We argue that we can be confident
of both assumptions. We find the luminosity function is well-described by the
local 100um luminosity function of Rowan-Robinson, Helou & Walker (1987). {\it
Assuming} this local normalisation, we derive luminosity evolution of
(1+z)^{2.45\pm0.85} (95% confidence). We argue that star formation dominates
the bolometric luminosities of these galaxies and we derive comoving star
formation rates in broad agreement with the Flores et al. (1999) and
Rowan-Robinson et al. (1997) mid-IR-based estimates.


title:
Photoevaporating flows from the cometary knots in the Helix nebula (NGC
  7293)

abstract:
  We explain the Ha emission of the cometary knots in the Helix Nebula (NGC
7293) with an analytical model that describes the emission of the head of the
globules as a photoevaporated flow produced by the incident ionizing radiation
of the central star.We compare these models with the Ha emission obtained from
the HST archival images of the Helix Nebula. From a comparison of the Ha
emission with the predictions of the analytical model we obtain a rate of
ionizing photons from the central star of about 5e45 s^-1, which is consistent
with estimates based on the total Hb flux of the nebula. We also model the
tails of the cometary knots as a photoevaporated wind from a neutral shadow
region produced by the diffuse ionizing photon field of the nebula. A
comparison with the HST images allows us to obtain a direct determination of
the value of the diffuse ionizing flux. We compare the ratio of diffuse to
direct stellar flux as a function of radius inside an HII region with those
obtained from the observational data through the analytical tail and head wind
model. The agreement of this model with the values determined from the
observations of the knots is excellent.


title: Saving Astronomical Treasures

abstract:
  The time domain is under-exploited in an astrophysical context, because the
large photographic plate collections are almost never consulted by young
astronomers. This is a result of lack of education of the more recent
generations of astronomers, and of the deluge of terabyte-size datasets
produced by new observations. Yet astronomical plates represent a unique set of
resources and their quality does NOT improve with time. We point out valuable
scientific projects that can be conducted with archival images and describe a
first step to realize this at the Uccle Observatory, in Belgium.


title:
Stellar Populations in Dwarf Galaxies: A Review of the Contribution of
  HST to our Understanding of the Nearby Universe

abstract:
  This review aims to give an overview of the contribution of the Hubble Space
Telescope to our understanding of the detailed properties of Local Group dwarf
galaxies and their older stellar populations. The exquisite stable high spatial
resolution combined with photometric accuracy of images from the Hubble Space
Telescope have allowed us to probe further back into the history of star
formation of a large variety of different galaxy types with widely differing
star formation properties. We have learnt several important things about dwarf
galaxy evolution from these studies. Firstly we have found that no two galaxies
have identical star formation histories; some galaxies may superficially look
the same today, but they have invariably followed different paths to this
point. Now that we have managed to probe deep into the star formation history
of dwarf irregular galaxies in the Local Group it is obvious that there are a
number of similarities with the global properties of dwarf
elliptical/spheroidal type galaxies, which were previously thought to be quite
distinct. The previous strong dichotomy between these two classes has been
weakened by these new results and may stem from the differences in the
environment in which these similar mass galaxies were born into or have
inhabited for most of their lives. The more detailed is our understanding of
star formation processes and their effect on galaxy evolution in the nearby
Universe the better we will understand the results from studies of the
integrated light of galaxies in the high-redshift Universe.


title:
Gravitational Microlensing of Gamma-Ray Burst Afterglows by Single and
  Binary Stars

abstract:
  We calculate the magnification light curves due to stellar microlensing of
gamma-ray burst (GRB) afterglows. A GRB source appears on the sky as a thin
ring which expands faster than the speed of light and is maximally magnified as
it crosses the lens caustics. While a single star lens produces a single peak
in the magnification light curve, binary star lenses may produce multiple
peaks. The shape of the magnification light curve provides invaluable
information on the surface brightness distribution of the afterglow photosphere
on sub micro-arcsecond scales. We find that all afterglows are likely to show
variability at the level of a few percent about a year following the explosion,
due to stars which are separated by tens of Einstein radii from their
line-of-sight.


title:
Long-time behavior and relaxation of power-law correlation in
  one-dimensional self-gravitating system

abstract:
  Long-time behavior of spatial power-law correlation in one-dimensional
self-gravitating system is numerically investigated. It is found that the
power-law structure persists even after the system is virialized. The structure
gradually disappears owing to energy exchange among particles. Energy
distribution is quasi-stationary after the system is virialized.


title: Gamma-Ray Bursts: Astronomical Constraints

abstract:
  After presenting a short history of gamma-ray burst (GRB) studies, we discuss
the current constraints on GRB models which follows from astronomical
observations. We concentrate on the energetics of the GRBs with known redshifts
and the association of the well-localized GRBs with star forming regions in
remote galaxies. We also discuss implications of the observed GRB rate.
Arguments are given favoring possible connection of GRBs with core collapse of
massive Wolf-Rayet stars. The possibility of GRB to be a transient phenomenon
in the early history of galactic star formation related to evolution of very
massive metal-free stars is briefly outlined.


title: Search for companions around Sirius

abstract:
  Since the discovery of Sirius-B about 130 yr ago, there have been several
claims of a possible second companion around the brightest star Sirius-A. Such
a companion could, in particular, be responsible of the suspected colour change
of the star, now strongly suggested from two independent historical sources. We
reported here on a new observation of the sky region around Sirius, to search
for such a companion, using a coronographic device.
  By comparison of the new stellar field with a similar image obtained by us
$\sim$13 yr ago and using the Sirius proper motion, we are able to eliminate
the most obvious companion candidates down to a magnitude m$_v$$\sim$17 in a
field from 30 arcsec to 2.5 arcmin of the central star. None of the visible
stars appears consistent in magnitude and colours with what expected from
current theoretical models and observations of low-mass stars.
  From the study of the same field, it is also shown that the Sirius companion,
consistently reported by observers during the years 1920-1930, is most probably
an unrelated m$_g$$\simeq$12 background star, now $\sim$ 1 arcmin away but
located precisely on the Sirius proper motion trajectory. The closest apparent
conjunction with Sirius was realized in 1937 with a minimum angular distance of
6.9 arcsec, of the same order than the Sirius A-B binary separation.
  The reported observations do not eliminate the possibility of a second
companion but now confined the search to the more central 30 arcsec region
around Sirius. In particular, the existence of a long period companion cannot
definitively be ruled out since the arbitrary orientation of the orbit can
yield an observed projected position on sky inside this more central region.


title:
Modelling the Interstellar Medium of Low Surface Brightness Galaxies:
  Constraining Internal Extinction, Disk Color Gradients, and Intrinsic
  Rotation Curve Shapes

abstract:
  We use a combination of three-dimensional Monte Carlo radiative transfer
techniques and multi-wavelength (BRHK,H alpha) imaging data to investigate the
nature of the interstellar medium (ISM) in the edge-on, low surface brightness
(LSB) galaxy UGC7321. Using realistic models that incorporate multiple
scattering effects and clumping of the stars and the interstellar material, we
explore the distribution and opacity of the interstellar material (gas+dust),
and its effects on the observed stellar disk luminosity profiles, color
gradients, and rotation curve shape. We find that UGC7321 contains a small but
non-negligible dusty component to its ISM, yielding a B-band optical depth
tau_e,B~4.0 from disk edge to center. A significant fraction (~50+/-10%) of the
interstellar material in the innermost regions of UGC7321 appears to be
contained in a clumpy medium, indicating that LSB galaxies can support a
modest, multi-phase ISM structure. In spite of the clear presence of dust, we
conclude that the large radial optical color gradients observed in UGC7321 and
other similar LSB spiral galaxies cannot be accounted for by dust and must
result primarily from significant stellar population and/or metallicity
gradients. We show that realistic optical depth effects will have little impact
on the observed rotation curves of edge-on disk galaxies and cannot explain the
linear, slowly rising rotation curves seen in some edge-on LSB spirals.
Projection effects create a far larger uncertainty in recovering the true
underlying rotation curve shape of galaxies viewed at inclinations i>85
degrees.


title: A Massive Dark Object in the S0 galaxy NGC 4350

abstract:
  We present a new detection of a Massive Dark Object in the S0 Galaxy NGC
4350, obtained applying a new dynamical model on ground-based photometric and
kinematic data already present in literature.


title:
The 35-day cycle in Her X-1 as observational appearance of freely
  precessing neutron star and forcedly precessing accretion disk

abstract:
  A careful analysis of X-ray light curves and pulse profiles of Her X-1
obtained over more than 20 years strongly evidences for free precession of a
magnetized neutron star with rotational axis inclined to the orbital plane as a
central clock underlying the observed 35-day period. Strong asymmetric X-ray
illumination of the optical star atmosphere leads to the formation of gaseous
streams coming out of the orbital plane and forming a tilted accretion disk
around the neutron star. Such a disk precesses due to tidal forces and
dynamical action of gaseous streams from the secondary companion. The locking
of these torques with neutron star precession makes the net disk precession
period to be very close to that of the neutron star free precession.


title: Dynamical Evolution of Protoplanetary Disks

abstract:
  This paper reviews the theory of protostellar debris disks. After a brief
introduction to accretion disk physics, I describe coagulation models of planet
formation in the outer regions of planetesimal disks. Coagulation models for
the Kuiper Belt produce Pluto-sized objects on timescales of 10-40 Myr. These
models yield size distributions which agree with observations of Kuiper Belt
objects with red magnitudes, R = 20-27. Velocity stirring models for other
debris disk systems demonstrate that 500 km or larger objects can stir the
velocities of small objects up to the shattering limit needed to begin a
collisional cascade.


title:
The Luminosity Function of 81 Abell Clusters from the CRoNaRio
  catalogues

abstract:
  We present the composite luminosity function (hereafter LF) of galaxies for
81 Abell clusters studied in our survey of the Northern Hemisphere, using DPOSS
data processed by the CRoNaRio collaboration. The derived LF is very accurate
due to the use of homogeneous data both for the clusters and the control fields
and to the local estimate of the background, which takes into account the
presence of large-scale structures and of foreground clusters and groups. The
global composite LF is quite flat down to $M^*+5$ has a slope
$\alpha\sim-1.0\pm0.2$ with minor variations from blue to red filters, and
$M^*\sim-21.8,-22.0,-22.3$ mag ($H_0=50$ km s$^{-1}$ Mpc$^{-1}$) in the $g, r$
and $i$ filters, respectively (errors are detailed in the text). We find a
significant difference between rich and poor clusters thus arguing in favour of
a dependence of the LF on the properties of the environment.


title: The Dying Wind Around HD 56126, A Post-AGB Carbon Star

abstract:
  We have used the Keck I telescope to resolve at mid-infrared wavelengths the
dust emission from HD 56126 (IRAS 07134+1005), a post-Asymptotic Giant Branch
carbon star with a detached dust shell. The gross morphology of the image can
be explained by a strong wind which started to die about 1500 years ago. If the
star had an effective temperature near 2600 K when it was losing a large amount
of mass, then during the past 1500 years, the average value of dT/dt has been
+2.2 K/yr. With such a time variation of the effective temperture of the star,
the 11.7 micron image can be approximately reproduced if the mass loss rate
varied as T^(-8.26), as proposed in recent models for dust-driven winds. Since
the mass loss rate appears to be very sensitive to the effective temperature of
the star, we speculate that the observed deviations from spherical symmetry of
the dust shell can be explained by plausible variations in the surface
temperature of the mass-losing star caused by rotation and/or magnetic fields.


title:
Power spectrum normalization from the local abundance of rich clusters
  of galaxies

abstract:
  The number density of rich galaxy clusters still provides the most robust way
of normalizing the power spectrum of dark matter perturbations on scales
relevant to large-scale structure. We revisit this constraint in light of
several recent developments: (1) the availability of well-defined samples of
local clusters with relatively accurate X-ray temperatures; (2) new theoretical
mass functions for dark matter haloes which provide a good fit to large
numerical simulations; (3) more accurate mass-temperature relations from larger
catalogs of hydrodynamical simulations; (4) the requirement to consider closed
as well as open and flat cosmologies to obtain full multi-parameter likelihood
constraints for CMB and SNe studies. We present a new sample of clusters drawn
from the literature and use this sample to obtain improved results on sigma_8,
the normalization of the matter power spectrum on scales of 8 h^{-1} Mpc, as a
function of the matter density and cosmological constant in a Universe with
general curvature. We discuss our differences with previous work, and the
remaining major sources of uncertainty. Final results on the 68 per cent
confidence region, approximately independent of power spectrum shape, can be
expressed as constraints on sigma at an appropriate cluster normalization scale
R_Cl. We provide fitting formulas for R_Cl and sigma(R_Cl) for general
cosmologies, as well as for sigma_8 as a function of cosmology and shape
parameter Gamma. For flat models we find approximately sigma_8 \simeq
0.495^{+0.034}_{-0.037}) Omega_M^{-0.60} for Gamma=0.23, where the error bar is
dominated by uncertainty in the mass-temperature relation.


title: Evolution of Gas in Elliptical Galaxies

abstract:
  We review the origin and structure of hot (cooling flow) gas in elliptical
galaxies. X-ray observations can be used to determine the stellar mass to light
ratio, the mass profiles of dark matter halos, and the interstellar magnetic
field. Interstellar gas cools over a large volume, forming stars with a
bottom-heavy IMF. For consistency with the thin fundamental plane, young stars
must be optically luminous. Circular X-ray isophotes in rotating elliptical
galaxies indicate distributed radiative cooling or strong interstellar
turbulence.


title:
A molecular shell with star formation toward the supernova remnant
  G349.7+0.2

abstract:
  A field of ~38'x38' around the supernova remnant (SNR) G349.7+0.2 has been
surveyed in the CO J=1-0 transition with the 12 Meter Telescope of the NRAO,
using the On-The-Fly technique. The resolution of the observations is 54". We
have found that this remnant is interacting with a small CO cloud which, in
turn, is part of a much larger molecular complex, which we call the ``Large CO
Shell''. The Large CO Shell has a diameter of about 100 pc, an H_2 mass of
930,000 solar masses, and a density of 35 cm-3. We investigate the origin of
this structure and suggest that an old supernova explosion ocurred about 4
million years ago, as a suitable hypothesis. Analyzing the interaction between
G349.7+0.2 and the Large CO Shell, it is possible to determine that the shock
front currently driven into the molecular gas is a non-dissociative shock
(C-type), in agreement with the presence of OH 1720 MHz masers. The positional
and kinematical coincidence among one of the CO clouds that constitute the
Large CO Shell, an IRAS point-like source and an ultracompact H II region,
indicate the presence of a recently formed star. We suggest that the formation
of this star was triggered during the expansion of the Large CO Shell, and
suggest the possibility that the same expansion also created the progenitor
star of G349.7+0.2. The Large CO Shell would then be one of the few
observational examples of supernova-induced star formation.


title:
Charge Conjugation Violation in Supernovae and The Neutron Shortage for
  R-Process Nucelosynthesis

abstract:
  Core collapse supernovae are dominated by energy transport from neutrinos.
Therefore, some supernova properties could depend on symetries and features of
the standard model weak interactions. The cross section for neutrino capture is
larger than that for antineutrino capture by one term of order the neutrino
energy over the nucleon mass. This reduces the ratio of neutrons to protons in
the $\nu$-driven wind above a protoneutron star by approximately 20 % and may
significantly hinder r-process nucleosynthesis.


title:
CO observations toward supernova remnants with associated OH 1720 MHz
  masers

abstract:
  The environs of three supernova remnants (SNR) with associated OH 1720 MHz
masers, G349.7+0.2, CTB 37A and G16.7+0.1, have been surveyed in the CO J=1-0
transition with the 12 Meter Telescope of the NRAO, using the On-The-Fly
technique. These observations have revealed a number of molecular clouds
interacting with the SNR shock fronts. Most of the OH 1720 MHz masers have been
found to lie over CO concentrations, and the maser velocities are coincident
with the CO peak velocities to an accuracy better than 2 km/s. The present data
trace the interstellar medium (ISM) structures interacting with the SNRs;
however, to probe the shocked molecular gas in which the OH 1720 MHz emission
originates, higher excitation transitions and more complex species should be
observed. In CTB 37A, where the shock velocity into the molecular cloud could
be determined, it has been found to be of C-type, in agreement with theoretical
predictions. Part of the rim of G16.7+0.1 appears to be flattened by a dense
external cloud, yet the only associated OH 1720 MHz maser lies near the
opposite region of the remnant. This behavior, also observed in IC 443 and 3C
391, seems to contradict the suggestion that OH 1720 MHz maser emission occurs
mainly for transverse shocks.


title: A 2.14 ms Candidate Optical Pulsar in SN1987A

abstract:
  We have monitored Supernova 1987A in optical/near-infrared bands from a few
weeks following its birth until the present time in order to search for a
pulsar remnant. We have found an apparent pattern of emission near the
frequency of 467.5 Hz - a 2.14 ms pulsar candidate, first detected in data
taken on the remnant at the Las Campanas Observatory (LCO) 2.5-m Dupont
telescope during 14-16 Feb. 1992 UT. We detected further signals near the 2.14
ms period on numerous occasions over the next four years in data taken with a
variety of telescopes, data systems and detectors, at a number of ground- and
space-based observatories. The sequence of detections of this signal from Feb.
`92 through August `93, prior to its apparent subsequent fading, is highly
improbable (< 1.e-10) for any noise source). We also find evidence for
modulation of the 2.14 ms period with a ~1,000 s period which, when taken with
the high spindown of the source (2-3e-10 Hz/s), is consistent with precession
and spindown via gravitational radiation of a neutron star with a
non-axisymmetric oblateness of ~1e-6, and an implied gravitational luminosity
exceeding that of the Crab Nebula pulsar by an order of magnitude.


title: Dependence of Gas Phase Abundances in the ISM on Column Density

abstract:
  Sightlines through high- and intermediate-velocity clouds allow measurements
of ionic gas phase abundances, A, at very low values of HI column density,
N(HI). Present observations cover over 4 orders of magnitude in N(HI).
Remarkably, for several ions we find that the A vs N(HI) relation is the same
at high and low column density and that the abundances have a relatively low
dispersion (factors of 2-3) at any particular N(HI). Halo gas tends to have
slightly higher values of A than disk gas at the same N(HI), suggesting that
part of the dispersion may be attributed to the environment. We note that the
dispersion is largest for NaI; using NaI as a predictor of N(HI) can lead to
large errors. Important implications of the low dispersions regarding the
physical nature of the ISM are: (a) because of clumping, over sufficiently long
pathlengths N(HI) is a reasonable measure of the_local_ density of_most_ of the
H atoms along the sight line; (b) the destruction of grains does not mainly
take place in catastrophic events such as strong shocks, but is a continuous
function of the mean density; (c) the cycling of the ions becoming attached to
grains and being detached must be rapid, and the two rates must be roughly
equal under a wide variety of conditions; (d) in gas that has a low average
density the attachment should occur within denser concentrations.


title: The Fossil Starburst in M82

abstract:
  (Abridged) We present high-resolution HST imaging in the optical (WFPC2) and
near-infrared (NICMOS) of a disk region 1 kpc NE of the starburst core in the
nearby galaxy M82. This region, M82 ``B,'' has been suspected to be a fossil
starburst site in which an intense episode of star formation occurred over 100
Myr ago, and our new observations confirm this intepretation. We find a large,
evolved system of super star clusters in M82 B; we identify a total of 113
super star cluster candidates. The clusters range in absolute magnitude from
M_V^0 = -6 to -10, with a peak at -7.5. The derived age distribution suggests
steady, continuing cluster formation at a modest rate at early times (> 2 Gyr
ago), followed by a concentrated formation episode ~600 Myr ago and more recent
suppression of cluster formation. The peak episode coincides with independent
dynamical estimates for the last tidal encounter with M81. Our J and H band
observations resolve the bright giant population in M82's disk for the first
time. Star formation evidently continued in M82 B until about 20-30 Myr ago,
but none is found associated with the youngest generations in the nuclear
starburst (age <= 15 Myr). After correcting the cluster luminosity function to
a fiducial age of 50 Myr, we find that the bright end is characterized by a
power-law slope with alpha = -1.2 +/- 0.3. Cluster sizes (2.34 <= Reff <= 10
pc, or 2.4 <= Rcore <= 7.9 pc) and estimated masses (a median of 10^5 Msun) are
consistent with values found for young super star cluster populations in M82's
core and other galaxies and with the progenitors of globular clusters.


title: The McKee/Ostriker Model: Paradigm?

abstract:
  We summarize the current observational status of the interstellar medium in
terms of the McKee/Ostriker model. We find both agreement and
disagreement---hence the title of the paper. Some of the newest observations
differ from older ones, which underscores the need for both more and better
data


title:
Topology and Polarisation of Subbeams Associated With Pulsar 0943+10's
  ``Drifting''-Subpulse Emission: I. Analysis of Arecibo 430- and 111-MHz
  Observations

abstract:
  The ``drifting'' subpulses exhibited by some radio pulsars have fascinated
both observers and theorists for 30 years, and have been widely regarded as one
of the most critical and potentially insightful aspects of their emission.
Here, we report on detailed studies of pulsar B0943+10, whose nearly coherent
sequences of ``drifting'' subpulses have permitted us to identify their origin
as a system of subbeams that appear to circulate around the star's magnetic
axis. We introduce several new techniques of analysis, and we find that both
the primary and secondary features in the star's fluctuation spectra are
aliases of their actual values. We have also developed a method of tracing the
underlying pattern responsible for the observed sequences, using a
``cartographic'' transform and its inverse, permitting us to study the
characteristics of the polar-cap emission ``map'' and to confirm that such a
``map'' in turn represents the observed sequence. We apply these techniques to
the study of three different Arecibo observations. The ``B''-mode sequences are
consistent in revealing that the emission pattern consists of 20 subbeams,
which rotate around the magnetic axis in about 37 periods or 41 seconds. Even
in the ``Q'' mode sequence, we find evidence of a compatible circulation time.
The similarity of the subbeam patterns at different radio frequencies strongly
suggests that the radiation is produced within a set of columns, which extend
from close to the stellar surface up though the emission region and reflect
some manner of a ``seeding''phenomenon at their base. The subbeam emission is
then tied neither to the stellar surface nor to the field.


title:
Further Investigation of the Time Delay, Magnification Ratios, and
  Variability in the Gravitational Lens 0218+357

abstract:
  High precision VLA flux density measurements for the lensed images of
0218+357 yield a time delay of 10.1(+1.5-1.6)days (95% confidence). This is
consistent with independent measurements carried out at the same epoch (Biggs
et al. 1999), lending confidence in the robustness of the time delay
measurement. However, since both measurements make use of the same features in
the light curves, it is possible that the effects of unmodelled processes, such
as scintillation or microlensing, are biasing both time delay measurements in
the same way. Our time delay estimates result in confidence intervals that are
somewhat larger than those of Biggs et al., probably because we adopt a more
general model of the source variability, allowing for constant and variable
components. When considered in relation to the lens mass model of Biggs et al.,
our best-fit time delay implies a Hubble constant of H_o = 71(+17-23) km/s-Mpc
for Omega_o=1 and lambda_o=0 (95% confidence; filled beam). This confidence
interval for H_o does not reflect systematic error, which may be substantial,
due to uncertainty in the position of the lens galaxy. We also measure the flux
ratio of the variable components of 0218+357, a measurement of a small region
that should more closely represent the true lens magnification ratio. We find
ratios of 3.2(+0.3-0.4) (95% confidence; 8 GHz) and 4.3(+0.5-0.8) (15 GHz).
Unlike the reported flux ratios on scales of 0.1", these ratios are not
strongly significantly different. We investigate the significance of apparent
differences in the variability properties of the two images of the background
active galactic nucleus. We conclude that the differences are not significant,
and that time series much longer than our 100-day time series will be required
to investigate propagation effects in this way.


title:
Dark matter distribution in the universe and ultra-high energy cosmic
  rays

abstract:
  Two of the greatest mysteries of modern physics are the origin of the dark
matter in the universe and the nature of the highest energy particles in the
cosmic ray spectrum. We discuss here possible direct and indirect connections
between these two problems, with particular attention to two cases: in the
first we study the local clustering of possible sources of ultra-high energy
cosmic rays (UHECRs) driven by the local dark matter overdensity. In the second
case we study the possibility that UHECRs are directly generated by the decay
of weakly unstable super heavy dark matter.


title: Infall models of Class 0 protostars

abstract:
  We have carried out radiative transfer calculations of infalling, dusty
envelopes surrounding embedded protostars to understand the observed properties
of the recently identified ``Class 0'' sources. To match the far-infrared peaks
in the spectral energy distributions of objects such as the prototype Class 0
source VLA 1623, pure collapse models require mass infall rates
$\sim10^{-4}\msun$yr$^{-1}$. The radial intensity distributions predicted by
such infall models are inconsistent with observations of VLA 1623 at sub-mm
wavelengths, in agreement with the results of Andre et al. (1993) who found a
density profile of $\rho \propto r^{-1/2}$ rather than the expected $\rho
\propto r^{-3/2}$ gradient. To resolve this conflict, while still invoking
infall to produce the outflow source at the center of VLA 1623, we suggest that
the observed sub-mm intensity distribution is the sum of two components: an
inner infall zone, plus an outer, more nearly constant-density region. This
explanation of the observations requires that roughly half the total mass
observed within 2000 AU radius of the source lies in a region external to the
infall zone. The column densities for this external region are comparable to
those found in the larger Oph A cloud within which VLA 1623 is embedded. The
extreme environments of Class 0 sources lead us to suggest an alternative or
additional interpretation of these objects: rather than simply concluding with
Andre et al. that Class 0 objects only represent the earliest phases of
protostellar collapse, and ultimately evolve into older ``Class I'' protostars,
we suggest that many Class 0 sources could be the protostars of very dense
regions. (Shortened)


title: Optical and Infrared Colors of Stars Observed by 2MASS and SDSS

abstract:
  We discuss optical and infrared photometric properties of stars matched in
the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS)
commissioning data for 50 deg2 of sky. About 98% (63,000) of objects listed in
the 2MASS Point Source Catalog in the analyzed area are matched within 2 arcsec
to an SDSS source. The matched sources represent 8% of the about 800,000 SDSS
sources in this area, and 15% of them are resolved in SDSS imaging data,
although they are detected as point sources in 2MASS data.
  For about 14,000 stars with the smallest photometric errors (< 10%) in both
surveys, we present optical and infrared color-magnitude and color-color
diagrams. We use optical (SDSS) colors to identify the stellar spectral
sequence and show that stars of different spectral types can have similar
infrared colors, thus making the classification of stars based on only 2MASS
data very difficult. However, a broad separation into ``early'' and ``late''
spectral types (relative to type K0) is possible with a reliability of about
95% even with 2MASS colors alone.
  The distributions of matched sources in color-magnitude and color-color
diagrams are compared to the predictions of a stellar population synthesis
code. We find that the models are in fair overall agreement with the data. The
most significant discrepancies are found for the number ratio of ``early'' to
``late'' type stars (by about a factor of 2) and in the colors of M stars (up
to 0.2 mag).


title: Probing Planet Formation Among Nearby Young Stars

abstract:
  The recent identification of several groups of young stars within 100 parsecs
of the Sun has generated widespread interest. Given their proximity and
possible age differences, these systems are ideally suited for detailed studies
of disk evolution and planet formation. Here I discuss recent results and
prospects for the near-future.


title:
Central Elemental Abundance Ratios in the Perseus Cluster: Resonant
  Scattering or SN Ia Enrichment?

abstract:
  We have determined elemental abundance ratios in the core of the Perseus
cluster for several elements. These ratios indicate a central dominance of SN
Ia ejecta similar to that found for A496, A2199 and A3571 (Dupke & White 2000).
Simultaneous analysis of ASCA spectra from SIS1, GIS 2&3 shows that the ratio
of Ni to Fe abundances is ~ (3.4 +- 1.1) times Solar within the central 4'.
This ratio is consistent with (and more precise than) that observed in other
clusters whose central regions are dominated by SN Ia ejecta. Such a large Ni
over-abundance is predicted by "Convective Deflagration" explosion models for
SN Ia such as "W7" but is inconsistent with delayed detonation models. We note
that with current instrumentation the NiK(alpha) line is confused with
FeK(beta) and that the Ni over-abundance we observe has been interpreted by
others as an anomalously large ratio of FeK(beta) to FeK(alpha) caused by
resonant scattering in the FeK(alpha) line. We argue that a central enhancement
of SN Ia ejecta and hence a high ratio of Ni to Fe is naturally explained by
scenarios that include the generation of chemical gradients by suppressed SN Ia
winds or ram-pressure stripping of cluster galaxies. It is not necessary to
suppose that the intracluster gas is optically thick to resonant scattering of
the FeK(alpha) line.


title: The Salpeter plasma correction for solar fusion reactions

abstract:
  We review five different derivations that demonstrate that the Salpeter
formula for the plasma corrections to fusion rates is valid at the center of
the sun with insignificant errors (~ percent). We point out errors in several
recent papers that have obtained a variety of answers, some even with the wrong
sign or the wrong functional dependence.

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


title:
The surface brightness of dark matter: unique signatures of neutralino
  annihilation in the Galactic halo

abstract:
  We use high resolution numerical simulations of the formation of cold dark
matter halos to simulate the background of decay products from neutralino
annihilation, such as gamma-rays or neutrinos. Halos are non-spherical, have
steep singular density profiles and contain many thousands of surviving dark
matter substructure clumps. This leads to several unique signatures in the
gamma-ray background that may be confirmed or rejected by the next generation
of gamma-ray experiments. Most importantly, the diffuse background is enhanced
by over two orders of magnitude due to annihilation within substructure halos.
The largest dark substructures are easily visibly above the background and may
account for the unidentified EGRET sources. A deep strip survey of the
gamma-ray background would allow the shape of the Galactic halo to be
quantified.