title:
Systematic effects and a new determination of the primordial abundance
  of 4He and dY/dZ from observations of blue compact galaxies

abstract:
  We use spectroscopic observations of a sample of 82 HII regions in 76 blue
compact galaxies to determine the primordial helium abundance Yp and the slope
dY/dZ from the Y-O/H linear regression. To improve the accuracy of the dY/dZ
measurement, we have included new spectrophotometric observations of 33 HII
regions which span a large metallicity range, with oxygen abundance 12+log(O/H)
varying between 7.43 and 8.30 (Zsun/30<Z<Zsun/4). For a subsample of 7 HII
regions, we derive the He mass fraction taking into account known systematic
effects, including collisional and fluorescent enhancements of HeI emission
lines, collisional excitation of hydrogen emission, underlying stellar HeI
absorption and the difference between the temperatures Te(HeII) in the He^+
zone and Te(OIII) derived from the collisionally excited [OIII] lines. We find
that the net result of all the systematic effects combined is small, changing
the He mass fraction by less than 0.6%. By extrapolating the Y vs. O/H linear
regression to O/H=0 for 7 HII regions of this subsample, we obtain
Yp=0.2421+/-0.0021 and dY/dO=5.7+/-1.8, which corresponds to dY/dZ=3.7+/-1.2,
assuming the oxygen mass fraction to be O=0.66Z. In the framework of the
standard Big Bang nucleosynthesis theory, this Yp corresponds to Omega_b h^2 =
0.012^+0.003_-0.002, where h is the Hubble constant in units of 100 km/s/Mpc.
This is smaller at the 2sigma level than the value obtained from recent
deuterium abundance and microwave background radiation measurements. The linear
regression slope dY/dO=4.3+/-0.7 (corresponding to dY/dZ=2.8+/-0.5) for the
whole sample of 82 HII regions is similar to that derived for the subsample of
7 HII regions, although it has a considerably smaller uncertainty.


title: Superhumps, Magnetic Fields and the Mass-ratio in AM Canum Venaticorum

abstract:
  We show that the observed K-velocities and periodicities of AM CVn can be
reconciled given a mass ratio of 0.22 and a secondary star with a modest
magnetic field of surface strength of order 1 Tesla. We see that the new mass
ratio implies that the secondary is most likely semi-degenerate. The effect of
the field on the accretion disc structure is examined. The theory of precessing
discs and resonant orbits is generalised to encompass higher order resonances
than 3:2 and shown to retain consistency with the new mass ratio.


title: SPI/INTEGRAL observation of the Cygnus region

abstract:
  We present the analysis of the first observations of the Cygnus region by the
SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing
${\sim}$ 600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375
were clearly detected. Our data illustrate the temporal variability of Cyg X-1
in the energy range from 20 keV to 300 keV. The spectral analysis shows a
remarkable stability of the Cyg X-1 spectra when averaged over one day
timescale. The other goal of these observations is SPI inflight calibration and
performance verification. The latest objective has been achieved as
demonstrated by the results presented in this paper.


title: Velocity Fields as a Probe of Cosmology

abstract:
  Analyses of peculiar velocity surveys face several challenges, including low
signal--to--noise in individual velocity measurements and the presence of
small--scale, nonlinear flows. I will present three new analyses that attempt
to address these inherent problems. The first is geared towards the better
understanding of the estimated errors in the surveys, specifically sampling
errors, and the resolution of the seeming disagreements between the surveys.
Another develops a new statistic that does not suffer from the usual problems
and gives robust results that are galaxy--morphology and distance--estimator
independent. The third introduces a formalism that allows for the accounting of
most of the non--linear signal whereby the signal to noise is increased and
small--scale aliasing is removed.


title: On the Correlated X-ray and Optical Evolution of SS Cygni

abstract:
  We have analyzed the variability and spectral evolution of the prototype
dwarf nova system SS Cygni using RXTE data and AAVSO observations. A series of
pointed RXTE/PCA observations allow us to trace the evolution of the X-ray
spectrum of SS Cygni in unprecedented detail, while 6 years of optical AAVSO
and RXTE/ASM light curves show long-term patterns. Employing a technique in
which we stack the X-ray flux over multiple outbursts, phased according to the
optical light curve, we investigate the outburst morphology. We find that the
3-12 keV X-ray flux is suppressed during optical outbursts, a behavior seen
previously, but only in a handful of cycles. The several outbursts of SS Cygni
observed with the more sensitive RXTE/PCA also show a depression of the X-rays
during optical outburst. We quantify the time lags between the optical and
X-ray outbursts, and the timescales of the X-ray recovery from outburst. The
optical light curve of SS Cygni exhibits brief anomalous outbursts. During
these events the hard X-rays and optical flux increase together. The long-term
data suggest that the X-rays decline between outburst. Our results are in
general agreement with modified disk instability models (DIM), which invoke a
two-component accretion flow consisting of a cool optically thick accretion
disk truncated at an inner radius, and a quasi-spherical hot corona-like flow
extending to the surface of the white dwarf. We discuss our results in the
framework of one such model, involving the evaporation of the inner part of the
optically thick accretion disk, proposed by Meyer & Meyer-Hofmeister (1994).


title:
Superhumps and Repetitive Rebrightenings of the WZ Sge-Type Dwarf Nova,
  EG Cancri

abstract:
  We report on time-resolved photometric observations of the WZ Sge-type dwarf
nova, EG Cnc (Huruhata's variable, see also
http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/egcnc.html), during its
superoutburst in 1996-1997. EG Cnc, after the main superoutburst accompanied
with development of superhumps typical of a WZ Sge-type dwarf nova, exhibited a
series of six major rebrightenings. During these rebrightenings and the
following long fading tail, EG Cnc persistently showed superhumps having a
period equal to the superhump period observed during the main superoutburst.
The persistent superhumps had a constant superhump flux with respect to the
rebrightening phase. These findings suggest the superhumps observed during the
rebrightening stage and the fading tail are a "remnant" of usual superhumps,
and are not newly triggered by rebrightenings. By comparison with the 1977
outburst of this object and outbursts of other WZ Sge-type dwarf novae, we
propose an activity sequence of WZ Sge-type superoutbursts, in which the
current outburst of EG Cnc is placed between a single-rebrightening event and
distinct outbursts separated by a dip. The post-superoutburst behavior of WZ
Sge-type dwarf novae can be understood in the presence of considerable amount
of remnant matter behind the cooling front in the outer accretion disk, even
after the main superoutburst. We consider the premature quenching of the hot
state due to the weak tidal effect under the extreme mass ratio of the WZ
Sge-type binary is responsible for the origin of the remnant mass.


title:
The impact of unresolved binaries on searches for white dwarfs in open
  clusters

abstract:
  Many open clusters have a deficit of observed white dwarfs (WDs) compared
with predictions of the number of stars to have evolved into WDs. We evaluate
the number of WDs produced in open clusters and the number of those WDS
detectable using photometric selection techniques. This calculation includes
the effects of varying the initial-mass function (IMF), the maximum progenitor
masses of WDs, and the binary fraction. Differences between the calculated
number of observable WDs and the actual number of WDs observed in a specific
cluster then indicate the true deficit of WDs that must be explained through
effects such as dynamical evolution of the cluster or close binary evolution.
Observations of WDs in three open clusters, the Hyades, Pleiades, and Praesepe,
are compared to the calculated observable populations in those clusters. The
results suggest that a large portion of the white dwarf deficit may be
explained by the presence of WDs in unresolved binary systems. However, the
calculated WD populations still over-predict the number of observable WDs in
each cluster. While these calculations cannot determine the cause of this
residual white dwarf deficit, potential explanations include a steep high-mass
IMF, dynamical evolution of the cluster, or an increased likelihood of
equal-mass components in a binary system. Observations of complete WD samples
in open clusters covering a range of ages and mass can help to distinguish
between these possibilities.


title:
Bering - The first deep space mission to map asteroidal diversity,
  origin and transportation

abstract:
  Asteroids are remnants of the material from which the Solar System formed.
Fragments of asteroids, in the form of meteorites, include samples of the first
solid matter to form in our Solar System 4.5 mia years ago. Spectroscopic
studies of asteroids show that they, like the meteorites, range from very
primitive objects to highly evolved small Earth-like planets that
differentiated into core mantle and crust. The asteroid belt displays
systematic variations in abundance of asteroid types from the more evolved
types in the inner belt to the more primitive objects in the outer reaches of
the belt thus bridging the gap between the inner evolved apart of the Solar
System and the outer primitive part of the Solar System. High-speed collisions
between asteroids are gradually resulting in their break-up. The size
distribution of kilometer-sized asteroids implies that the presently
un-detected population of sub-kilometer asteroids far outnumber the known
larger objects. Sub-kilometer asteroids are expected to provide unique insight
into the evolution of the asteroid belt and to the meteorite-asteroid
connection. We propose a space mission to detect and characterize sub-kilometer
asteroids between Jupiter and Venus. The mission is named Bering after the
famous navigator and explorer Vitus Bering. A key feature of the mission is an
advanced payload package, providing full on board autonomy of both object
detection and tracking, which is required in order to study fast moving objects
in deep space. The autonomy has the added advantage of reducing the cost of
running the mission to a minimum, thus enabling science to focus on the main
objectives.


title: Obtaining Global Galaxy Metallicities Using Emission Line EWs

abstract:
  We develop a prescription for estimating the interstellar medium oxygen
abundances of distant star-forming galaxies using the ratio EWR_{23} formed
from the equivalent widths of the [O II] 3727, [O III] 4959,5007 and Hbeta
nebular emission lines. This EWR_{23} approach essentially identical to the
widely-used R_{23} method of Pagel etal (1979). Using data from three
spectroscopic surveys of nearby galaxies, we conclude that the emission line
equivalent width ratios are a good substitute for emission line flux ratios in
galaxies with active star formation. The RMS dispersion between EWR_{23} and
the reddening-corrected R_{23} values is sigma(log R_{23})\leq0.08 dex. This
dispersion is comparable to the emission-line measurement uncertainties for
distant galaxies in many spectroscopic galaxy surveys, and is somewhat smaller
than the uncertainties of sigma(O/H)~0.15 dex inherent in strong-line
metallicity calibrations. Because equivalent width ratios are partially
insensitive to interstellar reddening effects, emission line equivalent width
ratios should be superior to flux ratios when reddening corrections are not
available. The EWR_{23} method presented here is likely to be most useful for
statistically estimating the mean metallicities for large samples of galaxies
to trace their chemical properties as a function of redshift or environment.
The approach developed here is used in a companion paper (Kobulnicky etal 2003)
to measure the metallicities of star-forming galaxies at z=0.2 - 0.8 in the
Deep Extragalactic Evolutionary Probe spectroscopic survey of the Groth Strip.


title: Asteroid and NEA detection models

abstract:
  We determine the possible detection rate of asteroids with the Bering
mission. In particular we examine the outcome of the Bering mission in relation
to the populations of Near-Earth Asteroids and main belt asteroids. This is
done by constructing synthetic populations of asteroids, based on the current
best estimates of the asteroid size-distributions. From the detailed
information obtained from the simulations, the scientific feasibility of Bering
is demonstrated and the key technical requirement for the scientific
instruments on Bering is determined.


title: On the Structure of Quasi-Universal Jets for Gamma-Ray Bursts

abstract:
  The idea that GRBs originate from uniform jets has been used to explain
numerous observations of breaks in the GRB afterglow lightcurves. We explore
the possibility that GRBs instead originate from a structured jet that may be
quasi-universal, where the variation in the observed properties of GRBs is due
to the variation in the observer viewing angle. We test how various models
reproduce the jet data of Bloom, Frail, & Kulkarni (2003), which show a
negative correlation between the isotropic energy output and the inferred jet
opening angle (in a uniform jet configuration). We find, consistent with
previous studies, that a power-law structure for the jet energy as a function
of angle gives a good description. However, a Gaussian jet structure can also
reproduce the data well, particularly if the parameters of the Gaussian are
allowed some scatter. We place limits on the scatter of the parameters in both
the Gaussian and power-law models needed to reproduce the data, and discuss how
future observations will better distinguish between these models for the GRB
jet structure. In particular, the Gaussian model predicts a turnover at small
opening angles and in some cases a sharp cutoff at large angles, the former of
which may already have been observed. We also discuss the predictions each
model makes for the observed luminosity function of GRBs and compare these
predictions with the existing data.


title:
Imaging and Demography of the Host Galaxies of High-Redshift Type Ia
  Supernovae

abstract:
  We present the results of a study of the host galaxies of high redshift Type
Ia supernovae (SNe Ia). We provide a catalog of 18 hosts of SNe Ia observed
with the Hubble Space Telescope (HST) by the High-z Supernova Search Team
(HZT), including images, scale-lengths, measurements of integrated (Hubble
equivalent) BVRIZ photometry in bands where the galaxies are brighter than m ~
25 mag, and galactocentric distances of the supernovae. We compare the
residuals of SN Ia distance measurements from cosmological fits to measurable
properties of the supernova host galaxies that might be expected to correlate
with variable properties of the progenitor population, such as host galaxy
color and position of the supernova. We find mostly null results; the current
data are generally consistent with no correlations of the distance residuals
with host galaxy properties in the redshift range 0.42 < z < 1.06. Although a
subsample of SN hosts shows a formally significant (3-sigma) correlation
between apparent V-R host color and distance residuals, the correlation is not
consistent with the null results from other host colors probed by our largest
samples. There is also evidence for the same correlations between SN Ia
properties and host type at low redshift and high redshift. These similarities
support the current practice of extrapolating properties of the nearby
population to high redshifts pending more robust detections of any correlations
between distance residuals from cosmological fits and host properties.


title: Radio Cores of Bipolar Nebulae: Search for Collimated Winds

abstract:
  We present results of our search for collimated ionized winds in bipolar
nebulae using the Very Large Array (VLA) and the Australia Telescope Compact
Array (ATCA). Our search is motivated by the discovery of an ionized jet in the
bipolar nebula M 2-9 (Lim & Kwok 2003) that may be responsible for sculpting
the nebula's mirror-symmetric structure. To determine if such jets are a common
feature of bipolar nebulae, we searched for optically-thick radio cores - a
characteristic signature of ionized jets - in 11 northern nebulae with the VLA
at 1.3 cm and 0.7 cm, and in 5 southern nebulae with the ATCA at 6 cm and 3.6
cm. Two northern objects, 19W32 and M 1-91, and two southern objects, He2-84
and and Mz 3, exhibit a compact radio core with a rising spectrum consistent
with an ionized jet. Th 2-B exhibits a steeply falling spectrum characteristic
of nonthermal radio emission. Here we present a preliminary analysis of these
five radio cores and discuss the implications of our results.


title: VLA observations of 6-cm excited OH

abstract:
  The VLA was used to determine precise positions for 4765-MHz OH maser
emission sources toward star-forming regions which had been observed about
seven months earlier with the Effelsberg 100-meter telescope. The observations
were successful for K3-50, DR21EX, W75N, and W49A. No line was detected toward
S255: this line had decreased to less than 5 per cent of the flux density
observed only seven months earlier. The time-variability of the observed
features during the past 30 years is summarised. In addition, to compare with
the Effelsberg observations, the 4750-MHz and 4660-MHz lines were observed in
W49A. These lines were found to originate primarily from an extended region
which is distinguished as an exceptional collection of compact continuum
components as well as by being the dynamical centre of the very powerful H_2 O
outflow.


title: An Intermediate-Mass Black Hole in the Dwarf Seyfert 1 Galaxy POX 52

abstract:
  We describe new observations of POX 52, a previously known but nearly
forgotten example of a dwarf galaxy with an active nucleus. While POX 52 was
originally thought to be a Seyfert 2 galaxy, the new data reveal an
emission-line spectrum very similar to that of the dwarf Seyfert 1 galaxy NGC
4395, with clear broad components to the permitted line profiles. The host
galaxy appears to be a dwarf elliptical; this is the only known case of a
Seyfert nucleus in a galaxy of this type. Applying scaling relations to
estimate the black hole mass from the broad H-beta linewidth and continuum
luminosity, we find M_BH ~ 1.6x10^5 solar masses. The stellar velocity
dispersion in the host galaxy is 36+/-5 km/s, also suggestive of a black hole
mass of order 10^5 solar masses. Further searches for AGNs in dwarf galaxies
can provide crucial constraints on the demographics of black holes in the mass
range below 10^6 solar masses.


title: Black Holes in Active Galaxies

abstract:
  Recent years have seen tremendous progress in the quest to detect
supermassive black holes in the centers of nearby galaxies, and gas-dynamical
measurements of the central masses of active galaxies have been valuable
contributions to the local black hole census. This review summarizes
measurement techniques and results from observations of spatially resolved gas
disks in active galaxies, and reverberation mapping of the broad-line regions
of Seyfert galaxies and quasars. Future prospects for the study of black hole
masses in active galaxies, both locally and at high redshift, are discussed.


title:
The Gemini Deep Deep Survey: II. Metals in Star-Forming Galaxies at
  Redshift 1.3<z<2

abstract:
  The goal of the Gemini Deep Deep Survey (GDDS) is to study an unbiased sample
of K<20.6 galaxies in the redshift range 0.8<z<2.0. Here we determine the
statistical properties of the heavy element enrichment in the interstellar
medium (ISM) of a subsample of 13 galaxies with 1.34<z<1.97 and UV absolute
magnitude M_2000 < -19.65. The sample contains 38% of the total number of
identified galaxies in the first two fields of the survey with z>1.3. The
selected objects have colors typical of irregular and Sbc galaxies. Strong
[OII] emission indicates high star formation activity in the HII regions
(SFR~13-106 M_sun/yr). The high S/N composite spectrum shows strong ISM MgII
and FeII absorption, together with weak MnII and MgI lines. The FeII column
density, derived using the curve of growth analysis, is logN_FeII =
15.54^{+0.23}_{-0.13}. This is considerably larger than typical values found in
damped Ly-alpha systems (DLAs) along QSO sight lines, where only 10 out of 87
(~11%) have logN_FeII > 15.2. High FeII column densities are observed in the
z=2.72 Lyman break galaxy cB58 (logN_FeII ~ 15.25) and in gamma-ray burst host
galaxies (logN_FeII ~ 14.8-15.9). Given our measured FeII column density and
assuming a moderate iron dust depletion (delta_Fe ~ 1 dex), we derive an
optical dust extinction A_V ~ 0.6. If the HI column density is log N(HI)<21.7
(as in 98% of DLAs), then the mean metallicity is Z/Z_sun > 0.2. The high
completeness of the GDDS sample implies that these results are typical of
star-forming galaxies in the 1<z<2 redshift range, an epoch which has
heretofore been particularly challenging for observational programs.


title:
The near-IR luminosity-metallicity relationship for dwarf irregular
  galaxies

abstract:
  We briefly describe our on-going investigation of the near-IR
luminosity-metallicity relationship for dwarf irregular galaxies in nearby
groups of galaxies. The motivations of the project and the observational
databases are introduced, and a preliminary result is presented. The
12+log(O/H) vs.H plane must be populated with more low-luminosity galaxies
before a definite conclusion can be drawn.


title: Direct Search for Dark Matter Particles With Very Large Detectors

abstract:
  We briefly discuss the expected level of supersymmetric dark matter
cross-sections as a reference for dark matter detectors. We then discuss the
current ZEPLIN II program as a prototype of large liquid Xenon detectors.
Cryoarray is a possible cryogenic detector. Finally we discuss ZEPLIN IV and
other one ton liquid Xenon detectors and the limiting backgrounds for such
detectors.


title: Scaling Relations of Local Spiral Galaxies.I. Observational Foundations

abstract:
  (Abridged) This paper presents an exploration of two fundamental scaling
relations of spiral galaxies, the luminosity-rotation speed (or Tully-Fisher;
TF) relation, and the size-luminosity (SL) relation, and the dependences of
their scatter, at red and IR bands. We verify that the observed virial
relations of disk galaxies are given by Vobs \prop L^0.31 and Rd \prop L^0.33
using distance-redshift surveys of high surface brightness (HSB) and low
surface brightness (LSB) non-interacting galaxies. Thus the galaxy surface
brightness (SB) is Sigma \prop Rd \prop Vobs \prop Mvir^0.33. We derive the
first extensive J-band TF and SL relations using 2MASS data products. The TF
residuals are fully independent of SB and other tested observables. TF
relations (TFRs) for various morphological types have different zero points,
but a common slope, such that early-type (redder) disks rotate faster than
later-types (bluer) of the same luminosity. This dependence of the TFR is a
direct consequence of the more fundamental dependence on color, which itself is
related to the galaxy star formation history. The SL relation scatter is mostly
dominated by SB, but color also plays a small role. The TF and SL residuals for
HSB and LSB galaxies are weakly correlated, in agreement with the earlier claim
by Courteau & Rix (1999). This suggests that spiral disks of all color,
brightness, and barredness are, on average, dominated by dark matter even in
their inner parts. The observed scaling relations of disk galaxies are likely
the result of the simplest scenario of galaxy formation, but their color
dependence remains a challenge to hierarchical structure formation models. The
scaling relations and their derivatives are contrasted against galaxy formation
models in our companion paper.


title: Nitrogen Overabundance: Globular Cluster and Halo Formation

abstract:
  Halo globular clusters pose four succinct issues that must be solved in any
scenario of their formation: single-age, single metallicity stellar
populations; a lower limit ([Fe/H] ~ -2.3) to their average metallicity;
comprising only 1% of the stellar halo mass, and being among the oldest stars
in our Galaxy. New spectra are presented of Galactic stars and integrated
spectra of Galactic globular clusters which extend to 3250 angstroms. These
spectra show show that the most metal-poor and among the best-studied Galactic
globular clusters show strong NH3360 absorption, even though their spectral
energy distributions in the near-UV are dominated by blue horizontal branch,
AF-type stars. These strong NH features must be coming from the main sequence
stars in these clusters. These new data are combined with existing data on the
wide range of carbon and nitrogen abundance in very metal-poor ([Fe/H] < -3.5)
halo giant and dwarf stars, together with recent models of zero-metal star
formation, to make a strawman scenario for globular cluster formation that can
reproduce three of the above four issues, and well as related two of the three
issues pertaining to nitrogen overabundance. This strawman proposal makes
observational and theoretical predictions that are testable, needing specific
help from the modelers to understand all of the elemental constraints on
globular cluster and halo formation.


title:
X-ray Scattering Halos from the Galactic Center: Implications for
  Diffuse Emission Around SgrA*

abstract:
  We consider the absorption and scattering of X-rays observed from the
Galactic center. One objective is to characterize the intrinsic X-ray emission
from the central black hole, SgrA*, in its quiescent and flaring states. We
correct the fluxes observed by the Chandra and XMM telescopes for absorption
and scattering, using realistic models for the dust grain size distribution,
gas and dust abundances and spatial distributions. However, there are still
large uncertainties. Since much of the intervening dust is close to SgrA*, the
scattered halo of X-ray photons is very concentrated: its intensity can
dominate the Chandra PSF inside 1", and so affects estimates of the point
source flux. It also broadens the radial intensity profiles of Galactic center
sources - observations of this effect can help constrain models of the spatial
distribution of the dust. We estimate that the combined scattering halos from
observed Galactic center sources within 10" of SgrA* contribute up to ~10% of
the observed diffuse emission in this region. Dust-scattered photons suffer a
time delay relative to the photons that arrive directly. For dust that is 100
pc towards us from the Galactic center, this delay is about 1000 s at angles of
1", and 100 ks at 10". We illustrate how the evolution of the scattering halo
following X-ray flares from SgrA* or other sources can also help to constrain
the dust's line of sight distribution. We discuss the implications of X-ray
scattering halos for the intensity of diffuse emission that has been reported
within a few arcseconds of SgrA*: in the most extreme, yet viable, model we
consider, ~1/3 of it is due to dust scattering of an unresolved source. The
remainder results from an extended source of emission.


title:
The Era of Massive Population III Stars: Cosmological Implications and
  Self-Termination

abstract:
  The birth and death of the first generation of stars have important
implications for the thermal state and chemical properties of the intergalactic
medium (IGM) in the early universe. Sometime after recombination, the neutral,
chemically pristine gas was reionized by ultraviolet photons emitted from the
first stars, but also enriched with heavy elements when these stars ended their
lives as energetic supernovae. Using the results from previous high-resolution
cosmological simulations of early structure formation that include radiative
transfer, we show that a significant volume fraction of the IGM can be
metal-polluted, as well as ionized, by massive Population III stars formed in
small-mass (10^6-10^7 Msun) halos early on. If most of the early generation
stars die as pair-instability supernovae with energies up to 10^{53} ergs, the
volume-averaged mean metallicity will quickly reach Z ~ 10^{-4}Zsun by a
redshift of 15-20, possibly causing a prompt transition to the formation of a
stellar population that is dominated by low-mass stars. In this scenario, the
early chemical enrichment history should closely trace the reionization history
of the IGM, and the end of the Population III era is marked by the completion
of reionization and pre-enrichment by z=15. We conclude that, while the
pre-enrichment may partially account for the ``metallicity-floor'' in
high-redshift Lyman-alpha clouds, it does not significantly affect the
elemental abundance in the intracluster medium.


title:
Globular cluster abundances in the light of 3D hydrodynamical model
  atmospheres

abstract:
  The new generation of 3D hydrodynamical model atmospheres have been employed
to study the impact of a realistic treatment of stellar convection on element
abundance determinations of globular cluster stars for a range of atomic and
molecular lines. Due to the vastly different temperature structures in the
optically thin atmospheric layers in 3D metal-poor models compared with
corresponding hydrostatic 1D models, some species can be suspected to be
hampered by large systematic errors in existing analyses. In particular, 1D
analyses based on minority species and low excitation lines may overestimate
the abundances by >0.3 dex. Even more misleading may be the use of molecular
lines for metal-poor globular clusters. However, the prominent observed
abundance (anti-)correlations and cluster variations are largely immune to the
choice of model atmospheres.


title: Uncertainties in stellar abundance analyses

abstract:
  Over the last half-century quantitative stellar spectroscopy has made great
progress. However, most stellar abundance analyses today still employ rather
simplified models, which can introduce severe systematic errors swamping the
observational errors. Some of these uncertainties for late-type stars are
briefly reviewed here: atomic and molecular data, stellar parameters, model
atmospheres and spectral line formation.


title: A Dynamical Model for Hot Gas in the Galactic Center

abstract:
  Winds from massive stars supply ~ 10^{-3} solar masss/year of gas to the
central parsec of the Galactic Center. Spherically symmetric hydrodynamic
calculations show that ~ 1 % of this gas, or ~ 10^{-5} solar masses/year, flows
in towards the central massive black hole Sgr A*; the remaining gas, ~ 10^{-3}
solar masses/year, is thermally driven out of the central star cluster in a
wind. This dynamical model accounts for the level of diffuse X-ray emission
observed in the Galactic Center by Chandra and the extended X-ray source
coincident with Sgr A*; the latter is a direct signature of gas being
gravitational captured by the black hole.


title: Perhaps they are not Globular Clusters after all

abstract:
  Our 2dF Fornax Cluster Spectroscopic Survey (FCSS) and follow-up work in the
Virgo Cluster have shown that the cores of both galaxy clusters contain a
previously-unknown class of object, ultra-compact dwarf (UCD) galaxies. We
present high resolution spectroscopy and deep multicolour imaging to show that
these enigmatic objects are dynamically distinct from both globular clusters
(GCs) and nucleated dwarf galaxies (dE,Ns). Our hypothesis for their origin may
explain the observed high ``specific frequency'' of GCs in central cluster
galaxies.


title: Galaxy Disruption Caught in the Act

abstract:
  Direct evidence of stellar material from galaxy disruption in the
intra-cluster medium (ICM) relies on challenging observations of individual
stars, planetary nebulae and diffuse optical light. Here we show that the
ultra-compact dwarf galaxies (UCDs) we have discovered in the Fornax Cluster
are a new and easy-to-measure probe of disruption in the ICM. We present
spectroscopic observations supporting the hypothesis that the UCDs are the
remnant nuclei of tidally ``threshed'' dwarf galaxies. Deep optical imaging of
the cluster has revealed a 43-kpc long arc of tidal debris, flanking a
nucleated dwarf elliptical (dE,N) cluster member. We may be witnessing galaxy
threshing in action.


title: The Ghosts of Galaxies: Tidal Debris in Clusters

abstract:
  Gravitational interactions in rich clusters can strip material from the outer
parts of galaxies or even completely disrupt entire systems, giving rise to
large scale, low surface brightness ghostly features stretching across
intergalactic space. The nearby Coma and Centaurus clusters both have striking
examples of galaxy ghosts, in the form of 100 kpc-long plumes of intergalactic
debris. By searching HST archival images, we have found numerous other examples
of galaxy ghosts in rich clusters at low redshift, evidence that galaxy
destruction and recycling are ubiquitous, important in cluster formation and
evolution, and continue to mold clusters at the present epoch. Many ghosts
appear in X-ray bright clusters, perhaps signaling a connection with energetic
subcluster mergers. The fate of such material has important ramifications for
cluster evolution. Our new HST WFPC2 V & I images of a portion of the Centaurus
plume reveal that it contains an excess of discrete objects with -12 < M_v <
-6, consistent with being globular clusters or smaller dwarf galaxies. This
tidally liberated material is being recycled directly into the intracluster
population of stars, dwarf galaxies, globular clusters, and gas, which may have
been built largely from a multitude of similar events over the life of the
cluster.


title: Cross-correlating the Microwave Sky with Galaxy Surveys

abstract:
  We present results for the cross-correlation between the WMAP 1st-year cosmic
microwave background (CMB) anisotropy data and optical galaxy surveys: the APM
and SDSS DR1 catalogs. Our measurement of a positive CMB-galaxy correlation on
large angles (\theta > 4 deg) yields significant detections of the Integrated
Sachs-Wolfe (ISW) effect and provides a new estimate of dark-energy in the
universe, \Omega_\Lambda=0.69-0.86 (2 \sigma range). In addition, the
correlated signal on small angles (\theta<1 deg) reveals the imprint left by
hot intra-cluster gas in the CMB photons: the thermal Sunyaev-Zeldovich (SZ)
effect


title:
Observational manifestations of young neutron stars: Spin-powered
  pulsars

abstract:
  The largest number of known young neutron stars are observed as spin-powered
pulsars. While the majority of those are detected at radio frequencies, an
increasing number can be studied at other parts of the electromagnetic spectrum
as well. The Crab pulsar is the prototype of a young pulsar which can be
observed from radio to gamma-ray frequencies, providing a red thread of
discussion during a tour through the pulsar properties observed across the
electromagnetic spectrum. The basic observational features of pulsar emission
are presented, preparing the ground for more detailed reviews given in these
proceedings. Here, particular attention will be paid to those emission features
which may provide a link between the radio and high-energy emission processes.


title: Are the quasars the missing "accretor isolated neutron stars" ?

abstract:
  The accretion of a cloud of hydrogen at the surface of a small, heavy star
produces a high energy mostly dissipated by electromagnetic radiation.
  The combination of the absorption and the redshift of this radiation by
hydrogen explains all spectral observations: shapes of the broad lines, and
their anti-correlation with the radio-loudness, lack of lines in front of the
Lyman forest, value zb = 0.062 of the periodicity of the redshifts, correlation
of a high redshift with a thermal spectrum attributed to dust.
  As a large part of the redshift is intrinsic, the quasars are not extremely
far, the may be the missing "accretor isolated neutron stars".
  These properties are deduced from usual laws of physics without new
parameters, they do not require any non baryonic matter.


title:
Relationship between environment and the broad-band optical properties
  of galaxies in the SDSS

abstract:
  We examine the relationship between environment and the luminosities, surface
brightnesses, colors, and profile shapes of luminous galaxies in the Sloan
Digital Sky Survey (SDSS). For the SDSS sample, galaxy color is the galaxy
property most predictive of the local environment. Galaxy color and luminosity
jointly comprise the most predictive pair of properties. At fixed luminosity
and color, density is not closely related to surface brightness or to Sersic
index -- the parameter in this study that astronomers most often associate with
morphology. In the text, we discuss what measureable residual relationships
exist, generally finding that at red colors and fixed luminosity, the mean
density decreases at the highest surface brightnesses and Sersic indices. In
general, these results suggest that the morphological properties of galaxies
are less closely related to galaxy environment than are their masses and
star-formation histories.


title: New Pulsars Discovered in Arecibo Drift-Scan Searches

abstract:
  We report on new pulsars discovered in Arecibo drift-scan data. Processing of
2200 square degrees of data has resulted in the detection of 41 known and 12
new pulsars. New pulsars include two millisecond pulsars, one solitary and one
binary recycled pulsar, and one pulsar with very unusual pulse profile
morphology and complex drifting subpulse behavior.


title: Two Radio Pulsars with Magnetar Fields

abstract:
  PSRs J1847-0130 and J1718-37184 have inferred surface dipole magnetic fields
greater than those of any other known pulsars and well above the ``quantum
critical field'' above which some models predict radio emission should not
occur.These fields are similar to those of the anomalous X-ray pulsars (AXPs),
which growing evidence suggests are ``magnetars''. The lack of AXP-like X-ray
emission from these radio pulsars (and the non-detection of radio emission from
the AXPs) creates new challenges for understanding pulsar emission physics and
the relationship between these classes of apparently young neutron stars.


title:
Effective temperatures and radii of planet-hosting stars from IR
  photometry

abstract:
  In this paper we present and analyse determinations of effective temperatures
of planet-hosting stars using infrared (IR) photometry. One of our goals is the
comparison with spectroscopic temperatures to evaluate the presence of
systematic effects that could alter the determination of metal abundances. To
estimate the stellar temperatures we have followed a new approach based on
fitting the observed 2MASS IR photometry with accurately calibrated synthetic
photometry. Special care has been put in evaluating all sources of possible
errors and incorporating them in the analysis. A comparison of our temperature
determinations with spectroscopic temperatures published by different groups
reveals the presence of no systematic trends and a scatter compatible with the
quoted uncertainties of 0.5-1.3%. This mutual agreement strengthens the results
of both the spectroscopic and IR photometry analyses. Comparisons with other
photometric temperature calibrations, generally with poorer performances, are
also presented. In addition, the method employed of fitting IR photometry
naturally yields determinations of the stellar semi-angular diameters, which,
when combined with the distances, results in estimations of the stellar radii
with remarkable accuracies of ~2-4%. A comparison with the only star in the
sample with an empirically determined radius (HD 209458 -- from transit
photometry) indicates excellent agreement.


title: The Anomaly in the Candidate Microlensing Event PA-99-N2

abstract:
  The lightcurve of PA-99-N2, one of the recently announced microlensing
candidates towards M31, shows small deviations from the standard Paczynski
form. We explore a number of possible explanations, including correlations with
the seeing, the parallax effect and a binary lens. We find that the
observations are consistent with an unresolved RGB or AGB star in M31 being
microlensed by a binary lens. We find that the best fit binary lens mass ratio
is about one hundredth, which is one of most extreme values found for a binary
lens so far. If both the source and lens lie in the M31 disk, then the standard
M31 model predicts the probable mass range of the system to be 0.02-3.6 solar
masses (95 % confidence limit). In this scenario, the mass of the secondary
component is therefore likely to be below the hydrogen-burning limit. On the
other hand, if a compact halo object in M31 is lensing a disk or spheroid
source, then the total lens mass is likely to lie between 0.09-32 solar masses,
which is consistent with the primary being a stellar remnant and the secondary
a low mass star or brown dwarf. The optical depth (or alternatively the
differential rate) along the line of sight toward the event indicates that a
halo lens is more likely than a stellar lens provided that dark compact objects
comprise no less than 15 per cent (or 5 per cent) of haloes.


title: Radio halos in star forming galaxies

abstract:
  We study the relation between radio halos, the energy input by supernovae in
the disk and the galaxy mass. We find that both the energy input by supernovae
as well as the galaxy mass are important parameters for understanding the
formation of radio halos. Galaxies with a high energy input by supernovae per
star forming area and a low galaxy mass generally possess radio halos whereas
galaxies with the opposite characteristics do not. Furthermore, there is a
tentative correlation between the observed scale height and the expected height
in a simple gravitational approximation.


title:
Comprehensive modelling of the planetary nebula LMC-SMP 61 and its
  [WC]-type central star

abstract:
  We present a comprehensive study of the Magellanic Cloud planetary nebula SMP
61 and of its nucleus, a Wolf-Rayet type star classified [WC 5-6]. We have
performed a detailed spectral analysis of the central star, using the Potsdam
code for expanding atmospheres in non-LTE. The fluxes from the model stellar
atmosphere were used to compute photoionization models of the nebula. All the
available observations, within their error bars, were used to constrain these
models. We find that the ionizing fluxes predicted by the stellar model are
basically consistent with the fluxes needed by the photoionization model to
reproduce the nebular emission, within the error margins. However, there are
indications that the stellar model overestimates the number and hardness of
Lyman continuum photons. The photoionization models imply a clumped density
structure of the nebular material. The observed CIII] 1909/CII 4267 line ratio
implies the existence of carbon-rich clumps in the nebula. Such clumps are
likely produced by stellar wind ejecta, possibly mixed with the nebular
material. We discuss our results with regard to the stellar and nebular
post-AGB evolution.


title: Non-Gaussianity from Warm Inflation in the Weak Dissipative Regime

abstract:
  The generic prediction for the perturbations generated during slow--roll,
single--field inflation, as they appear in the cosmic microwave background
(CMB), is a flat, close--to--Gaussian spectrum. We calculate the general
solution for a warm inflationary scenario with weak dissipation, reviewing the
dissipative dynamics of the two--fluid system, and calculate the bispectrum of
the gravitational field fluctuations generated in the case where dissipation of
the vacuum potential during inflation is the mechanism for structure formation,
but is the sub--dominant effect in the dynamics of the scalar field.


title: Long term X-ray spectral variability of the nucleus of M81

abstract:
  We have analysed the soft X-ray emission from the nuclear source of the
nearby spiral galaxy M81, using the available data collected with ROSAT, ASCA,
BeppoSAX and Chandra. The source flux is highly variable, showing (sometimes
dramatic: a factor of 4 in 20 days) variability at different timescales, from 2
days to 4 years, and in particular a steady increase of the flux by a factor of
>~ 2 over 4 years, broken by rapid flares. After accounting for the extended
component resolved by Chandra, the nuclear soft X-ray spectrum (from
ROSAT/PSPC, BeppoSAX/LECS and Chandra data) cannot be fitted well with a single
absorbed power-law model. Acceptable fits are obtained adding an extra
component, either a multi-color black body (MCBB) or an absorption feature. In
the MCBB case the inner accretion disk would be far smaller than the
Schwartzchild radius for the 3-60X 10^6 solar masses nucleus requiring a
strictly edge-on inclination of the disk, even if the nucleus is a rotating
Kerr black hole. The temperature is 0.27 keV, larger than expected from the
accretion disk of a Schwartzchild black hole, but consistent with that expected
from a Kerr black hole. In the power-law + absorption feature model we have
either high velocity (0.3 c) infalling C_v clouds or neutral C_i absorption at
rest. In both cases the C:O overabundance is a factor of 10.


title:
Magnetic fields in barred galaxies III: The southern peculiar galaxy NGC
  2442

abstract:
  Observations of the southern peculiar galaxy NGC 2442 with the Australia
Telescope Compact Array in total and linearly polarized radio continuum at 6cm
are presented and compared with previously obtained H$\alpha$ data. The
distribution of polarized emission, a signature of regular magnetic fields,
reveals some physical phenomena which are unusual among spiral galaxies. We
find evidence for tidal interaction and/or ram pressure from the intergalactic
medium compressing the magnetic field at the northern and western edges of the
galaxy. The radial component of the regular magnetic field in the northern arm
is directed away from the centre of the galaxy, a finding which is in contrast
to the majority of galaxies studied to date. The oval distortion caused by the
interaction generates a sudden jump of the magnetic field pattern upstream of
the inner northern spiral arm, similar to galaxies with long bars. An unusual
``island'' of strong regular magnetic field east of the galaxy is probably the
brightest part of a magnetic arm frequently seen in spiral galaxies, which
appear to be phase-shifted images of the preceding optical arm. The strong
magnetic field of the ``island'' indicates a past phase of active star
formation when the preceding optical arm was exposed to ram pressure.


title:
The Different Fates of a Low-Mass X-ray Binary. I: Conservative Mass
  Transfer

abstract:
  We study the evolution of a low mass x-ray binary coupling a binary stellar
evolution code with a general relativistic code that describes the behavior of
the neutron star. We assume the neutron star to be low--magnetized (B~10^8 G).
In the systems investigated in this paper, our computations show that during
the binary evolution the companion transfers as much as 1 solar mass to the
neutron star, with an accretion rate of 10^-9 solar masses/yr. This is
sufficient to keep the inner rim of the accretion disc in contact with the
neutron star surface, thus preventing the onset of a propeller phase capable of
ejecting a significant fraction of the matter transferred by the companion. We
find that, for neutron stars governed by equations of state from soft up to
moderately stiff, an accretion induced collapse to a black hole is almost
unavoidable. The collapse to a black hole can occur either during the accretion
phase or after the end of the mass transfer when the neutron star is left in a
supramassive sequence. In this last case the collapse is driven by energy
losses of the fast spinning radio pulsar. For extremely supramassive neutron
stars these energy losses cause a spin up. As a consequence the pulsar will
have a much shorter lifetime than that of a canonical radio pulsar. This
behavior depends on the equation of state for ultra-dense matter and therefore
could be used to constrain the internal structure of the neutron star. If the
r-modes of the neutron star are excited during the accretion process, the
gravitational waves emisson limits the maximum spin attainable by a NS to
roughly 2 ms. In this case the collapse during the accretion phase is even more
common since the maximum mass achievable before the collapse to a black hole
during accretion is smaller due to the limited spin frequency.


title:
Dust obscuration studies along quasar sight lines using simulated
  galaxies

abstract:
  We use the results of a set of three-dimensional SPH-Treecode simulations
which model the formation and early evolution of disk galaxies, including the
generation of heavy elements by star formation, to investigate the effects of
dust absorption in quasar absorption line systems.
  Using a simple prescription for the production of dust, we have compared the
column density, zinc abundance and optical depth properties of our models to
the known properties of Damped Lyman alpha systems.
  We find that a significant fraction of our model galaxy disks have a higher
column density than any observed DLA system. We are also able to show that such
parts of the disk tend to be optically thick, implying that any background
quasar would be obscured through much of the disk. This would produce the
selection effect against the denser absorption systems thought to be present in
observations.


title: The thermal and kinematic Sunyaev-Zel'dovich effects revisited

abstract:
  This paper shows that a simple convolution integral expression based on the
mean value of the isotropic frequency distribution corresponding to photon
scattering off electrons leads to useful analytical expressions describing the
thermal Sunyaev-Zel'dovich effect. The approach, to first order in the Compton
parameter is able to reproduce the Kompaneets equation describing the effect.
Second order effects in the parameter $z=\frac{kT_{e}}{mc^{2}}$ induce a slight
increase in the crossover frequency.


title: Photometric study of two novae in M31

abstract:
  We report $R_cI_c$ light curves of 2 novae in the M31 galaxy which were
detected in the four year Nainital Microlensing Survey. One of these novae has
been tracked from the initial increase in flux while other has been observed
during its descending phase of brightness. The photometry of the first nova
during the outburst phase suggests its peak $R_c$ magnitude to be about 17.2
mag with a flux decline rate of 0.11 mag day$^{-1}$ which indicates that it was
a fast nova. A month after its outburst, it shows reddening followed by a
plateau in $I_c$ flux. The second nova exhibits a bump in $R_c$ and $I_c$,
possibly about three weeks after the outburst.


title:
Near-IR [Fe II] emission diagnostics applied to cold disk winds in young
  stars

abstract:
  We investigate the emissivity properties of the main near-IR transitions of
the Fe+ ion in the conditions prevailing in the inner regions of jets from
young stars, based on a simplified 16-level atom model. We present new
diagnostic diagrams involving prominent near-IR line ratios that allow us to
constrain the electronic density, temperature, and Fe gas phase abundance
ratio, independently of the heating process. Comparison with recent near-IR
observations of a sample of HH objects indicates gas phase Fe abundances
ranging from 15-50 % up to 100 % of the solar value in agreement with the
moderate depletions previously derived from optical line ratios or shock
models. Hence, it appears that Fe-bearing dust is efficiently destroyed in
stellar jets. We then use our Fe+ emissivity model to predict near-IR [Fe II]
emission maps for self-similar, cold MHD disk wind models. We show that
observations in [Fe II] with AMBER on the VLTI could severely constrain the MHD
solution and the inner launch radius of the jet. We also compare theoretical
predictions with recent observations in the near-IR [Fe II] lines of the
L1551-IRS5 and DG Tau jets. The cold disk wind model reproduces quite well the
two velocity components observed at -100 and -300 km/s, although the high
velocity component appears overestimated by a factor of 1.5 in the DG Tau jet.
However, the model predicts too little emission at intermediate-velocity and
insufficient densities. Denser disk winds with stronger heating at the jet
base, which have been invoked for optical jets, also appear needed in younger,
embedded Class I jet sources.


title:
RXTE and BeppoSAX Observations of MCG -5-23-16: Reflection From Distant
  Cold Material

abstract:
  We examine the spectral variability of the Seyfert 1.9 galaxy MCG -5-23-16
using RXTE and BeppoSAX observations spanning 2 years from April 1996 to April
1998. During the first year the X-ray source brightens by a factor of ~25% on
timescales of days to months. During this time, the reprocessed continuum
emission seen with RXTE does not respond measurably to the continuum increase.
However, by the end of the second year during the BeppoSAX epoch the X-ray
source has faded again. This time, the reprocessed emission has also faded,
indicating that the reprocessed flux has responded to the continuum. If these
effects are caused by time delays due to the distance between the X-ray source
and the reprocessing region, we derive a light crossing time of between ~1
light day and ~1.5 light years. This corresponds to a distance of 0.001 pc to
0.55 pc, which implies that the reprocessed emission originates between 3x10^15
cm and 1.6x10^18 cm from the X-ray source. In other words, the reprocessing in
MCG -5-23-16 is not dominated by the inner regions of a standard accretion
disk.


title: Variability Tests for Intrinsic Absorption Lines in Quasar Spectra

abstract:
  Quasar spectra have a variety of absorption lines whose origins range from
energetic winds expelled from the central engines to unrelated, intergalactic
clouds. We present multi-epoch, medium resolution spectra of eight quasars at
z~2 that have narrow ``associated'' absorption lines (AALs, within $\pm$5000 km
s^{-1} of the emission redshift). Two of these quasars were also known
previously to have high-velocity mini-broad absorption lines (mini-BALs). We
use these data, spanning ~17 years in the observed frame with two to four
observations per object, to search for line strength variations as an
identifier of absorption that occurs physically near (``intrinsic'' to) the
central AGN.
  Our main results are the following: Two out of the eight quasars with narrow
AALs exhibit variable AAL strengths. Two out of two quasars with high-velocity
mini-BALs exhibit variable mini-BAL strengths. We also marginally detect
variability in a high-velocity narrow absorption line (NAL) system, blueshifted
\~32,900 km s^{-1}$ with respect to the emission lines. No other absorption
lines in these quasars appeared to vary. The outflow velocities of the variable
AALs are 3140 km s^{-1} and 1490 km s^{-1}. The two mini-BALs identify much
higher velocity outflows of ~28,400 km s^{-1} and ~52,000 km s^{-1}. Our
temporal sampling yields upper limits on the variation time scales from 0.28 to
6.1 years in the quasar rest frames. The corresponding minimum electron
densities in the variable absorbers, based on the recombination time scale, are
\~40,000 cm^{-3} to ~1900 cm^{-3}. The maximum distances of the absorbers from
the continuum source, assuming photoionization with no spectral shielding,
range from ~1.8 kpc to ~7 kpc.


title:
HD 199143 and HD 358623: Two Recently Identified Members of the Beta
  Pictoris Moving Group

abstract:
  HD 199143 and HD 358623 (BD-17 6128) are two sets of binary stars which are
physically associated and 48 pc from Earth. We present heliocentric radial
velocities and high lithium abundances which establish these stars as members
of the 12 Myr-old Beta Pictoris Moving Group. We also present mid-IR
photometric measurements which show no firm evidence for warm dust around all
four stars.


title: Supernova Remnant and Pulsar Wind Nebula Interactions

abstract:
  I review several topics in the structure of supernova remnants. Hydrodynamic
instabilities in young remnants may give rise to the cellular structure that is
sometimes observed, although structure in the ejecta might also play a role.
The presence of ejecta close to the forward shock front of a young remnant can
be the result of ejecta clumps or the dynamical effects of cosmic rays. Slower
moving ejecta clumps can affect the outer shock structure of older remnants
such as Vela. Young remnants typically show a circular structure, but often
have a one-sided asymmetry; the likely reasons are an asymmetric circumstellar
medium, or pulsar velocities in the case of pulsar wind nebulae. In older
remnants, asymmetric pulsar wind nebulae can result from asymmetric reverse
shock flows and/or pulsar velocities.


title: The evolution of the C/O ratio in metal-poor halo stars

abstract:
  We report new measurements of carbon and oxygen abundances in 34 F and G
dwarf and subgiant stars belonging to the halo population and spanning a range
of metallicity from [Fe/H] = -0.7 to -3.2 . The survey is based on observations
of four permitted lines of C I near 9100 A, and the O I 7774 A triplet, all
recorded at high signal-to-noise ratios with the UVES echelle spectrograph on
the ESO VLT. The line equivalent widths were analysed with the 1D, LTE, MARCS
model atmosphere code to deduce C and O abundances; corrections due to non-LTE
and 3D effects are discussed. When combined with similar published data for
disk stars, our results confirm the metallicity dependence of the C/O ratio
known from previous stellar and interstellar studies: C/O drops by a factor of
3-4 as O/H decreases from solar to 1/10 solar. Analysed within the context of
standard models for the chemical evolution of the solar vicinity, this drop
results from the metallicity dependence of the C yields from massive stars with
mass loss, augmented by the delayed release of C from stars of low and
intermediate mass. The former is, however, always the dominant factor. Our
survey has also uncovered tentative evidence to suggest that, as the oxygen
abundance decreases below [O/H] = -1, [C/O] may not remain constant at [C/O] =
-0.5, as previously thought, but increase again, possibly approaching
near-solar values at the lowest metallicities ([O/H] approximately equal to
-3). With the current dataset this is no more than a 3 sigma effect and it may
be due to metallicity-dependent non-LTE corrections to the [C/O] ratio which
have not been taken into account. However, its potential importance as a window
on the nucleosynthesis by Population III stars is a strong incentive for future
work, both observational and theoretical, to verify its reality.


title: Particle decays during the cosmic dark ages

abstract:
  We consider particle decays during the cosmic dark ages with two aims: (1) to
explain the high optical depth reported by WMAP, and (2) to provide new
constraints to the parameter space for decaying particles. We delineate the
decay channels in which most of the decay energy ionizes and heats the IGM gas
(and thus affects the CMB), and those in which most of the energy is carried
away -- e.g. photons with energies 100 keV < E < 1 TeV -- and thus appears as a
contribution to diffuse x-ray and gamma-ray backgrounds. The new constraints to
the decay-particle parameters from the CMB power spectrum thus complement those
from the cosmic X-ray and gamma-ray backgrounds. Although decaying particles
can indeed produce an optical depth consistent with that reported by WMAP, in
so doing they produce new fluctuations in the CMB temperature/polarization
power spectra. For decay lifetimes less than the age of the Universe, the
induced power spectra generally violate current constraints, while the power
spectra are usually consistent if the lifetime is longer than the age of the
Universe.


title:
Optimizing wide-field coded aperture imaging: radial mask holes and
  scanning

abstract:
  Imaging at hard X-ray energies (~10-600 keV) over very large fields of view
(~60 deg per telescope) is required to conduct a high sensitivity all-sky and
all-time survey for black holes. The proposed Energetic X-ray Imaging Survey
Telescope (EXIST) could achieve the high sensitivity required for the mission
science objectives by scanning an array of widefield coded aperture telescopes
with aperture mask holes radially aligned to minimize auto-collimation by the
thick (~7mm) masks required for high energy imaging. Simulation results from a
preliminary design study are reported which quantify the improvement in
off-axis imaging sensitivity vs. the conventional case with mask holes all
perpendicular to the mask. Such masks can be readily constructed from a stacked
laminate of thin (1mm) laser-etched W sheets. An even more dramatic increase in
coded aperture imaging sensitivity, and dynamic range, for a realistic
telescope and imaging detector with typical systematic errors can be achieved
by continuously scanning the field of view of the telescope over the source
region to be imaged. Simulation results are reported for detectors with
systematic errors 1-10%, randomly distributed but unknown in each detector
pixel. For the simplified case of a 1-D coded aperture telescope scanning along
its pattern, the systematics are removed identically. Results are also
presented for the 2-D case with both 1-D and partial 2-D scanning which
demonstrate the feasibility of a coded aperture scanning telescope with
systematic errors achieving nearly Poisson-limited sensitivity for
signal/background ratios S/B ~ 10^-4, in constrast to limits typically ~10-
100X worse that have been actually achieved by pointed or dithered coded
aperture telescopes flown (or proposed) previously.


title: Cathode depth sensing in CZT detectors

abstract:
  Measuring the depth of interaction in thick Cadmium-Zinc-Telluride (CZT)
detectors allows improved imaging and spectroscopy for hard X-ray imaging above
100 keV. The Energetic X-ray Imaging Survey Telescope (EXIST) will employ
relatively thick (5 - 10 mm) CZT detectors, which are required to perform the
broad energy-band sky survey. Interaction depth information is needed to
correct events to the detector "focal plane" for correct imaging and can be
used to improve the energy resolution of the detector at high energies by
allowing event-based corrections for incomplete charge collection. Background
rejection is also improved by allowing low energy events from the rear and
sides of the detector to be rejected. We present experimental results of
interaction depth sensing in a 5 mm thick pixellated Au-contact IMARAD CZT
detector. The depth sensing was done by making simultaneous measurements of
cathode and anode signals, where the interaction depth at a given energy is
proportional to the ratio of cathode/anode signals. We demonstrate how a simple
empirical formula describing the event distributions in the cathode/anode
signal space can dramatically improve the energy resolution. We also estimate
the energy and depth resolution of the detector as a function of the energy and
the interaction depth. We also show a depth-sensing prototype system currently
under development for EXIST in which cathode signals from 8, 16 or 32 crystals
can be read-out by a small multi-channel ASIC board that is vertically
edge-mounted on the cathode electrode along every second CZT crystal boundary.
This allows CZT crystals to be tiled contiguously with minimum impact on
throughput of incoming photons. The robust packaging is crucial in EXIST, which
will employ very large area imaging CZT detector arrays.


title: A warm hot intergalactic medium towards 3C 120?

abstract:
  We observed the Seyfert I active galaxy/broad line radio galaxy 3C120 with
the Chandra high energy transmission gratings and present an analysis of the
soft X-ray spectrum. We identify the strongest absorption feature (detected at
>99.9% confidence) with O VIII Lya (FWHM=1010^{+295}_{-265} km/s), blueshifted
by -5500 +/- 140 km/s from systemic velocity. The absorption may be due to
missing baryons in warm/hot intergalactic medium (WHIGM) along the
line-of-sight to 3C 120 at z=0.0147 +/- 0.0005, or it could be intrinsic to the
jet of 3C 120. Assuming metallicities of 0.1 solar, we estimate an ionic column
density of N_{O VIII}>3.4 \times 10^{16} cm^{-2} for WHIGM and a filament depth
of <19 h^{-1}_{70} Mpc. We find a baryon overdensity >56 relative to the
critical density of a $\Lambda$-dominated cold dark matter universe, which is
in reasonable agreement with WHIGM simulations. We detect, at marginal
significance, absorption of O VIII Lya at z\sim 0 due to a hot medium in the
Local Group. We also detect an unidentified absorption feature at \sim 0.71
keV. Absorption features which might be expected along with O VIII Lya, were
not significant statistically. Relative abundances of metals in the WHIGM and
local absorbers may therefore be considerably different from solar.


title: The RR Lyrae Distance to the Draco Dwarf Spheroidal Galaxy

abstract:
  We present the first CCD variability study of the Draco dwarf spheroidal
galaxy. The data were obtained with the FLWO 1.2 m telescope on 22 nights, over
a period of 10 months, covering a 22 x 22 arcmin field centered at
RA=17:19:57.5, Dec=57:50:05, J2000.0. The analysis of the BVI images produced
163 variable stars, 146 of which were RR Lyrae: 123 RRab, 16 RRc, 6 RRd and one
RR12. The other variables include a SX Phe star, four anomalous Cepheids and a
field eclipsing binary. Using the short distance scale statistical parallax
calibration of Gould & Popowski and 94 RRab stars from our field, we obtain a
distance modulus of (m-M)_0=19.40 +/- 0.02 (stat) +/- 0.15 (syst) mag for
Draco, corresponding to a distance of 75.7 kpc +/- 0.7 (stat) +/- 5.4 (syst)
kpc. By comparing the spread in magnitudes of RRab stars in B,V and I, we find
no evidence for internal dust in the Draco dwarf spheroidal galaxy. The catalog
of all variables, as well as their photometry and finding charts, is available
electronically via anonymous ftp and the World Wide Web. The complete set of
the CCD frames is available upon request.


title: The Abundance of Low-luminosity Lyman alpha Emitters at High Redshift

abstract:
  We derive the luminosity function of high-redshift Lyman alpha emitting
sources from a deep, blind, spectroscopic survey that utilized strong-lensing
magnification by intermediate-redshift clusters of galaxies. We observed
carefully selected regions near 9 clusters, consistent with magnification
factors generally greater than 10 for the redshift range 4.5<z<6.7. Eleven
emission-line candidates were located in the range 2.2<z<5.6 whose
identification we justify as Lyman alpha, in most cases via further
spectroscopic observations. The selection function we constructed for our
survey takes into account our varying intrinsic Lyman alpha line sensitivity as
a function of wavelength and sky position. By virtue of the strong
magnification factor, we provide constraints on the Lyman alpha luminosity
function to unprecedented limits of 10^40 erg/s, corresponding to a
star-formation rate of 0.01 Msun/yr. Our cumulative z=5 Lyman alpha luminosity
function is consistent with a power law form, n(>L) proportional to L^-1 over
10^41 to 10^42.5 erg/s. When combined with the results of other surveys,
limited at higher luminosities, our results suggest evidence for the
suppression of star formation in low-mass halos, as predicted in popular models
of galaxy formation.


title: Chaotic scalar fields as models for dark energy

abstract:
  We consider stochastically quantized self-interacting scalar fields as
suitable models to generate dark energy in the universe. Second quantization
effects lead to new and unexpected phenomena is the self interaction strength
is strong. The stochastically quantized dynamics can degenerate to a chaotic
dynamics conjugated to a Bernoulli shift in fictitious time, and the right
amount of vacuum energy density can be generated without fine tuning. It is
numerically observed that the scalar field dynamics distinguishes fundamental
parameters such as the electroweak and strong coupling constants as
corresponding to local minima in the dark energy landscape. Chaotic fields can
offer possible solutions to the cosmological coincidence problem, as well as to
the problem of uniqueness of vacua.


title: Acceleration and Dissipation in Relativistic Winds

abstract:
  I argue that ideal MHD relativistic winds are always limited in practice to
asymptotic 4-velocity $\gamma_\infty \approx \sigma_0^{1/3}$ and asymptotic
magnetization $\sigma \sim \sigma_0^{2/3} \gg 1$, where $\sigma_0$ is the wind
magnetization with respect to the rest energy density, evaluated at the light
cylinder of the rotating, magnetized compact object that drives the flow. This
suggests that the observed low value of he asymptotic $\sigma$ in the
equatorial sectors of the winds driving Pulsar Wind Nebulae and the associated
high values of the asymptotic 4-velocity are a consequence of magentic
dissipation in the wind zone.


title:
Effects of Small-Scale Fluctuations of Neutrino Flux in Supernova
  Explosions

abstract:
  We examine effects of small-scale fluctuations with angle in the neutrino
radiation in core-collapse supernova explosions. As the mode number of
fluctuations increases, the results approach those of spherical explosion. We
conclude that global anisotropy of the neutrino radiation is the most effective
mechanism of increasing the explosion energy when the total neutrino luminosity
is given.


title: Unveiling the multi-wavelength phenomenology of Anomalous X-ray Pulsars

abstract:
  During 2002-2003 the number of IR-identified counterparts to the Anomalous
X-ray Pulsars (AXPs) has grown to four (4U0142+614, 2E2259+584, 1E 1048-59 and
1RXS J170849-400910) out of the six assessed objects of this class, plus two
candidates. More importantly, some new common observational characteristics
have been identified, such as the IR variability, the IR flattening in the
broad band energy spectrum, the X-ray spectral variability as a function of
pulse phase (which are not predicted by the magnetar model), and the SGR-like
bursts (which can not be explained in terms of standard accretion models). We
present the results obtained from an extensive multi-wavelength observational
campaign carried out collecting data from the NTT, CFHT for the optical/IR
bands, and XMM, Chandra (plus BeppoSAX archival data) in the X-rays. Based on
these results and those reported in the literature, the IR-to-X-ray band
emission of AXPs has been compared and studied.


title: Magnetic field decay, or just period-dependent beaming?

abstract:
  Several recent papers conclude that radio-pulsar magnetic fields decay on a
time-scale of 10 Myr, apparently contradicting earlier results. We have
implemented the methods of these papers in our code and show that this
preference for rapid field decay is caused by the assumption that the beaming
fraction does not depend on the period. When we do include this dependence, we
find that the observed pulsar properties are reproduced best when the modelled
field does not decay.
  When we assume that magnetic fields of new-born neutron stars are from a
distribution sufficiently wide to explain magnetars, the magnetic field and
period distributions we predict for radio are pulsars wider than observed.
Finally we find that the observed velocities overestimate the intrinsic
velocity distribution.


title: Reception of radio waves from pulsars

abstract:
  The beamed emission by relativistic sources moving along the magnetic dipolar
field lines occur in the direction of tangents to the field lines. To receive
such a beamed radiation line-of-sight must align with the tangent within the
beaming angle 1/gamma, where gamma is the particle Lorentz factor. By solving
the viewing geometry, in an inclined and rotating dipole magnetic field, we
show that at any given pulse phase observer can receive the radiation only from
the specific altitudes. We find the outer conal emission is received from the
higher altitudes than the inner conal components including the core. At any
pulse phase, low frequency emission comes from the higher altitudes than the
high frequency emission. As an application of our model, we have applied it to
explain the emission heights of conal components in PSR B0329+54.


title:
Image-Subtraction Photometry of the Globular Cluster M3: identification
  of new double-mode RR Lyrae stars

abstract:
  We have applied the image subtraction method to the M3 dataset previously
analyzed by Corwin & Carney (2001; CC01). The new analysis produced light
curves and periods for 15 variables, bringing to 222 the total number of RR
Lyrae stars in CC01 M3 dataset. We have identified three new candidate
double-mode (RRd) variables (V13, V200, and V251) in M3. Of the newly
discovered RRd's V13 is unusual in that it has the fundamental as the dominant
pulsation mode. Two of the new candidate RRd's (V13 and V200) have period
ratios as low as 0.738-0.739. They lie separated from all previously known
RRd's in the Petersen diagram, in positions implying a large spread in mass
and/or, less likely, in heavy element mass fraction, among the M3 horizontal
branch (HB) stars. We explore mass transfer and helium enhancement as possible
explanations for the apparent spread in HB masses. We also note that the masses
derived from the RRd analyses now favor little mass loss on the red giant
branch. V200 has changed its dominant pulsation mode from fundamental to first
overtone, while V251 has changed its dominant mode from first overtone to
fundamental in the interval 1992 to 1993. Together with M3-V166 this is the
first time that RRd variables are observed to switch their dominant pulsation
modes while remaining RRd's. The phenomenon is found to occur in a one year
time-span thus suggesting that these stars are undergoing a rapid evolutionary
phase, and that both redward and blueward evolution may take place among the HB
stars in M3. The unusual behavior of the M3 RRd's is discussed and compared to
that of the RRd's identified so far in globular clusters and in the field of
our and other Local Group galaxies. We find lack of correlation between the
presence of RRd variables and any of the cluster structural parameters.


title: Centrifugal Acceleration in Pulsar Magnetosphere

abstract:
  We present a relativistic model of pulsar radio emission by plasma
accelerated along the rotating magnetic field lines projected on to a 2D plane
perpendicular to the rotation axis. We have derived the expression for the
trajectory of a particle, and estimated the spectrum of radio emission by the
plasma bunches. We used the parameters given in the paper by Peyman and
Gangadhara (2002). Further the analytical expressions for the Stokes parameters
are obtained, and compared their values with the observed profiles. The one
sense of circular polarization, observed in many pulsars, can be explained in
the light of our model.


title: Motion properties of satellites around external spiral galaxies

abstract:
  We are analyzing a sample of closeby galaxy systems, each comprising a bright
isolated spiral and its satellites. We find an excess (56%) of prograde
satellites over retrograde, which basically holds for all angular displacements
from the primary major axis. Monte Carlo simulations show that interlopers and
mixing systems at different distances in the sample should not affect
porcentages sensibly.


title: Orbital structure of triaxial galaxies

abstract:
  We have developed a method to construct realistic triaxial dynamical models
for elliptical galaxies, allowing us to derive best-fitting parameters, such as
the mass-to-light ratio and the black hole mass, and to study the orbital
structure. We use triaxial theoretical Abel models to investigate the
robustness of the method.


title: A search for starlight reflected from HD 75289 b

abstract:
  We have used a doppler tomographic analysis to conduct a deep search for the
starlight reflected from the planetary companion to HD 75289. In 4 nights on
VLT2/UVES in January 2003, we obtained 684 high resolution echelle spectra with
a total integration time of 26 hours. We establish an upper limit on the
planet's geometric albedo p < 0.12 (to the 99.9% significance level) at the
most probable orbital inclination i ~ 60 degrees, assuming a grey albedo, a
Venus-like phase function and a planetary radius R_p = 1.6 R_Jup. We are able
to rule out some combinations of the predicted planetary radius and atmospheric
albedo models with high, reflective cloud decks.


title:
Mid-Infrared Imaging and Modelling of the Dust Shell around Post-AGB
  star HD 187885 (IRAS 19500-1709)

abstract:
  We present 10 and 20 micron images of IRAS 19500-1709 taken with the
mid-infrared camera, OSCIR, mounted on the Gemini North Telescope. We use a 2-D
dust radiation transport code to fit the spectral energy distribution from UV
to sub-mm wavelengths and to simulate the images.


title: Induced radio and X-ray emission from an accretion disk

abstract:
  Radio and X-ray emission from compact sources with accretion disks (active
galactic nuclei, pulsars and X-ray binaries) is considered. It is shown that
both radio and X-ray emission from these sources can be interpreted as emission
of a hot ($T \geqslant 3 \times 10^{7}K$) plasma in the inner part of an
accretion disk or in the disk corona. Radio emission is produced by the maser
amplification of thermal radio emission in a hot plasma and corresponds to the
transitions between highly located energy levels (somewhat similarly to the
recombination lines). The X-ray emission is either thermal radiation from dense
filaments or is produced by the coherent inverse Compton scattering of radio
photons in the same dense filaments. The same mechanism, which gives rise to
the maser amplification at radio wavelengths, produces also laser amplification
in optical in X-ray binaries.


title: The high energy emission line spectrum of NGC 1068

abstract:
  We present and discuss the high energy (E>4 keV) XMM-Newton spectrum of the
Seyfert 2 galaxy, NGC 1068. Possible evidence for flux variability in both the
neutral and ionized reflectors with respect to a BeppoSAX observation taken 3.5
years before is found. Several Fe and Ni emission lines, from both neutral and
highly ionized material, are detected. The intensity of the iron K$\alpha$
Compton shoulder implies that the neutral reflector is Compton--thick, likely
the visible inner wall of the $N_H > 10^{25}$ cm$^{-2}$ absorber. From the
equivalent width of the ionized iron lines a column density of a few $\times
10^{21}$ cm$^{-2}$ is deduced for the hot ionized reflector. Finally, an iron
(nickel) overabundance, when compared to solar values, of about 2 (4) with
respect to lower Z elements, is found.


title:
The merger history of clusters and its effect on the X-ray properties of
  the intracluster medium

abstract:
  We investigate the growth over time of 20 massive (> 3 keV) clusters in a
hydrodynamical simulation of the LambdaCDM cosmology with radiative cooling.
The clusters show a variety of formation histories: some accrete most of their
mass in major mergers; others more gradually. During major mergers the
long-term (temporally-smoothed) luminosity increases such that the cluster
moves approximately along the Lx-Tx relation; between times it slowly
decreases, tracking the drift of the Lx-Tx relation. We identify several
different kinds of short-term luminosity and temperature fluctuations
associated with major mergers including double-peaked mergers in which the
global intracluster medium merges first (Lx and Tx increase together) and then
the cluster cores merge (Lx increases and Tx decreases). At both luminosity
peaks, clusters tend to appear spherical and relaxed, which may lead to biases
in high-redshift, flux-limited samples. There is no simple relationship between
scatter in the Lx-Tx relation and either recent or overall merger activity or
cluster formation time. The scatter in the Lx-M and Tx-M relations is reduced
if properties are measured within R_500 rather than R_vir.


title: AM CVn stars in the UCT CCD CV survey

abstract:
  High speed photometry of the helium-transferring binary ES Cet - taken over a
two-year period (2001 October - 2003 October) - shows a very stable photometric
period of 620.211437 +/- 0.000038 s, with a tentative indication of curvature
in the O-C diagram suggesting a change in period at a rate of dP/dt ~
1.6x10^-11. Phase-resolved spectroscopy of ES Cet obtained with the
Hobby-Eberly Telescope shows a clear modulation on the photometric period. We
have followed a newly identified AM CVn star (`2003aw') photometrically through
its 2003 February/March outburst during which it varied in brightness over a
range of V = 16.5 - 20.3; we find a superhump period of 2041.5 +/- 0.3 s.
Questions are raised about the reality of the detected spin-up in RX J0806
(Hakala et al. 2003; Strohmayer 2003).


title:
Reducing and constraining the intrinsic galaxy alignment contamination
  to weak lensing measurements

abstract:
  We present a method for removal of the contaminating effects of intrinsic
galaxy alignments, in measurements of cosmic shear from multi-colour weak
lensing surveys. The method down-weights pairs which are likely to be close in
three dimensions, based on spectroscopic or photometric redshifts. Results are
dramatic: the intrinsic contamination of the low-redshift Sloan photometric
redshift survey could be 80 times the lensing signal, but this can be almost
completely removed, leaving random shot noise errors of the order of 10%.
Intrinsic galaxy alignments, although an annoying contaminant for cosmic shear
studies, are interesting in their own right, and we therefore present a new
observational constraint for their amplitude from the aperture mass B-mode in
the Red-Sequence Cluster Survey. The small measured B-mode rules out the
published intrinsic alignment models from numerical simulations, which assume
no evolution in galaxy clustering.


title:
Homogeneity of bright radio sources at 15 GHz on the sky and in the
  space

abstract:
  A revised sample of the 2 cm Very Long Baseline Array (VLBA) survey is
studied to test the isotropic distribution of radio sources on the sky and
their uniform distribution in space. The revised sample is complete to
flux-density limits of 1.5 Jy for positive declinations and 2 Jy for
declinations between 0 and -20 degrees. At present the active galactic nuclei
sample comprises 122 members. Application of the two-dimensional
Kolmogorov-Smirnov (K-S) test shows that there is no significant deviation from
the homogenous distribution in the sky, while the V/Vmax test shows that the
space distribution of active nuclei is not uniform at high confidence level
(99.9%). This is indicative of a strong luminosity and/or density evolution
implying that active nuclei (or jet activity phenomena) were more populous at
high redshifts, z~2.


title: The Galactic Halo and CDM

abstract:
  This paper reviews the available information on the central density
distribution and shape of the Milky Way's halo. At present, there is no strong
evidence that the Milky Way's halo properties conflict with the predictions of
cold dark matter (CDM): a primordial central power law cusp can be accommodated
by the observations, and the current constraints on flattening are also
consistent with the predictions of the theory. If you want to pick a fight with
CDM, then the Milky Way is probably not the place to do it.


title: From the production of primordial perturbations to the end of inflation

abstract:
  In addition to generating the appropriate perturbation power spectrum, an
inflationary scenario must take into account the need for inflation to end
subsequently. In the context of single-field inflation models where inflation
ends by breaking of the slow-roll condition, we constrain the first and second
derivatives of the inflaton potential using this additional requirement. We
compare this with current observational constraints from the primordial
spectrum and discuss several issues relating to our results.


title:
Radio Emission Associated with Ultraluminous X-ray Sources in the Galaxy
  Merger NGC 3256

abstract:
  We present new 6, 3.6, and 2 cm VLA radio observations of the nearby merger
system NGC 3256, with resolutions of ~100 pc, which reveal compact radio
sources embedded in more diffuse emission at all three wavelengths. The two
radio nuclei are partially resolved, but the two dominant compact sources that
remain coincide with the two most powerful compact Ultraluminous X-ray sources
(ULXs) recently reported by Lira et al. The radio/X-ray ratios for these two
sources are too high by factors of >100-1000 to be normal X-ray binaries.
However, their radio and X-ray powers and ratios are consistent with
low-luminosity active galactic nuclei (LLAGNs), and optical emission lines
suggest the presence of a nuclear disk around the northern nucleus. If the two
nuclear ULXs are LLAGNs, their associated black holes are separated by only
\~1kpc, about 6 times closer to one another than those found recently in the
merger galaxy NGC 6240. A third ULX on the outskirts of the merger is also a
radio source, and probably is a collection of supernova remnants. The remaining
ULXs are not coincident with any source of compact radio emission, and are
consistent with expectations for beamed X-ray binaries or intermediate-mass
black holes.


title: HI and OVI high-velocity clouds and the Local Group

abstract:
  I examine some of the evidence relevant to the idea that high-velocity clouds
(HVCs) are gas clouds distributed throughout the Local Group, as proposed by
Blitz et al. (1999) and Braun & Burton (1999). This model makes several
predictions: a) the clouds have low metallicities; b) there should be no
detectable Halpha emission; c) analogues near other galaxies should exist; and
d) many faint HVCs in the region around M31 can be found. Low metallicities are
indeed found in several HVCs, although they are also expected in several other
models. Halpha emission detected in most HVCs and, when examined more closely,
distant (D>200 kpc) HVCs should be almost fully ionized, implying that most
HVCs with HI must lie near the Milky Way. No clear extragalactic analogues have
been found, even though the current data appear sensitive enough. The final
prediction (d) has not yet been tested. On balance there appears to be no
strong evidence for neutral gas clouds distributed throughout the Local Group,
but there may be many such clouds within 100 or so kpc from the Milky Way (and
M31). On the other hand, some (but not all) of the high-velocity OVI recently
discovered may originate in hot gas distributed throughout the Local Group.


title: The Early Optical Afterglow of GRB 030418 and Progenitor Mass Loss

abstract:
  The ROTSE-IIIa telescope and the SSO-40 inch telescope, both located at
Siding Spring Observatory, imaged the early time afterglow of GRB 030418. In
this report we present observations of the early afterglow, first detected by
the ROTSE-IIIa telescope 211 s after the start of the burst, and only 76 s
after the end of the gamma-ray activity. We detect optical emission that rises
for ~600 s, slowly varies around R=17.3 mag for ~1400 s, and then fades as a
power law of index alpha=-1.36. Additionally, the ROTSE-IIIb telescope, located
at McDonald Observatory, imaged the early time afterglow of GRB 030723. The
behavior of this light curve was qualitatively similar to that of GRB 030418,
but two magnitudes dimmer. These two afterglows are dissimilar to other
afterglows such as GRB 990123 and GRB 021211. We investigate whether the early
afterglow can be attributed to a synchrotron break in a cooling synchrotron
spectrum as it passes through the optical band, but find this model is unable
to accurately describe the early light curve. We present a simple model for
gamma-ray burst emission emerging from a wind medium surrounding a massive
progenitor star. This model provides an effective description of the data, and
suggests that the rise of the afterglow can be ascribed to extinction in the
local circumburst environment. In this interpretation, these events provide
further evidence for the connection between gamma-ray bursts and the collapse
of massive stars.


title:
Dust emission in the diffuse interstellar medium from far-infrared to
  millimeter: new constraints from WMAP

abstract:
  This paper proposes a short review on our knowledge on the dust emission in
the diffuse sky from far-IR to the mm wavelength. The current understanding is
based mainly on the analysis of the COBE data combined with several templates
of gas tracers (HI and Halpha). In the millimeter, emphasis is given to the new
WMAP results on the so-called ``anomalous microwave emission''.


title: On the jet speeds of classical double radio sources

abstract:
  A simple integral relation is obtained for the distribution functions of jet
speeds and jet-counterjet flux asymmetries of classical double radio sources.
Analytic expressions relating the mean jet speed and the mean jet flux
asymmetry, and their variances are derived. The results are considered in the
light of orientation-based unified schemes, and an analytical equation for the
critical angle separating quasars and radio galaxies is derived. The mean jet
speeds of classical double radio sources are estimated using the asymmetry of
jet-counterjet flux densities taken from the 3CRR and B2 samples. For FRI radio
sources the mean jet speed is ~0.54c (with a standard error SE=0.03c), while
for FRII low-redshift radio galaxies and intermediate redshift quasars the
values found are ~0.4c (SE=0.06c) and >0.6c respectively.


title: ULTRACAM photometry of the eclipsing cataclysmic variable OU Vir

abstract:
  We present high-speed, three-colour photometry of the faint eclipsing
cataclysmic variable OU Vir. For the first time in OU Vir, separate eclipses of
the white dwarf and bright spot have been observed. We use timings of these
eclipses to derive a purely photometric model of the system, obtaining a mass
ratio of q = 0.175 +/- 0.025, an inclination of i = 79.2 +/- 0.7 degrees and a
disc radius of Rd/a = 0.2315 +/- 0.0150. We separate the white dwarf eclipse
from the lightcurve and, by fitting a blackbody spectrum to its flux in each
passband, obtain a white dwarf temperature of T = 21700 +/- 1200 K and a
distance of D = 650 +/- 210 pc. Assuming that the primary obeys the Nauenberg
(1972) mass-radius relation for white dwarfs and allowing for temperature
effects, we also find a primary mass Mw/Msun = 0.90 +/- 0.19, primary radius
Rw/Rsun = 0.0097 +/- 0.0031 and orbital separation a/Rsun = 0.75 +/- 0.05.


title:
Future Evolution of the Intergalactic Medium in a Universe Dominated by
  a Cosmological Constant

abstract:
  We simulate the evolution of the intergalactic medium (IGM) in a universe
dominated by a cosmological constant. We find that within a few Hubble times
from the present epoch, the baryons will have two primary phases: one phase
composed of low-density, low-temperature, diffuse, ionized gas which cools
exponentially with cosmic time due to adiabatic expansion, and a second phase
of high-density, high-temperature gas in virialized dark matter halos which
cools much more slowly by atomic processes. The mass fraction of gas in halos
converges to ~40% at late times, about twice its calculated value at the
present epoch. We find that in a few Hubble times, the large scale filaments in
the present-day IGM will rarefy and fade away into the low-temperature IGM, and
only islands of virialized gas will maintain their physical structure. We do
not find evidence for fragmentation of the diffuse IGM at later times. More
than 99% of the gas mass will maintain a steady ionization fraction above 80%
within a few Hubble times. The diffuse IGM will get extremely cold and dilute
but remain highly ionized, as its recombination time will dramatically exceed
the age of the universe.


title: X-Ray Sources Overdensity Around 3C 295

abstract:
  We present a statistical analysis of the Chandra observation of the source
field around the 3C 295 galaxy cluster ($z=0.46$). Three different methods of
analysis, namely a chip by chip logN-logS, a two dimentional Kolmogorov-Smirnov
(KS) test, and the angular correlation function (ACF) show a strong overdensity
of sources in the North-East of the field, that may indicate a filament of the
large scale structure of the Universe toward 3C 295.


title: Non-linear shock acceleration in the presence of seed particles

abstract:
  Particles crossing repeatedly the surface of a shock wave can be energized by
first order Fermi acceleration. The linear theory is successful in describing
the acceleration process as long as the pressure of the accelerated particles
remains negligible compared to the kinetic pressure of the incoming gas (the
so-called test particle approximation). When this condition is no longer
fulfilled, the shock is modified by the pressure of the accelerated particles
in a nonlinear way, namely the spectrum of accelerated particles and the shock
structure determine each other. In this paper we present the first description
of the nonlinear regime of shock acceleration when the shock propagates in a
medium where seed particles are already present. This case may apply for
instance to supernova shocks propagating into the interstellar medium, where
cosmic rays are in equipartition with the gas pressure. We find that the
appearance of multiple solutions, previously found in alternative descriptions
of the nonlinear regime, occurs also for the case of reacceleration of seed
particles. Moreover, for parameters of concern for supernova shocks, the shock
is likely to turn nonlinear mainly due to the presence of the pre-existing
cosmic rays, rather than due to the acceleration of new particles from the
thermal pool. We investigate here the onset of the nonlinear regime for the
three following cases: 1) seed particles in equipartition with the gas
pressure; 2) particles accelerated from the thermal pool; 3) combination of 1)
and 2).


title: X-ray Absorption Toward Abell 2029 due to a Foreground Spiral

abstract:
  We have detected an X-ray absorption feature against the core of the galaxy
cluster Abell 2029 (z=0.0767) which we identify with the foreground galaxy UZC
J151054.6+054313 (z=0.0221). Optical observations (B, V, R, and I) indicate
that it is an Scd galaxy seen nearly edge-on at an inclination of 87 \pm 3
degrees. HI observations give a rotation velocity of 108 kms and an atomic
hydrogen mass of M_{HI} = 3.1 X 10^9 d_{90}^2 \msun, where d_{90} is the
distance to the galaxy in units of 90 Mpc. X-ray spectral fits to the Chandra
absorption feature yield a hydrogen column density of (2.0 \pm 0.4) X 10^{21}
cm^{-2} assuming solar abundances. If the absorber is uniformly distributed
over the disk of the galaxy, the implied hydrogen mass is M_H = (6.2 \pm 1.2) X
10^8 d_{90}^2 \msun. Since the absorbing gas in the galaxy is probably
concentrated to the center of the galaxy and the middle of the disk, this is a
lower limit to the total hydrogen mass. On the other hand, the absorption
measurements imply that the dark matter in UZC J151054.6+054313 is not
distributed in a relatively uniform diffuse gas.


title: Future Facilities for Gamma-Ray Pulsar Studies

abstract:
  Pulsars seen at gamma-ray energies offer insight into particle acceleration
to very high energies, along with information about the geometry and
interaction processes in the magnetospheres of these rotating neutron stars.
During the next decade, a number of new gamma-ray facilities will become
available for pulsar studies. This brief review describes the motivation for
gamma-ray pulsar studies, the opportunities for such studies, and some specific
discussion of the capabilities of the Gamma-ray Large Area Space Telescope
(GLAST) Large Area Telescope (LAT) for pulsar measurements.


title:
Thermal and Magnetorotational Instability in the ISM: Two-Dimensional
  Numerical Simulations

abstract:
  The structure and dynamics of diffuse gas in the Milky Way and other disk
galaxies may be strongly influenced by thermal and magnetorotational
instabilities (TI and MRI) on scales of about 1-100 pc. We initiate a study of
these processes, using two-dimensional numerical hydrodynamic and
magnetohydrodynamic (MHD) simulations with conditions appropriate for the
atomic interstellar medium (ISM). We demonstrate, consistent with previous
work, that nonlinear development of ``pure TI'' produces a network of filaments
that condense into cold clouds at their intersections, yielding a distinct
two-phase warm/cold medium within about 20 Myr. TI-driven turbulent motions of
the clouds saturate at subsonic amplitudes for uniform initial P/k=2000 K
cm^-3. MRI has previously been studied in near-uniform media; our simulations
include both TI+MRI models, which begin from uniform-density conditions, and
cloud+MRI models, which begin with a two-phase cloudy medium. Both the TI+MRI
and cloud+MRI models show that MRI develops within a few galactic orbital
times, just as for a uniform medium. The mean separation between clouds can
affect which MRI mode dominates the evolution. Provided intercloud separations
do not exceed half the MRI wavelength, we find the MRI growth rates are similar
to those for the corresponding uniform medium. This opens the possibility, if
low cloud volume filling factors increase MRI dissipation times compared to
those in a uniform medium, that MRI-driven motions in the ISM could reach
amplitudes comparable to observed HI turbulent linewidths.