title:
BeppoSAX spectroscopy of MR 2251-178: a test for ionized reflection in
  radio quiet QSOs

abstract:
  We present the 0.1-200 keV BeppoSAX spectrum of MR 2251-178 observed at two
epochs in 1998 separated by 5 months. Both epochs show identical spectral shape
and X-ray flux. Analysis of the combined spectra allow us to confirm the
presence of the ionized Fe K-alpha line detected by ASCA and to test the
presence of reflection from ionized material. The best self-consistent spectral
fit is obtained when including a contribution from a mildly ionized reflector
(Xi(0.01-100) ~ 1625 erg cm s-1, i.e. U(0.1-10) ~ 0.14) with a reflection
fraction R_ion ~ 0.11. An exponential cut-off to the direct power-law continuum
is then required at E ~ 100 keV. The low energy spectrum is absorbed by ionized
matter with a column density N_W = (8.1 (-1.2/+2.1))*10^21 cm^-2 and an X-ray
ionization parameter U(0.1-10)= 0.06 +/- 0.01. The warm absorber column is
slightly lower than that measured with ASCA. This change could be caused by
bulk motion. The BeppoSAX absorber ionization parameter globally agrees with
the ``U versus Flux'' correlation found for MR 2251-178 with EXOSAT, Ginga and
ASCA. This suggests that the absorber is in a state of instantaneous ionization
equilibrium.


title: The Neutral Hydrogen Content of Fornax Cluster Galaxies

abstract:
  We present a new set of deep HI observations of member galaxies of the Fornax
cluster. We detected 35 cluster galaxies in HI. The resulting sample, the most
comprehensive to date, is used to investigate the distribution of HI in the
cluster galaxies. We compare the HI content of the detected cluster galaxies
with that of field galaxies by measuring HI mass-to-light ratios and the HI
deficiency parameter of Solanes et al. (1996). The mean HI mass-to-light ratio
of the cluster galaxies is 0.68+/-0.15, significantly lower than for a sample
of HI-selected field galaxies (1.15+/-0.10), although not as low as in the
Virgo cluster (0.45+/-0.03). The mean HI deficiency for the cluster is
0.38+/-0.09 (for T=1-6), significantly greater than for the field sample
(0.05+/-0.03). Both these tests show that Fornax cluster galaxies are
HI-deficient compared to field galaxies. The kinematics of the cluster galaxies
suggests that the HI deficiency may be caused by ram-pressure stripping of
galaxies on orbits that pass close to the cluster core.
  We also derive the most complete B-band TF relation of inclined spiral
galaxies in Fornax. A subcluster in the South-West of the main cluster
contributes considerably to the scatter. The scatter for galaxies in the main
cluster alone is 0.50mag, which is slightly larger than the intrinsic scatter
of 0.4mag. We use the TF relation to derive a distance modulus of Fornax
relative to the Virgo cluster of -0.38+/-0.14mag. The galaxies in the
subcluster are 1.0+/-0.5mag brighter than the galaxies of the main cluster,
indicating that they are situated in the foreground. With their mean velocity
95km/s higher than that of the main cluster we conclude that the subcluster is
falling into the main Fornax cluster.


title: Hydrodynamic simulations of merging clusters of galaxies

abstract:
  We present the results of high-resolution AP3M+SPH simulations of merging
clusters of galaxies. We find that the compression and shocking of the core gas
during a merger can lead to large increases in bolometric X-ray luminosities
and emission-weighted temperatures of clusters. Cooling flows are completely
disrupted during equal-mass mergers, with the mass deposition rate dropping to
zero as the cores of the clusters collide. The large increase in the cooling
time of the core gas strongly suggests that cooling flows will not recover from
such a merger within a Hubble time. Mergers with subclumps having 1/8th of the
mass of the main cluster are also found to disrupt a cooling flow if the merger
is head-on. However, in this case the entropy injected into the core gas is
rapidly radiated away and the cooling flow restarts within a few Gyr of the
merger. Mergers in which the subcluster has an impact parameter of 500kpc do
not disrupt the cooling flow, although the mass deposition rate is reduced by
\~30%. Finally, we find that equal mass, off-centre mergers can effectively mix
gas in the cores of clusters, while head on mergers lead to very little mixing.
Gas stripped from the outer layers of subclumps results in parts of the outer
layers of the main cluster being well mixed, although they have little effect
on the gas in the core of the cluster. None of the mergers examined here
resulted in the ICM being well mixed globally.


title:
Mass ratios of the components in T Tauri binary systems and implications
  for multiple star formation

abstract:
  Using near-infrared speckle interferometry we have obtained resolved
JHK-photometry for the components of 58 young binary systems. From these
measurements, combined with other data taken from literature, we derive masses
and particularly mass ratios of the components. We use the J-magnitude as an
indicator for the stellar luminosity and assign the optical spectral type of
the system to the primary. On the assumption that the components within a
binary are coeval we can then place also the secondaries into the HRD and
derive masses and mass ratios for both components by comparison with different
sets of current theoretical pre-main sequence evolutionary tracks. The
resulting distribution of mass ratios is comparatively flat for M(2)/M(1) >
0.2, but depends on assumed evolutionary tracks. The mass ratio is neither
correlated with the primary's mass or the components' separation. These
findings are in line with the assumption that for most multiple systems in T
associations the components' masses are principally determined by fragmentation
during formation and not by the following accretion processes. Only very few
unusually red objects were newly found among the detected companions. This
finding shows that the observed overabundance of binaries in the Taurus-Auriga
association compared to nearby main sequence stars should be real and not the
outcome of observational biases related to infrared observing.


title: AGB variables in Baade's windows

abstract:
  In this work, a sample of luminous M-type giants in the Baade's Windows
towards the inner Galactic Bulge is investigated in the near-infrared. The
ISOGAL survey at 7 and 15 micron has given information concerning the mass-loss
rates of these stars and their variability characteristics have been extracted
from the MACHO database. Most are known to be semi-regular variables (SRVs).
Here we discuss how their IJHK-region colours depend on period and the presence
or absence of mass-loss, using results mainly taken from the DENIS and 2MASS
surveys.
  In order to compare their colours with solar neighbourhood stars, photometric
colours on the DENIS, 2MASS and ESO photometric systems have been synthesized
for objects in the spectrophotometric atlas of Lancon and Wood (2000). In
addition, they have been used to predict the differences in colour indicies
when stars with strong molecular bands are observed using different photometric
systems.
  The SRVs are found to inhabit the upper end of the J-K, K colour-magnitude
diagram, lying just below the Miras. High mass-loss rates are associated with
high luminosity. The near-infrared colours of the semi-regular variables
increase in a general way with period and are reddest for the stars with
significant mass-loss. The average colours of Mira variables, whose periods
start at around 200 days in the Bulge, are bluer than those of the
semi-regulars at this period, particularly in J-H, thanks to the association of
deep water-vapour bands with large amplitude.


title: Monte Carlo transition probabilities

abstract:
  Transition probabilities governing the interaction of energy packets and
matter are derived that allow Monte Carlo NLTE transfer codes to be constructed
without simplifying the treatment of line formation. These probabilities are
such that the Monte Carlo calculation asymptotically recovers the local
emissivity of a gas in statistical equilibrium. Numerical experiments with
one-point statistical equilibrium problems for Fe II and Hydrogen confirm this
asymptotic behaviour. In addition, the resulting Monte Carlo emissivities are
shown to be far less sensitive to errors in the populations of the emitting
levels than are the values obtained with the basic emissivity formula.


title:
Constraining the quintessence equation of state with SnIa data and CMB
  peaks

abstract:
  Quintessence has been introduced as an alternative to the cosmological
constant scenario to account for the current acceleration of the universe. This
new dark energy component allows values of the equation of state parameter
$w_{Q}^0\geq-1$, and in principle measurements of cosmological distances to
Type Ia supernovae can be used to distinguish between these two types of
models. Assuming a flat universe, we use the supernovae data and measurements
of the position of the acoustic peaks in the Cosmic Microwave Background (CMB)
spectra to constrain a rather general class of Quintessence potentials,
including inverse power law models and recently proposed Supergravity inspired
potentials. In particular we use a likelihood analysis, marginalizing over the
dark energy density $\Omega_{Q}$, the physical baryon density $\Omega_{b}h^2$
and the scalar spectral index $n$, to constrain the slopes of our Quintessence
potential. Considering only the first Doppler peak the best fit in our range of
models gives $w_{Q}^0\sim-0.8$. However, including the SnIa data and the three
peaks, we find an upper limit on the present value of the equation of state
parameter, $-1\leq w_{Q}^0\leq-0.93$ at $2\sigma$, a result that appears to
rule out a class of recently proposed potentials.


title:
Sersic 159-03: discovery of the brightest soft X-ray excess emitting
  cluster of galaxies

abstract:
  The soft X-ray excess emission in the southern cluster Sersic 159-03
represents hiterto the strongest effect of its kind. Emission in the ~0.2-0.4
keV passband is detected far in excess of the expected contribution from the
hot phase of the intra-cluster medium, and extends to the X-ray signal limit of
the cluster. Our analysis of ROSAT PSPC observations reveal that the soft
excess can be interpreted as either a thermal or non-thermal effect, and the
high data quality allows to place tight constraints on the two currently
competing models. However, each model now implies major revisions to our
understanding of clusters of galaxies: either `warm' gas masses in similar
amounts to the hot gas, or relativistic particles in or above equipartition
with the hot phase, appear to be unavoidable.


title:
A Chandra observation of the long-duration X-ray transient KS 1731-260
  in quiescence: too cold a neutron star?

abstract:
  After more than a decade of actively accreting at about a tenth of the
Eddington critical mass accretion rate, the neutron-star X-ray transient KS
1731-260 returned to quiescence in early 2001. We present a Chandra/ACIS-S
observation taken several months after this transition. We detected the source
at an unabsorbed flux of ~2 x 10^{-13} erg/cm^2/s (0.5-10 keV). For a distance
of 7 kpc, this results in a 0.5-10 keV luminosity of ~1 x 10^{33} erg/s and a
bolometric luminosity approximately twice that. This quiescent luminosity is
very similar to that of the other quiescent neutron star systems. However, if
this luminosity is due to the cooling of the neutron star, this low luminosity
may indicate that the source spends at least several hundreds of years in
quiescence in between outbursts for the neutron star to cool. If true, then it
might be the first such X-ray transient to be identified and a class of
hundreds of similar systems may be present in the Galaxy. Alternatively,
enhanced neutrino cooling could occur in the core of the neutron star which
would cool the star more rapidly. However, in that case the neutron star in KS
1731-260 would be more massive than those in the prototypical neutron star
transients (e.g., Aql X-1 or 4U 1608-52).


title: Relativistic effects in the solar EOS

abstract:
  We study the sensitivity of the sound speed to relativistic corrections of
the equation of state (EOS) in the standard solar model by means of a
helioseismic forward analysis. We use the latest GOLF/SOHO data for $\ell =
0,1,2,3$ modes to confirm that the inclusion of the relativistic corrections to
the adiabatic exponent $\Gamma_1$ computed from both OPAL and MHD EOS leads to
a more reliable theoretical modelling of the innermost layers of the Sun.


title: Vela, its X-ray nebula, and the polarization of pulsar radiation

abstract:
  The recent identification of the perpendicular mode of radio polarization as
the primary one in the Vela pulsar by Lai et al. (2001) is interpreted in terms
of the maser mechanism proposed by Luo & Melrose (1995). We suggest that such a
mechanism may also be operative for the parallel mode which opens up the
possibility of accounting for all types of polarization observed in pulsars. We
propose an alternative interpretation of the arcs in the nebular X-radiation
observed by Pavlov et al.(2000) & Helfand et al. (2001) with the Chandra
Observatory, and interpreted by the latter as an equatorial wind. We interpret
the arcs as traces of the particle beams from the two magnetic poles at the
shock front. We also propose that the alignment with the rotation axis of the
jet-like feature bisecting the arcs is an effect of projection on the sky plane
and that there is no physical jet along the axis of rotation.


title: Fast Clustering Analysis of Inhomogeneous Megapixel CMB maps

abstract:
  Szapudi et al (2001) introduced the method of estimating angular power
spectrum of the CMB sky via heuristically weighted correlation functions. Part
of the new technique is that all (co)variances are evaluated by massive Monte
Carlo simulations, therefore a fast way to measure correlation functions in a
high resolution map is essential. This letter presents a new algorithm to
calculate pixel space correlation functions via fast spherical harmonics
transforms. Our present implementation of the idea extracts correlations from a
MAP-like CMB map (HEALPix resolution of 512, i.e. $ \simeq 3 \times 10^6$
pixels) in about 5 minutes on a 500MHz computer, including $C_\ell$ inversion;
the analysis of one Planck-like map takes less then one hour. We use heuristic
window and noise weighting in pixel space, and include the possibility of
additional signal weighting as well, either in $\ell$ or pixel space. We apply
the new code to an ensemble of MAP simulations, to test the response of our
method to the inhomogenous sky coverage/noise of MAP. We show that the
resulting $C_\ell$'s are very close to the theoretical expectations. The
HEALPix based implementation of the method, SpICE (Spatially Inhomogenous
Correlation Estimator) will be available to the public from the authors.


title: Optimal detection of sources on a homogeneous and isotropic background

abstract:
  This paper introduces the use of pseudo-filters that optimize the
detection/extraction of sources on a background. We assume as a first approach
that such sources are described by a spherical (central) profile and that the
background is represented by a homogeneous and isotropic random field. We make
an n-dimensional treatment making emphasis in astrophysical applications for
spectra, images and volumes, for the cases of exponential and Gaussian source
profiles and scale-free power spectra to represent the background.


title:
A photometric and spectroscopic study of dwarf and giant galaxies in the
  Coma cluster - II. Spectroscopic observations

abstract:
  This is the second paper in a series studying the photometric and
spectroscopic properties of galaxies of different luminosities in the Coma
cluster. The sample selection, spectroscopic observations and completeness
functions are presented here. To study the spectral properties of galaxies as a
function of their local environment, two fields were selected for spectroscopic
observations to cover both the core (Coma1) and outskirts (ie. south-west of
the core and centered on NGC4839)- (Coma3) of the cluster. Medium resolution
spectroscopy (6-9 \AA) was carried out for a total of 490 galaxies in both
fields (302 in Coma1 and 188 in Coma3), using the WYFFOS multi-fiber
spectrograph on the William Herschel Telescope. The galaxies cover a range of
$12 < R < 20$, corresponding to -23 < M_R < -15 (H0=65 km/sec/Mpc). The
redshifts are measured with an accuracy of 100 km/sec. The spectral line
strengths and equivalent widths are also measured for the same galaxies and
analysed in Poggianti et al (2001- paper III). A total of 189 (Coma1) and 90
(Coma3) galaxies are identified as members of the Coma cluster. An analysis of
the colors show that only two members of the Coma cluster in our sample have
B-R > 2. The completeness functions for the spectroscopic sample is presented.


title: Cosmological observations in scalar-tensor quintessence

abstract:
  The framework for considering the astronomical and cosmological observations
in the context of scalar-tensor quintessence in which the quintessence field
also accounts for a time dependence of the gravitational constant is developed.
The constraints arising from nucleosynthesis, the variation of the constant,
and the post-Newtonian measurements are taken into account. A simple model of
supernovae is presented in order to extract the dependence of their light
curves with the gravitational constant; this implies a correction when fitting
the luminosity distance. The properties of perturbations as well as CMB
anisotropies are also investigated.


title: X-ray Novae and the Evidence for Black Hole Event Horizons

abstract:
  We discuss new observations of X-ray novae which provide strong evidence that
black holes have event horizons. Optical observations of 13 X-ray novae
indicate that these binary stars contain collapsed objects too heavy to be
stable neutron stars. The objects have been identified as black hole
candidates. X-ray observations of several of these X-ray novae in quiescence
with the Chandra X-ray Observatory show that the systems are approximately 100
times fainter than nearly identical X-ray novae containing neutron stars. The
advection-dominated accretion flow model provides a natural explanation for the
difference. In this model, the accreting gas reaches the accretor at the center
with a large amount of thermal energy. If the accretor is a black hole, the
thermal energy will disappear through the event horizon, and the object will be
very dim. If the accretor is a neutron star or any other object with a surface,
the energy will be radiated from the surface, and the object will be bright. We
discuss alternate interpretations of the data that eliminate the need for
advection-dominated accretion. Most of these alternatives still require an
event horizon to explain the unusually low X-ray luminosities of the black hole
candidates. Some of the alternatives are also inconsistent with observations.


title: Stellar Collisions and the Interior Structure of Blue Stragglers

abstract:
  Collisions of main sequence stars occur frequently in dense star clusters. In
open and globular clusters, these collisions produce merger remnants that may
be observed as blue stragglers. Detailed theoretical models of this process
require lengthy hydrodynamic computations in three dimensions. However, a less
computationally expensive approach, which we present here, is to approximate
the merger process (including shock heating, hydrodynamic mixing, mass
ejection, and angular momentum transfer) with simple algorithms based on
conservation laws and a basic qualitative understanding of the hydrodynamics.
These algorithms have been fine tuned through comparisons with the results of
our previous hydrodynamic simulations. We find that the thermodynamic and
chemical composition profiles of our simple models agree very well with those
from recent SPH (smoothed particle hydrodynamics) calculations of stellar
collisions, and the subsequent stellar evolution of our simple models also
matches closely that of the more accurate hydrodynamic models. Our algorithms
have been implemented in an easy to use software package, which we are making
publicly available (see http://vassun.vassar.edu/~lombardi/mmas/). This
software could be used in combination with realistic dynamical simulations of
star clusters that must take into account stellar collisions.


title: On the Possible Sources of D/H Dispersion at High Redshift

abstract:
  Recent observations suggest the existence of a white dwarf population in the
Galactic halo, while others suggest that deuterium has been astrated in systems
at high redshift and low metallicity. We propose that these observations could
be signatures of an early population of intermediate-mass stars. Such a
population requires a Population III initial mass function different from that
of the solar neighborhood, as perhaps also suggested by the observed cosmic
infrared background. Also, to avoid overproduction of C and N, it is required
that the Z=0 yields of these stars have low ($\sim 10^{-3}$ solar) abundances
as suggested by some recent calculations. Under these assumptions, we present a
model which reproduces the observed D vs Si trend, and predicts a high cosmic
Type Ia supernova rate, while producing a white dwarf population that accounts
for only $\sim$ 1.5% of the dark halo. This scenario can be tested by
observations of the cosmic supernova rate, and by confirmation and further
studies of the putative white dwarf halo population.


title:
Atomic and molecular gas in the merger galaxy NGC 1316 (Fornax A) and
  its environment

abstract:
  We present and interpret observations of atomic and molecular gas toward the
southern elliptical galaxy NGC 1316 (Fornax A), a strong double-lobe radio
source with a disturbed optical morphology that includes numerous shells and
loops. The 12CO(1-0), 12CO(2-1), and HI observations were made with SEST and
the VLA. CO emission corresponding to a total molecular hydrogen mass of 5x10^8
Msun was detected toward the central position as well as northwest and
southeast of the nucleus in the regions of the dust patches. The origin of that
gas is likely external and due to accretion of one or several small gas-rich
galaxies. HI was not detected in the central region of NGC1316, but ~2x10^7
Msun of atomic gas was found toward the giant HII region discovered by
Schweizer (1980) located 6.7 arcmin (or 36.2 kpc) from the nucleus. HI was also
found at three other locations in the outer part of NGC 1316. The HI
distributions and kinematics of the two nearby spiral companions of NGC 1316,
NGC 1317 (a barred galaxy to the north) and NGC 1310 (to the west) could be
studied. Both galaxies have unusually small HI disks that may have been
affected by ram-pressure stripping.


title:
Cepheid Calibration of the Peak Brightness of SNe Ia. XI. SN 1998aq in
  NGC 3982

abstract:
  Repeated imaging observations have been made of NGC 3982 with the Hubble
Space Telescope between March and May 2000, over an interval of 53 days. Images
were obtained on 12 epochs in the F555W band and on five epochs in the F814W
band. The galaxy hosted the type Ia supernova SN1998aq.
  A total of 26 Cepheid candidates were identified, with periods ranging from
10 to 45 days, using photometry with the DoPHOT program. The de-reddened
distance to NGC 3982 is estimated from these data using various criteria to
maximize signal to noise and reliability: the values lie between 31.71 and
31.82, with uncertainties in the mean of typically +/- 0.14 mag for each case.
A parallel analysis using photometry with HSTphot discovered 13 variables,
yielding a distance modulus of 31.85 +/- 0.16. The final adopted modulus is
(M-m)_0 = 31.72 +/- 0.14 (22 +/- 1.5 Mpc).
  Photometry of 1998aq that is available in the literature is used in
combination with the derived distance to NGC 3982 to obtain the peak absolute
magnitude of this supernova. The lower limit (no extinction within the host
galaxy) for M_V is -19.47 +/- 0.15 mag. Corrections for decline rate and
intrinsic color to carry these to the reduced system of Parodi et al. (2000)
have been performed. The derived luminosities at hand are fully consistent with
the mean of the 8 normal SNe Ia previously calibrated with Cepheids. Together
they yield H_0 ~ 60 +/- 2 (internal) km s-1 Mpc-1 based on an assumed LMC
distance modulus of 18.50. We point out that correcting some of the systematic
errors and including uncertainty estimates due to them leads to H_0 = 58.7 +/-
6.3 (internal) km s-1 Mpc-1.


title:
The Chandra Deep Field North Survey. VII. X-ray Emission from Lyman
  Break Galaxies

abstract:
  We present results from stacking analyses, using the 1 Ms Chandra Deep Field
North data, that constrain the X-ray emission of Lyman break galaxies at z =
2-4. Stacking the counts from 24 individually undetected Lyman break galaxies
located within the Hubble Deep Field North, we have obtained average detections
of these objects in the resulting 0.5-8.0 keV and 0.5-2.0 keV images; these
images have effective exposure times of 22.4 Ms (260 days). Monte Carlo testing
empirically shows the detections to be highly significant. The average
rest-frame 2-8 keV luminosity of a Lyman break galaxy is derived to be 3.2 x
10^{41} erg s^{-1}, comparable to that of the most X-ray luminous starbursts in
the local Universe. The observed ratio of X-ray to B-band luminosity is
somewhat, but not greatly, higher than that seen from local starbursts. The
X-ray emission probably arises from a combination of high-mass X-ray binaries,
"super-Eddington" X-ray sources, and low-luminosity active galactic nuclei.


title:
Synergy Between Observations of AGN with GLAST and MAXI - Detecting
  X-ray Precursors of Gamma-ray Flares in Blazars

abstract:
  The EGRET instrument onboard of CGRO detected a number of gamma-ray flares
from blazars, and it is expected that GLAST, to be launched in 2006, should
detect many more such flares. These flares should be preceded by X-ray
precursors, and the MAXI All-Sky Monitor, to be deployed around the time of
launch of GLAST, is likely to detect such precursors. This paper highlights the
interesting new insights into the structure of jets in blazars that may result
from simultaneous X-ray and gamma-ray observations. In particular, it addresses
the expected temporal relationship between the precursors and flares, and the
expected luminosities of the precursors.


title: Heating of the intergalactic medium due to structure formation

abstract:
  We estimate the heating of the intergalactic medium due to shocks arising
from structure formation. Heating of the gas outside the collapsed regions,
with small overdensities (${n_b \over {\bar n_b}}\ll 200$) is considered here,
with the aid of Zel'dovich approximation. We estimate the equation of state of
this gas, relating the density with its temperature, and its evolution in time,
considering the shock heating due to one-$\sigma$ density peaks as being the
most dominant. We also estimate the mass fraction of gas above a given
temperature as a function of redshift. We find that the baryon fraction above
$10^6$ K at $z=0$ is $\sim 10 %$. We estimate the integrated Sunyaev-Zel'dovich
distortion from this gas at present epoch to be of order $10^{-6}$.


title: Lane-Emden Equation: Picard vs Pade

abstract:
  The very accurate analytical solutions are found to Lane-Emden equation of
arbitrary index, n, using Picard type iteration scheme and rational Pade
approximants. For n=2 the dimensionless polytropic "radius" and "mass" are
4.35287459595 and 2.4110450121, with the largest ever accuracy.


title: An XMM-Newton view of the serendipitous sources in the PKS0312-770 field

abstract:
  We describe an XMM-Newton observation of the PKS0312-770 field, which
facilitates the spectral analysis of serendipitous sources previously detected
by CHANDRA. The combination of larger effective area and longer exposure
duration allows a significant increase in detected photons, and a lower limit
in source detection sensitivity. In particular the hard X-ray normal galaxy
unveiled by Fiore et al (2000) is most likely explained as a moderately
absorbed (N_H ~ 1e22 cm^-2) AGN. We detect 52 sources (45 previously
unreported) at a limiting flux of ~2e-15 cgs in the 0.5-2keV band. The
LogN-LogS curve is consistent with that derived from by XMM-Newton observations
of the Lockman Hole field. The flux determinations allow to check for any
inconsistency between the calibrations of the two observatories, which is
discussed.


title: A proposed theoretical basis for a MOND cosmology: I. The inertial frame

abstract:
  This first of two papers is a speculation on the nature of Mach's Principle,
derived from the formulation of two questions: (A) Can a globally inertial
space and time be associated with a non-trivial global matter distribution? (B)
If so, what are the general properties of such a global distribution? The
answers are yes subject to the condition that mass is distributed fractally
with D=2. Such a prediction is supported, for example, in Joyce, Montuori,
Labini astro-ph/9901290.
  The second paper then shows how gravitational phenomena arise as consequences
of perturbations of this equilibrium D=2 distribution, and applies this theory
to spiral galaxy dynamics. Specifically, the second paper derives a
gravitational model for an idealized spiral, defined to have perfect
cylindrical symmetry. One of the main results of this analysis is that, *in the
disc*, V_rot = A/R^alpha where (A, alpha) are constants which vary between
spirals. See astro-ph/0107305, which concludes that a power-law model is
powerfully confirmed for ORCs as a statistical generality over large samples,
and astro-ph/0107300 for new phenomonology discovered via this analysis.
  Thus, unlike MOND, we have only been concerned with model predictions made
for idealized matter distributions, and tested over very large numbers of ORCs.
But, like those of MOND, the predictions are very powerfully supported on the
data. For this reason, we hypothesize that perspectives of MOND are buried
within our own formalism. This remains a topic for future work.


title: Recent Progress in CdTe and CdZnTe Detectors

abstract:
  Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been
regarded as promising semiconductor materials for hard X-ray and Gamma-ray
detection. The high atomic number of the materials (Z_{Cd} =48, Z_{Te} =52)
gives a high quantum efficiency in comparison with Si. The large band-gap
energy (Eg ~ 1.5 eV) allows us to operate the detector at room temperature.
However, a considerable amount of charge loss in these detectors produces a
reduced energy resolution. This problem arises due to the low mobility and
short lifetime of holes. Recently, significant improvements have been achieved
to improve the spectral properties based on the advances in the production of
crystals and in the design of electrodes. In this overview talk, we summarize
(1) advantages and disadvantages of CdTe and CdZnTe semiconductor detectors and
(2) technique for improving energy resolution and photopeak efficiencies.
Applications of these imaging detectors in future hard X-ray and Gamma-ray
astronomy missions are briefly discussed.


title:
On the GRB progenitors: possible consequences for supernovae connection
  with gamma-ray bursts

abstract:
  Unique data on $BVRI$ light curves of the optical transient (OT) of GRB
970508 obtained with the 6-m telescope have been interpreted in the framework
of the idea of a straightforward link between supernovae (SNe) and long
duration gamma-ray bursts (GRBs). The effect must be maximum in the $I_{c}$
band as for OT GRB 970228. The peak absolute ($M_{B}$) magnitude of the
suggested SN must be around -19.5 for the OT of GRB 970508. So, in addition to
the characteristic "shoulders" on the light curves of the OTs of GRB 970228,
GRB 980326, 990712, 991208, more evidence of the link between GRBs and Type
Ib/c SNe (or core-collapse SNe) was found, which could be an argument in favor
of the idea of massive stars as progenitors of long duration GRBs. If all or
the main part of long duration GRBs are associated with the SNe, GRB host
galaxies (for ground-based observations, at least) must be dimmer than the peak
magnitude of a SN. If some GRB/SN relation really exists, and if all or at
least the main part of long duration GRBs are associated with SNe, then as a
consequence we have a very strong $\gamma$-ray beaming with a solid angle of up
to $\Omega_{beam} \sim (10^{-5} - 10^{-6})\cdot 4\pi$. Besides, the
observations of K$_{\alpha}$ lines of iron in the X-ray afterglow spectra of
GRBs (970508, 970828, 991216, 000214) and the observation of redshifted
absorption feature of neutral iron (7.1 keV) simultaneously with GRB 990705 are
also evidence in favor of massive stars -- progenitors of GRBs.


title: AMS, a particle spectrometer in space

abstract:
  The results of the AMS01 experiment are reviewed. The proton flux measured
below the geomagnetic cutoff is interpreted. Some Physics prospects for AMS02
on the International Space Station are outlined.


title:
M31 Globular Clusters in the HST Archive: I. Cluster Detection and
  Completeness

abstract:
  Globular clusters at the distance of M31 have apparent angular sizes of a few
arcseconds. While many M31 GCs have been detected and studied from ground-based
images, the high spatial resolution of HST allows much more robust detection
and characterization of star cluster properties. We present the results of a
search of 157 HST/WFPC2 images of M31: we found 82 previously-cataloged
globular cluster candidates as well as 32 new globular cluster candidates and
20 open cluster candidates. We present images of the new candidates and
photometry for all clusters. We assess existing cluster catalogs' completeness
and use the results to estimate the total number of GCs in M31 as 460+/-70. The
specific frequency is S_N = 1.2+/-0.2 and the mass specific frequency T =
2.4+/-0.4; these values are at the upper end of the range seen for spiral
galaxies.


title: Gravity's smoking gun?

abstract:
  We present a new constraint on the biased galaxy formation picture.
Gravitational instability theory predicts that the two-point mass density
correlation function, \xi(r), has an inflection point at the separation r=r_0,
corresponding to the boundary between the linear and nonlinear regime of
clustering, \xi = 1. We show how this feature can be used to constrain the
square of the biasing parameter, b^2 = \xi_g / \xi on scales r = r_0, where
\xi_g is the galaxy-galaxy correlation function, allowed to differ from \xi. We
apply our method to real data: the \xi_g(r), estimated from the APM galaxy
survey. Our results suggest that the APM galaxies trace the mass at separations
r > 5 Mpc/h, where h is the Hubble constant in units of 100 km/s Mpc. The
present results agree with earlier studies, based on comparing higher order
correlations in the APM with weakly non-linear perturbation theory. Both
approaches constrain the "b" factor to be within 20% of unity. If the existence
of the feature we identified in the APM \xi_g(r) -- the inflection point near
\xi_g = 1 -- is confirmed by more accurate surveys, we may have discovered
gravity's smoking gun: the long awaited ``shoulder'' in \xi, predicted by Gott
and Rees 25 years ago.


title: Galaxy Evolution with ALMA

abstract:
  The submillimeter and millimeter domains are privileged for the exploration
of galaxies at high redshift, because of the negative K-correction: the peak of
the dust emission at 60-100 microns is red-shifted in these domains. Already
blind surveys in blank fields with today instrumentation have discovered in the
continuum of the order of one object per square arcmin, with large limitations
due to confusion. In the molecular lines, the K-correction is not so favorable,
and it has been until now difficult to detect the objects, except when they are
starbursting monsters, or gravitationally lensed (about a dozen galaxies have
been detected). ALMA will bring more than one order of magnitude improvement,
and will not be affected by confusion. Normal star-forming objects will be
detected, and in particular those enshrouded in dust, so the instrument will be
complementary to the optical ones, such as NGST or ELTs.


title:
Towards a Mass and Radius Determination of the Nearby Isolated Neutron
  Star RX J185635-3754

abstract:
  We discuss efforts to determine the mass, radius, and surface composition of
the nearby compact object RX J185635-3754 from its multi-wavelength spectral
energy distribution. We compute non-magnetized model atmospheres and emergent
spectra for selected compositions and gravities, and discuss efforts to fit
existing and new observational data from ROSAT, EUVE and the HST. The spectral
energy distribution matches that expected from a heavy-element dominated
atmosphere, but not from a uniform temperature blackbody. Non-magnetic light
element atmospheres cannot be simultaneously reconciled with the optical and
X-ray data. We extend previous studies, which were limited to one fixed neutron
star mass and radius. For uniform temperature models dominated by heavy
elements, the redshift z is constrained to be 0.3 < z < 0.4 and the best-fit
mass and radius are M approx 0.9 solar masses and R approx 6 km (for a 61 pc
distance). These values for M and R together are not permitted for any
plausible equation of state, including that of a self-bound strange quark star.
A simplified two-temperature model allows masses and radii up to about 50%
larger, or a factor of 2 in the case of a black body. The observed luminosity
is consistent with the thermal emission of an isolated neutron star no older
than about 1 million years, the age inferred from available proper motion and
parallax information


title: BZ Cam during its 1999/2000 optical low state

abstract:
  We report optical observations of the VY Scl star BZ Cam during its previous
optical low state in 1999/2000. We find drastic variations in the line
profiles. Narrow-band imaging observations show that its nebula extends farther
than previously known and seems to be composed of two components. We determine
the [OIII] line intensity of BZ Cam's nebula to 4.8 * 10^-13 erg/cm^2/s. We
discover a proper motion of BZ Cam of 25+-2 mas/yr which together with the
systemic radial velocity yields a space velocity of 125 km/s. We re-interpret
the nebula as being photo-ionized by hypothesized transient, luminous,
supersoft X-ray emission during optical low states, and shaped by the
transverse motion of BZ Cam.


title: Parallel Programming with MatlabMPI

abstract:
  MatlabMPI is a Matlab implementation of the Message Passing Interface (MPI)
standard and allows any Matlab program to exploit multiple processors.
MatlabMPI currently implements the basic six functions that are the core of the
MPI point-to-point communications standard. The key technical innovation of
MatlabMPI is that it implements the widely used MPI ``look and feel'' on top of
standard Matlab file I/O, resulting in an extremely compact (~100 lines) and
``pure'' implementation which runs anywhere Matlab runs. The performance has
been tested on both shared and distributed memory parallel computers. MatlabMPI
can match the bandwidth of C based MPI at large message sizes. A test image
filtering application using MatlabMPI achieved a speedup of ~70 on a parallel
computer.


title: Penetrating the Mask: The Gravitational Torque of Bars

abstract:
  The Hubble classification scheme of galaxies is based on blue-light
appearance. Atlases reveal the rich variety of responses of the Population I
component (the "mask") of gas and dust to the underlying, older, stellar
population. However, the Population I component may only constitute 5 percent
of the dynamical mass of the galaxy; furthermore, dusty masks are highly
effective in hiding bars. In the 1960s, Ken Freeman presented a meticulous
study of the dynamics of bars at a time when nonbarred galaxies were called
"normal" spirals and barred galaxies were regarded as curiosities. Now we know
that it is more "normal" for a galaxy to be barred than to be nonbarred. What
is the range for gravitational torques of bars? We describe here a recently
developed method for deriving relative bar torques by using gravitational
potentials inferred from near-infrared light distributions. We incorporate a
bar torque class into the Block/Puerari dust-penetrated galaxy classification
system. We find a huge overlap in relative bar torque between Hubble (Sa, Sb,
  ...) and (SBa, SBb, ...) classifications. Application of the method to the
high redshift universe is briefly discussed.


title: Theory of Turbulent Accretion Disks

abstract:
  In low-mass disks, turbulent torques are probably the most important way of
redistributing angular momentum. Here we present the theory of turbulent
accretion disks. We show the molecular viscosity is far too small to account
for the evolutionary timescale of disks, and we describe how turbulence may
result in enhanced transport of (angular) momentum. We then turn to the
magnetorotational instability, which thus far is the only mechanism that has
been shown to initiate and sustain turbulence in disks. Finally, we present
both the basis and the structure of alpha disk models.


title:
Three-Dimensional Spectral Classification of Low-Metallicity Stars Using
  Artificial Neural Networks

abstract:
  We explore the application of artificial neural networks (ANNs) for the
estimation of atmospheric parameters (Teff, logg, and [Fe/H]) for Galactic F-
and G-type stars. The ANNs are fed with medium-resolution (~ 1-2 A) non
flux-calibrated spectroscopic observations. From a sample of 279 stars with
previous high-resolution determinations of metallicity, and a set of (external)
estimates of temperature and surface gravity, our ANNs are able to predict Teff
with an accuracy of ~ 135-150 K over the range 4250 <= Teff <= 6500 K, logg
with an accuracy of ~ 0.25-0.30 dex over the range 1.0 <= logg <= 5.0 dex, and
[Fe/H] with an accuracy ~ 0.15-0.20 dex over the range -4.0 <= [Fe/H] <= +0.3.
Such accuracies are competitive with the results obtained by fine analysis of
high-resolution spectra. It is noteworthy that the ANNs are able to obtain
these results without consideration of photometric information for these stars.
We have also explored the impact of the signal-to-noise ratio (S/N) on the
behavior of ANNs, and conclude that, when analyzed with ANNs trained on spectra
of commensurate S/N, it is possible to extract physical parameter estimates of
similar accuracy with stellar spectra having S/N as low as 13. Taken together,
these results indicate that the ANN approach should be of primary importance
for use in present and future large-scale spectroscopic surveys.


title:
The formation of black hole low-mass X-ray binaries: through case B or
  case C mass transfer?

abstract:
  The formation of low-mass X-ray binaries containing a rather massive (M >~ 7
\msun) black hole is problematic because in most recent stellar evolutionary
calculations the immediate progenitors of these black holes (Wolf-Rayet stars)
lose so much mass via their stellar wind that their final masses are well below
the observed black hole masses. We discuss the recently proposed solution that
these binaries are formed through case C mass transfer (i.e. mass transfer
after core helium burning is completed), avoiding a long Wolf-Rayet phase and
thus significant mass loss. We show that only some of the currently available
models for the evolution of massive stars allow this formation channel. We also
investigate the effect of the downward revised Wolf-Rayet mass-loss rate as is
suggested by observations, and conclude that in that case Wolf-Rayet stars end
their lives with significantly higher masses than previously found and may be
able to form a black holes.


title: Variable gamma-ray emission from the Be/X-ray transient A0535+26?

abstract:
  We present a study of the unidentified gamma-ray source 3EG J0542+2610. This
source is spatially superposed to the supernova remnant G180.0-1.7, but its
time variability makes unlikely a physical link. We have searched into the
EGRET location error box for compact radio sources that could be the low energy
counterpart of the gamma-ray source. Although 29 point-like radio sources were
detected and measured, none of them is strong enough as to be considered the
counterpart of a background gamma-ray emitting AGN. We suggest that the only
object within the 95 % error box capable of producing the required gamma-ray
flux is the X-ray transient A0535+26. We show that this Be/accreting pulsar can
produce variable hadronic gamma-ray emission through the mechanism originally
proposed by Cheng & Ruderman (1989), where a proton beam accelerated in a
magnetospheric electrostatic gap impacts the transient accretion disk.


title:
Magnetic Helix Formation Driven by Keplerian Disk Rotation in an
  External Plasma Pressure --- The Initial Expansion Stage

abstract:
  We study the evolution of a magnetic arcade that is anchored to an accretion
disk and is sheared by the differential rotation of a Keplerian disk. By
including an extremely low external plasma pressure at large distances, we
obtain a sequence of axisymmetric magnetostatic equilibria and show that there
is a fundamental difference between field lines that are affected by the plasma
pressure and those are not (i.e., force-free). Force-free fields, while being
twisted by the differential rotation of the disk, expand outward at an angle of
$\sim 60^\circ$ away from the rotation axis, consistent with the previous
studies. These force-free field lines, however, are enclosed by the outer field
lines which originate from small disk radii and come back to the disk at large
radii. These outer fields experience most of the twist, and they are also
affected most by the external plasma pressure. At large cylindrical radial
distances, magnetic pressure and plasma pressure are comparable so that any
further radial expansion of magnetic fields is prevented or slowed down greatly
by this pressure. This hindrance to cylindrical radial expansion causes most of
the added twist to be distributed on the ascending portion of the field lines,
close to the rotation axis. Since these field lines are twisted most, the
increasing ratio of the toroidal $B_{\phi}$ component to the poloidal component
$B_{R,z}$ eventually results in the collimation of magnetic energy and flux
around the rotation axis. We discuss the difficulty with adding a large number
of twists within the limitations of the magnetostatic approximation.


title: Measurement of the bias parameter from weak lensing

abstract:
  We have measured the correlation between the lensing signal induced by (dark)
matter and number counts of galaxies on scales ranging from 0.15-3.0
h_{50}^{-1} Mpc (which correspond to aperture radii of 1-15 arcminutes). This
provides a direct probe of the scale dependence of the ratio of the classical
bias parameter b and the galaxy-mass correlation coefficient r. The results
presented here are based on 16 deg^2 of R_C band data taken with the CFHT as
part of the Red-Sequence Cluster Survey. We used a sample of lens galaxies with
19.5<R_C<21, and a sample of source galaxies with 21.5<R_C<24. The results are
consistent with a scale independent value of b/r, which provides valuable
constraints on models of galaxy formation on scales that can only be probed
through weak lensing. For the currently favored cosmology (\Omega_m=0.3,
\Omega_\Lambda=0.7) we find b/r=1.05^{+0.12}_{-0.10}, similar to what is found
on larger scales (~10 h_{50}^{-1} Mpc) from local dynamical estimates. These
results support the hypothesis that light traces mass on scales ranging from
0.15 out to ~10 h_{50}^{-1} Mpc. The accuracy of the measurement will improve
significantly in the coming years, enabling us to measure both b and r
separately as a function of scale.


title:
HST STIS Observations of PG 0946+301: the Highest Quality UV Spectrum of
  a BALQSO

abstract:
  We describe deep (40 orbits) HST/STIS observations of the BALQSO PG 0946+301
and make them available to the community. These observations are the major part
of a multi-wavelength campaign on this object aimed at determining the
ionization equilibrium and abundances (IEA) in broad absorption line (BAL)
QSOs. We present simple template fits to the entire data set, which yield firm
identifications for more than two dozen BALs from 18 ions and give lower limits
for the ionic column densities. We find that the outflow's metalicity is
consistent with being solar, while the abundance ratio of phosphorus to other
metals is at least ten times solar. These findings are based on diagnostics
that are not sensitive to saturation and partial covering effects in the BALs,
which considerably weakened previous claims for enhanced metalicity. Ample
evidence for these effects is seen in the spectrum. We also discuss several
options for extracting tighter IEA constraints in future analyses, and present
the significant temporal changes which are detected between these spectra and
those taken by the HST/FOS in 1992.


title: Photoionization Models for BALQSO PG 0946+301

abstract:
  This is a companion paper to the manuscript entitled: ``HST STIS Observations
Of PG 0946+301: The Highest Quality UV Spectrum of a BALQSO'' (Arav et al.
2001; accepted for publication in ApJ). Here we present
photoionization-modeling results for ALL the ionic column density constraints
found in these data, most of which we were unable to include in the printed
version of the paper.


title:
Analysis of Systematic Effects and Statistical Uncertainties in Angular
  Clustering of Galaxies from Early SDSS Data

abstract:
  The angular distribution of galaxies encodes a wealth of information about
large scale structure. Ultimately, the Sloan Digital Sky Survey (SDSS) will
record the angular positions of order 10^8 galaxies in five bands, adding
significantly to the cosmological constraints. This is the first in a series of
papers analyzing a rectangular stripe 2.5x90 degrees from early SDSS data. We
present the angular correlation function for galaxies in four separate
magnitude bins on angular scales ranging from 0.003 degrees to 15 degrees. Much
of the focus of this paper is on potential systematic effects. We show that the
final galaxy catalog -- with the mask accounting for regions of poor seeing,
reddening, bright stars, etc. -- is free from external and internal systematic
effects for galaxies brighter than r* = 22. Our estimator of the angular
correlation function includes the effects of the integral constraint and the
mask. The full covariance matrix of errors in these estimates is derived using
mock catalogs with further estimates using a number of other methods.


title: The Angular Correlation Function of Galaxies from Early SDSS Data

abstract:
  The Sloan Digital Sky Survey is one of the first multicolor photometric and
spectroscopic surveys designed to measure the statistical properties of
galaxies within the local Universe. In this Letter we present some of the
initial results on the angular 2-point correlation function measured from the
early SDSS galaxy data. The form of the correlation function, over the
magnitude interval 18<r*<22, is shown to be consistent with results from
existing wide-field, photographic-based surveys and narrower CCD galaxy
surveys. On scales between 1 arcminute and 1 degree the correlation function is
well described by a power-law with an exponent of ~ -0.7. The amplitude of the
correlation function, within this angular interval, decreases with fainter
magnitudes in good agreement with analyses from existing galaxy surveys. There
is a characteristic break in the correlation function on scales of
approximately 1-2 degrees. On small scales, < 1', the SDSS correlation function
does not appear to be consistent with the power-law form fitted to the 1'<
theta <0.5 deg data. With a data set that is less than 2% of the full SDSS
survey area, we have obtained high precision measurements of the power-law
angular correlation function on angular scales 1' < theta < 1 deg, which are
robust to systematic uncertainties. Because of the limited area and the highly
correlated nature of the error covariance matrix, these initial results do not
yet provide a definitive characterization of departures from the power-law form
at smaller and larger angles. In the near future, however, the area of the SDSS
imaging survey will be sufficient to allow detailed analysis of the small and
large scale regimes, measurements of higher-order correlations, and studies of
angular clustering as a function of redshift and galaxy type.


title: The Angular Power Spectrum of Galaxies from Early SDSS Data

abstract:
  We compute the angular power spectrum C_l from 1.5 million galaxies in early
SDSS data on large angular scales, l<600. The data set covers about 160 square
degrees, with a characteristic depth of order 1 Gpc/h in the faintest (21<r<22)
of our four magnitude bins. Cosmological interpretations of these results are
presented in a companion paper by Dodelson et al (2001). The data in all four
magnitude bins are consistent with a simple flat ``concordance'' model with
nonlinear evolution and linear bias factors of order unity. Nonlinear evolution
is particularly evident for the brightest galaxies. A series of tests suggest
that systematic errors related to seeing, reddening, etc., are negligible,
which bodes well for the sixtyfold larger sample that the SDSS is currently
collecting. Uncorrelated error bars and well-behaved window functions make our
measurements a convenient starting point for cosmological model fitting.


title:
KL Estimation of the Power Spectrum Parameters from the Angular
  Distribution of Galaxies in Early SDSS Data

abstract:
  We present measurements of parameters of the 3-dimensional power spectrum of
galaxy clustering from 222 square degrees of early imaging data in the Sloan
Digital Sky Survey. The projected galaxy distribution on the sky is expanded
over a set of Karhunen-Loeve eigenfunctions, which optimize the signal-to-noise
ratio in our analysis. A maximum likelihood analysis is used to estimate
parameters that set the shape and amplitude of the 3-dimensional power
spectrum. Our best estimates are Gamma=0.188 +/- 0.04 and sigma_8L = 0.915 +/-
0.06 (statistical errors only), for a flat Universe with a cosmological
constant. We demonstrate that our measurements contain signal from scales at or
beyond the peak of the 3D power spectrum. We discuss how the results scale with
systematic uncertainties, like the radial selection function. We find that the
central values satisfy the analytically estimated scaling relation. We have
also explored the effects of evolutionary corrections, various truncations of
the KL basis, seeing, sample size and limiting magnitude. We find that the
impact of most of these uncertainties stay within the 2-sigma uncertainties of
our fiducial result.


title: Time and entropy

abstract:
  This paper presents alternative ideas on the physics of time that lead to a
new interpretation of cosmological redshifts. These ideas are based on the
close relationship between the speed of time and entropy processes in our
universe. I give numerical estimates and describe laboratory experiments and
observational effects that can test the new theory.


title:
The 3D Power Spectrum from Angular Clustering of Galaxies in Early SDSS
  Data

abstract:
  Early photometric data from the Sloan Digital Sky Survey (SDSS) contain
angular positions for 1.5 million galaxies. In companion papers, the angular
correlation function $w(\theta)$ and 2D power spectrum $C_l$ of these galaxies
are presented. Here we invert Limber's equation to extract the 3D power
spectrum from the angular results. We accomplish this using an estimate of
$dn/dz$, the redshift distribution of galaxies in four different magnitude
slices in the SDSS photometric catalog. The resulting 3D power spectrum
estimates from $w(\theta)$ and $C_l$ agree with each other and with previous
estimates over a range in wavenumbers $0.03 < k/{\rm h Mpc}^{-1} < 1$. The
galaxies in the faintest magnitude bin ($21 < \rstar < 22$, which have median
redshift $z_m=0.43$) are less clustered than the galaxies in the brightest
magnitude bin ($18 < \rstar < 19$ with $z_m=0.17$), especially on scales where
nonlinearities are important. The derived power spectrum agrees with that of
Szalay et al. (2001) who go directly from the raw data to a parametric estimate
of the power spectrum. The strongest constraints on the shape parameter
$\Gamma$ come from the faintest galaxies (in the magnitude bin $21 < \rstar <
22$), from which we infer $\Gamma = 0.14^{+0.11}_{-0.06}$ (95% C.L.).


title: Long-Term RXTE Monitoring of Anomalous X-ray Pulsars

abstract:
  We report on the long-term monitoring of three anomalous X-ray pulsars using
the Rossi X-ray Timing Explorer (RXTE). We present a phase-coherent timing
ephemeris for 4U 0142+61, and show that it has rotated with high stability over
4.4 yr, with RMS phase deviations of 7% of the pulse period from a simple fit
including only $\nu$ and $\dot{\nu}$. We report on the continued timing
stability of 1E 2259.1+586, for which phase coherence has now been maintained
over 4.5 yr, as well as on the detection of a significant $\ddot{\nu}$ in 1.4
yr of monitoring of RXS J170849.0-400910, consistent with recovery following a
glitch. We note a correlation in which timing stability in AXPs decreases with
increasing $\dot{\nu}$. The timing stability of soft gamma repeaters in
quiescence is consistent with this trend, given their large spin-down rates.
This trend is similar to one seen in radio pulsars, suggesting a connection
between the three populations. We find no large variability in pulse morphology
as a function of time. We present high signal-to-noise ratio average pulse
profiles for each AXP, and consider them as a function of energy. We find a
variety of different behaviors, and consider possible trends in the data. We
also find no large variations in pulsed flux, and set 1 $\sigma$ upper limits
of ~20-30% of the mean. Assuming a constant pulsed fraction, either more than
one of the AXPs are coincidentally in a much more quiescent state during our
RXTE monitoring than in the past, or past claims of large flux variations are
incorrect.


title:
Dark Matter in the center of galaxies and galaxy clusters: ruling out
  the CDM scenario?

abstract:
  This work is focused on the preliminary results of the observations of
H\alpha rotation curves for some of the late type dwarf and LSB galaxies
carried out at the TNG telescope. In light of the observational data and of the
N-body simulations we have performed recently, we discuss some of the
implications on the nature of the DM particles and the formation of the dark
haloes.


title: Soft Cores in Late-Type Dwarf and LSB Galaxies from H\alpha Observations

abstract:
  We present high spatial resolution H\alpha rotation curves of late-type dwarf
and LSB galaxies. From our analysis we find good agreement between our H\alpha
data and the HI observations taken from the literature, concluding that the HI
rotation curves for these galaxies suffer very little from beam smearing. A
preliminary analysis of our data rules out the CDM model in the inner regions
of these galaxies.


title: Star Formation in the Interacting Pair NGC7733/34

abstract:
  The problem of star formation within the interacting pair NGC7733/34 has been
studied, based on the UBVRI photometry of the source. The distribution of the
colors of selected regions within the galaxies is used to infer an estimate for
the age distribution of the star forming regions. The results seem to indicate
the presence of numerous extended young star-forming regions in the disk of one
of the two galaxies, NGC 7733, with ages in the range of $10^6$--$10^8$ yr.
However, there exist no evidence for any violent star formation activity, in
the past $10^8$ yr, in the nuclei of the two galaxies. The pair seems to be a
merger bound system with the brightest, youngest, site of star forming activity
lying at the disk interface.


title: Photospheric Abundances: Problems, Updates, Implications

abstract:
  Current problems encountered in the spectroscopic determination of
photospheric abundances are outlined and exemplified in a reevaluation of C, N,
O, Ne, Mg, Si, and Fe, taking effects of NLTE and granulation into account.
Updated abundances of these elements are given in Table 2.
  Specific topics addressed are (1) the correlation between photospheric matter
and CI chondrites, and the condensation temperature below which it breaks down
(Figure 1), (2) the question whether the metallicity of the Sun is typical for
its age and position in the Galaxy.


title: The Status of the STACEE Observatory

abstract:
  The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is a
ground-based instrument designed to study astrophysical sources of gamma
radiation in the energy range of 50 to 500 GeV. STACEE uses an array of large
heliostat mirrors at the National Solar Thermal Test Facility in Albuquerque,
New Mexico, USA. The heliostats are used to collect Cherenkov light produced in
gamma-ray air showers. The light is concentrated onto an array of
photomultiplier tubes located near the top of a tower. The construction of
STACEE started in 1997 and has been completed in 2001. During the 1998-99
observing season, we used a portion of the experiment, STACEE-32, to detect
gamma-rays from the Crab Nebula. The completed version of STACEE uses 64
heliostat mirrors, having a total collection area of 2300 m^2. During the last
year, we have also installed custom electronics for pulse delay and triggering,
and 1 GHz Flash ADCs to read out the photomultiplier tubes. The commissioning
of the full STACEE instrument is underway. Preliminary observations and
simulation work indicate that STACEE will have an energy threshold below 70 GeV
and a reach for extragalactic gamma-ray sources out to redshift of ~1.0. In
this paper we describe the design and performance of STACEE.


title: A Perturbed Tri-Polytropic Model of the Sun

abstract:
  Based on the Solar Standard Model SSM of Bahcall and Pinsonneault
(SSM-BP2000) we developed a solar model in hydrostatic equilibrium using three
polytropes, each one associated to the nuclear, the radiative and the
convective regions of the solar interior. Then, we apply small periodic and
adiabatic perturbations on this tri-polytropic model in order to obtain proper
frequencies and proper functions which are in the p-modes range of low order
0<l<5; for l=2,3 and 4 these values agrees with GOLF observational data within
a few percent.


title:
Galactic origin of the alleged extragalactic gamma-ray background
  radiation

abstract:
  The diffuse gamma-ray background radiation (GBR) at high Galactic latitudes
could be dominated by inverse Compton scattering (ICS) of cosmic ray (CR)
electrons on the cosmic microwave background radiation (CBR) and on starlight
(SL) in an extended CR halo of our galaxy. Assuming the locally observed CR
electron spectrum beyond a few GeV, which follows from equilibrium between
Fermi acceleration and radiative cooling, to be a universal spectrum throughout
our galaxy and its CR halo, we reproduce the observed spectral index, the
intensity and the angular dependence of the GBR, in directions away from the
galactic disk and centre, without recourse to hypothetical extragalactic
sources.


title:
Some Consequences of the Law of Local Energy Conservation in the
  Gravitational Field

abstract:
  At gravitational interactions of bodies and particles there appears the
defect of masses, i.e. the energy yields since the bodies (or particles) are
attracted. It is shown that this changing of the effective mass of the body (or
the particle) in the external gravitational field leads to changes the
measurement units: velocity and length (relative to the standard measurement
units). The expression describing the advance of the perihelion of the planet
(the Mercury) has been obtained. This expression is mathematically identical to
Einstein's equation for the advance of the perihelion of the Mercury.


title:
Shapes and Shears, Stars and Smears: Optimal Measurements for Weak
  Lensing

abstract:
  We present the theoretical and analytical bases of optimal techniques to
measure weak gravitational shear from images of galaxies. We first characterize
the geometric space of shears and ellipticity, then use this geometric
interpretation to analyse images. The steps of this analysis include:
measurement of object shapes on images, combining measurements of a given
galaxy on different images, estimating the underlying shear from an ensemble of
galaxy shapes, and compensating for the systematic effects of image distortion,
bias from PSF asymmetries, and `"dilution" of the signal by the seeing. These
methods minimize the ellipticity measurement noise, provide calculable shear
uncertainty estimates, and allow removal of systematic contamination by PSF
effects to arbitrary precision. Galaxy images and PSFs are decomposed into a
family of orthogonal 2d Gaussian-based functions, making the PSF correction and
shape measurement relatively straightforward and computationally efficient. We
also discuss sources of noise-induced bias in weak lensing measurements and
provide a solution for these and previously identified biases.


title:
Synchrotron Self-Comptonized Emission of Low Energy Cosmic Ray Electrons
  in the Universe: I) Individual Sources

abstract:
  Most of the Universe's populations of low energy cosmic ray electrons in the
energy range of 1-100 MeV still manage to elude from detection by our
instruments, since their synchrotron emission is at too low frequencies. We
investigate a mechanism which can lead to observable emission of such electron
populations: synchrotron-self Comptonization (SSC). The inverse Compton (IC)
scattering can shift an otherwise unobservable low-frequency 10 kHz-10 MHz
photons into observable radio, infrared (IR) or even more energetic wave-bands.
The resulting emission should be polarized. We also consider IC scattering of
the cosmic microwave background (CMB) and the cosmic radio background (CRB).
Electron spectral aging due to synchrotron, IC and adiabatic losses or gains
influences the resulting spectrum. The predicted radiation spectrum is a strong
function of the history of the source, of the low energy spectrum of
relativistic electrons, and of redshift. It has typically two maxima, and a
decrement in between at CMB frequencies. Detection will give a sensitive probe
of the environment of radio galaxies. We demonstrate that the fossil remnants
of powerful radio galaxies are promising detection candidates, especially when
they are embedded in a dense intra-cluster medium (ICM). GHz peaked sources
(GPS) have very low SSC luminosities, which may, however, extend into the X-ray
or even the gamma ray regime. Clusters of galaxies with relativistic electron
populations may be another detectable sources. Fossil radio plasma released by
our own Galaxy could be revealed by its large angular scale SSC flux. We
discuss the expected detectability of these sources with new and upcoming
instruments as LOFAR, GMRT, EVLA, ATA, ALMA, PLANCK, and HERSCHEL.


title: Wide field weak lensing observations of A1689

abstract:
  We present a mass profile for A1689 from 0.13 h^{-1} Mpc < r < 2 h^{-1} Mpc
from a weak lensing analysis of a 34'x34' R-band image from the ESO/MPG Wide
Field Imager. We detect the gravitational shearing of a 23<R<25.5 background
galaxy population even at the edge of the image with a 4-sigma significance,
and find a two-dimensional mass reconstruction has a 13.4-sigma significance
mass peak centered on the brightest cluster galaxy. This peak is well fit by
both a 1028+-35 km/s singular isothermal sphere and a r200 = 1.28 Mpc, c = 6
universal CDM profile, although the universal CDM profile provides a better fit
with 95.5% confidence. These mass measurements are lower than most of those
derived by other means and we discuss possible reasons for weak lensing
providing an underestimate of the true mass of the cluster. We find that the
correction factors needed to reconcile the weak lensing mass models with the
strong lensing Einstein radius would result is a much larger fraction of faint
stars and foreground and cluster dwarf galaxies in the 23<R<25.5 object catalog
than is seen in other fields.


title: Cosmological parameters from the clustering of AGN

abstract:
  We attempt to put constraints on different cosmological and biasing models by
combining the recent clustering results of X-ray sources in the local ($z\le
0.1$) and distant universe ($z\sim 1$).


title:
PMN J0134-0931: A gravitationally lensed quasar with an unusual radio
  morphology

abstract:
  The radio-loud quasar PMN J0134-0931 was discovered to have an unusual
morphology during our search for gravitational lenses. In VLA and MERLIN
images, there are 5 compact components with maximum separation 681
millarcseconds. All of these components have the same spectral index from 5 GHz
to 43 GHz. In a VLBA image at 1.7 GHz, a curved arc of extended emission joins
two of the components in a manner suggestive of gravitational lensing. At least
two of the radio components have near-infrared counterparts. We argue that this
evidence implies that J0134-0931 is a gravitational lens, although we have not
been able to devise a plausible model for the foreground gravitational
potential. Like several other radio-loud lenses, the background source has an
extraordinarily red optical counterpart.


title:
Energetics of Tev Blazars and Physical Constraints on their Emission
  Regions

abstract:
  Using multi-frequency spectra from TeV blazars in quiescent states, we obtain
the physical parameters of the emission region of blazars within the framework
of the one-zone synchrotron self-Compton (SSC) model. We numerically calculate
the steady-state energy spectra of electrons by self-consistently taking into
account the effects of radiative cooling with a proper account of the
Klein-Nishina effects. Here electrons are assumed to be injected with a
power-law spectrum and to escape on a finite time scale, which naturally leads
to the existence of a break energy scale. Although we do not use time
variabilities but utilize a model of electron escape to constrain the size of
the emission region, the resultant size turns out to be similar to that
obtained based on time variabilities. Through detailed comparison of the
predicted emission spectra with observations, we find that for Mrk 421, Mrk
501, and PKS 2155--304, the energy density of relativistic electrons is about
an order of magnitude larger than that of magnetic fields with an uncertainty
within a factor of a few.


title: The build-up of halos within Press-Schechter theory

abstract:
  Modelling the build-up of halos is important for linking the formation of
galaxies with cosmological models. A simple model of halo growth is provided by
Press-Schechter (PS) theory, where the initial field of density fluctuations is
smoothed using spherically symmetric filters centred on a given position to
obtain information about the likelihood of later collapse on varying scales. In
this paper the predicted halo mass growth is compared for three filter shapes:
Gaussian, top-hat and sharp k-space. Preliminary work is also presented
analysing the build-up of halos within numerical simulations using a
friends-of-friends group finder. The best-fit to the simulation mass function
was obtained using PS theory with a top-hat filter. By comparing both the
backwards conditional mass function, which gives the distribution of halo
progenitors, and the distribution of halo mergers in time, the build-up of
halos in the simulations is shown to be better fitted by PS theory with a sharp
k-space filter. This strengthens previous work, which also found the build-up
of halos in simulations to be well matched to PS theory with a sharp k-space
filter by providing a direct comparison of different filters and by extending
the statistical tools used to analyse halo mass growth. The usefulness of this
work is illustrated by showing that the cosmological evolution in the
proportion of halos that have undergone recent merger is predicted to be
independent of mass and power spectrum and to only depend upon cosmology.
Recent results from observations of field galaxies are shown to match the
evolution expected, but are not sufficiently accurate to usefully distinguish
between cosmological parameters.


title: Galactic Superwinds Circa 2001

abstract:
  In this contribution I summarize our current knowledge of the nature and
significance of starburst-driven galactic winds (``superwinds''). Superwinds
are complex multiphase outflows of cool, warm, and hot gas, dust, and
magnetized relativistic plasma. The observational manifestations of superwinds
result from the hydrodynamical interaction between the primary energy-carrying
wind fluid and the ambient interstellar medium. Superwinds are ubiquitous in
galaxies in which the global star-formation rate per unit area exceeds roughly
10$^{-1}$ M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$. This criterion is met by local
starbursts and the high-z Lyman Break galaxies. Several independent datasets
and techniques imply that the total mass and energy outflow rates in a
superwind are comparable to the starburst's star-formation-rate and mechanical
energy injection rate, respectively. Outflow speeds in interstellar matter
entrained in the wind range from $\sim 10^2$ to $10^3$ km/s, but the primary
wind fluid itself may reach velocities as high as $\sim$3000 km s$^{-1}$. The
available X-ray and far-UV ($FUSE$) data imply that radiative losses in
superwinds are not significant. Superwinds may have established the
mass-metallicity relation in ellipticals and bulges, polluted the present-day
inter-galactic medium to a metallicity of $\sim$ 10 to 30% solar, heated the
inter-galactic medium, and ejected enough dust into the inter-galactic medium
to have potentially observable consequences.


title:
Fabry-Perot Kinematics of HH 202, 203-204 in the Orion Nebula: Are they
  part of a Big Bipolar Outflow?

abstract:
  We present a kinematic study of the Herbig-Haro objects HH 202, 203 and 204
using Halpha and [NII] Fabry-Perot velocity maps. For HH 202 we find new
features that could belong to this HH object or that perhaps are associated
with an outflow different from HH 202. Because of its high velocity (up to 100
km/seg) this outflow probably can be a HH flow not catalogued previously. Large
internal motions are found in the fainter regions of HH 203-204, as well as
evidence of transverse density gradients. We show that the apex of HH 204 is
the zone of maximum velocity in agreement with bow shock models. From our
studies, we find kinematic evidence that suggests that HH 203-204 and HH 202
are part of a single and large (approx 0.55 pc) HH flow.


title: Classification of Planetary Nebulae by their Departure from Axisymmetry

abstract:
  We propose a scheme to classify planetary nebulae (PNe) according to their
departure from axisymmetric structure. We consider only departure along and
near the equatorial plane, i.e., between the two sides perpendicular to the
symmetry axis of the nebula. We consider 6 types of departure from axisymmetry:
(1) PNe whose central star is not at the center of the nebula; (2) PNe having
one side brighter than the other; (3) PNe having unequal size or shape of the
two sides; (4) PNe whose symmetry axis is bent, e.g., the two lobes in bipolar
PNe are bent toward the same side; (5) PNe whose main departure from
axisymmetry is in the outer regions, e.g., an outer arc; (6) PNe which show no
departure from axisymmetry, i.e., any departure, if it exists, is on scales
smaller than the scale of blobs, filaments, and other irregularities in the
nebula. We discuss the connection between departure types and the physical
mechanisms that may cause them, mainly due to the influence by a stellar binary
companion. We find that about 50 percents of all PNe possess large-scale
departure from axisymmetry. This number is larger than that expected from the
influence of binary companions, namely 25-30 percents. We argue that this
discrepancy comes from many PNe whose departure from axisymmetry, mainly
unequal size, shape, or intensity, results from the presence of long-lived and
large, hot or cool, spots on the surface of their AGB progenitors. Such spots
locally enhance mass loss rate, leading to a deparure from axisymmetry, mainly
near the equator, in the descendant PN.


title: The Reddest Quasars

abstract:
  In a survey of quasar candidates selected by matching the FIRST and 2MASS
catalogs, we have found two extraordinarily red quasars. FIRST J013435.7-093102
is a 1 Jy source at z=2.216 and has B-K > 10, while FIRST J073820.1+275045 is a
2.5 mJy source at z=1.985 with B-K = 8.4. FIRST J073820.1+275045 has strong
absorption lines of MgII and CIV in the rest frame of the quasar and is highly
polarized in the rest frame ultraviolet, strongly favoring the interpretation
that its red spectral energy distribution is caused by dust reddening local to
the quasar. FIRST J073820.1+275045 is thus one of the few low radio-luminosity,
highly dust-reddened quasars known. The available observational evidence for
FIRST J013435.7-093102 leads us to conclude that it too is reddened by dust. We
show that FIRST J013435.7-093102 is gravitationally lensed, increasing the
number of known lensed, extremely dust-reddened quasars to at least three,
including MG0414-0534 and PKS1830-211. We discuss the implications of whether
these objects are reddened by dust in the host or lensing galaxies. If reddened
by their local environment, then we estimate that between 10 and 20% of the
radio-loud quasar population is reddened by dust in the host galaxy. The
discovery of FIRST J073820.1+275045 and objects now emerging from X-ray surveys
suggests the existence of an analogous radio-quiet red quasar population. Such
objects will be entirely missed by standard radio or optical quasar surveys. If
dust in the lensing galaxies is primarily responsible for the extreme redness
of the lensed quasars, then an untold number of gravitationally lensed quasars
are being overlooked.


title:
The Central Mass and Phase-Space Densities of Dark Matter Halos:
  Cosmological Implications

abstract:
  Current data suggest that the central mass densities $\rho_0$ and phase-space
densities $Q\equiv\rho_0/\sigma_V^3$ of cosmological halos in the present
universe are correlated with their velocity dispersions $\sigma_V$ over a very
wide range of $\sigma_V$ from less than 10 to more than 1000 $\rm km s^{-1}$.
Such correlations are an expected consequence of the statistical correlation of
the formation epochs of virialized objects in the CDM model with their masses;
the smaller-mass halos typically form first and merge to form larger-mass halos
later. We have derived the $Q-\sigma_V$ and $\rho_0-\sigma_V$ correlations for
different CDM cosmologies and compared the predicted correlations with the
observed properties of a sample of low-redshift halos ranging in size from
dwarf spheroidal galaxies to galaxy clusters. Our predictions are generally
consistent with the data, with preference for the currently-favored, flat
$\Lambda$CDM model. Such a comparison serves to test the basic CDM paradigm
while constraining the background cosmology and the power-spectrum of
primordial density fluctuations, including larger wavenumbers than have
previously been constrained.


title: Can HST Measure the Mass of the Isolated Neutron Star RX J185635-3754 ?

abstract:
  In June 2003 the isolated neutron star RX J185635-3754 will pass within 0.3''
of a 26.5 mag star, changing its position by about 0.6 mas. The displacement,
caused by gravitational lensing, will be proportional to the neutron star mass.
The total event duration will be approximately 1 year.


title: X-ray source population of the Galactic center region obtained with ASCA

abstract:
  From the ASCA X-ray point-source list in the Galactic center 5x5 degree^2
region, we found the clear correlation between the position of the sources and
the absorption. This fact implies that the major part of the absorption is due
to the cold interstellar matter (ISM) in the line of sight. Using the
correlation, we estimate the distribution of the cold ISM. We also found that
the ratio of high mass binaries to low mass binaries is significantly smaller
than that in the whole Galaxy or SMC, which implies that the past starburst
activity in the Galactic center region was rather quiet.


title: SSC of MAXI experiment

abstract:
  Monitor of All-sky X-ray Image (MAXI) on the International Space Station
(ISS) has two kinds of X-ray detectors: the Gas Slit Camera (GSC) and the
Solid-state Slit Camera (SSC). SSC is an X-ray CCD array, consisting of 16
chips, which has the best energy resolution as an X-ray all-sky monitor in the
energy band of 0.5 to 10 keV. Each chip consists of 1024x1024 pixels with a
pixel size of 24$\mu$m, thus the total area is ~200 cm^2. We have developed an
engineering model of SSC, i.e., CCD chips, electronics, the software and so on,
and have constructed the calibration system. We here report the current status
of the development and the calibration of SSC.


title:
The SCUBA 8-mJy survey - I: Sub-millimetre maps, sources and number
  counts

abstract:
  We present maps, source lists, and number counts from the largest, unbiassed,
extragalactic sub-mm survey so far undertaken with the SCUBA camera on the
JCMT. Our maps cover 260 sq. arcmin, to a noise level S(850)=2.5 mJy/beam. We
have reduced the data using both SURF, and our own pipeline which produces
zero-footprint maps and noise images. The uncorrelated noise maps produced by
the latter approach have allowed application of a maximum-likelihood method to
measure the statistical significance of each peak, leading to properly
quantified flux-density errors for all potential sources. We detect 19 sources
with S/N > 4, 38 with S/N > 3.5, and 72 with S/N > 3. To assess completeness
and the impact of source confusion we have applied our source extraction
algorithm to a series of simulated images. The result is a new estimate of the
sub-mm source counts in the flux-density range S(850)=5-15mJy, which we compare
with other estimates, and with model predictions. Our estimate of the
cumulative source count at S(850) > 8 mJy is 320 (+80,-100) per square degree.
Assuming that the majority of sources have z > 1.5, the co-moving number
density of high-z galaxies forming stars at a rate >1000 solar masses per year
is 10^-5 per Mpc^3, with only a weak dependence on the precise redshift
distribution. This number density corresponds to that of massive ellipticals
with L > 3-4 L* at low redshift and is also the same as the co-moving number
density of comparably massive, passively-evolving objects in the redshift band
1<z<2 inferred from recent surveys of extremely red objects. Thus the bright
sub-mm sources can plausibly account for the formation of all present-day
massive ellipticals. Improved z constraints, and a proper measurement of sub-mm
clustering can refine or refute this picture.


title: The Clustering Properties of Lyman-Break Galaxies at Redshift z~3

abstract:
  We present a new measure of the angular two-point correlation function of
Lyman-break galaxies (LBGs) at z~3, obtained from the variance of galaxy counts
in 2-dimensional cells. By avoiding binning of the angular separations, this
method is significantly less affected by shot noise than traditional measures,
and allows for a more accurate determination of the correlation function. We
used a sample of about 1,000 galaxies with R<=25.5 extracted from the survey by
Steidel and collaborators, and found the following results. At scales in the
range 30<~theta<~100 arcsec, the angular correlation function w(theta) can be
accurately described as a power law with slope beta=0.50 +0.25-0.50(1 sigma
random)-0.10(systematic), shallower than the measure presented by Giavalisco et
al. However, the spatial correlation length, derived by Limber deprojection, is
in very good agreement with the previous measures, confirming the strong
spatial clustering of these sources. We discuss in detail the effects of both
random and systematic errors, in particular of the so called ``integral
constraint'' bias, to which we set a lower limit using numerical simulations.
This suggests that the current samples do not yet provide a ``fair
representation'' of the large-scale distribution of LBGs at z~3. An intriguing
result of our analysis is that at angular separations smaller than theta<~30
arcsec the correlation function seems to depart from the power-law fitted at
larger scales and become smaller. This feature is detected at the ~90 per cent
confidence level and, if real, it can provide information on the number density
and spatial distribution of LBGs within their host halos as well as the size
and the mass of the halos.


title:
The Luminosity Function and Surface Brightness Distribution of HI
  Selected Galaxies

abstract:
  We measure the z=0 B-band optical luminosity function (LF) for galaxies
selected in a blind HI survey. The total LF of the HI selected sample is flat,
with Schechter parameters M*=-19.38_{-0.62}^{+1.02} + 5 log h mag and
alpha=-1.03_{-0.15}^{+0.25}, in good agreement with LFs of optically selected
late-type galaxies. Bivariate distribution functions of several galaxy
parameters show that the HI density in the local Universe is more widely spread
over galaxies of different size, central surface brightness, and luminosity
than is the optical luminosity density. The number density of very low surface
brightness (>24.0 mag/arcsec^2) gas-rich galaxies is considerably lower than
that found in optical surveys designed to detect dim galaxies. This suggests
that only a part of the population of LSB galaxies is gas rich and that the
rest must be gas poor. However, we show that this gas-poor population must be
cosmologically insignificant in baryon content. The contribution of gas-rich
LSB galaxies (>23.0 mag/arcsec^2) to the local cosmological gas and luminosity
density is modest (18_{-5}^{+6} and 5_{-2}^{+2} per cent respectively); their
contribution to Omega_matter is not well-determined, but probably < 11 per
cent. These values are in excellent agreement with the low redshift results
from the Hubble Deep Field.


title:
Far Ultraviolet and H-alpha Imaging of Nearby Spirals: The OB Stellar
  Population in the Diffuse Ionized Gas

abstract:
  (Abridged) We have compared H-alpha and far ultraviolet (FUV) images of 10
nearby spirals, with the goal of understanding the contribution of field OB
stars to the ionization of the diffuse ionized gas (DIG) in spiral galaxies.
The FUV images were obtained by the Ultraviolet Imaging Telescope (UIT) and the
H-alpha images were obtained using various ground-based telescopes. In all of
the galaxies, the F_H-alpha/F_UIT flux ratio is lower in the DIG than in the
HII regions. This is likely an indication that the mean spectral type for OB
stars in the field is later than that in HII regions. Comparison of the
N_Lyc/L_UIT ratio with models of evolving stellar populations shows that the
stellar population in the DIG is consistent with either an older single burst
population or a steady state model with constant star formation and an initial
mass function (IMF) slope steeper than alpha=2.35. We compared the
F_H\alpha/F_UIT ratio in the DIG of these galaxies with that in M33. If the
mean spectral types of stars in HII regions and in the DIG are the same as in
M33, and the difference in extinction between DIG and HII regions is constant
among galaxies, then the analysis suggests that field stars are important
sources of ionization in most galaxies, and may be the dominant source in some
galaxies.


title:
The Chandra Deep Field North Survey. VI. The Nature of the Optically
  Faint X-ray Source Population

abstract:
  We provide constraints on the nature of the optically faint (I>=24) X-ray
source population from a 1 Ms Chandra exposure of a 8.4x8.4 arcmin region
containing the Hubble Deep Field North. We detect 47 (2,400 deg^-2) optically
faint X-ray sources. The fraction of optically faint X-ray sources is
approximately constant (at approx 35%) for 0.5-8.0 keV fluxes from 3x10^-14 cgs
down to the X-ray flux limit. A considerable fraction (approx 30%) of the
sources are Very Red Objects (I-K>=4). Analysis of the optical and X-ray
properties suggests a large number of optically faint X-ray sources are likely
to host obscured AGN activity at z= 1-3. From these results we calculate that a
significant fraction (approx 5-45%) could be obscured QSOs at z<=3. Given the
number of X-ray sources without I-band counterparts, there are unlikely to be
more than approx 15 sources at z>6. We provide evidence that the true number of
z>6 sources is considerably lower. Nine optically faint X-ray sources have
micro-Jy radio counterparts; approx 53% of the optically faint micro-Jy radio
sources in this region. The most likely origin of the X-ray emission in these
X-ray detected, optically faint micro-Jy radio sources is obscured AGN
activity. However, two of these sources have been previously detected at
sub-millimeter wavelengths and the X-ray emission from these sources could be
due to luminous star formation activity. Assuming the SED of NGC 6240, we
estimate the 175 micron flux of a typical optically faint X-ray source to be
<10 mJy. As expected for sources with AGN activity, the two optically faint
X-ray sources within the most sensitive area of the ISOCAM region have faint
(approx 50 micro-Jy) 15 micron counterparts. (ABRIDGED).


title:
A small area faint KX redshift survey for QSOs in the ESO Imaging Survey
  Chandra Deep Field South

abstract:
  In this paper we present preliminary spectroscopic results from a small area
faint K-excess (KX) survey, and compare KX selection against UVX selection. The
aim of the KX method is to produce complete samples of QSOs flux-limited in the
K band, in order to minimize any selection bias in samples of QSOs from the
effects of reddening and extinction. Using the photometric catalogue of the ESO
Imaging Survey Chandra Deep Field South (48 arcmin^2) we have identified
compact objects with J-K colours redder than the stellar sequence, that are
brighter than K=19.5. We have obtained spectra of 33 candidates, using the
LDSS++ spectrograph on the AAT. Amongst the 11 bluer candidates, with V-J<3,
three are confirmed as QSOs. Identification of the 22 redder candidates with
V-J>3 is substantially incomplete, but so far no reddened QSOs have been found.
Near-infrared spectroscopy will be more effective in identifying some of these
targets. Only two UVX (U-B<-0.2) sources brighter than K=19.5 are found which
are not also KX selected. These are both identified as galactic stars. Thus KX
selection appears to select all UVX QSOs. The surface density of QSOs in the
blue subsample (V-J<3) at K<19.5 is 325^+316_-177 deg^-2. Because
identification of the red subsample (V-J>3) is substantially incomplete, the
2sigma upper limit on the density of reddened QSO is large, <1150 deg^-2. As
anticipated, at these faint magnitudes the KX sample includes several compact
galaxies. Of the 14 with measured redshifts, there are roughly equal numbers of
early and late type objects. Nearly all the early type galaxies are found in a
single structure at z=0.66.


title: Evolution of X-ray Luminous Clusters from z=0.3 to z=0.8

abstract:
  Observations of the highest redshift clusters provide the longest lever arm
in the attempt to evaluate the evolution of their bulk properties. I present
the most recent results on galaxy cluster evolution based on data from the
ROSAT North Ecliptic Pole survey. At $z>0.3$ there is a deficit of clusters
with respect to the local universe which is significant at $>$ 4.7$\sigma$. The
evolution appears to begin at L$_{0.5-2.0} > 1.8\times10^{44}$ erg s$^{-1}$ in
the NEP survey data and goes in the same direction as the original EMSS result.
At lower redshifts there is no evidence for evolution, a result in agreement
with all the existing cluster surveys.


title:
Future Island Universes in a Background Universe Accelerated by
  Cosmological Constant and by Quintessence

abstract:
  We study bound object formation in a background universe accelerated by
cosmological constant and by quintessence. If the acceleration lasts forever,
due to the existence of event horizon, one would have naively expected the
universe to approach a state of cold death. However, we find that many local
regions in the universe can in fact be protected by their own gravity to form
mini-universes, provided that their present matter densities exceed some
critical value. In the case with cosmological constant ($\Lambda$CDM cosmology)
the condition of forming mini-universe is that the ratio of present density
parameters $\Omega_{i}^0/\Omega_\Lambda$ ought to be larger than a critical
value 3.63. Such mini-universes typically weigh less than $2\times 10^{14}$
solar masses, with the lighter ones having tight and compact configurations. In
the case with quintessence, the final ratio $\Omega_i/\Omega_q$ of a
mini-universe is found to be always larger than $w_q^2-w_q$, where $w_q$ is the
equation of state parameter.


title: Gradient Particle Magnetohydrodynamics

abstract:
  We introduce Gradient Particle Magnetohydrodynamics (GPM), a new Lagrangian
method for magnetohydrodynamics based on gradients corrected for the locally
disordered particle distribution. The development of a numerical code for MHD
simulation using the GPM algorithm is outlined. Validation tests simulating
linear and nonlinear sound waves, linear MHD waves, advection of magnetic
fields in a magnetized vortex, hydrodynamical shocks, and three-dimensional
collapse are presented, demonstrating the viability of an MHD code using GPM.
The characteristics of a GPM code are discussed and possible avenues for
further development and refinement are mentioned. We conclude with a view of
how GPM may complement other methods currently in development for the next
generation of computational astrophysics.


title:
VLT optical observations of V821 Ara(=GX339-4) in an extended "off"
  state

abstract:
  We report on low-resolution spectroscopy of GX339-4 during its current,
extended X-ray `off' state in May 2000 (r=20.1) obtained with the VLT Focal
Reducer/low dispersion Spectrograph (FORS1). Although we do not positively
detect the secondary star in GX339-4 we place an upper limit of 30 percent on
the contribution of a ``normal'' K-type secondary star spectrum to the observed
flux. Using this limit for the observed magnitude of the secondary star, we
find a lower limit for the distance of GX339-4 to be 5.6 kpc.


title: A source of high-velocity white dwarfs

abstract:
  We investigate whether the recently-observed population of high-velocity
white dwarfs can be derived from a population of binaries residing initially
within the thin disk of the Galaxy. In particular we consider binaries where
the primary is sufficiently massive to explode as a type II supernova. A large
fraction of such binaries are broken up when the primary then explodes as a
supernova owing to the combined effects of the mass loss from the primary and
the kick received by the neutron star on its formation. For binaries where the
primary evolves to fill its Roche lobe, mass transfer from the primary leads to
the onset of a common envelope phase during which the secondary and the core of
the primary spiral together as the envelope is ejected. Such binaries are the
progenitors of X-ray binaries if they are not broken up when the primary
explodes. For those systems which are broken up, a large number of the
secondaries receive kick velocities ~100 - 200 km/s and subsequently evolve
into white dwarfs. We compute trajectories within the Galactic potential for
this population of stars and relate the birthrate of these stars over the
entire Galaxy to those seen locally with high velocities relative to the LSR.
We show that for a reasonable set of assumptions concerning the Galactic
supernova rate and the binary population, our model produces a local number
density of high-velocity white dwarfs compatible with that inferred from
observations. We therefore propose that a population of white dwarfs
originating in the thin disk may make a significant contribution to the
observed population of high-velocity white dwarfs.


title: A Practical Relativistic Model of Microarcsecond Astrometry in Space

abstract:
  This paper is devoted to a practical model for relativistic reduction of
positional observations with an accuracy of 1 \muas which is expected to be
attained in the future space astrometry missions. All relativistic effects
which are caused by the gravitational field of the Solar system and which are
of practical importance for this accuracy level are thoroughly calculated and
discussed. The model includes relativistic modeling of the motion of observer,
modeling of relativistic aberration and gravitational light deflection as well
as a relativistic treatment of parallax and proper motion suitable for the
accuracy of 1 \muas. The model is formulated both for remote sources (stars,
quasars, etc.) and for Solar system objects (asteroids, etc.). The suggested
model is formulated within the framework of Parametrized Post-Newtonian
Formalism with parameters $\beta$ and $\gamma$. However, for general relativity
($\beta=\gamma=1$) the model is fully compatible with the IAU Resolutions
(2000) on relativity in celestial mechanics, astrometry and metrology. The
model is presented in a form suitable for implementation in a software system
for data processing or simulation. The changes which should be applied to the
model to attain the accuracy of 0.1 \muas are reviewed. Potentially important
relativistic effects caused by additional gravitational fields which are
generated outside of the Solar system are also briefly discussed.