title: Is cosmology compatible with sterile neutrinos?

abstract:
  By combining data from cosmic microwave background (CMB) experiments
(including the recent WMAP third year results), large scale structure (LSS) and
Lyman-alpha forest observations, we constrain the hypothesis of a fourth,
sterile, massive neutrino. For the 3 massless + 1 massive neutrino case we
bound the mass of the sterile neutrino to m_s<0.26eV (0.44eV) at 95% (99.9%)
c.l.. These results exclude at high significance the sterile neutrino
hypothesis as an explanation of the LSND anomaly. We then generalize the
analysis to account for active neutrino masses (which tightens the limit to
m_s<0.23eV 0.42eV) and the possibility that the sterile abundance is not
thermal. In the latter case, the contraints in the (mass, density) plane are
non-trivial. For a mass of >1eV or <0.05eV the cosmological energy density in
sterile neutrinos is always constrained to be omega_nu <0.003 at 95 c.l..
However, for a sterile neutrino mass of ~0.25eV, omega_nu can be as large as
0.01.


title:
AGN Feedback and Cooling Flows: Problems with Simple Hydrodynamical
  Models

abstract:
  In recent years it has become increasingly clear that Active Galactic Nuclei,
and radio-galaxies in particular, have an impact on large scale structure and
galaxy formation. In principle, radio-galaxies are energetic enough to halt the
cooling of the virialized intracluster medium (ICM) in the inner regions of
galaxy clusters, solving the cooling flow problem and explaining the high-mass
truncation of the galaxy luminosity function. We explore this process through a
series of high resolution, three dimensional hydrodynamic simulations of jetted
active galaxies that act in response to cooling-mediated accretion of an ICM
atmosphere. We find that our models are incapable of producing a long term
balance of heating and cooling; catastrophic cooling can be delayed by the jet
action but inevitably takes hold. At the heart of the failure of these models
is the formation of a low density channel through which the jet can freely
flow, carrying its energy out of the cooling core. It is possible that this
failure is due to an over-simplified treatment of the fast jet (which may
underestimate the ``dentist drill'' effect). However, it seems likely that
additional complexity (large-angle jet precession or ICM turbulence) or
additional physics (magnetohydrodynamic effects and plasma transport processes)
is required to produce a spatial distribution of jet heating that can prevent
catastrophic cooling. This work also underscores the importance of including
jet dynamics in any feedback model as opposed to the isotropically inflated
bubble approach taken in some previous works.


title:
WLM-1: A Non-Rotating, Gravitationally Unperturbed, Highly Elliptical
  Extragalactic Globular Cluster

abstract:
  Globular clusters have long been known for presenting (at times) significant
deviations from spherical symmetry. While rotation has been the main proposed
explanation, other complicating factors such as their constant interaction with
the strong gravitational potential of their host galaxy have made it difficult
for a consensus to be reached. To address this question we have obtained
high-resolution spectra of WLM-1, the lone globular cluster associated with the
isolated, low-mass dwarf irregular galaxy WLM. Using archival HST WFPC2 data,
we measure the radial ellipticity profile of WLM-1, finding it to be highly
elliptical, with a mean value of 0.17 in the region 0.5-5" -- which is
comparable to what is found in our Galaxy for the most elliptical globular
clusters. There is no evidence of isophote twisting, except for the innermost
regions of the cluster (r < 0.5"). To investigate whether the observed
flattening can be ascribed to rotation, we have obtained long-slit
high-resolution VLT/UVES spectra of this cluster along and perpendicular to the
axis of flattening. Using cross-correlation we find that the velocity profile
of the cluster is consistent with zero rotation along either axis. Thus neither
cluster rotation nor galactic tides can be responsible for the flattened
morphology of WLM-1. We argue that the required velocity dispersion anisotropy
between the semi-major and semi-minor axes that would be required to account
for the observed flattening is relatively small, of order 1 km/s. Even though
our errors preclude us from conclusively establishing that such a difference
indeed exists, velocity anisotropy remains at present the most plausible
explanation for the shape of this cluster.


title:
A data-driven Bayesian approach for finding young stellar populations in
  early-type galaxies from their UV-optical spectra

abstract:
  We present the results of a novel application of Bayesian modelling
techniques, which, although purely data driven, have a physically interpretable
result, and will be useful as an efficient data mining tool. We base our
studies on the UV-to-optical spectra (observed and synthetic) of early-type
galaxies. A probabilistic latent variable architecture is formulated, and a
rigorous Bayesian methodology is employed for solving the inverse modelling
problem from the available data. A powerful aspect of our formalism is that it
allows us to recover a limited fraction of missing data due to incomplete
spectral coverage, as well as to handle observational errors in a principled
way. We apply this method to a sample of 21 well-studied early-type spectra,
with known star-formation histories. We find that our data-driven Bayesian
modelling allows us to identify those early-types which contain a significant
stellar population <~ 1 Gyr old. This method would therefore be a very useful
tool for automatically discovering various interesting sub-classes of galaxies.
(abridged)


title: The Detection of 3He+ in a Planetary Nebula Using the VLA

abstract:
  We used the VLA to search for 3He+ emission from two Galactic planetary
nebulae (PNe): NGC6572 and J320}. Standard stellar models predict that the
3He/H abundance ratios for PNe should be 1-2 orders of magnitude higher than
the primordial value (3He/H ~ 1e-5 by number) determined from Galactic HII
region abundances and confirmed by WMAP cosmic microwave background results.
Chemical evolution models suggest that fewer than 5% of all PNe enrich the
interstellar medium (ISM) with 3He at the level of standard stellar models. Our
target PNe are therefore anomalous in that they were selected from a sample
deliberately biased to contain objects with properties that maximized the
likelihood of a 3He detection by the VLA. We have detected the 8.665 GHz
hyperfine 3He+ transition in J320 at the 4 sigma level. The 3He/H abundance
ratio is 1.9e-3 with roughly a factor of two uncertainty. For NGC 6572 we find
an upper limit of 3He/H <= 1e-3. This detection of 3He in J320 makes it the
second PN known to have an anomalously high 3He abundance confirming that at
least some low-mass stars produce significant amounts of 3He that survives to
the PN stage and enriches the ISM.


title:
Protostars, Dust Globules, and a Herbig-Haro Object in the LMC
  Superbubble N51D

abstract:
  Using Spitzer Space Telescope and Hubble Space Telescope observations of the
superbubble N51D, we have identified three young stellar objects (YSOs) in dust
globules, and made the first detection of a Herbig-Haro object outside the
Galaxy. The spectral energy distributions of these YSOs suggest young massive
stars with disk, envelope, and outflow cavities. The interstellar conditions
are used to assess whether the star formation was spontaneous or induced by
external pressure.


title:
Flares in long and short Gamma-Ray Bursts: a common origin in a
  hyperaccreting accretion disk

abstract:
  Early-time X-ray observations of GRBs with the Swift satellite have revealed
a more complicated phenomenology than was known before. In particular, the
presence of flaring activity on a wide range of time scales probably requires
late-time energy production within the GRB engine. Since the flaring activity
is observed in both long and short GRBs, its origin must be within what is in
common for the two likely progenitors of the two classes of bursts: a
hyperaccreting accretion disk around a black hole of a few solar masses. Here,
we show that some of the observational properties of the flares, such as the
duration-time scale correlation, and the duration-peak luminosity
anticorrelation displayed by most flares within a given burst, are
qualitatively consistent with viscous disk evolution, provided that the disk at
large radii either fragments or otherwise suffers large amplitude variability.
We discuss the physical conditions in the outer parts of the disk, and conclude
that gravitational instability, possibly followed by fragmentation, is the most
likely candidate for this variability.


title:
Infrared power-law galaxies in the Chandra Deep Field South: AGN and
  ULIRGs

abstract:
  We investigate the nature of a sample of 92 Spitzer/MIPS 24 micron selected
galaxies in the CDFS, showing power law-like emission in the Spitzer/IRAC 3.6-8
micron bands. The main goal is to determine whether the galaxies not detected
in X-rays (47% of the sample) are part of the hypothetical population of
obscured AGN not detected even in deep X-ray surveys. The majority of the IR
power-law galaxies are ULIRGs at z>1, and those with LIRG-like IR luminosities
are usually detected in X-rays. The optical to IR spectral energy distributions
(SEDs) of the X-ray detected galaxies are almost equally divided between a
BLAGN SED class (similar to an optically selected QSO) and a NLAGN SED (similar
to the BLAGN SED but with an obscured UV/optical continuum). A small fraction
of SEDs resemble warm ULIRG galaxies (e.g., Mrk231). Most galaxies not detected
in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically
fainter, and possibly more obscured. Moreover, the IR power-law galaxies have
SEDs significantly different from those of high-z (z_sp>1) IR (24 micron)
selected and optically bright (VVDS I_AB<=24) star-forming galaxies whose SEDs
show a very prominent stellar bump at 1.6 micron. The galaxies detected in
X-rays have 2-8 keV rest-frame luminosities typical of AGN. The galaxies not
detected in X-rays have global X-ray to mid-IR SED properties that make them
good candidates to contain IR bright X-ray absorbed AGN. If all these sources
are actually obscured AGN, we would observe a ratio of obscured to unobscured
24 micron detected AGN of 2:1, whereas models predict a ratio of up to 3:1.
Additional studies using Spitzer to detect X-ray-quiet AGN are likely to find
more such obscured sources.


title: The signature of a wind reverse shock in Gamma-ray bursts afterglows

abstract:
  Explosions of massive stars are believed to be the source of a significant
fraction of gamma-ray bursts (GRBs). If this is indeed the case, then the
explosion blast wave propagates into a complex density structure, composed of a
stellar wind bounded by two shock waves - a wind reverse shock and a forward
shock. As the explosion blast wave reaches R_0, the radius of the wind reverse
shock, it splits into two shock waves - a reverse and a forward shock wave. We
show that the reverse shock thus produced is not strong, therefore full
analytical treatment is required in calculating its properties. We calculate
the dynamics of the flow and the evolution of the blast waves in all of the
different stages. We show that the fluid Lorentz factor at r>R_0 is equal to
0.725 times the blast wave Lorentz factor as it reaches R_0, and is time (and
r) independent as long as the blast wave reverse shock exists. Following the
calculation of the blast wave evolution, we calculate the radiation expected in
different energy bands. We show that about a day after the main explosion, as
the blast wave reaches R_0, the observed afterglow flux starts to rise. It
rises by a factor of about 2 in a few hours, during which the blast wave
reverse shock exists, and then declines. We show that the power law index
describing light curve time evolution is different at early (before the rise)
and late times, and is frequency dependent. We present light curves in the
different energy bands for this scenario.


title:
Measurement of the Spatial Cross-Correlation Function of Damped Lyman
  Alpha Systems and Lyman Break Galaxies

abstract:
  We present the first spectroscopic measurement of the spatial
cross-correlation function between damped Lyman alpha systems (DLAs) and Lyman
break galaxies (LBGs). We obtained deep u'BVRI images of nine QSO fields with
11 known z ~ 3 DLAs and spectroscopically confirmed 211 R < 25.5
photometrically selected z > 2 LBGs. We find strong evidence for an overdensity
of LBGs near DLAs versus random, the results of which are similar to that of
LBGs near other LBGs. A maximum likelihood cross-correlation analysis found the
best fit correlation length value of r_0 = 2.9^(+1.4)_(-1.5) h^(-1)Mpc using a
fixed value of gamma = 1.6. The implications of the DLA-LBG clustering
amplitude on the average dark matter halo mass of DLAs are discussed.


title: A review of optical sky brightness and extinction at Dome C, Antarctica

abstract:
  The recent discovery of exceptional seeing conditions at Dome C, Antarctica,
raises the possibility of constructing an optical observatory there with unique
capabilities. However, little is known from an astronomer's perspective about
the optical sky brightness and extinction at Antarctic sites. We review the
contributions to sky brightness at high-latitude sites, and calculate the
amount of usable dark time at Dome C. We also explore the implications of the
limited sky coverage of high-latitude sites and review optical extinction data
from the South Pole. Finally, we examine the proposal of Baldry and
Bland-Hawthorn (2001) to extend the amount of usable dark time through the use
of polarising filters.


title:
Testing the beamed inverse-Compton model for jet X-ray emission:
  velocity structure and deceleration?

abstract:
  By considering a small sample of core-dominated radio-loud quasars with X-ray
jets, I show, as has been argued previously by others, that the observations
require bulk jet deceleration if all of the X-ray emission is to be explained
using the widely adopted beamed inverse-Compton model, and argue that jets even
in these powerful objects must have velocity structure in order to reconcile
their radio and X-ray properties. I then argue that the deceleration model has
several serious weaknesses, and discuss the viability of alternative models for
the decline in X-ray/radio ratio as a function of position. Although
inverse-Compton scattering from the jets is a required process and must come to
dominate at high redshifts, adopting an alternative model for the X-ray
emission of some nearby, well-studied objects can greatly alleviate some of the
problems posed by these observations for the beamed inverse-Compton model.


title: Dynamics of Quintessential Inflation

abstract:
  In this paper, we study a realistic model of quintessential inflation with
radiation and matter. By the analysis of the dynamical system and numerical
work about the evolution of the equation of state and cosmic density parameter,
we show that this model is a good match for the current astronomical
observation. The conclusion we obtain is in favor of the model where the
modular part of complex field plays the role of the inflaton whereas the
argument part is the quintessence field. The numerical calculation shows that a
heteroclinic orbit (solution of dynamical system) which interpolates between
early-time de Sitter phase (an unstable critical point) and a late-time de
Sitter attractor.


title: Extended X-Ray Emission from QSOs

abstract:
  We report Chandra ACIS observations of the fields of 4 QSOs showing strong
extended optical emission-line regions. Two of these show no evidence for
significant extended X-ray emission. The remaining two fields, those of 3C
249.1 and 4C 37.43, show discrete (but resolved) X-ray sources at distances
ranging from ~10 to ~40 kpc from the nucleus. In addition, 4C 37.43 also may
show a region of diffuse X-ray emission extending out to ~65 kpc and centered
on the QSO. It has been suggested that extended emission-line regions such as
these may originate in the cooling of a hot intragroup medium. We do not detect
a general extended medium in any of our fields, and the upper limits we can
place on its presence indicate cooling times of at least a few 10^9 years. The
discrete X-ray emission sources we detect cannot be explained as the X-ray jets
frequently seen associated with radio-loud quasars, nor can they be due to
electron scattering of nuclear emission. The most plausible explanation is that
they result from high-speed shocks from galactic superwinds resulting either
from a starburst in the QSO host galaxy or from the activation of the QSO
itself. Evidence from densities and velocities found from studies of the
extended optical emission around QSOs also supports this interpretation.


title:
Flux upper limits of diffuse TeV gamma rays from the Galactic plane
  using the effective area of the Tibet-II and -III arrays

abstract:
  We obtained new upper limits on the diffuse gamma rays from the inner
Galactic (IG) and outer Galactic (OG) planes in 3.10 TeV region, using the
Tibet air shower data and new Monte Carlo simulation results. A difference of
the effective area of the air-shower array for observing gamma rays and cosmic
rays was carefully taken into account in this analysis, resulting in that the
flux upper limits of the diffuse TeV gamma rays were reduced by factors of
4.0.3.7 for 3.10 TeV than those in our previous results (Amenomori, M., Ayabe,
S., Cui, S.W., et al. Observation of multi-TeV diffuse gamma rays from the
Galactic plane with the Tibet air shower array. Astrophys. J. 580, 887.895,
2002.). This new result suggests that the inverse power index of the energy
spectrum of source electrons responsible for generating diffuse TeV gamma rays
through inverse Compton effect should be steeper than 2.2 and 2.1 for IG and OG
planes, respectively, with 99%C.L.


title: Radiative Transfer Along Rays in Curved Spacetimes

abstract:
  Radiative transfer in curved spacetimes has become increasingly important to
understanding high-energy astrophysical phenomena and testing general
relativity in the strong field limit. The equations of radiative transfer are
physically equivalent to the Boltzmann equation, where the latter has the
virtue of being covariant. We show that by a judicious choice of the basis of
the phase space, it is generally possible to make the momentum derivatives in
the Boltzmann equation vanish along an arbitrary (including nongeodesic) path,
thus reducing the problem of radiative transfer along a ray to a path integral
in coordinate space.


title: A 70 kpc X-ray tail in the cluster A3627

abstract:
  We present the discovery of a 70 kpc X-ray tail behind the small late-type
galaxy ESO137-001 in the nearby, hot (T=6.5 keV) merging cluster A3627, from
both Chandra and XMM observations. The tail has a length-to-width ratio of ~
10. It is luminous (L_{0.5-2 keV} ~ 10^41 ergs s^-1, with a temperature of ~
0.7 keV and an X-ray M_gas of ~ 10^9 M_solar (~ 10% of the galaxy's stellar
mass). We interpret this tail as the stripped interstellar medium of ESO137-001
mixed with the hot cluster medium, when this blue galaxy is being converted
into a gas-poor galaxy. Three X-ray point sources are detected in the axis of
the tail, which may imply active star formation in the tail. The straightness
and narrowness of the tail also implies that the ICM turbulence is not strong
on scales of 20 - 70 kpc.


title:
Amplitude and Phase Fluctuations for Gravitational Waves Propagating
  through Inhomogeneous Mass Distribution in the Universe

abstract:
  When a gravitational wave (GW) from a distant source propagates through the
universe, its amplitude and phase change due to gravitational lensing by the
inhomogeneous mass distribution. We derive the amplitude and phase
fluctuations, and calculate these variances in the limit of a weak
gravitational field of density perturbation. If the scale of the perturbation
is smaller than the Fresnel scale $\sim 100 {pc} (f/{mHz})^{-1/2}$ ($f$ is the
GW frequency), the GW is not magnified due to the diffraction effect. The rms
amplitude fluctuation is $1-10 %$ for $f > 10^{-10}$ Hz, but it is reduced less
than 5% for a very low frequency of $f < 10^{-12}$ Hz. The rms phase
fluctuation in the chirp signal is $\sim 10^{-3}$ radian at LISA frequency band
($10^{-5} - 10^{-1}$ Hz). Measurements of these fluctuations will provide
information about the matter power spectrum on the Fresnel scale $\sim 100$ pc.


title: r-Process Calculations and Galactic Chemical Evolution

abstract:
  While the origin of r-process nuclei remains a long-standing mystery, recent
spectroscopic studies of extremely metal-poor stars in the Galactic halo
strongly suggest that it is associated with core-collapse supernovae. In this
article, an overview of the recent theoretical studies of the r-process is
presented with a special emphasis on the astrophysical scenarios related to
core-collapse supernovae. We also review a recent progress of the Galactic
chemical evolution studies as well as of the spectroscopic studies of extremely
metal-poor halo stars, which provide us important clues to better understanding
of the astrophysical r-process site.


title: A Smart Pixel Camera for future Cherenkov Telescopes

abstract:
  The Smart Pixel Camera is a new camera for imaging atmospheric Cherenkov
telescopes, suited for a next generation of large multi-telescope ground based
gamma-ray observatories. The design of the camera foresees all electronics
needed to process the images to be located inside the camera body at the focal
plane. The camera has a modular design and is scalable in the number of pixels.
The camera electronics provides the performance needed for the next generation
instruments, like short signal integration time, topological trigger and short
trigger gate, and at the same time the design is optimized to minimize the cost
per channel. In addition new features are implemented, like the measurement of
the arrival time of light pulses in the pixels on the few hundred psec
timescale. The buffered readout system of the camera allows to take images at
sustained rates of O(10 kHz) with a dead-time of only about 0.8 % per kHz.


title:
A Possible Rossby Wave Instability Origin for the Flares in Sagittarius
  A*

abstract:
  In recent years, near-IR and X-ray flares have been detected from the
Galaxy's central radio point source, Sagittarius A* (Sgr A*), believed to be a
\~3.10^6 solar masses supermassive black hole. In some cases, the transient
emission appears to be modulated with a (quasi-)periodic oscillation (QPO) of ~
17-20 minutes. The implied ~ 3 r_S size of the emitter (where r_S = 2GM/c^2 is
the Schwarzschild radius) points to an instability - possibly induced by
accretion - near the Marginally Stable Orbit (MSO) of a slowly spinning object.
But Sgr A* is not accreting via a large, `standard' disk; instead, the low
density environment surrounding it apparently feeds the black hole with low
angular momentum clumps of plasma that circularize within ~ 10-300 r_S and
merge onto a compact, hot disk. In this Letter, we follow the evolution of the
disk following such an event, and show that a Rossby wave instability,
particularly in its magnetohydrodynamic (MHD) form, grows rapidly and produces
a period of enhanced accretion lasting several hours. Both the amplitude of
this response, and its duration, match the observed flare characteristics
rather well.


title: Perturbations to the Hubble diagram

abstract:
  We compute the linear responses of the Hubble diagram to small scalar
perturbations in the Robertson-Walker metric and to small peculiar velocities
of emitter and receiver. We discuss the monotonicity constraint of the Hubble
diagram in the light of these responses.


title: The Birth-Cluster of the Galactic Luminous Blue Variable WRA751

abstract:
  We present the results of NTT/VLT UBV imaging of a 260 square arcmin region
containing the Galactic Luminous Blue Variable WRA751, in search for its
birth-cluster, i.e. a cluster of young and massive stars spatially and
physically associated with it. On the basis of the classical reddening-free
parameter Q, we have identified a sample of 24 early-type stars with colours
typical of spectral types earlier than B3. Interestingly, these stars are
clustered within a radius of 1 arcmin from WRA751, corresponding to about 1% of
the imaged field. These stars tightly distribute around (B-V) = 1.67, which in
turn defines a mean extinction A(V) = 6.1 mag. The 5 brighter (V > 16.2) and
bluer (Q < -0.9) stars of the sample have been subsequently observed with FORS1
and classified as 3 late O- and 2 early B- stars. The absence of stars earlier
than O8 indicates an age of the cluster older than 4 Myr, although it could be
due to an incomplete sampling of the upper end of the main sequence.
Nevertheless, the detection of OB stars of class I certainly indicates an age
of a few million years. At an assumed distance of 6 kpc, we estimate a cluster
radius of 3.4 pc and a total mass of 2200 solar masses. Our discovery is only
the second known instance of a Galactic Luminous Blue Variable associated with
its birth-cluster.


title: The young, highly relativistic binary pulsar J1906+0746

abstract:
  We report the discovery of PSR J1906+0746, a young 144-ms pulsar in a highly
relativistic 3.98-hr orbit with an eccentricity of 0.085 and expected
gravitational wave coalescence time of 300 Myr. The new pulsar was found during
precursor survey observations with the Arecibo 1.4-GHz feed array system and
retrospectively detected in the Parkes Multibeam plane pulsar survey data. From
radio follow-up observations with Arecibo, Jodrell Bank, Green Bank, and
Parkes, we have measured the spin-down and binary parameters of the pulsar and
its basic spectral and polarization properties. We also present evidence for
pulse profile evolution, which is likely due to geodetic precession, a
relativistic effect caused by the misalignment of the pulsar spin and total
angular momentum vectors. Our measurements show that PSR J1906+0746 is a young
object with a characteristic age of 112 kyr. From the measured rate of orbital
periastron advance 7.57+/-0.03 deg/yr, we infer a total system mass of
2.61+/-0.02 Msun. While these parameters suggest that the PSR J1906+0746 binary
system might be a younger version of the double pulsar system, intensive
searches for radio pulses from the companion have so far been unsuccessful. It
is therefore not known whether the companion is another neutron star or a
massive white dwarf. Regardless of the nature of the companion, a simple
calculation suggests that the Galactic birth rate of binaries similar to PSR
J1906+0746 is 60/Myr. This implies that PSR J1906+0746 will make a significant
contribution to the computed cosmic inspiral rate of compact binary systems.


title: Metallicity effects on distances based on double-mode Cepheids

abstract:
  We test the effect of systematic metallicity difference between the two types
of double-mode Cepheids in the Magellanic Clouds. We show that lowering the
metallicity for the short-periodic Cepheids leaves the distances at their
canonical values and, at the same time, improves the agreement between the
observed and model periods.


title: Large Silicon Abundance in Photodissociation Regions

abstract:
  We have made one-dimensional raster-scan observations of the rho Oph and
sigma Sco star-forming regions with two spectrometers (SWS and LWS) on board
the ISO. In the rho Oph region, [SiII] 35um, [OI] 63um, 146um, [CII] 158um, and
the H2 pure rotational transition lines S(0) to S(3) are detected, and the PDR
properties are derived as the radiation field scaled by the solar neighborhood
value G_0~30-500, the gas density n~250--2500 /cc, and the surface temperature
T~100-400 K. The ratio of [SiII] 35um to [OI] 146um indicates that silicon of
10--20% of the solar abundance must be in the gaseous form in the
photodissociation region (PDR), suggesting that efficient dust destruction is
undergoing even in the PDR and that part of silicon atoms may be contained in
volatile forms in dust grains. The [OI] 63um and [CII] 158um emissions are too
weak relative to [OI] 146um to be accounted for by standard PDR models. We
propose a simple model, in which overlapping PDR clouds along the line of sight
absorb the [OI] 63um and [CII] 158um emissions, and show that the proposed
model reproduces the observed line intensities fairly well. In the sigma Sco
region, we have detected 3 fine-structure lines, [OI] 63um, [NII] 122um, and
[CII] 158um, and derived that 30-80% of the [CII] emission comes from the
ionized gas. The upper limit of the [SiII] 35um is compatible with the solar
abundance relative to nitrogen and no useful constraint on the gaseous Si is
obtained for the sigma Sco region.


title:
Luminous Compact Blue Galaxies in Intermediate Redshift Galaxy Clusters:
  A Significant But Extreme Butcher-Oemler Population

abstract:
  We identify a population of Luminous Compact Blue Galaxies (LCBGs) in two
galaxy clusters: MS0451.6-0305 (z=0.54) and Cl1604+4304 (z=0.9). LCBGs are
identified via photometric characteristics and photometric redshifts derived
from broad and narrow band images taken with the WIYN telescope and the Hubble
Space Telescope. We analyze their surface densities and clustering properties
to find they compose a statistically significant portion (42% and 53%) of the
Butcher-Oemler galaxies in both clusters, and their spatial distributions are
best characterized by a shell model. The enhancement of the projected
space-density of LCBGs with M_B<-18.5 in the clusters relative to the field is
3-10 times higher than the BO population as a whole, but 2 times lower than the
red population, except in the core where LCBGs are absent. Assuming some
fading, a natural descendant would be small, low-luminosity galaxies found
preferentially in today's clusters, such as dEs.


title:
Long-term evolution of accretion disks around the neutron star in
  Be/X-ray binaries

abstract:
  we study the long-term evolution of the accretion disk around the neutron
star in Be/X-ray binaries. We confirm the earlier result by Hayasaki & Okazaki
(2004) that the disk evolves via a two-stage process, which consists of the
initial developing stage and the later developed stage. The peak mass-accretion
rate is distributed around apastron after the disk is fully developed. This
indicates that the modulation of the mass accretion rate is essentially caused
by an inward propagation of the one-armed spiral wave. The X-ray luminosity
peak around the apastron could provide circumstatial evidence for an persistent
disk around the neutron star in Be/X-ray binaries.


title: Beyond the perfect fluid hypothesis for dark energy equation of state

abstract:
  Abandoning the perfect fluid hypothesis, we investigate here the possibility
that the dark energy equation of state (EoS) $w$ is a nonlinear function of the
energy density $\rho$. To this aim, we consider four different EoS describing
classical fluids near thermodynamical critical points and discuss the main
features of cosmological models made out of dust matter and a dark energy term
with the given EoS. Each model is tested against the data on the dimensionless
coordinate distance to Type Ia Supernovae and radio galaxies, the shift and the
acoustic peak parameters and the positions of the first three peaks in the
anisotropy spectrum of the comic microwave background radation. We propose a
possible interpretation of each model in the framework of scalar field
quintessence determining the shape of the self interaction potential $V(\phi)$
that gives rise to each one of the considered thermodynamical EoS. As a general
result, we demonstrate that replacing the perfect fluid EoS with more generar
expressions gives both the possibility of successfully solving the problem of
cosmic acceleration escaping the resort to phantom models.


title:
SPH simulations of accretion flow via Roche lobe overflow and via mass
  transfer from Be disk

abstract:
  We compare the accretion flow onto the neutron star induced by Roche lobe
overflow with that by the overflow from the Be disk, in a zero eccentricity,
short period binary with the same mass transfer rate, performing
three-dimensional Smoothed Particle Hydrodynamics simulations. We find that a
persistent accretion disk is formed around the neutron star in both cases. The
circularization radius of the material transferred via Roche lobe overflow is
larger than that of the material transfered from the Be disk. Thus, the growth
of the accretion disk in the former case becomes significantly slower than in
the latter case. In both cases, the mass accretion rate is very small and
varies little with orbital phase, which is consistent with the observed X-ray
behaviour of Be/X-ray binaries with circular orbits (e.g. XTE J1543-568).


title: Dark Matter in the Central Regions of Early Type Galaxies

abstract:
  We investigate the well-known correlations between the dynamical
mass-to-light ratio M/L and other global observables of elliptical (E) and
lenticular (S0) galaxies. We construct two-integral Jeans and three-integral
Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON
integral-field stellar kinematics to about one effective (half-light) radius
R_e. The comparison of the dynamical M/L with the (M/L)_pop inferred from the
analysis of the stellar population, indicates that dark matter in early-type
galaxies contributes ~30% of the total mass inside one R_e, in agreement with
previous studies, with significant variations from galaxy to galaxy. Our
results suggest a variation in M/L at constant (M/L)_pop, which seems to be
linked to the galaxy dynamics. We speculate that fast rotating galaxies have
lower dark matter fractions than the slow rotating and generally more massive
ones.


title:
Calibration of the Rossi X-ray Timing Explorer Proportional Counter
  Array

abstract:
  We present the calibration and background model for the Proportional Counter
Array (PCA) aboard the Rossi X-ray Timing Explorer (RXTE). The energy
calibration is systematics limited below 10 keV with deviations from a
power-law fit to the Crab nebula plus pulsar less than 1%. Unmodelled
variations in the instrument background amount to less than 2% of the observed
background below 10 keV and less than 1% between 10 and 20 keV. Individual
photon arrival times are accurate to 4.4 micro-seconds at all times during the
mission and to 2.5 micro-seconds after 29 April 1997. The peak pointing
direction of the five collimators is known to a precision of a few arc-seconds


title: The Physical Properties and Detectability of Reionization-Epoch Galaxies

abstract:
  We present predictions drawn from cosmological hydrodynamic simulations for
the physical, photometric and emission line properties of galaxies present
during the latter stages of reionization from z=9-6. We find significant
numbers of galaxies that have stellar masses exceeding 10^8 Mo during this
epoch, with metallicities exceeding one-thirtieth solar. Far from primeval
"first-star" objects,these objects are likely to have reionized their infall
regions prior to z=9, are dominated by atomic rather than molecular cooling,
and are not expected to be forming Population III stars. Galaxies exhibit a
slowly evolving comoving autocorrelation length from z=9-6, continuing a trend
seen at lower redshifts in which the rapidly dropping bias counteracts the
rapidly increasing matter clustering. These sources can be marginally detected
using current instruments, but modest increases in sensitivity or survey area
would yield significantly increased samples. We compare to current observations
of the z~6 rest-UV and Ly-alpha line luminosity functions, and find good
agreement. We also compare with the z~7 object observed by Egami et al., and
find that such systems are ubiquitous in our simulations. The intrinsic
Ly-alpha luminosity function evolves slowly from z=9-6, meaning that it should
also be possible to detect these objects with upcoming narrow band surveys such
as DAzLE. We make predictions for near-IR surveys with JWST, and show that
while a high density of sources will be found, Population III objects may
remain elusive. We present and compare simulations with several recipes for
superwind feedback, and show that while our broad conclusions are insensitive
to this choice, a feedback model based on momentum-driven winds is favored in
comparisons with available data. (abridged)


title:
Clues on the Physical Origin of the Fundamental Plane from
  Self-consistent Hydrodynamical Simulations

abstract:
  We report on a study of the parameters characterizing the mass and velocity
distributions of two samples of relaxed elliptical-like objects (ELOs)
identified, at z=0, in a set of self-consistent hydrodynamical simulations
operating in the context of a concordance cosmological model. Star formation
(SF) has been phenomenologically implemented in the simulations in the
framework of the turbulent sequential scenario through a threshold gas density
and an efficiency parameter. Each ELO sample is characterized by the values
these parameters take. We have found that the (logarithms of the) ELO stellar
masses, projected stellar half-mass radii, and stellar central line-of-sight
(LOS) velocity dispersions define dynamical fundamental planes (FPs). Zero
points depend on the particular values that the SF parameters take, while
slopes do not change. The ELO samples have been found to show systematic trends
with the mass scale in both the relative content and the relative distributions
of the baryonic and the dark mass ELO components. The physical origin of these
trends lies in the systematic decrease, with increasing ELO mass, of the
relative dissipation experienced by the baryonic mass component along ELO mass
assembly, resulting in a tilt of the dynamical FP relative to the virial plane.
The dynamical FPs shown by the two ELO samples are consistent with that shown
by the SDSS elliptical sample in the same variables, with no further need for
any relevant contribution from stellar population effects to explain the
observed tilt. These effects could, however, have contributed to the scatter of
the observed FP, as the dynamical FPs have been found to be thinner than the
observed one. The results we report on hint, for the first time, at a possible
way to understand the tilt of the observed FP in a cosmological context.


title: Primordial Nucleosynthesis: Successes And Challenges

abstract:
  Primordial nucleosynthesis provides a probe of the Universe during its early
evolution. Given the progress exploring the constituents, structure, and recent
evolution of the Universe, it is timely to review the status of Big Bang
Nucleosynthesis (BBN) and to confront its predictions, and the constraints
which emerge from them, with those derived from independent observations of the
Universe at much later epochs in its evolution. Following an overview of the
key physics controlling element synthesis in the early Universe, the
predictions of the standard models of cosmology and particle physics are
presented, along with those from some non-standard models. The observational
data used to infer the primordial abundances are described, with an emphasis on
the distinction between precision and accuracy. These relic abundances are
compared with predictions, testing the internal consistency of BBN and enabling
a comparison of the BBN constraints with those derived from the WMAP Cosmic
Background Radiation data. Emerging from these comparisons is a successful
standard model along with constraints on (or hints of) physics beyond the
standard models of particle physics and of cosmology.


title:
High Energy Neutrinos from Cosmic Ray Interactions in Clusters of
  Galaxies

abstract:
  The spatial clustering of galaxies in galaxy clusters implies that the
background of infrared (IR) light in the intracluster medium (ICM) may exceed
the universal background. Cosmic rays injected within the ICM propagate
diffusively and at low enough energies are trapped there for cosmological
times. The photopion production interactions of cosmic rays with the IR photons
are responsible for the generation of neutrinos whose detection may shed some
light on the origin and propagation of high energy cosmic rays in the universe.
Here we discuss our calculations of the flux of neutrinos from single clusters
as well as the contribution of photopion production in clusters of galaxies to
the diffuse neutrino background.


title:
A possible approach to understand nonlinear gravitational clustering in
  expanding background

abstract:
  A new approach to study the nonlinear phase of gravitational clustering in an
expanding universe is explored. This approach is based on an
integro-differential equation, for the evolution of the gravitational potential
in the Fourier space, which is obtained by using a physically motivated closure
condition. I show how this equation allows one to understand several aspects of
nonlinear gravitational clustering and provides insight in to the transfer of
power from one scale to another through nonlinear mode coupling.


title: X-ray reflections on AGN

abstract:
  X-ray reflection generates much of the spectral complexity in the X-ray
spectra of AGN. It is argued that strong relativistic blurring of the
reflection spectrum should commonly be expected from objects accreting at a
high Eddington rate. The good agreement found between the local density in
massive black holes and the energy density in quasar and AGN light requires
that the accretion which built massive black holes was radiatively efficient,
involving thin discs extending within 6 gravitational radii. The soft excess
found in the spectra of many AGN can be explained by X-ray reflection when such
blurring is included in the spectral analysis. Some of the continuum
variability and in particular the puzzling variability of the broad iron line
can be explained by the strong light bending expected in the region immediately
around a black hole. Progress in understanding this behaviour in the brightest
sources can be made now with long observations using instruments on XMM-Newton
and Suzaku. Future missions like Xeus and Con-X, with large collecting areas,
are required to expand the range of accessible objects and to make
reverberation studies possible.


title: RODEO: a new method for planet-disk interaction

abstract:
  In this paper we describe a new method for studying the hydrodynamical
problem of a planet embedded in a gaseous disk. We use a finite volume method
with an approximate Riemann solver (the Roe solver), together with a special
way to integrate the source terms. This new source term integration scheme
sheds new light on the Coriolis instability, and we show that our method does
not suffer from this instability. The first results on flow structure and gap
formation are presented, as well as accretion and migration rates. For Mpl <
0.1 M_J and Mpl > 1.0 M_J (M_J = Jupiter's mass) the accretion rates do not
depend sensitively on numerical parameters, and we find that within the disk's
lifetime a planet can grow to 3-4 M_J. In between these two limits numerics
play a major role, leading to differences of more than 50 % for different
numerical parameters. Migration rates are not affected by numerics at all as
long as the mass inside the Roche lobe is not considered. We can reproduce the
Type I and Type II migration for low-mass and high-mass planets, respectively,
and the fastest moving planet of 0.1 M_J has a migration time of only 2.0 10^4
yr.


title:
XMM-Newton observations of the black hole X-ray transient XTE J1650-500
  in quiescence

abstract:
  We report the result of an XMM-Newton observation of the black-hole X-ray
transient XTE J1650-500 in quiescence. The source was not detected and we set
upper limits on the 0.5-10 keV luminosity of 0.9e31-1.0e31 erg/s (for a newly
derived distance of 2.6 kpc). These limits are in line with the quiescent
luminosities of black-hole X-ray binaries with similar orbital periods (~7-8
hr)


title:
An Optical Study of Stellar and Interstellar Environments of Seven
  Luminous and Ultraluminous X-Ray Sources

abstract:
  We have studied the stellar and interstellar environments of two luminous
X-ray sources and five ultraluminous X-ray sources (ULXs) in order to gain
insight into their nature. Archival Hubble Space Telescope images were used to
identify the optical counterparts of the ULXs Ho IX X-1 and NGC 1313 X-2, and
to make photometric measurements of the local stellar populations of these and
the luminous source IC 10 X-1. We obtained high-dispersion spectroscopic
observations of the nebulae around these seven sources to search for He II
lambda-4686 emission and to estimate the expansion velocities and kinetic
energies of these nebulae. Our observations did not detect nebular He II
emission from any source, with the exception of LMC X-1; this is either because
we missed the He III regions or because the nebulae are too diffuse to produce
He II surface brightnesses that lie within our detection limit. We compare the
observed ionization and kinematics of the supershells around the ULXs Ho IX X-1
and NGC 1313 X-2 with the energy feedback expected from the underlying stellar
population to assess whether additional energy contributions from the ULXs are
needed. In both cases, we find insufficient UV fluxes or mechanical energies
from the stellar population; thus these ULXs may be partially responsible for
the ionization and energetics of their supershells. All seven sources we
studied are in young stellar environments and six of them have optical
counterparts with masses >~7 M_sun; thus, these sources are most likely
high-mass X-ray binaries.


title:
Discovery of excess O I absorption towards the z = 6.42 QSO SDSS
  J1148+5251

abstract:
  We present a search for O I in the spectra of nine 4.9 < z_qso < 6.4 QSOs
taken with Keck/HIRES. We detect six systems with N(O I) > 10^13.7 cm^{-2} in
the redshift intervals where O I 1302 falls redward of the Ly-alpha forest.
Four of these lie towards SDSS J1148+5251 (z_qso = 6.42). This imbalance is
unlikely to arise from variations in sensitivity among our data or from a
statistical fluctuation. The excess O I occurs over a redshift interval that
also contains transmission in Ly-alpha and Ly-beta. Therefore, if these O I
systems represent pockets of neutral gas, then they must occur within or near
regions of the IGM that are highly ionized. In contrast, no O I is detected
towards SDSS J1030+0524 (z_qso = 6.30), whose spectrum shows complete
absorption in Ly-alpha and Ly-beta over \Delta z ~ 0.2. Assuming no ionization
corrections, we measure mean abundance ratios <[O/Si]> = -0.04 +/- 0.06,
<[C/O]> = -0.31 +/- 0.09, and <[C/Si]> = -0.34 +/- 0.07 (2 sigma), which are
consistent with enrichment dominated by Type II supernovae. The O/Si ratio
limits the fraction of silicon in these systems contributed by metal-free very
massive stars to < 30%, a result which is insensitive to ionization
corrections. The ionic comoving mass densities along the z_qso > 6.2
sightlines, including only the detected systems, are \Omega(O I) = (7.0 +/-
0.6) * 10^{-8}, \Omega(Si II) = (9.6 +/- 0.9) * 10^{-9}, and \Omega(C II) =
(1.5 +/- 0.2) * 10^{-8}.


title: The Cosmological Significance of High-Velocity Cloud Complex H

abstract:
  We have used infrared and radio observations to search for a dwarf galaxy
associated with the high-velocity cloud (HVC) known as Complex H. Complex H is
a large (> 400 deg^2) and probably nearby (d = 27 kpc) HVC whose location in
the Galactic plane has hampered previous investigations of its stellar content.
The HI mass of the cloud is 2.0 x 10^7 (d/27 kpc)^2 Msun, making Complex H one
of the most massive HVCs if its distance is > ~20 kpc. Virtually all similar HI
clouds in other galaxy groups are associated with LSB dwarf galaxies. We
selected mid-IR MSX sources in the direction of Complex H that appeared likely
to be star-forming regions and observed them at the wavelength of the CO 1-0
transition. 59 of the 60 observed sources show emission at Milky Way
velocities, and we detected no emission at velocities consistent with that of
Complex H. We use these observations to set an upper limit on the ongoing star
formation rate in the HVC of < 5 x 10^-4 Msun yr^-1. We also searched the 2MASS
database for evidence of any dwarf-galaxy-like stellar population in the
direction of the HVC and found no trace of a distant red giant population, with
an upper limit on the stellar mass of ~10^6 Msun. Given the lack of evidence
for either current star formation or an evolved population, we conclude that
Complex H cannot be a dwarf galaxy with properties similar to those of known
dwarfs. Complex H is therefore one of the most massive known HI clouds without
stars. If Complex H is self-gravitating, then it is one of the few known dark
galaxy candidates. These findings may offer observational support for the idea
that the Cold Dark Matter substructure problem is related to the difficulty of
forming stars in low-mass dark matter halos; alternatively, Complex H could be
an example of a cold accretion flow onto the Milky Way. [slightly abridged]


title: Of pNGB QuiNtessence

abstract:
  We review the pNGB quintessence models, and point out that the reason why the
large decay constants $f_a \ga {\cal O}(1)M_{Pl}$ are really needed is to tame
a tachyonic instability present for a wide range of initial $vev$s. Starting
very close to potential maxima does not help because quantum fluctuations
during early inflation at a scale $H_I$ perturb the quintessence $vev$,
displacing it from the maxima. This issue is quite interesting for pNGB dark
energy in light of the recently discussed difficulties with embedding models
with $f_a > M_{Pl}$ in fundamental theory. A possible way around is provided by
models with several ultralight pNGBs, which can drive a short burst of very
late inflation {\it together} even if all of their decay constants obey $f_a <
M_{Pl}$. Starting with their $vev \sim f_a$, the pNGBs will hold each other up
on the potential for a longer time period. Their effective dynamics is captured
by a collective mode, containing admixtures of all of the rolling pNGBs, which
behaves as an ultralight field with $f_{eff} > M_{Pl}$. We point out that there
may be potentially observable large scale disturbances in the sea of dark
energy in such models.


title: The Fundamental Plane of Quasars

abstract:
  We present results from an archival study of 70 medium-redshift QSOs observed
with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. The
QSOs have magnitudes M_V < -23 (total nuclear plus host light) and redshifts
0.06 < z < 0.46.
  A close relationship between QSO host and nucleus is found by examining
multiple parameters at once. A principal components analysis shows that 3
nuclear and host properties are related in a kind of fundamental plane: nuclear
luminosity and the size and effective surface magnitude of the bulge. Using
optical nuclear luminosity, this relationship explains 95.9% of the variance in
the overall sample, while 94.9% of the variance is accounted for if we use
x-ray nuclear luminosity.
  The form of this QSO fundamental plane shows similarities to the well-studied
fundamental plane of elliptical galaxies, and we examine the possible
relationship between them as well as the difficulties involved in establishing
this connection. The key to the relationship might lie in the fueling mechanism
of the central black hole.


title:
Simulating Radiating and Magnetized Flows in Multi-Dimensions with
  ZEUS-MP

abstract:
  This paper describes ZEUS-MP, a multi-physics, massively parallel, message-
passing implementation of the ZEUS code. ZEUS-MP differs significantly from the
ZEUS-2D code, the ZEUS-3D code, and an early "version 1" of ZEUS-MP distributed
publicly in 1999. ZEUS-MP offers an MHD algorithm better suited for
multidimensional flows than the ZEUS-2D module by virtue of modifications to
the Method of Characteristics scheme first suggested by Hawley and Stone
(1995), and is shown to compare quite favorably to the TVD scheme described by
Ryu et. al (1998). ZEUS-MP is the first publicly-available ZEUS code to allow
the advection of multiple chemical (or nuclear) species. Radiation hydrodynamic
simulations are enabled via an implicit flux-limited radiation diffusion (FLD)
module. The hydrodynamic, MHD, and FLD modules may be used in one, two, or
three space dimensions. Self gravity may be included either through the
assumption of a GM/r potential or a solution of Poisson's equation using one of
three linear solver packages (conjugate-gradient, multigrid, and FFT) provided
for that purpose. Point-mass potentials are also supported. Because ZEUS-MP is
designed for simulations on parallel computing platforms, considerable
attention is paid to the parallel performance characteristics of each module.
Strong-scaling tests involving pure hydrodynamics (with and without
self-gravity), MHD, and RHD are performed in which large problems (256^3 zones)
are distributed among as many as 1024 processors of an IBM SP3. Parallel
efficiency is a strong function of the amount of communication required between
processors in a given algorithm, but all modules are shown to scale well on up
to 1024 processors for the chosen fixed problem size.


title: Detection of an optical filament in the Monogem Ring

abstract:
  The Monogem Ring is a huge bright soft X-ray enhancement with a diameter of ~
25$\degr$. This 0.3 kpc distant structure is a peculiar Galactic supernova
remnant in that it is obviously visible only in X-rays, due to its expansion
into a region of extremely low ambient density: hence, practically no optical
emission or a neutral HI shell was expected to be detectable. - Here we report
on the discovery of a very faint arc-like nebula on a POSS II R film copy, at
the south-eastern borders of the MR. Spectroscopy revealed this filament to
have a very large [SII]$\lambda$ 6716+6731/Halpha ratio of up to ~ 1.8,
indicating shock excitation, and a low density of N_e <100 cm^{-3}. There is no
hint of [OIII] emission in the spectra. On deep wide-field direct images in
Halpha and in [SII] the nebula appears as a ~ 20 arcmin long, thin (~ 1
arcmin), structured filament, stretching N-S. We believe that this filament
belongs to the MR and became visible due to the interaction of the expanding
remnant with a mild density increase in the interstellar medium. Only one other
possible optical filament of the MR has been reported in the literature, but no
spectrum was provided.


title: Lensing Reconstruction using redshifted 21cm Fluctuations

abstract:
  We investigate the potential of second generation measurements of redshifted
21 cm radiation from before and during the epoch of reionization (EOR) to
reconstruct the matter density fluctuations along the line of sight. To do so
we generalize the quadratic methods developed for the Cosmic Microwave
Background (CMB) to 21 cm fluctuations. We show that the three dimensional
signal can be decomposed into a finite number of line of sight Fourier modes
that contribute to the lensing reconstruction. Our formalism properly takes
account of correlations along the line of sight and uses all the information
contained in quadratic combinations of the signal. In comparison with the CMB,
21 cm fluctuations have the disadvantage of a relatively scale invariant
unlensed power spectrum which suppresses the lensing effect. The smallness of
the lensing effect is compensated by using information from a range of observed
redshifts. We estimate the size of experiments that are needed to measure this
effect. With a square kilometer of collecting area and a maximal baseline of 3
km one can achieve lensing reconstruction noise levels an order of magnitude
below CMB quadratic estimator constraints at L=1000, and map the deflection
field out to less then a tenth of a degree (L> 2000) within a season of
observations on one field. Statistical lensing power spectrum detections will
be possible to sub-arcminute scales, even with the limited sky coverage that
currently conceived experiments have. One should be able to improve constraints
on cosmological parameters by using this method. With larger collecting areas
or longer observing times, one could probe arcminute scales of the lensing
potential and thus individual clusters. We address the effect that foregrounds
might have on lensing reconstruction with 21 cm fluctuations.


title:
Formation of Hydrogen, Oxygen, and Hydrogen Peroxide in Electron
  Irradiated Crystalline Water Ice

abstract:
  Water ice is abundant both astrophysically, for example in molecular clouds,
and in planetary systems. The Kuiper belt objects, many satellites of the outer
solar system, the nuclei of comets and some planetary rings are all known to be
water-rich. Processing of water ice by energetic particles and ultraviolet
photons plays an important role in astrochemistry. To explore the detailed
nature of this processing, we have conducted a systematic laboratory study of
the irradiation of crystalline water ice in an ultrahigh vacuum setup by
energetic electrons holding a linear energy transfer of 4.3 +/- 0.1 keV mm-1.
The irradiated samples were monitored during the experiment both on line and in
situ via mass spectrometry (gas phase) and Fourier transform infrared
spectroscopy (solid state). We observed the production of hydrogen and oxygen,
both molecular and atomic, and of hydrogen peroxide. The likely reaction
mechanisms responsible for these species are discussed. Additional formation
routes were derived from the sublimation profiles of molecular hydrogen (90-140
K), molecular oxygen (147 -151 K) and hydrogen peroxide (170 K). We also
present evidence on the involvement of hydroxyl radicals and possibly oxygen
atoms as building blocks to yield hydrogen peroxide at low temperatures (12 K)
and via a diffusion-controlled mechanism in the warming up phase of the
irradiated sample.


title:
Ultraluminous X-ray Sources Powered by Radiatively Efficient Two-Phased
  Super-Eddington Accretion onto Stellar Mass Black holes

abstract:
  The radiation spectra of many of the brightest ultraluminous X-ray sources
(ULXs) are dominated by a hard power law component, likely powered by a hot,
optically thin corona that Comptonizes soft seed photons emitted from a cool,
optically thick black hole accretion disk. Before its dissipation and
subsequent conversion into coronal photon power, the randomized gravitational
binding energy responsible for powering ULX phenomena must separate from the
mass of its origin by a means other than, and quicker than, electron
scattering-mediated radiative diffusion. Therefore, the release of accretion
power in ULXs is not necessarily subject to Eddington-limited photon trapping,
as long as it occurs in a corona. Motivated by these basic considerations, we
present a model of ULXs powered by geometrically thin accretion onto stellar
mass black holes. We argue that the radiative efficiency of the flow remains
high if the corona is magnetized or optically thin and the majority of the
accretion power escapes in the form of radiation rather than an outflow. Within
the context of the current black hole X-ray binary paradigm, our ULX model may
be viewed as an extension of the very high state observed in Galactic sources.
(abridged)


title: Cross-Correlation analysis of WMAP and EGRET in Wavelet Space

abstract:
  We cross correlate the Wilkinson Microwave Anisotropy Probe (WMAP) first year
data and the diffuse gamma-ray intensity maps from the Energetic Gamma Ray
Experiment Telescope (EGRET) using spherical wavelet approaches. Correlations
at 99.7% significance level have been detected, at scales around $15^{\circ}$
in the WMAP foreground cleaned W-band and Q-band maps, based on data from
regions that are outside the most conservative WMAP foreground mask; no
significant correlation is found with the Tegmark cleaned map. The detected
correlation is most likely of Galactic origin, and thus can help us probing the
origins of possible Galactic foreground residuals and ultimately removing them
from measured microwave sky maps.


title:
Microlensing of Circumstellar Envelopes. III. Line profiles from stellar
  winds in homologous expansion

abstract:
  This paper examines line profile evolution due to the linear expansion of
circumstellar material obsverved during a microlensing event. This work extends
our previous papers on emission line profile evolution from radial and
azimuthal flow during point mass lens events and fold caustic crossings. Both
''flavours'' of microlensing were shown to provide effective diagnostics of
bulk motion in circumstellar envelopes. In this work a different genre of flow
is studied, namely linear homologous expansion, for both point mass lenses and
fold caustic crossings. Linear expansion is of particular relevance to the
effects of microlensing on supernovae at cosmological distances. We derive line
profiles and equivalent widths for the illustrative cases of pure resonance and
pure recombination lines, modelled under the Sobolev approximation. The
efficacy of microlensing as a diagnostic probe of the stellar environs is
demonstrated and discussed.


title: Extending the X-ray luminosity function of AGN to high redshift

abstract:
  X-ray surveys of the extragalactic universe are now able to detect
significant numbers of AGN out to high redshift (z~5). We highlight some
results from the Chandra Multiwavelength Project (ChaMP) to measure the X-ray
luminosity function out to these early epochs. At z > 3, we show that the
comoving space density of luminous (log Lx > 44.5) AGN has a behavior similar
to the optical QSO luminosity function. With a newly compiled sample of AGN
from ChaMP supplemented with those from additional surveys including the
Chandra Deep fields, we present a preliminary measure of the luminosity
function in the hard (2-8 keV) band. With 37 AGN at z > 3, we continue to see a
decline in the space density at high redshift over a wider range in luminosity.
We discuss the need to identify a larger sample of obscured AGN at high
redshift to determine if an early epoch of hidden supermassive black hole
growth occurred.


title:
Proper Motions and CCD-photometry of Stars in the Region of the Open
  Cluster Trumpler 2

abstract:
  The results of the complex study of galactic open cluster Trumpler 2 are
presented. In order to obtain the proper motions the positions of 2600 stars up
to the limit magnitude B ~ 16.25 mag in the area 80x80 arcmin around the
cluster were measured on 6 plates with the maximal epoch difference of 63
years. The root-mean error of the relative proper motions is 4.2 mas/yr. The
catalogue of BV magnitudes of all the stars in the investigated area was
compiled. Astrometric selection of the cluster members within the region of
R<16 arcmin from the center of the cluster was made by means of the W.Sanders
method. In that field 192 stars were found to have the individual membership
probability greater then 85%, 148 of them are situated within the
+/-3sigma_(B-V) band around the main sequence of the cluster. They are
considered to be cluster members by two criteria. The U-B ~ B-V diagram plotted
for the astrometrical cluster members by the data taken from the Washington
catalogue of the UBV photometry in the galactic cluster fields (Hoag et
al.1961) made it possible to redefine the value of the color excess E(B-V)=0.40
mag. The superposition of the MS of the cluster with the ZAMS Schmidt-Kaler
leads to the coincidence at the value of the apparent distance module
(V-Mv)=10.50 which corresponds to the distance r=725 pc. The luminosity and
mass functions of the Trumpler 2 were constructed and the value of the slope
Gamma=-1.90+/-0.22 was determined. The cluster age of 8.913x10^7 yr was
determined. It is shown that the red giant on the late stage of the evolution
(st N.1095) belongs to cluster and indicates the brightness variability. The
possibility that the number of both known and recently discovered variables are
cluster members was considered. Tables 2,3,3A,5 will be only available in the
electronic form.


title:
Clustering and properties of K-band companion galaxies around USS radio
  sources

abstract:
  We have analyzed galaxy properties in the environment of a sample of 70 Ultra
Steep Spectrum (USS) radio sources selected from the Sydney University Molonglo
sky Survey and the NRAO VLA Sky Survey catalogues, using near-IR data complete
down to Ks=20. We have quantified galaxy excess around USS targets using an
Abell-type measurement N0.5 (Hill & Lilly 1991). We find that most of the USS
fields studied are compatible with being Abell class 0 richness clusters. A
statistical analysis of the distribution of companion galaxies around USS radio
sources show a pronounced tendency for such objects to be found in the
direction defined by the radio axis, suggesting that they may be related to the
presence of the radio sources. We have also measure the central concentration
of light of the USS sample and compare these to the values obtained for field
galaxies and galaxies selected through other methods. By using Spearman
statistics to disentangle richnesses and concentration indices dependences, we
detect a weak, but significant, positive correlation. We find that at z > 2 USS
radio sources are more concentrated than field galaxies at similar redshifts,
indicating that these objects trace the most massive systems at high redshift.


title:
Neutrino spectrum from the pair-annihilation process in the hot stellar
  plasma

abstract:
  An new method of calculating the energy spectrum of neutrinos and
antineutrinos produced in the electron-positron annihilation processes in hot
stellar plasma is presented. Detection of these neutrinos, produced copiously
in the presupernova which is evolutionary advanced neutrino-cooled star, may
serve in future as a trigger of pre-collapse early warning system. Also,
observation of neutrinos will probe final stages of thermonuclear burning in
the presupernova.
  The spectra obtained with the new method are compared to Monte Carlo
simulations. To achieve high accuracy in the energy range of interest,
determined by neutrino detector thresholds, differential cross-section for
production of the antineutrino, previously unknown in an explicit form, is
calculated as a function of energy in the plasma rest frame. Neutrino spectrum
is obtained as a 3-dimensional integral, computed with the use of the Cuhre
algorithm of at least 5% accuracy. Formulae for the mean neutrino energy and
its dispersion are given as a combination of Fermi-Dirac integrals. Also,
useful analytical approximations of the whole spectrum are shown.


title:
The Lack of Structural and Dynamical Evolution of Elliptical Galaxies
  since z ~ 1.5: Clues from Self-Consistent Hydrodynamical Simulations

abstract:
  We present results of a study on the evolution of the parameters
characterizing the structure and dynamics of the relaxed elliptical-like
objects (ELOs) identified at z=0, z=1 and z=1.5 in a set of hydrodynamical,
self-consistent simulations operating in the context of a concordance
cosmological model. The values of the stellar mass, the stellar half-mass
radius and the stellar mean-square velocity have been measured in each ELO and
found to populate, at any z, a flattened ellipsoid close to a plane (the
dynamical plane, DP). Our simulations indicate that, at the intermediate zs
considered, individual ELOs evolve, increasing the values of these parameters
as a consequence of on-going mass assembly, but, nevertheless, their DP is
roughly preserved within its scatter, in agreement with observations of the
Fundamental Plane of ellipticals at different zs. We briefly discuss how this
lack of significant dynamical and structural evolution in ELO samples arises,
in terms of the two different phases operating in the mass aggregation history
of their dark matter halos. According with our simulations, most dissipation
involved in ELO formation takes place at the early violent phase, causing the
stellar mass, the stellar half-mass radius and the stellar mean-square velocity
parameters to settle down to the DP, and, moreover, the transformation of most
of the available gas into stars. In the subsequent slow phase, ELO stellar mass
growth preferentially occurs through non-dissipative processes, so that the DP
is preserved and the ELO star formation rate considerably decreases. These
results hint, for the first time, to a possible way of explaining, in the
context of cosmological simulations, different apparently paradoxical
observational results on ellipticals.


title: Universe scenarios from loop quantum cosmology

abstract:
  Loop quantum cosmology is an application of recent developments for a
non-perturbative and background independent quantization of gravity to a
cosmological setting. Characteristic properties of the quantization such as
discreteness of spatial geometry entail physical consequences for the structure
of classical singularities as well as the evolution of the very early universe.
While the singularity issue in general requires one to use difference equations
for a wave function of the universe, phenomenological scenarios for the
evolution are based on effective equations implementing the main quantum
modifications. These equations show generic bounces as well as inflation in
diverse models, which have been combined to more complicated scenarios.


title: Massive star formation in the central regions of spiral galaxies

abstract:
  Context: The morphology of massive star formation in the central regions of
galaxies is an important tracer of the dynamical processes that govern the
evolution of disk, bulge, and nuclear activity. Aims: We present optical
imaging of the central regions of a sample of 73 spiral galaxies in the H alpha
line and in optical broad bands, and derive information on the morphology of
massive star formation. Methods: We obtained images with the William Herschel
Telescope, mostly at a spatial resolution of below one second of arc. For most
galaxies, no H alpha imaging is available in the literature. We outline the
observing and data reduction procedures, list basic properties, and present the
I-band and continuum-subtracted H alpha images. We classify the morphology of
the nuclear and circumnuclear H alpha emission and explore trends with host
galaxy parameters. Results: We confirm that late-type galaxies have a patchy
circumnuclear appearance in H alpha, and that nuclear rings occur primarily in
spiral types Sa-Sbc. We identify a number of previously unknown nuclear rings,
and confirm that nuclear rings are predominantly hosted by barred galaxies.
Conclusions: Other than in stimulating nuclear rings, bars do not influence the
relative strength of the nuclear H alpha peak, nor the circumnuclear H alpha
morphology. Even though our selection criteria led to an over-abundance of
galaxies with close massive companions, we do not find any significant
influence of the presence or absence of a close companion on the relative
strength of the nuclear H alpha peak, nor on the H alpha morphology around the
nucleus.


title:
Cosmological constraints with GRBs: homogeneous medium vs wind density
  profile

abstract:
  We present the constraints on the cosmological parameters obtained with the
$E_{\rm peak}$--$E_{\gamma}$ correlation found with the most recent sample of
19 GRBs with spectroscopically measured redshift and well determined prompt
emission spectral and afterglow parameters. We compare our results obtained in
the two possible uniform jet scenarios, i.e. assuming a homogeneous density
profile (HM) or a wind density profile (WM) for the circumburst medium. Better
constraints on $\Omega_{M}$ and $\Omega_{\Lambda}$ are obtained with the
(tighter) $E_{\rm peak}$--$E_{\gamma}$ correlation derived in the wind density
scenario. We explore the improvements to the constraints of the cosmological
parameters that could be reached with a large sample, $\sim$ 150 GRBs, in the
future. We study the possibility to calibrate the slope of these correlations.
Our optimization analysis suggests that $\sim 12$ GRBs with redshift
$z\in(0.9,1.1)$ can be used to calibrate the $E_{\rm peak}$--$E_{\gamma}$ with
a precision better than 1%. The same precision is expected for the same number
of bursts with $z\in(0.45,0.75)$. This result suggests that we do not
necessarily need a large sample of low z GRBs for calibrating the slope of
these correlations.


title:
A closer look at the X-ray transient XTE J1908+094: identification of
  two new near-infrared candidate counterparts

abstract:
  We had reported in Chaty, Mignani, Israel (2002) on the near-infrared (NIR)
identification of a possible counterpart to the black hole candidate XTE
J1908+094 obtained with the ESO/NTT. Here, we present new, follow-up, CFHT
adaptive optics observations of the XTE J1908+094 field, which resolved the
previously proposed counterpart in two objects separated by about 0.8".
Assuming that both objects are potential candidate counterparts, we derive that
the binary system is a low-mass system with a companion star which could be
either an intermediate/late type (A-K) main sequence star at a distance of 3-10
kpc, or a late-type ($>$K) main sequence star at a distance of 1-3 kpc.
However, we show that the brighter of the two objects (J ~ 20.1, H ~ 18.7, K' ~
17.8) is more likely to be the real counterpart of the X-ray source. Its
position is more compatible with our astrometric solution, and colours and
magnitudes of the other object are not consistent with the lower limit of 3 kpc
derived independently from the peak bolometric flux of XTE J1908+094. Further
multi-wavelength observations of both candidate counterparts are crucial in
order to solve the pending identification.


title:
Ionisation state, excited populations and emission of impurities in
  dynamic finite density plasmas. I: The generalised collisional-radiative
  model for light elements

abstract:
  The paper presents an integrated view of the population structure and its
role in establishing the ionisation state of light elements in dynamic, finite
density, laboratory and astrophysical plasmas. There are four main issues, the
generalised collisional-radiative picture for metastables in dynamic plasmas
with Maxwellian free electrons and its particularising to light elements, the
methods of bundling and projection for manipulating the population equations,
the systematic production/use of state selective fundamental collision data in
the metastable resolved picture to all levels for collisonal-radiative
modelling and the delivery of appropriate derived coefficients for experiment
analysis. The ions of carbon, oxygen and neon are used in illustration. The
practical implementation of the methods described here is part of the ADAS
Project.


title: On the Stability of Phantom K-essence Theories

abstract:
  We show that phantom dark energy, if it is described by a K-essence theory,
has three fundamental problems: first, its hamiltonian is unbounded from below.
Second, classical stability precludes the equation of state from crossing the
``Lambda-barrier'', $w_\Lambda=-1$. Finally, both the equation of state and the
sound speed are unbounded -- the first, from below, the second, from above --
if the kinetic term is not bounded by dynamics.


title:
Counting individual galaxies from deep 24 micron Spitzer surveys: beyond
  the confusion limit

abstract:
  We address the question of how to deal with confusion limited surveys in the
mid-infrared domain by using informations from higher frequency observations
over the same sky regions. Such informations, once applied to apparently
extended mid-infrared sources, which are indeed ``blends'' of two or more
different sources, allow us to disentangle the single counterparts and to split
the measured flux density into different components. We present the application
of this method to the 24 micron Spitzer archival data in the GOODS-EN1 test
field, where apparently extended, ``blended'' sources constitute about 20% of a
reliable sample of 983 sources detected above the 5-sigma threshold down to 23
microJy. As higher frequency data-set we have considered the public IRAC images
and catalogues on the same field. We show that the 24 micron sample is almost
unbiased down to ~40 microJy and the careful application of the deblending
procedure does not require any statistical completeness correction (at least at
the flux level considered). This is probed by direct comparison of our results
with those of Chary et al. (2004), who analysed the same data-set through
extensive Monte Carlo simulations. The deblending procedure reduces of about
30% the confusion limit of the MIPS 24 micron survey, allowing one to obtain
reliable source counts down to ~40 microJy. The extrapolation of the source
counts down to fainter fluxes suggests that our 24 micron sample is able to
resolve ~62% of the cosmic background down to a flux level of 38 microJy.


title: Effects of Dust Growth and Settling in T Tauri Disks

abstract:
  We present self-consistent disk models for T Tauri stars which include a
parameterized treatment of dust settling and grain growth, building on
techniques developed in a series of papers by D'Alessio etal. The models
incorporate depleted distributions of dust in upper disk layers along with
larger-sized particles near the disk midplane, as expected theoretically and as
we suggested earlier is necessary to account for mm-wave emission, SEDs,
scattered light images, and silicate emission features simultaneously. By
comparing the models with recent mid- and near-IR observations, we find that
the dust to gas mass ratio of small grains at the upper layers should be < 10 %
of the standard value. The grains that have disappeared from the upper layers
increase the dust to gas mass ratio of the disk interior; if those grains grow
to maximum sizes of the order of mm during the settling process, then both the
millimeter-wave fluxes and spectral slopes can be consistently explained.
Depletion and growth of grains can also enhance the ionization of upper layers,
enhancing the possibility of the magnetorotational instability for driving disk
accretion.


title: The Slingshot Revisited

abstract:
  (Abridged) In this celebratory contribution, we present some new data from
standard star cluster modelling containing primordial binaries and triples, as
well as results from a binary black hole simulation with two massive members.
In the star cluster case, the process of mass loss from evolving stars,
together with general mass segregation, promotes favourable interactions
involving compact subsystems of binaries and triples in the central region.
Three-body interactions often lead to energetic ejections, with one or more of
the components attaining relatively large terminal velocities which can be
observed in principle. The second type of stellar system to be discussed is
based on the scenario of two approaching galactic cores with density cusps,
each having a massive black hole. After the subsystems become well mixed, the
two massive components soon form a hard binary which gains energy by ejecting
other members. Such a massive binary has a large cross section and can be very
effective in depleting bound stars from the core. Again high-velocity escapers
are produced, with their terminal speeds related to the shrinking binary size
which eventually leads to coalescence.


title:
Spitzer Observations of Red Galaxies: Implication for High-Redshift Star
  Formation

abstract:
  My colleagues and I identified distant red galaxies (DRGs) with J-K>2.3 mag
in the GOODS-S field. These galaxies reside at z~1-3.5, (<z>=2.2) and based on
their ACS (0.4-1 micron), ISAAC (1-2.2 micron), and IRAC (3-8 micron)
photometry, they typically have inferred stellar masses > 10^11 solar masses.
Interestingly, more than 50% of these objects have 24 micron flux densities >50
micro-Jy. Attributing the IR emission to star-formation implies SFRs of
\~100-1000 solar masses per year. As a result, galaxies with stellar masses
>10^11 solar masses have specific SFRs equal to or exceeding the global value
at z~1.5-3. In contrast, galaxies with >10^11 solar masses z~0.3-0.75 have
specific SFRs less than the global average, and more than an order of magnitude
lower than that for massive DRGs at z~1.5-3. Thus, the bulk of star formation
in massive galaxies is largely complete by z~1.5. The red colors and large
inferred stellar masses in the DRGs suggest that much of the star formation in
these galaxies occurred at redshifts z>5-6. Using model star-formation
histories that match the DRG colors and stellar masses at z~2-3, and
measurements of the UV luminosity density at z>5-6, we consider what
constraints exist on the stellar initial mass function in the progenitors of
the massive DRGs at z~2-3.


title: Constraining global properties of the Draco dwarf spheroidal galaxy

abstract:
  By fitting a flexible stellar anisotropy model to the observed surface
brightness and line-of-sight velocity dispersion profiles of Draco we derive a
sequence of cosmologically plausible two-component (stars + dark matter) models
for this galaxy. The models are consistent with all the available observations
and can have either cuspy Navarro-Frenk-White or flat-cored dark matter density
profiles. The dark matter halos either formed relatively recently (at z~2...7)
and are massive (up to ~5x10^9 M_Sun), or formed before the end of the
reionization of the universe (z~7...11) and are less massive (down to ~7x10^7
M_Sun). Our results thus support either of the two popular solutions of the
"missing satellites" problem of Lambda cold dark matter cosmology - that dwarf
spheroidals are either very massive, or very old. We carry out high-resolution
simulations of the tidal evolution of our two-component Draco models in the
potential of the Milky Way. The results of our simulations suggest that the
observable properties of Draco have not been appreciably affected by the
Galactic tides after 10 Gyr of evolution. We rule out Draco being a "tidal
dwarf" - a tidally disrupted dwarf galaxy. Almost radial Draco orbits (with the
pericentric distance <15 kpc) are also ruled out by our analysis. The case of a
harmonic dark matter core can be consistent with observations only for a very
limited choice of Draco orbits (with the apocentric-to-pericentric distances
ratio of <2.5).


title:
An explanation for the soft X-ray excess in AGN (Conference proceedings
  version)

abstract:
  We present a large sample of type 1 AGN spectra taken with XMM-Newton. We fit
them with the relativistically blurred photoionized disc model of Ross & Fabian
(2005). This model is based on an illuminated accretion disc of fluorescing and
Compton-scattering gas, and includes relativistic Doppler effects due to the
rapid motion of the disc and general relativistic effects such as gravitational
redshift due to presence of the black hole. The disc model successfully
reproduces the X-ray continuum shape, including the soft excess, of all the
sources. It provides a natural explanation for the observation that the soft
excess is at a constant temperature over a wide range of AGN properties. The
model also reproduces many features that would conventionally be interpreted as
absorption edges. We use the model to measure properties of the AGN such as
inclination, black hole rotation, and metallicity.


title: A possible mechanism for QPOs modulation in neutron star sources

abstract:
  It was pointed out by Paczynski (1987) that the X-ray luminosity of accreting
neutron stars is very sensitive to the physical properties of the accretion
flow close to the innermost stable circular orbit. The X-ray radiation is
dominated by that emitted in the boundary layer, where accreted matter hits a
star surface. The X-ray luminosity of the boundary layer is proportional to the
local accretion rate. In this note, we estimate local accretion rate variations
from the disk that undergoes non-stationary axisymmetric perturbations. The
perturbations are given by the poloidal-velocity potential. We obtain a simple
formula describing the modulation of the accretion rate for the particular case
of global vertical disk oscillations that have been recently studied by
Abramowicz et al. (2005).


title: Inflation: Homogeneous Limit

abstract:
  I review the motivation for the early-time cosmic acceleration stage in
expanding universe and discuss simple inflationary scenarios. Preheating and
reheating are considered in great detail. This is a sample chapter from my book
"Physical Foundations of Cosmology" published by Cambridge University Press
(2005).


title:
Further constraints on the evolution of Ks-selected galaxies in the
  GOODS/CDFS field

abstract:
  We have selected and analysed the properties of a sample of 2905 Ks<21.5
galaxies in ~ 131 sq.arcmin of the Great Observatories Origins Deep Survey
(GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the
evolution of Ks-selected galaxies with respect to the results already obtained
in previous studies. We made use of the public deep multiwavelength imaging
from the optical B through the infrared (IR) 4.5 micron bands, in conjunction
with available spectroscopic and COMBO17 data in the CDFS, to construct an
optimised redshift catalogue for our galaxy sample. We computed the Ks-band LF
and determined that its characteristic magnitude has a substantial brightening
and a decreasing total density from z=0 to <z>=2.5. We also analysed the
colours and number density evolution of galaxies with different stellar masses.
Within our sample, and in contrast to what is observed for less massive
systems, the vast majority (~ 85-90%) of the most massive (M>2.5x10^11 Msun)
local galaxies appear to be in place before redshift z ~1. Around 65-70% of the
total assemble between redshifts z=1 and z=3 and most of them display extremely
red colours, suggesting that plausible star formation in these very massive
systems should mainly proceed in obscured, short-timescale bursts. The
remaining fraction (up to ~ 20%) could be in place at even higher redshifts
z=3-4, pushing the first epoch of formation of massive galaxies beyond the
limits of current near-IR surveys.


title: Chromaticity in all-reflective telescopes for astrometry

abstract:
  Chromatic effects are usually associated with refractive optics, so
reflective telescopes are assumed to be free from them. We show that
all-reflective optics still bears significant levels of such perturbations,
which is especially critical to modern micro-arcsecond astrometric experiments.
We analyze the image formation and measurement process to derive a precise
definition of the chromatic variation of the image position, and we evaluate
the key aspects of optical design with respect to chromaticity. The fundamental
requirement related to chromaticity is the symmetry of the optical design and
of the wavefront errors. Finally, we address some optical engineering issues,
such as manufacturing and alignment, providing recommendations to minimize the
degradation that chromaticity introduces into astrometry.


title: A Bayesian analysis of the primordial power spectrum

abstract:
  We present a Bayesian analysis of large-scale structure and cosmic microwave
background data to constrain the form of the primordial power spectrum. We have
extended the usual presumption of a scale invariant spectrum to include: (i) a
running spectral index; (ii) a broken spectrum arising perhaps from an
interruption of the potential driving inflation; (iii) a large scale cutoff in
power as the first year WMAP results appear to indicate; (iv) a reconstruction
of the spectrum in eight bins in wavenumber; and (v) a spectrum resulting from
a cosmological model proposed by Lasenby & Doran, which naturally exhibits an
exponential drop in power on very large scales. The result of our complete
Bayesian analysis includes not only the posterior probability distribution from
which parameter estimates are inferred but also the Bayesian evidence. This
evidence value is greater for a model with fewer parameters unless a more
complicated model provides a significantly better fit to the data, thus
allowing a powerful method of model selection. We find that those models
exhibiting any form of cutoff in power on large scales consistently produce
higher evidences than either the Harrison-Zel'dovich or single spectral index
spectra. In particular, within the best-fit concordance cosmology, we find the
Lasenby & Doran spectrum to show significantly larger evidence as compared to
the other models.


title:
Metallicity and colours in galaxy pairs in chemical hydrodynamical
  simulations

abstract:
  Using chemical hydrodynamical simulations consistent with a Lambda-CDM model,
we study the role played by mergers and interactions in the regulation of the
star formation activity, colours and the chemical properties of galaxies in
pairs. A statistical analysis of the orbital parameters in galaxy pairs (r <100
kpc/h) shows that the star formation (SF) activity correlates strongly with the
relative separation and weakly with the relative velocity, indicating that
close encounters (r <30 kpc/h) can increase the SF activity to levels higher
than that exhibit in galaxies without a close companion. Analysing the internal
properties of interacting systems, we find that their stability properties also
play a role in the regulation the SF activity (Perez et al 2005a).
Particularly, we find that the passive star forming galaxies in pairs are
statistically more stable with deeper potential wells and less leftover gas
than active star forming pairs. In order to compare our results with
observations, we also build a projected catalog of galaxy pairs (2D-GP: rp <100
kpc/h and Vr <350 km/s), constructed by projecting the 3D sample in different
random directions. In good agreement with observations (Lambas et al 2003), our
results indicate that galaxies with rp < 25 kpc/h (close pairs) show an
enhancement of the SF activity with respect to galaxies without a close
companion. (Abridged.)


title: Thick Pixelated CZT Detectors With Isolated Steering Grids

abstract:
  We explore the possibility to improve the performance of 0.5 cm thick Cadmium
Zinc Telluride (CZT) detectors with the help of steering grids on the anode
side of the detectors. Steering grids can improve the energy resolution of CZT
detectors by enhancing the small pixel effect; furthermore, they can increase
their detection efficiency by steering electrons to the anode pixels which
otherwise would drift to the area between pixels. Previously, the benefit of
steering grids had been compromised by additional noise associated with
currents between the steering grids and the anode pixels. We use thin film
deposition techniques to isolate the steering grid from the CZT substrate by a
150 nm thick layer of the isolator Aluminiumoxide. While the thin layer does
not affect the beneficial effect of the steering grid on the weighting
potentials and the electric field inside the detector, it suppresses the
currents between the steering grid and the anode pixels. In this contribution,
we present first results from a 2 x 2 x 0.5 cm CZT detector with 8 x 8 pixels
that we tested before and after deposition of an isolated steering grid. The
steering grid improves the 662 keV energy resolution of the detector by a
factor of 1.3 (from about 2% to about 1.5%), while not reducing the detection
efficiency. To gain further insights into the detector response in the region
between pixels, we measured energy spectra with a collimated Cs137 source. The
collimator measurements can be used to enhance our understanding of energy
spectra measured under flood illumination of the detectors.


title:
Discovery of an Afterglow Extension of the Prompt Phase of Two Gamma Ray
  Bursts Observed by Swift

abstract:
  BAT and XRT observations of two recent well-covered GRBs observed by Swift,
GRB 050315 and GRB 050319, show clearly a prompt component joining the onset of
the afterglow emission. By fitting a power law form to the gamma-ray spectrum,
we extrapolate the time dependent fluxes measured by the BAT, in the energy
band 15-350 keV, into the spectral regime observed by the XRT 0.2-10 keV, and
examine the functional form of the rate of decay of the two light curves. We
find that the BAT and XRT light curves merge to form a unified curve. There is
a period of steep decay up to ~300 s, followed by a flatter decay. The duration
of the steep decay, ~100 s in the source frame after correcting for
cosmological time dilation, agrees roughly with a theoretical estimate for the
deceleration time of the relativistic ejecta as it interacts with circumstellar
material. For GRB 050315, the steep decay can be characterized by an
exponential form, where one e-folding decay time t_e(BAT) ~ 24+/-2 s, and
t_e(XRT) ~ 35+/-2 s. For GRB 050319, a power law decay -(d ln f/d ln t) = n,
where n is about 3, provides a reasonable fit. The early time X-ray fluxes are
consistent with representing the lower energy tail of the prompt emission, and
provide our first quantitative measure of the decay of the prompt gamma-ray
emission over a large dynamic range in flux. The initial steep decay is
expected due to the delayed high latitude photons from a curved shell of
relativistic plasma illuminated only for a short interval. The overall
conclusion is that the prompt phase of GRBs remains observable for hundreds of
seconds longer than previously thought.


title: Evaluation of 5 mm-thick CdTe Detectors from the Company Acrorad

abstract:
  Using 2.0 cm x 2.0 cm x 0.5 cm Cadmium Telluride (CdTe) substrates from the
company Acrorad, we have fabricated detectors with planar cathode contacts and
8x8 anode pixels. We investigate the I-V characteristics and energy resolution
of the detectors for different contact materials and surface treatments. After
biasing the detectors for a certain period of time, the dark currents increase
dramatically. Out studies show that the time before breakdown decreases for
higher detector temperatures and higher applied bias voltages. We obtained the
best results with a Pt cathode and In anode pixels when we heat the detector to
90 C for 30 minutes prior to depositing the In contacts. Flood-illuminating the
detector with 662 keV X-rays, we measured the pulse length distribution and
derived an electron mobility of ~860 cm^(2)/V/s. We show that the energy
resolution can be improved by correcting the anode signals for the depth of the
primary interaction. Operated at -40 C and cathode bias of -500 V, the best
pixels of the best detector achieved full width half maximum (FWHM) energy
resolutions of 8 keV (6.4%) and 23 keV (3.4%) at 122 keV and 662 keV,
respectively.


title:
Semi-empirical analysis of Sloan Digital Sky Survey galaxies: II. The
  bimodality of the galaxy population revisited

abstract:
  We revisit the bimodal distribution of the galaxy population commonly seen in
the local universe. Here we address the bimodality observed in galaxy
properties in terms of spectral synthesis products, such as mean stellar ages
and stellar masses, derived from the application of this powerful method to a
volume-limited sample, with magnitude limit cutoff M_r = -20.5, containing
about 50 thousand luminous galaxies from the SDSS Data Release 2. In addition,
galaxies are classified according to their emission line properties in three
distinct spectral classes: star-forming galaxies, with young stellar
populations; passive galaxies, dominated by old stellar populations; and, hosts
of active nuclei, which comprise a mix of young and old stellar populations. We
show that the extremes of the distribution of some galaxy properties,
essentially galaxy colours, 4000 A break index, and mean stellar ages, are
associated to star-forming galaxies at one side, and passive galaxies at
another. We find that the mean light-weighted stellar age of galaxies is the
direct responsible for the bimodality seen in the galaxy population. The
stellar mass, in this view, has an additional role since most of the
star-forming galaxies present in the local universe are low-mass galaxies. Our
results also give support to the existence of a 'downsizing' in galaxy
formation, where massive galaxies seen nowadays have stellar populations formed
at early times.


title:
An origin for short g-ray bursts unassociated with current star
  formation

abstract:
  Two short (<2 s) g-ray bursts (GRBs) have recently been localized and fading
afterglow counterparts detected. The combination of these two results left
unclear the nature of the host galaxies of the bursts, because one was a
star-forming dwarf, while the other was probably an elliptical galaxy. Here we
report the X-ray localization of a short burst (GRB 050724) with unusual g-ray
and X-ray properties. The X-ray afterglow lies off the centre of an elliptical
galaxy at a redshift of z=0.258, coincident with the position determined by
ground-based optical and radio observations. The low level of star formation
typical for elliptical galaxies makes it unlikely that the burst originated n a
supernova explosion. A supernova origin was also ruled out for GRB 050709, even
though that burst took place in a galaxy with current star formation. The
isotropic energy for the short bursts is 2-3 orders of magnitude lower han that
for the long bursts. Our results therefore suggest that an alternative source
of bursts -- the of binary systems of neutron stars or a neutron star-black
hole pair -- are the progenitors of short bursts.