title:
The cosmological significance of Low Surface Brightness galaxies found
  in a deep blind neutral-hydrogen survey

abstract:
  We have placed limits on the cosmological significance of gas-rich low
surface-brightness (LSB) galaxies as a proportion of the total population of
gas-rich galaxies by carrying out a very deep survey (HIDEEP) for neutral
hydrogen (HI) with the Parkes multibeam system. Such a survey avoids the
surface-brightness selection effects that limit the usefulness of optical
surveys for finding LSB galaxies. To complement the HIDEEP survey we have
digitally stacked eight 1-hour R-band Tech Pan films from the UK Schmidt
Telescope covering 36 square degrees of the survey area to reach a very deep
isophotal limit of 26.5 R mag/sq. arcsec. At this level, we find that all of
the 129 HI sources within this area have optical counterparts and that 107 of
them can be identified with individual galaxies. We have used the properties of
the galaxies identified as the optical counterparts of the HI sources to
estimate the significance of LSB galaxies (defined to be those at least 1.5
magnitudes dimmer in effective surface-brightness than the peak in the observed
distribution seen in optical surveys). We calculate the contribution of LSB
galaxies to the total number, neutral hydrogen density, luminosity density,
baryonic mass density, dynamical mass density and cross-sectional area of
gas-rich galaxies. We do not find any `Crouching Giant' LSB galaxies such as
Malin 1, nor do we find a population of extremely low surface-brightness
galaxies not previously found by optical surveys. Such objects must either be
rare, gas-poor or outside the survey detection limits.


title: Structure formation, CMB and LSS in a mirror dark matter scenario

abstract:
  In the mirror world hypothesis the mirror baryonic component emerges as a
possible dark matter candidate. Here we study the behaviour of the mirror dark
matter and the differences from the more familiar CDM candidate for structure
formation, cosmic microwave background and large scale structure. We show
mirror models for CMB and LSS power spectra and compare them with observations,
obtaining bounds on the mirror parameter space.


title: Cosmology with mirror dark matter I: linear evolution of perturbations

abstract:
  This is the first paper of a series devoted to the study of the cosmological
implications of the parallel mirror world with the same microphysics as the
ordinary one, but having smaller temperature, with a limit set by the BBN
constraints. The difference in temperature of the ordinary and mirror sectors
generates shifts in the key epochs for structure formation, which proceeds in
the mirror sector under different conditions. We consider adiabatic scalar
primordial perturbations as an input and analyze the trends of all the relevant
scales for structure formation (Jeans length and mass, Silk scale, horizon
scale) for both ordinary and mirror sectors, comparing them with the CDM case.
These scales are functions of the fundamental parameters of the theory (the
temperature of the mirror plasma and the amount of mirror baryonic matter), and
in particular they are influenced by the difference between the cosmological
key epochs in the two sectors. Then we used a numerical code to compute the
evolution in linear regime of density perturbations for all the components of a
Mirror Universe: ordinary baryons and photons, mirror baryons and photons, and
possibly cold dark matter. We analyzed the evolution of the perturbations for
different values of mirror temperature and baryonic density, and obtained that
for x=T'/T less than a typical value x_eq, for which the mirror baryon-photon
decoupling happens before the matter-radiation equality, mirror baryons are
equivalent to the CDM for the linear structure formation process. Indeed, the
smaller the value of x, the closer mirror dark matter resembles standard cold
dark matter during the linear regime.


title:
Super-strong interacting gravitons as a main engine of the universe
  without expansion or dark energy

abstract:
  The basic cosmological conjecture about the Dopplerian nature of redshifts
may be false if gravitons are super-strong interacting particles. A quantum
mechanism of classical gravity and the main features of a new cosmological
paradigm based on it are described here.


title:
A multiwavelength study of the galaxy content and environmental effects
  in the dense group of galaxies around IC 65

abstract:
  We have carried out surface photometry of four bright known members and a
number of new possible LSB companions of the IC 65 (LGG 16) group of galaxies.
The purpose of the present study is twofold: (a) a search for new LSB dwarf
members and measuring of their global photometric characteristics, and (b) a
search for possible effects of mutual interactions on the morphology and
photometric characteristics of luminous and faint group members. This study is
based on our BRI CCD observations performed with the 1.23 m and 2.2 m
telescopes at Calar Alto, which were supplemented by the deep gri frames
obtained from the DSS 2, and the NIR JHK frames from the 2MASS database. In
addition, we have used the HI imaging data from literature and the results of
new pilot HI observations of selected dwarf-galaxy candidates made by W.
Huchtmeier with the Effelsberg 100 m radiotelescope. We have found four new
probable LSB dwarf members of the group, two of which have been marginally
detected in HI. The isophotal analysis in optical wavelengths revealed the
presence of minor disturbances in the outer isophotes of some bright regular
member galaxies. The HI emission appears generally more disturbed, compared to
the emission in the optical passbands. The new dwarf companion candidates
generally contain blue star-forming regions. The drift of optical isophotes
together with the warping of HI isophotes outside the optical image of regular
galaxies, as well as evidence for the enhanced star-forming activity in fragile
dwarf galaxies indicate that this dense group of at least 8 late type galaxies
is gravitationally bound and mutually interacting. (abridged)


title:
Cosmology with mirror dark matter II: Cosmic Microwave Background and
  Large Scale Structure

abstract:
  This is the second paper of a series devoted to the study of the cosmological
implications of the existence of mirror dark matter. The parallel hidden mirror
world has the same microphysics as the observable one and couples the latter
only gravitationally. The primordial nucleosynthesis bounds demand that the
mirror sector should have a smaller temperature T' than the ordinary one T, and
by this reason its evolution can be substantially deviated from the standard
cosmology. In this paper we took scalar adiabatic perturbations as the input in
a flat Universe, and computed the power spectra for ordinary and mirror CMB and
LSS, changing the cosmological parameters, and always comparing with the CDM
case. We found differences in both the CMB and LSS power spectra, and we
demonstrated that the LSS spectrum is particularly sensitive to the mirror
parameters, due to the presence of both the oscillatory features of mirror
baryons and the collisional mirror Silk damping. For x<0.3 the mirror
baryon-photon decoupling happens before the matter-radiation equality, so that
CMB and LSS power spectra in linear regime are equivalent for mirror and CDM
cases. For higher x-values the LSS spectra strongly depend on the amount of
mirror baryons. Finally, qualitatively comparing with the present observational
limits on the CMB and LSS spectra, we show that for x<0.3 the entire dark
matter could be made of mirror baryons, while in the case x>0.3 the pattern of
the LSS power spectrum excludes the possibility of dark matter consisting
entirely of mirror baryons, but they could present as admixture (up to 50%) to
the conventional CDM.


title: Simultaneous Doppler maps of IP Peg in outburst

abstract:
  IP Pegasi is an eclipsing dwarf nova lying above the period gap with an
orbital period of 3.8h. It is the first cataclysmic variable to show evidence
of spiral arms in its accretion disc. We present new time-resolved echelle
spectroscopic observations of IP Peg, covering the 3900-7700 Angstrom range.
This allows us to produce simultaneous Doppler Maps in 9 emission lines.


title: An extended frame for cosmology by integrable Weyl geometry

abstract:
  A conservative extension of general relativity by integrable Weyl geometry is
formulated, and a new class of cosmological models ({\em Weyl universes}) is
introduced and studied. A short discussion of how these new models behave in
the light of observational evidence follows. It turns out that the subclass of
Weyl universes with positive ex-ante curvature of spatial sections ({\em
Einstein-Weyl universes}) forms an empirically contentful conceptual frame for
cosmology. Recent high precision data (supernovae Ia, quasar frequencies,
microwave background) are well represented in this type of Weyl geometry and
several of the anomalies of the standard approach are avoided or become
meaningless.


title: The Peculiar 2004 Superoutburst in the Helium Dwarf Nova, 2003aw

abstract:
  We conducted a time-resolved photometric campaign of the helium dwarf nova,
2003aw in 2004 May--June. 2003aw stayed at 14.7--15.7 mag for the first several
days during this campaign, which is the plateau phase of this superoutburst.
This variable then rapidly decayed to $\sim$18.0 mag, still brighter by about 2
mag than its quiescence magnitude, and maintained this brightness for about 20
days, having short flares of $\sim$2 mag. A long fading tail followed it. We
detected superhumps with a period of 0.02357(4) d [= 2036(3) s] during the
plateau phase. The whole light curve of the superoutburst in 2003aw, taking
into account the present data and those in the literature, perfectly resembles
that of the 1996-1997 superoutburst of the peculiar WZ Sge-type hydrogen-rich
dwarf nova, EG Cnc.


title: Observing Gravitational Radiation with QSO Proper Motions and the SKA

abstract:
  We discuss the ability of the SKA to observe QSO proper motions induced by
long-wavelength gravitational radiation. We find that the SKA, configured for
VLBI with multiple beams at high frequency (8 GHz), is sensitive to a
dimensionless characteristic strain of roughly $10^{-13}$, comparable to (and
with very different errors than) other methods in the 1/yr frequency band such
as pulsar timing.


title:
What can XMM-Newton tell us about the spin periods of Intermediate
  Polars?

abstract:
  XMM-Newton's unprecedented combination of spectral resolution and high
throughput allows us to perform the best phase-resolved X-ray analysis of
intermediate polars to date. The Optical Monitor gives optical/UV photometry
simultaneously with the X-ray data. We present a comprehensive study of X-ray
spin pulses in IPs, giving spin-pulses and hardness ratios for every IP looked
at with XMM-Newton to date.


title: The Cosmological Context of Extraplanar Gas

abstract:
  I review evidence that galaxies form from gas that falls into potential wells
cold, rather than from virialized gas, and that formation stops once an
atmosphere of trapped virialized gas has accumulated. Disk galaxies do not have
such atmospheres, so their formation is ongoing. During galaxy formation
feedback is an efficient process, and the nuclear regions of disk galaxies blow
winds. The cold infalling gas that drives continued star formation has a
significant component of angular momentum perpendicular to that of the disk.
Extraplanar gas has to be understood in the context set by nuclear outflows and
cold skew-rotating cosmic infall.


title: The spin temperature of neutral hydrogen during cosmic pre-reionization

abstract:
  We re-examine the role of collisions in decoupling the HI 21-cm spin
temperature from the cosmic microwave background (CMB). The cross section for
de-exciting the 21-cm trasition in collisions with free electrons is more than
10 times larger than it is in collisions with other atoms. If the fraction of
free electrons in the diffuse cosmic gas is between 10 and 30 per cent then
collisions alone can decouple the spin temperature from the cosmic microwave
background (CMB), even in moderately under-dense regions at z >15. This
decoupling is especially important during the very early stages of
re-ionization when a Ly-alpha continuum background had yet to be established.
As a detailed example, we develop a semi-analytic model to quantify 21-cm
emission signatures from a diffuse gas which is partially ionized at z>10 by an
X-ray background. We find 21-cm differential brightness temperature
fluctuations with a mean of ~8 mK and a rms value as large as 5 mK, for a
frequency resolution bandwidth of 100 KHz and a beamsize of 3 arcmin. Another
example where free electron-atom collisions are important is during the
recombination of bubbles ionized by short-lived UV sources. When the ionized
fraction in these bubbles drops to 10-20 per cent their differential
temperature can be as high as 10 mK. We also consider the correlation of the
21-cm temperature as a function of frequency. By isotropy, a comparison with
the angular projected correlation in the plane of the sky should yield an
estimate for the matter density parameter, Omega_m, and the dark energy
component. This variant of the Alcock-Paczyski test is applicable for any
reionization scenario.


title: LOPES Detecting Radio Emission from Cosmic Ray Air Showers

abstract:
  Radio pulses emitted in the atmosphere during the air shower development of
high-energy primary cosmic rays were measured during the late 1960ies in the
frequency range from 2 MHz to 520 MHz. Mainly due to difficulties with radio
interference these measurements ceased in the late 1970ies.
  LOFAR (Low Frequency Array) is a new digital radio interferometer under
development. Using high bandwidth ADCs and fast data processing it will be able
to filter out most of the interference. By storing the whole waveform
information in digital form one can analyze transient events like air showers
even after they have been recorded.
  To test this new technology and to demonstrate its ability to measure air
showers a "LOFAR Prototype Station" (LOPES) is set up to operate in conjunction
with an existing air shower array (KASCADE-Grande).
  The first phase consisting of 10 antennas is already running. It operates in
the frequency range of 40 to 80 MHz, using simple short dipole antennas and
direct 2nd Nyquist sampling of the incoming wave. It has proven to be able to
do simple astronomical measurements, like imaging of a solar burst. It has also
demonstrated how digital interference suppression and beamforming can overcome
the problem of radio interference and pick out air shower events.


title: s-process branching at 185W revised

abstract:
  The neutron capture cross section of the unstable s-process branching nucleus
185W has been derived from experimental data of the inverse 186W(g,n)185W
photodisintegration taken with monochromatic photon beams from laser Compton
scattering. The result of sigma = 553 +- 60 mb at kT = 30 keV leads to a
relatively high effective neutron density in the classical s-process of N_n =
4.7 \times 10^8 cm^-3. A realistic model for the s-process in thermally pulsing
AGB stars overestimates the abundance of 186Os significantly because of the
relatively small neutron capture cross section of 185W.


title: The recognition of blazars and the blazar spectral sequence

abstract:
  We analyse a group of radio sources, a subset of the 200 mJy sample, all of
which have core-jet radio structures measured with VLBI and have flat spectra
stretching from the radio to the millimetre/sub-millimetre band. Thus the
objects have most of the properties expected of blazars. However, they display
varied optical properties ranging from ``Seyfert-like'' objects, through BL Lac
objects, to ``normal'' elliptical galaxies. We investigate the distribution of
synchrotron peak frequencies in their Spectral Energy Distributions (SEDs) and
find a broad distribution between 10^12 and 10^16 Hz. Our conclusion is that we
should consider virtually all objects in the sample as blazars since much of
the diversity in their classification based on traditional optical criteria
arises from differences in the frequency at which the non-thermal emission
begins to decline. Specifically, an object is only classified as BL Lac when
its peak frequency falls in the near IR/optical range.
  We determine peak frequencies using the same method for objects from other
blazar samples. An important result is that our objects do not follow the
blazar spectral sequence proposed by Fossati et al. and Ghisellini et al. in
which, on average, peak frequencies increase as the radio luminosity decreases.
Most of our low radio-luminosity sources have peaks in their SEDs at low
frequencies, not at the expected high frequencies. We suggest that at least
part of the systematic trend seen by Fossati et al. and Ghisellini et al.
results from selection effects.


title: Diamonds in HD 97048

abstract:
  We present adaptive optics high angular resolution ($\sim0\farcs$1)
spectroscopic observations in the 3 $\mu$m region of the Herbig Ae/Be star HD
97048. For the first time, we spatially resolve the emission in the diamond
features at 3.43 and 3.53 $\mu$m and in the adjacent continuum. Using both the
intensity profiles along the slit and reconstructed two-dimensional images of
the object, we derive full-width at half-maximum sizes consistent with the
predictions for a circumstellar disk seen pole-on. The diamond emission
originates in the inner region ($R \lesssim 15$ AU) of the disk.


title:
Bunching instability of rotating relativistic electron layers and
  coherent synchrotron radiation

abstract:
  We study the stability of a collisionless, relativistic, finite-strength,
cylindrical layer of charged particles in free space by solving the linearized
Vlasov-Maxwell equations and compute the power of the emitted electromagnetic
waves. The layer is rotating in an external magnetic field parallel to the
layer. This system is of interest to understanding the high brightness
temperature of pulsars which cannot be explained by an incoherent radiation
mechanism. Coherent synchrotron radiation has also been observed recently in
bunch compressors used in particle accelerators. We consider equilibrium layers
with a `thermal' energy spread and therefore a non-zero radial thickness. The
particles interact with their retarded electromagnetic self-fields. The effect
of the betatron oscillations is retained. A short azimuthal wavelength
instability is found which causes a modulation of the charge and current
densities. The growth rate is found to be an increasing function of the
azimuthal wavenumber, a decreasing function of the Lorentz factor, and
proportional to the square root of the total number of electrons. We argue that
the growth of the unstable perturbation saturates when the trapping frequency
of electrons in the wave becomes comparable to the growth rate. Owing to this
saturation we can predict the radiation spectrum for a given set of parameters.
Our predicted brightness temperatures are proportional to the square of the
number of particles and scale by the inverse five-third power of the azimuthal
wavenumber which is in rough accord with the observed spectra of radio pulsars.


title: Draco 119: A Remarkable Heavy Element-deficient Giant

abstract:
  We report the abundance analysis of new high S/N spectra of the most
metal-poor ([Fe/H] $= -2.95$) star presently known to be a member of a dwarf
galaxy, the Draco dSph red giant, D119. No absorption lines for elements
heavier than Ni are detected in two Keck HIRES spectra covering the
$\lambda\lambda$ 3850--6655 \AA{} wavelength range, phenomenon not previously
noted in any other metal-poor star. We present upper limits for several heavy
element abundances. The most stringent limits, based on the non-detection of
\ion{Sr}{2} and \ion{Ba}{2} lines, indicate that the total s- and r-process
enrichment of D119 is at least 100 times smaller than Galactic stars of similar
metallicity. The light element abundances are consistent with the star having
formed out of material enciched primarily by massive Type II supernovae (M $>
20$--25 M$_{\odot}$). If this is the case, we are forced to conclude that
massive, metal-poor Type II supernovae did not contribute to the r-process in
the proto-Draco environment. We compare the abundance pattern observed in D119
to current predictions of prompt enrichement and pair-instability supernovae
and find that the model predictions fail by an order or maginitude or more for
many elements.


title: Time-resolved observations of the short period CV SDSS J123813.73-033933

abstract:
  We present simultaneous spectral and photometric observations of SDSS
J123813.73-033933.0. From Ha radial velocity measurements we determined the
orbital period of the system to be 0.05592+/-0.00002 days (80.53 min). The
spectrum shows double Balmer emission lines flanked by strong, broad
absorption, indicating a dominant contribution from the white dwarf. The
photometric light curve shows complex variability. The system undergoes cyclic
brightening up to 0.4 mag which are semi-periodical on short time scales with
periods of the order of 7-12 hours. We also detect 40.25 min variability (~0.15
mag) in the light curve, that corresponds to half the orbital period. Its
amplitude increases with the cyclic brightening of the system.


title: The Spreading Layer and Dwarf Nova Oscillations

abstract:
  We describe recent theoretical work on the final stage of accretion when
material passes from an accretion disk onto a white dwarf surface. Our
calculations focus on understanding the latitudinal spreading and
differentially rotating profile of this material, so we call it the ``spreading
layer'' (SL) model. The SL typically extends to an angle of 0.01-0.1 radians,
with respect to the equator. At low accretion rates ($\dot{M}\la10^{18} {\rm g
s}^{-1}$) the amount of spreading is small, so that the dissipated energy is
radiated back into the accretion disk. When the accretion rate is high, such as
in dwarf novae, symbiotic binaries, and supersoft sources, the material spreads
to higher latitudes to be more easily observed. The SL may contain shallow
surface modes, and we propose that such waves could produce dwarf nova
oscillations (DNOs). This hypothesis naturally explains many key properties of
DNOs, including their frequency range, sinusoidal nature, sensitivity to
accretion rate, and why they are only seen during outburst.


title: Decaying Higgs Fields and Cosmological Dark Energy

abstract:
  The observed dark energy in the universe might give particles inertial mass.
We investigate one realization of this idea, that the dark energy field might
be a decayed scalar component of a supermultiplet field in the early universe
that creates inertial mass through spontaneous symmetry breaking, e.g. a Higgs
field. To investigate this possibility, the cosmological Friedmann equation of
energy balance is augmented in a standard way to incorporate a minimally
coupled cosmological Higgs. For epochs where the expansion of the universe is
driven by matter and radiation and not the scalar field, the observed hidden
nature of the Higgs field can be codified into a single differential equation
that we call the "hidden higgs" condition. The resulting differential equation
is solved for the time dependant scalar field and a simple and interesting
solution is found analytically. Such a Higgs field decays from Planck scale
energies rapidly and approximately exponentially from onset, leaving only the
initially negligible constant term of the potential as a final cosmological
constant. Such evolution replaces the hierarchy problem with the problem of
explaining why such evolution is physically justified.


title:
Mismatch between X-ray and emission-weighted temperatures in galaxy
  clusters: cosmological implications

abstract:
  The thermal properties of hydrodynamical simulations of galaxy clusters are
usually compared to observations by relying on the emission-weighted
temperature T_ew, instead of on the spectroscopic X-ray temperature T_spec,
which is obtained by actual observational data. In a recent paper Mazzotta et
al. show that, if the cluster is thermally complex, T_ew fails at reproducing
T_spec, and propose a new formula, the spectroscopic-like temperature, T_sl,
which approximates T_spec better than a few per cent. By analyzing a set of
hydrodynamical simulations of galaxy clusters, we find that T_sl is lower than
T_ew by 20-30 per cent. As a consequence, the normalization of the M-T_sl
relation from the simulations is larger than the observed one by about 50 per
cent. If masses in simulated clusters are estimated by following the same
assumptions of hydrostatic equilibrium and \beta--model gas density profile, as
often done for observed clusters, then the M-T relation decreases by about 40
per cent, and significantly reduces its scatter. Based on this result, we
conclude that using the observed M-T relation to infer the amplitude of the
power spectrum from the X-ray temperature function could bias low \sigma_8 by
10-20 per cent. This may alleviate the tension between the value of \sigma_8
inferred from the cluster number density and those from cosmic microwave
background and large scale structure.


title: The Origin of the Binary Pulsar J0737-3039B

abstract:
  Evolutionary scenarios suggest that the progenitor of the new binary pulsar
J0737-3039B \cite{ref1,ref2} was a He-star with $M > 2.1-2.3~\Ms$
\cite{ref3,ref4}. We show that this case implies that the binary must have a
large ($>120$ km/s) center of mass velocity. However, the location, $\sim 50$
pc from the Galactic plane, suggests that the system has, at high likelihood, a
significantly smaller center of mass velocity and a progenitor more massive
than 2.1~$\Ms$ is ruled out (at 97% c.l.). A progenitor mass around 1.45~$\Ms$,
involving a new previously unseen gravitational collapse, is kinematically
favored. The low mass progenitor is consistent with the recent scintillations
based velocity measurement of 66$\pm 15$ km/s \cite{ref12new} (and which also
rules out the high mass solution at 99% c.l.) and inconsistent with the higher
earlier estimates of 141$\pm 8.5$ km/s \cite{ref11new}. Direct proper motion
measurements, that should be available within a year or so, should better help
to distinguish between the two scenarios.


title: Cluster Alignments and Ellipticities in LCDM Cosmology

abstract:
  The ellipticities and alignments of clusters of galaxies, and their evolution
with redshift, are examined in the context of a Lambda-dominated cold dark
matter cosmology. We use a large-scale, high-resolution N-body simulation to
model the matter distribution in a light cone containing ~10^6 clusters out to
redshifts of z=3. Cluster ellipticities are determined as a function of mass,
radius, and redshift, both in 3D and in projection. We find strong cluster
ellipticities: the mean ellipticity increases with redshift from 0.3 at z=0 to
0.5 at z=3, for both 3D and 2D ellipticities; the evolution is well-fit by
e=0.33+0.05z. The ellipticities increase with cluster mass and with cluster
radius; the main cluster body is more elliptical than the cluster cores, but
the increase of ellipticities with redshift is preserved. Using the fitted
cluster ellipsoids, we determine the alignment of clusters as a function of
their separation. We find strong alignment of clusters for separations <100
Mpc/h; the alignment increases with decreasing separation and with increasing
redshift. The evolution of clusters from highly aligned and elongated systems
at early times to lower alignment and elongation at present reflects the
hierarchical and filamentary nature of structure formation. These measures of
cluster ellipticity and alignment will provide a new test of the current
cosmological model when compared with upcoming cluster surveys.


title: Searching for Planetary Transits in Galactic Open Clusters: EXPLORE/OC

abstract:
  Open clusters potentially provide an ideal environment for the search for
transiting extrasolar planets since they feature a relatively large number of
stars of the same known age and metallicity at the same distance. With this
motivation, over a dozen open clusters are now being monitored by four
different groups. We review the motivations and challenges for open cluster
transit surveys for short-period giant planets. Our photometric monitoring
survey (EXPLORE/OC) of Galactic southern open clusters was designed with the
goals of maximizing the chance of finding and characterizing planets, and of
providing for a statistically valuable astrophysical result in the case of no
detections. We use the EXPLORE/OC data from two open clusters NGC 2660 and NGC
6208 to illustrate some of the largely unrecognized issues facing open cluster
surveys including severe contamination by Galactic field stars ($>$ 80%) and
relatively low number of cluster members for which high precision photometry
can be obtained. We discuss how a careful selection of open cluster targets
under a wide range of criteria such as cluster richness, observability,
distance, and age can meet the challenges, maximizing chances to detect planet
transits. In addition, we present the EXPLORE/OC observing strategy to optimize
planet detection which includes high-cadence observing and continuously
observing individual clusters rather than alternating between targets.


title:
TALON - The Telescope Alert Operation Network System: Intelligent
  Linking of Distributed Autonomous Robotic Telescopes

abstract:
  The internet has brought about great change in the astronomical community,
but this interconnectivity is just starting to be exploited for use in
instrumentation. Utilizing the internet for communicating between distributed
astronomical systems is still in its infancy, but it already shows great
potential. Here we present an example of a distributed network of telescopes
that performs more efficiently in synchronous operation than as individual
instruments. RAPid Telescopes for Optical Response (RAPTOR) is a system of
telescopes at LANL that has intelligent intercommunication, combined with
wide-field optics, temporal monitoring software, and deep-field follow-up
capability all working in closed-loop real-time operation. The Telescope ALert
Operations Network (TALON) is a network server that allows intercommunication
of alert triggers from external and internal resources and controls the
distribution of these to each of the telescopes on the network. TALON is
designed to grow, allowing any number of telescopes to be linked together and
communicate. Coupled with an intelligent alert client at each telescope, it can
analyze and respond to each distributed TALON alert based on the telescopes
needs and schedule.


title:
Proving the conservation of surface brightness during the strong and
  weak lensing of light by an isothermal sphere

abstract:
  An analytical proof of the conservation of surface brightness during the
strong and weak lensing of light by a singular isothermal sphere is provided.
It is shown that the movement of asymptotic rays provide room for precisely the
extra solid angle claimed by the magnification of the centrally passing rays.
Previous claim of a violation of this conservation law, leading to a problem
over the COBE all sky CMB flux, is hereby withdrawn.


title: Is Double Reionization Physically Plausible?

abstract:
  Recent observations of z~6 quasars and the cosmic microwave background imply
a complex history to cosmic reionization. Such a history requires some form of
feedback to extend reionization over a long time interval, but the nature of
the feedback and how rapidly it operates remain highly uncertain. Here we focus
on one aspect of this complexity: which physical processes can cause the global
ionized fraction to evolve non-monotonically with cosmic time? We consider a
range of mechanisms and conclude that double reionization is much less likely
than a long, but still monotonic, ionization history. We first examine how
galactic winds affect the transition from metal-free to normal star formation.
Because the transition is actually spatially inhomogeneous and temporally
extended, this mechanism cannot be responsible for double reionization given
plausible parameters for the winds. We next consider photoheating, which causes
the cosmological Jeans mass to increase in ionized regions and hence suppresses
galaxy formation there. In this case, double reionization requires that small
halos form stars efficiently, that the suppression from photoheating is strong
relative to current expectations, and that ionizing photons are preferentially
produced outside of previously ionized regions. Finally, we consider H_2
photodissociation, in which the buildup of a soft ultraviolet background
suppresses star formation in small halos. This can in principle cause the
ionized fraction to temporarily decrease, but only during the earliest stages
of reionization. Finally, we briefly consider the effects of some of these
feedback mechanisms on the topology of reionization.


title: Uncertainties in the S-Z selected cluster angular power spectrum

abstract:
  Large SZ selected galaxy cluster surveys are beginning imminently. We compare
the dependence of the galaxy cluster angular power spectrum on cosmological
parameters, different modeling assumptions and statistical observational
errors. We quantify the degeneracies between theoretical assumptions such as
the mass function and cosmological parameters such as $\sigma_8$. We also
identify a rough scaling behavior of this angular power spectrum with
$\sigma_8$ alone.


title:
Observational Tests and Predictive Stellar Evolution II: Non-standard
  Models

abstract:
  We examine contributions of second order physical processes to results of
stellar evolution calculations amenable to direct observational testing. In the
first paper in the series (Young et al. 2001) we established baseline results
using only physics which are common to modern stellar evolution codes. In the
current paper we establish how much of the discrepancy between observations and
baseline models is due to particular elements of new physics. We then consider
the impact of the observational uncertainties on the maximum predictive
accuracy achievable by a stellar evolution code. The sun is an optimal case
because of the precise and abundant observations and the relative simplicity of
the underlying stellar physics. The Standard Model is capable of matching the
structure of the sun as determined by helioseismology and gross surface
observables to better than a percent. Given an initial mass and surface
composition within the observational errors, and no additional constraints for
which the models can be optimized, it is not possible to predict the sun's
current state to better than ~7%. Convectively induced mixing in radiative
regions, seen in multidimensional hydrodynamic simulations, dramatically
improves the predictions for radii, luminosity, and apsidal motions of
eclipsing binaries while simultaneously maintaining consistency with observed
light element depletion and turnoff ages in young clusters (Young et al. 2003).
Systematic errors in core size for models of massive binaries disappear with
more complete mixing physics, and acceptable fits are achieved for all of the
binaries without calibration of free parameters. The lack of accurate abundance
determinations for binaries is now the main obstacle to improving stellar
models using this type of test.


title: Early Spectra of Supernovae

abstract:
  We briefly describe the current version of the PHOENIX code. We then present
some results on the modeling of Type II supernovae and show that fits to
observations can be obtained, when account is taken for spherically symmetric,
line-blanketed, expanding atmospheres. We describe the SEAM method of obtaining
distances to supernovae and briefly discuss its future prospects.


title: Chandra HETG Spectra of SS Cyg and U Gem in Quiescence and Outburst

abstract:
  Chandra HETG spectra of the prototypical dwarf novae SS Cyg and U Gem in
quiescence and outburst are presented and discussed. When SS Cyg goes into
outburst, it becomes dimmer in hard X-rays and displays a dramatic shift in its
relative line strengths, whereas when U Gem goes into outburst, it becomes
brighter in hard X-rays and displays only a minor shift in its relative line
strengths. In both systems, the emission lines become significantly broader in
outburst, signaling the presence of high velocity gas either in Keplerian
orbits around the white dwarf or flowing outward from the system.


title: WHIM emission and the cluster soft excess: a model comparison

abstract:
  The confirmation of the cluster soft excess (CSE) by XMM-Newton has rekindled
interest as to its origin. The recent detections of CSE emission at large
cluster radii together with reports of OVII line emission associated with the
CSE has led many authors to conjecture that the CSE is, in fact, a signature of
the warm-hot intergalactic medium (WHIM). In this paper we test the scenario by
comparing the observed properties of the CSE with predictions based on models
of the WHIM. We find that emission from the WHIM in current models is 3 to 4
orders of magnitude too faint to explain the CSE. We discuss different
possibilities for this discrepancy including issues of simulation resolution
and scale, and the role of small density enhancements or galaxy groups. Our
final conclusion is that the WHIM alone is unlikely to be able to accout for
the observed flux of the CSE.


title: X-ray Observation of SS 433 with RXTE

abstract:
  Apart from regular monitoring by ASM, the compact object SS 433 was observed
with RXTE several times last two/three years. We present the first analysis of
these observations. We also include the results of the recent exciting TOO
campaign made during donour inferior (orbital phase $\phi=0$) and superior
($\phi=0.5$) conjunctions which took place on Oct. 2nd, 2003, and on March
13th, 2004 respectively, when the jet itself was directly pointing towards us
(i.e., precessional phase $\psi \sim 0$). Generally, we found that two distinct
lines fit the spectra taken on all these days. We present some of the
light-curves and the X-ray spectra, and show that the Doppler shifts of the
emitted lines roughly match those predicted by the kinematic model for the
jets. We find that the line with a higher energy can be best identified with a
FeXXVI Ly-$\alpha$ transition while the line with lower energy can be
identified with a FeXXV (1s2p - 1s$^2$) transition. We observe that the X-ray
flux on March 13th, 2004 (when the base of the jet is exposed) is more than
twice compared to that on Oct. 2nd, 2003 (when the base is covered by the
companion). We find the flux to continue to remain high at least till another
orbital period. We believe that this is because SS 433 was undergoing a weak
flaring activity during the recent observation.


title:
The Origin and Distribution of Diffuse Hot Gas in the Spiral Galaxy NGC
  3184

abstract:
  Deep Chandra exposures reveal the presence of diffuse X-ray emission with a
luminosity of 1.3x10^{39} ergs s^{-1} from the spiral galaxy NGC 3184. This
appears to be truly diffuse thermal emission distinct from the low-luminosity
LMXB emission. While the unresolved emission from older LMXBs is more uniformly
distributed across the galaxy, the diffuse X-ray emission is concentrated in
areas of younger stellar populations and star forming regions. The surface
brightness of the diffuse emission over the spiral arms is five times greater
than in off-arm regions, and eight times brighter in H II regions than in non-H
II regions. Spectral fits to the diffuse thermal emission are consistent with a
low temperature component, T ~ 1.5 x 10^6 K, plus a higher temperature
component, T ~ 5 x 10^6 K.


title: Properties of Accretion Shocks in Viscous Flows with Cooling Effects

abstract:
  Low angular momentum accretion flows can have standing and oscillating shock
waves. We study the region of the parameter space in which multiple sonic
points occur in viscous flows in presence of various cooling effects such as
bremsstrahlung and Comptonization. We also quantify the parameter space in
which shocks are steady or oscillating. We find that cooling induces effects
opposite to heating by viscosity even in modifying the topology of the
solutions, though one can never be exactly balanced by the other due to their
dissimilar dependence on dynamic and thermodynamic parameters. We show that
beyond a critical value of cooling, the flow ceases to contain a shock wave.


title:
High resolution spectroscopy of the hot post-AGB stars : IRAS13266-5551
  (CPD-55 5588) and IRAS17311-4924 (Hen3-1428)

abstract:
  The high resolution spectra covering the wavelength range 4900 A to 8250 A of
the hot post-AGB stars IRAS13266-5551 (CPD-55 5588) and IRAS17311-4924
(Hen3-1428) reveal absorption lines of CII, NII, OII, AlIII, SiIII and FeIII
and a rich emission line spectrum consisting of HI, HeI, CII, NI, OI, MgII,
AlII, SiII, VI, MnI, FeIII, [FeII] and [CrII]. The presence of [NII] and [OI]
lines and absence of [OIII] indicate low excitation nebulae around these stars.
The components of NaI absorption lines indicate the presence of neutral
circumstellar envelopes in addition to the low excitation nebulae around these
two hot post-AGB stars. The H-alpha lines show P-Cygni profiles indicating
ongoing post-AGB mass loss. From the absorption lines, we derived heliocentric
radial velocities of 65.31 +/- 0.34 km/s and 27.55 +/- 0.74 km/s for
IRAS13266-5551 and IRAS17311-4924 respectively. High galactic latitude and
large radial velocity of IRAS13266-5551 indicate that it belongs to the old
disk population. Preliminary estimates for the CNO abundances in IRAS13266-5551
are obtained.


title: Reflections on Reflexions: I. Light Echoes in Type Ia Supernovae

abstract:
  In the last ten years, observational evidences about a possible connection
between Type Ia Supernovae (SNe) properties and the environment where they
explode have been steadily growing. In this paper I discuss, from a theoretical
point of view but with an observer's perspective, the usage of light echoes
(LEs) to probe the CSM around SNe of Type Ia since, in principle, they give us
a unique opportunity of getting a three-dimensional description of the SN
environment. In turn, this can be used to check the often suggested association
of some Ia's with dusty/star forming regions, which would point to a young
population for the progenitors. After giving a brief introduction to the LE
phenomenon in single scattering approximation, I derive analytical and
numerical solutions for the optical light and colour curves for a few simple
dust geometries. A fully 3D multiple scattering treatment has also been
implemented in a Monte Carlo code, which I have used to investigate the effects
of multiple scattering. In particular, I have explored in detail the LE colour
dependency from time and dust distribution, since this is a promising tool to
determine the dust density and derive the effective presence of multiple
scattering from the observed properties. Finally, again by means of Monte Carlo
simulations, I have studied the effects of multiple scattering on the LE linear
polarization, analyzing the dependencies from the dust parameters and geometry.
Both the analytical formalism and MC codes described in this paper can be used
for any LE for which the light curve of the central source is known.


title: The role of the SW Sextantis stars in the picture of CV evolution

abstract:
  The SW Sextantis stars are novalike cataclysmic variables (CVs) which exhibit
intricate behaviour which is still a matter of debate. For years the common
belief has been that these systems were the``outlaws'' of the CVs, mainly
because of the lack of an overall understanding. We are now realising that a
large percentage (~30%) of all novalikes in the ~3-4 hour period range are SW
Sex stars. The study of the dominance of this class just above the period gap
will provide clues on the evolution of CVs. Here we present the discovery of 7
new SW Sex stars from the CVs found in the Hamburg Quasar Survey.


title:
Detection of the white dwarf and the secondary star in the new SU UMa
  dwarf nova HS 2219+1824

abstract:
  We report the discovery of a new, non-eclipsing SU UMa-type dwarf nova, HS
2219+1824. Photometry obtained in quiescence (V ~ 17.5) reveals a double-humped
light curve from which we derive an orbital period of ~ 86.2 min. Additional
photometry obtained during a superoutburst reaching V ~ 12.0 clearly shows
superhumps with a period of ~ 89.05 min. The optical spectrum contains
double-peaked Balmer and HeI emission lines from the accretion disc as well as
broad absorption troughs of Hbeta, Hgamma, and Hdelta from the white dwarf
primary star. Modelling of the optical spectrum implies a white dwarf
temperature of 13000 K <~ Twd <~ 17000 K, a distance of 180 pc <~ d <~ 230 pc,
and suggests that the spectral type of the donor star is later than M5.
Phase-resolved spectroscopy obtained during quiescence reveals a narrow Halpha
emission line component which has a radial velocity amplitude and phase
consistent with an origin on the secondary star, possibly on the irradiated
hemisphere facing the white dwarf. This constitutes the first detection of line
emission from the secondary star in a quiescent SU UMa star.


title: Is GRS 1915+105 a microquasar?

abstract:
  The large mechanical luminosity of the jets of GRS 1915+105 should give rise
to luminous emission regions, similar to those observed in radio galaxies,
where the jets interact with the gas surrounding the source. However, no radio
synchrotron emission of the expected morphology has been found. Here we present
the results of a study suggesting that radio bremsstrahlung from the compressed
and heated ISM in front of the jets should be detectable, while the synchrotron
lobes may be too faint. We identify these jet impact sites with two well-known
IRAS regions. This identification suggests a distance of GRS 1915+105 of
$6.5\pm1.6$ kpc, significantly closer than the usually assumed distance of 11
to 12 kpc. We discuss the implications of this reduced distance estimate. The
apparent motion of small-scale jet components is not superluminal, so if
superluminal motion is required for an object to be termed a microquasar, GRS
1915+105 actually does not qualify. The mass of the black hole in the system is
increased to $21\pm9$ M$_{\odot}$ while the mechanical luminosity of the jets
is reduced to 14% of the Eddington luminosity.


title:
The XMM-{\em Newton}/2dF Survey - VI: Clustering and Bias of the Soft
  X-ray Point Sources

abstract:
  We study the clustering properties of X-ray sources detected in the wide area
($\sim 2 $deg$^{2}$) bright, contiguous XMM-{\em Newton}/2dF survey. We detect
432 objects to a flux limit of $5\times 10^{-15}$ ergcm$^{-2}$s$^{-1}$ in the
soft 0.5-2 keV band. Performing the standard angular correlation function
analysis, a $\sim 3\sigma$ correlation signal between 0 and 150 arcsec is
detected: $w(\theta<150^{''})\simeq 0.114\pm 0.037$. If the angular correlation
function is modeled as a power law,
$w(\theta)=(\theta_{\circ}/\theta)^{\gamma-1}$, then for its nominal slope of
$\gamma=1.8$ we estimate, after correcting for the integral constraint and the
amplification bias, that $\theta_{\circ}\simeq 10.4 \pm 1.9$ arcsec. Using a
clustering evolution model which is constant in comoving coordinates
($\epsilon=-1.2$), a luminosity dependent density evolution model for the X-ray
luminosity function and the concordance cosmological model ($\Omega_{\rm
m}=1-\Omega_{\Lambda}=0.3$) we obtain, by inverting Limber's integral equation,
a spatial correlation length of $r_{\circ}\sim 16$ $h^{-1}$ Mpc. This value is
larger than that of previous {\sc ROSAT} surveys as well as of the optical
two-degree quasar redshift survey. Only in models where the clustering remains
constant in physical coordinates ($\epsilon=-3$), do we obtain an $r_{\circ}$
value ($\sim 7.5$ $h^{-1}$ Mpc) which is consistent with the above surveys.


title: Time delays between the soft and hard X-ray bands in GRS 1915+105

abstract:
  The hard X-ray lightcurves exhibit delays of $\sim 1$ s with respect to the
soft X-ray lightcurves when the microquasar GRS 1915+105 is in the state of
frequent, regular outbursts (states $\rho$ and $\kappa$ of Belloni et al.
2000). Such outbursts are supposed to be driven by the radiation pressure
instability of the inner disc parts. The hard X-ray delays are then caused by
the time needed for the adjustment of the corona to changing conditions in the
underlying disc. We support this claim by the computation of the time evolution
of the disc, including a non-stationary evaporation of the disc and mass
exchange with the corona.


title:
Implications of WMAP observations on Li abundance and stellar evolution
  models

abstract:
  The WMAP determination of the baryon-to-photon ratio implies, through Big
Bang nucleosynthesis, a cosmological Li abundance larger, by a factor of 2 to
3, than the Li abundance plateau observed in the oldest Pop II stars. It is
however inescapable that there be a reduction by a factor of at least 1.6 to
2.0 of the surface Li abundance during the evolution of Pop II field stars with
[Fe/H] < -1.5. That the observed Li be lower than cosmologically produced Li is
expected from stellar evolution models. Since at turnoff most of the Li
abundance reduction is caused by gravitational settling, the presence of
Lithium 6 in some turnoff stars is also understood. Given that the WMAP
implications for Li cosmological abundance and the Li Spite plateau can be
naturally explained by gravitational settling in the presence of weak
turbulence, there appears little need for exotic physics as suggested by some
authors. Instead, there is a need for a better understanding of turbulent
transport in the radiative zones of stars. This requires simulations from first
principles. Rather strict upper limits to turbulent transport are determined
for the Sun and Pop II stars.


title:
The visibility of the Galactic bulge in optical surveys. Application to
  the Gaia mission

abstract:
  The bulge is a region of the Galaxy which is of tremendous interest for
understanding Galaxy formation. However, measuring photometry and kinematics in
it raises several inherent issues, like high extinction in the visible and
severe crowding. Here we attempt to estimate the problem of the visibility of
the bulge at optical wavelengths, where large CCD mosaics allow to easily cover
wide regions from the ground, and where future astrometric missions are
planned. Assuming the Besancon Galaxy model and high resolution extinction
maps, we estimate the stellar density as a function of longitude, latitude and
apparent magnitude and we deduce the possibility of reaching and measuring
bulge stars. The method is applied to three Gaia instruments, the BBP and MBP
photometers, and the RVS spectrograph. We conclude that, while in the BBP most
of the bulge will be accessible, in the MBP there will be a small but
significant number of regions where bulge stars will be detected and accurately
measured in crowded fields. Assuming that the RVS spectra may be extracted in
moderately crowded fields, the bulge will be accessible in most regions apart
from the strongly absorbed inner plane regions, because of high extinction, and
in low extinction windows like the Baades's window where the crowding is too
severe.


title: Gamma-Ray Line Astronomy

abstract:
  Gamma-ray lines from radioactive isotopes, ejected into interstellar space by
cosmic nucleosynthesis events, are observed with new space telescopes. The
Compton Observatory had provided a sky survey for the isotopes 56Co, 22Na,
44Ti, and 26Al, detecting supernova radioactivity and the diffuse glow of
long-lived radioactivity from massive stars in the Galaxy. High-resolution
spectroscopy is now being exploited with Ge detectors: Since 2002, with ESA's
INTEGRAL satellite and the RHESSI solar imager two space-based Ge-gamma-ray
telescopes are in operation, measuring Doppler broadenings and line shape
details of cosmic gamma-ray lines. First year's results include a detection and
line shape measurement of annihilation emission, and 26Al emission from the
inner Galaxy and from the Cygnus region. 60Fe gamma-ray intensity is
surprisingly low; it may have been detected by RHESSI at 10% of the 26Al
brightness, yet is not seen by INTEGRAL. 44Ti emission from Cas A and SN1987A
is being studied; no other candidate young supernova remnants have been found
through 44Ti. 22Na from novae still is not seen.


title: 3C 223.1: A source with unusual spectral properties

abstract:
  Analysis of Giant Metrewave Radio Telescope low frequency data for an
X-shaped source, 3C 223.1 has revealed an unusual result. The radio
morphologies of it at 240 and 610 MHz show well defined X-shape with a pair of
active jets along the north-south axis and a pair of wings along the east-west
axis, that pass symmetrically through the undetected radio core. The wings (or
low surface brightness jets) have flatter spectral indices with respect to the
high surface brightness jets, which confirms the earlier marginal result
obtained at high frequency by Dennett-Thorpe et al. (2002). Although unusual,
it is a valuable result which puts stringent constraints on the formation
models and nature of these sources. This result clearly shows the value of
mapping the sample of X-shaped sources at low frequencies.


title: AM CVn stars

abstract:
  I review our observational and theoretical knowledge of AM CVn stars,
focusing on recent developments. These include newly discovered systems, the
possibility that two recently discovered extremely short period objects are AM
CVn stars and an update on X-ray, UV an optical studies. Theoretical advances
include the study of the details of both the donor and accretor, and the
physics of the helium accretion discs. I review our (limited) knowledge of the
formation of AM CVn stars and the apparent success of the now more than 25 year
old suggestion that in these objects the mass transfer is driven by
gravitational wave radiation losses. The exciting prospect of directly
detecting these gravitational waves and the possibilities this brings conclude
this contribution.


title: Population Synthesis for Progenitors of Type Ia Supernovae

abstract:
  We discuss application of population synthesis for binary stars to
progenitors of SN Ia. We show that the only candidate systems able to support
the rate of SNe Ia $\sim 10^{-3} yr^{-1}$ both in old and young populations are
merging white dwarfs. In young populations ($\sim 1$ Gyr) edge-lit detonations
in semidetached systems with nondegenerate helium star donors are also able to
support a similar rate. The estimated current Galactic rate of SN Ia with
single-degenerate progenitors is $\sim 10^{-4} yr^{-1}$.


title: Time dependent mixing in He-burning cores: the case of NGC1866

abstract:
  We examine the convective core helium burning phase of intermediate mass
stars, and investigate the role of coupling of nuclear burning and mixing on
the extension and duration of the blue loop phase. We compare the theoretical
scenario with the distribution of stars in the colour-magnitude (CM) diagram of
the Large Magellanic Cloud (LMC) cluster NGC1866, whose largely populated clump
of He-burning stars is equally populated in the blue and red side. We compare
the distributions expected by adopting either a diffusive scheme within the
instability regions, in which nuclear burning and mixing are self-consistently
coupled, or the traditional instantaneous mixing approximation. We analyze with
particular care the sensitivity of the results to: a) the e-folding distance
with which the velocity of convective eddies decays outside the formal border
of the convective regions fixed by the Schwarzschild criterion; b) the
convective model adopted to evaluate the temperature gradient; c) the rate of
reaction C12+alpha -> O16. Models not including convective overshoot are also
commented.


title: The Leo Triplet: Common origin or late encounter?

abstract:
  The kinematics, structure, and stellar population properties in the centers
of two early-type spiral galaxies of the Leo Triplet, NGC 3623 and NGC 3627,
are studied by means of integral-field spectroscopy. Unlike our previous
targets, NGC 3384/NGC 3368 in the Leo I group and NGC 5574/NGC 5576 in LGG379,
NGC 3623 and NGC 3627 do not appear to experience a synchronous evolution. The
mean ages of their circumnuclear stellar populations are quite different, and
the magnesium overabundance of the nucleus in NGC 3627 is evidence for a very
brief last star formation event 1 Gyr ago whereas the evolution of the central
part of NGC 3623 looks more quiescent. In the center of NGC 3627 we observe
noticeable gas radial motions, and the stars and the ionized gas in the center
of NGC 3623 demonstrate more or less stable rotation. However, NGC 3623 has a
chemically distinct core -- a relic of a past star formation burst -- which is
shaped as a compact, dynamically cold stellar disk with a radius of about
250-350 pc which has been formed not later than 5 Gyr ago.


title: Collapse and Fragmentation in Finite Sheets

abstract:
  We present two-dimensional simulations of finite, self-gravitating gaseous
sheets. Unlike the case of infinite sheets, such configurations do not
constitute equilibrium states but instead are subject to global collapse unless
countered by pressure forces or rotation. The initial effect of finite geometry
is to promote concentrations of material at the edges of the sheet. If the
sheet is not perfectly circular, gravitational focussing results in enhanced
concentrations of mass. In the second-most simple geometry, that of an
elliptical outer boundary, the general result is collapse to a filamentary
structure with the densest concentrations of mass at the ends of the filament.
We suggest that these simple calculations have interesting implications for the
gravitational evolution of overall molecular cloud structure, envisioning that
such clouds might originate as roughly sheetlike sections of gas accumulated as
a result of large-scale flows in the local interstellar medium. We show some
examples of local clouds with overall filamentary shape and denser
concentrations of mass and star clusters near the ends of the overall extended
structure, suggestive of our simple ellipse collapse calculations. We suggest
that cluster-forming gas is often concentrated as a result of gravity acting on
irregular boundaries; this mechanism can result in very rapid infall of gas
which may be of importance to the formation of massive stars. This picture
suggests that much of the supersonic ``turbulence'' observed in molecular
clouds might be gravitationally-generated. Our results may provide impetus for
further theoretical explorations of global gravitational effects in molecular
clouds and their implications for generating the substructure needed for
fragmentation into stars and clusters.


title: The ultimate outcome of black hole - neutron star mergers

abstract:
  We present a simple, semi--analytical description for the final stages of
mergers of black hole (BH) -- neutron star (NS) systems. Such systems are of
much interest as gravitational wave sources and gamma--ray burst progenitors.
Numerical studies show that in general the neutron star is not disrupted at the
first phase of mass transfer. Instead, what remains of the neutron star is left
on a wider, eccentric, orbit. We consider the evolution of such systems as they
lose angular momentum via gravitational radiation and come into contact for
further phases of mass transfer. During each mass transfer event the neutron
star mass is reduced until a critical value where mass loss leads to a rapid
increase in the stellar radius. At this point Roche lobe overflow shreds what
remains of the neutron star, most of the mass forming a disc around the black
hole. Such a disc may be massive enough to power a gamma--ray burst. The mass
of the neutron star at the time of disruption (and therefore the disc mass) is
largely independent of the initial masses of the black hole and neutron star,
indicating that BH--NS star mergers may be standard candles.


title:
Pure Luminosity Evolution Models: Too Few Massive Galaxies at
  Intermediate and High Redshift

abstract:
  We compare pure luminosity evolution (PLE) models with recent data at low and
high redshift. These models assume that massive galaxies were assembled and
formed most of their stars at high redshift (z > 3) and have evolved without
merging or substantial dust obscuration since then. Our models span the full
range of plausible metallicities, initial mass functions (IMF's) and star
formation histories. We require them to reproduce the abundance of galaxies by
colour and luminosity in the Sloan Digital Sky Survey and we investigate
whether they can simultaneously fit (i) the observed galaxy counts as a
function of redshift in magnitude limited surveys with K < 20, and (ii) the
colour and M/L ratio evolution of red sequence galaxies in clusters. All models
that are consistent with (ii) predict galaxy counts at 1.5 < z < 3 which lie
above the observations. Models with an IMF slope similar to the Salpeter value
lie far above the data. We conclude that the majority of massive galaxies were
either assembled relatively late in this redshift interval or were
substantially obscured by dust at these redshifts.


title: Mg II chromospheric radiative loss rates in cool active and quiet stars

abstract:
  The Mg II k emission line is a good indicator of the level of chromospheric
activity in late-type stars. We investigate the dependence of this activity
indicator on fundamental stellar parameters. To this purpose we use IUE
observations of the Mg II k line in 225 late-type stars of luminosity classes
I-V, with different levels of chromospheric activity. We first re-analyse the
relation between Mg II k line luminosity and stellar absolute magnitude,
performing linear fits to the points. The ratio of Mg II surface flux to total
surface flux is found to be independent of stellar luminosity for evolved stars
and to increase with decreasing luminosity for dwarfs. We also analyse the Mg
II k line surface flux-metallicity connection. The Mg II k emission level turns
out to be not dependent on metallicity. Finally, the Mg II k line surface
flux-temperature relation is investigated by treating separately, for the first
time, a large sample of very active and normal stars. The stellar surface
fluxes in the k line of normal stars are found to be strongly dependent on the
temperature and slightly dependent on the gravity, thus confirming the validity
of recently proposed models. In contrast, data relative to RS CVn binaries and
BY Dra stars, which show very strong chromospheric activity, are not justified
in the framework of a description based only on acoustic waves and uniformly
distributed magnetic flux tubes so that they require more detailed models.


title: From heaviness to lightness during inflation

abstract:
  We study the quantum fluctuations of scalar fields with a variable effective
mass during an inflationary phase. We consider the situation where the
effective mass depends on a background scalar field, which evolves during
inflation from being frozen into a damped oscillatory phase when the Hubble
parameter decreases below its mass. We find power spectra with suppressed
amplitude on large scales, similar to the standard massless spectrum on small
scales, and affected by modulations on intermediate scales. We stress the
analogies and differences with the parametric resonance in the preheating
scenario. We also discuss some potentially observable consequences when the
scalar field behaves like a curvaton.


title: Non-stationary variability in AGN: the case of 3C 390.3

abstract:
  We use data from a two-year intensive RXTE monitoring campaign of the
broad-line radio galaxy 3C 390.3 to investigate its stationarity. In order to
exploit the potential information contained in a time series more efficiently,
we use a multi-technique approach. Specifically, the temporal properties are
first studied with a technique borrowed from non-linear dynamics. Then we
utilize traditional linear techniques both in the Fourier domain, by estimating
the power spectral density, and in the time domain with a structure function
analysis. Finally we investigate directly the probability density function
associated with the physical process underlying the signal. All the methods
demonstrate the presence of non-stationarity. The structure function analysis,
and (at a somewhat lower significance level) the power spectral density suggest
that 3C 390.3 is not even second order stationarity. This result indicates, for
the first time, that the variability properties of the active galactic nuclei
light curves may also vary with time, in the same way as they do in Galactic
black holes, strengthening the analogy between the X-ray variability properties
of the two types of objects.


title:
Infrared Properties of Cataclysmic Variables in the 2MASS All Sky Data
  Release

abstract:
  We present results from our analysis of the near-infrared (J, H, and Ks)
photometry for all cataclysmic variables from the catalog of Downes et al.
(2001) that are detected in the (final) All Sky Data Release from the Two
Micron All Sky Survey (2MASS).


title:
Evidence that powerful radio jets have a profound influence on the
  evolution of galaxies

abstract:
  The relationships between supermassive black holes and the properties of
their associated dark-matter halos imply that outflows from accreting black
holes provide a feedback mechanism regulating galaxy formation. Accreting black
holes with weak or undetectable radio jets (radio-quiet quasars) outnumber
those with powerful jets (radio-loud quasars) by a factor ~10-100, so
powerful-jet outflows are often neglected. However, whenever powerful jets are
triggered, there is a dramatic (factor >100) step-function increase in the
efficiency of feedback. We use a feedback model, together with the measured
space density of flat-spectrum radio-loud quasars, to show that a powerful-jet
episode probably occurred in every protocluster in the Universe. Before jet
triggering, there was time for gravitational collapse to create many (~10-100)
surrounding protogalaxies massive enough to host radio-quiet quasars. After
triggering, the powerful jet pushes back and heats ionized gas so that it
cannot fall onto these protogalaxies and cool. Once neutral/molecular gas
reservoirs become exhausted, there is a synchronized shut down in both
star-formation and black-hole activity throughout the protocluster. These
considerations imply that radio-loud quasars have a profound influence on the
evolution of all the galaxies seen in clusters today.


title:
Generalized Regularization Techniques With Constraints For The Analysis
  Of Solar Bremsstrahlung X-Ray Spectra

abstract:
  Hard X-ray spectra in solar flares provide knowledge of the electron spectrum
that results from acceleration and propagation in the solar atmosphere.
However, the inference of the electron spectra from solar X-ray spectra is an
ill-posed inverse problem. Here we develop and apply an enhanced regularization
algorithm for this process making use of physical constraints on the form of
the electron spectrum. The algorithm incorporates various features not
heretofore employed in the solar flare context: Generalized Singular Value
Decomposition (GSVD) to deal with different orders of constraints; rectangular
form of the cross-section matrix to extend the solution energy range;
regularization with various forms of the smoothing operator; and
"preconditioning" of the problem. We show by simulations that this technique
yields electron spectra with considerably more information and higher quality
than previous algorithms.


title:
On the transmission- to reprocessing-dominated spectral state
  transitions in Seyfert 2 galaxies

abstract:
  We present Chandra and XMM-Newton observations of a small sample (11 objects)
of optically-selected Seyfert~2 galaxies, for which ASCA and BeppoSAX had
suggested Compton-thick obscuration of the Active Nucleus (AGN). The main goal
of this study is to estimate the rate of transitions between "transmission-"
and "reprocessing-dominated" states. We discover one new transition in NGC4939,
with a possible additional candidate in NGC5643. This indicates a typical
occurrence rate of at least ~0.02/year. These transitions could be due to large
changes of the obscuring gas column density, or to a transient dimming of the
AGN activity, the latter scenario being supported by detailed analysis of the
best studied events. Independently of the ultimate mechanism, comparison of the
observed spectral dynamics with Monte-Carlo simulations demonstrates that the
obscuring gas is largely inhomogeneous, with multiple absorbing components
possibly spread through the whole range of distances from the nucleus between a
fraction of parsecs up to several hundreds parsecs. As a by-product of this
study, we report the first measurement ever of the column density covering the
AGN in NGC3393 (N_H ~ 4.4x10^{24} atoms/cm/cm), and the discovery of soft X-ray
extended emission, apparently aligned along the host galaxy main axis in
NGC5005. The latter object hosts most likely an historically misclassified
low-luminosity Compton-thin AGN.


title: 2-D Models of Protostars: III. Effects of Stellar Temperature

abstract:
  We model how the mid-infrared colors of Young Stellar Objects (YSOs) vary
with stellar temperature. The spectral energy distribution (SED) of each object
has contributions from thermal emission of circumstellar dust, from direct
stellar photospheric emission, and from scattered stellar emission. We first
isolate the effects of stellar contributions (direct+scattered) to the SED
using homologous "Class I" models, where the shape of the thermal contribution
to the SED remains constant. Stellar light contributes relatively more to the
MIR emission of YSOs with lower temperature stars (Tstar ~4000 K) because the
emission peak wavelength of the star is closer to that of the thermal
radiation. Next we consider realistic Class 0, I, and II source models and find
that the other dominant effect of varying stellar temperature on YSO SEDs is
that of the inner disk wall: In high-Tstar models, the dust destruction radius
is much further out with a consequently larger inner disk wall that contributes
relatively more to the 2-10 um flux. This effect partially offsets that of the
stellar contribution leading to varying behaviors of the 2-10 um flux.
  Our modeled MIR protostellar colors have implications for interpretations of
Spitzer IRAC observations of star formation regions: It is commonly assumed
that the slope of the SED at 1-10 um is directly related to evolutionary state.
We show that inclination effects, aperture size, scattered light, and stellar
temperature cause a broad spread in the colors of a source at a single
evolutionary state. Color magnitude diagrams can help sort out these effects by
separating sources with different Tstar based on their different brightness
(for sources at the same distance).


title:
Determination Of Electron Flux Spectra In A Solar Flare With An
  Augmented Regularization Method: Application To Rhessi Data

abstract:
  Kontar et al. (2004) have shown how to recover mean source electron spectra
in solar flares through a physical constraint regularization analysis of the
bremsstrahlung photon spectra that they produce. They emphasize the use of
non-square inversion techniques, and preconditioning combined with physical
properties of the spectra to achieve the most meaningful solution to the
problem. Higher-order regularization techniques may be used to generate
${overline F}(E)$ forms with certain desirable properties (e.g., higher order
derivatives). They further note that such analyses may be used to infer
properties of the electron energy spectra at energies well above the maximum
photon energy observed. In this paper we apply these techniques to data from a
solar flare observed by RHESSI on 26 February, 2002. Results using different
orders of regularization are presented and compared for various time intervals.
Clear evidence is presented for a change in the value of the high-energy cutoff
in the mean source electron spectrum with time. We also show how the
construction of the injected (accelerated) electron spectrum $F_0(E_0)$
(assuming that Coulomb collisions in a cold target dominate the electron
energetics) is facilitated by the use of higher-order regularization methods.


title: G65.2+5.7: A Thermal Composite Supernova Remnant With a Cool Shell

abstract:
  This paper presents archival ROSAT PSPC observations of the G65.2+5.7
supernova remnant (also known as G65.3+5.7). Little material obscures this
remnant and so it was well observed, even at the softest end of ROSAT's
bandpass (~0.11 to 0.28 keV). These soft X-ray images reveal the remnant's
centrally-filled morphology which, in combination with existing radio frequency
observations, places G65.2+5.7 in the thermal composite (mixed morphology)
class of supernova remnants. Not only might G65.2+5.7 be the oldest known
thermal composite supernova remnant, but owing to its optically revealed cool,
dense shell, this remnant supports the proposal that thermal composite
supernova remnants lack X-ray bright shells because they have evolved beyond
the adiabatic phase. These observations also reveal a slightly extended point
source centered on RA = 19h 36m 46s, dec = 30deg 40' 07'' and extending 6.5
arcmin in radius in the band 67 map. The source of this emission has yet to be
discovered, as there is no known pulsar at this location.


title: A NLTE line blanketed model of a solar type star

abstract:
  We present LTE and NLTE atmospheric models of a star with solar parameters,
and study the effect of treating many thousands of Iron group lines out of LTE
on the computed atmospheric structure, overall absolute flux distribution, and
the moderately high resolution spectrum in the visible and near UV bands. Our
NLTE modeling includes the first two or three ionization stages of 20 chemical
elements, up to and including much of the Fe-group, and includes about 20000 Fe
I and II lines. We investigate separately the effects of treating the light
metals and the Fe-group elements in NLTE. Our main conclusions are that 1) NLTE
line blanketed models with direct multi-level NLTE for many actual transitions
gives qualitatively similar results as the more approximate treatment of
Anderson (1989) for both the Fe statistical equilibrium and the atmospheric
temperature structure, 2) models with many Fe lines in NLTE have a temperature
structure that agrees more closely with LTE semi-empirical models based on
center-to-limb variation and a wide variety of spectra lines, whereas LTE
models agree more with semi-empirical models based only on an LTE calculation
of the Fe I excitation equilibrium, 3) the NLTE effects of Fe-group elements on
the model structure and flux distribution are much more important than the NLTE
effects of all the light metals combined, and serve to substantially increases
the violet and near UV flux level as a result of NLTE Fe over-ionization. These
results suggest that there may still be important UV opacity missing from the
models.


title:
A constraint on any topological lensing hypothesis in the spherical
  case: it must be a root of the identity

abstract:
  Three-dimensional catalogues of objects at cosmological distances can
potentially yield candidate topologically lensed pairs of sets of objects,
which would be a sign of the global topology of the Universe. In the spherical
case, a necessary condition, which does not exist for either null or negative
curvature, can be used to falsify such hypotheses, without needing to loop
through a list of individual spherical 3-manifolds. This condition is that the
isometry between the two sets of objects must be a root of the identity
isometry in the covering space S^3. This enables numerical falsification of
topological lensing hypotheses without needing to assume any particular
spherical 3-manifold. By embedding S^3 in R^4, this condition can be expressed
as the requirement that M^n = I for an integer n, where M is the matrix
representation of the hypothesised lensing isometry and I is the identity.
Moreover, this test becomes even simpler with the requirement that the two
rotation angles, theta, phi, corresponding to the given isometry, satisfy 2\pi
/ \theta, 2\pi / \phi \in Z. The calculation of this test involves finding the
two eigenplanes of the matrix M. A GNU General Public Licence numerical
package, called eigenplane, is made available at
http://cosmo.torun.pl/GPLdownload/eigen/ for finding the rotation angles and
eigenplanes of an arbitrary isometry M of S^3.


title:
Elemental Abundances in Two High Column Density Damped Lyman Alpha
  Systems at z < 1.5

abstract:
  We present Keck/HIRES abundance measurements and metal-line kinematic
profiles of the damped Lyman alpha systems (DLAs) towards the quasars Q0933+733
(z_abs=1.479) and Q0948+433 (z_abs=1.233). These two DLAs have among the five
highest HI column densities at any redshift: N(HI)=4.2E21 cm^{-2}. The
metal-line data, presented here for the first time, reveal that these DLAs are
noteworthy for several other reasons as well. 1) The Q0933+733 DLA exhibits
simple kinematic structure with unusually narrow velocity widths as measured
from its unsaturated metal lines (delta v=16 km/s). At 2.6% solar, it has the
second lowest metallicity at z<2. 2) The Q0948+433 DLA has among the strongest
metal-line transitions of any known DLA. The saturated SiII1808 line implies a
high metallicity ([Si/H]> -1) and a significant alpha-enhancement. The strong
metal lines of this DLA have made possible the detection of TiII1910, CoII2012,
and MgI2026. 3) We find that the relative gas-phase abundances of both DLAs
follow the general trend seen at high redshift, e.g., enhanced Zn/Fe and Si/Fe,
and sub-solar Mn/Fe, indicating that there is little evolution in the
nucleosynthetic patterns of DLAs down to this epoch. 4) Their high HI column
densities imply that these DLAs dominate the column density-weighted cosmic
mean metallicity, <Z>, of the universe at z<1.5. Using the 15 DLAs with
measured metallicities in the redshift interval 0.4<z<1.5, we find <Z> =
-0.89^{+0.40}_{-0.33}, where the uncertainties are 95% confidence limits.


title:
Infall, the Butcher-Oemler Effect, and the Descendants of Blue Cluster
  Galaxies at z~0.6

abstract:
  Using wide-field HST/WFPC2 imaging and extensive Keck/LRIS spectroscopy, we
present a detailed study of the galaxy populations in MS2053--04, a massive,
X-ray luminous cluster at z=0.5866. Analysis of 149 confirmed cluster members
shows that MS2053 is composed of two structures that are gravitationally bound
to each other; their respective velocity dispersions are 865 km/s (113 members)
and 282 km/s (36 members). MS2053's total dynamical mass is 1.2x10^15 Msun.
MS2053 is a classic Butcher-Oemler cluster with a high fraction of blue members
(24%) and an even higher fraction of star-forming members (44%), as determined
from their [OII] emission. The number fraction of blue/star-forming galaxies is
much higher in the infalling structure than in the main cluster. This result is
the most direct evidence to date that the Butcher-Oemler effect is linked to
galaxy infall. In terms of their colors, luminosities, estimated internal
velocity dispersions, and [OII] equivalent widths, the infalling galaxies are
indistinguishable from the field population. MS2053's deficit of S0 galaxies
combined with its overabundance of blue spirals implies that many of these
late-types will evolve into S0 members. The properties of the blue cluster
members in both the main cluster and infalling structure indicate they will
evolve into low mass, L<L* galaxies with extended star formation histories like
that of low mass S0's in Coma. Our observations show that most of MS2053's blue
cluster members, and ultimately most of its low mass S0's, originate in the
field. Finally, we measure the redshift of the giant arc in MS2053 to be
z=3.1462; this object is one in only a small set of known strongly lensed
galaxies at z>3.


title: Quasars and the Big Blue Bump

abstract:
  We investigate the ultraviolet-to-optical spectral energy distributions
(SEDs) of 17 active galactic nuclei (AGNs) using quasi-simultaneous
spectrophotometry spanning 900-9000 Angstrom (rest frame). We employ data from
the Far Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope
(HST), and the 2.1-meter telescope at Kitt Peak National Observatory (KPNO).
Taking advantage of the short-wavelength coverage, we are able to study the
so-called "big blue bump," the region where the energy output peaks, in detail.
Most objects exhibit a spectral break around 1100 Angstrom. Although this
result is formally associated with large uncertainty for some objects, there is
strong evidence in the data that the far-ultraviolet spectral region is below
the extrapolation of the near-ultraviolet-optical slope, indicating a spectral
break around 1100 Angstrom. We compare the behavior of our sample to those of
non-LTE thin-disk models covering a range in black-hole mass, Eddington ratio,
disk inclination, and other parameters. The distribution of ultraviolet-optical
spectral indices redward of the break, and far-ultraviolet indices shortward of
the break, are in rough agreement with the models. However, we do not see a
correlation between the far-ultraviolet spectral index and the black hole mass,
as seen in some accretion disk models. We argue that the observed spectral
break is intrinsic to AGNs, although intrinsic reddening as well as
Comptonization can strongly affect the far-ultraviolet spectral index. We make
our data available online in digital format.


title: The Third VLBA Calibrator Survey

abstract:
  This paper presents the third extension to the Very Large Baseline Array
(VLBA) Calibrator Survey, containing 360 new sources not previously observed
with very long baseline interferometry (VLBI). The survey, based on three 24
hour VLBA observing sessions, fills the areas on the sky above declination -45
degrees where the calibrator density is less than one source within a 4 degrees
radius disk at any given direction. The positions were derived from astrometric
analysis of the group delays determined at 2.3 and 8.6 GHz frequency bands
using the Calc/Solve software package. The VCS3 catalogue of source positions,
plots of correlated flux density versus the length of projected baseline,
contour plots and fits files of naturally weighted CLEAN images as well as
calibrated visibility function files are available on the Web at
http://gemini.gsfc.nasa.gov/vcs3


title:
Type II quasar candidates in the Sloan Digital Sky Survey: evidence for
  X-ray obscuration

abstract:
  Recent X-ray surveys with Chandra and XMM-Newton have found several genuine
Type II quasars, the long sought-after population of high-luminosity
(high-redshift) Seyfert 2 galaxies, and a sizable number of Type II quasar
candidates. However, at present it is hard to know whether the on-going X-ray
surveys are providing a reliable and nearly complete census of the Type II
quasar population. In order to address this open issue and shed light on the
broad-band properties of Type II quasars, we used the sample of 291
high-ionization narrow emission-line AGN at z=0.3-0.83 selected from the Sloan
Digital Sky Survey by Zakamska et al. (2003). Using archival X-ray information,
we were able to place constraints on the X-ray emission of 17 of these objects
(three X-ray detections and 14 upper limits). Using the [O III]5007 line
luminosities to predict the intrinsic X-ray power of the AGN, we found that at
least 47% of the objects in the observed sample provides evidence for the
presence of X-ray absorption (with N_H>10^22 cm^-2), including the four highest
luminosity sources with predicted unobscured luminosities of ~10^45 erg/s. For
the only source with moderate-quality XMM-Newton spectral data, all of the
pieces of the puzzle (2-10 keV luminosity of ~4x10^44 erg/s, N_H~1-3x10^22
cm^-2, and unobscured magnitude M_B=-26 assure that this is a genuine Type II
quasar.


title:
Sloan Digital Sky Survey Imaging of Low Galactic Latitude Fields:
  Technical Summary and Data Release

abstract:
  The Sloan Digital Sky Survey (SDSS) mosaic camera and telescope have obtained
five-band optical-wavelength imaging near the Galactic plane outside of the
nominal survey boundaries. These additional data were obtained during
commissioning and subsequent testing of the SDSS observing system, and they
provide unique wide-area imaging data in regions of high obscuration and star
formation, including numerous young stellar objects, Herbig-Haro objects and
young star clusters. Because these data are outside the Survey regions in the
Galactic caps, they are not part of the standard SDSS data releases. This paper
presents imaging data for 832 square degrees of sky (including repeats), in the
star-forming regions of Orion, Taurus, and Cygnus. About 470 square degrees are
now released to the public, with the remainder to follow at the time of SDSS
Data Release 4. The public data in Orion include the star-forming region NGC
2068/NGC 2071/HH24 and a large part of Barnard's loop.


title: The spin of accreting stars: dependence on magnetic coupling to the disc

abstract:
  We formulate a general, steady-state model for the torque on a magnetized
star from a surrounding accretion disc. For the first time, we include the
opening of dipolar magnetic field lines due to the differential rotation
between the star and disc, so the magnetic topology then depends on the
strength of the magnetic coupling to the disc. This coupling is determined by
the effective slip rate of magnetic field lines that penetrate the diffusive
disc. Stronger coupling (i.e., lower slip rate) leads to a more open topology
and thus to a weaker magnetic torque on the star from the disc. In the expected
strong coupling regime, we find that the spin-down torque on the star is more
than an order of magnitude smaller than calculated by previous models. We also
use our general approach to examine the equilibrium (`disc-locked') state, in
which the net torque on the star is zero. In this state, we show that the
stellar spin rate is roughly an order of magnitude faster than predicted by
previous models. This challenges the idea that slowly-rotating, accreting
protostars are disc locked. Furthermore, when the field is sufficiently open
(e.g., for mass accretion rates > 5 x 10^{-9} M_sun / yr, for typical accreting
protostars), the star will receive no magnetic spin-down torque from the disc
at all. We therefore conclude that protostars must experience a spin-down
torque from a source that has not yet been considered in the star-disc torque
models--possibly from a stellar wind along the open field lines.


title:
Particle Acceleration and Magnetic Field Generation in Electron-Positron
  Relativistic Shocks

abstract:
  Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., Buneman, Weibel and
other two-stream instabilities) created in collisionless shocks are responsible
for particle (electron, positron, and ion) acceleration. Using a 3-D
relativistic electromagnetic particle (REMP) code, we have investigated
particle acceleration associated with a relativistic electron-positron jet
front propagating into an ambient electron-positron plasma with and without
initial magnetic fields. We find small differences in the results for no
ambient and modest ambient magnetic fields. New simulations show that the
Weibel instability created in the collisionless shock front accelerates jet and
ambient particles both perpendicular and parallel to the jet propagation
direction. Furthermore, the non-linear fluctuation amplitudes of densities,
currents, electric, and magnetic fields in the electron-positron shock are
larger than those found in the electron-ion shock studied in a previous paper
at the comparable simulation time. This comes from the fact that both electrons
and positrons contribute to generation of the Weibel instability. Additionally,
we have performed simulations with different electron skin depths. We find that
growth times scale inversely with the plasma frequency, and the sizes of
structures created by the Weibel instability scale proportional to the electron
skin depth. This is the expected result and indicates that the simulations have
sufficient grid resolution. The simulation results show that the Weibel
instability is responsible for generating and amplifying nonuniform,
small-scale magnetic fields which contribute to the electron's (positron's)
transverse deflection behind the jet head.


title:
Simulations of core convection and resulting dynamo action in rotating
  A-type stars

abstract:
  We present the results of 3--D nonlinear simulations of magnetic dynamo
action by core convection within A-type stars of 2 solar masses, at a range of
rotation rates. We consider the inner 30% by radius of such stars, with the
spherical domain thereby encompassing the convective core and a portion of the
surrounding radiative envelope. The compressible Navier-Stokes equations,
subject to the anelastic approximation, are solved to examine highly nonlinear
flows that span multiple scale heights, exhibit intricate time dependence, and
admit magnetic dynamo action. Small initial seed magnetic fields are found to
be amplified greatly by the convective and zonal flows. The central columns of
strikingly slow rotation found in some of our progenitor hydrodynamic
simulations continue to be realized in some simulations to a lesser degree,
with such differential rotation arising from the redistribution of angular
momentum by the nonlinear convection and magnetic fields. We assess the
properties of the magnetic fields thus generated, the extent of convective
penetration, the magnitude of the differential rotation, and the excitation of
gravity waves within the radiative envelope.


title: Diffuse X-rays from the Arches and Quintuplet clusters

abstract:
  The origin and initial mass function of young stellar clusters near the
Galactic center are still poorly understood. Two of the more prominent ones,
the Arches and Quintuplet clusters, may have formed from a shock-induced burst
of star formation, given their similar age and proximity to each other. Their
unusual mass distribution, however, may be evidence of a contributing role
played by other factors, such as stellar capture from regions outside the
clusters themselves. Diffuse X-ray emission from these sources provides us with
a valuable, albeit indirect, measure of the stellar mass-loss rate from their
constituents. Using recent data acquired with Chandra, we can study the nature
and properties of the outflow to not only probe the pertinent physical
conditions, such as high metallicity, the magnetic field, and so forth, but
also to better constrain the stellar distribution within the clusters, in order
to identify their formative history. In this paper, we present a set of
three-dimensional smoothed particle hydrodynamics simulations of the wind-wind
interactions in both the Arches and Quintuplet clusters. We are guided
primarily by the currently known properties of the constituent stars, though we
vary the mass-loss rates in order to ascertain the dependence of the measured
X-ray flux on the assumed stellar characteristics. Our results are compared
with the latest observations of the Arches cluster. Our analysis of the
Quintuplet cluster may be used as a basis for comparison with future X-ray
observations of this source.


title: On the Origin of Isophotal Shapes in Elliptical Galaxies

abstract:
  Using semi-analytical models of galaxy formation, the origin of boxy and
disky elliptical galaxies is investigated. We find that the simple scenario,
motivated by N-body simulations, in which the isophotal shape is only dependent
on the mass ratio of the last major merger, is not able to reproduce the
observation that the fraction of boxy and disky ellipticals depends on galaxy
luminosity. The observations can however be reproduce with the following
reasonable assumptions: (i) equal-mass mergers lead to boxy ellipticals and
unequal-mass mergers produce disky ellipticals (as motivated by N-body
simulations) (ii) major mergers between bulge-dominated galaxies result always
in boxy ellipticals, independent of the mass ratio, (iii) merger remnants that
subsequently accrete gas leading to a secondary stellar disk with more than $20
%$ the total stellar fraction are always disky. Boxy and disky ellipticals can
be divided into two subclasses, depending on their formation history. Boxy
ellipticals either formed by equal mass mergers of disk galaxies or by major
mergers of early-type galaxies. We find that disky ellipticals are indicators
of unequal-mass mergers or late gas infall. Disky ellipticals with high
luminosities preferentially are 1-component systems that result from unequal
mass mergers whereas low-luminosity disky ellipticals are more likely to harbor
secondary disk components. In addition, the fraction of disky ellipticals with
secular disk components should increase in regions with higher galaxy
densities. Taking into account the conversion of cuspy cores into flat
low-density cores by black hole merging we find that disky ellipticals should
contain central density cusps whereas boxy ellipticals should in general be
characterized by flat cores.


title:
Chemical Abundances for Seven Giant Stars in M68 (NGC 4590) : A Globular
  Cluster with Abnormal Silicon and Titanium Abundances

abstract:
  We present a detailed chemical abundance study of seven giant stars in M68
including six red giants and one post-AGB star. We find significant differences
in the gravities determined using photometry and those obtained from ionization
balance, which suggests that non-LTE effects are important for these
low-gravity, metal-poor stars. We adopt an iron abundance using photometric
gravities and Fe II lines to minimize those effects, finding [Fe/H] = -2.16 +/-
0.02. For element-to-iron ratios,we rely on neutral lines vs. Fe I and ionized
lines vs. FeII (except for [O/Fe]) to also minimize non-LTE effects.
  We find variations in the abundances of sodium among the program stars.
However, there is no correlation (or anti-correlation) with the oxygen
abundances. Further, the post-AGB star has a normal (low) abundance of sodium.
Both of these facts add further support to the idea that the variations seen
among some light elements within individual globular clusters arises from
primordial variations, and not from deep mixing.
  M68, like M15, shows elevated abundances of silicon compared to other
globular clusters and comparable metallicity field stars. But M68 deviates even
more in showing a relative underabundance of titanium. We speculate that in
M68, titanium is behaving like an iron-peak element rather than its more
commonly observed adherence to enhancements seen in the "alpha" elements such
as magnesium, silicon, and calcium. We interpret this result as implying that
the chemical enrichment seen in M68 may have arisen from contributions from
supernovae with somewhat more massive progenitors than contribute normally to
abundances seen in other globular clusters.


title: Simulating the Soft X-ray excess in clusters of galaxies

abstract:
  The detection of excess of soft X-ray or Extreme Ultraviolet (EUV) radiation,
above the thermal contribution from the hot intracluster medium (ICM), has been
a controversial subject ever since the initial discovery of this phenomenon. We
use a large--scale hydrodynamical simulation of a concordance $\Lambda$CDM
model, to investigate the possible thermal origin for such an excess in a set
of 20 simulated clusters having temperatures in the range 1--7 keV. Simulated
clusters are analysed by mimicking the observational procedure applied to
ROSAT--PSPC data, which for the first time showed evidences for the soft X-ray
excess. For cluster--centric distances $0.4< R/R_{\rm vir}< 0.7$ we detect a
significant excess in most of the simulated clusters, whose relative amount
changes from cluster to cluster and, for the same cluster, by changing the
projection direction. In about 30 per cent of the cases, the soft X-ray flux is
measured to be at least 50 per cent larger than predicted by the
one--temperature plasma model. We find that this excess is generated in most
cases within the cluster virialized regions. It is mainly contributed by
low--entropy and high--density gas associated with merging sub--halos, rather
than to diffuse warm gas. Only in a few cases the excess arises from
fore/background groups observed in projection, while no evidence is found for a
significant contribution from gas lying within large--scale filaments. We
compute the distribution of the relative soft excess, as a function of the
cluster--centric distance, and compare it with the observational result by
Bonamente et al. (2003) for the Coma cluster. Similar to observations, we find
that the relative excess increases with the distance from the cluster center,
with no significant excess detected for $R<0.4R_{\rm vir}$. (abridged)


title: Coevolution of the galactic cores and spiral galaxies

abstract:
  Using high-resolution N-body/SPH simulations with $2\times 10^6$ particles,
we investigate the evolution of stellar and gaseous galactic cores during the
hierarchical formation of a spiral galaxy. We find that the galactic core ($r <
300 $ pc) coevolves with the host galaxy. The average mass ratio between the
baryonic core and the halo is nearly constant, $\sim $ 0.04 from $z \sim 10$ to
$z \sim 2$. However, there are several `rapid-growing phases' during the
evolution, in which the rate of mass accretion to the central sub-kpc region is
ten times higher ($\sim 1 M_\odot$ yr pc$^{-1}$) than the average accretion
rate. The rapid growth of the inner core is associated with the major merger
events with a time-delay. We also find that the spin-axis of the gas core
frequently changes. As a result, the angular momentum vector of the central
part of the galaxy is independent of the rotation of the outer part. Our
results suggest that if a constant fraction of the baryonic mass in the central
several 100 pc of a galaxy is converted into a massive black hole, the black
hole mass should correlate with the total mass of the galaxies.