title: Launching of jets and the vertical structure of accretion disks

abstract:
  The launching of magnetohydrodynamic outflows from accretion disks is
considered. We formulate a model for the local vertical structure of a thin
disk threaded by a poloidal magnetic field of dipolar symmetry. The model
consists of an optically thick disk matched to an isothermal atmosphere. The
disk is supposed to be turbulent and possesses an effective viscosity and an
effective magnetic diffusivity. In the atmosphere, if the magnetic field lines
are inclined sufficiently to the vertical, a magnetocentrifugal outflow is
driven and passes through a slow magnetosonic point close to the surface. We
determine how the rate of mass loss varies with the strength and inclination of
the magnetic field. In particular, we find that for disks in which the mean
poloidal field is sufficiently strong to stabilize the disk against the
magnetorotational instability, the mass loss rate decreases extremely rapidly
with increasing field strength, and is maximal at an inclination angle of 40-50
degrees. For turbulent disks with weaker mean fields, the mass loss rate
increases monotonically with increasing strength and inclination of the field,
but the solution branch terminates before achieving excessive mass loss rates.
Our results suggest that efficient jet launching occurs for a limited range of
field strengths, and a limited range of inclination angles in excess of 30
degrees. In addition, we determine the direction and rate of radial migration
of the poloidal magnetic flux, and discuss whether configurations suitable for
jet launching can be maintained against dissipation.


title:
1-5 micron imaging of 3CRR galaxies: The K-z relation and the geometry
  of the torus

abstract:
  It has been claimed by Taylor et al. that the low-redshift end of the K-z
relation for radio galaxies is too bright by about half a magnitude due to
contributions from the obscured quasar nuclei. Such a result has major
implications for the use of the K-band Hubble diagram in understanding the
cosmological evolution of radio galaxies. In this paper we present 1-5 micron
imaging data of a nearly-complete sample of low-redshift radio galaxies; this
approach allows us to accurately determine the strengths of any unresolved
nuclear components in the galaxies. We detect nuclear sources in five targets,
whose broad-band colours are consistent with reddened quasar spectra. In all
five cases the ratio of the inferred intrinsic near-infrared luminosity to the
narrow-line luminosity is typical of quasars. We find a correlation between the
inferred nuclear extinction and core-to-lobe ratio, which places constraints on
the geometry of the torus. We find evidence for a shift of the K-z relation to
fainter magnitudes, but by a much smaller amount (~0.1 mag) than Taylor et al.
determined. Under the assumption that the nuclear sources in radio galaxies
have the same intrinsic near-infrared spectra as quasars, our multi-wavelength
images allow us to limit any possible shift to less than 0.3 magnitudes.


title: The Cosmological Mass Function in the Zel'dovich Approximation

abstract:
  The Press-Schechter theory of the cosmological mass function and its
modifications allow to constraint cosmological scenarios of the structure
formation. Recently a few new models have been suggested that explored the
influence of anisotropic collapse on the shape of the mass function. I discuss
in more detail a particular model that assumes that a fluid particle becomes a
part of a gravitationally bound halo when the smallest eigenvalue of the
deformation tensor of the filtered initial density field reaches a certain
threshold (like the filtered density contrast reaches the threshold in the
Press-Schechter formalism). Choosing the smallest eigenvalue guarantees that
the fluid particle in question experiences collapse along all three axes. The
model shows a better agreement with the N-body simulations than the standard
Press-Schechter model.


title: Stewart-Lyth Inverse Problem

abstract:
  In this paper the Stewart-Lyth inverse problem is introduced. It consists of
solving two non-linear differential equations for the first slow-roll parameter
and finding the inflaton potential. The equations are derived from the
Stewart--Lyth equations for the scalar and tensorial perturbations produced
during the inflationary period. The geometry of the phase planes transverse to
the trajectories is analyzed, and conclusions about the possible behaviour for
general solutions are drawn.


title:
Bardeen-Petterson Effect and Quasi-Periodic Oscillations in X-Ray
  Binaries

abstract:
  The Bardeen-Petterson effect around a rapidly-rotating compact object causes
a tilted accretion disk to warp into the equatorial plane of the rotating body.
Viscous forces cause the accretion flow to divide into two distinct regions -
an inner aligned accretion disk and an outer tilted accretion disk. The
transition between these two occurs at a characteristic radius that depends on
the mass and angular momentum of the central object and possibly on the
accretion rate through the disk. We propose that accreting material passing
through the transition region may generate quasi-periodic brightness
oscillations (QPOs) such as have been observed in a number of X-ray binaries.
We show that this effect may be present in the black-hole X-ray binary GRO
J1655-40. We also argue that the QPO frequency range predicted by this model is
consistent with observed QPO frequencies in both black-hole and neutron-star
low-mass X-ray binaries.


title: Gravitational Time Delay Effects on CMB Anisotropies

abstract:
  We study the effect of gravitational time delay on the power spectra and
bispectra of the cosmic microwave background (CMB) temperature and polarization
anisotropies. The time delay effect modulates the spatial surface at
recombination on which temperature anisotropies are observed, typically by ~1
Mpc. While this is a relatively large shift, its observable effects in the
temperature and polarization fields are suppressed by geometric considerations.
The leading order effect is from its correlation with the closely related
gravitational lensing effect. The change to the temperature-polarization cross
power spectrum is of order 0.1% and is hence comparable to the cosmic variance
for the power in the multipoles around l~1000. While unlikely to be extracted
from the data in its own right, its omission in modeling would produce a
systematic error comparable to this limiting statistical error and, in
principle, is relevant for future high precision experiments. Contributions to
the bispectra result mainly from correlations with the Sachs-Wolfe effect and
may safely be neglected in a low density universe.


title: A Global Photometric Analysis of 2MASS Calibration Data

abstract:
  We present results from the application of a global photometric calibration
(GPC) procedure to calibration data from the first 2 years of The Two Micron
All Sky Survey (2MASS). The GPC algorithm uses photometry of both primary
standards and moderately bright `tracer' stars in 35 2MASS calibration fields.
During the first two years of the Survey, each standard was observed on
approximately 50 nights, with about 900 individual measurements. Based on the
photometry of primary standard stars and secondary tracer stars and under the
assumption that the nightly zeropoint drift is linear, GPC ties together all
calibration fields and all survey nights simultaneously, producing a globally
optimized solution. Calibration solutions for the Northern and Southern
hemisphere observatories are found separately, and are tested for global
consistency based on common fields near the celestial equator.
  Several results from the GPC are presented, including establishing candidate
secondary standards, monitoring of near-infrared atmospheric extinction
coefficients, and verification of global validity of the standards. The
solution gives long-term averages of the atmospheric extinction coefficients,
A_J=0.096, A_H=0.026, A_{K_s}=0.066 (North) and A_J=0.092, A_H=0.031,
A_{K_s}=0.065 (South), with formal error of 0.001. The residuals show small
seasonal variations, most likely due to changing atmospheric content of water
vapor. Extension of the GPC to approximately 100 field stars in each of the 35
calibration fields yields a catalog of more than two thousand photometric
standards ranging from 10th to 14th magnitude, with photometry that is globally
consistent to $\sim 1%$.


title: Mapping the Galactic Halo II: Photometric Survey

abstract:
  We present imaging results from a high Galactic latitude survey designed to
examine the structure of the Galactic halo. The objective of the survey is to
identify candidate halo stars which can be observed spectroscopically to obtain
radial velocities and confirm halo membership. The Washington filter system is
used for its ability to distinguish between dwarfs and giants, as well as
provide a metallicity indicator. Our most successful imaging run used the BTC
camera on the CTIO 4m telescope in April 1999. Photometric conditions during
these observations provided superb photometry, with average errors for a star
at $M=18.5$ of 0.009, 0.008, 0.011, and 0.009 for $C$, $M$, $DDO51$, and $T2$
respectively. These data are available with the electronic version of this
paper, as well as through ADC (http://adc.gsfc.nasa.gov/). We use these data as
a template to describe the details of our photometric reduction process. It is
designed to perform CCD reductions and stellar photometry automatically during
the observation run without the aid of external packages, such as IRAF and IDL.
We describe necessary deviations from this procedure for other instruments used
in the survey up to June 2000. Preliminary results from spectroscopic
observations indicate a 97% efficiency in eliminating normal dwarfs from halo
giant candidates for $M<18.5$. Unfortunately, low-metallicity subdwarfs cannot
be photometrically distinguished from giants using the Washington filters.
These major contaminates unavoidably reduced the overall giant identification
efficiency to 66% for $M<18.5$. Our improved knowledge of these stars will
increase this efficiency for future spectroscopic observations.


title:
Infrared Star Count Models and Their Application to the Subaru Deep
  Field

abstract:
  We construct infrared star count models of the Galaxy applicable at faint
magnitudes. In addition to dwarfs and subdwarfs, we also take into account L
dwarfs, T dwarfs, and white dwarfs of both disk and halo. As a test case of the
models, we analyze the infrared imaging data at J and K' obtained during the
Subaru Deep Field Survey to study stellar objects. Infrared star count models
we have obtained predict that the Next Generation Space Telescope will
primarily see T dwarfs, M subdwarfs, and old halo white dwarfs at faint
magnitudes.


title: Phase Diagram for Spinning and Accreting Neutron Stars

abstract:
  Neutron star configurations are considered as thermodynamical systems for
which a phase diagram in the angular velocity (Omega) - baryon number (N) plane
is obtained with a dividing line N_{crit}(Omega) for quark core configurations.
Trajectories of neutron star evolution in this diagram are studied for
different scenarios defined by the external torque acting on the star due to
radiation and/or mass accretion. They show a characteristic change in the
rotational kinematics when the star enters the quark core regime. For isolated
pulsars the braking index signal for deconfinement has been studied in its
dependence on the mass of the star. Model calculations of the spin evolution of
accreting low-mass X-ray binaries in the phase diagram have been performed for
different values of the initial magnetic field, its decay time as well as
initial mass and mass accretion rate. Population clustering of these objects at
the line N_{crit}(Omega) in the phase diagram is suggested as an observable
signal for the deconfinement phase transition if it exists for spinnning and
accreting neutron stars.


title:
The Narrow-Line Region of Seyfert Galaxies: Narrow-Line Seyfert 1
  Galaxies versus Broad-Line Seyfert 1 Galaxies

abstract:
  It is known that the spectral energy distribution (SED) of the nuclear
radiation of narrow-line Seyfert 1 galaxies (NLS1s) has different shapes with
respect to that of ordinary broad-line Seyfert 1 galaxies (BLS1s), particularly
in wavelengths of X-ray. This may cause some differences in the ionization
degree and the temperature of gas in narrow-line regions (NLRs) between NLS1s
and BLS1s. This paper aims to examine whether or not there are such differences
in the physical conditions of NLR gas between them. For this purpose, we have
compiled the emission-line ratios of 36 NLS1s and 83 BLS1s from the literature.
Comparing these two samples, we have found that the line ratios of [O {\sc
i}]$\lambda$6300/[O {\sc iii}]$\lambda$5007 and [O {\sc iii}]$\lambda$4363/[O
{\sc iii}]$\lambda$5007, which represent the ionization degree and the gas
temperature respectively, are statistically indistinguishable between NLS1s and
BLS1s. Based on new photoionization model calculations, we show that these
results are not inconsistent with the difference of the SED between them. The
influence of the difference of SEDs on the highly ionized emission lines is
also briefly discussed.


title:
Recent Progress in Understanding Nucleosynthesis via Rapid Neutron
  Capture

abstract:
  I discuss the recent progress in our understanding of nucleosynthesis via
rapid neutron capture, the r-process, based on meteoritic data for the early
solar system and observations of stars at low metallicities. At present, all
data require that there be two distinct kinds of r-process events and suggest
that supernovae are associated with these events. The diversity of supernova
sources for the r-process may depend on whether a neutron star or black hole is
formed in an individual supernova. This dependence, if substantiated by future
observations discussed here, has important implications for properties of
nuclear matter.


title:
Determining the Microlens Mass Function from Quasar Microlensing
  Statistics

abstract:
  The first investigations of the response of the microlensing magnification
pattern (at an optical depth of order unity) to the mass function of the
microlenses found that the resulting statistics depend only on the mean
microlens mass <m>. In particular the mean microlensing caustic crossing rate
was found to be proportional to the squareroot of <m>. We show that while this
is true in the limit of mass functions with a narrow range of mass, in general
the magnification pattern shows structure that reflects the contribution to the
optical depth of microlenses with different masses. We present a better
approximation, relating the microlens mass function to light-curve statistics.
We show that the variability statistics of quasar microlensing light-curves can
(in principle) be inverted to obtain the mass function of the microlenses in
the mass range over which the mass density remains comparable, ie. p(m)dm~C/m.
A preliminary analysis of the structure function for Q2237+0305 suggests that
there is not a significant contribution to the optical depth from very low mass
objects (0.001 solar mass). However observations of multiple microlensed
quasars for a period of ~20 years may in the future yield a detailed p(m)dm. In
the mass range where the number density is comparable, ie. p(m)dm~const., the
distribution of flux factors could be inverted to find the microlens mass
function. This may be used as a probe of the abundance of planets with orbital
radii >100 AU.


title: Gravitational Microlensing of Gamma Ray Bursts at Medium Optical Depth

abstract:
  Gravitational lensing of a gamma ray burst (GRB) by a single point mass will
produce a second, delayed signal. Several authors have discussed using
microlensed GRBs to probe a possible cosmological population of compact
objects. We analyse a closely related phenomenon; the effect of microlensing by
low to medium optical depth in compact objects on the averaged observed
light-curve of a sample of GRBs. We discuss the cumulative measured flux as a
function of time resulting from delays due to microlensing by cosmological
compact objects. The time-scale and curvature of this function describe unique
values for the compact object mass and optical depth. For GRBs with durations
larger than the detector resolution, limits could be placed on the mass and
optical depth of cosmological compact objects. The method does not rely on the
separation of lensed bursts from those which are spatially coincident.


title:
Abundance profiles of CH3OH and H2CO toward massive young stars as
  evolutionary tracers

abstract:
  The chemical evolution of thirteen regions of massive star formation is
studied through single-dish and interferometer line observations at
submillimeter wavelengths. The wealth of CH3OH and H2CO lines covering a large
range of excitation conditions allows us to calculate radial abundance
profiles, using the physical structures of the sources derived earlier from
submillimeter continuum and CS lines. The data indicate three types of
abundance profiles: flat profiles at CH3OH/H2 ~10^-9 for the coldest sources,
profiles with a jump in its abundance from ~10^-9 to ~10^-7 for the warmer
sources, and flat profiles at CH3OH/H2 ~few 10^-8 for the hot cores. The
location of the jump at T~100 K suggests that it is due to evaporation of grain
mantles, followed by destruction in gas-phase reactions in the hot core stage.
In contrast, the H2CO data can be well fit with a constant abundance of a few x
10^-9 throughout the envelope, providing limits on its grain surface formation.
These results indicate that T_rot(CH3OH) can be used as evolutionary indicator
during the embedded phase of massive star formation, independent of source
optical depth or orientation.


title: The detection of oxygen in the low-density intergalactic medium

abstract:
  The abundances of metals in the intergalactic medium (IGM) can be used to
constrain the amount of star formation at high redshift and the spectral shape
of the ionizing background radiation. For both purposes it is essential to
measure the abundances in regions of low density, away from local sources of
metals and ionizing photons. Here we report the first detection of OVI in the
low-density IGM at high redshift. We perform a pixel-by-pixel search for OVI
absorption in eight high quality quasar spectra spanning the redshift range z =
2.0-4.5. At 2 ~< z ~< 3, we clearly detect OVI in the form of a positive
correlation between the HI Ly-alpha optical depth and the optical depth in the
corresponding OVI pixel, down to an HI optical depth of 0.1. This is an order
of magnitude lower in HI optical depth than the best CIV measurements can probe
and constitutes the first clear detection of metals in underdense gas. The
non-detection of OVI at z > 3 is consistent with the enhanced photoionization
from a hardening of the UV background below z ~ 3 but could also be caused by
the high level of contamination from Ly series lines.


title: The Subluminous Type Ia Supernova 1998de in NGC 252

abstract:
  We present spectroscopic and extensive photometric observations of supernova
(SN) 1998de in the S0 galaxy NGC 252, discovered during the course of the Lick
Observatory Supernova Search. These data, which span a time period of 8 days
before to 76 days after $B$-band maximum, unambigously establish SN 1998de as a
peculiar and subluminous SN Ia with strong similarities to SN 1991bg, the
prototype of these intrinsically dim SNe Ia. We find that subluminous SNe Ia
with the same Delta m_{15}(B) can have slightly different light curves at
longer wavelengths. The notable spectroscopic similarities between SN 1998de
and SN 1991bg are the wide Ti II trough at 4100-4500 A, the strong Ca II
features, and the early onset of the nebular phase. We observe that
spectroscopic deviations of SN 1998de from SN 1991bg increase toward redder
wavelenghts. These deviations include the absence of the conspicuous Na I D
absorption found in SN 1991 at 5700 A, and the evolution of a region (6800-7600
A) from featureless to feature-rich. Several lines of evidence suggest that SN
1998de was a slightly more powerful explosion than SN 1991bg. We discuss the
implications of our observations for progenitor models and the explosion
mechanism of peculiar, subluminous SNe Ia. The extensive photometric data make
SN 1998de a better template than SN 1991bg for calibrating the low-luminosity
end of the luminosity vs. decline-rate relationship.


title:
Triggered Star Formation in the Scorpius-Centaurus OB Association (Sco
  OB2)

abstract:
  We explore the star formation history of the Upper Scorpius OB association,
the youngest part of Sco OB2. A wide field (160 square-degree) survey for
low-mass pre-main sequence (PMS) stars enabled us to increase the number of
known low-mass members of Upper Scorpius to nearly 100 stars. In a detailed
analysis of the locations of these stars in the HR diagram, taking proper
account of the uncertainties and the effects of unresolved binaries, we find a
mean stellar age of about 5 Myr and no evidence for a significant age
dispersion among these stars. This implies that the star formation history of
the Upper Scorpius association was dominated by a short star-burst, which
started about 5 Myr ago and ended probably not more than one or two Myr later.
Interestingly, the structure and kinematics of the HI shells surrounding the
Sco OB2 association show that the shock wave of a supernova explosion in the
nearby Upper Centaurus-Lupus association, the oldest part of Sco OB2, crossed
Upper Scorpius just about 5 Myr ago. This strongly suggests that this supernova
shock wave triggered the star-burst in Upper Scorpius.


title: Multiplicity of massive stars

abstract:
  We discuss the observed multiplicity of massive stars and implications on
theories of massive star formation. After a short summary of the literature on
massive star multiplicity, we focus on the O- and B-type stars in the Orion
Nebula Cluster, which constitute a homogenous sample of very young massive
stars. 13 of these stars have recently been the targets of a bispectrum speckle
interferometry survey for companions. Considering the visual and also the known
spectroscopic companions of these stars, the total number of companions is at
least 14. Extrapolation with correction for the unresolved systems suggests
that there are at least 1.5 and perhaps as much as 4 companions per primary
star on average. This number is clearly higher than the mean number of about
0.5 companions per primary star found for the low-mass stars in the general
field population and also in the Orion Nebula cluster. This suggests that a
different mechanism is at work in the formation of high-mass multiple systems
in the dense Orion Nebula cluster than for low-mass stars.


title: Deflection of jets induced by jet-cloud & jet-galaxy interactions

abstract:
  The model first introduced by Raga & Canto (1996) in which astrophysical jets
are deflected on passing through an isothermal high density region is
generalised by taking into account gravitational effects on the motion of the
jet as it crosses the high density cloud. The problem is also generalised for
relativistic jets in which gravitational effects induced by the cloud are
neglected. Two further cases, classical and relativistic, are discussed for the
cases in which the jet is deflected on passing through the interstellar gas of
a galaxy in which a dark matter halo dominates the gravitational potential.
  The criteria for the stability of jets due to the formation of internal
shocks are discussed.


title:
Optical Spectroscopy of GX339-4 during the High-Soft and Low-Hard States
  II: Line Ionisation and Emission Region

abstract:
  We have carried out observations of the X-ray transient GX339-4 during its
high-soft and low-hard X-ray spectral states. Our high-resolution spectroscopic
observation in 1999 April suggests that the H-alpha line has a single-peaked
profile in the low-hard state as speculated in our previous paper. The HeII
4686 line, however, has a double-peaked profile in both the high-soft and
low-hard states. This suggests that the line-emission mechanism is different in
the two states. Our interpretation is that double-peaked lines are emitted from
a temperature-inversion layer on the accretion-disk surface when it is
irradiatively heated by soft X-rays. Single-peaked lines may be emitted from
outflow/wind matter driven by hard X-ray heating. We have constructed a simple
plane-parallel model and we use it to illustrate that a temperature-inversion
layer can be formed at the disk surface under X-ray illumination. We also
discuss the conditions required for the formation of temperature inversion and
line emission. Based on the velocity separations measured for the double-peaked
lines in the high-soft state, we propose that GX339-4 is a low-inclination
binary system. The orbital inclination is about 15 deg if the orbital period is
14.8 hours.


title: Convective cores in galactic cooling flows

abstract:
  We use hydrodynamic simulations with adaptive grid refinement to study the
dependence of hot gas flows in X-ray luminous giant elliptical galaxies on the
efficiency of heat supply to the gas. We consider a number of potential heating
mechanisms including Type Ia supernovae and sporadic nuclear activity of a
central supermassive black hole. As a starting point for this research we use
an equilibrium hydrostatic recycling model (Kritsuk 1996). We show that a
compact cooling inflow develops, if the heating is slightly insufficient to
counterbalance radiative cooling of the hot gas in the central few kiloparsecs.
An excessive heating in the centre, instead, drives a convectively unstable
outflow. We model the onset of the instability and a quasi-steady convective
regime in the core of the galaxy in two-dimensions assuming axial symmetry.
  Provided the power of net energy supply in the core is not too high, the
convection remains subsonic. The convective pattern is dominated by buoyancy
driven large-scale mushroom-like structures. Unlike in the case of a cooling
inflow, the X-ray surface brightness of an (on average) isentropic convective
core does not display a sharp maximum at the centre. A hybrid model, which
combines a subsonic peripheral cooling inflow with an inner convective core,
appears to be stable. We also discuss observational implications of these
results.


title: Calculations at Series Limits in One-Electron Systems

abstract:
  As soon as Lyman or Balmer lines overlap, the net absorption cross section
rapidly approaches the value at the series limit. Independent of the difficult
question of the relative contributions of line and continuous opacity, we can
get a good estimate of their sum.


title: A physical model for the hard X-ray background

abstract:
  We combine a semi-analytic galaxy formation model (Nulsen and Fabian 1997)
with a prescription for the obscured growth of massive black holes (Nulsen and
Fabian 2000; Fabian 1999), to reproduce the hard X-ray background (XRB), the
local 2-10keV AGN luminosity function and the source counts, including recent
Chandra results. The model also complies with constraints on the AGN
contribution to the far-infrared and sub-mm backgrounds.
  The co-moving density of luminous AGN [L(2-10keV)>1E44 erg/s, in the
unabsorbed rest- frame] in the model declines sharply since z=2, mimicking the
observed evolution of the quasar population. The abundance of lower luminosity
AGN simultaneously increases, and we identify such objects with the Seyfert
galaxies. These features reflect an epoch-dependent rate of Bondi accretion
from the hot, cooling atmosphere: at z<2.5 most AGN are fed at much less than
10 per cent of the Eddington rate, whilst at z>2.5 most accrete at 10-50 per
cent Eddington. Unlike other models for quasar and galaxy formation, we do not
consider major mergers between normal galaxies.
  The model produces an excess soft XRB below 4keV which can be removed by
modifying the wind expulsion model of Fabian (1999) to incorporate anisotropic
ejection.


title: Further daemon detection experiments

abstract:
  The experiments on detection of daemons captured into geocentric orbits,
which are based on the postulated fast decay of daemon-containing nuclei, have
been continued. By properly varying the experimental parameters, it has become
possible to reveal and formulate some relations governing the interaction of
daemons with matter. Among them are, for instance, the emission of energetic
Auger-type electrons in the capture of an atomic nucleus, the possibility of
charge exchange involving the capture of a heavier nucleus etc. The decay time
of a daemon-containing proton has been measured to be D \tau ~ approx 2 mks.
The daemon flux at the Earth's surface is f ~ 10^{-7} cm^-2 s^-1. One should
point out, on the one hand, the reproducibility of the main results, and on the
other, the desirability of building up larger statistics and employing more
sophisticated experimental methods to reveal finer details in the daemon
interaction with matter.


title: Large scale jets in AGN: multiwavelength mapping

abstract:
  X-ray emission from large scale extragalactic jets is likely to be due to
inverse Compton scattering of relativistic particles off seed photons of both
the cosmic microwave background field and the blazar nucleus. The first process
dominates the observed high energy emission of large scale jets if the plasma
is moving at highly relativistic speeds and if the jet is aligned with the line
of sight, i.e. in powerful flat radio spectrum quasars. The second process is
relevant when the plasma is moving at mildly bulk relativistic speeds, and can
dominate the high energy emission in misaligned sources, i.e. in
radio-galaxies. We show that this scenario satisfactorily accounts for the
spectral energy distribution detected by Chandra from the jet and core of PKS
0637-752.


title:
Genetic-Algorithm-based Asteroseismological Analysis of the DBV White
  Dwarf GD 358

abstract:
  White dwarf asteroseismology offers the opportunity to probe the structure
and composition of stellar objects governed by relatively simple physical
principles. The observational requirements of asteroseismology have been
addressed by the development of the Whole Earth Telescope (WET), but the
analytical procedures still need to be refined before this technique can yield
the complete physical insight that the data can provide. Toward this end, we
have utilized a genetic-algorithm-based optimization method to fit our models
to the observed pulsation frequencies of the DBV white dwarf GD 358 obtained
with the WET in 1990. This new approach has finally exploited the sensitivity
of our models to the core composition, and will soon yield some interesting
constraints on nuclear reaction cross-sections.


title:
Electron-Ion Recombination Rate Coefficients and Photoionization Cross
  Sections for Astrophysically Abundant Elements. V. Relativistic calculations
  for Fe XXIV and Fe XXV for X-ray modeling

abstract:
  Photoionization and recombination cross sections and rate coefficients are
calculated for Li-like Fe XXIV and He-like Fe XXV using the Breit-Pauli
R-matrix (BPRM) method. A complete set of total and level-specific parameters
is obtained to enable X-ray photoionization and spectral modeling. The ab
initio calculations for the unified (e + ion) recombination rate coefficients
include both the non-resonant and the resonant recombination (radiative and
di-electronic recombination, RR and DR, respectively) for (e + Fe XXV) -> Fe
XXIV and (e + Fe XXVI) -> Fe XXV. The level specific rates are computed for all
fine structure levels up to n = 10, enabling accurate computation of
recombination-cascade matrices and effective rates for the X-ray lines. The
total recombination rate coefficients for both Fe XXIV and Fe XXV differ
considerably, by several factors, from the sum of RR and DR rates currently
used to compute ionization fractions in astrophysical models. As the
photoionization/recombination calculations are carried out using an identical
eigenfunction expansion, the cross sections for both processes are
theoretically self-consistent; the overall uncertainty is estimated to be about
10-20%. All data for Fe XXIV and Fe XXV (and also for H-like Fe XXVI, included
for completeness) are available electronically.


title:
Four Years of Extreme Ultraviolet Observations of Markarian 421. I:
  Spectral Analysis

abstract:
  We analyzed the ~950 ks of spectroscopic data accumulated by the Extreme
Ultraviolet Explorer (EUVE) satellite between 1994 and 1997 for the BL Lacertae
object Markarian 421. The EUV spectrum is well detected in the 70-110 A
(112-177 eV) range and can be fitted by a power law model plus an absorption
feature in the ~71-75 A range. Previous studies of EUV absorption features in
MRK 421 and in the other EUV bright BL Lac object, PKS2155-304, explain this
absorption feature as a superposition of Doppler-smeared absorption lines
(mainly L- and M-shell transitions of Mg and Ne) originating in high-velocity
gas clouds ionized by the beamed continuum of the associated relativistic jet.
We show that, for example, Fe IX L could also be a possibility consistent with
the marginal detection of oxygen absorption lines in the X-ray range. However
physical models are highly sensitive to the assumptions on the photoionizing
continuum and the surrounding gas.


title: Silicate Emission in the TW Hydrae Association

abstract:
  The TW Hydrae Association is the nearest young stellar association. Among its
members are HD 98800, HR 4796A, and TW Hydrae itself, the nearest known
classical T Tauri star. We have observed these three stars spectroscopically
between 3 and 13 microns. In TW Hya the spectrum shows a silicate emission
feature that is similar to many other young stars with protostellar disks. The
11.2 micron feature indicative of significant amounts of crystalline olivine is
not as strong as in some young stars and solar system comets. In HR 4796A, the
thermal emission in the silicate feature is very weak, suggesting little in the
way of (small silicate) grains near the star. The silicate band of HD 98800
(observed by us but also reported by Sylvester and Skinner (1996)) is
intermediate in strength between TW Hya and HR 4796.


title: The Distribution of Redshifts in New Samples of Quasi-stellar Objects

abstract:
  Two new samples of QSOs have been constructed from recent surveys to test the
hypothesis that the redshift distribution of bright QSOs is periodic in
$\log(1+z)$. The first of these comprises 57 different redshifts among all
known close pairs or multiple QSOs, with image separations $\leq$ 10\arcsec,
and the second consists of 39 QSOs selected through their X-ray emission and
their proximity to bright comparatively nearby active galaxies. The redshift
distributions of the samples are found to exhibit distinct peaks with a
periodic separation of $\sim 0.089 $ in $\log(1+z)$ identical to that claimed
in earlier samples but now extended out to higher redshift peaks $z = 2.63,
3.45$ and 4.47, predicted by the formula but never seen before. The periodicity
is also seen in a third sample, the 78 QSOs of the 3C and 3CR catalogues. It is
present in these three datasets at an overall significance level $10^{-5}$ -
$10^{-6}$, and appears not to be explicable by spectroscopic or similar
selection effects. Possible interpretations are briefly discussed.


title:
The Effect of Dust on Photometric Redshift Measurement; A
  Self-consistent Technique

abstract:
  A new method is developed for estimating photometric redshifts to galaxies,
using realistic template SEDs, extending over four decades in wavelength (i.e.
from 0.05 micron to 1 mm). The template SEDs are constructed for four different
spectral types of galaxies (elliptical, spiral, irregular and starburst),
satisfying the following characteristics: a). they are normalised to produce
the observed colours of galaxies at z ~ 0; b). incorporate the
chemo-photometric spectral evolution of galaxies of different types, in
agreement with the observations; c). allow treatment of dust contribution and
its evolution with redshift, consistent with the spectral evolution model; d).
include absorption and re-emission of radiation by dust and hence, realistic
estimates of the far-infrared radiation; e). include correction for
inter-galactic absorption by Lyman continuum and Lyman forest. Using these
template SEDs, the photometric redshifts are estimated to an accuracy of ~
0.11. The effect on the estimated photometric redshifts, due to assumptions in
the evolutionary population synthesis models, are investigated and discussed.
  The simultaneous and self-consistent modelling of both the photometric and
chemical evolution of galaxies and the effect of dust, makes this technique
particularly useful for high redshift galaxies. Moreover, since the template
SEDs (at different redshifts) cover the range from UV to far-infrared and
sub-mm wavelengths, one could consistently use the optimised SEDs to estimate
the contribution from individual galaxies to these wavelengths, where no
observational data are available.


title: Baryonic Dark Matter in Galaxies

abstract:
  Cosmological nucleosynthesis calculations imply that many of the baryons in
the Universe must be dark. We discuss the likelihood that some of these dark
baryons may reside in the discs or halos of galaxies. If they were in the form
of compact objects, they would then be natural MACHO candidates, in which case
they are likely to be the remnants of a first generation of pregalactic or
protogalactic Population III stars. Various candidates have been proposed for
such remnants - brown dwarfs, red dwarfs, white dwarfs, neutron stars or black
holes - and we review the many types of observations (including microlensing
searches) which can be used to constrain or exclude them.


title:
The Redshift and the Host Galaxy of GRB 980613: A Gamma-Ray Burst From a
  Merger-Induced Starburst?

abstract:
  We present optical and near-IR identification and spectroscopy of the host
galaxy of GRB 980613. The burst was apparently associated with the optically
(restframe UV) brightest component of a system of at least five galaxies or
galaxy fragments at a redshift of z = 1.0969. The component we identify as the
host galaxy shows a moderately high unobscured star formation rate, SFR = 5
M_solar/yr, but a high SFR per unit mass, indicative of a starburst. The image
components show a broad range of (R-K) colors, with two of them being very red,
possibly due to dust. Overall morphology of the system can be naturally
interpreted as a strong tidal interaction of two or more galaxies, at a
redshift where such events were much more common than now. Given the well
established causal link between galaxy mergers and starbursts, we propose that
this is a strong case for a GRB originating from a merger-induced starburst
system. This supports the proposed link between GRBs and massive star
formation.


title: B3 0003+387: AGN Marked Large-Scale Structure at z=1.47?

abstract:
  We present evidence for a significant overdensity of red galaxies, as much as
a factor of 14 over comparable field samples, in the field of the z=1.47 radio
galaxy B3 0003+387. The colors and luminosities of the brightest red galaxies
are consistent with their being at z>0.8. The radio galaxy and one of the red
galaxies are separated by 5" and show some evidence of a possible interaction.
However, the red galaxies do not show any strong clustering around the radio
galaxy nor around any of the brighter red galaxies. The data suggest that we
are looking at a wall or sheet of galaxies, possibly associated with the radio
galaxy at z=1.47. Spectroscopic redshifts of these red galaxies will be
necessary to confirm this large-scale structure.


title: Discovery of mHz UV Quasiperiodic Oscillations in Hercules X-1

abstract:
  Observations of the ultraviolet continuum of the X-ray binary system Her
X-1/HZ Herculis with the Space Telescope Imaging Spectrograph on the Hubble
Space Telescope show quasiperiodic oscillations (QPOs) at frequencies of 8+/-2
and 43+/-2 mHz, with rms amplitudes of 2 and 4% of the steady flux.
Observations with the Keck telescope confirm the presence of the higher
frequency QPO in the optical continuum, with a rms amplitude of 1.6+/-0.2%. The
QPOs are most prominent in the HST data near phi=0.5 (where phi=0 is the middle
of the X-ray eclipse), suggesting that they arise not in the accretion disk but
on the X-ray heated face of the companion star. We discuss scenarios in which
the companion star reprocesses oscillations in the disk which are caused by
either Keplerian rotation or a beat frequency between the neutron star spin and
Keplerian rotation at some radius in the accretion disk.


title:
Atomic data from the Iron Project XLV. Relativistic transition
  probabilities for carbon-like Ar XIII and Fe XXI using Breit-Pauli R-matrix
  method

abstract:
  The Breit-Pauli R-matrix method developed under the Iron Project has been
used to obtain extensive sets of oscillator strengths and transition
probabilities for dipole allowed and intercombination fine structure
transitions in carbon like ions, Ar XIII and Fe XXI. The complete set consists
of 1274 fine structure bound energy levels and 198,259 oscillator strengths for
Ar XIII, and 1611 bound levels and 300,079 oscillator strengths for Fe XXI.
These correspond to levels of total angular momenta of 0 <= J <= 7 of even and
odd parities formed from total spin of 2S+1=5,3,1, and orbital angular momenta
0 <= L <= 9 with n <= 10, 0 <= l <= 9 for each ion. The relativistic effects
are included in the Breit-Pauli approximation. The close coupling wavefunction
expansion for each ion is represented by the lowest 15 fine structure levels of
target configuations, 2s2.2p, 2s.2p2 and 2p3. The energy levels are identified
spectroscopically using a newly developed identification procedure. The
procedure also makes a correspondence between the fine strucure energy levels
and LS terms. This provides the check for completeness of the calculated
levels. Comparison is made of the present energies and the f-values with the
available observed and theoretical values. Present transition probabilitis
agree very well with the relativistic atomic structure calculations of Mendoza
et al. for the intercombination transitions, 2s.2p3(5So)2 -
2s2.2p2(3P){1,2},(1D)2. This further indicates that the importance of the
neglected Breit interaction decreases with ion charge and constrains the
uncertainty in the present calculations to within 15% even for the weak
transitions.


title: Fun for Two

abstract:
  We performed populations synthesis calculations of single stars and binaries
and show that binary evolution is extremely important for Galactic astronomy.
We review several binary evolution models and conclude that they give quite
different results. These differences can be understood from the assumptions
related to how mass is transfered in the binary systems. Most important are 1)
the fraction of mass that is accreted by the companion star during mass
transfer, 2) the amount of specific angular momentum which is carried away with
the mass that leaves the binary system.


title: Near-infrared and Br_gamma observations of post-AGB stars

abstract:
  We investigate the infrared properties of the IRAS sources not confirmed as
PNe in Van de Steene & Pottasch (1993). We observed 28 objects in the N-band of
which 20 were detected and 5 were resolved. We obtained medium resolution
Br_gamma spectra and we took high resolution JHKL images of these 20 objects.
We critically assessed the identification of the IRAS counterpart in the
images. Of sixteen positively identified objects, seven show Br_gamma in
absorption, another six objects show Br_gamma in emission on top of a
continuum. In another three objects, no clear Br_gamma absorption or emission
was visible. Our detection rate of emission line objects is higher compared to
previous studies. None of the objects with Br_gamma in emission were detected
above a detection limit of 0.6 mJy/beam at 6 cm, while they should have been
easily detected if the radio flux was optically thin and Case B recombination
was applicable. Their SED's are typical for post-AGB stars. We also constructed
various color-color diagrams using the near-infrared and IRAS magnitudes. No
distinction can be made between the objects showing Br_gamma in emission,
absorption, or a flat spectrum in the near and far-infrared color-color
diagrams. The near-infrared color-color diagrams show evidence for a very large
range of extinction, which in part is of circumstellar origin. Near-infrared
versus far-infrared color-color diagrams show trends that are consistent with
the expected evolution of the circumstellar shell. This sample of post-AGB
stars show a larger range in color and are generally closer to the galactic
plane than the ones known so far.


title: X-Ray Lines from Hot Flows around White Dwarfs. Application to SS Cygni

abstract:
  Rather than accreting via a disk, some White Dwarfs (WDs) in quiescent Dwarf
Novae (DN) could accrete via an Advection-Dominated Accretion Flow (ADAF)
possibly responsible for the X-ray Bremsstrahlung emission observed. Such a hot
accretion flow is also expected to produce characteristic thermal line
emission. Using SS Cyg as a specific example, we show that knowing a priori the
inclination and the WD mass in quiescent DN makes X-ray line diagnostics
powerful probes of the flow structure in these systems. Current X-ray
instruments can discriminate, from their width, between lines emitted from a
flow with a Keplerian rotation rate and those emitted at a substantially
sub-Keplerian rate. This could be used to observationally test the property of
energy advection, which is at the origin of the partial radial pressure support
by the hot gas and the sub-Keplerian rotation rate in an ADAF.


title: PMN J1838-3427: A new gravitationally lensed quasar

abstract:
  We report the discovery of a new double-image quasar that was found during a
search for gravitational lenses in the southern sky. Radio source PMN
J1838-3427 is composed of two flat-spectrum components with separation 1", flux
density ratio 14:1 and matching spectral indices, in VLA and VLBA images.
Ground-based BRI images show the optical counterpart (total I=18.6) is also
double with the same separation and position angle as the radio components. An
HST/WFPC2 image reveals the lens galaxy. The optical flux ratio (27:1) is
higher than the radio value probably due to differential extinction of the
components by the lens galaxy. An optical spectrum of the bright component
contains quasar emission lines at z=2.78 and several absorption features,
including prominent Ly-alpha absorption. The lens galaxy redshift could not be
measured but is estimated to be z=0.36 +/- 0.08. The image configuration is
consistent with the simplest plausible models for the lens potential. The flat
radio spectrum and observed variability of PMN J1838-3427 suggest the time
delay between flux variations of the components is measurable, and could thus
provide an independent measurement of H_0.


title: CLASS B0739+366: A new two-image gravitational lens system

abstract:
  We present the discovery of CLASS B0739+366, a new gravitational lens system
from the Cosmic Lens All-Sky Survey. Radio imaging of the source with the Very
Large Array (VLA) shows two compact components separated by $0\farcs54$, with a
flux density ratio of $\sim$ 6:1. High-resolution follow-up observations using
the Very Long Baseline Array (VLBA) at 1.7 GHz detect weak, parity-reversed jet
emission from each of the radio components. Hubble Space Telescope NICMOS F160W
observations detect infrared counterparts to the lensed images, as well as an
extended object between them which we identify as the lensing galaxy. Redshifts
for the galaxy and lensed source have not yet been obtained. For typical lens
and source redshifts of $z=0.5$ and $z=1.5$, respectively, preliminary mass
modeling predicts a time delay of $\sim7h^{-1}$ days in a flat $\Omega_{M}=1.0$
universe. The small predicted time delay and weak radio components will make
CLASS B0739+366 a challenging target for Hubble constant determination.


title:
The He II Emitting Nebula N44C in the LMC: Optical/UV Spectroscopy of
  the Nebula and its Ionizing Star

abstract:
  We present HST spectroscopy and imaging, along with new ground-based
spectroscopy and ROSAT HRI imaging, of the He II emitting nebula N44C and its
ionizing star. A GHRS spectrogram of the ionizing star yields a spectral type
of about O7 for the star. The lack of P Cygni profiles for Si IV and C IV
indicates that the star is not a supergiant. The nebular abundances in the
ionized gas are consistent with average abundances for LMC H II regions, with
the possible exception that nitrogen may be enhanced. Enrichment by a former
evolved companion star is not evident. A long-slit echelle spectrogram in
H-alpha + [N II] shows no evidence for high-velocity gas in N44C. This rules
out high-velocity shocks as the source of the nebular He II emission. A 108 ks
ROSAT HRI image of N44C shows no X-ray point source to a 3-sigma upper limit
L(X) < 10^34 erg s^-1 in the 0.1-2.0 keV band. Based on new measurements of the
electron density in the He II emitting region, we derive recombination
timescales of approximately 20 yrs for He^+2 and approximately 4 yrs for Ne^+4.
If N44C is a fossil X-ray ionized nebula, this places severe constraints on
when the putative X-ray source could have turned off. The presence of strong
[Ne IV] emission in the nebula is puzzling if the ionizing source has turned
off. It is possible the system is related to the Be X-ray binaries, although
the O star in N44C does not show Be characteristics at the present time.
Monitoring of X-rays and He II emission from the nebula, as well as a radial
velocity study of the ionizing star, are needed to fully understand the
emission line spectrum of N44C.


title:
Particle number density fluctuations and pressure effects on structure
  formation

abstract:
  We provide a covariant and gauge-invariant approach to the question of how a
first order pressure can be incorporated self-consistently in a cosmological
scenario. The approximation is relevant, in the linear regime, to weakly
self-interacting or warm dark matter models. We also derive number density
fluctuations in which new modes appear because the number density fluctuations
are no longer simply proportional to the density fluctuations.


title: The First Six Days of The Universe

abstract:
  The early stage of the Universe is discussed and the time lengths of its
first six days, as well as its age, are given. There seems to be no
contradiction with the Bible's ascertain that the Universe was created in six
days.


title: Constraints on Cosmological Anisotropy out to z=1 from Supernovae Ia

abstract:
  A combined sample of 79 high and low redshift supernovae Ia (SNe) is used to
set constraints on the degree of anisotropy in the Universe out to $z\simeq1$.
First we derive the global most probable values of matter density $\Omega_M $,
the cosmological constant $\Omega_\Lambda $, and the Hubble constant $H_0$, and
find them to be consistent with the published results from the two data sets of
Riess et al. 1998 (R98) and Perlmutter et al. 1999 (P99). We then examine the
Hubble diagram (HD, i.e., the luminosity-redshift relation) in different
directions on the sky by utilising spherical harmonic expansion. In particular,
via the analysis of the dipole anisotropy, we divide the sky into the two
hemispheres that yield the most discrepant of the three cosmological
parameters, and the scatter $\chi^2_{\rm HD}$ in each case. The most discrepant
values roughly move along the locus $-4\Omega_M +3 \Omega_{\Lambda} = 1$ (cf.
P99), but by no more than $\Delta \approx 2.5$ along this line. For a perfect
FRW universe, Monte Carlo realizations that mimic the current set of SNe yield
values higher than the measured $\Delta$ in $\sim 1/5$ of the cases. We discuss
implications for the validity of the Cosmological Principle, and possible
calibration problems in the SNe data sets.


title: The Radio Structure of the Supernova Remnant MSH14-63

abstract:
  G315.4-2.3 is an extended shell supernova remnant (SNR) with some
characteristics of evolutionarily young remnants and some of older ones. To
further elucidate some of its characteristics, we present imaging and
polarimetry of this SNR at a frequency of 1.34 GHz with a resolution of 8
arcsec made with the Australia Telescope Compact Array.
  The indicators of youth are: Morphologically, the radio emission arises in a
smooth shell without the fine scale filaments seen in the optical. Many of the
optical filaments are Balmer dominated. Where measurable, the orientation of
the magnetic field appears to be radial with respect to the center of the
remnant. There may have been a supernova in that region in AD185.
  Indications of older age include: Particularly in RCW86, the bright optical
nebula in the southwestern corner of this extended SNR, but also in other
locations there are several filaments with bright [S II] emission
representative of older shocked filaments in radiative equilibrium. If the
remnant lies at the kinematical distance of 2.8 kpc, it has a diameter of 37 pc
which would be large for a remnant less than two thousand years old.
  The remnant seems to be expanding inside a cavity outlined by infrared
emission and so it could well be young and large. Where it is encountering the
walls of the cavity it is slowing rapidly and we observe the radiative
filaments. RCW86 itself is encountering a dense clump of material but may also
be the remains of a more compact lump of ejecta ploughing into the
surroundings.


title:
Measurement of air shower cores to study the cosmic ray composition in
  the knee energy region

abstract:
  Since 1996, a hybrid experiment consisting of an emulsion chamber and a burst
detector array and the Tibet-II air shower array has been operated at
Yangbajing (4300 m above sea level) in Tibet. This experiment can detect
air-shower cores, called burst events, accompanied by air showers in excess of
about 100 TeV. Using the burst event data observed by this experiment, we
discuss the primary cosmic ray composition around the knee in comparison with
the Monte Carlo simulations. In this paper, we show that all the features of
burst events are wholly compatible with the heavy enriched composition in the
knee energy region.


title: Extended line emission around seven radio-loud quasars at redshift z~2

abstract:
  We present near-infrared spectra of seven radio-loud quasars with a median
redshift of 2.1, five of which were previously known to have Ly alpha nebulae.
Extended [OIII]5007 and H alpha emission are evident around six objects, at the
level of a few times 1E-16 erg/cm^2/arcsec^2/s within 2 arcsec of the nucleus
(16 kpc in the adopted cosmology). Nuclear [OII]3727 is detected in three of
the 5 quasars studied at this wavelength, and clearly extended in one of them.
  The extended [OIII] tends to be brighter on the side of the nucleus with the
stronger, jet-like radio emission, indicating at least that the extranuclear
gas is distributed anisotropically. It is also redshifted by several hundred
km/s from the nuclear [OIII], perhaps because the latter is blueshifted from
the systemic velocity of the host galaxy. Alternatively, the velocity shifts
could be due to infall (which is suggested by line widths ~1000 km/s FWHM) in
combination with a suitable dust geometry. Lyalpha/Halpha ratios well below the
case B value suggest that some dust is present.
  Photoionization modelling of the [OIII]/[OII] ratios in the extended gas
suggests that its pressure is around or less than a few times 1E7 cm^-3 K; any
confining intracluster medium may thus host a strong cooling flow. A comparison
with lower-redshift work suggests that there has been little evolution in the
nuclear emission line properties of radio-loud quasars between redshifts 1 and
2.


title:
The Lyman-alpha Forest Flux Distribution at z\sim 5.2 and the Evolution
  of the Ionizing Background

abstract:
  We use the redshift evolution of the lyman-alpha forest mean transmitted flux
at z>2.5 to infer the evolution of the intensity of the ionizing background,
using theoretical predictions for the density distribution of the intergalactic
gas giving rise to the lyman-alpha forest. The proper background intensity
declines gradually with redshift, decreasing by a factor \sim 3 between z=3 and
z=5.
  The gravitational structure formation theory of the lyman-alpha forest
implies that, given the observed mean transmitted flux of \bar{F}=0.1 in the
highest redshift quasar (with a mean lyman-alpha forest redshift z=5.2), only
about 3% of the lyman-alpha spectrum should have a flux higher than 50% of the
continuum, and less than 0.5% of pixels should have flux above 75% of the
continuum, assuming a uniform ionizing background intensity. We show that this
is consistent with the spectrum shown in Fan et al.


title: Polytropes: Implications for Molecular Clouds and Dark Matter

abstract:
  Polytropic models are reasonably successful in acounting for the observed
features of molecular clouds. Multi-pressure polytropes include the various
pressure components that are important in molecular clouds, whereas composite
polytropes provide a representation for the core halo structure.
  Small, very dense (n~10^{11} cm^{-3}) molecular clouds have been proposed as
models for both dark matter and for extreme scattering events. Insofar as the
equation of state in these clouds can be represented by a single polytropic
relation (pressure varies as a power of the density), such models conflict with
observation. It is possible to contrive composite polytropes that do not
conflict with observation, but whether the thermal properties of the clouds are
consistent with such structure remains to be determined.


title:
Scaling and fluctuations in galaxy distribution: two tests to probe
  large scale structures

abstract:
  We present a brief introduction to the statistical properties of systems with
large fluctuations. We point out that for such systems the relevant statistical
quantities are scaling exponents and the nature of fluctuations is completely
different from the one belonging to system with small fluctuations. We then
propose two test to be performed on galaxy counts data as a function of
apparent magnitude, which may clarify in a direct way the nature of the large
scale galaxy clustering


title: Solar Oscillations and Convection: II. Excitation of Radial Oscillations

abstract:
  Solar p-mode oscillations are excited by the work of stochastic,
non-adiabatic, pressure fluctuations on the compressive modes. We evaluate the
expression for the radial mode excitation rate derived by Nordlund and Stein
(Paper I) using numerical simulations of near surface solar convection. We
first apply this expression to the three radial modes of the simulation and
obtain good agreement between the predicted excitation rate and the actual mode
damping rates as determined from their energies and the widths of their
resolved spectral profiles. We then apply this expression for the mode
excitation rate to the solar modes and obtain excellent agreement with the low
l damping rates determined from GOLF data. Excitation occurs close to the
surface, mainly in the intergranular lanes and near the boundaries of granules
(where turbulence and radiative cooling are large). The non-adiabatic pressure
fluctuations near the surface are produced by small instantaneous local
imbalances between the divergence of the radiative and convective fluxes near
the solar surface. Below the surface, the non-adiabatic pressure fluctuations
are produced primarily by turbulent pressure fluctuations (Reynolds stresses).
The frequency dependence of the mode excitation is due to effects of the mode
structure and the pressure fluctuation spectrum. Excitation is small at low
frequencies due to mode properties -- the mode compression decreases and the
mode mass increases at low frequency. Excitation is small at high frequencies
due to the pressure fluctuation spectrum -- pressure fluctuations become small
at high frequencies because they are due to convection which is a long time
scale phenomena compared to the dominant p-mode periods.


title: Resolving Gamma-Ray Burst 000301C with a Gravitational Microlens

abstract:
  The afterglow of the Gamma-Ray Burst (GRB) 000301C exhibited achromatic,
short time-scale variability that is difficult to reconcile with the standard
relativistic shock model. We interpret the observed light curves as a
microlensing event superimposed on power-law flux decays typical of afterglows.
In general, a relativistic GRB shock appears on the sky as a thin ring
expanding at a superluminal speed. Initially the ring is small relative to its
angular separation from the lens and so its flux is magnified by a constant
factor. As the ring grows and sweeps across the lens its magnification reaches
a maximum. Subsequently, the flux gradually recovers its unlensed value. This
behavior involves only three free parameters in its simplest formulation and
was predicted theoretically by Loeb & Perna (1998). Fitting the available
R-band photometric data of GRB 000301C to a simple model of the microlensing
event and a broken power-law for the afterglow, we find reasonable values for
all the parameters and a reduced chi^2/DOF parameter of 1.48 compared with 2.99
for the broken power-law fit alone. The peak magnification of ~2 occurred 3.8
days after the burst. The entire optical-IR data imply a width of the GRB ring
of order 10% of its radius, similar to theoretical expectations. The angular
resolution provided by microlensing is better than a micro-arcsecond. We infer
a mass of approximately 0.5 M_Sun for a lens located half way to the source at
z_s=2.04. A galaxy 2'' from GRB 000301C might be the host of the stellar lens,
but current data provides only an upper-limit on its surface brightness at the
GRB position.


title:
Detection of X-ray Emission from Gravitationally Lensed Submillimeter
  Sources in the Field of Abell 370

abstract:
  We report the detection by Chandra of SMM J02399-0134 and SMM J02399-0136,
two distant (z=1.06 and z=2.81, respectively) submillimeter sources
gravitationally magnified by the galaxy cluster Abell 370. These are
high-significance (> 7-sigma) X-ray detections of the high-redshift
submillimeter source population. The X-ray positions are coincident with the
optical positions to within one arcsecond. The X-ray spectra, while of low
signal-to-noise ratio, are quite hard. Absorbed power law models with fixed
photon indices of $\Gamma=2.0$ imply local absorbing columns $>2 \times
10^{23}$ cm$^{-2}$ and unabsorbed luminosities $>10^{44}$ erg s$^{-1}$ in both
sources. These results imply that nuclear activity is responsible for the bulk
of the luminosity in SMM J02399-0134, and for at least 20% of the luminosity of
SMM J02399-0136, consistent with previous optical observations. We also place
an upper limit on the X-ray flux of a third submillimeter source, SMM
J02400-0134. Considered together with previously published Chandra upper limits
on X-ray flux from submillimeter sources, our results imply that
$20^{+30}_{-16}$ % of submillimeter sources exhibit X-ray emission from AGN
(90% confidence), consistent with expectations of their contribution to the
diffuse X-ray background.


title:
Caltech Faint Galaxy Redshift Survey XIV: Galaxy Morphology in the HDF
  (North) and its Flanking Fields to z=1.2

abstract:
  Morphological classifications are reported for Hubble Space Telescope (HST)
images of 241 galaxies in the Hubble Deep Field (HDF) and its Flanking Fields
(FF) with measured redshifts in the interval 0.25 < z < 1.2, drawn from a
magnitude-limited redshift survey to R = 24.0. The galaxies are divided into
three groups with redshifts in the intervals [0.25,0.6], [0.6,0.8], [0.8,1.2].
R606 images from the first group and I814 images from the second and third
groups are compared with B-band images of nearby galaxies. All classifications
were therefore made at approximately the same rest wavelength. Selection biases
are discussed. We corroborate and extend the results of earlier investigations
by observing that: Most intermediate and late-type galaxies with $z\gtrsim0.5$
have morphologies that are dramatically different from those of local galaxies
and cannot be shoehorned into the Hubble ``tuning fork'' classification scheme.
Grand-design spirals appear to be rare or absent for $z\gtrsim0.3$. Many Sa and
Sb spirals with $z\gtrsim0.6$ do not exhibit well-defined spiral arms. The arms
of distant Sc galaxies appear more chaotic than those of their nearby
counterparts. (abridged) On the basis of these and similar observations, it is
inferred that the development of pronounced spiral structure was delayed until
\~5 Gyr and that most bulges are probably not formed by disintegrating bars.
Major morphological changes were still taking place only ~5 Gyr ago even though
changes in the integrated light of most galaxies were then much slower than
they were ~10 Gyr ago.


title:
Mid-infrared imaging of the massive young star AFGL 2591: Probing the
  circumstellar environment of an outflow source

abstract:
  Most, if not all, stars are now believed to produce energetic outflows during
their formation. Yet, almost 20 years after the discovery of bipolar outflows
from young stars, the origins of this violent phenomenon are not well
understood. One of the difficulties of probing the outflow process,
particularly in the case of massive embedded stars, is a deficit of high
spatial resolution observations. Here, we present sub-arcsecond-resolution
mid-infrared images of one massive young stellar object, AFGL 2591, and its
immediate surroundings. Our images, at 11.7, 12.5 and 18.0 microns, reveal a
knot of emission ~6'' SW of the star, which may be evidence for a recent
ejection event or an embedded companion star. This knot is roughly coincident
with a previously seen near-infrared reflection nebula and a radio source, and
lies within the known large-scale CO outflow. We also find a new faint NW
source which may be another embedded lower-luminosity star. The IRAS
mid-infrared spectrum of AFGL 2591 shows a large silicate absorption feature at
10 microns, implying that the primary source is surrounded by an optically
thick dusty envelope. We discuss the interrelationship of these phenomena and
suggest that mid-infrared imaging and spectroscopy provide powerful tools for
probing massive star birth.


title: The Flared Disc Project: RXTE and ASCA Observations of X 1822-371

abstract:
  We present archival RXTE and simultaneous ASCA data of the eclipsing low mass
X-ray binary (LMXB) X 1822-371. Our spectral analysis shows that a variety of
simple models can fit the spectra relatively well. Of these models, we explore
two in detail through phase resolved fits. These two models represent the case
of a very optically thick and a very optically thin corona. While systematic
residuals remain at high energies, the overall spectral shape is
well-approximated. The same two basic models are fit to the X-ray light curve,
which shows sinusoidal modulations interpreted as absorption by an opaque disc
rim of varying height. The geometry we infer from these fits is consistent with
previous studies: the disc rim reaches out to the tidal truncation radius,
while the radius of the corona (approximated as spherical) is very close to the
circularization radius. Timing analysis of the RXTE data shows a time lag from
hard to soft consistent with the coronal size inferred from the fits. Neither
the spectra nor the light curve fits allow us to rule out either model, leaving
a key ingredient of the X 1822-371 puzzle unsolved. Furthermore, while previous
studies were consistent with the central object being a 1.4 Msol neutron star,
which has been adopted as the best guess scenario for this system, our light
curve fits show that a white dwarf or black hole primary can work just as well.
Based on previously published estimates of the orbital evolution of X 1822-371,
however, we suggest that this system contains either a neutron star or a low
mass (~ 2.5 Msol) black hole and is in a transitional state of duration
shortward of 10^7 years.


title: New Pulsars from an Arecibo Drift Scan Search

abstract:
  We report the discovery of pulsars J0030+0451, J0711+0931, and J1313+0931
that were found in a search of 470 square degrees at 430 MHz using the 305m
Arecibo telescope. The search has an estimated sensitivity for long period, low
dispersion measure, low zenith angle, and high Galactic latitude pulsars of ~1
mJy, comparable to previous Arecibo searches. Spin and astrometric parameters
for the three pulsars are presented along with polarimetry at 430 MHz. PSR
J0030+0451, a nearby pulsar with a period of 4.8 ms, belongs to the less common
category of isolated millisecond pulsars. We have measured significant
polarization in PSR J0030+0451 over more than 50% of the period, and use these
data for a detailed discussion of its magnetospheric geometry. Scintillation
observations of PSR J0030+0451 provide an estimate of the plasma turbulence
level along the line of sight through the local interstellar medium.


title:
First Detection of Submillimeter [C I] Emission in the Small Magellanic
  Cloud

abstract:
  We report the first detection of [CI] (3P1-3P0) emission at 609 um in a
region of the Small Magellanic Cloud (N27). Environments poor in heavy elements
and dust such as the SMC are thought to be dominated by photodissociation
regions. This is the lowest metallicity source where submillimeter neutral
carbon emission has been detected. Studying the [CI]/CO intensity ratio in
several sources spanning more than an order of magnitude in metallicity, Z, we
find that the [CI]/CO ratio increases for decreasing Z. The existence of such a
trend points to a photodissociation origin for most of neutral carbon in
molecular clouds, in agreement with standard PDR models. We also report ISO FIR
spectroscopic observations of N27, and use them to derive its physical
properties. Comparison between the density and radiation field revealed by FIR
diagnostics (n~300-1000 cm-3, Xuv~30-100 Xo) and those derived from millimeter
and submillimeter data (n~10^5 cm-3, Xuv<30 Xo) suggests that the FIR lines
originate in more diffuse gas, and are perhaps dominated by the interclump
medium. Regardless of the cause, analysis of the FIR and mm-submm data produces
a discrepancy of two orders of magnitude for the density of this source.


title: Stellar Mass-to-Light Ratios and the Tully-Fisher relation

abstract:
  We use spiral galaxy evolution models to argue that there are substantial
variations in stellar mass-to-light ratio (M/L) within and among galaxies. Our
models show a strong correlation between stellar M/L and galaxy color. We
compare the colors and maximum-disk M/L values of a sample of galaxies to the
model color-M/L relation, finding that a Salpeter IMF is too massive but that
an IMF with fewer low mass stars fits the observations well. Applying our
color-M/L relation to the Tully-Fisher (TF) relation, we find a stellar mass
TF-relation that is independent of originating passband. Adding the HI gas
mass, we find that the maximum slope of the baryonic TF-relation is 3.5.


title: Evidence from Type Ia Supernovae for an Accelerating Universe

abstract:
  We review the use of Type Ia supernovae for cosmological distance
determinations. Low-redshift SNe Ia (z < 0.1) demonstrate that the Hubble
expansion is linear, that H_0 = 65 +/- 2 (statistical) km/s/Mpc, and that the
properties of dust in other galaxies are similar to those of dust in the Milky
Way. We find that the light curves of high-redshift (z = 0.3-1) SNe Ia are
stretched in a manner consistent with the expansion of space; similarly, their
spectra exhibit slower temporal evolution (by a factor of 1 + z) than those of
nearby SNe Ia. The luminosity distances of our first set of 16 high-redshift
SNe Ia are, on average, 10-15% farther than expected in a low mass-density
(Omega_M=0.2) universe without a cosmological constant. Preliminary analysis of
our second set of 9 SNe Ia is consistent with this. Our work supports models
with positive cosmological constant and a current acceleration of the
expansion. We address the main potential sources of systematic error; at
present, none of them appears to reconcile the data with Omega_Lambda=0 and q_0
>= 0. The dynamical age of the Universe is estimated to be 14.2 +/- 1.7 Gyr,
consistent with the ages of globular star clusters.


title:
Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu
  Cephei

abstract:
  We report a detection of water in emission in the spectrum of the M2
supergiant atar mu Cep (M2Ia) observed by the Short Wavelength Spectrometer
(SWS) aboard Infrared Space Observatory (ISO) and now released as the ISO
Archives. The emission first appears in the 6 micron region (nu2 fundamental)
and then in the 40 micron region (pure rotation lines) despite the rather
strong dust emission. The intensity ratios of the emission features are far
from those of the optically thin gaseous emission. Instead, we could reproduce
the major observed emission features by an optically thick water sphere of the
inner radius about two stellar radii (1300Rsun), Tex = 1500K, and Ncol (H2O) =
3.0E+20/cm2. This model also accounts for the H2O absorption bands in the near
infrared (1.4, 1.9, and 2.7 micron) as well. The detection of water in emission
provides strong constraints on the nature of water in the early M supergiant
stars, and especially its origin in the outer atmosphere is confirmed against
other models such as the large convective cell model. We finally confirm that
the early M supergiant star is surrounded by a huge optically thick sphere of
the warm water vapor, which may be referred to as MOLsphere for simplicity.
Thus, the outer atmosphere of M supergiant stars should have a complicated
hierarchical and/or hybrid structure with at least three major constituents
including the warm MOLsphere (T about 1.0E+3K) together with the previously
known hot chromosphere (T about 1.0E+4K) and cool expanding gas-dust envelope
(T about 1.0E+2K).


title: Cygnus X-1 from RXTE: Monitoring the short term variability

abstract:
  We present temporal and spectral results from monitoring Cygnus X-1 with the
Rossi X-ray Timing Explorer (RXTE) in 1998 and 1999. We concentrate on the long
term evolution of the hard state timing properties, comparing it to the 1996
soft state evolution. This leads to the following results: 1. the hard and soft
state time lag spectra are very similar, 2. during state transitions, the lags
in the 1-10 Hz range increase by more than an order of magnitude, 3. in the
hard state itself, flaring events can be seen --- the temporal and spectral
evolution during the flare of 1998 July identifies it as a ``failed state
transition''. During (failed) state transitions, the time lag spectra and the
power spectra change predominantly in the 1-10 Hz range. We suggest that this
additional variability is produced in ejected coronal material disrupting the
synchrotron radiation emitting outflows present in the hard state.


title: First results of UVES at VLT: revisiting RR Tel

abstract:
  We present here the first results of UVES observations of RR Tel. The
exceptional performances of the instrument have allowed the detection of new
spectral features and have led to an improvement in the identifications of
several emission lines. A direct comparison with the IUE observations in the
range 3045-3300 A has revealed the appearance of many weak and shallow lines,
most of them lacking a convincing identification. The Balmer lines are visible
up to H38 and are accompanied by the He II lines of the Pickering series. Also,
all of the He II emissions of the Pfund series, from 5858 A to 6408 A have been
detected. We made definite identifications of additional TiO bands at 4955 A
(alpha R_2 1-0), 5167 A (alpha R_2 0-0), 5445 A (alpha R_2 0-1), 5598 A (beta
R_1 0-0), 5847 A (gamma 'R_1 1-0), and 6148 A (gamma ' {^S} R_21 0-0). The
Halpha line has very wide wings, extending to at least 5000 km/s, which are
similar to those reported for the planetary nebula IC 4997 and attributed to
Raman scattering by Ly beta photons. A selective pumping mechanism via the HeII
237 A emission is proposed to explain the intensity of the high-lying lines of
O IV mult. 1 and 2.


title:
Carbon Star Survey of Local Group Dwarf Galaxies. II. Pegasus, DDO 210
  and Tucana

abstract:
  We present the latest results of our ongoing four filter photometric survey
of C stars in Local Group dwarf irregular galaxies. Observations of the two low
luminosity dwarf irregular galaxies, Pegasus and DDO 210, revealed respectively
40 and 3 C stars, assuming that the reddening of Pegasus is negligible. No C
stars were identified in Tucana. Our observations permit the estimation of the
CMD contamination by foreground M dwarf thus yielding reliable C/M ratios. Our
R, I photometry of the C stars cannot be used to solve the extinction
controversy toward Pegasus. The three C stars in DDO 210 are quite bright when
compared to C star populations in dwarf galaxies. A larger fainter population
in that galaxy seems however improbable. The statistics of C stars, currently
on hand for dwarf galaxies, show a well-defined trend with the absolute
magnitude of galaxies.


title: Dynamics of Stars and Globular Clusters in M87

abstract:
  We examine the dynamics of the stars and globular clusters in the nearby
giant galaxy M87 and constrain the mass distribution, using all the available
data over a large range of radii, including higher-order moments of the stellar
line-of-sight velocity distributions and the discrete velocities of over two
hundred globular clusters. We introduce an extension of spherical orbit
modeling methods that makes full use of all the information in the data, and
provides very robust constraints on the mass models. We conclusively rule out a
constant mass-to-light ratio model, and infer that the radial density profile
of the galaxy's dark halo falls off more slowly than 1/r^2, suggesting that the
potential of the Virgo Cluster is already dominant at r ~ 300" ~ 20 kpc.


title: Origin of the highest energy cosmic rays observed

abstract:
  Introducing a simple Galactic wind model patterned after the solar wind we
show that back-tracing the orbits of the highest energy cosmic events suggests
that they may all come from the Virgo cluster, and so probably from the active
radio galaxy M87. This confirms a long standing expectation. Those powerful
radio galaxies that have their relativistic jets stuck in the interstellar
medium of the host galaxy, such as 3C147, will then enable us to derive limits
on the production of any new kind of particle, expected in some extensions of
the standard model in particle physics. New data from HIRES will be crucial in
testing the model proposed here.


title: A Structure for Quasars

abstract:
  This paper proposes a simple, empirically derived, unifying structure for the
inner regions of quasars. This structure is constructed to explain the broad
absorption line (BAL) regions, the narrow `associated' ultraviolet and X-ray
warm absorbers (NALs); and is also found to explain the broad emission line
regions (BELR), and several scattering features, including a substantial
fraction of the broad X-ray Iron-K emission line, and the bi-conical extended
narrow emission line region (ENLR) structures seen on large kiloparsec scales
in Seyfert images. Small extensions of the model to allow luminosity dependent
changes in the structure may explain the UV and X-ray Baldwin effects and the
greater prevalence of obscuration in low luminosity AGN.


title:
The European Large Area ISO Survey III: 90micron extragalactic source
  counts

abstract:
  We present results and source counts at 90micron extracted from the
Preliminary Analysis of the European Large Area ISO Survey (ELAIS). The survey
covered about 11.6 square degrees of the sky in four main areas and was carried
out with the PHOT instrument onboard the Infrared Space Observatory (ISO). The
survey is at least an order of magnitude deeper than the IRAS 100micron survey
and is expected to provide constraints on the formation and evolution of
galaxies. The majority of the detected sources are associated with galaxies on
optical images. In some cases the optical associations are interacting pairs or
small groups of galaxies suggesting the sample may include a significant
fraction of luminous infrared galaxies. The source counts extracted from a
reliable subset of the detected sources are in agreement with strongly evolving
models of the starburst galaxy population.


title: Supernova Remnants in the Sedov Expansion Phase: Thermal X-Ray Emission

abstract:
  Improved calculations of X-ray spectra for supernova remnants (SNRs) in the
Sedov-Taylor phase are reported, which for the first time include reliable
atomic data for Fe L-shell lines. This new set of Sedov models also allows for
a partial collisionless heating of electrons at the blast wave and for energy
transfer from ions to electrons through Coulomb collisions. X-ray emission
calculations are based on the updated Hamilton-Sarazin spectral model. The
calculated X-ray spectra are succesfully interpreted in terms of three
distribution functions: the electron temperature and ionization timescale
distributions, and the ionization timescale averaged electron temperature
distribution. The comparison of Sedov models with a frequently used single
nonequilibrium ionization (NEI) timescale model reveals that this simple model
is generally not an appropriate approximation to X-ray spectra of SNRs. We find
instead that plane-parallel shocks provide a useful approximation to X-ray
spectra of SNRs, particularly for young SNRs. Sedov X-ray models described
here, together with simpler plane shock and single ionization timescale models,
have been implemented as standard models in the widely used XSPEC v11 spectral
software package.


title: Cosmological Studies from Radio Source Samples

abstract:
  I review some recent cosmological studies based on redshift surveys of radio
sources selected at low frequencies. The accretion rate onto the central black
hole is identified as the basis of a crude physical division of the
low-frequency population into two sub-populations: the first comprises
`Eddington-tuned' (high accretion rate) quasars and their torus-hidden
counterparts; the second comprises `starved quasars' like M87. There exist
remarkable similarities between the shapes and evolutionary behaviours of the
luminosity functions of radio sources and radio-quiet quasars; all luminous AGN
are $\sim300-$times rarer at epochs corresponding to $z \sim 0$ than at $z \sim
2.5$. I argue that any evidence that quasars were intrinsically rarer at $z
\sim 5$ than at $z \sim 2.5$ is as yet both tentative and indirect. A simple
calculation suggests that the radio source population has been over-looked as a
potentially important contributor to the entropy budget of the Universe. A
recent sub-mm survey of radio sources is used to demonstrate a connection
between the events which trigger jets and intense bursts of star formation, and
a close link between the histories of star formation and AGN activity is
proposed. I discuss the aims and methods of future large redshift surveys of
radio sources, emphasising the importance of dovetailing these with the
development of robust physical models for radio sources and their
epoch-dependent environments.


title: A spectroscopic survey for strong galaxy-galaxy lenses

abstract:
  We present a spectroscopic survey for strong galaxy-galaxy lenses. Exploiting
optimal sight-lines to massive, bulge-dominated galaxies at redshifts $z \sim
0.4$ with wide-field, multifibre spectroscopy, we anticipate the detection of
10-20 lensed Lyman-$\alpha$ emitting galaxies at redshifts $z \simgreat 3$ from
a sample of 2000 deflectors. Initial spectroscopic observations are described
and the prospects for constraining the emission-line luminosity function of the
Lyman-$\alpha$ emitting population are outlined.


title: Binary quasars

abstract:
  Quasar pairs are either physically distinct binary quasars or the result of
gravitational lensing. The majority of known pairs are in fact lenses, with a
few confirmed as binaries, leaving a population of objects that have not yet
been successfully classified. Building on the arguments of Kochanek, Falco &
Munoz (1999), it is shown that there are no objective reasons to reject the
binary interpretation for most of these. In particular, the similarity of the
spectra of the quasar pairs appears to be an artifact of the generic nature of
quasar spectra. The two ambiguous pairs discovered as part of the Large Bright
Quasar Survey (Q 1429-053 and Q 2153-0256) are analysed using principle
components analysis, which shows that their spectral similarities are not
greater than expected for a randomly chosen pair of quasars from the survey.
The assumption of the binary hypothesis allows the dynamics, time-scales and
separation distribution of binary quasars to be investigated and constrained.
The most plausible model is that the quasars' activity is triggered by tidal
interactions in a galatic merger, but that the (re-)activation of the galactic
nuclei occurs quite late in the interaction, when the nuclei are within 80+/-30
kpc of each other. A simple dynamical friction model for the decaying orbits
reproduces the observed distribution of projected separations, but the decay
time inferred is comparable to a Hubble time. Hence it is predicted that binary
quasars are only observable as such in the early stages of galactic collisions,
after which the quiescent super-massive black holes orbit in the merger remnant
for some time.


title: Bayesian joint estimation of non-Gaussianity and the power spectrum

abstract:
  We propose a rigorous, non-perturbative, Bayesian framework which enables one
jointly to test Gaussianity and estimate the power spectrum of CMB
anisotropies. It makes use of the Hilbert space of an harmonic oscillator to
set up an exact likelihood function, dependent on the power spectrum and on a
set of parameters $\alpha_i$, which are zero for Gaussian processes. The latter
can be expressed as series of cumulants; indeed they perturbatively reduce to
cumulants. However they have the advantage that their variation is essentially
unconstrained. Any truncation(i.e.: finite set of $\alpha_i$) therefore still
produces a proper distribution - something which cannot be said of the only
other such tool on offer, the Edgeworth expansion. We apply our method to Very
Small Array (VSA) simulations based on signal Gaussianity, showing that our
algorithm is indeed not biased.


title:
The local space density of Sb-Sdm galaxies as function of their
  scalesize, surface brightness and luminosity

abstract:
  We investigate the dependence of the local space density of spiral galaxies
on luminosity, scalesize and surface brightness. We derive bivariate space
density distributions in these quantities from a sample of about 1000 Sb-Sdm
spiral galaxies, corrected for selection effects in luminosity and surface
brightness. The structural parameters of the galaxies were corrected for
internal extinction using a description depending on galaxy surface brightness.
We find that the bivariate space density distribution of spiral galaxies in the
(luminosity, scalesize)-plane is well described by a Schechter luminosity
function in the luminosity dimension and a log-normal scale size distribution
at a given luminosity. This parameterization of the scalesize distribution was
motivated by a simple model for the formation of disks within dark matter
halos, with halos acquiring their angular momenta through tidal torques from
neighboring objects, and the disk specific angular momentum being proportional
to that of the parent halo. However, the fractional width of the scalesize
distribution at a given luminosity is narrower than what one would expect from
using the distribution of angular momenta of halos measured in N-body
simulations. We present several possible explanations for the narrowness of the
observed distribution. Using our bivariate distribution, we find that
determinations of the local luminosity function of spiral galaxies should not
be strongly affected by the bias against low surface brightness galaxies, even
when the galaxies are selected from photographic plates. This may not be true
for studies at high redshift, where (1+z)^4 surface brightness dimming can
cause a significant selection bias against lower surface brightness galaxies.


title:
Spatially Resolved Circumstellar Structure of Herbig Ae/Be Stars in the
  Near-Infrared

abstract:
  We have conducted the first systematic study of Herbig Ae/Be stars using the
technique of long baseline stellar interferometry in the near-infrared. The
principal result of this paper is that the IOTA interferometer resolves the
source of infrared excess in 11 of the 15 systems surveyed.
  The visibility data for all the sources has been interpreted within the
context of four simple models which represent a range of plausible
representations for the brightness distribution of the source of excess
emission: a Gaussian, a narrow uniform ring, a flat blackbody disk with a
single temperature power law, and an infrared companion. We find that the
characteristic sizes of the near-infrared emitting regions are larger than
previously thought (0.5-5.9 AU, as given by the FWHM of the Gaussian
intensity). A further major result of this paper is that the sizes measured,
when combined with the observed spectral energy distributions, essentially rule
out accretion disk models represented by blackbody disks with the canonical
radial temperature law with exponent -3/4. We also find that, within the range
observed in this study, none of the sources (except the new binary) shows
varying visibilities as the orientation of the interferometer baseline changes.
  Taken as an ensemble, with no clear evidence in favor of axi-symmetric
structure, the observations favor the interpretation that the circumstellar
dust is distributed in spherical envelopes (the Gaussian model) or thin shells
(the ring model).


title: The Spallagenic Production Rates of Lithium, Beryllium and Boron

abstract:
  We calculate the production rates of Li6, Li7, Be9, B10 and B11 via
spallation of Carbon, Nitrogen and Oxygen nuclei by protons and alpha-particles
and by alpha-alpha fusion reactions. We include recent measurements of the
cross sections of alpha-alpha fusion reactions and find that the computations
yield rates of Li6 and Li7 production that are nearly a factor of two smaller
than previously calculated. We begin by using the `straight ahead'
approximation for the fragment energy and the `leaky-box' model for product
capture in the Galaxy. In addition we test the straight ahead approximation by
recalculating the production rates using an empirical description of the
fragment energy distribution and find that the results closely match. We have
also calculated the rates for various cosmic ray spectra and find that the
hardest spectra tested decrease the rates with CR CNO by approximately an order
of magnitude relative to our chosen standard. Finally we have computed the
Population I elemental ratios and the Population II scaling relations for our
standard and find that our computations predict an abundance of Lithium for a
given abundance of Beryllium that is 1/4 smaller than previously derived.


title: Galaxy Collisions and Star Formation

abstract:
  We present a brief overview of some recent observations of colliding galaxies
and relevant numerical simulations. These are compared, and details of the
locations and history of collision induced star formation are explored, with
possible application to star formation at earlier epochs.


title: The Galactic Thick Disk Stellar Abundances

abstract:
  We present first results from a program to measure the chemical abundances of
a large (N>30) sample of thick disk stars with the principal goal of
investigating the formation history of the Galactic thick disk. Our analysis
confirms previous studies of O and Mg in the thick disk stars which reported
enhancements in excess of the thin disk population. Furthermore, the
observations of Si, Ca, Ti, Mn, Co, V, Zn, Al, and Eu all argue that the thick
disk population has a distinct chemical history from the thin disk. With the
exception of V and Co, the thick disk abundance patterns match or tend towards
the values observed for halo stars with [Fe/H]~-1. This suggests that the thick
disk stars had a chemical enrichment history similar to the metal-rich halo
stars. With the possible exception of Si, the thick disk abundance patterns are
in excellent agreement with the chemical abundances observed in the metal-poor
bulge stars suggesting the two populations formed from the same gas reservoir
at a common epoch.
  We discuss the implications for the formation of the thick disk, new insights
presented for theories of nucleosynthesis, and the impact on interpretations of
the abundance patterns of the damped Lya systems at high redshift.
[significantly abridged]


title:
The Interaction of Type Ia Supernovae with their Surroundings: The
  Exponential profile in 2D

abstract:
  The evolution of Type Ia supernovae in the surrounding medium is studied
using 2-dimensional numerical hydrodynamic simulations. The ejecta are assumed
to be described by an exponential density profile, following the work of
Dwarkadas & Chevalier (1998). The case of a circumstellar (CS) region formed by
mass loss from the progenitor or a companion star is also considered. The
decelerating contact discontinuity is found to be Rayleigh-Taylor (R-T)
unstable, as expected, and the nature of the instability is studied in detail
for 2 cases: 1) a constant density ambient medium, and 2) a CS medium whose
density goes as r^{-2}. The nature of the instability is found to be different
in both cases. In the case of a CS medium the instability is much better
resolved, and a fractal-like structure is seen. In the case of a constant
density medium the extent of growth is less, and the R-T fingers are found to
be limited by the presence of Kelvin-Helmholtz mushroom caps at the tips of the
fingers. The unstable region is far enough away from the reverse shock that the
latter is not affected by the mixing taking place in the interaction region. In
contrast the reverse shock in the case of a CS medium is found to be rippled
due to the formation of instabilities. In neither case is the outer shock front
affected. These results are consistent with similar studies of power-law ejecta
profiles conducted by Chevalier, Blondin & Emmering (1992). Our results are
then applied to Tycho's supernova remnant.


title: Study of Hadronic Decays of the Z Boson at LEP

abstract:
  This report summarizes four recent papers on the characteristics of the
hadronic decays of the Z by the LEP collaborations ALEPH, DELPHI and OPAL.


title:
Limits on the Abundance of Galactic Planets From Five Years of Planet
  Observations

abstract:
  We search for signatures of planets in 43 intensively monitored microlensing
events that were observed between 1995 and 1999. Planets would be expected to
cause a short duration (~1 day) deviation on the smooth, symmetric light curve
produced by a single-lens. We find no such anomalies and infer that less than
1/3 of the ~0.3 M_sun stars that typically comprise the lens population have
Jupiter-mass companions with semi-major axes in the range of 1.5 AU <a < 4 AU.
Since orbital periods of planets at these radii are 3-15 years, the outer
portion of this region is currently difficult to probe with any other
technique.


title: Gravitational lensing by elliptical galaxies

abstract:
  The fraction of high-redshift sources which are multiply-imaged by
intervening galaxies is strongly dependent on the cosmological constant, and so
can be a useful probe of the cosmological model. However its power is limited
by various systematic (and random) uncertainties in the calculation of lensing
probabilities, one of the most important of which is the dynamical
normalisation of elliptical galaxies. Assuming ellipticals' mass distributions
can be modelled as isothermal spheres, the mass normalisation depends on: the
velocity anisotropy; the luminosity density; the core radius; and the area over
which the velocity dispersion is measured. The differences in the lensing
probability and optical depth produced by using the correct normalisation can
be comparable to the differences between even the most extreme cosmological
models. The existing data is not sufficient to determine the correct
normalisation with enough certainty to allow lensing statistics to be used to
their full potential. However, as the correct lensing probability is almost
certainly higher than is usually assumed, upper bounds on the cosmological
constant are not weakened by these possibilities.


title: Antlia: an outskirt Local Group Galaxy

abstract:
  Deep (I,V-I) and (I,B-I) color-magnitude diagrams (CMDs) of the Antlia dwarf
galaxy, based on Science Verification (SV) data collected with the FORS I
camera on the ESO Very Large Telescope (VLT) are presented.
  By adopting the new calibration of the Tip of the Red Giant Branch (TRGB)
provided by Salaris & Cassisi (1998) we estimated that the Antlia distance
modulus is (m-M)o=25.98 with an error of 0.10 mag.
  We suggest an improvement of the classical TRGB method based on infrared H
and K magnitudes of TRGB stars. Such a method should overcome the well-known
limit of the "classical" TRGB method when dealing with metal-rich stellar
populations.


title: The statistics of wide-separation lensed quasars

abstract:
  The absence of any wide-separation gravitational lenses in the Large Bright
Quasar Survey is used to place limits on the population of cluster-sized halos
in the universe, and hence constrain a number of cosmological parameters. The
results agree with previous investigations in strongly ruling out the standard
cold dark matter model but they are consistent with low-density universes in
which the primordial fluctuation spectrum matches both cluster abundances and
cosmic microwave background measurements. These conclusions are essentially
independent of the cosmological constant, which is in stark contrast to the
statistics of galaxy lenses. The constraints presented here are nullified if
clusters have core radii of more than 10 kpc, but are free of a number of
potential systematic errors, due to the homogeneity of the data.