title: Forced oscillations in magnetized accretion disks and QPOs

abstract:
  We propose a new model for these QPOs based on forced oscillations induced in
the accretion disk due to the stellar magnetic field.
  First, it is shown that a magnetized accretion disk evolving in a rotating
nonaxisymmetric magnetic field anchored to a neutron star will be subject to
three kinds of resonances: a corotation resonance, a Lindblad resonance due to
a driving force, and a parametric resonance due to the time varying epicyclic
frequencies. In the second part of the paper, we focus on the linear response
of a thin accretion disk, developing the density perturbation as the sum of
free wave solutions and non-wavelike disturbances. In the last part, we show
results of 2D numerical simulations of a simplified version of the accretion
disk consisting of a column of plasma threaded by a vertical magnetic field. It
is argued that the nearly periodic motion induced in the disk will produce high
quality factor QPOs.


title: Orientation and size of the `Z' in `X'-shaped radio galaxies

abstract:
  Some X-shaped radio galaxies show a Z-symmetric morphology in the less
luminous secondary lobes. Within the scenario of a merger between two galaxies,
each hosting a supermassive black hole in its center, this structure has been
explained before: As the smaller galaxy spirals towards the common center, it
releases gas to the ISM of the larger active galaxy. The ram pressure of this
streaming gas will bend the lobes of the pre-merger jet into a Z-shape. After
the black holes have merged the jet propagates in a new direction that is
aligned with the angular momentum of the binary black hole. In this article we
deproject the pre- and post-merger jets. Taking into account the expected
angles between the jet pairs and with the assumption that their directions are
uncorrelated, we show that one of three possible orientations of the jets with
respect to the line of sight is more likely than the others. This actually
depends on the distance where the bending occurs. Another result of our
deprojection is that the streaming gas bends the jet into a Z-shape in a range
between about 30 and 100 kpc distance to the center of the primary galaxy. We
confirm this finding by comparing our predictions for the properties of the
rotational velocity field and its radius with observations and numerical
simulations of merging galaxies. Thus our results support the merger scenario
as explanation for X- and Z-shaped radio galaxies with the jet pointing along
the former axis of orbital angular momentum of the binary.


title: The Formation of Primordial Luminous Objects

abstract:
  In these lecture notes we review the current knowledge about the formation of
the first luminous objects. We start from the cosmological context of
hierarchical models of structure formation, and discuss the main physical
processes which are believed to lead to primordial star formation, i.e. the
cooling processes and the chemistry of molecules (especially H2) in a
metal-free gas. We then describe the techniques and results of numerical
simulations, which indicate that the masses of the first luminous objects are
likely to be much larger than that of present-day stars. Finally, we discuss
the scenario presented above, exposing some of the most interesting problems
which are currently being investigated, such as that of the feedback effects of
these objects.


title:
On the formation and evolution of magnetic chemically peculiar stars in
  the solar neighborhood

abstract:
  In order to put strict observational constraints on the evolutionary status
of the magnetic chemically peculiar stars (CP2) of the upper main sequence, we
have investigated a well established sample of galactic field CP2 objects
within a radius of 200pc from the Sun in the (X,Y) plane. In total, 182 stars
with accurate parallax measurements from the Hipparcos satellite were divided
into Si, SiCr and SrCrEu subgroups based on classification resolution data from
the literature. Primarily, it was investigated if the CP2 phenomenon occurs at
very early stages of the stellar evolution, significantly before these stars
reach 30% of their life-time on the main sequence. This result is especially
important for theories dealing with stellar dynamos, angular momentum loss
during the pre- as well as main sequence and stellar evolutionary codes for CP2
stars. For the calibration of the chosen sample, the well-developed framework
of the Geneva 7-color and Stromgren uvbybeta photometric system was used. We
are able to show that the CP2 phenomenon occurs continuously at the zero age
main sequence for masses between 1.5 and 4.5M(sun}. The magnetic field
strengths do not vary significantly during the evolution towards the terminal
age main sequence. Only the effective temperature and magnetic field strength
seem to determine the kind of peculiarity for those stars. We found several
effects during the evolution of CP2 stars at the main sequence, i.e. there are
two "critical" temperatures where severe changes take place. There is a
transition between Si, SiCr and SrCrEu stars at 10000K whereas a significant
decrease to almost zero of evolved SrCrEu objects with masses below 2.25M(sun)
at 8000K occurs.


title:
Quality studies of the data taking conditions for the Auger Fluorescence
  Detector

abstract:
  As more than half of the Fluorescence Detector (FD) of the Auger Observatory
is completed, data taking is becoming a routine job. It is then necessary to
follow strict procedures to assure the quality of the data. An overview of the
data taking methods is given. The nature of the FD background signal is due to
the night sky brightness (stars and planet faint light, moonlight, twilight,
airglow, zodiacal and artificial light) and to the electronic background
(photomultiplier and electronic noise). The analysis of the fluctuations in the
FADC signal (variance analysis), directly proportional to the background mean
light level, performed for each night of data taking is used to monitor the FD
background signal. The data quality is analysed using different techniques,
described in detail. Examples of trigger rates, number of stereo events, dead
time due to moonlight, weather or hardware problems are given. The analysis
comprises several months of data taking, giving an overview of the FD
capabilities, performance and allowing a systematic study of data and their
correlation with the environment.


title:
Binary Encounters With Supermassive Black Holes: Zero-Eccentricity LISA
  Events

abstract:
  Current simulations of the rate at which stellar-mass compact objects merge
with supermassive black holes (called extreme mass ratio inspirals, or EMRIs)
focus on two-body capture by emission of gravitational radiation. The
gravitational wave signal of such events will likely involve a significant
eccentricity in the sensitivity range of the Laser Interferometer Space Antenna
(LISA). We show that tidal separation of stellar-mass compact object binaries
by supermassive black holes will instead produce events whose eccentricity is
nearly zero in the LISA band. Compared to two-body capture events, tidal
separations have a high cross section and result in orbits that have a large
pericenter and small apocenter. Therefore, the rate of interactions per binary
is high and the resulting systems are very unlikely to be perturbed by other
stars into nearly radial plunges. Depending on the fraction of compact objects
that are in binaries within a few parsecs of the center, the rate of
low-eccentricity LISA events could be comparable to or larger than the rate of
high-eccentricity events.


title:
Formation of Galactic Systems in Light of the Magnesium Abundance in
  Field Stars: The Thick Disk

abstract:
  The space velocities and Galactic orbital elements of stars calculated from
the currently available high-accuracy observations in our summary catalog of
spectroscopic magnesium abundances in dwarfs and subgiants in the solar
neighborhood are used to identify thick-disk objects. The relative magnesium
abundances in thick-disk stars are shown to lie within the range
0.0<[Mg/Fe]<0.5 and to decrease with increasing metallicity starting from
[Fe/H]=-1.0. This is interpreted as evidence for a longer duration of the star
formation process in the thick disk. We have found vertical gradients in
metallicity (grad_Z[Fe/H]=-0.13\pm 0.04 kpc^{-1}) and relative magnesium
abundance (grad_Z [Mg/Fe]=0.06\pm 0.02 kpc^{-1}), which can be present in the
subsystem only in the case of its formation in a slowly collapsing protogalaxy.
The large spread in relative magnesium abundance (-0.3<[Mg/Fe]<0.5) in the
stars of the metal-poor "tail" of the thick disk which constitute 8% of the
subsystem, can be explained in terms of their formation inside isolated
interstellar clouds that interacted weakly with the matter of a single
protogalactic cloud. We have found a statistically significant negative radial
gradient in relative magnesium abundance in the thick disk (grad_R
[Mg/Fe]=-0.03\pm 0.01 kpc^{-1}) instead of the expected positive gradient. The
smaller perigalactic orbital radii and the higher eccentricities for
magnesium-richer stars, which among other stars, are currently located in a
small volume of the Galactic space near the Sun are assumed to be responsible
for the gradient inversion. A similar but statistically less significant
inversion is also observed in the subsystem for the radial metallicity
gradient.


title:
Two-dimensional hydrodynamic core-collapse supernova simulations with
  spectral neutrino transport. I. Numerical method and results for a 15 M_sun
  star

abstract:
  Supernova models with a full spectral treatment of the neutrino transport are
presented, employing the Prometheus/Vertex neutrino-hydrodynamics code with a
``ray-by-ray plus'' approximation for treating two- (or three-) dimensional
problems. The method is described in detail and critically assessed with
respect to its capabilities, limitations, and inaccuracies in the context of
supernova simulations. In this first paper of a series, 1D and 2D core-collapse
calculations for a (nonrotating) 15 M_sun star are discussed, uncertainties in
the treatment of the equation of state -- numerical and physical -- are tested,
Newtonian results are compared with simulations using a general relativistic
potential, bremsstrahlung and interactions of neutrinos of different flavors
are investigated, and the standard approximation in neutrino-nucleon
interactions with zero energy transfer is replaced by rates that include
corrections due to nucleon recoil, thermal motions, weak magnetism, and nucleon
correlations. Models with the full implementation of the ``ray-by-ray plus''
spectral transport were found not to explode, neither in spherical symmetry nor
in 2D with a 90 degree lateral wedge. The success of previous 2D simulations
with grey, flux-limited neutrino diffusion can therefore not be confirmed.
Omitting the radial velocity terms in the neutrino momentum equation leads to
``artificial'' explosions by increasing the neutrino energy density in the
convective gain layer by about 20--30% and thus the integral neutrino energy
deposition in this region by about a factor of two. (abbreviated)


title: Phase-Dependent Properties of Extrasolar Planet Atmospheres

abstract:
  Recently the Spitzer Space Telescope observed the transiting extrasolar
planets, TrES-1 and HD209458b. These observations have provided the first
estimates of the day side thermal flux from two extrasolar planets orbiting
Sun-like stars. In this paper, synthetic spectra from atmospheric models are
compared to these observations. The day-night temperature difference is
explored and phase-dependent flux densities are predicted for both planets. For
HD209458b and TrES-1, models with significant day-to-night energy
redistribution are required to reproduce the observations. However, the
observational error bars are large and a range of models remains viable.


title: On water ice formation in interstellar clouds

abstract:
  A model is proposed for the formation of water ice mantles on grains in
interstellar clouds. This occurs by direct accretion of monomers from the gas,
be they formed by gas or surface reactions. The model predicts the existence of
a threshold in interstellar light extinction, A(v), which is mainly determined
by the adsorption energy of water molecules on the grain material; for
hydrocarbon material, chemical simulation places this energy between 0.5 and 2
kcal/mole, which sets the visible exctinction threshold at a few magnitudes, as
observed. Once the threshold is crossed, all available water molecules in the
gas are quickly adsorbed, forming an ice mantle, because the grain cools down
and the adsorption energy on ice is higher than on bare grain. The model also
predicts that the thickness of the mantle, and, hence, the optical thickness at
3 mu, grow linearly with A(v), as observed, with a slope which depends upon the
total amount of water in the gas. Chemical simulation was also used to
determine the adsorption sites and energies of O and OH on hydrocarbons, and
study the dynamics of formation of water molecules by surface reactions with
gaseous H atoms, as well as their chances of sticking in situ.


title:
The Temperature Scale of Metal-Poor Dwarfs: Lithium and Oxygen
  Abundances

abstract:
  We employ a new Infrared Flux Method (IRFM) temperature scale (Ramirez &
Melendez 2005, ApJ 626, 446; ApJ 626, 465) in order to determine Li, O, and Fe
NLTE abundances in a sample of relatively unevolved (dwarfs, turn-off,
subgiants) metal-poor stars. We show that the analysis of the permitted OI
triplet and FeII lines leads to a plateau in [OI/FeII] over the broad
metallicity range -3.2 < [Fe/H] < -0.7, independent of temperature and
metallicity, and with a star-to-star scatter of only 0.1 dex. The Li abundance
in halo stars is also found to be independent of temperature and metallicity
(Spite plateau), with a star-to-star scatter of just 0.06 dex over the
metallicity range -3.4 < [Fe/H] < -1. Our Li abundance (Melendez & Ramirez
2004, ApJ 615, L33) is higher than previously reported values, but still lower
than the primordial abundance suggested by WMAP data and BBN.


title:
Absolute Calibration of the Infrared Array Camera on the Spitzer Space
  Telescope

abstract:
  The Infrared Array Camera (IRAC) on the Spitzer Space Telescope is absolutely
calibrated by comparing photometry on a set of A stars near the north ecliptic
pole to predictions based on ground-based observations and a stellar atmosphere
model. The brightness of point sources is calibrated to an accuracy of 3%,
relative to models for A star stellar atmospheres, for observations performed
and analyzed in the same manner as the calibration stars. This includes
corrections for location of the star in the array and the location if the
centroid within the peak pixel. Long-term stability of the IRAC photometry was
measured by monitoring the brightness of A dwarfs and K giants (near the north
ecliptic pole) observed several times per month; the photometry is stable to
1.5% (rms) over a year. Intermediate-time-scale stability of the IRAC
photometry was measured by monitoring at least one secondary calibrator (near
the ecliptic plane) every 12 hr while IRAC is in nominal operations; the
intermediate-term photometry is stable with a 1% dispersion (rms). One of the
secondary calibrators was found to have significantly time-variable (5%)
mid-infrared emission, with period (7.4 days) matching the optical light curve;
it is possibly a Cepheid variable.


title:
Can Remote Observing be Good Observing? Reflections on Procrustes and
  Antaeus

abstract:
  Remote observing seeks to simulate the presence of the astronomer at the
telescope. While this is useful, and necessary in some circumstances,
simulation is not reality. The drive to abstract the astronomer from the
instrument can have unpleasant consequences, some of which are prefigured in
the ancient tales of Procrustes and Antaeus. This article, written in 1992 for
a conference proceedings on remote observing, is reprinted here with only
slight editorial changes and the addition of a short Afterword. I consider some
of the human factors involved in remote observing, and suggest that our aim be
to enhance rather than supplant the astronomer at the telescope.


title: Accretion Disks, Jets and Blazar Variability

abstract:
  Although blazar variability is probably dominated by emission from
relativistic jets, accretion disks should be present in all blazars. These
disks produce emission over most of the electromagnetic spectrum; various
unstable processes operate in those disks which lead to variable emission. Here
I summarize some of the most relevant disk mechanisms for AGN variability. I
also discuss some aspects of jet variability, focusing on the possibility that
ultrarelativisitic jets of modest opening angle can reconcile TeV blazar
emission with the many subluminal VLBI knots seen in those sources. Finally, I
present recently illuminated characteristics of optical microvariability of
different classes of AGN which have important implications for the dominant
processes involved.


title:
Constraints on dark matter and the shape of the Milky Way dark halo from
  the 511 keV line

abstract:
  About one year ago, it was speculated that decaying or annihilating Light
Dark Matter (LDM) particles could explain the flux and extension of the 511 keV
line emission in the galactic centre. Here we present a thorough comparison
between theoretical expectations of the galactic positron distribution within
the LDM scenario and observational data from INTEGRAL/SPI. Unlike previous
analyses, there is now enough statistical evidence to put tight constraints on
the shape of the dark matter halo of our galaxy, if the galactic positrons
originate from dark matter. For annihilating candidates, the best fit to the
observed 511 keV emission is provided by a radial density profile with inner
logarithmic slope gamma=1.03+-0.04. In contrast, decaying dark matter requires
a much steeper density profile, gamma>1.5, rather disfavoured by both
observations and numerical simulations. Within the annihilating LDM scenario, a
velocity-independent cross-section would be consistent with the observational
data while a cross-section purely proportional to v^2 can be rejected at a high
confidence level. Assuming the most simplistic model where the galactic
positrons are produced as primaries, we show that the LDM candidate should be a
scalar rather than a spin-1/2 particle and obtain a very stringent constraint
on the value of the positron production cross-section to explain the 511 keV
emission. One consequence is that the value of the fine structure constant
should differ from that recommended in the CODATA. This is a very strong test
for the LDM scenario and an additional motivation in favour of experiments
measuring alpha directly. Our results finally indicate that an accurate
measurement of the shape of the dark halo profile could have a tremendous
impact on the determination of the origin of the 511 keV line and vice versa.


title:
The Infrared Array Camera component of the Spitzer Space Telescope
  Extragalactic First Look Survey

abstract:
  We present Infrared Array Camera (IRAC) data and source catalogs from the
Spitzer Space Telescope Extragalactic First Look Survey. The data were taken in
four broad bands centered at nominal wavelengths of 3.6, 4.5, 5.8 and 8.0
microns. A set of mosaics and catalogs have been produced which are ~80%
complete and ~99% reliable to their chosen flux density limits. The main field
survey covers 3.8 deg^2, and has flux density limits of 20muJy, 25muJy, 100muJy
and 100muJy at wavelengths of 3.6, 4.5, 5.8 and 8.0 microns,respectively. The
deeper ``verification'' survey covers 0.25 deg^2 with limits of 10muJy, 10muJy,
30muJy and 30muJy, respectively. We also include deep data in the ELAIS-N1
field which covers 0.041deg^2 with limits of 4muJy, 3muJy, 10muJy and 10muJy,
respectively, but with only two wavelength coverage at a given sky position.
The final bandmerged catalogs contain 103193 objects in the main field, 12224
in the verification field and 5239 in ELAIS-N1. Flux densities of high
signal-to-noise objects are accurate to about 10%, and the residual systematic
error in the absolute flux density scale is ~2-3%. We have successfully
extracted sources at source densities as high as 100000 deg^-2 in our deepest
3.6 and 4.5 micron data. The mosaics and source catalogs will be made available
through the Spitzer Science Center archive and the Infrared Science Archive.


title: The faint-end of the galaxy luminosity function in groups

abstract:
  We compute the galaxy luminosity function in spectroscopically selected
nearby groups and clusters. Our sample comprises 728 systems extracted from the
third release of the Sloan Digital Sky Survey in the redshift range $0.03 < z <
0.06$ with virial mass range $10^{11}M_\odot < M_{vir} < 2\times
10^{14}M_\odot$. In order to compute the galaxy luminosity function, we apply a
statistical background subtraction method following usually adopted techniques.
In the $r$ band, the composite galaxy luminosity function shows a slope
$\alpha=-1.3$ in the bright--end, and an upturn of the slope in the faint--end,
$M_r\ga -18+5log(h)$, to slopes $-1.9<\alpha<-1.6$. We find that this feature
is present also in the $i,g$ and $z$ bands, and for all explored group
subsamples, irrespective of the group mass, number of members, integrated color
or the presence of a hot intra-cluster gas associated to X-ray emission.


title: X-ray Pulsations in the Supersoft X-ray Binary CAL 83

abstract:
  X-ray data reveal that the supersoft X-ray binary CAL 83 exhibits 38.4 minute
pulsations at some epochs. These X-ray variations are similar to those found in
some novae and are likely to be caused by nonradial pulsations the white dwarf.
This is the first detection of pulsations in a classical supersoft X-ray
binary.


title:
Early and Rapid Merging as a Formation Mechanism of Massive Galaxies:
  Empirical Constraints

abstract:
  We present the results of a series of empirical computations regarding the
role of major mergers in forming the stellar masses of modern galaxies based on
measurements of galaxy merger and star formation histories from z~0.5-3. We
re-construct the merger history of normal field galaxies from z~3 to z~0 as a
function of initial mass using published pair fractions and merger fractions
from structural analyses. We calibrate the observed merger time-scale and mass
ratios for galaxy mergers using self-consistent N-body models of mergers,
composed of dark matter and stars, with mass ratios from 1:1 to 1:5 with
various orbital properties and viewing angles. We use these simulations to
determine the time-scales and mass ratios that produce structures that would be
identified as major mergers. Based on these calculations we argue that a
typical massive galaxy at z~3 with M_{*} > 10^{10} M_0 undergoes
4.4^{+1.6}_{-0.9} major mergers at z > 1. We find that by z~1.5 the stellar
mass of an average massive galaxy is relatively established, a scenario
qualitatively favored in a lambda dominated universe. We argue that the final
masses of these systems increases by as much as a factor of 100 allowing
Lyman-break galaxies, which tend to have low stellar masses, to become the most
massive galaxies in today's universe with M > M^{*}. Induced star formation
however only accounts for 10-30% of the stellar mass formed in these galaxies
at z < 3. A comparison to semi-analytic models of galaxy formation shows that
Cold Dark Matter (CDM) models consistently under-predict the merger fraction,
and rate of merging, of massive galaxies at high redshift. This suggests that
massive galaxy formation occurs through more merging than predicted in CDM
models, rather than a rapid early collapse.


title:
Late-time Radio Observations of 68 Type Ibc Supernovae: Strong
  Constraints on Off-Axis Gamma-ray Bursts

abstract:
  We present late-time radio observations of 68 local Type Ibc supernovae,
including six events with broad optical absorption lines (``hypernovae''). None
of these objects exhibit radio emission attributable to off-axis gamma-ray
burst jets spreading into our line-of-sight. Comparison with our afterglow
models reveals the following conclusions: (1) Less than $\sim 10%$ of Type Ibc
supernovae are associated with typical gamma-ray bursts initially directed away
from our line-of-sight; this places an empirical constraint on the GRB beaming
factor of $<f_b^{-1}> \lesssim 10^4$ corresponding to an average jet opening
angle, $\theta_j \gtrsim 0.8$ degrees. (2) This holds in particular for the
broad-lined supernovae (SNe 1997dq, 1997ef, 1998ey, 2002ap, 2002bl and 2003jd)
which have been argued to host GRB jets. Our observations reveal no evidence
for typical (or even sub-energetic) GRBs and rule out the scenario in which
every broad-lined SN harbors a GRB at the 84% confidence level. Their large
photospheric velocities and asymmetric ejecta (inferred from spectropolarimetry
and nebular spectroscopy) appear to be characteristic of the non-relativistic
supernova explosion and do not necessarily imply the existence of associated
GRB jets.


title: The Accelerated Acceleration of the Universe

abstract:
  We present a simple mechanism which can mimic dark energy with an equation of
state w < -1 as deduced from the supernova data. We imagine that the universe
is accelerating under the control of a quintessence field, which is moving up a
very gently sloping potential. As a result, the potential energy and hence the
acceleration increases at lower redshifts. Fitting this behavior with a dark
energy model with constant w would require w<-1. In fact we find that the
choice of parameters which improves the fit to the SNe mimics w = -1.4 at low
redshifts. Running up the potential in fact provides the best fit to the SN
data for a generic quintessence model. However, unlike models with phantoms,
our model does not have negative energies or negative norm states. Future
searches for supernovae at low redshifts 0.1 < z < 0.5 and at high redshifts
z>1 may be a useful probe of our proposal.


title: Kuiper Binary Object Formation

abstract:
  It has been observed that binary Kuiper Belt Objects (KBOs) exist contrary to
theoretical expectations. Their creation presents problems to most current
models. However, the inclusion of a third body (for example, one of the outer
planets) may provide the conditions necessary for the formation of these
objects. The presence of a third massive body not only helps to clear the
primordial Kuiper Belt but can also result in long lived binary Kuiper belt
objects. The gravitational interaction between the KBOs and the third body
causes one of four effects; scattering into the Oort cloud, collisions with the
growing protoplanets, formation of binary pairs, or creation of a single Kuiper
belt object. Additionally, the initial location of the progenitors of the
Kuiper belt objects also has a significant effect on binary formation.


title:
First Estimate of the Primary Cosmic Ray Energy Spectrum above 3 EeV
  from the Pierre Auger Observatory

abstract:
  Measurements of air showers are accumulating at an increasing rate while
construction proceeds at the Pierre Auger Observatory. Although the southern
site is only half complete, the cumulative exposure is already similar to those
achieved by the largest forerunner experiments. A measurement of the cosmic ray
energy spectrum in the southern sky is reported here. The methods are simple
and robust, exploiting the combination of fluorescence detector (FD) and
surface detector (SD). The methods do not rely on detailed numerical simulation
or any assumption about the chemical composition.


title:
Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7
  Pre-Main Sequence Stars

abstract:
  In January 2003, the Chandra Orion Ultradeep Project (COUP) detected about
1400 young stars during a 13.2 day observation of the Orion Nebula Cluster
(ONC). This paper studies a well-defined sample of 28 solar-mass COUP sources
to characterize the magnetic activity of analogs of the young Sun and thereby
to improve understanding of the effects of solar X-rays on the solar nebula
during the era of planet formation.
  We find that active young Suns spend 70% of their time in a characteristic
state with relatively constant flux and magnetically confined plasma with
temperatures kT_2 = 2.1 * kT_1. During characteristic periods, the 0.5-8 keV
X-ray luminosity is about 0.03% of the bolometric luminosity. One or two
powerful flares per week with peak luminosities logL_x ~ 30-32 erg/s are
typically superposed on this characteristic emission accompanied by heating of
the hot plasma component from ~2.4 keV to ~7 keV at the flare peak. The energy
distribution of flares superposed on the characteristic emission level follows
the relationship dN/dE ~ E^-1.7. The flare rates are consistent with the
production of sufficiently energetic protons to spawn a spallogenic origin of
some important short-lived radionuclides found in ancient meteorites. The
X-rays can ionize gas in the circumstellar disk at a rate of 6 10^-9
ionizations per second at 1 AU from the central star, orders of magnitude above
cosmic ray ionization rates. The estimated energetic particle fluences are
sufficient to a account for many isotopic anomalies observed in meteoritic
inclusions.


title:
On how much X-ray and UV radiation processes are coupled in accretion
  disks: AGN case

abstract:
  Within the standard accretion disk theory for active galactic nuclei (AGN),
the observed X-rays are often modeled by Compton up-scattering of ultraviolet
(UV) disk photons inside a hot disk corona. Here, we point out that for many
AGN, radiation pressure due to the very same UV disk photons can drive a flow
from the disk into the corona and couple the processes producing X-rays and UV
photons. This coupling could lead to quenching of the disk corona because the
regions above the UV disk will be too dense, too opaque, and consequently too
cold. We discuss various consequences of this new type of the X-ray/UV coupling
on the dynamical and radiative properties of AGN.


title: Evolutionary and structural properties of mirror star MACHOs

abstract:
  There can exist a hidden sector of the Universe in the form of parallel
''mirror'' world which has the same particle physics as the observable world
and interacts with the latter only gravitationally. Big Bang Nucleosynthesis
bounds demand that the mirror sector should have a smaller temperature than the
ordinary one. This implies that the mirror matter could play a role of dark
matter, and in addition its chemical content should be dominated by helium.
Here we study the evolutionary and structural properties of the mirror stars
which essentially are similar to that of the ordinary stars but with higher
helium contents. Being invisible in terms of photons, they could be observed
only as MACHOs in the microlensing experiments. Using a numerical code, we
compute evolution of stars with large helium abundances (Y = 0.30-0.80) and a
wide range of masses, from 0.5 to 10 solar masses. We found that helium
dominated mirror star should have much faster evolutionary time (up to a factor
30) than the ordinary star with the same mass. In addition, we show the
diagrams of luminosities, effective temperatures, central temperatures and
densities, and compute the masses of the He core at ignition and the minimum
mass for carbon ignition, for different chemical compositions. The general
conclusion is that mirror stars evolve faster as compared to ordinary ones, and
explode earlier as type II supernovae, thus enriching the galactic halo of
processed mirror gas with higher metallicity, with implications for MACHO
observations and galaxy evolution.


title: Ursa Major: a missing low-mass CDM halo?

abstract:
  The recently discovered Ursa Major dwarf spheroidal (dSph) galaxy candidate
is about five to eight times less luminous than the faintest previously known
dSphs And IX, Draco, and UMi. In this Letter, we present velocity measurements
of seven color-magnitude selected UMajor candidate stars. Two of them are
apparent non-members based on metallicity and velocity, and the remaining five
stars yield a systemic heliocentric velocity of v=-52.45 +/-4.27 km/s and a
central line of sight velocity dispersion of 9.3 (+11.7 -1.2) km/s, with 95%
confidence that the dispersion is >6.5 km/s. Assuming that UMajor is in
dynamical equilibrium, it is clearly dark matter dominated, and cannot be a
purely stellar system like a globular cluster. It has an inferred central
mass-to-light ratio of M/L~500 and, based on our studies of other dSphs, may
possess a much larger total mass to light ratio. UMajor is unexpectedly massive
for its low luminosity -- indeed, UMajor appears to be the most dark-matter
dominated galaxy yet discovered. The presence of so much dark matter in UMajor
immediately suggests that it may be a member of the missing population of
low-mass galaxies predicted by the Cold Dark Matter (CDM) paradigm. Given the
weak correlation between dSph mass and luminosity, it is entirely likely that a
population of dark dwarfs surrounds our Galaxy.


title: Integrated spectrum of the planetary nebula NGC 7027

abstract:
  We present deep optical spectra of the archetypal young planetary nebula (PN)
NGC 7027, covering a wavelength range from 3310 to 9160 A. The observations
were carried out by uniformly scanning a long slit across the entire nebular
surface, thus yielding average optical spectra for the whole nebula. A total of
937 emission features are detected. The extensive line list presented here
should prove valuable for future spectroscopic analyses of emission line
nebulae. The optical data, together with the archival IUE and ISO spectra, are
used to probe the temperature and density structures and to determine the
elemental abundances from lines produced by different excitation mechanisms.
The C++/H+, N++/H+, O++/H+ and Ne++/H+ ionic abundance ratios derived from
optical recombination lines (ORLs) are found to be only slightly higher than
those derived from collisionally excited lines (CELs). We conclude that
whatever mechanism is causing the BJ/CEL temperature discrepanies and the
ORL/CEL abundance discrepancies that have been observed in many PNe, it has an
insignificant effect on this bright young compact PN. The properties of the
central star are also discussed. Based on the integrated spectrum and using the
energy-balance method, we have derived an effective temperature of 219 000 K
for the ionizing star. Finally, we report the first detection in the spectrum
of this bright young PN of Raman-scattered O VI features at 6830 and 7088 A,
pointing to the existence of abundant neutral hydrogen around the ionized
regions. (abridged)


title:
Near room temperature X-ray and Gamma ray spectroscopic detectors for
  future space experiments

abstract:
  New generation Cadmium Telluride (CZT & CdTe) solid state detectors can
provide high quantum efficiency with reasonably good energy resolution and can
operate at near room temperature; an unique advantage for space experiments. We
present here results of our study of small diode detectors as well as large
area pixel detectors. Our study is aimed at developing near room temperature
hard X-ray spectroscopy detectors for ASTROSAT and other future Indian space
science missions.We have studied a Si-PIN detector in the energy range 5 - 60
keV and CZT & CdTe Schottky diode detectors in the energy region 10 - 1330 keV.
We have studied large area (64 cm$^2$) CZT pixel detectors with pixel size
close to the small CZT detector. We have studied individual pixels as well as
CZT detector as a whole (summed over all the 1024 pixels). The energy
resolution behaviour of the large area CZT detector is similar to that of small
diode detectors in the low energy region. The change in operating temperature
from room temperature ~20 to ~70$ degree C drastically affects both the energy
resolutionas well as the peak area due to a sharp rise in the thermal
noise.These results suggest that the cooling of detector system will provide
better energy resolution as well as detection efficiency.


title: The ASTRO-F Mission : Large Area Infrared Survey

abstract:
  ASTRO-F is the first Japanese satellite mission dedicated for large area
surveys in the infrared. The 69cm aperture telescope and scientific instruments
are cooled to 6K by liquid Helium and mechanical coolers. During the expected
mission life of more than 500 days, ASTRO-F will make the most advanced all-sky
survey in the mid- to far-infrared since the Infrared astronomical Satellite
(IRAS). The survey will be made in 6 wavebands and will include the first all
sky survey at >100-160(mu)m. Deep imaging and spectroscopic surveys with
pointed observations will also be carried out in 13 wavelength bands from
2-160(mu)m. ASTRO-F should detect more than a half million galaxies tracing the
large-scale structure of the Universe out to redshifts of unity, detecting
rare, exotic extraordinarily luminous objects at high redshift, numerous brown
dwarfs, Vega-like stars, protostars, and will reveal the large-scale structure
of nearby galactic star forming regions. ASTRO-F is a perfect complement to
Spitzer Space Telescope in respect of its wide sky and wavelength coverage.
Approximately 30 percent of pointed observations will be allocated to an
open-time opportunity. Updated pre-flight ensitivities as well as the
observation plan including the large-area surveys are described.


title: Asteroids. From Observations to Models

abstract:
  We will discuss some specific applications to the rotation state and the
shapes of moderately large asteroids, and techniques of observations putting
some emphasis on the HST/FGS instrument.


title:
Why Newton's gravity is practically reliable in the large-scale
  cosmological simulations

abstract:
  Until now, it has been common to use Newton's gravity to study the non-linear
clustering properties of the large-scale structures. Without confirmation from
Einstein's theory, however, it has been unclear whether we can rely on the
analysis, for example, near the horizon scale. In this work we will provide a
confirmation of using Newton's gravity in cosmology based on relativistic
analysis of weakly non-linear situations to the third order in perturbations.
We will show that, except for the gravitational wave contribution, the
relativistic zero-pressure fluid equations perturbed to the second order in a
flat Friedmann background coincide exactly with the Newtonian results. We will
also present the pure relativistic correction terms appearing in the third
order. The third-order correction terms show that these are the linear-order
curvature perturbation strength higher than the second-order
relativistic/Newtonian terms. Thus, the pure general relativistic corrections
in the third order are independent of the horizon scale and are small in the
large-scale due to the low-level temperature anisotropy of the cosmic microwave
background radiation. Since we include the cosmological constant, our results
are relevant to currently favoured cosmology. As we prove that the Newtonian
hydrodynamic equations are valid in all cosmological scales to the second
order, and that the third-order correction terms are small, our result has a
practically important implication that one can now use the large-scale
Newtonian numerical simulation more reliably as the simulation scale approaches
and even goes beyond the horizon.


title: Radio Detection of Extensive Air Showers with CODALEMA

abstract:
  The principle and performances of the CODALEMA experimental device, set up to
study the possibility of high energy cosmic rays radio detection, are
presented. Radio transient signals associated to cosmic rays have been
identified, for which arrival directions and shower's electric field topologies
have been extracted from the antenna signals. The measured rate, about 1 event
per day, corresponds to an energy threshold around 5.10^16 eV. These results
allow to determine the perspectives offered by the present experimental design
for radiodetection of UHECR at a larger scale.


title:
VLT L-band mapping of the Galactic Center IRS 3-IRS 13 region Evidence
  for new Wolf-Rayet type stars

abstract:
  This paper presents L-band ISAAC and NAOS/CONICA (VLT) spectroscopic
observations of the IRS~3-IRS~13 Galactic Center region. The ISAAC data allowed
us to build the first spectroscopic data cube of the region in the L-band
domain corrected for the foreground extinction. Maps of the water ice and
hydrocarbon absorption line strength were then derived. These maps are
important diagnostics of the interstellar and circumstellar medium (resp. ISM
and CSM). They support our previous results that the absorption features are
most probably occuring in the local Galactic center medium and can be
associated with the individual sources. Moreover, turbulence seems to affect
the studied region of the minispiral which appears like a mixture of a dense
and diffuse medium. The Br alpha and Pf gamma emission line maps allowed us to
find three sources with broad lines corresponding to a FWHM deconvolved line
width of about 1100 km/s and moving towards us with a radial velocity of about
-300km/s. These sources are most probably new Wolf-Rayet type stars located in
projection to the north and west of IRS 3. Their derived radial velocities and
proper motions show that only two of them might belong to the two rotating
disks of young stars reported by Genzel et al. (2003) and Levin & Beloborodov
(2003)...


title: Abundances on the Main Sequence of the Globular Cluster Omega Centauri

abstract:
  Using the 2dF multi-fibre instrument on the AAT, moderate resolution spectra
have been obtained for a large sample of stars on the main sequence and at the
turnoff in the unusual globular cluster omega Centauri. We investigate the
behaviour of CH, CN and SrII line strength indices as a function of overall
abundance for the main sequence sample. A number of stars do not follow the
relations defined by the majority. These anomalous objects can be categorised
into (at least) three types. (1) Carbon enhanced stars, which represent about
5% of the sample, and which are found at all metallicities. Spectrum synthesis
calculations show that the atmospheres of these stars are typically enhanced in
C by factors of between 3 and 10. (2) Nitrogen enhanced stars, revealed for
[Fe/H] > -1.3 by strong CN indices, which make up ~40% of the cluster main
sequence population above this metallicity. These stars are enhanced in N by
factors of up to 100. Our data, however, provide no constraints of their
relative numbers at lower [Fe/H]. (3) Stars with enhancements of the s-process
element Sr by factors of 30 to 60. The possible origins for these abundance
anomalies are discussed.


title:
Dense and Warm Molecular Gas between Double Nuclei of the Luminous
  Infrared Galaxy NGC 6240

abstract:
  High spatial resolution observations of the 12CO(1-0), HCN(1-0), HCO+(1-0),
and 13CO(1-0) molecular lines toward the luminous infrared merger NGC 6240 have
been performed using the Nobeyama Millimeter Array and the RAINBOW
Interferometer. All of the observed molecular emission lines are concentrated
in the region between the double nuclei of the galaxy. However, the
distributions of both HCN and HCO+ emissions are more compact compared with
that of 12CO, and they are not coincident with the star-forming regions. The
HCN/12CO line intensity ratio is 0.25; this suggests that most of the molecular
gas between the double nuclei is dense. A comparison of the observed high
HCN/13CO intensity ratio, 5.9, with large velocity gradient calculations
suggests that the molecular gas is dense [n(H_2)=10^{4-6} cm^-3] and warm
(T_kin>50 K). The observed structure in NGC 6240 may be explained by time
evolution of the molecular gas and star formation, which was induced by an
almost head-on collision or very close encounter of the two galactic nuclei
accompanied with the dense gas and star-forming regions.


title:
Photometric monitoring of the doubly imaged quasar UM673: possible
  evidence for chromatic microlensing

abstract:
  We present the results of two-band CCD photometric monitoring of the
gravitationally lensed quasar Q 0142-100 (UM 673).The data, obtained at ESO-La
Silla with the 1.54 m Danish telescope in the Gunn i-band (October 1998 -
September 1999) and in the Johnson V-band (October 1998 to December 2001), were
analyzed using three different photometric methods. The light-curves obtained
with all methods show variations, with a peak-to-peak amplitude of 0.14
magnitude in $V$. Although it was not possible to measure the time delay
between the two lensed QSO images, the brighter component displays possible
evidence for microlensing: it becomes bluer as it gets brighter, as expected
under the assumption of differential magnification of a quasar accretion disk


title:
Obscured Activity: AGN, Quasars, Starbursts and ULIGs observed by the
  Infrared Space Observatory

abstract:
  Some of the most active galaxies in the Universe are obscured by large
quantities of dust and emit a substantial fraction of their bolometric
luminosity in the infrared. Observations of these infrared luminous galaxies
with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed
view to the sources fuelling this active emission. The improved sensitivity,
spatial resolution and spectroscopic capability of ISO over its predecessor
Infrared Astronomical Satellite (IRAS), has enabled significant advances in the
understanding of the infrared properties of active galaxies. ISO surveyed a
wide range of active galaxies which, in the context of this review, includes
those powered by intense bursts of star-formation as well as those containing a
dominant active galactic nucleus (AGN). Mid infrared imaging resolved for the
first time the dust enshrouded nuclei in many nearby galaxies, while a new era
in infrared spectroscopy was opened by probing a wealth of atomic, ionic and
molecular lines as well as broad band features in the mid and far infrared.
This was particularly useful since it resulted in the understanding of the
power production, excitation and fuelling mechanisms in the nuclei of active
galaxies including the intriguing but so far elusive ultraluminous infrared
galaxies. Detailed studies of various classes of AGN and quasars greatly
improved our understanding of the unification scenario. Far-infrared imaging
and photometry also revealed the presence of a new very cold dust component in
galaxies and furthered our knowledge of the far-infrared properties of faint
starbursts, ULIGs and quasars. We summarise almost nine years of key results
based upon ISO data spanning the full range of luminosity and type of active
galaxies.


title: The Dipole Anisotropy of the 2 Micron All-Sky Redshift Survey

abstract:
  We estimate the acceleration on the Local Group (LG) from the Two Micron All
Sky Redshift Survey (2MRS). The sample used includes about 23,200 galaxies with
extinction corrected magnitudes brighter than K_s=11.25 and it allows us to
calculate the flux weighted dipole. The near-infrared flux weighted dipoles are
very robust because they closely approximate a mass weighted dipole, bypassing
the effects of redshift distortions and require no preferred reference frame.
This is combined with the redshift information to determine the change in
dipole with distance. The misalignment angle between the LG and the CMB dipole
drops to 12 degrees at around 50 Mpc/h, but then increases at larger distances,
reaching 21 degrees at around 130 Mpc/h. Exclusion of the galaxies Maffei 1,
Maffei 2, Dwingeloo 1, IC342 and M87 brings the resultant flux dipole to 14
degrees away from the CMB velocity dipole In both cases, the dipole seemingly
converges by 60 Mpc/h. Assuming convergence, the comparison of the 2MRS flux
dipole and the CMB dipole provides a value for the combination of the mass
density and luminosity bias parameters Omega_m^0.6/b_L=0.40+/-0.09.


title:
An explanation for the kHz-QPO twin peaks separation in slow and fast
  rotators

abstract:
  In this Letter we further explore the idea, suggested previously by
Klu{\'z}niak and collaborators, that the high frequency QPOs may be explained
as a resonant coupling between the neutron star spin and two epicyclic modes of
accretion disk oscillations. We confirm result of Lee, Abramowicz and
Klu{\'z}niak (\cite{Lee2004}) that the strongest response occurs when the
frequency difference of the two modes equals either the spin frequency (for
``slow rotators'') or half of it (for ``fast rotators''). New points discussed
in this Letter are: (1) We suggest that the coupling is gravitational, and due
to a non-axially symmetric structure of the rotating neutron star. (2) We found
that two excited modes may be both connected to vertical oscillations of the
disk, and that strong gravity is not needed to excite the modes.


title: The Stellar Populations of dSph Galaxies in Nearby Groups

abstract:
  In this contribution initial results are presented from a program to study in
detail the stellar populations of dwarf Spheroidal (dSph) galaxies in three
nearby groups. The long-term aim of the program is to assess the influence of
environment in governing the evolution of these low-luminosity systems.
Specific results described here include the detection and measurement of
intermediate-age upper-AGB populations in dSphs in the M81 and Cen A groups,
and the discovery that four of the five low-luminosity early-type dwarfs in the
low density Sculptor group contain modest amounts of neutral hydrogen gas.


title: UV properties of early-type galaxies in the Virgo cluster

abstract:
  We study the UV properties of a volume limited sample of early-type galaxies
in the Virgo cluster combining new GALEX far- (1530 A) and near-ultraviolet
(2310 A) data with spectro-photometric data available at other wavelengths. The
sample includes 264 ellipticals, lenticulars and dwarfs spanning a large range
in luminosity (M(B)<-15). While the NUV to optical or near-IR color magnitude
relations (CMR) are similar to those observed at optical wavelengths, with a
monotonic reddening of the color index with increasing luminosity, the (FUV-V)
and (FUV-H) CMRs show a discontinuity between massive and dwarf objects. An
even more pronounced dichotomy is observed in the (FUV-NUV) CMR. For
ellipticals the (FUV-NUV) color becomes bluer with increasing luminosity and
with increasing reddening of the optical or near-IR color indices. For the
dwarfs the opposite trend is observed. These observational evidences are
consistent with the idea that the UV emission is dominated by hot, evolved
stars in giant systems, while in dwarf ellipticals residual star formation
activity is more common.


title: Prospects for Dark Energy Evolution: a Frequentist Multi-Probe Approach

abstract:
  A major quest in cosmology is the understanding of the nature of dark energy.
It is now well known that a combination of cosmological probes is required to
break the underlying degeneracies on cosmological parameters. In this paper, we
present a method, based on a frequentist approach, to combine probes without
any prior constraints, taking full account of the correlations in the
parameters. As an application, a combination of current SNIa and CMB data with
an evolving dark energy component is first compared to other analyses. We
emphasise the consequences of the implementation of the dark energy
perturbations on the result for a time varying equation of state. The impact of
future weak lensing surveys on the measurement of dark energy evolution is then
studied in combination with future measurements of the cosmic microwave
background and type Ia supernovae. We present the combined results for future
mid-term and long-term surveys and confirm that the combination with weak
lensing is very powerful in breaking parameter degeneracies. A second
generation of experiment is however required to achieve a 0.1 error on the
parameters describing the evolution of dark energy.


title: Hinting at primary composition using asymmetries in time distributions

abstract:
  Evidence of azimuthal asymmetries in the time structure and signal size have
been found in non-vertical showers at the Pierre Auger Observatory. It has been
previously shown that the asymmetry in time distributions offers a new
possibility for the determination of the mass composition. New studies have
demonstrated that the dependence of the asymmetry parameter in the rise-time
and fall-time distributions with sec(theta) shows a clear peak. Both, the
position of the peak, X_asymax, and the size of the asymmetry at X_asymax are
sensitive to primary mass composition and have a small dependence on energy. In
this paper a study of the discriminating power of the new observables to
separate primary species is presented.


title: Methanol emission from low mass protostars

abstract:
  We present observations of methanol lines in a sample of Class 0 low mass
protostars. Using a 1-D radiative transfer model, we derive the abundances in
the envelopes. In two sources of the sample, the observations can only be
reproduced by the model if the methanol abundance is enhanced by about two
order of magnitude in the inner hot region of the envelope. Two other sources
show similar jumps, although at a lower confidence level. The observations for
the other three sources are well reproduced with a constant abundance, but the
presence of a jump cannot be ruled out. The observed methanol abundances in the
warm gas around low mass protostars are orders of magnitude higher than gas
phase chemistry models predict. Hence, in agreement with other evidences, this
suggest that the high methanol abundance reflects recent evaporation of ices
due to the heating by the newly formed star. The observed abundance ratios of
CH3 OH, H2 CO, and CO are in good agreement with grain surface chemistry
models. However, the absolute abundances are more difficult to reproduce and
may point towards the presence of multiple ice components in these regions.


title: On the nature of X-Ray Flashes

abstract:
  We discuss the origin of X-Ray Flashes (XRFs), a recently discovered class of
Gamma-Ray Bursts (GRBs). Using a simplified model for internal shocks we check
if XRFs can be intrinsically soft due to some specific values of the parameters
describing the relativistic outflow emerging from the central engine. We
generate a large number of synthetic events and find that XRFs are obtained
when the contrast Gamma_max/Gamma_min of the Lorentz factor distribution is
small while the average Lorentz factor Gamma is large. A few XRFs may be GRBs
at large redshifts but we exclude this possibility for the bulk of the
population. If outflows with a small contrast are commonly produced, even a
large population of XRFs could be explained. If conversely the Lorentz factor
distribution within the wind is broad, one should then rely on extrinsic
causes, such as viewing angle effects or high redshift.


title:
A new constraint on the time dependence of the proton-to-electron mass
  ratio. Analysis of the Q 0347-383 and Q 0405-443 spectra

abstract:
  A new limit on the possible cosmological variation of the proton-to-electron
mass ratio \mu=m_p/m_e is estimated by measuring wavelengths of H_2 lines of
Lyman and Werner bands from two absorption systems at z_abs = 2.5947 and 3.0249
in the spectra of quasars Q 0405-443 and Q 0347-383, respectively. Data are of
the highest spectral resolution (R = 53000) and S/N ratio (30\div70) for this
kind of study. We search for any correlation between z_i, the redshift of
observed lines, determined using laboratory wavelengths as references, and K_i,
the sensitivity coefficient of the lines to a change of \mu, that could be
interpreted as a variation of \mu over the corresponding cosmological time. We
use two sets of laboratory wavelengths, the first one, Set (A) (Abgrall et
al.), based on experimental determination of energy levels and the second one,
Set (P) (Philip et al.), based on new laboratory measurements of some
individual rest-wavelengths. We find \Delta\mu/\mu = (3.05+-0.75)10^-5 for Set
(A), and \Delta\mu/\mu = (1.65+-0.74)10^-5 for Set (P). The second
determination is the most stringent limit on the variation of \mu over the last
12 Gyrs ever obtained. The correlation found using Set (A) seems to show that
some amount of systematic error is hidden in the determination of energy levels
of the H$_2$ molecule.


title: Exploring the Hard X-/soft gamma-ray Continuum Spectra with Laue Lenses

abstract:
  The history of X-ray astronomy has shown that any advancement in our
knowledge of the X-ray sky is strictly related to an increase in instrument
sensitivity. At energies above 60 keV, there are interesting prospects for
greatly improving the limiting sensitivity of the current generation of direct
viewing telescopes (with or without coded masks), offered by the use of Laue
lenses. We will discuss below the development status of a Hard X-Ray focusing
Telescope (HAXTEL) based on Laue lenses with a broad bandpass (from 60 to 600
keV) for the study of the X-ray continuum of celestial sources. We show two
examplesof multi-lens configurations with expected sensitivity orders of
magnitude better ($\sim 1 \times 10^{-8}$ photons cm$^{-2}$ s$^{-1}$ keV$^{-1}$
at 200 keV) than that achieved so far. With this unprecedented sensitivity,
very exciting astrophysical prospects are opened.


title: Simulating field-aligned diffusion of a cosmic ray gas

abstract:
  The macroscopic behaviour of cosmic rays in turbulent magnetic fields is
discussed. An implementation of anisotropic diffusion of cosmic rays with
respect to the magnetic field in a non-conservative, high-order,
finite-difference magnetohydrodynamic code is discussed. It is shown that the
standard implementation fails near singular X-points of the magnetic field,
which are common if the field is random. A modification to the diffusion model
for cosmic rays is described and the resulting telegraph equation (implemented
by solving a dynamic equation for the diffusive flux of cosmic rays) is used;
it is argued that this modification may better describe the physics of cosmic
ray diffusion. The present model reproduces several processes important for the
propagation and local confinement of cosmic rays, including spreading
perpendicular to the local large-scale magnetic field, controlled by the
random-to-total magnetic field ratio, and the balance between cosmic ray
pressure and magnetic tension. Cosmic ray diffusion is discussed in the context
of a random magnetic field produced by turbulent dynamo action. It is argued
that energy equipartition between cosmic rays and other constituents of the
interstellar medium do not necessarily imply that cosmic rays play a
significant role in the balance of forces.


title:
On the frequency of close binary systems among very low-mass stars and
  brown dwarfs

abstract:
  We have used Monte Carlo simulation techniques and published radial velocity
surveys to constrain the frequency of very low-mass star (VLMS) and brown dwarf
(BD) binary systems and their separation (a) distribution. Gaussian models for
the separation distribution with a peak at a = 4 au and 0.6 =< sigma(log(a/au))
=< 1.0 correctly predict the number of observed binaries, yielding a close
(a<2.6 au) binary frequency of 17-30 per cent and an overall VLMS/BD binary
frequency of 32-45 per cent. We find that the available N-body models of
VLMS/BD formation from dynamically decaying protostellar multiple systems are
excluded at >99 per cent confidence because they predict too few close binary
VLMS/BDs. The large number of close binaries and high overall binary frequency
are also very inconsistent with recent smoothed particle hydrodynamical
modelling and argue against a dynamical origin for VLMS/BDs.


title: Intergalactic HeII absorption towards QSO 1157+3143

abstract:
  We report the discovery of a further line of sight allowing detection of HeII
Ly alpha absorption by the intergalactic medium. A HST/STIS survey of 32 bright
z ~ 3 quasars selected from the Hamburg Quasar Surveys yielded one detection
toward QSO 1157+3143 (z ~ 3, B ~ 17). A 10 orbit follow-up spectrum reveals a
UV spectrum significantly supressed by two intervening Lyman limit systems at
z=2.77 and 2.94, but with the continuum flux recovering sufficiently shortward
of ~ 1700 A to allow study of the HeII absorption spectrum in the redshift
range 2.75 < z < 2.97. The absorption is characterized by alternating voids and
dense filament structures seen in both HeII and HI. Attempts to model the HeII
opacity in terms of HI Ly alpha forest absorption are not successful in the
voids, suggesting that HeII reionization is not complete between z=2.77 and
2.97 or that an optically thin Lyman limit system with z ~ 0.3 is responsible
for the additional opacity.


title:
Source blending effects on microlensing time-histograms and optical
  depth determination

abstract:
  Source blending in microlensing experiments is known to modify the Einstein
time of the observed events. In this paper, we have conducted Monte-Carlo
calculations, using the analytical relationships derived by Han (1999) to
quantify the effect of blending on the observed event time distribution and
optical depth. We show that short-time events are affected significantly by
source blending and that, for moderately blended sources, the optical depth
$\tau$ is globally overestimated, because of an underestimation of the
exposure. For high blending situations, on the opposite, blending leads to an
{\it under}estimation of the optical depth. Our results are in agreement with
the most recent optical depth determinations toward the Galactic Center of the
MACHO collaboration (Popowski et al. 2004) and the OGLE-II collaboration (Sumi
et al. 2005) that use clump giants (less affected by the blending effect) as
sources. The blending-corrected, lower optical depth toward the Galactic Bulge
is now in good agreement with the value inferred from galactic models,
reconciling theoretical and observational determinations.


title:
Oligarchic and giant impact growth of terrestrial planets in the
  presence of gas giant planet migration

abstract:
  We present the results of N--body simulations which examine the effect that
gas giant planet migration has on the formation of terrestrial planets. The
models incorporate a 0.5 Jupiter mass planet undergoing type II migration
through an inner protoplanet--planetesimal disk, with gas drag included. Each
model is initiated with the inner disk being at successively increased levels
of maturity, so that it is undergoing either oligarchic or giant impact style
growth as the gas giant migrates. In all cases, a large fraction of the disk
mass survives the passage of the giant, either by accreting into massive
terrestrial planets shepherded inward of the giant, or by being scattered into
external orbits. Shepherding is favored in younger disks where there is strong
dynamical friction from planetesimals and gas drag is more influential, whereas
scattering dominates in more mature disks where dissipation is weaker. In each
scenario, sufficient mass is scattered outward to provide for the eventual
accretion of a set of terrestrial planets in external orbits, including within
the system's habitable zone. An interesting result is the generation of
massive, short period, terrestrial planets from compacted material pushed ahead
of the giant. These planets are reminiscent of the short period Neptune mass
planets discovered recently, suggesting that such `hot Neptunes' could form
locally as a by-product of giant planet migration.


title: The Spherical Accretion Shock Instability in the Linear Regime

abstract:
  We use time-dependent, axisymmetric, hydrodynamic simulations to study the
linear stability of the stalled, spherical accretion shock that arises in the
post-bounce phase of core-collapse supernovae. We show that this accretion
shock is stable to radial modes, with decay rates and oscillation frequencies
in close agreement with the linear stability analysis of Houck and Chevalier.
For non-spherical perturbations we find that the l=1 mode is always unstable
for parameters appropriate to core-collapse supernovae. We also find that the
l=2 mode is unstable, but typically has a growth rate smaller than that for
l=1. Furthermore, the l=1 mode is the only mode found to transition into a
nonlinear stage in our simulations. This result provides a possible explanation
for the dominance of an l=1 'sloshing' mode seen in many two-dimensional
simulations of core-collapse supernovae.


title: The Detectability of Pair-Production Supernovae at z < 6

abstract:
  Nonrotating, zero metallicity stars with initial masses 140 < M < 260 solar
masses are expected to end their lives as pair-production supernovae (PPSNe),
in which an electron-positron pair-production instability triggers explosive
nuclear burning. Interest in such stars has been rekindled by recent
theoretical studies that suggest primordial molecular clouds preferentially
form stars with these masses. Since metal enrichment is a local process, the
resulting PPSNe could occur over a broad range of redshifts, in pockets of
metal-free gas. Using the implicit hydrodynamics code KEPLER, we have
calculated a set of PPSN light curves that addresses the theoretical
uncertainties and allows us to assess observational strategies for finding
these objects at intermediate redshifts. The peak luminosities of typical PPSNe
are only slightly greater than those of Type Ia, but they remain bright much
longer (~ 1 year) and have hydrogen lines. Ongoing supernova searches may soon
be able to limit the contribution of these very massive stars to < 1% of the
total star formation rate density out to z=2 which already provides useful
constraints for theoretical models. The planned Joint Dark Energy Mission
satellite will be able to extend these limits out to z=6.


title:
First results from the Canada-France High-z Quasar Survey: Constraints
  on the z=6 quasar luminosity function and the quasar contribution to
  reionization

abstract:
  We present preliminary results of a new quasar survey being undertaken with
multi-colour optical imaging from the Canada-France-Hawaii Telescope. The
current data consists of 3.83 sq. deg. of imaging in the i' and z' filters to a
10 sigma limit of z'<23.35. Near-infrared photometry of 24 candidate 5.7<z<6.4
quasars confirms them all to be low mass stars including two T dwarfs and four
or five L dwarfs. Photometric estimates of the spectral type of the two T
dwarfs are T3 and T6. We use the lack of high-redshift quasars in this survey
volume to constrain the z=6 quasar luminosity function. For reasonable values
of the break absolute magnitude M*_1450 and faint-end slope alpha, we determine
that the bright-end slope beta>-3.2 at 95% confidence. We find that the
comoving space-density of quasars brighter than M_1450=-23.5 declines by a
factor >25 from z=2 to z=6, mirroring the decline observed for high-luminosity
quasars. We consider the contribution of the quasar population to the ionizing
photon density at z=6 and the implications for reionization. We show that the
current constraints on the quasar population give an ionizing photon density
<<30% that of the star-forming galaxy population. We conclude that active
galactic nuclei make a negligible contribution to the reionization of hydrogen
at z~6.


title:
Probing Cosmic Acceleration Beyond the Equation of State: Distinguishing
  between Dark Energy and Modified Gravity Models

abstract:
  If general relativity is the correct theory of physics on large scales, then
there is a differential equation that relates the Hubble expansion function,
inferred from measurements of angular diameter distance and luminosity
distance, to the growth rate of large scale structure. For a dark energy fluid
without couplings or an unusual sound speed, deviations from this consistency
relationship could be the signature of modified gravity on cosmological scales.
We propose a procedure based on this consistency relation in order to
distinguish between some dark energy models and modified gravity models. The
procedure uses different combinations of cosmological observations and is able
to find inconsistencies when present. As an example, we apply the procedure to
a universe described by a recently proposed 5-dimensional modified gravity
model. We show that this leads to an inconsistency within the dark energy
parameter space detectable by future experiments.


title:
Chandra Deep X-ray Observation of a Typical Galactic Plane Region and
  Near-Infrared Identification

abstract:
  Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I),
we have carried out a deep hard X-ray observation of the Galactic plane region
at (l,b) ~ (28.5, 0.0), where no discrete X-ray source had been reported
previously. We have detected 274 new point X-ray sources (4 sigma confidence)
as well as strong Galactic diffuse emission within two partially overlapping
ACIS-I fields (~250 arcmin^2in total). Sum of all the detected point source
fluxes accounts for only ~ 10 % of the total X-ray flux in the field of view.
Even hypothesizing a new population of much dimmer and numerous Galactic point
sources, the total observed X-ray flux cannot be explained. Therefore, we
conclude that X-ray emission from the Galactic plane has truly diffuse origin.
Only 26 point sources were detected both in the soft and hard bands, indicating
that there are two distinct classes of the X-ray sources distinguished by the
spectral hardness ratio. Surface number density of the hard sources is only
slightly higher than that measured at the high Galactic latitude regions,
indicating that majority of the hard sources are background AGNs. Following up
the Chandra observation, we have performed a near-infrared (NIR) survey with
SOFI at ESO/NTT. Almost all the soft X-ray sources have been identified in NIR
and their spectral types are consistent with main-sequence stars, suggesting
most of them are nearby X-ray active stars. On the other hand, only 22 % of the
hard sources had NIR counterparts, which are presumably Galactic. From X-ray
and NIR spectral study, they are most likely to be quiescent cataclysmic
variables. We have also carried out a precise spectral study of the Galactic
diffuse X-ray emission excluding the point sources.


title:
Multipole vector anomalies in the first-year WMAP data: a cut-sky
  analysis

abstract:
  We apply the recently defined multipole vector framework to the
frequency-specific first-year WMAP sky maps, estimating the low-l multipole
coefficients from the high-latitude sky by means of a power equalization
filter. While most previous analyses of this type have considered only heavily
processed (and foreground-contaminated) full-sky maps, the present approach
allows for greater control of residual foregrounds, and therefore potentially
also for cosmologically important conclusions. The low-l spherical harmonics
coefficients and corresponding multipole vectors are tabulated for easy
reference.
  Using this formalism, we re-assess a set of earlier claims of both
cosmological and non-cosmological low-l correlations based on multipole
vectors. First, we show that the apparent l=3 and 8 correlation claimed by Copi
et al. (2004) is present only in the heavily processed map produced by Tegmark
et al. (2003), and must therefore be considered an artifact of that map.
Second, the well-known quadrupole-octopole correlation is confirmed at the 99%
significance level, and shown to be robust with respect to frequency and sky
cut. Previous claims are thus supported by our analysis. Finally, the low-l
alignment with respect to the ecliptic claimed by Schwarz et al. (2004) is
nominally confirmed in this analysis, but also shown to be very dependent on
severe a-posteriori choices. Indeed, we show that given the peculiar
quadrupole-octopole arrangement, finding such a strong alignment with the
ecliptic is not unusual.


title: The [O III] Veil: Astropause of Eta Carinae's Wind?

abstract:
  We present narrowband images of eta Carinae in the light of [O III] 5007
obtained with HST/WFPC2, as well as a ground-based image in the same emission
line with a larger field of view. These images show a thin veil of [O III]
emission around eta Car and its ejecta, confirming the existence of an
oxygen-bearing ``cocoon'' inferred from spectra. This [O III] veil may be the
remnant of the pre-outburst wind of eta Car, and its outer edge probably marks
the interface where eta Car's ejecta meet the stellar wind of the nearby O4
V((f)) star HD303308 or other ambient material -- i.e., it marks the
``astropause'' in eta Car's wind. This veil is part of a more extensive [O III]
shell that appears to be shaped and ionized by HD303308. A pair of HST images
with a 10 yr baseline shows no proper motion, limiting the expansion speed away
from eta Car to 12pm13 km/s, or an expansion age of a few times 10^4 yr. Thus,
this is probably the decelerated pre-outburst LBV wind of eta Car. The [O III]
morphology is very different from that seen in [N II], which traces young knots
of CNO-processed material; this represents a dramatic shift in the chemical
makeup of material recently ejected by eta Car. This change in the chemical
abundances may have resulted from the sudden removal of the star's outer
envelope during eta Car's 19th century outburst or an earlier but similar
event.


title: Tracing the spiral arms in IP Pegasi

abstract:
  We report the analysis of time-resolved spectroscopy of IP Pegasi in outburst
with eclipse mapping techniques to investigate the location and geometry of the
observed spiral structures. We were able to obtain an improved view of the
spiral structures with the aid of light curves extracted in velocity bins
matching the observed range of velocities of the spiral arms combined with a
double default map tailored for reconstruction of asymmetric structures.
Two-armed spiral structures are clearly seen in all eclipse maps. The arms are
located at different distances from the disc centre. The ``blue'' arm is
farther out in the disc (R= 0.55 +/- 0.05 R_{L1}) than the ``red'' arm (R= 0.30
+/- 0.05 R_{L1}). There are evidences that the velocity of the emitting gas
along the spiral pattern is lower than the Keplerian velocity for the same disc
radius. The discrepancy is smaller in the outer arm (measured velocities 10-15
per cent lower than Keplerian) and is more significant in the inner arm
(observed velocities up to 40 per cent lower than Keplerian). We measured the
opening angle of the spirals from the azimuthal intensity distribution of the
eclipse maps to be \phi= 25 +/- 3 degrees. A comparison with similar
measurements on data at different outburst stages reveals that the opening
angle of the spiral arms in IP Peg decreases while the outbursting accretion
disc cools and shrinks, in agreement with the expected evolution of a tidally
driven spiral wave. The sub-Keplerian velocities along the spiral pattern and
the clear correlation between the opening angle of the spirals and the outburst
stage favors the interpretation of these asymmetric structures as
tidally-induced spiral shocks.


title: Hot Accretion With Saturated Conduction

abstract:
  Observations of the hot gas surrounding Sgr A* and a few other nearby
galactic nuclei imply electron and proton mean free paths comparable to the gas
capture radius: hot accretion likely proceeds under weakly-collisional
conditions in these systems. As a result, thermal conduction, rather than
convection, may be important on all scales and affect the global flow
properties. The self-similar ADAF solution of Narayan & Yi (1994) is
generalized to include a saturated form of thermal conduction, as is
appropriate for the weakly-collisional regime of interest. Conduction provides
extra heating and yet it reduces the free-free radiative efficiency of the
accretion flow (by potentially large factors). These idealized solutions
suggest that thermal conduction may be an important physical ingredient to
understand hot accretion onto dim accreting black holes. Conduction could also
play a role in reducing the rate at which black holes capture ambient gas and
in providing an evaporation mechanism for an underlying cold thin disk.


title:
Exclusion Limits on the WIMP-Nucleon Cross-Section from the First Run of
  the Cryogenic Dark Matter Search in the Soudan Underground Lab

abstract:
  The Cryogenic Dark Matter Search (CDMS-II) employs low-temperature Ge and Si
detectors to seek Weakly Interacting Massive Particles (WIMPs) via their
elastic scattering interactions with nuclei. Simultaneous measurements of both
ionization and phonon energy provide discrimination against interactions of
background particles. For recoil energies above 10 keV, events due to
background photons are rejected with >99.99% efficiency. Electromagnetic events
very near the detector surface can mimic nuclear recoils because of reduced
charge collection, but these surface events are rejected with >96% efficiency
by using additional information from the phonon pulse shape. Efficient use of
active and passive shielding, combined with the the 2090 m.w.e. overburden at
the experimental site in the Soudan mine, makes the background from neutrons
negligible for this first exposure. All cuts are determined in a blind manner
from in situ calibrations with external radioactive sources without any prior
knowledge of the event distribution in the signal region. Resulting
efficiencies are known to ~10%. A single event with a recoil of 64 keV passes
all of the cuts and is consistent with the expected misidentification rate of
surface-electron recoils. Under the assumptions for a standard dark matter
halo, these data exclude previously unexplored parameter space for both
spin-independent and spin-dependent WIMP-nucleon elastic scattering. The
resulting limit on the spin-independent WIMP-nucleon elastic-scattering
cross-section has a minimum of 4x10^-43 cm^2 at a WIMP mass of 60 GeV/c^2. The
minimum of the limit for the spin-dependent WIMP-neutron elastic-scattering
cross-section is 2x10^-37 cm^2 at a WIMP mass of 50 GeV/c^2.


title:
BIMA Array Observations of the Highly Unusual SiO Maser Source with a
  Bipolar Nebulosity, IRAS 19312+1950

abstract:
  We report the results of mapping observations of the bipolar nebula with SiO
maser emission, IRAS 19312+1950, in the CO (J=1-0 and J=2-1), 13CO (J=1-0 and
J=2-1), C18O (J=1-0), CS (J=2-1), SO (J_K=3_2-2_1) and HCO+ (J=3-2) lines with
the Berkeley-Illinois-Maryland Association array. Evolutional status of this
source has been evoking a controversy since its discovery, though SiO maser
sources are usually identified as late-type stars with active mass loss. In
line profiles, two kinematical components are found as reported in previous
single-dish observations: a broad pedestal component and a narrow component.
Spatio-kinetic properties of a broad component region traced by 12CO lines are
roughly explained by a simple spherical outflow model with a typical expanding
velocity of an AGB star, though some properties of the broad component region
still conflict with properties of a typical AGB spherical outflow. A narrow
component region apparently exhibits a bipolar flow. The angular size of the
narrow component region is spatially larger than that of a broad component
region. Intensity distribution of the CS emission avoids the central region of
the source, and that of an SO broad component emission exhibits a small feature
peaked exactly at the mapping center. According to the present results, if a
broad component really originates in a spherical outflow, an oxygen-rich
evolved stellar object seems to be a natural interpretation for the central
star of IRAS 19312+1950.


title:
Gamma-ray bursts as dark energy-matter probes in the context of the
  generalized Chaplygin gas model

abstract:
  In this paper we consider the use of Gamma Ray Bursts (GRBs) as distance
markers to study the unification of dark energy and dark matter in the context
of the so-called Generalized Chaplygin Gas (GCG) model. We consider that the
GRB luminosity may be estimated from its variability, time-lag, and also use
the so-called Ghirlanda relation. We evaluate the improvements one may expect
once more GRBs and their redshift become available. We show that although GRBs
allow for extending the Hubble diagram to higher redshifts, its use as a dark
energy probe is limited when compared to SNe Ia. We find that the information
from GRBs can provide some bounds on the amount of dark matter and dark energy
independently of the equation of state. This is particularly evident for
XCDM-type models, which are, for low-redshifts ($z\leq2$), degenerate with the
GCG.


title:
Inflaton field potential producing the exactly flat spectrum of
  adiabatic perturbations

abstract:
  Presented is the exact solution of the problem of finding a potential of an
inflaton scalar field for which adiabatic perturbations generated during a de
Sitter (inflationary) stage in the early Universe have the exactly flat (or,
the Harrison-Zeldovich) initial spectrum. This solution lies outside the scope
of the slow-roll approximation and higher-order corrections to it. The
potential found depends on two arbitrary physical constants, one of those
determines an amplitude of perturbations. For small (zero) values of the other
constant, a long (infinite) inflationary stage with slow rolling of the
inflaton field exists.


title: Morphology of synchrotron emission in young supernova remnants

abstract:
  In the framework of test-particle and cosmic-ray modified hydrodynamics, we
calculate synchrotron emission radial profiles in young ejecta-dominated
supernova remnants (SNRs) evolving in an ambient medium which is uniform in
density and magnetic field. We find that, even without any magnetic field
amplification by Raleigh-Taylor instabilities, the radio synchrotron emission
peaks at the contact discontinuity because the magnetic field is compressed and
is larger there than at the forward shock. The X-ray synchrotron emission
sharply drops behind the forward shock as the highest energy electrons suffer
severe radiative losses.


title: Virialization in Dark Energy Cosmology

abstract:
  We discuss the issue of energy nonconservation in the virialzation process of
spherical collapse model with homogeneous dark energy. We propose an
approximation scheme to find the virialization radius. By comparing various
schemes and estimating the parameter characterizing the ratio of dark energy to
dark matter at the turn-around time, we conclude that the problem of energy
nonconservation may have sizable effects in fitting models to observations.


title:
The relativistic shift of narrow spectral features from black-hole
  accretion discs

abstract:
  Transient spectral features have been discovered in the X-ray spectra of
Active Galactic Nuclei, mostly in the 5--7 keV energy range. Several
interpretations were proposed for the origin of these features. We examined a
model of Doppler boosted blue horns of the iron line originating from a spot in
a black hole accretion disc, taking into account different approximations of
general relativistic light rays and the resulting shift of energy of photons.
We provide a practical formula for the blue horn energy of an intrinsically
narrow line and assess its accuracy by comparing the approximation against an
exact value, predicted under the assumption of a planar accretion disc. The
most accurate approximation provides excellent agreement with the spot orbital
radius down to the marginally stable orbit of a non-rotating black hole.


title: Light-cone Simulations: Evolution of dark matter haloes

abstract:
  We present a new fast method for simulating pencil-beam type light-cones,
using the MLAPM-code (Multi Level Adaptive Particle Mesh) with light-cone
additions. We show that by a careful choice of the light-cone orientation, it
is possible to avoid extra periodicities in the light-cone. As an example, we
apply the method to simulate a 6 Gpc deep light-cone, create the dark matter
halo catalogue for the light-cone and study the evolution of haloes from $z=6$
up to the present time. We determine the spatial density of the haloes, their
large-scale correlation function, and study the evolution of the mass function.
We find a surprisingly simple relation for the dependence of halo maximum mass
on redshift, and apply it to derive redshift limits for bright quasars.


title:
Probing the outer edge of an accretion disk: A Her X-1 turn-on observed
  with RXTE

abstract:
  We present the analysis of Rossi X-ray Timing Explorer (RXTE) observations of
the turn-on phase of a 35 day cycle of the X-ray binary Her X-1. During the
early phases of the turn-on, the energy spectrum is composed of X-rays
scattered into the line of sight plus heavily absorbed X-rays. The energy
spectra in the 3-17 keV range can be described by a partial covering model,
where one of the components is influenced by photoelectric absorption and
Thomson scattering in cold material plus an iron emission line at 6.5 keV. In
this paper we show the evolution of spectral parameters as well as the
evolution of the pulse profile during the turn-on. We describe this evolution
using Monte Carlo simulations which self-consistently describe the evolution of
the X-ray pulse profile and of the energy spectrum.


title: Radiation-induced solitary waves in hot plasmas of accretion disks

abstract:
  It is shown that the existence of radiation-induced solitary waves in hot
plasmas of accretion disks depends on the radial temperature profile.


title: Discovery of nine quasars behind the Large Magellanic Cloud

abstract:
  We present the discovery of nine quasars behind the Large Magellanic Cloud,
with emission redshifts ranging from 0.07 to 2.0. Six of them were identified
as part of the systematic variability-based search for QSOs in the objects from
the OGLE-II database. Combination of variability-based selection of candidates
with the candidates' colours appears to be a powerful technique for identifying
quasars, potentially reaching ca. 50% efficiency. We report an apparent
correlation between variability magnitude and variability timescale, which - if
confirmed - could put even more constraints on QSO candidate selection. The
remaining three quasars were identified via followup spectroscopy of optical
counterparts to X-ray sources found serendipitously by the Chandra X-ray
Observatory satellite. Even though the locations of the candidates were quite
uniformly distributed over the LMC bar, the confirmed QSOs all appear near the
bar's outskirts.


title: The Coughing Pulsar Magnetosphere

abstract:
  Polar magnetospheric gaps consume a fraction of the electric potential that
develops accross open field lines. This effect modifies significantly the
structure of the axisymmetric pulsar magnetosphere. We present numerical
stead-state solutions for various values of the gap potential. We show that a
charge starved magnetosphere contains significantly less electric current than
one with freely available electric charges. As a result, electromagnetic
neutron star braking becomes inefficient. We argue that the magnetosphere may
spontaneously rearrange itself to a lower energy configuration through a
dramatic release of electromagnetic field energy and magentic flux. Our results
might be relevant in understanding the recent December 27, 2004 burst observed
in SGR 1806-20.


title: CH stars at High Galactic Latitudes

abstract:
  In the present work we report on several CH stars identified in a sample of
Faint High Latitude Carbon stars from Hamburg survey and discuss their medium
resolution spectra covering a wavelength range 4000 - 6800 \AA . Estimation of
the depths of bands (1,0) $^{12}$C$^{12}$C ${\lambda}$4737 and (1,0)
$^{12}$C$^{13}$C ${\lambda}$4744 in these stars indicate isotopic ratio
$^{12}$C/$^{13}$C ${\sim}$ 3, except for a few exceptions; these ratios are
consistent with existing theories of CH stars evolution. The stars of Hamburg
survey, a total of 403 objects were reported to be carbon star candidates with
strong C$_{2}$ and CN molecular bands.
  In the first phase of observation, we have acquired spectra of ninety one
objects. Inspection of the objects spectra show fifty one objects with C$_{2}$
molecular bands in their spectra of which thirteen stars have low flux below
about 4300 \AA . Twenty five objects show weak or moderate CH and CN bands,
twelve objects show weak but detectable CH bands in their spectra and there are
three objects which do not show any molecular bands due to C$_{2}$, CN or CH in
their spectra. Objects with C$_{2}$ molecular bands and with good signals
bluewards of 4300 \AA which show prominent CH bands in their spectra are
potential candidate CH stars. Thirty five such candidates are found in the
present sample of ninty one objects observed so far. The set of CH stars
identified could be the targets of subsequent observation at high resolution
for a detail and comprehensive analysis for understanding their role in early
Galactic chemical evolution.


title: Pairwise velocities in the Halo Model: Luminosity and Scale Dependence

abstract:
  We investigate the properties of the pairwise velocity dispersion as a
function of galaxy luminosity in the context of a halo model. We derive the
distribution of velocities of pairs at a given separation taking into account
both one-halo and two-halo contributions. We show that pairwise velocity
distribution in real space is a complicated mixture of host-satellite,
satellite-satellite and two-halo pairs. The peak value is reached at around
1$h^{-1}$Mpc and does not reflect the velocity dispersion of a typical halo
hosting these galaxies, but is instead dominated by the satellite-satellite
pairs in high mass clusters. This is true even for cross-correlations between
bins separated in luminosity. As a consequence the velocity dispersion at a
given separation can decrease with luminosity, even if the underlying typical
halo host mass is increasing, in agreement with recent observations. We compare
our findings to numerical simulations and find a good agreement. Numerical
simulations also suggest a luminosity dependent velocity bias, which depends on
the subhalo mass. We develop models of the auto- and cross-correlation function
of luminosity subsamples of galaxies in the observable $r_\proj - \pi$ space
and calculate the inferred velocity dispersion as a function of wave vector if
dispersion model is fit to the redshift space power spectrum. We find that so
derived pairwise velocity dispersion also exhibits a bump at $k\sim 1 h/{\rm
Mpc}$.


title:
The kinematics of the large western knot in the halo of the young
  planetary nebula NGC 6543

abstract:
  A detailed analysis is presented of the dominant ionised knot in the halo of
the planetary nebula NGC 6543. Observations were made at high spectral and
spatial resolution of the [OIII] 5007 line using the Manchester echelle
spectrometer combined with the 2.1-m San Pedro Martir Telescope. A 20-element
multislit was stepped across the field to give almost complete spatial coverage
of the knot and surrounding halo. The spectra reveal, for the first time, gas
flows around the kinematically inert knot. The gas flows are found to have
velocities comparable to the sound speed as gas is photo-evaporated off an
ionised surface. No evidence is found of fast wind interaction with the knot
and we find it likely that the fast wind is still contained in a
pressure-driven bubble in the core of the nebula. This rules out the
possibility of the knot having its origin in instabilities at the interface of
the fast and AGB winds. We suggest that the knot is embedded in the slowly
expanding Red Giant wind and that its surfaces are being continually
photoionised by the central star.


title: Neutrino Cooled disk in GRB central engine

abstract:
  At the extreme densities and temperatures typical of the central engine of
GRBs, the accreting torus is cooled mainly by advection and by neutrino
emission. The latter process is dominated by electron and positron capture onto
nucleons ($\beta$ reactions). We calculate the reaction rates and the nuclear
composition of matter, assuming that the torus consists of helium,
eletron-positron pairs, free neutrons and protons. After determining the
equation of state and solving for the disk structure for a given initial
accretion rate, we subsequently follow its time evolution. We find that, for
accretion rates of the order of $10 M_{\odot}$/s, likely typical for the early
stages of the accretion event, the disk becomes unstable, giving rise to
variable energy output. This instability may play an important role for
producing internal shocks.


title: The mass of the neutron star in SMC X-1

abstract:
  We present new optical spectroscopy of the eclipsing binary pulsar Sk 160/SMC
X-1. From the He I absorption lines, taking heating corrections into account,
we determine the radial velocity semi-amplitude of Sk 160 to be 21.8 +/- 1.8
km/s. Assuming Sk 160 fills its Roche-lobe, the inclination angle of the system
is i=65.3 deg +/- 1.3 deg and in this case we obtain upper limits for the mass
of the neutron star as Mx = 1.21 +/- 0.10 Msolar and for Sk 160 as Mo= 16.6 +/-
0.4 Msolar. However if we assume that the inclination angle is i=90 deg, then
the ratio of the radius of Sk 160 to the radius of its Roche-lobe is beta =
0.79 +/- 0.02, and the lower limits for the masses of the two stars are Mx =
0.91 +/- 0.08 Msolar and Mo = 12.5 +/- 0.1 Msolar. We also show that the HeII
4686A emission line tracks the motion of the neutron star, but with a radial
velocity amplitude somewhat less than that of the neutron star itself. We
suggest that this emission may arise from a hotspot where material accreting
via Roche lobe overflow impacts the outer edge of an accretion disc.


title: Observations of Selected AGN with H.E.S.S

abstract:
  A sample of selected active galactic nuclei (AGN) was observed in 2003 and
2004 with the High Energy Stereoscopic System (H.E.S.S.), an array of imaging
atmospheric-Cherenkov telescopes in Namibia. The redshifts of these candidate
very-high-energy (VHE, >100 GeV) gamma-ray emitters range from z=0.00183 to
z=0.333. Significant detections were already reported for some of these
objects, such as PKS 2155-304 and Markarian 421. Marginal evidence (3.1 sigma)
for a signal is found from large-zenith-angle observations of Markarian 501,
corresponding to an integral flux of I(>1.65 TeV) = (1.5 +/- 0.6 (stat) +/- 0.3
(syst)) x 10^{-12} cm^{-2} s^{-1} or ~15% of the Crab Nebula flux. Integral
flux upper limits for 19 other AGN, based on exposures of ~1 to ~8 hrs live
time, and with average energy thresholds between 160 GeV and 610 GeV, range
from 0.4% to 5.1% of the Crab Nebula flux. All the upper limits are the most
constraining ever reported for these objects.


title: Cosmic Backgrounds from Miniquasars

abstract:
  A large population of Intermediate Mass Black Holes (IMBHs) might be produced
at early cosmic times as a left over of the evolution of the very massive first
stars. Accretion onto IMBHs provides a source of (re)ionizing radiation. We
show that the baryon mass fraction locked into IMBHs and their growth is
strongly constrained by the observed residual Soft X-ray Background (SXRB)
intensity. Thus, unless they are extremely X-ray quiet, miniquasars must be
quite rare and/or have a short shining phase. As a byproduct, we find that
miniquasars can not be the only source of reionization and that their alleged
contribution to the near infrared bands is completely negligible.


title: High-Ionization Emission in Metal-Deficient Blue Compact Dwarf Galaxies

abstract:
  Primordial stars are expected to be very massive and hot, producing copious
amounts of hard ionizing radiation. The best place to study hard ionizing
radiation in the local universe is in very metal-deficient Blue Compact Dwarf
(BCD) galaxies. We have carried out a MMT spectroscopic search for [Ne V] 3426
(ionization potential of 7.1 Ryd), [Fe V] 4227 (ionization potential of 4 Ryd)
and He II 4686 (ionization potential of 4 Ryd) emission in a sample of 18 BCDs.
We have added data from previous work and from the Data Release 3 of the Sloan
Digital Sky Survey. In total, we have assembled a BCD high-ionization sample
with [Ne V] emission in 4 galaxies, [Fe V] emission in 15 galaxies and He II
emission in 465 galaxies. With this large sample, we have reached the following
conclusions. There is a general trend of higher [Ne V], [Fe V] and He II
emission at lower metallicities. However metallicity is not the only factor
which controls the hardness of the radiation. High-mass X-ray binaries and
main-sequence stars are probably excluded as the main sources of the very hard
ionizing radiation responsible for [Ne V] emission. The most likely source of
[Ne V] emission is probably fast radiative shocks moving with velocities > 450
km/s through a dense interstellar medium with an electron number density of
several hundreds per cm^-3 and associated with supernova explosions of the most
massive stars. These have masses of ~ 50 - 100 Msun and are formed in very
compact super-star clusters. The softer ionizing radiation required for He II
emission is likely associated with less massive evolved stars and/or radiative
shocks moving through a less dense interstellar medium.


title: Optical Depths and Timescale Distributions in Galactic Microlensing

abstract:
  We present microlensing calculations for a Galactic model based on Han &
Gould (2003), which is empirically normalised by star counts. We find good
agreement between this model and data recently published by the MACHO and OGLE
collaborations for the optical depth in various Galactic fields, and the trends
thereof with Galactic longitude l and latitude b. We produce maps of optical
depth and, by adopting simple kinematic models, of average event timescales for
microlensing towards the Galactic bulge. We also find that our model
predictions are in reasonable agreement with the OGLE data for the expected
timescale distribution. We show that the fractions of events with very long and
short timescales due to a lens of mass M are weighted by M^2 n(M)dM and M^(-1)
n(M)dM respectively, independent of the density and kinematics of the lenses.