title:
A Survey of Merger Remnants II: The Emerging Kinematic and Photometric
  Correlations

abstract:
  This paper is the second in a series exploring the properties of 51 {\it
optically} selected, single-nuclei merger remnants. Spectroscopic data have
been obtained for a sub-sample of 38 mergers and combined with previously
obtained infrared photometry to test whether mergers exhibit the same
correlations as elliptical galaxies among parameters such as stellar luminosity
and distribution, central stellar velocity dispersion ($\sigma$$_{\circ}$), and
metallicity. Paramount to the study is to test whether mergers lie on the
Fundamental Plane. Measurements of $\sigma$$_{\circ}$ have been made using the
Ca triplet absorption line at 8500 {\AA} for all 38 mergers in the sub-sample.
Additional measurements of $\sigma$$_{\circ}$ were made for two of the mergers
in the sub-sample using the CO absorption line at 2.29 $\micron$. The results
indicate that mergers show a strong correlation among the parameters of the
Fundamental Plane but fail to show a strong correlation between
$\sigma$$_{\circ}$ and metallicity (Mg$_{2}$). In contrast to earlier studies,
the $\sigma$$_{\circ}$ of the mergers are consistent with objects which lie
somewhere between intermediate-mass and luminous giant elliptical galaxies.
However, the discrepancies with earlier studies appears to correlate with
whether the Ca triplet or CO absorption lines are used to derive
$\sigma$$_{\circ}$, with the latter almost always producing smaller values.
Finally, the photometric and kinematic data are used to demonstrate for the
first time that the central phase-space density of mergers are equivalent to
elliptical galaxies. This resolves a long-standing criticism of the merger
hypothesis.


title: To Understand the UV-optical Excess of RX J1856.5-3754

abstract:
  The enigma source, RX J1856.5-3754, is one of the so-called dim thermal
neutron stars. Two puzzles of RXJ1856.5-3754 exist: (1) the observational X-ray
spectrum is completely featureless; (2) the UV-optical intensity is about seven
times larger than that given by the continuation of the blackbody model yielded
by the X-ray data. Both the puzzles would not exist anymore if RX J1856.5-3754
is a low mass bare strange quark star, which is in a propeller phase with a low
accretion rate. A boundary layer of RX J1856.5-3754 is suggested and modelled,
from which the UV-optical emission is radiated. Free-free absorption dominates
the opacity of the boundary layer, which results in the opacity to be high in
UV-optical but low in X-ray bands. The star's magnetic field, spin period, as
well as the accretion rate are constrained by observations.


title:
A Modeling of the Super-Eddington Luminosity in Nova Outbursts: V1974
  Cygni

abstract:
  We have modeled nova light curves exceeding the Eddington luminosity. It has
been suggested that a porous structure develops in nova envelopes during the
super Eddington phase and the effective opacity is much reduced for such a
porous atmosphere. Based on this reduced opacity model, we have calculated
envelope structures and light curves of novae. The optically thick wind model
is used to simulate nova winds. We find that the photospheric luminosity and
the wind mass-loss rate increase inversely proportional to the reducing factor
of opacities, but the wind velocity hardly changes. We also reproduce the
optical light curve of V1974 Cygni (Nova Cygni 1992) in the super-Eddington
phase, which lasts 13 days from the optical peak 1.7 mag above the Eddington
luminosity.


title:
The Galaxy Hosts and Large-Scale Environments of Short-Hard Gamma-Ray
  Bursts

abstract:
  The rapid succession of discovery of short--duration hard--spectrum GRBs has
led to unprecedented insights into the energetics of the explosion and nature
of the progenitors. Yet short of the detection of a smoking gun, like a burst
of coincident gravitational radiation or a Li-Paczynski mini-supernova, it is
unlikely that a definitive claim can be made for the progenitors. As was the
case with long--duration soft--spectrum GRBs, however, the expectation is that
a systematic study of the hosts and the locations of short GRBs could begin to
yield fundamental clues about their nature. We present the first aggregate
study of the host galaxies of short--duration hard--spectrum GRBs. In
particular, we present the Gemini--North and Keck discovery spectra of the
galaxies that hosted three short GRBs and a moderate--resolution (R~6000)
spectrum of a fourth host. We find that these short--hard GRBs originate in a
variety of low-redshift (z<1) environments that differ substantially from those
of long--soft GRBs, both on individual galaxy scales and on galaxy--cluster
scales. Specifically, three of the bursts are found to be associated with old
and massive galaxies with no current (< 0.1 Msol/hr) or recent star formation.
Two of these galaxies are located within a cluster environment. These
observations support an origin from the merger of compact stellar remnants,
such as double neutron stars of a neutron star--black hole binary. The fourth
event, in contrast, occurred within a dwarf galaxy with a star formation rate
exceeding 0.5 Msol/yr. Therefore, it appears that like supernovae of Type Ia,
the progenitors of short--hard bursts are created in all galaxy types,
suggesting a corresponding class with a wide distribution of delay times
between formation and explosion.


title:
On Temperature and Abundance Effects During an X-Ray Flare on Sigma
  Geminorum

abstract:
  We compare quiescent and flare X-ray spectra of the RS CVn binary Sigma Gem
obtained with the Chandra and XMM-Newton grating spectrometers. We find that in
addition to an overall 25% flux increase, which can be ascribed to variations
in the system's quiescence activity over the 15 months that passed between the
observations, there is a hot plasma component of kT_e > 3 keV that arises with
the flare. The hot component is manifested primarily by emission from high
charge states of Fe and by a vast continuum. The cooler (kT_e < 2 keV) plasma
remains undisturbed during the flare. We find no significant variations in the
relative abundances during the flare except for a slight decrease (<30%) of O
and Ne.


title: Dark energy - dark matter - and black holes: The music of the universe

abstract:
  Here we review the recent evidence for dark energy, dark matter and black
holes as components of an expanding universe, for the vantage point of a
non-expert; we speculate on a specific DM particle.


title: Galactic Stellar Populations

abstract:
  The history of the formation and evolution of the Milky Way Galaxy is found
in the spatial distribution, kinematics, age and chemical abundance
distributions of long-lived stars. From this fossil record one can in principle
extract the star formation histories of different components, their chemical
evolution, the stellar Initial Mass Function, the merging history -- what
merged and when did it merge? -- and compare with theoretical models.
Observations are driving models, and we live in exciting times.


title: Supernova Cosmology and the ESSENCE project

abstract:
  The proper usage of Type Ia supernovae (SNe Ia) as distance indicators has
revolutionized cosmology, and added a new dominant component to the energy
density of the Universe, dark energy. Following the discovery and confirmation
era, the currently ongoing SNe Ia surveys aim to determine the properties of
the dark energy. ESSENCE is a five year ground-based supernova survey aimed at
finding and characterizing 200 SNe Ia in the redshift domain z=[0.2-0.8]. The
goal of the project is to put constraints on the equation of state parameter,
w, of the dark energy with an accuracy of <10%. This paper presents these
ongoing efforts in the context of the current developments in observational
cosmology.


title:
Improving Foreground Subtraction in Statistical Observations of 21 cm
  Emission from the Epoch of Reionization

abstract:
  Statistical observations of the Epoch of Reionization using the 21 cm line of
neutral hydrogen have the potential to revolutionize our understanding of
structure formation and the first luminous objects. However, these observations
are complicated by a host of strong foreground sources. Several foreground
removal techniques have been proposed in the literature, and it has been
assumed that these would be used in combination to reveal the Epoch of
Reionization (EOR) signal. By studying the characteristic subtraction errors of
the proposed foreground removal techniques, we identify an additional
subtraction stage that can further reduce the EOR foreground contamination, and
study the interactions between the foreground removal algorithms. This enables
us to outline a comprehensive foreground removal strategy that incorporates all
previously proposed subtraction techniques. Using this foreground removal
framework and the characteristic subtraction errors, we discuss the
complementarity of different foreground removal techniques and the implications
for array design and the analysis of EOR data.


title:
High Spectral Resolution Observations of the Massive Stars in the
  Galactic Center

abstract:
  We present high-resolution near-infrared spectra, obtained with the NIRSPEC
spectrograph on the W. M. Keck II Telescope, of a collection of hot, massive
stars within the central 25 arcseconds of the Galactic center. We have
identified a total of twenty-one emission-line stars, seven of which are new
radial velocity detections with five of those being classified as He I
emission-line stars for the first time. These stars fall into two categories
based on their spectral properties: 1) those with narrow 2.112, 2.113 micron He
I doublet absorption lines, and 2) those with broad 2.058 micron He I emission
lines. These data have the highest spectral resolution ever obtained for these
sources and, as a result, both components of the absorption doublet are
separately resolved for the first time. We use these spectral features to
measure radial velocities. The majority of the measured radial velocities have
relative errors of 20 kms, smaller than those previously obtained with
proper-motion or radial velocity measurements for similar stellar samples in
the Galactic center. The radial velocities estimated from the He I absorption
doublet are more robust than those previously estimated from the 2.058 micron
emission line, since they do not suffer from confusion due to emission from the
surrounding ISM. Using this velocity information, we agree that the stars are
orbiting in a somewhat coherent manner but are not as defined into a disk or
disks as previously thought. Finally, multi-epoch radial velocity measurements
for IRS 16NE show a change in its velocity presumably due to an unseen stellar
companion.


title: Satellites of the largest Kuiper belt objects

abstract:
  We have searched the four brightest objects in the Kuiper belt for the
presence of satellites using the newly commissioned Keck Observatory Laser
Guide Star Adaptive Optics system. Satellites are seen around three of the four
objects: Pluto (whose satellite Charon is well-known), 2003 EL61, and 2003
UB313. The object 2005 FY9, the brightest Kuiper belt object after Pluto, does
not have a satellite detectable within 0.4 arcseconds with a brightness of more
than 0.5% of the primary. The presence of satellites to 3 of the 4 brightest
Kuiper belt objects is inconsistent with the fraction of satellites in the
Kuiper belt at large at the 99.1% confidence level, suggesting a different
formation mechanism for these largest KBO satellites. The satellites of 2003
EL61 and 2003 UB313, with fractional brightnesses of 5% and 2% of their
primaries, respectively, are significantly fainter relative to their primaries
than other known Kuiper belt object satellites, again pointing to possible
differences in their origin.


title: Non-Gaussianity in Nonminimally Coupled Scalar Field Theory

abstract:
  We consider the non-Gaussianity of the nonlinear density perturbations in a
single-field inflationary model when a scalar field couples nonminimally with
gravity. Gravity theories with a nonminimal coupling can be transformed into
the Einstein gravity with canonical kinetic terms by using a suitable conformal
transformation. We find that a nonlinear generalization of the gauge invariant
quantity $\zeta_i$ is invariant under the conformal transformation. With the
help of this conformal invariant property, we calculate the non-Gaussianity,
which is characterized by a nonlinear parameter $f_{NL}$, in nonminimal coupled
scalar field theory.


title:
Comment on ``Nonextensive theory of dark matter and gas density
  profiles''

abstract:
  Self-gravitating systems with nonlocal, long-range interactions are described
by nonextensive statistics. Recently, Leubner demonstrated that the
nonextensivity parameter $\kappa$ should be negative for self-gravitating,
pressureless systems, such as dark matter halos. The equation for the
spherically symmetric nonextensive dark matter halos has also been derived.
Here we demonstrate that this equation is identical to the classical Lane-Emden
equation describing the structure of self-gravitating polytropic spheres. This
establishes an intimate connection between self-gravitating polytropes and
nonextensive thermostatistics. Moreover, based on this fact and observational
data, we put a stronger constraint on $\kappa$, namely $\kappa<-3.4$.


title:
Tracing the base of protostellar wind(s) towards the high-mass star
  forming region AFGL 5142: VLA continuum and VLBA water maser observations

abstract:
  We have conducted phase-reference multi-epoch observations of the 22.2 GHz
water masers using the VLBA and multi-frequency study of the continuum emission
using the VLA towards the high-mass SFR AFGL 5142. The water maser emission
comes from two elongated structures (indicated as Group I and Group II), with
the measured proper motions aligned along the structures' elongation axes. Each
group consists of two (blue- and red-shifted) clusters of features separated by
a few hundreds and thousands of AU respectively for Group I and Group II. The
maser features of Group II have both positions and velocities aligned along a
direction close to the axis of the outflow traced by HCO+ and SiO emission on
angular scales of tens of arcsec. We predict that the maser emission arises
from dense, shocked molecular clumps displaced along the axis of the molecular
outflow. The two maser clusters of Group I are oriented on the sky along a
direction forming a large angle (> 60 degrees) with the axis of the jet/outflow
traced by Group II maser features. We have detected a compact (8.4 and 22 GHz)
continuum source that falls close to the centroid of Group I masers, indicating
that the source ionizing the gas is also responsible for the excitation of the
water masers. The kinematic analysis indicates that the Group I masers trace
outflowing rather than rotating gas, discarding the Keplerian disk scenario
proposed in a previous paper for Group I. Since the axis joining the two maser
clusters of Group II does not cross the position of the continuum source, Group
II masers might be excited by an (undetected) massive YSO, distinct from the
one (pinpointed by the VLA continuum emission) responsible for the excitation
of the Group I masers.


title: Classical Cepheids as Age Indicators

abstract:
  Theoretical Period-Age and Period-Age-Color relations for different chemical
compositions have been recently derived using an updated homogeneous set of
evolutionary and pulsational models. We apply these relations to Cepheids in
the Magellanic Clouds to constrain the recent star formation history of these
dwarf galaxies. Finally, we also compare the radial distribution of classical
Cepheids with young clusters and star forming regions.


title:
NGC 7679: an anomalous, composite Seyfert 1 galaxy whose, X-ray luminous
  AGN vanishes at optical wavelengths

abstract:
  Morphological disturbances and gas kinematics of the SB0 galaxy NGC 7679=Arp
216 are investigated to get clues to the history of this highly composite
object, where AGN and starburst signatures dominate each other in the X-ray and
optical/IR regime, respectively. Perturbations of the ionized gas velocity
field appear quite mild within 15'' (~5 kpc) from the center, so as it can be
straightforwardly modeled as a circularly rotating disk. On the contrary,
outside that radius, significant disturbances show up. In particular, the
eastern distorted arm as well as the huge neutral hydrogen bridge connecting
NGC 7679 with the nearby Seyfert spiral NGC 7682 unambiguously represent the
vestige of a close encounter of the two objects dating back ~500 Myr ago. The
relationship of such past event with the much more recent, centrally located
starburst (not older than 20 Myr) cannot be easily established. Altogether, the
classification of NGC 7679, turns out to be less extreme than that proposed in
the past, being simply a (disturbed) galaxy where starburst and AGN activity
cohexist with a starburst dominating the bolometric luminosity.


title: A search for binarity using FUSE observations of DAO white dwarfs

abstract:
  We report on a search for evidence of binarity in Far-Ultraviolet
Spectroscopic Explorer (FUSE) observations of DAO white dwarfs. Spectra
recorded by FUSE are built up from a number of separate exposures. Observation
of changes in the position of photospheric heavy element absorption lines
between exposures, with respect to the stationary interstellar medium lines,
would reveal radial velocity changes - evidence of the presence of a binary
system. This technique is successful in picking out all the white dwarfs
already known to be binaries, which comprise 5 out of the sample of 16, but
significant radial velocity shifts were found for only one additional star, Ton
320. This object is also known to have an infrared excess. DAOs can be
separated broadly into low or normal mass objects. Low mass white dwarfs can be
formed as a result of binary evolution, but it has been suggested that the
lower mass DAOs evolve as single stars from the extended horizontal branch, and
we find no evidence of binarity for 8 out of the 12 white dwarfs with
relatively low mass. The existence of higher mass DAOs can also be explained if
they are within binary systems, but of the four higher mass stars in the sample
studied, PG 1210+533 and LB 2 do not exhibit significant radial velocity
shifts, although there were only two exposures for the former object and the
latter has an infrared excess.


title: Recent results on Pre-main sequence delta Scuti stars

abstract:
  Intermediate mass Pre-main sequence stars (1.5 $M_{\odot}< M < 5M_{\odot}$)
cross the instability strip on their way to the main sequence. They are
therefore expected to be pulsating in a similar way as the $\delta$ Scuti
stars. In this contribution we present the status of the observational studies
of pulsations in these stars with special emphasis on recent results from our
group. The prospects for future investigations of these objects from the ground
and from space are discussed.


title: New list of peculiar velocities of RFGC galaxies

abstract:
  We present a new version of the list of peculiar velocities of 1561 flat
edge-on spirals from the RFGC catalogue. It differs from the previous version
by 233 new data and 34 corrected data. A new regression was used for distances
estimation based on the Tully-Fisher relationship in the "linear diameter - HI
line width" variant. Moreover, we present velocities for 3 models of galaxies
collective motion. They are a D-model (dipole, Hubble expansion + bulk motion
with constant speed), DQ-model (a quadrupole terms are added) and DQO-model
(DQ-model + octopole).


title: Accretion-powered millisecond pulsars

abstract:
  I review X-ray observations of accretion-powered millisecond pulsars and
current theories for formation of their spectra and pulse profiles.


title: An X-ray emission line spectrum of Nova V382 Velorum 1999

abstract:
  We report on the analysis of an X-ray grating spectrum of the Classical Nova
V382 Vel (1999), obtained with the LETG+HRC-S instrument on board CHANDRA,
which shows emission lines dominating over any continuum. Lines of Si, Mg, Ne,
O, N, and C are identified, but no Fe lines are detected. The total luminosity
in the lines is 4x10^27erg/s (corrected for N_H=1.2x10^21cm^-2). The lines have
broad profiles with FWHM corresponding to a velocity 2900+-200km/s. Some
structure is identified in the profiles, but for different elements we find
different profile structures. While lines of O show a broadened Gaussian
profile, those of Ne are double-peaked, suggesting a fragmented emitting
plasma. Using the emission measure distribution we derive relative element
abundances and find abundances of Ne and N that are significantly enhanced
relative to that of O, while Fe is not over-abundant. The lack of any source
emission longwards of 50A and the OVIII Ly_alpha/Ly_beta line ratio support
previous values of the hydrogen column-density. We find weak continuum emission
from the white dwarf, consistent with a black-body spectrum with an upper limit
to the temperature of T=3x10^5K, assuming a source radius of 6000km. The upper
limit for the integrated black-body luminosity is 2x10^36erg/s. The BeppoSAX
and Chandra ACIS observations of V382 Vel show that the nova was bright and in
the Super Soft phase as late as 1999 December 30. Our LETG observation obtained
6 weeks later, as well as all subsequent X-ray observations, showed a
remarkable fading to a nearly pure emission line phase which suggests that
nuclear burning on the white dwarf had turned off by February. In the absence
of a photoionizing source the emission lines were formed in a collisionally
ionized and excited expanding shell.


title:
XMM-Newton view of PKS 2155-304: hardness ratio and cross-correlation
  analysis of EPIC pn observations

abstract:
  With currently available XMM-Newton EPIC pn observations spanned over about 3
years, we present a detailed spectral and temporal variability of the 0.2--10
keV X-ray emission from the X-ray bright BL Lac object PKS 2155-304. The
spectral variability is examined with a model independent hardness ratio
method. We find that the spectral evolution of the source follows the light
curves well, indicating that the spectra harden when the fluxes increase. The
plots of hardness ratios versus count rates show that the spectral changes are
particularly significant during flares. The cross-correlation functions (CCFs)
show that the light curves in the different energy bands are well correlated at
different time lags. The CCF peaks (i.e., the maximum correlation coefficients)
tend to become smaller with larger energy differences, and the variability in
the different energy bands are more correlated for the flares than for the
other cases. In most cases the higher energy band variations lead the lower
energy band, but in two cases we observed the opposite behavior that the lower
energy variability possibly leads the higher energy variability. The time lags
increase with the energy differences between the two cross-correlated light
curves. The maximum lag is found to be up to about one hour, in support with
the findings obtained with previous low Earth orbit X-ray missions. We discuss
our results in the context of the particle acceleration, cooling and light
crossing timescales.


title: Acceleration of adaptive optics simulations using programmable logic

abstract:
  Numerical Simulation is an essential part of the design and optimisation of
astronomical adaptive optics systems. Simulations of adaptive optics are
computationally expensive and the problem scales rapidly with telescope
aperture size, as the required spatial order of the correcting system
increases. Practical realistic simulations of AO systems for extremely large
telescopes are beyond the capabilities of all but the largest of modern
parallel supercomputers. Here we describe a more cost effective approach
through the use of hardware acceleration using field programmable gate arrays.
By transferring key parts of the simulation into programmable logic, large
increases in computational bandwidth can be expected. We show that the
calculation of wavefront sensor image centroids can be accelerated by a factor
of four by transferring the algorithm into hardware. Implementing more
demanding parts of the adaptive optics simulation in hardware will lead to much
greater performance improvements, of up to 1000 times.


title: A tomographic study of the classical nova RR Pic

abstract:
  We present the results of spectrophotometric observations of the old nova RR
Pic performed in two spectral ranges, one centered in the Ha line and other
covering Hb and Hg spectral lines. From the Hb radial velocity study we found a
primary radial semi-amplitude of K1 = 37(1) km/s and a systemic velocity of g =
1.8(2) km/s. With this new values a mass diagram is constructed, constraining
the possible mass intervals for the system. The possible orbital inclination
range was restricted using the fact that RR Pic presents shallow eclipses. A
secondary mass range below the limit of a main sequence star filling its Roche
lobe indicate an evolved companion. We also calculated the Ha, Hb, Hg, HeI 6678
and HeII 4686 Doppler tomograms. The most conspicuous differences are found
between the HeI and HeII tomograms, the former has a ring shape, while the
second is filled at low velocities, suggesting that the low velocity emission
is not coming from the accretion disk. Radial emissivity profiles for these
lines were also derived.


title:
Extreme helium stars: non-LTE matters Helium and hydrogen spectra of the
  unique objects V652 Her and HD144941

abstract:
  Quantitative analyses of low-mass hydrogen-deficient (super-)giant stars -
so-called extreme helium stars - to date face two major difficulties. First,
theory fails to reproduce the observed helium lines in their entirety, wings
and line cores. Second, a general mismatch exists for effective temperatures
derived from ionization equilibria and from spectral energy distributions.
Here, we demonstrate how the issue can be resolved using state-of-the-art
non-LTE line-formation for these chemically peculiar objects. Two unique
high-gravity B-type objects are discussed in detail, the pulsating variable
V652 Her and the metal-poor star HD144941. In the first case atmospheric
parameters from published LTE analyses are largely recovered, in the other a
systematic offset is found. Hydrogen abundances are systematically smaller than
previously reported, by up to a factor ~2. Extreme helium stars turn out to be
important testbeds for non-LTE model atoms for helium. Improved non-LTE
computations show that analyses assuming LTE or based on older non-LTE model
atoms can predict equivalent widths, for the HeI 10830A transition in
particular, in error by up to a factor ~3.


title:
PKS 0743$-$67: An Ultra-luminous Accretion Disk and a High Kinetic
  Luminosity Jet

abstract:
  In this letter, deep radio observations of the quasar PKS 0743$-$67 are
presented that reveal a central engine capable of driving jets with enormous
kinetic luminosity, $Q>4.1 \times 10^{46}\mathrm{ergs/s}$. This result is
significant because archival optical spectral data indicates that the accretion
disk has a thermal luminosity, $L_{bol}>2\times 10^{47}\mathrm{ergs/s}$.
Furthermore, estimates of the central black hole mass from line widths indicate
that $L_{bol}/L_{Edd}\approx 1$. This suggests that neither a large $L_{bol}$
nor $L_{bol}/L_{Edd}$ suppresses jet power in quasars, despite claims that they
do in the recent literature. Earlier studies have found $L_{bol}$ and $Q$ are
correlated in blazars. However, by removing the BL-Lacs and leaving only the
quasars in the sample, we found that $Q$ is very weakly correlated with
$L_{bol}$ in the subsample.


title: Unobscured QSO2: A New Class of Objects?

abstract:
  We present in this paper optical and X-ray follow up observations for three
X-ray selected objects extracted from the ROSAT North Ecliptic Pole survey
which is a flux-limited, completely identified survey. All three objects have
X-ray luminosities in the 10^44 erg/s regime and show narrow emission lines in
their optical discovery spectra, typical of QSO2 type objects. Spectroscopic
data for the three QSO2 candidates, obtained with the Telescopio Nazionale
Galileo, confirm the widths of the Halpha or Hbeta emission lines are less than
750 km/s. On the other hand XMM-Newton data do not show any sign of obscuration
as expected for this class of objects. The X-ray spectra of the three objects
are all well fit by a single power law model with Gamma~1.7 with low energy
absorption fixed to the Galactic value along the line of sight to each object.
Most observational evidence supports the scenario where optical and X-ray
obscurations are linked, contrary to our findings. We discuss the unanticipated
results of these observations, and compute the space density in soft X-ray
surveys of this possibly new class of objects. Their spatial density in the
ROSAT NEP survey is 2.8{+2.7 / -1.5} 10^-8 h^3 Mpc^-3 in a Lambda-CDM model
with h=0.7. Unobscured QSO\2 candidates could go unrecognized in current X-ray
surveys where the low hydrogen column density is inferred by a hardness ratio
rather than a more precise X-ray spectrum measurement.


title:
Simultaneous XMM-Newton and ESO VLT observations of SN 1995N: probing
  the wind/ejecta interaction

abstract:
  We present the results of the first {\it XMM-Newton} observation of the
interacting type IIn supernova 1995N, performed in July 2003. We find that the
0.2--10.0 keV unabsorbed flux dropped at a value of $\simeq 1.8 \times
10^{-13}$ erg cm$^{-2}$ s$^{-1}$, almost one order of magnitude lower than that
of a previous {\it ASCA} observation of January 1998. From all the available
X-ray measurements, an interesting scenario emerges where the X-ray light
emission may be produced by a two-phase (clumpy/smooth) circumstellar medium.
The X-ray spectral analysis shows statistically significant evidence for the
presence of two distinct components, that can be modeled with emission from
optically thin, thermal plasmas at different temperatures. The exponent of the
ejecta density distribution inferred from these temperatures is $n\simeq 6.4$.
  From the fluxes of the two spectral components we derive an estimate of the
mass loss rate of the supernova progenitor, ${\dot M} \sim 2 \times 10^{-4}
M_\odot {\rm yr}^{-1}$, at the upper end of the interval exhibited by red
super-giants. Coordinated optical and infrared observations allow us to
reconstruct the simultaneous infrared to X-ray flux distribution of SN 1995N.
We find that, at $\sim$ 9 years after explosion, the direct X-ray thermal
emission due to the wind/ejecta interaction is $\sim 5$ times larger than the
total reprocessed IR/optical flux.


title:
vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open
  Cluster NGC 2420

abstract:
  CCD photometry on the intermediate-band vbyCaHbeta system is presented for
the metal-deficient open cluster, NGC 2420. Restricting the data to probable
single members of the cluster using the CMD and the photometric indices alone
generates a sample of 106 stars at the cluster turnoff. The average E(b-y) =
0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors
refer to internal errors alone. With this reddening, [Fe/H] is derived from
both m1 and hk, using b-y and Hbeta as the temperature index. The agreement
among the four approaches is reasonable, leading to a final weighted average of
[Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades
has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and
from recalibrated low-resolution spectroscopy, the mean metallicity becomes
[Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster
abundances based upon either DDO data or low-resolution spectroscopy are
consistently reliable to 0.05 dex or better, contrary to published attempts to
establish an open cluster metallicity scale using simplistic offset corrections
among different surveys.


title:
Elodie metallicity-biased search for transiting Hot Jupiters I. Two Hot
  Jupiters orbiting the slightly evolved stars HD118203 and HD149143

abstract:
  We report the discovery of a new planet candidate orbiting the subgiant star
HD118203 with a period of P=6.1335 days. The best Keplerian solution yields an
eccentricity e=0.31 and a minimum mass m2sin(i)=2.1MJup for the planet. This
star has been observed with the ELODIE fiber-fed spectrograph as one of the
targets in our planet-search programme biased toward high-metallicity stars,
on-going since March 2004 at the Haute-Provence Observatory. An analysis of the
spectroscopic line profiles using line bisectors revealed no correlation
between the radial velocities and the line-bisector orientations, indicating
that the periodic radial-velocity signal is best explained by the presence of a
planet-mass companion. A linear trend is observed in the residuals around the
orbital solution that could be explained by the presence of a second companion
in a longer-period orbit. We also present here our orbital solution for another
slightly evolved star in our metal-rich sample, HD149143, recently proposed to
host a 4-d period Hot Jupiter by the N2K consortium. Our solution yields a
period P=4.09 days, a marginally significant eccentricity e=0.08 and a
planetary minimum mass of 1.36MJup. We checked that the shape of the spectral
lines does not vary for this star as well.


title: X-ray luminosity function of faint point sources in the Milky Way

abstract:
  We assess the contribution to the X-ray (above 2 keV) luminosity of the Milky
Way from different classes of low-mass binary systems and single stars. We
begin by using the RXTE Slew Survey of the sky at |b|>10 to construct an X-ray
luminosity function (XLF) of nearby X-ray sources in the range
10^30<Lx(erg/s)<10^34 (where Lx is the luminosity over 2-10 keV), occupied by
coronally active binaries (ABs) and cataclysmic variables (CVs). We then extend
this XLF down to Lx~10^27.5 erg/s using the Rosat All-Sky Survey in soft X-rays
and available information on the 0.1-10 keV spectra of typical sources. We find
that the local cumulative X-ray (2-10 keV) emissivities (per unit stellar mass)
of ABs and CVs are (2.0+/-0.8)x10^27 and (1.1+/-0.3)x10^27 erg/s/Msol,
respectively. In addition to ABs and CVs, representing old stellar populations,
young stars emit locally (1.5+/-0.4)x10^27 erg/s/Msol. We finally attach to the
XLF of ABs and CVs a high luminosity branch (up to ~10^39 erg/s) composed of
neutron-star and black-hole low-mass X-ray binaries (LMXBs), derived in
previous work. The combined XLF covers ~12 orders of magnitude in luminosity.
The estimated combined contribution of ABs and CVs to the 2-10 keV luminosity
of the Milky Way is ~2x10^38 erg/s, or ~3% of the integral luminosity of LMXBs
(averaged over nearby galaxies). The XLF obtained in this work is used
elsewhere (Revnivtsev et al.) to assess the contribution of point sources to
the Galactic ridge X-ray emission.


title: Origin of the Galactic ridge X-ray emission

abstract:
  We analyze a map of the Galactic ridge X-ray emission (GRXE) constructed in
the 3-20 keV energy band from RXTE/PCA scan and slew observations. We show that
the GRXE intensity closely follows the Galactic near-infrared surface
brightness and thus traces the Galactic stellar mass distribution. The GRXE
consists of two spatial components which can be identified with the bulge/bar
and the disk of the Galaxy. The parameters of these components determined from
X-ray data are compatible with those derived from near-infrared data. The
inferred ratio of X-ray to near-infrared surface brightness I(3-20 keV) (1e-11
erg/s/cm2/deg2)/I_(3.5micron)(MJy/sr)=0.26+/-0.05, and the ratio of X-ray to
near-infrared luminosity L_(3-20 keV)/L_(3-4 micron)=(4.1+/-0.3)e-5. The
corresponding ratio of the 3-20 keV luminosity to the stellar mass is
L_x/M_Sun=
  (3.5\pm0.5) 10^{27} erg/s, which agrees within the uncertainties with the
cumulative emissivity per unit stellar mass of point X-ray sources in the Solar
neighborhood, determined in an accompanying paper (Sazonov et al.). This
suggests that the bulk of the GRXE is composed of weak X-ray sources, mostly
cataclysmic variables and coronally active binaries. The fractional
contributions of these classes of sources to the total X-ray emissivity
determined from the Solar neighborhood data can also explain the GRXE energy
spectrum. Based on the luminosity function of local X-ray sources we predict
that in order to resolve 90% of the GRXE into discrete sources a sensitivity
limit of ~10^{-16} erg/s/cm2 (2--10 keV) will need to be reached in future
observations.


title: Evolution of a Kerr-Newman black hole in a dark energy universe

abstract:
  This paper deals with the study of the accretion of dark energy with equation
of state $p=w\rho$ onto Kerr-Newman black holes. We have obtained that when
$w>-1$ the mass and specific angular momentum increase, and that whereas the
specific angular momentum increases up to a given plateau, the mass grows up
unboundedly. On the regime where the dominant energy condition is violated our
model predicts a steady decreasing of mass and angular momentum of black holes
as phantom energy is being accreted. Masses and and angular momenta of all
black holes tend to zero when one approaches the big rip. The results that
cosmic censorship is violated and that the black hole size increases beyond the
universe size itself are discussed in terms of considering the used models as
approximations to a more general descriptions where the metric is
time-dependent.


title: Primordial black hole constraints on non-gaussian inflation models

abstract:
  We determine the abundance of primordial black holes (PBHs) formed in the
context of non-gaussian models with primordial density perturbations. We
consider models with a renormalized $\chi^2$ probability distribution function
parametrized by the number, $\nu$, of degrees of freedom. We show that if $\nu$
is not too large then the PBH abundance will be altered by several orders of
magnitude with respect to the standard gaussian result obtained in the $\nu \to
\infty$ limit. We also study the dependence of the spectral index constraints
on the nature of the cosmological perturbations for a power-law primordial
power spectrum.


title:
Frequency spectrum of gravitational radiation from global hydromagnetic
  oscillations of a magnetically confined mountain on an accreting neutron star

abstract:
  Recent time-dependent, ideal-magnetohydrodynamic (ideal-MHD) simulations of
polar magnetic burial in accreting neutron stars have demonstrated that stable,
magnetically confined mountains form at the magnetic poles, emitting
gravitational waves at $f_{*}$ (stellar spin frequency) and $2 f_{*}$. Global
MHD oscillations of the mountain, whether natural or stochastically driven, act
to modulate the gravitational wave signal, creating broad sidebands (full-width
half-maximum $\sim 0.2f_*$) in the frequency spectrum around $f_{*}$ and $2
f_{*}$. The oscillations can enhance the signal-to-noise ratio achieved by a
long-baseline interferometer with coherent matched filtering by up to 15 per
cent, depending on where $f_*$ lies relative to the noise curve minimum.
Coherent, multi-detector searches for continuous waves from nonaxisymmetric
pulsars should be tailored accordingly.


title: Simulations of Early Galaxy Formation

abstract:
  We present the predictions for the photometric and emission line properties
of galaxies present during the latter stages of reionization from z=8 to 6.
These preliminary predictions are made from cosmological hydrodynamic
simulations that include star formation and feedback, but not the effects of
radiative transfer. We find significant numbers of galaxies that have stellar
masses exceeding 10^8 Mo by z=8, with metallicities in the range of one-tenth
solar. These galaxies are just beyond the reach of current near-infrared
surveys, but should be found in large numbers by next-generation programs. The
Lyman alpha luminosity function does not evolve much from z=6 to z=8, meaning
that it should also be possible to detect these objects in significant numbers
with upcoming narrow band surveys, unless the escape fraction of Ly-alpha
evolves significantly between those epochs.


title: The evolution of disk galaxies in clusters and the field

abstract:
  We describe our project to examine the evolution of distant disk galaxies,
and present the results of our work based on the Tully-Fisher relation.
Comparing matched cluster and field samples we find evidence that the cluster
galaxies are on average 0.7+-0.2 mag brighter than those in the field.
Considering the field sample alone we find a brightening with redshift
amounting to 1.0+-0.5 mag by z=1, which is likely to be an upper limit,
considering the selection effects. We also give brief details of the ESO
Distant Clusters Survey (EDisCS) and describe our plans for expanding our
studies using data from this survey.


title: GDDS Highlights: Galaxy Evolution Revealed

abstract:
  The Gemini Deep Deep Survey, GDDS, produced several significant results
relating to the evolution of galaxies. All of these results are consistent with
the "downsizing" concept of galaxy formation and evolution, i.e., that the
active periods of star formation moved progressively from very massive galaxies
at high redshift to much lower mass galaxies at the present epoch. Spectra of
massive red galaxies at z ~ 1.7 demonstrates that they contain old stellar
populations and hence must have formed their stars in the first ~3 Gyr of
cosmic history; indicators of star formation activity show that the star
formation rate in the most massive galaxies was much higher at z = 2 than
today, that the activity in intermediate mass galaxies peaked near z ~ 1.5,
while, since z ~ 1 the activity is primarily confined to lower mass galaxies.
The GDDS also uncovered a relatively high percentage of post-starburst galaxies
at z ~ 1, a result that is anticipated given all the activity seen at higher
redshifts. Measurements of the strengths of metal lines of a subsample of the
GDDS and CFRS galaxies at z ~ 0.7 reveal that, at a given mass, they had lower
metallicities than at present. The evolution in the mass-metallicity relation
is consistent with a model in which star formation lasts longest in less
massive galaxies, again an expected result in the downsizing scenario.


title: Mutual Friction in Superfluid Neutron Stars

abstract:
  We discuss vortex-mediated mutual friction in the two-fluid model for
superfluid neutron star cores. Our discussion is based on the general formalism
developed by Carter and collaborators, which makes due distinction between
transport velocity and momentum for each fluid. This is essential for an
implementation of the so-called entrainment effect, whereby the flow of one
fluid imparts momentum in the other and vice versa. The mutual friction follows
by balancing the Magnus force that acts on the quantised neutron vortices with
a resistive force due to the scattering of electrons off of the magnetic field
with which each vortex core is endowed. We derive the form of the macroscopic
mutual friction force which is relevant for a model based on smooth-averaging
over a collection of vortices. We discuss the coefficients that enter the
expression for this force, and the timescale on which the two interpenetrating
fluids in a neutron star core are coupled. This discussion confirms that our
new formulation accords well with previous work in this area.


title:
Gamma--Ray Bursts associated with Supernovae: A systematic analysis of
  BATSE GRB candidates

abstract:
  We examined the properties of a sample of BATSE Gamma--Ray Bursts (GRBs)
comprising events which have indications of association with a supernova (SN),
some on the basis of indications of re--brightening in the optical afterglow
light curve, but in most cases based only on the `loose' temporal and
directional coincidence inferred from the cross correlation of catalogs.
Despite of the large uncertainties in the latter selection method, the temporal
and spectral analysis reveal three interesting statistical results when the
sample is compared with that of all the BATSE GRBs: the GRBs tentatively
associated with SNe are found to predominantly (in $\sim$ 80% of the cases)
have single-peaked light curves, a softer spectrum (i.e. low energy power law
index $\alpha \sim$ --1.5) and tend not to follow the Lag-Luminosity and
Isotropic Energy--Peak Energy correlations. These three independent statistical
properties point toward the existence of a significant number of
under-luminous,GRB 980425-like events constituting -- at least from an
observational point of view -- a tail or a separate class with respect to the
whole of the BATSE GRB events. The unusually high percentage of SN Ibc among
those identified by the catalog cross--correlation (factor $\sim 4$ higher than
expected from SN catalog statistics) reinforces the non-randomness of (some of)
the selected events.


title: Insights into Dark Energy: Interplay Between Theory and Observation

abstract:
  The nature of Dark Energy is still very much a mystery, and the combination
of a variety of experimental tests, sensitive to different potential Dark
Energy properties, will help elucidate its origins. This white paper briefly
surveys the array of theoretical approaches to the Dark Energy problem and
their relation to experimental questions.


title:
Accretion-powered Stellar Winds as a Solution to the Stellar Angular
  Momentum Problem

abstract:
  We compare the angular momentum extracted by a wind from a pre-main-sequence
star to the torques arising from the interaction between the star and its
Keplerian accretion disk. We find that the wind alone can counteract the
spin-up torque from mass accretion, solving the mystery of why accreting
pre-main-sequence stars are observed to spin at less than 10% of break-up
speed, provided that the mass outflow rate in the stellar winds is ~10% of the
accretion rate. We suggest that such massive winds will be driven by some
fraction $\epsilon$ of the accretion power. For observationally constrained
typical parameters of classical T-Tauri stars, $\epsilon$ needs to be between a
few and a few tens of percent. In this scenario, efficient braking of the star
will terminate simultaneously with accretion, as is usually assumed to explain
the rotation velocities of stars in young clusters.


title:
Does Low Frequency X-ray QPO Behavior in GRS 1915+105 Influence
  Subsequent X-ray and Infrared Evolution?

abstract:
  Using observations with the Rossi X-ray Timing Explorer, we examine the
behavior of 2-10 Hz quasi-periodic oscillations (QPOs) during spectrally-hard
dips in the x-ray light curve of GRS 1915+105 that are accompanied by infrared
flares. Of the twelve light-curves examined, nine are beta-class and three are
alpha-class following the scheme of Belloni et al. (2000). In most cases, the
QPO frequency is most strongly correlated to the power law flux, which
partially contradicts some earlier claims that the strongest correlation is
between QPO frequency and blackbody flux. Seven beta-class curves are highly
correlated to blackbody features. In several cases, the QPO evolution appears
to decouple from the spectral evolution. We find that beta-class light-curves
with strong correlations can be distinguished from those without by their
``trigger spike'' morphology. We also show that the origin and strength of the
subsequent infrared flare may be causally linked to the variations in QPO
frequency evolution and not solely tied to the onset of soft x-ray flaring
behavior. We divide the twelve alpha- and beta-class light-curves into three
groups based on the evolution of the QPO, the morphology of the trigger spike,
and the infrared flare strength. An apparent crossover case leads us to
conclude that these groups are not unique modes but represent part of a
continuum of accretion behaviors. We believe the QPO behavior at the initiation
of the hard dip can ultimately be used to determine the terminating x-ray
behavior, and the following infrared flaring behavior.


title: XMM-NEWTON Observations of Red AGN

abstract:
  XMM-Newton spectra of five red, 2MASS AGN, selected from a sample observed by
Chandra to be relatively X-ray bright and to cover a range of hardness ratios,
confirm the presence of substantial absorbing material in three sources with
optical classifications ranging from Type 1 to Type 2. A flat (hard), power law
continuum is observed in the other two. The combination of X-ray absorption and
broad optical emission lines suggests either a small (nuclear) absorber or a
favored viewing angle so as to cover the X-ray source but not the broad
emission line region (BELR). A soft excess is detected in all three Type 1
sources. We speculate that this may arise in an extended region of ionised gas,
perhaps linked with the polarised (scattered) optical light present in these
sources. The spectral complexity revealed by XMM-Newton emphasizes the
limitations of the low S/N \chandra data. The new results strengthen our
earlier conclusions that the observed X-ray continua of red AGN are unusually
hard at energies >2 keV. Their observed spectra are consistent with
contributing significantly to the missing hard/absorbed population of the
Cosmic X-ray Background (CXRB) although their intrinsic power law slopes are
typical of broad-line (Type 1) AGN (Gamma ~1.7-1.9). This suggests that the
missing X-ray-absorbed CXRB population may include Type 1 AGN/QSOs in addition
to the Type 2 AGN generally assumed.


title: Observed Metallicity Dependence of Winds from WR stars

abstract:
  A review of observational evidence in favour of a metallicity dependence of
WN and WC stars is presented. New near-IR studies of Milky Way, LMC and SMC
early-type WN stars are presented, with weake winds amongst WN stars containing
hydrogen. A metallicity dependence is supported for WN stars with hydrogen,
with dM/dt propto Z^alpha with alpha approx 0.8 +/- 0.2 The influence of CNO
content upon WN subtypes is discussed. Earlier WN spectral types are expected
(and observed) at lower metallicity due to the abundance sensitivity of NIII-IV
classification diagnostics. Recent physical and chemical results of WC stars in
the Milky Way and LMC are discussed, suggesting a metallicity dependence of
alpha approx 0.6 +/- 0.1. Earlier WC spectral types are predicted (and
observed) in lower metallicity galaxies, due to the dependence of the CIII
classification diagnostic on wind density. WO stars reveal lower wind
velocities at lower metallicity, whilst the situation for WN and WC stars is
unclear. Finally, the influence of a WR metallicity dependence upon the
ionizing flux distributions and optical line luminosities is addressed, with
particular regard to I Zw 18. Weaker winds at low metallicity would imply
harder ionizing flux distributions and lower line luminosities, arguing for an
substantially increased number of WR stars with respect to standard
calibrations, exacerbating difficulties with single star evolutionary models at
very low metallicity.


title:
Effects of Mergers and Core Structure on the Bulk Properties of Nearby
  Galaxy Clusters

abstract:
  We use morphological measurements and the scatter of clusters about observed
and simulated scaling relations to examine the impact of merging and
core-related phenomena on the structure of galaxy clusters. All relations
constructed from emission-weighted mean temperature and intracluster medium
mass, X-ray luminosity, isophotal size, or near-IR luminosity show a separation
between cool core (CC) and non-cool core (NCC) clusters. We attribute this
partially to a temperature bias in CC clusters, and partially to other cool
core-related structural changes. We attempt to minimize CC/NCC separation in
scaling relations by applying a uniform scale factor to CC cluster temperatures
and determining the scale factor for each relation that minimizes the
separation between CC and NCC populations, and by introducing central surface
brightness as a third parameter in relations. The latter approach reduces
scatter in relations more than temperature scaling. We compare the scatter
within subsamples split by CC/NCC and morphological merger indicators. CC
clusters and clusters with less substructure generally exhibit higher scatter
about relations. The larger structural variations in CC clusters exit well
outside the core, suggesting that a process more global than core radiative
instability is at work. Simulations without cooling mechanisms also show no
correlation between substructure and larger scatter about relations, indicating
that any merger-related scatter increases are subtle. The results indicate that
cool core related phenomena, not merging processes, are the primary contributor
to scatter in scaling relations. Our analysis does not appear to support the
scenario in which clusters evolve cool cores over time unless they experience
major mergers. (Abridged)


title: Environmental Dependence of the Structure of Brightest Cluster Galaxies

abstract:
  We measure the Petrosian structural properties of 33 brightest cluster
galaxies (BCGs) at redshifts z<0.1 in X-ray selected clusters with a wide range
of X-ray luminosities. We find that some BCGs show distinct signatures in their
Petrosian profiles, likely to be due to cD haloes. We also find that BCGs in
high X-ray luminosity clusters have shallower surface brightness profiles than
those in low X-ray luminosity clusters. This suggests that the BCGs in high
X-ray luminosity clusters have undergone up to twice as many equal-mass mergers
in their past as those in low X-ray luminosity clusters. This is qualitatively
consistent with the predictions of hierarchical structure formation.


title: Observations of Global and Local Infall in NGC 1333

abstract:
  We report ``infall asymmetry'' in the HCO$^+$ (1--0) and (3--2) lines toward
NGC 1333, extended over $\sim 0.39 {\rm pc}^2$, a larger extent than has been
reported be fore, for any star-forming region. The infall asymmetry extends
over a major portion of the star-forming complex, and is not limited to a
single protostar, or to a single dense core, or to a single spectral line. It
seems likely that the infall asymmetry represents inward motions, and that
these motions are physically associated with the complex. Both blue-asymmetric
and red-asymmetric lines are seen, but in both the (3--2) and (1--0) lines of
HCO$^+$ the vast majority of the asymmetric lines are blue, indicating inward
motions. The (3--2) line, tracing denser gas, has the spectra with the
strongest asymmetry and these spectra are associated with the protostars IRAS
4A and 4B, which most likely indicates a warm central source is affecting the
line profiles. The (3--2) and (1--0) lines usually have the same sense of
asymmetry in common positions, but their profiles differ significantly, and the
(1--0) line appears to trace motions on much larger spatial scales than does
the (3--2) line. Line profile models fit the spectra well, but do not strongly
constrain their parameters. The mass accretion rate of the inward motions is of
order 10$^{-4}$ M$_\odot$/yr, similar to the ratio of stellar mass to cluster
age.


title:
A Method For Eclipsing Component Identification In Large Photometric
  Datasets

abstract:
  We describe an automated method for assigning the most likely physical
parameters to the components of an eclipsing binary (EB), using only its
photometric light curve and combined color. In traditional methods (e.g. WD and
EBOP) one attempts to optimize a multi-parameter model over many iterations, so
as to minimize the chi-squared value. We suggest an alternative method, where
one selects pairs of coeval stars from a set of theoretical stellar models, and
compares their simulated light curves and combined colors with the
observations. This approach greatly reduces the EB parameter-space over which
one needs to search, and allows one to determine the components' masses, radii
and absolute magnitudes, without spectroscopic data. We have implemented this
method in an automated program using published theoretical isochrones and
limb-darkening coefficients. Since it is easy to automate, this method lends
itself to systematic analyses of datasets consisting of photometric time series
of large numbers of stars, such as those produced by OGLE, MACHO, TrES, HAT,
and many others surveys.


title: The Phenomenology of Dvali-Gabadadze-Porrati Cosmologies

abstract:
  Cosmologists today are confronted with the perplexing reality that the
universe is currently accelerating in its expansion. Nevertheless, the nature
of the fuel that drives today's cosmic acceleration is an open and tantalizing
mystery. There exists the intriguing possibility that the acceleration is not
the manifestation of yet another mysterious ingredient in the cosmic gas tank
(dark energy), but rather our first real lack of understanding of gravity
itself, and even possibly a signal that there might exist dimensions beyond
that which we can currently observe. The braneworld model of Dvali, Gabadadze
and Porrati (DGP) is a theory where gravity is altered at immense distances by
the excruciatingly slow leakage of gravity off our three-dimensional Universe
and, as a modified-gravity theory, has pioneered this line of investigation. I
review the underlying structure of DGP gravity and those phenomenological
developments relevant to cosmologists interested in a pedagogical treatment of
this intriguing model.


title: Wave Excitation in Three-Dimensional Disks by External Potential

abstract:
  We study the excitation of density and bending waves and the associated
angular momentum transfer in gaseous disks with finite thickness by a rotating
external potential. The disk is assumed to be isothermal in the vertical
direction and has no self-gravity. The disk perturbations are decomposed into
different modes, each characterized by the azimuthal index m and the vertical
index n, which specifies the nodal number of the density perturbation along the
disk normal direction. The n=0 modes correspond to the two-dimensional density
waves previously studied by Goldreich & Tremaine and others. In a
three-dimensional disk, waves can be excited at both Lindblad resonances (for
modes with n=0,1,2...) and vertical resonances (for the $n\ge 1$ modes only).
The torque on the disk is positive for waves excited at outer Linblad/vertical
resonances and negative at inner Lindblad/vertical resonances. While the n=0
modes are evanescent around corotation, the $n\ge 1$ modes can propagate into
the corotation region where they are damped and deposit their angular momenta.
We have derived analytical expressions for the amplitudes of different wave
modes excited at Lindblad and/or vertical resonances and the resulting torques
on the disk. It is found that for $n\ge 1$, angular momentum transfer through
vertical resonances is much more efficient than Lindblad resonances. This
implies that in some situations (e.g., a circumstellar disk perturbed by a
planet in an inclined orbit), vertical resonances may be an important channel
of angular momentum transfer between the disk and the external potential. We
have also derived new formulae for the angular momentum deposition at
corotation and studied wave excitations at disk boundaries.


title:
Linking stellar mass and star formation in Spitzer/MIPS 24 micron
  galaxies

abstract:
  We present deep Ks<21.5 (Vega) identifications, redshifts and stellar masses
for most of the sources composing the bulk of the 24 micron background in the
GOODS/CDFS. Our identified sample consists of 747 Spitzer/MIPS 24 micron
objects, and includes ~94% of all the 24 micron sources in the GOODS-South
field which have fluxes Snu(24)>83 microJy (the 80% completeness limit of the
Spitzer/GTO 24 micron catalog). 36% of our galaxies have spectroscopic
redshifts (mostly at z<1.5) and the remaining ones have photometric redshifts
of very good quality, with a median of |dz|=|zspec-zphot|/(1+zspec)=0.02. We
find that MIPS 24 micron galaxies span the redshift range z~0-4, and that a
substantial fraction (28%) lie at high redshifts z>1.5. We determine the
existence of a bump in the redshift distribution at z~1.9, indicating the
presence of a significant population of galaxies with PAH emission at these
redshifts. Massive (M>10^11 Msun) star-forming galaxies at redshifts 2<z<3 are
characterized by very high star-formation rates (SFR>500 Msun/yr), and some of
them are able to construct a mass of 10^10-10^11 Msun in a single burst
lifetime (~0.01-0.1 Gyr). At lower redshifts z<2, massive star-forming galaxies
are also present, but appear to be building their stars on long timescales,
either quiescently or in multiple modest burst-like episodes. At redshifts
z~1-2, the ability of the burst-like mode to produce entire galaxies in a
single event is limited to some lower (M<7x10^10 Msun) mass systems, and it is
basically negligible at z<1. Our results support a scenario where
star-formation activity is differential with assembled stellar mass and
redshift, and where the relative importance of the burst-like mode proceeds in
a down-sizing way from high to low redshifts. (abridged)


title: Sub-arcsecond Radio Observations of the Dwarf Starburst Galaxy NGC 3077

abstract:
  We present the first sub-arcsecond radio observations of the nearby dwarf
starburst galaxy NGC 3077 obtained with the MERLIN interferometer. We have
detected two resolved sources which are coincident with the positions of two
discrete X-ray sources detected by Chandra. One of the radio sources is
associated with a supernova remnant and the observed radio flux is consistent
with having a non-thermal origin. The age of the SNRs of about 760 years is
between the average age of the SNRs detected in M82 and those detected in the
Milky Way and the Large Magellanic Cloud. We use this detection to calculate a
star formation rate (SFR) of 0.28 M_sun year-1 which is similar to the SFR
calculated by using far infrared and millimeter observations but larger than
the SFR given by optical recombination lines corrected for extinction. The
other compact radio source detected by MERLIN which is coincident with the
position of an X-ray binary, has the properties of an HII region with a flux
density of about 747 microJy which corresponds to an ionizing flux of 6.8x10^50
s-1. A young massive stellar cluster with a mass of about 2x10^5 M_sun,
detected by the Hubble Space Telescope could be the responsible for the
production of the ionizing flux.


title: Star formation in the merging galaxy cluster Abell 3921

abstract:
  Through a combined optical and radio analysis, we have investigated the
possible connection between the dynamical state of the merging cluster A3921
and its star formation properties, reaching the conclusion that the on-going
merger is triggering a SF episode in the collision region.


title: Beta Cephei stars in the inner part of the Galaxy

abstract:
  From the Fourier analysis of the catalogue of ~200,000 variable candidates in
the OGLE-II Galactic fields, we found a sample of about 230 short-period
low-amplitude variable stars. From their position in the colour-magnitude
diagram and the observed periods (multiple in most cases), we identify the
stars as a mixture of Beta Cephei and Delta Scuti stars. Beta Cephei stars from
this sample are located in the Galactic disk at distances from 3 to 6 kpc. Many
of them shows large range of the excited periods, an indication of high
metallicity. We estimate that even a half of the sample of 230 short-period
variables we found, can be Beta Cephei stars. The periods alone, however, are
rarely sufficient to distinguish between both types of pulsators. We point out,
how this can be done observationally.


title:
On the population of primordial star clusters in the presence of UV
  background radiation

abstract:
  We use the algorithm of Cole et al. (2000) to generate merger trees for the
first star clusters in a Lambda CDM cosmology under an isotropic UV background
radiation field, parametrized by J_21. We have investigated the problem in two
ways: a global radiation background and local radiative feedback surrounding
the first star clusters.
  Cooling in the first halos at high redshift is dominated by molecular
hydrogen, H_2 - we call these Generation 1 objects. At lower redshift and
higher virial temperature, T_vir > 10^4K, electron cooling dominates - we call
these generation 2. Radiation fields act to photo-dissociate H_2, but also
generate free electrons that can help to catalyse its production. At modest
radiation levels, J_{21}/(1+z)^3 ~ 10^{-12}-10^{-7}, the nett effect is to
enhance the formation of Generation 1 star-clusters. At higher fluxes the
heating from photo-ionisation dominates and halts their production. With a
realistic build-up of flux over time, the period of enhanced H_2 cooling is so
fleeting as to be barely discernable and the nett effect is to move primordial
star cluster formation towards Generation 2 objects at lower redshift. A
similar effect is seen with local feedback. Provided that enough photons are
produced to maintain ionization of their host halo, they will suppress the
cooling in Generation 1 halos and boost the numbers of primordial star clusters
in Generation 2 halos. Significant suppression of Generation~1 halos occurs for
specific photon fluxes in excess of about 10^{43} ph s^{-1} Msun^{-1}.


title: Large-scale alpha^2-dynamo in low-mass stars and brown dwarfs

abstract:
  We develop a model based on 3D mean-field MHD for the generation of large
scale magnetic fields in fully convective objects like low-mass stars, brown
dwarfs and possibly gaseous planets. The dynamo process is of alpha^2 type and
thus differs from the shell-dynamo at work in more massive stars.The alpha^2
dynamo becomes supercritical for Rossby numbers Ro\la 10. It generates a
large-scale, non-axisymmetric, steady field that is symmetric with respect to
the equatorial plane. Saturation of the alpha^2-generated field at the
equipartition yields strengths of several kGauss, in agreement with
observations of active M dwarfs, and provides a qualitative explanation for the
observed activity saturation in late M stars. For brown dwarfs with a
conductive core, as occurs at the center of the most massive and oldest of
these objects, we have also studied an alpha^2-Omega dynamo, i.e. the effect of
differential rotation. In this case the field is predominantly toroidal,
axisymmetric and oscillatory, like the solar field. The topology of the field
in the fully convective objects exhibits a high order multipole character that
differs from the aligned dipole field generated by the alpha-Omega dynamo. The
strong reduction of the dipolar component due to the field non-axisymmetry
should considerably reduce the Alfven radius and thus the efficiency of
magnetic braking, providing an appealing explanation for the decreasing angular
momentum loss rate observed in low-mass stars and brown dwarfs. This may have
also implications for cataclysmic variables below the period gap. In spite of
this large-scale field, the decreasing conductivity in the dominantly neutral
atmosphere of these objects prevents the current generation necessary to
support a chromosphere and thus activity. (Abridged)


title:
RR Lyrae variables in Galactic Globular Clusters: distribution of
  periods and synthetic models

abstract:
  We present some applications of our Synthetic Horizontal Branches (SHB)
simulations, aimed to reproduce the peculiar period distributions of RR Lyrae
belonging to the Galactic Globular Clusters M3 and M5. We show some evidence,
supporting the importance of SHBs in obtaining parameters such as the mass
distribution inside the instability strip.


title:
The CNOC2 sample of intermediate redshift galaxy groups - the powerhouse
  of galaxy evolution

abstract:
  The evolution of galaxies in groups may have important implications for the
global evolution of star formation rate in the Universe, since many processes
which operate in groups may suppress star formation, and the fraction of
galaxies bound in groups at the present day is as high as ~60%. We present an
analysis of our sample of 0.3<=z<=0.55 groups, selected from the CNOC2 redshift
survey and supplemented with deep spectroscopy and HST ACS imaging. We find
that these groups contain significantly more passive galaxies than the field,
with excesses of S0, elliptical and passive spiral galaxy types. The
morphological composition is closely matched to that of more massive irregular
clusters at a similar epoch. Contrasting with galaxy samples in a variety of
environments and epochs, we find that the fraction of passive galaxies
(EW[OII]<5A), is strongly evolving in the group environment, with parallel
evolution in the (global) field population, whilst little evolution is observed
in cluster cores since z~1.


title:
The Recently-Discovered Dwarf Nova System ASAS J002511+1217.2: A New WZ
  Sagittae Star

abstract:
  The cataclysmic variable ASAS J002511+1217.2 was discovered in outburst by
the All-Sky Automated Survey in September 2004, and intensively monitored by
AAVSO observers through the following two months. Both photometry and
spectroscopy indicate that this is a very short-period system. Clearly defined
superhumps with a period of 0.05687 +/- 0.00001 days (1-sigma) are present
during the superoutburst, 5 to 18 days following the ASAS detection. We observe
a change in superhump profile similar to the transition to ``late superhumps''
observed in other short-period systems; the superhump period appears to
increase slightly for a time before returning to the original value, with the
resulting superhump phase offset by approximately half a period. We detect
variations with a period of 0.05666 +/- 0.00003 days (1-sigma) during the
four-day quiescent phase between the end of the main outburst and the single
echo outburst. Weak variations having the original superhump period reappear
during the echo and its rapid decline. Time-resolved spectroscopy conducted
nearly 30 days after detection and well into the decline yields an orbital
period measurement of 82 +/- 5 minutes. Both narrow and broad components are
present in the emission line spectra, indicating the presence of multiple
emission regions. The weight of the observational evidence suggests that ASAS
J002511+1217.2 is a WZ Sge-type dwarf nova, and we discuss how this system fits
into the WZ classification scheme.


title:
The multi-phase gaseous halos of star forming late-type galaxies - I.
  XMM-Newton observations of the Hot Ionized Medium

abstract:
  This study presents first results from an X-ray mini-survey carried out with
XMM-Newton to investigate the diffuse Hot Ionized Medium in the halos of nine
nearby star-forming edge-on spiral galaxies. Diffuse gaseous X-ray halos are
detected in eight of our targets, covering a wide range of star formation rates
from quiescent to starburst cases. For four edge-on spiral galaxies, namely
NGC3044, NGC3221, NGC4634, and NGC5775, we present the first published high
resolution/sensitivity detections of extended soft X-ray halos. EPIC X-ray
contour maps overlaid onto Halpha imaging data reveals that in all cases the
presence of X-ray halos is correlated with extraplanar Diffuse Ionized Gas.
Moreover, these halos are also associated with non-thermal cosmic ray halos, as
evidenced by radio continuum observations. Supplemental UV-data obtained with
the OM-telescope at 210nm show Diffuse Ionized Gas to be well associated with
UV emission originating in the underlying disk. Beside NGC891, NGC4634 is the
second non-starburst galaxy with a diffuse soft X-ray halo (|z|<4kpc). In case
of NGC3877, for which we also present the first high resolution X-ray imaging
data, no halo emission is detectable. EPIC pn spectra (0.3-12keV) of the
diffuse X-ray emission are extracted at different offset positions from the
disk, giving evidence to a significant decrease of gas temperatures, electron
densities, and gas masses with increasing distance to the plane. A comparison
between dynamical and radiative cooling time scales implies that the outflow in
all targets is likely to be sustained. We find very strong indications that
spatially correlated multi-phase gaseous halos are created by star forming
activity in the disk plane.


title: The evolution of actively star forming galaxies in the mid infrared

abstract:
  In this paper we analyze the evolution of actively star forming galaxies in
the mid-infrared (MIR). This spectral region, characterized by continuum
emission by hot dust and by the presence of strong emission features generally
ascribed to polycyclic aromatic hydrocarbon (PAH) molecules, is the most
strongly affected by the heating processes associated with star formation
and/or active galactic nuclei (AGN). Following the detailed observational
characterization of galaxies in the MIR by ISO, we have updated the modelling
of this spectral region in our spectro-photometric model GRASIL (Silva et al.
1998). In the diffuse component we have updated the treatment of PAHs according
to the model by Li & Draine (2001). As for the dense phase of the ISM
associated with the star forming regions, the molecular clouds, we strongly
decrease the abundance of PAHs as compared to that in the cirrus, basing on the
observational evidences of the lack or weakness of PAH bands close to the newly
formed stars, possibly due to the destruction of the molecules in strong UV
fields. The robustness of the model is checked by fitting near infrared to
radio broad band spectra and the corresponding detailed MIR spectra of a large
sample of galaxies (Lu et al. 2003), at once. With this model, we have analyzed
the larger sample of actively star forming galaxies by Dale et al. (2000). We
show that the observed trends of galaxies in the ISO-IRAS-Radio color-color
plots can be interpreted in terms of different evolutionary phases of star
formation activity, and the consequent different dominance in the spectral
energy distribution (SED) of the diffuse or dense phase of the ISM.


title: Generating long streams of $1/f^alpha$ noise

abstract:
  We review existing methods for generating long streams of 1/f^alpha noise
($0<\alpha\le 2$) focusing on the digital filtering of white noise. We detail
the formalism to conceive an efficient random number generator (white outside
some bounds) in order to generate very long streams of noise without an
exhaustive computer memory load. For $\alpha=2$ it is shown why the process is
equivalent to a random-walk and can be obtained simply by a first order
filtering of white noise. As soon as $\alpha<2$ the problem becomes non linear
and we show why the exact digital filtering method becomes inefficient.
Instead, we work out the formalism of using several 1/f^2 filters spaced
logarithmically, to approximate the spectrum at the percent level. Finally,
from work on logistic maps, we give hints on how to design generators with
$\alpha>2$. The software is available from
http://planck.lal.in2p3.fr/article.php3?id\_article=8


title:
HST Images Do Not Support the Presence of Three High Velocity, Low-Mass
  Stars in the Core of the Orion Nebula Cluster

abstract:
  A recent article has employed the determination from groundbased images of
high proper motions in the Orion Nebula Cluster to argue that JW 349, JW 355,
and JW 451 are high velocity (38 km/s, 89 km/s, and 69 km/s, respectively) low
mass runaway stars. We report on measurement of the proper motions of these
stars using images made by the Hubble Space Telescope's WFPC2 imager and find
that there is no evidence for motions above 6.2 km/s for JW 349 and 7.9 km/s
for JW 355, while the motion of 5.5 km/s for JW 451 is only slightly larger
than the measurement uncertainty of 3.9 km/s. We conclude that there is no
observational support for these stars being high velocity runaway stars.


title:
Stellar populations in the CFHTLS. I. New constraints on the IMF at low
  mass

abstract:
  We present a stellar populations analysis of the first release of the CFHTLS
(Canada-France-Hawai Telescope Legacy Survey) data. A detailed comparison
between the Besan\c{c}on model of the Galaxy and the first data release of the
CFHTLS-Deep survey is performed by implementing the MEGACAM photometric system
in this model using stellar atmosphere model libraries. The reliability of the
theoretical libraries to reproduce the observed colours in the MEGACAM system
is investigated. The locations of various stellar species like subdwarfs, white
dwarfs, late-type and brown dwarfs, binary systems are identified. The
contamination of the stellar sample by quasars and compact galaxies is
quantified using spectroscopic data from the VIMOS-VLT Deep Survey (VVDS) as a
function of $i'$ magnitude and $r'-i'$ colour. A comparison between simulated
counts using the standard IMF at low masses show that the number of very low
mass dwarfs may have been underestimated in previous studies. These
observations favour a power law IMF following $d(n)/dm \propto m^{-\alpha}$
with $\alpha=2.5$ for $m < $ 0.25 \Msun or $\alpha=3.0$ for $m < $ 0.2 \Msun
for single stars. The resulting LF is in agreement with the local LF as
measured from the 5 or 25 pc samples. It is in strong disagreement with the
Zheng et al (2001) LF measured from deep HST data. We show that this
discrepancy can be understood as an indication of a different IMF at low masses
at early epochs of the Galaxy compared to the local thin disc IMF.


title:
SPI/INTEGRAL observation of the Galactic central radian: contribution of
  discrete sources and implication for the diffuse emission

abstract:
  The INTEGRAL observatory has been performing a deep survey of the Galactic
central radian since 2003, with the goal of both extracting a catalog of
sources and gaining insight into the Galactic diffuse emission. This paper
concentrates on the estimation of the total point sources emission
contribution. It is now clear that unresolved point sources contribute to the
observed diffuse emission; the increasing sensitivity of instruments with time
has lead to a steady decrease in estimates of this ``diffuse emission''.
  We have analysed the first year data obtained with the spectrometer and
imager SPI on board INTEGRAL. First, a catalog of 63 hard X-ray sources
detected, time-averaged, during our 2003 Galactic plane survey, is derived.
Second, after extracting the spectra of the sources detected by SPI, their
combined contribution is compared to the total (resolved and unresolved)
emission from the Galactic ridge. The data analysis is complex: it requires us
to split the total emission into several components, as discrete sources and
diffuse emission are superimposed in SPI data. The main result is that point
source emission dominates in the hard X-ray/soft $\gamma$-ray domain, and
contributes around 90 % of the total emission around 100 keV, while above 250
keV, diffuse electron-positron annihilation, through its three-photon
positronium continuum with a positronium fraction $\sim$ 0.97 and the 511 keV
electron-positron line, dominates over the sources.


title: VLT Observations of the Ultraluminous X-ray Source NGC 1313 X-2

abstract:
  We present archive ESO VLT photometric and spectroscopic data of the
Ultraluminous X-ray source NGC 1313 X-2. The superb quality of the VLT images
reveals that two distinct objects, with R magnitudes 23.7 and 23.6, are visible
inside the Chandra error box. The two objects, separated by 0.75 arcsec, were
unresolved in our previous ESO 3.6 m+EFOSC image. We show that both are stars
in NGC 1313, the first a B0-O9 main sequence star of ~20 Msun, while the second
a G supergiant of ~10 Msun. Irrespectively of which of the two objects the
actual counterpart is, this implies that NGC 1313 X-2 is a high mass X-ray
binary with a very massive donor.


title:
ISM properties in low-metallicity environments I. mid-infrared spectra
  of dwarf galaxies

abstract:
  We present new ISOCAM mid-infrared spectra of three starbursting nearby dwarf
galaxies, NGC1569, IIZw40, NGC1140 and the 30Dor region of the LMC and explore
the properties of the ISM in low-metallicity environments, also using
additional sources from the literature. We analyse the various components of
the ISM probed by the mid-infrared observations and compare them with other
Galactic and extragalactic objects. The MIR spectra of the low-metallicity
starburst sources are dominated by the [NeIII] and [SIV] lines, as well as a
steeply rising dust continuum. PAH bands are generaly faint, both locally and
averaged over the full galaxy, in stark contrast to dustier starburst galaxies,
where the PAH features are very prominant and even dominate on global scales.
The hardness of the modeled interstellar radiation fields for the dwarf
galaxies increases as the presence of PAH band emission becomes less
pronounced. The [NeIII]/[NeII] ratios averaged over the full galaxy are
strikingly high, often >10. Thus, the hard radiation fields are pronounced and
pervasive. We find a prominent correlation between the PAHs/VSGs and the
[NeIII]/[NeII] ratios for a wide range of objects, including the low
metallicity galaxies as well as Galactic HII regions and other metal-rich
galaxies. This effect is consistent with the hardness of the interstellar
radiation field playing a major role in the destruction of PAHs in the low
metallicity ISM. We see a PAHs/VSGs and metallicity correlation, also found by
Engelbracht et al. (2005) for a larger survey. Combined effects of metallicity
and radiation field seem to be playing important roles in the observed behavior
of PAHs in the low metallicity systems.


title:
Chemical telemetry of OH observed to measure interstellar magnetic
  fields

abstract:
  We present models for the chemistry in gas moving towards the ionization
front of an HII region. When it is far from the ionization front, the gas is
highly depleted of elements more massive than helium. However, as it approaches
the ionization front, ices are destroyed and species formed on the grain
surfaces are injected into the gas phase. Photodissociation removes gas phase
molecular species as the gas flows towards the ionization front. We identify
models for which the OH column densities are comparable to those measured in
observations undertaken to study the magnetic fields in star forming regions
and give results for the column densities of other species that should be
abundant if the observed OH arises through a combination of the liberation of
H2O from surfaces and photodissociation. They include CH3OH, H2CO, and H2S.
Observations of these other species may help establish the nature of the OH
spatial distribution in the clouds, which is important for the interpretation
of the magnetic field results.


title: Alternative Approaches to Dark Matter Puzzle

abstract:
  We study the dark matter problem with particular reference to a candidate
particle within the Standard Model: the $H$ dibaryon. We consider as well a
scenario which aims to connect the dark matter origin to the Baryon Asymmetry
of the Universe, studying the examples of $H$ and of a BSM particle $X$.
Strongly attractive color forces in the flavor singlet channel may lead to a
tightly bound and compact $H$ dibaryon. We find that the observation of
$\Lambda$ decays from doubly-strange hypernuclei puts a constraint on the $H$
wavefunction which is plausibly satisfied. In this case the $H$ is long-lived
as we calculate. We also show that an $H$ or another compact, flavor singlet
hadron is unlikely to bind to nuclei, so that experimental bounds on exotic
isotopes do not exclude their existence. Remarkably, the $H$ appears to evade
other experimental constraints as well, when account is taken of its expected
compact spatial wavefunction. We check whether the $H$ is a viable DM candidate
by considering DM experiments sensitive to light particles. Taking into account
the DM interaction in the crust above underground detectors we find a window in
the exclusion limits in the micro-barn, $m\lsi 2.4$ GeV, range which coincides
with the range expected for the tightly bound $H$. Finally, we present a
scenario in which DM carries (anti-)baryon number and which offers a mechanism
to generate the baryon asymmetry observed in the Universe. If $\sigma^{annih}
_{\bar{X}} < \sigma^{annih}_{X}$, the $\bar{X}$'s freeze out at a higher
temperature and have a larger relic density than $X$'s. If $m_X \lsi 4.5 B_X$
GeV and the annihilation cross sections differ by 10% or more, this type of
scenario naturally explains the observed $\Omega_{DM} \simeq 5 \Omega_b$. Two
examples are given, the $H$ and an hypothetical BSM candidate $X$.


title:
Using Line Profiles to Test the Fraternity of Type Ia Supernovae at High
  and Low Redshifts

abstract:
  Using archival data of low-redshift (z < 0.01) Type Ia supernovae (SN Ia) and
recent observations of high-redshift (0.16 < z <0.64; Matheson et al. 2005) SN
Ia, we study the "uniformity'' of the spectroscopic properties of nearby and
distant SN Ia. We find no difference in the measures we describe here. In this
paper, we base our analysis solely on line-profile morphology, focusing on
measurements of the velocity location of maximum absorption (vabs) and peak
emission (vpeak). We find that the evolution of vabs and vpeak for our sample
lines (Ca II 3945, Si II 6355, and S II 5454, 5640) is similar for both the
low- and high-redshift samples. We find that vabs for the weak S II 5454, 5640
lines, and vpeak for S II 5454, can be used to identify fast-declining [dm15 >
1.7] SN Ia, which are also subluminous. In addition, we give the first direct
evidence in two high-z SN Ia spectra of a double-absorption feature in Ca II
3945, an event also observed, though infrequently, in low-redshift SN Ia
spectra (6/22 SN Ia in our local sample). We report for the first time the
unambiguous and systematic intrinsic blueshift of peak emission of optical
P-Cygni line profiles in Type Ia spectra, by as much as 8000 km/s. All the
high-z SN Ia analyzed in this paper were discovered and followed up by the
ESSENCE collaboration, and are now publicly available.


title: A Unified Near Infrared Spectral Classification Scheme for T Dwarfs

abstract:
  A revised near infrared classification scheme for T dwarfs is presented,
based on and superseding prior schemes developed by Burgasser et al. and
Geballe et al., and defined following the precepts of the MK Process. Drawing
from two large spectroscopic libraries of T dwarfs identified largely in the
Sloan Digital Sky Survey and the Two Micron All Sky Survey, nine primary
spectral standards and five alternate standards spanning spectral types T0 to
T8 are identified that match criteria of spectral character, brightness,
absence of a resolved companion and accessibility from both northern and
southern hemispheres. The classification of T dwarfs is formally made by the
direct comparison of near infrared spectral data of equivalent resolution to
the spectra of these standards. Alternately, we have redefined five key
spectral indices measuring the strengths of the major H$_2$O and CH$_4$ bands
in the 1-2.5 micron region that may be used as a proxy to direct spectral
comparison. Two methods of determining T spectral type using these indices are
outlined and yield equivalent results. These classifications are also
equivalent to those from prior schemes, implying that no revision of existing
spectral type trends is required. The one-dimensional scheme presented here
provides a first step toward the observational characterization of the lowest
luminosity brown dwarfs currently known. Future extensions to incorporate
spectral variations arising from differences in photospheric dust content,
gravity and metallicity are briefly discussed. A compendium of all currently
known T dwarfs with updated classifications is presented.


title: Spectroscopic Binaries in Planetary Nebulae

abstract:
  It is already known that about 10% of central stars of PNe are very
short-period binaries (hours to days), which are detected through photometric
variations. These must have been formed through common-envelope interactions in
initially wide binaries, accompanied by ejection of the envelope and its
subsequent photoionization as a PN. Radial-velocity observations by ourselves
and others are now suggesting that an even larger fraction of planetary nuclei
may be spectroscopic binaries, making the total binary fraction very large.
However, we have not as yet been able to rule out the possibility that the
apparent velocity changes are actually due to stellar-wind variations. Pending
follow-up spectroscopic observations with large telescopes, it presently
appears plausible that binary-star ejection is the major formation channel for
planetary nebulae.


title: On the Ages of Exoplanet Host Stars

abstract:
  We obtained spectra, covering the CaII H and K region, for 49 exoplanet host
(EH) stars, observable from the southern hemisphere. We measured the
chromospheric activity index, Rhk. We compiled previously published values of
this index for the observed objects as well as the remaining EH stars in an
effort to better smooth temporal variations and derive a more representative
value of the average chromospheric activity for each object. We used the
average index to obtain ages for the group of EH stars. In addition we applied
other methods, such as: Isochrone, lithium abundance, metallicity and
transverse velocity dispersions, to compare with the chromospheric results. The
kinematic method is a less reliable age estimator because EH stars lie red-ward
of Parenago's discontinuity in the transverse velocity dispersion vs dereddened
B-V diagram. The chromospheric and isochrone techniques give median ages of 5.2
and 7.4 Gyr, respectively, with a dispersion of 4 Gyr. The median age of F and
G EH stars derived by the isochrone technique is 1--2 Gyr older than that of
identical spectral type nearby stars not known to be associated with planets.
However, the dispersion in both cases is large, about 2--4 Gyr. We searched for
correlations between the chromospheric and isochrone ages and Lir/L* (the
excess over the stellar luminosity) and the metallicity of the EH stars. No
clear tendency is found in the first case, whereas the metallicy dispersion
seems to slightly increase with age.


title: Atomic X-ray Spectroscopy of Accreting Black Holes

abstract:
  Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.


title:
Drop of coherence of the lower kilo-Hz QPO in neutron stars: is there a
  link with the innermost stable circular orbit?

abstract:
  Using all available archival data from the Rossi X-ray Timing Explorer
(RXTE), we follow the frequency of the kilo-Hz QPOs in three low luminosity
neutron star low mass X-ray binaries; namely 4U 1636-536, 4U 1608-522, and
4U1735-44. Following earlier work, we focus our analysis on the lower kilo-Hz
QPO, for which we study the dependency of its quality factor (Q) amplitude as a
function of frequency over a range covering from 500 Hz to 1000 Hz. As
previously found for 4U 1636-536, we show that the quality factor of the lower
kilo-Hz increases with frequency up to a maximum frequency around 800 Hz,
beyond which an abrupt drop of its coherence is observed down to a limiting
frequency where the QPO disappears completely. Simultaneously the amplitude of
the QPOs is almost constant below the peak frequency and starts to decrease
smoothly afterwards. The peak frequency is 850 Hz, 820 Hz, 740 Hz whereas the
limiting frequency is 920 Hz, 900 Hz and 830 Hz for 4U 1636-536, 4U 1608-522
and 4U 1735-44 respectively. A ceiling of the lower QPO frequencies is also
seen clearly in a frequency versus count rate diagram for all sources. This
behavior is reproducible within an object and between objects. We suggest here
that the drop of coherence of the lower QPO may be a geometry-related effect,
which could be related to the last stable circular orbit.


title: Ultraviolet studies of interacting binaries

abstract:
  Interacting Binaries consist of a variety of stellar objects in different
stages of evolution and those containing accreting compact objects still
represent a major challenge to our understanding of not only close binary
evolution but also of the chemical evolution of the Galaxy. These end-points of
binary star evolution are ideal laboratories for the study of accretion and
outflow processes, and provide insight on matter under extreme physical
conditions. One of the key-questions of fundamental relevance is the nature of
SNIa progenitors. The study of accreting compact binary systems relies on
observations over the entire electromagnetic spectrum and we outline here those
unresolved questions for which access to the ultraviolet range is vital, as
they cannot be addressed by observations in any other spectral region.


title: The optical afterglow of the short gamma-ray burst GRB 050709

abstract:
  It has long been known that there are two classes of gamma-ray bursts (GRBs),
mainly distinguished by their durations. The breakthrough in our understanding
of long-duration GRBs (those lasting more than ~2 s), which ultimately linked
them with energetic Type Ic supernovae, came from the discovery of their
long-lived X-ray and optical afterglows, when precise and rapid localizations
of the sources could finally be obtained. X-ray localizations have recently
become available for short (duration <2 s) GRBs, which have evaded optical
detection for more than 30 years. Here we report the first discovery of
transient optical emission (R-band magnitude ~23) associated with a short
burst; GRB 050709. The optical afterglow was localized with subarcsecond
accuracy, and lies in the outskirts of a blue dwarf galaxy. The optical and
X-ray afterglow properties 34 h after the GRB are reminiscent of the afterglows
of long GRBs, which are attributable to synchrotron emission from
ultrarelativistic ejecta. We did not, however, detect a supernova, as found in
most nearby long GRB afterglows, which suggests a different origin for the
short GRBs.


title: Virial masses and the baryon fraction in galaxies

abstract:
  We have measured the weak lensing signal as a function of restframe
luminosity for a sample of `isolated' galaxies. These results are based on
four-band photometry from the Red-Sequence Cluster Survey, enabling us to
determine photometric redshifts for a large number of galaxies. We select a
secure sample of lenses with photometric redshifts 0.2<z<0.4 and study the
relation between the virial mass and baryonic contents. In addition, we discuss
the implications of the derived photometric redshift distribution for published
cosmic shear studies. The virial masses are derived from a fit to the observed
lensing signal. For a galaxy with a fiducial luminosity of 10^10 h^-2 L_Bsun we
obtain a mass M_vir=9.9^{+1.5}_{-1.3}\times 10^11 h^-1 M_sun. The virial mass
as a function of luminosity is consistent with a power-law ~L^1.5, with similar
slopes for the three filters considered here. These findings are in excellent
agreement with results from the Sloan Digital Sky Survey and semi-analytic
models of galaxy formation. We measure the fraction of mass in stars and the
baryon fraction in galaxies by comparing the virial mass-to-light ratio to
predicted stellar mass-to-light ratios. We find that star formation is
inefficient in converting baryons into stars, with late-type galaxies
converting ~33% and early-type galaxies converting only ~14% of baryons into
stars. Our results imply that the progenitors of early-type galaxies must have
low stellar mass fractions, suggestive of a high formation redshift.


title: The host galaxy cluster of the short gamma-ray burst GRB 050509B

abstract:
  The first arcsecond localization of a short gamma-ray burst, GRB 050509B, has
enabled detailed studies of a short burst environment. We here report on
studies of the environment of GRB 050509B using the Swift X-ray Telescope
(XRT). The XRT error circle of the burst overlaps with an elliptical galaxy in
the cluster of galaxies ZwCl 1234.0+02916. Based on the measured X-ray flux of
the cluster we estimate that the probability for a chance superposition of GRB
050509B and a cluster at least as X-ray bright as this cluster is $< 2\times
10^{-3}$, presenting the first strong case of a short burst located in a
cluster of galaxies. We also consider the case for GRB 050509B being located
behind ZwCl 1234.0+02916 and gravitationally lensed. From the velocity
dispersion of the elliptical galaxy and the temperature of hot intracluster
gas, we model the mass distribution in the elliptical galaxy and the cluster,
and calculate the gravitational lensing magnification within the XRT error
circle. We find that, if GRB050509B would be positioned significantly behind
the cluster, it is most likely magnified by a factor less than two, but that
the burst could be strongly lensed if it is positioned within 2 arcsec of the
center of the bright elliptical galaxy. Further mapping of arcsecond size short
burst error boxes is a new promising route to determine the spatial
distribution of old stars throughout the Universe.