title:
Rest-frame optical and far-infrared observations of extremely bright
  Lyman-break galaxy candidates at z ~ 2.5

abstract:
  We have investigated the rest-frame optical and far-infrared properties of a
sample of extremely bright candidate Lyman-break galaxies (LBG) identified in
the Sloan Digital Sky Survey. Their high ultraviolet luminosities and lack of
strong ultraviolet emission lines are suggestive of massive starbursts,
although it is possible that they are more typical luminosity LBGs which have
been highly magnified by strong gravitational lensing. Alternatively, they may
be an unusual class of weak-lined quasars. If the ultraviolet and submillimetre
properties of these objects mirror those of less luminous, starburst LBGs, then
they should have detectable rest-frame far-infrared emission. However, our
submm photometry fails to detect such emission, indicating that these systems
are not merely scaled-up (either intrinsically or as a result of lensing)
examples of typical LBGs. In addition we have searched for the morphological
signatures of strong lensing, using high-resolution, near-infrared imaging, but
we find none. Instead, near-infrared spectroscopy reveals that these systems
are, in fact, a rare class of broad absorption-line (BAL) quasars.


title:
A Wide Field, Low Frequency Radio Image of the Field of M31: II. --
  Source Classification and Discussion

abstract:
  We have previously presented the results of a 325 MHz radio survey of M31,
conducted with the A-configuration of the Very Large Array. In this survey, a
total of 405 radio sources between <6" and 170" in extent were mapped with a
resolution of 6" and a sensitivity of ~0.6 mJy/beam. Here, we compare the
resultant source list and image with other radio, IR, optical, X-ray
observations and catalogs of the region. Through this, we were able to identify
five supernova remnant (SNR) candidates and three pulsar wind nebula (PWN)
candidates in M31, as well as three Milky Way radio stars, a possible Milky Way
Planetary Nebula, and a bevy of interesting extragalactic objects: a BL Lac, a
Giant Radio Galaxy, a galaxy merger, and several high-z radio galaxy
candidates. In addition, a large number of compact (<6") extremely steep
spectrum sources ($\alpha \leq -1.6; S_{\nu} \propto \nu^{\alpha}$) were
detected whose nature is unknown.


title: Molecular Hydrogen Formation on Porous Dust Grains

abstract:
  Recent laboratory experiments on interstellar dust analogues have shown that
H_2 formation on dust grain surfaces is efficient in a range of grain
temperatures below 20 K. These results indicate that surface processes may
account for the observed H_2 abundance in cold diffuse and dense clouds.
However, high abundances of H_2 have also been observed in warmer clouds,
including photon-dominated regions (PDRs), where grain temperatures may reach
50 K, making the surface processes extremely inefficient. It was suggested that
this apparent discrepancy can be resolved by chemisorption sites. However,
recent experiments indicate that chemisorption processes may not be efficient
at PDR temperatures. Here we consider the effect of grain porosity on H_2
formation. It is found that porosity extends the efficiency of the
recombination process to higher temperatures. This is because H atoms that
desorb from the internal surfaces of the pores may re-adsorb many times and
thus stay longer on the surface. However, this porosity-driven extension may
enable efficient H_2 formation in PDRs only if porosity also contributes to
significant cooling of the grains, compared to non-porous grains.


title: Crossing into the substellar regime in Praesepe

abstract:
  We present the results of a deep optical 2.6 square degree survey with near
infrared follow-up measurements of the intermediate-aged Praesepe open cluster.
The survey is complete to I=21.3, Z=20.5, corresponding to ~0.06 Solar Masses
assuming a cluster age of 0.5 Gyrs. Using 3-5 pass-bands to constrain cluster
membership, we identify 32 new low mass cluster members, at least 4 of which
are likely to be substellar. We use the low mass census to trace the region
where the sequence moves away from the NEXTGEN towards the Dusty regime at Teff
= 2200K. In doing so, we identify four unresolved binaries, yielding a
substellar binary fraction of ~30 percent. The binary fractions appear to
decrease below 0.1 Solar Masses, in contrast to the rising fractions found in
the Pleiades. We also identify a paucity of late M dwarfs, thought to be due to
a steepening in the mass-luminosity relation at these spectral types, and
compare the properties of this gap in the sequence to those observed in younger
clusters. We note an overdensity of faint sources in the region of the
so-called subcluster (possibly an older smaller cluster within Praesepe), and
subsequently derive the luminosity and mass functions for the main Praesepe
cluster, revealing a turn-over near the substellar boundary. We conclude by
presenting astrometric measurements for low mass Praesepe candidates from the
literature, and rule out as a likely foreground dwarf RPr1, hitherto thought to
be a substellar member.


title: Far Ultraviolet Spectroscopy of (Non-magnetic) Cataclysmic Variables

abstract:
  HST and FUSE have provided high signal-to-noise, high-resolution spectra of a
variety of cataclysmic variables and have allowed a detailed characterization
of FUV emission sources in both high and low states. Here, I describe how this
has advanced our understanding of non-magnetic CVs and the substantial
interpretive challenges still posed by the observations. In the high state, the
FUV spectra are dominated by disk emission that is modified by scattering in
high and low velocity material located above the disk photosphere. Progress is
being made toward reproducing the high-state spectra using kinematic
prescriptions of the velocity field and new ionization and radiative transfer
codes. In conjunction with hydrodynamical simulations of the outflows, accurate
estimates of the mass loss rates and determination of the launching mechanism
are likely forthcoming. In quiescence, the FUV spectra reveal contributions
from the WD and the disk. Quantitative analyses have lead to solid measurements
of the temperatures and abundances of a number of WDs in CVs, and of a
determination of the response of the WD to an outburst. Basic challenges exist
in terms of understanding the other components of the emission in quiescence,
however, and these are needed to better understand the structure of the disk
and the physical mechanisms resulting in ongoing accretion in quiescence.


title: Catalog of Galactic Beta Cephei Stars

abstract:
  We present an extensive and up-to-date catalog of Galactic Beta Cephei stars.
This catalog is intended to give a comprehensive overview of observational
characteristics of all known Beta Cephei stars. 93 stars could be confirmed to
be Beta Cephei stars. For some stars we re-analyzed published data or conducted
our own analyses. 61 stars were rejected from the final Beta Cephei list, and
77 stars are suspected to be Beta Cephei stars. A list of critically selected
pulsation frequencies for confirmed Beta Cephei stars is also presented. We
analyze the Beta Cephei stars as a group, such as the distributions of their
spectral types, projected rotational velocities, radial velocities, pulsation
periods, and Galactic coordinates. We confirm that the majority of these stars
are multiperiodic pulsators. We show that, besides two exceptions, the Beta
Cephei stars with high pulsation amplitudes are slow rotators. We construct a
theoretical HR diagram that suggests that almost all 93 Beta Cephei stars are
MS objects. We discuss the observational boundaries of Beta Cephei pulsation
and their physical parameters. We corroborate that the excited pulsation modes
are near to the radial fundamental mode in frequency and we show that the mass
distribution of the stars peaks at 12 solar masses. We point out that the
theoretical instability strip of the Beta Cephei stars is filled neither at the
cool nor at the hot end and attempt to explain this observation.


title:
Evolution of protoplanetary disks: Constraints from DM Tauri and GM
  Aurigae

abstract:
  We present a one-dimensional model of the formation and viscous evolution of
protoplanetary disks. The formation of the early disk is modeled as the result
of the gravitational collapse of an isothermal molecular cloud. The disk's
viscous evolution is integrated according to two parameterizations of
turbulence: The classical $\alpha$ representation and a $\beta$
parameterization, representative of non-linear turbulence driven by the
keplerian shear. We apply the model to DM Tau and GM Aur, two classical T-Tauri
stars with relatively well-characterized disks, retrieving the evolution of
their surface density with time. We perform a systematic Monte-Carlo
exploration of the parameter space (i.e. values of the $\alpha$-$\beta$
parameters, and of the temperature and rotation rate in the molecular cloud) to
find the values that are compatible with the observed disk surface density
distribution, star and disk mass, age and present accretion rate. We find that
the observations for DM Tau require $0.001<\alpha<0.1$ or $2\times
10^{-5}<\beta<5\times 10^{-4}$. For GM Aur, we find that the turbulent
viscosity is such that $4\times 10^{-4}<\alpha<0.01$ or $2\times
10^{-6}<\beta<8\times 10^{-5}$. These relatively large values show that an
efficient turbulent diffusion mechanism is present at distances larger than
$\sim 10 $AU. This is to be compared to studies of the variations of accretion
rates of T-Tauri stars versus age that mostly probe the inner disks, but also
yield values of $\alpha\sim 0.01$. We show that the mechanism responsible for
turbulent diffusion at large orbital distances most probably cannot be
convection because of its suppression at low optical depths.


title: Low Power Compact Radio Galaxies at High Angular Resolution

abstract:
  We present sub-arcsecond resolution multi-frequency (8 and 22 GHz)
  VLA images of five low power compact (LPC) radio sources, and phase
referenced VLBA images at 1.6 GHz of their nuclear regions. At the VLA
resolution we resolve the structure and identify component positions and flux
densities. The phase referenced VLBA data at 1.6 GHz reveals flat-spectrum,
compact cores (down to a few milliJansky) in four of the five sources. The
absolute astrometry provided by the phase referencing allows us to identify the
center of activity on the VLA images. Moreover, these data reveal rich
structures, including two-sided jets and secondary components. On the basis of
the arcsecond scale structures and of the nuclear properties, we rule out the
presence of strong relativistic effects in our LPCs, which must be
intrinsically small (deprojected linear sizes <~ 10 kpc). Fits of continuous
injection models reveal break frequencies in the GHz domain, and ages in the
range 10^5-10^7 yrs. In LPCs, the outermost edge may be advancing more slowly
than in more powerful sources or could even be stationary; some LPCs might also
have ceased their activity. In general, the properties of LPCs can be related
to a number of reasons, including, but not limited to: youth, frustration, low
kinematic power jets, and short-lived activity in the radio.


title: SBS 0335-052W: The Lowest-Metallicity Star-Forming Galaxy Known

abstract:
  We present 4-meter Kitt Peak telescope and 6.5-meter MMT spectrophotometry of
the extremely low-metallicity galaxy SBS 0335-052W, the western companion of
the blue compact dwarf galaxy SBS 0335-052E. These observations have been
combined with published 10-meter Keck data to derive for the brightest region
of SBS 0335-052W an oxygen abundance 12+logO/H=7.12+/-0.03. This makes SBS
0335-052W the lowest metallicity star-forming galaxy known in the local
universe. Using a Monte Carlo technique, we fit the spectral energy
distribution of SBS 0335-052W to derive the age of the oldest stars
contributing to its optical light. We find that star formation in SBS 0335-052W
began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.


title: Detectability of Cosmic Topology in Generalized Chaplygin Gas Models

abstract:
  If the spatial section of the universe is multiply connected, repeated images
or patterns are expected to be detected observationally. However, due to the
finite distance to the last scattering surface, such pattern repetitions could
be unobservable. This raises the question of whether a given cosmic topology is
detectable, depending on the values of the parameters of the cosmological
model. We study how detectability is affected by the choice of the model itself
for the matter-energy content of the universe, focusing our attention on the
generalized Chaplygin gas (GCG) model for dark matter and dark energy
unification, and investigate how the detectability of cosmic topology depends
on the GCG parameters. We determine to what extent a number of topologies are
detectable for the current observational bounds on these parameters. It emerges
from our results that the choice of GCG as an alternative to the $\Lambda$CDM
matter-energy content model has an impact on the detectability of cosmic
topology.


title: Hydrogen Burning of 17-O in Classical Novae

abstract:
  We report on the observation of a previously unknown resonance at
E=194.1+/-0.6 keV (lab) in the 17-O(p,alpha)14-N reaction, with a measured
resonance strength omega_gamma(p,alpha)=1.6+/-0.2 meV. We studied in the same
experiment the 17-O(p,gamma)18-F reaction by an activation method and the
resonance-strength ratio was found to be
omega_gamma(p,alpha)/omega_gamma(p,gamma)=470+/-50. The corresponding
excitation energy in the 18-F compound nucleus was determined to be
5789.8+/-0.3 keV by gamma-ray measurements using the 14-N(alpha,gamma)18-F
reaction. These new resonance properties have important consequences for 17-O
nucleosynthesis and gamma-ray astronomy of classical novae.


title:
Discovery of an M4 Spectroscopic Binary in Upper Scorpius: A Calibration
  Point for Young Low-Mass Evolutionary Models

abstract:
  We report the discovery of a new low-mass spectroscopic (SB2) stellar binary
system in the star-forming region of Upper Scorpius. This object, UScoCTIO5,
was discovered by Ardila (2000), who assigned it a spectral class of M4. A
KeckI HIRES spectrum revealed it to be double-lined, and we then carried out a
program at several observatories to determine its orbit. The orbital period is
34 days, and the eccentricity is nearly 0.3. The importance of such a discovery
is that it can be used to help calibrate evolutionary models at low masses and
young ages. This is one of the outstanding problems in the study of formation
mechanisms and initial mass functions at low masses. The orbit allows us to
place a lower limit of 0.64 +- 0.02 M_sol on the total system mass. The
components appear to be of almost equal mass. We are able to show that this
mass is significantly higher than predicted by evolutionary models for an
object of this luminosity and age, in agreement with other recent results. More
precise determination of the temperature and surface gravity of the components
would be helpful in further solidifying this conclusion.


title: Interstellar Isomers: The Importance of Bonding Energy Differences

abstract:
  We present strong detections of methyl cyanide, vinyl cyanide, ethyl cyanide
and cyanodiacetylene molecules with the Green Bank Telescope (GBT) toward the
Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide
isomers were only successful in the case of methyl isocyanide for its
J(K)=1(0)-0(0) transition, which is the first interstellar report of this line.
To determine the spatial distribution of methyl isocyanide, we used archival
Berkeley-Illinois-Maryland Association (BIMA) array data for the J(K)=4(K)-3(K)
(K=0-3) transitions but no emission was detected. From ab initio calculations,
the bonding energy difference between the cyanide and isocyanide molecules is
>8500 cm^-1 (>12,000 K). That we detect methyl isocyanide emission with a
single antenna (Gaussian beamsize(Omega_B)=1723 arcsec^2) but not with an
interferometer (Omega_B=192 arcsec^2), strongly suggests that methyl isocyanide
has a widespread spatial distribution toward the Sgr B2(N) region. Thus,
large-scale, non-thermal processes in the surrounding medium may account for
the conversion of methyl cyanide to methyl isocyanide while the LMH hot core,
which is dominated by thermal processes, does not produce a significant amount
of methyl isocyanide. Ice analog experiments by other investigators have shown
that radiation bombardment of methyl cyanide can produce methyl isocyanide,
thus supporting our observations. We conclude that isomers separated by such
large bonding energy differences are distributed in different interstellar
environments, making the evaluation of column density ratios between such
isomers irrelevant unless it can be independently shown that these species are
co-spatial.


title: Global X-ray properties of the Orion Nebula region

abstract:
  Based on the Chandra Orion Ultradeep Project (COUP) observation, we establish
the global X-ray properties of the stellar population associated with the Orion
Nebula. Three components contribute roughly equally to the integrated COUP
luminosity in the hard (2-8 keV) X-ray band: several OB stars, 822 lightly
obscured cool stars in the Orion Nebula Cluster (ONC), and 559 heavily obscured
stars. ONC stars 0.5-2 pc from the center show a spatial asymmetry consistent
with violent relaxation in the stellar dynamics. The obscured COUP sources
concentrate around both OMC-1 molecular cores; these small-scale structures
indicate ages t < 0.1 Myr. The X-ray luminosity function (XLF) of the lightly
obscured sample is roughly lognormal in shape. The obscured population is
deficient in lower-luminosity stars, perhaps due to localized circumstellar
material. Mass-stratified XLFs show that one-third of the Orion Nebula region
hard-band emission is produced by the bright O6 star theta-1 Ori C and half is
produced by lower mass pre-main sequence stars with masses 0.3 < M < 3 Mo. Very
low mass stars contribute little to the cluster X-ray emission.
  Using the hard band emission, we show that young stellar clusters like the
ONC can be readily detected and resolved with Chandra across the Galactic disk,
even in the presence of heavy obscuration. The Orion Nebula sample is a
valuable template for studies of distant clusters. For example, the peak of the
XLF shape can serve as a standard candle for a new distance measure to distant
young stellar clusters, and the presence of a neon emission line complex around
1 keV can serve as a diagnostic for young stars.


title:
INTEGRAL observations of the Be/X-ray binary EXO 2030+375 during
  outburst

abstract:
  We present a type-I outburst of the high-mass X-ray binary EXO 2030+375,
detected during INTEGRAL's Performance and Verification Phase in December 2002
(on-source time about 10e+06 seconds). In addition, six more outbursts have
been observed during INTEGRAL's Galactic Plane Scans. X-ray pulsations have
been detected with a pulse period of 41.691798+-0.000016 s. The X-ray
luminosity in the 5-300 keV energy range was 9.7*10e+36 erg/s, for a distance
of 7.1 kpc. Two unusual features were found in the light curve, with an initial
peak before the main outburst and another possible spike after the maximum.
RXTE observations confirm only the existence of the initial spike. Although the
initial peak appears to be a recurrent feature, the physical mechanisms
producing it and the possible second spike are unknown. Moreover, a four-day
delay between periastron passage and the peak of the outburst is observed. We
present for the first time a 5-300 keV broad-band spectrum of this source. It
can be modelled by the sum of a disk black body (kT_bb~8 keV) with either a
power law model with Gamma=2.04+-0.11 keV or a Comptonized component (spherical
geometry, kT_e=30 keV, tau=2.64, kT_W=1.5 keV).


title: A Unique Dust Formation Episode in the SC-Type Star UY Cen

abstract:
  We report the first detection of new dust formation in an SC star. The
prototype of the SC stars, UY Cen, underwent a decline of 2 magnitudes in the
V-band. The SC stars show pulsational variations and have 60 micron excesses
indicating past dust formation. It has been suggested that as a star evolves
from oxygen rich to carbon rich, there is a short period of time when C/O$~1
that the star appears spectroscopically as an SC star and ceases to produce
dust. The SC star, BH Cru, has shown large spectroscopic and pulsation period
variations in only 30 years, indicating rapid evolution but it has shown no
sign of new dust formation. UY Cen has not shown any pulsation or spectroscopic
variations accompanying the onset of its dust formation. In addition, UY Cen
did not show emission in the resonance lines of Na I, K I or Rb I when it was
at its faintest, although these lines were a feature of the carbon stars R Lep
and V Hya during similar faint phases.


title: Singularity-Free Collapse through Local Inflation

abstract:
  In common relativistic models of gravitational collapse, the interior
experiences a bubble-like local inflation, allowing radii to diverge rather
than converge toward a singularity. This proves a conjecture of Shatskiy. At
the horizon, the solution locally resembles the neck of a wormhole from the
exterior to the interior. The implied limiting curvature is at the horizon not
the Planck level.


title:
Probing the Birth of Super Star Clusters: Implications for Massive Star
  Formation

abstract:
  Super Star Clusters are one of the most extreme star forming environments in
the universe, and the most massive and dense of these may be proto globular
clusters. Like individual massive stars, the earliest stages of super star
cluster evolution are deeply obscured, and therefore our knowledge about their
birth environments is currently very incomplete. However, the study of natal
super star clusters has become somewhat of a cottage industry in recent years,
and the sample of such objects has been growing rapidly with high-quality
long-wavelength data now available from a number of observatories. The natal
super star clusters identified in thermal-infrared and radio observations
represent the youngest stage of massive star cluster evolution yet observed.
Their properties appear to be similar to those of ultracompact HII regions in
the Milky Way, but scaled up in total mass and luminosity. I will overview what
we think we know about these objects based on existing observations, discuss
their relationship to ultracompact HII regions, present new models of their
spectral energy distributions based on 3-D simulations, and outline some of the
most significant gaps in our current understanding.


title:
Why is the Fast Solar Wind Fast and the Slow Solar Wind Slow? A Survey
  of Geometrical Models

abstract:
  Four decades have gone by since the discovery that the solar wind at 1 AU
seems to exist in two relatively distinct states: slow and fast. There is still
no universal agreement concerning the primary physical cause of this apparently
bimodal distribution, even in its simplest manifestation at solar minimum. In
this presentation we review and extend a series of ideas that link the
different states of solar wind to the varying superradial geometry of magnetic
flux tubes in the extended corona. Past researchers have emphasized different
aspects of this relationship, and we attempt to disentangle some of the
seemingly contradictory results. We apply the hypothesis of Wang and Sheeley
(as well as Kovalenko) that Alfven wave fluxes at the base are the same for all
flux tubes to a recent model of non-WKB Alfven wave reflection and turbulent
heating, and we predict coronal heating rates as a function of flux tube
geometry. We compare the feedback of these heating rates on the locations of
Parker-type critical points, and we discuss the ranges of parameters that yield
a realistic bifurcation of wind solutions into fast and slow. Finally, we
discuss the need for next-generation coronagraph spectroscopy of the extended
corona - especially measurements of the electron temperature above 1.5 solar
radii - in order to confirm and refine these ideas.


title:
Capabilities of UV Coronagraphic Spectroscopy for Studying the Source
  Regions of Solar Energetic Particles and the Solar Wind

abstract:
  We summarize the unique capabilities of UV coronagraphic spectroscopy for
determining the detailed plasma properties (e.g., density, temperature, outflow
speed, composition) of the source regions of both transient phenomena such as
CMEs, flares, and solar energetic particles (SEPs) and more time-steady solar
wind streams. UVCS/SOHO observations have provided the first detailed
diagnostics of the physical conditions of CME plasma in the extended corona. It
provided new insights into the roles of shock waves, reconnection, and magnetic
helicity in CME eruptions. We summarize past observations and discuss the
diagnostic potential of UV coronagraphic spectroscopy for characterizing two
possible sites of SEP production: CME shocks and reconnection current sheets.
UVCS/SOHO has also led to fundamentally new views of the acceleration region of
the solar wind. Understanding the physical processes in this region, which
ranges from the low corona (1.1 to 1.5 Rsun) past the sonic points (greater
than 5 Rsun), is key to linking the results of solar imaging to in situ
particle and field detection. Despite the advances that have resulted from
UVCS/SOHO, more advanced instrumentation could determine properties of
additional ions with a wider sampling of charge/mass combinations. This would
provide much better constraints on the specific kinds of waves that are present
as well as the specific collisionless damping modes. Electron temperatures and
departures from Maxwellian velocity distributions could also be measured. The
instrumentation capable of making the above observations will be described.


title: The age dependence of halo clustering

abstract:
  We use a very large simulation of the concordance LCDM cosmogony to study the
clustering of dark matter haloes. For haloes less massive than about
1e13Msun/h, the amplitude of the two-point correlation function on large scales
depends strongly on halo formation time. Haloes that assembled at high redshift
are substantially more clustered than those that assembled more recently. The
effect is a smooth function of halo formation time and its amplitude increases
with decreasing halo mass. At 1e11 Msun/h the ``oldest'' 10% of haloes are more
than 5 times more strongly correlated than the ``youngest'' 10%. This
unexpected result is incompatible with the standard excursion set theory for
structure growth, and it contradicts a fundamental assumption of the halo
occupation distribution models often used to study galaxy clustering, namely
that the galaxy content of a halo of given mass is statistically independent of
its larger scale environment.


title:
The Spectral Evolution of Transient Anomalous X-ray Pulsar XTE
  J1810--197

abstract:
  (Abridged) We present a multi-epoch spectral study of the Transient Anomalous
X-ray Pulsar XTE J1810-197 obtained with the XMM X-ray telescope. Four
observations taken over the course of a year reveal strong spectral evolution
as the source fades from outburst. The origin of this is traced to the
individual decay rates of the pulsar's spectral components. A 2-T fit at each
epoch requires nearly constant temperatures of kT=0.25 & 0.67 keV while the
component luminosities decrease exponentially with tau=900 & 300d,
respectively. One possible interpretation is that the slowly decaying cooler
component is the radiation from a deep heating event that affected a large
fraction of the crust, while the hotter component is powered by external
surface heating at the foot-points of twisted magnetic field lines, by
magnetospheric currents that are decaying more rapidly. The energy-dependent
pulse profile of XTE J1810-197 is well modeled at all epochs by the sum of a
sine and triangle function. These profiles peak at the same phase, suggesting a
concentric surface emission geometry. The spectral and pulse evolution together
argue against the presence of a significant ``power-law'' contribution to the
X-ray spectrum below 8 keV. The extrapolated flux is projected to return to the
historic quiescent level, characterized by an even cooler blackbody spectrum,
by the year 2007.


title:
Possible Optical Detection of the Anomalous X-ray Pulsar CXOU
  J010043.1-721134

abstract:
  Archival Hubble Space Telescope Wide Field/Planetary Camera 2 observations of
the Small Magellanic Cloud serendipitously reveal a possible counterpart to the
Anomalous X-ray Pulsar CXOU J010043.1-721134. The candidate is faint, but its
location and strange colours make it an interesting object. We estimate, that
the probability of such a detection being due to a non-physical source is less
than 1.5%. We have tried to confirm the identification with Gemini-South and
Magellan, but the conditions were insufficiently favourable. If confirmed, the
object will allow the first detailed studies of the optical and ultraviolet
emission of magnetars.


title: Dust Extinction in Compact Planetary Nebulae

abstract:
  The effects of dust extinction on the departure from axi-symmetry in the
morphology of planetary nebulae (PNs) are investigated through a comparison of
the radio free-free emission and hydrogen recombination line images. The dust
exctinction maps of five compact PNs are derived using high-resolution (~ 0".1)
H-alpha and radio images maps of the HST and VLA. These extinction maps are
then analyzed by an ellipsoidal shell ionization model including the effects of
dust extinction to infer the nebulae's intrinsic structure and orientation in
the sky. This method provides a quantitative analysis of the morphological
structure of PNs and represents a step beyond qualitative classification of
morphological types of PNs.


title:
The H II Region/PDR Connection: Self-Consistent Calculations of Physical
  Conditions in Star-Forming Regions

abstract:
  We have performed a series of calculations designed to reproduce infrared
diagnostics used to determine physical conditions in star forming regions. We
self-consistently calculate the thermal and chemical structure of an H II
region and photodissociation region (PDR) that are in pressure equilibrium.
This differs from previous work, which used separate calculations for each gas
phase. Our calculations span a wide range of stellar temperatures, gas
densities, and ionization parameters. We describe improvements made to the
spectral synthesis code Cloudy that made these calculations possible. These
include the addition of a molecular network with ~1000 reactions involving 68
molecular species and improved treatment of the grain physics. Data from the
Spitzer First Look Survey, along with other archives, are used to derive
important physical characteristics of the H II region and PDR. These include
stellar temperatures, electron densities, ionization parameters, UV radiation
flux, and PDR density. Finally, we calculate the contribution of the H II
region to PDR emission line diagnostics, which allows for a more accurate
determination of physical conditions in the PDR.


title: A Strong X-Ray Burst from the Low Mass X-Ray Binary EXO0748-676

abstract:
  We have observed an unusually strong X-ray burst as a part of our regular
eclipse timing observations of the low mass binary system EXO0748-676. The
burst peak flux was 5.2x10^-8 ergs cm^-2 s^-1, approximately five times the
normal peak X-ray burst flux observed from this source by RXTE. Spectral fits
to the data strongly suggest that photospheric radius expansion occurred during
the burst. In this Letter we examine the properties of this X-ray burst, which
is the first example of a radius expansion burst from EXO0748-676 observed by
RXTE. We find no evidence for coherent burst oscillations. Assuming that the
peak burst luminosity is the Eddington luminosity for a 1.4 solar mass neutron
star we derive a distance to EXO0748-676 of 7.7 kpc for a helium-dominated
burst photosphere and 5.9 kpc for a hydrogen-dominated burst photosphere.


title: Preheating by Previrialization and its Impact on Galaxy Formation

abstract:
  We use recent observations of the HI-mass function to constrain galaxy
formation. The data conflicts with the standard model where most of the gas in
a low-mass dark matter halo is assumed to settle into a disk of cold gas that
is depleted by star formation and supernova-driven outflows until the disk
becomes gravitationally stable. A consistent model can be found if low-mass
haloes are embedded in a preheated medium, with a specific gas entropy ~ 10Kev
cm^2. Such a model simultaneously matches the faint-end slope of the galaxy
luminosity function. We propose a preheating model where the medium around
low-mass haloes is preheated by gravitational pancaking. Since gravitational
tidal fields suppress the formation of low-mass haloes while promoting that of
pancakes, the formation of massive pancakes precedes that of the low-mass
haloes within them. We demonstrate that the progenitors of present-day dark
matter haloes with M<10^{12}h^{-1}\msun were embedded in pancakes of masses
$~5x10^{12}h^{-1}\msun$ at z~2. The formation of such pancakes heats the gas to
a temperature of 5x10^5K and compresses it to an overdensity of ~10. Such gas
has a cooling time that exceeds the age of the Universe at z~2, and has a
specific entropy of ~15Kev cm^2, almost exactly the amount required to explain
the stellar and HI mass functions. (Abridged)


title:
Hi-Res Spectroscopy of a Volume-Limited Hipparcos Sample within 100
  parsec

abstract:
  We obtain high-resolution echelle spectra of evolved Hipparcos stars within
100 parsec for detailed abundance analysis. We are particularly interested in
subgiants because their ages can be derived accurately. Here, we present
preliminary results for 10 subgiants and discuss the future work for this
project. Our main scientific interest is to incorporate our results to
constrain the star formation history in the solar neighborhood.


title: Measuring Galaxy Environments with Deep Redshift Surveys

abstract:
  We study the applicability of several galaxy environment measures
(n^th-nearest-neighbor distance, counts in an aperture, and Voronoi volume)
within deep redshift surveys. Mock galaxy catalogs are employed to mimic
representative photometric and spectroscopic surveys at high redshift (z ~ 1).
We investigate the effects of survey edges, redshift precision, redshift-space
distortions, and target selection upon each environment measure. We find that
even optimistic photometric redshift errors (\sigma_z = 0.02) smear out the
line-of-sight galaxy distribution irretrievably on small scales; this
significantly limits the application of photometric redshift surveys to
environment studies. Edges and holes in a survey field dramatically affect the
estimation of environment, with the impact of edge effects depending upon the
adopted environment measure. These edge effects considerably limit the
usefulness of smaller survey fields (e.g. the GOODS fields) for studies of
galaxy environment. In even the poorest groups and clusters, redshift-space
distortions limit the effectiveness of each environment statistic; measuring
density in projection (e.g. using counts in a cylindrical aperture or a
projected n^th-nearest-neighbor distance measure) significantly improves the
accuracy of measures in such over-dense environments. For the DEEP2 Galaxy
Redshift Survey, we conclude that among the environment estimators tested the
projected n^th-nearest-neighbor distance measure provides the most accurate
estimate of local galaxy density over a continuous and broad range of scales.


title:
On making predictions in a multiverse: conundrums, dangers, and
  coincidences

abstract:
  The notion that there are many "universes" with different properties is one
answer to the question of "why is the universe so hospitable to life?" This
notion also naturally follows from current ideas in eternal inflation and
string/M theory. But how do we test such a "multiverse" theory: which of the
many universes do we compare to ours? This paper enumerates would would seem to
be essential ingredients for making testable predictions, outlines different
strategies one might take within this framework, then discusses some of the
difficulties and dangers inherent in these approaches. Finally, I address the
issue of whether there may be some general, qualitative predictions that
multiverse theories might share.


title:
Dark Matter Annihilation: the origin of cosmic gamma-ray background at
  1-20 MeV

abstract:
  The origin of the cosmic gamma-ray background at 1-20 MeV remains a mystery.
We show that gamma-ray emission accompanying annihilation of 20 MeV dark matter
particles explains most of the observed signal. Our model satisfies all of the
current observational constraints, and naturally provides the origin of
"missing" gamma-ray background at 1-20 MeV and 511 keV line emission from the
Galactic center. We conclude that gamma-ray observations support the existence
of 20 MeV dark matter particles. Improved measurements of the gamma-ray
background in this energy band undoubtedly test our proposal.


title:
Kinematic Properties and Stellar Populations of Faint Early-Type
  Galaxies. I. Velocity Dispersion Measurements of Central Coma Galaxies

abstract:
  We present velocity dispersion measurements for 69 faint early-type galaxies
in the core of the Coma cluster, spanning -22.0<M_R<-17.5 mag. We examine the
L-\sigma relation for our sample and compare it to that of bright ellipticals
from the literature. The distribution of the the faint early-type galaxies in
the L-sigma plane follows the relation L ~ \sigma^{2.01\pm0.36}, which is
significantly shallower from L ~ \sigma^4 as defined for the bright
ellipticals. While increased rotational support for fainter early-type galaxies
could account for some of the difference in slope, we show that it cannot
explain it. We also investigate the Colour-\sigma relation for our Coma
galaxies. Using the scatter in this relation, we constrain the range of galaxy
ages as a function of their formation epoch for different formation scenarios.
Assuming a strong coordination in the formation epoch of faint early-type
systems in Coma, we find that most had to be formed at least 6 Gyrs ago and
over a short 1 Gyr period.


title:
The INT/WFC survey of the Monoceros Ring: Accretion origin or Galactic
  Anomaly?

abstract:
  We present the results of a wide-field camera survey of the stars in the
Monoceros Ring, thought to be an additional structure in the Milky Way of
unknown origin. Lying roughly in the plane of the Milky Way, this may represent
a unique equatorial accretion event which is contributing to the Thick Disk of
the Galaxy. Alternatively, the Monoceros Ring may be a natural part of the Disk
formation process. With ten pointings in symmetric pairs above and below the
plane of the Galaxy, this survey spans 90 degrees about the Milky Way's
equator. Signatures of the stream of stars were detected in three fields, ({\it
l},{\it b}) = (118,+16)$^\circ$ and (150,+15)$^\circ$ plus a more tentative
detection at (150,-15)$^\circ$. Galactocentric distance estimates to these
structures gave $\sim$17, $\sim$17, and $\sim$13 kpc respectively. The
Monoceros Ring seems to be present on both sides of the Galactic plane, in a
form different to that of the Galactic suggestive of a tidal origin with
streams multiply wrapping the Galaxy. A new model of the stream has shown a
strong coincidence with our results and has also provided the opportunity to
make several more detections in fields in which the stream is less significant.
The confirmed detection at ({\it l},{\it b}) = (123,-19)$^\circ$ at $\sim$14,
kpc from the Galactic centre allows a re-examination revealing a tentative new
detection with a Galactocentric distance of $\sim$21 kpc. (Abridged)


title:
Spatially resolved stellar populations in the isolated elliptical NGC
  821

abstract:
  We present the analysis of Lick absorption-line indices from three separate
long-slit spectroscopic observations of the nearby isolated elliptical galaxy
NGC 821. The three data sets present a consistent picture of the stellar
population within one effective radius, in which strong gradients are evident
in both luminosity-weighted age and metallicity. The central population
exhibits a young age of ~4 Gyr and a metallicity ~3 times solar. At one
effective radius the age has risen to ~12 Gyr and the metallicity fallen to
less than 1/3 solar. The low metallicity population around one effective radius
appears to have an exclusively red horizontal branch, with no significant
contribution from the blue horizontal branch evident in some globular clusters
of the same age and metallicity. Despite the strong central age gradient, we
demonstrate that only a small fraction (<10%) of the galaxy's stellar mass can
have been created in recent star formation events. We consider possible star
formation histories for NGC 821 and find that the most likely cause of the
young central population was a minor merger or tidal interaction that caused
NGC 821 to consume its own gas in a centrally concentrated burst of star
formation 1 to 4 Gyr ago.


title: Interstellar Extinction by Spheroidal Dust Grains

abstract:
  Observations of interstellar extinction and polarization indicate that the
interstellar medium consists of aligned non-spherical dust grains which show
variation in the interstellar extinction curve for wavelengths ranging from NIR
to UV. To model the extinction and polarization, one cannot use the Mie theory
which assumes the grains as solid spheres. We have used a T-matrix based method
for computing the extinction efficiencies of spheroidal silicate and graphite
grains of different shapes (axial ratios) and sizes and used these efficiencies
to evaluate the interstellar extinction curve in the wavelength range 3.4--1.0
microns. A best fit linear combination of silicate and graphite grains of not
very large axial ratio, fits the observed extinction curve reasonably well.
  We calculate the volume extinction factor Vc, which is an important parameter
from the point of view of the cosmic abundance, for the spheroidal grain models
that reproduce the interstellar extinction curve. We find that the shape of the
grains do not affect the volume extinction factor.
  Finally we have also studied the extinction and linear polarization
efficiencies for aligned spheroids. The results show that the shape of grains
affects the linear polarization efficiencies considerably for various
orientation angles of the spheroids.


title:
A Damped Ly-alpha Absorption-line System in an Apparent Void at Redshift
  2.38

abstract:
  We study the contents of an apparent void in the distribution of Ly-alpha
emitting galaxies at redshift 2.38. We show that this void is not empty, but
contains a damped Ly-alpha absorption-line system, seen in absorption against
background QSO 2138-4427. Imaging does not reveal any galaxy associated with
this absorption-line system, but it contains metals (Fe/H ~ -1.3), and its
large velocity range (~ 180 km/s) implies a significant mass.


title:
The Origin of T Tauri X-ray Emission: New Insights from the Chandra
  Orion Ultradeep Project

abstract:
  We use the data of the Chandra Orion Ultradeep Project (COUP) to study the
nearly 600 X-ray sources that can be reliably identified with optically well
characterized T Tauri stars (TTS) in the Orion Nebula Cluster. We detect X-ray
emission from more than 97% of the optically visible late-type (spectral types
F to M) cluster stars. This proofs that there is no ``X-ray quiet'' population
of late-type stars with suppressed magnetic activity. All TTS with known
rotation periods lie in the saturated or super-saturated regime of the relation
between activity and Rossby numbers seen for main-sequence (MS) stars, but the
TTS show a much larger scatter in X-ray activity than seen for the MS stars.
Strong near-linear relations between X-ray luminosities, bolometric
luminosities and mass are present. We also find that the fractional X-ray
luminosity rises slowly with mass over the 0.1 - 2 M_sun range. The plasma
temperatures determined from the X-ray spectra of the TTS are much hotter than
in MS stars, but seem to follow a general solar-stellar correlation between
plasma temperature and activity level. The large scatter about the relations
between X-ray activity and stellar parameters seems to be related to the
influence of accretion on the X-ray emission. While the X-ray activity of the
non-accreting TTS is consistent with that of rapidly rotating MS stars, the
accreting stars are less X-ray active (by a factor of ~2-3 on average) and
produce much less well defined correlations than the non-accretors. We discuss
possible reasons for the suppression of X-ray emission by accretion and the
implications of our findings on long-standing questions related to the origin
of the X-ray emission from young stars.


title:
The exact solution of the Riemann problem in relativistic MHD with
  tangential magnetic fields

abstract:
  We have extended the procedure to find the exact solution of the Riemann
problem in relativistic hydrodynamics to a particular case of relativistic
magnetohydrodynamics in which the magnetic field of the initial states is
tangential to the discontinuity and orthogonal to the flow velocity. The wave
pattern produced after the break up of the initial discontinuity is analogous
to the non--magnetic case and we show that the problem can be understood as a
purely relativistic hydrodynamical problem with a modified equation of state.
The new degree of freedom introduced by the non-zero component of the magnetic
field results in interesting effects consisting in the change of the wave
patterns for given initial thermodynamical states, in a similar way to the
effects arising from the introduction of tangential velocities. Secondly, when
the magnetic field dominates the thermodynamical pressure and energy, the wave
speeds approach the speed of light leading to fast shocks and fast and
arbitrarily thin rarefaction waves. Our approach is the first non-trivial exact
solution of a Riemann problem in relativistic magnetohydrodynamics and it can
also be of great interest to test numerical codes against known analytical or
exact solutions.


title: Dynamical insight into dark-matter haloes

abstract:
  We investigate, using the spherical Jeans equation, self-gravitating
dynamical equilibria satisfying a relation rho/sigma_r^3 propto r^-alpha, which
holds for simulated dark-matter haloes over their whole resolved radial range.
Considering first the case of velocity isotropy, we find that this problem has
only one solution with realistic density profile, which occurs only for a
critical value of alpha_crit = 35/18 ~= 1.94, which is consistent with the
empirical value of 1.9+/-0.05. We extend our analysis in two ways: first we
introduce a parameter epsilon to allow for a more general relation
rho/\sigma_r^epsilon propto r^-alpha; second we consider velocity anisotropy.
If we assume beta(r) := 1- sigma_theta^2 / sigma_r^2 to be linearly related to
the logarithmic density slope gamma(r) := -dln(rho)/dln(r), which is in
agreement with simulations, the problem remains analytically tractable and is
equivalent to the simpler isotropic case: there exists only one physical
solution, which occurs at a critical alpha value. Remarkably, this value of
alpha and the density and velocity-dispersion profiles depend only on epsilon
and the value beta_0 := beta(r=0), but not on the slope of the linear
beta-gamma relation. For epsilon=3, alpha_crit = 35/18 - 2beta_0/9 and the
resulting density profile is fully analytic (as are the velocity dispersion and
circular speed) with an inner cusp rho propto r^{-(7+10beta_0)/9} and a very
smooth transition to a steeper outer power-law asymptote. These models are in
excellent agreement with the density, velocity-dispersion and anisotropy
profiles of simulated dark-matter haloes over their full resolved radial range.
If epsilon=3 is a universal constant, some scatter in beta_0 ~= 0 may account
for some diversity in the density profiles. (ABRIDGED)


title: The Galactic globular cluster system as a fossil record of reionization

abstract:
  We propose that structural, kinematical, and chemical properties of the
Galactic globular clusters (GCs) can contain fossil information of the cosmic
reionization history. We first summarize possible observational evidences for
the influence of reionization on the Galactic GC formation. We then show how
structural properties of the GC system (GCS) in the Galaxy can be influenced by
suppression of GC formation due to reionization during the Galaxy formation
through hierarchical merging of subgalactic clumps, by using numerical
simulations with and without suppression of GC formation by reionization. In
particular, we show that if GC formation in dwarf galaxies that are building
blocks of the Galaxy and virialized after reionization era ($z_{reion}$) are
completely suppressed, the present-day radial distribution of the Galactic GCs
depends strongly on $z_{reion}$. Our numerical results imply that if GC
formation after $z_{reion}$ $\sim$ 15 is strongly suppressed, the origin of the
observed structural properties of the Galactic GCS can be more naturally
explained in the framework of the hierarchical clustering scenario.


title:
Spectral Indications of thermal Sunyaev-Zel'dovich Effect in Archeops
  and WMAP Data

abstract:
  In this paper, we present a joint cross-correlation analysis of the Archeops
CMB maps at 143 and 217 GHz and the WMAP CMB maps at 41, 61 and 94 GHz with sky
templates of projected galaxy density constructed from the 2MASS Extended
Source catalog. These templates have been divided in patches sorted in
decreasing galaxy density with a fixed number of pixels (we considered patches
having 32, 64 and 128 pixels) and the cross correlation has been performed
independently for each of these patches. We find that the densest patch shows a
strong temperature decrement in the Q, V, W bands of WMAP and in the 143 GHz
channel of Archeops, but not in the 217 GHz channel. Furthermore, we find that
the spectral behavior of the amplitude of this decrement is compatible with
that expected for the non-relativistic thermal Sunyaev-Zel'dovich effect, and
is incompatible (at 4.5 sigma level) with the null hypothesis of having only
CMB, noise and a dust component (nu^2) in those pixels. We find that the first
32-pixel sized patch samples the cores of 11 known massive nearby galaxy
clusters. Under the assumption that the decrement found in this patch is due
entirely to the thermal Sunyaev-Zel'dovich effect, we obtain an average
comptonization parameter for those sources of y = (0.41 +- 0.08) x 10^(-4) at
13 arcmin angular scales. This value is compatible at 1 sigma with the
expectation, y = 0.49 x 10^(-4), from a model of the cluster flux number counts
based on the standard Lambda-CDM cosmology. The observed value of y is slightly
diluted when computed for the first patch of 64 and 128 pixels, presumably due
to the inclusion of less massive clusters, and the dilution factor inferred is
also compatible with the quoted model.


title:
The spectral-type/luminosity and the spectral type/satellite-density
  relations in the 2dFGRS

abstract:
  We examine the relative fractions of passive (Type 1), quiet-SF (Type 2) and
active-SF (Type 3+4) galaxies as a function of luminosity and number of
neighbours in several volume limited samples selected from the 2dFGRS.
Neighbours are counted within 1 $h_{75}^{-1}$ Mpc projected distance, and $\pm$
1000 km s$^{-1}$ depth. We apply a maximum magnitude difference criterion and
require neighbours to be fainter than the galaxy itself. We show that, whatever
the environment, passive galaxies dominate in bright samples and active-SF
galaxies in faint samples, whereas quiet-SF galaxies never dominate. We further
show that in bright samples (M$_{B}$ -- 5 $\log$ $h_{75}$ $\leq$$
  - 19$) the fraction of passive galaxies grows steadily with fainter neighbour
density, whereas in faint samples a threshold like dependence is observed. This
suggests that the spectral-type / density ($\approx$ morphology / density)
relation extends to intermediate dense environment, but only in the surrounding
of luminous galaxies and that it reflects an enhancement of the number of
satellites rather than stronger clustering among galaxies themselves. Our
analysis indicates that, in general, luminosity is a good tracer of a galaxy
halo mass and that it dominates over environment (satellite density) in setting
the spectral type mix of a population. However, minority populations exist,
such as luminous SF galaxies and faint passive galaxies, whose luminosity is an
unfair tracer of halo mass.


title:
Gauge-invariant perturbations at second order: multiple scalar fields on
  large scales

abstract:
  We derive the governing equations for multiple scalar fields minimally
coupled to gravity in a flat Friedmann-Robertson-Walker (FRW) background
spacetime on large scales. We include scalar perturbations up to second order
and write the equations in terms of physically transparent gauge-invariant
variables at first and second order. This allows us to write the perturbed
Klein-Gordon equation at second order solely in terms of the field fluctuations
on flat slices at first and second order.


title: A new intermediate mass protostar in the Cepheus A HW2 region

abstract:
  We present the discovery of the first molecular hot core associated with an
intermediate mass protostar in the CepA HW2 region. The hot condensation was
detected from single dish and interferometric observations of several high
excitation rotational lines (from 100 to 880K above the ground state) of SO2 in
the ground vibrational state and of HC3N in the vibrationally excited states
v7=1 and v7=2. The kinetic temperature derived from both molecules is 160K. The
high-angular resolution observations (1.25'' x 0.99'') of the SO2
J=28(7,21)-29(6,24) line (488K above the ground state) show that the hot gas is
concentrated in a compact condensation with a size of 0.6''(430AU), located
0.4'' (300AU) east from the radio-jet HW2. The total SO2 column density in the
hot condensation is 10E18cm-2, with a H2 column density ranging from 10E23 to 6
x 10E24cm-2. The H2 density and the SO2 fractional abundance must be larger
than 10E7cm-3 and 2 x 10E-7 respectively. The most likely alternatives for the
nature of the hot and very dense condensation are discussed. From the large
column densities of hot gas, the detection of the HC3N vibrationally excited
lines and the large SO2 abundance, we favor the interpretation of a hot core
heated by an intermediate mass protostar of 10E3 Lo. This indicates that the
CepA HW2 region contains a cluster of very young stars.


title: On cosmic acceleration without dark energy

abstract:
  We elaborate on the proposal that the observed acceleration of the Universe
is the result of the backreaction of cosmological perturbations, rather than
the effect of a negative-pressure dark-energy fluid or a modification of
general relativity. Through the effective Friedmann equations describing an
inhomogeneous Universe after smoothing, we demonstrate that acceleration in our
local Hubble patch is possible even if fluid elements do not individually
undergo accelerated expansion. This invalidates the no-go theorem that there
can be no acceleration in our local Hubble patch if the Universe only contains
irrotational dust. We then study perturbatively the time behavior of
general-relativistic cosmological perturbations, applying, where possible, the
renormalization group to regularize the dynamics. We show that an instability
occurs in the perturbative expansion involving sub-Hubble modes. Whether this
is an indication that acceleration in our Hubble patch originates from the
backreaction of cosmological perturbations on observable scales requires a
fully non-perturbative approach.


title: CN and HCN in Dense Interstellar Clouds

abstract:
  We present a theoretical investigation of CN and HCN molecule formation in
dense interstellar clouds. We study the gas-phase CN and HCN production
efficiencies from the outer photon-dominated regions (PDRs) into the opaque
cosmic-ray dominated cores. We calculate the equilibrium densities of CN and
HCN, and of the associated species C+, C, and CO, as functions of the
far-ultraviolet (FUV) optical depth. We consider isothermal gas at 50 K, with
hydrogen particle densities from 10^2 to 10^6 cm^-3. We study clouds that are
exposed to FUV fields with intensities 20 to 2*10^5 times the mean interstellar
FUV intensity. We assume cosmic-ray H2 ionization rates ranging from 5*10^-17
s^-1, to an enhanced value of 5*10^-16 s^-1. We also examine the sensitivity of
the density profiles to the gas-phase sulfur abundance.


title:
Two 2MASS-Selected Young Stellar Clusters: Photometry, Spectroscopy, and
  the IMF

abstract:
  We present near-infrared J, H, and K_s images and K-band spectroscopy of two
newly discovered stellar clusters at different stages of evolution. Our spectra
suggest the presence of massive YSOs in the heavily embedded cluster in the
star-forming region near radio source G353.4-0.4 and an O5-O6V star in the
cluster near radio source G305+00.2. We determine a K-band luminosity function
(KLF) for both clusters and an initial mass function (IMF) for the cluster near
G305+00.2. The derived IMF slope is -1.5 if the KLF is used to derive the IMF
and is -0.98 if the color-magnitude diagram and spectra are used. The more
reliable CMD-based slope is flatter than the Salpeter value usually found for
stellar clusters. We find that using the KLF alone to derive an IMF is likely
to produce an overly steep slope in stellar clusters subject to variable
extinction.


title: 2-D models of layered protoplanetary discs: I. The ring instability

abstract:
  In this work we use the radiation hydrodynamic code TRAMP to perform a
two-dimensional axially symmetric model of the layered disc. Using this model
we follow the accumulation of mass in the dead zone due to the radially varying
accretion rate. We found a new type of instability which causes the dead zone
to split into rings. This "ring instability" works due to the positive feedback
between the thickness of the dead zone and the mass accumulation rate.
  We give an analytical description of this instability, taking into account
non-zero thickness of the dead zone and deviations from the Keplerian
rotational velocity. The analytical model agrees reasonably well with results
of numerical simulations. Finally, we speculate about the possible role of the
ring instability in protoplanetary discs and in the formation of planets.


title:
The dwarf galaxy DDO 47 as a dark matter laboratory: testing cusps
  hiding in triaxial halos

abstract:
  We present an analysis of high resolution HI data of the dwarf galaxy DDO 47,
aimed at testing the hypothesis that dark halo triaxiality might induce
non-circular motions resulting in rotation curves best fitted by cored halos,
even if the dark matter halo is intrinsically cuspy. This hypothesis could be
invoked in order to reconcile the predictions of the standard LambdaCDM theory
with the rotation curves of disk galaxies. DDO 47 is an ideal case to test this
hypothesis because it has a very regular velocity field, its rotation curve is
best fitted by a cored halo and a NFW halo is inconsistent with the data. We
analysed the velocity field through the higher-order harmonic terms in order to
search for kinematical signatures of alleged non-circular motions needed to
"hide" a cusp: the result is that globally non-circular motions are at a level
of 2-3 km/s, and they are more likely to be associated to the presence of some
spiral structure than to a global elongated potential (e.g. a triaxial halo).
These non-circular motions are far from being sufficient to account for the
discrepancy with the LambdaCDM predictions. We therefore conclude that the dark
matter halo around the dwarf galaxy DDO 47 is truly cored and that a cusp
cannot be hidden by non-circular motions.


title: The ages and metallicities of galaxies in the local universe

abstract:
  We derive stellar metallicities, light-weighted ages and stellar masses for a
magnitude-limited sample of 175,128 galaxies drawn from the Sloan Digital Sky
Survey Data Release Two (SDSS DR2). We compute median-likelihood estimates of
these parameters using a large library of model spectra at medium-high
resolution, covering a comprehensive range of star formation histories. The
constraints we derive are set by the simultaneous fit of five spectral
absorption features, which are well reproduced by our population synthesis
models. By design, these constraints depend only weakly on the alpha/Fe element
abundance ratio. Our sample includes galaxies of all types spanning the full
range in star formation activity, from dormant early-type to actively
star-forming galaxies. We show that, in the mean, galaxies follow a sequence of
increasing stellar metallicity, age and stellar mass at increasing 4000AA-break
strength (D4000). For galaxies of intermediate mass, stronger Balmer absorption
at fixed D4000 is associated with higher metallicity and younger age. We
investigate how stellar metallicity and age depend on total galaxy stellar
mass. Low-mass galaxies are typically young and metal-poor, massive galaxies
old and metal-rich, with a rapid transition between these regimes over the
stellar mass range 3x10^9<M/Msun<3x10^10. Both high- and low-concentration
galaxies follow these relations, but there is a large dispersion in stellar
metallicity at fixed stellar mass, especially for low-concentration galaxies of
intermediate mass. Despite the large scatter, the relation between stellar
metallicity and stellar mass is similar to the correlation between gas-phase
oxygen abundance and stellar mass for star-forming galaxies. [abriged]


title: Generation of Gaussian Density Fields

abstract:
  This document describes analytical and numerical techniques for the
generation of Gaussian density fields, which represent cosmological density
perturbations. The mathematical techniques involved in the generation of
density harmonics in k-space, the filtering of the density fields, and the
normalization of the power spectrum to the measured temperature fluctuations of
the Cosmic Microwave Background, are presented in details. These techniques are
well-known amongst experts, but the current literature lacks a formal
description. I hope that this technical report will prove useful to new
researchers moving into this field, sparing them the task of reinventing the
wheel.


title: Cool carbon stars in the halo II. A study of 25 new objects

abstract:
  We present new results from an ongoing survey of carbon-rich asymptotic giant
(AGB) stars in the halo of our Galaxy. After selecting candidates primarily
through their 2MASS colours, slit spectroscopy was achieved at the ESO NTT
telescope. Twenty-one new AGB carbon stars were discovered, increasing the
total of presently known similar AGB C stars to about 120. A further four were
observed again in order to confirm their carbon-rich nature and measure radial
velocities. Two main findings emerge from this work. First, we found a C star
located at about 130 kpc from the Sun and at b = -62 degrees. This distant star
is remarkably close (5 kpc) to the principal plane of the Stream of the
Sagittarius dwarf galaxy, and is likely to be a tracer of a distant poorly
populated southern warp of the Stream. etc etc


title: Detection of a massive dust shell around the Type II supernova SN 2002hh

abstract:
  Dust emission from the Type II supernova SN 2002hh in NGC 6946 has been
detected at mid-infrared wavelengths by the Spitzer Space Telescope from 590 to
758 days after outburst and confirmed by higher angular resolution Gemini-N
mid-IR observations. The day-600 5.8-24 micron emission can be fit by a 290-K
blackbody having a luminosity of 1.6E+7 L_Sol. The minimum emitting radius of
1.1E+17 cm is too large for the emitting dust to have been formed in the
supernova ejecta. Using radiative transfer models and realistic dust grain
parameters, fits to the observed flux distribution could be obtained with an
optically thick dust shell having a mass of 0.10-0.15 M_Sol, corresponding to a
total dust+gas mass in excess of 10 M_Sol, suggesting a massive M supergiant or
luminous blue variable precursor to this self-obscured object.


title: Zipf's law for fractal voids and a new void-finder

abstract:
  Voids are a prominent feature of fractal point distributions but there is no
precise definition of what is a void (except in one dimension). Here we propose
a definition of voids that uses methods of discrete stochastic geometry, in
particular, Delaunay and Voronoi tessellations, and we construct a new
algorithm to search for voids in a point set. We find and rank-order the voids
of suitable examples of fractal point sets in one and two dimensions to test
whether Zipf's power-law holds. We conclude affirmatively and, furthermore,
that the rank-ordering of voids conveys similar information to the
number-radius function, as regards the scaling regime and the transition to
homogeneity. So it is an alternative tool in the analysis of fractal point
distributions with crossover to homogeneity and, in particular, of the
distribution of galaxies.


title: GRB 021004 modelled by multiple energy injections

abstract:
  GRB 021004 is one of the best sampled gamma-ray bursts (GRB) to date,
although the nature of its light curve is still being debated. Here we present
a large amount (107) of new optical, near-infrared (NIR) and millimetre
observations, ranging from 2 hours to more than a year after the burst. Fitting
the multiband data to a model based on multiple energy injections suggests that
at least 7 refreshed shocks took place during the evolution of the afterglow,
implying a total energy release (collimated within an angle of 1.8 deg) of ~
8x10^51 erg. Analysis of the late photometry reveals that the GRB 021004 host
is a low extinction (Av ~ 0.1) starburst galaxy with M_B ~ -22.0.


title: A Multi-wavelength study of the Pulsar PSR B1929+10 and its X-ray trail

abstract:
  We report on the emission properties of PSR B1929+10 and its putative X-ray
trail from a multi-wavelength study performed with XMM-Newton, the ESO NTT, the
HST, the Effelsberg 100m Radio Telescope and the Jodrell Bank Radio
Observatory. The XMM-Newton observations confirm the existence of the diffuse
emission with a trail morphology lying in a direction opposite to the
transverse motion of the pulsar. The trail has a length of ~15 arcmin. Its
spectrum is non-thermal and produced by electron-synchrotron emission in the
shock between the pulsar wind and the surrounding medium. Assuming that the
electron lifetime against synchrotron cooling is comparable to the source
transit time over the X-ray trail length, the magnetic field strength in the
trail emitting region is inferred to be ~5 uG. Inspecting data from the
Effelsberg 11cm radio continuum survey of the Galactic plane we discovered an
elongated feature apparently coincident with the X-ray trail. The emission
properties observed from PSR 1929+10 are found to finally challenge the picture
of the emission properties of old non-recycled rotation powered pulsars. Both,
the temporal and spectral X-ray emission properties of PSR 1929+10 are in
excellent agreement with a non-thermal and, thus, magnetospheric radiation
dominated emission scenario. A flux contribution from the thermal emission of
heated polar caps of ~7% is inferred from a best fitting composite Planckian
and power law spectral model. The X-ray pulse profile is found to be markedly
different from the broad sinusoidal pulse profile seen in the low statistic
ROSAT data. Simulations in the framework of an outer-gap emission model are
able to reproduce the observed X-ray pulse profile and its phase relation
relative to the radio pulse.


title:
A Unique Detector for Proton Decay and Neutrino Oscillations Study
  (LANNDD) for a Usa Dusel

abstract:
  We discuss the major scientific issues of the search for proton decay to
$10^{35}$ years lifetime and search for CP violation with a VLBL superbeam
(~2000 km distance). The 100 kT LANNDD liquid Argon TPC is well matched to
these goals. We describe the progress in the R&D program for the detector as
well as the possible location in an underground laboratory in the USA called
DUSEL.


title: The peculiar velocities of satellites of external disk galaxies

abstract:
  We analyze the angular distribution and the orbital rotation directions of a
sample of carefully-selected satellite galaxies extracted from the Sloan
Digital Sky Survey (SDSS). We also study these statistics in an N-body
simulation of cosmological structure formation set within the LCDM paradigm
under various assumptions for the orientations of disk angular momenta.
Assuming that the angular momenta of the disks are aligned with the angular
momenta of the inner regions of their host dark matter halos, we find that the
fraction of simulated satellite halos that exhibit prograde motion is
0.55-0.60, with larger satellites more likely to be prograde. In our
observational sample, approximately 60% of the satellites exhibit prograde
motion, a result that is broadly consistent with the simulated sample. Contrary
to several recent studies, our observational sample of satellite galaxies show
no evidence for being anisotropically distributed about their primary disks.
Again, this result is broadly consistent with our simulated sample of
satellites under the assumption that disk and halo angular momenta are aligned.
However, the small size of our observational sample does not yet allow us to
distinguish between various assumptions regarding the orientations of disks in
their halos. Finally, we assessed the importance of contamination by
interlopers on the measured prograde and retrograde statistics.


title:
Constraints on the acceleration of the solar system from high-precision
  timing

abstract:
  Many astronomers have speculated that the solar system contains undiscovered
massive planets or a distant stellar companion. The acceleration of the solar
system barycenter can constrain the mass and position of the putative
companion. In this paper we use the most recent timing data on accurate
astronomical clocks (millisecond pulsars, pulsars in binary systems and
pulsating white dwarfs) to constrain this acceleration. No evidence for
non-zero acceleration has been found; the typical sensitivity achieved by our
method is a/c=a few times 10^{-19} s^{-1}, comparable to the acceleration due
to a Jupiter-mass planet at 200 AU. The acceleration method is limited by the
uncertainties in the distances and by the timing precision for pulsars in
binary systems, and by the intrinsic distribution of the period derivatives for
millisecond pulsars. Timing data provide stronger constraints than residuals in
the motions of comets or planets if the distance to the companion exceeds a few
hundred AU. The acceleration method is also more sensitive to the presence of a
distant companion (> 300-400 AU) than existing optical and infrared surveys. We
outline the differences between the effects of the peculiar acceleration of the
solar system and the background of gravitational waves on high-precision
timing.


title:
The impact of lens galaxy environments on the image separation
  distribution

abstract:
  We study the impact of lens galaxy environments on the image separation
distribution of lensed quasars. We account for both environmental convergence
and shear, using a joint distribution derived from galaxy formation models
calibrated by galaxy-galaxy lensing data and number counts of massive
elliptical galaxies. We find that the external field enhances lensing
probabilities, particularly at large image separations; the increase is ~30% at
\theta=3'' and ~200% at \theta=5'', when we adopt a power-law source luminosity
function \Phi(L) \propto L^-2.1. The enhancement is mainly driven by
convergence, which boosts both the image separation and magnification bias (for
a fixed lens galaxy mass). These effects have been neglected in previous
studies of lens statistics. Turning the problem around, we derive the posterior
convergence and shear distributions and point out that they are strong
functions of image separation; lens systems with larger image separations are
more likely to lie in dense environments.


title: Diffraction Analysis of 2-D Pupil Mapping for High-Contrast Imaging

abstract:
  Pupil-mapping is a technique whereby a uniformly-illuminated input pupil,
such as from starlight, can be mapped into a non-uniformly illuminated exit
pupil, such that the image formed from this pupil will have suppressed
sidelobes, many orders of magnitude weaker than classical Airy ring
intensities. Pupil mapping is therefore a candidate technique for coronagraphic
imaging of extrasolar planets around nearby stars. Unlike most other
high-contrast imaging techniques, pupil mapping is lossless and preserves the
full angular resolution of the collecting telescope. So, it could possibly give
the highest signal-to-noise ratio of any proposed single-telescope system for
detecting extrasolar planets. Prior analyses based on pupil-to-pupil
ray-tracing indicate that a planet fainter than 10^{-10} times its parent star,
and as close as about 2 lambda/D, should be detectable. In this paper, we
describe the results of careful diffraction analysis of pupil mapping systems.
These results reveal a serious unresolved issue. Namely, high-contrast pupil
mappings distribute light from very near the edge of the first pupil to a broad
area of the second pupil and this dramatically amplifies diffraction-based edge
effects resulting in a limiting attainable contrast of about 10^{-5}. We hope
that by identifying this problem others will provide a solution.


title: The Extended Chandra Deep Field-South Survey: X-ray Point-Source Catalog

abstract:
  The Extended Chandra Deep Field-South (ECDFS) survey consists of 4 Chandra
ACIS-I pointings and covers $\approx$ 1100 square arcminutes ($\approx$ 0.3
deg$^2$) centered on the original CDF-S field to a depth of approximately 228
ks. This is the largest Chandra survey ever conducted at such depth, and only
one XMM-Newton survey reaches a lower flux limit in the hard 2.0--8.0 keV band.
We detect 651 unique sources -- 587 using a conservative source detection
threshold and 64 using a lower source detection threshold. These are presented
as two separate catalogs. Of the 651 total sources, 561 are detected in the
full 0.5--8.0 keV band, 529 in the soft 0.5--2.0 keV band, and 335 in the hard
2.0--8.0 keV band. For point sources near the aim point, the limiting fluxes
are approximately $1.7 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ and $3.9
\times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ in the 0.5--2.0 keV and 2.0--8.0 keV
bands, respectively. Using simulations, we determine the catalog completeness
as a function of flux and assess uncertainties in the derived fluxes due to
incomplete spectral information. We present the differential and cumulative
flux distributions, which are in good agreement with the number counts from
previous deep X-ray surveys and with the predictions from an AGN population
synthesis model that can explain the X-ray background. In general, fainter
sources have harder X-ray spectra, consistent with the hypothesis that these
sources are mainly obscured AGN.


title: The infrared Hourglass cluster in M8

abstract:
  A detailed study of the Hourglass Nebula in the M8 star forming region is
presented. The study is mainly based on recent subarcsec-resolution JHKs images
taken at Las Campanas Observatory and complemented with archival HST images and
longslit spectroscopy retrieved from the ESO Archive Facility. Using the new
numerical code CHORIZOS, we estimate the distance to the earliest stars in the
region to be 1.25 kpc. Infrared photometry of all the sources detected in the
field is given. From analysis of the JHKs colour-colour diagrams, we find that
an important fraction of these sources exhibit significant infrared excess.
These objects are candidates to be low- and intermediate-mass pre-main sequence
stars. Based on HST observations, the spatial distribution of gas, dust and
stars in the region is analyzed. The morphological analysis of these images
also reveals a rich variety of structures related to star formation (proplyds,
jets, bow shocks), similar to those observed in M16 and M42, along with the
detection of the first four Herbig-Haro objects in the region. Furthermore, a
longslit spectrum obtained with NTT confirms the identification of one of them
(HH 870) in the core of the Hourglass nebula, providing the first direct
evidence of active star formation by accretion in M8.


title: 2-D and 3-D Radiation Transfer Models of High-Mass Star Formation

abstract:
  2-D and 3-D radiation transfer models of forming stars generally produce
bluer 1-10 micron colors than 1-D models of the same evolutionary state and
envelope mass. Therefore, 1-D models of the shortwave radiation will generally
estimate a lower envelope mass and later evolutionary state than
multidimensional models. 1-D models are probably reasonable for very young
sources, or longwave analysis (wavelengths > 100 microns). In our 3-D models of
high-mass stars in clumpy molecular clouds, we find no correlation between the
depth of the 10 micron silicate feature and the longwave (> 100 micron) SED
(which sets the envelope mass), even when the average optical extinction of the
envelope is >100 magnitudes. This is in agreement with the observations of
Faison et al. (1998) of several UltraCompact HII (UCHII) regions, suggesting
that many of these sources are more evolved than embedded protostars.
  We have calculated a large grid of 2-D models and find substantial overlap
between different evolutionary states in the mid-IR color-color diagrams. We
have developed a model fitter to work in conjunction with the grid to analyze
large datasets. This grid and fitter will be expanded and tested in 2005 and
released to the public in 2006.


title:
Particle Acceleration and the Production of Relativistic Outflows in
  Advection-Dominated Accretion Disks with Shocks

abstract:
  Relativistic outflows (jets) of matter are commonly observed from systems
containing black holes. The strongest outflows occur in the radio-loud systems,
in which the accretion disk is likely to have an advection-dominated structure.
In these systems, it is clear that the binding energy of the accreting gas is
emitted primarily in the form of particles rather than radiation. However, no
comprehensive model for the disk structure and the associated outflows has yet
been produced. In particular, none of the existing models establishes a direct
physical connection between the presence of the outflows and the action of a
microphysical acceleration mechanism operating in the disk. In this paper we
explore the possibility that the relativistic protons powering the jet are
accelerated at a standing, centrifugally-supported shock in the underlying
accretion disk via the first-order Fermi mechanism. The theoretical analysis
employed here parallels the early studies of cosmic-ray acceleration in
supernova shock waves, and the particle acceleration and disk structure are
treated in a coupled, self-consistent manner based on a rigorous mathematical
approach. We find that first-order Fermi acceleration at standing shocks in
advection-dominated disks proves to be a very efficient means for accelerating
the jet particles. Using physical parameters appropriate for M87 and SgrA*, we
verify that the jet kinetic luminosities computed using our model agree with
estimates based on observations of the sources.


title:
The VLT-UVES survey for molecular hydrogen in high-redshift damped
  Lyman-alpha systems: Physical conditions in the neutral gas

abstract:
  We study the physical conditions in DLAs, using a sample of 33 systems toward
26 QSOs acquired for a recently completed survey of H_2 by Ledoux et al.
(2003). We use the column densities of H_2 in different rotational levels,
together with those of C I, C I*, C I**, C II* and singly ionized atomic
species to discuss the kinetic temperature, the density of hydrogen and the
electronic density in the gas together with the ambient UV radiation field.
Detailed comparisons are made between the observed properties in DLAs, the
interstellar medium (ISM) of the Galaxy, LMC and SMC. The mean kinetic
temperature of the gas corresponding to DLA subcomponents in which H_2
absorption line is detected, derived from the ortho-to-para ratio (153+/-78 K),
is higher than that measured in the ISM (77+/-17 K) and the Magellanic clouds
(82+/-21 K). Typical pressure in these components (corresponding to T = 100-300
K and n = 10-200 cm^-3), measured using C I fine-structure excitation, are
higher than what is measured along ISM sightlines. This is consistent with the
corresponding higher values for N(H_2,J=2)/N(H_2,J=0) seen in DLAs. From the
column densities of the high-J rotational levels, we derive that the typical
radiation field in the H_2 bearing components is of the order of or slightly
higher than the mean UV field in the Galactic ISM. Determination of electron
density in the gas with H_2 and C I show the ionization rate is similar to that
of a cold neutral medium (CNM) in a moderate radiation field. This, together
with the fact that we see H_2 in 13-20% of the DLAs, can be used to conclude
that DLAs at z>1.9 could contribute as much as 50% star formation rate density
seen in Lyman break galaxies (LBGs). (Abridged)


title: Molecular hydrogen in the diffuse interstellar medium at high redshift

abstract:
  Physical conditions within DLAs can reveal the star formation history,
determine the chemical composition of the associated ISM, and hence document
the first steps in the formation of present day galaxies. Here we present
calculations that self-consistently determine the gas ionization, level
populations (atomic fine-structure levels and rotational levels of H_2), grain
physics, and chemistry. We show that for a low-density gas (n< 0.1 cm^-3) the
meta-galactic UV background due to quasars is sufficient to maintain H_2 column
densities below the detection limit (i.e N(H_2)< 10^14 cm^-2) irrespective of
the metallicity and dust content in the gas. Such a gas will have a 21 cm spin
temperature in excess of 7000 K and very low C I and C II* column densities for
H I column densities typically observed in DLAs. We show that the observed
properties of the ~15% per cent of the DLAs that do show detectable H_2
absorption cannot be reproduced with only the quasar dominated meta-galactic UV
radiation field. Gas with higher densities (n>10 cm^-3), a moderate radiation
field (flux density one to ten times that of the background radiation of the
Galactic ISM), the observed range of metallicity and dust-to-gas ratio
reproduce all the observed properties of the DLAs that show H_2 absorption
lines. This favors the presence of ongoing star formation in DLAs with H_2. The
absence of detectable H_2 and C I absorption in a large fraction of DLAs can be
explained if they originate either in a low-density gas or in a high-density
gas with a large ambient radiation field. The absence of 21 cm absorption and C
II* absorption will be consistent with the first possibility. The presence of
21 cm absorption and strong C II* without H_2 and C I absorption will suggest
the second alternative. (Abridged)


title:
A short note on climbing gravity improbable: Superradiant ring
  fellowship of launching the high Lorentz-factor outflows/jets

abstract:
  The spin energy extraction from a rotating black hole by amplification of
scalar waves inside superradiance resonance wedge cavity (ring), followed by
jet formation via magnetic reconnection assisted by the amplified scalar
fields, is proposed. This mechanism may explain the availability of energy for
as well as the formation of relativistic jets with high Lorentz-factor in
microquasars and quasars. It is speculated that it may also explain that the
spin of the central black hole, which facilitates the formation of
superradiance cavity, which in turn would produce the amplified scalar waves by
taking the hole's spin energy, is the source for the distinction between
radio-loud and radio-quiet active galaxies.


title: Flow equations in generalized braneworld scenarios

abstract:
  We discuss the flow equations in the context of general braneworld
cosmologies with a modified Friedmann equation, for either an ordinary scalar
field or a Dirac-Born-Infeld tachyon as inflaton candidates. The 4D,
Randall-Sundrum, and Gauss-Bonnet cases are compared, using the patch formalism
which provides a unified description of these models. The inflationary dynamics
is described by a tower of flow parameters that can be evolved in time to
select a particular subset of points in the space of cosmological observables.
We analyze the stability of the fixed points in all the cosmologies (our
results in the 4D case already extending those in the literature). Numerical
integration of the flow equations shows that the predictions of the
Gauss-Bonnet braneworld differ significantly as compared to the Randall-Sundrum
and 4D scenarios, whereas tachyon inflation gives tensor perturbations smaller
than those in the presence of a normal scalar field. These results are extended
to the realization of a noncommutative space-time preserving maximal symmetry.
In this case the tensor-to-scalar signal is unchanged, while blue-tilted
spectra are favoured.


title: Gamma-Ray Bursts, Collisionless Shocks and Synthetic Spectra

abstract:
  The radiation from afterglows of gamma-ray bursts (GRB) is generated in
collisionless plasma shocks. The two main ingredients behind the radiation are
high-energy, non-thermal electrons and a strong magnetic field. I argue that in
order to make the right conclusions about gamma-ray burst and afterglow
parameters from observations, it is crucial to have a firm understanding of the
microphysics of collisionless shock. I present the results of self-consistent,
three-dimensional particle-in-cell computational simulations of the collision
of weakly magnetized plasma shells: The experiments show how a plasma
instability generates a magnetic field in the shock. The field has strength up
to percents of the equipartition value. The experiments also reveal a new,
non-thermal electron acceleration mechanism that differs substantially from
Fermi acceleration. Finally, I present the results from a new numerical tool
that enables us to extract synthetic radiation spectra directly from the
experiments. The preliminary results differ from synchrotron radiation but are
consistent with GRB afterglow observations. I conclude that strong magnetic
field generation, non-thermal particle acceleration and the emission of
radiation that is consistent with GRB afterglow observations, are all
unavoidable consequences of the collision between two relativistic plasma
shells.


title: Caustic and Weak Lensing Estimators of Galaxy Cluster Masses

abstract:
  There are only two methods for estimating the mass distribution in the outer
regions of galaxy clusters, where virial equilibrium does not hold: weak
gravitational lensing and identification of caustics in redshift space. For the
first time, we apply both methods to three clusters: A2390, MS1358 and Cl 0024.
The two measures are in remarkably good agreement out to ~2 Mpc/h from the
cluster centers. This result demonstrates that the caustic technique is a
valuable complement to weak lensing. With a few tens of redshifts per (Mpc/h)^2
within the cluster, the caustic method is applicable for any z<~0.5.


title:
The VIMOS VLT Deep Survey: Evolution of the non-linear galaxy bias up to
  z=1.5

abstract:
  We present the first measurements of the Probability Distribution Function
(PDF) of galaxy fluctuations in the VIMOS-VLT Deep Survey (VVDS) cone, covering
0.4x0.4 deg between 0.4<z<1.5. The second moment of the PDF, i.e. the rms
fluctuations of the galaxy density field, is with good approximation constant
over the full redshift baseline investigated: we find that, in redshift space,
sigma_8 for galaxies brighter than M=-20+5log h has a mean value of 0.94\pm0.07
in the redshift interval 0.7<z<1.5. The third moment, i.e. the skewness,
increases with cosmic time: we find that the probability of having underdense
regions is greater at z~0.7 than it was at z~1.5. By comparing the PDF of
galaxy density contrasts with the theoretically predicted PDF of mass
fluctuations we infer the redshift-, density-, and scale-dependence of the
biasing function b(z, \delta, R) between galaxy and matter overdensities up to
redshift z=1.5. Our results can be summarized as follows: i) the galaxy bias is
an increasing function of redshift: evolution is marginal up to z~0.8 and more
pronounced for z>0.8; ii) the formation of bright galaxies is inhibited below a
characteristic mass-overdensity threshold whose amplitude increases with
redshift and luminosity; iii) the biasing function is non linear in all the
redshift bins investigated with non-linear effects of the order of a few to 10%
on scales >5Mpc.


title:
QSO Host Galaxy Luminosity and [OIII] Line Width as a Surrogate for
  Stellar Velocity Distribution

abstract:
  Supermassive black holes in galactic nuclei show a close relationship between
the black hole mass, luminosity, and stellar velocity dispersion (sigma_*) of
the host galaxy bulge. Probing these relationships at high redshift may shed
light on the link between the formation of the galactic bulge and central black
hole, but direct measurements of stellar velocity dispersion at high redshift
are difficult. We show that [OIII] line widths provide a useful surrogate for
sigma_* by comparing sigma_[OIII] with the value of sigma_* predicted by the
Faber-Jackson relation for QSOs with measured host galaxy luminosity. Over a
wide range of AGN luminosity, sigma_[OIII] tracks sigma_*, albeit with
considerable scatter. [OIII] line widths are narrower by ~0.1 dex in radio-loud
QSOs than in radio-quiet QSOs of similar host luminosity. In low redshift QSOs,
the ratio of star formation rate to black hole growth rate is much smaller than
the typical ratio of bulge mass to black hole mass.


title:
A Hydrogen Atmosphere Spectral Model Applied to the Neutron Star X7 in
  the Globular Cluster 47 Tucanae

abstract:
  Current X-ray missions are providing high-quality X-ray spectra from neutron
stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated
us to calculate new hydrogen-atmosphere models, including opacity due to
free-free absorption and Thomson scattering, thermal electron conduction, and
self-irradiation by photons from the compact object. We have constructed a
self-consistent grid of neutron star models covering a wide range of surface
gravities as well as effective temperatures, which we make available to the
scientific community.
  We present multi-epoch Chandra X-ray observations of the qLMXB X7 in the
globular cluster 47 Tuc, which is remarkably nonvariable on timescales from
minutes to years. Its high-quality X-ray spectrum is adequately fit by our
hydrogen-atmosphere model without any hard power-law component or narrow
spectral features. If a mass of 1.4 Msol is assumed, our spectral fits require
that its radius be in the range R=14.5^{+1.8}_{-1.6} km (90% confidence),
larger than expected from currently preferred models of NS interiors. If its
radius is assumed to be 10 km, then a mass of M=2.20^{+0.03}_{-0.16} Msol is
required. Using models with the appropriate surface gravity for each value of
the mass and radius becomes important for interpretation of the highest quality
data.


title: Spiders in Lyot Coronagraphs

abstract:
  In principle, suppression of on-axis stellar light by a coronagraph is easier
on an unobscured aperture telescope than on one with an obscured aperture.
Recent designs such as the apodized pupil Lyot coronagraph, the `band-limited'
Lyot coronagraph, and several variants of phase mask coronagraphs work best on
unobscured circular aperture telescopes. These designs are developed to enable
the discovery and characterization of nearby jovian or even terrestrial
exoplanets. All of today's major space-based and adaptive optics-equipped
ground based telescopes are obscured aperture systems, with a secondary mirror
held in place by secondary support `spider' vanes. The presence of a secondary
obscuration can be dealt with by ingenious coronagraph designs, but the spider
vanes themselves cause diffracted light that can hamper the search for jovian
exoplanets around nearby stars. We look at the problem of suppressing spider
vane diffraction in Lyot coronagraphs, including apodized pupil and
band-limited designs. We show how spider vane diffraction can be reduced
drastically, and in fact contained, in the final coronagraphic image, within
one resolution element of the geometric image of the focal plane mask's
occulting spot. This makes adaptive optics coronagraphic searches for
exojupiters possible on the next generation of adaptive optics systems being
developed for 8-10 m class telescopes such as Gemini and the Very Large
Telescopes.


title:
Where does the hard X-ray diffuse emission in clusters of galaxies come
  from?

abstract:
  The surface brightness produced by synchrotron radiation in Clusters of
Galaxies with a radio-halo sets a degenerate constraint on the magnetic field
strength, the relativistic electron density and their spatial distributions.
Using the Coma radio-halo as a case-study, predictions are made for the
brightness profile expected in the 20-80 keV band due to ICS by the
relativistic electrons on the CMB, for a range of central values of the
magnetic field B_0 and models of its radial dependence. We show that the
presence of B-field scalar fluctuations on small scales tends to systematically
depress the electron density required by the radio data, hence to decrease the
ICS brightness expected. These predictions are useful to evaluate the
sensitivity required in future imaging HXR instruments, in order to obtain
direct information on the spatial distribution and content of relativistic
electrons, hence on the magnetic field properties. If compared with the flux in
the Coma HXR tail - interpreted as ICS from within the radius R_h - the
predictions lead to values of B_0 which are lower than those obtained from
Faraday Rotation measurements. The discrepancy is somewhat reduced if the
radio-halo profile is extrapolated out to R_{vir}, i.e. about 3 R_h, or if it
is assumed that B(r) \propto n_{th}(r) (Dolag et al. 2002). Note that in the
latter case, n_{rel}(r) has its minimum value at the center of the cluster. If
real and from ICS, the bulk of the HXR tail should then be contributed by
electrons other than those responsible for the bulk of the radio-halo emission.
This case illustrates the need for spatially resolved spectroscopy in the HXR,
in order to obtain solid information on the non-thermal content of Clusters of
Galaxies.


title:
The Double Pulsar J0737--3039: Testing the Neutron Star Equation of
  State

abstract:
  The double pulsar J0737--3039 has become an important astrophysical
laboratory for testing fundamental physics. Here we demonstrate that the low
measured mass of Pulsar B can be used to constrain the equation of state of
neutron star matter {\em under the assumption} that it formed in an
electron-capture supernova. We show that the observed orbital parameters as
well as the likely evolutionary history of the system support such a hypothesis
and discuss future refinements that will improve the constraints this test may
provide.


title: How is the blazar GeV emission really produced?

abstract:
  We show that the external Compton (EC) model for the production of the GeV
emission in blazars makes specific predictions for the spectrum and variability
of those blazars characterized by a high Compton dominance (Compton to
synchrotron luminosity ratio). These unavoidable features have not been
observed, casting doubt on the validity of this popular model. We argue that
synchrotron-self Compton (SSC) models including the higher orders of Compton
scattering are more promising, and we briefly discuss the implications of our
findings for the geometry of the broad line region (BLR).


title: A Survey of Eclipsing Binary Stars in the Eastern Spiral Arm of M31

abstract:
  Results of an archival survey are presented using B-band imaging of the
eastern spiral arm of M31. Focusing on the eclipsing binary star population, a
matched-filter technique has been used to identify 280 binary systems. Of
these, 127 systems (98 of which are newly discovered) have sufficient phase
coverage to allow accurate orbital periods to be determined. At least nine of
these binaries are detached systems which could, in principle, be used for
distance determination. The light curves of the detached and other selected
systems are presented along with a discussion of some of the more interesting
binaries. The impact of unresolved stellar blends on these lightcurves is
considered.


title:
The Transit Light Curve Project. IV. Five Transits of the Exoplanet
  OGLE-TR-10b

abstract:
  We present I and B photometry of five distinct transits of the exoplanet
OGLE-TR-10b. By modeling the light curves, we find the planetary radius to be
R_P = 1.06 +/- 0.08 R_Jup and the stellar radius to be R_S = 1.10 +/- 0.07
R_sun. The uncertainties are dominated by statistical errors in the photometry.
Our estimate of the planetary radius is smaller than previous estimates that
were based on lower-precision photometry, and hence the planet is not as
anomalously large as was previously thought. We provide updated determinations
of all the system parameters, including the transit ephemerides.


title: Non-Gaussianity from Cosmic Magnetic Fields

abstract:
  Magnetic fields in the early universe could have played an important role in
sourcing cosmological perturbations. While not the dominant source, even a
small contribution might be traceable through its intrinsic non-Gaussianity.
Here we calculate analytically the one, two and three point statistics of the
magnetic stress energy resulting from tangled Gaussian fields, and confirm
these with numerical realizations of the fields. We find significant
non-Gaussianity, and importantly predict higher order moments that will appear
between the scalar, vector and tensor parts of the stress energy (e.g.
scalar-tensor-tensor moments). Such higher order cross correlations are a
generic feature of non-linear theories and could prove to be an important probe
of the early universe.