title: The DEEP2 Redshift Survey

abstract:
  The DEIMOS spectrograph is nearing completion in the UC Lick shops and will
be delivered to the Keck Observatory in 2001. Once it is operational, a team of
astronomers will initiate DEEP2, a major redshift survey of galaxies that will
consume approximately 120 nights at the Keck Observatory over a three year
period. Our goal is to gather high-quality spectra of ~60,000 galaxies with
Z>0.7 in order to study the properties and large scale clustering of galaxies
at $Z \approx 1$. The survey will be done at high spectral resolution,
R=\lambda/\Delta \lambda ~3500, allowing us to work between the bright OH sky
emission lines and to infer linewidths for many of the target galaxies. The
linewidth data will facilitate the execution of the classical redshift-volume
cosmological test, which can provide a precision measurement of the equation of
state of the Universe.


title:
Chandra Discovers a Very High Density X-ray Plasma on the O-Star Zeta
  Orionis

abstract:
  We report on a Chandra line spectrum observation of the O supergiant, Zeta
Orionis (O9.7 Ib). A 73.4 ks HETGS observation shows a wide range of ionization
stages and line strengths over the wavelength range of 5 to 26 A. The observed
emission lines indicate a range in temperature of 2 to 10 MK which is
consistent with earlier X-ray observations of Zeta Ori. Many lines are
spectrally resolved showing Doppler broadening of 900 +/- 200 km/s. The
observed He-like ions (O VII, Ne IX, Mg XI, and Si XIII) provide information
about the spatial distribution of the X-ray emission. Although the observations
support a wind distribution of X-ray sources, we find three conflicting
results. First, line diagnostics for SIXIII indicate that this line emission
forms very close to the stellar surface, where the density is of order 10^{12}
cm^{-3}, but the velocity there is too small to produce the shock jump required
for the observed ionization level. Second, the strong X-ray line profiles are
symmetric and do not show any evidence of Doppler blue-shifted line centroids
which are expected to accompany an outwardly moving source in a high density
wind. Third, the observed velocity dispersions do not appear to correlate with
the associated X-ray source radii velocities, contrary to expectations of wind
distributed source models. A composite source model involving wind shocks and
some magnetic confinement of turbulent hot plasma in a highly non-symmetric
wind, appears to be needed to explain the line diagnostic anomalies.


title: Confusion of Diffuse Objects in the X-ray Sky

abstract:
  Most of the baryons in the present-day universe are thought to reside in
intergalactic space at temperatures of 10^5-10^7 K. X-ray emission from these
baryons contributes a modest (~10%) fraction of the ~ 1 keV background whose
prominence within the large-scale cosmic web depends on the amount of
non-gravitational energy injected into intergalactic space by supernovae and
AGNs. Here we show that the virialized regions of groups and clusters cover
over a third of the sky, creating a source-confusion problem that may hinder
X-ray searches for individual intercluster filaments and contaminate
observations of distant groups.


title: A Multivariate Analysis of Galaxies in the Hubble Deep Field North

abstract:
  We use the ultraviolet and optical WFPC2 and near-infrared NICMOS images of
the Hubble Deep Field North to measure and statistically compare an array of
parameters for over 250 of the galaxies it contains. These parameters include
redshift, rest-frame visible asymmetry and concentration, bolometric luminosity
and extinction-corrected star formation rate. We find only one strong
correlation, between bolometric luminosity and star formation rate, from which
early-type galaxies noticeably deviate. When our asymmetry measurements are
combined with those of a sample of nearby galaxies covering the full Hubble
sequence, we find a weak correlation between redshift and rest-frame visible
asymmetry, consistent with the qualitative evidence of galaxy morphological
evolution from these and other deep Hubble Space Telescope images. The mean
values of these asymmetry measurements show a monotonic increase with redshift
interval over the range 0 < z < 2, increasing by a factor of approximately
three. If this trend is real, it suggests that galaxy morphological evolution
is a gradual process that is continuing through the present cosmological epoch.
There is evidence that the dominant source of this evolution is the "minor"
mergers of disk galaxies with smaller companions, which could also transform
late-type spiral galaxies into early-type spiral galaxies. Interestingly, in
contrast to local galaxies we find no correlations between star formation rate
and either UV or visible asymmetry. This could arise if the star formation of
high-redshift galaxies proceeds in episodes that are short (~ 100 Myr) relative
to the time scales over which galaxy mergers produce strong asymmetries (~ 500
Myr), a result suggested by the high star formation rates of Lyman break
galaxies.


title:
HST/STIS observations of the HeII Gunn-Peterson effect towards HE
  2347-4342

abstract:
  We present an HST STIS spectrum of the HeII Gunn-Peterson effect towards
HE2347-4342. Compared to the previous HST GHRS data obtained by Reimers et al.
(1997), the STIS spectrum has a much improved resolution. The 2-D detector also
allows us to better characterize the sky and dark background. We confirm the
presence of two spectral ranges of much reduced opacity, the opacity gaps, and
provide improved lower limits on the HeII G-P opacity in the high opacity
regions. We use the STIS spectrum together with a Keck--HIRES spectrum covering
the corresponding HI Lya forest to calculate a 1-D map of the softness S of the
ionization radiation along the line of sight towards HE 2347-4342, where S is
the ratio of the HI to HeII photoionization rates. We find that S is generally
large but presents important variations, from S ~ 30 in the opacity gaps to a 1
sigma lower limit of 2300 at z~2.86, in a region which shows an extremely low
HI opacity over a 6.5 A range. We note that a large S naturally accounts for
most of the large SiIV to CIV ratios seen in other quasar absorption line
spectra. We present a simple model that reproduces the shape of the opacity
gaps in absence of large individual absorption lines. We extend the model
described in Heap et al. (2000) to account for the presence of sources close to
the line of sight of the background quasar. As an alternative to the delayed
reionization model suggested by Reimers et al. (1997), we propose that the
large softness observed at z~2.86 is due to the presence of bright soft sources
close to the line of sight, i.e. for which the ratio between the number of HI
to HeII ionizing photons reaching the IGM is large. We discuss these two models
and suggest ways to discriminate between them.


title:
Accretion onto nearby supermassive black holes: Chandra constraints on
  the dominant cluster galaxy NGC 6166

abstract:
  Chandra observations of low-luminosity supermassive black holes in nearby
elliptical galaxies provide tight limits on both their nuclear luminosities and
on their Bondi accretion rates. We examine Chandra constraints on NGC 6166, the
dominant galaxy in the cluster Abell 2199, which hosts a \sim 10^9 \Msun black
hole. We measure a nuclear X-ray luminosity L_{x} \sim 10^{40} erg/s and show
that the density and temperature profiles of the hot interstellar medium imply
a Bondi accretion rate of Mdot_{Bondi} \sim 3 10^{-2} Msun/yr. This accretion
rate predicts a nuclear luminosity of \sim 10^{44} erg/s for a canonical
radiative efficiency of 10%. Unless the Bondi estimate is inappropriate and/or
the accretion rate onto the black hole is significantly reduced, the observed
nuclear flux constrains the radiative efficiency of the accretion flow to be
\eta \sim 10^{-5}. We show that low-radiative efficiency accretion flows with
radial density profiles \rho \approxpropto r^{-3/2} (and not significantly
flatter) can explain the observed nuclear X-ray luminosity but that the power
output from the jets in NGC 6166 is also important to the energetics of the
system.


title: Planck-scale quintessence and the physics of structure formation

abstract:
  In a recent paper we considered the possibility of a scalar field providing
an explanation for the cosmic acceleration. Our model had the interesting
properties of attractor-like behavior and having its parameters of O(1) in
Planck units. Here we discuss the effect of the field on large scale structure
and CMB anisotropies. We show how some versions of our model inspired by
"brane" physics have novel features due to the fact that the scalar field has a
significant role over a wider range of redshifts than for typical "dark energy"
models. One of these features is the additional suppression of the formation of
large scale structure, as compared with cosmological constant models. In light
of the new pressures being placed on cosmological parameters (in particular
H_0) by CMB data, this added suppression allows our "brane" models to give
excellent fits to both CMB and large scale structure data.


title: CMB anisotropy from spatial correlations of clusters of galaxies

abstract:
  The SZ effect from clusters of galaxies is a dominant source of secondary CMB
anisotropy in the low-redshift universe. We present analytic predictions for
the CMB power spectrum from massive halos arising from the SZ effect. Since
halos are discrete, the power spectrum consists of a Poisson and a correlation
term. The latter is always smaller than the former, which is dominated by
nearby bright rich clusters. In practice however, those bright clusters are
easy to indentify and can thus be subtracted from the map. After this
subtraction, the correlation term dominates degree-scale fluctuations over the
Poisson term, as the main contribution to the correlation term comes from
distant clusters. We find that the correlation term is detectable by Planck
experiment. Since the degree scale spectrum is quite insensitive to the highly
uncertain core structures of halos, our predictions are robust on these scales.
Measuring the correlation term on degree scales thus cleanly probes the
clustering of distant halos. This has not been measured yet, mainly because
optical and X-ray surveys are not sufficiently sensitive to include such
distant clusters and groups. Our analytic predictions are also compared to
adiabatic hydrodynamic simulations. The agreement is remarkably good, down to
ten arcminutes scales, indicating that our predictions are robust for the
Planck experiment. Below ten arcminute scales, where the details of the core
structure dominates the power spectrum, our analytic and simulated predictions
might fail. In the near future, interferometer and bolometer array experiments
will measure the SZ power spectrum down to arcminutes scales, and yield new
insight into the physics of the intrahalo medium.


title:
The cosmic microwave background bispectrum as a test of the physics of
  inflation and probe of the astrophysics of the low-redshift universe

abstract:
  Why is non-Gaussianity interesting? One of generic predictions from
inflationary scenarios is that primordial fluctuations are exactly Gaussian in
linear order; however, the non-linearity in the inflation will produce weak
non-Gaussianity. Thus, measuring the non-Gaussianity in the cosmic microwave
background radiation anisotropy is a probe of the non-linear physics in the
very early universe. Since the angular three point function is zero for the
Gaussian field, it is sensitive to the non-Gaussianity. We predict its harmonic
transform counterpart, the angular {\it Bispectrum}, down to arcminutes angular
scales, including the full effect of the radiation transfer function. We find
that even the Planck experiment cannot detect the primary bispectrum from the
inflation, as long as the single field slow-roll inflation is right.
Non-linearities in the low redshift universe also produce the non-Gaussianity.
We find that secondary bispectra are detectable by both MAP and Planck
experiments. The secondary bispectra probe the non-linear physics of the
low-redshift universe. Although this could be a contaminant to the primary
signal, MAP and Planck experiments are found to be able to separate the primary
from secondary effects well. We present a tentative comparison of the primary
bispectrum to the published COBE 4 year bispectrum. The data put a weak
constraint on the parameter, and the constraint would become much tighter when
we use all modes available in the COBE data, and certainly forthcoming
satellite experiments. As a conclusion, the bispectrum is a key measure to
confirm or destroy the simple inflationary scenario in non-linear order that
seems quite successful in linear order.


title:
Models of Rapidly Rotating Neutron Stars: Remnants of Accretion Induced
  Collapse

abstract:
  Equilibrium models of differentially rotating nascent neutron stars are
constructed, which represent the result of the accretion induced collapse of
rapidly rotating white dwarfs. The models are built in a two-step procedure:
(1) a rapidly rotating pre-collapse white dwarf model is constructed; (2) a
stationary axisymmetric neutron star having the same total mass and angular
momentum distribution as the white dwarf is constructed. The resulting
collapsed objects consist of a high density central core of size roughly 20 km,
surrounded by a massive accretion torus extending over 1000 km from the
rotation axis. The ratio of the rotational kinetic energy to the gravitational
potential energy of these neutron stars ranges from 0.13 to 0.26, suggesting
that some of these objects may have a non-axisymmetric dynamical instability
that could emit a significant amount of gravitational radiation.


title: Formation Mechanisms for Spirals in Barred Galaxies

abstract:
  We consider a scenario of formation of the spiral structure in barred
galaxies. This scenario includes the new non-resonant mechanism of elongation
of spirals, due to the characteristic behaviour of the gravitational potential
beyond the principal spiral arms.


title:
Source-lens clustering effects on the skewness of the lensing
  convergence

abstract:
  The correlation between source galaxies and lensing potentials causes a
systematic effect on measurements of cosmic shear statistics, known as the
source-lens clustering (SLC) effect. The SLC effect on the skewness of lensing
convergence, $S_3$, is examined using a nonlinear semi-analytic approach and is
checked against numerical simulations. The semi-analytic calculations have been
performed in a wide variety of generic models for the redshift distribution of
source galaxies and power-law models for the bias parameter between the galaxy
and dark matter distributions. The semi-analytic predictions are tested
successfully against numerical simulations. We find the relative amplitude of
the SLC effect on $S_3$ to be of the order of five to forty per cent. It
depends significantly on the redshift distribution of sources and on the way
the bias parameter evolves. We discuss possible measurement strategies to
minimize the SLC effects.


title:
Conservative General Relativistic Radiation Hydrodynamics in Spherical
  Symmetry and Comoving Coordinates

abstract:
  The description of general relativistic radiation hydrodynamics in spherical
symmetry is presented in natural coordinate choices. For hydrodynamics,
comoving coordinates are chosen, and the momentum phase space for the radiation
particles is described in comoving frame four momenta. We also investigate a
description of the momentum phase space in terms of particle impact parameter
and energy at infinity and derive a simple approximation to the general
relativistic Boltzmann equation. Further developed are, however, the exact
equations in comoving coordinates, because the description of the interaction
between matter and radiation particles is best described in the closely related
orthonormal basis comoving with the fluid elements. We achieve a conservative
and concise formulation of radiation hydrodynamics that is well suited for
numerical implementation by a variety of methods. The contribution of radiation
to the general relativistic jump conditions at shock fronts is discussed, and
artificial viscosity is consistently included in the derivations in order to
support approaches relying on this option.


title: Cluster Mass Profiles from Weak Lensing II

abstract:
  In Schneider, King & Erben (2000) we developed likelihood techniques to
compare the constraints on cluster mass profiles that can be obtained using the
shear and magnification information. This work considered circularly symmetric
power-law models for clusters at fairly low redshifts where the redshift
distribution of source galaxies could be neglected. Here this treatment is
extended to encompass NFW profiles which are a good description of clusters
from cosmological N-body simulations, and NFW clusters at higher redshifts
where the influence of various scenarios for the knowledge of the redshift
distribution are examined. Since in reality the overwhelming majority of
clusters have ellipsoidal rather than spherical profiles, the singular
isothermal ellipsoid (SIE) is investigated. We also briefly consider the impact
of substructure on such a likelihood analysis. In general, we find that the
shear information provides a better constraint on the NFW profile under
consideration, so this becomes the focus of what follows. The ability to
differentiate between the NFW and power-law profiles strongly depends on the
size of the data field, and on the number density of galaxies for which an
ellipticity can be measured. For higher redshift NFW profiles, there is very
little reduction (~1.5%) in the dispersion of parameter estimates when
spectroscopic redshifts, as opposed to photometric redshift estimates, are
available for the galaxies used in the lensing analysis.


title:
Young Collapsed Supernova Remnants: Similarities and Differences in
  Neutron Stars, Black Holes, and More Exotic Objects

abstract:
  Type Ia supernovae are thought to explode completely, leaving no condensed
remnant, only an expanding shell. Other types of supernovae are thought to
involve core collapse and are expected to leave a condensed remnant, which
could be either a neutron star or a black hole, or just possibly, something
more exotic, such as a quark orstrange star, a naked singularity, a frozen
star, a wormhole or a red hole. It has proven surprisingly difficult to
determine which type of condensed remnant has been formed in those cases where
the diagnostic highly regular pulsar signature of a neutron star is absent. We
consider possible observational differences between the two standard
candidates, as well as the more speculative alternatives.
  We classify condensed remnants according to whether they do or do not possess
three major features: 1)a hard surface, 2)an event horizon, and 3)a
singularity. Black holes and neutron stars differ on all three criteria. Some
of the less frequently considered alternatives are "intermediate," in the sense
that they possess some of the traits of a black hole and some of the traits of
a neutron star. This possibility makes distinguishing the various possibilities
even more difficult.


title:
First Results from the Anglo-Australian Planet Search - A Brown Dwarf
  Candidate and a 51 Peg-like Planet

abstract:
  We report results from the Anglo-Australian Planet Search -- a survey for
planets around 200 solar-type stars in the southern hemisphere, which is being
carried out on the 3.9m Anglo-Australian Telescope. Limiting Doppler precisions
of 3m/s have been demonstrated from the first 2.5 years of operation, making
this the highest precision planet search in the southern hemisphere. From these
data we report results for two new sub-stellar detections. The first is a "51
Peg"-like planet around the star HD179949 with Msin i = 0.84 Mjup. Photometric
study reveals this is not a transiting system. The second is a brown dwarf or
very low-mass star companion to HD164427 in an eccentric orbit with Msin i =
46Mjup. Hipparcos data indicate this latter object is unlikely to have a mass
greater than 0.18 Msol.


title: Cosmological matter perturbations

abstract:
  We investigate matter density perturbations in models of structure formation
with or without causal/acausal source. Under the fluid approximation in the
linear theory, we first derive full perturbation equations in flat space with a
cosmological constant $\Lambda$. We then use Green-function technique to obtain
analytic solutions for matter perturbations in a flat $\Lambda=0$ model. Some
incorrect solutions in the literature are corrected here. A simple yet accurate
extrapolation scheme is then proposed to obtain solutions in curved or
$\Lambda\neq 0$ cosmologies. Some general features of these solutions are
revealed. In particular, we analytically prove that the resulting matter
density perturbations are independent of the way the causal source was
compensated into the background contents of the universe when it was first
formed. We also use our Green-function solutions to investigate the
compensation mechanism for perturbations with causal seeds, and yield a
mathematically and physically explicit formin interpreting it. We found that
the compensation scale depends not only on the dynamics of the universe, but
also on the properties of the seeds near the horizon scale. It can be
accurately located by employing our Green functions.


title: New method of extracting non-Gaussian signals

abstract:
  We propose a new general method of extracting non-Gaussian features in a
given field. It sets the mean of the field to zero and renormalizes its Fourier
(or multipole) power to white noise, while keeping the phase information
unchanged. Using simulated cosmic microwave background (CMB) as an example, we
demonstrate the power of this method under many challenging circumstances. In
particular, we show its capability of detecting cosmic strings in the CMB.


title: Cluster abundance and large scale structure

abstract:
  We use the presently observed number density of large X-ray clusters and the
linear mass power spectra to constrain $\sigma_8$ and the redshift distortion
parameter $\beta$, in both OCDM and $\Lambda$CDM models. The best fit to the
observed mass power spectra gives $n=0.84\pm 0.67$ and
$\Gamma=0.27^{+0.42}_{-0.16}$, with the theoretically expected degeneracy
$\Gamma'=0.247\Gamma\exp(1.4n)=0.220^{+0.036}_{-0.031}$ (all at 95% confidence
level). Based on this, we then calculate the cluster-abundance-normalized
$\sigma_8$, using different models of mass function: Press & Schechter (1974),
Sheth & Tormen (1999), and Lee & Shandarin (1999). The $\sigma_8$ based on the
non-spherical-collapse models (ST & LS) are significantly lower, mainly due to
the larger mass function within the scale range of our interest. In particular,
we found $\sigma_{8{\rm (ST+LS)}}=0.477\Omega_{\rm m0}^\alpha$, where
$\alpha=-0.3-0.17\Omega_{\rm m0}^{0.34}-0.13\Omega_{\Lambda 0}$. We also derive
the probability distribution function of cluster formation redshift using the
Lacey-Cole formalism (1993), but with modifications to incorporate
non-spherical collapse. The uncertainties in our $\sigma_8$ are mainly
contributed from the normalization in the virial mass-temperature relation. We
also obtain for the IRAS galaxies $\sigma_{8\rm (I)}=0.78\pm 0.06$ (at 95%
confidence level), and found $\beta_{\rm I(ST+LS)}=0.613\Omega_{\rm
m0}^{0.24-0.16(\Omega_{\rm m0}+\Omega_{\Lambda 0})}$. This is more consistent
with the recent observations than the result based on the PS formalism.


title:
The DIRECT Project: Catalogs of Stellar Objects in Nearby Galaxies. I.
  The Central Part of M33

abstract:
  The DIRECT project aims to determine direct distances to two important
galaxies in the cosmological distance ladder -- M31 and M33 -- using detached
eclipsing binaries (DEBs) and Cepheids. The search for these variables requires
time-series photometry of large areas of the target galaxies and yields
magnitudes and positions for tens of thousands of stellar objects, which may be
of use to the astronomical community at large.
  During the first phase of the project, between September 1996 and October
1997, we were awarded 95 nights on the F. L. Whipple Observatory 1.2 m
telescope and 36 nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search
for DEBs and Cepheids in the M31 and M33 galaxies. This paper, the first in our
series of stellar catalogs, lists the positions, three-color photometry, and
variability indices of 57,581 stars with 14.4 < V < 23.6 in the central part of
M33. The catalog is available from our FTP site at
ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/star_catalog/M33ABC/


title: Superfluidity in Neutron Star Matter

abstract:
  Superfluidity of nuclear matter relevant for neutron star physics is
reviewed.


title: Helicity in Hydro and MHD Reconnection

abstract:
  Helicity, a measure of the linkage of flux lines, has subtle and largely
unknown effects upon dynamics. Both magnetic and hydrodynamic helicity are
conserved for ideal systems and could suppress nonlinear dynamics. What
actually happens is not clear because in a fully three-dimensional system there
are additional channels whereby intense, small-scale dynamics can occur. This
contribution shows one magnetic and one hydrodynamic case where for each the
presence of helicity does not suppress small-scale intense dynamics of the type
that might lead to reconnection.


title:
First Intrinsic Anisotropy Observations with the Cosmic Background
  Imager

abstract:
  We present the first results of observations of the intrinsic anisotropy of
the cosmic microwave background radiation with the Cosmic Background Imager
from a site at 5080 m altitude in northern Chile. Our observations show a sharp
decrease in C_l in the range l=400 - 1500. The broadband amplitudes we have
measured are deltaT(band) = 58.7 (-6.3, +7.7) microK for l = 603 (-166, +180)
and 29.7 (-4.2, +4.8) microK for l = 1190 (-224, +261), where these are
half-power widths in l. Such a decrease in power at high l is one of the
fundamental predictions of the standard cosmological model, and these are the
first observations which cover a broad enough l range to show this decrease in
a single experiment. The C_l we have measured enable us to place limits on the
density parameter, Omega(tot) <= 0.4 or $Omega(tot) >= 0.7 (90% confidence).


title: The Cosmic Background Imager

abstract:
  The Cosmic Background Imager (CBI) is an instrument designed to make images
of the cosmic microwave background radiation and to measure its statistical
properties on angular scales from about 3 arc minutes to one degree (spherical
harmonic scales from l ~ 4250 down to l ~ 400). The CBI is a 13-element
interferometer mounted on a 6 meter platform operating in ten 1-GHz frequency
bands from 26 GHz to 36 GHz. The instantaneous field of view of the instrument
is 45 arcmin (FWHM) and its resolution ranges from 3 to 10 arcmin; larger
fields can be imaged by mosaicing. At this frequency and resolution, the
primary foreground is due to discrete extragalactic sources, which are
monitored at the Owens Valley Radio Observatory and subtracted from the CBI
visibility measurements. The instrument has been making observations since late
1999 of both primordial CMB fluctuations and the Sunyaev-Zeldovich effect in
clusters of galaxies from its site at an altitude of 5080 meters near San Pedro
de Atacama, in northern Chile. Observations will continue until August 2001 or
later. We present preliminary results from the first few months of
observations.


title: Evidence for a Supermassive Black Hole in the S0 Galaxy NGC 3245

abstract:
  The S0 galaxy NGC 3245 contains a circumnuclear disk of ionized gas and dust
with a radius of 1.1" (110 pc), making it an ideal target for dynamical studies
with the Hubble Space Telescope. We have obtained spectra of the nuclear disk
with the Space Telescope Imaging Spectrograph, using an 0.2"-wide slit at five
parallel positions. Measurements of the H-alpha and [N II] emission lines are
used to map out the kinematic structure of the disk in unprecedented detail.
The data reveal a rotational velocity field with a steep velocity gradient
across the innermost 0.4". We construct dynamical models for a thin gas disk in
circular rotation, using HST optical images to map out the gravitational
potential due to stars. The H-alpha+[N II] surface brightness measured from an
HST narrow-band image is folded into the models, and we demonstrate that many
of the apparent small-scale irregularities in the observed velocity curves are
the result of the patchy distribution of emission-line surface brightness. A
central dark mass of (2.1+/-0.5)x10^8 solar masses is required for the models
to reproduce the steep central velocity gradient. This value for the central
mass is consistent with recently discovered correlations between black-hole
mass and bulge velocity dispersion.


title: The MAP satellite mission to map the CMB anisotropy

abstract:
  The Microwave Anisotropy Probe (MAP) satellite is scheduled to launch in
mid-2001. MAP's goal is to produce a map of the anisotropy in the cosmic
microwave background of unprecedented accuracy and precision. The guiding
design principle has been the minimization of systematic effects. The
instrument design and mapping strategy work in concert to take advantage of the
unique opportunities afforded by deep space. We give an overview of the mission
and compare the projected MAP error bars to recent measurements.


title: Temperature Structure of Four Merging Clusters Obtained with Chandra

abstract:
  We present preliminary Chandra results on z=0.2 clusters A665, A2163 and
A2218, and a z=0.05 cluster A754. For A754, A665 and A2163, we have derived
first high-resolution projected gas temperature maps. All three show strong
spatial temperature variations in the inner r<0.5-1 Mpc regions, indicating
ongoing mergers. The maps reveal a probable shock in front of a moving cluster
core in A665, a rather complicated temperature distribution in the center of
A2163, and possibly a merger of three subclusters in A754. At greater
off-center distances, radial profiles for A2163 and A2218 show a temperature
decline, in agreement with earlier ASCA results.


title: Evidence for a source size of less than 2000 AU in Quasar 2237+0305

abstract:
  Recently, OGLE team have reported clear quasar microlensing signal in
Q2237+0305. We have analyzed the microlens event of ``image C'' by using their
finely and densely sampled lightcurves. From lightcurve fitting, we can
unambiguously set the source size of $\lsim 0.98$ Einstein Ring radius as a
conservative limit. This limit corresponds to $2000 {\rm (AU)}$, if we adopt
  $M_{\rm lens} \sim 0.1M_{\odot}$ obtained by a recent statistical study of
mean mass of lens object. This gives a clear evidence for the existence of an
accretion disk in the central region of the quasar.


title:
On the origin of the Ca-Ti-Cr isotopic anomalies in the inclusion
  EK-1-4-1 of the Allende Meteorite

abstract:
  In the framework of our investigation to explain the nucleosynthesis origin
of the correlated Ca-Ti-Cr isotopic anomalies in the Ca-Al-rich ''FUN''
inclusion EK-1-4-1 of the Allende meteorite, the nuclear-physics basis in the
neutron-rich N=28 region has been updated by including recent experimental data
on beta-decay properties and microscopic predictions of neutron-capture cross
sections. Charged-particle and subsequent r-process calculations within an
entropy-based approach were performed using a complete reaction network. It is
shown that there exist two astrophysical scenarios within which the observed
isotopic anomalies can be reproduced simultaneously; one at low entropies
(about 10) which confirms the earlier suggestrd Sn Ia mechanism, and another at
high entropies (about 150) which could be compatible with the neutrino-wind
scenario of a SN II.


title: Helium-like ions as powerful X-ray plasma diagnostics

abstract:
  We revisited the calculations of the ratios of the Helium-like ion
``triplet'' (resonance, intercombination, and forbidden lines) for Z=6 to 14 (C
V, N VI, O VII, Ne IX, Mg XI, Si XIII) in order to provide temperature, density
and ionization diagnostics for the new high-resolution spectroscopic data of
Chandra and XMM-Newton. Comparing to earlier computations, collisional rates
are updated and the best experimental values for radiative transition
probabilities are used. The influence of an external radiation field
(photo-excitation) and the contribution from unresolved dielectronic satellite
lines to the line ratios are discussed. Collision-dominated plasmas (e.g.
stellar coronae), photo-ionized plasmas (e.g. AGNs) or transient plasmas (e.g.
SNRs) are considered.


title: Luminosity function of clusters of galaxies

abstract:
  The composite galaxy luminosity function (hereafter LF) of 39 Abell clusters
of galaxies is derived by computing the statistical excess of galaxy counts in
the cluster direction with respect to control fields. Due to the wide field
coverage of the digitised POSS-II plates, we can measure field counts around
each cluster in a fully homogeneous way. Furthermore, the availability of
virtually unlimited sky coverage allows us to directly compute the LF errors
without having to rely on the estimated variance of the background. The wide
field coverage also allows us to derive the LF of the whole cluster, including
galaxies located in the cluster outskirts. The global composite LF has a slope
alpha ~ -1.1+/-0.2 with minor variations from blue to red filters, and M* ~
-21.7,-22.2,-22.4 mag (H_0=50 km/s/Mpc) in g, r and i filters, respectively.
These results are in quite good agreement with several previous determinations
and in particular with the LF determined for the inner region of a largely
overlapping set of clusters, but derived making use of a completely different
method for background subtraction. The similarity of the two LFs suggests the
existence of minor differences between the LF in the cluster outskirts and in
the central region, or a negligible contribution of galaxies in the cluster
outskirts to the global LF.


title: Far Ultraviolet Spectra of B Stars near the Ecliptic

abstract:
  Spectra of B stars in the wavelength range of 911-1100 A have been obtained
with the EURD spectrograph onboard the Spanish satellite MINISAT-01 with ~5 A
spectral resolution. IUE spectra of the same stars have been used to normalize
Kurucz models to the distance, reddening and spectral type of the corresponding
star. The comparison of 8 main-sequence stars studied in detail (alpha Vir,
epsilon Tau, lambda Tau, tau Tau, alpha Leo, zeta Lib, theta Oph, and sigma
Sgr) shows agreement with Kurucz models, but observed fluxes are 10-40% higher
than the models in most cases. The difference in flux between observations and
models is higher in the wavelength range between Lyman alpha and Lyman beta. We
suggest that Kurucz models underestimate the FUV flux of main-sequence B stars
between these two Lyman lines. Computation of flux distributions of
line-blanketed model atmospheres including non-LTE effects suggests that this
flux underestimate could be due to departures from LTE, although other causes
cannot be ruled out. We found the common assumption of solar metallicity for
young disk stars should be made with care, since small deviations can have a
significant impact on FUV model fluxes. Two peculiar stars (rho Leo and epsilon
Aqr), and two emission line stars (epsilon Cap and pi Aqr) were also studied.
Of these, only epsilon Aqr has a flux in agreement with the models. The rest
have strong variability in the IUE range and/or uncertain reddening, which
makes the comparison with models difficult.


title: Investigating ULIRGs in the Near-Infrared: Imaging & Spectroscopy

abstract:
  We present imaging and spectroscopic observations of 2 nearby (z<0.1) ULIRGs
from a larger sample, and address the question of whether the JHK continuum
colours and slope might be effective probes of the nuclear region in searches
for AGN. Certainly there is evidence for significant quantities of hot dust
emission at temperatures >1000K; but it may be that rather than pointing to an
AGN, this instead tells us more about the environment and evolution of the star
formation.


title: The microwave background temperature at the redshift of 2.33771

abstract:
  The Cosmic Microwave Background radiation is a fundamental prediction of Hot
Big Bang cosmology. The temperature of its black-body spectrum has been
measured at the present time, $T_{\rm CMBR,0}$ = 2.726$\pm$ 0.010 K, and is
predicted to have been higher in the past. At earlier time, the temperature can
be measured, in principle, using the excitation of atomic fine structure levels
by the radiation field. All previous measurements however give only upper
limits as they assume that no other significant source of excitation is
present. Here we report the detection of absorption from the first {\sl and}
second fine-structure levels of neutral carbon atoms in an isolated remote
cloud at a redshift of 2.33771. In addition, the unusual detection of molecular
hydrogen in several rotational levels and the presence of ionized carbon in its
excited fine structure level make the absorption system unique to constrain,
directly from observation, the different excitation processes at play. It is
shown for the first time that the cosmic radiation was warmer in the past. We
find 6.0 < T_{\rm CMBR} < 14 K at z = 2.33771 when 9.1 K is expected in the Hot
Big Bang cosmology.


title:
Helium-like triplet density diagnostics: Applications to CHANDRA--LETGS
  X-ray observations of Capella and Procyon

abstract:
  Electron density diagnostics based on the triplets of Helium-like CV, NVI,
and OVII are applied to the X-ray spectra of Capella and Procyon measured with
the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra
X-ray Observatory. New theoretical models for the calculation of the line
ratios between the forbidden (f), intercombination (i), and the resonance (r)
lines of the helium-like triplets are used. The derived densities are quite
typical of densities found in the solar active regions, and also pressures and
temperatures in Procyon's and Capella's corona at a level of T=10^6K are quite
similar. We find no evidence for densities as high as measured in solar flares.
Comparison of our Capella and Procyon measurements with the Sun shows little
difference in the physical properties of the layers producing the CV, NVI, and
OVII emission. Assuming the X-ray emitting plasma to be confined in magnetic
loops, we obtain typical loop length scales of L_Capella > 8 L_Procyon from the
loop scaling laws, implying that the magnetic structures in Procyon and Capella
are quite different. The total mean surface fluxes emitted in the helium- and
hydrogen-like ions are quite similar for Capella and Procyon, but exceed
typical solar values by one order of magnitude. We thus conclude that Procyon's
and Capella's coronal filling factors are larger than corresponding solar
values.


title:
Variability in ultra cool dwarfs: evidence for the evolution of surface
  features

abstract:
  We present photometric light curves for a sample of 21 ultra cool M and L
dwarfs in the field and in the young open clusters sigma Orionis and the
Pleiades. Evidence for variability with RMS amplitudes (in the I band) of 0.01
to 0.055 magnitudes on timescales of 0.4 to 100 hours is discovered in half of
these objects. Power spectral analysis using the CLEAN algorithm was performed
to search for evidence of periodic variability. Some objects show strong
periodicities at around a few hours, which could be due to rotational
modulation of the light curve by surface features. However, several objects do
not have any significant periodicities to explain their variability. The vsini
values of a similar population of objects makes it very likely that our time
sampling was sensitive to the expected range of rotation periods, and
simulations show that we would have detected these if they were caused by
long-lived surface features. We argue that this absence of periodicity is due
to the evolution of the brightness, and presumably also the physical size, of
surface features on timescales of a few to a few tens of hours. This is
supported in the case of 2M1145 for which two light curves have been obtained
one year apart and show no common periodicity. The surface features could
plausibly be photospheric dust clouds or magnetically-induced spots. The
recently observed decline in chromospheric activity for late type M and L
dwarfs hints towards the former explanation for at least our later-type
objects. Furthermore, our sample suggests that variability to be more common in
objects later than M9, indicating that the variability may be related to dust
formation. One light curve shows a brief, but significant, dip, which could be
a short-lived feature or possibly an eclipse by a companion. (abridged)


title: Effective stability of the Trojan asteroids

abstract:
  We study the spatial circular restricted problem of three bodies in the light
of Nekhoroshev theory of stability over large time intervals. We consider in
particular the Sun-Jupiter model and the Trojan asteroids in the neighborhood
of the Lagrangian point $L_4$. We find a region of effective stability around
the point $L_4$ such that if the initial point of an orbit is inside this
region the orbit is confined in a slightly larger neighborhood of the
equilibrium (in phase space) for a very long time interval. By combining
analytical methods and numerical approximations we are able to prove that
stability over the age of the universe is guaranteed on a realistic region, big
enough to include one real asteroid. By comparing this result with the one
obtained for the planar problem we see that the regions of stability in the two
cases are of the same magnitude.


title: Cosmic Dust: The Ulysses perspective

abstract:
  The Ulysses spacecraft, launched in October 1990, orbits the Sun on a polar
trajectory. The spacecraft is equipped with a highly sensitive impact-
ionization dust detector which can in situ measure cosmic dust grains in the
mass range 10^-9 to 10^-19 kg. With the Ulysses dust detector dust streams
originating from Jupiter's volcanically active moon Io have been discovered as
well as interstellar dust particles sweeping through the solar system. The
distribution of interplanetary dust grains has been measured at high ecliptic
latitudes with Ulysses for the first time. The Ulysses measurements of
interplanetary dust, dust grains interacting electromagnetically with the
magnetosphere of Jupiter and measurements of interstellar dust in the solar
system are reviewed.


title:
The Cannonball Model of Gamma Ray Bursts: Spectral and Temporal
  Properties of the Gamma Rays

abstract:
  Recent observations suggest that gamma ray bursts (GRBs) and their afterglows
are produced by highly relativistic jets emitted in supernova explosions. We
have proposed that the result of the event is not just a compact object plus
the ejecta: within days, a fraction of the parent star falls back to produce a
thick accretion disk. The subsequent accretion generates jets and constitutes
the GRB ``engine'', as in the observed ejection of relativistic ``cannonballs''
of plasma by microquasars and active galactic nuclei. Here we investigate the
production of a GRB as the jetted cannonballs exit the supernova shell reheated
by their collision with it, emitting highly forward-collimated radiation. Each
cannonball corresponds to an individual pulse in a GRB. We cannot predict the
timing sequence of these pulses, but the Cannonball Model fares very well in
describing the total energy, energy spectrum, and time-dependence of the
individual pulses.


title: The Nature of Flat-Spectrum Nuclear Radio Emission in Seyfert Galaxies

abstract:
  Parsec-scale VLBA imaging of five Seyfert galaxies with flat-spectrum radio
nuclei was conducted to determine whether the flat spectrum represents thermal
emission from the accretion disk/obscuring torus or nonthermal, synchrotron
self-absorbed emission. Four of the five show emission consistent with
synchrotron self-absorption, with intrinsic sizes ~0.05-0.2 pc (or 10^4
gravitational radii for a 10^8 Msun black hole for the smallest). In contrast,
NGC 4388, which was detected with MERLIN but not the VLBA, shows thermal
emission with similar properties to that detected in NGC 1068. It is notable
that the two Seyfert galaxies with detected thermal nuclear radio emission both
have large X-ray absorbing columns, suggesting that columns in excess of
\~10^{24} cm^{-2} are needed for such disks to be detectable.


title: Subparsec-scale HI in the nucleus of NGC 4151

abstract:
  We present sensitive, high-resolution 21-cm VLBA+VLA observations of the
radio jet and nuclear HI absorption in NGC 4151. The 25-mas (1.6-pc) resolution
continuum image reveals a highly collimated radio jet, underlying the discrete
components seen previously with MERLIN and the VLA. Spatially and kinematically
complex HI absorption is detected against the whole 3-pc extent of the
continuum component predicted by Ulvestad et al. to contain the AGN. Instead,
we suggest the component against which the absorption is detected is part of
the eastern counterjet, ruling it out as the location for the AGN.


title: The Gaseous Environment of Seyfert Galaxies

abstract:
  The VLA has been used to image HI in a heterogeneous sample of nine Seyferts
as part of a continuing investigation of the role of galactic host gas in the
triggering and fuelling of nuclear activity. Where previous single-dish
observations indicated complex, poorly understood kinematics, improved angular
resolution and sensitivity reveal tidal tails and intragroup gas, distinguish
dwarfs from main disks and resolve non-linear gas dynamical features such as
shocks in bars. Seyferts may be abnormally gas-rich, but a larger,
statistically significant comparison of HI properties of normal and active
galaxies is now required.


title: VLBI, MERLIN and HST observations of the giant radio galaxy 3C236

abstract:
  We present VLBI and MERLIN data at 1.66 and 4.99 GHz on the central component
coincident with the nucleus of the giant radio galaxy, 3C236. The nuclear radio
structure is composed of two complexes of emission which are resolved on scales
from 1 milli-arcsec (mas) to 1 arcsec. Oscillations with an amplitude of about
5 degrees can be seen in the compact radio structure. Spectral index
distributions are plotted at angular resolutions of 10 and 25 mas and allow us
to identify the core component in the south-east emission complex.
Re-examination of the HST WFPC-2 image of 3C236 by de Koff et al. (2000), shows
that the normal to the dust disk in the nucleus is ~30 degrees from the plane
of the sky and within 12 degrees of parallel to the overall orientation of the
radio source. We suggest that the radio axis is also at an angle of ~30 degrees
to the plane of the sky and that the north-west jet is on the approaching side.
This orientation implies an overall size of 4.5 Mpc (H_o = 75 km/s/Mpc, q_o =
0.5) for 3C236. The coincidence of a dust feature and the south-east compact
jet, within the astrometric errors, leads us to suggest that the dust may be in
the form of a cloud encountered by the jet in the first ~400 pc of its journey
out from the nucleus. One-sided emission at 5 GHz on 1 mas scales would suggest
that the jets are ejected initially at <= 35 degrees to the line of sight, but
this is difficult to reconcile with the obvious orientation stability of the
jet system as a whole. Free-free absorption of the counter-jet may be an
alternative explanation for the one-sideness.


title: Metallicity Gradients in X-ray Clusters of Galaxies

abstract:
  We present the projected metallicity profiles for a sample of 17 rich galaxy
clusters observed by BeppoSAX. We find that the 8 non-cooling flow clusters
have flat metallicity profiles. On the contrary, a strong enhancement in the
abundance is found in the central regions of the cooling flow clusters. All the
non-cooling flow clusters present evidence of recent merger activity suggesting
that the merger events redistributes efficiently the metal content of the
intracluster medium. For the cooling flow clusters with better statistics and
available optical data (A85, A496, A2029 and Perseus) we have tested whether
the observed abundance excess is due to metals ejected from the galaxies
located in the cluster core. We find that at a resolution > 100 kpc the
observed projected abundance excess profiles are consistent with originating
from a deprojected metal excess distribution tracing the optical light
distribution. In the one case (i.e. Perseus) with higher resolution (~ 50 kpc),
we find that the observed metal abundance excess distribution is broader than
the predicted one. Such a difference can be reconciled if we assume that the
metals have drifted away from their parent ejecting galaxies by a few tens of
kpc, or, alternatively, if we assume that the cluster light profile has become
significantly more centrally peaked because of the formation process of the
central dominant cluster galaxy since the last major merger occurred.


title: Neutralino Dark Matter and Caustic Ring Signals

abstract:
  We have studied the effects on the gamma-ray flux on Earth by neutralino
annihilations in caustic rings of dark matter in the Galactic halo. The caustic
ring model by Sikivie has been used where dark matter particles are assumed to
possess angular momentum with respect to the Galactic centre. The computer code
DarkSUSY was then used to examine the supersymmetric implications on the flux.
We conclude that a small signal might be detectable under very optimistic
assumptions, but under these only.


title: DarkSUSY - A numerical package for dark matter calculations in the MSSM

abstract:
  The question of the nature of the dark matter in the Universe remains one of
the most outstanding unsolved problems in basic science. One of the best
motivated particle physics candidates is the lightest supersymmetric particle,
assumed to be the lightest neutralino. We here describe DarkSUSY, an advanced
numerical FORTRAN package for supersymmetric dark matter calculations which we
release for public use. With the help of this package, the masses and
compositions of various supersymmetric particles can be computed, for given
input parameters of the minimal supersymmetric extension of the Standard Model
(MSSM). For the lightest neutralino, the relic density is computed, using
accurate methods which include the effects of resonances, pair production
thresholds and coannihilations. Accelerator bounds are checked to identify
viable dark matter candidates. Finally, detection rates are computed for a
variety of detection methods, such as direct detection and indirect detection
through antiprotons, gamma-rays and positrons from the Galactic halo or
neutrinos from the center of the Earth or the Sun.


title:
A new population of WIMPs in the solar system and indirect detection
  rates

abstract:
  A new Solar System population of Weakly Interacting Massive Particle (WIMP)
dark matter has been proposed to exist. We investigate the implications of this
population on indirect signals in neutrino telescopes (due to WIMP
annihilations in the Earth) for the case when the WIMP is the lightest
neutralino of the MSSM, the minimal supersymmetric extension of the standard
model. The velocity distribution and capture rate of this new population is
evaluated and the flux of neutrino-induced muons from the center of the Earth
in neutrino telescopes is calculated. We show that the effects of the new
population can be crucial for masses around 60-120 GeV, where enhancements of
the predicted muon flux from the center of the Earth by up to a factor of 100
compared to previously published estimates occur. As a result of the new WIMP
population, neutrino telescopes should be able to probe a much larger region of
parameter space in this mass range.


title:
The Galaxy Environment of Quasars in the Clowes-Campusano Large Quasar
  Group at z~1.3

abstract:
  The Clowes-Campusano Large Quasar Group (LQG) is the largest known structure
at high redshifts, with at least 18 quasars at z~1.3 forming a structure ~200
Mpc across. We are conducting an ultra-deep optical and deep NIR study to
examine the galaxy environment of quasars in this LQG to determine if, and how,
LQGs trace large-scale structure at early epochs. We report significant
associated clustering in the field of a z=1.226 quasar from this LQG in the
form of a factor ~11 overdensity of I-K>3.75 galaxies, and red sequences of
15-18 galaxies at I-K~4.3,V-K~6.9, indicative of a population of massive
ellipticals at the quasar redshift. The quasar is located between two groups of
these galaxies, with further clustering extending over 2-3 Mpc. Within 30
arcsec of the quasar we find a concentration of blue (V-I<1) galaxies in a band
that bisects the two groups of red sequence galaxies. This band is presumed to
correspond to a region of enhanced star-formation. We suggest that the merging
of the two groups of red sequence galaxies has triggered both the quasar and
the band of star-formation. Quasars at z~1.3 are located in a variety of
environments, but those with associated clustering are found on the cluster
peripheries.


title: Runaway Collisions in Star Clusters

abstract:
  We study the occurrence of physical collisions between stars in young and
compact star cluster. The calculations are performed on the GRAPE-4 with the
starlab software environment which include the dynamical evolution and the
nuclear evolution of all stars and binaries. The selection of the initial
conditions is based on existing and well observed star clusters, such as R136
in the 30 Doradus region in the Large Magellanic Cloud and the Arches and
Quintuplet star clusters in the vicinity of the Galactic center.
  Collisions between stars occurred rather frequently in our models. At any
time a single star dominates the collision history of the system. The collision
rate of this runaway merger scales with the initial relaxation time of the
cluster and is independent on other cluster parameters, such as the initial
mass function or the initial density profile of the cluster. Subsequent
encounters result in a steady grow in mass of the coagulating star, until it
escapes or explodes in a supernova. The collision rate in these models is about
0.00022 collisions per star per Myr for a cluster with an initial relaxation
time of 1 Myr.


title:
ORFEUS echelle spectra: Molecular hydrogen in disk, IVC, and HVC gas in
  front of the LMC

abstract:
  In front of the LMC molecular hydrogen is found in absorption near 0 km/s,
being local disk gas, near +60 km/s in an intermediate velocity cloud, and near
+120 km/s, in a high velocity halo cloud. The nature of the gas is discussed
based on four ORFEUS far UV spectra of LMC stars and including data from the
ground and from the IUE satellite. The local gas is cool and, given a span of
sight lines of only 2.5 deg, rather fluffy. The fractional abundance of H_2
varies from log(f)=-5.4 to -3.3. Metal depletions (up to -1.7 dex for Fe) are
typical for galactic disk gas. In the IV and HV gas an apparent underabundance
of neutral oxygen points to an ionization level of the gas of about 90%. H_2 is
detected in IV and HV gas toward HD 269546. In the IV gas we find an H_2 column
density of log(N)\simeq15.6. The H_2 excitation indicates that the line of
sight samples a cloud at a temperature below 150 K. Column densities are too
small to detect the higher UV pumped excitation levels. The high velocity H_2
(log(N)\simeq15.6) is highly excited and probably exposed to a strong radiation
field. Its excitation temperature exceeds 1000 K. Due to the radial velocity
difference between the halo gas and the Milky Way disk, the unattenuated disk
radiation is available for H_2 excitation in the halo. We do not find evidence
for an intergalactic origin of this gas; a galactic as well as a Magellanic
Cloud origin is possible.


title: Helioseismology and solar neutrinos: an update

abstract:
  We review recent advances concerning helioseismology, solar models and solar
neutrinos. Particularly we address the following points: i) helioseismic tests
of recent SSMs; ii) predictions of the Beryllium neutrino flux based on
helioseismology; iii) helioseismic tests regarding the screening of nuclear
reactions in the Sun.


title:
Sheared helical turbulence and the helicity constraint in large-scale
  dynamos

abstract:
  The effect of shear on the growth of large scale magnetic fields in helical
turbulence is investigated. The resulting large-scale magnetic field is also
helical and continues to evolve, after saturation of the small scale field, on
a slow resistive time scale. This is a consequence of magnetic helicity
conservation. Because of shear, the time scale needed to reach an
equipartition-strength large scale field is shortened proportionally to the
ratio of the resulting toroidal to poloidal large scale fields.


title: The Optical Spectroscopic Evolution of V1974 Cygni (Nova Cygni 1992)

abstract:
  Optical observations of nova V1974 Cygni (Cygni 1992), spanning a 4 year
period, have been used to study its spectroscopic evolution. The data cover a
wavelength range from $\sim 3200 - 8000$ \AA and follows the nebular
evolutionary phase of the ejecta. We have modeled the integrated fluxes by
means of the photoionization code CLOUDY. The models were run at a {\it fixed}
abundance value for the most prominent elements (i.e. H, He, C, O, N, Ne, Fe,
etc) over the entire time sequence. It is possible to constrain from this
simple model some of the physical conditions of the gaseous emitting region,
like temperature and density. Compared with previous studies of the gas
abundances of the heavy elements, we found that smaller enhancements of S, N
and Ar, and comparable values for O and Fe, are able to reproduce the
observations. The time evolution of the surface temperature of the ionizing
source and the high-ionization iron lines [Fe VII] 6087 \AA and [Fe X] 6374
\AA, is similar to what it is observed in the soft X-rays. The early line
profiles can be reproduced using a simple kinematical model consisting of an
equatorial ring and polar caps, expanding at a velocity of $\sim 1100$ km/s.
This simple model also approximates the structure of the resolved shell
observed by HST. Considering the complicated structure of the shell, the lack
of well defined values of its gas density and our limited knowledge of the time
evolution of the surface temperature of the photoionization source, the
comparison between models and observations agrees remarkably well.


title:
Singular Isothermal Disks: II. Nonaxisymmetric Bifurcations and
  Equilibria

abstract:
  We review the difficulties of the classical fission and fragmentation
hypotheses for the formation of binary and multiple stars. A crucial missing
ingredient in previous theoretical studies is the inclusion of dynamically
important levels of magnetic fields. As a minimal model for a candidate
presursor to the formation of binary and multiple stars, we therefore formulate
and solve the problem of the equilibria of isopedically magnetized, singular
isothermal disks, without the assumption of axial symmetry. Considerable
analytical progress can be made if we restrict our attention to models that are
scale-free, i.e., that have surface densities that vary inversely with distance
from the rotation axis of the system. In agreement with earlier analysis by
Syer and Tremaine, we find that lopsided (M=1) configurations exist at any
dimensionless rotation rate, including zero. Multiple-lobed (M = 2, 3, 4, ...)
configurations bifurcate from an underlying axisymmetric sequence at
progressively higher dimensionless rates of rotation, but such nonaxisymmetric
sequences always terminate in shockwaves before they have a chance to fission
into M=2, 3, 4, ... separate bodies. On the basis of our experience in this
paper, and the preceding Paper I, we advance the hypothesis that binary and
multiple star-formation from smooth (i.e., not highly turbulent) starting
states that are supercritical but in unstable mechanical balance requires the
rapid (i.e., dynamical) loss of magnetic flux at some stage of the ensuing
gravitational collapse.


title: Low-latitude gamma-ray sources: correlations and variability

abstract:
  A review of the main characteristics of low-latitude sources in the third
EGRET catalog is presented. There are 75 unidentified gamma-ray sources
detected by EGRET at less than 10 degrees from the galactic plane. About a half
of these sources are spatially correlated with potential galactic gamma-ray
emitters such as supernova remnants, OB associations and early-type stars with
very strong stellar winds. The other half is formed by sources without
positional correlation with known galactic objects capable to generate a gamma
ray flux significant enough as to be detected by EGRET. A variability analysis
shows that this second group of sources contains several objects with high
levels of gamma-ray variability. These variable sources resemble very much the
AGNs detected by EGRET, but without their typical strong radio emission. To
establish the nature of these sources is one of the most urgent problems of
high-energy astrophysics.


title: The Binary Origins of Hot Subdwarfs: New Radial Velocities

abstract:
  Multiple radial velocity observations have been obtained for a large sample
of local field subdwarf B (sdB) stars over a period of two years. SdB stars
appear to fall into three distinct groups based on their kinematic and
spectroscopic properties. The sdB's in Group I have no detectable spectral
lines from a cool companion, and show only small or insignificant velocity
variations. They represent about 35% of all sdB stars, which defines the upper
limit for the total fraction of non-binary sdB's. Group II sdB's are
single-lined spectroscopic binaries, comprising about 45% of the sample. Their
spectra resemble those in the first group, but they have significant or large
velocity variations and probable orbital periods on the order of a day. The
third group contains the remaining 20% of sdB's, those showing additional
spectral lines from a cool (FGK) main sequence or subgiant companion. All Group
III sdB's have slowly varying or nearly constant velocities, indicating periods
of many months to several years. Group II sdB's are obvious post-common
envelope systems, in strong contrast to the wide binaries of Group III. Current
data are insufficient to rule out the possibility that some sdB's in Group I
might be analogs of Group III binaries, with undetectably faint companions. The
clear division into three groups with such disparate properties suggests very
different evolutionary histories even though the current physical states are
essentially indistinguishable.


title: Emission line imaging of QSOs with high resolution

abstract:
  We report the first detection of emission line gas within the host galaxies
of high redshift QSOs. This was done using narrow-band imaging at the
redshifted wavelengths of [O III] and H alpha, using the PUEO adaptive optics
camera of the CFHT. The QSOs are all radio-quiet or very compact radio sources.
In all five observed QSOs, which have redshifts 0.9 to 2.4, we find extended
line emission that lies within 0.5" (a few Kpc) of the nucleus. The emission
(redshifted) equivalent widths range from 35 to 300A. Where there is radio
structure, the line emission is aligned with it. We also report on continuum
fluxes and possible companions. Two of the QSOs are very red, and have high
resolved continuum flux.


title: On the Origin of Subdwarf B Stars and Related Metal-Rich Binaries

abstract:
  Mounting evidence from subdwarf B (sdB) stars in the galactic field and their
recently discovered counterparts in old open clusters indicates that at least
two thirds of local disk sdB stars are binaries. Our recent radial velocity
survey showed that sdB binaries naturally divide into two groups with
contrasting spectroscopic and kinematic properties. Those with detectable
spectral lines from a cooler companion invariably have periods longer than a
year, while very short period sdB's have essentially invisible companions. We
derive typical orbital separations for the components of the composite spectrum
sdB's from their velocities. The current systems must have been produced by
Roche lobe overflow/mass transfer from low mass, metal-rich giants near the
first red giant branch tip, without undergoing common envelope envolution. The
same process should also occur at slightly lower red giant luminosities,
producing a wide binary with a helium white dwarf instead of an sdB star. Most
short period sdB's probably result from a common envelope following Roche lobe
overflow of the initial secondary onto the white dwarf. Rare post-common
envelope sdB + main sequence (MS) binaries also exist, but available data
suggest that most such systems involving lower MS companions end up merging.
The small and nearly identical masses of the two known MS survivors in short
period sdB binaries imply that both components must have lost a large fraction
of their initial mass in the common envelope process.


title: Turbulent Velocity Structure in Molecular Clouds

abstract:
  We compare velocity structure in the Polaris Flare molecular cloud at scales
ranging from 0.015 pc to 20 pc to simulations of supersonic hydrodynamic and
MHD turbulence computed with the ZEUS MHD code. We use several different
statistical methods to compare models and observations. The Delta-variance
wavelet transform is most sensitive to characteristic scales and scaling laws,
but is limited by a lack of intensity weighting. The scanning-beam
size-linewidth relation is more robust with respect to noisy data. Obtaining
the global velocity scaling behaviour requires that large-scale trends in the
maps not be removed but treated as part of the turbulent cascade. We compare
the true velocity PDF in our models to velocity centroids and average line
profiles in optically thin lines, and find that the line profiles reflect the
true PDF better unless the map size is comparable to the total line-of-sight
thickness of the cloud. Comparison of line profiles to velocity centroid PDFs
can thus be used to measure the line-of-sight depth of a cloud. The observed
density and velocity structure is consistent with supersonic turbulence with a
driving scale at or above the size of the molecular cloud and dissipative
processes below 0.05 pc. Ambipolar diffusion could explain the dissipation. The
velocity PDFs exclude small-scale driving such as that from stellar outflows as
a dominant process in the observed region. In the models, large-scale driving
is the only process that produces deviations from a Gaussian PDF shape
consistent with observations. Strong magnetic fields impose a clear anisotropy
on the velocity field, reducing the velocity variance in directions
perpendicular to the field. (abridged)


title: The Sunyaev-Zel'dovich Effect with the Cosmic Background Imager

abstract:
  We are engaged in a program with the Cosmic Background Imager (CBI), a
13-element interferometer recently installed at 5000 m in the Chilean Andes, to
measure H_0 with 10% accuracy through observations of the Sunyaev-Zel'dovich
effect in a sample of nearby clusters. We discuss the capabilities of this new
instrument and present our cluster sample and selection criteria, along with
results from detailed simulations. We also present preliminary observations of
Abell 478.


title:
Clustering Segregation With UV Luminosity in Lyman-Break Galaxies at z~3
  and Its Implications

abstract:
  We report on the clustering properties of Lyman-break galaxies (LBGs) at z~3.
The correlation length of flux-limited samples of LBGs depends on their
rest-frame ultraviolet (UV) luminosity at lambda ~1700 Angstrom, with fainter
galaxies being less strongly clustered in space. It decreases by a factor ~3
over the range of limiting magnitudes that we have probed, namely 25<R<27,
suggesting that fainter samples include galaxies with smaller mass. We find
that: 1) the clustering strength of LBGs follows, within the errors, the same
scaling law with the volume density predicted for cold dark matter (CDM) halos;
2) the scaling law predicted for the galaxies using the halos mass spectrum and
a number of models for the relationship that maps the halos' mass into the
galaxies' UV luminosity depends only on how tightly mass and UV luminosity
correlate, but is otherwise insensitive to the details of the models. These
results provide additional evidence that the strong spatial clustering of LBGs
is due to galaxy biasing, supporting biased galaxy formation and gravitational
instability as the primary mechanism for the formation of structure. We also
find that 1) a scale invariant relationship between mass and UV luminosity
(e.g. a power law) is not supported, suggesting that the properties of star
formation of galaxies change along the mass spectrum of the observed LBGs; 2)
the scatter of the UV luminosity of LBGs of given mass must be relatively small
for massive LBGs, suggesting that the mass is an important parameter in
regulating the activity of star formation in these systems, and that the
fraction of massive halos at z~3 that are not observed in UV-selected surveys
is not large.


title: The Intracluster Medium in z > 1 Galaxy Clusters

abstract:
  The Chandra X-ray Observatory was used to obtain a 190 ks image of three high
redshift galaxy clusters in one observation. The results of our analysis of
these data are reported for the two z > 1 clusters in this Lynx field,
including the most distant known X-ray selected cluster. Spatially-extended
X-ray emission was detected from both these clusters, indicating the presence
of hot gas in their intracluster media. A fit to the X-ray spectrum of RX
J0849+4452, at z=1.26, yields a temperature of kT = 5.8^{+2.8}_{-1.7} keV.
Using this temperature and the assumption of an isothermal sphere, the total
mass of RX J0849+4452 is found to be 4.0^{+2.4}_{-1.9} X 10^{14} h_{65}^{-1}
M_{\sun} within r = 1 h_{65}^{-1} Mpc. The T_x for RX J0849+4452 approximately
agrees with the expectation based on its L_{bol} = 3.3^{+0.9}_{-0.5} X 10^{44}$
erg s$^{-1} according to the low redshift L_x - T_x relation. The very
different distributions of X-ray emitting gas and of the red member galaxies in
the two z > 1 clusters, in contrast to the similarity of the optical/IR colors
of those galaxies, suggests that the early-type galaxies mostly formed before
their host clusters.


title: Models of Quasi-Periodic Variability in Neutron Stars and Black Holes

abstract:
  Black holes and weakly-magnetic accreting neutron stars show strong
quasi-periodic variability over timescales that span a very wide range. This
property offer us a unique opportunity to improve our understanding of basic
physical processes in strong gravitational fields as it reveals, for the first
time, phenomena that occur on the most fundamental timescales near accreting
compact objects. In this article, I review our current understanding of the
variability properties of accretion flows onto neutron stars and black holes. I
discuss a number of challenges faced by theoretical models, in order to
identify open questions in accretion physics that need to be addressed.
Finally, I discuss the relation to and implications for variability models of
the detection of nearly coherent oscillations during type I X-ray bursts in
several neutron-star sources.


title:
Ram-Pressure Stripping of Galaxies in High-Redshift Clusters and
  Influence of ICM Heating

abstract:
  We have investigated the ram-pressure stripping of disk galaxies in clusters
at various redshifts and in cluster progenitors; the clusters grow up on a
hierarchical clustering scenario. We consider a radially infalling galaxy whose
initial position and velocity are given by a spherical collapse model of
structure formation. Moreover, since observations show that the intracluster
medium (ICM) of nearby clusters is non-gravitationally heated, we study the
effect of the non-gravitational heating on the ram-pressure stripping. For a
given redshift, we find that ram-pressure stripping has more influence on
galaxies in more massive clusters. On the other hand, for a given mass, it has
more influence on galaxies in the clusters at higher redshifts. In particular,
we predict that in rich clusters at z ~> 1, most of the galaxies are affected
by the ram-pressure stripping. While the non-gravitational heating
significantly reduces the influence of ram-pressure stripping on galaxies in
clusters with mass smaller than 1-5 10^13 M_sun, it does not affect the
influence in richer clusters. If the ICM is heated non-gravitationally at z>>1,
ram-pressure stripping does not occur at z ~ 1-2 in the progenitors of clusters
observed at 0 ~< z ~< 0.5, because the heat makes the ICM fraction of the
cluster progenitors small. On the other hand, if the ICM is heated
non-gravitationally at z ~ 0 for the first time, the ram-pressure stripping
occurs even at z ~ 3. We compare the results with the observations of galaxies
in clusters at various redshifts.


title: Weak Lensing Constraints on Cluster Structural Parameters

abstract:
  We study the reliability of dark matter (DM) profile determinations for rich
clusters of galaxies based on weak gravitational lensing measurements. We
consider three functional forms for the mass distribution: a softened
isothermal sphere (SIS), the Navarro, Frenk, & White model (NFW) and the
Klypin, Kravstov, Bullock, & Primack model (KKBP). A maximum likelihood
parametric method is developed and applied to simulated images of background
galaxies (z=2.0) lensed by clusters at z=0.2, 0.5, and 0.8. The images have
field size (~10 arcmin) and angular resolution (~0.5 arcsec) characteristic of
the new generation of 8-10 meter-class ground-based telescopes. The method
recovers the correct virial mass of the DM halo, M_{200}, to within ~10% at all
redshifts. The recovered values of \delta_c and r_s are only accurate to ~25%;
however, their correlated errors are such that greater accuracy is obtained for
the mass. Clusters with an SIS density profile are recognized by the method,
while NFW and KKBP clusters are recognized as not being SIS. The method does
not discriminate between NFW and KKBP profiles for clusters of a given mass,
because they are too similar in their outer regions. Strongly lensed arcs near
the cluster centers would be needed to distinguish NFW from KKBP.


title: Optical/Infrared Survey of Galaxy Clusters

abstract:
  In this contribution the ongoing effort to build a statistical sample of
clusters of galaxies over a wide range of redshifts to study the evolution of
clusters and member galaxies is reviewed. The starting point for this project
has been the list of candidate clusters identified from the I-band EIS-WIDE
survey data. Since the completion of this survey, new optical/infrared
observations have become available and have been used to confirm some of these
candidates using the photometric data alone or in combination with the results
of follow-up spectroscopic observations. Our preliminary results show that the
yield of real physical associations from the original catalog is conservatively
>60% and that a large sample of clusters in the southern hemisphere, extending
to high-redshifts, is within reach.


title: In search for the oldest star forming regions in Holmberg II

abstract:
  We present an X-ray study of the irregular dwarf galaxy Holmberg II based on
deep ROSAT PSPC observations. Holmberg II is one of the most famous examples of
an irregular dwarf galaxy with a disrupted interstellar medium (ISM): expanding
HI holes are present across the entire face of the galaxy. Huge HI cavities of
kpc extent are found even outside current starforming regions. We search for
faint X-ray sources (stellar end points as well as hot gas), touching the
limits of the ROSAT PSPC detector and link the newly detected X-ray sources to
features detected in other wavelengths. Using an X-ray hardness ratio
color-color diagram we show that it is possible to differentiate between
thermal plasma and power-law X-ray spectra, which helps to track down the
physical nature of the individual sources.


title: On the atmospheric fragmentation of small asteroids

abstract:
  It is known, from observational data recorded from airbursts, that small
asteroids breakup at dynamical pressures lower than their mechanical strength.
This means that actual theoretical models are inconsistent with observations.
In this paper, we present a detailed discussion about data recorded from
airbursts and about several theoretical models. We extend and improve a theory
previously outlined for the fragmentation of small asteroids in the Earth
atmosphere. The new condition for fragmentation is given by the shock
wave-turbulence interaction, which results in sudden outburst of the dynamical
pressure.


title: On the broadening of emission lines in active galactic nuclei

abstract:
  Recent works, both theoretical and observational, have suggested that
turbulence could play a non-negligible role in the broadening of emission lines
in active galactic nuclei. The purpose of this note is to show how shock
wave-turbulence interaction, under unsteady regime, can affect the broadening
of emission lines.


title: Leonid Electrophonic Bursters

abstract:
  We investigate the conditions under which Leonid meteoroids might generate
short duration (burster) electrophonic sounds. A `first order' theory is
employed to estimate the approximate electron number density in the meteoroid
ablation column as a function of time. Using the threshold conditions discussed
in an earlier communication (Beech and Foschini 1999) we find that Leonid
meteoroids more massive than about 0.1 kg can potentially generate short
duration electrophonic bursters.


title:
The "Number - Flux Density" Relation for Milliarcsecond Structures in
  Extragalactic Radio Sources

abstract:
  ``Number - flux density'' distributions for total and correlated flux
densities at various interferometer spacings in 355 extragalactic radio sources
are analysed. Qualitative conclusions on the population of milliarcsecond
components in these sources are presented.


title:
Effect of Magnetic Field on the Phase Transition from Nuclear Matter to
  Quark Matter during Proto-Neutron Star Evolution

abstract:
  We have studied phase transition from hadron matter to quark matter in the
presence of high magnetic fields incorporating the trapped electron neutrinos
at finite temperatures. We have used the density dependent quark mass (DDQM)
model for the quark phase while the hadron phase is treated in the frame-work
of relativistic mean field theory. It is seen that the nuclear energy at phase
transition decreases with both magnetic field and temperature. A brief
discussion of the effect of magnetic field in supernova explosions and
proto-neutron star evolution is given.


title: A census with ROSAT of low-luminosity X-ray sources in globular clusters

abstract:
  I analyze 101 observations from the ROSAT archive to search for X-ray sources
in or near 55 globular clusters. New sources are found in the cores of NGC362
(a double source), NGC6121 (marginally significant), NGC6139, and NGC6266; and
outside the cores of NGC6205, NGC6352 and NGC6388. More accurate positions are
determined for the X-ray sources in some ten clusters. The improved position
for the source in NGC6341 excludes the suggested ultraviolet counterpart. It is
shown that one of the two sources reported near the core NGC6626 is spurious,
as is the detection of a pulsar period in the PSPC data of this cluster; the
central source is resolved in three sources. One source reported previously in
NGC6304 is demoted to an upper limit. For 20 cluster cores better upper limits
to the X-ray luminosity are obtained.
  From a statistical analysis I argue that several sources outside the cluster
cores may well belong to the clusters. All spectral energy distributions
observed so far are relatively soft, with bremsstrahlung temperatures =~0.9keV;
there is evidence however that bremsstrahlung spectra do not correctly describe
the spectra. The X-ray luminosity per unit mass for the cluster as a whole does
not depend on the concentration; the luminosity per unit mass for the core may
increase with the cluster concentration.


title:
Accretion discs models with the "beta"-viscosity prescription derived
  from laboratory experiments

abstract:
  We examine under which conditions one may apply, to steady state keplerian
accretion discs, the "beta"-viscosity prescription which has been derived from
rotating shear flow experiments (Richard & Zahn 1999). Using a vertically
averaged model, we show that this law may be suitable for all three families of
known systems: in young stellar objects, evolved binary stars and Active
Galactic Nuclei discs (except in their outer gas pressure dominated regions
where turbulence becomes hypersonic). According to the standard criterion for
viscous stability, "beta"-discs are always stable throughout. Using realistic
opacities and equation of state, we demonstrate that these discs are thermally
unstable in the temperature domain where hydrogen recombines, when they are
optically thick, and this could lead to limit cycle behavior. Radiation
pressure dominated regions are thermally stable, in contrast with
"alpha"-discs. This results in a fully stable solution for the innermost parts
of AGN discs.


title: Physical Parameter Eclipse Mapping

abstract:
  The tomographic method "Physical Parameter Eclipse Mapping" is a tool to
reconstruct spatial distributions of physical parameters (like temperatures and
surface densities) in accretion discs of cataclysmic variables. After
summarizing the method, we apply it to multi-colour eclipse light curves of
various dwarf novae and nova-likes like VZ Scl, IP Peg in outburst, UU Aqr,
V2051 Oph and HT Cas in order to derive the temperatures (and surface
densities) in the disc, the white dwarf temperature, the disc size, the
effective temperatures and the viscosities. The results allows us to establish
or refine a physical model for the accretion disc. Our maps of HT Cas and V2051
Oph, for example, indicate that the (quiescent) disc must be structured into a
cool, optically thick inner disc sandwiched by hot, optically thin
chromospheres. In addition, the disc of HT Cas must be patchy with a covering
factor of about 40% caused by magnetic activity in the disc.


title: Brownian Motion of a Massive Binary

abstract:
  The dynamical friction and diffusion coefficients are derived for a massive
binary that moves against a uniform background of stars. The random impulses
exerted on the binary's center of mass by the field stars are greater than
those exerted on a point particle due to inelastic scattering. The frictional
force acting on the binary is less than that acting on a point particle due to
randomization of the trajectories of field stars that pass near the binary.
Both effects tend to increase the random motion of a binary compared with that
of a point mass. If the maximum effective impact parameter for gravitational
encounters is comparable to the radius of gravitational influence of the
binary, its Brownian velocity can be increased by a modest factor compared with
that of a single particle. This condition is probably fulfilled in the case of
binary supermassive black holes in galactic nuclei.


title: Anisotropic Stars: Exact Solutions

abstract:
  We study the effects of anisotropic pressure on the properties of spherically
symmetric, gravitationally bound objects. We consider the full general
relativistic treatment of this problem and obtain exact solutions for various
form of equations of state connecting the radial and tangential pressures. It
is shown that pressure anisotropy can have significant effects on the structure
and properties of stellar objects. In particular, the maximum value of 2M/R can
approach unity (2M/R < 8/9 for isotropic objects) and the surface redshift can
be arbitrarily large.


title:
The ROSAT-ESO Flux Limited X-Ray (REFLEX) Galaxy Cluster Survey I: The
  Construction of the Cluster Sample

abstract:
  We describe the construction of an X-ray flux-limited sample of galaxy
clusters, the REFLEX survey catalogue, to be used for cosmological studies. The
survey is based on the ROSAT All-Sky Survey and on extensive follow-up
observations conducted in the frame of an ESO key program. In the paper we
document the process by which the primary cluster candidate catalogue is
constructed prior to the optical follow-up observations. We describe the
reanalysis of the RASS source catalogue which enables us to impose a proper
flux limit cut to the X-ray source list without introducing a severe bias
against extended sources. We discuss the correlation of the X-ray and optical
(COSMOS) data to find galaxy density enhancements at the RASS X-ray source
positions and the further evaluation of the nature of these cluster candidates.
Based also on the results of the follow-up observations we provide a
statistical analysis of the completeness and contamination of the final cluster
sample and show results on the cluster number counts. The final sample of
identified X-ray clusters reaches a flux limit of 3e-12 erg s-1 cm-2 in the 0.1
- 2.4 keV band and comprises 452 clusters. The results imply a completeness of
the REFLEX cluster sample well in excess of 90% and a contamination by
non-cluster X-ray sources of less than 9%, an accuracy sufficient for the use
of this cluster sample for cosmological tests.


title: Master Equation for Hydrogen Recombination on Grain Surfaces

abstract:
  Recent experimental results on the formation of molecular hydrogen on
astrophysically relevant surfaces under conditions similar to those encountered
in the interstellar medium provided useful quantitative information about these
processes. Rate equation analysis of experiments on olivine and amorphous
carbon surfaces provided the activation energy barriers for the diffusion and
desorption processes relevant to hydrogen recombination on these surfaces.
However, the suitability of rate equations for the simulation of hydrogen
recombination on interstellar grains, where there might be very few atoms on a
grain at any given time, has been questioned. To resolve this problem, we
introduce a master equation that takes into account both the discrete nature of
the H atoms and the fluctuations in the number of atoms on a grain. The
hydrogen recombination rate on microscopic grains, as a function of grain size
and temperature, is then calculated using the master equation. The results are
compared to those obtained from the rate equations and the conditions under
which the master equation is required are identified.


title: Gamma-Ray Pulsars: Models and Predictions

abstract:
  Pulsed emission from gamma-ray pulsars originates inside the magnetosphere,
from radiation by charged particles accelerated near the magnetic poles or in
the outer gaps. In polar cap models, the high energy spectrum is cut off by
magnetic pair production above an energy that is dependent on the local
magnetic field strength. While most young pulsars with surface fields in the
range B = 10^{12} - 10^{13} G are expected to have high energy cutoffs around
several GeV, the gamma-ray spectra of old pulsars having lower surface fields
may extend to 50 GeV. Although the gamma-ray emission of older pulsars is
weaker, detecting pulsed emission at high energies from nearby sources would be
an important confirmation of polar cap models. Outer gap models predict more
gradual high-energy turnovers at around 10 GeV, but also predict an inverse
Compton component extending to TeV energies. Detection of pulsed TeV emission,
which would not survive attenuation at the polar caps, is thus an important
test of outer gap models. Next-generation gamma-ray telescopes sensitive to
GeV-TeV emission will provide critical tests of pulsar acceleration and
emission mechanisms.


title:
Coronal cooling and its signatures in the rapid aperiodic variability of
  Galactic black-hole candidates

abstract:
  The most popular models for the complex phase and time lags in the rapid
aperiodic variability of Galactic X-ray binaries are based Comptonization of
soft seed photons in a hot corona, where small-scale flares are induced by
flares of the soft seed photon input (presumably from a cold accretion disc).
However, in their original version, these models have neglected the additional
cooling of the coronal plasma due to the increased soft seed photon input, and
assumed a static coronal temperature structure. In this paper, our
Monte-Carlo/Fokker-Planck code for time-dependent radiation transfer and
electron energetics is used to simulate the self-consistent coronal response to
the various flaring scenarios that have been suggested to explain phase and
time lags observed in some Galactic X-ray binaries. It is found that the
predictions of models involving slab-coronal geometries are drastically
different from those deduced under the assumption of a static corona. However,
with the inclusion of coronal cooling they may even be more successful than in
their original version in explaining some of the observed phase and time lag
features. The predictions of the model of inward-drifting density perturbations
in an ADAF-like, two-temperature flow also differ from the static-corona case
previously investigated, but may be consistent with the alternating phase lags
seen in GRS 1915+105 and XTE J1550-564. Models based on flares of a cool disc
around a hot, inner two-temperature flow may be ruled out for most objects
where significant Fourier-frequency-dependent phase and time lags have been
observed.


title: The Merging History of the Milky Way Disk

abstract:
  The stellar populations of the stellar halo and of the thick disk of the
Milky Way reveal much about the merging history that our Galaxy, a typical
large disk galaxy, has experienced. Our current understanding, described here,
implies a rather quiet evolution for the disk, back to redshifts of order 2.


title:
Extragalactic Background Light, MACHOs, and the Cosmic Stellar Baryon
  Budget

abstract:
  The optical/far-IR extragalactic background light (EBL) from both resolved
and unresolved extragalactic sources is an indicator of the total luminosity of
cosmic structures, as the cumulative emission from young and evolved galactic
systems, as well as from active galactic nuclei (AGNs), is recorded in this
radiation. This is a brief review of some of the implications of the observed
brightness of the night sky for the stellar mass density and average
metallicity of the universe today, and of the possible contribution of MACHO
progenitors and QSOs to the EBL. Assuming a Salpeter initial mass function with
a cutoff below 0.6 M_sun, a lower limit of Omega_{g+s}h^2>0.0015 I_{60} can be
derived to the visible (recycled gas + stars) mass density required to generate
an EBL at a level of I_{EBL}=60 I_{60} nW/m^2/sr: our latest, best-guess
estimate is Omega_{g+s}h^2 ~ 0.0023 I_{60}, which implies a mean metallicity at
the present-epoch of y_Z Omega_{g+s}/Omega_b ~ 0.2 Z_sun. If massive dark halos
around spiral galaxies are partially composed of faint, old white dwarfs, i.e.
if a non-negligible fraction (a few percent) of the nucleosynthetic baryons is
locked in the remnants (MACHOs) of intermediate-mass stars forming at very high
redshifts, then the bright early phases of such halos should contribute
significantly to the observed EBL. Assuming a standard black hole accretion
model for quasar activity and using recent observations of the quasar
population and new synthesis models for the cosmic X-ray background, we
estimate a present mass density of QSO remnants of rho_{BH} ~ 3e5 M_sun/Mpc^3
for a 10% efficiency of accreted mass-to-radiation conversion. The quasar
contribution to the brightness of the night sky is I_QSO ~ 2 nW/m^2/sr.


title:
Adiabatic Losses and Stochastic Particle Acceleration in Gamma-Ray Burst
  Blast Waves

abstract:
  We treat the problem of adiabatic losses and stochastic particle acceleration
in gamma-ray burst (GRB) blast waves that decelerate by sweeping up matter from
an external medium. The shocked fluid is assumed to be represented by a
homogeneous expanding shell. The energy lost by nonthermal particles through
adiabatic expansion is converted to the bulk kinetic energy of the outflow,
permitting the evolution of the bulk Lorentz factor Gamma of the blast wave to
be self-consistently calculated. The behavior of the system is shown to
reproduce the hydrodynamic self-similar solutions in the relativistic and
nonrelativistic limits, and the formalism is applicable to scenarios that are
intermediate between the adiabatic and fully radiative regimes. Nonthermal
particle energization through stochastic gyroresonant acceleration with
magnetic turbulence in the blast wave is treated by employing energy-gain rates
and diffusive escape timescales based upon expressions derived in the
quasilinear regime. If the magnetic field in the shocked fluid approaches its
equipartition value, this process can accelerate escaping particles to
>~10^{20} eV energies, consistent with the hypothesis that ultra-high energy
cosmic rays (UHECRs) are accelerated by GRB blast waves. Due to particle
trapping by the magnetic turbulence, only the highest energy particles can
escape during the prompt and afterglow phases of a GRB for acceleration by a
Kolmogorov spectrum of MHD turbulence. Lower energy particles begin to escape
as the blast wave becomes nonrelativistic and shock Fermi acceleration becomes
more important.


title: In-flight main beam reconstruction for Planck-LFI

abstract:
  In-flight measurement of the antenna main beams of the Planck instruments is
a crucial input to the data analysis pipeline. We study the main beam
reconstruction achievable through external planets using a flight simulator to
model their observation. We restrict our analysis to the 30 GHz LFI channel but
the method can be easily extended to higher frequency channels. We show that it
is possible to fit the antenna response from Jupiter and Saturn to obtain an
accurate, robust, simple and fast reconstruction of the main beam properties
under very general conditions, independently of the calibration accuracy.
  In addition, we find that a bivariate Gaussian approximation of the main beam
shapes represents a significant improvement with respect to a symmetric
representation.
  We also show that it is possible to combine the detection of the planet's
transit and Planck's very accurate in-flight calibration to measure the
planet's temperature at millimetric wavelengths with an accuracy at the %
level.
  This work is based on Planck-LFI activities.


title:
Discovery of a Magnetic DZ White Dwarf with Zeeman-Split Lines of Heavy
  Elements

abstract:
  A spectroscopic survey of previously-unstudied Luyten Half Second proper
motion stars has resulted in the discoveries of two new cool magnetic white
dwarfs. One (LHS 2273) is a routine DA star, T= 6,500K, with Zeeman-split H
alpha and H beta, for which a simple model suggests a polar field strength of
18.5 MG viewed close to equator-on. However, the white dwarf LHS 2534 proves to
be the first magnetic DZ showing Zeeman-split Na I and Mg I components, as well
as Ca I and Ca II lines for which Zeeman components are blended. The Na I
splittings result in a mean surface field strength estimate of 1.92 MG. Apart
from the magnetic field, LHS 2534 is one of the most heavily-blanketed and
coolest DZ white dwarfs at T ~ 6,000K.


title: Near-Infrared Spectral Classification of late-M and L Dwarfs

abstract:
  We present near-infrared (1 to 2.5 micron) low-resolution spectroscopy of
eleven ultracool dwarfs with spectral types ranging from M7 to L8. Combining
our observations with data published previously by Leggett et al. (2001), we
have measured equivalent widths for the strongest atomic features and
constructed narrowband indices to gauge the strength of the strongest molecular
features. Those measurements show that the behaviourr at near-infrared
wavelengths is well correlated with spectral type, where the latter is defined
from observations between 6300 and 10000 Angstroms. In particular, four indices
designed to measure absorption in the wings of the 1.4 and 1.85 micron steam
bands exhibit a linear, monotonic correlation with spectral type on the
Kirkpatrick et al. (1999) system, allowing consistent calibration from both
optical and near-infrared spectroscopy.


title:
An Upgraded Data Acquisition System for the Balloon-Borne Liquid Xenon
  Gamma-Ray Telescope LXeGRIT

abstract:
  LXeGRIT is a balloon-borne Compton telescope for MeV gamma-ray astrophysics,
based on a liquid xenon time projection chamber (LXe-TPC) with charge and light
readout. The first balloon flights in 1997 revealed limitations of the trigger
electronics and the data acquisition (DAQ) system, leading to their upgrade.
New electronics was developed to handle the xenon scintillation light trigger.
The original processor module was replaced by a commercial VME processor. The
telemetry rate was doubled to 2 x 500 kbps and onboard data storage on hard
disks was implemented. Relying on a robust real-time operating system, the new
DAQ software adopts an object oriented design to implement the diverse tasks of
trigger handling, data selection, transmission, and storage, as well as DAQ
control and monitor functions. The new systems performed well during two
flights in Spring 1999 and Fall 2000. In the 2000 flight, the DAQ system was
able to handle 300-350 triggers/s out of a total of about 650 Hz, including
charged particles.