title: Measuring Supernova Neutrino Temperatures using Lead Perchlorate

abstract:
  Neutrino interactions with lead produce neutrons in numbers that depend on
neutrino energy and type. A detector based on lead perchlorate, for example,
would be able to measure the energy deposited by electrons and gammas in
coincidence with the number of neutrons produced. Sorting the electron energy
spectra by the number of coincident neutrons permits the identification of the
neutrino type that induced the reaction. This separation allows an analysis
which can determine the temperatures of electron neutrinos and electron
anti-neutrinos from a supernova in one experiment. The neutrino reaction
signatures of lead perchlorate and the fundamentals of using this material as a
neutrino detector are described.


title:
Time Domain Analysis of Variability in Cygnus X-1: Constraints on the
  Emission Models

abstract:
  We use time domain analysis techniques to investigate the rapid variability
of Cygnus X-1. We show that the cross-correlation functions between hard and
soft energy bands reach values very close to unity and peak at a lag of less
than 2 millisecond for energies separated by a factor of 10. This confirms that
the process that produces X-ray photons at different energies is extremely
coherent on short time scales and strongly constrains emission models proposed
to explain Fourier-frequency-dependent time lags. We present autocorrelation
functions at different energies, and note their widths decrease with increasing
energy. We show that the extended Compton corona model produces
auto-correlation functions whose widths increase with increasing energy, that
the model of cylindrical waves moving inward through a transition disk has too
large a peak lag in the cross-correlation function. Models of magnetic flaring
and of drifting blobs in a hot corona can qualitatively fit the observations.


title: Digital Sky Surveys: Software Tools and Technologies

abstract:
  Large digital sky surveys, over a broad range of wavelengths, both from the
ground and from space observatories, are becoming a major source of
astronomical data. Some examples include the Sloan Digital Sky Survey (SDSS)
and the Digital Palomar Observatory Sky Survey (DPOSS) in the visible, the
Two-Micron All-Sky Survey (2MASS) in the near-infrared, the NRAO VLA Sky Survey
(NVSS) and the Faint Images of the Radio Sky at Twenty centimeters (FIRST) in
the radio. Many others surveys are planned or expected, in addition to the
previously named surveys. While most surveys are exclusively imaging,
large-scale spectroscopic surveys also exist. In addition, a number of
experiments with specific scientific goals, e.g., microlensing surveys for
MACHOs, searches for near-Earth asteroids, are generating comparable data
volumes. Typical sizes of resulting data sets (as of the late 1990's) are in
the range of tens of Terabytes of digital information, with detections of many
millions or even billions of sources, and several tens of parameters measured
for each detected source. This vast amount of new information presents both a
great scientific opportunity and a great technological challenge: how to
process, and calibrate the raw data; how to store, combine, and access them
using modern computing hardware and networks; and how to visualize, explore and
analyses these great data sets quickly and efficiently.


title: Surveys for z > 3 Damped Lyman-alpha Absorption Systems

abstract:
  We have completed spectroscopic observations using LRIS on the Keck 1
telescope of 30 very high redshift quasars, 11 selected for the presence of
damped Ly-alpha absorption systems and 19 with redshifts z > 3.5 not previously
surveyed for absorption systems. We have surveyed an additional 10 QSOs with
the Lick 120'' and the Anglo-Australian Telescope. We have combined these with
previous data resulting in a statistical sample of 646 QSOs and 85 damped
Ly-alpha absorbers with column densities N(HI) >= 2 x 10^20 atoms/cm^2 covering
the redshift range 0.008 <= z <= 4.694. To make the data in our statistical
sample more readily available for comparison with scenarios from various
cosmological models, we provide tables that includes all 646 QSOs from our new
survey and previously published surveys. They list the minimum and maximum
redshift defining the redshift path along each line of sight, the QSO emission
redshift, and when an absorber is detected, the absorption redshift and
measured HI column density. [see the paper for the complete abstract]


title:
Energetic particle acceleration in a 3D magnetic field reconnection
  model: a role of MHD turbulence

abstract:
  The role of MHD turbulence in the cosmic ray acceleration process in a volume
with a reconnecting magnetic field is studied by means of Monte Carlo
simulations. We performed modelling of proton acceleration with the 3D analytic
model of stationary reconnection of Craig et al. (1995) providing the
unperturbed background conditions. Perturbations of particle trajectories due
to a turbulent magnetic field component were simulated using small-amplitude
pitch-angle momentum scattering, enabling modelling of both small and large
amplitude turbulence in a wide wave vector range. Within the approach, no
second-order Fermi acceleration process is allowed. Comparison of the
acceleration process in models involving particle trajectory perturbations to
the unperturbed one reveals that the turbulence can substantially increase the
acceleration efficiency, enabling much higher final particle energies and flat
particle spectra.


title: Analysis of Four A-F Supergiants in M31 from Keck HIRES Spectroscopy

abstract:
  The first stellar abundances in M31 are presented, based on Keck I HIRES
spectroscopy and model atmospheres analyses of three A-F supergiants, 41-2368,
41-3712, and A-207. We also present the preliminary analysis of a fourth star,
41-3654. We find that the stellar oxygen abundances are in good agreement with
those determined from nebular studies, even though the stars do {\it not} show
a clear radial gradient in oxygen. The uncertainties in the stellar abundances
are smaller than the range in the nebular results, making these stars ideal
objects for further studies of the distribution of oxygen in M31. We show that
the stars can be used to study the abundance distributions of other elements as
well, including iron-group and heavier elements.
  The A-F supergiants also provide direct information on the metallicity and
reddening of nearby Cepheid stars. We have examined the metallicity and
reddening assumptions used for Cepheids within 1' of our targets and noted the
differences from values used in the literature.


title:
On the Relation Between Peak Luminosity and Parent Population of Type Ia
  Supernovae: A New Tool for Probing the Ages of Distant Galaxies

abstract:
  We study the properties of Type Ia Supernovae (SNe Ia) as functions of the
radial distance from their host galaxy centers. Using a sample of 62 SNe Ia
with reliable luminosity, reddening, and decline rate determinations, we find
no significant radial gradients of SNe Ia peak absolute magnitudes or decline
rates in elliptical+S0 galaxies, suggesting that the diversity of SN properties
is not related to the metallicity of their progenitors. We do find that the
range in brightness and light curve width of supernovae in spiral galaxies
extends to brighter, broader values. These results are interpreted as support
for an age, but not metallicity, related origin of the diversity in SNe Ia. If
confirmed with a larger and more accurate sample of data, the age-luminosity
relation would offer a new and powerful tool to probe the ages and age
gradients of stellar populations in galaxies at redshift as high as $z\sim1-2$.
The absence of significant radial gradients in the peak $\rm (B-V)_0$ and $\rm
(V-I)_0$ colors of SNe Ia supports the redding correction method of Phillips et
al (1999). We find no radial gradient in residuals from the SN Ia
luminosity-width relation, suggesting that the relation is not affected by
properties of the progenitor populations and supporting the reliability of
cosmological results based upon the use of SNe Ia as distance indicators.


title: Dwarf Galaxy Rotation Curves and the Core Problem of Dark Matter Halos

abstract:
  The standard cold dark matter (CDM) model has recently been challenged by the
claim that dwarf galaxies have dark matter halos with constant density cores.
Consequently, numerous alternative dark matter candidates have recently been
proposed. In this paper, we scrutinize the observational evidence for the
incongruity between dwarf galaxies and the CDM model. To this end, we analyze
the rotation curves of 20 late-type dwarf galaxies studied by Swaters (1999).
Taking the effects of beam-smearing and adiabatic contraction into account, we
fit mass models to these rotation curves with dark matter halos with different
cusp slopes, ranging from constant density cores to r^{-2} cusps. Uncertainties
in the stellar mass-to-light ratio and the limited spatial sampling of the
halo's density distribution hamper a unique mass decomposition. Consequently,
the rotation curves in our sample cannot be used to discriminate between dark
halos with constant density cores and r^{-1} cusps. We show that the dwarf
galaxies analyzed here are consistent with cold dark matter halos in a LCDM
cosmology, and that there is thus no need to abandon the idea that dark matter
is cold and collisionless. However, the data is also consistent with any
alternative dark matter model that produces dark matter halos with central
cusps less steep than r^{-1.5}. In fact, we argue that based on existing
rotation curves alone at best weak limits can be obtained on cosmological
parameters and/or the nature of the dark matter.


title: Non-LTE treatment of molecules in the photospheres of cool stars

abstract:
  We present a technique to treat systems with very many levels, like
molecules, in non-LTE. This method is based on a superlevel formalism coupled
with rate operator splitting. Superlevels consist of many individual levels
that are assumed to be in LTE relative to each other. The usage of superlevels
reduces the dimensionality of the rate equations dramatically and, thereby,
makes the problem computationally more easily treatable. Our superlevel
formalism retains maximum accuracy by using direct opacity sampling (dOS) when
calculating the radiative transitions and the opacities. We developed this
method in order to treat molecules in cool dwarf model calculations in non-LTE.
Cool dwarfs have low electron densities and a radiation field that is far from
a black body radiation field, both properties may invalidate the conditions for
the common LTE approximation. Therefore, the most important opacity sources,
the molecules, need to be treated in non-LTE. As a case study we applied our
method to carbon monoxide. We find that our method gives accurate results since
the conditions for the superlevel method are very well met for molecules. Due
to very high collisional cross sections with hydrogen, and the high densities
of H_2 the population of CO itself shows no significant deviation from LTE.


title:
Magnetic field measurements in white dwarfs. Magnetic field, rotation
  and spectrum of 40 Eri B

abstract:
  This paper describes results of magnetic field measurements of white dwarfs
carried out on the 6-m telescope for the last years. A magnetic field of about
Be ~ 28 kG has been discovered in the degenerate star WD 1953-011.
  A rotational period of WD 0009+501, 1.83 hours, has been discovered, the
average magnetic field of the star is <Be> = -42.3 +/- 5.4 kG and its
semi-amplitude of the rotational variability is 32.0 +/- 6.8 kG. The variable
magnetic field of the bright normal (non-magnetic) degenerate star 40 Eridani B
was confirmed in January 1999 by Zeeman time-resolved spectroscopy. Both the
Halpha and the Hbeta lines give about the same results, we have selected two
best periods in the magnetic field variability, 2h25m and 5h17m. The
semi-amplitude of the rotational variations B_ max ~ 4000-5000 G and the
average field is about zero +/- 500 G. If the magnetic field of 40 Eridani B is
a central dipole, then the rotational axis inclination to the line of sight is
i ~ 90 DEG, and the magnetic axis inclination to the rotational axis is about
the same, beta ~ 90 DEG. For the first time an ultra-high signal-to-noise
spectrum of the white dwarf has been obtained (S/N > 1000). We have found in
this hydrogen-rich DA white dwarf 40 Eridani B (16500 K) that helium abundance
is low (N(He)/N(H) < 10^{-7}), but the spectrum is rich in ultra-weak
absorption lines of metals in low ionization states. It was proposed that these
lines were produced in both circumstellar and interstellar gas.


title:
Power Density Spectra of Gamma-Ray Burst Light Curves: Implications on
  Theory and Observation

abstract:
  We study the power density spectrum (PDS) of artificial light curves of
observed gamma-ray bursts (GRBs). We investigate statistical properties of GRB
light curves by comparing the reported characteristics in the PDSs of the
observed GRBs with those that we model, and discuss implications on
interpretations of the PDS analysis results. Results of PDS analysis of
observed GRBs suggest that the averaged PDS of GRBs follows a power law over
about two decades of frequency with the power law index, -5/3, and the
distribution of individual power follows an exponential distribution. Though an
attempt to identify the most sensitive physical parameter has been made on the
basis of the internal shock model, we demonstrate that conclusions of this kind
of approach should be derived with due care. It is indicative that the physical
information extracted from the slope can be misleading. We show that the
reported slope and the distribution can be reproduced by adjusting the sampling
interval in the time domain for a given decaying timescale of individual pulse
in a specific form of GRB light curves. In particular, given that the temporal
feature is modeled by a two-sided exponential function, the power law behavior
with the index of -5/3 and the exponential distribution of the observed PDS is
recovered at the 64 ms trigger time scale when the decaying timescale of
individual pulse is $\sim 1$ second, provided that the pulse sharply rises.
Another way of using the PDS analysis is an application of the same method to
individual long bursts in order to examine a possible evolution of the decaying
timescale in a single burst.


title: Iterative map-making for scanning experiments

abstract:
  We describe here an iterative method for jointly estimating the noise power
spectrum from a scanning experiment's time-ordered data, together with the
maximum-likelihood map. We test the robustness of this method on simulated
datasets with colored noise, like those of bolometer receivers in CMB
experiments.


title:
A Fundamental Relation Between Supermassive Black Holes and Their Host
  Galaxies

abstract:
  The masses of supermassive black holes correlate almost perfectly with the
velocity dispersions of their host bulges, M(BH) ~ sigma^alpha, where alpha
=4.8 +/- 0.5$. The relation is much tighter than the relation between M(BH) and
bulge luminosity, with a scatter no larger than expected on the basis of
measurement error alone. Black hole masses estimated by Magorrian et al. (1998)
lie systematically above the M(BH)-sigma relation defined by more accurate mass
estimates, some by as much as two orders of magnitude. The tightness of the
M(BH)-sigma relation implies a strong link between black hole formation and the
properties of the stellar bulge.


title:
X-ray emission from Seyfert 2 galaxies with optical polarized broad
  lines

abstract:
  We analyze the 0.5-10 keV spectra of six Seyfert 2 galaxies observed with the
X-ray satellite ASCA: Mrk 3, Mrk 348, Mrk 1210, Mrk 477, NGC 7212, and Was 49b.
These galaxies were selected based on their possession of optical polarized
broad lines. In the 2-10 keV band, their spectra are heavily absorbed, with
2-10 keV absorption-corrected X-ray luminosities ranging from 10^{42} to
10^{43} erg/s. The observed X-ray emission is generally only about one tenth
that predicted based on their known infrared and H_beta luminosities. This
apparent X-ray weakness can be understood if a considerable fraction of the
nuclear activity is completely blocked from view by thick matter along our line
of sight to the nucleus.
  All of these galaxies possess significant soft X-ray emission whose origin
appears to be scattered light from their nuclear emission. Based on this
hypothesis, we estimate a typical scattering efficiency for X-rays to be about
10%. This efficiency is larger than the few % found for ordinary Seyfert 2
galaxies with no report of optical polarized broad lines. A large scattering
efficiency is best explained by an apparent weakness of the hard X-ray
luminosity rather than unusually strong scattered light in the soft band. The
difference of the apparent weakness is probably associated with viewing angle.


title: Iron K line Variability in the Low-Luminosity AGN NGC 4579

abstract:
  We present results of new ASCA observations of the low-luminosity AGN (LLAGN)
NGC 4579 obtained on 1998 December 18 and 28, and we report on detection of
variability of an iron K emission line. The X-ray luminosities in the 2--10 keV
band for the two observations are nearly identical (LX $\approx$
2$\times10^{41}$ ergs/s), but they are $\sim$35% larger than that measured in
1995 July by Terashima et al. An Fe K emission line is detected at
$6.39\pm0.09$ keV (source rest frame) which is lower than the line energy
$6.73^{+0.13}_{-0.12}$ keV in the 1995 observation. If we fit the Fe lines with
a blend of two Gaussians centered at 6.39 keV and 6.73 keV, the intensity of
the 6.7 keV line decreases, while the intensity of the 6.4 keV line increases,
within an interval of 3.5 yr. This variability rules out thermal plasmas in the
host galaxy as the origin of the ionized Fe line in this LLAGN. The detection
and variability of the 6.4 keV line indicates that cold matter subtends a large
solid angle viewed from the nucleus and that it is located within $\sim1$ pc
from the nucleus. It could be identified with an optically thick standard
accretion disk. If this is the case, a standard accretion disk is present at
the Eddington ratio of $L_{\rm Bol}/L_{\rm Eddington} \sim 2\times10^{-3}$. A
broad disk-line profile is not clearly seen and the structure of the innermost
part of accretion disk remains unclear.


title: An $\dot{f}(f)$-frequency dynamics algorithm for gravitational waves

abstract:
  Coalescence of low mass compact binaries of neutron stars and black holes are
primary burst sources for LIGO and VIRGO.Of importance in the early stages of
observations will be the classification of candidate detections by source-type.
The diversity in source parameters and serendipity in any new window of
observations suggest to consider model-independent detection algorithms. Here a
frequency dynamics algorithm is described which extracts a trajectory in the
$\dot{f}(f)$-plane from the noisy signal. The algorithm is studied in simulated
binary coalescence. Robust results are obtained with experimental noise data.
Experiments show the method to be superior to matched filtering in the presence
of model imperfections.


title: The Disturbed ISM of the Local Group Dwarf Galaxy NGC 6822

abstract:
  We present a wide-field, high spatial and velocity resolution map of the
entire extended HI distribution of the nearby Local Group dwarf galaxy NGC
6822. The observations were obtained with the Parkes single-dish telescope and
the Australia Telescope Compact Array in mosaicing mode. NGC 6822 has an
extended HI-disk which is shaped by the presence of numerous HI holes and
shells, including a supergiant shell, and the effects of tidal interaction, in
the form of a tidal arm and an infalling or interacting HI complex. These tidal
features are not obvious in lower resolution data, and only the proximity of
NGC 6822 enables us to see them clearly. This suggests that the importance of
minor interactions in dwarf galaxies may be larger than previously assumed.


title: Gas in Galaxies

abstract:
  The interstellar medium (ISM) can be thought of as the galactic atmosphere
which fills the space between stars. When clouds within the ISM collapse, stars
are born. When the stars die, they return their matter to the surrounding gas.
Therefore the ISM plays a vital role in galactic evolution. The medium includes
starlight, gas, dust, planets, comets, asteroids, fast moving charged particles
(cosmic rays) and magnetic fields. The gas can be further divided into hot,
warm and cold components, each of which appear to exist over a range of
densities, and therefore pressures. Remarkably, the diverse gas components,
cosmic rays, magnetic fields and starlight all have very roughly the same
energy density of about 1 eV cm$^{-3}$. All the major constituents (or phases)
of the interstellar medium appear to be identified now, although complete
multi-phase studies are extremely difficult beyond a few thousand parsecs from
the Sun. The interstellar medium is a highly complex environment which does not
lend itself to simple analysis. However, this has not stopped astrophysicists
from producing basic models of the ISM in order to make sense of the great
wealth of data coming in from ground-based telescopes and from satellites.


title: Tunable Imaging Filters in Astronomy

abstract:
  While tunable filters are a recent development in night time astronomy, they
have long been used in other physical sciences, e.g. solar physics, remote
sensing and underwater communications. With their ability to tune precisely to
a given wavelength using a bandpass optimized for the experiment, tunable
filters are already producing some of the deepest narrowband images to date of
astrophysical sources. Furthermore, some classes of tunable filters can be used
in fast telescope beams and therefore allow for narrowband imaging over angular
fields of more than a degree over the sky.


title:
The stars near the centre of supergiant shell LMC4: Further constraints
  on triggering scenarios

abstract:
  The huge supergiant shell (SGS) LMC4, next to the giant HII region 30 Doradus
the second most impressive feature of the Large Magellanic Cloud (LMC), has
been the subject of many studies and was used to test various models of star
forming mechanisms. In this paper we present a B, V photometry of the very
centre of this SGS. The new data yield an age of 11(2)Myr and a colour excess
E(B-V) = 0.10(3)mag. Additionally, the two clusters near the geometric centre
are too old to be related to the formation of LMC4: HS343 being ~0.1Gyr and
KMHK1000 being ~0.3Gyr of age. This and existing photometries support that the
young stellar population covering the entire inner region is nearly coeval. We
compare these findings with predictions of models proposed for the creation
mechanism of SGSs. We conclude that the large-scale trigger, necessary to
explain the observations, comes from hydrodynamic interaction of the galactic
halo with gas in the leading edge of the moving LMC.


title:
Simultaneous radio and X-ray observations of Galactic Centre low mass
  X-ray binaries

abstract:
  We have performed simultaneous X-ray and radio observations of thirteen
Galactic centre low-mass X-ray binaries in 1998 April using the Wide-Field
Cameras onboard BeppoSAX and the Australia Telescope Compact Array, the latter
simultaneously at 4.8 and 8.64 GHz. We detect two Z sources, GX 17+2 and GX
5-1, and the unusual `hybrid' source GX 13+1. Upper limits, which are
significantly deeper than previous non-detections, are placed on the radio
emission from two more Z sources and seven atoll sources. Hardness-Intensity
diagrams constructed from the Wide-Field Camera data reveal GX 17+2 and GX 5-1
to have been on the lower part of the horizontal branch and/or the upper part
of the normal branch, at the time of the observations, and the two non-detected
Z sources, GX 340+0 and GX 349+2, to have been on the lower part of the normal
branch. This is consistent with the previous empirically-determined relation
between radio and X-ray emission from Z sources, in which radio emission is
strongest on the Horizontal branch and weakest on the Flaring branch. For the
first time we have information on the X-ray state of atoll sources, which are
clearly radio-quiet relative to the Z sources, during periods of observed radio
upper limits. We place limits on the linear polarisation from the three
detected sources, and use accurate radio astrometry of GX 17+2 to confirm that
it is probably not associated with the optical star NP Ser. Additionally we
place strong upper limits on the radio emission from the X-ray binary 2S
0921-630, disagreeing with suggestions that it is a Z-source viewed edge-on.


title: Comparison of the ENEAR Peculiar Velocities with the PSCz Gravity Field

abstract:
  We present a comparison between the peculiar velocity field measured from the
ENEAR all-sky $D_n-\sigma$ catalog and that derived from the galaxy
distribution of the IRAS PSCz redshift survey. The analysis is based on a modal
expansion of these data in redshift space by means of spherical harmonics and
Bessel functions. The effective smoothing scale of the expansion is almost
linear with redshift reaching 1500km/s at 3000km/s. The general flow patterns
in the filtered ENEAR and PSCz velocity fields agree well within 6000km/s,
assuming a linear biasing relation between the mass and the PSCz galaxies. The
comparison allows us to determine the parameter $\beta=\Omega^{0.6}/b$, where
$\Omega$ is the cosmological density parameter and $b$ is the linear biasing
factor. A likelihood analysis of the ENEAR and PSCz modes yields $\beta=0.5 +-
0.1$, in good agreement with values obtained from Tully-Fisher surveys.


title: Quasar environments at 0.5 < z < 0.8

abstract:
  Over the past few years, we have been collecting data with the Nordic Optical
Telescope (NOT) on the galaxy environments around active galactic nuclei (AGN).
Here we present some results from a sample of 21 radio-loud and 20 radio-quiet
quasars in the redshift range 0.5 < z < 0.8. We find a few quasars in very rich
environments, perhaps as rich as Abell class 1-2 clusters, but more often the
quasars seem to prefer groups and poorer clusters. We also find that on average
the galaxy environments around radio-loud and radio-quiet quasars are
indistinguishable, consistent with the findings that both powerful radio-loud
and radio-quiet quasars appear to be hosted by luminous galaxies with
luminosities higher than the break in the luminosity function (Dunlop et al.
1993; Taylor et al. 1996). Comparing the galaxy richnesses in the radio-loud
quasar fields with quasar fields in the literature, we find a weak, but
significant, correlation between quasar radio luminosity and environmental
richness.


title:
Fine phase resolved spectroscopy of the X-ray emission of the Crab
  pulsar (PSR B0531+21) observed with BeppoSAX

abstract:
  The Crab Nebula and the Pulsar have been pointed several times by the
BeppoSAX satellite. We analysed all these observations, summed together, to
study the main spectral properties with a good phase resolution. A new accurate
estimate of the hydrogen column density in the Crab direction N_H=3.23 x
10^(21) cm^(-2) is given as derived from the analysis of the off-pulse emission
at low energies. We studied the changes of the spectral index with the pulse
phase and showed that in the interpeak region it is systematically harder than
in the main peaks of about 0.4. We observed also a significant spectral
steepening of the pulsed emission and showed that this distribution can be
represented by a unique law with a linear variable log slope and apply it to
the spectrum of the first peak. A two component model is proposed to explain
the phase evolution of the spectrum. One component has the same profile
observed in the optical while the other presents a maximum at the phase 0.4
with essentially the spectrum of the interpeak region. Two possible
interpretations for the origin of the latter component are discussed.


title: Observational signatures of feedback in QSO absorption spectra

abstract:
  Models for the formation of galaxies and clusters of galaxies require strong
feedback in order to explain the observed properties of these systems. We
investigate whether such feedback has observational consequences for the
intergalactic medium, as probed in absorption towards background quasars. A
typical quasar sight-line intersects one proto-cluster per unit redshift, and
significant feedback from forming galaxies or AGN, heating the proto-cluster
gas, will result in a large clearing of reduced absorption in the Lyman
alpha-forest. Such a gap could be detected at redshift > 3 when the mean
opacity is high. Feedback from Lyman-break galaxies in proto-clusters can be
probed by the absorption lines produced in their winds. Strong feedback from
galaxies has a major impact on the number and properties of absorption lines
with neutral hydrogen column densities of 10^16/ cm^2. This feedback can be
probed with multiple sight-lines and by studying the unsaturated higher-order
lines of the Lyman series. Galactic winds from dwarf galaxies should break-up
into clouds, in order not to over produce the number of absorption lines. These
clouds can then coast to large distances.


title:
The 1-point PDF of the Initial Conditions of our Local Universe from the
  IRAS PSC redshift catalogue

abstract:
  The algorithm ZTRACE of Monaco & Efstathiou (1999) is applied to the IRAS
PSCz catalogue to reconstruct the initial conditions of our local Universe with
a resolution down to ~5 Mpc/h. The 1-point PDF of the reconstructed initial
conditions is consistent with the assumptions that (i) IRAS galaxies trace mass
on scales of ~5 Mpc/h, and (ii) the statistics of primordial density
fluctuations is Gaussian. We use simulated PSCz catalogues, constructed from
N-body simulations with Gaussian initial conditions, to show that local
non-linear bias can cause the recovered initial PDF (assuming no bias) to be
non-Gaussian. However, for plausible bias models, the distortions of the
recovered PDF would be difficult to detect using the volume finely sampled by
the PSCz catalogue. So, for Gaussian initial conditions, a range of bias models
remain compatible with our PSCz reconstruction results.


title: General considerations on the illumination of galactic nebulae

abstract:
  The interpretation of observations over different wavelength domains, which
now exist over a large fraction of the sky, will be used to determine
relationships between a nebula and its' illuminating source.
  The illuminating source of a high latitude nebula must be behind the cloud
and e.g. at close angular distance. It is either a point source behind the
nebula or the average radiation field created by all the background stars. In
the latter case it is possible to estimate the maximum surface brightness a
nebula can reach. Illumination by the galactic plane is always negligible in up
to date observations.
  The red color of some nebulae, when they are not HII regions, is more likely
to be due to large column densities than to an emission process.
  Concerning interstellar grain properties, the same data will be used to
support the well known property that grains scatter starlight in forward
direction.


title: Is there ERE in bright nebulae?

abstract:
  In 1986 Witt & Schild studied the optical emission of selected bright
nebulae. Comparison of the data to a model led the authors to conclude the
nebulae have too high a level of I-band emission to be explained solely by the
scattering of starlight. The excess is explained as a broad band I emission
which originates in the nebulae. This phenomenum is known as Extended Red
Emission (ERE).
  Given Witt & Schild's data, the model they employed, and the estimate of
observational errors, I've reached a different conclusion: Witt & Schild's
observations are compatible with classical scattering and therefore cannot be
used to prove the existence of ERE.


title: First Observations of the Magnetic Field Geometry in Pre-stellar Cores

abstract:
  We present the first published maps of magnetic fields in pre-stellar cores,
to test theoretical ideas about the way in which the magnetic field geometry
affects the star formation process. The observations are JCMT-SCUBA maps of 850
micron thermal emission from dust. Linear polarizations at typically ten or
more independent positions in each of three objects, L1544, L183 and L43 were
measured, and the geometries of the magnetic fields in the plane of the sky
were mapped from the polarization directions. The observed polarizations in all
three objects appear smooth and fairly uniform. In L1544 and L183 the mean
magnetic fields are at an angle of around 30 degrees to the minor axes of the
cores. The L43 B-field appears to have been influenced in its southern half,
such that it is parallel to the wall of a cavity produced by a CO outflow from
a nearby T Tauri star, whilst in the northern half the field appears less
disturbed and has an angle of 44 degrees to the core minor axis. We briefly
compare our results with published models of magnetized cloud cores and
conclude that no current model can explain these observations simultaneously
with previous ISOCAM data.


title: No diffuse H2 in the metal deficient galaxy I Zw 18

abstract:
  The metal deficient starburst galaxy IZw18 has been observed with FUSE in a
search for H2 molecules. The spectrum obtained with an aperture covering the
full galaxy shows no absorption lines of diffuse H2 at the radial velocity of
the galaxy. The upper limit for the diffuse H2 column density is found to be
very low: N(H2) <~ 10^15 cm-2 (10 sigma), unlike our Galaxy where H2 is
generally present for even low HI column densities. Although the HI column
density is here as high as N(HI) ~ 2.10^21 cm-2, we observe 2N(H2)/N(HI)<<
10^-6. We cannot exclude the possibility that some H2 could be in very dense,
small and discrete clumps which cannot be detected with the present
observation. However, the remarkable absence of diffuse H2 in this metal-poor
galaxy can be explained by the low abundance of dust grains (needed to form
this molecule from H-atoms), the high ultraviolet flux and the low density of
the HI cloud surrounding the star-forming regions. Thus having eliminated
diffuse H2 as a significant contributor to the total mass, it appears that the
gas of the galaxy is dominated by HI, and that the high dynamical mass is not
composed of cold and diffuse baryonic dark matter.


title: A pot of gold at the end of the cosmic "raynbow"?

abstract:
  We critically review the common belief that ultrahigh energy cosmic rays are
protons or atomic nuclei with masses not exceeding that of iron. We find that
heavier nuclei are indeed possible, and discuss possible sources and
acceleration mechanisms for such primaries. We also show detailed simulations
of extensive air showers produced by ``superheavy'' nuclei, and discuss
prospects for their detection in future experiments.


title: A Powerful Radio Halo in the Hottest Known Cluster of Galaxies 1E0657-56

abstract:
  We report the detection of a diffuse radio halo source in the hottest known
cluster of galaxies 1E0657-56 (RXJ0658-5557). The radio halo has a morphology
similar to the X-ray emission from the hot intracluster medium. The presence of
a luminous radio halo in such a hot cluster is further evidence for a steep
correlation between the radio halo power and the X-ray temperature. We favour
models for the origin of radio halo sources involving a direct connection
between the X-ray emitting thermal particles and the radio emitting
relativistic particles.


title: Transport phenomena in stochastic magnetic mirrors

abstract:
  Parallel thermal conduction along stochastic magnetic field lines may be
reduced because the heat conducting electrons become trapped and detrapped
between regions of strong magnetic field (magnetic mirrors). The problem
reduces to a simple but realistic model for diffusion of mono-energetic
electrons based on the fact that when there is a reduction of diffusion, it is
controlled by a subset of the mirrors, the principle mirrors. The diffusion
reduction can be considered as equivalent to an enhancement of the pitch angle
scattering rate. Therefore, in deriving the collision integral, we modify the
pitch angle scattering term. We take into account the full perturbed
electron-electron collision integral, as well as the electron-proton collision
term. Finally, we obtain the four plasma transport coefficients and the
effective thermal conductivity. We express them as reductions from the
classical values. We present these reductions as functions of the ratio of the
magnetic field decorrelation length to the electron mean free path at the
thermal speed $V_T=\sqrt{2kT/m_e}$. We briefly discuss an application of our
results to clusters of galaxies.
  Key words: magnetic fields: conduction --- magnetic fields: diffusion ---
methods: analytical --- plasmas


title: Dark matter phase space densities

abstract:
  The low velocity part of a kinetic equilibrium dark matter distribution has
higher phase space density and is more easily incorporated in formation of a
low mass galaxy than the high velocity part. For relativistically decoupling
fermions (bosons), this explains one (two) orders of magnitude of the observed
trend, that phase space densities in dark matter halo cores are highest in the
smallest systems, and loosens constraints on particle masses significantly. For
non-relativistic decoupling and/or finite chemical potentials even larger
effects may occur. It is therefore premature to dismiss dissipationless
particle distributions as dark matter on the basis of phase space arguments.


title:
Optical Spectrum of Main-, Inter- and Off-pulse Emission from Crab
  Pulsar

abstract:
  A dedicated stroboscopic device was used to obtain optical spectra of the
Crab main-pulse and inter-pulse as well as the spectrum of the underlying
nebula when the pulsar is turned off. As the nebular emission is very
inhomogeneous, our ability to effectively subtract the nebular background
signal is crucial.
  No spectral lines intrinsic to the pulsar are detected. The main-pulse and
the inter-pulse behave as power laws, both with the same de-reddened index
Alpha = +0.2 +- 0.1. This value was obtained by subtracting the nebular
spectrum at the exact position of the pulsar. The underlying nebula is redder,
Alpha = -0.4 +- 0.1. Its emission lines are split into approaching (sim. -1200
km/s) and receding (sim. +600 km/s) components. The strength of emission line
components and the flux in nebular continuum vary on arcsec scale. The nebular
line and continuum intensities along the N-S slit are given.


title: X-ray spectral features from GRBs: Predictions of progenitor models

abstract:
  We investigate the potentially observable prompt or delayed X-ray spectral
features from the currently popular gamma-ray burst (GRB) models. During the
evolution of many GRB progenitors, a disk around the central GRB source is
produced. Shock heating as the GRB ejecta collide with the disk may produce
observable X-ray features. We first summarize predictions deduced from previous
calculations which invoke photoionization and relativistic blast waves. We then
calculate the quasi-thermal X-ray line features produced assuming the ejecta
are nonrelativistic (which is more likely for the disk interactions of many GRB
models). In the framework of the Hypernova/Collapsar model, delayed (a few days
- several months after the GRB) bursts of line-dominated, thermal X-ray
emission may be expected. The He-merger scenario predicts similar X-ray
emission line bursts <~ a few days after the GRB. These X-ray signatures should
be observable with Chandra and XMM-Newton out to at least z ~ 1. Weak emission
line features <~ a few days after the GRB may also result from the supranova
GRB scenario. In all three cases, significant X-ray absorption features, in
particular during the prompt GRB phase, are expected. No significant X-ray
spectral features might result from compact-object binary mergers.


title: Perturbation Spectra in the Warm Inflationary Scenario

abstract:
  We investigate the phenomenology of warm inflation and present generic
results about the evolution of the inflaton and radiation fields. The general
conditions required for warm inflation to take place are derived and discussed.
A comprehensive approach is presented for the generation of thermally induced
adiabatic and isocurvature perturbations and the amplitude of their spectra
calculated. In addition we derive the ratio of tensor-to-scalar perturbations
and find the spectral indices for adiabatic, isocurvature and tensor
perturbations formed in the warm inflationary era. These results are presented
in a simplified and compact approach that is generally applicable. Our results
are illustrated by inflation models with polynomial and exponential potentials.
We compare our analytic results against numerical models and find excellent
agreement. Finally, presently available data is used to put constraints on warm
inflation and we discuss how near--future observations may distinguish the warm
inflationary scenario from standard supercooled inflation. The main observable
difference is the different scalar-to- tensor ratio, and that the consistency
relation between this and the slope of tensor perturbations does not hold for
warm inflation.


title: Constraints on Cluster Properties Using X-ray and Optical Data

abstract:
  In this work we show that combining different cluster data sets is a powerful
tool to constrain both, the cosmology and cluster properties. We assume a model
with 9 parameters and fit them to 5 cluster data sets. From that fit, we
conclude that only low density universes are compatible with the previous data
and we also get some interesting conclusions on the rest of parameters.


title:
Impact of Few-Body Reactions on Explosive Nucleosynthesis: The Big-Bang
  and Supernovae

abstract:
  We study the few body reactions in explosive nucleosynthesis of
light-to-heavy mass elements in various astrophysical conditions. In
neutrino-driven winds of gravitational core collapse of SNeII, several light
nuclei as well as heavy unstable nuclei paly significant roles in producing
r-process elements. We discuss how the three-body reaction $^4$He$(\alpha n,
\gamma)^9$Be, whose cross section is poorly known, plays very critical role. We
make note that several other reactions in the r-process are relevant to a
Big-Bang nucleosynthesis. We discuss briefly a Galactic chemical evolution.


title: Optical and Infrared photometry of the type IIn SN 1998S:Days 11-146

abstract:
  We present contemporaneous optical and infrared photometric observations of
the type IIn SN 1998S covering the period between 11 and 146 days after
discovery. The infrared data constitute the first ever infrared light curves of
a type IIn supernova. We use blackbody and spline fits to the photometry to
examine the luminosity evolution. During the first 2--3 months, the luminosity
is dominated by the release of shock-deposited energy in the ejecta. After
$\sim$100 days the luminosity is powered mostly by the deposition of
radioactive decay energy from 0.15$\pm$0.05 M$_{\odot}$ of $^{56}$Ni which was
produced in the explosion. We also report the discovery of an astonishingly
high infrared (IR) excess, $K-L'=2.5$, that was present at day 130. We
interpret this as being due to thermal emission from dust grains in the
vicinity of the supernova. We argue that to produce such a high IR luminosity
so soon after the explosion, the dust must be {\it pre-existing} and so is
located in the circumstellar medium of the progenitor. The dust could be heated
either by the UV/optical flash (IR echo) or by the X-rays from the interaction
of the ejecta with the circumstellar material


title: On the redshift cut-off for flat-spectrum radio sources

abstract:
  We use data from the Parkes Half-Jansky Flat-Spectrum (PHJFS) sample
(Drinkwater et al. 1997) to constrain the cosmic evolution in the co-moving
space density of radio sources in the top decade of the flat-spectrum radio
luminosity function (RLF). A consistent picture for the high-redshift evolution
is achieved using both simple parametric models, which are the first to allow
for distributions in both radio luminosity and spectral index, and variants of
the V / V_max test, some of which incorporate the effects of radio spectral
curvature. For the most luminous flat-spectrum objects, the PHJFS sample is
extremely similar to that used by Shaver et al. (1996, 1998) to argue for an
abrupt `redshift cut-off': a decrease by a factor ~30 in space density between
a peak redshift z~2.5 and z~5. Our analysis finds that the observable co-moving
volume is too small to make definitive statements about any redshift cut-off
for the most luminous flat-spectrum sources, although both constant-space
density (no cut-off) models and models with cut-offs as abrupt as those
envisaged by Shaver et al. are outside the 90% confidence region. The inference
that the decline in space density is most likely to be gradual, by a factor ~4
between z~2.5 and z~5, is in accordance with previous work on the RLF by Dunlop
& Peacock (1990), but different to the abrupt decline favoured by studies of
optically-selected quasars. Dust obscuration provides one explanation for this
difference. We show that a significant fraction of the most radio-luminous
flat-spectrum objects are Giga-Hertz Peaked Spectrum (GPS) rather than
Doppler-Boosted (DB) sources, complicating any interpretation of the redshift
cut-off.


title: A Model of Metallicity Evolution in the Early Universe

abstract:
  We apply the phenomenological model used to explain the abundances of Fe and
r-process elements in very metal-poor stars in the Galaxy to [Fe/H] of damped
Ly alpha systems. It is assumed that the first stars formed after the Big Bang
were very massive and promptly enriched the interstellar medium to [Fe/H] ~ -3,
at which metallicity formation of normal stars took over. Subsequent Fe
enrichment was provided by Type II supernovae. The range of [Fe/H] at a given
redshift z for damped Ly alpha systems is explained by the time t* after the
Big Bang at which normal star formation started in an individual protogalactic
system. The average t* is approx 80% the age of the universe for damped Ly
alpha systems at z approx 1.5 to 4.5, indicating a long delay between the Big
Bang and the turn-on of protogalaxies. It is inferred that a substantial
fraction of the total baryonic matter may not have been aggregated into
protogalaxies where normal star formation had occurred down to z ~ 1.5. The
data near z = 2.2 suggest that the rate of turn-on of protogalaxies was
initially very low and slowly reached a maximum at ~ 3 Gyr after the Big Bang.
This may be important in understanding the rate of formation of quasars.


title: Clumps into Voids

abstract:
  We consider a spherically symmetric distribution of dust and show that it is
possible, under general physically reasonable conditions, for an overdensity to
evolve to an underdensity (and vice versa). We find the conditions under which
this occurs and illustrate it on a class of regular Lemaitre-Tolman-Bondi
solutions. The existence of this phenomenon, if verified, would have the result
that the topology of density contours, assumed fixed in standard structure
formation theories, would have to change and that luminous matter would not
trace the dark matter distribution so well.


title: Cold gas and star formation in a merging galaxy sequence

abstract:
  We explore the evolution of the cold gas and star-formation activity during
galaxy interactions, using a merging galaxy sequence comprising both pre- and
post-mergers. Data for this study come from the literature but supplemented by
new radio observations presented here. Firstly, we confirm that the
star-formation efficiency (SFE) increases close to nuclear coalescence. At
post-merger stages there is evidence that the SFE declines to values typical of
ellipticals. This trend can be attributed to M(H_2) depletion due to
interaction induced star-formation. However, there is significant scatter,
likely to arise from differences in the interaction details of individual
systems. Secondly, we find that the central molecular hydrogen surface density,
increases close to the final stages of the merging of the two nuclei. Such a
trend is also predicted by numerical simulations. Furthermore, there is
evidence for a decreasing fraction of cold gas mass from early interacting
systems to merger remnants, attributed to gas conversion into other forms. The
evolution of the total-radio to blue-band luminosity ratio, reflecting the
disk+nucleus star-formation activity, is also investigated. Although this ratio
is on average higher than that of isolated spirals, we find a marginal increase
along the merging sequence, attributed to the relative insensitivity of disk
star-formation to interactions. However, a similar result is also obtained for
the nuclear radio emission, although galaxy interactions are believed to
significantly affect the activity in the central galaxy regions. Finally, we
find that the FIR--radio flux ratio distribution of interacting galaxies is
consistent with star-formation being the main energising source.


title:
Investigating the structure of the accretion disk in WZ Sge from
  multi-wave-band, time-resolved spectroscopic observations: Paper II

abstract:
  We present our second paper describing multi-wave-band, time-resolved
spectroscopy of WZ Sge. We analyze the evolution of both optical and IR
emission lines throughout the orbital period and find evidence, in the Balmer
lines, for an optically thin accretion disk and an optically thick hot-spot.
Optical and IR emission lines are used to compute radial velocity curves. Fits
to our radial velocity measurements give an internally inconsistent set of
values for K1, gamma, and the phase of red-to-blue crossing. We present a
probable explanation for these discrepancies and provide evidence for similar
behaviour in other short orbital period dwarf-novae. Selected optical and IR
spectra are measured to determine the accretion disk radii. Values for the disk
radii are found to be strongly dependent on the assumed WD mass and binary
orbital inclination. However, the separation of the peaks in the optical
emission line (i.e. an indication of the outer disk radius) has been found to
be constant during all phases of the super-cycle period over the last 40 years.


title: AU-Scale Synchrotron Jets and Superluminal Ejecta in GRS 1915+105

abstract:
  Radio imaging of the microquasar GRS 1915+105 with the Very Long Baseline
Array (VLBA) during various flaring, quiescent, or oscillatory states of the
black hole binary, always resolves the nucleus as a compact jet of length about
10.lambda_cm AU. On scales of 2.5-7AU, the nucleus has brightness temperature
T_B > 10^9 K, and its properties are better fit by a synchrotron jet, rather
than a thermal jet. The nuclear jet varies in 10-60min during minor X-ray/radio
outbursts, and re-establishes within 18hrs of a major outburst, indicating the
robustness of the disk/jet system to disruption. At lower resolution
(80-240AU), time-lapse images reveal discrete superluminal ejecta at 500-600 AU
separation from the nucleus. The measured velocity is 1.5c+-0.1c(D/12 kpc) for
the approaching component, consistent with ballistic motion of the ejecta from
500AU outwards, perhaps even since birth. The axis of the ejecta differs by
<12deg clockwise from the axis of the AU-scale jet, measured in the same
observation. Both axes are stable for years. The black hole is astrometrically
located to +-1.5mas, after accounting for its secular parallax from Galactic
rotation of 5.8+-1.5mas/yr at the distance of 12kpc, and a limit of <100km/s is
placed on its proper-motion with respect to its neighbourhood. Our observations
suggest that the unresolved flat-spectrum radio cores of accreting black holes
are compact quasi-continuous synchrotron jets.


title:
Chandra X-ray Observatory Study of the Orion Nebula Cluster and BN/KL
  Region

abstract:
  About 1000 X-ray emitting young pre-main sequence (PMS) stars distributed in
mass from 0.05 to 50 solar masses are detected in an image of the Orion Nebula
obtained with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray
Observatory. This is the richest field of sources ever obtained in X-ray
astronomy. ACIS sources include 85-90% of V<20 stars, plus a substantial
fraction of deeply embedded stars with extinctions as high as A_V~60.
  The relationships between X-ray and other PMS stellar properties suggest that
X-ray luminosity of lower-mass PMS stars depends more on mass, and possibly
stellar rotation, than on bolometric luminosity as widely reported. A subsample
of unabsorbed solar-mass stars show high X-ray luminosities around L_x ~ 2 x
10^30 erg/s for the first ~2 My but diverge during 2-10 My with X-ray emission
plummeting in some stars but remaining high in others. This behavior is
consistent with theories of stellar rotational history and magnetic dynamos.
  The Becklin-Neugebauer/Kleinman-Low (BN/KL) region of massive star formation
shows both unabsorbed and embedded low-mass members of the Orion Nebula
Cluster, the luminous infrared Source n, and a class of sources without
photospheric counterparts that may be new magnetically active embedded PMS
stars. Several X-ray sources are also variable radio emitters. Faint X-ray
emission is seen close to, but apparently not coincident with the BN object.
Its nature is not clear.


title:
Multiperiodicity in semiregular variables II. Systematic amplitude
  variations

abstract:
  We present a detailed lightcurve analysis for a sample of bright semiregular
variables based on long-term (70--90 years) visual magnitude estimates carried
out by amateur astronomers. Fundamental changes of the physical state
(amplitude and/or frequency modulations, mode change and switching) are studied
with the conventional Fourier- and wavelet analysis.
  The light curve of the carbon Mira Y Per showing a gradual amplitude decrease
has been re-analysed after collecting and adding current data to earlier ones.
The time scales of the sudden change and convection are compared and their
similar order of magnitude is interpreted to be a possible hint for strong
coupling between pulsation and convection. The periods of the biperiodic
low-amplitude light curve and their ratios suggest a pulsation in the first and
third overtone modes. An alternative explanation of the observed behaviour
could be a period halving due to the presence of weak chaos.
  Beside two examples of repetitive mode changes (AF Cyg and W Cyg) we report
three stars with significant amplitude modulations (RY Leo, RX UMa and RY UMa).
A simple geometric model of a rotationally induced amplitude modulation in RY
UMa is outlined assuming low-order nonradial oscillation, while the observed
behaviour of RX UMa and RY Leo is explained as a beating of two closely
separated modes of pulsation. This phenomenon is detected unambiguously in V
CVn, too. The period ratios found in these stars (1.03-1.10) suggest either
high-order overtone or radial+non-radial oscillation.


title:
Formulae for Growth Factors In Expanding Universes Containing Matter and
  a Cosmological Constant

abstract:
  Formulae are presented for the linear growth factor D/a and its logarithmic
derivative dlnD/dlna in expanding Friedmann-Robertson-Walker Universes with
arbitrary matter and vacuum densities. The formulae permit rapid and stable
numerical evaluation. A fortran program is available at
http://casa.colorado.edu/~ajsh/growl/ .


title:
VLT-ISAAC near-IR Spectroscopy of ISO selected Hubble Deep Field South
  Galaxies

abstract:
  We report the results of near-infrared VLT-ISAAC spectroscopy of a sample of
12 galaxies at z = 0.4-1.4, drawn from the ISOCAM survey of the Hubble Deep
Field South. We find that the rest frame R-band spectra of the ISOCAM galaxies
resemble those of powerful dust-enshrouded starbursts. Halpha emission is
detected in 11 out of 12 objects down to a flux limit of 7x10^(-17) erg/cm^2/s,
corresponding to a luminosity limit of 10^41 erg/s at z = 0.6, (for an Ho = 50
and Omega = 0.3 cosmology). From the Halpha luminosities in these galaxies we
derive estimates of the star formation rate in the range 2--50 Mo/yr for
stellar masses 1--100 Mo. The raw Halpha-based star formation rates are an
order of magnitude or more lower than SFR(FIR) estimates based on ISOCAM LW3
fluxes. If the Halpha emission is corrected for extinction the median offset is
reduced to a factor of 3. The sample galaxies are part of a new population of
optically faint but infrared--luminous active starburst galaxies, which are
characterized by an extremely high rate of evolution with redshift up to z~1.5
and expected to contribute significantly to the cosmic far-IR extragalactic
background.


title: A Comptonization Model for Phase Lag Variability in GRS 1915+105

abstract:
  In this Letter we propose a simple thermal comptonization model to account
for the observed properties of the phase lags associated to the ``plateau''
intervals of GRS 1915+105. By invoking a temperature stratification in a corona
and assuming that the optical depth of the comptonizing region increases as the
disk inner radius moves inward, we are able to reproduce both the observed
colors and time lags in the continuum.


title:
Rejection of the hypothesis that Markarian 501 TeV photons are pure
  Bose-Einstein condensates

abstract:
  The energy spectrum of the Blazar type galaxy Markarian 501 (Mrk 501) as
measured by the High-Energy-Gamma-Ray Astronomy (HEGRA) air Cerenkov telescopes
extends beyond 16 TeV and constitutes the most energetic photons observed from
an extragalactic object. A fraction of the emitted spectrum is possibly
absorbed in interactions with low energy photons of the diffuse extragalactic
infrared radiation, which in turn offers the unique possibility to measure the
diffuse infrared radiation density by TeV spectroscopy. The upper limit on the
density of the extragalactic infrared radiation derived from the TeV
observations imposes constraints on models of galaxy formation and stellar
evolution. One of the recently published ideas to overcome severe absorption of
TeV photons is based upon the assumption that sources like Mrk 501 could
produce Bose-Einstein condensates of coherent photons. The condensates would
have a higher survival probability during the transport in the diffuse
radiation field and could mimic TeV air shower events. The powerful
stereoscopic technique of the HEGRA air Cerenkov telescopes allows to test this
hypothesis by reconstructing the penetration depths of TeV air shower events:
Air showers initiated by Bose-Einstein condensates are expected to reach the
maximum of the shower development in the atmosphere earlier than single photon
events. By comparing the energy-dependent penetration depths of TeV photons
from Mrk 501 with those from the TeV standard-candle Crab Nebula and simulated
air shower events, we can reject the hypothesis that TeV photons from Mrk 501
are pure Bose-Einstein condensates.


title:
Equations of motion for the mass centers in a scalar theory of
  gravitation

abstract:
  A scalar theory of gravitation with a preferred reference frame (PRF) is
considered, that accounts for special relativity and reduces to it if the
gravitational field cancels. The gravitating system consists of a finite number
of perfect-fluid bodies. An " asymptotic " post-Newtonian (PN) approximation
scheme is used, allowing an explicit weak-field limit with all fields expanded.
Exact mass centers are defined and their exact equations of motion are derived.
The PN expansion of these equations is obtained: the zero-order equations are
those of Newtonian gravity (NG), and the equations for the first-order (PN)
corrections depend linearly on the PN fields. For PN corrections to the motion
of the mass centers, especially in the solar system, one may assume "
very-well-separated " rigidly moving bodies with spherical self-fields of the
zero-order approximation. The PN corrections reduce then to a time integration
and include spin effects, which might be significant. It is shown that the
Newtonian masses are not correct zero-order masses for the PN calculations. An
algorithm is proposed, in order to minimize the residual and to assess the
velocity in the PRF.


title:
Three high-redshift millimeter sources and their radio and near-infrared
  identifications

abstract:
  We present millimeter wavelength detections of three faint sources that are
most likely high-redshift starburst galaxies. For one of the sources, which was
previously discovered with SCUBA at 850 mu m, we present a detection with the
IRAM interferometer at 240 GHz (1.25 mm) that shows the object unresolved at an
angular resolution of 2.''5, and coincident within 1'' with a radio source and
a galaxy detected in the near-infrared. The two other sources were discovered
in a deep 250 GHz (1.2 mm) survey with the Max-Planck Millimeter Bolometer
(MAMBO) array at the IRAM 30m telescope. Both have fluxes of ~4 mJy and radio
counterparts with a 1.4 GHz flux density of ~75 muJy. Their radio-to-mm flux
ratios suggest redshifts larger than 2. Both sources are faint in the optical
and near-infrared, one showing a 20.5 mag K-band counterpart. From our data and
that available in the literature, we estimate the redshift distribution of
twenty-two faint mm and sub-mm sources and conclude that the majority of them
are likely to be at z>2.


title: High-energy $\gamma$-ray emission from GRBs

abstract:
  GRBs are nowadays a rather well understood phenomenon in the soft (KeV-MeV)
$\gamma$-ray energy band, while only a few GRBs have been observed at high
photon energies ($E_{\gamma} \ut > 1$ GeV). It is also widely recognized that
GRBs accelerate protons to relativistic energies and that dense media are often
present nearby the sources. Within this framework we compute in detail the
high-energy $\gamma$-ray flux from the decay of neutral pions produced through
the interaction of accelerate protons with nucleons in the surrounding medium.
We also take into account the local and intergalactic $\gamma$-ray absorption.
The presence of magnetic fields around the GRB sources causes the deflection of
the accelerated protons and so a temporal spread of the produced high-energy
$\gamma$-rays with respect to the signal in the soft $\gamma$-ray band.
Moreover, we analyze the possibility to detect the $\gamma$-ray signal in the
GeV-TeV energy range by the ARGO detector under construction in Tibet.


title: Constraints on the Space Density of Extragalactic HVCs

abstract:
  High Velocity Clouds (HVCs) have recently attracted renewed attention as
being long lived, massive dark matter dominated clouds of primordial
composition distributed throughout the Local Group. In this picture the HVCs
would contain a few times 10^7 M_sun of HI and would be at distances of a few
hundred kpc to 1.5 Mpc from the Local Group barycenter. If this extragalactic
interpretation of HVCs is true, similar clouds are expected in other galaxy
groups and around galaxies. We discuss the limits blind HI surveys and QSO
absorption line studies put on this proposed population of clouds.


title: On non-Gaussianity in the Cosmic Microwave Background

abstract:
  We consider a cosmological model with non-Gaussian initial perturbations,
which in principle could be generated in non-standard inflationary scenarios
with two or more scalar fields. In particular we focus our attention on the
model proposed by Linde & Mukhanov (1997) perturbations are quadratic in a
Gaussian field. These perturbations, if they exist, have to be observable as a
non-Gaussian distribution of the CMB signal on the sky. In order to efficiently
pick up the non-Gaussian signal in CMB maps of degree resolution, one can use
Minkowski Functionals and peak statistics. Our paper contains the theoretical
predictions of the properties for Minkowski Functionals and distributions of
peaks of the CMB anisotropy in the model with "squared" Gaussian statistics.
Likelihood comparison of the four-year COBE DMR data to this non-Gaussian model
and the standard Gaussian model does not select any of them as most likely. We
also suggest an efficient algorithm for fast simulation of CMB maps on the
whole sky. Using a cylindrical partition of the sphere, we rewrite the
spherical harmonics analysis as a Fourier transform in flat space, which makes
the problem accessible to numerically advantageous FFT methods.


title:
Nonzero angular momentum states of the helium atom in a strong magnetic
  field

abstract:
  The electronic structure of the helium atom in the magnetic field regime
B=0-100a.u. is investigated, using a full configuration interaction approach
which is based on a nonlinearly optimized anisotropic Gaussian basis set of
one-particle functions. The corresponding generalized eigenvalue problem is
solved for the magnetic quantum number M=-1 and for both even and odd z-parity
as well as singlet and triplet spin symmetry. Accurate total electronic
energies of the ground state and the first four excitations in each subspace as
well as their one-electron ionization energies are presented as a function of
the magnetic field. Additionally we present energies for electromagnetic
transitions within the M=-1 subspace and between the M=-1 subspace and the M=0
subspace treated in a previous work. A complete table of wavelengths and field
strengths for the detected stationary points is given.


title: Superbubbles and the Galactic evolution of Li, Be and B

abstract:
  From a recent re-analysis of the available data, Be and B Galactic evolution
appears to show evidence for a two-slope behaviour with respect to O. The
inferred Be/O abundance ratio in halo stars is constant at very low metallicity
(primary behaviour) and increases proportionally to O/H at high metallicity
(secondary behaviour). We show that this can be explained in the framework of
one single model, the `superbubble model', in which Li, Be and B are produced
by spallation reactions induced by energetic particles accelerated out of a
mixture of supernova (SN) ejecta and ambient interstellar medium inside
superbubbles (SBs). All the qualitative and quantitative constraints, including
the energetics, the value of the transition metallicity and the 6Li/9Be
isotopic ratio, are satisfied provided that the energetic particles have a
spectrum flattened at low energy (in E^-1) and that the proportion of the SN
ejecta inside SBs is of the order of a few percent. This lends support to
Bykov's acceleration mechanism inside SBs and to the SB dynamical evolution
model of Mac Low & McCray (1988).


title:
Tidal Tails Around 20 Galactic Globular Cluster: Observational Evidence
  for Gravitational Disk/Bulge Shocking

abstract:
  Large-field multi-color images of 20 galactic globular clusters are used to
investigate the presence of tidal tails around these stellar systems. Field and
cluster stars are sorted with the help of color-magnitude diagrams, and
star-count analysis is performed on the selected cluster stars in order to
increase the signal-to-noise ratio of their surface density. We study the
overdensities of these stars using the wavelet transform of the star counts in
order to filter the background density noise and to detect the weak structures,
at large scale, formed by the numerous stars previously members of the
clusters. We associate these stellar overdensities with the stars evaporated
from the clusters because of dynamical relaxation and/or tidal stripping from
the clusters by the galactic gravitational field. Most of the globular clusters
in our sample display strong evidence of tidal interactions with the galactic
plane in the form of large and extended deformations. These tidal tails exhibit
projected directions preferentially towards the galactic center. All the
clusters observed, which do not suffer from strong observational biases,
present such tidal tails, tracing their dynamical evolution (evaporation, tidal
shocking, tidal torquing, and bulge shocking) in the Galaxy. The clusters
exhibit different regimes of mass loss rate, detected using the radial density
slope in the outer parts of the clusters. For NGC 5139 ($\omega$ Centauri), we
estimate, taking into account the possible presence of mass segregation in its
outer parts, that about 0.6 to 1% of its mass has been lost during the crossing
(Abridged)


title: Collimated outflows of rapidly rotating young stellar objects

abstract:
  We present an analytical model for the magnetic flux surfaces for rapidly
rotating magnetized young stellar objects which is based on ideal, stationary,
axisymmetric magnetohydrodynamics. The resulting cold wind solutions reproduce
observed wind velocities of a few hundred \kms$ $ and the outer jet radi us for
a collimated jet of several thousand stellar radii. The theory of axisymmetric
magnetospheres around rapidly rotating stellar sources is outlined including
electric fields due to the rapid rotation. Gravity of the central object is
consistently built into this theory. A consistent wind theory is developed
which contains the Newtonian theory as a classical limit. Current--carrying
plasma flows will lead to a collimation of the magnetospheric structure into a
cylindrical shape. We show that the asymptotic structure is essentially
determined by electric forces in the pinch equation, and not by centrifugal and
pressure forces.


title:
The Effect of Expansion on Mass Entrainment and Stability of
  Super-Alfv\'enic Jets

abstract:
  We extend investigations of mass entrainment by jets, which previously have
focused on cylindrical supermagnetosonic jets and expanding trans-Alfv\'enic
jets, to a set of expanding supermagnetosonic jets. We precess these jets at
the origin to excite the helical mode of the Kelvin-Helmholtz (or KH)
instability, in order to compare the results with predictions from linear
stability analysis. We analyze this simulation set for the spatial development
of magnetized mass, which we interpret as jet plus entrained, initially
unmagnetized external mass. As with the previous simulation sets, we find that
the growth of magnetized mass is associated with the growth of the KH
instability through linear, nonlinear, and saturated stages and with the
expansion of magnetized material in simulated observations of the jet. From
comparison of measured wavelengths and wave speeds with the predictions from
linear stability analysis, we see evidence that the KH instability is the
primary cause for mass entrainment in these simulations, and that the expansion
reduces the rate of mass entrainment. This reduced rate can be observed as a
somewhat greater distance between the two transition points separating the
three stages of expansion.


title: Median Statistics, H_0, and the Accelerating Universe

abstract:
  (Abridged) We develop median statistics that provide powerful alternatives to
chi-squared likelihood methods and require fewer assumptions about the data.
Applying median statistics to Huchra's compilation of nearly all estimates of
the Hubble constant, we find a median value H_0=67 km/s/Mpc. Median statistics
assume only that the measurements are independent and free of systematic
errors. This estimate is arguably the best summary of current knowledge because
it uses all available data and, unlike other estimates, makes no assumption
about the distribution of measurement errors. The 95% range of purely
statistical errors is +/- 2 km/s/Mpc. The statistical precision of this result
leads us to analyze the range of possible systematic errors in the median,
which we estimate to be roughly +/- 5 km/s/Mpc (95% limits), dominating over
the statistical errors. A Bayesian median statistics treatment of high-redshift
Type Ia supernovae (SNe Ia) apparent magnitude versus redshift data from Riess
et al. yields a posterior probability that the cosmological constant Lambda > 0
of 70 or 89%, depending on the prior information used. The posterior
probability of an open universe is about 47%. Analysis of the Perlmutter et al.
high-redshift SNe Ia data show the best-fit flat-Lambda model favored over the
best-fit Lambda = 0 open model by odds of 366:1; corresponding Riess et al.
odds are 3:1 (assuming prior odds of 1:1).Median statistics analyses of the SNe
Ia data do not rule out a time-variable Lambda model, and may even favor it
over a time-independent Lambda and a Lambda = 0 open model.


title: The radial distribution of OB star formation in the Galaxy

abstract:
  We present the azimuthally averaged radial distribution of 748 regions of OB
star formation in the whole galactic disk, based on our previous CS(2-1) survey
of UC H II regions. Embedded massive stars produce a total FIR luminosity of
1.39E8 Lsun within the range 0.2<R/Ro<2 in galactocentric radius. We find 492
massive star forming regions within the solar circle, producing 81% of the
total FIR luminosity. Separate analyses of the 349 sources in the I and II
quadrant (north), and of the 399 sources in the III and IV quadrant (south),
yield FIR luminosities (extrapolated to the complete galactic disk) of 1.17E8
Lsun and of 1.60E8 Lsun, respectively. Massive star formation is distributed in
a layer with its centroid Zo(R) following that of molecular gas for all
galactocentric radii, both north and south. Its thickness for R<Ro is ~73 pc
(FWHM), 62% the thickness of the molecular gas disk. The FIR luminosity
produced by massive stars has a well defined maximum at R=0.55Ro, with a
gaussian FWHM of 0.28Ro - compared with 0.51Ro for the H2 surface density
distribution. Toward the outer Galaxy, down from the maximum, the face-on FIR
surface luminosity decays exponentially with a scale length of 0.21Ro, compared
with 0.34Ro for the H2 surface density. Massive star formation per unit H2 mass
is maximum for R~0.55Ro in the southern Galaxy, with a FIR surface luminosity
to H2 surface density ratio of 0.41Lsun/Msun, compared with 0.21Lsun/Msun at
the same radius in the north, and with an average of ~0.18Lsun/Msun for the
whole galactic disk within the solar circle.


title: On the Internal Structure of Relativistic Jets

abstract:
  A magnetohydrodynamic model is constructed for a cylindrical jet immersed in
an external uniform magnetic field. It is shown that, as in the force-free
case, the total electric current within the jet can be zero. The particle
energetics and the magnetic field structure are determined in a self-consistent
way; all jet parameters depend on the physical conditions in the external
medium. In particular, we show that a region with subsonic flow can exist in
the central jet regions. In actual relativistic jets, most of the energy is
transferred by the electromagnetic field only when the magnetization parameter
is sufficiently large, $\sigma>10^6$. We also show that, in general, the
well-known solution with a central core, $B_z = B_0/(1+\varpi^2/\varpi_c^2)$,
can not be realized in the presence of an external medium.


title: RX J0911+05: A Massive Cluster Lens at z=0.769

abstract:
  We report the detection of a massive high-redshift cluster of galaxies near
the quadruple quasar RX J0911+05, using the LRIS instrument on the Keck-II
telescope. The cluster is found to have a mean redshift of <z>=0.7689+/-0.002
and a velocity dispersion of sigma=836{+180-200} km/s, based on redshift
measurements for 24 member galaxies. This massive high-redshift cluster is the
origin of the unusually large external shear required by lensing models of the
quadruple quasar system. We predict the expected time delay depending on the
exact contribution of the cluster. A measurement of the time delay and further
deep lensing and X-ray observations will unravel useful properties of this
serendipitously discovered high-redshift cluster, and may put interesting
cosmological constraints on H0.


title: R-modes of neutron stars with a solid crust

abstract:
  We investigate the properties of $r$-mode oscillations of a slowly rotating
neutron star with a solid crust, by taking account of the effects of the
Coriolis force. For the modal analysis we employ three-component neutron star
models that are composed of a fluid core, a solid crust and a surface fluid
ocean. For the three-component models, we find that there exist two kinds of
$r$-modes, that is, those confined in the surface fluid ocean and those
confined in the fluid core, which are most important for the $r$-mode
instability. The $r$-modes do not have any appreciable amplitudes in the solid
crust if rotation rate of the star is sufficiently small. We find that the core
$r$-modes are strongly affected by mode coupling with the crustal torsional
(toroidal) modes and lose their simple properties of the eigenfunction and
eigenfrequency as functions of the angular rotation velocity $\Omega$. This
indicates that the extrapolation formula, which is obtained in the limit of
$\Omega\to 0$, cannot be used to examine the $r$-mode instability of rapidly
rotating neutron stars with a solid crust unless the effects of mode coupling
with the crustal torsional modes are correctly taken into account.


title: Muon Bremsstrahlung and Muonic Pair Production in Air Showers

abstract:
  The objective of this work is to report on the modifications in air shower
development due to muon bremsstrahlung and muonic pair production. In order to
do that we have implemented new muon bremsstrahlung and muonic pair production
procedures in the AIRES air shower simulation system, and have used it to
simulate ultra high energy showers in different conditions.
  The influence of the mentioned processes in the global development of the air
shower is important for primary particles of large zenith angles, while they do
not introduce significant changes in the position of the shower maximum.


title: The Impact of Galaxy Formation on the X-ray Evolution of Clusters

abstract:
  We present a new model for the X-ray properties of the intracluster medium
that explicitly includes heating of the gas by the energy released during the
evolution of cluster galaxies. We calculate the evolution of clusters by
combining the semi-analytic model of galaxy formation of Cole et al. with a
simple model for the radial profile of the intracluster gas. We focus on the
cluster X-ray luminosity function and on the relation between X-ray temperature
and luminosity. We show that cooling alone is not enough to account for the
flatness of the observed T-L relation or for the lack of strong redshift
evolution in the observed X-ray luminosity function. Gas heating, on the other
hand, can solve these two problems: in the \Lambda-CDM cosmology, our model
reproduces fairly well the T-L relation and the X-ray luminosity function.
Furthermore, it predicts only weak evolution in these two properties out to
z=0.5, in agreement with recent observational data. A successful model requires
an energy input of 1--2 x 10^49 ergs per solar mass of stars formed. This is
comparable to the total energy released by the supernovae associated with the
formation of the cluster galaxies. Thus, unless the transfer of supernovae
energy to the intracluster gas is very (perhaps unrealistically) efficient,
additional sources of energy, such as mechanical energy from AGN winds are
required. However, the amplification of an initial energy input by the response
of the intracluster medium to protocluster mergers might ease the energy
requirements. Our model makes definite predictions for the X-ray properties of
groups and clusters at high redshift which may soon be tested with data from
the Chandra and Newton satellites.


title:
Kinematics of elliptical galaxies with a diffuse dust component - II.
  Dust effects on kinematic modelling

abstract:
  Observations have demonstrated the presence of substantial amounts of
interstellar dust in elliptical galaxies, most of which is believed to be
distributed diffusely over the galaxy. Absorption by dust grains has a major
impact on the transfer of stellar radiation, and affects the projection of each
physical (and kinematic) quantity. In a previous paper, we have investigated
the effects of a diffusely distributed dust component on the observed
kinematics of spherical galaxies. In this paper we investigate the effect of
not taking dust into account in dynamical modelling procedures. We use a set of
semi-analytical dusty galaxy models to create synthetic LOSVD data sets, which
we then model as if no dust were present.
  We find some considerable differences between the best-fitting models and the
input models, and we find that these differences are dependent on the orbital
structure of the input galaxy. For radial and isotropic models on the one hand,
we find that the dynamical mass of the models decreases nearly linearly with
optical depth, with an amount of 5 per cent per optical depth unit, whereas
their orbital structure is hardly affected. For tangential models on the other
hand, the dynamical mass decrease is smaller, but their orbital structure is
affected: their distribution functions appears less tangentially anisotropic.
For all models the mass-to-light ratio will be underestimated, by a factor of
around 20 per cent per optical depth unit.
  We discuss these results in the light of the limited effects of dust
extinction on the LOSVDs, as obtained in paper I, and conclude that the
determination of the dynamical mass and the kinematic structure of galaxies...
(for full abstract, see paper)


title: Theoretical and Experimental Topics on Ultra High Energy Cosmic Rays

abstract:
  Since their first observation in 1962, the existence of Ultra High Energy
Cosmic Rays (UHECR) remains a mystery in modern astrophysics. Those cosmic
rays, with energies well above 50 EeV ($50\times 10^{18}$eV), can hardly be
accelerated, even in the most active parts of our universe such as FR-II radio
galaxies or AGNs, nor can they travel on distances larger than 100 Mpc. In the
following some of the production and acceleration models for UHECR are reviewed
and some of the transport issues are exposed. Finally the detection and
identification on Earth of those ``cosmic bullets'' are presented.


title:
On the spectrum of Ultrahigh Energy Cosmic Rays and the Gamma Ray Burst
  Origin Hypothesis

abstract:
  It has been suggested that cosmological gamma-ray bursts (GRBs) can produce
the observed flux of cosmic rays at the highest energies. However, recent
studies of GRBs indicate that their redshift distribution likely follows that
of the average star formation rate and that GRBs were more numerous at high
redshifts. As a consequence, we show that photomeson production energy losses
suffered by ultrahigh energy cosmic rays coming from GRBs would produce too
sharp a spectral high energy cutoff to be consistent with the air shower data.
Furthermore, we show that cosmological GRBs fail to supply the energy input
required to account for the cosmic ray flux above 10 EeV by a factor of
100-1000.


title:
The response of an accretion disc to an inclined dipole with application
  to AA Tau

abstract:
  We compute the warping of a disc induced by an inclined dipole. We consider a
magnetised star surrounded by a thin Keplerian diamagnetic disc with an inner
edge that corotates with the star. We suppose the stellar field is a dipole
with an axis that is slightly misaligned with the stellar rotation axis. The
rotation axes of the disc material orbiting at large distances from the star
and that of the star are supposed to coincide. The misalignment of the magnetic
and rotation axes results in the magnetic pressure not being the same on the
upper and lower surfaces of the disc. The resultant net vertical force produces
a warp which appears stationary in a frame corotating with the star. We find
that, if viscosity is large enough (alpha on the order of 0.01-0.1) to damp
bending waves as they propagate away, a smoothly varying warp of the inner
region of the disc is produced. The amplitude of the warp can easily be on the
order of ten percent of the disc inner radius for reasonably small misalignment
angles (less than 30 degrees). Viscous damping also introduces a phase shift
between the warp and the forcing torque, which results in the locations of
maximum elevation above the disc forming a trailing spiral pattern. We apply
these results to recent observations of AA Tau, and show that the variability
of its light curve, which occurs with a period comparable to the expected
stellar rotation period, could be due to obscuration produced by a warp
configuration of the type we obtain.


title: Azimuthally symmetric MHD and two-fluid equilibria with arbitrary flows

abstract:
  Magnetohydrodynamic (MHD) and two-fluid quasi-neutral equilibria with
azimuthal symmetry, gravity and arbitrary ratios of (nonrelativistic) flow
speed to acoustic and Alfven speeds are investigated. In the two-fluid case,
the mass ratio of the two species is arbitrary, and the analysis is therefore
applicable to electron-positron plasmas. The methods of derivation can be
extended in an obvious manner to several charged species. Generalized
Grad-Shafranov equations, describing the equilibrium magnetic field, are
derived. Flux function equations and Bernoulli relations for each species,
together with Poisson's equation for the gravitational potential, complete the
set of equations required to determine the equilibrium. These are
straightforward to solve numerically. The two-fluid system, unlike the MHD
system, is shown to be free of singularities. It is demonstrated analytically
that there exists a class of incompressible MHD equilibria with magnetic
field-aligned flow. A special sub--class first identified by S. Chandrasekhar,
in which the flow speed is everywhere equal to the local Alfven speed, is
compatible with virtually any azimuthally symmetric magnetic configuration.
Potential applications of this analysis include extragalactic and stellar jets,
and accretion disks.


title:
Wide Field Imaging. I. Applications of Neural Networks to object
  detection and star/galaxy classification

abstract:
  [Abriged] Astronomical Wide Field Imaging performed with new large format CCD
detectors poses data reduction problems of unprecedented scale which are
difficult to deal with traditional interactive tools. We present here NExt
(Neural Extractor): a new Neural Network (NN) based package capable to detect
objects and to perform both deblending and star/galaxy classification in an
automatic way. Traditionally, in astronomical images, objects are first
discriminated from the noisy background by searching for sets of connected
pixels having brightnesses above a given threshold and then they are classified
as stars or as galaxies through diagnostic diagrams having variables choosen
accordingly to the astronomer's taste and experience. In the extraction step,
assuming that images are well sampled, NExt requires only the simplest a priori
definition of "what an object is" (id est, it keeps all structures composed by
more than one pixels) and performs the detection via an unsupervised NN
approaching detection as a clustering problem which has been thoroughly studied
in the artificial intelligence literature. In order to obtain an objective and
reliable classification, instead of using an arbitrarily defined set of
features, we use a NN to select the most significant features among the large
number of measured ones, and then we use their selected features to perform the
classification task. In order to optimise the performances of the system we
implemented and tested several different models of NN. The comparison of the
NExt performances with those of the best detection and classification package
known to the authors (SExtractor) shows that NExt is at least as effective as
the best traditional packages.


title: The Importance of Einstein Rings

abstract:
  We develop a theory of Einstein rings and demonstrate it using the infrared
Einstein ring images of the quasar host galaxies observed in PG1115+080,
B1608+656 and B1938+666. The shape of an Einstein ring accurately and
independently determines the shape of the lens potential and the shape of the
lensed host galaxy. We find that the host galaxies of PG1115+080, B1608+656 and
B1938+666 have axis ratios of 0.58+/-0.02, 0.69+/-0.02 and 0.62+/-0.15
including the uncertainties in the lens models. The Einstein rings break the
degeneracies in the mass distributions or Hubble constants inferred from
observations of gravitational lenses. In particular, the Einstein ring in
PG1115+080 rules out the centrally concentrated mass distributions that lead to
a high Hubble constant (H_0>60 km/s Mpc) given the measured time delays. Deep,
detailed observations of Einstein rings will be revolutionary for constraining
mass models and determining the Hubble constant from time delay measurements.


title: FUSE Observations of the Active Cool Star AB Doradus

abstract:
  Far ultraviolet spectra were obtained of the active cool star AB Doradus (HD
36705) during the calibration and checkout period of the FUSE satellite.
Observations in this early phase of the mission were taken at a resolving power
of 12000-15000 (~20-25 km/s) and covered the spectral range 905-1187 A. The
integrated spectrum exhibits strong, rotationally broadened stellar emission
from C III (977, 1175) and O VI (1032, 1037), and many weaker lines. Strong
emission lines of C III and O VI exhibit broad wings. The C III 977 profile
shows blue-shifted absorption at ~30 km/s and C II 1036 absorption appears
superposed on emission in the wing of O VI 1037. Rotational modulation of C III
and O VI is present, in harmony with its photometric variability. Flares were
detected in the brightest lines and subexposures were analyzed to examine flux
and profile variations. Downflows that extend to 600 km/s during a flare are
found in the O VI profiles. These early observations demonstrate that FUSE will
be an exceptional instrument for studying chromospheres in cool stars.


title: Tentative Detection of Galaxy Spin Correlations in the Tully Catalogue

abstract:
  We report a tentative detection of spin correlations in the Tully catalogue
of nearby galaxies. We define a simple but nontrivial spin correlation
function, and find an analytic estimate of it in the frame of the linear
perturbation theory. Then, we present the observed spin correlation signal from
the Tully galaxies with error bars. The three dimensional spin correlation
turns out to be significant at the 97% confidence level, detected out to a few
$h^{-1}$ Mpc. This observed correlation is consistent with the theoretical
prediction based on the gravitational instability picture of galaxy formation.
An analysis of systematic errors is also presented. The observed strength of
correlation may be sufficient to significantly affect blank field of weak
lensing searches.


title:
On the Integrated Spectrum of the X-ray Binaries and the Origin of Soft
  X-ray Emission from the Bulge of M31

abstract:
  Using ROSAT PSPC data, we have performed several tests aimed at understanding
the origin of the soft X-ray spectral component detected from the bulge of M31.
We find that a significant soft component in the spectrum of the bulge is
spatially correlated with the unresolved X-ray emission near the core of M31,
which is probably a hot interstellar medium or perhaps a population of multiple
faint sources. For the first time, we extracted the spectrum of this unresolved
emission, by removing point sources dominating the integral spectrum of the
bulge, and found it to be responsible for the most of soft excess. A soft
spectral component is not at all needed to fit the point source spectrum that
remains after subtracting the unresolved emission. The integral spectra of
bright point sources, both inside and outside of the M31 bulge, can be fitted
with a single power-law in the ROSAT band. Our analysis rules out the previous
suggestion that all bulge emission in M31 may be generated by low mass X-ray
binaries (Irwin & Bregman, 1999).


title: A Search of the Zone of Avoidance in Scorpius

abstract:
  An optical search of the Scorpius region - close to the Galactic bulge - has
revealed some 1400 partially-obscured galaxies. Redshifts have been obtained
for nearly a hundred of these objects. Preliminary indications of large-scale
structures are reported.


title: An Overview of Optical Galaxy Searches and their Completeness

abstract:
  Dust and stars in the Milky Way create a ``Zone of Avoidance'' (ZOA) in the
distribution of optically visible galaxies of about 25% of the sky. To reduce
this gap, optical searches for partially obscured galaxies have been performed.
The status of these deep searches, in particular their completeness as a
function of foreground extinction are discussed. Using existing sky surveys,
over 50000 previously unknown galaxies have been identified. The surveys cover
practically the whole ZOA. It is shown that these surveys are complete for
galaxies with extinction-corrected diameters D^o ge 1.3 arcmin to extinction
levels of A_B le 3.0 mag. Incorporating these new data in a whole-sky map of
galaxies complete to D^o ge 1.3 arcmin finds the ZOA reduced by a factor of
about 2 to 2.5, respectively from extinction levels of A_B = 1.0 mag to A_B =
3.0 mag (see Fig.~4).


title: The HI mass function in Ursa Major

abstract:
  A deep blind HI survey of the nearby spiral rich Ursa Major cluster has been
performed with the VLA in parallel with a wide-field R-band imaging campaign of
most VLA fields with the CFHT. The goal is to measure the slope of the HI mass
function down to HI masses of 10^7 Msun as well as the slope of the faint-end
of the luminosity function down to M(R)=-10. The VLA survey sampled 16% of the
Ursa Major cluster volume. Both the HIMF and the LF in Ursa Major are nearly
flat at their faint-ends. No free- floating HI clouds were detected.


title:
R-modes in Neutron Stars with Crusts: Turbulent Saturation, Spin-down,
  and Crust Melting

abstract:
  Rossby waves (r-modes) have been suggested as a means to regulate the spin
periods of young or accreting neutron stars, and also to produce observable
gravitational wave radiation. R-modes involve primarily transverse,
incompressive motions of the star's fluid core. However, neutron stars gain
crusts early in their lives: therefore, r-modes also imply shear in the fluid
beneath the crust. We examine the criterion for this shear layer to become
turbulent, and derive the rate of dissipation in the turbulent regime. Unlike
dissipation from a viscous boundary layer, turbulent energy loss is nonlinear
in mode energy and can therefore cause the mode to saturate at amplitudes
typically much less than unity. This energy loss also reappears as heat below
the crust. We study the possibility of crust melting as well as its
implications for the spin evolution of low-mass X-ray binaries. Lastly, we
identify some universal features of the spin evolution that may have
observational consequences.


title:
A combined analysis of cluster mass estimates from strong lensing, X-ray
  measurement and the universal density profile

abstract:
  (Abridged)We present a combined analysis of mass estimates in the central
cores of galaxy clusters from the strong lensing, the X-ray measurements and
the universal density profile (NFW). Special attention is paid to the questions
(1)whether the previously claimed mass discrepancy between the strong lensing
and X-ray measurements is associated with the presence of cooling/non-cooling
flows, (2)whether the cusped NFW density model can provide a consistent cluster
mass with the strong lensing result and (3)whether a non-zero cosmological
constant can be of any help to reducing the strong lensing - X-ray mass ratios.
We analyse a sample of 26 arc-like images among 21 clusters. The X-ray and NFW
cluster masses are obtained by assuming that the intracluster gas is isothermal
and in hydrostatic equilibrium with the underlying gravitational potential of
the clusters. A statistical comparison of these three mass estimates reveals
that the mass discrepancies for all the events are well within a factor of 2.
We confirm the result of Allen that the larger mass discrepancy is only
detected in the intermediate cooling, especially non-cooling flow clusters,
thus attributing the mass discrepancy to the local dynamical activities in the
central regions. We show that the NFW profile yields a consistent cluster mass
with the conventional X-ray measurement, and any difference between these two
models must occur at even smaller radii (e.g. within the arc-like images) or at
large radii. Finally, a non-zero cosmological constant is able to moderately
reduce the mass ratios of m_lens to m_xray.


title:
On the radial density profile of intracluster gas tracing the isothermal
  dark halo with a finite core

abstract:
  The cusped NFW universal density profile suggested by typical CDM models has
been challenged in recent years by the discoveries of the soft cores for a
broad range of masses from dwarf galaxies to clusters of galaxies. It is thus
desirable that a new, analytic model would instead become available for
virialized dark halos. One promising candidate is probably the empirical
density profile proposed by Burkert, which resembles an isothermal profile with
a constant core in the inner region and matches the NFW profile at large radii.
Meanwhile, such a revised dark halo (RDH) profile has turned out a great
success on galactic scales. This stimulates us to apply the RDH profile to more
massive systems like clusters of galaxies. In this paper we have made an
attempt to derive the radial density profile of intracluster gas from the RDH
profile, and compare it with those revealed by X-ray observations and inferred
from the NFW profile. It is shown that the RDH predicted gas density can be
well represented by the conventional beta model with a typical beta parameter
of 0.7-0.9. Fitting the theoretically predicted X-ray surface brightness
profile to an ensemble of 45 X-ray clusters, we find that the RDH and NFW
profiles become to be almost indistinguishable. Yet, the RDH profile allows us
to work out straightforwardly the central dark matter density of clusters from
X-ray measurements. Using the 45 clusters, we find that the central densities
of clusters have an average value of ~0.01 solar mass pc^{-3}, in agreement
with the result estimated on galactic scales, which reinforces the claim for
the presence of the soft halo cores over the entire mass range.