title: Accretion mode changes in Centaurus X-3

abstract:
  We report here discovery of the existence of two different accretion modes in
the high mass X-ray binary pulsar Cen X-3 during its high states. The multiband
X-ray light curves of Cen X-3 lasting for more than 3400 days obtained with the
All Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE) shows many
episodes of high and low X-ray intensities. The high intensity phases last
between a few to upto 110 days and the separation between two high intensity
phases also varies widely. One remarkable feature deduced from the RXTE-ASM
light curves is that during these high intensity phases, Cen X-3 manifests in
two very distinct spectral states. When the source makes a transition from the
low intensity phase to the high intensity phase, it adopts one of these two
spectral states and during the entire high intensity phase remains in that
particular spectral state. During December 2000 to April 2004, all the high
intensity episodes showed a hardness ratio which is significantly larger than
the same during all the high states prior to and subsequent to this period. It
is also found that most of the soft outbursts reach a nearly constant peak flux
in the 5--12 keV band. For comparison, similar analysis was carried out on the
long term X-ray light curves of three other X-ray binary pulsars Her X-1, Vela
X-1, and SMC X-1. Results obtained with these sources are also presented here
and we found that none of the other sources show such a behaviour. From these
observations, we suggest that Cen X-3 has two different accretion modes and in
the course of nine years it has exhibited two switch overs between these.


title: Testing Primordial Non-Gaussianity in CMB Anisotropies

abstract:
  Recent second-order perturbation computations have provided an accurate
prediction for the primordial gravitational potential $\Phi(x)$ in scenarios in
which cosmological perturbations are generated either during or after
inflation. This enables us to make realistic predictions for a non-Gaussian
part of $\Phi(x)$, which is generically written in momentum space as a double
convolution of its Gaussian part with a suitable kernel, f_NL(k1,k2). This
kernel defines the amplitude and angular structure of the non-Gaussian signals
and originates from the evolution of second-order perturbations after the
generation of the curvature perturbation. We derive a generic formula for the
CMB angular bispectrum with arbitrary f_NL(k1,k2) and examine the detectability
of the primordial non-Gaussian signals from various scenarios such as
single-field inflation, inhomogeneous reheating, and curvaton scenarios. Our
results show that in the standard slow-roll inflation scenario the signal
actually comes from the momentum-dependent part of f_NL(k1,k2), and thus it is
important to include the momentum dependence in the data analysis. In the other
scenarios the primordial non-Gaussianity is comparable to or larger than these
post-inflationary effects. We find that WMAP cannot detect non-Gaussian signals
generated by these models. Numerical calculations for l>500 are still
computationally expensive, and we are not yet able to extend our calculations
to Planck's angular resolution; however, there is an encouraging trend which
shows that Planck may be able to detect these non-Gaussian signals.


title: Observational Constraints on Silent Quartessence

abstract:
  We derive new constraints set by SNIa experiments (`gold' data sample of
Riess et al.), X-ray galaxy cluster data (Allen et al. Chandra measurements of
the X-ray gas mass fraction in 26 clusters), large scale structure (Sloan
Digital Sky Survey spectrum) and cosmic microwave background (WMAP) on the
quartessence Chaplygin model. We consider both adiabatic perturbations and
intrinsic non-adiabatic perturbations such that the effective sound speed
vanishes (Silent Chaplygin). We show that for the adiabatic case, only models
with equation of state parameter $ |\alpha |\lesssim 10^{-2}$ are allowed: this
means that the allowed models are very close to \LambdaCDM. In the Silent case,
however, the results are consistent with observations in a much broader range,
-0.3<\alpha<0.7.


title: Observations of Stripped Edge-on Virgo Cluster Galaxies

abstract:
  We present observations of highly inclined, HI deficient, Virgo cluster
spiral galaxies. Our high-resolution VLA HI observations of edge-on galaxies
allow us to distinguish extraplanar gas from disk gas. All of our galaxies have
truncated H-alpha disks, with little or no disk gas beyond a truncation radius.
While all the gas disks are truncated, the observations show evidence for a
continuum of stripping states: symmetric, undisturbed truncated gas disks
indicate galaxies that were stripped long ago, while more asymmetric disks
suggest ongoing or more recent stripping. We compare these timescale estimates
with results obtained from two-dimensional stellar spectroscopy of the outer
disks of galaxies in our sample. One of the galaxies in our sample, NGC 4522 is
a clear example of active ram-pressure stripping, with 40% of its detected HI
being extraplanar. As expected, the outer disk stellar populations of this
galaxy show clear signs of recent (and, in fact, ongoing) stripping. Somewhat
less expected, however, is the fact that the spectrum of the outer disk of this
galaxy, with very strong Balmer absorption and no observable emission, would be
classified as ``k+a'' if observed at higher redshift. Our observations of NGC
4522 and other galaxies at a range of cluster radii allow us to better
understand the role that clusters play in the structure and evolution of disk
galaxies.


title:
Critical Metallicity and Fine-Structure Emission of Primordial Gas
  Enriched by the First Stars

abstract:
  The influence of the first stars on the formation of second-generation
objects at high redshift may be determined, in part, by their metal enrichment
of surrounding gas. At a critical metallicity, Zcrit, primordial gas cools more
efficiently by fine-structure lines of CII (157.74 um), OI (63.18 um, 145.5
um), SiII (34.8 um), and FeII (25.99 um, 35.35 um) than by HI or H2 emission.
This cooling may alter the process of fragmentation into smaller units. We
study the time-dependent cooling of primordial gas enriched by heavy elements
from early massive stars, particularly O, Si, and Fe. We define Zcrit as the
point when the total cooling rate by metals plus H2 equals the adiabatic
compressional heating. We explore two metallicity scenarios: (1) a single
metallicity for all heavy elements; (2) individual metallicities (Z_C, Z_O,
Z_Si, Z_Fe) from theoretical supernova yields. For dense gas [n > 10^3 cm^(-3)]
with metals in relative solar abundances, fragmentation occurs at Zcrit ~
10^(-3.5) Z_sun. However, for lower density gas, [n = 1-100 cm^(-3)],
particularly in halos enriched in Si, O, and Fe, we find Zcrit = 0.1-1% Zsun.
The critical metallicity approaches a minimum value at high-n set by efficient
LTE cooling, with thermalized level populations of fine-structure states and H2
rotational states (J = 2 and J = 3). Primordial clouds of 10^8 Msun at 200K are
detectable in redshifted fine-structure lines, with far-infrared fluxes between
10^-22 and 10^-21 W/m^2. For metallicities Z_O = 10^(-3) and molecular
fractions f(H2) = 10^(-3) the fine-structure emission lines of OI, SiII, and
FeII could be 10^2 - 10^3 times stronger than the H2 rotational lines at 28.22
um (J = 2-0) and 17.03 um (J = 3-1).


title: Chemical Abundances of DEEP2 Star-forming Galaxies at 1.0<z<1.5

abstract:
  We present the results of near-infrared spectroscopic observations for a
sample of 12 star-forming galaxies at 1.0<z<1.5, drawn from the DEEP2 Galaxy
Redshift Survey. H-beta, [OIII], H-alpha, and [NII] emission-line fluxes are
measured for these galaxies. Application of the O3N2 and N2 strong-line
abundance indicators implies average gas-phase oxygen abundances of 50-80%
solar. We find preliminary evidence of luminosity-metallicity (L-Z) and
mass-metallicity (M-Z) relationships within our sample, which spans from
M_B=-20.3 to -23.1 in rest-frame optical luminosity, and from 4x10^9 to 2x10^11
Msun in stellar mass. At fixed oxygen abundance, these relationships are
displaced from the local ones by several magnitudes towards brighter absolute
B-band luminosity and more than an order of magnitude towards larger stellar
mass. If individual DEEP2 galaxies in our sample follow the observed global
evolution in the B-band luminosity function of blue galaxies between z~1 and
z~0 they will fade on average by ~1.3 magnitudes in M_B. To fall on local (L-Z)
and (M-Z) relationships, these galaxies must increase by a factor of 6-7 in
M/L_B between z~1 and z~0, and by factor of two in both stellar mass and
metallicity. Emission line diagnostic ratios indicate that the z>1 DEEP2
galaxies in our sample are significantly offset from the excitation sequence
observed in nearby HII regions and SDSS emission-line galaxies. This offset
implies that physical conditions are different in the HII regions of distant
galaxies hosting intense star formation, and may affect the chemical abundances
derived from strong-line ratios for such objects (Abridged).


title: Combined reconstruction of weak and strong lensing data with WSLAP

abstract:
  We describe a method to estimate the mass distribution of a gravitational
lens and the position of the sources from combined strong and weak lensing
data. The algorithm combines weak and strong lensing data in a unified way
producing a solution which is valid in both the weak and strong lensing
regimes. We study how the result depends on the relative weighting of the weak
and strong lensing data and on choice of basis to represent the mass
distribution. We find that combining weak and strong lensing information has
two major advantages: it eliminates the need for priors and/or regularization
schemes for the intrinsic size of the background galaxies (this assumption was
needed in previous strong lensing algorithms) and it corrects for biases in the
recovered mass in the outer regions where the strong lensing data is less
sensitive. The code is implemented into a software package called WSLAP (Weak &
Strong Lensing Analysis Package) which is publicly available at
http://darwin.cfa.harvard.edu/SLAP/


title:
Submillimeter observations of Distant Red Galaxies: uncovering the 1mJy
  850um-population

abstract:
  We present a study of the submillimeter (submm) emission of Distant Red
Galaxies (DRGs). The DRGs are selected by the criterion (J-K)>2.3, and are
generally massive galaxies at redshifts higher than 2, with red rest-frame
optical colors. Using a deep SCUBA submm image of a field centred on the
cluster MS1054-03, we obtain a statistical detection of the DRGs at redshift
z=2-3.5, with an average 850um flux density of 1.11+-0.28mJy. The detection
implies an average star formation rate (SFR) of 127+-34 M_sun/yr (lensing
corrected), assuming that the far-infrared (FIR) spectral energy distribution
(SED) is well-described by a modified blackbody. The SFR derived from the submm
agrees well with SFRs derived from SED fitting of optical-near-infrared data
and average X-ray emission. Constant Star Formation models imply ages of 2Gyr,
extinction A_V=2.4 mag, which is consistent with the FIR to rest-frame optical
luminosity ratio of ~15. DRGs are older and have lower SFRs relative to optical
luminosity than (ultra-)luminous infrared galaxies, although their FIR
luminosities are similar. The DRGs at 2<z<3.5 and the Extremely Red Objects
((I-K)>4) at 1<z<2, which were also investigated, contribute 5.7 and 5.9 Jy
deg^-2 respectively to the submm background. Simple estimates suggest that
these populations contribute ~50% of the flux from sources with 0.5 < f_850 < 5
mJy, which is where the peak of energy is produced. We have therefore uncovered
one of the most important populations of galaxies contributing to the sub-mm
background.


title:
Probing Post-Newtonian Gravity near the Galactic Black Hole with Stellar
  Doppler Measurements

abstract:
  Stars closely approaching the massive black hole in the center of the Galaxy
provide a unique opportunity to probe post-Newtonian physics in a yet
unexplored regime of celestial mechanics. Recent advances in infrared stellar
spectroscopy allow the precise measurement of stellar Doppler shift curves and
thereby the detection of beta-squared post-Newtonian effects (gravitational
redshift in the black hole's potential and the transverse Doppler shift). We
formulate a detection procedure in terms of a simplified post-Newtonian
parametrization. We then use simulations to show that these effects can be
decisively detected with existing instruments after about a decade of
observations. We find that neglecting these effects can lead to statistically
significant systematic errors in the derived black hole mass and distance.


title:
The Rest-Frame FUV Morphologies of Star-Forming Galaxies at z ~ 1.5 and
  z ~ 4

abstract:
  We apply a new approach to quantifying galaxy morphology and identifying
galaxy mergers to the rest-frame far-ultraviolet images of 82 z ~ 4 Lyman break
galaxies (LBGs) and 55 1.2 < z < 1.8 emission-line galaxies in the GOODS and
Ultra Deep Fields. We compare the distributions of the Gini coefficient (G),
second-order moment of the brightest 20% of galaxy light (M20), and
concentration (C) for high-redshift and low-redshift galaxies with average
signal to noise per pixel > 2.5 and Petrosian radii > 0.3 arcsec. Ten of the 82
LBGs have M20 >= -1.1 and possess bright double or multiple nuclei, implying a
major-merger fraction of star-forming galaxies ~ 10-25% at M_{FUV} < -20,
depending on our incompleteness corrections. Galaxies with bulge-like
morphologies (G >= 0.55, M20 < -1.6) make up ~ 30% of the z ~ 4 LBG sample,
while the remaining ~ 50% have G and M20 values higher than expected for smooth
bulges and disks and may be star-forming disks, minor-mergers or post-mergers.
The star-forming z ~ 1.5 galaxy sample has a morphological distribution which
is similar to the UDF z ~ 4 LBGs, with an identical fraction of major-merger
candidates but fewer spheroids. The observed morphological distributions are
roughly consistent with current hierarchical model predictions for the
major-merger rates and minor-merger induced starbursts at z ~ 1.5 and ~4. We
also examine the rest-frame FUV-NUV and FUV-B colors as a function of
morphology and find no strong correlations at either epoch.


title: The Star Formation Threshold in NGC 6822

abstract:
  We investigate the star formation threshold in NGC 6822, a nearby Local Group
dwarf galaxy, on sub-kpc scales using high-resolution, wide-field, deep HI,
Halpha and optical data. In a study of the HI velocity profiles we identify a
cool and warm neutral component in the Interstellar Medium of NGC 6822. We show
that the velocity dispersion of the cool component (~4 km/s) when used with a
Toomre-Q criterion gives an optimal description of ongoing star formation in
NGC 6822, superior to that using the more conventional dispersion value of 6
km/s. However, a simple constant surface density criterion for star formation
gives an equally superior description. We also investigate the two-dimensional
distribution of Q and the star formation threshold and find that these results
also hold locally. The range in gas density in NGC 6822 is much larger than the
range in critical density, and we argue that the conditions for star formation
in NGC 6822 are fully driven by this density criterion. Star formation is
local, and in NGC 6822 global rotational or shear parameters are apparently not
important.


title:
Some comments on the high energy emission from regions of star formation
  beyond the galaxy

abstract:
  Regions that currently are or have been subject to a strong process of star
formation are good candidates to be intense gamma-ray and neutrino emitters.
They may even perhaps be sites where ultra high energy cosmic rays are
produced. Outside the Galaxy, the more powerful sites of star formation are
found within very active galaxies such as starbursts (SGs) and Luminous or
Ultra-Luminous Infrared Galaxies (LIRGs or ULIRGs). Some general characteristic
of these objects are herein reviewed from the point of view of their possible
status as high energy emitters. Revised estimations of the high energy
gamma-ray yield of Arp 220 are presented.


title:
The Low Quiescent X-Ray Luminosity of the Transient X-Ray Burster EXO
  1747-214

abstract:
  We report on X-ray and optical observations of the X-ray burster EXO
1747-214. This source is an X-ray transient, and its only known outburst was
observed in 1984-1985 by the EXOSAT satellite. We re-analyzed the EXOSAT data
to derive the source position, column density, and a distance upper limit using
its peak X-ray burst flux. We observed the EXO 1747-214 field in 2003 July with
the Chandra X-ray Observatory to search for the quiescent counterpart. We found
one possible candidate just outside the EXOSAT error circle, but we cannot rule
out the possibility that the source is unrelated to EXO 1747-214. Our
conclusion is that the upper limit on the unabsorbed 0.3-8 keV luminosity is L
< 7E31 erg/s, making EXO 1747-214 one of the faintest neutron star transients
in quiescence. We compare this luminosity upper limit to the quiescent
luminosities of 19 neutron star and 14 black hole systems and discuss the
results in the context of the differences between neutron stars and black
holes. Based on the theory of deep crustal heating by Brown and coworkers, the
luminosity implies an outburst recurrence time of >1300 yr unless some form of
enhanced cooling occurs within the neutron star. The position of the possible
X-ray counterpart is consistent with three blended optical/IR sources with
R-magnitudes between 19.4 and 19.8 and J-magnitudes between 17.2 and 17.6. One
of these sources could be the quiescent optical/IR counterpart of EXO 1747-214.


title: Black Hole Spectral States and Physical Connections

abstract:
  The dramatic changes seen in the X-ray spectral and timing properties of
accreting black hole candidates (BHCs) provide important clues about the
accretion and jet formation processes that occur in these systems. Dividing the
different source behaviors into spectral states provides a framework for
studying BHCs. To date, there have been three main classification schemes with
Luminosity-based, Component-based, or Transition-based criteria. The canonical,
Luminosity-based criteria and physical models that are based on this concept do
not provide clear explanations for several phenomena, including hysteresis of
spectral states and the presence of jets. I discuss the re-definitions of
states, focusing on an application of the Component-based states to more than
400 RXTE observations of the recurrent BHC 4U 1630-47. We compare the X-ray
properties for the recent 2002-2004 outburst to those of an earlier (1998)
outburst, during which radio jets were observed. The results suggest a
connection between hysteresis of states and major jet ejections, and it is
possible that both of these are related to the evolution of the inner radius of
the optically thick accretion disk.


title:
Extrasolar planets and brown dwarfs around A-F type stars. I.
  Performances of radial velocity measurements, first analyses of variations

abstract:
  We present the performances of a radial velocity measurement method that we
developed for A-F type stars. These perfomances are evaluated through an
extensive set of simulations, together with actual radial velocity observations
of such stars using the ELODIE and HARPS spectrographs. We report the case of
stars constant in radial velocity, the example of a binary detection on HD
48097 (an A2V star, with vsini equal to 90 km/s) and a confirmation of the
existence of a 3.9 MJup planet orbiting around HD 120136 (Tau Boo). The
instability strip problem is also discussed. We show that with this method, it
is in principle possible to detect planets and brown dwarfs around A-F type
stars, thus allowing further study of the impact of stellar masses on planetary
system formation over a wider range of stellar masses than is currently done.


title:
Extrasolar planets and brown dwarfs around A-F type stars. II. A planet
  found with ELODIE around the F6V star HD 33564

abstract:
  We present here the detection of a planet orbiting around the F6V star HD
33564. The radial velocity measurements, obtained with the ELODIE echelle
spectrograph at the Haute-Provence Observatory, show a variation with a period
of 388 days. Assuming a primary mass of 1.25 Mo, the best Keplerian fit to the
data leads to a minimum mass of 9.1 MJup for the companion.


title: Abundances in the high-redshift Intergalactic Medium

abstract:
  The enrichment of the intergalactic medium (IGM) with heavy elements provides
us with a record of past star formation and with an opportunity to study the
interactions between galaxies and their environments. We summarize current data
analysis methods and observational constraints on abundances in the diffuse,
high-redshift (z > 2) IGM. This review is targeted at interested outsiders and
attempts to answer the following questions: Why should you care? What do we
want to measure? How do we do it? What do we know? What are the common
misconceptions?


title:
Oxygen Gas Abundances at 0.4<z<1.5: Implications for the Chemical
  Evolution History of Galaxies

abstract:
  We report VLT-ISAAC and Keck-NIRSPEC near-infrared spectroscopy for a sample
of 30 0.47<z<0.92 CFRS galaxies and five [OII]-selected, M_B,AB<-21.5, z~1.4
galaxies. We have measured Halpha and [NII] line fluxes for the CFRS galaxies
which have [OII], Hbeta and [OIII] line fluxes available from optical
spectroscopy. For the z~1.4 objects we measured Hbeta and [OIII] emission line
fluxes from J-band spectra, and Halpha line fluxes plus upper limits for [NII]
fluxes from H-band spectra. We derive the extinction and oxygen abundances for
the sample using a method based on a set of ionisation parameter and oxygen
abundance diagnostics, simultaneously fitting the [OII], Hbeta, [OIII], Halpha
and [NII] line fluxes. Our most salient conclusions are: a) the source of gas
ionisation in the 30 CFRS and in all z~1.4 galaxies is not due to AGN activity;
b) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have
substantially lower metallicities than local galaxies with similar luminosities
and star formation rates; c) comparison with a chemical evolution model
indicates that these low metallicity galaxies are unlikely to be the
progenitors of metal-poor dwarf galaxies at z~0, but more likely the
progenitors of massive spirals; d) the z~1.4 galaxies are characterized by the
high [OIII]/[OII] line ratios, low extinction and low metallicity that are
typical of lower luminosity CADIS galaxies at 0.4<z<0.7, and of more luminous
Lyman Break Galaxies at z~3.1, but not seen in CFRS galaxies at 0.4<z<1.0; e)
the properties of the z~1.4 galaxies suggest that the period of rapid chemical
evolution takes place progressively in lower mass systems as the universe ages,
and thus provides further support for a downsizing picture of galaxy formation,
at least from z~1.4 to today.


title: The nuclei of comets 7P/Pons-Winnecke, 14P/Wolf and 92P/Sanguin

abstract:
  Jupiter Family comets (JFCs) are short period comets which have recently
entered the inner solar system, having previously orbited in the Kuiper Belt
since the formation of the planets. We used two nights on the 3.6m New
Technology Telescope (NTT) at the European Southern Observatory, to obtain VRI
photometry of three JFCs; 7P/Pons-Winnecke, 14P/Wolf and 92P/Sanguin. These
were observed to be stellar in appearance. We find mean effective radii of 2.24
\pm 0.02 km for 7P, 3.16 \pm 0.01 km for 14P and 2.08 \pm 0.01 km for 92P,
assuming a geometric albedo of 0.04. From light-curves for each comet we find
rotation periods of 7.53 \pm 0.10 and 6.22 \pm 0.05 hours for 14P and 92P
respectively. 7P exhibits brightness variations which imply a rotation period
of 6.8 \le P_rot \le 9.5 hours. Assuming the nuclei to be ellipsoidal the
measured brightness variations imply minimum axial ratios a/b of 1.3 \pm 0.1
for 7P and 1.7 \pm 0.1 for both 14P and 92P. This in turn implies minimum
densities of 0.23 \pm 0.08 g cm^{-3} for 7P, 0.32 \pm 0.02 g cm^{-3} for 14P
and 0.49 \pm 0.06 g cm^{-3} for 92P. Finally, we measure colour indices of
(V-R) = 0.40 \pm 0.05 and (R-I) = 0.41 \pm 0.06 for 7P/Pons-Winnecke, (V-R) =
0.57 \pm 0.07 and (R-I) = 0.51 \pm 0.06 for 14P/Wolf, and (V-R) = 0.54 \pm 0.04
and (R-I) = 0.54 \pm 0.04 for 92P/Sanguin.


title:
Active Galactic Nuclei In Cosmological Simulations - I. Formation of
  black holes and spheroids through mergers

abstract:
  The Active Galactic Nuclei In Cosmological Simulations (AGNICS) project
includes AGN into the GalICS hybrid (N-body + semi-analytic) model to explore
the quasar-galaxy link in a cosmological perspective. The key problems are the
quasar fuelling mechanism, the origin of the BH to bulge mass relation, the
causal and chronological link between BH growth and galaxy formation, the
properties of quasar hosts and the role of AGN feedback in galaxy formation.
This first paper has two goals: to describe the general structure and the
assumptions of the method, and to apply AGNICS to studying the joint formation
of BHs and spheroids in galaxy mergers. We investigate under what conditions
this scenario can reproduce the local BH distribution and the evolution of the
quasar population. AGNICS contains two star formation modes: a quiescent one in
discs and a starburst one in protospheroids, the latter triggered by mergers
and disc instabilities. We assume that BH growth is linked to the starburst
mode. The simplest version of this scenario, in which the BH accretion rate and
the star formation rate in the starburst component are simply related by a
constant of proportionality, does not to reproduce the cosmic evolution of the
quasar population. A model in which this relation is modulated by a scaling
with the square root of the starburst gas density can explain the evolution of
the quasar luminosity function in B-band and X-rays (accounting for the
obscuration inferred from X-ray studies). The scatter and the tilt that this
model introduces in the BH-to-bulge mass relation are within the observational
constraints. The quasar contribution grows with bolometric luminosity and for a
given bulge mass the most massive BHs are in the bulges with the oldest stars.


title: INTEGRAL three years later

abstract:
  The ESA INTErnational Gamma-Ray Astrophyisics Laboratory (INTEGRAL) is
composed of two main instruments (IBIS and SPI) for the gamma-ray astrophysics
(20 keV - 10 MeV), plus two monitors (JEM-X and OMC) for X-ray and optical
counterparts. It was launched on October 17th, 2002, from the Baikonur
cosmodrome (Kazakhstan) and it will be active at least up to 2008. A selection
of its main scientific contributions obtained to date are presented.


title: Neutrons and antiprotons in ultrahigh energy cosmic rays

abstract:
  The neutron fraction in the very high energy cosmic rays near the
Greisen-Zatsepin-Kuzmin (GZK) cutoff energy is analyzed by taking into account
the time dilation effect of the neutron decays and also the pion
photoproduction behaviors above the GZK cutoff. We predict a non-trivial
neutron fraction above the GZK cutoff and a negligibly small neutron fraction
below. However, there should be a large antiproton fraction in the high energy
cosmic rays below the GZK cutoff in several existing models for the observed
cosmic-ray events above and near the GZK cutoff. Such a large antiproton
fraction can manifest itself by the muon charge ratio $\mu^+/\mu^-$ in the
collisions of the primary nucleon cosmic rays with the atmosphere, if there is
no neutron contribution. We suggest to use the muon charge ratio as one of the
information to detect the composition of the primary cosmic rays near or below
the GZK cutoff.


title: On the evolutionary status of Be stars. I. Field Be stars near the Sun

abstract:
  A sample of 97 galactic field Be stars were studied by taking into account
the effects induced by the fast rotation on their fundamental parameters. All
program stars were observed in the BCD spectrophotometric system in order to
minimize the perturbations produced by the circumstellar environment on the
spectral photospheric signatures. This is one of the first attempts at
determining stellar masses and ages by simultaneously using model atmospheres
and evolutionary tracks, both calculated for rotating objects. The stellar ages
($\tau$) normalized to the respective inferred time that each rotating star can
spend in the main sequence phase ($\tau\_{\rm MS}$) reveal a mass-dependent
trend. This trend shows that: a) there are Be stars spread over the whole
interval $0 \la \tau/\tau\_{\rm MS} \la 1$ of the main sequence evolutionary
phase; b) the distribution of points in the ($\tau/\tau\_{\rm
MS},M/M\_{\odot}$) diagram indicates that in massive stars ($M \ga
12M\_{\odot}$) the Be phenomenon is present at smaller $\tau/\tau\_{\rm MS}$
age ratios than for less massive stars ($M \la 12M\_{\odot}$). This
distribution can be due to: $i$) higher mass-loss rates in massive objets,
which can act to reduce the surface fast rotation; $ii$) circulation time
scales to transport angular momentum from the core to the surface, which are
longer the lower the stellar mass.


title: Discovery of Ultra-Compact Dwarf Galaxies in the Virgo Cluster

abstract:
  We have discovered nine ultra-compact dwarf galaxies (UCDs) in the Virgo
Cluster, extending samples of these objects outside the Fornax Cluster. Using
the 2dF multi-fiber spectrograph on the Anglo-Australian Telescope, the new
Virgo members were found among 1500 color-selected, star-like targets with 16.0
< b_j < 20.2 in a two-degree diameter field centered on M87 (NGC4486). The
newly-found UCDs are comparable to the UCDs in the Fornax Cluster, with sizes
<~ 100 pc, -12.9 < M_B < -10.7, and exhibiting red, absorption-line spectra,
indicative of an older stellar population. The properties of these objects
remain consistent with the tidal threshing model for the origin of UCDs from
the surviving nuclei of nucleated dwarf ellipticals disrupted in the cluster
core, but can also be explained as objects that were formed by mergers of star
clusters created in galaxy interactions. The discovery that UCDs exist in Virgo
shows that this galaxy type is probably a ubiquitous phenomenon in clusters of
galaxies; coupled with their possible origin by tidal threshing, the UCD
population is a potential indicator and probe of the formation history of a
given cluster.
  We also describe one additional bright UCD with M_B = -12.0 in the core of
the Fornax Cluster. We find no further UCDs in our Fornax Cluster Spectroscopic
Survey down to b_j = 19.5 in two additional 2dF fields extending as far as 3
degrees from the center of the cluster. All six Fornax bright UCDs identified
with 2dF lie within 0.5 degree (projected distance of 170 kpc) of the central
elliptical galaxy NGC1399.


title: Rotation velocities of white dwarfs determined from the CaII K line

abstract:
  We determine projected rotation velocities v sini in DAZ white dwarfs, for
the first time using the rotational broadening of the CaII K line. The results
confirm previous findings that white dwarfs are very slow rotators, and set
even more stringent upper limits of typically less than 10 km/s. The few
exceptions include 3 stars known or suspected to be variable ZZ Ceti stars,
where the line broadening is very likely not due to rotation. The results
demonstrate that the angular momentum of the core cannot be preserved
completely between main sequence and final stage.


title: Ultrahigh Energy Cosmic Rays Detection

abstract:
  The paper describes methods used for the detection of cosmic rays with
energies above 10^18 eV (UHECR, UltraHigh Energy Cosmic Rays). It had been
anticipated there would be a cutoff in the energy spectrum of primary cosmic
rays around 3 10^19 eV induced by their interaction with the 2.7 K primordial
photons. This has become known as the GZK cutoff. However, several showers have
been detected with estimated primary energy exceeding this limit.


title: INTEGRAL observations of AGN in the Galactic Plane

abstract:
  We present results on approximately one year of INTEGRAL observations of six
AGN detected during the regular scans of the Galactic Plane. The sample is
composed by five Seyfert 2 objects (MCG -05-23-16, NGC 4945, the Circinus
galaxy, NGC 6300, ESO 103-G35) and the radio galaxy Centaurus A. The continuum
emission of each of these sources is well represented by a highly absorbed (NH
> 1e22 1/cm^2) power law, with average spectral index Gamma = 1.9 +/- 0.3. A
high energy exponential cut-off at Ec ~ 50 keV is required to fit the spectrum
of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC
4945 and no cut-off has been detected for NGC 6300 in the energy range covered
by these INTEGRAL data. The flux of Centaurus A was found to vary by a factor
of ~ 2 in 10 months, showing a spectral change between the high and low state,
which can be modelled equally well by a change in the absorption (NH from 17e22
to 33e22 1/cm^2) or by the presence of a cut-off at >~ 120 keV in the low state
spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a
general agreement with INTEGRAL results. The high energy cut-off in the hard
X-ray spectra appears to be a common but not universal characteristic of
Seyfert 2 and to span a wide range of energies.


title: Most supermassive black hole growth is obscured by dust

abstract:
  We present an alternative method to X-ray surveys for hunting down the
high-redshift type-2 quasar population, using Spitzer and VLA data on the
Spitzer First Look Survey. By demanding objects to be bright at 24 microns but
faint at 3.6 microns, and combining this with a radio criterion, we find 21
type-2 radio-quiet quasar candidates at the epoch at which the quasar activity
peaked. Optical spectroscopy with the WHT confirmed 10 of these objects to be
type-2s with 1.4 < z < 4.2 while the rest are blank. There is no evidence for
contamination in our sample, and we postulate that our 11 blank-spectrum
candidates are obscured by kpc-scale dust as opposed to dust from a torus
around the accretion disk. By carefully modelling our selection criteria, we
conclude that, at high redshift, 50-80 % of the supermassive black hole growth
is obscured by dust.


title:
Open clusters in the Third Galactic Quadrant. II. The intermediate age
  open clusters NGC 2425 and NGC 2635

abstract:
  We analyse CCD broad band (UBV(RI)c) photometric data obtained in the fields
of the poorly studied open clusters NGC 2425 and NGC 2635. Both clusters are
found to be of intermediate age thus increasing the population of open clusters
known to be of the age of, or older than, the Hyades. More explicitly, we find
that NGC 2425 is a 2.2 Gyr old cluster, probably of solar metallicity, located
at 3.5 kpc from the Sun. NGC 2635 is a Hyades age (600 Myr) cluster located at
a distance of 4.0 kpc from the Sun. Its Colour Magnitude Diagram reveals that
it is extremely metal poor for its age and position, thus making it a very
interesting object in the context of Galactic Disk chemical evolution models.


title:
The life-time of galactic bars: central mass concentrations and gravity
  torques

abstract:
  Bars in gas-rich spiral galaxies are short-lived. They drive gas inflows
through their gravity torques, and at the same time self-regulate their
strength. Their robustness has been subject of debate, since it was thought
that only the resulting central mass concentrations (CMCs) were weakening bars,
and only relatively rare massive CMCs were able to completely destroy them.
Through numerical simulations including gas dynamics, we find that with the gas
parameters of normal spiral galaxies, the CMC is not sufficient to fully
dissolve the bar. But another overlooked mechanism, the transfer of angular
momentum from the infalling gas to the stellar bar, can also strongly weaken
the bar. In addition, we show that gravity torques are correctly reproduced in
simulations, and conclude that bars are transient features, with life-time of
1-2 Gyr in typical Sb-Sc galaxies, because of the combined effects of CMCs and
gravity torques, while most existing works had focussed on the CMC effects
alone.


title:
Molecular cloud evolution. I. Molecular cloud and thin CNM sheet
  formation

abstract:
  We discuss molecular cloud formation by large-scale supersonic compressions
in the diffuse warm neutral medium (WNM). Initially, a shocked layer forms, and
within it, a thin cold layer. An analytical model and high-resolution 1D
simulations predict the thermodynamic conditions in the cold layer. After $\sim
1$ Myr of evolution, the layer has column density $\sim 2.5 \times 10^{19}
\psc$, thickness $\sim 0.03$ pc, temperature $\sim 25$ K and pressure $\sim
6650$ K $\pcc$. These conditions are strongly reminiscent of those recently
reported by Heiles and coworkers for cold neutral medium sheets. In the 1D
simulations, the inflows into the sheets produce line profiles with a central
line of width $\sim 0.5 \kms$ and broad wings of width $\sim 1 \kms$. 3D
numerical simulations show that the cold layer develops turbulent motions and
increases its thickness, until it becomes a fully three-dimensional turbulent
cloud. Fully developed turbulence arises on times ranging from $\sim 7.5$ Myr
for inflow Mach number $\Mr = 2.4$ to $> 80$ Myr for $\Mr = 1.03$. These
numbers should be considered upper limits. The highest-density turbulent gas
(HDG, $n > 100 \pcc$) is always overpressured with respect to the mean WNM
pressure by factors 1.5--4, even though we do not include self-gravity. The
intermediate-density gas (IDG, $10 < n [{\rm cm}^ {-3}] < 100$) has a
significant pressure scatter that increases with $\Mr$, so that at $\Mr = 2.4$,
a significant fraction of the IDG is at a higher pressure than the HDG. Our
results suggest that the turbulence and at least part of the excess pressure in
molecular clouds can be generated by the compressive process that forms the
clouds themselves, and that thin CNM sheets may be formed transiently by this
mechanism, when the compressions are only weakly supersonic.


title: Deep spectroscopy of a young radio source at z=0.521

abstract:
  9C J1503+4528 is a very young CSS radio galaxy, with an age of order 10^4
years. This source is an ideal laboratory for the study of the intrinsic host
galaxy/IGM properties, radio source interactions, evidence for young stellar
populations and the radio source triggering mechanism. Here we present the
results of a spectroscopic analysis of this source, considering each of these
aspects of radio source physics.


title: Outflows and shocks in compact radio sources

abstract:
  We report some key results from the optical emission line study of a complete
sample of compact radio sources. We find strong evidence for jet-driven
outflows in the circum-nuclear emission line gas namely: 1) highly broadened
and blueshifted emission line components (up to 2000 km/s), 2) shock ionised
gas (broader, shifted components), 3) consistency in the scales of the emission
line gas and the radio source and 4) trends between the maximum outflow
velocity and radio source size (and orientation). Full details can be found in
Holt (2005).


title:
Analytic Solutions to the Constraint Equation for a Force-Free
  Magnetosphere around a Kerr Black Hole

abstract:
  The Blandford-Znajek constraint equation for a stationary, axisymmetric
black-hole force-free magnetosphere is cast in a 3+1 absolute space and time
formulation, following Komissarov (2004). We derive an analytic solution for
fields and currents to the constraint equation in the far-field limit that
satisfies the Znajek condition at the event horizon. This solution generalizes
the Blandford-Znajek monopole solution for a slowly rotating black hole to
black holes with arbitrary angular momentum. Energy and angular momentum
extraction through this solution occurs mostly along the equatorial plane. We
also present a nonphysical, reverse jet-like solution.


title: The far-infrared properties of the most isolated galaxies

abstract:
  Although it is widely accepted that galaxy interactions stimulate secular
evolutionary effects (e.g. enhanced star formation) the amplitude of this
effect and the processes for accomplishing them, are not well quantified. The
goal of the project AMIGA (Analysis of the Interstellar Medium of Isolated
Galaxies) is to provide a sizable reference sample (n=1050) of the most
isolated galaxies as a basis for the study of the influence of the environment
on galaxy properties. Here, we present the far-infrared (FIR) properties of
1030 galaxies of the sample for which IRAS data are available. We improved the
detection rate and accuracy of the IRAS data with respect to the Point Source
and Faint Source Catalog by redoing the data reduction with the IPAC utility
ADDSCAN/SCANPI. Comparing the FIR to the blue luminosities, we find a slightly
non-linear relation. Furthermore, we find that interacting galaxies tend to
have an enhanced FIR emission.


title:
Deep Near-Infrared Imaging and Photometry of the Antennae Galaxies with
  WIRC

abstract:
  We present deep near-infrared images of the Antennae galaxies, taken with the
Palomar Wide-Field Infrared Camera WIRC. The images cover a 4.33' x 4.33'
(24.7kpc x 24.7kpc) area around the galaxy interaction zone. We derive J and
K_s band photometric fluxes for 172 infrared star clusters, and discuss details
of the two galactic nuclei and the overlap region. We also discuss the
properties of a subset of 27 sources which have been detected with WIRC, HST
and the VLA. The sources in common are young clusters of less than 10 Myr,
which show no correlation between their infrared colors and 6 cm radio
properties. These clusters cover a wide range in infrared color due to
extinction and evolution. The average extinction is about A_V~2 mag while the
reddest clusters may be reddened by up to 10 magnitudes.


title:
Outburst of the X-ray transient SAX J1818.6-1703 detected by INTEGRAL in
  September 2003

abstract:
  During the observation of the Galactic-center field by the INTEGRAL
observatory on September 9, 2003, the IBIS/ISGRI gamma-ray telescope detected a
short (several-hours-long) intense (~380 mCrab at the peak) outburst of hard
radiation from the X-ray transient SAX J1818.6-1703. Previously, this source
was observed only once in 1998 during a similar short outburst. We present the
results of our localization, spectral and timing analyses of the object and
briefly discuss the possible causes of the outburst. The release time of the
bulk of the energy in such an outburst is appreciably shorter than the
accretion (viscous) time that characterizes the flow of matter through a
standard accretion disk.


title:
Radial velocity survey for planets and brown dwarf companions to very
  young brown dwarfs and very low-mass stars in ChaI with UVES at the VLT

abstract:
  We present results of a radial velocity (RV) survey for planets and brown
dwarf (BD) companions to very young BDs and (very) low-mass stars (VLMSs) in
ChaI. High-resolution echelle spectra of ChaHa1-8 and 12 (M6-M8), and B34,
CHXR74, Sz23 (M2.5-M5) were taken with UVES / VLT between 2000 and 2004. The
achieved precision (40 to 670 m/s) is sufficient to detect Jupiter mass planets
around the targets. This first RV survey of very young BDs probes multiplicity
which is a key parameter for formation in an as yet unexplored domain, in terms
of age, mass, and orbital separation. We find that the subsample of ten BDs and
VLMSs (M<0.12 Msun, M5-M8) has constant RVs on time scales of <40 days. For
them, estimates of upper limits for masses of hypothetical companions are 0.1
to 1.5 MJup (assuming 0.1 AU). This hints at a rather small multiplicity
fraction for very young BDs/VLMSs at <0.1 AU. Furthermore, the non-variable
objects demonstrate the lack of any significant RV noise due to stellar
activity down to the precision necessary to detect giant planets. Thus, very
young BDs and VLMSs are suitable targets for RV surveys for planets. Three
objects of the sample exhibit significant RV variations. For Sz23, they might
be attributed to surface activity, while for ChaHa8 (M6.5) and CHXR74 (M4.5),
the detected RV variations are on times scales of >150 days, which cannot be
explained by rotational modulation. An alternative explanation are giant
planets / BDs of at least a few Jupiter masses orbiting with periods of several
months or longer. Thus, the presented RV data indicate that orbital periods of
companions to very young BDs and (V)LMSs are possibly several months or longer,
and that orbital separations are > 0.2 AU. This parameter range has not been
covered for all targets yet, but will be probed by follow-up observations.


title:
A Snapshot Survey for Gravitational Lenses Among z>=4.0 Quasars: II.
  Constraints on the 4.0<z<4.5 Quasar Population

abstract:
  We report on i-band snapshot observations of 157 Sloan Digital Sky Survey
(SDSS) quasars at 4<z<5.4 using the Advanced Camera for Surveys on the Hubble
Space Telescope (HST) to search for evidence of gravitational lensing of these
sources. None of the quasars appear to be strongly lensed and multiply imaged
at the angular resolution (~0.1") and sensitivity of HST. The non-detection of
strong lensing in these systems constrains the z=4-5 luminosity function to an
intrinsic slope of beta>-3.8 (3 sigma), assuming a break in the quasar
luminosity function at M_1450^star=-24.5. This constraint is considerably
stronger than the limit of beta>-4.63 obtained from the absence of lensing in
four z>5.7 quasars. Such constraints are important for our understanding of the
true space density of high-redshift quasars and the ionization state of the
early universe.


title:
XMM Spectroscopy of the Transient Supersoft Source RX J0513.9-6951:
  probing the dynamic white dwarf photosphere

abstract:
  The highly luminous (> 10^37 erg s^-1) supersoft X-ray sources (SSS) are
believed to be Eddington limited accreting white dwarfs undergoing surface
hydrogen burning. The current paradigm for SSS involves thermally unstable mass
transfer from a 1-2 solar mass companion. However this model has never been
directly confirmed and yet is crucial for the evolution of cataclysmic
variables in general, and for the establishment of SSS as progenitors of type
Ia supernovae in particular. The key SSS is RX J0513.9-6951 which has recurrent
X-ray outbursts every 100-200 d (lasting for ~40 d) during which the optical
declines by 1 mag. We present the first XMM-Newton observations of RX
J0513.9-6951 through one of its optical low states. Our results show that as
the optical low state progresses the temperature and the X-ray luminosity
decrease, behaviour that is anti-correlated with the optical and UV emission.
We find that as the optical (and UV) intensity recover the radius implied by
the spectral fits increases. The high resolution spectra show evidence of deep
absorption features which vary during the optical low state. Our results are
consistent with the predictions of the white dwarf photospheric contraction
model proposed by Southwell et al. 1996.


title: Spherical Isothermal Self-Similar Shock Flows

abstract:
  We explore self-similar dynamical processes in a spherical isothermal
self-gravitational fluid with an emphasis on shocks and outline astrophysical
applications of such shock solutions. The previous similarity shock solutions
of Tsai & Hsu and of Shu et al. may be classified into two types: Class I
solutions with downstream being free-fall collapses and Class II solutions with
downstream being Larson-Penston (LP) type solutions. By the analyses of Lou &
Shen and Shen & Lou, we further construct similarity shock solutions in the
`semi-complete space'. These general shock solutions can accommodate and model
dynamical processes of radial outflows (wind), inflows (accretion or
contraction), subsonic oscillations, and free-fall core collapses all with
shocks in various settings such as star-forming molecular clouds, `champagne
flows' in H{\sevenrm II} regions around luminous massive OB stars or
surrounding quasars, dynamical connection between the asymptotic giant branch
phase to the proto-planetary nebula phase with a central hot white dwarf as
well as accretion shocks around compact objects such as white dwarfs, neutron
stars, and supermassive black holes. By a systematic exploration, we are able
to construct families of infinitely many discrete Class I and Class II
solutions matching asymptotically with a static outer envelope of singular
isothermal sphere; the shock solutions of Tsai & Hsu form special subsets.
These similarity shocks travel at either subsonic or supersonic constant
speeds. We also construct twin shocks as well as an `isothermal shock'
separating two fluid regions of two different yet constant temperatures.


title: The Radio Luminosity Function of the NEP Distant Cluster Radio Galaxies

abstract:
  A complete sample of 18 X-ray selected clusters of galaxies belonging to the
ROSAT North Ecliptic Pole (NEP) survey has been observed with the Very Large
Array at 1.4 GHz. These are the most distant clusters in the X-ray survey with
redshift in the range 0.3 < z < 0.8.Seventy-nine radio sources are detected
within half an Abell radius with an observed peak brightness >=0.17 mJy/beam,
except for three sources, belonging to the same cluster, which have a higher
peak brightness limit of 0.26 mJy/beam. The NEP field source counts are in good
agreement with the source counts of a comparison survey, the VLA-VIRMOS deep
field survey, indicating that the NEP sample is statistically complete.
Thirty-two out of the 79 sources are within 0.2 Abell radii, twenty-two of them
are considered cluster members based on spectroscopic redshifts or their
optical magnitude and morphological classification. The cluster radio galaxies
are used to construct the Radio Luminosity Function (RLF) of distant X-ray
selected clusters. A comparison with two nearby cluster RLFs shows that the NEP
RLF lies above the local ones, has a steeper slope at low radio powers (<=
10^(24) W/Hz) and shows no evidence for a break at about 6 X 10^(24) W/Hz which
is observed in the nearby cluster RLFs. We discuss briefly the origin and
possible explanations of the differences observed in the radio properties of
nearby and distant clusters of galaxies. The main result of this study is that
the RLF of the distant X-ray clusters is very different from that of the local
rich Abell clusters.


title: On the evolutionary connection between AGB stars and PNe

abstract:
  The `O-rich AGB sequence' is a sequence of colours describing the location of
O-rich AGB stars in the IRAS two-colour diagram [12]--[25] vs [25]--[60]. We
propose an evolutionary scenario for this sequence in which all stars,
independent of their progenitor mass, start the AGB phase in the blue part of
the `O-rich AGB sequence' and then evolve toward redder colors, although only
the more massive stars would reach the very end of the `O-rich AGB sequence'.
The sources located in the blue part of the sequence are mainly Mira variables,
whose mean period is increasing with the IRAS colours. Most of them will evolve
into O-rich Type II (and III) Planetary Nebulae. Part of the stars located in
the red part of the sequence will change their chemical composition from O-rich
to C-rich during their evolution in the AGB phase, and might evolve into C-rich
Type II Planetary Nebulae. Hot bottom burning may prevent the conversion to
carbon stars of the rest of sources located in the red part of the sequence and
they will end up as N-rich Type I Planetary Nebulae.


title:
Detection of inclined and horizontal showers in the Pierre Auger
  Observatory

abstract:
  The Pierre Auger Observatory can detect with high efficiency the air showers
induced by ultra-high energy cosmic rays incident at large (> 60 deg.) zenith
angles. We describe here the specific characteristics of inclined and
horizontal showers, as well as the characteristics of their signal in the
surface detector. We point out their relevance both to extend the potential of
the detector, and in the context of the detection of high-energy cosmic
neutrinos.


title: Clustering of primordial black holes: Basic results

abstract:
  We investigate the spatial clustering properties of primordial black holes
(PBHs). With minimal assumptions, we show that PBHs created in the radiation
era are highly clustered. Using the peaks theory model of bias, we compute the
PBH two-point correlation function and power spectrum. For creation from an
initially adiabatic power spectrum of perturbations, the PBH power spectrum
contains both isocurvature and adiabatic components. The absence of observed
isocurvature fluctuations today constrains the mass range in which PBHs may
serve as dark matter. We briefly discuss other consequences of PBH clustering.


title:
Do observed metallicity gradients of early-type galaxies support a
  hybrid formation scenario?

abstract:
  We measure radial gradients of the Mg2 index in 15 E-E/S0 and 14 S0 galaxies.
Our homogeneous data set covers a large range of internal stellar velocity
dispersions (2.0<logsigma<2.5) and Mg2 gradients (dMg2/dlogr/re* up to
-0.14mag/dex). We find for the first time, a noticeable lower boundary in the
relation between Mg2 gradient and sigma along the full range of sigma, which
may be populated by galaxies predominantly formed by monolithic collapse. At
high sigma, galaxies showing flatter gradients could represent objects which
suffered either important merging episodes or later gas accretion. These
processes contribute to the flattening of the metallicity gradients and their
increasing importance could define the distribution of the objects above the
boundary expected by the ``classical'' monolithic process. This result is in
marked contrast with previous works which found a correlation between
dMg2/dlogr/re* and sigma confined to the low mass galaxies, suggesting that
only galaxies below some limiting sigma were formed by collapse whereas the
massive ones by mergers. We show observational evidence that a hybrid scenario
could arise also among massive galaxies. Finally, we estimated d[Z/H] from Mg2
and Hbeta measurements and single stellar population models. The conclusions
remain the same, indicating that the results cannot be ascribed to age effects
on Mg2.


title: The Antennae Ultraluminous X-Ray Source, X-37, Is A Background Quasar

abstract:
  In this paper we report that a bright, X-ray source in the Antennae galaxies
(NGC 4038/9), previously identified as an ultra-luminous X-ray source, is in
fact a background quasar. We identify an isolated infrared and optical
counterpart within 0.3+/-0.5 arcseconds the X-ray source X-37. After acquiring
an optical spectrum of its counterpart, we use the narrow [OIII] and broad
H_alpha emission lines to identify X-37 as a quasar at a redshift of z=0.26.
Through a U, V, and K_s photometric analysis, we demonstrate that most of the
observable light along this line of sight is from the quasar. We discuss the
implications of this discovery and the importance of acquiring spectra for
optical and IR counterparts to ULXs.


title:
Optical emission from GRB 050709: a short/hard GRB in a star forming
  galaxy

abstract:
  We present optical observations of the short/hard gamma-ray burst GRB 050709,
the first such event with an identified optical counterpart. The object is
coincident with a weak X-ray source and is located inside a galaxy at redshift
z = 0.1606 +- 0.0002. Multiband photometry allowed us to study the broad-band
spectral energy distribution. Late-time monitoring places strong limits on any
supernova simultaneous with the GRB. The host galaxy is not of early type.
Spectra show that the dominant stellar population is relatively young (~ 1
Gyr), and that ongoing star formation is present at a level of 2-3 (L/L*)
Msun/yr. This is at least 2 orders of magnitude larger than that observed in
the elliptical hosts of the short GRB 050509B and GRB 050724. This shows that
at least some short GRBs originate in a young population. Short/hard GRB models
based on the merger of a binary degenerate system are compatible with the host
galaxy characteristics, although there is still the possibility of a connection
between young stars and at least a fraction of such events.


title: van der Kruit to Spitzer: A New Look at the FIR-Radio Correlation

abstract:
  We present an initial look at the far infrared-radio correlation within the
star-forming disks of four nearby, nearly face-on galaxies (NGC~2403, NGC~3031,
NGC~5194, and NGC~6946). Using {\it Spitzer} MIPS imaging and WSRT radio
continuum data, we are able to probe variations in the logarithmic
70~$\mu$m/22~cm ($q_{70}$) flux density ratios across each disk at sub-kpc
scales. We find general trends of decreasing $q_{70}$ with declining surface
brightness and with increasing radius. We also find that the dispersion in
$q_{70}$ within galaxies is comparable to what is measured {\it globally} among
galaxies at around 0.2 dex. We have also performed preliminary phenomenological
modeling of cosmic ray electron (CR$e^{-}$) diffusion using an image-smearing
technique, and find that smoothing the infrared maps improves their correlation
with the radio maps. The best fit smoothing kernels for the two less active
star-forming galaxies (NGC~2403 and NGC~3031) have much larger scale-lengths
than that of the more active star-forming galaxies (NGC~5194 and NGC~6946).
This difference may be due to the relative deficit of recent CR$e^{-}$
injection into the interstellar medium (ISM) for the galaxies having largely
quiescent disks.


title:
XMM-Newton Spectroscopy of the Highly Polarized and Luminous Broad
  Absorption Line Quasar CSO 755

abstract:
  We present the results from XMM-Newton observations of the highly optically
polarized broad absorption line quasar (BALQSO) CSO 755. By analyzing its X-ray
spectrum with a total of ~3000 photons we find that this source has an X-ray
continuum of `typical' radio-quiet quasars, with a photon index of
Gamma=1.83^{+0.07}_{-0.06}, and a rather flat (X-ray bright) intrinsic
optical-to-X-ray spectral slope of alpha_ox=-1.51. The source shows evidence
for intrinsic absorption, and fitting the spectrum with a neutral-absorption
model gives a column density of N_H~1.2x10^{22} cm^{-2}; this is among the
lowest X-ray columns measured for BALQSOs. We do not detect, with high
significance, any other absorption features in the X-ray spectrum. Upper limits
we place on the rest-frame equivalent width of a neutral (ionized) Fe Ka line,
<=180 eV (<=120 eV), and on the Compton-reflection component parameter, R<=0.2,
suggest that most of the X-rays from the source are directly observed rather
than being scattered or reflected; this is also supported by the relatively
flat intrinsic alpha_ox we measure. The possibility that most of the X-ray flux
is scattered due to the high level of UV-optical polarization is ruled out.
Considering data for 46 BALQSOs from the literature, including CSO 755, we have
found that the UV-optical continuum polarization level of BALQSOs is not
correlated with any of their X-ray properties. A lack of significant short- and
long-term X-ray flux variations in the source may be attributed to a large
black-hole mass in CSO 755. We note that another luminous BALQSO, PG 2112+059,
has both similar shallow C IV BALs and moderate X-ray absorption.


title:
Properties of Galaxy Groups in the SDSS: I.-- The Dependence of Colour,
  Star Formation, and Morphology on Halo Mass

abstract:
  Using a large galaxy group catalogue constructed from the SDSS, we
investigate the correlation between various galaxy properties and halo mass. We
split the population of galaxies in early types, late types, and intermediate
types, based on their colour and specific star formation rate. At fixed
luminosity, the early type fraction increases with increasing halo mass. Most
importantly, this mass dependence is smooth and persists over the entire mass
range probed, without any break or feature at any mass scale. We argue that the
previous claim of a characteristic feature on galaxy group scales is an
artefact of the environment estimators used. At fixed halo mass, the luminosity
dependence of the type fractions is surprisingly weak: galaxy type depends more
strongly on halo mass than on luminosity. We also find that the early type
fraction decreases with increasing halo-centric radius. Contrary to previous
studies, we find that this radial dependence is also present in low mass
haloes. The properties of satellite galaxies are strongly correlated with those
of their central galaxy. In particular, the early type fraction of satellites
is significantly higher in a halo with an early type central galaxy than in a
halo of the same mass but with a late type central galaxy. This phenomenon,
which we call `galactic conformity', is present in haloes of all masses and for
satellites of all luminosities. Finally, the fraction of intermediate type
galaxies is always ~20 percent, independent of luminosity, independent of halo
mass, independent of halo-centric radius, and independent of whether the galaxy
is a central galaxy or a satellite galaxy. We discuss the implications of all
these findings for galaxy formation and evolution.


title: The Evidence of Absence: Galaxy Voids in the Excursion Set Formalism

abstract:
  We present an analytic model for the sizes of voids in the galaxy
distribution. Peebles and others have recently emphasized the possibility that
the observed characteristics of voids may point to a problem in galaxy
formation models, but testing these claims has been difficult without any clear
predictions for their properties. In order to address such questions, we build
a model to describe the distribution of galaxy underdensities. Our model is
based on the "excursion set formalism," the same technique used to predict the
dark matter halo mass function. We find that, because of bias, galaxy voids are
typically significantly larger than dark matter voids and should fill most of
the universe. We show that voids selected from catalogs of luminous galaxies
should be larger than those selected from faint galaxies: the characteristic
radii range from ~5-10h^{-1} Mpc for galaxies with absolute r-band magnitudes
M_r-5 log(h) < -16 to -20. These are reasonably close to, though somewhat
smaller than, the observed sizes. The discrepancy may result from the void
selection algorithm or from their internal structure. We also compute the halo
populations inside voids. We expect small haloes (M<10^{11} Msun) to be up to a
factor of two less underdense than the haloes of normal galaxies. Within large
voids, the mass function is nearly independent of the size of the underdensity,
but finite-size effects play a significant role in small voids (R<7h^{-1} Mpc).


title: Ultraluminous Starbursts from SMBH-induced outflows

abstract:
  I argue that there are two modes of global star formation. Disks and smaller
spheroids form stars relatively inefficiently as a consequence of
supernova-triggered negative feedback via a sequence of ministarbursts (S
mode), whereas massive spheroids formed rapidly with high efficiency via the
impact of AGN jet-triggered positive feedback (J mode) that generates and
enhances ultraluminous starbursts. Supermassive black hole growth by accretion
is favoured in the gas-rich protospheroid environment as mergers build up the
mass of the host galaxy and provide a centrally concentrated gas supply.
Quasi-spherical outflows arise and provide the source of porosity as the
energetic jets from the accreting central SMBH are isotropised by the
inhomogeneous interstellar medium in the protospheroid core. Super-Eddington
outflows occur and help generate both the SMBH at high redshift and the strong
positive feedback on protospheroid star formation that occurs as dense
interstellar clouds are overpressured and collapse. SMBH form before the bulk
of spheroid stars, and the correlation between spheroid velocity dispersion and
supermassive black hole mass arises as AGN-triggered outflows limit the gas
reservoir for spheroid star formation. The super-Eddington phase plausibly
triggers a top-heavy IMF in the region of influence of the SMBH. The
Compton-cooled Eddington-limited outflow phase results in a spheroid core whose
phase space density scales as the inverse 5/2 power of the core mass, and whose
mass scales as the 3/2 power of SMBH mass. This latter scaling suggests that
SMBH growth (and hence spheroid formation) is anti-hierarchical.


title: Near-Field Cosmology with Local Group Dwarf Spheroidals

abstract:
  The Local Group offers an excellent laboratory for near-field cosmology by
permitting us to use the resolved stellar content of its constituent galaxies
as probes of galaxy formation and evolution, which in turn is an important
means for testing cosmological models of hierarchical structure formation. In
this review, we discuss the the least massive, yet most numerous type of galaxy
in the Local Group, the dwarf spheroidal galaxies, and compare their properties
to cosmological predictions. In particular, we point out problems found with a
simple building block scenario and with effects expected from reionization. We
show that the star formation histories of dSphs are inconsistent with the
predicted cessation of star formation after reionization; instead, extended
star formation episodes are observed. The Galactic dSphs contain in part
prominent intermediate-age populations, whereas the Galactic halo does not.
Conversely, the M31 dSphs are almost entirely old, while the M31 halo contains
a substantial intermediate-age population. These differences in the population
structure as well as the differences in the modes of star formation inferred
from [alpha/Fe] ratios make dSphs unlikely major contributors to the build-up
of the Galactic and M31 halo unless most of the accretion occurred at early
epochs. On the other hand, there is clear evidence for ongoing harassment and
accretion of a number of dSphs.


title:
Metal Enrichment of the Intergalactic Medium and Production of Massive
  Black Holes

abstract:
  A model for the chemical evolution of the intergalactic medium (IGM) is
presented using theoretical yields of very massive stars (VMSs) and Type II
supernovae (SNe II). It is shown that if [Si/C] is indeed as high as ~0.7 in
the IGM, then VMSs associated with pair-instability supernovae (PI-SNe) in
low-mass halos at high redshift must produce at least 50% of the Si. The
remainder is from later galactic outflows of SN II debris, which also provide
most of the C and O. Both sources are required to account for the metal
inventory in the IGM. The early VMS production must continue until redshift
z~15 so that the efficiency of VMS formation per low-mass halo is significantly
below unity. Contributions from the later galactic outflows mainly occur at
z~4-6. Using a Salpeter initial mass function, we infer that the number of VMSs
producing massive black holes (MBHs) is 0.72 times the the number of VMSs
associated with PI-SNe. The amount of metals (particularly Si) in the IGM that
is attributable to PI-SNe is thus closely coupled with the total mass of MBHs
produced in epochs prior to galaxy formation. Production of ~50% of the Si in
the IGM by PI-SNe corresponds to an early inventory of MBHs that is comparable
to the global mass budget of the central supermassive black holes in
present-day galaxies. (Abridged)


title: Galactic Open Clusters

abstract:
  The study of open clusters has a classic feel to it since the subject
predates anyone alive today. Despite the age of this topic, I show via an ADS
search that its relevance and importance in astronomy has grown faster in the
last few decades than astronomy in general. This is surely due to both
technical reasons and the interconnection of the field of stellar evolution to
many branches of astronomy. In this review, I outline what we know today about
open clusters and what they have taught us about a range of topics from stellar
evolution to Galactic structure to stellar disk dissipation timescales. I argue
that the most important astrophysics we have learned from open clusters is
stellar evolution and that its most important product has been reasonably
precise stellar ages. I discuss where open cluster research is likely to go in
the next few years, as well as in the era of 20m telescopes, SIM, and GAIA. Age
will continue to be of wide relevance in astronomy, from cosmology to planet
formation timescales, and with distance errors soon no longer a problem,
improved ages will be critically important to many of the most fascinating
astrophysical questions.


title: Error Analysis for Dual-Beam Optical Linear Polarimetry

abstract:
  In this paper we present an error analysis for polarimetric data obtained
with dual-beam instruments. After recalling the basic concepts, we introduce
the analytical expressions for the uncertainties of polarization degree and
angle. These are then compared with the results of Monte-Carlo simulations,
which are also used to briefly discuss the statistical bias. Then we approach
the problem of background subtraction and the errors introduced by a
non-perfect Wollaston prism, flat-fielding and retarder plate defects. We
finally investigate the effects of instrumental polarization and we propose a
simple test to detect and characterize it. The application of this method to
real VLT-FORS1 data has shown the presence of a spurious polarization, which is
of the order of 1.5% at the edges of the field of view. The cause of this
effect has been identified with the presence of rather curved lenses in the
collimator, combined with the non complete removal of reflections by the
coatings. This problem is probably common to all focal-reducer instruments
equipped with a polarimetric mode. An additional spurious and asymmetric
polarization field, whose cause is still unclear, is visible in the B band.


title:
A new approach for constraining the Hubble constant from proper motions
  of radio jets

abstract:
  Withdrawn due to a mistake in jets' Doppler factor modeling. An updated
version will appear after revisiting this work.


title:
Probing the Coevolution of Supermassive Black Holes and Quasar Host
  Galaxies

abstract:
  At low redshift, there are fundamental correlations between the mass of
supermassive black holes (MBH) and the mass (Mbulge) and luminosity of the host
galaxy bulge. We investigate the same relation at z>=1. Using virial mass
estimates for 11 quasars at z >~2 to measure their black hole mass, we find
that black holes at high z fall nearly on the same MBH versus R-band magnitude
(MR) relation (to ~0.3 mag) as low-redshift active and inactive galaxies,
without making any correction for luminosity evolution. Using a set of
conservative assumptions about the host galaxy stellar population, we show that
at z>~2 (10 Gyrs ago) the ratio of MBH/Mbulge was 3--6 times larger than today.
Barring unknown systematic errors on the measurement of MBH, we also rule out
scenarios in which moderately luminous quasar hosts at z>~2 were fully formed
bulges that passively fade to the present epoch. On the other hand, 5 quasar
hosts at z~1 are consistent with current day MBH-MR relationship after taking
into account evolution, appropriate for that of E/S0 galaxies. Therefore, z~1
host galaxies appear to fit the hypothesis they are fully formed early-type
galaxies. We also find that most quasar hosts with absolute magnitudes brighter
than MR = -23 cannot fade below L* galaxies today, regardless of their stellar
population makeup, because their black hole masses are too high and they must
arrive at the local MBH-MR relationship by z=0.


title:
XMM-Newton Observation of Diffuse Gas and LMXBs in the Elliptical Galaxy
  NGC 4649 (M60)

abstract:
  (Abridged) We present an XMM-Newton X-ray observation of the X-ray bright E2
elliptical galaxy NGC 4649. In addition to bright diffuse emission, we resolve
158 discrete sources, ~50 of which are likely to be low-mass X-ray binaries
(LMXBs) associated with NGC 4649. We find evidence for variability in three
sources between this observation and a previous Chandra observation.
Additionally, we detect five sources that were not detected with Chandra
despite its better detection limit, suggesting that these sources have since
brightened. The total X-ray spectrum of the resolved sources is well-fit by a
hard power-law, while the diffuse spectrum requires a hard and a soft
component, presumably due to the relatively soft diffuse gas and the harder
unresolved sources. A deprojection of the diffuse emission revealed a radial
temperature gradient that is hot in the center, drops to a minimum at about
20-50" (1.6-4.1 kpc), and rises again in the outer regions. The diffuse
emission appears to require a two-temperature model with heavy element
abundance ratios that differ from the solar values. We have verified the
existence of faint radial features extending out from the core of NGC 4649 that
had previously been seen with Chandra. The fingers are morphologically similar
to radial features seen in hydrodynamic simulations of cooling flows in
elliptical galaxies. We also find evidence for a longer, previously undetected
filament that extends to the northeastern edge of NGC 4649. We conclude that
the filament may be the result of a tidal interaction, possibly with NGC 4647,
though more work is necessary to verify this conclusion.


title:
Preliminary Results from a Spectrosopic LyA Survey at Redshift 5.7 with
  IMACS

abstract:
  We describe preliminary results from an ultra-sensitive, spectroscopic
emission-line survey and illustrate the challenges inherent in identifying
high-redshift LyA emitters. Our multi-slit windows technique complements other
types of emission-line surveys. Narrowband imaging surveys cover large areas of
sky but only detect much brighter objects. Longslit spectra taken along cluster
caustics yield intrinsically fainter lensed LyA emitters but probe small
volumes of space. We have observed the COSMOS deep field and a field at 15h
+00. To a line flux of a few times 10^-18 erg/s/cm^2, we found 150
emission-line sources (with no detectable continuum) among 4 masks. These
candidates are being re-observed with broad spectral coverage to determine the
line identity. To date, the interloper to LyA ratio is about 8:1. The sky
positions of the LyA candidates generally do not coincide with those of
foreground objects in ultra-deep r band or i' images -- consistent with the
presence of a strong Lyman break.


title:
The Complex Symmetry Gravitational Theory as a New Alternative of Dark
  Energy

abstract:
  We propose that complex symmetry gravitational theory (CSGT) explain the
accelerating expansion of universe. In this paper universe is taken as the
double complex symmetric space. Cosmological solution is obtained within CSGT.
The conditions of the accelerating expansion of universe are discussed within
CSGT. Moreover, the range of equation of state of matter $\omega_\epsilon$ is
given in the hyperbolic imaginary space.


title: Tail Emission of Prompt Gamma-Ray Burst Jets

abstract:
  Tail emission of the prompt gamma-ray burst (GRB) is discussed using a
multiple emitting sub-shell (inhomogeneous jet, sub-jets or mini-jets) model,
where the whole GRB jet consists of many emitting sub-shells. One may expect
that such a jet with angular inhomogeneity should produce spiky tail emission.
  However, we found that the tail is not spiky but is decaying roughly
monotonically. The global decay slope of the tail is not so much affected by
the local angular inhomogeneity but affected by the global sub-shell energy
distribution. The fact that steepening breaks appeared in some events prefers
the structured jets. If the angular size of the emitting sub-shell is around
0.01-0.02 rad, some bumps or fluctuations appear in the tail emission observed
frequently in long GRBs. If the parameter differences of sub-shell properties
are large, the tail has frequent changes of the temporal slope observed in a
few bursts. Therefore, the multiple emitting sub-shell model has the advantage
of explaining the small-scale structure in the observed rapid decay phase.


title:
The X-ray emission properties and the dicothomy in the central stellar
  cusp shapes of early-type galaxies

abstract:
  Hubble Space Telescope revealed a dicothomy in the central surface brightness
profiles of early-type galaxies, that subsequently have been grouped into two
families: core, boxy, anisotropic systems and cuspy ("power law"), disky,
rotating ones. Here we investigate whether a dicothomy is present also in the
X-ray properties of the two families. We consider both their total soft
emission (Lsx,tot), that is a measure of the galactic hot gas content, and
their nuclear hard emission (Lhx,nuc), mostly coming from Chandra observations,
that is a measure of the nuclear activity. At any optical luminosity, the
highest Lsx,tot values are reached by core galaxies; this is explained with
their being central dominant galaxies of groups, subclusters or clusters, in
many of the logLsx,tot(erg/s)>~41.5 cases. The highest Lhx,nuc values, similar
to those of classical AGNs, in this sample are hosted only by core galaxies; at
low luminosity AGN levels, Lhx,nuc is independent of the central stellar
profile shape. The presence of optical nuclei (also found by HST) is unrelated
with the level of Lhx,nuc, even though the highest Lhx,nuc are all associated
with optical nuclei. The implications of these findings for the galaxy
evolution and the accretion modalities at the present epoch are discussed.


title: Sulphur abundances in metal-poor stars

abstract:
  We investigate the debated "sulphur discrepancy" found among metal-poor stars
of the Galactic halo with [Fe/H] < -2. This discrepancy stems in part from the
use of two different sets of sulphur lines, the very weak triplet at 8694-95 A
and the stronger triplet lines at 9212 - 9237 A. For three representative cases
of metal-poor dwarf, turnoff and subgiant stars, we argue that the abundances
from the 8694-95 lines have been overestimated which has led to a continually
rising trend of [S/Fe] as metallicity decreases. Given that the near-IR region
is subject to CCD fringing, these weak lines become excessively difficult to
measure accurately in the metallicity regime of [Fe/H] < -2. Based on
homogeneously determined spectroscopic stellar parameters, we also present
updated [S/Fe] ratios from the 9212-9237 lines which suggest a plateau-like
behaviour similar to that seen for other alpha elements.


title: GQ Lup and its common proper motion companion

abstract:
  Recently, Neuhaeuser et al. (2005) presented evidence for a sub-stellar,
common proper motion companion to GQ Lup. With two theoretical mass estimates,
both below the Deuterium burning minimum mass limit, the companion is probably
a planet imaged directly. We present here a more detailed astrometric analysis
of the GQ Lup system, using all the (different) proper motions published for
the primary. The common proper motion is significant in all cases, also when
taking into account the error in parallax or distance (140 +- 50 pc). When
using the weighted mean, the significance for common proper motion of GQ Lup
and its companion is 7 + 4 sigma for no change in separation plus 8 sigma for
no change in position angle. We also discuss the question, whether GQ Lup and
its common-proper motion companion are not bound, but share the same or similar
proper motion as two independent members of the Lupus T association, which is a
moving group, where most members should have the same motion anyway. Given our
discussion, this hypothesis can be rejected by several sigma: The probability
to find by chance an L-dwarf fainter than Ks = 14 mag within 0.7325 arcsec with
(almost) the same proper motion of GQ Lup is only < 3 10^{-10}. The orbital
motion of the system is not yet detected (1.4 +- 2.2 mas/yr), but is probably
smaller than the escape velocity (5.3 +- 2.1 mas/yr), so that the system may
well be gravitationally bound and stable. This is different for the
2MASSWJ1207334-393254 system, as we also show.


title: Do we Observe Quantum Gravity Effects at Galactic Scales?

abstract:
  The nonperturbative renormalization group flow of Quantum Einstein Gravity
(QEG) is reviewed. It is argued that there could be strong renormalization
effects at large distances, in particular a scale dependent Newton constant,
which mimic the presence of dark matter at galactic and cosmological scales.


title: Swift XRT Observations of the Breaking X-ray Afterglow of GRB 050318

abstract:
  We report the results of Swift X-Ray Telescope (XRT) observations of GRB
050318. This event triggered the Burst Alert Telescope (BAT) aboard Swift and
was followed-up with XRT and UVOT for 11 consecutive orbits starting from 54
minutes after the trigger. A previously unknown fading X-ray source was
detected and accurately monitored. The source was found to decrease in
intensity with time and a clear temporal break occurring at ~18000 s after the
trigger was observed. The X-ray light curve was found to be consistent with a
broken power-law with decay indices -1.17 +/- 0.08 and -2.10 (+0.22) (-0.24)
before and after the break. The spectrum of the X-ray afterglow was well
described by a photoelectrically absorbed power-law with energy index of -1.09
+/-0.09. No evidence of spectral evolution was found. We compare these results
with those obtained with UVOT and separately reported and refine the data
analysis of BAT. We discuss our results in the framework of a collimated
fireball model and a synchrotron radiation emission mechanism. Assuming the GRB
redshift derived from the farthest optical absorption complex (z = 1.44), the
event is fully consistent with the E_p-E_iso correlation.


title: Low Mass Companions to White Dwarfs

abstract:
  This paper summarizes the results of over 17 years of work searching for low
mass stellar and substellar companions to more than 370 nearby white dwarfs.
Roughly 60 low mass, unevolved companions were found and studied all together,
with over 20 discovered in the last few years, including the first unambiguous
brown dwarf companion to a white dwarf, GD 1400B. The resulting spectral type
distributions for companions to white dwarfs and nearby cool field dwarfs are
compared, and the implications for binary star formation are discussed. A brief
analysis of GD 1400B, including new data, is also presented


title:
The limb darkening of alpha Cen B: Matching 3D hydrodynamical models
  with interferometric measurements

abstract:
  For the nearby dwarf star alpha Cen B (K1 V), we present limb darkening
predictions from a 3D hydro-dynamical radiative transfer model of its
atmosphere. We first compare the results of this model to a standard Kurucz's
atmosphere. Then we use both predictions to fit the new interferometric
visibility measurements of alpha Cen B obtained with the VINCI instrument of
the VLT Interferometer. Part of these new visibility measurements were obtained
in the second lobe of the visibility function, that is sensitive to stellar
limb darkening. The best agreement is found for the 3D atmosphere limb
darkening model and a limb darkened angular diameter of theta\_3D =
6.000+-0.021 mas, corresponding to a linear radius of 0.863+-0:003Ro (assuming
pi = 747.1+-1.2 mas). Ournew linear radius is in good agreement with the
asteroseismic value predicted by Thevenin et al. (2002). In view of future
observations of this star with the VLTI/AMBER instrument, we also present limb
darkening predictions in the J, H and K bands.


title: An origin in the local Universe for some short gamma-ray bursts

abstract:
  Gamma-ray bursts (GRBs) divide into two classes: "long", which typically have
initial durations of T90>2s, and "short", with durations of T90<2s (where T90
is the time to detect 90% of the observed fluence). Long bursts, which on
average have softer gamma-ray spectra, are known to be associated with with
stellar core-collapse events-- in some cases simultaneously producing powerful
Type Ic supernovae. In contrast, the origin of short bursts has remained
mysterious until recently. A subsecond intense "spike" of gamma-rays during a
giant flare from the Galactic soft gamma-ray repeater, SGR 1806-20, reopened an
old debate over whether some short GRBs could be similar events seen in
galaxies out to ~70Mpc (redshift z=0.016). Shortly after that, localizations of
a few short GRBs (with optical afterglows detected in two cases) have shown an
apparent association with a variety of host galaxies at moderate redshifts.
Here we report a correlation between the locations of previously observed short
bursts and the positions of galaxies in the local Universe, indicating that
between 10 and 25 per cent of short GRBs originate at low redshifts (z<0.025).


title: Identification of a new short-period comet near the sun

abstract:
  We present the identification of comet C/1999 R1 (SOHO) with comet C/2003 R5
(SOHO). Both apparitions were only observed with the Solar and Heliospheric
Observatory (SOHO) at distances smaller than 0.1 AU from the sun with the LASCO
coronagraphs onboard the spacecraft. Although SOHO comets usually have poor
orbital coverage, the 1999 and 2003 arcs are sufficient to generate a link that
seems to satisfy all observations. We also analyze comet C/2002 R5 (SOHO) which
has similar orbital elements. A fragmentation scenario is proposed and
discussed which would support the linkage of C/1999 R1 and C/2003 R5 and thus
its short periodic nature.


title: Evolution of Galactic Field be Stars

abstract:
  Galactic field Be stars were studied by taking into account the effects
induced by the fast rotation on their fundamental parameters. Fractional ages
$\tau/\tau\_{\rm MS}$ ($\tau\_{\rm MS}$ = time spent in the MS) against stellar
mass reveal that: a) Be stars spread over the whole interval $0<\tau/\tau\_{\rm
MS}<1$; b) the Be phenomenon in massive stars ($M>12M\_{\odot}$) is present at
smaller age ratios than for less massive stars ($M<12M\_{\odot}$); c) there is
a lack of Be stars with $M<7M\_{\odot}$ in the first half of the MS. Low mass
fast rotators ($M<7M\_{\odot}$), called Bn stars, could be "becoming" Be stars.


title: On the Frequency of Field Galactic Be Stars

abstract:
  Since Be stars belong to the high velocity tail of a single B star velocity
distribution, the appearance of the Be phenomenon must be independent of the
stellar mass. In the present paper we show that the shape of the distribution
of the number fraction N(Be)/N(Be+B) against the spectral type can be explained
in terms of the Balmer line emission efficiency as a function of the effective
temperature.


title: The winds of the hot massive first stars

abstract:
  We study dynamical aspects of circumstellar environment around massive
zero-metallicity first stars. For this purpose we apply our NLTE wind models.
We show that the hydrogen-helium stellar wind from stationary massive first
generation (Population III) stars (driven either by the line (bound-bound) or
continuum (bound-free and free-free) transitions) is unlikely. The possibility
of expulsion of chemically homogeneous wind and the role of minor isotopes are
also discussed. Finally, we estimate the importance of hydrogen and helium
lines for shutting off the initial accretion onto first stars and its influence
on initial mass function of first stars.


title: Accretion modes and jet production in black hole X-ray binaries

abstract:
  We review our current understanding of the radio properties of black hole
X-ray binaries in connection with the X-ray spectral states, and discuss them
in the framework of the recently proposed unified model for the jet-accretion
coupling in these systems.


title: Achernar Can be a Differential Rotator

abstract:
  We take advantage of interferometric measurements of Achernar to inquire on
its internal rotational law. The reinterpretation of interferome-tric data and
the use of fundamental parameters corrected for gravitational darkening effects
and models of 2D-models of internal stellar structures, lead us to the
conclusion that the star could not be a rigid, near critical, rotator but a
differential rotator with the core rotating $\sim3$ times faster than the
surface.


title: Primordial magnetic seeds from string cosmology

abstract:
  After a discussion of the inflationary production of primordial magnetic
seeds, and a short review of various possible mechanisms, we concentrate on the
analysis of the photon-dilaton coupling typical of string theory models.
Particular attention is paid to the constraints to be imposed on the primordial
seed spectrum, and to the possibility of obtaining phenomenological signatures
of heterotic and Type I superstrings, in principle accessible to present (or
near-future) observations.


title: Zams Rotational Velocities of be Stars

abstract:
  We show that Be stars belong to a high velocity tail of a single B-type star
rotational velocity distribution in the main sequence (MS). We studied 127
galactic field Be stars and obtained their true equatorial velocity at the ZAMS
using models of stellar evolution with rotation. There is a sharp
mass-dependent cut in the ZAMS under which there is no Be star. Velocities
above this cut follow a Gaussian-tail distribution. B stars with ZAMS
rotational velocities lower than the cut probably cannot become Be.


title: An Observationally Motivated Framework for AGN Heating of Cluster Cores

abstract:
  The cooling-flow problem is a long-standing puzzle that has received
considerable recent attention, in part because the mechanism that quenches
cooling flows in galaxy clusters is likely to be the same mechanism that
sharply truncates the high end of the galaxy luminosity function. Most of the
recent models for halting cooling in clusters have focused on AGN heating, but
the actual heating mechanism has remained mysterious. Here we present a
framework for AGN heating derived from a Chandra survey of gas entropy profiles
within cluster cores. This set of observations strongly suggests that the inner
parts of cluster cores are shock-heated every ~10^8 years by intermittent AGN
outbursts, driven by a kinetic power output of ~ 10^45 erg/sec and lasting at
least 10^7 years. Beyond ~30 kpc these shocks decay to sound waves, releasing
buoyant bubbles that heat the core's outer parts. Between heating episodes,
cooling causes the core to relax toward an asymptotic pure-cooling profile. The
density distribution in this asymptotic profile is sufficiently peaked that the
AGN shock does not cause a core entropy inversion, allowing the cluster core to
retain a strong iron abundance gradient, as observed.


title: Dark energy, curvature, and cosmic coincidence

abstract:
  The fact that the energy densities of dark energy and matter are similar
currently, known as the coincidence problem, is one of the main unsolved
problems of cosmology. We present here a model in which a spatial curvature of
the universe can lead to a transition in the present epoch from a matter
dominated universe to a scaling dark energy dominance in a very natural way. In
particular, we show that if the exponential potential of the dark energy field
depends linearly on the spatial curvature density of a closed universe, the
observed values of some cosmological parameters can be obtained assuming
acceptable values for the present spatial curvature of the universe, and
without fine tuning in the only parameter of the model. We also comment on
possible variations of this model, and realistic scenarios in which it could
arise.


title: Properties of Regions Forming the FeII Emission Lines in Be Stars

abstract:
  We study FeII and Balmer hydrogen emission lines observed simultaneously of
18 southern Be stars. We use the self-absorption-curve method (SAC) to
determine the optical depth regime of FeII emission lines and to derive first
insights on the physical properties of their forming regions.


title: Fast Rotation vs. Metallicity

abstract:
  Fast rotation seems to be the major factor to trigger the Be phenomenon.
Surface fast rotation can be favored by initial formation conditions such as
metal abundance. Models of fast rotating atmospheres and evolutionary tracks
are used to determine the stellar fundamental parameters of 120 Be stars
situated in spatially well-separated regions to imply there is between them
some gradient of metallicity. We study the effects of the incidence of this
gradient on the nature of the studied stars as fast rotators.


title: The Long-Term H$\alpha$ Emission Line Variation in $\alpha$ Eri

abstract:
  The long-term variation of the H$\alpha$ line in $\alpha$ Eri has 14-15 years
cyclic \bbe phase transitions. The disc formation time scales, interpreted as
the periods during which the H$\alpha$ line emission increases from zero to its
maximum, agree with the viscous decretion model. On the other hand, the time
required for the disc dissipation ranges from 6 to 12 years which questions the
viscous disc model predictions.


title: Morphology of the coronal line region in active galactic nuclei

abstract:
  We present new images of the coronal line region, as traced by [Si VII] 2.48
\um, in some of the nearest Seyfert 2 galaxies. In each of these galaxies, the
coronal line emission comprises a bright, compact central source and extended
emission showing broad alignment along a particular direction, usually
coinciding with that defined by the radio emission or the extended narrow line
region. The full extent of the coronal line emission ranges from few tens of pc
to $\sim$ 150 pc radius from the nucleus and is a factor $\sim 10$ smaller than
that seen in the extended, lower-ionization gas. With a spatial resolution of
10 pc or better, the coronal region shows diffuse and filamentary structure in
all cases, and it is difficult to see whether it breaks down into discrete
blobs as those seen in lower-ionization-lines- or radio- images of comparable
resolution. The extent of the coronal line emission is larger than would be
predicted by photoionization models, which argues for additional in-situ gas
excitation, the most plausible energy source being shock-excitation.
  Based on observations carried out under ESO / VLT programs 70.B-0409 and
74.B-0404.


title:
A Fabry-Perot Imaging Search for Lyman-alpha Emission in Quasar
  Absorbers at z ~ 2.4

abstract:
  We have carried out a deep narrow-band imaging survey of six fields with
heavy-element quasar absorption lines, using the Goddard Fabry-Perot (FP)
system at the Apache Point Observatory (APO) 3.5-meter telescope. The aim of
these observations was to search for redshifted Ly-$\alpha$ emission from the
galaxies underlying the absorbers at $z = 2.3-2.5$ and their companion
galaxies. The 3 $\sigma$ sensitivity levels ranged between
  $1.9 \times 10^{-17}$ and $5.4 \times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$ in
observed-frame Ly-$\alpha$ flux. No significant Ly-$\alpha$ emitters were
detected at $> 3 \sigma$ level. The absence of significant Ly-$\alpha$ emission
implies limits on the star formation rate (SFR) of 0.9-2.7 $M_{\odot}$
yr$^{-1}$ per 2-pixel x 2-pixel region, if no dust attenuation is assumed. We
compare our results with those from other emission-line studies of absorber
fields and with predictions for global average SFR based on the models of
cosmic chemical evolution. Our limits are among the tightest existing
constraints on Ly-$\alpha$ emission from galaxies in absorber fields, but are
consistent with many other studies. In the absence of dust attenuation, these
studies suggest that SFRs in a large fraction of objects in the absorber fields
may lie below the global mean SFR. However, it is possible that dust
attenuation is responsible for the low emission line fluxes in some objects. It
is also possible that the star-forming regions are compact and at smaller
angular separations from the quasar than the width of our point spread function
and, get lost in the quasar emission. We outline future observations that could
help to distinguish between the various possibilities.


title:
Hierarchical Growth and Cosmic Star Formation: Enrichment, Outflows and
  Supernova Rates

abstract:
  The cosmic star formation histories are evaluated for different minimum
masses of the initial halo structures, with allowance for realistic gas
outflows. With a minimum halo mass of 10^{7} - 10^{8} M_odot and a moderate
outflow efficiency, we reproduce both the current baryon fraction and the early
chemical enrichment of the IGM. The intensity of the formation rate of
``normal'' stars is also well constrained by the observations: it has to be
dominated by star formation in elliptical galaxies, except perhaps at very low
redshift. The fraction of baryons in stars is predicted as are also the type Ia
and II supernova event rates. Comparison with SN observations in the redshift
range z=0-2 allows us to set strong constraints on the time delay of type Ia
supernovae (a total delay of \sim 4 Gyr is required to fit the data), the lower
end of the mass range of the progenitors (2 - 8 M_odot) and the fraction of
white dwarfs that reproduce the type Ia supernova (about 1 per cent). The
intensity in the initial starburst of zero metallicity stars below 270 M_\odot
must be limited in order to avoid premature overenrichment of the IGM. Only
about 10 - 20 % of the metals present in the IGM at z = 0 have been produced by
population III stars at very high z. The remaining 80 - 90 % are ejected later
by galaxies forming normal stars, with a maximum outflow efficiency occurring
at a redshift of about 5. We conclude that 10^{-3} of the mass in baryons must
lie in first massive stars in order to produce enough ionizing photons to allow
early reionization of the IGM by z \sim 15.


title:
Scalings between Physical and their Observationally related Quantities
  of Merger Remnants

abstract:
  We present scaling relations between the virial velocity (V) and the
one-dimensional central velocity dispersion (Sig0); the gravitational radius
(Rv) and the effective radius (Re); and the total mass (M) and the luminous
mass (ML) found in N-body simulations of binary mergers of spiral galaxies.
These scalings are of the form V^2 ~ Sig0^alpha, Rv ~ Re^beta and M ~ ML^gamma.
The particlar values obtained for (alpha,beta,gamma) depend on the method of
fitting used [ordinary least-squares (ols) or orthogonal distance regression
(odr)], the assumed profile [de Vaucouleurs (deV) or Sersic (S)], and the size
of the radial interval where the fit is done. The alpha and gamma indexes turn
out more sensitive to the fitting procedure, obtaining for the ols a mean
alpha_ols=1.51 and gamma_ols=0.69, while for the odr alpha_odr=2.35 and
gamma_odr=0.76. The beta index depends more on the adopted type of profile,
with beta_deV=0.13 and beta_S=0.27. We conclude that dissipationless formed
remnants of mergers have a strong breaking of structural and kinematical
homology.