title: Microjansky radio sources in DC0107-46 (Abell 2877)

abstract:
  The cluster DC0107-46 (Abell 2877) lies within the Phoenix Deep Survey, made
at 1.4 GHz with the Australia Telescope Compact Array. Of 89 known optical
cluster members, 70 lie within the radio survey area. Of these 70 galaxies, 15
(21%) are detected, with luminosities as faint as 10^20 W/Hz. Spectroscopic
observations are available for 14/15 of the radio-detected cluster galaxies.
Six galaxies show only absorption features and are typical low-luminosity AGN
radio sources. One galaxy hosts a Seyfert 2 nucleus, two are star-forming
galaxies, and the remaining five may be star-forming galaxies, AGNs, or both.


title: Predicting Future Duration from Present Age: A Critical Assessment

abstract:
  Using a temporal version of the Copernican principle, Gott has proposed a
statistical predictor of future longevity based on present age [J. R. Gott III,
Nature 363, 315 (1993)] and applied the predictor to a variety of examples,
including the longevity of the human species. Though Gott's proposal contains a
grain of truth, it does not have the universal predictive power that he
attributes to it.


title: Measuring the Diffuse Optical Light in Abell 1651

abstract:
  Using drift scan data, a new approach to determining surface brightness
profiles, and techniques for detecting low surface brightness signals, we fit
the light profile of the brightest cluster galaxy (BCG) in the rich cluster
Abell 1651 out to 670 h^{-1} kpc. This radius is a significant fraction of the
virial radius of the cluster (2 h^{-1} Mpc; Girardi et al. 1998), indicating
that the sizes of the BCG and the cluster are comparable. We find that the
profile is consistent with a de Vaucouleurs profile over the radial range
probed. We also find that the integrated light profile of the BCG in Abell 1651
contributes 36% of the total cluster light within 500 h^{-1} kpc. Including all
luminous components, we obtain M/L_I~160 h for the cluster, which would be
overestimated by ~20% without the BCG halo. Furthermore, the relatively red
color of the BCG at large radii suggests that recent disruption and tidal
stripping of spirals and dwarf ellipticals do not contribute significantly to
the halo luminosity. The color and the form of the profile are consistent with
a scenario in which the BCG forms from filamentary collapse during the epoch of
cluster formation, with relatively little evolution in the past 5 Gyrs
(Dubinski 1998). We remove the BCG and other detected galaxies from the image
and construct a two dimensional surface brightness map of the cluster core.
Several knots of excess emission are found, but the total diffuse component is
constrained to contribute less than 5% of the cluster light.


title: Magnetic field and unstable accretion during AM Herculis low states

abstract:
  A study of AM Her low states in September 1990 and 1991 and June-July 1997 is
reported from a coordinated campaign with observations obtained at the
Haute-Provence observatory, at the 6-m telescope of the Special Astrophysical
Observatory and at the 2.6m and 1.25m telescopes of the Crimean observatory.
Spectra obtained at different dates when the source was in low states at a
comparable V magnitude, show the presence of strong Zeeman absorption features
and marked changes in emission lines with a day-to-day reappearance of the HeII
(4686\AA) emission lines in 1991. Despite this variability, the magnetic field
inferred from the fitting of the absorption spectrum with Zeeman hydrogen
splitting, is remarkably constant with a best value of (12.5$\pm$0.5)MG.
Detailed analysis of the UBVRI light curves shows the presence of repetitive
moderate amplitude ($\sim$ 0.3-0.5 mag) flares predominantly red in colour.
These flares are attributed to small accretion events and are compared to the
large ($\sim$ 2 mag.) blue flare reported by Shakhovskoy et al. (1993). We
suggest that the general flaring activity observed during the low states is
generated by accretion events. The different characteristics of the flares
(colour and polarization) are the results of different shock geometries
depending on the net mass accretion flux.


title: OGLE Cepheids have Lower Amplitudes in SMC than in LMC

abstract:
  We selected cepheids from the OGLE database for the Magellanic Clouds in the
period range 10^{1.1} < P < 10^{1.4} days. There were 33 objects in the LMC and
35 in the SMC. We find that the median amplitude of cepheids in the LMC is 18%
larger than in the SMC, a 4 sigma effect. This implies that the period - flux
amplitude relation is not universal, and cannot be used to measure distances
accurately.


title: The Magnetic Fields of the Universe and Their Origin

abstract:
  Recent rotation measure observations of a dozen or so galaxy clusters have
revealed a surprisingly large amount of magnetic fields, whose estimated energy
and flux are, on average, $\sim 10^{58}$ ergs and $\sim 10^{41}$ G cm$^2$,
respectively. These quantities are so much larger than any coherent sums of
individual galaxies within the cluster that an efficient galactic dynamo is
required. We associate these fields with single AGNs within the cluster and
therefore with all galaxies during their AGN phase. Only the central, massive
black hole (BH) has the necessary binding energy, $\sim 10^{61}$ ergs. Only the
accretion disk during the BH formation has the winding number, $\sim 10^{11}$
turns, necessary to make the gain and magnetic flux. We present a model of the
BH accretion disk dynamo that might create these magnetic fields, where the
helicity of the $\alpha - \Omega$ dynamo is driven by star-disk collisions. The
back reaction of the saturated dynamo forms a force-free field helix that
carries the energy and flux of the dynamo and redistributes them within the
clusters.


title:
Constraints on Photometric Calibration from Observations of
  High-Redshift Type Ia Supernovae

abstract:
  The good match of the type Ia supernova (SNIa) Hubble Diagram to the
prediction of a not-unreasonable cosmological world model shows that
measurements of standard stars and their comparison with point sources down to
m=25 mag is good to better than +/-0.5 mag over an 11 mag range. It also shows
that the true spectral energy distribution (SED) shapes of standard stars are
known to better than +/-0.5 mag over an octave in wavelength. On the other
hand, the SNIa argument for an accelerating Universe assumes that the magnitude
system is good to much better than ~0.1 mag over the 11 mag range, and that SED
shapes are known to much better than ~10 percent over an octave in wavelength.
There is no independent empirical evidence for these plausible assumptions.


title: Screw Instability and Blandford-Znajek Mechanism

abstract:
  When magnetic field lines thread a rotating black hole's horizon and connect
with remote astrophysical loads, the rotational energy of the black hole can be
extracted through the Blandford-Znajek mechanism. Due to the rotation of the
black hole, the magnetic field lines are twisted and toroidal components are
generated. So poloidal electric currents are induced and the black hole's
rotational energy is transported to the astrophysical loads through Poynting
flux. The Blandford-Znajek mechanism has been considered to be a possible
process for powering extragalactic jets.
  In this paper we show that due to the screw instability of magnetic field,
the toroidal components of the magnetic field, and thus the poloidal currents,
cannot exceed the limits given by the Kruskal-Shafranov criterion. This
significantly lowers the power of the Blandford-Znajek mechanism when the loads
are far from the black hole. So the Blandford-Znajek mechanism can only work
efficiently within the neighborhood of the black hole. The implications of the
results for the scenario of extragalactic jets powered by the Blandford-Znajek
mechanism are discussed.


title: A Natural Formalism for Microlensing

abstract:
  If the standard microlensing geometry is inverted so that the Einstein ring
is projected onto the observer plane rather than the source plane, then the
relations between the observables (\theta_E,\tilde r_E) and the underlying
physical quantities (M,\pi_rel) become immediately obvious. Here \theta_E and
\tilde r_E are the angular and projected Einstein radii, M is the mass of the
lens, and \pi_rel is the lens-source relative parallax. I recast the basic
formalism of microlensing in light of this more natural geometry and in terms
of observables. I then find that the relations between observable and physical
quantities assume an exceptionally simple form. In an appendix, I propose a set
of notational conventions for microlensing.


title: Gas Stripping of Dwarf Galaxies in Clusters of Galaxies

abstract:
  Many clusters of galaxies contain an appreciable amount of hot gas, the
intracluster medium. As a consequence, gas will be stripped from galaxies that
move through the inter cluster medium, if the ram pressure exceeds the internal
gravitational force. We study the interaction between the intracluster medium
and an extended gas component of dwarf galaxies confined by a surrounding cold
dark matter halo analytically and numerically, using axisymmetric
two-dimensional hydrodynamical simulations at high resolution. The results show
that the gas within the dark matter halo is totally stripped in a typical
galactic cluster. The process of ram pressure stripping therefore must have
played an important role during the chemo-dynamical evolution of dwarf galaxies
in galactic clusters. Our results predict that most of the chemical evolution
of dwarf galaxies must have occurred at high redshift, before the virialized
cluster had formed.


title:
BeppoSAX and Chandra Observations of SAXJ0103.2-7209=2E0101.5-7225: a
  new Persistent 345s X-ray Pulsar in the SMC

abstract:
  We report the results of a 1998 July BeppoSAX observation of a field in the
SMC which led to the discovery of 345s pulsations in the X-ray flux of
SAXJ0103.2-7209. The BeppoSAX X-ray spectrum is well fit by an absorbed
power-law with photon index 1.0 plus a black body component with kT=0.1keV. The
unabsorbed luminosity in the 2-10 keV energy range is 1.2x10^{36} erg/s. In a
very recent Chandra observation the 345s pulsations are also detected. The
available period measurements provide a constant period derivative of -1.7s/yr
over the last three years making SAXJ0103.2-7209 one of the most rapidly
spinning-up X-ray pulsars known. The BeppoSAX position is consistent with that
of the Einstein source 2E0101.5-7225 and the ROSAT source RXJ0103.2-7209. This
source was detected at a luminosity level of few 10^{35}-10^{36} erg/s in all
datasets of past X-ray missions since 1979. The ROSAT HRI and Chandra positions
are consistent with that of a m_V=14.8 Be spectral type star already proposed
as the likely optical counterpart of 2E0101.5-7225. We conclude that
SAXJ0103.2-7209 and 2E0101.5-7225 are the same source, a relatively young and
persistent X-ray pulsar in the SMC.


title: Stellar Dynamics and the implications on the merger evolution in NGC6240

abstract:
  We report near-infrared integral field spectroscopy of the luminous merging
galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by
1.6arcsec are the central parts of inclined, rotating disk galaxies with equal
mass bulges. The dynamical masses of the nuclei are much larger than the
stellar mass derived from the K-band light, implying that the progenitor
galaxies were galaxies with massive bulges. The K-band light is dominated by
red supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 years
ago, possibly by the most recent perigalactic approach. Strong feedback effects
of a superwind and supernovae are responsible for a short duration burst
(~5x10^6 years) which is already decaying. The two galaxies form a
prograde-retrograde rotating system and from the stellar velocity field it
seems that one of the two interacting galaxies is subject to a prograde
encounter. Between the stellar nuclei is a prominent peak of molecular gas
(H_2, CO). The stellar velocity dispersion peaks there indicating that the gas
has formed a local, self-gravitating concentration decoupled from the stellar
gravitational potential. NGC 6240 has previously been reported to fit the
paradigm of an elliptical galaxy formed through the merger of two galaxies.
This was based on the near-infrared light distribution which follows a
r^1/4-law. Our data cast strong doubt on this conclusion: the system is by far
not relaxed, rotation plays an important role, as does self-gravitating gas,
and the near-infrared light is dominated by young stars.


title: Black Hole Formation and Gamma Ray Bursts

abstract:
  Recent work on the dyadosphere of a black hole is reviewed with special
emphasis on the explanation of gamma ray bursts. A change of paradigm in the
observations of black holes is presented.


title: Early Galactic Evolution of Carbon, Nitrogen and Oxygen

abstract:
  We present results on carbon, nitrogen, and oxygen abundances for a sample of
unevolved metal-poor stars with metallicities in the range -0.3< [Fe/H]< -3.
Oxygen abundances derived from different indicators are compared showing
consistently that in the range 0.3 >[Fe/H]>-3.0, the [O/Fe] ratio increases
from approximately 0 to 1. We find a good agreement between abundances based on
the forbidden line, the OH and IR triplet lines when gravities based on
Hipparcos} parallaxes are considered for the sample stars. Gravities derived
from LTE ionization balance in metal-poor stars with [Fe/H]< -1 are likely too
low, and could be responsible for an underestimation of the oxygen abundances
derived using the [OI] line. [C/Fe] and [N/Fe] ratios appear to be constant,
independently of metallicity, in the same range. However, they show larger
scatter than oxygen at a given metallicity, which could reflect the larger
variety of stellar production sites for these other elements.


title: Note on the Origin of the Highest Energy Cosmic Rays

abstract:
  In this note we argue that the galactic model chosen by E.-J. Ahn, G.
Medina-Tanco, P.L. Bierman and T. Stanev in their paper discussing the origin
of the highest energy cosmic rays, is alone responsible for the focussing of
positive particles towards the North galactic pole. We discuss the validity of
this model, in particular in terms of field reversals and radial extensions. We
conclude that with such a model one cannot retreive any directional information
from the observed direction of the cosmic rays. In particular one cannot
identify point sources at least up to energies of about 200 EeV. Therefore the
apparent clustering of the back-traced highest energy cosmic rays observed to
date cannot be interpreted as an evidence for a point source nor for the
identification of M87, which happens to be close to the North pole, as being
such a source.


title: Stellar Dynamics in the Galactic centre: Proper Motions and Anisotropy

abstract:
  We report a new analysis of stellar dynamics in the Galactic centre, based on
improved sky and LOS velocities for >100 stars within a few arcsec of SgrA*.
Overall the motions do not deviate strongly from isotropy. For 32 stars with
all 3 components determined the absolute, LOS and sky velocities agree well, as
for a spherical cluster. The projected radial and tangential motions of all 104
pm stars are also consistent with overall isotropy. However, the projected
velocities of the young, early type stars have a strong radial dependence. Most
of the bright HeI stars 1-10" from SgrA* are on tangential orbits. This
anisotropy of the HeI stars and most of the brighter IRS16 complex members is
largely caused by a CW and counter-rotating, coherent rotation pattern. The
overall rotation of the young star cluster probably is a remnant of the angular
momentum in the cloud these stars formed from. The fainter, fast stars within
\~1" of SgrA* appear to be largely moving on radial or very elliptical orbits.
We have not detected nonlinear motion for any of them. Most of the SgrA*
cluster members also are on CW orbits. Spectroscopy shows them to be early type
stars. We propose that the SgrA* cluster stars are those members of the early
type cluster with small angular momentum which can plunge to the vicinity of
SgrA*. Our anisotropy-independent estimate of the Sun-GC distance is 7.8-8.2
kpc (+/- 0.9 kpc). We include velocity anisotropy in estimating the central
mass distribution. We confirm previous conclusions that a compact central mass
concentration is present and dominates the potential from 0.01-1 pc. The
central mass ranges from 2.6-3.3E6 M_sun. (abridged)


title: Comptonization of the Cosmic Microwave Background by Relativistic Plasma

abstract:
  (Abridged) We investigate the spectral distortion of the cosmic microwave
background (CMB) caused by relativistic plasma. Within the Thomson regime, an
exact analytic expression for the photon scattering kernel of a momentum
power-law electron distribution is given. The ultra-relativistic
Sunyaev-Zeldovich (SZ) decrement measures the electron number and not the
energy content. On the other hand, the relativistic SZ increment at higher
frequencies depends strongly on the spectral shape of the electrons. We
calculate the expected Comptonization due to the energy release of radio
galaxies, which we estimate to be 3 10^66 erg Gpc^-3. We investigate
Comptonization from (a) the part of the released energy which is thermalized
and (b) the relativistic, remnant radio plasma, which may form a second,
relativistic phase in the inter galactic medium, nearly unobservable for
present day instruments (presence of so called 'radio ghosts'). We find a
thermal Comptonization parameter due to (a) of y = 10^-6 and (b) an optical
depth of relativistic electrons in old radio plasma of tau_rel < 10^-7. If a
substantial fraction of the volume of clusters of galaxies is filled with such
old radio plasma the SZ effect based determination of the Hubble constant is
biased to lower values. Finally, it is shown that a supra-thermal population of
electrons in the Coma cluster would produce a signature in the Wien-tail of the
CMB, which is marginally detectable with a multifrequency measurement by the
Planck satellite. Such a population is expected to exist, since its
bremsstrahlung would explain Coma's recently reported high energy X-ray excess.


title: Outbursts of EX Hydrae: mass-transfer events or disc instabilities?

abstract:
  We present the 45-yr record of EX Hya's lightcurve and discuss the
characteristics of its 15 observed outbursts. We then concentrate on the 1998
outburst, reporting the first outburst X-ray observations. We discover an X-ray
beat-cycle modulation, indicating that an enhanced accretion stream couples
directly with the magnetosphere in outburst, confirming our previous
prediction. Optical eclipse profiles late in outburst show that the visible
light is dominated by an enhanced mass-transfer stream overflowing the
accretion disc. We are uncertain whether the enhanced mass transfer is
triggered by a disc instability, or by some other cause. While in outburst, EX
Hya shows some of the characteristics of SW Sex stars.


title: A GRB Tool Shed

abstract:
  We describe the design of a suite of software tools to allow users to query
Gamma-Ray Burst (GRB) data and perform data mining expeditions. We call this
suite of tools a shed (SHell for Expeditions using Datamining). Our schedule is
to have a completed prototype (funded via the NASA AISRP) by February, 2002.
Meanwhile, interested users will find a partially functioning tool shed at
http://grb.mankato.msus.edu.


title: Power filtration of CMB observational data

abstract:
  We propose a power filter Gp for linear reconstruction of the CMB signal from
observational maps. This Gp filter preserves the power spectrum of the CMB
signal in contrast to the Wiener filter which diminishes the power spectrum of
the reconstructed CMB signal. We demonstrate how peak statistics and a cluster
analysis can be used to estimate the probability of the presence of a CMB
signal in observational records. The efficiency of the Gp filter is
demonstrated on a toy model of an observational record consisting of a CMB
signal and noise in the form of foreground point sources.


title:
Theoretical Implications of Diffuse Non-Thermal Emission from Clusters
  of Galaxies

abstract:
  A short review on theoretical implications of non-thermal emission (radio,
extreme ultraviolet, high energy X-ray) from the intra-cluster medium is given.
The origin of cluster radio halos and cluster radio relics is discussed within
the framework of a network of processes producing a non-thermal electron
population. Emphasis is given to the role of old, remnant, presently invisible
relativistic plasma released by former radio galaxies.


title: Broad-band colour evolution of star clusters

abstract:
  We briefly review the main features in the broad-band colour evolution of
star clusters, over the complete age interval from 10^7 to 10^(10) yr. The
emphasis is in the problem of age-dating distant young clusters (<2 Gyr) from
their integrated colours. It is shown that U-B and B-V are less sensitive to
metallicity than colours involving red pass-bands, like V-I, at least up to
ages of some few Gyr. Since U-B and B-V are determined by well-understood and
well-populated evolutionary stages, they are also less affected by theoretical
uncertainties and by the ubiquitous effect of stochastic colour dispersion. The
latter effects become important for the V-K colour. Thus, we argue that U-B and
B-V are, presently, the more suitable broad-band colours for age-dating distant
clusters. For other potentially useful colours like V-R and V-I, empirical
tests of their evolution are still missing.


title:
The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large
  Magellanic Cloud

abstract:
  We present a 9 million star color-magnitude diagram (9M CMD) of the LMC bar.
The 9M CMD reveals a complex superposition of different age and metallicity
stellar populations, with important stellar evolutionary phases occurring over
3 orders of magnitude in number density. First, we count the non-variable
supergiants, the associated Cepheids, and measure the effective temperatures
defining the instability strip. Lifetime predictions of stellar evolution
theory are tested, with implications for the origin of low-luminosity Cepheids.
The highly-evolved AGB stars have a bimodal distribution in brightness, which
we interpret as discrete old populations (>1 Gyr). The faint AGB may be
metal-poor and very old. We identify the clusters NGC 411 and M3 as templates
for the admixture of old stellar populations. However, there are indications
that the old and metal-poor field population has a red HB morphology: the RR
Lyraes lie on the red edge of the instability strip, the AGB-bump is very red,
and the ratio of AGB-bump stars to RR Lyraes is quite large. If the HB second
parameter is age, the old and metal-poor field population likely formed after
the oldest clusters. Lifetime predictions of stellar evolution theory lead us
to associate a significant fraction of the red HB clump giants with the same
old and metal-poor population producing the RR Lyraes and the AGB-bump. In this
case, compared to the age-dependent luminosity predictions of stellar evolution
theory, the red HB clump is too bright relative to the RR Lyraes and AGB-bump.
Last, the surface density profile of RR Lyraes is fit by an exponential,
favoring a disk-like rather than spheroidal distribution. We conclude that the
age of the LMC disk is probably similar to the age of the Galactic disk.
(ABRIDGED)


title: X-Ray Afterglows of Gamma-Ray Bursts

abstract:
  The afterglow emission has become the main stream of Gamma-Ray burst research
since its discovery three years ago. With the distance-scale enigma solved, the
study of the late-time GRB emission is now the most promising approach to
disclose the origin of these explosions and their relationship with the
environment of the host galaxy in the early phase of the Universe. In this
contribution I will review X-ray observations and their implication on our
undertstanding on the GRB phenomenon. These measurements are providing a direct
probe into the nature of the progenitor and a measurement of the GRB beaming
properties, crucial to establish the total energy output. Some evidence of iron
lines connects the GRB explosion with massive progenitors, thence with
star-forming regions. Furthermore a comparison of the spectral properties with
the temporal evolution indicates that the fireball expansion should not be - on
average - highly collimated, with a jet angle $>10 \deg$.


title: SAX J1810.8-2609: A New Hard X-ray Bursting Transient

abstract:
  The transient X-ray source SAX J1810.8-2609 was discovered on 1998, March 10
with the Wide Field Cameras on board the BeppoSAX satellite, while observing
the Galactic Bulge in the 2-28 keV energy range. On March 11, a strong type-I
X-ray burst was detected with evidence of photospheric radius expansion. A
follow-up target of opportunity observation with the Narrow-Field Instruments
(NFI) was performed on March 11 and 12, for a total elapsed time of 8.51 x
10^{4} s. The wide band spectral data (0.1-200 keV) obtained with the NFI show
a remarkable hard X-ray spectrum detected up to ~200 keV, which can be
described by a power law with photon spectral index Gamma=1.96\pm0.04, plus a
soft component which is compatible with blackbody radiation of temperature
kT~0.5 keV.
  The detection of the type-I X-ray burst is a strong indication that the
compact object is a neutron star in a low mass X-ray binary system. Assuming
standard burst parameters and attributing the photospheric radius expansion to
near Eddington luminosity, we estimate a distance of ~5 kpc. The inferred 2-10
keV X-ray luminosity is ~ 9 x 10^{35} erg/s at the time of the discovery.


title: Prompt Optical Observations of Gamma-ray Bursts

abstract:
  The Robotic Optical Transient Search Experiment (ROTSE) seeks to measure
simultaneous and early afterglow optical emission from gamma-ray bursts (GRBs).
A search for optical counterparts to six GRBs with localization errors of 1
square degree or better produced no detections. The earliest limiting
sensitivity is m(ROTSE) > 13.1 at 10.85 seconds (5 second exposure) after the
gamma-ray rise, and the best limit is m(ROTSE) > 16.0 at 62 minutes (897 second
exposure). These are the most stringent limits obtained for GRB optical
counterpart brightness in the first hour after the burst. Consideration of the
gamma-ray fluence and peak flux for these bursts and for GRB990123 indicates
that there is not a strong positive correlation between optical flux and
gamma-ray emission.


title: Hydrodynamic Simulations of the Bardeen-Petterson Effect

abstract:
  We present SPH simulations of accretion discs in orbit about rotating compact
objects such as black holes and neutron stars, and study the structure of
warped discs produced by the Bardeen-Petterson effect. We calculate the
transition radius out to which the disc specific angular momentum vector is
aligned with that of the black hole. We focus on the parameter regime where the
warp dynamics are controlled by bending wave propagation, but also consider
models in which warps are subject to diffusion rather than wave transport, and
are able to consider the fully nonlinear regime. Because of hydrodynamic or
pressure effects, for the parameter range investigated, the transition radius
is always found to be much smaller than that obtained by Bardeen & Petterson
(1975). For discs with midplane Mach numbers of about 10, the transition occurs
between 10 - 16 gravitational radii, whereas for a Mach number of about 30 it
occurs at around 30 gravitational radii. A thicker disc with a Mach number of 5
is found to produce no discernible warped structure. The rate of black hole -
disc alignment is found to be consistent with the ideas of Ress (1978), with
the alignment torque behaving as if it arises from the accreted material
transferring its misaligned component of angular momentum at the larger
transition radius of Bardeen & Petterson (1975). The inclusion of Einstein
precession in the calculations modified both the warped disc structure and,
consistent with linear analysis, produced an increased alignment rate by up to
a factor of 4 because of the effect that a non Keplerian potential has on the
propagation of warps.


title:
Estimating reaction rates and uncertainties for primordial
  nucleosynthesis

abstract:
  We present a Monte Carlo method for direct incorporation of nuclear inputs in
primordial nucleosynthesis calculations. This method is intended to remedy
shortcomings of current error estimation, by eliminating intermediate data
evaluations and working directly with experimental data, allowing error
estimation based solely on published experimental uncertainties. This technique
also allows simple incorporation of new data and reduction of errors with the
introduction of more precise data. Application of our method indicates that
previous error estimates on the calculated abundances were too large by as much
as a factor of three. Since uncertainties in the BBN calculation currently
dominate inferences drawn from light-element abundances, the re-estimated
errors have important consequences for cosmic baryon density, neutrino physics,
and lithium depletion in halo stars. Our direct method allows detailed
discussion of the status of the nuclear inputs, by identifying clearly the
places where improved cross section measurements would be most useful.


title: Geometrodynamics of Variable-Speed-of-Light Cosmologies

abstract:
  This paper is dedicated to the memory of Dennis Sciama.
  Variable-Speed-of-Light (VSL) cosmologies are currently attracting interest
as an alternative to inflation. We investigate the fundamental geometrodynamic
aspects of VSL cosmologies and provide several implementations which do not
explicitly break Lorentz invariance (no "hard" breaking). These "soft"
implementations of Lorentz symmetry breaking provide particularly clean answers
to the question "VSL with respect to what?". The class of VSL cosmologies we
consider are compatible with both classical Einstein gravity and low-energy
particle physics. These models solve the "kinematic" puzzles of cosmology as
well as inflation does, but cannot by themselves solve the flatness problem,
since in their purest form no violation of the strong energy condition occurs.
We also consider a heterotic model (VSL plus inflation) which provides a number
of observational implications for the low-redshift universe if chi contributes
to the "dark energy" either as CDM or quintessence. These implications include
modified gravitational lensing, birefringence, variation of fundamental
constants and rotation of the plane of polarization of light from distant
sources.


title: RR Lyrae - Theory vs Observation

abstract:
  The luminosities, effective temperatures and metallicities that are derived
empirically by Kovacs and Jurcsik from the light curves of a large number of
globular cluster and field RRab and RRc stars are compared to theoretical RR
Lyrae models. The strong luminosity dependence of the empirical blue and red
edges (Log L vs Log Teff diagram) is in disagreement with that of both
radiative and convective models. A reexamination of the theoretical
uncertainties in the modelling leads us to conclude that the disagreement is
irreconcilable.


title: Scale Dependent Dimension of Luminous Matter in the Universe

abstract:
  We present a geometrical model of the distribution of luminous matter in the
universe, derived from a very simple reaction-diffusion model of turbulent
phenomena. The apparent dimension of luminous matter, $D(l)$, depends linearly
on the logarithm of the scale $l$ under which the universe is viewed: $D(l)
\sim 3\log(l/l_0)/\log(\xi/l_0)$, where $\xi$ is a correlation length.
Comparison with data from the SARS red-shift catalogue, and the LEDA database
provides a good fit with a correlation length $\xi \sim 300$ Mpc. The
geometrical interpretation is clear: At small distances, the universe is
zero-dimensional and point-like. At distances of the order of 1 Mpc the
dimension is unity, indicating a filamentary, string-like structure; when
viewed at larger scales it gradually becomes 2-dimensional wall-like, and
finally, at and beyond the correlation length, it becomes uniform.


title: Possible solar cycle variations in the convection zone

abstract:
  Using data from the Global Oscillations Network Group (GONG) that covers the
period from 1995 to 1998 we study the change in frequencies of solar
oscillations with solar activity. From these frequencies we attempt to
determine any possible variation in solar structure with solar activity. We do
not find any evidence of a change in the convection zone depth or extent of
overshoot below the convection zone during the solar cycle.


title:
The FIR-Radio Correlation of Wolf-Rayet Galaxies and the Role of Star
  Formation in LINERs

abstract:
  We find that a preliminary classification of LINERs' energetics may be made
in terms of the FIR-radio correlation of Wolf-Rayet galaxies. The AGN- or
starburst-supported LINERs can be distinguished by their FIR-to-radio ratio,
$Q\equiv L(1.4{\rm GHz})/$ $L(60\mu{\rm m})>$ or $<0.01$. It is interesting to
note that almost all the LINERs with inner rings might be starburst- supported,
indicating reduced AGN activities compared with those of the AGN-supported
ones. We also find that a shock-heating phase for the warm dust component might
be important for some starbursts at the burst age of $\ge 10^{7}$ yr, with
$Q<0.001$.


title: Preheated Advection Dominated Accretion Flow

abstract:
  All high temperature accretion solutions including ADAF are physically thick,
so outgoing radiation interacts with the incoming flow, sharing as much or more
resemblance with classical spherical accretion flows as with disk flows. We
examine this interaction for the popular ADAF case. We find that without
allowance for Compton preheating, a very restricted domain of ADAF solution is
permitted and with Compton preheating included a new high temperature PADAF
branch appears in the solution space. In the absence of preheating, high
temperature flows do not exist when the mass accretion rate mdot == Mdot c^2 /
L_E >~ 10^-1.5. Below this mass accretion rate, a roughly conical region around
the hole cannot sustain high temperature ions and electrons for all flows
having mdot >~ 10^-4, which may lead to a funnel possibly filled with a tenuous
hot outgoing wind. If the flow starts at large radii with the usual equilibrium
temperature ~10^4 K, the critical mass accretion rate is much lower, mdot
\~10^-3.7 above which level no self-consistent ADAF (without preheating) can
exist. However, above this critical mass accretion rate, the flow can be
self-consistently maintained at high temperature if Compton preheating is
considered. These solutions constitute a new branch of solutions as in
spherical accretion flows. High temperature PADAF flows can exist above the
critical mass accretion rate in addition to the usual cold thin disk solutions.
We also find solutions where the flow near the equatorial plane accretes
normally while the flow near the pole is overheated by Compton preheating,
possibly becoming, a polar wind, solutions which we designate WADAF.


title:
Growth of a Vortex Mode during Gravitational Collapse Resulting in Type
  II Supernova

abstract:
  We investigate stability of a gravitationally collapsing iron core against
non-spherical perturbation. The gravitationally collapsing iron core is
approximated by a similarity solution for dynamically collapsing polytropic gas
sphere. We find that the similarity solution is unstable against non-spherical
perturbations. The perturbation grows in proportion to $ (t - t_0) ^{-\sigma} $
while the the central density increases in proportion to $ (t - t_0) ^{-2} $.
The growth rate is $ \sigma = 1/3 + \ell (\gamma - 4/3) $, where $ \gamma $ and
$ \ell $ denote the polytropic index and the parameter $ \ell $ of the
spherical harmonics, $ Y_{\ell} ^m (\theta, \phi) $, respectively. The growing
perturbation is dominated by vortex motion. Thus it excites global convection
during the collapse and may contribute to material mixing in a type II
supernova.


title:
Evaporation and Condensation Processes of Giant Molecular Clouds in a
  Hot Plasma

abstract:
  2d hydrodynamical simulations are performed to examine the evaporation and
condensation processes of giant molecular clouds in the hot phase of the
interstellar medium. The evolution of cold and dense clouds is calculated in
the subsonic stream of a hot tenuous plasma. Our code includes self-gravity,
heating and cooling processes and heat conduction by electrons. Significant
differences occur between simulations with and without heat conduction.


title:
Optical surface photometry of radio galaxies - II. Observations and data
  analysis

abstract:
  Optical imaging observations for 50 radio galaxies are presented. For each
object isophotal contours, photometric profiles, structural parameters
(position angle, ellipticity, Fourier coefficients), and total magnitudes are
given. These observations, obtained in the Cousins R band, complement the data
presented in a previous paper and are part of a larger project aimed at
studying the optical properties of low redshift (z<0.12) radio galaxies (Govoni
et al. 1999). Comments for each individual source are reported.


title:
Frequency resolved spectroscopy of Cyg X-1: fast variability of the
  reflected emission in the soft state

abstract:
  Using the RXTE/PCA data we study the fast variability of the reflected
emission in the soft spectral state of Cyg X-1 by means of Fourier frequency
resolved spectroscopy. We find that the rms amplitude of variations of the
reflected emission has the same frequency dependence as the primary radiation
down to time scales of <30-50 msec. This might indicate that the reflected flux
reproduces, with nearly flat response, variations of the primary emission. Such
behavior differs notably from the hard spectral state, in which variations of
the reflected flux are significantly suppressed in comparison with the primary
emission, on time scales shorter than ~0.5-1 sec. If related to the finite
light crossing time of the reflector, these results suggest that the
characteristic size of the reflector -- presumably an optically thick accretion
disk, in the hard spectral state is larger by a factor of >5-10 than in the
soft spectral state. Modeling the transfer function of the disk, we estimate
the inner radius of the accretion disk R_in~100R_g in the hard and R_in<10R_g
in the soft state for a 10M_sun black hole.


title: Superwind-Driven Intense H_2 Emission in NGC 6240

abstract:
  We have performed a long-slit K band spectroscopic observation of the
luminous infrared galaxy NGC 6240. The peak position of the H_2 v=1-0 S(1)
emission in the slit is located ~0.3" - 0.4" north of the southern nucleus. It
is almost the midpoint between the southern nucleus and the peak position of
the ^12CO J=1-0 emission. Based on the line-ratio analyses, we suggest the
excitation mechanism of H_2 is pure thermal at most positions. In the southern
region we find the following three velocity components in the H_2 emission: the
blueshifted shell component (~-250 km s^-1 with respect to V_sys) which is
recognized as a distinct C-shape distortion in the velocity field around the
southern nucleus, the high-velocity blueshifted ``wing'' component (~-1000 km
s^-1 with respect to V_sys), and the component indicating possible line
splitting of ~500 km s^-1. The latter two components are extended to the south
from the southern nucleus. We show that the kinematic properties of these three
components can be reproduced by expanding motion of a shell-like structure
around the southern nucleus. The offset peak position of the H_2 emission can
be understood if we assume that the shell expanding to the north interacts with
the extragalactic molecular gas. At the interface between the shell and the
molecular gas concentration the cloud-crushing mechanism proposed by Cowie et
al. (1981) may work efficiently, and the intense H_2 emission is thus expected
there. All these findings lead us to propose a model that the most H_2 emission
is attributed to the shock excitation driven by the superwind activity of the
southern nucleus.


title: Dusty Tori of Seyfert Nuclei

abstract:
  Dusty tori around active galactic nuclei (AGNs) play an important role in the
classification of Seyfert galaxies. Therefore, physical properties of dusty
tori are of great interest. We briefly introduce three statistical studies
investigating properties of dusty tori; 1) physical sizes of dusty tori based
on water-vapor maser emission, 2) ionization condition of the inner wall of
tori based on high-ionization emission lines, and 3) viewing angle toward dusty
tori based on mid-infrared color.


title: On continued gravitational collapse

abstract:
  According to a widespread idee fixe, the spherically-symmetric collapse of a
sufficiently massive celestial body of spherical shape should generate a black
hole. I prove that this process generates simply an ordinary point mass. My
argument is model-independent.


title:
Near-Infrared-Spectroscopy with Extremely Large Telescopes:
  Integral-Field- versus Multi-Object-Instruments

abstract:
  Integral-field-spectroscopy and multi-object-spectroscopy provide the high
multiplex gain required for efficient use of the upcoming generation of
extremely large telescopes. We present instrument developments and designs for
both concepts, and how these designs can be applied to cryogenic near-infrared
instrumentation. Specifically, the fiber-based concept stands out the
possibility to expand it to any number of image points, and its modularity
predestines it to become the new concept for multi-field-spectroscopy. Which of
the three concepts --- integral-field-, multi-object-, or
multi-field-spectroscopy --- is best suited for the largest telescopes is
discussed considering the size of the objects and their density on the sky.


title: Low Frequency Insights Into Supernova Remnants

abstract:
  Low frequency observations at 330 and 74 MHz can provide new insights into
supernova remnants (SNR). We can test theoretical predictions for spectral
index variations. Nonlinear models of shock acceleration predict that the
spectra from young SNR should be slightly concave rather than power laws --
flattening toward higher energies. However, few SNR are bright and compact
enough to be studied at millimeter wavelengths, restricting studies to the
small range from 6 to 20 cm (a factor of 1.7 in electron energies).
Observations at 330 MHz increase the electron energy baseline to a factor of 4,
while providing sensitivity to larger spatial scales that are resolved out by
centimeter-wavelength interferometers. Such observations can also separate
thermal from nonthermal emission and detect excess free-free absorption
associated with cool gas in remnants. Wide field images also provide an
efficient census of both thermal and nonthermal sources over a large region.


title:
A Search for Sub-millisecond Pulsations in Unidentified FIRST and NVSS
  Radio Sources

abstract:
  We have searched 92 unidentified sources from the FIRST and NVSS 1400 MHz
radio survey catalogs for radio pulsations at 610 MHz. The selected radio
sources are bright, have no identification with extragalactic objects, are
point-like and are more than 5% linearly polarized. Our search was sensitive to
sub-millisecond pulsations from pulsars with dispersion measures (DMs) less
than 500 pc cm-3 in the absence of scattering. We have detected no pulsations
from these sources and consider possible effects which might prevent detection.
We conclude that as a population, these sources are unlikely to be pulsars.


title: The present rate of Supernovae

abstract:
  We present and discuss the most recent determination of the rate of
Supernovae in the local Universe. A comparison with other results shows a
general agreement on the gross values but still significant differences on the
values of the rates of various SN rates in different kinds of galaxies. The
rate of SNe, used as a probe of Star Formation, confirms the young progenitor
scenario for SNII+Ib/c. The increasing diversity of SNe reflects also in the SN
yields which may affect the chemical evolution of the Galaxy but, because of
the limited statistics, we cannot estimate the contributions of the new
subtypes yet. It is also expected that in a few years observational
determinations of the SN rates at various look-back times will be available.


title: The X-ray spectrum of a disk illuminated by ions

abstract:
  The X-ray spectrum from a cool disk embedded in an ion supported torus is
computed. The interaction of the hot ions with the disk increases the hard
X-ray luminosity of the system}. A surface layer of the disk is heated by the
protons from the torus. The Comptonized spectrum produced by this layer has a
shape that depends only weakly on the incident energy flux and the distance
from the accreting compact object. It consists of a `blue bump' of
unComptonized soft photons and a flat high energy tail, reminiscent of the
observed spectra. The hard tail becomes flatter as the thermalization depth in
the cool disk is increased. Further evidence for ion illumination are the Li
abundance in the secondaries of low mass X-ray binaries and the 450 keV lines
sometimes seen in black-hole transient spectra.


title:
High-resolution radio observations of Seyfert galaxies in the extended
  12-micron sample - I. The observations

abstract:
  We present 8.4 GHz VLA A-configuration observations of 87 sources from the
mid-infrared-selected AGN sample of Rush et al (1993). These 0.25 arcsec
resolution observations allow elongated radio structures tens of parsecs in
size to be resolved and enable radio components smaller than 3.5 arcsec to be
isolated from diffuse galactic disc emission. When combined with previous data,
matched radio observations covering ninety percent of the sample have been
collected and these represent the largest sub-arcsecond-resolution radio
imaging survey of a homogeneously-selected sample of Seyfert galaxies to date.
We use our observations to identify 5 radio-loud AGN in the sample. The nature
of the radio emission from Seyfert nuclei will be discussed in subsequent
papers.


title:
Transient X--Ray Sources Observed with the Rxte All-Sky Monitor after
  3.5 Years

abstract:
  We present light curves of a sample of "transient" sources observed with the
All-Sky Monitor (ASM) of the Rossi X-ray Timing Explorer (RXTE). The light
curves extend over 3.5 years. They are presented in three groups: six
neutron-star systems, eight black-hole-candidate systems, and an additional
diverse set of six objects that are either transient sources (in the sense of
usually being undetectable) or persistent sources showing transient behavior.
The outburst profiles of these sources show reproducible characteristics within
one source and from source to source, as well as large variations. These
profiles together with the profiles of the hardness ratios from the ASM are a
valuable resource for the understanding of accretion instabilities. We
summarize briefly some recent work by observers on these somewhat arbitrarily
selected sources.


title: The Mid-Infrared Spectra of Normal Galaxies

abstract:
  The mid-infrared spectra (2.5 to 5 and 5.7 to 11.6 mu) obtained by ISO-PHOT
reveal the interstellar medium emission from galaxies powered by star formation
to be strongly dominated by the aromatic features at 6.2, 7.7, 8.6 and 11.3 mu.
Additional emission appears in-between the features, and an underlying
continuum is clearly evident at 3-5 mu. This continuum would contribute about a
third of the luminosity in the 3 to 13 mu range. The features together carry 5
to 30% of the 40-to-120 mu `FIR' luminosity. The relative fluxes in individual
features depend very weakly on galaxy parameters such as the far-infrared
colors, direct evidence that the emitting particles are not in thermal
equilibrium. The dip at 10 mu is unlikely to result from silicate absorption,
since its shape is invariant among galaxies. The continuum component has a f_nu
\~ nu^{0.65} shape between 3 and 5 mu and carries 1 to 4% of the FIR
luminosity; its extrapolation to longer wavelengths falls well below the
spectrum in the 6 to 12 mu range. This continuum component is almost certainly
of non-stellar origin, and is probably due to fluctuating grains without
aromatic features. The spectra reported here typify the integrated emission
from the interstellar medium of the majority of star-forming galaxies, and
could thus be used to obtain redshifts of highly extincted galaxies up to z=3
with SIRTF.


title: Competitive Accretion in Clusters and the IMF

abstract:
  Observations have revealed that most stars are born in clusters. As these
clusters typically contain more mass in gas than in stars, accretion can play
an important role in determining the final stellar masses. Numerical
simulations of gas accretion in stellar clusters have found that the stars
compete for the available reservoir of gas. The accretion rates are highly
nonuniform and are determined primarily by each star's position in the cluster.
Stars in the centre accrete more gas, resulting in initial mass segregation.
This competitive accretion naturally results in a mass spectrum and is
potentially the dominant mechanism for producing the initial mass function.
Furthermore, accretion on to the core of a cluster forces it to shrink, which
may result in formation of massive stars through collisions.


title: Gravitational waves emitted by extrasolar planetary systems

abstract:
  In this paper we consider the Extra-solar Planetary Systems recently
discovered in our Galaxy as potential sources of gravitational waves. We
estimate the frequency and characteristic amplitude of the radiation they emit
due to the orbital motion, using the quadrupole formalism. In addition, we
check whether the conditions needed for the resonant excitation of the f- and
g-modes of the central star can be fulfilled. By a Roche-lobe analysis, we show
that there could exist systems in which the low-order g-modes could be excited,
although this does not happen in the systems discovered up to now.


title:
The Role of Electron Captures in Chandrasekhar Mass Models for Type Ia
  Supernovae

abstract:
  The Chandrasekhar mass model for Type Ia Supernovae (SNe Ia) has received
increasing support from recent comparisons of observations with light curve
predictions and modeling of synthetic spectra. It explains SN Ia events via
thermonuclear explosions of accreting white dwarfs in binary stellar systems,
being caused by central carbon ignition when the white dwarf approaches the
Chandrasekhar mass. As the electron gas in white dwarfs is degenerate,
characterized by high Fermi energies for the high density regions in the
center, electron capture on intermediate mass and Fe-group nuclei plays an
important role in explosive burning. Electron capture affects the central
electron fraction Y_e, which determines the composition of the ejecta from such
explosions. Up to the present, astrophysical tabulations based on shell model
matrix elements were only available for light nuclei in the sd-shell. Recently
new Shell Model Monte Carlo (SMMC) and large-scale shell model diagonalization
calculations have also been performed for pf-shell nuclei. These lead in
general to a reduction of electron capture rates in comparison with previous,
more phenomenological, approaches. Making use of these new shell model based
rates, we present the first results for the composition of Fe-group nuclei
produced in the central regions of SNe Ia and possible changes in the
constraints on model parameters like ignition densities and burning front
speeds.


title: Optical/Multiwavelength Observations of GRB Afterglows

abstract:
  I review gamma-ray burst optical/multiwavelength afterglow observations since
1997, when the first counterparts to GRBs were discovered. I discuss what we
have learned from multiwavelength observations of GRB afterglows in relation to
the `standard' fireball plus relativistic blast-wave models. To first order the
`standard' model describes the afterglow observations well, but a wealth of
information can be gathered from the deviations of GRB afterglow observations
from this `standard' model. These deviations provide information on the nature
of the progenitor and on the physics of GRB production. In particular I focus
on the possible connection of GRBs to supernovae, on jet and circumstellar wind
models, on the early-time afterglow, and on the emission from the reverse
shock.


title: LiBeB Evolution: Three Models

abstract:
  We consider the three principal LiBeB evolutionary models, CRI in which the
cosmic-ray source at all epochs of Galactic evolution is the average ISM,
CRI+LECR in which metal enriched low energy cosmic rays (LECRs) are
superimposed onto the CRI cosmic rays, and CRS in which the cosmic-ray source,
accelerated in superbubbles, is constant, independent of the ISM metallicity.
By considering the evolutionary trend of log(Be/H) vs. both [Fe/H] and [O/H],
we demonstrate that the CRI model is energetically untenable. We present
evolutionary trends for B-11/B-10 and B/Be which, combined with future
precision measurements, could distinguish between the CRS and CRI+LECR models.
We show that delayed LiBeB synthesis in the CRS model, due to the transport of
the cosmic rays, could explain why log(Be/H) is steeper vs. [O/H] than vs.
[Fe/H]. We also show that delayed deposition of Fe into star forming regions,
due to its incorporation into high velocity dust, could provide an explanation
for the possible rise of [O/Fe] with decreasing [Fe/H]. Observations of
refractory and volatile alpha-elements could test this scenario. There seems to
be a need for pregalactic or extragalactic Li-6 sources.


title:
Quark phases in neutron stars and a "third family" of compact stars as a
  signature for phase transitions

abstract:
  The appearance of quark phases in the dense interior of neutron stars
provides one possibility to soften the equation of state (EOS) of neutron star
matter at high densities. This softening leads to more compact equilibrium
configurations of neutron stars compared to pure hadronic stars of the same
mass. We investigate the question to which amount the compactness of a neutron
star can be attributed to the presence of a quark phase. For this purpose we
employ several hadronic EOS in the framework of the relativistic mean-field
(RMF) model and an extended MIT bag model to describe the quark phase. We find
that - almost independent of the model parameters - the radius of a pure
hadronic neutron star gets typically reduced by 20-30% if a pure quark phase in
the center of the star does exist. For some EOS we furthermore find the
possibility of a "third family" of compact stars which may exist besides the
two known families of white dwarfs and neutron stars. We show how an
experimental proof of the existence of a third family by mass and radius
measurements may provide a unique signature for a phase transition inside
neutron stars.


title: The spatial and age distribution of stellar populations in DDO 190

abstract:
  The spatial distribution of stellar populations, the star formation history,
and other properties of the dIrr galaxy DDO 190 have been analyzed using
color--magnitude diagrams (CMDs) of about 3900 resolved stars and the Ha fluxes
of HII regions. From the mean color index of the red giant branch, a mean
metallicity [Fe/H]=-2.0 is obtained. The I magnitude of the TRGB has been used
to estimate the distance. DDO 190 is 2.9+/-0.2 Mpc from the Milky Way, 2.1 Mpc
from the M 94 group (CnV-I), 2.4 Mpc from the M 81 group and 2.9 Mpc from the
barycenter of the Local Group, all indicating that it is an isolated, field
galaxy. The surface-brightness distribution of the galaxy is well fitted by
ellipses of ellipticity e=1-a/b=0.1 and P.A.=82deg. The radial star density
distribution follows an exponential law of scale length a=43."4, corresponding
to 611 pc. The Holmberg semi-major axis to mu_B=26.5 is estimated to be
r^B_(26.5)=3.'0. Stellar populations of different ages in DDO 190 show strong
spatial decoupling, the oldest population appearing much more extended than the
youngest. Stars younger than 0.1 Gyr occupy only the central 40'' (0.55 kpc);
stars younger than a few (~4) Gyr extend out to ~80'' (125 kpc), and for larger
galactocentric distances only older stars seem to be present. This behavior is
found in all the dIrr galaxies for which spatially extended studies have been
performed and could be related with the kinematical history of the galaxy.


title:
Gravitational Lensing Effects on High Redshift Type II Supernova Studies
  with NGST

abstract:
  We derive the expected Type II SN differential number counts, N(m), and
Hubble diagram for SCDM and LCDM cosmological models, taking into account the
effects of gravitational lensing (GL) produced by the intervening cosmological
mass. The mass distribution of dark matter halos (ie the lenses) is obtained by
means of a Monte Carlo method applied to the Press-Schechter mass function. The
halos are assumed to have a NFW density profile, in agreement with recent
simulations of hierarchical cosmological models. Up to z=15, the (SCDM, LCDM)
models predict a total number of (857, 3656) SNII/yr in 100 surveyed 4' times
4' fields of the Next Generation Space Telescope. NGST will be able to reach
the peak of the N(m) curve, located at AB approx 30(31) for SCDM(LCDM) in J and
K wavelength bands and detect (75%, 51%) of the above SN events. This will
allow a detailed study of the early cosmic star formation history, as traced by
SNIIe. N(m) is only very mildly affected by the inclusion of lensing effects.
In addition, GL introduces a moderate uncertainty in the determination of
cosmological parameters from Hubble diagrams, when these are pushed to higher
$z$. For example, for a ``true'' LCDM with (Omega_M= 0.4, Omega_Lambda=0.6),
without proper account of GL, one would instead derive
(Omega_{M}=0.36^{+0.15}_{-0.12}, Omega_{Lambda}=0.60^{+0.12}_{-0.24}). We
briefly compare our results with previous similar work and discuss the
limitations of the model.


title:
Harmonizing the RR Lyrae and Clump Distance Scales - Stretching the
  Short Distance Scale to Intermediate Ranges?

abstract:
  I explore the consequences of making the RR Lyrae and clump giant distance
scales consistent in the solar neighborhood, Galactic bulge and Large
Magellanic Cloud (LMC). I employ two major assumptions: 1) that the absolute
magnitude - metallicity, M_V(RR) - [Fe/H], relation for RR Lyrae stars is
universal, and 2) that absolute I-magnitudes of clump giants, M_I(RC), in
Baade's Window are known (e.g., can be inferred from the local Hipparcos-based
calibration or theoretical modeling). A comparison between the solar
neighborhood and Baade's Window sets M_V(RR) at [Fe/H] = -1.6 in the range
(0.59 +/- 0.05, 0.70 +/- 0.05), somewhat brighter than the statistical parallax
solution. More luminous RR Lyrae stars imply younger ages of globular cluster,
which would be in better agreement with the conclusions from the currently
favored stellar evolution and cosmological models. A comparison between Baade's
Window and the LMC sets the M_I^{LMC}(RC) in the range (-0.33 +/- 0.09, -0.53
+/- 0.09). The distance modulus to the LMC, mu^{LMC}, is between 18.24 +/- 0.08
and 18.44 +/- 0.07. Unlike M_I^{LMC}(RC), this range in mu^{LMC} does NOT
depend on the adopted value of the dereddened LMC clump magnitude,
I_0^{LMC}(RC). I argue that the currently available information is insufficient
to select the correct distance scale with high confidence.


title:
The Effect of a Non-Thermal Tail on the Sunyaev-Zeldovich Effect in
  clusters of galaxies

abstract:
  We study the spectral distortions of the cosmic microwave background
radiation induced by the Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies
when the target electrons have a modified Maxwell-Boltzmann distribution with a
high-energy non-thermal tail. Bremsstrahlung radiation from this type of \\
electron distribution may explain the supra-thermal X-ray emission observed in
some clusters such as the Coma cluster and A2199 and serve as an alternative to
the classical but problematic inverse Compton scattering interpretation. We
show that the SZ effect can be used as a powerful tool to probe the electron
distribution in clusters of galaxies and discriminate among these different
interpretations of the X-ray excess. The existence of a non-thermal tail can
have important consequences for cluster based estimators of cosmological
parameters.


title: Faint Infrared Flares from the Microquasar GRS 1915+105

abstract:
  We present simultaneous infrared and X-ray observations of the Galactic
microquasar GRS 1915+105 using the Palomar 5-m telescope and Rossi X-ray Timing
Explorer on July 10, 1998 UT. Over the course of 5 hours, we observed 6 faint
infrared (IR) flares with peak amplitudes of $\sim 0.3-0.6 $ mJy and durations
of $\sim 500-600 $ seconds. These flares are associated with X-ray
soft-dip/soft-flare cycles, as opposed to the brighter IR flares associated
with X-ray hard-dip/soft-flare cycles seen in August 1997 by Eikenberry et al.
(1998). Interestingly, the IR flares begin {\it before} the X-ray oscillations,
implying an ``outside-in'' origin of the IR/X-ray cycle. We also show that the
quasi-steady IR excess in August 1997 is due to the pile-up of similar faint
flares. We discuss the implications of this flaring behavior for understanding
jet formation in microquasars.


title:
Radio-optical identification of very-steep spectrum radio sources from
  the UTR-2 catalogue

abstract:
  We used radio source catalogues accessible from the CATS database
(http://cats.sao.ru) to establish radio continuum spectra for decametric radio
sources in the UTR-2 catalogue (Braude et al., 1978--1994). From these, we
select a sample of 23 sources with ultra steep radio spectra (\alpha<=-1.2, S ~
\nu^{\alpha}) and present accurate positions and sizes from FIRST and NVSS. The
search for optical counterparts from the APM (object) and DSS (image)
databases, as well as infrared and X-ray identifications of these UTR sources
are in progress.


title: LiBeB Production and Associated Astrophysical Sites

abstract:
  The various modes of spallative LiBeB production are summarized, and
classified according to their dependence or independence on the abundance of
medium heavy elements (CNO) illustrated by that of oxygen in the interstellar
medium.
  The predictions of the models are confronted to the available observational
correlations (Be, B vs O). Clearly, a primary mechanism should lead to a slope
one in the lg(Be/H) vs [O/H] plot and a secondary mechanism to a slope two. Due
to the ambiguity of the O data, another criterion, based on energetics, can
help us to select an adequate model. A purely secondary origin in the very
early Galaxy is much more energy demanding than a primary one. Indeed,
magnesium seems to be a possible surrogate of oxygen and iron since i) it is
spectroscopically more easy to cope with and ii) its nucleosynthetic yield is
independent of the mass cut and does not depend on metallicity.


title:
Investigations of the Local Supercluster Velocity Field III. Tracing the
  backside infall with distance moduli from the direct Tully-Fisher relation

abstract:
  We have extended the discussion of Paper II (Ekholm et al. 1999) to cover
also the backside of the Local Supercluster (LSC) by using 96 galaxies within
Theta<30 deg from the adopted centre of LSC and with distance moduli from the
direct B-band Tully-Fisher relation. In order to minimize the influence of the
Malmquist bias we required log V_max>2.1 and sigma_{B_T}<0.2 mag.
  We found out that if R_Virgo<20 Mpc this sample fails to follow the expected
dynamical pattern from the Tolman-Bondi (TB) model. When we compared our
results with the Virgo core galaxies given by Federspiel et al. (1998) we were
able to constrain the distance to Virgo: R_Virgo=20-24 Mpc.
  When analyzing the TB-behaviour of the sample as seen from the origin of the
metric as well as that with distances from the extragalactic Cepheid
PL-relation we found additional support to the estimate R_Virgo=21 Mpc given in
Paper II. Using a two-component mass-model we found a Virgo mass estimate
M_Virgo= (1.5-2)M_virial, where M_virial=9.375.10^14M_sun for R_Virgo=21 Mpc.
This estimate agrees with the conclusion in Paper I (Teerikorpi et al. 1992).
  Our results indicate that the density distribution of luminous matter is
shallower than that of the total gravitating matter when q_0<=0.5. The
preferred exponent in the density power law, alpha\approx2.5, agrees with
recent theoretical work on the universal density profile of dark matter
clustering in an Einstein-deSitter universe (Tittley & Couchman 1999).


title: Young Stellar Populations Around SN1987A

abstract:
  We present the results of a study of the stellar population in a region of 30
pc radius around SN1987A, based on an analysis of multi-band HST-WFPC2 images.
  The effective temperature, radius and, possibly, reddening of each star were
determined for 21,955 stars by fitting the measured broad band magnitudes to
the ones calculated with model atmospheres. In addition, we have identified all
stars with Halpha equivalent widths in excess of 8 A, amounting to a total of
492 stars.
  An inspection to the HR diagram reveals the presence of several generations
of young stars, with ages between 1 and 150 Myrs, superposed on a much older
field population (0.6-6 Gyrs). A substantial fraction of young stars have ages
around 12 Myrs which is the stellar generation coeval to SN 1987A progenitor.
The youngest stars in the field appear to be strong-line T Tauri stars. This
constitute the first positive detection of low mass (about 1-2 Mo) Pre Main
Sequence (PMS) stars outside the Milky Way. Their positions in the HR diagram
appear to require that star formation in the LMC occurs with accretion rates
about 10 times higher than in the Milky Way, i.e. ~10^{-4} Mo/yr.
  SN1987A appears to belong to a loose, young cluster 12+/-2 Myrs old, in which
the slope of the present mass function is almost identical to Salpeter's for
masses above 3 Mo, but becomes much flatter for lower masses. On a large scale,
we find that the spatial distribution of massive stars and low-mass PMS stars
are conclusively different. This results casts doubts on the validity of an IMF
concept on a small scale (say, less than 10 pc). A preliminary analysis, done
for the whole field as a single entity, shows that the IMF slope for the young
population present over the entire region is steeper than Gamma ~ -1.7.


title:
The Elliptical Galaxy formerly known as the Local Group: Merging the
  Globular Cluster Systems

abstract:
  Prompted by a new catalogue of M31 globular clusters, we have collected
together individual metallicity values for globular clusters in the Local
Group. Although we briefly describe the globular cluster systems of the
individual Local Group galaxies, the main thrust of our paper is to examine the
collective properties. In this way we are simulating the dissipationless merger
of the Local Group, into presumably an elliptical galaxy. Such a merger is
dominated by the Milky Way and M31, which appear to be fairly typical examples
of globular cluster systems of spiral galaxies.
  The Local Group `Elliptical' has about 700 +/- 125 globular clusters, with a
luminosity function resembling the `universal' one. The metallicity
distribution has peaks at [Fe/H] ~ -1.55 and -0.64 with a metal-poor to
metal-rich ratio of 2.5:1. The specific frequency of the Local Group Elliptical
is initially about 1 but rises to about 3, when the young stellar populations
fade and the galaxy resembles an old elliptical. The metallicity distribution
and stellar population corrected specific frequency are similar to that of some
known early type galaxies. Based on our results, we briefly speculate on the
origin of globular cluster systems in galaxies.


title:
Conversion of neutron stars to strange stars as the central engine of
  gamma-ray bursts

abstract:
  We study the conversion of a neutron star to a strange star as a possible
energy source for gamma-ray bursts. We use different recent models for the
equation of state of neutron star matter and strange quark matter. We show that
the total amount of energy liberated in the conversion is in the range of (1-4)
10^{53} ergs (one order of magnitude larger than previous estimates) and is in
agreement with the energy required to power gamma-ray burst sources at
cosmological distances.


title: On the absence of winds in ADAFs

abstract:
  We show that recently published assertions that advection dominated accretion
flows (ADAFs) require the presence of strong winds are unfounded because they
assume that low radiative efficiency in flows accreting at low rates onto black
holes implies vanishing radial energy and angular momentum fluxes through the
flow (which is also formulated in terms of the `Bernoulli function' being
positive). This, however, is a property only of self-similar solutions which
are an inadequate representation of global accretion flows. We recall general
properties of accretion flows onto black holes and show that such, necessarily
transonic, flows may have either positive or negative Bernoulli function
depending on the flow viscosity. Flows with low viscosities (alpha<0.1 in the
alpha-viscosity model) have a negative Bernoulli function. Without exception,
all 2-D and 1-D numerical models of low viscosity flows constructed to date
experience no significant outflows. At high viscosities the presence of
outflows depends on the assumed viscosity, the equation of state and on the
outer boundary condition. The positive sign of the Bernoulli function invoked
in this context is irrelevant to the presence of outflows. As an illustration,
we recall 2-D numerical models with moderate viscosity that have positive
values of the Bernoulli function and experience no outflows. ADAFs, therefore,
do not differ from this point of view from thin Keplerian discs: they may have,
but they do not have to have strong winds.


title:
Relations Between Timing Features and Colors in the X-Ray Binary 4U
  0614+09

abstract:
  We study the correlations between timing and X-ray spectral properties in the
low mass X-ray binary 4U 0614+09 using a large (265-ks) data set obtained with
the Rossi X-ray Timing Explorer. We find strong quasi-periodic oscillations
(QPOs) of the X-ray flux, like the kilohertz QPOs in many other X-ray binaries
with accreting neutron stars, with frequencies ranging from 1329 Hz down to 418
Hz and, perhaps, as low as 153 Hz. We report the highest frequency QPO yet from
any low mass X-ray binary at 1329+-4 Hz, which has implications for neutron
star structure. This QPO has a 3.5-sigma single-trial significance, for an
estimated 40 trials the significance is 2.4-sigma. Besides the kilohertz QPOs,
the Fourier power spectra show four additional components: high frequency noise
(HFN), described by a broken power-law with a break frequency between 0.7 and
45 Hz, very low frequency noise (VLFN), which is fitted as a power-law below 1
Hz, and two broad Lorentzians with centroid frequencies varying from 6 to 38 Hz
and 97 to 158 Hz, respectively. We find strong correlations between the
frequencies of the kilohertz QPOs, the frequency of the 6 to 38 Hz broad
Lorentzian, the break frequency of the HFN, the strength of both the HFN and
the VLFN and the position of the source in the hard X-ray color vs. intensity
diagram. The frequency of the 97 to 158 Hz Lorentzian does not correlate with
these parameters. We also find that the relation between power density and
break frequency of the HFN is similar to that established for black hole
candidates in the low state. We suggest that the changing mass accretion rate
is responsible for the correlated changes in all these parameters.


title: Chi-Variable-Speed-of-Light Cosmologies

abstract:
  Variable-Speed-of-Light (VSL) cosmologies are currently attracting much
interest as a possible alternative to cosmological inflation. We discuss the
fundamental geometrodynamic aspects of VSL cosmologies, and provide several
alternative implementations. These implementations provide a large class of VSL
cosmologies that pass the zeroth-order consistency tests of being compatible
with both classical Einstein gravity and low-energy particle physics. While
they solve the ``kinematic'' puzzles as well as inflation does, VSL cosmologies
typically do not solve the flatness problem since in their purest form no
violation of the strong energy condition occurs. Nevertheless, these models are
easy to unify with inflation.


title:
Do statistically significant correlations exist between the Homestake
  solar neutrino data and sunspots?

abstract:
  It has been suggested by various authors that a significant anticorrelation
exists between the Homestake solar neutrino data and the sunspot cycle. Some of
these claims rest on smoothing the data by taking running averages, a method
that has recently undergone criticism. We demonstrate that no significant
anticorrelation can be found in the Homestake, data, or in standard 2- and
4-point averages of that data. However, when 3-, 5-, and 7-point running
averages are taken, an anticorrelation seems to emerge whose significance grows
as the number of points in the average increases. Our analysis indicates that
the apparently high significance of these anticorrelations is an artifact of
the failure to consider the loss of independence introduced in the running
average process. When this is considered, the significance is reduced to that
of the unaveraged data. Furthermore, when evaluated via parametric subsampling,
no statistically significant anticorrelation is found. We conclude that the
Homestake data can not be used to substantiate any claim of an anticorrelation
with the sunspot cycle.


title: The role of Star Formation in the evolution of spiral galaxies

abstract:
  Spiral galaxies offer a unique opportunity to study the role of star
formation in galaxy evolution and to test various theoretical star formation
schemes. I review some recent relevant work on the evolution of spiral
galaxies. Detailed models are used for the chemical and spectrophotometric
evolution, with metallicity dependent stellar yields, tracks and spectra. The
models are ``calibrated'' on the Milky Way disk and generalised to other
spirals with some simple scaling relations, obtained in the framework of Cold
Dark Matter models for galaxy formation. The results compare favourably to the
main observables of present day spirals, provided a crucial assumption is made:
massive disks form their stars earlier than low mass ones. It is not clear
whether this picture is compatible with currently popular hierarchical models
of galaxy evolution. The resulting abundance gradients are found to be
anticorrelated to the disk scalelength, support radially dependent star
formation efficiencies and point to a kind of ``homologuous evolution'' for
spirals.


title:
A High Sensitivity Measurement of the MeV Gamma-Ray Spectrum of Cygnus
  X-1

abstract:
  The Compton Gamma-Ray Observatory (CGRO) has observed the Cygnus region on
several occasions since its launch in 1991. The data collected by the COMPTEL
experiment on CGRO represent the most sensitive observations to date of Cygnus
X-1 in the 0.75-30 MeV range. A spectrum accumulated by COMPTEL over 10 weeks
of observation time shows significant evidence for emission extending out to
several MeV. We have combined these data with contemporaneous data from both
BATSE and OSSE to produce a broad-band gamma-ray spectrum, corresponding to the
low X-ray state of Cygnus X-1, extending from 50 keV up to approximately 5 MeV.
Although there is no evidence for any broad line-like emissions in the MeV
region, these data further confirm the presence of a hard tail at energies
above several hundred keV. In particular, the spectrum at MeV energies can be
described as a power-law with a photon spectral index of $\alpha$ = -3.2, with
no evidence for a cutoff at high energies. For the 200 keV to 5 MeV spectrum,
we provide a quantitative description of the underlying electron spectrum, in
the context of a hybrid thermal/non-thermal model for the emission. The
electron spectrum can be described by a thermal Maxwellian with a temperature
of $kT_e$ = 86 keV and a non-thermal power-law component with a spectral index
of $p_e$ = 4.5. The spectral data presented here should provide a useful basis
for further theoretical modeling.


title: The Spectral Variability of Cygnus X-1 at MeV Energies

abstract:
  In previous work, we have used data from the first three years of the CGRO
mission to assemble a broad-band $\gamma$-ray spectrum of the galactic black
hole candidate Cygnus X-1. Contemporaneous data from the COMPTEL, OSSE and
BATSE experiments on CGRO were selected on the basis of the hard X-ray flux
(45--140 keV) as measured by BATSE. This provided a spectrum of Cygnus X-1 in
its canonical low X-ray state (as measured at energies below 10 keV), covering
the energy range from 50 keV to 5 MeV. Here we report on a comparison of this
spectrum to a COMPTEL-OSSE spectrum collected during a high X-ray state of
Cygnus X-1 (May, 1996). These data provide evidence for significant spectral
variability at energies above 1 MeV. In particular, whereas the hard X-ray flux
{\it decreases} during the high X-ray state, the flux at energies above 1 MeV
{\it increases}, resulting in a significantly harder high energy spectrum. This
behavior is consistent with the general picture of galactic black hole
candidates having two distinct spectral forms at soft $\gamma$-ray energies.
These data extend this picture, for the first time, to energies above 1 MeV.


title: Search for Binary Protostars

abstract:
  In an effort to shed more light on the formation process of binary stars, we
have started a program to study multiplicity among nearby low- and
intermediate-mass protostars using the OVRO Millimeter Array. Here, we describe
the project and present the first results on the protostellar core in the Bok
globule CB230 (L1177). At 10 arcsec resolution, the molecular core is resolved
into two components separated by 5000 AU. The morphology and kinematics of the
double core suggest that it formed from a single cloud core due to rotational
fragmentation.


title:
The Impact of Nuclear Reaction Rate Uncertainties on Evolutionary
  Studies of the Nova Outburst

abstract:
  The observable consequences of a nova outburst depend sensitively on the
details of the thermonuclear runaway which initiates the outburst. One of the
more important sources of uncertainty is the nuclear reaction data used as
input for the evolutionary calculations. A recent paper by Starrfield, Truran,
Wiescher, & Sparks (1998) has demonstrated that changes in the reaction rate
library used within a nova simulation have significant effects, not just on the
production of individual isotopes (which can change by an order of magnitude),
but on global observables such as the peak luminosity and the amount of mass
ejected. We present preliminary results of systematic analyses of the impact of
reaction rate uncertainties on nova nucleosynthesis.


title: Infrared Properties of High Redshift and X-ray Selected AGN Samples

abstract:
  The NASA/ISO Key Project on active galactic nuclei (AGN) seeks to better
understand the broad-band spectral energy distributions (SEDs) of these sources
from radio to X-rays, with particular emphasis on infrared properties. The ISO
sample includes a wide variety of AGN types and spans a large redshift range.
Two subsamples are considered herein: 8 high-redshift (1 < z < 4.7) quasars;
and 22 hard X-ray selected sources.
  The X-ray selected AGN show a wide range of IR continuum shapes, extending to
cooler colors than the optical/radio sample of Elvis et al. (1994). Where a
far-IR turnover is clearly observed, the slopes are < 2.5 in all but one case
so that non-thermal emission remains a possibility. The highest redshift
quasars show extremely strong, hot IR continua requiring ~ 100 solar masses of
500 - 1000 Kelvin dust with ~ 100 times weaker optical emission. Possible
explanations for these unusual properties include: reflection of the optical
light from material above/below a torus; strong obscuration of the optical
continuum; or an intrinsic deficit of optical emission.


title:
Colour Change Measurements of Gravitational Microlensing Events by Using
  the Difference Image Analysis Method

abstract:
  Detecting colour changes of a gravitational microlensing event induced by the
limb-darkened extended source effect is important to obtain useful information
both about the lens and source star. However, precise measurements of the
colour changes are hampered by blending, which also causes colour changes of
the event. In this paper, we show that although the colour change measured from
the subtracted image by using the recently developed photometric method of the
``difference image analysis'' (DIA) differs from the colour change measured by
using the conventional method based on the extraction of the individual source
stars' point spread functions, the curve of the colour changes (colour curve)
constructed by using the DIA method enables one to obtain the same information
about the lens and source star, but with significantly reduced uncertainties
due to the absence of blending. We investigate the patterns of the DIA colour
curves for both single lens and binary lens events by constructing colour
change maps.


title:
Detection of Stellar Spots from the Observations of Caustic-Crossing
  Binary-Lens Gravitational Microlensing Events

abstract:
  Recently, Heyrovsk\'y & Sasselov (1999) investigated the sensitivity of {\it
single-lens} gravitational microlensing event light curves to small spots and
found that during source transit events spots can cause deviations in
amplification larger than 2%, and thus be detectable. In this paper, we explore
the feasibility of spot detection from the observations of {\it
caustic-crossing binary-lens} microlensing events instead of single-lens
events. For this we investigate the sensitivity of binary-lens event light
curves to spots and compare it to that of single-lens events. From this
investigation, we find that during caustic crossings the fractional
amplification deviations of microlensing light curves from those of spotless
source events are equivalent to the deviations of single-lens events, implying
that spots can also be detected with a similar photometric precision to that
required for spot detection by observing single-lens events. We discuss the
relative advantages of observing caustic-crossing binary-lens events over the
observations of single-lens events in detecting stellar spots.


title:
Better Astrometric Deblending of Gravitional Microlensing Events by
  Using the Difference Image Analysis Method

abstract:
  Due to the choice of very dense star fields for a higher event rate, the
current microlensing searches suffer from large uncertainties caused by
blending effect. To measure light variations of microlensing events free from
the effect of blending, a newly developed method of Differential Image Analysis
(DIA) was proposed for microlensing searches. However, even with the light
variation curve obtained by using the DIA method, dramatic reduction of the
uncertainty in the determined Einstein time scale is not expected due to the
difficulty in determining the baseline flux of a source star.
  However, we show in this paper that if the blending effect is investigated by
detecting the shift of a source star image centroid, the DIA method will allow
one to detect the blending effect with a significantly enhanced efficiency
compared the efficiency of the current method based on PSF photometry (PSF
method). This is because for a given event the centroid shift measurable by
using the DIA method, $\delta\theta_{\rm c,DIA}$, is {\it always} larger than
the centroid shift measurable by using the PSF method, $\delta\theta_{\rm
c,PSF}$. We find that the ratio $\delta\theta_{\rm c,DIA}/\delta\theta_{\rm
c,DIA}$ rapidly increases with increasing fraction of blended light. In
addition, for events affected by the same fraction of blended light, the ratio
$\delta\theta_{\rm c,DIA}/ \delta \theta_{\rm c,DIA}$ is larger for the event
with a lower amplification. Therefore, centroid shift measurements by using the
DIA method will be an efficient method to detect the blending effect especially
of highly blended events, for which the uncertainties in the determined
Einstein time scale are large, as well as of low amplification events, for
which the current method is highly inefficient.


title: Mapping the Galactic Halo I. The `Spaghetti' Survey

abstract:
  We describe a major survey of the Milky Way halo designed to test for
kinematic substructure caused by destruction of accreted satellites. We use the
Washington photometric system to identify halo stars efficiently for
spectroscopic followup. Tracers include halo giants (detectable out to more
than 100 kpc), blue horizontal branch stars, halo stars near the main sequence
turnoff, and the ``blue metal-poor stars'' of Preston et al (1994). We
demonstrate the success of our survey by showing spectra of stars we have
identified in all these categories, including giants as distant as 75 kpc. We
discuss the problem of identifying the most distant halo giants. In particular,
extremely metal-poor halo K dwarfs are present in approximately equal numbers
to the distant giants for V fainter than 18, and we show that our method will
distinguish reliably between these two groups of metal-poor stars. We plan to
survey 100 square degrees at high galactic latitude, and expect to increase the
numbers of known halo giants, BHB stars and turnoff stars by more than an order
of magnitude. In addition to the strong test that this large sample will
provide for the question `was the Milky Way halo accreted from satellite
galaxies?', we will improve the accuracy of mass measurements of the Milky Way
beyond 50 kpc via the kinematics of the many distant giants and BHB stars we
will find. We show that one of our first datasets constrains the halo density
law over galactocentric radii of 5-20 kpc and z heights of 2-15 kpc. The data
support a flattened power-law halo with b/a of 0.6 and exponent -3.0. More
complex models with a varying axial ratio may be needed with a larger dataset.


title: Analytic model for galaxy and dark matter clustering

abstract:
  We investigate an analytic model to compute nonlinear power spectrum of dark
matter, galaxies and their cross-correlation. The model is based on
Press-Schechter halos, which cluster and have realistic dark matter profiles.
The total power spectrum is a sum of two contributions, one from correlations
betwen the halos and one from correlations within the same halo. We show that
such a model can give dark matter power spectra which match well with the
results of N-body simulations, provided that concentration parameter decreases
with the halo mass.
  Galaxy power spectrum differs from dark matter power spectrum because pair
weighted number of galaxies increases less rapidly than the halo mass, as
predicted by theoretical models and observed in clusters. In this case the
resulting power spectrum becomes a power law with the slope closed to the
observed. Such a model also predicts a later onset of nonlinear clustering
compared to the dark matter, which is needed to reconcile the CDM models with
the data. Generic prediction of this model is that bias is scale dependent and
nonmonotonic. For red or elliptical galaxies bias in power spectrum may be
scale dependent even on very large scales.
  Our predictions for galaxy-dark matter correlations, which can be observed
through the galaxy-galaxy lensing, show that these cannot be interpreted simply
as an average halo profile of a typical galaxy, because different halo masses
dominate at different scales and because larger halos host more than one
galaxy. We discuss the prospects of using cross-correlations in combination
with galaxy clustering to determine the dark matter power spectrum (ABRIDGED).


title:
Electromagnetic Energy for a Charged Kerr Black Hole in a Uniform
  Magnetic Field

abstract:
  With the Komar mass formula we calculate the electromagnetic energy for a
charged Kerr black hole in a uniform magnetic field. We find that the total
electromagnetic energy takes the minimum when the Kerr black hole possesses a
non-zero net charge $Q = 2\xi B_0 J_H$ where $B_0$ is the strength of the
magnetic field, $J_H$ is the angular momentum of the black hole, $\xi$ is a
dimensionless parameter determined by the spin of the black hole.


title:
The Properties of Poor Groups of Galaxies: III. The Galaxy Luminosity
  Function

abstract:
  We obtain R-band photometry for galaxies in six nearby poor groups for which
we have spectroscopic data, including 328 new galaxy velocities. For the five
groups with luminous X-ray halos, the composite group galaxy luminosity
function (GLF) is fit adequately by a Schechter function with Mstar = -21.6 +/-
0.4 + 5log h and alpha = -1.3 +/- 0.1. We also find that (1) the ratio of
dwarfs to giants is significantly larger for the five groups with luminous
X-ray halos than for the one marginally X-ray detected group, (2) the composite
GLF for the luminous X-ray groups is consistent in shape with that for rich
clusters, (3) the composite group GLF rises more steeply at the faint end than
that of the field, (4) the shape difference between the field and composite
group GLF's results mostly from the population of non-emission line galaxies,
whose dwarf-to-giant ratio is larger in the denser group environment than in
the field, and (5) the non-emission line dwarfs are more concentrated about the
group center than the non-emission line giants. This last result indicates that
the dwarfs and giants occupy different orbits (i.e., have not mixed completely)
and suggests that the populations formed at a different times. Our results show
that the shape of the GLF varies with environment and that this variation is
due primarily to an increase in the dwarf-to-giant ratio of quiescent galaxies
in higher density regions, at least up to the densities characteristic of X-ray
luminous poor groups. This behavior suggests that, in some environments, dwarfs
are more biased than giants with respect to dark matter. This trend conflicts
with the prediction of standard biased galaxy formation models. (Abridged)


title: Modeling Galaxy Lenses

abstract:
  In order to use a gravitational lens to measure the Hubble constant
accurately, it is necessary to derive a reliable model of the lens surface
potential. If the analysis is restricted to the locations and magnifications of
point images, the derived Hubble constant depends upon the class of mass models
used to fit the data. However, when there is extended emission from an Einstein
ring, it may be possible to derive a potential from the observed surface
brightness in a model-independent manner. This procedure is illustrated with
reference to B1608+656. The multi-band images are de-reddened, de-convolved and
de-contaminated so that the luminous matter and the surface brightness contours
in the Einstein ring are both faithfully mapped. This intensity distribution
can then be used to reconstruct the potential. Progress in implementing this
program is reported.
  The observed incidence of multiple-imaged galaxies on the Hubble Deep Fields
is an order of magnitude smaller than naively predicted on the basis of radio
lens surveys, like CLASS, but consistent with the rate computed using surface
photometry of candidate lens galaxies assuming standard mass to light ratios.
In order to resolve this paradox, it is suggested that most galaxy lenses are
located in compact groups.


title: Spectral Evolution of the Peculiar Ic Supernova 1998bw

abstract:
  SN 1998bw holds the record for the most energetic Type Ic explosion, one of
the brightest radio supenovae and probably the first supernova associated with
a gamma-ray burst. In this paper we present spectral observations of SN 1998bw
observed in a cooperative monitoring campaign using the AAT, UKST and the SSO
2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94
days after V_band maximum in comparison to well-studied examples of Type Ic SNe
in order to quantify the unusual properties of this supernova event. Though the
early spectra differ greatly from the observations of classical Ic SNe, we find
that the evolution from the photospheric to the nebular phases is slow but
otherwise typical. The spectra differ predominantly in the extensive line
blending and blanketing which has been attributed to the high velocity of the
ejecta. We find that by day 19, the absorption line minima blueshifts are 10% -
50% higher than other SNe and on day 94 emission lines are 45% broader, as
expected if the progenitor had a massive envelope. However, it is difficult to
explain the extent of line blanketing entirely by line broadening, and we argue
that additional contribution from other species is present, indicating unusual
relative abundances or physical conditions in the envelope.


title: Current Issues

abstract:
  Cosmic explosions are observed in many astrophysical environments. They range
in scale from hydromagnetic instabilities in the terrestrial magnetotail and
solar ``nanoflares'' to cosmological gamma ray bursts, supernovae and the
protracted intervals of nuclear activity that produce the giant quasars and
radio galaxies. There are many parallels in the analyses of the explosion sites
that are highlighted at this workshop, specifically stellar coronae, accretion
disks, supernovae and compact objects. In this introductory talk, some general
issues are discussed and some more specific questions relating to the
individual sites are raised.


title: Quasar Jets and their Fields

abstract:
  Observations of jets from quasars and other types of accreting black hole are
briefly summarized. The importance of beaming and $\gamma$-ray observations for
understanding the origin of these jets is emphasised. It is argued that both
the power source and the collimation are likely to be magnetic in origin,
although the details remain controversial. Ultrarelativistic jets may be formed
by the spinning hole and collimated by a hydromagnetic disc wind. Progress in
understanding jets has been handicapped by our inadequate knowledge of how
magnetic field really behaves under cosmic conditions. Fortunately, significant
insights are coming from solar observations, numerical simulation and
laboratory plasma experiments. Some possible, evolutionary ramifications are
briefly discussed and it is suggested that it is the mass of the black hole
relative to that of the galaxy which determines the eventual galaxy morphology.


title: The Host Galaxy of the Lensed Quasar Q 0957+561

abstract:
  Infrared images of the Q 0957+561 gravitational lens obtained with the Hubble
Space Telescope show two large (\sim 5 arcsec) lensed images of the z_s=1.41
quasar host galaxy. Parts of the host galaxy are doubly-imaged like the quasar,
while other parts are quadruply-imaged. The distortions of the host galaxy
offer the best probe yet of the global structure of the lensing potential,
which is essential for determining the Hubble constant from the measured time
delay. The distortions are inconsistent with the predictions of previously
published lens models, which invalidates those models and their implications
for H_0. New models show that the distortions finally break the long-standing
degeneracy between the shape of the lens galaxy and the tidal shear contributed
by the cluster containing the lens galaxy. The shape of the lens galaxy's mass
distribution must be remarkably similar to the shape of its luminosity
distribution, and most models that produce reasonable values for the Hubble
constant roughly match the observed ellipticity gradient and isophote twist of
the lens galaxy. Also, the cluster must be non-spherical and produce a
relatively small tidal shear. Although there are still degeneracies in the lens
models that lead to a 25% uncertainty in the derived value of the Hubble
constant, there are also strong prospects for new observations to further
improve the constraints and reduce the uncertainties.


title: Internal shock model for Microquasars

abstract:
  We present a model for the radio outbursts of microquasars based on the
assumption of quasi-continuous jet ejection. The jets are `lit up' by shock
fronts traveling along the jets during outbursts. The observed comparatively
flat decay light curves combined with gradually steepening spectral slopes are
explained by a superposition of the radiation of the aging relativistic
particle population left behind by the shocks. This scenario is the low energy,
time-resolved equivalent to the internal shock model for GRBs. We show that
this model predicts energy contents of the radiating plasma similar to the
plasmon model. At the same time, the jet model relaxes the severe requirements
on the central source in terms of the rate at which this energy must be
supplied to the jet. Observations of `mini-bursts' with flat spectral slopes
and of infrared emission far from the source centre suggest two different
states of jet ejections: (i) A `mini-burst' mode with relatively stable jet
production and weak radio emission with flat spectra and (ii) an outburst mode
with strong variations in the jet bulk velocities coupled with strong radio
emission with steeper spectra. We also show that the continuous jets in
microquasars should terminate in strong shocks and possibly inflate radio lobes
similar to extragalactic jet sources. Finally, we investigate the possibility
of testing the predictions of this model with resolved radio observations.