title:
VLT identification of the optical afterglow of the gamma-ray burst GRB
  000131 at z=4.50

abstract:
  We report the discovery of the gamma-ray burst GRB 000131 and its optical
afterglow. The optical identification was made with the VLT 84 hours after the
burst following a BATSE detection and an Inter Planetary Network localization.
GRB 000131 was a bright, long-duration GRB, with an apparent precursor signal
62 s prior to trigger. The afterglow was detected in ESO VLT, NTT, and DK1.54m
follow-up observations. Broad-band and spectroscopic observations of the
spectral energy distribution reveals a sharp break at optical wavelengths which
is interpreted as a Ly-alpha absorption edge at 6700 A. This places GRB 000131
at a redshift of 4.500 +/- 0.015. The inferred isotropic energy release in
gamma rays alone was approximately 10^54 erg (depending on the assumed
cosmology). The rapid power-law decay of the afterglow (index alpha=2.25,
similar to bursts with a prior break in the lightcurve), however, indicates
collimated outflow, which relaxes the energy requirements by a factor of < 200.
The afterglow of GRB 000131 is the first to be identified with an 8-m class
telescope.


title: Torsional oscillations in the solar convection zone

abstract:
  Recent analysis of the helioseismic observations indicate that the previously
observed surface torsional oscillations extend significantly downwards into the
solar convection zone.
  In an attempt to understand these oscillations, we study the nonlinear
coupling between the magnetic field and the solar differential rotation in the
context of a mean field dynamo model, in which the nonlinearity is due to the
action of the azimuthal component of the Lorentz force of the dynamo generated
magnetic field on the solar angular velocity. The underlying zero order angular
velocity is chosen to be consistent with the most recent helioseismic data.
  The model produces butterfly diagrams which are in qualitative agreement with
the observations. It displays torsional oscillations that penetrate into the
convection zone, and which with time migrate towards the equator. The period of
these oscillations is found to be half that of the period of the global
magnetic fields. This is compatible with the observed period of the surface
torsional oscillations. Inside the convection zone, this is a testable
prediction that is not ruled out by the observations so far available.


title:
Constraining the cosmological parameters from gravitational lenses with
  several families of images

abstract:
  The knowledge of the redshift of multiple images in cluster-lenses allows to
determine precisely the total projected mass within the Einstein radius. The
observation of various multiple images in a same cluster is opening new
possibilities to constrain the curvature of the universe. Indeed, although the
influence of $\Omega_m$ and $\Omega_\lambda$ on the images formation is of the
second order, observations of many multiple images at different redshifts
formed by a regular cluster-lens should allow to constrain very accurately the
mass distribution of the cluster and to start to be sensitive to the
cosmological parameters entering the diameter angular distances. We present,
analytical expressions and numerical simulations that allow us to compute the
expected error bars on the cosmological parameters provided an HST/WFPC2
resolution image and spectroscopic redshifts for the multiple images. Numerical
tests on simulated data confirm the rather small uncertainties we could obtain
this way for the two popular cosmological world models: $\Omega_m=0.3{\pm
0.24}$, $\Omega_\lambda=0.7{\pm 0.5}$ or $\Omega_m=1.{\pm 0.33}$,
$\Omega_\lambda=0.{\pm 1.2}$. Our method can be applied from now on, on real
clusters.


title: Chaotic Mixing in Galactic Dynamics

abstract:
  This talk summarises what is currently understood about the phenomenon that
has come to be known as {\it chaotic mixing}. The first part presents a concise
statement as to what chaotic mixing actually is, and then explains why it
should be important in galactic dynamics. The second discusses in detail what
is currently known, describing the manifestations of chaotic mixing both for
flows in time-independent Hamiltonian systems and for systems subjected to
comparatively weak time-dependent perturbations. The third part discusses what
one might expect if one were to allow for a strongly time-dependent potential,
including possible implications for violent relaxation.


title: Dynamics of Cuspy Triaxial Galaxies with a Supermassive Black Hole

abstract:
  This talk provides a progress report on an extended collaboration which has
aimed to address two basic questions, namely: Should one expect to see cuspy,
triaxial galaxies in nature? And can one construct realistic cuspy, triaxial
equilibrium models that are robust? Three technical results are described: (1)
Unperturbed chaotic orbits in cuspy triaxial potentials can be extraordinarily
sticky, much more so than orbits in many other three-dimensional potentials.
(2) Even very weak perturbations can be important by drastically reducing,
albeit not completely eliminating, this stickiness. (3) A simple toy model
facilitates a simple understanding of why black holes and cusps can serve as an
effective source of chaos. These results suggest that, when constructing models
of galaxies using Schwarzschild's method or any analogue thereof, astronomers
would be well advised to use orbital building blocks that have been perturbed
by `noise' or other weak irregularities, since such building blocks are likely
to be more nearly time-independent than orbits evolved in the absence of all
perturbations.


title: Strong constraints on cosmology from galaxy clusters

abstract:
  In this work we show how galaxy clusters can be used to discriminate among
different cosmological models. We have used available X-ray & optical cluster
data to constrain the cosmological parameters as well as the cluster scaling
relations, T-M and L-T. We also show the power of future SZE data to constrain
even more these parameters.


title:
An XMM-Newton detection of the z=5.80 X-ray weak quasar SDSSp
  J104433.04-012502.2

abstract:
  We report on an XMM-Newton observation of the most distant known quasar,
SDSSp J104433.04-012502.2, at z=5.80. We have detected this quasar with high
significance in the rest-frame 3.4-13.6 keV band, making it the most distant
cosmic object detected in X-rays; 32 +/- 9 counts were collected. SDSSp
J104433.04-012502.2 is notably X-ray weak relative to other luminous, optically
selected quasars, with alpha_ox=-1.91 +/- 0.05 and a 3.4-13.6 keV luminosity of
about 1.8 x 10^{44} erg/s. The most likely reason for its X-ray weakness is
heavy absorption with N_H greater than about 10^{24} 1/cm^2, as is seen in some
Broad Absorption Line quasars and related objects; we discuss this and other
possibilities. High-quality spectroscopy from 0.95-1.10 microns to search for
blueshifted C IV absorption may elucidate the origin of the X-ray weakness.


title:
The Cosmic Electron Background in Low Energy IACTs. Effect of the
  Geomagnetic Field

abstract:
  A new generation of low threshold Imaging Atmospheric Cherenkov Telescopes
(IACTs) may reach gamma-ray energies about 10 GeV with high sensitivities and
very large collection areas. At these low energies cosmic electrons
significantly contribute to the telescope background and are in principle
indistinguishable from gamma-rays. In this paper we estimate the electron
background expected for two configurations of the low energy IACT MAGIC. We
discuss in particular the reduction of the background caused by the geomagnetic
field at different locations on the Earth's surface.


title: Tests of Gaussianity of CMB maps

abstract:
  We study two different methods to test Gaussianity in CMB maps. One of them
is based on the partition function and the other on the morphology of hot and
cold spots. The partition function contains information on all the moments and
scales, being a useful quantity to compress the large data sets expected from
future space missions like Planck. In particular, it contains much richer
information than the one available through the radiation power spectrum. The
second method utilizes morphological properties of hot and cold spots such as
the eccentricity and number of spots in CMB maps. We study the performance of
both methods in detecting non-Gaussian features in small scale CMB simulated
maps as those which will be provided by the Planck mission.


title: Simulated Performance of a Germanium Compton Telescope

abstract:
  To build upon the goals of the upcoming INTEGRAL mission, the next generation
soft gamma-ray (0.2-20 MeV) observatory will require improved sensitivity to
nuclear line emission while maintaining high spectral resolution. We present
the simulated performance of a germanium Compton telescope (GCT) design, which
will allow a factor of ten improvement in sensitivity over INTEGRAL/SPI. We
also discuss a number of issues concerning reconstruction techniques and event
cuts, and demonstrate how these affect the overall performance of the
telescope.


title: The fading of SN 1997D

abstract:
  We present a new set of spectroscopic and photometric data extending the
observations of SN 1997D to over 400 days after the explosion. These
observations confirm the peculiar properties of SN 1997D, such as the very low
abundance of 56Co (0.002 Msolar) and the low expansion velocity of the ejecta
(~1000 km/s). We discuss the implications of these observations for the
character of the progenitor and the nature of the remnant showing that a
Crab-like pulsar or an accreting neutron star formed in the explosion of a low
mass progenitor should already have produced a detectable luminosity at this
epoch, in contrast with photometric data. On the other hand, the explosion of a
high mass progenitor with the formation of a black hole is consistent with the
available observations. The consequences of this conclusion regarding the
nature of the explosion and the prospects of directly identifying the black
hole are also addressed.


title:
Statistical Power, the Bispectrum and the Search for Non-Gaussianity in
  the CMB Anisotropy

abstract:
  We use simulated maps of the cosmic microwave background anisotropy to
quantify the ability of different statistical tests to discriminate between
Gaussian and non-Gaussian models. Despite the central limit theorem on large
angular scales, both the genus and extrema correlation are able to discriminate
between Gaussian models and a semi-analytic texture model selected as a
physically motivated non-Gaussian model. When run on the COBE 4-year CMB maps,
both tests prefer the Gaussian model. Although the bispectrum has comparable
statistical power when computed on the full sky, once a Galactic cut is imposed
on the data the bispectrum loses the ability to discriminate between models.
Off-diagonal elements of the bispectrum are comparable to the diagonal elements
for the non-Gaussian texture model and must be included to obtain maximum
statistical power.


title:
High resolution spectroscopy of H II Galaxies: Structure and Supersonic
  line widths

abstract:
  We present high resolution echelle spectroscopy of a sample of H II galaxies.
In all galaxies we identify different H(alpha) emitting knots along the slit
crossing the nucleus. All of these have been isolated and separately analyzed
through luminosity and size vs diagnosis plots. We find that in all cases, for
a particular galaxy, the bulk of emission comes from their main knot and
therefore, at least for the compact class galaxies we are dealing with,
luminosity and sigma values measured using single aperture observations would
provide similar results to what is obtained with spatially resolved
spectroscopy. In the size vs plots as expected there is a shift in the
correlations depending on whether we are including all emission in a single
point or we split it in its different emitting knots. The problem of a proper
determination of the size of the emitting region so that it can be used to
determine the mass of the system remains open. From the data set gathered,
using the highest surface brightness points as recently proposed by
Fuentes-Masip et al. (2000), the best luminosity vs correlation turns out to be
consistent with a Virial model.


title: The morphology of extremely red objects

abstract:
  We present a quantitative study of the morphology of 41 Extremely Red Objects
(EROs). The analysis is based on deep otical and near-infrared images from the
Hubble Space Telescope public archive, and performed by fitting to each galaxy
image a PSF-convolved bi-dimensional model brightness distribution. Relying
both on the visual inspection of the data and on the results of the fitting
procedure, we are able to determine the fraction of irregular and/or
interacting EROs, and to identify those that more closely resemble local
ellipticals. To the former class, whose members are probably high-redshift
dusty starburst, belongs about 15% of the whole sample, whereas the
elliptical-like objects are between 50 and 80% of the total. A few galaxies,
although characterized by a compact morphology, are best fitted by an
exponential distribution, more typical of local spirals. Our data also suggest
that irregular EROs are found predominantly in the field, and that - on average
- they tend to be characterized by the reddest colors. Finally, we plot the
rest-frame Kormendy Relation ($\mu_e$ vs. $R_e$) for a sample of 6 EROs with
spectroscopic redshifts ($z \sim 1.3$), and estimate its evolution with respect
to the local relation.


title:
Evolution from Canonical to Millisecond Pulsar through the X-ray
  Accretion Stage

abstract:
  We model the evolution of canonical pulsars from the death line to
millisecond pulsars through the X-ray neutron star stage of accretion from a
low-mass companion. We trace this evolution in magnetic field strength starting
at $B=10^{12}$ to $10^8$ G and in period of about 1 s to milliseconds.
Important factors are accretion rate and the decay rate of the magnetic field.
A broad swathe is traced in the $B-P$ plane according to the value of these
factors, which represent different conditions of the binary pair. An important
ingredient is the dependence of the stellar moment of inertia on rotation
frequency (time).


title: Known and unknown SCUBA sources

abstract:
  Summary and discussion of some projects to use SCUBA to target sources
selected at other wavebands, as well as to find new sub-mm galaxies in `blank
fields': FIRBACK galaxies; Lyman break galaxies and `the Blob'; HDF flanking
fields and the Groth Strip; survey of lensing cluster fields.


title:
Upper Limits On Periodic, Pulsed Radio Emission from the X-Ray Point
  Source in Cassiopeia A

abstract:
  The Chandra X-ray Observatory recently discovered an X-ray point source near
the center of Cassiopeia A, the youngest known Galactic supernova remnant. We
have conducted a sensitive search for radio pulsations from this source with
the Very Large Array, taking advantage of the high angular resolution of the
array to resolve out the emission from the remnant itself. No convincing
signatures of a dispersed, periodic source or of isolated dispersed pulses were
found, whether for an isolated or a binary source. We derive upper limits of 30
and 1.3 mJy at 327 and 1435 MHz for the phase-averaged pulsed flux density from
this source. The corresponding luminosity limits are lower than those for any
pulsar with age less than 10^4 years. The sensitivities of our search to single
pulses were 25 and 1.0 Jy at 327 and 1435 MHz. For comparison, the Crab pulsar
emits roughly 80 pulses per minute with flux densities greater than 100 Jy at
327 MHz and 8 pulses per minute with flux densities greater than 50 Jy at 1435
MHz. These limits are consistent with the suggestion that the X-ray point
source in Cas A adds to the growing number of neutron stars which are not radio
pulsars.


title: Is the LMA solar-neutrino solution ruled out by SN1987A data?

abstract:
  The development of new supernova neutrino detectors relies on the expected
hard energy spectrum of the nu_mu and nu_tau emitted in the supernova. We show
that SN1987A was sensitive to the large mixing angle (LMA) and "just so"
solution to the solar neutrino problem. We review the previous analysis of the
SN1987A data and propose a new analysis. The results of this analysis strongly
disfavor the LMA solution, provided the nu_mu and nu_tau are hard as predicted


title: A Comparison of UIT Far-Ultraviolet and H alpha Star Formation Rates

abstract:
  We have used archival ultraviolet (UV) imaging of 50 nearby star-forming
galaxies obtained with the Ultraviolet Imaging Telescope (UIT) to derive
integrated near-UV and far-UV magnitudes, and have combined these data with H
alpha, far-infrared, and thermal radio continuum measurements to explore the
consistency of UV and H alpha star formation rates (SFRs). In agreement with
previous studies, we find that the UV and H alpha SFRs are qualitatively
consistent, even before corrections for extinction are applied. The uncorrected
UV SFRs are systematically lower by a factor of 1.5 (with a factor of two
scatter) among luminous galaxies with SFRs over 1 solar mass per year,
indicating a higher effective attenuation of the far-UV radiation. Among less
luminous galaxies there is no significant offset between the H alpha and far-UV
SFR scales. Far-infrared and thermal radio continuum data available for a
subset of our sample allow us to estimate the attenuation in the UV and at H
alpha independently. The UV and H alpha attenuations appear to be correlated,
and confirm systematically higher attenuations in the UV. Although the galaxies
in our sample show modest levels of attenuation (with median values of 0.9 mag
at H alpha and 1.4 mag at 1550 Angstroms), the range across the sample is
large, around 4 mag for H alpha and around 5 mag in the far-UV (1550
Angstroms). This indicates that the application of a single characteristic
extinction correction to H alpha or UV SFRs is only realistic for large,
well-defined and well-studied galaxy samples, and that extinction bias may be
important for UV or emission-line selected samples of star-forming galaxies.


title: Performance of the STACEE Atmospheric Cherenkov Telescope

abstract:
  The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is located
at the National Solar Thermal Test Facility of Sandia National Laboratories in
Albuquerque, New Mexico, USA. The field of solar tracking mirrors (heliostats)
around a central receiver tower is used to direct Cherenkov light from
atmospheric showers onto secondary mirrors on the tower, which in turn image
the light onto cameras of photomultiplier tubes. The STACEE Collaboration has
previously reported a detection of the Crab Nebula with approximately 7
standard deviation significance, using 32 heliostats (STACEE-32). This result
demonstrates both the viability of the technique and the suitability of the
site. We are in the process of completing an upgrade to 48 heliostats
(STACEE-48) en route to an eventual configuration using 64 heliostats
(STACEE-64) in early 2001. In this paper, we summarize the results obtained on
the sensitivity of STACEE-32 and our expectations for STACEE-48 and STACEE-64.


title:
A Dust-Penetrated Classification Scheme for Bars as Inferred from their
  Gravitational Force Fields

abstract:
  The division of galaxies into ``barred'' (SB) and ``normal'' (S) spirals is a
fundamental aspect of the Hubble galaxy classification system. This ``tuning
fork'' view was revised by de Vaucouleurs, whose classification volume
recognized apparent ``bar strength'' (SA, SAB, SB) as a continuous property of
galaxies called the ``family''. However, the SA, SAB, and SB families are
purely visual judgments that can have little bearing on the actual bar strength
in a given galaxy. Until very recently, published bar judgments were based
exclusively on blue light images, where internal extinction or star formation
can either mask a bar completely or give the false impression of a bar in a
nonbarred galaxy. Near-infrared camera arrays, which principally trace the old
stellar populations in both normal and barred galaxies, now facilitate a
quantification of bar strength in terms of their gravitational potentials and
force fields. In this paper, we show that the maximum value, Qb, of the ratio
of the tangential force to the mean radial force is a quantitative measure of
the strength of a bar. Qb does not measure bar ellipticity or bar shape, but
rather depends on the actual forcing due to the bar embedded in its disk. We
show that a wide range of true bar strengths characterizes the category ``SB'',
while de Vaucouleurs category ``SAB'' corresponds to a much narrower range of
bar strengths. We present Qb values for 36 galaxies, and we incorporate our bar
classes into a dust-penetrated classification system for spiral galaxies.


title:
The FUSE Spectrum of PG0804+761: A Study of Atomic and MolecularGas in
  the Lower Galactic Halo and Beyond

abstract:
  We present an analysis of interstellar and intergalactic absorption lines in
the FUSE spectrum of the low-redshift quasar PG0804+761 (z=0.100) at
intermediate resolution (FWHM=25 km/s) in the direction l=138.3, b=31.0. With a
good signal-to-noise ratio and the presence of several interesting Galactic and
extragalactic absorption components along the sight line, this spectrum
provides a good opportunity to demonstrate the ability of FUSE to do both
interstellar and extragalactic science. Although the spectrum of PG0804+761 is
dominated by strong absorption from local Galactic gas, we concentrate our
study on absorption by molecular hydrogen and neutral neutral and ionized
metals related to an intermediate-velocity cloud in the lower Galactic halo at
-55 km/s, and on absorption from OVI extended to negative velocities. In the
IVC, weak molecular hydrogen absorption is found in 5 lines for rotational
levels 0 and 1, leading to a total H_2 column density of log N = 14.71(+-0.30).
We derive an OI gas-phase abundance for the IVC of 1.03(+0.71-0.42) solar.
Absorption by OVI is found at velocities as negative as -110 km/s, but no
absorption from any species is found at velocities of -180 km/ where absorption
from the nearby high-velocity Complex A would be expected. We suggest that the
extended OVI absorption traces hot gas above the Perseus spiral arm. Finally,
we find intergalactic absorption by an intervening HI Ly betax absorber at
z=0.019 and absorption by HI, CIII and OVI in an associated system at z=0.102.
No intervening OVI absorbers are seen in the spectrum of PG0804+761.


title: The Effects of Noise and Sampling on the Spectral Correlation Function

abstract:
  The effects of noise and sampling on the ``Spectral Correlation Function''
(SCF) introduced by Rosolowsky et al. 1999 are studied using observational
data, numerical simulations of magneto-hydrodynamic turbulence, and simple
models of Gaussian spectral line profiles. The most significant innovations of
this paper are: i) the normalization of the SCF based on an analytic model for
the effect of noise; ii) the computation of the SCF as a function of the
spatial lag between spectra within a map. By computing of the dependence of the
SCF on the spatial lag, S_o(dr), we have been able to conclude that: 1) S_o(dr)
is a power law, with slope in the range of scales l_i-l_o. 2) The correlation
outer scale, l_o, is determined by the size of the map, and no evidence for a
true departure from self-similarity on large scales has been found. 3) The
correlation inner scale, l_i, is a true estimate of the smallest self-similar
scale in a map. 4) The spectral slope in a given region, is independent of
velocity resolution (above a minimum resolution threshold), spatial resolution,
and average spectrum quality. 5) Molecular transitions which trace higher gas
density yield larger values of the spectral slope than transitions tracing
lower gas density. 6) Nyquist sampling, bad pixels in detector arrays, and
reference sharing data acquisition need to be taken into account for a correct
determination of the SCF at lag dr=1. The value of the spectral slope, however,
can be computed correctly without a detailed knowledge of observational
procedures.


title: Hydrodynamic Simulation of the Cosmological X-ray Background

abstract:
  (Abridged) We use a hydrodynamic simulation of a LambdaCDM model to predict
the extragalactic X-ray background (XRB), focussing on emission from the
intergalactic medium (IGM). We also include X-rays from point sources
associated with galaxies in the simulation, and make maps of the angular
distribution of the emission. We find that filaments in the maps are not
evident, being diluted by projection. In the soft (0.5-2 keV) band, the mean
intensity of radiation from intergalactic and cluster gas is 2.3*10^-12
ergdeg^-2cm^-2s^-1, 35% of the total soft band emission. This is compatible at
the ~1 sigma level with estimates of the unresolved soft background from ROSAT
and {\it Chandra}. Only 4% of the hard (2-10 keV) emission is associated with
the IGM. Relative to AGN flux, the IGM component peaks at a lower redshift
(median z~0.45) so its clustering makes an important contribution to that of
the total XRB. The angular correlations on 0.1-10 arcmin scales are
significant, with an amplitude roughly consistent with an extrapolation of
recent ROSAT results to small scales. A cross-correlation of the XRB against
nearby galaxies taken from a simulated redshift survey also yields a strong
signal from the IGM. Although some recent papers have argued that the expected
soft band intensity from gas in galaxy, group, and cluster halos would exceed
XRB limits unless much of the gas is expelled by supernova feedback, we obtain
reasonable compatibility with current observations in a simulation that
incorporates cooling, star formation, and only modest feedback. A prediction of
our model is that the unresolved portion of the soft XRB will remain mostly
unresolved.


title:
Solar Models: current epoch and time dependences, neutrinos, and
  helioseismological properties

abstract:
  We calculate accurate solar models and report the detailed time dependences
of important solar quantities. We use helioseismology to constrain the
luminosity evolution of the sun and report the discovery of semi-convection in
evolved solar models that include diffusion. In addition, we compare the
computed sound speeds with the results of p-mode observations by BiSON, GOLF,
GONG, LOWL, and MDI instruments. We contrast the neutrino predictions from a
set of eight standard-like solar models and four deviant (or deficient) solar
models with the results of solar neutrino experiments. For solar neutrino and
for helioseismological applications, we present present-epoch numerical
tabulations of characteristics of the standard solar model as a function of
solar radius, including the principal physical and composition variables, sound
speeds, neutrino fluxes, and functions needed for calculating solar neutrino
oscillations.


title: Binary Stars in Young Clusters - a Theoretical Perspective

abstract:
  The preponderance of binary systems in all known stellar populations makes
them exciting dynamical agents for research on topics as varied as star
formation, star-cluster dynamics and the interiors of young and old stars.
Today we know that the Galactic-field binary population is probably a
dynamically evolved version of the Taurus-Auriga pre-main sequence population,
and that the initial distributions of binary-star orbital elements are probably
universal. Furthermore, N-body calculations tentatively suggest that OB stars
form in energetic binaries near cluster cores, and that binaries with
'forbidden' orbital elements that are produced in stellar encounters, may turn
out to be very useful windows into stellar interiors, potentially allowing
tests of pre-main sequence evolution theory as well as of models of
main-sequence stars.


title: Does the Mass Accretion Rate Depend On the Radius of the Accreting Star?

abstract:
  In some circumstances, the mass accretion rate M^dot onto a compact star may
depend not only on external boundary conditions, but also on the radius R of
the star. Writing the dependence as a power-law in which M^dot is proportional
to R^p, we estimate the power-law index, p, for transient binary systems in a
quiescent state. We use the observed luminosities $L$ of accreting neutron
stars (R=10^6 cm) in soft X-ray transients and white dwarfs (R=10^9 cm) in
similar cataclysmic variables, and estimate M^dot in each system through the
relation L=(GM/R)*M^dot, where M is the mass of the star. From the available
data we infer that p~0.9+-0.5. This radial dependence is consistent with
radiatively inefficient accretion flows that either are convective or lose mass
via a wind.


title:
Lagrangian description of fluid flow with pressure in relativistic
  cosmology

abstract:
  The Lagrangian description of fluid flow in relativistic cosmology is
extended to the case of flow accelerated by pressure. In the description, the
entropy and the vorticity are obtained exactly for the barotropic equation of
state. In order to determine the metric, the Einstein equation is solved
perturbatively, when metric fluctuations are small but entropy inhomogeneities
are large. Thus, the present formalism is applicable to the case when the
inhomogeneities are small in the large scale but locally nonlinear.


title: Disks at High Redshift: Interactions, Mergers, and Starbursts

abstract:
  Do disk galaxies exist at redshifts much greater than unity, and how might
they look different from local disks? How does the morphological mix of
galaxies change with redshift? What can we learn from current observations
about the properties of high redshift galactic disks? I present theoretical
predictions based on semi-analytic hierarchical models, focussing on the role
played by interactions, mergers, and starbursts in determining the observable
properties of disk galaxies at high redshift, and discuss the interpretation of
high redshift observations of possible proto-disks (damped Lyman-$\alpha$
systems and Lyman-break galaxies) in light of these predictions.


title: Gravitational Lensing Statistics as a Probe of Dark Energy

abstract:
  By using the comoving distance, we derive an analytic expression for the
optical depth of gravitational lensing, which depends on the redshift to the
source and the cosmological model characterized by the cosmic mass density
parameter $\Omega_m$, the dark energy density parameter $\Omega_x$ and its
equation of state $\omega_x = p_x/\rho_x$. It is shown that, the larger the
dark energy density is and the more negative its pressure is, the higher the
gravitational lensing probability is. This fact can provide an independent
constraint for dark energy.


title: Power Spectra Estimation for Weak Lensing

abstract:
  We develop a method for estimating the shear power spectra from weak lensing
observations and test it on simulated data. Our method describes the shear
field in terms of angular power spectra and cross correlation of the two shear
modes which differ under parity transformations. Two of the three power spectra
can be used to monitor unknown sources of noise in the data. The power spectra
are decomposed in a model independent manner in terms of ``band-powers'' which
are then extracted from the data using a quadratic estimator to find the
maximum of the likelihood and its local curvature (for error estimates). We
test the method against simulated data from Gaussian realizations and
cosmological N-body simulations. In the Gaussian case, the mean bandpowers and
their covariance are well recovered even for irregular (or sparsely) sampled
fields. The mild non-Gaussianity of the N-body realizations causes a slight
underestimation of the errors that becomes negligible for scales much larger
than several arcminutes and does not bias the recovered band powers.


title: Neutrinos from Gamma Ray Bursts

abstract:
  The observed fluxes of cosmic rays and gamma rays are used to infer the
maximum allowed high-energy neutrino flux allowed for Gamma Ray Bursts (GRBs),
following Mannheim, Protheroe, and Rachen (2000). It is shown that if GRBs
produce the ultrahigh-energy cosmic rays, they should contribute (a) at least
10% of the extragalactic gamma ray background between 3 MeV and 30 GeV,
contrary to their observed energy flux which is only a minute fraction of this
flux, and (b) a cumulative neutrino flux a factor of 20 below the AMANDA
(Neutrino 2000) limit on isotropic neutrinos. This could have two implications,
either GRBs do not produce the ultrahigh energy cosmic rays or that the GRBs
are strongly beamed and emit most of their power at energies well above 100 GeV
implausibly increasing the energy requirements, but consistent with the
marginal detections of a few low-redshift GRBs by MILAGRITO, HEGRA-AIROBICC,
and the Tibet-Array. All crucial measurements to test the models will be
available in the next few years. These are measurements of (i) high-energy
neutrinos with AMANDA-ICECUBE or an enlarged ANTARES/NESTOR ocean detector,
(ii) GRB redshifts from HETE-2 follow-up studies, and (iii) GRB spectra above
10 GeV with low-threshold imaging air Cherenkov telescopes such as MAGIC and
the space telescopes AGILE and GLAST.


title: Truncations in stellar disks

abstract:
  The presence of radial truncations in stellar disks is reviewed. There is
ample evidence that many disk galaxies have relatively shaprt truncations in
their disks. These often are symmetric and independent of the wavelength band
of the observations. The ratio of the truncation radius R_{max} to the disk
scalelength h appears often less then 4.5, as expected on a simple model for
the disk collapse. Current samples of galaxies observed may however not be
representative and heavily biased towards disks with the largest scalelengths.
Many spiral galaxies also have HI warps and these generally start at the
truncation radius of the stellar disk. The HI surface density suddenly becomes
much flatter with radius. In some galaxies the start of the warp and the
position of the disk truncation radius is accompanied by a drop in the rotation
velocity. In the regiosn beyond the dis truncation in the HI layer some star
formation does occur, but the heavy element abundance and the dust content are
very low. All evidence is consistent with the notion that the outer gas parts
of the disks constitute recently accreted material, at least accreted after
formation of what is now the stellar thin disk. Although various models exist
for the origin of the truncations in the stellar disks, this at present remains
unclear.


title: X-ray imaging of the Seyfert 2 galaxy Circinus with Chandra

abstract:
  We present results from the zeroth-order imaging of a Chandra HETGS
observation of the nearby Seyfert 2 galaxy Circinus. Twelve X-ray sources were
detected in the ACIS-S image of the galaxy, embedded in diffuse X-ray emission.
The latter shows a prominent (~18arcsec) soft ``plume'' in the N-W direction,
coincident with the [OIII] ionization cone. The radial profiles of the
brightest X-ray source at various energies are consistent with an unresolved
(FWHM ~0.8arcsec) component, which we identify as the active nucleus, plus two
extended components with FWHMs ~ 2.3arcsec and 18arcsec, respectively. In a
radius of 3arcsec, the nucleus contributes roughly the same flux as the
extended components at the softest energies (< 2 keV). However, at harder
energies (> 2 keV), the contribution of the nucleus is dominant. The
zeroth-order ACIS spectrum of the nucleus exhibits emission lines at both soft
and hard X-rays, including a prominent Fe Kalpha line at 6.4 keV, showing that
most of the X-ray lines previously detected with ASCA originate in a compact
region (<15 pc). Based on its X-ray spectrum, we argue that the 2.3arcsec
extended component is scattered nuclear radiation from nearby ionized gas. The
large-scale extended component includes the emission from the N-W plume and
possibly from the outer starburst ring.


title:
High-resolution X-ray spectroscopy of the Seyfert 2 galaxy Circinus with
  Chandra

abstract:
  Results from a 60 ks Chandra HETGS observation of the nearby Seyfert 2
Circinus are presented. The spectrum shows a wealth of emission lines at both
soft and hard X-rays, including lines of Ne, Mg, Si, S, Ar, Ca, and Fe, and a
prominent Fe Kalpha line at 6.4 keV. We identify several of the He-like
components and measure several of the Lyman lines of the H-like ions. The
lines' profiles are unresolved at the limited signal-to-noise ratio of the
data. Our analysis of the zeroth-order image in a companion paper constrains
the size of the emission region to be 20-60 pc, suggesting that emission within
this volume is almost entirely due to the reprocessing of the obscured central
source. Here we show that a model containing two distinct components can
reproduce almost all the observed properties of this gas. The ionized component
can explain the observed intensities of the ionized species, assuming
twice-solar composition and an N \propto r^{-1.5} density distribution. The
neutral component is highly concentrated, well within the 0.8arcsec point
source, and is responsible for almost all of the observed Kalpha (6.4 keV)
emission. Circinus seems to be different than Mkn~3 in terms of its gas
distribution.


title:
A simple tool for assessing the completeness in apparent magnitude of
  magnitude-redshift samples

abstract:
  A new tool is proposed for finding out the completeness limit in apparent
magnitude of a magnitude-redshift sample. The technique, closely related to the
statistical test proposed by Efron & Petrosian (1992), presents a real
improvement compared to standard completeness tests. Namely, no a priori
assumptions are required concerning the redshift space distribution of the
sources. It means in particular that neither the clustering nor the evolution
of the mean number density of the galaxies do affect the result of the search.


title: The Amount of Dark Matter in Spiral Galaxies

abstract:
  The `maximum' disk hypothesis of galactic disks imbedded in dark matter halos
is examined. First, decompositions of the rotation curves of NGC 2613, 3198,
6503, and 7184 are analyzed. For these galaxies the radial velocity dispersions
of the stars have been measured. If the parameters of the decompositions are
chosen according to the `maximum' disk hypothesis, the Toomre Q stability
parameter is sytematically less than one, which is a strong argument against
the `maximum' disk hypothesis. Next, density wave theory arguments are used to
describe the morphology of the spiral arms of NGC 3223, 157, and 7083. It is
shown that the `maximum' disk hypothesis is not consistent with the observed
morphologies of the galaxies.


title: Stellar Variability in the Globular Cluster Terzan 5

abstract:
  We present the results of a search for variability in and near the core of
the metal-rich, obscured globular cluster Terzan 5, using NICMOS on HST. This
extreme cluster has approximately solar metallicity and a central density that
places it in the upper few percent of all clusters. It is estimated to have the
highest interaction rate of any galactic globular cluster. The large extinction
towards Terzan 5 and the severe stellar crowding near the cluster center
present a substantial observational challenge. Using time series analysis we
discovered two variable stars in this cluster. The first is a RRab Lyrae
variable with a period of ~0.61 days, a longer period than that of field stars
with similar high metallicities. This period is, however, shorter than the
average periods of RR Lyraes found in the metal-rich globular clusters NGC
6441, NGC 6388 and 47 Tuc. The second variable is a blue star with a 7-hour
period sinusoidal variation and a likely orbital period of 14 hours. This star
is probably an eclipsing blue straggler, or (less likely) the infrared
counterpart to the low mass X-ray binary known in Terzan 5. Due to the extreme
crowding and overlapping Airy profile of the IR PSF, we fall short of our
original goal of detecting CVs via Palpha emission and detecting variable
infrared emission from the location of the binary MSP in Terzan 5.


title:
The Optical Gravitational Lensing Experiment. Ages of about 600 Star
  Clusters from the LMC

abstract:
  We present results of age determination based on the standard procedure of
isochrone fitting for about 600 star clusters younger than about 1.2 Gyr from
the central parts of the LMC. Comparison of age distributions of star clusters
from the LMC and the SMC shows that cluster formation histories are different
in these galaxies. The age distribution of the LMC clusters reveals bursty
nature of cluster formation in this galaxy, with contrast to the relatively
uniform distribution of cluster ages in the SMC. We detected three extended
peaks in the distribution of ages of LMC clusters, located at about 7 Myr, 125
Myr and 0.8 Gyr. All detected peaks have complex structure. While the structure
of the youngest and the oldest peaks may be spurious due to accuracy of age
determination, in the middle peak two evident sub-peaks at 100 Myr and 160 Myr
are clearly seen. Similar peaks are seen in the distribution of ages of
clusters from the SMC, which indicates that increased cluster formation ratio
during these periods might be caused by the last encounter between the
Magellanic Clouds. The sample of clusters from the LMC is overabundant in very
young (<10 Myr) and old (>400 Myr) clusters, and underabundant in clusters
having ages in the range from 80 to 15 Myr with respect to the studied sample
of clusters from the SMC.


title:
Astronomical Constraints on the Cosmic Evolution of the Fine Structure
  Constant and Possible Quantum Dimensions

abstract:
  We present measurements of absorption by the 21cm hyperfine transition of
neutral hydrogen toward radio sources at substantial look-back times. These
data are used in combination with observations of rotational transitions of
common interstellar molecules, to set limits on the evolution of the fine
structure constant: (dot alpha)/alpha < 3.5e-15/yr to a look-back time of 4.8
Gyr. The neutral hydrogen observations employed Very Long Baseline
Interferometry in order to mitigate the substantial uncertainty arising from
the fact that observations at very different wavelengths may probe different
lines-of-site due to frequency dependent structure of the background source. We
discuss the implication of these results on theories unifying natural forces
based on compact quantum dimensions. In the context of string theory, the limit
on the secular evolution of the scale factor of these compact dimensions, R, is
(dot R)/R < 1e-15/yr. Including terrestrial and other astronomical measurements
places limits (2sigma) on slow oscillations of R from the present to the epoch
of cosmic nucleosynthesis, just seconds after the big bang, of (Delta R)/R <
1e-5.


title: X-ray Spectroscopy of the Cluster of Galaxies Abell 1795 with XMM-Newton

abstract:
  The initial results from XMM-Newton observations of the rich cluster of
galaxies Abell 1795 are presented. The spatially-resolved X-ray spectra taken
by the European Photon Imaging Cameras (EPIC) show a temperature drop at a
radius of $\sim 200$ kpc from the cluster center, indicating that the ICM is
cooling. Both the EPIC and the Reflection Grating Spectrometers (RGS) spectra
extracted from the cluster center can be described by an isothermal model with
a temperature of $\sim 4$ keV. The volume emission measure of any cool
component ($<1$ keV) is less than a few % of the hot component at the cluster
center. A strong OVIII Lyman-alpha line was detected with the RGS from the
cluster core. The O abundance and its ratio to Fe at the cluster center is
0.2--0.5 and 0.5--1.5 times the solar value, respectively.


title:
Faint Scattering Around Pulsars: Probing the Interstellar Medium on
  Solar System Size Scales

abstract:
  We have made high-resolution, high-sensitivity dynamic spectra of a sample of
strong pulsars at 430 MHz with the Arecibo radiotelescope. For 4 pulsars we
find faint but sharply delineated features in the secondary spectra. These are
examples of the previously observed ``crisscross'' or ``multiple drift slope''
phenomenon presumed to be due to multiple imaging of the pulsar by the
interstellar medium. The unprecedented resolution and dynamic range of our
observations allow a deeper level of analysis. Distances to the dominant
scattering screen along the line of sight are determined and are shown to agree
well with those inferred from other scintillation phenomena. Multiple imaging
of the pulsar by the ISM is required. A compact central image surrounded by a
faint scattering halo, roughly circularly symmetric, is consistent with the
data. Scattering from filaments may also be consistent. The angular extent of
the scattering material parallel to the direction of the pulsar velocity is
roughly 5 mas, corresponding to a linear extent of about 2 AU. Further
observations of these features should allow better discrimination between
models and an identification of the scattering structures.


title:
Gaussianity of Cosmic Velocity Fields and Linearity of the
  Velocity-Gravity Relation

abstract:
  We present a numerical study of the relation between the cosmic peculiar
velocity field and the gravitational acceleration field. We show that on mildly
non-linear scales (4-10 Mpc Gaussian smoothing), the distribution of the
Cartesian coordinates of each of these fields is well approximated by a
Gaussian. In particular, their kurtoses and negentropies are small compared to
those of the velocity divergence and density fields. We find that at these
scales the relation between the velocity and gravity field follows linear
theory to good accuracy. Specifically, the systematic errors in
velocity-velocity comparisons due to assuming the linear model do not exceed 6%
in beta. To correct for them, we test various nonlinear estimators of velocity
from density. We show that a slight modification of the alpha-formula proposed
by Kudlicki et al. yields an estimator which is essentially unbiased and has a
small variance.


title: The role of Z=0 AGB stars on the early chemical enrichment

abstract:
  We present theoretical evolutionary models for Z=0 stars in the mass range 4<
M/Mo <8 from the pre-main sequence up to the AGB phase. Contrary to previous
calculations we found that these stars develop normal thermal pulses and third
dredge-up episodes. Special attention is devoted to analyze the chemical
enrichment in the envelope due to the above mechanisms. As a consequence, we
show that these stars become carbon and nitrogen rich. Using different IMFs
proposed in the literature for the Population III stars, we study their
contribution to the pre-galactic chemical enrichment. It is found that Z=0 AGB
stars could significantly contribute to 7Li, 12C and 14N and produce extreme
non-solar 24Mg/25Mg/26Mg ratios. However, the net contribution is very
sensitive to the IMF adopted and to the fraction of primordial matter which
goes into stars.


title: Detection Limits for Super-Hubble Suppression of Causal Fluctuations

abstract:
  We investigate to what extent future microwave background experiments might
be able to detect a suppression of fluctuation power on large scales in flat
and open universe models. Such suppression would arise if fluctuations are
generated by causal processes, and a measurement of a small suppression scale
would be problematic for inflation models, but consistent with many defect
models. More speculatively, a measurement of a suppression scale of the order
of the present Hubble radius could provide independent evidence for a
fine-tuned inflation model leading to a low-density universe. We find that,
depending on the primordial power spectrum, a suppression scale modestly larger
than the visible Horizon can be detected, but that the detectability drops very
rapidly with increasing scale. For models with two periods of inflation, there
is essentially no possibility of detecting a causal suppression scale.


title: The first XMM-Newton spectrum of a high redshift quasar - PKS 0537-286

abstract:
  We present XMM-Newton observations of the high redshift z=3.104, radio-loud
quasar PKS 0537-286. The EPIC CCD cameras provide the highest signal-to-noise
spectrum of a high-z quasar to date. The EPIC observations show that PKS
0537-286 is extremely X-ray luminous (Lx=2x10^47 erg/s), with an unusually hard
X-ray spectrum (Gamma=1.27+/-0.02). The flat power-law emission extends over
the whole observed energy range; there is no evidence of intrinsic absorption,
which has been claimed in PKS 0537-286 and other high z quasars.
  However, there is evidence for weak Compton reflection. A redshifted iron K
line, observed at 1.5 keV - corresponding to 6.15 keV in the quasar rest frame
- is detected at 95% confidence. If confirmed, this is the most distant iron K
line known. The line equivalent width is small (33eV), consistent with the
`X-ray Baldwin effect' observed in other luminous quasars. The reflected
continuum is also weak (R=0.25). We find the overall spectral energy
distribution of PKS 0537-286 is dominated by the X-ray emission, which,
together with the flat power-law and weak reflection features, suggests that
the X-radiation from PKS 0537-286 is dominated by inverse Compton emission
associated with a face-on relativistic jet.


title:
Type Ia supernovae: differences due to progenitors within delayed
  detonation explosions

abstract:
  At this moment, the use of SNIa for cosmology lies on the assumption that the
SNe at high redshifts are equal to the local ones. However, some observations
indicate a correlation between the light curve (LC) properties and the
morphological type of the host galaxy. This could indicate a dependence with
the age (mass/composition) of the underlying population. In this work we have
chosen the delayed detonation explosion model in CO Chandrasekhar mass WDs to
explore the dependence of the SNIa LC and nucleosynthesis with the initial mass
and composition of the WD progenitor. The progenitor influences the final SNIa
via the mass of the CO core formed and the C/O ratio within it (1D explosion
models). We have followed the evolution of stars with masses between 1.5 and 8
Mo and metallicity, Z=0, 1.E-05, 0.001 and 0.02, from the pre-main sequence to
the TP-AGB phase. The differences obtained in the final C/O ratio within the
explosive WD are smaller than 22%. This results in a difference at maximum of
0.03 mag and of 0.1 mag when the brightness-decline relation is applied.


title:
First XMM-Newton observations of a Cataclysmic Variable I: Timing
  studies of OY Car

abstract:
  We present XMM-Newton observations of the eclipsing, disc accreting,
cataclysmic variable OY Car which were obtained as part of the performance
verification phase of the mission. The star was observed 4 days after an
outburst and then again 5 weeks later when it was in a quiescent state. There
is a quasi-stable modulation of the X-rays at ~2240 sec, which is most
prominent at the lowest energies. We speculate that this may be related to the
spin period of the white dwarf. The duration of the eclipse ingress and egress
in X-rays is 20--30 sec. This indicates that the bulk of the X-ray emission
originates from the boundary layer which has a negligible height above the
surface of the white dwarf. The eclipse profile implies a white dwarf of mass
M_{1}=0.9-1.1Msun and a secondary star of M_{2}=0.08-0.11Msun.


title: Deducing the Source of Ultrahigh Energy Cosmic Rays

abstract:
  The apparent lack of suitable astrophysical sources for cosmic rays with E >
10^{19.7} eV (UHECRs) is the "GZK Paradox". We argue that whatever mechanism
produces them must also account for events down to ~10^{18.7} eV, including
their isotropy and spectral smoothness. This rules out galactic sources,
distributed sources such as topological defects, and Gamma Ray Bursts (GRBs).
We are lead to identify the powerful radio galaxy Cen A, at 3.4 Mpc, as the
probable source of most UHECRs observed at Earth today, and to estimate the
extragalactic magnetic field to be ~0.3 microG.


title:
HST Color-Magnitude Data for Globular Clusters: I. Transformations
  Between STIS LP Magnitudes and WFPC2 F606W and F814W Magnitudes

abstract:
  We present deep Hubble Space Telescope optical imaging observations of two
Galactic globular clusters, 47 Tuc and M15, using the Space Telescope Imaging
Spectrograph (STIS) longpass (LP) filter and the Wide Field and Planetary
Camera 2 (WFPC2) F606W and F814W filters. These globular clusters have very
different metallicities ([Fe/H] = -0.7 dex for 47 Tuc, and [Fe/H] = -2.2 dex
for M15), essentially spanning the metallicity distribution of the entire Milky
Way globular cluster system, and were chosen to investigate the relationship
between magnitudes in the non-standard STIS LP system and the better
characterized WFPC2 magnitudes. We determine this relationship by combining our
new STIS data with archival WFPC2 data, taking care to provide a robust and
reliable transformation. Examining the 47 Tuc and M15 data separately, there is
no evidence for a metallicity dependence in the transformation relations. This
allows us to combine the data for both clusters, and also include the stars in
the Small Magellanic Cloud that lie within the field of view of the 47 Tuc
images, to determine final transformations that are valid for main sequence
stars with colors in the range 0.3 < V606-I814 < 1.8. These final relations
predict STIS magnitudes within 0.05 mag (1 sigma) of those measured for stars
in both clusters. In an appendix, we discuss the differences between our
empirical transformation relations and those predicted by synthetic photometry.


title: The Beta Problem: A Study of Abell 262

abstract:
  We present an investigation of the dynamical state of the cluster A262.
Existing optical line of sight velocities for select cluster galaxies have been
augmented by new data obtained with the Automated Multi-Object Spectrograph at
Lick Observatory. We find evidence for a virialized early-type population
distinct from a late-type population infalling from the Pisces-Perseus
supercluster ridge. We also report on a tertiary population of low luminosity
galaxies whose velocity dispersion distinguishes them from both the early and
late-type galaxies. We supplement our investigation with an analysis of
archival X-ray data. A temperature is determined using ASCA GIS data and a gas
profile is derived from ROSAT HRI data. The increased statistics of our sample
results in a picture of A262 with significant differences from earlier work. A
previously proposed solution to the "beta-problem" in A262 in which the gas
temperature is significantly higher than the galaxy temperature is shown to
result from using too low a velocity dispersion for the early-type galaxies.
Our data present a consistent picture of A262 in which there is no
"beta-problem", and the gas and galaxy temperature are roughly comparable.
There is no longer any requirement for extensive galaxy-gas feedback to
drastically overheat the gas with respect to the galaxies. We also demonstrate
that entropy-floor models can explain the recent discovery that the beta values
determined by cluster gas and the cluster core radii are correlated.


title: Magnetic Helicity Conservation and Astrophysical Dynamos

abstract:
  We construct a magnetic helicity conserving dynamo theory which incorporates
a calculated magnetic helicity current. In this model the fluid helicity plays
a small role in large scale magnetic field generation. Instead, the dynamo
process is dominated by a new quantity, derived from asymmetries in the second
derivative of the velocity correlation function, closely related to the `twist
and fold' dynamo model. The turbulent damping term is, as expected, almost
unchanged. Numerical simulations with a spatially constant fluid helicity and
vanishing resistivity are not expected to generate large scale fields in
equipartition with the turbulent energy density. The prospects for driving a
fast dynamo under these circumstances are uncertain, but if it is possible,
then the field must be largely force-free. On the other hand, there is an
efficient analog to the $\alpha-\Omega$ dynamo. Systems whose turbulence is
driven by some anisotropic local instability in a shearing flow, like real
stars and accretion disks, and some computer simulations, may successfully
drive the generation of strong large scale magnetic fields, provided that
$\partial_r\Omega< \partial_\theta v_z\omega_\theta>>0$. We show that this
criterion is usually satisfied. Such dynamos will include a persistent,
spatially coherent vertical magnetic helicity current with the same sign as
$-\partial_r\Omega$, that is, positive for an accretion disk and negative for
the Sun. We comment on the role of random magnetic helicity currents in storing
turbulent energy in a disordered magnetic field, which will generate an
equipartition, disordered field in a turbulent medium, and also a declining
long wavelength tail to the power spectrum. As a result, calculations of the
galactic `seed' field are largely irrelevant.


title:
Proper Motion Measurements with the VLA: I. Wide-field Imaging and Pulse
  Gating Techniques

abstract:
  The pulsar velocity distribution provides information about the binary
history of pulsar progenitors as well as asymmetries of the supernova events in
which pulsars are born. Studies of local pulsars present a biased view of this
distribution, since they preferentially select low velocity pulsars that have
remained near their birthplaces in the Galactic plane. Using the VLA, we have
studied the proper motions of a large sample of distant pulsars. These pulsars
are generally faint, and the expected proper motions are small. In this paper,
we describe the data analysis techniques that we have developed to allow
precise astrometric measurements of faint sources with the VLA. These
techniques include ``gating'' the VLA correlator to increase the
signal-to-noise ratio of the pulsar by gathering data only during the pulse.
Wide-field imaging techniques, including multiband imaging to account for
bandwidth smearing, were used to allow identification of multiple in-beam
background sources for astrometric calibration. We present the analysis of
three pulsars, and demonstrate that astrometric accuracy of about ten
milliarcseconds can be obtained for individual sources with our technique,
allowing measurement of proper motions with errors of only a few
milliarcseconds per year over our seven year baseline.


title: The Tail of the HI Mass Function

abstract:
  The contribution of extragalactic objects with HI masses below $10^8 M_\odot$
to the HI mass function remains uncertain. Several aspects of the detection of
low-mass sources in HI surveys are not always considered, and as a result
different analysis techniques yield widely different estimates for their number
density. It is suggested at one extreme that the number density of galaxies
follows a shallow Schechter power-law slope, and at the other extreme that it
follows a steep faint-end rise like that found for field optical sources. Here
we examine a variety of selection effects, issues of completeness, and
consequences of LSS. We derive results for the large Arecibo Dual Beam Survey
which indicate that the field mass function does rise steeply, while within the
Virgo Cluster environs, the slope appears to be much shallower. Dependence on
the local density of galaxies may partially explain differences between
surveys.


title:
The Arecibo Dual-Beam Survey: Filling the Gap in the Extragalactic
  Census

abstract:
  We present the Arecibo Dual-Beam Survey (ADBS), a "blind" 21cm survey for
galaxies. The ADBS is the largest to date with the Arecibo radio telescope. We
were able to achieve an rms sensitivity of 3-4 mJy in only 7 seconds. The ADBS
covers substantially more volume than the Spitzak & Schneider (1998) and the
Zwaan et al. (1997) surveys. It is surpassed by the Parkes HIPASS survey
(Kilborn et al. 1999) but has much better angular resolution and sensitivity.
We will discuss the HI sample and our efforts to quantify the completeness and
reliability.
  This is the first survey to use synthetic sources to establish the relation
between the flux, line width, and completeness of the survey. An empirical
understanding of these quantities is vital to the determination of the mass
function. Even if we do not understand all of the reasons why we do not detect
galaxies, the empirical understanding allows us to account for them properly.
  In addition to the more general discussion of the ADBS survey, we will
discuss galaxies which have large ratios of HI mass to optical area and
probably have extended HI disks. We detect a much higher percentage of these
high HI mass to optical area galaxies than are seen in optical surveys
indicating that optical surveys miss these galaxies. Among these galaxies are
also 7 galaxies with HI masses < 10^8 M_sun. Based on the mass function of
Schneider & Rosenberg (this volume), the low mass galaxies are an important
part of the general galaxy population.


title: Evidence for the Heating of Atomic Interstellar Gas by PAHs

abstract:
  We report a strong correlation between the [CII] 158 micron cooling line and
the mid-infrared flux in the 5-10 micron range in a wide variety of
star-forming galaxies. The mid-infrared flux is dominated by Aromatic Feature
Emission (AFE), which is thought to arise from large polycyclic aromatic
hydrocarbon molecules or `PAHs' and generally associated with the smallest
interstellar grains. The [CII] line is the dominant gas coolant in most regions
of atomic interstellar gas, and therefore reflects the heating input to the
gas. The ratio of these two quantities, [CII]/AFE, remains nearly constant with
the ratio of the IRAS 60 micron band flux to the 100 micron band flux,
R(60/100). This is in contrast to the drop in the [CII]/FIR ratio with
increasing R(60/100), which signal higher dust temperatures and more intense
radiation fields. We interpret the stable [CII]/AFE ratio as evidence that gas
heating is dominated by the PAHs or small grains which are also AFE carriers
over a wide range of conditions. The trend of decreasing [CII]/FIR with
increasing radiation field suggests a decrease in the importance of PAHs or
small grains relative to large grains both in gas heating and in dust cooling.
We summarize the observed trends and suggest two plausible scenarios.


title: Emission Mechanisms in X-Ray Faint Galaxies

abstract:
  Hot gas dominates the emission in X-ray luminous early-type galaxies, but in
relatively X-ray faint systems, integrated X-ray emission from discrete
stellar-like sources is thought to be considerable, although the amount of the
contribution is controversial. To help resolve this issue, we examine the
radial X-ray surface brightness distribution of 17 X-ray faint galaxies
observed with the ROSAT HRI and PSPC. We assume that the stellar contribution
follows a de Vaucouleurs law while the hot gas component follows a King beta
model. For some galaxies, both models fit equally well, but for a number of
systems, a dual component model yields the best fit, from which upper bounds
are placed on the stellar contribution. Best-fit values for the stellar
contribution are inconsistent with (lower than) that suggested by Fabbiano,
Gioia, & Trinchieri (1989) and estimated from the bulge of M31, but are
consistent with the Forman, Jones, & Tucker (1985) estimate of the stellar
fraction in X-ray faint elliptical and S0 galaxies. Our results indicate an
upper limit to discrete sources of L_X/L_B = 1.6 x 10^29 ergs/s/L(solar).


title:
Kinematics from spectroscopy with a wide slit: detecting black holes in
  galaxy centres

abstract:
  We consider long-slit emission-line spectra of galactic nuclei when the slit
is wider than the instrumental PSF, and the target has large velocity
gradients. The finite width of the slit generates complex distributions of
brightness at a given spatial point in the measured spectrum, which can be
misinterpreted as coming from additional physically distinct nuclear
components. We illustrate this phenomenon for the case of a thin disc in
circular motion around a nuclear black hole (BH). We develop a new method for
estimating the mass of the BH that exploits a feature in the spectrum at the
outer edge of the BH's sphere of influence, and therefore gives higher
sensitivity to BH detection than traditional methods. Moreover, with this
method we can determine the black hole mass and the inclination of the
surrounding disc separately, whereas the traditional approach to black-hole
estimation requires two long-slit spectra to be taken. We show that with a
given spectrograph, the detectability of a BH depends on the sense of rotation
of the nuclear disc. We apply our method to estimate the BH mass in M84 from a
publicly available spectrum, and recover a value 4 times lower than that
published previously from the same data.


title: Temperature Map of the Virgo Cluster of Galaxies Observed with ASCA

abstract:
  The temperature distribution of the intracluster medium (ICM) in the Virgo
cluster of galaxies has been derived from extensive mapping observations with
ASCA covering an area of 19 deg^2. In the spectral analysis, the inner region
within a radius of ~60' from M87 is characterized by an ICM temperature of kT
\~2.5 keV with little variation. On the other hand, the outer regions indicate
significant variation of the temperature with an amplitude of about 1 keV. The
temperature map was produced from the hardness ratio (H.R.) values with a
resolution of about 5'. Besides the previously reported hot region with kT > 4
keV between M87 and M49, several hot regions with kT = 3-4 keV are detected in
the cluster outskirts. The auto-correlation function for the H.R. variation
shows that the temperature variation is correlated within a size of about 300
kpc, suggesting that gas blobs falling in the Virgo cluster have a typical size
of groups of galaxies. A correlation with the velocity dispersion of member
galaxies shows that only the north-west region indicates an unusually large
beta_spec value of 2-4. The upper limit for extended non-thermal emission in
the Virgo cluster is obtained to be L_X ~9 x 10^41 ergs/s in the 2 - 10 keV
band. We discuss that these features consistently indicate that the Virgo
cluster is in a relatively early stage of the cluster evolution.


title:
Successive Measurements of Cosmic-Ray Antiproton Spectrum in a Positive
  Phase of the Solar Cycle

abstract:
  The energy spectrum of cosmic-ray antiprotons has been measured by BESS
successively in 1993, 1995, 1997 and 1998. In total, 848 antiprotons were
clearly identified in energy range 0.18 to 4.20 GeV. From these successive
measurements of the antiproton spectrum at various solar activity, we discuss
about the effect of the solar modulation and the origin of cosmic-ray
antiprotons. Measured antiproton ratios were nearly identical during this
period, and were consistent with a prediction taking the charge dependent solar
modulation into account.


title: Kinematics of 1200 km/s Jets in He 3-1475

abstract:
  Spectroscopic observations of a proto-planetary nebula He 3-1475 with the
Space Telescope Imaging Spectrograph (STIS) reveal the kinematics of its high
(1200 km/s) velocity jets. The jets are formed at a large (0.15 pc) distance
from its central star by collimation of an asymmetric stellar wind in a pair of
conical shocks seen in Wide Field Planetary Camera (WFPC2) images. The jets
consist of several pairs of knots symmetrically distributed with respect to the
central star, with most knots exhibiting a head-tail morphology. Large (up to
650 km/s) radial velocity gradients are seen within the knots on subarcsec
scales, with velocities decreasing from the knot heads toward their trailing
tails. These large velocity gradients are a sign of efficient deceleration of
jets by a much slower bipolar outflow. The inclination angle of the bipolar
outflow is equal to 40 degrees, based on Doppler shifts of the scattered
stellar Halpha line. Its velocity is equal to 140 km/s at a distance of 0.23 pc
from the star, and increases monotonically with the radial distance from the
star. A comparison of new WFPC2 [N II] 6584 images with older WFPC2 images
reveals expansion of the jets. The measured jet proper motions in combination
with their radial velocities imply that He 3-1475 is a Galactic Bulge star at a
distance of 8 kpc, located 800 pc above the Galactic plane. Its very high
luminosity (25,000 solar luminosities) implies that He 3-1475 must be
significantly more massive than a typical AGB star within the Galactic Bulge,
perhaps because of a past mass transfer and/or a merger event in an interacting
binary system.


title: Self-Gravitating N-Body Systems out of Equilibrium

abstract:
  Real physical systems are often maintained off equilibrium by energy or
matter flows. If these systems are far from equilibrium then the
thermodynamical branch become unstable and fluctuations can lead them to other
more stable states. These new states are often endowed with higher degrees of
organization. In order to explore whether an energy-flow in combination with
self-gravity can lead to complex, inhomogeneous structures, like observed in
the interstellar medium (ISM), we perform N-body simulations of
self-gravitating systems subjected to an energy-flow. Moreover we perform some
simple gravo-thermal N-body experiments and compare them with theoretical
results. We find negative specific heat in an energy range as predicted by
Follana & Laliena (1999).


title: AGN and Starburst Galaxies Seen through Radio Surveys

abstract:
  The emergence of a new population of radio galaxies at mJy and sub-mJy levels
is responsible for the change in the slope of the radio source counts. This
population seems to include both star forming galaxies and classical
(AGN-powered) radio sources, but the relative importance of the two classes is
still debated. We present results from the ATESP radio survey and its optical
follow-up and show that the fraction of starburst galaxies changes from ~15% at
fluxes >1 mJy to >50% at lower fluxes.


title:
Dehydrogenation of polycyclic aromatic hydrocarbons in the diffuse
  interstellar medium

abstract:
  We present a model for the hydrogenation states of Polycyclic Aromatic
Hydrocarbons (PAHs) in the diffuse interstellar medium. First, we study the
abundance of hydrogenation and charge states of PAHs due to photo-ionization,
photo-dissociation in the interstellar UV field, electron recombination and
chemical reactions between PAH cations and H or H_2. For PAH cations, we find
that the dehydrogenation effects are dominant. The hydrogenation state of PAHs
depends strongly on the H density, the size of the molecule and UV field. In
diffuse clouds with low H density and normal UV radiation, PAHs containing less
than 40 C are completely or strongly dehydrogenated whereas at high H density,
they are normally hydrogenated. The partially dehydrogenated species dominate
in intermediate density clouds. PAHs above 40 C are quite stable and are fully
hydrogenated, which would favor their spectroscopic search in near IR surveys
of Diffuse Interstellar Bands (DIBs).


title:
XMM-Newton Detection of a Comptonized Accretion Disc in the Quasar
  PKS0558-504

abstract:
  We present XMM-Newton observations of the bright quasar PKS0558-504. The
0.2-10 keV spectrum is dominated by a large, variable soft X-ray excess. The
fastest flux variations imply accretion onto a Kerr black hole. The XMM-Newton
data suggest the presence of a `big blue bump' in PKS0558-504 extending from
the optical band to ~3 keV. The soft X-ray spectrum shows no evidence for
significant absorption or emission-line features. The most likely explanation
for the hot big blue bump is Comptonization by the multi-temperature corona of
a thermal accretion disc running at a high accretion rate.


title:
Maximum-entropy reconstruction of gravitational lenses using shear
  and/or magnification data

abstract:
  We demonstrate that the maximum-entropy method for gravitational lens
reconstruction presented in Bridle et al. (1998) may be applied even when only
shear \emph{or} magnification information is present. We also demonstrate that
the method can easily handle irregularly shaped observing fields and, because
shear is a non-local function of the lensing mass, reconstructions that use
shear information can successfully bridge small gaps in observations. For our
simulations we use a mass density distribution that is realistic for a z=0.4
cluster of total mass around 10^15 h^-1 M_solar. Using HST-quality shear data
alone, covering the area of four WFPC2 observations, we detect 60 per cent of
the mass of the cluster within the area observed, despite the mass sheet
degeneracy. This is qualitatively because the shear provides information about
the variations in the mass distribution, and our prior includes a positivity
constraint. We investigate the effect of using various sizes of observing field
and find that 50 to 100 per cent of the cluster mass is detected, depending on
the observing strategy and cluster shape. Finally we demonstrate how this
method can cope with strong lensing regions of a mass distribution.


title: The Chemical Evolution of Galaxy Disks

abstract:
  We discuss the main ingredients necessary to build models of chemical
evolution of spiral galaxies and in particular the Milky Way galaxy. These
ingredients include: the star formation rate, the initial mass function, the
stellar yields and the gas flows. Then we discuss models for the chemical
evolution of galaxy disks and compare their predictions with the main
observational constraints available for the Milky Way and other spirals. We
conclude that it is very likely that the disk of our Galaxy and other spirals
formed through an ``inside-out'' mechanism, where the central parts collapsed
much faster than the external ones. This mechanism has important consequences
for the appearance of galaxy disks as a function of redshift.


title: Halo Formation in Warm Dark Matter Models

abstract:
  Discrepancies have emerged between the predictions of standard cold dark
matter (CDM) theory and observations of clustering on sub-galactic scales. Warm
dark matter (WDM) is a simple modification of CDM in which the dark matter
particles have initial velocities due either to their having decoupled as
thermal relics, or having been formed via non-equilibrium decay. We investigate
the nonlinear gravitational clustering of WDM with a high resolution N-body
code, and identify a number of distinctive observational signatures. Relative
to CDM, halo concentrations and core densities are lowered, core radii are
increased, and large halos emerge with far fewer low mass satellites. The
number of small halos is suppressed, and those present are formed by `top down'
fragmentation of caustics, as part of a `cosmic web' connecting massive halos.
Few small halos form outside this web. If we identify small halos with dwarf
galaxies, their number, spatial distribution, and formation epoch appear in
better agreement with the observations for WDM than they are for CDM.


title: The formation of G-band bright points. I: Standard LTE modelling

abstract:
  Assuming LTE, we synthesise solar G band spectra from the semiempirical
flux-tube model of Briand Solanki (1995). The results agree with observed
G-band bright-point contrasts within the uncertainty set by the amount of
scattered light. We find that it is the weakening of spectral lines within the
flux tube that makes the bright-point contrast in the G band exceed the
continuum contrast. We also synthesise flux-tube spectra assuming LTE for the
full wavelength range from UV to IR, and identify other promising passbands for
flux-tube observations.


title:
Submillimeter Wave Astronomy Satellite Observations of Extended Water
  Emission in Orion

abstract:
  We have used the Submillimeter Wave Astronomy Satellite to map the
ground-state 1_{10}-1_{01} transition of ortho-water at 557 GHz in the Orion
molecular cloud. Water emission was detected in Orion over an angular extent of
about 20 arcmin, or nearly 3 pc. The water emission is relatively weak, with
line widths (3-6 km s^{-1}) and V_{LSR} velocities (9-11 km s^{-1}) consistent
with an origin in the cold gas of the molecular ridge. We find that the
ortho-water abundance relative to H_2 in the extended gas in Orion varies
between 1 and 8x10^{-8}, with an average of 3x10^{-8}. The absence of
detectable narrow-line ortho-H_2^{18}O emission is used to set a 3-sigma upper
limit on the relative ortho-water abundance of 7x10^{-8}.


title: The Distribution of Water Emission in M17SW

abstract:
  We present a 17-point map of the M17SW cloud core in the 1_{10}-1_{01}
transition of ortho-water at 557 GHz obtained with the Submillimeter Wave
Astronomy Satellite. Water emission was detected in 11 of the 17 observed
positions. The line widths of the water emission vary between 4 and 9 km
s^{-1}, and are similar to other emission lines that arise in the M17SW core. A
direct comparison is made between the spatial extent of the water emission and
the ^{13}CO J = 5\to4 emission; the good agreement suggests that the water
emission arises in the same warm, dense gas as the ^{13}CO emission. A spectrum
of the H_2^{18}O line was also obtained at the center position of the cloud
core, but no emission was detected. We estimate that the average abundance of
ortho-water relative to H_2 within the M17 dense core is approximately
1x10^{-9}, 30 times smaller than the average for the Orion core. Toward the H
II region/molecular cloud interface in M17SW the ortho-water abundance may be
about 5 times larger than in the dense core.


title: Water Abundance in Molecular Cloud Cores

abstract:
  We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the
1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud
cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL
2591, W3, W3(OH), Mon R2, and W33, and was not detected in TMC-1, L134N, and
B335. We also present a small map of the water emission in S140. Observations
of the H_2^{18}O line were obtained toward S140 and NGC 7538, but no emission
was detected. The abundance of ortho-water relative to H_2 in the giant
molecular cloud cores was found to vary between 6x10^{-10} and 1x10^{-8}. Five
of the cloud cores in our sample have previous water detections; however, in
all cases the emission is thought to arise from hot cores with small angular
extents. The water abundance estimated for the hot core gas is at least 100
times larger than in the gas probed by SWAS. The most stringent upper limit on
the ortho-water abundance in dark clouds is provided in TMC-1, where the
3-sigma upper limit on the ortho-water fractional abundance is 7x10^{-8}.


title: Extended [C I] and ^{13}CO(5-4) Emission in M17SW

abstract:
  We mapped a 13 by 22 pc region in emission from 492 GHz [C I] and, for the
first time, 551 GHz ^{13}CO(5-4) in the giant molecular cloud M17SW, using the
Submillimeter Wave Astronomy Satellite. The morphologies of the [C I] and
^{13}CO emission are strikingly similar. The extent and intensity of the [C I]
and ^{13}CO(5-4) emission is explained as arising from photodissociation
regions on the surfaces of embedded molecular clumps. Modeling of the
^{13}CO(5-4) emission in comparison to ^{13}CO(1-0) indicates a temperature
gradient across the cloud, peaking to at least 63 K near the M17 ionization
front and decreasing to at least 20 K at the western edge of the cloud. We see
no correlation between gas density and column density. The beam-averaged column
density of C I in the core is 1x10^{18} cm^-2, and the mean column density
ratio N(C I)/N(CO) is about 0.4. The variations of N(C I)/N(CO) with position
in M17SW indicate a similar clump size distribution throughout the cloud.


title: The Complete Bispectrum of COBE-DMR Four Year Maps

abstract:
  We extend a previous bispectrum analysis of the COBE-DMR 4 year maps,
allowing for the presence of correlations between all possible angular scales.
We find that the non-Gaussian signal found earlier for bispectrum components
including adjacent modes does not extend to triplets of modes with larger
separations. Indeed for all separations $\Delta\ell >1$ we find that the
COBE-DMR data is very Gaussian. The implication seems to be that the previously
detected non-Gaussian scale-scale correlation falls off very quickly with mode
separation.


title: Variability Modes of Blazars from Intensive Optical Monitoring

abstract:
  We report the main results of our six year long intensive optical monitoring
on blazars ON 231 (W Com), BL Lac, and 3C 273. Intensive optical monitoring is
an indispensable tool to obtain well sampled light curves and thus to
understand the correlation with the variability in other bands and to
discriminate among the proposed emission models. The curves based on our work
show different variability modes: intermittent mode, quasi-regular mode and
mixed mode. It is not clear if different variability modes can be present, at
various times, in the life of an object suggesting that their occurrence can be
related to the evolution of blazars. An optimized and nearly continuous optical
monitoring is the only way to know the activity status of the sources and to
retrieve useful information on their physical dynamics. Also, the rapid
availability of information about the luminosity of a source is very important
to trigger space based observations and to activate large multifrequency
collaborations. We stress that a significant sample of blazars can be observed
with small size telescopes (0.35-0.80 cm) equipped with CCD cameras. A
world-wide network of several instruments in different countries, is very
useful to increase the time coverage and to reduce the number of nights lost
for bad meteorological conditions.


title: The Ephemeris and Dipping Spectral Behavior of X1624-490

abstract:
  We present striking results from Rossi X-ray Timing Explorer (RXTE)
observations of the 21-hr low mass X-ray binary X1624-490, showing five complex
dips in unprecedented detail. For the first time, dipping is detected up to 15
keV. Prominent flares are also observed in the light curves, limited to
energies above 8 keV. Spectra selected by intensity during dip episodes can be
well fit with a two-component model consisting of a point-like blackbody from
the neutron star and progressive covering of an extended Comptonized region,
presumably an accretion disk corona (ADC), corrected for photons scattered into
and out of the X-ray beam by a interstellar dust halo. We find that the outer
regions of the absorber are highly ionized and that electron scattering is
totally responsible for the X-ray attenuation during shallow dipping. The
timescales of dip ingress and egress indicate that the envelope of material
absorbing the ADC has smaller angular size than the ADC itself, and that the
ADC is likely limited to a height-to-radius ratio of 10%, rather than being
spherical in extent. In addition, we have analyzed 4.5 yrs of RXTE All Sky
Monitor (ASM) coverage to derive the first accurate orbital ephemeris for
X1624-490, with phase zero (the time of dip centers) well-described by the
relation 2450088.63918(69) + N*0.869907(12) (JD).


title:
Black Hole Formation in Core-Collapse Supernovae and Time-of-Flight
  Measurements of the Neutrino Masses

abstract:
  Early black hole formation in core-collapse supernovae may be triggered by
mass accretion or a change in the high-density equation of state. We consider
the possibility that black hole formation happens when the flux of neutrinos is
still measurably high. If this occurs, then the neutrino signal from the
supernova will be terminated abruptly (the transition takes $\lesssim 0.5$ ms).
The properties and duration of the signal before the cutoff are important
measures of both the physics and astrophysics of the cooling proto-neutron
star. For the event rates expected in present and proposed detectors, the
cutoff will generally appear sharp, thus allowing model-independent
time-of-flight mass tests for the neutrinos after the cutoff. If black hole
formation occurs relatively early, within a few ($\sim 1$) seconds after core
collapse, then the expected luminosities are of order $L_{BH} = 10^{52}$ erg/s
per flavor. In this case, the neutrino mass sensitivity can be extraordinary.
For a supernova at a distance $D = 10$ kpc, SuperKamiokande can detect a
$\bar{\nu}_e$ mass down to 1.8 eV by comparing the arrival times of the
high-energy and low-energy neutrinos in $\bar{\nu}_e + p \to e^+ + n$. This
test will also measure the cutoff time, and will thus allow a mass test of
$\nu_\mu$ and $\nu_\tau$ relative to $\bar{\nu}_e$. Assuming that $\nu_\mu$ and
$\nu_\tau$ are nearly degenerate, as suggested by the atmospheric neutrino
results, masses down to about 6 eV can be probed with a proposed lead detector
of mass $M_D = 4$ kton (OMNIS). Remarkably, the neutrino mass sensitivity
scales as $(D/L_{BH} M_D)^{1/2}$. Therefore, {\it direct} sensitivity to all
three neutrino masses in the interesting few-eV range is realistically
possible; {\it there are no other known techniques that have this capability}.

categories: astro-ph gr-qc hep-ex hep-ph nucl-ex nucl-th


title: Ground-state OH observations towards NGC 6334

abstract:
  We have made observations of the four hyperfine transitions of the 2Pi(3/2),
J=3/2 ground state of OH at 1612, 1665, 1667 and 1720 MHz and the related
1.6-GHz continuum emission, towards NGC 6334 using the Australia Telescope
Compact Array. The observations covered all the major radio continuum
concentrations aligned along the axis of NGC 6334 (V, A to F). We have detected
seven OH masers plus a possible faint eighth maser; two of these masers are
located towards NGC 6334-A. Absorption at 1665 and 1667 MHz was detected
towards almost all the continuum distribution. All transitions showed non-LTE
behaviour. The 1667-/1665-MHz intensity ratios ranged from 1.0 to 1.2,
significantly less than their LTE value of 1.8. The results of the OH `Sum
Rule' suggest that this discrepancy cannot be explained solely by high optical
depths. The 1612- and 1720-MHz line-profiles showed conjugate behaviour whereby
one line was in absorption and the other in emission. In addition, the profiles
commonly showed a flip from absorption to emission and vice versa, which has
been interpreted as a density gradient. The OH line-to-continuum distribution,
optical depth and velocity trends are consistent with a bar-like shape for the
molecular gas which wraps around the continuum emission.


title: Photon Splitting and Pair Creation in Highly Magnetized Pulsars

abstract:
  The absence of radio pulsars with long periods has lead to the popular notion
of a high P ``death line.'' In the standard picture, beyond this boundary,
pulsars with low spin rates cannot accelerate particles above the stellar
surface to high enough energies to initiate pair cascades, and the pair
creation needed for radio emission is strongly suppressed. In this paper we
explore the possibility of another pulsar ``death line'' in the context of
polar cap models, corresponding to high magnetic fields B in the upper portion
of the period-period derivative diagram, a domain where few radio pulsars are
observed. The origin of this high B boundary, which may occur when B becomes
comparable to or exceeds $B_{\rm cr} = 4.4 \times 10^{13}$ Gauss, is also due
to the suppression of magnetic pair creation, but primarily because of
ineffective competition with magnetic photon splitting. Threshold pair creation
also plays a prominent role in the suppression of cascades. We present Monte
Carlo calculations of the pair yields in photon splitting/pair cascades which
show that, in the absence of scattering effects, pair production is effectively
suppressed, but only if all three modes of photon splitting allowed by QED are
operating in high fields. This paper describes the probable shape and position
of the new ``death line,'' above which pulsars are expected to be radio quiet,
but perhaps still X-ray and gamma-ray bright. The hypothesized existence of
radio-quiet sources finds dramatic support in the recent discovery of
ultra-strong fields in Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars.
Guidelines for moderate to high B pulsar searches at radio wavelengths and also
in the soft and hard gamma-ray bands are presented.


title:
The Relative Star Formation Histories of Spiral Bulges and Elliptical
  Galaxies in the Hubble Deep Fields

abstract:
  Hierarchical galaxy formation models make specific predictions concerning the
relative assembly rates and star formation histories of spiral bulges and field
ellipticals. Independently of the cosmological model and initial power spectrum
of fluctuations, at all epochs the stellar populations in spiral bulges should
be older and redder than those in typical ellipticals selected at the same
redshift. To test this simple prediction, we analyze the internal optical
colors of a complete sample of I<24 mag early-type and spiral galaxies from the
Northern and Southern Hubble Deep Fields (HDF). The subset of galaxies in the
Northern HDF are also investigated in the near-infrared using NICMOS
photometry. We compare the central (inner 5% radius) colors of those spirals
with clearly visible bulges with the integrated colors of ellipticals in our
sample. Comparisons are possible to a redshift z~1 at which point well-defined
bulges become difficult to locate. While spiral bulges are systematically
redder in their optical colors than their associated disks at all redshifts, we
find that the majority are significantly bluer than the red locus occupied by
most field ellipticals at similar redshifts. In the near-infrared, similar
trends are found at redshifts z<0.6, but at higher redshifts some bulges as red
as the reddest ellipticals are found. We conclude that a significant
rejuvenation may have occurred in the inner stellar populations of many spiral
galaxies at intermediate redshifts.


title:
Resonant Gaps in the Scattered Cometary Population of the
  Trans-Neptunian Region

abstract:
  Our numerical simulations of the Edgeworth-Kuiper belt objects
gravitationally scattered by the four giant planets accounting for mean motion
resonances reveal numerous resonant gaps in the distribution of the scattered
population.


title:
Exploring the gravitationally lensed system HE1104-1805: VLT
  spectroscopy of the lens at z=0.729

abstract:
  Using FORS2, mounted on Kueyen (UT2 of the VLT), we have obtained the
redshift of the lensing galaxy in the gravitational lens system HE1104-1805. We
measure z=0.729, in good agreement with previous estimates based on the time
delay and the position of the lens on the fundamental plane. It also coincides
with one of the metal line absorption systems that are seen in high resolution
spectra of HE1104-1805.


title: CMB with Quintessence: Analytic Approach and CMBFAST

abstract:
  A particular kind of quintessence is considered, with equation of motion
$p_Q/\rho_Q = -1$, corresponding to a cosmological term with time-dependence
$\Lambda(t) = \Lambda(t_0) (R(t_0)/R(t))^{P}$ which we examine initially for $0
\leq P < 3$. Energy conservation is imposed, as is consistency with big-bang
nucleosynthesis, and the range of allowed $P$ is thereby much restricted to $0
\leq P < 0.2$. The position of the first Doppler peak is computed analytically
and the result combined with analysis of high-Z supernovae to find how values
of $\Omega_m$ and $\Omega_{\Lambda}$ depend on $P$. Some comparison is made to
the CMBFAST public code.


title: The Birth, Evolution and Death of Star Clusters

abstract:
  A dense-enough gas-accumulation evolves, over a few Myr of intensifying star
formation, to an embedded cluster. If it contains a sufficient amount of mass,
O stars form and explosively expel the remaining gas, whereas poorer clusters
reduce their embryonic gas content more gradually. The sudden expulsion of gas
unbinds most of a rich cluster, but a significant fraction of it can condense
by two-body interactions to become an open cluster despite a star-formation
efficiency as low as 30 per cent. Poorer clusters survive their gradual mass
loss more easily, but have short, relaxation-limited life-times. Pleiades-like
clusters may thus form as nuclei of expanding OB associations, by filling their
tidal radii and having large (1-2 pc) core-radii. A 'main-sequence' of clusters
is thus established. Ultimately, a cluster dies an explosive death through the
ever shortening relaxation time, and leaves a remnant that consists of about
4-10 stars arranged in a highly hierarchical and thus long-lived system.
Dynamical mass segregation in very young clusters is extremely rapid, and heats
a cluster substantially, which is partially off-set by the cooling from the
disruption of primordial binaries.


title:
The KPNO International Spectroscopic Survey. II. H-alpha Selected Survey
  List 1

abstract:
  The KPNO International Spectroscopic Survey (KISS) is a new objective-prism
survey for extragalactic emission-line objects. It combines many of the
features of previous slitless spectroscopic surveys with the advantages of
modern CCD detectors, and is the first purely digital objective-prism survey
for emission-line galaxies. Here we present the first list of emission-line
galaxy candidates selected from our red spectral data, which cover the spectral
range 6400 to 7200 Angstroms. In most cases, the detected emission line is
H-alpha. The current survey list covers a one-degree-wide strip located at Dec
(1950) = 29.5 degrees and spanning the RA range 12h 15m to 17h 0m. An area of
62.2 sq. degrees is covered. A total of 1128 candidate emission-line objects
have been selected for inclusion in the survey list (18.1 per sq. degree). We
tabulate accurate coordinates and photometry for each source, as well as
estimates of the redshift and emission-line flux and equivalent width based on
measurements of the digital objective-prism spectra. The properties of the KISS
emission-line galaxies are examined using the available observational data.


title: The vertical structure and kinematics of HI in spiral galaxies

abstract:
  We discuss the distribution and kinematics of neutral hydrogen in the halos
of spiral galaxies. We focus in particular on new results obtained for the
nearby Sc galaxy NGC 2403 which have revealed the presence of extended HI
emission (here referred to as the `beard') at anomalous velocities with respect
to the `cold' HI disk. Modeling shows that this component has a mass of about
1/10 of the total HI mass and is probably located in the halo region. Its
kinematics differs from that of the thin HI disk: it rotates more slowly and
shows radial inflow. The origin of this anomalous gas component is unknown. It
could be the result of a galactic fountain or of accretion of extragalactic
`primordial' gas.


title:
Particle Creation in Pre-Big-Bang Cosmology: theory and observational
  consequences

abstract:
  We present some phenomenological aspects of the pre-big-bang cosmological
model inspired by the duality properties of string theory. In particular,
assuming the spatial sections of the homogeneous background geometry to be
isotropic, we discuss the quantum production of perturbations of the background
fields (gravitons, dilatons, moduli fields), as well as the production of
particles which do not contribute to the background, which we call ``seeds''.
As such we consider the cases of electromagnetic and axionic seeds. We also
discuss their possible observational consequences, for example, we study
whether they can provide the origin of primordial galactic magnetic fields, and
whether they can generate the initial fluctuations leading to the formation of
large-scale structure and the measured cosmic microwave background
anisotropies. We finally analyze axion and photon production in four
dimensional anisotropic pre-big-bang cosmological models.


title: From Messier to Abell: 200 years of science with galaxy clusters

abstract:
  I review the history of scientific research on galaxy clusters, from 1784,
the year of publication of Messier's catalogue, to 1983, the year of George O.
Abell's premature death.
  My review covers four main topics:
  1) the distribution of clusters,
  2) the cluster components,
  3) the cluster structure,
  4) the evolution of clusters.
  I consider both theoretical and observational aspects, but not technical
aspects, such as the development of new telescopes and instruments.
  In total, 529 papers are cited in this review.


title: A High Resolution Radio Survey of Class I Protostars

abstract:
  We report the results of a survey of low mass Class I protostars in the cm
continuum. In the initial survey, seven sources in the Taurus star formation
were observed with the VLA at 0``.25 resolution. All seven sources drive CO
outflows and display Herbig-Haro flows in the optical or near infrared
wavebands. 4/7 sources were detected, two of which are new discoveries in
systems of very low luminosity, one being the lowest luminosity system detected
to date in the cm continuum. Notably, three sources were not detected to a
3-sigma limit of 0.10 mJy/beam, which indicates that significant cm continuum
emission is not a universal feature of Class I systems with outflow activity.
Subsequent observations of HH30, a more evolved Class II system, found no
emission to a 3-sigma limit of 0.03 mJy/beam. After comparison with near
infrared data, we suggest that the discriminating feature of the detected
systems is a relatively high ionisation fraction in the stellar wind. Temporal
variability of the outflow may also play a role. The one relatively bright
source, IRAS 04016+2610 (L1489 IRS), is clearly resolved on a 0``.4 scale at 2
cm and 3.5 cm. Follow-up imaging with MERLIN did not detect this source with a
0``.04 beam, indicating that the radio emission is generated in a region with a
radius of about 25 au, which is broadly similar to the radius of the bipolar
cavities inferred from models of near infrared data. Interpretation of this
system is complicated by the existence of a quadrupolar outflow, which we
originally detected through polarimetric imaging. We present a near infrared H2
image in which a bow shock in the secondary outflow is clearly seen. This
complicated structure may have been caused by a gravitational interaction
between two protostars.