title:
Nonlinear evolution of spherical perturbation in a non-flat Universe
  with cosmological constant

abstract:
  We generalize the spherical collapse model for the formation of bound objects
to apply in a Universe with arbitrary positive cosmological constant. We
calculate the critical condition for collapse of an overdense region and give
exact values of the characteristic densities and redshifts of its evolution.


title: Are granules good tracers of solar surface velocity fields?

abstract:
  Using a numerical simulation of compressible convection with radiative
transfer mimicking the solar photosphere, we compare the velocity field derived
from granule motions to the actual velocity field of the plasma. We thus test
the idea that granules may be used to trace large-scale velocity fields at the
sun's surface. Our results show that this is indeed the case provided the scale
separation is sufficient. We thus estimate that neither velocity fields at
scales less than 2500 km nor time evolution at scales shorter than 0.5 hr can
be faithfully described by granules. At larger scales the granular motions
correlate linearly with the underlying fluid motions with a slope of ~< 2
reaching correlation coefficients up to ~0.9.


title:
Accelerated Electrons in Cassiopeia A: Thermal and Electromagnetic
  Effects

abstract:
  We consider in more detail a model previously proposed for the hard X-ray
(>10 keV) emission observed from the supernova remnant Cas A, whereby electrons
are accelerated by lower-hybrid waves and radiate bremsstrahlung. We consider
both cold and thermal plasma limits of the modified two-stream instability that
generates the lower-hybrid waves, and by studying time dependent ionization
balance for various components of the Cas A ejecta and shocked circumstellar
medium, find locations within the shell where one or other of the instabilities
may occur. Either instability can be effective, with the cold plasma
instability imposing fewer constraints on the shocked reflected ion population
responsible for exciting the waves. The instability must be located in the
ejecta shocked at the earliest times and therefore closest to the contact
discontinuity where magnetic fields are expected to be the strongest. The
energy deposited in this ejecta by collisions between accelerated and ambient
electrons is broadly consistent with that required to reheat this ejecta to
observed temperatures.


title: The SuperCOSMOS Sky Survey. Paper I: Introduction and Description

abstract:
  In this, the first in a series of three papers concerning the SuperCOSMOS Sky
Survey (SSS), we give an introduction and user guide to the survey programme.
We briefly describe other wide-field surveys and compare with our own. We give
examples of the data, and make a comparison of the accuracies of the various
image parameters available with those from the other surveys providing similar
data; we show that the SSS database and interface offer advantages over these
surveys. Some science applications of the data are also described and some
limitations discussed. The series of three papers constitutes a comprehensive
description and user guide for the SSS.


title: The Quiescence of Dwarf Novae and X-ray Transients

abstract:
  Our understanding of the structure and properties of accretion disks in
quiescent Dwarf Novae and X-ray Transients is very limited. Observations during
quiescence challenge some of the standard Disk Instability Model (DIM)
predictions. Our ignorance of the nature of viscosity may be the main source of
uncertainties in quiescent disk models. A ``layered accretion'' alternative to
the DIM, in which accretion proceeds via X-ray ionized surface layers,
illustrates the magnitude of these uncertainties. A detection of molecular
hydrogen in quiescent disks may provide direct constraints on the nature of
viscosity.


title: Small Scale Anisotropies of UHECRs from Super-Heavy Halo Dark Matter

abstract:
  The decay of very heavy metastable relics of the Early Universe can produce
ultra-high energy cosmic rays (UHECRs) in the halo of our own Galaxy. In this
model, no Greisen-Zatsepin-Kuzmin cutoff is expected because of the short
propagation distances. We show here that, as a consequence of the hierarchical
build up of the halo, this scenario predicts the existence of small scale
anisotropies in the arrival directions of UHECRs, in addition to a large scale
anisotropy, known from previous studies. We also suggest some other observable
consequences of this scenario which will be testable with upcoming experiments,
as Auger, EUSO and OWL.


title:
Extending Lagrangian perturbation theory to a fluid with velocity
  dispersion

abstract:
  We formulate a perturbative approximation to gravitational instability, based
on Lagrangian hydrodynamics in Newtonian cosmology. We take account of
`pressure' effect of fluid, which is kinematically caused by velocity
dispersion, to aim hydrodynamical description beyond shell crossing. Master
equations in the Lagrangian description are derived and solved perturbatively
up to second order. Then, as an illustration, power spectra of density
fluctuations are computed in a one-dimensional model from the Lagrangian
approximations and Eulerian linear perturbation theory for comparison. We find
that the results by the Lagrangian approximations are different from those by
the Eulerian one in weakly non-linear regime at the scales smaller than the
Jeans length. We also show the validity of the perturbative Lagrangian
approximations by consulting difference between the first-order and the
second-order approximations.


title:
The SuperCOSMOS Sky Survey. Paper II: Image detection, parameterisation,
  classification and photometry

abstract:
  In this, the second in a series of three papers concerning the SuperCOSMOS
Sky Survey, we describe the methods for image detection, parameterisation,
classification and photometry. We demonstrate the internal and external
accuracy of our object parameters. Using examples from the first release of
data, the South Galactic Cap survey, we show that our image detection
completeness is close to 100% to within 1.5 mag of the nominal plate limits. We
show that for the Bj survey data, the image classification is externally > 99%
reliable to Bj = 19.5. Internally, the image classification is reliable at a
level of > 90% to Bj=21, R=19. The photometric accuracy of our data is
typically 0.3 mag with respect to external data for m > 15. Internally, the
relative photometric accuracy in restricted position and magnitude ranges can
be as accurate as 5% for well exposed stellar images. Colours (B-R or R-I) are
externally accurate to 0.07 mag at Bj = 16.5 rising to 0.16 mag at Bj = 20.


title: The SuperCOSMOS Sky Survey. Paper III: Astrometry

abstract:
  In this, the third in a series of three papers concerning the SuperCOSMOS Sky
Survey, we describe the astrometric properties of the database. We describe the
algorithms employed in the derivation of the astrometric parameters of the
data, and demonstrate their accuracies by comparison with external datasets
using the first release of data, the South Galactic Cap survey. We show that
the celestial coordinates, which are tied to the International Celestial
Reference Frame via the Tycho-2 reference catalogue, are accurate to better
than +/- 0.2 arcsec at J,R=19,18 rising to +/- 0.3 arcsec at J,R=22,21 with
positional dependent systematic effects from bright to faint magnitudes at the
+/- 0.1 arcsec level. The proper motion measurements are shown to be accurate
to typically +/- 10 mas/yr at J,R=19,18 rising to +/- 50 mas/yr at J,R=22,21
and are tied to zero using the extragalactic reference frame. We show that the
zeropoint errors in the proper motions are < 1 mas/yr for R > 17 and are no
larger than 10 mas/yr for R < 17 mas/yr.


title:
A Long-Wavelength View on Galaxy Evolution from Deep Surveys by the
  Infrared Space Observatory

abstract:
  We discuss the constraints set on galaxy evolution by data from deep surveys
performed in the mid-IR and far-IR with ISO and with mm telescopes at longer
wavelengths. These reveal extremely high rates of evolution for IR galaxies.
According to our model, the deep ISO surveys at 15 micron may have already
resolved more than 50% of the CIRB intensity, hence allowing to investigate the
origin of the CIRB. From our fits to the observed optical-IR SEDs, these
objects appear to involve massive galaxies hosting luminous starbursts (SFR 100
Mo/yr). Our evolutionary scheme considers a bimodal star formation (SF),
including long-lived quiescent SF, and enhanced SF taking place during
transient events recurrently triggered by interactions and merging. We
interpret the strong observed evolution as an increase with z of the rate of
interactions between galaxies (density evolution) and an increase of their IR
luminosity due to the more abundant fuel available in the past (luminosity
evolution). Very schematically, we associate the origin of the bulk of the
optical/NIR background to the quiescent evolution, while the CIRB is
interpreted as mostly due the dusty starburst phase (the latter possibly
leading to the formation of galaxy spheroids). The large energy contents in the
CIRB and optical backgrounds are not easily explained, considering the moderate
efficiency of energy generation by stars: a top-heavy stellar IMF associated
with the starburst phase (and compared with a more standard IMF during the
quiescent SF) would alleviate the problem. IR data suggest that the strong
observed evolution to z~1 should turn over at higher z: scenarios in which a
dominant fraction of stellar formation occurs at very high-z are not supported
by our analysis.


title: Microlensing planets in M22: free-floating or bound?

abstract:
  We use detailed numerical simulations and theoretical estimates to show that,
if confirmed, the unusually brief microlensing events observed by Sahu et al.
(2001) in the field of the globular cluster M22 might be explained as a result
of microlensing by a population of clustered MACHOs, a dark cluster or RAMBO,
not associated with the globular cluster. If real, this dark cluster would be
located between M22 and the Galactic bulge and could include at least $10^6$
substellar members with a typical size of 1-3 pc. Bound planets in wide or/and
eccentric orbits are also able to reproduce the observed microlensing
behaviour, but only if multiplanet systems (including large Kuiper-belt-like
objects) are abundant, although, our calculations argue against the latter
scenario as the ionization rate in M22 is very high. Dynamically ejected or
lone planets are, in principle, incompatible with the observational findings as
they either escape their parent cluster in a relatively short time-scale after
ejection or segregate toward the outskirts of the cluster. We discuss
additional implications of the dark cluster scenario, including the existence
of a population of RAMBOs toward the Galactic bulge.


title:
Interstellar gas in the Galaxy and the X-ray luminosity of Sgr A* in the
  recent past

abstract:
  Information about the X-ray luminosity of the supermassive black hole located
at the Galactic center (GC), Sgr A*, and its temporal variations in the past is
imprinted in the scattered emission observed today in the direction towards
giant molecular clouds (GMCs) located in our Galaxy. Due to light travel time
effects these clouds probe the activity of Sgr A* at different times in the
past depending on their position relative to the GC and the observer. In this
paper we combine results of recent ASCA observations along the Galactic plane,
providing upper limits for the scattered flux in the 4-10 keV range produced in
a given direction, with data from CO surveys of the same regions. These CO
surveys map the position and mass of the molecular gas which the GMCs are made
up of. Demanding the scattered flux to be not larger than the observed one,
this data enables us to derive upper limits for the 4-10 keV luminosity of Sgr
A* at certain times during the last 40.000 years down to about 8*10^40 erg/s.
At other times the limits are less tight, of the order of 10^41-10^42 erg/s.
The more extended and continuous HI distribution in the Galactic disk, which
also scatters the radiation emitted by Sgr A*, allows us to extend the time
coverage further into the past, back to about 110.000 years, albeit the limits
are becoming less tight. We thereby can rule out a long term X-ray activity
phase of Sgr A* at one per cent of its Eddington level ending less than about
80.000 years ago. The limits presented in this paper can be improved by
observations of emission in the fluorescent iron K_alpha-line. We study the
feasibility of these methods to investigate past nuclear activity in other
spiral galaxies observed with the angular resolution of X-ray telescopes like
Chandra and XMM-Newton.


title:
Non-Critical Liouville String Escapes Constraints on Generic Models of
  Quantum Gravity

abstract:
  It has recently been pointed out that generic models of quantum gravity must
contend with severe phenomenological constraints imposed by gravitational
Cerenkov radiation, neutrino oscillations and the cosmic microwave background
radiation. We show how the non-critical Liouville-string model of quantum
gravity we have proposed escapes these constraints. It gives energetic
particles subluminal velocities, obviating the danger of gravitational Cerenkov
radiation. The effect on neutrino propagation is naturally flavour-independent,
obviating any impact on oscillation phenomenology. Deviations from the expected
black-body spectrum and the effects of time delays and stochastic fluctuations
in the propagation of cosmic microwave background photons are negligible, as
are their effects on observable spectral lines from high-redshift astrophysical
objects.


title: Resolving Microlens Blends Using Image Subtraction

abstract:
  Blended light is an important source of degeneracy in the characterization of
microlensing events, particularly in binary-lens and high magnification events.
We show how the techniques of image subtraction can be applied to form an image
of the blend with the source removed. In many cases, it should be possible to
construct images with very high signal-to-noise ratio. Analysis of these images
can help distinguish between competing models that have different blend
fractions, and in some cases should allow direct detection of the lens.


title: The Role of Active Regions in the Generation of Torsional Oscillations

abstract:
  We present a model for torsional oscillations where the inhibiting effect of
active region magnetic fields on turbulence locally reduces turbulent viscous
torques, leading to a cycle- and latitude-dependent modulation of the
differential rotation. The observed depth dependence of torsional oscillations
as well as their phase relationship with the sunspot butterfly diagram are
reproduced quite naturally in this model. The resulting oscillation amplitudes
are significantly smaller than observed, though they depend rather sensitively
on model details. Meridional circulation is found to have only a weak effect on
the oscillation pattern.


title: How Did Globular Clusters Form?

abstract:
  It is suggested that there have been at least two physically distinct epochs
of massive cluster formation. The first generation of globular clusters may
have formed as halo gas was compressed by shocks driven inward by ionization
fronts generated during cosmic reionization at z ~ 6. On the other hand a
second generation of massive clusters might have been formed at later times by
compression, and subsequent collapse, of giant molecular clouds. In some cases
this compression may have been triggered by heating of the interstellar medium
via collisions between gas-rich disk galaxies. It is also suggested that the
present specific globular cluster frequency in galaxies was mainly determined
by the peak rate of star creation, with elevated peak rates of star formation
per unit area resulting in high present specific globular cluster frequencies.


title: BVRI Photometry of Supernovae

abstract:
  We present optical photometry of one Type IIn supernova (1994Y) and nine Type
Ia supernovae (1993Y, 1993Z, 1993ae, 1994B, 1994C, 1994M, 1994Q, 1994ae, and
1995D). SN 1993Y and SN 1993Z appear to be normal SN Ia events with similar
rates of decline, but we do not have data near maximum brightness. The colors
of SN 1994C suggest that it suffers from significant reddening or is
intrinsically red. The light curves of SN 1994Y are complicated; they show a
slow rise and gradual decline near maximum brightness in $VRI$ and numerous
changes in the decline rates at later times. SN 1994Y also demonstrates color
evolution similar to that of the SN IIn 1988Z, but it is slightly more luminous
and declines more rapidly than SN 1988Z. The behavior of SN1994Y indicates a
small ejecta mass and a gradual strengthening of the H$\alpha$ emission
relative to the continuum.


title: Kolmogorov-Burgers Model for Star Forming Turbulence

abstract:
  The process of star formation in interstellar molecular clouds is believed to
be controlled by driven supersonic magnetohydrodynamic turbulence. We suggest
that in the inertial range such turbulence obeys the Kolmogorov law, while in
the dissipative range it behaves as Burgers turbulence developing shock
singularities. On the base of the She-Leveque analytical model we then predict
the velocity power spectrum in the inertial range to be E_k ~ k^{-1.74}. This
result reproduces the observational Larson law, <u^2_l>~ l^{0.74...0.76},
[Larson, MNRAS 194 (1981) 809] and agrees well with recent numerical findings
by Padoan and Nordlund [astro-ph/0011465]. The application of the model to more
general dissipative structures, with higher fractal dimensionality, leads to
better agreement with recent observational results.

categories: astro-ph cond-mat nlin.CD physics.flu-dyn


title: Interpreting the M22 Spike Events

abstract:
  Recently Sahu et al., using the Hubble Space Telescope to monitor stars in
the direction of the old globular cluster M22, detected six events in which
otherwise constant stars brightened by ~50% during a time of <1 day. They
tentatively interpret these unresolved events as due to microlensing of
background bulge stars by free-floating planets in M22. I show that if these
spike events are due to microlensing, the lensing objects are unlikely to be
associated with M22, and unlikely to be part of a smoothly distributed Galactic
population. Thus either there happens to be a massive, dark cluster of planets
along our line-of-sight to M22, or the spike events are not due to
microlensing. The lensing planets cannot be bound to stars in the core of M22:
if they were closer than 8 AU, the lensing influence of the parent star would
have been detectable. Moreover, in the core of M22, all planets with
separations > 1 AU would have been ionized by random stellar encounters. Most
unbound planets would have escaped the core via evaporation which
preferentially affects such low-mass objects. Bound or free-floating planets
can exist in the outer halo of M22; however, for reasonable assumptions, the
maximum optical depth to such a population falls short of the observed optical
depth, tau ~ 3x10^{-6}, by a factor of 5-10. Therefore, if real, these events
represent the detection of a significant free-floating Galactic planet
population. The optical depth to these planets is comparable to and mutually
exclusive from the optical depth to resolved events measured by microlensing
survey collaborations toward the bulge, and thus implies a similar additional
mass of lensing objects. Such a population is difficult to reconcile with both
theory and observations.


title: The Consequences of the Cosmic Star-Formation Rate: X-ray Number Counts

abstract:
  We discuss the observable consequences for the detection of galaxies in the
X-ray bandpass resulting from a peak in the cosmic star-formation rate at a
redshift > 1. Following White & Ghosh, we assume a large evolution in the
X-ray/B luminosity ratio at z ~ 0.5-1.5 resulting from the X-ray binaries that
have evolved from stars formed at z > 1-2. Using the HDF-N redshift survey data
and the locally observed X-ray/B luminosity ratio as a guide, we estimate a
median X-ray flux (2-10 keV) on the order of 8 x 10^-18 ergs/s/cm^2 for
galaxies in the HDF-N, which is consistent with a signal derived from a
stacking analysis of the HDF-N Chandra data by Brandt et al. (2001). We also
predict the number counts in deep X-ray surveys expected from normal galaxies
at high redshift.


title:
The Decline of the Source Population of Gamma-Ray Bursts and Their
  Luminosity Function

abstract:
  The source population of gamma-ray bursts (GRBs) declines towards the present
epoch being consistent with the measured decline of the star formation rate. We
show this using the brightness distribution of 3255 long BATSE GRBs found in an
off-line scan of the BATSE continuous 1.024 s count rate records. The
significance of this conclusion is enhanced by the detection of three GRBs with
known redshifts brighter than 10^{52} erg/s during the last two years. This is
an argument in favor of the generally believed idea that GRBs are strongly
correlated with the star production, at least on cosmological time scales, and
favors the association of long GRBs with collapses of supermassive stars.
However, we still cannot rule out neutron star mergers if the typical delay
time for binary system evolution is relatively short. If we assume a steep
decline of the GRB population at z>1.5, then their luminosity function can be
clearly outlined. The luminosity function is close to a power law, dN/dL ~
L^{-1.4}, for low luminosities over at least 1.7 orders of magnitude. Then the
luminosity function breaks to a steeper slope or to an exponential decline
around L = 3*10^{51} erg/s in the 50-300 keV range assuming isotropic emission.


title:
Velocity distribution of high-energy particles and the solar neutrino
  problem

abstract:
  High energy infers high velocity and high velocity is a concept of special
relativity. The Maxwellian velocity distribution is corrected to be consistent
with special relativity. The corrected distribution reduces to the Maxwellian
distribution for small velocities, contains a relatively depleted high-energy
tail and vanishes at the velocity of light. This corrected distribution will
lower solar neutrino fluxes and change solar neutrino energy spectra but keep
solar sound speeds.


title:
Cosmic Ray Electrons in Groups and Clusters of Galaxies: Primary and
  Secondary Populations from a Numerical Cosmological Simulation

abstract:
  We study the generation and distribution of high energy electrons in cosmic
environment and their observational consequences by carrying out the first
cosmological simulation that includes directly cosmic ray (CR) particles.
Starting from cosmological initial conditions we follow the evolution of
primary and secondary electrons (CRE), CR ions (CRI) and a passive magnetic
field. CRIs and primary CREs are injected and accelerated at large scale
structure shocks. Secondary CREs are continuously generated through inelastic
p-p collisions. We include spatial transport, adiabatic expansion/compression,
Coulomb collisions, bremsstrahlung, synchrotron (SE)and inverse Compton (IC)
emission. We find that, from the perspective of cosmic shock energy and
acceleration efficiency, the few detections of hard X-ray radiation excess
could be explained in the framework of IC emission of primary CREs in clusters
undergoing high accretion/merger phase. Instead, IC emission from both primary
and secondary CREs accounts at most for a small fraction of the radiation
excesses detected in the extreme-UV (except for the Coma cluster as reported by
Bowyer et al.1999). Next, we calculate the SE after normalizing the magnetic
field so that for a Coma-like cluster <B^2>^1/2~3 \muG. Our results indicate
that the SE from secondary CREs reproduces several general properties of radio
halos, including the recently found P_1.4GHz vs T relation, the morphology and
polarization of the emitting region and, to some extent, the spectral index.
Moreover, SE from primary CREs turns out sufficient to power extended regions
resembling radio relics observed at the outskirts of clusters. Again we find
striking resemblance between morphology, polarization and spectral index of our
synthetic maps and those reported in the literature.


title: Eliminating the Coriols Effect in Liquid Mirrors

abstract:
  If uncorrected, the Coriolis force due to the rotation of the Earth causes
significant aberration of images produced by large liquid-mirror telescopes. We
show that this problem can be eliminated by a fixed compensating tilt of the
liquid-mirror rotation axis. The required tilt angle, which is a function of
latitude and mirror rotation rate, is of order 10 arcsec for current
telescopes. This result removes the last fundamental obstacle to achieving
diffraction-limited performance with large liquid mirrors.


title:
Effects of Heavy Elements and Excited States in the Equation of State of
  the Solar Interior

abstract:
  Although 98% of the solar material consists of hydrogen and helium, the
remaining chemical elements contribute in a discernible way to the
thermodynamic quantities. The contribution of various heavy elements in a set
of thermodynamic quantities has been examined. It has emerged that prominent
signatures of individual elements exist, and that these effects are greatest in
the ionization zones, typically located near the bottom of the convection zone.
The main result is that part of the features found here depend strongly both on
the given species (atom or ion) and its detailed internal partition function,
whereas other features only depend on the presence of the species itself, not
on details such as the internal partition function. The latter features are
obviously well suited for a helioseismic abundance determination, while the
former features present a unique opportunity to use the sun as a laboratory to
test the validity of physical theories of partial ionization in a relatively
dense and hot plasma. This domain of plasma physics has so far no competition
from terrestrial laboratories. [shortened version of original abstract]


title: Cluster Morphologies as a Test of Different Cosmological Models

abstract:
  We investigate how cluster morphology is affected by the cosmological
constant in low-density universes. Using high-resolution cosmological
N-body/SPH simulations of flat (\Omega_0 = 0.3, \lambda_0 = 0.7, \Lambda CDM)
and open (\Omega_0 = 0.3, \lambda_0 = 0, OCDM) cold dark matter universes, we
calculate statistical indicators to quantify the irregularity of the cluster
morphologies. We study axial ratios, center shifts, cluster clumpiness, and
multipole moment power ratios as indicators for the simulated clusters at z=0
and 0.5. Some of these indicators are calculated for both the X-ray surface
brightness and projected mass distributions. In \Lambda CDM all these
indicators tend to be larger than those in OCDM at z=0. This result is
consistent with the analytical prediction of Richstone, Loeb, & Turner, that
is, clusters in \Lambda CDM are formed later than in OCDM, and have more
substructure at z=0. We make a Kolmogorov-Smirnov test on each indicator for
these two models. We then find that the results for the multipole moment power
ratios and the center shifts for the X-ray surface brightness are under the
significance level (5%). We results also show that these two cosmological
models can be distinguished more clearly at z=0 than z = 0.5 by these
indicators.


title:
Positional Coincidence between the High-latitude Steady Unidentified
  Gamma-ray Sources and Possibly Merging Clusters of Galaxies

abstract:
  We report an evidence for the first time that merging clusters of galaxies
are a promising candidate for the origin of high galactic-latitude, steady
unidentified EGRET gamma-ray sources. Instead of using past optical catalogs of
eye-selected clusters, we made a matched-filter survey of galaxy clusters over
$4\arcdeg \times 4\arcdeg$ areas around seven steady unidentified EGRET sources
at $|b|>45\arcdeg$ together with a 100 $\sq \arcdeg$ area near the South
Galactic Pole as a control field. In total, 154 Abell-like cluster candidates
and 18 close pairs/groups of these clusters, expected to be possibly merging
clusters, were identified within estimated redshift $z_{est}\leq 0.15$. Five
among the seven EGRET sources have one or two cluster pairs/groups (CPGs)
within 1$\arcdeg$ from them. We assess the statistical significance of this
result by several methods, and the confidence level of the real excess is
maximally 99.8% and 97.8% in a conservative method. In contrast, we found no
significant correlation with single clusters. In addition to the spatial
correlation, we also found that the richness of CPGs associated with EGRET
sources is considerably larger than those of CPGs in the control field. These
results imply that a part of the steady unidentified EGRET sources at
high-latitude are physically associated with close CPGs, not with single
clusters. We also discuss possible interpretations of these results. We argue
that, if these associations are real, they are difficult to explain by hadronic
processes, but best explained by the inverse-Compton scattering by high energy
electrons accelerated in shocks of cluster formation, as recently proposed.


title:
Variability Time Scales of TeV Blazars Observed in the ASCA Continuous
  Long-Look X-ray Monitoring

abstract:
  Three uninterrupted, long (lasting respectively 7, 10, and 10 days) ASCA
observations of the well-studied TeV-bright blazars Mrk 421, Mrk 501 and PKS
2155-304 all show continuous strong X-ray flaring. Despite the relatively faint
intensity states in 2 of the 3 sources, there was no identifiable quiescent
period in any of the observations. Structure function analysis shows that all
blazars have a characteristic time scale of ~ a day, comparable to the
recurrence time and to the time scale of the stronger flares. On the other
hand, examination of these flares in more detail reveals that each of the
strong flares is not a smooth increase and decrease, but exhibits substructures
of shorter flares having time scales of ~10 ks. We verify via simulations that
in order to explain the observed structure function, these shorter flares
("shots") are unlikely to be fully random, but in some way are correlated with
each other. The energy dependent cross-correlation analysis shows that
inter-band lags are not universal in TeV blazars. This is important since in
the past, only positive detections of lags were reported. In this work, we
determine that the sign of a lag may differ from flare to flare; significant
lags of both signs were detected from several flares, while no significant lag
was detected from others. However, we also argue that the nature of the
underlying component can affect these values. The facts that all flares are
nearly symmetric and that fast variability shorter than the characteristic time
scale is strongly suppressed, support the scenario where the light crossing
time dominates the variability time scales of the day-scale flares.


title:
Detecting TeV Gamma Rays from Gamma Ray Bursts by Ground Based Muon
  Detectors

abstract:
  The possibility of detecting Gamma-Ray Bursts (GRB) in TeV energy range using
large area muon detectors like AMANDA and Lake Baikal detector is examined.
These detectors can detect TeV energy photons by detecting the secondary muons
created by the TeV photons in the Earth's atmosphere. We calculate the expected
number of muons and the signal to square root of noise ratios in these
detectors due to TeV gamma-rays from individual GRBs for various assumption on
their luminosity, distance from the observer (redshift), gamma-ray integral
spectral index, maximum energy cutoff of the photon spectrum and duration
including the effect of the absorption of TeV photons in the intergalactic
infrared radiation background. We also calculate the expected rate of
detectable TeV-GRB events in these detectors using a recent determination of
the luminosity and redshift distributions of GRBs in the Universe.


title:
Optical Gravitational Lensing Experiment. OGLE-1999-BUL-32: the Longest
  Ever Microlensing Event -- Evidence for a Stellar Mass Black Hole?

abstract:
  We describe the discovery of the longest microlensing event ever observed,
OGLE-1999-BUL-32, also independently identified by the MACHO collaboration as
MACHO-99-BLG-22. This unique event has an Einstein radius crossing time of 641
days. The high quality data obtained with difference image analysis shows a
small but significant parallax signature. This parallax effect allows one to
determine the Einstein radius projected onto the observer plane as rE^hat ~
29.2AU. The transverse velocity projected onto the observer plane is about
79km/s. We argue that the lens is likely to be have a mass of at least a few
solar masses, i.e., it could be a stellar black hole. The black hole hypothesis
can be tested using the astrometric microlensing signature with the soon-to-be
installed Advanced Camera for Surveys on board the Hubble Space Telescope. Deep
X-ray and radio images may also be useful for revealing the nature of the
object.


title:
The FIR/Radio correlation of high redshift glaxies in the region of the
  HDF-N

abstract:
  The correlation between the far-infrared (FIR) and radio emission is well
established for nearby star forming galaxies. Many applications, in particular
the radio-to-submm spectral index redshift indicator, tacitly assume that the
relation holds well beyond our local neighbourhood, to systems located at
cosmological distances. In order to test this assumption I have constructed a
sample of 22 HDF-N galaxies, all with measured spectroscopic redshifts, and all
detected by both ISO and the WSRT at 15 micron and 1.4 GHz respectively. The
galaxies span a wide range of redshift with a median value of z ~ 0.7. The ISO
15 micron data were k-corrected and extrapolated to the FIR (60 and 100 micron)
by assuming a starburst (M82) spectral energy distribution (SED) for the entire
sample. An initial analysis of the data suggests that the correlation between
the FIR and the radio emission continues to apply at high redshift with no
obvious indication that it fails to apply beyond z ~ 1.3. The sample is
``contaminated'' by at least 1 distant (z=4.4), radio-loud AGN, VLA
J123642+621331. This source has recently been detected by the first deep field
VLBI observations of the HDF-N and is clearly identified as an ``outlier'' in
the FIR/radio correlation. I briefly comment on the impact upgraded and next
generation radio instruments (such as e-MERLIN and the Square Km Array) can
have in studies of star formation in the early Universe.


title:
On the detectability of gravitational waves background produced by gamma
  ray bursts

abstract:
  In this paper we discuss a new strategy for the detection of gravitational
radiation likely emitted by cosmological gamma ray burst. Robust and
conservative estimates lead to the conclusion that the uncorrelated
superimposition of bursts of gravitational waves can be detected by
interferometric detectors like VIRGO or LIGO. The expected signal is predicted
to carry two very distinctive signatures: the cosmological dipole anisotropy
and a characteristic time scale in the auto correlation spectrum, which might
be exploited, perhaps with ad hoc modifications and/or upgrading of the planned
experiments, to confirm the non-instrumental origin of the signal.


title: Fast Parameter Estimation from the CMB Power Spectrum

abstract:
  The statistical properties of a map of the primary fluctuations in the cosmic
microwave background (CMB) may be specified to high accuracy by a few thousand
power spectra measurements, provided the fluctuations are gaussian, yet the
number of parameters relevant for the CMB is probably no more than about 10-20.
There is consequently a large degree of redundancy in the power spectrum data.
In this paper, we show that the MOPED data compression technique can reduce the
CMB power spectrum measurements to about 10-20 numbers (one for each
parameter), from which the cosmological parameters can be estimated virtually
as accurately as from the complete power spectrum. This offers opportunities
for very fast parameter estimation from real and simulated CMB skies, with
accurate likelihood calculations at Planck resolution being speeded up by a
factor of around five hundred million.


title: The Electron Temperature and 44Ti Decay Rate in Cassiopeia A

abstract:
  The effects of plasma elemental composition and ionization state on the
effective decay rate of 44Ti are investigated. We essentially follow the
methods of the first authors to treat this topic, Mochizuki et al., but use
more realistic plasma models, including radiative cooling, to compute the
evolution of the charge state distribution behind the reverse shock. For
uniform density ejecta (i.e. no clumps or bubbles) we find a negligible change
to the decay rate of 44Ti. We discuss the effects of non-uniform ejecta. We
also briefly consider the effects on these calculations of collisionless
electron heating associated with weak secondary shocks propagating throughout
the Cas A shell as a result of foward or reverse shock encounters with density
inhomogeneities, recently suggested as an explanation for the hard X-ray tail
seen in BeppoSAX and RXTE/OSSE spectra.


title: Mid Infrared Polarisation of Ultraluminous Infrared Galaxies

abstract:
  The mid infrared polarisation properties of four Ultraluminous Infrared
Galaxies (ULIRGs) have been investigated by broad band filter observations with
the ISOCAM instrument on board the Infrared Space Observatory (ISO). The
wavelength region from 5 to 18 mic. was selected where the emission from the
putative torus peaks. We report detection of polarisation for all ULIRGs
studied. The fractional polarisation ranges from about 3% up to 8%. The highest
polarisation is recorded in Mrk231 which has a clear AGN signature, whereas the
lowest is for Arp220, which is generally thought to be powered predominantly by
star formation. We discuss the various mechanisms that could give rise to the
polarisation and conclude that the most likely interpretation is that it is due
to magnetically aligned elongated dust grains. This is the same mechanism
believed to be operating in a number of galactic sources. The position angle of
polarisation could give the projected magnetic field direction and therefore
constrain models for the formation of the tori.


title: CROMOS: A cryogenic near-infrared, multi-object spectrometer for the VLT

abstract:
  We discuss a cryogenic, multi-object near-infrared spectrometer as a second
generation instrument for the VLT. The spectrometer combines 20 to 40
independent integral eld units (IFUs), which can be positioned by a cryogenic
robot over the entire unvignetted eld of the VLT (~7'). Each IFU consists of a
contiguous cluster of 20 to 30 pixels (0.15 to 0.25" per pixel). The individual
IFUs have cold fore-optics and couple into the spectrograph with integrated
bers-microlenses. The spectrometer has lambda/d-lambda~4000 and simultaneously
covers the J-, H-, and K-bands with three HAWAII 2 detectors. The system is
designed for operation both in seeing limited and MCAO modes. Its speed is
approximately 3500 times greater than that of ISAAC and 60 times greater than
NIRMOS (in H-band). The proposed instrument aims at a wide range of science,
ranging from studies of galaxies/clusters in the high-z Universe (dynamics and
star formation in z>1 galaxies, evolution of ellipticals, properties of
distant, obscured far-IR and X-ray sources), to investigations of nearby
starbursts, star clusters and properties of young low mass stars and brown
dwarfs.


title: Dark matter and galactic halos - a quantum approach

abstract:
  Traditional quantum theory can be used to construct hypothetical very
large-scale gravitational stationary state structures from traditionally stable
atoms and subatomic particles. These so called "gravitational
macro-eigenstructures" have potential to explain the composition of
extra-galactic dark matter and galactic halos. It is shown that the eigenstates
within these structures can have radiative and stimulated lifetimes that are
longer than the age of the universe, and also that they cannot be easily
transformed or "destroyed" by many conventional galactic processes. Because of
the unique nature of stationary states, it is shown that gravitational
eigenstructures have the potential to remain largely undetected, provided
certain conditions are met. Speculatively, it is suggested that they could
provide a mechanism for the origin of high-energy cosmic rays, and also that,
if these hypothetical structures have been present from an early time in the
history of the universe, then they could have influenced the large- scale
structure of the universe.

categories: astro-ph math-ph math.MP physics.space-ph quant-ph


title: Sunyaev-Zel'dovich Effect and Morphology of Galaxy Clusters

abstract:
  We investigate the influence of the finite extension and the aspherical
geometry of a galaxy cluster on the estimate of the Hubble constant through the
Sunyaev-Zel'dovich effect. An analysis of a recent CHANDRA image of the galaxy
cluster RBS797 indicates a strong ellipticity and thus a pronounced aspherical
geometry. We estimate the total mass of RBS797 assuming spherical or
ellipsoidal geometry and show that in the latter case the mass is about 10-17 %
less than the one inferred for a spherical shape.


title: Excess GeV radiation and cosmic ray origin

abstract:
  Recent EGRET observations of the diffuse Galactic gamma-ray emission reveal a
spectrum which is incompatible with the assumption that the cosmic ray spectra
measured locally hold throughout the Galaxy: the spectrum above 1 GeV, where
the emission is supposedly dominated by pi^0-decay, is harder than that derived
from the local cosmic ray proton spectrum.
  We demonstrate that in case of a SNR origin of cosmic ray nucleons part of
this gamma-ray excess may be attributed to the dispersion of the spectral
indices in these objects. In global averages, as are gamma-ray line-of-sight
integrals, this dispersion leads to a positive curvature in the composite
spectrum, and hence to modified pi^0-decay gamma-ray spectra.


title: Nova-induced mass transfer variations

abstract:
  We investigate variations of the mass transfer rate in cataclysmic variables
(CVs) that are induced by nova outbursts. The ejection of nova shells leads to
a spread of transfer rates in systems with similar orbital period. The effect
is maximal if the specific angular momentum in the shell is the same as the
specific orbital angular momentum of the white dwarf. We show analytically that
in this case the nova-induced widening of the mass transfer rate distribution
can be significant if the system, in the absence of nova outbursts, is close to
mass transfer instability (i.e., within a factor of ~1.5 of the critical mass
ratio). Hence the effect is negligible below the period gap and for systems
with high-mass white dwarfs. At orbital periods between about 3 and 6 hrs the
width of the mass transfer rate distribution exceeds an order of magnitude if
the mass accreted on the white dwarf prior to the runaway is larger than a few
10^{-4} M_sun. At a given orbital period in this range, systems with the
highest transfer rate should on average have the largest ratio of donor to
white dwarf mass. We show results of population synthesis models which confirm
and augment the analytic results.


title: Possible 38 day X-ray period of KS1731-260

abstract:
  We report the detection of a 38 day period in the X-ray flux of the transient
burster KS1731-260. The narrow peak of periodicity was detected during ~TJD
10150--11050 when the source had a high and relatively stable X-ray flux. After
\~TJD 11100 the source became strongly variable on a time scale of months that
contaminates the search for the 38 day periodicity. The detected period can not
be a binary period. The binary with Roche lobe overflow has in this case large
radii of the secondary and of the accretion disk. Disk and secondary star
illumination by X-ray flux from luminous neutron star would lead to high
infrared brightness of the binary. That clearly contradicts the infrared data
even for the brightest infrared sources within CHANDRA error box of KS1731-260.
Remaining possibility is that observed periodicity is connected with the
accretion disk precession, similar to that was observed for SS 433, Her X-1,
Cyg X-1 etc.


title:
Iron K-alpha Emission from X-ray Reflection: Predictions for Gamma-Ray
  Burst Models

abstract:
  Recent observations of several gamma-ray burst (GRB) afterglows have shown
evidence for a large amount of X-ray line emitting material, possibly arising
from ionized iron. A significant detection of an X-ray spectral feature, such
as that found in the Chandra observation of GRB 991216, may provide important
constraints on the immediate environment of the burst and hence on progenitor
models. The large Fe K-alpha equivalent widths inferred from the X-ray
observations favor models in which the line is produced when the primary X-ray
emission from the source strikes Thomson-thick material and Compton scatters
into our line of sight. We present such reflection spectra here, computed in a
fully self-consistent manner, and discuss the range of ionization parameters
that may be relevant to different models of GRBs. We argue that the presence of
a strong hydrogen-like K-alpha line is unlikely, because Fe-XXVI photons would
be trapped resonantly and removed from the line core by Compton scattering. In
contrast, a strong narrow emission line from He-like Fe-XXV is prominent in the
model spectra. We briefly discuss how these constraints may affect the line
energy determination in GRB 991216.


title: Optimal Moments for the Analysis of Peculiar Velocity Surveys

abstract:
  We present a new method for the analysis of peculiar velocity surveys which
removes contributions to velocities from small scale, nonlinear velocity modes
while retaining information about large scale motions. Our method utilizes
Karhunen--Lo\`eve methods of data compression to construct a set of moments out
of the velocities which are minimally sensitive to small scale power. The set
of moments are then used in a likelihood analysis. We develop criteria for the
selection of moments, as well as a statistic to quantify the overall
sensitivity of a set of moments to small scale power. Although we discuss our
method in the context of peculiar velocity surveys, it may also prove useful in
other situations where data filtering is required.


title: Regular and chaotic motion in softened gravitational systems

abstract:
  The stability of the dynamical trajectories of softened spherical
gravitational systems is examined, both in the case of the full $N$-body
problem and that of trajectories moving in the gravitational field of
non-interacting background particles. In the latter case, for $N \ge 10000$,
some trajectories, even if unstable, had exceedingly long diffusion times,
which correlated with the characteristic e-folding timescale of the
instability. For trajectories of $N \approx 100000$ systems this timescale
could be arbitrarily large --- and thus appear to correspond to regular orbits.
For centrally concentrated systems, low angular momentum trajectories were
found to be systematically more unstable. This phenomenon is analogous to the
well known case of trajectories in generic centrally concentrated non-spherical
smooth systems, where eccentric trajectories are found to be chaotic. The
exponentiation times also correlate with the conservation of the angular
momenta along the trajectories. For $N$ up to a few hundred, the instability
timescales of $N$-body systems and their variation with particle number are
similar to those of the most chaotic trajectories in inhomogeneous
non-interacting systems. For larger $N$ (up to a few thousand) the values of
the these timescales were found to saturate, increasing significantly more
slowly with $N$. We attribute this to collective effects in the fully
self-gravitating problem, which are apparent in the time-variations of the time
dependent Liapunov exponents. The results presented here go some way towards
resolving the long standing apparent paradoxes concerning the local instability
of trajectories of gravitational systems (abridged).


title: Shaping the central structure in CDM halos

abstract:
  Coupling the dark matter (DM) and baryonic components in galaxies via
dynamical friction (by allowing the latter to be clumpy) leads to energy input
into the DM. The resulting expanding tendency in the DM component overcomes the
competing effect of adiabatic contraction, resulting from the shrinking gas
component, and leads to a nearly constant density core. The baryonic mass
inflow also leads to the coupling of the structure at the kpc scale and below
and that of the structure of the DM at the 10 kpc scale and above, with rate of
mass inflow being dependent on the initial halo central concentration. The
latter also determines the final halo core radius.


title:
Polarimetric variations of binary stars. III Periodic polarimetric
  variations of the Herbig Ae/Be star MWC 1080

abstract:
  We present polarimetric observations of a massive pre-main sequence
short-period binary star of the Herbig Ae/Be type, MWC 1080. The mean
polarization at 7660 A is 1.60% at 81.6 deg, or 0.6% at 139 deg if an estimate
of the interstellar polarization is subtracted. The intrinsic polarization
points to an asymmetric geometry of the circumstellar or circumbinary
environment while the 139 deg intrinsic position angle traces the axis of
symmetry of the system and is perpendicular to the position angle of the
outflow cavity. The polarization and its position angle are clearly variable,
at all wavelengths, and on time scales of hours, days, months, and years.
Stochastic variability is accompanied by periodic variations caused by the
orbital motion of the stars in their dusty environment. These periodic
polarimetric variations are the first phased-locked ones detected for a
pre-main sequence binary. The variations are not simply double-periodic (seen
twice per orbit) but include single-periodic (seen once per orbit) and
higher-order variations. The presence of single-periodic variations could be
due to non equal mass stars, the presence of dust grains, an asymmetric
configuration of the circumstellar or circumbinary material, or the
eccentricity of the orbit. MWC 1080 is an eclipsing binary with primary and
secondary eclipses occurring at phases 0.0 and 0.55. The signatures of the
eclipses are seen in the polarimetric observations.


title:
Pre-heating the ICM in high resolution simulations: the effect on the
  gas entropy

abstract:
  We present results from high-resolution Tree+SPH simulations of galaxy
clusters and groups, aimed at studying the effect of non-gravitational heating
on the entropy of the ICM. We simulate three systems, having emission-weighted
temperature T=0.6,1 and 3 keV, with spatial resolution better than 1% of the
virial radius. We consider the effect of different prescriptions for
non-gravitational ICM heating, such as SN energy feedback, as predicted by
semi-analytical models of galaxy formation, and two different minimum entropy
floors, S_fl=50 and 100 keV cm^2, imposed at z=3. Simulations with only
gravitational heating nicely reproduce predictions from self-similar ICM
models, while extra heating is shown to break the self-similarity, by a degree
which depends on total injected energy and on cluster mass. We use
observational results on the excess entropy in central regions of galaxy
systems, to constrain the amount of extra-heating required. We find that
setting the entropy floor S_fl=50 keV cm^2, which corresponds to an extra
heating energy of about 1 keV per particle, is able to reproduce the observed
excess of ICM entropy.


title: Relaxation times calculated from angular deflections

abstract:
  In this paper we measure the two-body relaxation time from the angular
deflection of test particles launched in a rigid configuration of field
particles. We find that centrally concentrated configurations have relaxation
times that can be shorter than those of the corresponding homogeneous
distributions by an order of magnitude or more. For homogeneous distributions
we confirm that the relaxation time is proportional to the number of particles.
On the other hand centrally concentrated configurations have a much shallower
dependence, particularly for small values of the softening. The relaxation time
increases with the inter-particle velocities and with softening. The latter
dependence is not very strong, of the order of a factor of two when the
softening is increased by an order of magnitude. Finally we show that
relaxation times are the same on GRAPE-3 and GRAPE-4, dedicated computer boards
with limited and high precision respectively.


title:
Planetary nebula or symbiotic Mira? Near infrared colours mark the
  difference

abstract:
  Nebulae around symbiotic Miras look very much like genuine planetary nebulae,
although they are formed in a slightly different way. We present near infrared
photometry of known and suspected symbiotic nebulae obtained with the Deep Near
Infrared Southern Sky Survey (DENIS). We demonstrate that the near infrared
colours are an excellent tool to distinguish symbiotic from genuine planetary
nebulae. In particular we find that the bipolar planetary nebulae M 2-9 and Mz
3 are in fact symbiotic Miras. Further observations on prototype symbiotic
Miras prove that the proposed classification scheme works generally.


title: Emission Line Diagnostics of Accretion Flows in Weak-Line Radio Galaxies

abstract:
  In recent surveys of Radio-loud AGN, a new sub-class of objects, known as
Weak-Line Radio Galaxies (WLRGs) has emerged. These radio galaxies have only
weak, low-ionization optical emission lines. In the X-ray band, these objects
are much fainter and have flatter spectra than broad-line and narrow-line radio
galaxies. In these respects, WLRGs are reminiscent of Low Ionization Nuclear
Emission Regions (LINERs). We have begun a multi-wavelength study of WLRGs to
better understand their possible connection to LINERs and the structure of the
accretion flow in both these systems. Here, we present new optical spectra of a
sample of WLRGs. We find that 81% of the objects have optical emission-line
properties that are similar to LINERs, indicating that these two classes of AGN
may be related. Future high resolution X-ray observations of WLRGs will be
critical in determining the true nature of the accretion flow in these objects.


title:
Quiet Sun coronal heating: analyzing large scale magnetic structures
  driven by different small-scale uniform sources

abstract:
  Recent measurements of quiet Sun heating events by Krucker and Benz (1998)
give strong support to Parker's (1988) hypothesis that small scale dissipative
events make the main contribution to the quiet heating. Moreover, combining
their observations with the analysis by Priest et al. (2000), it can be
concluded that the sources driving these dissipative events are also small
scale sources, typically of the order of (or smaller than) 2000 km and the
resolution of modern instruments. Thus arises the question of how these small
scale events participate into the larger scale observable phenomena, and how
the information about small scales can be extracted from observations. This
problem is treated in the framework of a simple phenomenological model
introduced in Krasnoselskikh et al. (2001), which allows to switch between
various small scale sources and dissipative processes. The large scale
structure of the magnetic field is studied by means of Singular Value
Decomposition (SVD) and a derived entropy, techniques which are readily
applicable to experimental data.


title: A first look at cataclysmic variable stars from the 2dF QSO survey

abstract:
  The 2dF QSO survey is a spectroscopic survey of 48,000 point-sources selected
by colour with magnitudes in the range 18.35 < B < 20.95. Amongst QSOs, white
dwarfs, narrow-line galaxies and other objects are some cataclysmic variables
(CVs). This survey should be sensitive to intrinsically faint CVs. In the
standard picture of CV evolution, these form the majority of the CV population.
We present the spectra of 6 CVs from this survey. Four have the spectra of
dwarf novae and two are magnetic CVs. We present evidence that suggests that
the dwarf novae have period P < 2 h and are indeed intrinsically less luminous
than average. However, it is not clear yet whether these systems are present in
the large numbers predicted.


title: Pismis 2, a poorly studied, intermediate age open cluster

abstract:
  We present CCD BVI photometry of the intermediate age open cluster Pismis 2,
covering from the brighter red giants to about 5 magnitudes below the main
sequence turn-off. The cluster is heavily reddened and is possibly affected by
a differential reddening of Delta E(B-V) ~= 0.04-0.06.
  Using the synthetic Colour - Magnitude Diagram method, we estimate in a
self-consistent way distance modulus, (n-M)0 ~= 12.5-12.7, and age ~= 1.1-1.2
Gyr. The cluster probably contains a significant fraction of binary systems.
The metallicity is most likely solar and the reddening E(B-V) ranges between
1.26 and 1.32 depending on the cluster region.


title:
Sulfur, Chlorine, and Argon in Planetary Nebulae. IIA: Observations of a
  Southern Sample

abstract:
  In this paper we present fully reduced and dereddened emission line strengths
for a sample of 45 southern Type II planetary nebulae (PNe). The
spectrophotometry for these PNe covers an extended optical/near-IR range from
3600 - 9600 Angstroms. This PN study and subsequent analysis (presented in a
companion paper), together with a similar treatment for a northern PN sample,
is aimed at addressing the lack of homogeneous, consistently observed, reduced,
and analyzed data sets that include the near-IR [S III] lines at 9069 and 9532
Angstroms. The use of Type II objects only is intended to select disk nebulae
that are uncontaminated by nucleosynthetic products of the progenitor star.
Extending spectra redward to include the strong [S III] lines enables us to
look for consistency between S++ abundances inferred from these lines and from
the more accessible, albeit weaker, [S III] line at 6312 Angstroms.


title: Oscillations of alpha UMa and other red giants

abstract:
  There is growing observational evidence that the variability of red giants
could be caused by excitation of global modes of oscillation. The most recent
evidence of such oscillations was reported for alpha UMa by Buzasi et
al.(2000). We address the problem of radial and nonradial mode excitation in
red giants from the theoretical point of view. In particular, we present the
results of numerical computations of oscillation properties of a model of alpha
UMa and of several models of a 2M_sun star in the red-giant phase. In the red
giant stars by far most of the nonradial modes are confined to to the deep
interior, where they have the g-mode character. Only modes at resonant
frequencies of the p-mode cavity have substantial amplitudes in the outer
layers. We have shown that such modes can be unstable with the linear growth
rates similar to those of corresponding to radial modes.
  We have been unable to explain the observed oscillation properties of alpha
UMa, either in terms of mode instability or in terms of stochastic excitation
by turbulent convection. Modes at the lowest frequencies, which exhibit the
largest amplitudes and may correspond to the first three radial modes, are
found stable if all effects of convection are taken into account. The observed
frequency dependence of amplitudes does not agree with what one expects from
stochastic excitation. The predicted fundamental mode amplitude is by about two
orders of magnitude smaller than those of high frequency modes, which is in
stark disagreement with the observations.


title:
Propagation of ultra-high energy protons in regular extragalactic
  magnetic fields

abstract:
  We study the proton flux expected from sources of ultra high energy cosmic
rays (UHECR) in the presence of regular extragalactic magnetic fields. It is
assumed that a local source of ultra-high energy protons and the magnetic field
are all in a wall of matter concentration with dimensions characteristic of the
supergalactic plane. For a single source, the observed proton flux and the
local cosmic ray energy spectrum depend strongly on the strength of the field,
the position of the observer, and the orientation of the field relative to the
observer's line of sight. Regular fields also affect protons emitted by sources
outside the local magnetic fields structure. We discuss the possibility that
such effects could contribute to an explanation of the excess of UHECR above
$5.10^{19}$ eV, and the possibility that sources of such particles may be
missed if such magnetic fields are not taken into account.


title:
The Three-Dimensional Structure of a Massive Gas Disk in the Galactic
  Central Region

abstract:
  Using high-resolution, three-dimensional hydrodynamical simulations, we
investigate the structure of the interstellar medium in the central hundred pc
region in galaxies, taking into account self-gravity of the gas, radiative
cooling from 10 K to $10^8$ K, and energy feedback from supernovae. Similar to
the previous two-dimensional results produced by Wada and Norman, we find that
a gravitationally and thermally unstable ISM evolves, in a self-stabilizing
manner, into a quasi-stable thin disk, which is characterized by a network of
cold ($T < 100$ K), dense clumps and filaments, and hot ($T > 10^6$ K), diffuse
medium. Supernova explosions blow the diffuse gases from the disk, and as a
result, a quasi-steady diffuse halo, which is not uniform but has a plume-like
structure, is formed. The density probability distribution function (PDF) in a
quasi-steady state is well fitted by a Log-Normal function over about seven
orders of magnitude.


title:
Shocks and dust survival in nearby active galaxies: implications for the
  alignment effect

abstract:
  One of the most popular explanations for the so-called alignment effect in
high redshift (z>0.7) radio galaxies is the scattering by dust of the hidden
quasar light. As shown by De Young (1998) a problem with the dust scattering
model is that the short destruction time-scale for dust grains means that they
will not survive the passage of the radio jet.
  We investigate the survival of dust in the extended ionised gas of nearby
active galaxies with jet/gas interactions. We discuss the implications on the
alignment effect of high redshift (>0.7) radio galaxies. We conclude that
although shocks are likely to destroy dust grains in regions of interaction,
dust might survive in enough quantities to scatter light from the active
nucleus and produce alignment between scattered light and the radio structures.
  We propose an observational test to investigate the existence of dust in
shocked regions based on the sensitivity of calcium to depletion onto dust
grains.


title:
Big Bang Nucleosynthesis and Cosmological Constraints on Neutrino
  Oscillation Parameters

abstract:
  We present a review of cosmological nucleosynthesis (CN) with neutrino
oscillations, discussing the different effects of oscillations on CN, namely:
increase of the effective degrees of freedom during CN, spectrum distortion of
the oscillating neutrinos, neutrino number density depletion, and growth of
neutrino-antineutrino asymmetry due to active-sterile oscillations. We discuss
the importance of these effects for the primordial yield of helium-4.
  Primordially produced He-4 value is obtained in a selfconsistent study of the
nucleons and the oscillating neutrinos. The effects of spectrum distortion,
depletion and neutrino-antineutrino asymmetry growth on helium-4 production are
explicitly calculated.
  An update of the cosmological constraints on active-sterile neutrino
oscillations parameters is presented, giving the values: delta m^2 sin^8 (2
theta) < 1.5 x 10^{-9} eV^2 for delta m^2 > 0, and |delta m^2| < 8.2 x 10^{-10}
eV^2 at large mixing angles for delta m^2 < 0. According to these constraints,
besides the active-sterile LMA solution, also the active-sterile LOW solution
to the solar neutrino problem is almost totally excluded.


title:
The effects of a comptonizing corona on the appearance of the reflection
  components in accreting black hole spectra

abstract:
  We discuss the effects of a comptonizing corona on the appearance of the
reflection components, and in particular of the reflection hump, in the X-rays
spectra of accreting black holes. Indeed, in the framework of a thermal corona
model, we expect that part (or even all, depending on the coronal covering
factor) of the reflection features should cross the hot plasma, and thus suffer
Compton scattering, before being observed. We have studied in detail the
dependence of these effects on the physical (i.e. temperature and optical
depth) and geometrical (i.e. inclination angle) parameters of the corona,
concentrating on the slab geometry . Due to the smoothing and shifting towards
high energies of the comptonized reflection hump, the main effects on the
emerging spectra appear above 100 keV. We have also investigated the importance
of such effects on the interpretation of the results obtained with the standard
fitting procedures. We found that fitting Comptonization models, taking into
account comptonized reflection, by the usual cut-off power law + uncomptonized
reflection model, may lead to an underestimation of the reflection
normalization and an overestimation of the high energy cut-off. We discuss and
illustrate the importance of these effects by analysing recent observational
results as those of the galaxy NGC 4258. We also find that the comptonizing
corona can produce and/or emphasize correlations between the reflection
features characteristics (like the iron line equivalent width or the covering
fraction) and the X-ray spectral index similar to those recently reported in
the literature. We also underline the importance of these effects when dealing
with accurate spectral fitting of the X-ray background.


title:
Searching for Millisecond Pulsars in Globular Clusters at Parkes:
  Further Results

abstract:
  We have discovered 12 new millisecond pulsars in 6 globular clusters in which
no pulsars were previously known, in the first two years of a search at 1.4 GHz
in progress at the Parkes radio telescope. Here we briefly describe the
motivation, the new hardware and software systems adopted for this survey, and
we present the results obtained thus far.


title: The Extragalactic Ionizing Background at Low Redshift

abstract:
  We present a measurement of the mean intensity of the hydrogen-ionizing
background radiation field at low redshift using 906 Ly-alpha absorption lines
in 151 quasar spectra from the archives of the Faint Object Spectrograph on the
Hubble Space Telescope. Using a maximum likelihood technique and the best
estimates possible for each QSO's Lyman limit flux and systemic redshift, we
find J(\nu_{0})= 7.6^{+9.4}_{-3.0} x 10^{-23} ergs s^{-1} cm^{-2} Hz^{-1}
sr^{-1} at 0.03 < z < 1.67. This is in good agreement with the mean intensity
expected from models of the background which incorporate only the known quasar
population. When the sample is divided into two subsamples, consisting of lines
with z < 1 and z > 1, the values of J(\nu_{0}) found are 6.5^{+38.}_{-1.6} x
10^{-23} ergs s^{-1} cm^{-2} Hz^{-1} sr^{-1}, and 1.0^{+3.8}_{-0.2} x 10^{-22}
ergs s^{-1} cm^{-2} Hz^{-1} sr^{-1}, respectively, indicating that the mean
intensity of the background is evolving over the redshift range of this data
set. Relaxing the assumption that the spectral shapes of the sample spectra and
the background are identical, the best fit HI photoionization rates are found
to be 6.7 x 10^{-13} s^{-1} for all redshifts, and 1.9 x 10^{-13} s^{-1} and
1.3 x 10^{-12} s^{-1} for z < 1 and z > 1, respectively.


title:
The constant-velocity highly collimated outflows of the planetary nebula
  He 2-90

abstract:
  We present high-dispersion echelle spectroscopic observations and a
narrow-band [N II] image of the remarkable jet-like features of He 2-90. They
are detected in the echelle spectra in the H-alpha and [N II] lines but not in
other nebular lines. The [N II]/H-alpha ratio is uniformly high, ~1. The
observed kinematics reveals bipolar collimated outflows in the jet-like
features and shows that the southeast (northwest) component expands towards
(away from) the observer at a remarkably constant line-of-sight velocity,
26.0+-0.5 km/s. The observed expansion velocity and the opening angle of the
jet-like features are used to estimate an inclination angle of ~5 degrees with
respect to the sky plane and a space expansion velocity of ~290 km/s. The
spectrum of the bright central nebula reveals a profusion of Fe lines and
extended wings of the H-alpha line, similar to those seen in symbiotic stars
and some young planetary nebulae that are presumed to host a mass-exchanging
binary system. If this is the case for He 2-90, the constant velocity and
direction of the jets require a very stable dynamic system against precession
and warping.


title: Exploration of Parameter Spaces in a Virtual Observatory

abstract:
  Like every other field of intellectual endeavor, astronomy is being
revolutionised by the advances in information technology. There is an ongoing
exponential growth in the volume, quality, and complexity of astronomical data
sets, mainly through large digital sky surveys and archives. The Virtual
Observatory (VO) concept represents a scientific and technological framework
needed to cope with this data flood. Systematic exploration of the observable
parameter spaces, covered by large digital sky surveys spanning a range of
wavelengths, will be one of the primary modes of research with a VO. This is
where the truly new discoveries will be made, and new insights be gained about
the already known astronomical objects and phenomena. We review some of the
methodological challenges posed by the analysis of large and complex data sets
expected in the VO-based research. The challenges are driven both by the size
and the complexity of the data sets (billions of data vectors in parameter
spaces of tens or hundreds of dimensions), by the heterogeneity of the data and
measurement errors, including differences in basic survey parameters for the
federated data sets (e.g., in the positional accuracy and resolution,
wavelength coverage, time baseline, etc.), various selection effects, as well
as the intrinsic clustering properties (functional form, topology) of the data
distributions in the parameter spaces of observed attributes. Answering these
challenges will require substantial collaborative efforts and partnerships
between astronomers, computer scientists, and statisticians.


title: Spectral cutoffs in EGRET gamma-ray sources

abstract:
  The EGRET instrument has measured detailed photon spectra between 30 MeV and
10 GeV, which are represented by means of single power-law fits for sources in
the 3EG catalog. However, various sources show indications of spectral cutoffs
at GeV energies, which are poorly represented by such simple fits. In the case
of well exposed or bright EGRET sources, a description of spectral cutoffs with
more complicated functional forms appears to be applicable. An application for
such multicomponent fits should be seen in extrapolations beyond the energies
accessible to EGRET, i.e. for detectability studies of low-threshold Imaging
Atmospheric Cherenkov Telescopes (IACTs). In cases of unidentified gamma-ray
sources positionally coincident with Supernova remnants, the spectral shape
beyond power-law extrapolations might observationally explain why such
prominent SNRs like gammaCygni, IC 443 and CTA1 have not been detected during
several observation campaigns performed by IACTs over the last years.


title: LogN-LogS Studies of EGRET Sources

abstract:
  A comprehensive investigation of logN-logS distributions of gamma-ray sources
discovered by EGRET has been performed for subsequent use in population
studies. Existing models explaining the spatial arrangement of unidentified
sources do not compare against an observed logN-logS distribution. However,
viable population models not only have to reproduce the logN-logS distribution
for different source classes globally, they have to correspond to apparent
differences among their spatial, spectral and variability characteristics.
Furthermore, it needs to be understood in which way results from selections
among the unidentified sources like "persistent" (Grenier 2000) or "steady"
sources (Gehrels et al. 2000) are related to the overall picture regarding
their logN-logS characteristics.


title: Kinematics in the Central Kiloparsec of Spiral Galaxies

abstract:
  Results from kinematic observations of the central regions of spiral galaxies
are reviewed, with particular emphasis on starburst and AGN hosts. While
morphological studies lead to important insight, a more complete understanding
of the physical processes that drive the evolution of the central regions can
be achieved with measurements of the kinematics of gas and stars. Here, a
variety of observational techniques at different wavelengths is critically
discussed, and specific areas of interest are highlighted, such as inflow in
barred galaxies and the origin of nuclear spiral arms. A brief discussion of a
number of case studies is presented to illustrate recent progress.


title: Free-Floating Planets: Not So Surprising

abstract:
  We find that free-floating planets can remain bound to a star cluster for
much longer than was previously assumed: of the order of the cluster half-mass
relaxation timescale as opposed to the crossing-time. This result is based on
N-body simulations performed with the new GRAPE-6 special purpose hardware and
is important in the context of the preliminary detection of a population of
free-floating sub-stellar objects in the globular cluster M22. The planets in
our N-body study are of Jupiter mass and are initially placed in circular
orbits of between 0.05 and 50 AU about a parent star whose mass is chosen from
a realistic initial mass function. The presence of the free-floating planets is
the result of dynamical encounters between planetary systems and the cluster
stars. Most planets are liberated from their parent star in, or near, the
cluster core, and then drift outwards on a timescale of ~ 10^{8-9} year. This
still implies the existence of many (~100) planets per star if the M22 result
is confirmed.


title: Testing models of X-ray reflection from irradiated disks

abstract:
  We model the reflected spectrum expected from localized magnetic flares above
an ionised accretion disk. We concentrate on the case of very luminous magnetic
flares above a standard accretion disk extending down to the last stable orbit,
and use a simple parameterisation to allow for an X-ray driven wind. Full disk
spectra including relativistic smearing are calculated. When fit with the
constant density reflection models, these spectra give both a low reflected
fraction and a small line width as seen in the hard spectra from Galactic Black
Hole Binaries and Active Galactic Nuclei. We fit our calculated spectra to real
data from the low/hard state of Nova Muscae and Cyg X-1 and show that these
models give comparable $\chi^2$ to those obtained from the constant density
reflection models which implied a truncated disk. This explicitally
demonstrates that the data are consistent with either magnetic flares above an
ionized disk extending down to the last stable orbit around a black hole, or
with non-ionized, truncated disks.


title:
The electron temperature of the inner halo of the Planetary Nebula NGC
  6543

abstract:
  We investigate the electron temperature of the inner halo and nebular core
regions of NGC 6543, using archival Hubble Space Telescope (HST) Wide Field
Planetary Camera 2 (WFPC2) images taken through narrow band [O III] filters.
Balick et al. (2001) showed that the inner halo consists of a number of
spherical shells. We find the temperature of this inner halo to be much higher
(~15000 K) than that of the bright core nebula (~8500 K). Photo-ionization
models indicate that hardening of the UV radiation from the central star cannot
be the main source of the higher temperature in the halo region. Using a
radiation hydrodynamic simulation, we show that mass loss and velocity
variations in the AGB wind can explain the observed shells, as well as the
higher electron temperature.


title: Observations of Mkn 421 using Pachmarhi Array of \v{C}erenkov Telescopes

abstract:
  Pachmarhi Array of \v{C}erenkov Telescopes (PACT), based on wavefront
sampling technique, has been used for detecting TeV gamma rays from galactic
and extra-galactic $\gamma $-ray sources. The Blazar, Mkn 421 was one such
extra-galactic source observed during the winter nights of 2000 and 2001. We
have carried out a preliminary analysis of the data taken during the nights of
January, 2000 and 2001. Results show a significant gamma ray signal from this
source during both these periods above a threshold energy of 900 GeV. The
source was contemporaneously observed by CAT imaging telescope during the first
episode of January 2000 while HEGRA CT1 was observing the source during the
second episode. Both these observations have detected variable $\gamma $-ray
emission this source and they reported that it was flaring during both these
periods. The light curve in the TeV gamma ray range derived from the first PACT
observations during both these episodes is in agreement with that reported by
other experiments. The analysis procedure and the preliminary results will be
presented and discussed.


title: The stability of the Circumnuclear Disk clouds in the Galactic Centre

abstract:
  The influence of rotation and magnetic fields on the physical properties of
isothermal gas clouds is discussed. The presence of rotation and/or magnetic
fields results in an increase of the critical cloud mass with respect to
gravitational instability for clouds of a given temperature and external
pressure. Rotating clouds have higher densities. Consequently, they are more
stable against tidal shear than non-rotating clouds. They can approach the
Galactic Centre up to a radius of ~2 pc without being disrupted by the tidal
shear due to the gravitational potential. For smaller radii the clouds either
collapse or become tidally disrupted. We suggest that this mechanism is
responsible for the formation of the inner edge of the Circumnuclear Disk in
the Galactic Centre.


title:
Globular Cluster Mass and Metallicity Distributions: Reconstructing the
  Events During Halo Formation

abstract:
  Globular clusters in most large galaxies are a mixture of metal-poor and
metal-rich (bimodal), but the halo stars are almost entirely metal-rich. This
and other lines of evidence argue that the metal-poor globular clusters formed
within widely distributed 10^8-10^9 Solar masses gas clouds (supergiant GMCs)
during an early burst in which most of the gas was ejected or unused till later
rounds of star formation. New simulations of the growth of pre-galactic
potential wells in the early universe now indicate that the initial power-law
form of the globular cluster mass distribution (dN/dM ~ M^-1.8) is a miniature
replica of the mass distribution of the SGMCs themselves, which grow
hierarchically in the CDM potential wells of large protogalaxies.


title:
Formation and dynamics of self-sustained neutron haloes in disk
  accreting sources

abstract:
  It has been recognized long ago that the presence of hot plasma in the inner
accretion disks around black holes could lead to the neutron production via
dissociation of helium nuclei. We show that, for a broad range of accretion
parameters, neutrons effectively decouple from protons and pile up in the inner
disk leading to the formation of self-sustained halo. This means that new
neutrons in the halo are supplied mainly by the splitting of helium nuclei in
their collisions with existing neutrons. Once formed, such a halo can exist
even if the proton temperature is much lower than the energy threshold of
helium dissociation. We show that neutron haloes can be the natural source of
relativistic electrons and positrons, providing characteristic comptonization
spectra and hard spectral tails observed in many black hole candidates, and
also giving rise to relativistic outflows. Deuterium gamma-ray line at 2.2 MeV
resulting from neutron capture is also expected at a level detectable by future
INTEGRAL mission. Furthermore, the presence of a neutron halo strongly affects
the dynamics of accretion and leads to the rich variety of transient dynamical
regimes.


title:
Relativistic Kinetic Equation for Induced Compton Scattering of
  Polarized Radiation

abstract:
  The relativistic kinetic equations describing time evolution and space
dependence of the density matrices of polarized photons and electrons
interacting via Compton scattering are deduced from the quantum Liouville
equation. The induced scattering and exclusion principle are taken into
account. The Bogoliubov method is used in the frame of quantum electrodynamics.
The equation for polarized radiation scattered by unpolarized electrons is
considered as a particular case and is reformulated in terms of the Stokes
parameters. The expressions for the scattering amplitudes and cross-sections
are derived simultaneously.


title: Two Decades of Hypergiant Research

abstract:
  This article is a brief review of the research by Dr. C. de Jager and
co-workers over the past twenty years into the physics of hypergiant
atmospheres. Various important results on the microturbulence, mass-loss,
circumstellar environment, atmospheric velocity fields, and the Yellow
Evolutionary Void of these enigmatic stars are summarized. Aspects of recent
developments and future work are also communicated.


title:
Dense cores in the L1630 molecular cloud: discovering new protostars
  with SCUBA

abstract:
  Maps of the 450 micron and 850 micron dust continuum emission from three
star-forming condensations within the Lynds 1630 molecular cloud, made with the
SCUBA bolometer array, reveal the presence of four new submillimetre sources,
each of a few solar masses, two of which are probably Class I, two Class 0, as
well as several sources whose existence was previously known. The sources are
located in filaments and appear elongated when observed at 450 microns. They
likely have dust temperatures in the range 10 to 20 K, in good agreement with
previous ammonia temperature estimates. Attempts to fit their structures with
power-law and Gaussian density distributions suggest that the central
distribution is flatter than expected for a simple singular isothermal sphere.
  Although the statistics are poor, our results suggest that the ratio of
`protostellar core' mass to total virial mass may be similar for both large and
small condensations.


title:
A New System of Parallel Isolated Nonthermal Filaments Near the Galactic
  Center: Evidence for a Local Magnetic Field Gradient

abstract:
  We report the discovery of a system of isolated nonthermal filaments
approximately 0.5 deg. northwest (75 pc in projection) of Sgr A. Unlike other
isolated nonthermal filaments which show subfilamentation, braiding of
subfilaments, and flaring at their ends, these filaments are simple linear
structures and more closely resemble the parallel bundled filaments in the
Galactic center radio arc. However, the most unusual feature of these filaments
is that the 20/90 cm spectral index uniformly decreases as a function of
length, in contrast to all other nonthermal filaments in the Galactic center.
This spectral gradient may not be due to simple particle aging but could be
explained by a curved electron energy spectrum embedded in a diverging magnetic
field. If so, the scale of the magnetic gradient is not consistent with a large
scale magnetic field centered on Sgr A* suggesting that this filament system is
tracing a local magnetic field.


title:
Discovery of an extremely red galaxy at z=0.65 with dusty star-formation
  and nuclear activity

abstract:
  In the course of the follow-up multiwavelength study of a deep radio survey
we have discovered that the milli-Jansky radio source PDFJ011423 is a
low-redshift (z = 0.65) extremely red galaxy (ERG) with K=15.3, R-K = 5.8 and
J-K = 3.1. Optical, infrared and radio photometry, together with optical and
near-infrared spectroscopy, reveal a heavily obscured galaxy (A_V=5-6, from the
observed Balmer decrement) undergoing vigorous star formation and presenting an
active galactic nucleus (AGN). PDFJ011423 is a representative member of the
dusty ERG population, providing a local counterpart for studying more distant
ERGs.


title:
All-sky astrophysical component separation with Fast Independent
  Component Analysis (FastICA)

abstract:
  We present a new, fast, algorithm for the separation of astrophysical
components superposed in maps of the sky, based on the fast Independent
Component Analysis technique (FastICA). It allows to recover both the spatial
pattern and the frequency scalings of the emissions from statistically
independent astrophysical processes, present along the line-of-sight, from
multi-frequency observations. We apply FastICA to simulated observations of the
microwave sky with angular resolution and instrumental noise at the mean
nominal levels for the Planck satellite, containing the most important known
diffuse signals: the Cosmic Microwave Background (CMB), Galactic synchrotron,
dust and free-free emissions. A method for calibrating the reconstructed maps
of each component at each frequency has been devised. The spatial pattern of
all the components have been recovered on all scales probed by the instrument.
In particular, the CMB angular power spectra is recovered at the percent level
up to $\ell_{max}\simeq 2000$. Frequency scalings and normalization have been
recovered with better than percent precision for all the components at
frequencies and in sky regions where their signal-to-noise ratio exceeds 1.5;
the error increases at ten percent level for signal-to-noise ratios about 1.
Runs have been performed on a Pentium III 600 MHz computer; FastICA typically
took a time of the order of 10 minutes for all-sky simulations with 3.5
arcminutes pixel size. We conclude that FastICA is an extremly promising
technique for analyzing the maps that will be obtained by the forthcoming high
resolution CMB experiments.


title: Stochastic excitation of stellar oscillations

abstract:
  Excitation of solar oscillations is attribued to turbulent motions in the
solar convective zone. It is also currently believed that oscillations of low
massive stars (M <2 Mo) - which possess an upper convective zone - are
stochastically excited by turbulent convection in their outer layers.
  A recent theoretical work (Samadi & Goupil, 2001 ; Samadi et al, 2001)
supplements and reinforces this theory. This allows the use of any available
model of turbulence and emphasizes some recent unsolved problems which are
brought up by these new theoretical developments.


title: Disc Instabilities in Soft X-ray Transients

abstract:
  I briefly review the theory of soft X-ray transient systems. Irradiation of
the accretion disc faces by the central X-ray source determines both the
occurrence and the nature of the outbursts, in particular forcing these to be
long viscous events and producing exponential decays at short orbital periods.
Soft X-ray transients constitute the majority of LMXBs, persistent systems
being largely confined to a subset of neutron-star LMXBs with periods P < 2 d.
It appears that LMXBs very frequently contain nuclear-evolved companions, even
at short orbital periods. In long-period transients (P > 20 d) the outburst
recurrence times must become extremely long (> 1500 yr). The outbursts are
highly super-Eddington, markedly reducing the accretion efficiency. Spinup of a
neutron-star primary to millisecond periods probably cannot occur for orbital
periods > 200 d, in agreement with observations of binary pulsars.


title:
MHD consistent cellular automata (CA) models II. Applications to solar
  flares

abstract:
  In Isliker et al. (2000b), an extended cellular automaton (X-CA) model for
solar flares was introduced. In this model, the interpretation of the model's
grid-variable is specified, and the magnetic field, the current, and an
approximation to the electric field are yielded, all in a way that is
consistent with Maxwell's and the MHD equations. Here, we reveal which relevant
plasma physical processes are implemented by the X-CA model and in what form,
and what global physical set-up is assumed by this model when it is in its
natural state (SOC). The basic results are: (1) On large-scales, all variables
show characteristic quasi-symmetries. (2) The global magnetic topology forms
either (i) closed magnetic field lines, or (ii) an arcade of field lines above
the bottom plane line, if the model is slightly modified. (3) In case of the
magnetic topology (ii), loading can be interpreted as if there were a plasma
which flows predominantly upwards, whereas in case of the magnetic topology
(i), as if there were a plasma flow expanding from the neutral line. (4) The
small-scale physics in the bursting phase represent localized diffusive
processes. (5) The local diffusivity usually has a value which is effectively
zero, and it turns locally to an anomalous value if a threshold is exceeded,
whereby diffusion dominates the quiet evolution (loading). (6) Flares
(avalanches) are accompanied by the appearance of localized, intense electric
fields. (7) In a variant on the X-CA model, the magnitude of the current is
used directly in the instability criterion. First results indicate that the SOC
state persists. (8) The current-dissipation during flares is spatially
fragmented into a large number of dissipative current-surfaces of varying
sizes, which show a highly dynamic temporal evolution.


title:
Transient Gamma Ray Spectrometer Measurements of Gamma-Ray Lines from
  Novae. III. The 478 keV Line from 7Be Decay

abstract:
  The "Wind" spacecraft carrying the Transient Gamma Spectrometer (TGRS) moves
in an extremely elliptical orbit that largely avoids Earth's trapped radiation
belts and albedo gamma-radiation. The TGRS therefore enjoys a relatively low
level of background that is also extremely stable. We show how this stability
enables modeling of the time variability of background lines, which in turn
enables a novel technique of background subtraction to be used in the detection
of transient astrophysical lines. We apply a simple version of this method to
the line at 478 keV that is expected to arise from nucleosynthesis of 7Be in
nearby novae. This search covers the entire southern ecliptic hemisphere during
1995-1997, including five known individual events, and possible undiscovered
individual events. The TGRS design also uses "Wind"'s 3 s rotation period to
modulate signals from the Galactic Center (GC). We use this feature of the
instrument to search for a quasi-constant level of 478 keV emission from the
accumulation of 7Be from several novae that are expected to occur in the
direction of the GC during that isotope's 53 d half-life. We derive upper
limits on the transient (single-nova) emission which improve on previous limits
by about an order of magnitude, and limits on the steady (many-nova) emission
which represent a factor 2 improvement. Only weak limits can be placed on the
key parameters in the nucleosynthesis and ejection of 7Be, however.


title:
The effects of dust in simple environments: Large Magellanic Cloud HII
  regions

abstract:
  We investigate the effects of dust on Large Magellanic Cloud (LMC) HII region
spectral energy distributions using arcminute-resolution far-ultraviolet (FUV),
H-alpha, far-infrared (FIR), and radio images. Widely-used indicators of the
amount of light lost to dust (attenuation) at H-alpha and in the FUV correlate
with each other, although often with substantial scatter. There are two
interesting systematic discrepancies. First, H-alpha attenuations estimated
from the Balmer decrement are lower than those estimated from the
H-alpha-to-thermal radio luminosity ratio. Our data, at this stage, cannot
unambiguously identify the source of this discrepancy. Second, the attenuation
at 1500 angstroms and UV spectral slope, beta, correlate, although the slope
and scatter are substantially different from the correlation first derived for
starbursting galaxies by Calzetti et al. Combining our result with those of
Meurer et al. for ultra-luminous infrared galaxies and Calzetti et al. for
starbursting galaxies, we conclude that no single relation between beta and
1500 angstrom attenuation is applicable to all star-forming systems.


title: GSH 138-01-94, an old supernova remnant in the far outer Galaxy

abstract:
  The properties of the Galactic HI shell GSH 138-01-94 are derived from data
of the Canadian Galactic Plane Survey. The basic parameters of GSH 138-01-94
were determined by fitting the expansion of a thin shell to the expansion
velocity field on the sky. The kinematic distance is 16.6 kpc for v_LSR=-94.2
$\pm$ 0.5 km/s. The radius is 180 $\pm$ 10 pc, the expansion velocity v_exp =
11.8 $\pm$ 0.9 km/s, and the mass 2 * 10^5 M_sun. No radio continuum
counterpart of the shell was detected at 21 cm or at 74 cm. Absorption of a
background continuum source constrains the spin temperature of \HI in the shell
to T_s=230^{367}_{173} K. The expansion age of GSH 138-01-94 is 4.3 Myr. These
observables are in excellent agreement with predictions from hydrodynamic
models for a supernova remnant in a low-density low-metallicity environment
such as the outer Galaxy. GSH 138-01-94 is then the largest and the oldest
supernova remnant known. It provides direct evidence for the release of
mechanical energy in the interstellar medium by stars in the outer galaxy. It
is argued that such old supernova remnants be found in low-density,
low-metallicity environments such as the outer Galaxy, dwarf galaxies and low
surface brightness galaxies.


title: Nonthermal Emission from Accreting and Merging Clusters of Galaxies

abstract:
  We compare the nonthermal emission from clusters of galaxies undergoing minor
mergers (``accreting'' clusters) and major mergers (``merging'' clusters). For
accreting clusters, the radial distribution of the nonthermal emission in the
clusters is also calculated. The relativistic electrons, which are the origin
of the nonthermal radiation through inverse Compton (IC) and synchrotron
mission, are assumed to be accelerated at shocks produced by accretion or
mergers. We estimate the typical accretion rate and merger probability
according to a hierarchical clustering model. We show that the total luminosity
of IC emission from accreting and merging clusters are similar. On the other
hand, the luminosity of synchrotron radio emission of the former is much
smaller than that of the latter. We show that about 10% of clusters at z~0
should have hard X-ray and radio nonthermal emissions due to their last major
merger, which are comparable to or dominate those due to ongoing accretion.
Moreover, 20-40% of clusters should have significant EUV emission due to their
last merger. We also investigate the case where the criterion of mergers is
relaxed. If we extend the definition of a merger to an increase in the mass of
the larger subcluster by at least 10% of its initial mass, about 20-30% of
clusters at z~0 should have hard X-ray and radio nonthermal emissions due to
the merger even in a low density universe. We compare the results with
observations. We find that the observed EUV emission from clusters is not
attributed to accretion. If the diffuse radio emission observed in clusters is
synchrotron emission from electrons accelerated via accretion or merging, the
magnetic fields of clusters are generally as small as ~0.1 mu G.


title: Extended King Models for Star Clusters

abstract:
  Models applied to galaxies in equilibrium configuration are based on the
solution of the collisionless Boltzmann equation and the Poisson equation for
gravitational interaction which are related to each other by a smoothed-out
mass density. This mass density is related to a distribution function
$f(\mathbf{x},\mathbf{v},t)$ and produces a gravitational potential $\phi
(\mathbf{x},t)$. The most popular models to describe spherically symmetric
systems are King models. These models are based on a truncated isothermal
sphere. They fit the surface brightness of globular clusters and some
elliptical galaxies well. A well-known example of a galaxy that King models
does not fit well is NGC 3379. In this work, we extend King models. Our models
are based on the Tsallis distribution function. There is a parameter $q$ in
this function and we can recover the King distribution function in the limit
$q\to 1$. We discuss the general behaviors of our models and, moreover, we use
them to fit the surface brightness of NGC 3379 and 47 TUC.


title:
The Ionization and Metallicity of the Intervening O VI Absorber at z =
  0.1212 in the Spectrum of H1821+643

abstract:
  We use high-resolution UV spectra of the radio-quiet QSO H1821+643 (z_em =
0.297), obtained with STIS and FUSE, to study the ionization and metallicity of
an intervening O VI absorption line system at z(abs) = 0.1212. This absorber
has the following notable properties: (1) Several galaxies are close to the
sight line at the absorber redshift, including an actively star-forming galaxy
at a projected distance of 144 kpc. (2) There is a complex cluster of H I lya
absorption lines near the O VI redshift, including at least five components
spread over a velocity range of ~700 km/s . (3) The strongest lya line in the
cluster appears to be composed of a mildly saturated component with a typical
b-value blended with a broad component with b = 85 km/s . (4) The O VI
absorption is not aligned with the strongest H I absorption, but instead is
well-aligned with the broad component. (5) The only detected species (>4sigma)
are O VI and H I despite coverage of strong transitions of other abundant
elements. Based on these constraints, we find that the absorption line
properties can be produced in collisionally ionized gas with roughly 5.3 < log
T < 5.6 and -1.8 < [O/H] < -0.6. However, we find that photoionization is also
viable if the pathlength l through the absorbing gas is long enough; simple
photoionization models require 85 < l < 1900 kpc and -1.1 < [O/H] < -0.3. We
briefly discuss how observations of X-ray absorption lines due to O VII and O
VIII could be used, in principle, to break the ionization mechanism degeneracy.