title: Collapse of Rotating Magnetized Molecular Cloud Cores and Mass Outflows

abstract:
  Collapse of the rotating magnetized molecular cloud core is studied with the
axisymmetric magnetohydrodynamical (MHD) simulations. Due to the change of the
equation of state of the interstellar gas, the molecular cloud cores experience
several different phases as collapse proce eds. In the isothermal run-away
collapse ($n \lesssim 10^{10}{\rm H_2 cm}^{-3}$), a pseudo-disk is formed and
it continues to contract till the opaque core is fo rmed at the center. In this
disk, a number of MHD fast and slow shock pairs appear running parallelly to
the disk. After the equation of state becomes hard, an adiabatic core is
formed, which is separated from the isothermal contracting pseudo-disk by the
accretion shock front facing radially outwards. By the effect of the magnetic
tension, the angular momentum is transferred from the disk mid-plane to the
surface. The gas with excess angular momentum near the surface is finally
ejected, which explains the molecular bipolar outflow. Two types of outflows
are observed. When the poloidal magnetic field is strong (magnetic energy is
comparable to the thermal one), a U-shaped outflow is formed in which fast
moving gas is confined to the wall whose shape looks like a capit al letter U.
The other is the turbulent outflow in which magnetic field lines and velocity
fi elds are randomly oriented. In this case, turbulent gas moves out almost
perpendicularly from the disk. The continuous mass accretion leads to the
quasistatic contraction of the first core. A second collapse due to
dissociation of H$_2$ in the first core follows. Finally another quasistatic
core is again formed by atomic hydrogen (the second core). It is found that
another outflow is ejected around the second atomic core, which seems to
correspond to the optical jets or the fast neutral winds.


title:
High Resolution X-ray Imaging of a Globular Cluster Core: Compact
  Binaries in 47Tuc

abstract:
  We have obtained high resolution (<1") deep x-ray images of the globular
cluster 47Tucanae (NGC 104) with the Chandra X-ray Observatory to study the
population of compact binaries in the high stellar density core. A 70 kilosec
exposure of the cluster reveals a centrally concentrated population of faint
(Lx ~10^{30-33} erg/s) x-ray sources, with at least 108 located within the
central 2arcmin X 2.5arcmin and at least half with Lx <10^{30.5} erg/s. All 15
millisecond pulsars (MSPs) recently located precisely by radio observations are
identified, though two are unresolved by Chandra. The x-ray spectral and
temporal characteristics, as well as initial optical identifications with the
Hubble Space Telescope, suggest that >~50% are millisecond pulsars, ~30% are
accreting white dwarfs, ~15% are main sequence binaries in flare outbursts and
only 2 to 3 are quiescent low mass x-ray binaries containing neutron stars, the
conventional progenitors of MSPs. An approximate upper limit of ~470Msun for
the mass of an accreting central black hole in the cluster is derived. These
observations provide the first x-ray "color-magnitude" diagram for a globular
cluster and census of its compact object and binary population.


title:
Molecular hydrogen, deuterium and metal abundances in the damped
  Ly-alpha system at z = 3.025 toward QSO 0347-3819

abstract:
  We have detected in high resolution spectra of the quasar Q0347--3819
obtained with the UVES spectrograph at the VLT/Kueyen telescope over 80
absorption features in the Lyman and Werner H2 bands at the redshift of a
damped Ly-alpha system at z = 3.025. The z = 3.025 system spans over 80 km/s
and exhibits a multicomponent velocity structure in the metal lines. The main
component at z = 3.024855 shows a total H2 column density N(H2) =
(4.10\pm0.21)*10^{14} cm^{-2} and a fractional molecular abundance f(H2) =
(1.94\pm0.10)*10^{-6} derived from the H2 lines arising from J=0 to 5
rotational levels of the ground electronic-vibrational state. For the first
time we unambiguously reveal a pronounced [alpha-element/iron-peak] enhancement
of [O,Si/Zn] = 0.6\pm0.1 (6 sigma c.l.) at high redshift. The simultaneous
analysis of metal and hydrogen lines leads to D/H = (3.75\pm0.25)*10^{-5}. This
value is consistent with standard big bang nucleosynthesis if the
baryon-to-photon ratio, eta, lies within the range 4.37*10^{-10} <= eta <=
5.32*10^{-10}, implying 0.016 <= Omega_b h^2_100 <= 0.020.


title: Triggered Star Formation

abstract:
  The star formation triggered in dense walls of expanding shells will be
discussed. The fragmentation process is studied using the linear and non-linear
perturbation theory. The influence of the energy input, the ISM distribution
and the speed of sound is examined analytically and by numerical simulations.
We formulate the condition for the gravitational fragmentation of expanding
shells: if the total surface density of the disc is higher than a certain
critical value, shells are unstable. This value depends on the energy of the
shell and the sound speed in the ISM. As an example the formation of OB
associations near the Sun will be discussed. We trace their orbits in the Milky
Way to see where they have been born: 10 - 12 Myr ago progenitors of
Scorpius-Centaurus OB associations and the Orion OB association resided
together within a sheet-like region elongated in the $l = 20-200degrees
direction, showing that the local OB associations may be formed as fragments of
an expanding supershell.


title: VHE observations of unidentified EGRET sources

abstract:
  Observations of unidentified EGRET sources were made with the Whipple 10m
imaging atmospheric Cherenkov telescope between Fall 1999 and Spring 2001.
During this period, a high resolution 490 pixel camera with 4 degree field of
view was present on the telescope. Characterization of the off-axis response of
this instrument was done using observations of the Crab Nebula. No significant
emission was detected from the eight unidentified EGRET sources observed and
upper limits are presented as a function of position.


title: On the question of trapped surfaces and black holes

abstract:
  There are many observational evidences for the detection of compact objects
with masses significantly larger (in galactic cases) or much larger (in
extragalactic cases) than the upper limits of masses of em cold Neutron Stars.
Such compact objects are commonly interpreted as Black Holes (BHs). However, we
point out that while such Black Hole Candidates (BHCs) must be similar to BHs
in many respects they, actually, can not be BHs because existence of Black
Holes would violate the basic tenet of the General Theory of Relativity that
the worldline of a material particle must be TIMELIKE at any regular region of
spacetime. We arrive at this unique conclusion by approaching the problem from
various directions. We feel that such ``operational'' Black Holes could be able
to explain hard X-ray tail found in the galactic BHCs because Lorentz factor of
the plasma accreting on such objects should be considerably higher than the
corresponding NS case.


title: A Useful Approximation to the Cooling Coefficient of Trace Elements

abstract:
  Radiative cooling is an important ingredient in hydrodynamical models
involving evolution of high temperature plasmas. Unfortunately, calculating an
accurate cooling coefficient generally requires the solution of over a hundred
differential equations to follow the ionization. We discuss here a simple
2-parameter approximation for the cooling coefficient due to elements heavier
than H and He, for the temperature range $T= 10^{4}-10^{8}$K. Tests of the
method show that it successfully tracks the ionization level in severe
dynamical environments, and accurately approximates the non-equilibrium cooling
coefficient of the trace elements, usually to within 10% in all cases for which
cooling is actually important. The error is large only when the temperature is
dropping so rapidly due to expansion that radiative cooling is negligible, but
even in this situation, the ionization level is followed sufficiently
accurately. The current approximation is fully implemented in publicly
available FORTRAN code. A second paper will discuss general approaches to
approximation methods of this type, other realizations which could be even more
accurate, and the potential for extension to calculations of non-equilibrium
spectra.


title:
The Real and Redshift Space Density Distribution Function for
  Large-Scale Structure in the Spherical Collapse Approximation

abstract:
  We use the spherical collapse (SC) approximation to derive expressions for
the smoothed redshift-space probability distribution function (PDF), as well as
the $p$-order hierarchical amplitudes $S_p$, in both real and redshift space.
We compare our results with numerical simulations, focusing on the $\Omega=1$
standard CDM model, where redshift distortions are strongest. We find good
agreement between the SC predictions and the numerical PDF in real space even
for $\sigma_L \simgt 1$, where $\sigma_L$ is the linearly-evolved rms
fluctuation on the smoothing scale. In redshift space, reasonable agreement is
possible only for $\sigma_L \simlt 0.4$. Numerical simulations also yield a
simple empirical relation between the real-space PDF and redshift-space PDF: we
find that for $\sigma \simlt 1$, the redshift space PDF, P[\delta_z], is, to a
good approximation, a simple rescaling of the real space PDF, P[\delta], i.e.,
P[\delta/\sigma] d[\delta/\sigma] = P[\delta_z/\sigma_z] d[\delta_z/\sigma_z],
where $\sigma$ and \sigma_z are the real-space and redshift-space rms
fluctuations, respectively. This result applies well beyond the validity of
linear perturbation theory, and it is a good fit for both the standard CDM
model and the Lambda-CDM model. It breaks down for SCDM at $\sigma \approx 1$,
but provides a good fit to the \Lambda-CDM models for $\sigma$ as large as 0.8.


title:
An Efficient Algorithm for Positioning Tiles in the Sloan Digital Sky
  Survey

abstract:
  The Sloan Digital Sky Survey (SDSS) will observe around 10^6 spectra from
targets distributed over an area of about 10,000 square degrees, using a
multi-object fiber spectrograph which can simultaneously observe 640 objects in
a circular field-of-view (referred to as a ``tile'') 1.49 degrees in radius. No
two fibers can be placed closer than 55'' during the same observation; multiple
targets closer than this distance are said to ``collide.'' We present here a
method of allocating fibers to desired targets given a set of tile centers
which includes the effects of collisions and which is nearly optimally
efficient and uniform. Because of large-scale structure in the galaxy
distribution (which form the bulk of the SDSS targets), a naive covering the
sky with equally-spaced tiles does not yield uniform sampling. Thus, we present
a heuristic for perturbing the centers of the tiles from the equally-spaced
distribution which provides more uniform completeness. For the SDSS sample, we
can attain a sampling rate greater than 92% for all targets, and greater than
99% for the set of targets which do not collide with each other, with an
efficiency greater than 90% (defined as the fraction of available fibers
assigned to targets).


title:
Mapping the Galactic Halo. V. Sgr dSph Tidal Debris 60 degrees from the
  Main Body

abstract:
  As part of the Spaghetti Project Survey (SPS) we have detected a
concentration of giant stars well above expectations for a smooth halo model.
The position (l~350, b~50) and distance (~50 kpc) of this concentration match
those of the Northern over-density detected by SDSS (Yanny et al. 2000, Ivezic
et al. 2000). We find additional evidence for structure at ~80 kpc in the same
direction. We present radial velocities for many of these stars, including the
first published results from the 6.5m Magellan telescope. The radial velocities
for stars in these structures are in excellent agreement with models of the
dynamical evolution of the Sgr dwarf tidal debris, whose center is 60 degrees
away. The metallicity of stars in these streams is lower than that of the main
body of the Sgr dwarf, which may indicate a radial metallicity gradient prior
to disruption.


title:
Studying the Accretion Disks in Black Hole X-ray Binaries with
  Monte-Carlo Simulations

abstract:
  Understanding the properties of the hot corona is very important for studying
the accretion disks in black hole X-ray binary systems. Using the Monte-Carlo
technique to simulate the inverse Compton scattering process between disk
photons and electrons in the hot corona, we have produced two table models in
the XSPEC package. Applying the models to the broad-band BeppoSAX observations
of the black hole candidate XTE J2012+381, we demonstrate the power of this
table model. Our results indicate that the electron distribution in the corona
has a powerlaw shape with a spectral index around 4 and the size of the corona
is just several tens of gravitational radius and the inclination angle of the
disk is around 60 degrees.


title:
Circumnuclear stellar population, morphology and environment of Seyfert
  2 galaxies: an evolutionary scenario

abstract:
  We investigate the relation between the characteristics of the circumnuclear
stellar population and both the galaxy morphology and the presence of close
companions for a sample of 35 Seyfert 2 nuclei. Fifteen galaxies present
unambiguous signatures of recent episodes of star formation within $\approx$300
pc from the nucleus. When we relate this property with the Hubble type of the
host galaxy, we find that the incidence of recent circumnuclear star formation
increases along the Hubble sequence, and seems to be larger than in non-Seyfert
galaxies for the early Hubble types S0 and Sa, but similar to that in
non-Seyfert galaxies for later Hubble types. Both in early-type and late-type
Seyferts, the presence of recent star-formation is related to the galaxy
morphology in the inner few kiloparsecs, as observed in HST images through the
filter F606W by Malkan et al., who has assigned a late ``inner Hubble type'' to
most Seyfert 2s with recent nuclear star-formation. This new classification is
due to the presence of dust lanes and spiral structures in the inner region.
The presence of recent star formation in Seyfert 2 nuclei is also related to
interactions: among the 13 galaxies of the sample with close companions or in
mergers, 9 have recent star formation in the nucleus. These correlations
between the presence of companions, inner morphology and the incidence of
recent star formation suggest an evolutionary scenario in which the interaction
is responsible for sending gas inwards which both feeds the AGN and triggers
star-formation. The starburst then fades with time and the composite Seyfert 2
+ Starburst nucleus evolves to a ``pure'' Seyfert 2 nucleus with an old stellar
population.


title: The Cosmic Infrared Background: Measurements and Implications

abstract:
  The cosmic infrared background records much of the radiant energy released by
processes of structure formation that have occurred since the decoupling of
matter and radiation following the Big Bang. In the past few years, data from
the Cosmic Background Explorer mission provided the first measurements of this
background, with additional constraints coming from studies of the attenuation
of TeV gamma-rays. At the same time there has been rapid progress in resolving
a significant fraction of this background with the deep galaxy counts at
infrared wavelengths from the Infrared Space Observatory instruments and at
submillimeter wavelengths from the Submillimeter Common User Bolometer Array
instrument. This article reviews the measurements of the infrared background
and sources contributing to it, and discusses the implications for past and
present cosmic processes.


title: Chandra Observations of a Cluster and Two Quasars at High Redshift

abstract:
  We observed MS 1054-0321, the highest redshift cluster of galaxies in the
Einstein Medium Sensitivity Survey (EMSS), with the Chandra ACIS-S detector. We
find the X-ray temperature of the cluster to be 10.4^{+1.7}_{-1.5} keV,
slightly lower than that inferred previously and in agreement with the observed
velocity dispersion and that found from weak lensing. We confirm significant
substructure in the form of two distinct clumps in the X-ray distribution. We
find the virial mass of the cluster to be at least 4.5 x 10^{14} h^{-1}
M_{\odot} and the existence of this cluster constrains Omega_m to be less than
one. If Omega_m = 1 and assuming Gaussian initial perturbations, we find the
probability of observing MS 1054 in the EMSS is ~ 7 x 10^{-4}. We also present
the first high-resolution X-ray spectra of two high-redshift quasars, S5
0836+710 and PKS 2149-306, obtained with the Chandra HETGS. The primary goal of
this observation is to use the high spectral resolving power of the HETGS to
detect X-ray absorption produced by a hot intergalactic medium. No significant
emission or absorption feature is detected in either source at +/-3sigma level.
Based on the detection limits we constrain the properties of possible emitters
and absorbers. We propose a method to constrain the cosmological parameters via
the X-ray forest theory, but current data do not give significant constraints.
We also find that combined with the constraints from the distortion of the CMB
spectrum, the X-ray Gunn-Peterson test can marginally constrain a uniform,
enriched IGM.


title:
Chandra Detection of a Hot Gaseous Corona Around the Edge-on Galaxy NGC
  4631

abstract:
  We present a Chandra X-ray observation that shows, unambiguously for the
first time, the presence of a giant diffuse X-ray-emitting corona around the
edge-on disk galaxy NGC 4631. This corona, with a characteristic thermal
temperature of 2-7\times10^6 K, extends as far as 8 kpc away from the galactic
plane. The X-ray morphology resembles the radio halo of the galaxy, indicating
a close connection between outflows of hot gas, cosmic rays, and magnetic field
from the galactic disk. Enhanced diffuse X-ray emission is apparently enclosed
by numerous H\alpha-emitting loops blistered out from the central disk of the
galaxy, as is evident in a comparison with our deep Hubble Space Telescope
imaging.


title:
On the Relationship between Stellar Rotation and Radius in Young
  Clusters

abstract:
  We examine the early angular momentum history of stars in young clusters via
197 photometric periods in the Orion Flanking Fields, 83 photometric periods in
NGC 2264, and 256 measurements of v sin i in the ONC. We show that PMS stars,
even those without observable disks, apparently do not conserve stellar angular
momentum as they evolve down their convective tracks, but instead evolve at
nearly constant angular velocity. This result is inconsistent with expectations
that convective stars lacking disks should spin up as they contract, but
paradoxically consistent with disk-locking models. We briefly explore possible
resolutions, including disk locking, birthline effects, stellar winds, and
planetary companions. We have found no plausible explanations for this paradox.


title: Neutrino Emission from HBLs and LBLs

abstract:
  The Synchrotron Proton Blazar model is a promising model to explain high
energy emission from gamma-ray loud BL Lac objects like Mkn 421. In contrast to
leptonic models, the hadronic explanation of gamma-ray emission predicts
ultrahigh energy neutrinos.
  The predicted neutrino spectra from a typical High-energy cutoff BL Lac
Object (HBL) and a Low-energy cutoff BL Lac Object (LBL) are presented. We find
that cooling due to muon synchrotron radiation causes a cutoff of the neutrino
spectrum at $\sim 10^{18}$ eV, with the exception of $\nu_\mu$ from kaon decay
which may extend to higher energies if meson production takes place in the
secondary resonance region of the cross section.
  The impact of the neutrino output from both source populations to the diffuse
neutrino background is discussed.


title: Radiation of neutron stars and the nature of quasars

abstract:
  The paper has been withdrawn because a new, substantially revised version of
the theory of neutron star radiation is completed by the author.


title:
Galaxy Number Counts from the Sloan Digital Sky Survey Commissioning
  Data

abstract:
  We present bright galaxy number counts in five broad bands ($u', g', r', i',
z'$) from imaging data taken during the commissioning phase of the Sloan
Digital Sky Survey (SDSS). The counts are derived from two independent stripes
of imaging scans along the Celestial Equator, one each toward the North and the
South Galactic cap, covering about 230 and 210 square degrees, respectively. A
careful study is made to verify the reliability of the photometric catalog. For
galaxies brighter than $r^* = 16$, the catalog produced by automated software
is examined against eye inspection of all objects. Statistically meaningful
results on the galaxy counts are obtained in the magnitude range $12 \le r^*
\le 21$, using a sample of 900,000 galaxies. The counts from the two stripes
differ by about 30% at magnitudes brighter than $r^*= 15.5$, consistent with a
local $2\sigma$ fluctuation due to large scale structure in the galaxy
distribution. The shape of the number counts-magnitude relation brighter than
$r^* = 16$ is well characterized by $N \propto 10^{0.6m}$, the relation
expected for a homogeneous galaxy distribution in a ``Euclidean'' universe. In
the magnitude range $ 16 < r^* < 21$, the galaxy counts from both stripes agree
very well, and follow the prediction of the no-evolution model, although the
data do not exclude a small amount of evolution. We use empirically determined
color transformations to derive the galaxy number counts in the $B$ and
$I_{814}$ bands. We compute the luminosity density of the universe at zero
redshift in the five SDSS bands and in the $B$ band. We find ${\cal L}_{B} =
2.4 \pm 0.4 \times 10^8L_\odot h $Mpc$^{-3}$, for a reasonably wide range of
parameters of the Schechter luminosity function in the $B$ band.


title:
New Photometry for the Intermediate-age LMC Globular Cluster NGC 2121
  and the Nature of the LMC Age Gap

abstract:
  We report new photometry for the cluster NGC 2121 in the Large Magellanic
Cloud, which shows a prominent hydrogen core exhaustion gap at the turnoff, and
a descending subgiant branch remniscent of Galactic open clusters. We achieve
an excellent fit using the Girardi isochrones, finding an age of 3.2 +/-
0.5Gyr, with [Fe/H]=-0.6 +/- 0.2. The isochrones fit the color and shape of the
turnoff and subgiant branch so precisely that we constrain the metallicity as
well as the age. The smae isochrones also fit SL 663 and NGC 2155, although our
photometry for these clusters has much larger errors. We find these clusters to
be 0.8 Gyr younger, and 0.4 dex more metal rich, than recently reported in the
literature. Consequently, we argue that NGC 2121, NGC 2155, and SL 663 are not
properly assigned to the age gap in the LMC, but instead are among the first
clusters to have formed int he relatively metal rich, younger group of LMC
clusters. We propose a new definition of the LMC Age Gap as extending from 3.2
to 13 Gyr, with ESO121-SCO3 still the only remaining candidate for membership
in the age gap.


title: Dark Energy and the Observable Universe

abstract:
  We consider ever-expanding Big Bang models with a cosmological constant,
$\Lambda$, and investigate in detail the evolution of the observable part of
the universe. We also discuss quintessence models from the same point of view.
  A new concept, the $\Lambda$-sphere (or $Q$-sphere, in the case of
quintessence) is introduced. This is the surface in our visible universe which
bounds the region where dark energy dominates the expansion, and within which
the universe is accelerating. We follow the evolution of this surface as the
universe expands, and we also investigate the evolution of the particle and
event horizons as well as the Hubble surface. We calculate the extent of the
observable universe and the portion of it that can be seen at different epochs.
Furthermore, we trace the changes in redshift, apparent magnitude and apparent
size of distant sources through cosmic history. Our approach is different from,
but complementary to, most other contemporary investigations, which concentrate
on the past light cone at the present epoch.
  When presenting numerical results we use the FRW world model with
$\Omega_{m0} = 0.30$ and $\Omega_{\Lambda0} = 0.70$ as our standard
cosmological model. In this model the $\Lambda$-sphere is at a redshift of
0.67, and within a few Hubble times the event horizon will be stationary at a
fixed proper distance of 5.1 Gpc (assuming $h_0 = 0.7$). All cosmological
sources with present redshift larger than 1.7 have by now crossed the event
horizon and are therefore completely out of causal contact.


title:
Clusters of Galaxies as Standard Candles for Global Observational
  Cosmology

abstract:
  As the largest gravitationally collapsed objects, and as objects with a
relatively low space density, clusters of galaxies offer one of the best sets
of standard candles for trying to measure basic cosmological parameters such as
the injectivity diameter 2r_{inj} (the shortest distance between two
topologically lensed images of any object, e.g. cluster) and the out-diameter
2r_{+} (the maximum `size' of the Universe). Present constraints indicate that
either of these may be smaller or larger than the horizon diameter.


title:
Electrodynamic Structure of an Outer-Gap Accelerator: Implausibility of
  Super Goldreich-Julian Current

abstract:
  We investigate a stationary pair production cascade in the outer
magnetosphere of a spinning neutron star. The charge depletion due to global
flows of charged particles, causes a large electric field along the magnetic
field lines. Migratory electrons and/or positrons are accelerated by this field
to radiate curvature gamma-rays, some of which collide with the X-rays to
materialize as pairs in the gap. The replenished charges partially screen the
electric field, which is self-consistently solved, together with the
distribution functions of particles and gamma-rays. By solving the Vlasov
equations describing this pair production cascade, we demonstrate the existence
of a stationary gap in the outer magnetosphere of PSR B1055-52 for a wide range
of current densities flowing in the accelerator: From sub to super
Goldreich-Julian values. However, we find that the expected GeV spectrum
becomes very soft if the current density exceeds the Goldreich-Julian value. We
also demonstrate that the GeV spectrum softens with decreasing magnetic
inclination and with increasing distance to this pulsar. We thus conclude that
a sub-Goldreich-Julian current, a large magnetic inclination, and a small
distance (500 pc, say) are plausible to account for EGRET observations.
Furthermore, it is found that the TeV flux due to inverse Compton scatterings
of infrared photons whose spectrum is inferred from the Rayleigh-Jeans side of
the soft blackbody spectrum is much less than the observational upper limit.


title: The Far Infrared and Submillimeter Diffuse Extragalactic Background

abstract:
  The cosmic infrared background (CIB) radiation was a long-sought fossil of
energetic processes associated with structure formation and chemical evolution
since the Big Bang. The COBE Diffuse Infrared Background Experiment (DIRBE) and
Far Infrared Absolute Spectrophotometer (FIRAS) were specifically designed to
search for this background from 1.25 microns to millimeter wavelengths. These
two instruments provided high quality, absolutely calibrated all-sky maps which
have enabled the first detections of the CIB, initially at far infrared and
submillimeter wavelengths, and more recently in the near infrared as well. The
aim of this paper is to review the status of determinations of the CIB based
upon COBE measurements. The results show that the energy in the CIB from far
infrared to millimeter wavelengths is comparable to that in the integrated
light of galaxies from UV to near infrared wavelengths: the universe had a
luminous but dusty past. On the assumption that nucleosynthesis in stars is the
energy source for most of this light, the results also imply that 1 to 8
percent of cosmic baryons has been converted to helium and heavier elements in
stars. The integrated background light from UV to millimeter wavelengths is
about 10 percent of that in the cosmic microwave background.


title: Gravitational lensing constraint on the cosmic equation of state

abstract:
  Recent redshift-distance measurements of Type Ia supernovae (SNe Ia) at
cosmological distances suggest that two-third of the energy density of the
universe is dominated by dark energy component with an effective negative
pressure. This dark energy component is described by the equation of state
$p_{x} = w \rho_{x}$ $(w \geq -1)$. We use gravitational lensing statistics to
constrain the equation of state of this dark energy. We use $n(\Delta\theta)$,
image separation distribution function of lensed quasars, as a tool to probe
$w$. We find that for the observed range of $\Omega_m \sim 0.2 - 0.4$, $w$
should lie between $-0.8 \leq w \leq -0.4$ in order to have five lensed quasars
in a sample of 867 optical quasars. This limit is highly sensitive to lens and
Schechter parameters and evolution of galaxies.


title:
Long Period Variable Stars: galactic populations and infrared luminosity
  calibrations

abstract:
  In this paper HIPPARCOS astrometric and kinematic data are used to calibrate
both infrared luminosities and kinematical parameters of Long Period Variable
stars (LPVs). Individual absolute K and IRAS 12 and 25 luminosities of 800 LPVs
are determined and made available in electronic form.
  The estimated mean kinematics is analyzed in terms of galactic populations.
LPVs are found to belong to galactic populations ranging from the thin disk to
the extended disk. An age range and a lower limit of the initial mass is given
for stars of each population. A difference of 1.3mag in K for the upper limit
of the Asymptotic Giant Branch is found between the disk and old disk galactic
populations, confirming its dependence on the mass in the main sequence.
  LPVs with a thin envelope are distinguished using the estimated mean IRAS
luminosities. The level of attraction (in the classification sense) of each
group for the usual classifying parameters of LPVs (variability and spectral
types) is examined.


title: A High Density Thin layer confining the HII region M42. HHT measurements

abstract:
  We present HHT observations in the N=3-2 rotational transition of the CN
radical toward selected positions of the Trapezium region and of the molecular
Ridge in the Orion molecular cloud. Two of the positions in the Ridge were also
observed in the N=2-1 line of CN and 13CN. The N=3-2 CN lines have been
combined with observations of the N=2-1 and N=1-0 transitions of CN, and of the
N=2-1 of 13CN to estimate the physical conditions and CN abundances in the
molecular gas. We analyze in detail the excitation of the CN lines and find
that the hyperfine ratios of the N=3-2 line are always close to the Local
Thermodynamic Equilibrium (LTE) optically thin values even in the case of
optically thick emission. This is due to different excitation temperatures for
the different hyperfine lines. From the line intensity ratios between the
different CN transitions we derive H_2 densities of ~10^5cm^-3 for the
molecular Ridge and of ~3x10^6cm^-3 for the Trapezium region. The CN column
densities are one order of magnitude larger in the Ridge than in the Trapezium
region, but the CN to H_2 ratio is similar both in the Trapezium and in the
Ridge. The combination of the low CN column densities, high H_2 densities and
relatively high CN abundances toward the Trapezium region requires that the CN
emission arises from a thin layer with a depth along the line of sight of only
\~5x10^15cm. This high density thin layer of molecular gas seems to be related
with material that confines the rear side of the HII region Orion A. However
the molecular layer is not moving as expected from the expansion of the HII
region, but it is ``static'' with respect to the gas in the molecular cloud. We
discuss the implication of a high density ``static'' layer in the evolution of
an HII region.


title: Physics Input from Multiwavelength Observations of AGN

abstract:
  The current status of leptonic jet models for blazars is reviewed.
Differences between the quasar and BL-Lac subclasses of blazars may be
understood in terms of the dominance of different radiation mechanisms in the
gamma-ray regime. Spectral variability patterns of different blazar subclasses
appear to be significantly different and require different intrinsic mechanisms
causing gamma-ray flares. As examples, recent results of long-term
multiwavelength monitoring of PKS 0528+134, 3C 279, and Mrk 501 are interpreted
in the framework of leptonic jet models. Short-term variability patterns give
important additional clues about the source geometry and the relevant radiation
mechanisms in blazars. Challenges for future observational efforts are
discussed.


title:
The discovery and study of the optical counterparts of the transient
  X-ray pulsars RXJ0052.1-7319 and XTEJ0111.2-7317 in the SMC

abstract:
  We report on the discovery and confirmation of the optical counterparts of
the two transient X-ray pulsars, RXJ0052.1-7319 and XTEJ0111.2-7317. In the
narrow (~3" radius) X-ray error circle of RXJ0052.1-7319 we found a V=14.6
(B-V=0.1) 09.5IIIe (a classification as a B0Ve star is also possible, since the
luminosity class depends on the uncertainty on the adopted reddening). Medium
resolution spectra for this object show Balmer lines in emission with an
equivalent width of Halpha=-12/-16A. In the X-ray error box of XTEJ0111.2-7317
we found a relatively bright object (V=15.4, B-V=0.06) which has been
classified as a B0.5-B1Ve star and that was later confirmed by Coe et al.
(2000) as the most plausible counterpart for XTEJ0111.2-7317. Also in this case
we easily detect Balmer emission lines with an Halpha equivalent width of about
-21A. There is also evidence for the presence of a surrounding nebula, possibly
a supernova remnant. A further bright B0Ve star was found just outside the
X-ray error circle of XTEJ0111.2-7317. We discuss the implication of these
results in the light of the current knowledge of Be/X-ray binary systems in the
Magellanic Clouds and within our Galaxy.


title: The HI supershell GS061+00+51 and its neighbours

abstract:
  We describe HI observations of a 4 x 4 degrees field in the Milky Way
centered on l=61 deg, b=0 deg made by the Effelsberg radiotelescope. The field
contains one previously identified HI supershell, GS061+00+51 (Heiles, 1979);
apart from it we find several new structures. We also study the HI distribution
in the vicinity of four HII regions, S86, S87, S88 and S89. We confirm the
existence of the shell GS061+00+51, and we find that it has two smaller
neighbours, spherical shells with a radius around 30 pc. We identify at least
one more regular shell at v_LSR = -18 km/s; and one blown-out shell at v_LSR =
-54 km/s. In two cases we are able to connect HII regions with features in the
HI distribution (S86 and S87), in two other cases no connection is found. Apart
from quite regular HI shells we see a number of non-coherent objects, which are
probably a result of the turbulence in the interstellar medium.


title:
Spectroscopic Classification of 42 LMC OB Stars: Selection of Probes for
  the Hot Gaseous Halo of the LMC

abstract:
  Interstellar C IV absorption line studies of the hot gaseous halo of the
Large Magellanic Cloud (LMC) have been hindered by non-ideal selections of
early-type probe stars in regions where C+3 can be produced locally via
photoionization, fast stellar winds, or supernovae. To observe stars outside
such regions, precise spectral classifications of OB stars in the field are
needed. Therefore, we have obtained medium-dispersion spectra of 42 early-type
stars in the LMC that are distributed outside superbubbles or supergiant
shells. The spectral classification of these stars is presented in this paper.
Nineteen of these program stars have spectral types between B1 and O7, and are
thus suitable probes for interstellar C IV absorption line studies of the hot
gaseous halo of the LMC.


title:
Galactic chemical evolution of Lithium: interplay between stellar
  sources"

abstract:
  In this paper we study the evolution of 7Li in the Galaxy considering the
contributions of various stellar sources: type II supernovae, novae, red giant
stars, and asymptotic giant branch (AGB) stars. We present new results for the
production of 7Li in AGB stars via the hot bottom burning process, based on
stellar evolutionary models by Frost (1997). In the light of recent
observations of dense circumstellar shells around evolved stars in the Galaxy
and in the Magellanic Clouds, we also consider the impact of a very high
mass-loss rate episode (superwind) before the evolution off the AGB phase on
the 7Li enrichment in the interstellar medium. We compare the Galactic
evolution of 7Li obtained with these new 7Li yields (complemented with a
critical re-analysis of the role of supernovae, novae and giant stars) with a
selected compilation of spectroscopic observations including halo and disk
field stars as well as young stellar clusters. We conclude that even allowing
for the large uncertainties in the theoretical calculation of mass-loss rates
at the end of the AGB phase, the superwind phase has a significant effect on
the 7Li enrichment of the Galaxy.


title:
Normal Branch Quasi-Periodic Oscillations in Sco X-1: Viscous
  Oscillations of a Spherical Shell Near the Neutron Star

abstract:
  We present a comprehensive classification of all observed QPOs within the
framework of the transition layer model using a large set of Rossi X-ray Timing
Explorer (RXTE) data for Sco X-1. The model assumes an optically thin material
along the observer's line of sight in the horizontal branch and an increasingly
optically thick material while in the other two branches that is consistent
with X-ray and radio observations and the disk transition layer model of QPOs.
We identify the ~ 6 Hz frequencies in the normal branch as acoustic
oscillations of a spherical shell around the neutron star (NS) that is formed
after radiation pressure near the Eddington accretion rate destroys the disk.
The size of the shell is on the order of one NS radii from the NS. We also
estimate the upper limit of Sco X-1's magnetic field to be 0.7 x 10^6 G at
about one NS radii above the NS surface while in the horizontal X-ray branch.


title: The ELAIS Deep X-ray Survey

abstract:
  We present initial follow-up results of the ELAIS Deep X-ray Survey which is
being undertaken with the Chandra and XMM-Newton Observatories. 235 X-ray
sources are detected in our two 75 ks ACIS-I observations in the well-studied
ELAIS N1 and N2 areas. 90% of the X-ray sources are identified optically to
R=26 with a median magnitude of R=24. We show that objects which are unresolved
optically (i.e. quasars) follow a correlation between their optical and X-ray
fluxes, whereas galaxies do not. We also find that the quasars with fainter
optical counterparts have harder X-ray spectra, consistent with absorption at
both wavebands. Initial spectroscopic follow-up has revealed a large fraction
of high-luminosity Type 2 quasars. The prospects for studying the evolution of
the host galaxies of X-ray selected Type 2 AGN are considered.


title: On the Near-Infrared Size of Vega

abstract:
  Near-infrared (2.2 um) long baseline interferometric observations of Vega are
presented. The stellar disk of the star has been resolved, and the data have
been fitted with a limb darkened stellar disk of diameter Theta_{LD} = 3.28 +/-
0.01 mas. The derived effective temperature is T_eff = 9553 +/- 111 K. However,
the residuals resulting from the stellar disk model appear to be significant
and display organized structure. Instrumental artifacts, stellar surface
structure, stellar atmosphere structure, and extended emission/scattering from
the debris disk are discussed as possible sources of the residuals. While the
current dataset cannot uniquely determine the origin of the residuals, the
debris disk is found to be the most likely source. A simple debris disk model,
with 3-6% of Vega's flux emanating from the disk at r < 4 AU, can explain the
residuals.


title: OPTICON: EC Optical Infrared Coordination Network for Astronomy

abstract:
  OPTICON, the ICN Optical Infrared Coordination Network for Astronomy, brings
together for the first time the operators of all Europe's medium to large
optical-infrared telescopes, the largest corresponding data archives, and
several user representatives. The OPTICON partners work with their communities
to identify those major challenges for the future development of European
optical-infrared astronomy which require Europe-wide collaboration. OPTICON
sponsors and coordinates developments towards these goals, involving the entire
astronomical community through workshops and meetings targeted towards these
agreed common goals of general importance.


title:
X-ray Structure in Cluster Cooling Flows and Its Relationship to Star
  Formation and Powerful Radio Sources

abstract:
  Analyses of Chandra's first images of cooling flow clusters find smaller
cooling rates than previously thought. Cooling may be occurring preferentially
near regions of star formation in central cluster galaxies, where the local
cooling and star formation rates agree to within factors of a few. The radio
sources in central cluster galaxies are interacting with and are often
displacing the hot, intracluster gas. X-ray ``bubbles'' seen in Chandra images
are used to measure the amount of energy radio sources deposit into their
surroundings, and they may survive as fossil records of ancient radio activity.
The bubbles are vessels that transport magnetic fields from giant black holes
to the outskirts of clusters.


title: Quintessential Haloes around Galaxies

abstract:
  The nature of the dark matter that binds galaxies remains an open question.
The favored candidate has been so far the neutralino. This massive species with
evanescent interactions is now in difficulty. It would actually collapse in
dense clumps and would therefore play havoc with the matter it is supposed to
shepherd. We focus here on a massive and non-interacting charged scalar field
as an alternate option to the astronomical missing mass. We investigate the
classical solutions that describe the Bose condensate of such a field in
gravitational interaction with matter. This simplistic model accounts quite
well for the dark matter inside low-luminosity spirals whereas the agreement
lessens for the brightest objects where baryons dominate. A scalar mass m=0.4
to 1.6 10^{-23} eV is derived when both high and low-luminosity spirals are
fitted at the same time. Comparison with astronomical observations is made
quantitative through a chi-squared analysis. We conclude that scalar fields
offer a promising direction worth being explored.


title:
The Super Star Cluster NGC 1569-A Resolved on Sub-Parsec Scales with
  Hubble Space Telescope Spectroscopy

abstract:
  We present 3000--10000 Ang HST/STIS long-slit spectroscopy of the bright
super star cluster A (SSC-A) in the dwarf starburst galaxy NGC 1569. The 0.05"
HST angular resolution allows, for the first time, to probe for spatial
variations in the stellar population of a ~ 10^6 M_sun SSC. Integrated
ground-based spectra of SSC-A have previously revealed young Wolf-Rayet (WR)
signatures that coexist with features from supposedly older, red supergiant
(RSG), populations. We find that the WR emission complexes come solely from the
subcluster A2, identified in previous HST imaging, and are absent from the main
cluster A1, thus resolving the question of whether the WR and RSG features
arise in a single or distinct clusters. The equivalent widths of the WR
features in A2 --- including the CIV 5808 complex which we detect in this
object for the first time --- are larger than previously observed in other WR
galaxies. Models with sub-solar metallicity, as inferred from the nebular
emission lines of this galaxy, predict much lower equivalent widths. On the
``clean'' side of A1, opposite to A2, we find no evidence for radial gradients
in the observed stellar population at 0.05"<R<0.40" (~0.5 to 5 pc), neither in
broad-band, low-resolution, spectra nor in medium-resolution spectra of the
infrared CaII triplet.


title: Infrared Emission from Clusters in the Starforming Disk of He2-10

abstract:
  We have made subarcsecond-resolution images of the central 10" of the
Wolf-Rayet dwarf galaxy He 2-10 at 11.7 microns, using the Long Wavelength
Spectrometer on the Keck Telescope. The spatial distribution of the infrared
emission roughly agrees with that of the rising spectrum radio sources seen by
Kobulnicky & Johnson (1999) and confirms that those sources are compact HII
regions rather than SNR or other objects. The infrared sources are more
extended than the subarcsecond rising spectrum radio sources, although the
entire complex is still less than 5" in extent. On sizescales of 1" the
infrared and radio emission are in excellent agreement, with each source
requiring several hundred to a thousand O stars for excitation. The nebulae lie
in a flattened disk-like distribution about 240 by 100 pc and provide all of
the flux measured by IRAS for the entire galaxy in the 12 micron band; 30% of
the total IRAS flux from the galaxy emanates from one 15-30 pc source. In this
galaxy, intense star formation, probably triggered by an accretion event, is
confined to a central disk which breaks up into distinct nebulae which
presumably mark the sites of young super star clusters.


title:
Cracking Open the Window for Strongly Interacting Massive Particles as
  the Halo Dark Matter

abstract:
  In the early 1990's, an analysis was completed by several theorists of the
available mass/cross-section parameter space for unusual particle candidates to
solve the dark matter problem, e.g. strongly interacting massive particles
(SIMPs). This analysis found several unconstrained windows, such that for SIMP
masses and cross-sections within these windows, SIMPs could still be the
dominant dark matter in our Galactic halo. Since the early 1990's, some of
these windows have been narrowed or closed, and some of these windows have been
widened further by more careful analysis. We summarize the present state of the
SIMP parameter space, and point to the cosmological salience of SIMPs as dark
matter, given some of the present inadequacies of the WIMP solution to the dark
matter problem.


title: Compact Symmetric Objects as Radio Flux Density Calibrators

abstract:
  We present results from the first intensive monitoring campaign of a sample
of Compact Symmetric Objects (CSOs). We observed seven CSOs at 8.5 GHz over a
period of eight months, with an average spacing between observations of 2.7
days. Our results show that, as predicted, the flux densities of the CSOs are
extremely stable; the mean RMS variability of the sample was 0.7% in flux
density. The low variability of the CSOs makes them excellent flux density
calibrators at this frequency. We recommend that at least four CSOs be included
in any VLA monitoring campaign which requires precise epoch-to-epoch
calibration, such as those to measure gravitational lens time delays. The CSO
data enable the correction of small systematic errors in the primary flux
calibration.


title: Direct Detection of Warm Dark Matter in the X-ray

abstract:
  We point out a serendipitous link between warm dark matter (WDM) models for
structure formation on the one hand and the high sensitivity energy range (1-10
keV) for x-ray photon detection on the Chandra and XMM-Newton observatories on
the other. This fortuitous match may provide either a direct detection of the
dark matter or exclusion of many candidates. We estimate expected x-ray fluxes
from field galaxies and clusters of galaxies if the dark matter halos of these
objects are composed of WDM candidate particles with rest masses in the
structure formation-preferred range (~1 keV to ~20 keV) and with small
radiative decay branches. Existing observations lead us to conclude that for
singlet neutrinos (possessing a very small mixing with active neutrinos) to be
a viable WDM candidate they must have rest masses < 5 keV in the zero lepton
number production mode. Future deeper observations may detect or exclude the
entire parameter range for the zero lepton number case, perhaps restricting the
viability of singlet neutrino WDM models to those where singlet production is
driven by a significant lepton number. The Constellation X project has the
capability to detect/exclude singlet neutrino WDM for lepton number values up
to 10% of the photon number. We also consider diffuse x-ray background
constraints on these scenarios. These same x-ray observations additionally may
constrain parameters of active neutrino and gravitino WDM candidates.


title: Dynamo and Electrical Jet in Hall Plasmas, Application to Astrophysics

abstract:
  The magnetic field in Hall plasmas is frozen in the electron component and is
advected not only with the plasma motion but also with the electrical current
flow. Its coupling with the plasma may be not as strong as characteristic of
the MHD approximation. The rotation and slipping of the magnetic field result
in a very different and less efficient magnetic field generation by dynamo -
rotating plasma disk in magnetic field. We found a some exact analytical
solutions of nonlinear equations describing the dynamo. In particular, the
dynamo may not dissipate the energy in the steady state limit. The 3-component
magnetic field and magnetic energy are generated and accumulated during the
transition time only. An electrical jet is the other unusual phenomenon for
MHD. It was investigated theoretically and experimentally for laboratory
plasmas during the last 15 years and now is used for fast current switching. We
found periodical or shock-like nonlinear wave traveling along a Hall plasma
column and not associated with plasma motion. A nonlinear equation describing a
possible steady state magnetic field distribution and current flow in Hall
plasma conductor is derived that differs from the Grad-Shafranov equation for
the low pressure MHD plasma. In conclusion we discuss application of our
results to astrophysical plasmas. This physics could be important for
understanding the evolution of dusty plasma disks and jets around new stars.


title:
Dynamics of the Globular Cluster System Associated with M87 (NGC 4486).
  I. New CFHT MOS Spectroscopy and the Composite Database

abstract:
  We present a comprehensive database of kinematic, photometric and positional
information for 352 objects in the field of M87 (NGC 4486), the central giant
elliptical galaxy in the Virgo cluster; the majority of the objects are
globular clusters associated with that galaxy. New kinematic information comes
from multi-slit observations with the Multi-Object Spectrograph (MOS) of the
Canada-France-Hawaii Telescope, an investigation which has added 96 new
velocities to and confirmed many of the earlier values in a pre-existing
dataset of 256 velocities published elsewhere. The photometry, consisting of
magnitudes and colors in the Washington T1, C-T1 system, is based on CCD
observations made at CTIO and KPNO. The composite database represents the
largest compilation of pure Population II dynamical tracers yet identified in
any external galaxy; moreover, it extends to larger spatial scales than have
earlier investigations. The inclusion of photometric information allows
independent study of the distinct red and blue sub-populations of the bimodal
GCS of M87. In a companion paper (Cote et al. 2001), we use this dataset to
analyse the present dynamical state of the M87 globular cluster system, and
consider the question of its interaction and formation history.


title:
Dynamics of the Globular Cluster System Associated with M87 (NGC 4486).
  II. Analysis

abstract:
  We present a dynamical analysis of the globular cluster system associated
with M87 (= NGC 4486), the cD galaxy near the dynamical center of the Virgo
cluster. The analysis utilizes a new spectroscopic and photometric database
which is described in a companion paper (Hanes et al. 2001). Using a sample of
278 globular clusters with measured radial velocities and metallicities, and
new surface density profiles based on wide-field Washington photometry, we
study the dynamics of the M87 globular cluster system both globally --- for the
entire cluster sample --- and separately --- for the metal-rich and metal-poor
globular cluster samples. This constitutes the largest sample of radial
velocities for pure Population II tracers yet assembled for any galaxy. We
discuss the implications of our findings for models for the formation of giant
elliptical galaxies, globular cluster systems, and the Virgo cluster.
(ABRIDGED)


title: The Kinematics of Intermediate Redshift Mg II Absorbers

abstract:
  [Abridged] We present 23 quasar absorption line systems selected by the MgII
doublet with W_r(2796)>0.3 Ang over the redshift range 0.4<z<1.2. The
kinematics are studied at ~6 km/s resolution to a 5-sigma detection threshold
of 0.015 Ang. Most absorbers are characterized by a dominant kinematic
subsystem with W_r>0.2 Ang and velocity spreads ranging from 10-50 km/s, in
proportion to the system equivalent width. Additional kinematic subsystems have
velocities out to ~400 km/s. The equivalent widths and velocity spreads of
these "outlying", weaker subsystems are anti-correlated with their velocities
and their equivalent width distribution turns down from a power law below
W_r~0.08 Ang. These "moderate" and "high velocity" subsystems and probably not
higher redshift analogues to Galactic high velocity clouds (HVCs). Weak
subsystems are asymmetrically distributed in velocity; they are either all
blueshifted or all redshifted with respect to the dominant subsystem. This
implies, that on a case-by-case basis, a given line of sight is apparently
probing a well defined spatial and kinematic structure. We investigate a simple
kinematic model that relies on a rotating disk to explain the observed
asymmetries. There are systematic differences, or trends, in both the subsystem
to subsystem velocity clustering and in the overall kinematics with increasing
equivalent width; we discuss how these may provide clues to the observed
differential evolution in the equivalent width distribution of MgII absorbers.


title:
X-Ray Spectroscopy of II Pegasi: Coronal Temperature Structure,
  Abundances, and Variability

abstract:
  We have obtained high resolution X-ray spectra of the coronally active
binary, II Pegasi (HD 224085), covering the wavelength range of 1.5-25
Angstroms. For the first half of our 44 ksec observation, the source was in a
quiescent state with constant X-ray flux, after which it flared, reaching twice
the quiescent flux in 12 ksec, then decreasing. We analyze the emission-line
spectrum and continuum during quiescent and flaring states. The differential
emission measure derived from lines fluxes shows a hot corona with a continuous
distribution in temperature. During the non-flare state, the distribution peaks
near log T = 7.2, and when flaring, near 7.6. High-temperature lines are
enhanced slightly during the flare, but most of the change occurs in the
continuum. Coronal abundance anomalies are apparent, with iron very deficient
relative to oxygen and significantly weaker than expected from photospheric
measurements, while neon is enhanced relative to oxygen. We find no evidence of
appreciable resonant scattering optical depth in line ratios of iron and
oxygen. The flare light curve is consistent with Solar two-ribbon flare models,
but with a very long reconnection time-constant of about 65 ks. We infer loop
lengths of about 0.05 stellar radii, to about 0.25 in the flare, if the flare
emission originated from a single, low-density loop.


title: Q-ball candidates for self-interacting dark matter

abstract:
  We show that non-topological solitons, known as Q-balls, are promising
candidates for self-interacting dark matter. They can satisfy the cross-section
requirements for a broad range of masses. Unlike previously considered
examples, Q-balls can stick together after collision, reducing the effective
self-interaction rate to a negligible value after a few collisions per
particle. This feature modifies predictions for halo formation. We also discuss
the possibility that Q-balls have large interaction cross-sections with
ordinary matter.


title: The Stellar IMF in Very Metal-Deficient Gas

abstract:
  In the context of the star formation through the fragmentation of an
extremely metal-deficient protogalactic cloud, the gravitational collapse of
filamentary gas clouds is explored with H$_2$ and HD chemistry. It is found by
1D hydrodynamical simulations that the cloud evolution is prescribed mainly by
the initial density ($n_0$) and H$_2$ abundance ($x_{\rm H_2,0}$). In
particular, it turns out that the evolution of low-density filaments ($n_0
\lesssim 10^5$ cm$^{-3}$) bifurcates at a critical H$_2$ abundance of $x_{\rm
H_2,cr}\simeq 3\times 10^{-3}$, beyond which HD cooling overwhelms H$_2$
cooling. The numerical results indicate that the stellar IMF is likely to be
double-peaked and deficient in sub-solar mass stars, where the high mass peak
of the IMF is around $10M_\odot$ or $10^2M_\odot$, dependently on the initial
density and H$_2$ abundance. If the gas in protogalactic clouds is photoionized
by UV radiation or shock-heated, the H$_2$ abundance could exceed
  $x_{\rm H_2,cr}\simeq 3\times 10^{-3}$ by H$^-$ reactions. Then, the high
mass peak would be $O(10) M_\odot$.


title:
Gravitational instability of expanding shells: Solution with nonlinear
  terms

abstract:
  A model of the thin shell expanding into a uniform ambient medium is
developed. Density perturbations are described using equations with linear and
quadratic terms, and the linear and the nonlinear solutions are compared. We
follow the time evolution of the fragmentation process and separate the well
defined fragments. Their mass spectrum is compared to observations and we also
estimate their formation time.


title:
Millimetric Observations of the Center of M81 : A Starved Nucleus with
  Intraday Variability

abstract:
  The central kiloparsec of M81 has been observed in the CO(J=1-0) line and the
3 mm continuum at 100 pc resolution in an attempt to probe molecular gas, and
to search for the nuclear inner Lindblad resonance (NILR), around the
low-luminosity AGN M81*. We found the following. (1) Molecular gas in the
central kpc is mainly on a ``pseudoring'' or a spiral arm at a radius of about
500 pc. (2) The region within ~300 pc from the nucleus is mostly devoid of
molecular gas except for diffuse one; in particular, there is neither a giant
molecular cloud that is now accreting on the nucleus nor a conspicuous gas
feature that can be identified as an NILR. (3) The 3 mm continuum emission
shows significant intraday variation, suggesting an emitting region of ~100 AU.
(4) The 3-sigma upper limit for CO absorption toward the continuum source is
tau_CO(0->1) dV < 0.1 for a linewidth of 10 km/s. The dearth of accreting
molecular gas in the vicinity of the nucleus may explain the low luminosity of
M81*.


title:
The 2dF QSO Redshift Survey - VI. Measuring Lambda and Beta from
  Redshift-space Distortions in the Power Spectrum

abstract:
  When the 2dF QSO Redshift Survey (2QZ) is complete, a powerful geometric test
for the cosmological constant will be available. By comparing the clustering
along and across the line of sight and modelling the effects of peculiar
velocities and bulk motions in redshift space, geometric distortions, which
occur if the wrong cosmology is assumed, can be detected.
  In this paper we investigate the effect of geometric and redshift-space
distortions in the power spectrum parallel and perpendicular to the observer's
line of sight. Ballinger et al. developed a model to estimate the cosmological
constant, $\Lambda$, and the important parameter $\beta \approx
\Omega_m^{0.6}/b$ from these distortions. We apply this model to a detailed
simulation of the final 25k 2QZ, produced using the Virgo Consortium's huge
{\it Hubble Volume} N-body $\Lambda$-CDM light cone simulation. We confirm the
conclusions of Ballinger et al.; the shape of the redshift-space and geometric
distortions are very similar. When all the uncertainties are taken into account
we find that only a joint $\Lambda - \beta$ constraint is possible.
  By combining this result with a second constraint based on mass clustering
evolution, however, we can make significant progress. We predict that this
method should allow us to constrain $\beta$ to approximately $\pm0.1$, and
$\Omega_{m}$ to $\pm0.25$ using the final catalogue. We apply the method to the
2QZ catalogue of 10000 QSOs and find that this incomplete catalogue marginally
favours a $\Lambda$ cosmology.


title: The RR Lyrae variables in M54 and the Sgr dwarf galaxy

abstract:
  We report on new B, V and I CCD photometry of the globular cluster M54 that
was aimed at the study of its variable stars. With respect to the previous most
recent work on M54 we have nearly doubled the number of detected variable
stars: M54 can now be classified as intermediate in the Oosterhoff groups. The
metallicity distribution for the cluster and the Sgr dSph field is obtained
from the red giant stellar population, and for the variables.


title:
The contribution of active galaxies to the far-infrared and
  submillimeter backgrounds

abstract:
  We present a simple model, developed to estimate the contribution of Active
Galactic Nuclei to the far--infrared background, closely linked to the AGN
synthesis model for the X-ray background. According to our calculation the AGN
contribution is never dominant, ranging from a few to 15 percent between 100
and 850 micron.


title: A Survey of M31 Globular Clusters using WFPC2 on board HST

abstract:
  We report new, as yet unpublished HST/WFPC2 V, I photometry of 9 globular
clusters in M31. These are part of a total sample of 19 clusters on M31 with
well observed CMDs from HST. The clusters have the full range of horizontal
branch morphologies from blue HB to red clump, but none are found with an
extreme (blue only) horizontal branch. Plots of HB type vs [Fe/H] are similar
to those of Galactic clusters, including a hint of second parameter clusters.
Sixteen halo fields adjacent to the observed clusters included in our images
have been analysed. The M31 halo metallicity distribution peaks at [Fe/H]=--0.7
with a tail toward low metallicity, resembling the halo of NGC 5128; metal rich
giants appear to be centrally concentrated.


title: Formation of Globular Clusters in Turbulent Molecular Clouds

abstract:
  The formation of massive stellar clusters in turbulent molecular clouds is
investigated. We include artificial star formation and energy feedback of newly
born stars. The obtained systems are not likely to survive. Case studies to
determine conditions necessary for forming bound clusters will be done in the
future.


title: Photometric observations of 9 Near-Earth Objects

abstract:
  We present new CCD observations of nine Near-Earth Asteroids carried out
between February, 1999 and July, 2000. The bulk of the data was acquired
through an R_C filter, while the minor planet 11405 was observed without
filter. We could determine synodic periods and amplitudes for 5 asteroids, 699:
3.3 h, 0.18 mag; 1866: 2.7 h, 0.12 mag; 1999 JD6: 7.68 h, 1.2 mag; 2000 GK137:
4.84 h, 0.27 mag; 2000 NM: 9.24 h, 0.30 mag. Based on observations taken at
different phases, we could infer a phase parameter m of 0.018+/-0.005 for 1865
Cerberus. An epoch-method yielded a sidereal period of 0.27024003(5) d for this
object with retrograde rotation. The remaining 3 objects have only partial
coverage, thus no firm conclusion on their synodic period is possible.


title: Modelling the uv/x-ray cosmic background with CUBA

abstract:
  In this paper, I will describe the features of the numerical code CUBA, aimed
at the solution of the radiative transfer equation in a cosmological context.
CUBA will be soon available for public use at the URL
http://pitto.mib.infn.it/~haardt/, allowing for several user-supplied input
parameters, such as favourite cosmology, luminosity functions, Type II object
evolution, stellar spectra, and many others. I will also present some new
results of the UV/X-ray cosmic background as produced by the observed
populations of QSOs and star forming galaxies, updating and extending our
previous works. The background evolution is complemented with a number of
derived quantities such as the ionization and thermal state of the IGM, the
HeII opacity, the HI and HeII ionization rates, and the HI, HeII and Compton
heating rates.


title:
The gravitational torque of bars in optically unbarred and barred
  galaxies

abstract:
  The relative bar torques for 45 galaxies observed at $K$- band with the 4.2m
William Herschel Telescope are determined by transforming the light
distributions into potentials and deriving the maximum ratios of the tangential
forces relative to the radial forces. The results are combined with the bar
torques for 30 other galaxies determined from our previous $K$-band survey
(Buta & Block 2001). Relative bar torques determine the degree of spiral arm
forcing, gas accretion, and bar evolution. They differ from other measures of
bar strength, such as the relative amplitude of the bar determined
photometrically, because they include the bulge and other disk light that
contributes to the radial component of the total force. If the bulge is strong
and the radial forcing large, then even a prominent bar can have a relatively
weak influence on the azimuthal motions in the disk. Here we find that the
relative bar torque correlates only weakly with the optical bar type listed in
the Revised Shapley-Ames and de Vaucouleurs systems. In fact, some classically
barred galaxies have weaker relative bar torques than classically unbarred
galaxies. The optical class is a poor measure of azimuthal disk forcing for two
reasons: some infrared bars are not seen optically, and some bars with strong
bulges have their azimuthal forces so strongly diluted by the average radial
force that they exert only small torques on their disks. The Hubble
classification scheme poorly recognizes the gravitational influence of bars.
Applications of our bar torque method to the high-redshift universe are briefly
discussed.


title:
Higher order corrections to primordial spectra from cosmological
  inflation

abstract:
  We calculate power spectra of cosmological perturbations at high accuracy for
two classes of inflation models. We classify the models according to the
behaviour of the Hubble distance during inflation. Our approximation works if
the Hubble distance can be approximated either to be a constant or to grow
linearly with cosmic time. Many popular inflationary models can be described in
this way, e.g., chaotic inflation with a monomial potential, power-law
inflation and inflation at a maximum. Our scheme of approximation does not rely
on a slow-roll expansion. Thus we can make accurate predictions for some of the
models with large slow-roll parameters.


title: The white dwarf revealed in the intermediate polar V709 Cassiopeiae

abstract:
  Results are presented from the first detailed spectroscopic observations of
the recently identified intermediate polar RXJ0028.8+5917/V709 Cas. The study
of the emission line radial velocities allows us to remove the uncertainties on
the different aliases of the orbital period and a best value is found at
(0.2225 +/- 0.0002) day. It is also found that the system shows significant EW~
(2-4)A, broad absorptions affecting the Balmer lines from Hdelta to Hbeta.
These broad absorptions are interpreted as the contribution of an underlying
white dwarf atmosphere. The characteristics of the absorptions are found to be
consistent with a DA log(g) = 8 white dwarf at a temperature of ~ 23 000 K,
contributing ~ 17 % (at 4500 A) to the overall flux. This is the first direct
detection of a white dwarf in an intermediate polar system. The absence of
significant Zeeman splitting indicates a magnetic field lower than 10 MG,
confirming that, at least in some cases, intermediate polars have weaker fields
than polars. Different possibilities are discussed to explain the substantial
contribution of the white dwarf to the overall flux.


title: Oscillations During Inflation and the Cosmological Density Perturbations

abstract:
  Adiabatic (curvature) perturbations are produced during a period of
cosmological inflation that is driven by a single scalar field, the inflaton.
On particle physics grounds -- though -- it is natural to expect that this
scalar field is coupled to other scalar degrees of freedom. This gives rise to
oscillations between the perturbation of the inflaton field and the
perturbations of the other scalar degrees of freedom, similar to the phenomenon
of neutrino oscillations. Since the degree of the mixing is governed by the
squared mass matrix of the scalar fields, the oscillations can occur even if
the energy density of the extra scalar fields is much smaller than the energy
density of the inflaton field. The probability of oscillation is resonantly
amplified when perturbations cross the horizon and the perturbations in the
inflaton field may disappear at horizon crossing giving rise to perturbations
in scalar fields other than the inflaton. Adiabatic and isocurvature
perturbations are inevitably correlated at the end of inflation and we provide
a simple expression for the cross-correlation in terms of the slow-roll
parameters.


title:
HST/STIS spectroscopy of the exposed white dwarf in the short-period
  dwarf nova EK TrA

abstract:
  We present high resolution Hubble Space Telescope ultraviolet spectroscopy of
the dwarf nova EK TrA obtained in deep quiescence. The Space Telescope Imaging
Spectrograph data reveal the broad Ly-alpha absorption profile typical of a
moderately cool white dwarf, overlayed by numerous broad emission lines of He,
C, N, and Si and by a number of narrow absorption lines, mainly of CI and SiII.
Assuming a white dwarf mass in the range 0.3-1.4Msun we derive
Teff=17500-23400K for the primary in EK TrA; Teff=18800K for a canonical mass
of 0.6Msun. From the narrow photospheric absorption lines, we measure the white
dwarf rotational velocity, v*sin i=200+-100kms. Even though the strong
contamination of the photospheric white dwarf absorption spectrum by the
emission lines prevents a detailed quantitative analysis of the chemical
abundances of the atmosphere, the available data suggest slightly sub-solar
abundances. The high time resolution of the STIS data allows us to associate
the observed ultraviolet flickering with the emission lines, possibly
originating in a hot optically thin corona above the cold accretion disk.


title: Intensity Distributions of Gamma-Ray Bursts

abstract:
  Observations of individual bursts chosen by the vagaries of telescope
availability demonstrated that bursts are not standard candles and that their
apparent energy can be as great as 10^54 erg. However, determining the
distribution of their apparent energy (and of other burst properties) requires
the statistical analysis of a well-defined burst sample; the sample definition
includes the threshold for including a burst in the sample. Thus optical groups
need to the criteria behind the decision to search for a spectroscopic
redshift. Currently the burst samples are insufficient to choose between
lognormal and power law functional forms of the distribution, and the parameter
values for these functional forms differ between burst samples. Similarly, the
actual intensity distribution may be broader than observed, with a low energy
tail extending below the detection threshold.


title:
Maximum-Entropy Reconstruction of the Distribution of Mass in Cluster
  MS1054-03 from Weak Lensing Data

abstract:
  Weak gravitational lensing studies of clusters of galaxies provide
complimentary information to that from X-ray data; the measured signal depends
only on the cluster's projected mass, independent of dynamical assumptions.
Here we apply a maximum-entropy method algorithm for reconstructing the
two-dimensional density distribution to two sets of shear data for the high
redshift cluster MS1054-03, courtesy of Clowe et al (2000) and Hoekstra et al
(2000).


title:
Open clusters or their remnants: B and V photometry of NGC 1901 and NGC
  1252

abstract:
  Photometry in the B and V bands is presented for the southern stellar groups
NGC 1901 and NGC 1252. NGC 1901 is often described as an open cluster while NGC
1252 consists of a concentration of about 20 stars centered approx 20' north of
the original New General Catalogue coordinates, and at the southwest edge of
the large region previously assigned to this object in the literature. NGC 1901
has a clear main sequence and shares similarities with the Hyades. We derive a
reddening value E(B-V) = 0.04, a distance from the Sun d = 0.45 kpc (Z = -0.23
kpc) and an age 0.6 +/- 0.1 Gyr. NGC 1901 is conclusively a physical system,
dynamically comparable to or more evolved than the Hyades. The colour-
magnitude diagram of NGC 1252 suggests a turnoff and main sequence, and a total
of 12 probable members. We simulated the Galactic field colour-magnitude
diagram in the same direction and found it to be a poor match to NGC 1252,
suggesting that NGC 1252 is not a field fluctuation. Isochrone fitting to the
probable members is consistent with E(B-V) = 0.02, a distance from the Sun d =
0.64 kpc (Z = -0.46 kpc) and an age 3 +/- 1 Gyr. NGC 1252 cannot be ruled out
as a physical group with the available data. If so, evidence is found that it
is not a classical open cluster, but rather an open cluster remnant.


title:
Resolving the X-ray Spectral Paradox: XMM-Newton Spectra of Faint
  Sources in the Lockman Hole

abstract:
  Using 100ks of XMM-Newton data on the Lockman Hole, we show how the X-ray
background 'spectral paradox' is being resolved. We find the summed spectra of
the Type I AGN, Type II AGN, and the unidentified objects. We conclude that the
hard slope of the XRB is caused predominantly by latter sources, i.e. the Type
II AGN and unidentified objects.


title:
First Results from the XMM-Newton Observation in the Groth-Westphal
  Survey Strip Region

abstract:
  We present the first results of the XMM-Newton observation on the
Groth-Westphal Strip Field. The scheduled exposure time was 70 [ks]. We first
analyzed about 50 [ks] of calibrated and cleaned EPIC-PN data, which were the
only ones we could successfully process with an early version of the SAS
software applicable to these observations. A total of about 110 sources have
been detected in the central 10 arcmin of the PN field of view (FOV). A
cross-correlation with the Hubble Space Telescope (HST) Medium Deep Survey
(MDS) database shows a range of morphological properties of host galaxies of
the X-ray source. Spectra of hard X-ray sources in our data indeed show
absorption in the range N_H~10^{22}-10^{23} [cm^{-2}] at z~1.


title: Chandra observations of the X-ray jet in 3C66B

abstract:
  Our Chandra observation of the FRI radio galaxy 3C66B has resulted in the
first detection of an X-ray counterpart to the previously known radio,
infra-red and optical jet. The X-ray jet is detected up to 7 arcsec from the
core and has a steep X-ray spectrum, alpha ~ 1.3 +/- 0.1. The overall X-ray
flux density and spectrum of the jet are consistent with a synchrotron origin
for the X-ray emission. However, the inner knot in the jet has a higher ratio
of X-ray to radio emission than the others. This suggests that either two
distinct emission processes are present or that differences in the acceleration
mechanism are required; there may be a contribution to the inner knot's
emission from an inverse-Compton process or it may be the site of an early
strong shock in the jet. The peak of the brightest radio and X-ray knot is
significantly closer to the nucleus in the X-ray than in the radio, which may
suggest that the knots are privileged sites for high-energy particle
acceleration. 3C66B's jet is similar both in overall spectral shape and in
structural detail to those in more nearby sources such as M87 and Centaurus A.


title: Detection of Bulk Motions in the ICM of the Centaurus Cluster

abstract:
  Several recent numerical simulations of off-center cluster mergers predict
that significant angular momentum with associated velocities of a few x 10^{3}
km/s can be imparted to the resulting cluster. Such gas bulk velocities can be
detected by the Doppler shift of X-ray spectral lines with ASCA spectrometers.
Using two ASCA observations of the Centaurus cluster, we produced a velocity
map for the gas in the cluster's central regions. We also detected radial and
azimuthal gradients in temperature and metal abundance distributions, which
seem to be associated with the infalling sub-group centered at NGC 4709 (Cen
45). More importantly, we found a significant (>99.8% confidence level)
velocity gradient along a line near-perpendicular to the direction of the
incoming sub-group and with a maximum velocity difference of ~3.4+-1.1 x 10^{3}
km/s. It is unlikely (P < 0.002) that the observed velocity gradient is
generated by gain fluctuations across the detectors. While the observed
azimuthal temperature and abundance variations can be attributed to the
interaction with Cen 45, we argue that the intracluster gas velocity gradient
is more likely due to a previous off-center merging event in the main body of
the Centaurus cluster.


title: A Pulsar Wind Nebula in the Oxygen-Rich Supernova Remnant G292.0+1.8

abstract:
  Using the Chandra X-ray Observatory we have discovered a diffuse,
center-filled region of hard X-ray emission within the young, oxygen-rich
supernova remnant (SNR) G292.0+1.8. Near the peak of this diffuse emission lies
a point-like source of X-ray emission that is well described by an absorbed
power-law spectrum with photon index $1.72\pm0.09$. This source appears to be
marginally extended; its extent of 1.3$^{\prime\prime}$ (FWHM) is greater than
that of a nearby serendipitous X-ray source with FWHM = $1.1^{\prime\prime}$.
This is strong evidence for the presence within SNR G292.0+1.8 of a young
rapidly-rotating pulsar and its associated pulsar wind nebula. From the
unabsorbed, 0.2-4 keV band X-ray luminosity of the pulsar wind nebula ($L_X\sim
4\times 10^{34} \rm ergs s^{-1}$), we infer a spin-down energy loss rate of
$\dot E \sim 7\times 10^{36} \rm ergs s^{-1}$ for the still undetected pulsar.
The pulsar candidate is $0.9^\prime$ from the geometric center of the SNR which
implies a transverse velocity of $\sim$$770 (D/4.8 {\rm kpc}) (t/1600 {\rm
yr})^{-1} \rm km s^{-1}$ assuming currently accepted values for the distance
and age of G292.0+1.8.


title: Ultra-Luminous Infrared Mergers: Elliptical Galaxies in Formation?

abstract:
  We report high quality near-infrared spectroscopy of 12 ultra-luminous
infrared galaxy mergers (ULIRGs). Our new VLT and Keck data provide ~0.5"
resolution, stellar and gas kinematics of these galaxies most of which are
compact systems in the last merger stages.
  We confirm that ULIRG mergers are 'ellipticals-in-formation'. Random motions
dominate their stellar dynamics, but significant rotation is common. Gas and
stellar dynamics are decoupled in most systems. ULIRGs fall on or near the
fundamental plane of hot stellar systems, and especially on its less evolution
sensitive, r(eff)-sigma projection. The ULIRG velocity dispersion distribution,
their location in the fundamental plane and their distribution of
v(rot)*sin(i)/sigma closely resemble those of intermediate mass (~L*),
elliptical galaxies with moderate rotation. As a group ULIRGs do not resemble
giant ellipticals with large cores and little rotation. Our results are in good
agreement with other recent studies indicating that disky ellipticals with
compact cores or cusps can form through dissipative mergers of gas rich, disk
galaxies while giant ellipticals with large cores have a different formation
history.


title:
A possible Universal Origin of Hadronic Cosmic Rays from
  Ultrarelativistic Ejecta of Bipolar Supernovae

abstract:
  Based on the ``cannonball model'' for gamma-ray bursts of Dar and De Rujula
it is proposed that masses of baryonic plasma (``cannonballs''), ejected in
bipolar supernova explosions in our Galaxy are the sources of hadronic Galactic
cosmic rays (CRs) at all energies. The propagation of the cannonballs in the
Galactic disk and halo is studied. Two mechanisms for the acceleration of the
observed CRs are proposed. The first is based on ultrarelativistic shocks in
the interstellar medium and could accelerate the bulk of CRs up to the ``knee''
energy of 4 x 10(15) eV. The second operates with second-order Fermi
acceleration within the cannonball. If the total initial energy of the ejected
plasmoids in a SN explosion is 10(53) ergs or higher this second mechanism may
explain the CR spectrum above the knee up to the highest observed energies. It
is shown that together with plausible assumptions about CR propagation in the
Galactic confinement volume the observed spectral indices of the CR spectrum
can be theoretically understood to first order. The model allows a natural
understanding of various basic CR observations like the absence of the
Greisen-Zatsepin cutoff, the anisotropy of arrival directions as function of
energy and the small Galactocentric gradient of the CR density.


title:
Accretion Disk Spectra of the Ultra-luminous Compact X-ray Sources in
  Nearby Galaxies and the Super-luminal Jet Sources

abstract:
  The Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and
the Galactic super-luminal jet sources share the common spectral characteristic
that they have extremely high disk temperatures which cannot be explained in
the framework of the standard accretion disk model in the Schwarzschild metric.
We examine several possibilities to solve this ``too-hot'' disk problem. In
particular, we have calculated an extreme Kerr disk model to fit the observed
spectra. We found that the Kerr disk will become significantly harder compared
to the Schwarzschild disk only when the disk is highly inclined. For
super-luminal jet sources, which are known to be inclined systems, the Kerr
disk model may work if we choose proper values for the black hole angular
momentum. For the ULXs, however, the Kerr disk interpretation will be
problematic, as it is highly unlikely that their accretion disks are
preferentially inclined.


title: The Case for Omega_M = 0.33 +/- 0.035

abstract:
  For decades, the determination of the mean density of matter(Omega_M) has
been tied to the distribution of light. This has led to a ``bias,'' perhaps as
large as a factor of 2, in determining a key cosmological parameter. Recent
measurements of the physical properties of clusters, cosmic microwave
background (CMB) anisotropy and the power spectrum of mass inhomogeneity now
allow a determination of Omega_M without ``visual bias.'' The early data lead
to a consistent picture of the matter and baryon densities, with Omega_B =
0.039 +/- 0.0075 and Omega_M = 0.33 +/- 0.035.


title: Photometric redshifts from reconstructed QSO templates

abstract:
  From SDSS commissioning photometric and spectroscopic data, we investigate
the utility of photometric redshift techniques to the task of estimating QSO
redshifts. We consider empirical methods (e.g. nearest-neighbor searches and
polynomial fitting), standard spectral template fitting and hybrid approaches
(i.e. training spectral templates from spectroscopic and photometric
observations of QSOs). We find that in all cases, due to the presence of strong
emission-lines within the QSO spectra, the nearest-neighbor and template
fitting methods are superior to the polynomial fitting approach. Applying a
novel reconstruction technique, we can, from the SDSS multicolor photometry,
reconstruct a statistical representation of the underlying SEDs of the SDSS
QSOs. Although, the reconstructed templates are based on only broadband
photometry the common emission lines present within the QSO spectra can be
recovered in the resulting spectral energy distributions. The technique should
be useful in searching for spectral differences among QSOs at a given redshift,
in searching for spectral evolution of QSOs, in comparing photometric redshifts
for objects beyond the SDSS spectroscopic sample with those in the well
calibrated photometric redshifts for objects brighter than 20th magnitude and
in searching for systematic and time variable effects in the SDSS broad band
photometric and spectral photometric calibrations.


title:
Proton synchrotron radiation of large-scale jets in active galactic
  nuclei

abstract:
  I propose a new mechanism for explanation of nonthernal X-ray emission of
large-scale AGN jets. Namely, I assume that this radiation has synchrotron
origin emitted by extremely high energy protons, and discuss implications of
this model for several prominent hot spots and knots resolved by Chandra in
Pictor A, 3C 120, PKS 0637-752, 3C 273.


title: Photometric Redshifts of Quasars

abstract:
  We demonstrate that the design of the Sloan Digital Sky Survey (SDSS) filter
system and the quality of the SDSS imaging data are sufficient for determining
accurate and precise photometric redshifts (``photo-z''s) of quasars. Using a
sample of 2625 quasars, we show that photo-z determination is even possible for
z<=2.2 despite the lack of a strong continuum break that robust photo-z
techniques normally require. We find that, using our empirical method on our
sample of objects known to be quasars, approximately 70% of the photometric
redshifts are correct to within delta z = 0.2; the fraction of correct
photometric redshifts is even better for z>3. The accuracy of quasar
photometric redshifts does not appear to be dependent upon magnitude to nearly
21st magnitude in i'. Careful calibration of the color-redshift relation to
21st magnitude may allow for the discovery of on the order of 10^6 quasars
candidates in addition to the 10^5 quasars that the SDSS will confirm
spectroscopically. We discuss the efficient selection of quasar candidates from
imaging data for use with the photometric redshift technique and the potential
scientific uses of a large sample of quasar candidates with photometric
redshifts.


title:
On the complex disc-corona interactions in the soft spectral states of
  Soft X-ray Transients

abstract:
  Accreting black holes show a complex and diverse behaviour in their soft
spectral states. Although these spectra are dominated by a soft, thermal
component which almost certainly arises from an accretion disc, there is also a
hard X-ray tail indicating that some fraction of the accretion power is instead
dissipated in hot, optically thin coronal material. During such states, best
observed in the early outburst of Soft X-ray Transients, the ratio of power
dissipated in the hot corona to that in the disc can vary from ~0 (pure disc
accretion) to ~1 (equal power in each). Here we present results of spectral
analyses of a number of sources, demonstrating the presence of complex features
in their energy spectra. Our main findings are: (1) the soft components are not
properly described by a thermal emission from accretion discs: they are
appreciably broader than can be described by disc blackbody models even
including relativistic effects, and (2) the spectral features near 5-9 keV
commonly seen in such spectra can be well described by reprocessing of hard
X-rays by optically thick, highly ionized, relativistically moving plasma.


title: The Globular Cluster Systems of Ellipticals and Spirals

abstract:
  In this overview of the key properties of globular cluster (GC) systems I
show that the GCs in elliptical and spiral host galaxies have more in common
than previously thought. After contrasting these properties I briefly comment
on GC formation.


title: Nature, Nurture or Not Sure? A Debate about SGRs and AXPs

abstract:
  Marsden, Lingenfelter, Rothschild & Higdon have given arguments against the
magnetar model for Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars
(AXPs), as forcefully advocated by R. Rothschild at this meeting. We critique
these arguments, showing: (1) The claim that SGRs and AXPs are born in
unusually dense regions of the ISM is not supported in any compelling way by
observations. (2) Even if this claim were true, it would not argue against the
magnetar model. Moreover, all observations can be accounted for if magnetars
have shorter observable lifetimes than do radiopulsars, in agreement with
theoretical expectations, but no systematically different ambient ISM
densities. (3) The suggestion that accretion onto the neutron star is directly
influenced by the ISM in a way that explains the difference between SGRs/AXPs
and radiopulsars, is not possible. The mass inflow rate during later stages of
supernova remnant expansion when accretion can be influenced by backpressure
from the ISM is many orders of magnitude too small. (4) Accretion-based models
are unable to account for the hyper-Eddington bursts and flares which are the
defining characteristic of SGRs. (5) Accretion disk models also predict optical
and IR emission with higher luminosities than are observed.


title:
Derivation of the Mass Distribution of Extrasolar Planets with MAXLIMA -
  a Maximum Likelihood Algorithm

abstract:
  We construct a maximum-likelihood algorithm - MAXLIMA, to derive the mass
distribution of the extrasolar planets when only the minimum masses are
observed. The algorithm derives the distribution by solving a numerically
stable set of equations, and does not need any iteration or smoothing. Based on
50 minimum masses, MAXLIMA yields a distribution which is approximately flat in
log M, and might rise slightly towards lower masses. The frequency drops off
very sharply when going to masses higher than 10 Jupiter masses, although we
suspect there is still a higher mass tail that extends up to probably 20
Jupiter masses. We estimate that 5% of the G stars in the solar neighborhood
have planets in the range of 1-10 Jupiter masses with periods shorter than 1500
days. For comparison we present the mass distribution of stellar companions in
the range of 100--1000 Jupiter masses, which is also approximately flat in log
M. The two populations are separated by the "brown-dwarf desert", a fact that
strongly supports the idea that these are two distinct populations. Accepting
this definite separation, we point out the conundrum concerning the
similarities between the period, eccentricity and even mass distribution of the
two populations.


title:
Investigating the central engine and excitation mechanisms of
  ultraluminous infrared galaxies: near infrared spectroscopy

abstract:
  We present NIR observations of a sample of mainly interacting ULIRGs,
comprising H and K band spectra. Our main aims are to investigate the power
source of these extremely luminous objects and the various excitation
mechanisms of the strong molecular hydrogen emission often seen in such
objects. Broadened emission lines were only detected in one object, IRAS 23498,
consistent with previous results for this galaxy. The [SiVI] emission line was
detected in IRAS17179 and IRAS20210, both classified as Sy2s. Two of the sample
were unclassified, IRAS00150 and IRAS23420, which exhibit neither [SiVI]
emission or broadened HI emission. However this does not rule out the presence
of an obscured AGN. Analysis of the molecular hydrogen emission showed that the
major excitation mechanism for most objects was thermal. Modelling of the more
luminous objects indicate for IRAS20210 10 per cent, and for both IRAS23365 and
IRAS23420, 30 per cent of their 1-0S(1) line emission has a non-thermal origin.


title: The AIRES system for air shower simulations. An update

abstract:
  A report on the characteristics of ultra-high energy air showers simulated
with the current version of the AIRES program is presented. The AIRES system
includes a fast simulating program, originally designed on the basis of the
well-known MOCCA program, and progressively improved and tested. The AIRES
algorithms are briefly described and some results coming from the simulations
are analyzed.


title: Gamma-Ray Spectral Variability of Cygnus X-1

abstract:
  We have used observations from CGRO to study the variation in the MeV
emission of Cygnus X-1 between its low and high X-ray states. These data
provide a measurement of the spectral variability above 1 MeV. The high state
MeV spectrum is found to be much harder than that of the low state MeV
spectrum. In particular, the power-law emission seen at hard X-ray energies in
the high state spectrum (with a photon spectral index of 2.6) is found to
extend out to at least 5 MeV, with no evidence for any cutoff. Here we present
the data and describe our efforts to model both the low state and high state
spectra using a hybrid thermal/nonthermal model in which the emission results
from the Comptonization of an electron population that consists of both a
thermal and nonthermal component.


title: Tests of Galactic Cosmic Ray Source Models

abstract:
  This report discusses the possibilities for observational tests of current
models and ideas regarding the origin of the Galactic Cosmic Rays using
facilities which are already available.


title: The Development of Coplanar CZT Detectors for Gamma-Ray Astronomy

abstract:
  The development of CdZnTe detectors with an orthogpnal coplanar anode
structure has important implications for future astrophysical instrumentation.
As electron-only devices, like pixel detectors, coplanar anode strip detectors
can be fabricated in the thickness required to be effective for photons with
energies in excess of 500 keV. Unlike conventional double-sided strip
detectors, the coplanar anode strip detectors require segmented contacts and
signal processing electronics on only one surface. This facilitates the
fabrication of closely-packed large area arrays that will be required for the
next generation of coded aperture imagers. These detectors provide both very
good energy resolution and sub-millimeter spatial resolution (in all three
spatial dimensions) with far fewer electronic channels than are required for
pixel detectors. Here we summarize results obtained from prototype detectors
having a thickness of 5 mm and outline a concept for large area applications.


title:
Signatures of Hierarchical Clustering in Dark Matter Detection
  Experiments

abstract:
  In the cold dark matter model of structure formation, galaxies are assembled
hierarchically from mergers and the accretion of subclumps. This process is
expected to leave residual substructure in the Galactic dark halo, including
partially disrupted clumps and their associated tidal debris. We develop a
model for such halo substructure and study its implications for dark matter
(WIMP and axion) detection experiments. We combine the Press-Schechter model
for the distribution of halo subclump masses with N-body simulations of the
evolution and disruption of individual clumps as they orbit through the
evolving Galaxy to derive the probability that the Earth is passing through a
subclump or stream of a given density. Our results suggest that it is likely
that the local complement of dark matter particles includes a 1-5% contribution
from a single clump. The implications for dark matter detection experiments are
significant, since the disrupted clump is composed of a `cold' flow of
high-velocity particles. We describe the distinctive features due to halo
clumps that would be seen in the energy and angular spectra of detection
experiments. The annual modulation of these features would have a different
signature and phase from that for a smooth halo and, in principle, would allow
one to discern the direction of motion of the clump relative to the Galactic
center.


title: Tidal Torques and Galactic Warps

abstract:
  We investigate the tilting and warping of galactic disks in response to tidal
torquing. The strength of the torque is determined from cosmological N-body
simulations. We find the tidal torques to be dominated by substructure in the
galactic halo, such as dwarf satellites, and by a misalignment between the disk
angular momentum and the figure axes of the dark matter halo. The radial
dependence of the torque can approximated by a power law of index -2.5. A
massless disk subjected to such a torque develops a trailing warp similar to
those seen in a large number of disk galaxies, i.e. the inner regions of the
disk tilt faster than the outer disk. In the case of massive disks, self
gravity causes the inner disk to stay locally flat and only the outer regions
show the signatures of warps. The radius outside of which a massive disk is
warped depends on the local surface density of the disk and on the product of
the strength of the torque and the exposure time to this torque.


title: A search for intergalactic HI gas in the NGC 1808 group of galaxies

abstract:
  A mosaic of six HI line observations with the Australia Telescope Compact
Array is used to search for intergalactic gas in the NGC 1808 group of
galaxies. Within the field of view of about 1.4 deg x 1.2 deg, no emission from
intergalactic HI gas is detected, either in the form of tidal plumes or tails,
intergalactic HI clouds, or as gas associated with tidal dwarf galaxies, with a
5-sigma limiting sensitivity of about 3x10^{18} cm^{-2} (or 1.4x10^7 M_sun at a
distance of 10.9 Mpc, for the given beam size of 127.9" x 77.3"). The HI data
of NGC 1792 and NGC 1808, with a velocity resolution of 6.6 km/s, confirm the
results of earlier VLA observations. Simultaneous wide-band 1.34 GHz continuum
observations also corroborate the results of earlier studies. However, the
continuum flux of NGC 1808 measured by us is almost 20% higher than reported
previously. No radio continuum emission was detected from the type Ia supernova
SN1993af in the north-eastern spiral arm of NGC 1808. A comparison of NGC 1792
and NGC 1808 shows that it is not primarily the total energy input that makes
the big difference between the starburst-related outflow in NGC 1808 and the
absence of such extraplanar features in NGC 1792, but the area over which the
energy released by stellar winds and supernovae is injected into the ISM.