title: Precise Chandra Localization of the Soft Gamma-ray Repeater SGR 1806-20

abstract:
  We present observations of the Soft Gamma-ray Repeater SGR 1806-20 taken with
the Chandra X-ray Observatory. We identify the X-ray counterpart of SGR 1806-20
based on detection of 7.5-s pulsations. Using three unrelated X-ray sources
(and USNO stars) as position references, we are able to determine that the SGR
is at alpha_{2000}=18h08m39.32s and delta_{2000}=-20o24'39.5", with rms
uncertainty of 0.3" in each coordinate. We find that SGR 1806-20 is located
within the 1-sigma error region determined by Interplanetary Network data and
is 14+/-0.5 arcsec distant from the non-thermal core of SNR G10.0-0.3,
excluding SGR 1806-20 as the origin of the core. We see evidence for a
significant deviation of the spin-down of SGR 1806-20 from its long-term trend,
demonstrating erratic spin-down behavior in this source similar to that seen in
other SGRs. Finally, we show that there is a broad X-ray halo surrounding SGR
1806-20 out to radii ~1' due to scattering in the interstellar medium.


title: Neutrino Annihilation between Binary Neutron Stars

abstract:
  We calculate the neutrino pair annihilation rate into electron pairs between
two neutron stars in a binary system. We present a closed formula for the
energy deposition rate at any point between the stars, where each neutrino of a
pair derives from each star, and compare this result to that where all
neutrinos derive from a single neutron star. An approximate generalization of
this formula is given to include the relativistic effects of gravity. We find
that this inter-star neutrino annihilation is a significant contributor to the
energy deposition between heated neutron star binaries. In particular, for two
neutron stars near their last stable orbit, inter-star neutrino annihilation
energy deposition is almost equal to that of single star energy deposition.


title: Quintessential perturbations during scaling regime

abstract:
  The scalar field with an exponential potential allows a scaling solution
where the the density of the field follows the density of the dominating fluid.
Such a scaling regime is often used as an important ingredient in many models
of quintessence. We analyse evolution of perturbations while the background
follows the scaling. As the results, the perturbed scalar field also scales
with the perturbed fluid, and the perturbations accompany the adiabatic as well
as the isocurvature mode between the fluid and the field.


title: Broad-band photometric evolution of star clusters

abstract:
  I briefly introduce a database of models that describe the evolution of star
clusters in several broad-band photometric systems. Models are based on the
latest Padova stellar evolutionary tracks - now including the alpha-enhanced
case and improved AGB models - and a revised library of synthetic spectra from
model atmospheres. As of today, we have revised isochrones in
Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Thuan-Gunn, and Washington
systems. Several other filter sets are included in a preliminary way, like
those used by the EIS and SDSS projects. The database contains also integrated
magnitudes of single-burst stellar populations and Monte-Carlo simulations that
show the stochastic dispersion of the colours as a function of cluster mass,
age, and metallicity. The models are useful for several kinds of studies,
including estimates of masses and ages of extragalactic star clusters observed
by means of broad-band photometry.


title: Correlated msec X-ray and optical emission from XTE J1118+480

abstract:
  We report on fast (msec) simultaneous observations in X-rays and optical
light of the black hole candidate XTE J1118+480, showing correlation on time
scales from 20msec to several seconds. The shape of the correlation is not
easily explained with existing models. We suggest that is is caused by optical
cyclosynchrotron emission in a dense, relatively slow outflow from the inner
regions of the accretion.


title:
Cosmological Aspects of Gamma-Ray Bursts: Luminosity Evolution and an
  Estimate of the Star Formation Rate at High Redshifts

abstract:
  Using 220 Gamma-Ray Burst (GRB) redshifts and luminosities derived from the
luminosity-variability relationship of Fenimore & Ramirez-Ruiz (2000), we show
that there exists a significant correlation between the GRB luminosity and
redshift. In particular, we find that the evolution of the average luminosity
can be parameterized as L ~ (1+z)^(1.4 +- 0.5), where z is the burst redshift.
We discuss the possible reasons behind this evolution and compare it to other
known sources that exhibit similar behavior. In addition, we use non-parametric
statistical techniques to independently estimate the distributions of the
luminosity and redshift of bursts, accounting for the evolution (in contrast to
previous studies which have assumed that the luminosity function is independent
of redshift). We present these distributions and discuss their implications.
Most significantly, we find a co-moving rate density of GRBs that continues to
increase to (1+z) ~ 10. From this estimate of the GRB rate density, we then use
the population synthesis codes of Fryer et al. (1999) to estimate the star
formation rate at high redshifts, based on different progenitor models of GRBs.
We find that no matter what the progenitor or population synthesis model, the
star formation rate increases or remains constant to very high redshifts (z ~
10).


title: The Accelerating Universe: A Gravitational Explanation

abstract:
  The problem of explaining the acceleration of the expansion of the universe
and the observational and theoretical difficulties associated with dark matter
and dark energy are discussed. The possibility that GR does not correctly
describe the large-scale structure of the universe is considered and an
alternative gravity theory is proposed as a possible resolution to the
problems.


title: Self-consistent axisymmetric Sridhar-Touma models

abstract:
  We construct phase-space distribution functions for the oblate, cuspy mass
models of Sridhar & Touma, which may contain a central point mass (black hole)
and have potentials of St\"ackel form in parabolic coordinates. The density in
the ST models is proportional to a power $r^{-\gamma}$ of the radius, with
$0<\gamma<1$. We derive distribution functions $f(E, L_z)$ for the scale-free
ST models (no black hole) using a power series of the energy $E$ and the
component $L_z$ of the angular momentum parallel to the symmetry axis. We use
the contour integral method of Hunter & Qian to construct $f(E, L_z)$ for ST
models with central black holes, and employ the scheme introduced by Dejonghe &
de Zeeuw to derive more general distribution functions which depend on $E$,
$L_z$ and the exact third integral $I_3$. We find that self-consistent two- and
three-integral distribution functions exist for all values $0 < \gamma < 1$.


title:
Observational Constraints on the Self Interacting Dark Matter Scenario
  and the Growth of Supermassive Black Holes

abstract:
  We consider the consequences of SIDM for a velocity dependent cross section
per unit mass. Accretion of SIDM onto seed black holes can produce supermassive
black holes that are too large for certain combinations of parameters,which is
used to obtain a new constraint on the dark matter interaction. Constraints due
to other considerations are presented and previous ones are generalized. The
black hole constraint is extremely sensitive to the slope \alpha, of the inner
density profile of dark halos. For the most probable value of \alpha=1.3, there
exists a narrow range in parameter space, such that all constraints are
satisfied. However, the adiabatic compression of the dark halo by baryons as
they cool and contract in normal galaxies yields a steeper cusp, \alpha=1.7.
This gives a tighter constraint, which would exclude SIDM as a possible
solution to the purported problems with CDM in the absence of other dynamical
processes. Nevertheless, SIDM with parameters consistent with this stronger
constraint, can explain the ubiquity of supermassive black holes in the centers
of galaxies. A ``best fit'' model is presented which reproduces the
supermassive black hole masses and their observed correlations with the
velocity dispersion of the host bulges. Specifically, the fourth power
dependence of black hole mass on velocity dispersion is a direct consequence of
the power spectrum having an index of n=-2. Although the dark matter collision
rates for this model are too small to directly remedy problems with CDM,
mergers between dark halos harboring supermassive black holes at high redshift
could ameliorate the cuspy halo problem. This scenario also explains the lack
of comparable supermassive black holes in bulgeless galaxies like M33.


title: CMB Analysis

abstract:
  We describe the subject of Cosmic Microwave Background (CMB) analysis - its
past, present and future. The theory of Gaussian primary anisotropies, those
arising from linear physics operating in the early Universe, is in reasonably
good shape so the focus has shifted to the statistical pipeline which confronts
the data with the theory: mapping, filtering, comparing, cleaning, compressing,
forecasting, estimating. There have been many algorithmic advances in the
analysis pipeline in recent years, but still more are needed for the forecasts
of high precision cosmic parameter estimation to be realized. For secondary
anisotropies, those arising once nonlinearity develops, the computational state
of the art currently needs effort in all the areas: the Sunyaev-Zeldovich
effect, inhomogeneous reionization, gravitational lensing, the Rees-Sciama
effect, dusty galaxies. We use the Sunyaev-Zeldovich example to illustrate the
issues. The direct interface with observations for these non-Gaussian signals
is much more complex than for Gaussian primary anisotropies, and even more so
for the statistically inhomogeneous Galactic foregrounds. Because all the
signals are superimposed, the separation of components inevitably complicates
primary CMB analyses as well.


title:
The Location of the Nucleus and the Morphology of Emission-Line Regions
  in NGC 1068

abstract:
  This paper presents NICMOS images of the nucleus and emission line regions in
NGC 1068. The location of the nucleus relative to the emission line features is
established and the physics underlying the morphology is discussed.


title: The High Resolution X-ray Spectrum of SS 433 using the Chandra HETGS

abstract:
  We present observations of SS 433 using the Chandra High Energy Transmission
Grating Spectrometer. Many emission lines of highly ionized elements are
detected with the relativistic blue and red Doppler shifts. The lines are
measurably broadened to 1700 km/s (FWHM) and the widths do not depend
significantly on the characteristic emission temperature, suggesting that the
emission occurs in a freely expanding region of constant collimation with
opening angle of 1.23 +/- 0.06 deg. The blue shifts of lines from low
temperature gas are the same as those of high temperature gas within our
uncertainties, again indicating that the hottest gas we observe to emit
emission lines is already at terminal velocity. Fits to the emission line
fluxes give a range of temperatures in the jet from 5e6 to 1e8 K. We derive the
emission measure as a function of temperature for a four component model that
fits the line flux data. Using the density sensitive Si XIII triplet, the
characteristic electron density is 1e14 cm^{-3}, where the gas temperature is
about 1.3e7 K. Based on an adiabatic expansion model of the jet, the electron
densities drop from ~2e15 to 4e13 cm^{-3} at distances of 2e10 to 2e11 cm from
the apex of the jet cone. The jet mass outflow rate is 1.5e-7 Msun / yr. The
kinetic power is 3.2e38 erg/s, which is x1000 larger than the unabsorbed 2-10
keV X-ray luminosity. The bremsstrahlung emission associated with the lines can
account for the entire continuum; we see no direct evidence for an accretion
disk. The image from zeroth order shows extended emission at a scale of ~2",
aligned in the general direction of the radio jets.


title:
Dynamo action by differential rotation in a stably stratified stellar
  interior

abstract:
  Magnetic fields can be created in stably stratified (non-convective) layers
in a differentially rotating star. A magnetic instability in the toroidal field
(wound up by differential rotation) replaces the role of convection in closing
the field amplification loop. Tayler instability is likely to be the most
relevant magnetic instability. A dynamo model is developed from these
ingredients, and applied to the problem of angular momentum transport in
stellar interiors. It produces a prodominantly horizontal field. This dynamo
process might account for the observed pattern of rotation in the solar core.


title:
Double-Peaked X-Ray Lines from the Oxygen/Neon-Rich Accretion Disk in
  4U1626-67

abstract:
  We report on a 39 ks observation of the 7.7-s low-mass X-ray binary pulsar
4U1626-67 with the High Energy Transmission Grating Spectrometer (HETGS) on the
Chandra X-Ray Observatory. This ultracompact system consists of a
disk-accreting magnetic neutron star and a very low mass, hydrogen-depleted
companion in a 42-min binary. We have resolved the previously reported Ne/O
emission line complex near 1 keV into Doppler pairs of broadened (2500 km/s
FWHM) lines from highly ionized Ne and O. In most cases, the blue and red line
components are of comparable strength, with blueshifts of 1550-2610 km/s and
redshifts of 770-1900 km/s. The lines appear to originate in hot (10^6 K),
dense material just below the X-ray-heated skin of the outer Keplerian
accretion disk, or else possibly in a disk wind driven from the pulsar's
magnetopause. The observed photoelectric absorption edges of Ne and O appear
nearly an order of magnitude stronger than expected from interstellar material
and are likely formed in cool, metal-rich material local to the source. Based
on the inferred local abundance ratios, we argue that the mass donor in this
binary is probably the 0.02 M_sun chemically fractionated core of a C-O-Ne or
O-Ne-Mg white dwarf which has previously crystallized.


title: Detectability of Microwave Background Polarization

abstract:
  [NOTE: Previous versions of this paper (both on astro-ph and published in
Phys. Rev. D) contain results that are in error. The power spectra C_l were
normalized incorrectly by a factor of 2 pi. All observing times in
detector-years in those versions are too large by a factor of 2 pi. The main
place these numbers appear is on the vertical axes of Figures 4 and 5. Note
that because all calculations were based on the same power spectra, all
conclusions pertaining to comparisons of different techniques remain unchanged.
This error has been corrected in the present version of the paper. An erratum
is being sent to Phys. Rev. D. I apologize for the error.]
  Using a Fisher-matrix formalism, we calculate the required sensitivities and
observing times for an experiment to measure the amplitudes of both E and B
components as a function of sky coverage, taking full account of the fact that
the two components cannot be perfectly separated in an incomplete sky map. We
also present a simple approximation scheme that accounts for mixing of E and B
components in computing predicted errors in the E-component power spectrum
amplitude. In an experiment with small sky coverage, mixing of the two
components increases the difficulty of detecting the subdominant B component by
a factor of two or more in observing time; however, for larger survey sizes the
effect of mixing is less pronounced. Surprisingly, mixing of E and B components
can enhance the detectability of the E component by increasing the effective
number of independent modes that probe this component


title: On physics of the Poynting-Robertson effect

abstract:
  Detailed discussion of university textbook statements (Harwit 1988)
concerning the Poynting-Robertson effect (P-R effect) is presented. Discussion
is concentrated on better physical understanding of the P-R effect. References
to complete correct equation of motion for real dust particle are also
presented.


title: Electromagnetic Radiation and Motion of Really Shaped Particle

abstract:
  Relativistically covariant form of equation of motion for real particle
(neutral in charge) under the action of electromagnetic radiation is derived.
Various formulations of the equation of motion in the proper frame of reference
of the particle are used.
  Main attention is devoted to the reformulation of the equation of motion in
the general frame of reference, e. g., in the frame of reference of the source
of electromagnetic radiation. This is the crucial form of equation of motion in
applying it to motion of particles (cosmic dust, asteroids, ...) in the
Universe if electromagnetic radiation acts on the particles.
  General relativistic equation of motion is presented.


title: Ages of S0 and elliptical galaxies in the Coma cluster

abstract:
  The ages of stellar populations in 52 elliptical and S0 galaxies in the Coma
cluster are investigated using a new spectroscopic sample. More than 40% of the
S0s are found to have experienced recent star formation in their central
regions during the last ~5 Gyrs, while such activity is absent in the
ellipticals. Galaxies in this sample have absolute magnitudes in the range
-20.5 < M_B < -17.5, and the fraction of S0 galaxies with recent star formation
is higher at fainter luminosities. The observed luminosity range of S0 galaxies
with signs of recent star formation activity is consistent with them being the
descendants of typical star-forming spirals at intermediate redshift whose star
formation has been halted as a consequence of the dense environment.


title:
Negative intensity patches in angular variations of CMB as a probe of
  the period of reionization

abstract:
  The observational tests for the period of reionization of the universe are
discussed. We show that this period can be observed as {\it negative} intensity
patches of the CMB radiation with the amplitude $\delta T/T\sim 10^{-5}$ and
the angular sizes $\theta_T\sim$10 angular seconds in range of the wavelength
0.1 cm$\leq\lambda\leq$1 cm. The expected number density and frequency
dependence of the amplitude permit to recognize this effect and to discriminate
it from the noise. This method applied to the small scale variations of CMB
temperature complements well the traditional spectral approach.
  The number density and the amplitude of observed 'negative' intensity patches
depend upon the redshift of reionization that allow to estimate roughly this
redshift. The ionized bubbles formed just before the period of reionization
could also be seen as the highest peaks. The expected results are sensitive to
the Jeans scale at the period of reionization, to the small scale shape of the
primordial power spectrum and to the mass of dark matter particles.


title:
Parallax Microlensing Events in the OGLE II Database Toward the Galactic
  Bulge

abstract:
  We present a systematic search for parallax microlensing events among a total
of 512 microlensing candidates in the OGLE II database for the 1997-1999
seasons. We fit each microlensing candidate with both the standard microlensing
model and also a parallax model that accounts for the Earth's motion around the
Sun. We then search for the parallax signature by comparing the chi^2 of the
standard and parallax models. For the events which show a significant
improvement, we further use the `duration' of the event and the signal-to-noise
ratio as criteria to separate true parallax events from other noisy
microlensing events. We have discovered one convincing new candidate,
sc33_4505, and seven other marginal cases. The convincing candidate (sc33_4505)
is caused by a slow-moving, and likely low-mass, object, similar to other known
parallax events. We found that irregular sampling and gaps between observing
seasons hamper the recovery of parallax events. We have also searched for
long-duration events that do not show parallax signatures. The lack of parallax
effects in a microlensing event puts a lower-limit on the Einstein radius
projected onto the observer plane, which in turn imposes a lower limit on the
lens mass divided by the relative lens-source parallax. Most of the constraints
are however quite weak.


title:
3-Gyr-old Globular Clusters in the Merger Remnant NGC 1316: Implications
  for the Fate of Globular Clusters Formed During Gas-rich Galaxy Mergers

abstract:
  The giant early-type merger remnant galaxy NGC 1316 is an ideal probe for
studying the long-term effects of a major merger on its globular cluster (GC)
system, given its spectroscopically derived merger age of 3 Gyr which we
reported in a recent paper. Here we report several pieces of photometric
evidence showing that the second-generation GCs in NGC 1316 are at an
evolutionary phase in between that of luminous GCs found in younger merger
remnants such as (e.g.) NGC 7252 and that of `red' GCs found in `normal, old'
ellipticals. The observation that massive, second-generation GCs formed during
major mergers can survive for at least 3 Gyr provides strong evidence that
these clusters can have `normal' mass functions including low-mass stars, and
hence that they can survive to reach `old age' similar to those of `normal'
ellipticals.


title:
Mapping Metal-Enriched High Velocity Clouds to Very Low HI Column
  Densities

abstract:
  Our galaxy is the nearest known quasar absorption line system, and it
uniquely provides us with an opportunity to probe multiple lines of sight
through the same galaxy. This is essential for our interpretations of the
complex kinematic profiles seen in the MgII absorption due to lines of sight
through intermediate redshift galaxies. The Milky Way halo has never been
probed for high velocity clouds below the 21-cm detection threshold of
N(HI)~10^18 cm-2. Through a survey of MgII absorption looking toward the
brightest AGNs and quasars, it will be possible to reach down a few orders of
magnitude in HI column density. The analogs to the high velocity components of
the MgII absorption profiles due to intermediate redshift galaxies should be
seen. We describe a program we are undertaking, and present some preliminary
findings.


title:
The Effects of Photoionization on Galaxy Formation - I: Model and
  Results at z=0

abstract:
  We develop a coupled model for the evolution of the global properties of the
intergalactic medium (IGM) and the formation of galaxies, in the presence of a
photoionizing background due to stars and quasars. We use this model to predict
the thermodynamic history of the IGM when photoionized by galaxies forming in a
cold dark matter (CDM) universe. The evolution of the galaxies is calculated
using a semi-analytical model, including a detailed treatment of the effects of
tidal stripping and dynamical friction on satellite galaxies orbiting inside
larger dark matter halos. We include in the model the negative feedback on
galaxy formation from the photoionizing background. Photoionization inhibits
galaxy formation in low-mass dark matter halos in two ways: (i) heating of the
IGM and inhibition of the collapse of gas into dark halos by the IGM pressure,
and (ii) reduction in the radiative cooling of gas within halos. The result of
our method is a self-consistent model of galaxy formation and the IGM. The IGM
is reheated twice (during reionization of HI and HeII), and we find that the
star formation rate per unit volume is slightly suppressed after each episode
of reheating. We find that galaxies brighter than L_* are mostly unaffected by
reionization, while the abundance of faint galaxies is significantly reduced,
leading to present-day galaxy luminosity functions with shallow faint end
slopes, in good agreement with recent observational data. Reionization also
affects other properties of these faint galaxies, in a readily understandable
way.


title:
The Effects of Photoionization on Galaxy Formation - II: Satellites in
  the Local Group

abstract:
  We use a self-consistent model of galaxy formation and the evolution of the
intergalactic medium to study the effects of the reionization of the universe
at high redshift on the properties of satellite galaxies like those seen around
the Milky Way. Photoionization suppresses the formation of small galaxies, so
that surviving satellites are preferentially those that formed before the
universe reionized. As a result, the number of satellites expected today is
about an order of magnitude smaller than the number inferred by identifying
satellites with subhalos in high-resolution simulations of the dark matter. The
resulting satellite population has an abundance and a distribution of circular
velocities similar to those observed in the Local Group. We explore many other
properties of satellite galaxies, including their gas content, metallicity and
star formation rate, and find generally good agreement with available data. Our
model predicts the existence of many as yet undetected satellites in the Local
Group. We quantify their observability in terms of their apparent magnitude and
surface brightness and also in terms of their constituent stars. A
near-complete census of the Milky Way's satellites would require imaging to
V~20 and to a surface brightness fainter than 26 V-band magnitudes per square
arcsecond. Satellites with integrated luminosity V=15 should contain of order
100 stars brighter than B=26, with central stellar densities of a few tens per
square arcminute. Discovery of a large population of faint satellites would
provide a strong test of current models of galaxy formation.


title: The Nature of [Ar III] Bright Knots in the Crab Nebula

abstract:
  The kinematic and morphological properties of a string of [Ar III] bright
knots in the Crab Nebula are examined using 1994 - 1999 HST WFPC-2 images of
the remnant. We find that five southern [Ar III] bright knots exhibit ordinary
radial motions away from the nebula's center of expansion with magnitudes
consistent with their projected radial displacements. These results do not
support the suggestion by MacAlpine et al.(1994) that these knots might be
moving rapidly away from the Crab pulsar due to a collimated wind. The HST
images also do not show that the [Ar III] knots have unusual morphologies
relative to other features in the remnant. Our proper motion results, when
combined with radial velocity estimates, suggest these knots have relatively
low space velocities implying relatively interior remnant locations thus
placing them closer to the ionizing radiation from the Crab's synchrotron
nebula. This might lead to higher knot gas temperatures thereby explaining the
knots' unusual line emission strengths as MacAlpine et al.(1994) suspected.


title: Multi(Scale)Gravity: A Telescope for the Micro-World

abstract:
  This is a talk presented at XXXVIth Rencontres de Moriond, ElectroWeak
Interactions and Unified Theories, March 2001. A short review of modern status
of multigravity, i.e. modification of gravity at both short and large distances
is given.


title: Structural Properties of Massive Young Clusters

abstract:
  We have retrieved multicolor WFPC2/HST data from the STScI archive for 27
nearby Massive (>= 3x10^4 M_Sun) Young (< 20 Myr) star Clusters (MYCs). The
data represents the most-complete-to-date sample of clearly resolved MYCs. We
have analyzed their structural properties and have found that they can be
classified as either Super Star Clusters (SSCs) or as Scaled OB Associations
(SOBAs). SSCs have a compact core possibly surrounded by a halo while SOBAs
have no core. A morphological sequence can be established from SSCs with weak
halos to SSCs with strong halos to SOBAs and we propose that this is linked to
the original mass distribution of the parent giant molecular clouds. Our
results indicate that a significant fraction of the stars in MYCs dissipate on
timescales of 10 Gyr or less due to the extended character of some of the
clusters. Also, SSCs with ages < 7 Myr have smaller cores on average than those
with ages > 7 Myr, confirming predictions of numerical simulations with mass
loss.


title:
Recent Dynamical Relaxation of Galaxy Clusters: Evidence for a
  Low-$\Omega_m$ Universe

abstract:
  We argue that there has been substantial evolution in the ellipticity of rich
galaxy clusters between 0 < z < 0.1, and suggest that this is additional
evidence for a low matter-density Universe.


title: Where is the Neutral Atomic Gas in Hickson Groups?

abstract:
  We have analyzed the total HI contents of 72 Hickson compact groups of
galaxies (HCGs) and the detailed spatial distributions and kinematics of HI
within a subset of 16 groups using the high angular resolution observations
obtained with the VLA in order to investigate a possible evolutionary scenario
for these densest systems in the present day galaxy hierarchy. For the more
homogeneous subsample of 48 groups, we found a mean HI deficiency of DefHI = 40
(40% of the expected HI for the LBs and morphological types of the member
galaxies). The individual galaxies show larger degrees of deficiency than the
groups globally, DefHI = 0.62 (24% of the expected HI), due in most cases to
efficient gas stripping from individual galaxies into the group environment
visible in the VLA maps. The degree of deficiency is found to be similar to the
central galaxies of Virgo and Coma cluster, and Coma I group, in spite of the
significantly different characteristics of these environments. Phase
transformation of the HI should explain the deficiency. The detection rate of
HCGs at X-ray wavelengths is larger for HI deficient groups. In the
evolutionary scenario we propose, the amount of detected HI would decrease
further with evolution, by continuous tidal stripping and/or heating. The H2
content also tends to be lower than expected for the galaxies in HI deficient
groups, this may suggest that the HI stripping by frequent tidal interaction
breaks the balance between the disruption of molecular clouds by star formation
and the replenishment from the ambient HI.


title:
Compound gravitational lensing as a probe of dark matter substructure
  within galaxy halos

abstract:
  We show how observations of multiply-imaged quasars at high redshift can be
used as a probe of dark matter clumps (subhalos with masses ~ 10^9 solar
masses) within the virialized extent of more massive lensing halos. A large
abundance of such satellites is predicted by numerical simulations of galaxy
formation in cold dark matter (CDM) cosmogonies. Small-scale structure within
galaxy halos affects the flux ratios of the images without appreciably changing
their positions. We use numerical simulations to quantify the effect of dark
matter substructure on the distribution of magnifications, and find that the
magnification ratio of a typical image pair will deviate significantly from the
value predicted by a smooth lensing potential if, near the Einstein radius,
only a few percent of the lens surface density is contained in subhalos. The
angular size of the continuum source dictates the range of subclump masses that
can have a detectable effect: to avoid confusion with gravitational
microlensing caused by stars in the lens galaxy, the background source must be
larger than the optical continuum-emitting region of a QSO. We also find that
substructure will cause distortions to images on milli-arcsecond scales and
bias the distribution of QSO magnification ratios -- two other possible methods
of detection.


title:
The Ursa Major Cluster of Galaxies. V ; HI Rotation Curve Shapes and the
  Tully-Fisher Relations

abstract:
  The Tully-Fisher relations for a complete sample of spirals in the Ursa Major
cluster is investigated. The merits of combining B, R, I and K' photometry with
HI rotation curves (RCs) have been exploited. In addition to the corrected HI
global profile widths W_{R,I}^i, the HI RCs allow direct measurements of the
maximum rotation Vmax and the amplitudes Vflat of the outer flat parts. The
dynamical state of the gas disks could also be determined in detail. For large
galaxy samples, the M^{b,i}_R - Log(W_{R,I}^i) correlation in conjunction with
strict selection criteria is preferred for distance determinations with a 7%
accuracy. Galaxies with rising RCs at the last measured point lie
systematically on the low velocity side of the TF-relation. Galaxies with
partly declining RCs (Vmax>Vflat) tend to lie on the high velocity side when
using W_{R,I}^i or Vmax. These trends are eliminated when Vflat is used. The
M^{b,i}_B - Log(2Vflat) residuals correlate consistently with morphology,
color, surface brightness and gas mass fraction. These correlations are absent
for the near-IR M^{b,i}_K' - Log(2Vflat) residuals. The tightest correlation
(Xred=1.1) is found for the M^{b,i}_K' - Log(2Vflat) relation with a slope of
-11.3 +/- 0.5 and a total scatter of 0.26^m with a most likely intrinsic
scatter of zero. The tightness of the near-IR correlation is preserved when
converting it into a baryonic TF-relation which has a slope of -10.0 for
(Mgas/L_K')=1.6 while a zero intrinsic scatter remains most likely. The
tightness of the near-IR and baryonic correlations suggests that the
TF-relation reflects a correlation between the dark matter halo mass, indicated
by Vflat, and the total baryonic mass Mbar where Mbar~Vflat^4. The distribution
of the baryons inside halos of similar mass is irrelevant for this relation.


title: Temporal variations of solar rotation rate at high latitudes

abstract:
  Frequency splitting coefficients from Global Oscillation Network Group (GONG)
and Michelson Doppler Imager (MDI) observations covering the period 1995--2001
are used to study temporal variations in the solar rotation rate at high
latitudes. The torsional oscillation pattern in the Sun is known to penetrate
to a depth of about $0.1R_\odot$ with alternate bands of faster and slower
rotating plasma. At lower latitudes the bands move towards equator with time.
At higher latitudes, however, the bands appear to move towards the poles. This
is similar to the observed pole-ward movement of large scale magnetic fields at
high latitudes. This also supports theoretical results of pole-ward moving
bands at high latitudes in some mean field dynamo models. The polar rotation
rate is found to decrease between 1995 and 1999 after which it has started
increasing.


title:
Ring diagram analysis of the characteristics of solar oscillation modes
  in active regions

abstract:
  The presence of intense magnetic fields in and around sunspots is expected to
modify the solar structure and oscillation frequencies. Applying the ring
diagram technique to data from the Michelson Doppler Imager (MDI) on board the
Solar and Heliospheric Observatory (SOHO), we analyze the characteristics of
high-degree f and p modes near active regions and compare them with the
characteristics of the modes in quiet regions. As expected from earlier
results, the f- and p-mode frequencies of high degree modes are found to be
significantly larger in magnetically active regions. In addition, we find that
the power in both f and p modes is lower in active regions, while the widths of
the peaks are larger, indicating smaller lifetimes. We also find that the
oscillation modes are more asymmetric in active regions than those in quiet
regions, indicating that modes in active regions are excited closer to the
surface. While the increase in mode frequency is monotonic in frequency, all
other characteristics show more complex frequency dependences.


title:
The 1 Ms Chandra Survey of the HDF-N: Populations at the Faintest X-ray
  Fluxes

abstract:
  The Chandra Deep Field-North survey, which has at its center the Hubble Deep
Field-North, has reached an exposure of 1 Ms and is now available to the public
for analysis. This great astronomical resource will soon be released to the
community in the form of a catalog paper with accurate X-ray fluxes in four
bands and astrometry good to approximately 0.6-1.2 arcseconds over the entire
ACIS-I field.
  The scientific focus of this contribution is the population of X-ray sources
detected at X-ray fluxes below the faintest detection limits of X-ray
observatories such as ROSAT and ASCA. These include fairly normal and
star-forming galaxies out to z=2, starburst galaxies from z=2-4 and possibly
very high redshift (z> 6) AGN. The exciting new prospects for studying these
populations in the X-ray band are discussed.


title: Diamagnetic Screening of the Magnetic Field in Accreting Neutron Stars

abstract:
  A possible mechanism for screening of the surface magnetic field of an
accreting neutron star, by the accreted material, is investigated. We model the
material flow in the surface layers of the star by an assumed 2-D velocity
field satisfying all the physical requirements. Using this model velocity we
find that, in the absence of magnetic buoyancy, the surface field is screened
(submergence of the field by advection) within the time scale of material flow
of the top layers. On the other hand, if magnetic buoyancy is present, the
screening happens over a time scale which is characteristic of the slower flow
of the deeper (hence, denser) layers. For accreting neutron stars, this longer
time scale turns out to be about $10^5$ years, which is of the similar order as
the accretion time scale of most massive X-ray binaries.


title:
Gravitational instability of finite isothermal spheres in general
  relativity. Analogy with neutron stars

abstract:
  We investigate the effects of relativity on the gravitational instability of
finite isothermal gaseous spheres. In the first part of the paper, we treat the
gravitational field within the framework of Newtonian mechanics but we use a
relativistic equation of state in the condition of hydrostatic equilibrium. In
the second part of the paper, we study the full general relativistic problem
for a gas described by an equation of state $p=q\epsilon$ such that the
pressure is proportional to the energy density (``isothermal'' distribution).
For $q=1/3$, this equation of state describes the core of neutron stars. The
mass-density diagram displays some damped oscillations and there exists a
critical value of mass-energy above which no equilibrium state is possible. We
show analytically that the mass peaks are associated with new modes of
instability. These results are strikingly similar to those obtained by Antonov
[Vest. Leningr. Gos. Univ. 7, 135 (1962)] and Lynden-Bell & Wood (1968) for a
classical isothermal gas. Our study completes the analogy between isothermal
spheres and neutron stars investigated by Yabushita [MNRAS 167, 95 (1974)].


title: Detection of several daemon populations in Earth-crossing orbits

abstract:
  Detection of negative daemons, DArk Electric Matter Objects, viz. Planckian
supermassive (~2*10^-5 g) particles, whose population has been detected in
March 2000 to populate near-Earth, almost circular, heliocentric orbits
(NEACHOs), is being continued. The NEACHO objects hit the Earth with a velocity
~10-15 km/s. The results of these and new experiments (April-June, 2001) are
now processed taking into account the scintillation shape depending on the
magnitude and sign of the velocity of the daemons crossing our detector. The
data accumulated during the time of the experiment and processed in this way
reveal also the presence of (1) a high-velocity (~35-50 km/s) daemon population
whose objects can be related to a population in the Galactic disk and/or that
in strongly elongated, Earth-crossing heliocentric orbits (SEECHOs), as well as
(2) a low-velocity (~3-10 km/s) population in geocentric Earth-surface-crossing
orbits (GESCOs), whose objects traverse repeatedly the Earth to suffer a
decrease in velocity by ~30-40% in a month in the process. An evolutionary
relation between all these three (four?) populations is discussed. Assumptions
concerning their manifestations in further observations are put forward. An
analysis of possible interaction processes of daemons, which may have different
velocities and directions of motion, with the detector components [ZnS(Ag)
layers, 0.3-mm thick tinned-iron sheets etc.] on the atomic (emission of Auger
electrons) and nuclear (nucleon evaporation from a nucleus excited in the
capture and, subsequently, the decay of its protons) levels has permitted
estimation of some characteristic times. In particular, the decay time of a
daemon-containing proton is ~10^-6 s.


title:
Analysis of astronomical data from optical superconducting tunnel
  junctions

abstract:
  Currently operating optical superconducting tunnel junction (STJ) detectors,
developed in ESA, can simultaneously measure the wavelength (delta lambda = 50
nm at 500 nm) and arrival time (to within ~5 micros) of individual photons in
the range 310-720 nm with an efficiency of ~70%, and with count rates of order
5,000 photons per second per junction. A number of STJ junctions placed in an
array format generates four-dimensional data: photon arrival time, energy, and
array element (X,Y). Such STJ cameras are ideally suited for, e.g., high time-
resolution spectrally-resolved monitoring of variable sources or low-resolution
spectroscopy of faint extragalactic objects.
  The reduction of STJ data involves detector efficiency correction, atmo-
spheric extinction correction, sky background subtraction, and, unlike that of
data from CCD-based systems, a more complex energy calibration, barycentric
arrival time correction, energy range selection, and time binning; these steps
are, in many respects, analogous to procedures followed in high-energy astro-
physics. This paper discusses these calibration steps in detail using a repre-
sentative observation of the cataclysmic variable UZ Fornacis; these data were
obtained with ESA's S-Cam2 6x6-pixel device. We furthermore discuss issues re-
lated to telescope pointing and guiding, differential atmospheric refraction,
and atmosphere-induced image motion and image smearing (`seeing') in the focal
plane. We also present a simple and effective recipe for extracting the evolu-
tion of atmospheric seeing with time from any science exposure, and discuss a
number of caveats in the interpretation of STJ-based time-binned data, such as
light curves and hardness ratio plots.


title: Deep Studies of the Resolved Stellar Populations in the Outskirts of M31

abstract:
  We discuss the first results from ongoing studies of the resolved stellar
populations in the outskirts of our nearest large neighbour, M31. Deep
HST/WFPC2 archival observations are used to construct colour-magnitude-diagrams
which reach well below the horizontal branch at selected locations in the outer
disk and halo, while a panoramic ground-based imaging survey maps spatial
density variations through resolved star counts to a projected radius of ~50
kpc.


title:
Neural Networks as a tool for parameter estimation in mega-pixel data
  sets

abstract:
  We present a neural net algorithm for parameter estimation in the context of
large cosmological data sets. Cosmological data sets present a particular
challenge to pattern-recognition algorithms since the input patterns (galaxy
redshift surveys, maps of cosmic microwave background anisotropy) are not fixed
templates overlaid with random noise, but rather are random realizations whose
information content lies in the correlations between data points. We train a
``committee'' of neural nets to distinguish between Monte Carlo simulations at
fixed parameter values. Sampling the trained networks using additional Monte
Carlo simulations generated at intermediate parameter values allows accurate
interpolation to parameter values for which the networks were never trained.
The Monte Carlo samples automatically provide the probability distributions and
truth tables required for either a frequentist or Bayseian analysis of the one
observable sky. We demonstrate that neural networks provide unbiased parameter
estimation with comparable precision as maximum-likelihood algorithms but
significant computational savings. In the context of CMB anisotropies, the
computational cost for parameter estimation via neural networks scales as
$N^{3/2}$. The results are insensitive to the noise levels and sampling schemes
typical of large cosmological data sets and provide a desirable tool for the
new generation of large, complex data sets.


title: Pulsar braking index: A test of emission models?

abstract:
  Pulsar braking torques due to magnetodipole radiation and to unipolar
generator are considered, which results in braking index being less than 3 and
could be employed to test the emission models. Improved equations to obtain
pulsar braking index and magnetic field are presented if we deem that the
rotation energy loss rate equals to the sum of the dipole radiation energy loss
rate and that of relativistic particles powered by unipolar generator. The
magnetic field calculated by conventional way could be good enough but only
modified by a factor of ~0.6 at most. Both inner and outer gaps may coexist in
the magnetosphere of the Vela pulsar.


title:
Newtonian hydrodynamics of the coalescence of black holes with neutron
  stars IV: Irrotational binaries with a soft equation of state

abstract:
  We present the results of three-dimensional hydrodynamical simulations of the
final stages of inspiral in a black hole-neutron star binary, when the
separation is comparable to the stellar radius. We use a Newtonian Smooth
Particle Hydrodynamics (SPH) code to model the evolution of the system, and
take the neutron star to be a polytrope with a soft (adiabatic index G=2 and
G=5/3) equation of state and the black hole to be a Newtonian point mass. The
only non-Newtonian effect we include is a gravitational radiation back reaction
force, computed in the quadrupole approximation for point masses. We use
irrotational binaries as initial conditions for our dynamical simulations,
which are begun when the system is on the verge of initiating mass transfer and
followed for approximately 23 ms. For all the cases studied we find that the
star is disrupted on a dynamical time-scale, and forms a massive (the disc mass
is approximately 0.2 solar masses) accretion torus around the spinning (Kerr)
black hole. The rotation axis is clear of baryons (less than 1.e-5 solar masses
within 10 degrees) to an extent that would not preclude the formation of a
relativistic fireball capable of powering a cosmological gamma ray burst. Some
mass (the specific amount is sensitive to the stiffness of the equation of
state) may be dynamically ejected from the system during the coalescence and
could undergo r-process nucleosynthesis. We calculate the waveforms,
luminosities and energy spectra of the gravitational radiation signal and show
how they reflect the global outcome of the coalescence process.


title: The mass of the neutron star in Vela X-1

abstract:
  We measured the radial-velocity curve of HD77581, the B-supergiant companion
of the X-ray pulsar Vela X-1, using 183 high-resolution optical spectra
obtained in a nine-month campaign. We derive radial-velocity amplitudes for
different lines and wavelength regions, and find all are consistent with each
other, as well as with values found in previous analyses. We show that one
apparent exception, an anomalously low value derived from ultra-violet spectra
obtained with the IUE, was due to an error in the analysis procedures. We
re-analyse all IUE spectra, and combine the resulting velocities with the ones
derived from the new optical spectra presented here, as well as those derived
from optical spectra published earlier. As in previous analyses, the radial
velocities show strong deviations from those expected for a pure Keplerian
orbit. The deviations likely are related to the pronounced line-profile
variations seen in our spectra. It turns out that systematic deviations as a
function of orbital phase are present. Our best estimate of the radial-velocity
amplitude, Kopt = 21.7 +/- 1.6 km/s, has an uncertainty not much reduced to
that found in previous analyses, in which the systematic deviations had not
been taken into account. Combining our velocity amplitude with the accurate
orbital elements of the X-ray pulsar, we infer M_ns sin^3i = 1.78 +/- 0.15
Msun.


title:
On the Formation of Galaxy Halos: Comparing NGC 5128 and the Local Group
  Members

abstract:
  The metallicity distribution function (MDF) for the old red-giant stars in
the halo of NGC 5128, the nearest giant elliptical galaxy, is virtually
identical with the MDF for the old-disk stars in the LMC and also strongly
resembles the halo MDF in M31. These galaxies all have high mean halo
metallicities (<m/H> ~ -0.4$) with very small proportions of low-metallicity
stars. These observations reinforce the view that metal-rich halos are quite
normal for large galaxies of all types. Such systems are unlikely to have built
up by accretion of pre-existing, gas-free small satellite galaxies, unless
these satellites had an extremely shallow mass distribution (d log N / d log M
> -1). We suggest that the halo of NGC 5128 is more likely to have assembled
from hierarchical merging of gas-rich lumps in which the bulk of star formation
took place during or after the merger stage.


title: The proximity effect in a close group of QSOs

abstract:
  We present an analysis of the proximity effect in a sample of ten 2 A
resolution QSO spectra of the Ly alpha forest at <z> = 2.9. Rather than
investigating variations in the number density of individual absorption lines
we employ a novel technique that is based on the statistics of the transmitted
flux itself. We confirm the existence of the proximity effect at the > 99 per
cent confidence level. We derive a value for the mean intensity of the
extragalactic background radiation at the Lyman limit of J = 3.5^{+3.5}_{-1.3}
x 10^{-22} ergs/s/cm^2/Hz/sr. This value assumes that QSO redshifts measured
from high ionization lines differ from the true systemic redshifts by ~800
km/s. We find evidence at a level of 2.6 sigma that the significance of the
proximity effect is correlated with QSO Lyman limit luminosity. Allowing for
known QSO variability the significance of the correlation reduces to 2.1 sigma.
The QSOs form a close group on the sky and the sample is thus well suited for
an investigation of the foreground proximity effect, where the Ly alpha forest
of a background QSO is influenced by the UV radiation from a nearby foreground
QSO. From the complete sample we find no evidence for the existence of this
effect, implying either that J > 20 x 10^{-22} ergs/s/cm^2/Hz/sr or that QSOs
emit at least a factor of 1.4 less ionizing radiation in the plane of the sky
than along the line of sight to Earth. We do however find one counter-example.
Our sample includes the fortunate constellation of a foreground QSO surrounded
by four nearby background QSOs. These four spectra all show underdense
absorption within +/-3000 km/s of the redshift of the foreground QSO.


title: Phase-resolved Crab Studies with a Cryogenic TES Spectrophotometer

abstract:
  We are developing time- and energy-resolved near-IR/optical/UV photon
detectors based on sharp superconducting-normal transition edges in thin films.
We report observations of the Crab pulsar made during prototype testing at the
McDonald 2.7m telescope with a fiber-coupled transition-edge sensor (TES)
system. These data show substantial (d[alpha]~0.3), rapid variations in the
spectral index through the pulse profile, with a strong phase-varying IR break
across our energy band. These variations correlate with X-ray spectral
variations, but no single synchrotron population can account for the full
Spectral Energy Distribution (SED). We also describe test
spectrophotopolarimetry observations probing the energy dependence of the
polarization sweep; this may provide a new key to understanding the radiating
particle population.


title: Orientation and Speed of the Parsec-Scale Jet in NGC4261 (3C270)

abstract:
  NGC4261 (3C270) is an elliptical galaxy containing a 300-parsec scale nuclear
disk of gas and dust imaged by the Hubble Space Telescope (HST), around a
central supermassive black hole. Previous VLBI observations of NGC4261 revealed
a gap in emission in the radio counterjet, presumably due to free-free
absorption in the inner parsec of the accretion disk. Here we present three 8
GHz VLBA observations of NGC4261 that allow us to monitor the location and
depth of the gap, and check for motions in the jet and counterjet. The
separation between the brightest peak and the gap is stable, with an upper
limit to its motion of 0.01 c, supporting the interpretation of the gap as
absorption by an accretion disk rather than an intrinsic jet feature. These
observations span a time of order that required for orbiting material in the
disk to transit the counterjet, so we are able to search for density changes
(clumps) in the disk by monitoring the optical depth of the gap. The optical
depth of the gap is stable to within 20% over 5 years at tau = 1.1 +/- 0.1,
corresponding to an electron density in the disk that is constant to within
10%. We measure an apparent speed in the jet of 0.52 +/- 0.07 c. An apparent
speed could not be measured for the counterjet due to a lack of identifiable
features. From the apparent jet speed and the jet to counterjet brightness
ratio, we calculate the viewing angle of the jet to be 63 +/- 3 degrees and its
intrinsic speed to be 0.46 +/- 0.02 c. From the inclination and position angles
of the parsec-scale radio jet and outer HST disk rotation axis we calculate a
difference between the parsec-scale radio jet and outer HST disk rotation axis
of 12 +/- 2 degrees.


title:
Multiwavelength observations revealing the outbursts of the soft X-ray
  transients XTE J1859+226 and XTE J1118+480

abstract:
  We report multiwavelength observations of the two soft X-ray transients
(SXTs) XTE J1859+226 and XTE J1118+480, which we observed with HST, RXTE and
UKIRT. The two sources exhibited very different behaviour. XTE J1859+226 showed
a thermal-viscous disc instability outburst modified by irradiation. XTE
J1118+480, which we also observed with EUVE since it is located at a very high
galactic latitude and suffers from very low extinction, is much more unusual.
It exhibits i) a low X-ray to optical flux ratio and ii) a strong non-thermal
contribution throughout the spectrum, which is likely to be due to synchrotron
emission. We concentrate here on their evolution in the course of their
outbursts.


title:
Gamma-Ray Burst in a Molecular Cloud: Destruction of Dust and H2, and
  Emergent Spectrum

abstract:
  A gamma ray burst with strong optical-UV emission occuring in a molecular
cloud will photodissociate H2, photoionize H2, H, and He, and destroy dust
grains. We model these processes, including time-dependent radiative transfer
in both continuum radiation and the resonance lines of H2. The UV will pump H2
into vibrationally-excited levels. We calculate the absorption spectrum
imprinted on radiation from the GRB at various times. In addition to the strong
absorption lines of H2(v=0) at lambda < 1110 Angstrom, due to cold ambient gas,
we find that radiation reaching us from the GRB and its afterglow will show
strong absorption lines due to vibrationally-excited H2 at 1110 < lambda < 1705
Angstrom. These absorption lines, if observed, would provide unequivocal
evidence for association of the GRB with molecular gas. Low-resolution spectra
will exhibit conspicuous features due to clustering of individual lines; a list
of the strongest such absorption features is given for spectral resolution R
approx 350 characteristic of the grism on the Swift UV-Optical Telescope.


title: Phenomemology of a Realistic Accelerating Universe Using Tracker Fields

abstract:
  We present a realistic scenario of tracking of scalar fields with varying
equation of state. The astrophysical constraints on the evolution of scalar
fields in the physical universe are discussed. The nucleosynthesis and the
galaxy formation constraints have been used to put limits on $\Omega_\phi$ and
estimate $\epsilon$ during cosmic evolution. Interpolation techniques have been
applied to estimate $\epsilon\simeq0.772$ at the present epoch. The epoch of
transition from matter to quintessence dominated era and consequent onset of
acceleration in cosmic expansion is calculated and taking the lower limit
$\Omega_n^0 = 0.2$ as estimated from $SN_e I_a$ data, it is shown that the
supernova observations beyond redshift $z=1$ would reveal deceleration in
cosmic expansion.


title: X-Ray Probes of Cosmic Star-Formation History

abstract:
  We discuss the imprints left by a cosmological evolution of the star
formation rate (SFR) on the evolution of X-ray luminosities Lx of normal
galaxies, using the scheme proposed by White and Ghosh (1998, WG98), wherein
the evolution of Lx of a galaxy is driven by the evolution of its X-ray binary
population. As indicated in WG98, the profile of Lx with redshift can both
serve as a diagnostic probe of the SFR profile and constrain evolutionary
models for X-ray binaries. We report here the first calculation of the expected
evolution of X-ray luminosities of galaxies, updating the WG98 work by using a
suite of more recently developed SFR profiles that span the currently plausible
range. The first Chandra deep imaging results on Lx are beginning to probe the
SFR profile of bright spirals: the early results are consistent with
predictions based on current SFR models. Using these new SFR profiles, the
resolution of the ``birthrate problem'' of low-mass X-ray binaries (LMXBs) and
recycled, millisecond pulsars (WG98) in terms of an evolving global SFR is more
complete. We discuss the possible impact of the variations in the SFR profile
of individual galaxies and galaxy-types.


title: SwSt 1: an O-rich planetary nebula around a C-rich central star

abstract:
  The hydrogen-deficient carbon-rich [WCL] type central star HD167362 and its
oxygen-rich planetary nebula (PN) SwSt~1 are investigated. The nebular
chemistry might indicate a recent origin for the carbon-rich stellar spectrum.
Its stellar and nebular properties might therefore provide further
understanding of the origin of the [WCL] central star class. The UV-IR stellar
spectra are modelled with state of the codes and show ~40kK central star with a
wind and a C/O~3, indicative of efficient third dredge-up. The synthetic
stellar flux distribution is used to model the high density, compact PN, which
has a solar C/O ratio, is still enshrouded by 1200K and 230K dust shells and,
reported here for the first time, in molecular hydrogen. Although it appears
that the change in C/O ratio has been recent, the published spectroscopy since
1895 has been re-examined and no clear spectral change is seen. If an event
occurred that has turned it into a hydrogen-deficient central star, it did not
happen in the last 100 years.


title: Search for Tracker Potentials in Quintessence Theory

abstract:
  We report a significant finding in Quintessence theory that the the scalar
fields with tracker potentials have a model-independent scaling behaviour in
the expanding universe. So far widely discussed exponential,power law or
hyperbolic potentials can simply mimic the tracking behaviour over a limited
range of redshift. In the small redshift range where the variation of the
tracking parameter $\epsilon$ may be taken to be negligible, the differential
equation of generic potentials leads to hyperbolic sine and hyperbolic cosine
potentials which may approximate tracker field in the present day universe. We
have plotted the variation of tracker potential and the equation of state of
the tracker field as function of the redshift $z$ for the model-independent
relation derived from tracker field theory; we have also plotted the variation
of $V(\Phi)$ in terms of the scalar field $\Phi$ for the chosen hyperbolic
cosine function and have compared with the curves obtained by reconstruction of
$V(\phi)$ from the real observational data from the supernovae.


title: High Mass, OB Star Formation in M51 : HST Halpha and Palpha Imaging

abstract:
  (first paragraph) We have obtained Halpha and Palpha emission line images
covering the central 3 - 4 arcmin of M51 using the WFPC2 and NICMOS cameras on
HST to study the high-mass stellar population. The 0.1 - 0.2 arcsec pixels
provide 4.6 - 9 pc resolution in M51 and the Halpha/Palpha line ratios are used
to obtain extinction estimates. A sample of 1373 Halpha emission regions is
catalogued using an automated and uniform measurement algorithm. Their sizes
are typically 10 - 100 pc. The luminosity function for the Halpha emission
regions is obtained over the range L_{Halpha} = 10^{36} to 2 times 10^{39} erg
s{-1}. The luminosity function is fit well by a power law with dN/dlnL
proportional to L^{-1.01}). The power law is significantly truncated and no
regions were found with observed L_{Halpha} above 2 times 10^{39} erg s^{-1}
(uncorrected for extinction; the maximum seen in ground-based studies is
approximately a factor of 5 higher, very likely due to blending of multiple
regions). The extinctions derived here increase the maximum intrinsic
luminosity to above 10^{40} erg s^{-1}). The logarithmically binned luminosity
function is also somewhat steeper (alpha = -1.01) than that found ground-based
imaging (alpha = -0.5 to -0.8)
  - probably also a result of our resolving regions which were blended in the
ground-based images. The 2-point correlation function for the HII regions
exhibits strong clustering on scales <= 2 arcsec or 96 pc.


title:
Optical spectroscopy of isolated planetary mass objects in the sigma
  Orionis cluster

abstract:
  We have obtained low resolution optical spectra of 15 isolated planetary mass
objects (IPMOs) in the sigma Orionis cluster, and derived spectral types by
comparison with nearby M and L dwarfs. The spectral types are in the range late
M - mid L, in agreement with our expectations based on colors and magnitudes
for bona fide members. Therefore, most of these objects have masses below the
deuterium burning limit. About 2/3 show H(alpha) in emission at our spectral
resolution. From our spectroscopic and photometric data, we infer that three
IPMOs in this sample may be binaries with components of similar masses. These
results confirm that the substellar mass function of the sigma Orionis cluster,
in the form dN/dM, keeps rising in the planetary domain.


title:
An eclipsing millisecond pulsar with a possible main-sequence companion
  in NGC 6397

abstract:
  We present the results of one year of pulse timing observations of PSR
J1740-5340, an eclipsing millisecond pulsar located in the globular cluster NGC
6397. We have obtained detailed orbital parameters and a precise position for
the pulsar. The radio pulsar signal shows frequent interactions with the
atmosphere of the companion, and suffers significant and strongly variable
delays and intensity variations over a wide range of orbital phases. These
characteristics and the binary parameters indicate that the companion may be a
bloated main-sequence star or the remnant (still filling its Roche lobe) of the
star that spun up the pulsar. In both cases, this would be the first binary
millisecond pulsar system with such a companion.


title: Detecting magnetic CMB polarization on an incomplete sky

abstract:
  The full sky cosmic microwave background polarization field can be decomposed
into `electric' and `magnetic' components. Working in harmonic space we
construct magnetic variables that can be measured from observations over only a
portion of the sky. Our construction is exact for azimuthally symmetric
patches, but should continue to perform well for arbitrary patches. For
isotropic, uncorrelated noise the variables have a very simple diagonal noise
correlation, and further analysis using them should be no harder than analysing
the temperature field. We estimate the tensor mode amplitude that could be
detected by the Planck satellite and discuss the sensitivity of future
experiments in the presence of a contaminating weak lensing signal.


title:
The bright optical companion to the eclipsing millisecond pulsar in NGC
  6397

abstract:
  We report the possible optical identification of the companion to the
eclipsing millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397. A
bright variable star with an anomalous red colour and optical variability which
nicely correlates to the orbital period of the pulsar has been found close to
the pulsar position. If confirmed, the optical light curve, reminiscent of
tidal distorsions similar to those observed in detached and contact binaries,
support the idea that this is the first case of a Roche lobe filling companion
to a millisecond pulsar.


title: Cluster-Cluster Lensing in Abell 2152

abstract:
  We discuss lensing properties of the nearby cluster Abell 2152. Recent work
shows that Abell 2152 is actually the projection of two different clusters, one
of which is a Hercules supercluster member at z=0.043, while the other is more
than 3 times as distant. The cluster centers have a projected separation of
only 2.4 arcmin, and our data indicate that the foreground cluster lenses
members of the background one. We have an ongoing program to measure the
magnification of the fundamental plane in the background cluster. The
magnification of this standard rod will provide an estimate of the foreground
cluster mass free from the uncertainty of the mass-sheet degeneracy which
affects mass estimates based on weak shear.


title:
A test of general relativity from the three-dimensional orbital geometry
  of a binary pulsar

abstract:
  Binary pulsars provide an excellent system for testing general relativity
because of their intrinsic rotational stability and the precision with which
radio observations can be used to determine their orbital dynamics.
Measurements of the rate of orbital decay of two pulsars have been shown to be
consistent with the emission of gravitational waves as predicted by general
relativity, providing the most convincing evidence for the self-consistency of
the theory to date. However, independent verification of the orbital geometry
in these systems was not possible. Such verification may be obtained by
determining the orientation of a binary pulsar system using only classical
geometric constraints, permitting an independent prediction of general
relativistic effects. Here we report high-precision timing of the nearby binary
millisecond pulsar PSR J0437-4715, which establish the three-dimensional
structure of its orbit. We see the expected retardation of the pulse signal
arising from the curvature of space-time in the vicinity of the companion
object (the `Shapiro delay'), and we determine the mass of the pulsar and its
white dwarf companion. Such mass determinations contribute to our understanding
of the origin and evolution of neutron stars.


title: Weak and Strong Lensing Statistics

abstract:
  After a brief introduction to gravitational lensing theory, a rough overview
of the types of gravitational lensing statistics that have been performed so
far will be given. I shall then concentrate on recent results of galaxy-galaxy
lensing, which indicate that galactic halos extend much further than can be
probed via rotation of stars and gas.


title: The Metallicity of Redshift 0.5<z<1 Field Galaxies

abstract:
  We are undertaking a program to measure emission line ratios in a selected
sample of $0.5 < z < 1.0$ CFRS starforming galaxies in order to compute their
Interstellar Medium metallicities. The latter are derived by means of the
empirically-calibrated $R_{23}$ estimator introduced by Pagel et al. (1979).
Here we focus on a subsample of 15 galaxies with $L_{H\beta} > 1.2 \times
10^{41}$ erg s$^{-1}$. In addition to the optical CFHT spectra discussed in
Carollo & Lilly (2001), where a preliminary account of this work can be found,
in this paper we also refer to new $J$-band Keck spectroscopy of the $H\alpha$
and [NII]6583 lines for several objects. These lines allow us to break the
degeneracy between low ($\lta 0.1Z_\odot$) and high ($\gta 0.5Z_\odot$)
metallicity of the $R_{23}$ estimator, and put on solid ground the finding that
the $0.5 < z < 1.0$ blue galaxies in the high-$L_{H\beta}$ sample are
significantly metal-enriched ($Z \gta 0.3Z_\odot$ up to $Z_\odot$). Therefore,
our results do not support previous suggestions in which the $0.5 < z < 1.0$
starforming galaxies are dwarf galaxies brightened by large bursts of
star-formation, but support instead a picture where at least a significant
fraction of them evolves to become today's massive metal-rich systems.


title: Discovery of a double ring in the core of eta Carinae

abstract:
  We report the discovery of a double ring structure in the waist of the nebula
surrounding eta Carinae. The rings are detected in the mid-IR dust continuum at
wavelengths of 7.9, 11.9, 12.9 and 20 micronmeter. The dust in the rings has a
temperature of about 300 K. The orientation of the rings is inclined with
respect to the axis of the homunculus by either 37 or 58 degrees. The central
star is not in the projected centre of the structure defined by the two rings.
This geometry is reminiscent of that seen in SN1987A and some planetary
nebulae. We discuss several possible origins for this remarkable geometry and
its orientation.


title: A Relativistic-Plasma Compton Maser

abstract:
  A relativistic pair-plasma which contains a high excitation of electrostatic
turbulence could produce intense radiation at brightness temperature in excess
of 10^22 K by stimulated scattering. Important relativistic effects would
include the broadband frequency response of the plasma and Compton-boosting of
the scattered radiation. In radio-frequency relativistic plasma, the optical
depth can be as small as hundreds of meters. When the plasma wave excitation
and particle distributions are one-dimensional, the frequency-dependent angular
distribution of the emission exhibits characteristics of pulsar emission.


title: The Anthropic Principle Revisited

abstract:
  The usage of the anthropic principle in modern cosmology is reviewed. It is
argued that its recent use to explain the observedvalues of cosmological
parameters as most probable values for an ensemble of universes, is not
justified. However, the anthropic principle can be invoked to argue that a vast
number of universes must exist, in which the cosmological parameters and
constants of nature take on different values. This argument lends support to
the hypothesis of eternal inflation and suggests that at least some of the
parameters of the Standard Model cannot be quantitatively derived from an
underlying theory.


title:
Prospects for Constraining Cosmology with the Extragalactic Cosmic
  Microwave Background Temperature

abstract:
  Observers have demonstrated that it is now feasible to measure the cosmic
microwave background (CMB) temperature at high redshifts. We explore the
possible constraints on cosmology which might ultimately be derived from such
measurements. Besides providing a consistency check on standard and alternative
cosmologies, possibilities include: constraints on the inhomogeneity and
anisotropy of the universe at intermediate redshift $z ^<_\sim 10$; an
independent probe of peculiar motions with respect to the Hubble flow; and
constraining the epoch of reionization. We argue that the best possibility is
as a probe of peculiar motions. We show, however, that the current measurement
uncertainty ($\Delta T= \pm 0.002 $K) in the local present absolute CMB
temperature imposes intrinsic limits on the use of such CMB temperature
measurements as a cosmological probe. At best, anisotropies at intermediate
redshift could only be constrained at a level of $^>_\sim 0.1%$ and peculiar
motions could only be determined to an uncertainty of $^>_\sim 311$ km
s$^{-1}$. If the high $z$ CMB temperature can only be measured with a precision
comparable to the uncertainty of the local interstellar CMB temperature, then
peculiar motions could be determined to an uncertainty of $1101 (1+z)^{-1}
[\Delta T_{CMB}(z)/0.01 K] km s^{-1}$.


title: Ultraluminous Infrared Galaxies: Atlas of Near-Infrared Images

abstract:
  A sample of 27 ultraluminous infrared galaxy (ULIRG) systems has been imaged
at 1.6 microns using the HST Near Infrared Camera and Multi-Object Spectrometer
(NICMOS). These ULIRGs are from a larger sample also imaged with HST in the
I-band. Images and catalog information for the NICMOS subsample, as well as
brief morphological descriptions of each system are presented. Inspection of
the infrared images and a comparison with optical images of these systems shows
that at least 85% are obviously composed of two or more galaxies involved in a
close interaction or merger event, with as many as 93% showing some signs of
interaction history. Approximately 37% of the systems show either spectroscopic
or morphological characteristics of an active galactic nucleus (AGN). The
infrared morphologies of these systems are generally less complicated or
disturbed than their optical morphologies, indicating that some of the
small-scale features seen in optical images are likely due to complicated
patterns of dust obscuration, as well as widely distributed star formation
activity. In some systems the high-resolution HST infrared images have revealed
nuclear remnants that are obscured or unidentified in ground-based imaging,
which has led to changes in previously determined interaction stage
classifications or system content. In general, however, the NICMOS images
support previous conclusions from previous HST optical imaging.


title:
The Radio Recovery of SN 1970G: The Continuing Radio Evolution of SN
  1970G

abstract:
  Using the Very Large Array, we have detected radio emission from the site of
SN 1970G in the Sc galaxy M101. These observations are 31 years after the
supernova event, making SN 1970G the longest monitored radio supernova. With
flux densities of 0.12 +/- 0.020 mJy at 6 cm and 0.16 +/- 0.015 mJy at 20 cm,
the spectral index of -0.24 +/- 0.20 appears to have flattened somewhat when
compared with the previously reported value of -0.56 +/- 0.11, taken in 1990.
The radio emission at 20 cm has decayed since the 1990 observations with a
power-law index of beta_20cm = -0.28 +/- 0.13. We discuss the radio properties
of this source and compare them to those of other Type II radio supernovae.


title:
Boron Abundances in Main Sequence B-type Stars: A Test of Rotational
  Depletion during Main Sequence Evolution

abstract:
  Boron abundances have been derived for seven main sequence B-type stars from
HST STIS spectra around the B III 2066 A line. In two stars, boron appears to
be undepleted with respect to the presumed initial abundance. In one star,
boron is detectable but it is clearly depleted. In the other four stars, boron
is undetectable implying depletions of 1 to 2 dex. Three of these four stars
are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only
rotationally induced mixing predicts that boron depletions are unaccompanied by
nitrogen enrichments. The inferred rate of boron depletion from our
observations is in good agreement with these predictions. Other boron-depleted
nitrogen-normal stars are identified from the literature. Also, several
boron-depleted nitrogen-rich stars are identified, and while all fall on the
boron-nitrogen trend predicted by rotationally-induced mixing, a majority have
nitrogen enrichments that are not uniquely explained by rotation.
  The spectra have also been used to determine iron-group (Cr, Mn, Fe, and Ni)
abundances. The seven B-type stars have near solar iron-group abundances, as
expected for young stars in the solar neighborhood. We have also analysed the
halo B-type star, PG0832+676. We find [Fe/H] = -0.88 +/- 0.10, and the absence
of the B III line gives the upper limit [B/H]<2.5. These and other published
abundances are used to infer the star's evolutionary status as a post-AGB star.


title: Spectral Structure in FRII Radio Galaxies and Jets

abstract:
  Using spectral tomography to separate overlapping spectral features in a
sample of FRII radio galaxies, we find a variety of spatial/spectral features
that are not easily described in the context of current models. In particular,
we find mixtures of flat and steep spectrum features in the hot spot regions,
and non-monotonic spectral index gradients along jets. Additional findings
include spectral gradients in compact hot spots and possible transitions in jet
properties at the downstream ends of the diffuse lobes. The complexity of
behaviors uncovered here points to the need for a thorough investigation of
numerical models for radio galaxies, as well as detailed observational studies
of larger, unbiased samples. We also perform the first quantitative assessment
of errors in the use of spectral tomography for spectral index measurements.


title: Chandra Exposes the Core Collapsed Globular Cluster NGC 6397

abstract:
  We report results of the Chandra deep imaging observation of the closest
post-core collapse globular cluster, NGC 6397. Some 25 sources are detected
within 2 arcmin of the cluster center of which about 20 are likely cluster
members with L_x ~ 3x10^29 erg/s. The x-ray spectra suggest identifications
with 1 quiescent low mass x-ray binary (qLMXB) detected by the thermal emission
from its neutron star (NS) and 9 cataclysmic variables (CVs), 8 of which are
identified in our deep HST imaging survey (reported separately). Three (of 16)
BY Draconis main sequence binary candidates identified in our earlier HST
imaging study (Taylor et al) are detected of which one is indeed the
counterpart of the eclipsing millisecond pulsar (MSP) recently located by
D'Amico et al. Two other BY Dra candidates are also detected, whereas none of
the probable He white dwarf (WD) binaries identified by Taylor et al are
indicating they do not contain MSP primaries. The x-ray color magnitude diagram
suggests that the remaining 5 probable cluster sources are a mixture of faint
CVs, BY Dra binaries and MSPs. Compact binaries containing WDs appear to
dominate this cluster, in contrast to those containing NSs in 47Tuc.


title: Modeling Galaxy Clustering by Color

abstract:
  We extend the mass-halo formalism for analytically generating power spectra
to allow for the different clustering behavior observed in galaxy
sub-populations. Although applicable to other separations, we concentrate our
methods on a simple separation by rest-frame color into ``red'' and ``blue''
sub-populations through modifications to the <N(M)> relations and halo
distribution functions for each of the sub-populations. This sort of separation
is within the capabilities of the current generations of simulations as well as
galaxy surveys, suggesting a potentially powerful observational constraint for
current and future simulations. In anticipation of this, we demonstrate the
sensitivity of the resulting power spectra to the choice of model parameters.


title: Column density distribution of galactic Ly-alpha absorption systems

abstract:
  A simple consistency argument for hypothesis of the galactic halo origin of
the Ly-alpha forest absorption lines is advanced, based on the recent
determination of column-density vs. impact parameter relation for the
low-redshift gaseous galactic haloes. It is shown that observations of neutral
hydrogen absorption around luminous galaxies are consistent with the index of
the power-law column density distribution derived from statistical analysis of
large samples of high-redshift Ly-alpha forest lines.


title: Qualitative Properties of Magnetic Fields in Scalar Field Cosmology

abstract:
  We study the qualitative properties of the class of spatially homogeneous
Bianchi VI_o cosmological models containing a perfect fluid with a linear
equation of state, a scalar field with an exponential potential and a uniform
cosmic magnetic field, using dynamical systems techniques. We find that all
models evolve away from an expanding massless scalar field model in which the
matter and the magnetic field are negligible dynamically. We also find that for
a particular range of parameter values the models evolve towards the usual
power-law inflationary model (with no magnetic field) and, furthermore, we
conclude that inflation is not fundamentally affected by the presence of a
uniform primordial magnetic field. We investigate the physical properties of
the Bianchi I magnetic field models in some detail.


title: $^1$S$_0$ Neutron Pairing vs Observations of Cooling Neutron Stars

abstract:
  As shown recently by Kaminker et al. (2001), current observations of thermal
emission of isolated middle-aged neutron stars (NSs) can be explained by
cooling of NSs of different masses with the cores composed of neutrons, protons
and electrons, assuming rather strong superfluidity (SF) of protons, weak
triplet-state SF of neutrons and neglecting singlet-state SF of neutrons. We
show that this explanation remains correct in the presence of singlet-state SF
of neutrons in the NS crust and outermost core but under stringent constraints
on the density profile of the SF critical temperature $T_{\rm cns}(\rho)$. In
order to explain observations of (young and hot) RX J0822--43 and (old and
warm) PSR 1055--52 and RX J1856--3754 as cooling not too massive NSs, the
maximum $T_{\rm cns}^{\rm max}$ should be rather high ($\ga 5 \times 10^9$ K)
and the decrease of $T_{\rm cns}(\rho)$ outside the maximum should be sharp.
These results place important constraints on the models of nucleon SF in dense
matter.


title:
Very high-energy gamma-ray observations of the Crab nebula and other
  potential sources with the GRAAL experiment

abstract:
  The ``Gamma Ray Astronomy at ALmeria'' (GRAAL) experiment uses 63
heliostat-mirrors with a total mirror area of ~ 2500 m2 from the CESA-1 field
at the ``Plataforma Solar de Almeria'' (PSA) to collect Cherenkov light from
air showers. The detector is located in a central solar tower and detects
photon-induced showers with an energy threshold of 250 +- 110 GeV and an
asymptotic effective detection area of about 15000 m2. A comparison between the
results of detailed Monte-Carlo simulations and data is presented. Data sets
taken in the period September 1999 - September 2000 in the direction of the
Crab pulsar, the active galaxy 3C 454.3, the unidentified gamma-ray source 3EG
1835+35 and a ``pseudo source'' were analyzed for high energy gamma-ray
emission.Evidence for a gamma-ray flux from the Crab pulsar with an integral
flux of 2.2 +- 0.4 (stat) ^+1.7_-1.3 (syst) x 10^-9 cm^-2 sec^-1 above
threshold and a significance of 4.5 sigma in a total measuring time of 7 hours
and 10 minutes on source was found. No evidence for emission from the other
sources was found. Some difficulties with the use of heliostat fields for
gamma-ray astronomy are pointed out. In particular the effect of field-of-view
restricted to the central part of a detected air shower on the lateral
distribution and timing properties of Cherenkov light are discussed. Upon
restriction the spread of the timing front of proton induced showers sharply
decreases and the reconstructed direction becomes biased towards the pointing
direction. This is shown to make efficient gamma-hadron separation difficult.


title: Improving the mass determination of Galactic Cepheids

abstract:
  We have selected a sample of Galactic Cepheids for which accurate estimates
of radii, distances, and photometric parameters are available. The comparison
between their pulsation masses, based on new Period-Mass-Radius (PMR)
relations, and their evolutionary masses, based on both optical and NIR
Color-Magnitude (CM) diagrams, suggests that pulsation masses are on average of
the order of 10% smaller than the evolutionary masses. Current pulsation masses
show, at fixed radius, a strongly reduced dispersion when compared with values
published in literature.The increased precision in the pulsation masses is due
to the fact that our predicted PMR relations based on nonlinear, convective
Cepheid models present smaller standard deviations than PMR relations based on
linear models. At the same time, the empirical radii of our Cepheid sample are
typically accurate at the 5% level. Our evolutionary mass determinations are
based on stellar models constructed by neglecting the effect of mass-loss
during the He burning phase. Therefore, the difference between pulsation and
evolutionary masses could be intrinsic and does not necessarily imply a problem
with either evolutionary and/or nonlinear pulsation models. The marginal
evidence of a trend in the difference between evolutionary and pulsation masses
when moving from short to long-period Cepheids is also briefly discussed. The
main finding of our investigation is that the long-standing Cepheid mass
discrepancy seems now resolved at the 10% level either if account for canonical
or mild convective core overshooting evolutionary models.


title: Reclassification of gamma-ray bursts

abstract:
  We have applied two different automatic classifier algorithms to the BATSE
Current GRB Catalog data and we obtain three different classes of GRBs. Our
results confirm the existence of a third, intermediate class of GRBs, with mean
duration \sim 25-50 s, as deduced from a cluster analysis and from a neural
network algorithm. Our analyses imply longer durations than those found by
Mukherjee et al. (1998) and Horvath (1998), whose intermediate class had
durations \sim 2-10 s. From the neural network analysis no difference in
hardness between the two longest classes is found, and from both methods we
find that the intermediate-duration class constitutes the most homogeneous
sample of GRBs in its space distribution while the longest-duration class
constitutes the most inhomogeneous one with <V/V_max> \sim 0.1, being thus the
deepest population of GRBs with z_max \sim 10. The trend previously found in
long bursts, of spatial inhomogeneity increasing with hardness, only holds for
this new longest-duration class.


title:
The redshift and scale dependence of the cosmic shear signal from
  numerical simulations

abstract:
  The weak lensing shear signal has been measured numerically in $N$-body
simulations at 14 different redshifts ($z_s = 0.1$ to 3.6) and on angular
scales of $\theta = 2'$ to 32'. In addition, the data have been validated by
analytical computations for an identical cosmology, with density parameter
$\Omega_m = 0.3$ and vacuum energy density parameter $\lambda_0 = 0.7$. This
paper reports on the scale and redshift dependence of the shear variance,
$<\gamma^2>$, which may be described by a simple formula of the form
$<\gamma^2>(\theta,z_s) = a(\theta)z_s^{b(\theta)}$. The redshift dependence
for source redshifts up to 1.6, is found to be close to $z_s^2$, which is a
stronger dependence than earlier analytical predictions ($<\gamma^2 > \propto
z_s^{1.52}$), although, at higher redshifts, the $z_s$ dependence of the shear
variance is clearly less steep. The strong redshift dependence further
emphasises the need to know the precise redshift distribution for the galaxy
sources in any given survey, so that they can be allocated to redshift bins
accordingly, and the cosmic shear signal correctly interpreted. Equations are
also given for the variance in the reduced shear, which is a more directly
measurable quantity observationally.


title:
Magnetoconvection and dynamo coefficients: Dependence of the
  alpha-effect on rotation and magnetic field

abstract:
  We present numerical simulations of three-dimensional compressible
magnetoconvection in a rotating rectangular box that represents a section of
the solar convection zone. The box contains a convectively unstable layer,
surrounded by stably stratified layers with overshooting convection. The
magnetic Reynolds number, Rm, is chosen subcritical, thus excluding spontaneous
growth of the magnetic field through dynamo action, and the magnetic energy is
maintained by introducing a constant magnetic field into the box, once
convection has attained a statistically stationary state. Under the influence
of the Coriolis force, the advection of the magnetic field results in a
non-vanishing contribution to the mean electric field, given by uxb. From this
electric field, we calculate the alpha-effect, separately for the stably and
the unstably stratified layers, by averaging over time and over suitably
defined volumes. From the variation of alpha we derive an error estimate, and
the dependence of alpha on rotation and magnetic field strength is studied.
Evidence is found for rotational quenching of the vertical alpha-effect, and
for a monotonic increase of the horizontal alpha-effect with increasing
rotation. For Rm~30, our results for both vertical and horizontal alpha-effect
are consistent with magnetic quenching by a factor 1/[1+Rm(B_0/B_eq)^2]. The
signs of the small-scale current helicity and of the vertical component of
alpha are found to be opposite to those for isotropic turbulence.


title: The Clustering of Galaxies around Quasars

abstract:
  We study the cross-correlation between quasars and galaxies by embedding
models for the formation and evolution of the two populations in cosmological
N-body simulations. We adopt the quasar evolution model of Kauffmann & Haehnelt
(2000), in which supermassive black holes are formed and fuelled during major
mergers. We define the `bias' parameter b_QG as the ratio of the
cross-correlation function xi_QG to the galaxy auto-correlation function xi_GG.
On scales larger than 1 h^{-1} Mpc, the values of b_QG predicted by our models
at low redshift depend very little on galaxy selection. They measure the
characteristic mass of the dark matter halos that host quasars and can be used
to estimate the typical quasar lifetime. In current redshift surveys, such
measurements will constrain the lifetimes of low z quasars more accurately than
measurements of the quasar auto-correlation function, because galaxies have
much higher space densities than quasars. On scales smaller than 1 h^{-1} Mpc,
the main contribution to xi_QG comes from quasar/galaxy pairs in the same dark
matter halo. The amplitude of xi_QG depends both on the location of the host
galaxy and on the density profile of other galaxies within the halo. As a
result, measurements on these scales yield information about the processes
responsible for fuelling super- massive black holes. At high redshifts, our
models predict that quasars of fixed luminosity are located in less massive
halos than at low redshift. They are therefore less biased relative to galaxies
of given luminosity or stellar mass. We have used the simulations to calculate
the evolution of the quasar auto- correlation function. We find that models
with quasar lifetimes in the range 10^6-10^7 years provide a good match to the
results of the 2dF QSO survey.


title: Dynamics of the solar tachocline I: an incompressible study

abstract:
  Gough & McIntyre have suggested that the dynamics of the solar tachocline are
dominated by the advection-diffusion balance between the differential rotation,
a large-scale primordial field and baroclinicly driven meridional motions. This
paper presents the first part of a study of the tachocline, in which a model of
the rotation profile below the convection zone is constructed along the lines
suggested by Gough & McIntyre and solved numerically. In this first part, a
reduced model of the tachocline is derived in which the effects of
compressibility and energy transport on the system are neglected; the
meridional motions are driven instead by Ekman-Hartmann pumping. It is shown
that there exists only a narrow range of magnetic field strengths for which the
system can achieve a nearly uniform rotation. The results are discussed with
respect to observations and to the limitations of this initial approach. A
following paper combines the effects of realistic baroclinic driving and
stratification with a model that follows closely the lines of work of Gough &
McIntyre.


title: Constraining H0 from Chandra Observations of Q0957+561

abstract:
  We report the detection of the lens cluster of the gravitational lens (GL)
system Q0957+561 from a deep observation with the Advanced CCD Imaging
Spectrometer on-board the Chandra X-ray Observatory. Intracluster X-ray
emission is found to be centered 4.3 +/- 1.3 arcsec east and 3.5(-0.6,+1.3)
arcsec north of image B, nearer than previous estimates. Its spectrum can be
modeled well with a thermal plasma model consistent with the emission
originating from a cluster at a redshift of 0.36. Our best-fit estimates of the
cluster temperature of T_e = 2.09(-0.54,+0.83) keV (90 percent confidence) and
mass distribution of the cluster are used to derive the convergence parameter
kappa, the ratio of the cluster surface mass density to the critical density
required for lensing. We estimate the convergence parameter at the location of
the lensed images A and B to be kappa_A = 0.22(+0.14,-0.07) and kappa_B =
0.21(+0.12,-0.07), respectively (90 percent confidence levels). The observed
cluster center, mass distribution and convergence parameter kappa provide
additional constraints to lens models of this system. Our new results break a
mass-sheet degeneracy in GL models of this system and provide better
constraints of ~ 29 percent (90 percent confidence levels) on the Hubble
constant. We also present results from the detection of the most distant X-ray
jet (z = 1.41) detected to date. The jet extends approximately 8 arcsec NE of
image A and three knots are resolved along the X-ray jet with flux densities
decreasing with distance from the core. The observed radio and optical flux
densities of the knots are fitted well with a synchrotron model and the X-ray
emission is modeled well with inverse Compton scattering of Cosmic Microwave
Background photons by synchrotron-emitting electrons in the jet.


title:
Highly-Ionized Intergalactic Gas at Low Redshifts: Constraints from QSO
  Absorption Lines

abstract:
  High-resolution UV spectroscopy of low-z QSOs with the Space Telescope
Imaging Spectrograph and the Far Ultraviolet Spectroscopic Explorer has
indicated that O VI absorption-line systems provide a valuable probe of the
low-z intergalactic medium. These observations and their implications are
briefly reviewed. Though still uncertain due to the small sample, the number of
O VI absorbers per unit redshift is quite high, and these absorbers appear to
trace an important baryon reservoir. The O VI systems are intervening; they are
highly displaced from the background QSO redshifts and are correlated with
foreground luminous galaxies. Their physical conditions are variable and
sometimes complicated. In some cases, there is clear evidence that the
absorbers have a multiphase nature. Some appear to be photoionized by the UV
background from QSOs, while others are probably collisionally ionized. However,
the majority of the O VI lines have b-values that suggest an origin in
collisionally ionized hot gas. The observations are in agreement with
hydrodynamic simulations of cosmological structure growth, which predict
substantial quantities of shock-heated, hot intergalactic gas at low z, but
more observational and theoretical work is needed to confirm the nature of the
O VI systems.


title:
Cluster Galaxy Evolution from a New Sample of Galaxy Clusters at 0.3 < z
  < 0.9

abstract:
  (Abridged) We analyze photometry and spectroscopy of a sample of 63 clusters
at 0.3<z<0.9 drawn from the Las Campanas Distant Cluster Survey to empirically
constrain models of cluster galaxy evolution. Specifically, by combining data
on our clusters with those from the literature we parametrize the redshift
dependence of 1) M*_I in the observed frame; 2) the V-I color of the E/S0 red
sequence in the observed frames; and 3) the I-K' color of the E/S0 red sequence
in the observed frame. Using the peak surface brightness of the cluster
detection, S, as a proxy for cluster mass, we find no correlation between S and
M* or the location of the red envelope in V-I. We suggest that these
observations can be explained with a model in which luminous early type
galaxies (or more precisely, the progenitors of current day luminous early type
galaxies) form the bulk of their stellar populations at high redshift (>~ 5)
and in which many of these galaxies, if not all, accrete mass either in the
form of evolved stellar populations or gas that causes only a short term
episode of star formation at lower redshifts (1.5 < z < 2). Our data are too
crude to reach conclusions regarding the evolutionary state of any particular
cluster or to investigate whether the morphological evolution of galaxies
matches the simple scenario we discuss, but the statistical nature of this
study suggests that the observed evolutionary trends are universal in massive
clusters.


title:
Understanding the Optimal Redshift Range for the Supernovae Hubble
  Diagram

abstract:
  The supernovae Hubble diagram traces the expansion history of the universe,
including the influence of dark energy. Its use to probe the cosmological model
can fruitfully be guided by heuristic study of the features of the model
curves. By relating these directly to the physics of the expansion we can
understand simply the optimal redshift range for supernovae observations,
requiring a survey depth of z=1.5-2 to distinguish evolution in dark energy
properties.


title: Vortex Unpinning in Precessing Neutron Stars

abstract:
  The neutron vortices thought to exist in the inner crust of a neutron star
interact with nuclei and are expected to pin to the nuclear lattice. Evidence
for long-period precession in pulsars, however, requires that pinning be
negligible. We estimate the strength of vortex pinning and show that
hydrodynamic forces present in a precessing star are likely sufficient to unpin
all of the vortices of the inner crust. In the absence of precession, however,
vortices could pin to the lattice with sufficient strength to explain the giant
glitches observed in many radio pulsars.


title: The Fundamental Line of the Local Group Satellites

abstract:
  We present a new correlation between the mass-to-light (M/L) ratio and the
mean metallicity for the satellites of the Local Group. This relation together
with their central surface brightness define a Fundamental Line where metal
poor and low surface brightness dwarfs are dark matter dominated while metal
rich high surface brightness systems will have a low M/L ratio. This
Fundamental Line is independent of distance to the central galaxy (M31 and the
Milky Way) and morphological type among other global parameters as their star
formation history. The new M/L-metallicity relation indicates that dwarf
spheroidal galaxies are dark matter confined. It can be interpreted if
satellites experienced a continuous loss of metals with a final episode of gas
ejection at the end of the star formation epoch. Only Globular Clusters are
found to lie outside the Fundamental Line of dwarf satellites. Unlike satellite
galaxies they are not dark matter confined.