title:
A Burst and Simultaneous Short-Term Pulsed Flux Enhancement from the
  Magnetar Candidate 1E 1048.1-5937

abstract:
  We report on the 2004 June 29 burst detected from the direction of the
Anomalous X-ray Pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing
Explorer (RXTE). We find a simultaneous increase of ~3.5 times the quiescent
value in the 2-10 keV pulsed flux of 1E 1048.1-5937 during the tail of the
burst which identifies the AXP as the burst's origin. The burst was overall
very similar to the two others reported from the direction of this source in
2001. The unambiguous identification of 1E 1048.1-5937 as the burster here
confirms it was the origin of the 2001 bursts as well. The epoch of the burst
peak was very close to the arrival time of 1E 1048.1-5937's pulse peak. The
burst exhibited significant spectral evolution with the trend going from hard
to soft. During the 11 days following the burst, the AXP was observed further
with RXTE, XMM-Newton and Chandra. Pre- and post-burst observations revealed no
change in the total flux or spectrum of the quiescent emission. Comparing all
three bursts detected thus far from this source we find that this event was the
most fluent (>3.3x10^-8 erg/cm^2 in the 2-20 keV band), had the highest peak
flux (59+/-9x10^-10 erg/s/cm^2 in the 2-20 keV band), and the longest duration
(>699 s). The long duration of the burst differentiates it from Soft Gamma
Repeater (SGR) bursts which have typical durations of ~0.1 s. Bursts that occur
preferentially at pulse maximum, have fast-rises and long X-tails containing
the majority of the total burst energy have been seen uniquely from AXPs. The
marked differences between AXP and SGRs bursts may provide new clues to help
understand the physical differences between these objects.


title: The 6.7-GHz and 25-GHz methanol masers in OMC-1

abstract:
  The Australia Telescope Compact Array (ATCA) has been used to search for
methanol maser emission at 6.7 GHz towards OMC-1. Two features peaking at 7.2
km/s and -1.1 km/s have been detected. The former has at least two components
close in both velocity and position. It is located south-east of the Orion
Kleinmann-Low (Orion-KL) nebula in the region of outflow traced by the 25-GHz
methanol masers and the 95-GHz methanol emission. It is shown by modelling that
in contrast to the widespread opinion that simultaneous masing of methanol
transitions of different classes is impossible there are conditions for which
simultaneous masing of the class II transition at 6.7-GHz and some class I
transitions (e.g. the series at 25 GHz) is possible. A relevant example is
provided, in which the pumping occurs via the first torsionally excited state
and is driven by radiation of the dust intermixed with the gas in the cloud. In
this regime the dust temperature is significantly lower (T is about 60 K) than
in the case of bright 6.7-GHz masers (T>150 K). The narrow spectral feature at
-1.1 km/s has a brightness temperature greater than about 1400 K, which
suggests that it is probably a maser. It emanates from the Orion South region
and is probably associated with the approaching part of outflow seen in CO. The
25-GHz maser associated with OMC-1 was observed quasi-simultaneously with the
6.7-GHz observations. No 25-GHz emission associated with the -1.1 km/s 6.7 GHz
feature towards Orion South was detected.


title:
Chandra Observation of the Interaction between the Hot Plasma Nebula
  RCW89 and the Pulsar Jet of PSR B1509-58

abstract:
  We present a Chandra observation of the H II region RCW89. The nebula lies on
10' north from the central pulsar PSR B1509-58, and it has been suggested that
the nebula is irradiated by the pulsar jet. We performed a spectral analysis of
the seven brightest emitting regions aligned in a ``horse-shoe'' shape, and
found that the temperature of the knots increases along the ``horse-shoe'' in
the clockwise direction, while, in contrast, the ionization parameter
decreases. This strongly supports a picture of energy transfer via the
precessing pulsar jet. We examined the energy budget assuming that RCW89 is
powered by the pulsar jet, and confirmed that the pulsar rotational energy loss
is sufficient to drive the nebula. The rate of energy injection into RCW89 by
the jet was estimated from the synchrotron radiation flux. We obtained a
heating time-scale of 1400 yr, which is consistent with the pulsar
characteristic age of 1700 yr. To explain the temperature gradient, we discuss
the cooling process for plasma clouds in RCW89. We argue that the plasma clouds
can be cooled down by the adiabatic expansion within 70 yr, and form the
temperature gradient reflecting the sequential heating by the precessing pulsar
jet. We also determined the velocities of the individual plasma clouds by
spectral fitting. The plasma clouds in RCW89 are moving away at 240 ~ 860 km/s,
which constrains the inclination angle of the pulsar spin axis i > 50 degree
and the expanding velocity of the shell as v > 1100 km/s.


title:
The dusty MOCASSIN: fully self-consistent 3D photoionisation and dust
  radiative transfer models

abstract:
  We present the first 3D Monte Carlo (MC) photoionisation code to include a
fully self-consistent treatment of dust radiative transfer (RT) within a
photoionised region. This is the latest development (Version 2.0) of the
gas-only photoionisation code MOCASSIN (Ercolano et al., 2003a), and employs a
stochastic approach to the transport of radiation, allowing both the primary
and secondary components of the radiation field to be treated
self-consistently, whilst accounting for the scattering of radiation by dust
grains mixed with the gas, as well as the absorption and emission of radiation
by both the gas and the dust components. A set of rigorous benchmark tests have
been carried out for dust-only spherically symmetric geometries and 2D disk
configurations. MOCASSIN's results are found to be in agreement with those
obtained by well established dust-only RT codes that employ various approaches
to the solution of the RT problem. A model of the dust and of the photoionised
gas components of the planetary nebula (PN) NGC 3918 is also presented as a
means of testing the correct functioning of the RT procedures in a case where
both gas and dust opacities are present. The two components are coupled via the
heating of dust grains by the absorption of both UV continuum photons and
resonance line photons emitted by the gas. The MOCASSIN results show agreement
with those of a 1D dust and gas model of this nebula published previously,
showing the reliability of the new code, which can be applied to a variety of
astrophysical environments.


title: High-Energy Neutrino Astronomy with the Super-Kamiokande Detector

abstract:
  The Super-Kamiokande experiment has collected a large sample of high-energy
neutrino events. These are primarily atmospheric neutrinos, but a bright enough
astrophysical source could also be visible. The data have been examined for
possible point and bursting neutrino sources, as well as possible WIMP
annihilation signatures. No significant evidence for such sources have been
found, and the resulting flux limits have been calculated.


title: Brightness constraint for cooling models of young neutron stars

abstract:
  We study the systematics of neutron star cooling curves with three
representative masses from the most populated interval of the estimated mass
distribution for compact objects. The cooling simulations are made in the
framework of the nuclear medium cooling (NMC) scenario using different
combinations of possible nucleon-nucleon pairing gaps. Possible heating or
enhanced cooling mechanisms in the crust are not considered. We define a
constraint on the highest possible temperatures for a given age of young
neutron stars and show that this limits the freedom of modeling pairing gaps
and crust properties.


title: Running Non-Gaussianities in DBI Inflation

abstract:
  We study the non-Gaussianity in the simplest infrared (IR) model of the DBI
inflation. We show that the non-Gaussianity in such a model is compatible with
the current observational bound, and is within the sensitivity of future
experiments. We also discuss the scale dependence of the non-Gaussianity. In
the DBI inflation, such a feature can be used as a probe to the properties of
the background geometry of the extra dimensions or internal space.


title:
High resolution numerical modeling of the force-free pulsar
  magnetosphere

abstract:
  We consider the force-free magnetosphere of an aligned rotator. Its structure
is well described by a Grad-Shafranov equation for poloidal magnetic field, the
so-called "pulsar equation". We solve this equation by a multigrid method with
high numerical resolution. On the fine numerical grid current layer along the
last closed field line could be accurately incorporated into the numerical
procedure and all physical properties of the solution such as Goldreich-Julian
charge density, drift velocity, energy losses etc. could be accurately
calculated. Here we report results of the simulations. Among other interesting
properties, the solution is not unique, i.e. the position of the last closed
field line, and hence the pulsar energy losses, are not determined by the
global magnetosphere structure and depend on kinetic of electromagnetic
cascades. We discuss the properties of the solutions and their implications for
pulsars. A model for pulsar magnetosphere evolution is proposed. In the frame
of this model values of the pulsar braking index less than 3 have natural
explanation.


title: A Complete Sample of Megaparsec Size Double Radio Sources from SUMSS

abstract:
  We present a complete sample of megaparsec-size double radio sources compiled
from the Sydney University Molonglo Sky Survey (SUMSS). Almost complete
redshift information has been obtained for the sample. The sample has the
following defining criteria: Galactic latitude |b| > 12.5 deg, declination <
-50 deg and angular size > 5 arcmin. All the sources have projected linear size
larger than 0.7 Mpc (assuming H_o = 71 km/s/Mpc). The sample is chosen from a
region of the sky covering 2100 square degrees. In this paper, we present
843-MHz radio images of the extended radio morphologies made using the Molonglo
Observatory Synthesis Telescope (MOST), higher resolution radio observations of
any compact radio structures using the Australia Telescope Compact Array
(ATCA), and low resolution optical spectra of the host galaxies from the 2.3-m
Australian National University (ANU) telescope at Siding Spring Observatory.
The sample presented here is the first in the southern hemisphere and
significantly enhances the database of known giant radio sources. The giant
radio sources with linear size exceeding 0.7 Mpc have an abundance of (215
Mpc)^(-3) at the sensitivity of the survey. In the low redshift universe, the
survey may be suggesting the possibility that giant radio sources with relict
lobes are more numerous than giant sources in which beams from the centre
currently energize the lobes.


title:
Dark and stellar matter in strong lensing galaxies from a joint lensing
  and stellar dynamics

abstract:
  We present Subaru spectroscopy of the early-type lensing galaxies in the lens
systems HST14113+5211 (z=0.464) and B2045+265 (z=0.868), being aimed at
measuring the velocity dispersion of the lensing galaxies as an important
component to their mass distributions and internal dynamics. For HST14113+5211
we have obtained 174+/-20km/s (1-sigma) inside an aperture of 0.9", and for
B2045+265 we have obtained 213+/-23km/s inside an aperture of 1.2". To extract
the significance of these information on the mass distributions and stellar
dynamics of the lensing galaxies, we construct two alternative models for both
the mass and velocity distributions. It is found that the mass-to-light ratios
as derived from a joint lensing and stellar dynamics analysis are virtually
consistent with those obtained from the use of the Fundamental Plane. Also, for
HST14113+5211, we find that the total mass distribution is well reproduced by a
power-law density profile with an index of 2, thereby suggesting that a
singular isothermal model is a good fit to the lensing galaxy. In contrast, the
corresponding slope for B2045+265 is flatter than isothermal, suggesting that
additional contributions to lensing mass from surrounding structures (possibly
the group of galaxies) provide the observed angular separations of multiple
images.


title:
On the Feasibility of Characterizing Lens Stars in Future Space-Based
  Microlensing Surveys

abstract:
  If a light-emitting star is responsible for a gravitational microlensing
event, the lens can be characterized by analyzing the blended light from the
lens. In this paper, we investigate the feasibility of characterizing lenses by
using this method in future space-based lensing surveys. To judge the
feasibility of the method, we estimate the portions of events whose blended
flux F_b can be firmly noticed and most of it can be attributed to the lens by
carrying out detailed simulations of Galactic bulge lensing events considering
various blending sources, including the lens, background stars, and binary
companions to the lens and source. From this, it is estimated that among the
events to be detected from a survey using a 1 m space telescope, ~27% will have
blending fractions of F_b/F\geq 10% and the blended flux of half of these
events will be contaminated more than (F_b-F_L)/F_b=20% by the flux from
blending sources other than the lens, implying the contamination of the blended
flux will be substantial. Although the contamination by the background stars
can be reduced by using an instrument with a higher resolution, it is estimated
that the blended flux of more than 1/3 of events will still be contaminated
(mostly by binary companions) even using a telescope equivalent to the {\it
Hubble Space Telescope}, assuming 50% binary frequency. We, therefore, conclude
that caution and consideration of the blending contaminants are required in
applying the lens-light analysis method.


title:
Effect of Binary Source Companions on the Microlensing Optical Depth
  Determination toward the Galactic Bulge Field

abstract:
  Currently, gravitational microlensing survey experiments toward the Galactic
bulge field utilize two different methods of minimizing blending effect for the
accurate determination of the optical depth \tau. One is measuring \tau based
on clump giant (CG) source stars and the other is using `Difference Image
Analysis (DIA)' photometry to measure the unblended source flux variation.
Despite the expectation that the two estimates should be the same assuming that
blending is properly considered, the estimates based on CG stars systematically
fall below the DIA results based on all events with source stars down to the
detection limit. Prompted by the gap, we investigate the previously
unconsidered effect of companion-associated events on $\tau$ determination.
Although the image of a companion is blended with that of its primary star and
thus not resolved, the event associated with the companion can be detected if
the companion flux is highly magnified. Therefore, companions work effectively
as source stars to microlensing and thus neglect of them in the source star
count could result in wrong \tau estimation. By carrying out simulations based
on the assumption that companions follow the same luminosity function of
primary stars, we estimate that the contribution of the companion-associated
events to the total event rate is ~5f_{bi}% for current surveys and can reach
up to ~6f_{bi}% for future surveys monitoring fainter stars, where f_{bi} is
the binary frequency. Therefore, we conclude that the companion-associated
events comprise a non-negligible fraction of all events. However, their
contribution to the optical depth is not large enough to explain the systematic
difference between the optical depth estimates based on the two different
methods.


title:
Topology Analysis of the Sloan Digital Sky Survey: I. Scale and
  Luminosity Dependences

abstract:
  We measure the topology of volume-limited galaxy samples selected from a
parent sample of 314,050 galaxies in the Sloan Digital Sky Survey(SDSS), which
is now complete enough to describe the fully three-dimensional topology and its
dependence on galaxy properties. We compare the observed genus statistic
G\nu_f) to predictions for a Gaussian random field and to the genus measured
for mock surveys constructed from new large-volume simulations of the LambdaCDM
cosmology. In this analysis we carefully examine the dependence of the observed
genus statistic on the Gaussian smoothing scale R_G from 3.5 to 11 h^-1Mpc and
on the luminosity of galaxies over the range -22.50<M_r<-18.5. The void
multiplicity A_V is less than unity at all smoothing scales. Because A_V cannot
become less than 1 through gravitational evolution, this result provides strong
evidence for biased galaxy formation in low density environments. We also find
clear evidence of luminosity bias of topology within the volume-limited
sub-samples. The shift parameter Delta nu indicates that the genus of brighter
galaxies shows a negative shift toward a ``meatball'' (i.e. cluster-dominated)
topology, while faint galaxies show a positive shift toward a ``bubble'' (i.e.
void-dominated) topology. The transition from negative to positive shift occurs
approximately at the characteristic absolute magnitude M_{r*}=-20.4. Even in
this analysis of the largest galaxy sample to date, we detect the influence of
individual large-scale structures, as the shift parameter Delta nu and cluster
multiplicity A_C reflect (at ~3 sigma) the presence of the Sloan Great Wall and
a X-shaped structure which runs for several hundred Mpc across the survey
volume.


title:
Morphological Classification of Galaxies using Photometric Parameters:
  the Concentration index versus the Coarseness parameter

abstract:
  We devise improved photometric parameters for the morphological
classification of galaxies using a bright sample from the First Data Release of
the Sloan Digital Sky Survey. In addition to using an elliptical aperture
concentration index for classification, we introduce a new texture parameter,
coarseness, which quantifies deviations from smooth galaxy isophotes. The
elliptical aperture concentration index produces morphological classifications
that are in appreciably better agreement with visual classifications than those
based on circular apertures. With the addition of the coarseness parameter,the
success rate of classifying galaxies into early and late types increases to
\~88% with respect to the reference visual classification. A reasonably high
success rate ~68% is also attained in classifying galaxies into three types,
early-type galaxies (E+S0), early- (Sa+Sb) and late- (Sc+Sdm+Im) type spiral
galaxies.


title: Medium Effects in Cooling of Neutron Stars and $3P_2$ Neutron Gap

abstract:
  We study the dependence of the cooling of isolated neutron stars on the
magnitude of the $3P_2$ neutron gap. It is demonstrated that our ``nuclear
medium cooling'' scenario is in favor of a suppressed value of the $3P_2$
neutron gap.


title: Molecular Hydrogen Excitation around Active Galactic Nuclei

abstract:
  We report R~3000 VLT ISAAC K-band spectroscopy of the nuclei (i.e. central
100-300pc) of 9 galaxies hosting an active galactic nucleus. For 5 of these we
also present spectra of the circumnuclear region out to 1kpc. We have measured
a number of H_2 lines in the v=1-0, 2-1, and 3-2 vibrational transitions, as
well as the Br_gamma and HeI recombination lines, and the NaI stellar
absorption. Although only 3 of the galaxies are classified as Seyfert 1s in the
literature, broad Br_gamma (FWHM 1000kms) is seen in 7 of the objects. The
v=1-0 emission appears thermalised at T~1000K. However, the v=2-1 and 3-2
emission show evidence of being radiatively excited by far-UV photons. The PDR
models that fit the data best are, as for the ultraluminous infrared galaxies
in Davies et al. (2003), those for which the H_2 emission arises in dense
clouds illuminated by intense FUV radiation. The NaI stellar absorption is
clearly seen in 6 of the nuclear spectra, indicating the presence of a
significant population of late type stars. It is possible that these stars are
a result of the same episode of star formation that gave rise to the stars
heating the PDRs. It seems unlikely that the AGN is the dominant source of
excitation for the near infrared H_2 emission: in two nuclei H_2 was not
detected at all, and in general we find no evidence of suppression of the
2-1S(3) line, which may occur in X-ray irradiated gas. Our data do not reveal
any significant difference between the nuclear and circumnuclear line ratios,
suggesting that the physical conditions of the dominant excitation mechanism
are similar both near the AGN and in the larger scale environment around it,
and that star formation is an important process even in the central 100pc
acround AGN.


title: Time-Delayed transfer functions simulations for LMXBs

abstract:
  Recent works (Steeghs & Casares 2002, Casares et al. 2003, Hynes et al. 2003)
have demonstrated that Bowen flourescence is a very efficient tracer of the
companion star in LMXBs. We present a numerical code to simulate time-delayed
transfer functions in LMXBs, specific to the case of reprocessing in emission
lines. The code is also able to obtain geometrical and binary parameters by
fitting observed (X-ray + optical) light curves using simulated annealing
methods. In this work we present the geometrical model for the companion star
and the analytical model for the disc and show synthetic time-delay transfer
functions for different orbital phases and system parameters.


title:
First evidence for a spatially resolved disk structure around the Herbig
  Ae star R CrA

abstract:
  We present mid-infrared interferometric observations of the Herbig Ae star R
CrA obtained with MIDI at the VLTI using several projected baselines in the
UT2-UT3 configuration. The observations show resolved circumstellar emission in
the wavelength range 8-13 micron on a ~6 AU scale with a non-symmetric
intensity distribution, providing support for an inclined disk geometry.
Visibilities are best fitted using a uniform ring model with outer radius in
the range 6-10 AU, in the wavelength range 8-13 micron. The inclination of the
ring with respect to the plane of the sky is found to be ~45 deg., consistent
with the 40 deg. suggested from near-infrared imaging polarimetry (Clark et al.
2000, MNRAS, 319, 337).


title: Sungrazing comets as source of pickup ions at Earth orbit and Ulysses

abstract:
  Most of the sungrazing comets observed by LASCO at SOHO belong to the Kreutz
group of comets and follow trajectories that are tightly clumped in space.
Statistical analysis of 9 years of SOHO observations suggests that the true
apparition rate of these comets is as high as one every other day. Practically
all these comets break up before perihelion passage. Their material is
dissociated and ionized, and subsequently transported away from the Sun as
pickup ions in the solar wind. Their mean mass flux is about $3.1 10^4 g/s.
Since the breakup occurs between 40 and 4 solar radii and the ionization is
almost immediate, the expected location of these ions in the phase space is
close to the location of the inner source of pickup ions. Assuming radial
propagation, the cometary pickups should be observable at Earth between August
and January, with peak probability at the end of September. At Ulysses, they
should be observable approximately between -25 and 40 degrees ecliptic latitude
during the fast latitude scans, the first of which occurred in 1995 and the
second in 2001. The population of cometary pickup ions should be augmented by
about 40% by solar wind protons as a result of charge exchange with the
cometary neutral hydrogen and oxygen atoms and subsequent reionization of the
newly-created Energetic Neutral Atoms, streaming with respect to the solar
wind. In total, the average flux of the pickup ions related to the sungrazing
comets at 1 AU should be about 1.6 10^5 g/s/sr within the detection area (and
null outside it). This value is comparable to the flux of the inner
source-pickup ions.


title: Multiband Echo Tomography of Sco X-1

abstract:
  We present preliminary results of a simultaneous X-ray/optical campaign of
the prototypical LMXB Sco X-1 at 1-10 Hz time resolution. Lightcurves of the
high excitation Bowen/HeII emission lines and a red continuum at lambda ~ 6000
Ang were obtained through narrow interference filters with ULTRACAM, and these
were cross-correlated with simultaneous RXTE X-ray lightcurves. We find
evidence for correlated variability, in particular when Sco X-1 enters the
Flaring Branch. The Bowen/HeII lightcurves lag the X-ray lightcurves with a
light travel time which is consistent with reprocessing in the companion star
while the continuum lightcurves have shorter delays consistent with
reprocessing in the accretion disc


title: Crossing of the w=-1 Barrier by D3-brane Dark Energy Model

abstract:
  We explore a possibility for the Universe to cross the w=-1 cosmological
constant barrier for the dark energy state parameter. We consider the Universe
as a slowly decaying D3-brane. The D3-brane dynamics is approximately described
by a nonlocal string tachyon interaction and a back reaction of gravity is
incorporated in the closed string tachyon dynamics. In a local effective
approximation this model contains one phantom component and one usual field
with a simple polynomial interaction. To understand cosmological properties of
this system we study toy models with the same scalar fields but with modified
interactions. These modifications admit polynomial superpotentials. We find
restrictions on these interactions under which it is possible to reach w=-1
from below at large time. Explicit solutions with the dark energy state
parameter crossing/non-crossing the barrier w=-1 at large time are presented.


title:
Hard X-ray and Gamma-ray Emission Induced by Ultra-High Energy Protons
  in Cluster Accretion Shocks and their Detectability

abstract:
  Protons can be plausibly accelerated to $\sim 10^{18}$-$10^{19}$ eV in strong
accretion shocks surrounding massive clusters of galaxies. Such protons
efficiently produce very high energy pairs through interactions with the CMB,
which then radiate synchrotron and inverse Compton emission with hard spectra,
peaking respectively in hard X-rays and TeV gamma-rays. We discuss the
prospects for detecting this emission from nearby clusters with current and
future facilities such as HESS and NeXT, which should provide a clear signature
of ultra-high energy proton acceleration and an important probe of magnetic
fields in the outermost regions of clusters.


title: Interstellar extinction towards open clusters and galactic structure

abstract:
  We study the distribution of interstellar matter near the galactic plane on
the basis of open star clusters and reviewed the correlation of extinction with
different physical parameters of the clusters to understand the galactic
structure. It is seen from the extinction towards open clusters that about 90%
of the absorbing material lie within -5<b<5 deg of the galactic plane. The mean
thickness of the absorbing material, which is determined in terms of half-width
value \beta, is estimated to be about 125+/-21 pc. We show that the
interstellar absorption follows a sinusoidal variation with galactic longitude
and maximum and minimum absorptions occur at l ~ 48+/-4 deg and l ~ 228+/-4 deg
respectively. It is found that the galactic plane defined by the reddening
material is inclined by an angle of 0.6+/-0.4 deg to the formal galactic plane
and inclination is maximum at l ~ 54+/-6 deg. The reddening analysis has been
used to constrain the Solar offset which is found to be about 22.8+/-3.3 pc
above the reddening plane. We obtained a scale height of 53+/-5 pc for the
distribution of open clusters while it is 186+/-25 pc for the distribution of
reddening material from the reddening plane.


title:
Molecular Gas in NUclei of GAlaxies (NUGA): IV. Gravitational Torques
  and AGN Feeding

abstract:
  We discuss the efficiency of stellar gravity torques as a mechanism to
account for the feeding of the central engines of four low luminosity AGN:
NGC4321, NGC4826, NGC4579 and NGC6951. These galaxies have been observed as
part of the NUGA CO project, aimed at the study of AGN fueling mechanisms. Our
calculations allow us to derive the characteristic time-scales for gas flows
and discuss whether torques from the stellar potentials are efficient enough to
drain the gas angular momentum in the inner 1 kpc of these galaxies. Results
indicate paradoxically that feeding should be thwarted close to the AGN: in the
four cases analyzed, gravity torques are mostly positive inside r~200pc,
resulting in no inflow on these scales. As a possible solution for the paradox,
we speculate that the agent responsible for driving inflow to still smaller
radii is transient and thus presently absent in the stellar potential.
Alternatively, the gravity torque barrier associated with the ILR of the bars
in these galaxies could be overcome by other mechanisms that become competitive
in due time against gravity torques. We find that viscosity can counteract
moderate--to--low gravity torques on the gas if it acts on a nuclear ring of
high gas surface density contrast and a few 100pc size. We propose an
evolutionary scenario in which gravity torques and viscosity act in concert to
produce recurrent episodes of activity during the typical lifetime of any
galaxy. In this scenario the recurrence of activity in galaxies is indirectly
related to that of the bar instabilities.


title:
Feeding the monster... the nucleus of NGC1097 at sub-arcsec scale in the
  IR with the VLT

abstract:
  Near-infrared images of the prototype LINER / Seyfert 1 galaxy NGC 1097
observed with the Very Large Telescope (VLT) using adaptive optics disclose
with unprecedented detail a complex central network of filamentary structure
spiralling down to the center of the galaxy. The structure, consisting of
several spiral arms, some almost completing a revolution about the center, is
most prominent within the radius of about 300 pc. Some filaments can be traced
further out, where they seem to connect with the nuclear star-forming ring at
0.7 kpc radius. Straight principal shocks running along the primary large-scale
bar of NGC 1097, seen in the optical images as prominent dust lanes, curve into
this ring, but radio polarization vectors cross the nuclear ring under a rather
large angle. Here we attempt to explain this morphology in terms of
three-dimensional gas flow in a barred galaxy. In our scenario, parts of the
principal shock, which propagate in the off-plane gas, can cross the nuclear
star-forming ring, and excite waves inward from it. If the dispersion relation
of the excited waves allows for their propagation, they will naturally take the
shape of the observed central spiral. The nuclear region of NGC 1097 remains
unresolved at sub-arcsec scales in the near-IR, with an upper size limit of <10
pc FWHM. Thus, any putative central dusty torus or gaseosus disk envisaged by
the AGN unified schemes has to be smaller than 10 pc in diameter at near-IR
wavelengths. The extinction in the region between the nuclear star-forming ring
and the nucleus increases very moderately, reaching A_v~1 at the immediate
surrounding of the nucleus. Thus, if the nuclear filaments are tracing cold
dust, they contribute to a very low extinction in the line of sight and are
likely to be distributed in a rather thin disk.


title:
Modeling optical and UV polarization of AGNs I. Imprints of individual
  scattering regions

abstract:
  [abridged] We investigate the effects of various AGN scattering region
geometries on the polarized flux. We introduce a new, publicly available Monte
Carlo radiative transfer code, Stokes, which models polarization induced by
scattering off free electrons and dust grains. We find that the shape of the
funnel of the dusty torus has a significant impact on the polarization
efficiency. A compact torus with a steep inner surface scatters more light
toward type-2 viewing angles than a large torus of the same half-opening angle,
theta0. For theta0 < 53 deg, the scattered light is polarized perpendicularly
to the symmetry axis, whilst for theta0 > 60 deg it is polarized parallel to
the symmetry axis. In between these intervals the orientation of the
polarization depends on the viewing angle. The degree of polarization ranges
between 0% and 20% and is wavelength-independent for a large range of theta0.
Observed wavelength-independent optical and near-UV polarization thus does not
necessarily imply electron scattering. For polar dust, scattering spectra are
reddened for type-1 viewing angles, and made bluer for type-2 viewing angles.
Polar electron-scattering cones are very efficient polarizers at type-2 viewing
angles, whilst the polarized flux of the torus is weak. We predict that the net
polarization of Seyfert-2 galaxies decreases with luminosity, and conclude that
the degree of polarization should be correlated with the relative strength of
the thermal IR flux. We find that a flattened, equatorial, electron-scattering
disk, of relatively low optical depth, reproduces type-1 polarization. This is
insensitive to the exact geometry, but the observed polarization requires a
limited range of optical depth.


title:
Supermassive Black Holes in Elliptical Galaxies: Switching from Very
  Bright to Very Dim

abstract:
  Relativistic outflows (mainly observed in the radio) are a characteristic
feature of both Galactic stellar mass black holes and supermassive black holes
(SMBHs). Simultaneous radio and X-ray observations of Galactic sources have
shown that the outflow is strong at low accretion rates, but it weakens
dramatically or disappears completely at high accretion rates, manifesting
structural changes in the accretion flow. It is reasonable to assume that SMBHs
follow the same trend. For low luminosity SMBHs in nearby elliptical galaxies
and clusters, recent observations strongly suggest that the outflows play the
central role in keeping the gas hot (mechanical feedback). If the outflow is
quenched in SMBHs at high accretion rates similarly to the behavior of galactic
sources, then the straightforward consequence is a relatively weak feedback of
rapidly accreting SMBHs. We argue that elliptical galaxies and their central
engines should then evolve through two stages. Early on, the central SMBH
rapidly grows by accreting cooling gas at a near-Eddington rate with high
radiative efficiency but with weak feedback on the infalling gas. This stage
terminates when the black hole has grown to a sufficiently large mass that its
feedback (radiative and/or mechanical), despite the low gas heating efficiency,
is able to suppress gas cooling. After that the system switches to a stable
state corresponding to passively evolving ellipticals, when the accretion rate
and radiative efficiency are very low, but the gas heating efficiency is high
and energy input from the relativistic outflow keeps the gas hot.


title: A combined optical/infrared spectral diagnostic analysis of the HH1 jet

abstract:
  Complete flux-calibrated spectra covering the spectral range from 6000 A to
2.5 um have been obtained along the HH1 jet and analysed in order to explore
the potential of a combined optical/near-IR diagnostic applied to jets from
young stellar objects. Important physical parameters have been derived along
the jet using various diagnostic line ratios. This multi-line analysis shows,
in each spatially unresolved knot, the presence of zones at different
excitation conditions, as expected from the cooling layers behind a shock
front. In particular, a density stratification in the jet is evident from
ratios of various lines of different critical density. In particular, [FeII]
lines originate in a cooling layer located at larger distances from the shock
front than that generating the optical lines, where the compression is higher
and the temperature is declining. The derived parameters were used to measure
the mass flux along the jet, adopting different procedures, the advantages and
limitations of which are discussed. dM/dt is high in the initial part of the
flow but decreases by about an order of magnitude further out. Conversely, the
mass flux associated with the warm molecular material is low and does not show
appreciable variations along the jet. We suggest that part of the mass flux in
the external regions is not revealed in optical and IR lines because it is
associated with a colder atomic component, which may be traced by the far-IR [O
I]63 um line.
  Finally, we find that the gas-phase abundance of refractory species is lower
than the solar value suggesting that a significant fraction of dust grains may
still be present in the jet beam.


title: Dynamics of perfect fluid Unified Dark Energy models

abstract:
  In this paper we show that a \emph{one-to-one} correspondence exists between
any dark energy model and an equivalent (from a cosmological point of view, in
the absence of perturbations) quartessence model in which dark matter and dark
energy are described by a single perfect fluid. We further show that if the
density fluctuations are small, the evolution of the sound speed squared,
$c_s^2$, is fully coupled to the evolution of the scale factor and that the
transition from the dark matter to the dark energy dominated epoch is faster
(slower) than in a standard $\Lambda$CDM model if $c_s^2 > 0$ ($c_s^2 < 0$). In
particular, we show that the mapping of the simplest quintessence scenario with
constant $w_Q \equiv p_Q/ \rho_Q$ into a unified dark energy model requires
$c_s^2 < 0$ at the present time (if $w_Q > -1$) contrasting to the Chaplygin
gas scenario where one has $c_s^2 > 0$. However, we show that non-linear
effects severely complicate the analysis, in particular rendering linear
results invalid even on large cosmological scales. Although a detailed analysis
of non-linear effects requires solving the full Einstein field equations, some
general properties can be understood in simple terms. In particular, we find
that in the context of Chaplygin gas models the transition from the dark matter
to the dark energy dominated era may be anticipated with respect to linear
expectations leading to a background evolution similar to that of standard
$\Lambda$CDM models. On the other hand, in models with $c_s^2 > 0$ the expected
transition from the decelerating to the accelerating phase may never happen.


title:
Mean Angular Diameters and Angular Diameter Amplitudes of Bright
  Cepheids

abstract:
  We predict mean angular diameters and amplitudes of angular diameter
variations for all monoperiodic Pop.I Cepheids brighter than <V> = 8.0mag. The
catalog is intended to aid selecting most promising Cepheid targets for future
interferometric observations.


title: Asteroseismic diagrams for solar-type stars

abstract:
  We explore the feasibility of applying the Christensen-Dalsgaard diagram to
real asteroseismic data and provide quantitative measures of the uncertainty
associated with the results. We also propose a new kind of seismic diagram,
based on the determination of the locations of sharp acoustic features inside a
star. We show that by combining the information about the position of the base
of the convective envelope or the HeII ionisation zone with a measure of the
average large separation, it is possible to constrain the unknown chemical
composition or the various parameters characterising the physical processes in
the stellar interior. We demonstrate the application of this technique to the
analysis of mock data for a CoRoT target star.


title:
The gravitational-wave spectrum of a non-axisymmetric torus around a
  rapidly spinning black hole

abstract:
  The gravitational-wave spectrum emitted by a non-axisymmetric torus rotating
at an angular velocity $\Omega_T$, is derived in terms of a structure function
representing a combination of sausage-tilt modes in the torus in the limit of
an incompressible fluid. The analysis of the gravitational-wave spectrum is
then applied to a model proposed recently, in which a highly magnetized torus
interacts with a stellar mass, Kerr black hole via poloidal field lines that
connect the torus and the horizon. The deformation of the torus results from
global magnetic instabilities when the magnetic field strength inside the torus
exceeds a few times $10^{15}$ Gauss. The dynamics of the system is illustrated
using a non-MHD toy model. It is found that, quite generally, most of the
gravitational-wave energy emitted is in the frequency range of sensitivity of
LIGO and Virgo.


title:
Planetary Detection Efficiency of the Magnification 3000 Microlensing
  Event OGLE-2004-BLG-343

abstract:
  OGLE-2004-BLG-343 was a microlensing event with peak magnification
A_{max}=3000+/-1100, by far the highest-magnification event ever analyzed and
hence potentially extremely sensitive to planets orbiting the lens star. Due to
human error, intensive monitoring did not begin until 43 minutes after peak, at
which point the magnification had fallen to A~1200, still by far the highest
ever observed. As the light curve does not show significant deviations due to a
planet, we place upper limits on the presence of such planets by extending the
method of Yoo et al. (2004b), which combines light-curve analysis with priors
from a Galactic model of the source and lens populations, to take account of
finite-source effects. This is the first event so analyzed for which
finite-source effects are important, and hence we develop two new techniques
for evaluating these effects. Somewhat surprisingly, we find that
OGLE-2004-BLG-343 is no more sensitive to planets than two previously analyzed
events with A_{max}~100, despite the fact that it was observed at ~12 times
higher magnification. However, we show that had the event been observed over
its peak, it would have been sensitive to almost all Neptune-mass planets over
a factor of 5 of projected separation and even would have had some sensitivity
to Earth-mass planets. This shows that some microlensing events being detected
in current experiments are sensitive to very low-mass planets. We also give
suggestions on how extremely high-magnification events can be more promptly
monitored in the future.


title: Dynamical virial masses of Lyman-break galaxy haloes at z=3

abstract:
  We improve on our earlier dynamical estimate of the virial masses of the
haloes of Lyman-break galaxies (LBGs) at redshift z=3 by accounting for the
effects of seeing, slit width, and observational uncertainties. From an
analysis of the small number of available rotation curves for LBGs we determine
a relation Vc7=(1.9+/-0.2)sigma between circular velocity at a radius of 7kpc,
and central line velocity width. We use this relation to transform the measured
velocity widths of 32 LBGs to the distribution of circular velocities, for the
population of LBGs brighter than R=25.5. We compare this distribution against
the predicted distribution for the 'massive-halo' model in which LBGs pinpoint
all of the highest mass dark matter haloes at that epoch. The observed LBG
circular velocities are smaller than the predicted circular velocities by a
factor >1.4+/-0.15. This is a lower limit as we have ignored any increase of
circular velocity caused by baryonic dissipation. The massive-halo model
predicts a median halo virial mass of 10^12.3 Msol, and a small spread of
circular velocities. Our median estimated dynamical mass is <10^(11.6+/-0.3)
Msol, which is significantly smaller; furthermore, the spread of our circular
velocities is much larger than the massive-halo prediction. These results are
consistent with a picture which leaves some of the most-massive haloes
available for occupation by other populations which do not meet the LBG
selection criteria. The median halo mass recently estimated by Adelberger et
al. from the measured clustering of LBGs is 10^(11.86+/-0.3) Msol. Our
dynamical analysis appears to favour lower masses and to be more in line with
the median mass predicted by the collisional starburst model of Somerville et
al., of 10^11.3 Msol. [abridged]


title: The Spatial Distribution of Metals in the Intergalactic Medium

abstract:
  We investigate the impact of environment on the metallicity of the diffuse
intergalactic medium. We use pixel correlation techniques to search for weak
CIV and OVI absorption in the spectrum of quasar Q1422+231 in regions of the
spectrum close to and far from galaxies at z ~ 3. This is achieved both by
using the positions of observed Lyman break galaxies and by using strong CIV
absorption as a proxy for the presence of galaxies near the line of sight. We
find that the metal line absorption is a strong function of not only the HI
optical depth (and thus gas density) but also proximity to highly enriched
regions (and so proximity to galaxies). The parameter ``proximity to galaxies''
can account for some, but not all, of the scatter in the strength of CIV
absorption for fixed HI. Finally, we find that even if we limit our analysis to
the two thirds of the pixels that are at least 600 km/s from any CIV line that
is strong enough to detect unambiguously (tau_CIV > 0.1), our statistical
analysis reveals only slightly less CIV for fixed HI than when we analyze the
whole spectrum. We conclude that while the metallicity is enhanced in regions
close to (Lyman-break) galaxies, the enrichment is likely to be much more
widespread than their immediate surroundings.


title:
The Hamburg/SAO survey for emission-line galaxies. VI. The sixth list of
  126 galaxies

abstract:
  We present the sixth list with results of the Hamburg/SAO Survey for
Emission-Line Galaxies. The final list resulted from follow-up spectroscopy
conducted with the 4.5m MMT telescope in 1996, and with 2.2m CAHA and 6m SAO
telescopes in 2000 to 2003. The data of this snap-shot spectroscopy survey
confirmed 134 emission-line objects out of 182 observed candidates and allowed
their quantitative spectral classification and redshift determination. We
classify 73 emission-line objects as definite or probable blue compact or HII
galaxies (BCG), 8 as QSOs, 4 as Seyfert 1 and 2 galaxies. 30 low-excitation
objects were classified as definite or probable starburst nuclei (SBN), 3 as
dwarf amorphous nuclei starburst galaxies (DANS) and 2 as LINERs. Due to the
low signal-to-noise ratio we could not classify 14 ELGs (NON). For another 9
galaxies we did not detect any significant emission lines. For 98 emission-line
galaxies, the redshifts and/or line intensities are determined for the first
time. For the remaining 28 previously-known ELGs we give either improved data
the line intensities or some independent measurements. The detection rate of
ELGs is ~70%. This paper completes the classification of strong-lined ELGs
found in the zone of the Hamburg/SAO survey. Together with previously known
BCG/HII galaxies in this zone, this sample of ~500 objects is the largest to
date in a well bound region.


title: Absolute calibration of imaging atmospheric Cherenkov telescopes

abstract:
  A calibrated laser pulse propagating through the atmosphere produces a flash
of Rayleigh scattered light with an intensity that can be calculated very
accurately when atmospheric conditions are good. This is used in a technique
developed for the absolute calibration of ultra high energy cosmic ray
fluorescence telescopes, and it can also be applied to imaging atmospheric
Cherenkov telescopes (IACTs). In this paper we present the absolute calibration
system being constructed and tested for the VERITAS project.


title:
Chemical Composition of Two H II Regions in NGC 6822 Based on VLT
  Spectroscopy

abstract:
  We present long slit spectrophotometry of regions V and X of the local group
irregular galaxy NGC 6822. The data consist of VLT FORS observations in the
3450 to 7500 A range. We have obtained electron temperatures and densities
using different line intensity ratios. We have derived the He, C, and O
abundances relative to H based on recombination lines, the abundance ratios
among these elements are almost independent of the temperature structure of the
nebulae. We have also determined the N, O, Ne, S, Cl, and Ar abundances based
on collisionally excited lines, the ratios of these abundances relative to that
of H depend strongly on the temperature structure of the nebulae. The chemical
composition of NGC 6822 V is compared with those of the Sun, the Orion nebula,
NGC 346 in the SMC, and 30 Doradus in the LMC. The O/H value derived from
recombination lines is in good agreement with the value derived by Venn et al.
(2001) from two A type supergiants in NGC 6822.


title: Cosmological nonlinear hydrodynamics with post-Newtonian corrections

abstract:
  The post-Newtonian (PN) approximation, based on the assumptions of weak
gravitational fields and slow motions, provides a way to estimate general
relativistic effects in the fully nonlinear evolution stage of the large-scale
cosmic structures. We extend Chandrasekhar's first order PN (1PN) hydrodynamics
based on the Minkowski background to the Robertson-Walker background. We assume
the presence of Friedmann's cosmological spacetime as a background. In the
background we include the three-space curvature, the cosmological constant and
general pressure. In the Newtonian order and 1PN order we include general
pressure, stress, and flux. The Newtonian hydrodynamic equations appear
naturally in the 0PN order. The spatial gauge degree of freedom is fixed in a
unique manner and the basic equations are arranged without taking the temporal
gauge condition. In this way we can conveniently try alternative temporal gauge
conditions. We investigate a number of temporal gauge conditions under which
all the remaining variables are equivalently gauge-invariant. Our aim is to
present the fully nonlinear 1PN equations in a form suitable for implementation
in conventional Newtonian hydrodynamic simulations with minimal extensions. The
1PN terms can be considered as relativistic corrections added to the well known
Newtonian equations. The proper arrangement of the variables and equations in
combination with suitable gauge conditions would allow the possible future 1PN
cosmological simulations to become more tractable. Our equations and gauges are
arranged for that purpose. We suggest ways of controlling the numerical
accuracy. The typical 1PN order terms are about $10^{-6} \sim 10^{-4}$ times
smaller than the Newtonian terms.


title: Orbital and spin variability of the Intermediate Polar BG CMi

abstract:
  Results of a CCD study of the variability of the cataclysmic variable BG CMi
obtained at the Korean 1.8m telescope in 2002-2005 are presented. The
"multi-comparison star" method had been applied for better accuracy estimates.
The linear ephemeris based on 19 mean maxima for 2002--2005 is HJD
2453105.31448(6)+0.01057257716(198)(E-764707). The period differs from that
predicted by the quadratic ephemeris by Pych et al. (1996) leading to a
possible cycle miscount. The statistically optimal ephemeris is a fourth-order
polynomial, as a quadratic or even a cubic ephemeris leads to unaceptably large
residuals: Min.HJD=$ 2445020.28095(28)+0.0105729609(57)E
-1.58(32)\cdot10^{-13}E^2-5.81(64)\cdot10^{-19}E^3+4.92(41)\cdot10^{-25}E^4.$
Thus the rate of the spin-up of the white dwarf is decreasing. An alternative
explanation is that the spin-up has been stopped during recent years. The
deviations between the amplutudes of the spin variability in V and R, as well
as between phases are not statistically significant. However, the orbital light
curves exhibit distinct difference; the corresponding color index shows a
nearly sinusoidal shape with a maximum at orbital phase $\sim0.2.$ The
variations of the amplitude of spin waves shows a short maximum at the phase of
the orbital dip. The corrected ephemeris for orbital minima is
Min.HJD=$2448368.7225(12)+0\fd13474841(6)\cdot(E-24849)$ with a narrow dip
occuring 0.07P later. The rate of the spin period variation seems to be
changed, justifying the necessity of regular observations of intermediate
polars.


title:
A photometric study of V1193 Ori: detection of orbital and negative
  superhump periods

abstract:
  We present the results obtained from unfiltered photometric CCD observations
of V1193 Ori made during 24 nights between November 2002 and January 2003. We
found periods of 0.1430 d, 0.1362 d and possibly 2.98 d in the data. The 0.1430
d period is consistent with the 1d^{-1} alias of the proposed orbital period of
P_{orb}=0.165 d (Ringwald et al., 1994, Papadaki et al., 2004). Thus and using
the known relation between the orbital and superhump periods, we interpret
these periods as the orbital period of 0.1430 d, the negative superhump period
of 0.1362 d and the precession period of 2.98 d. V1193 Ori can then be
classified as a permanent superhump system.


title: A dual emission mechanism in Sgr A*/L' ?

abstract:
  We have collected in 2004 adaptive optics corrected L' images of the Galactic
Center region with NAOS-CONICA at VLT. A strong variability was observed as
well as a correlation between the photocenter positions and fluxes of the
L'-band counterpart of Sgr A*. It is interpreted as the combined emission of a
point-like flaring source at the position of Sgr A*/IR itself and an extended
dust structure, 75 mas south west of Sgr A*/IR, which we name Sgr A*-f. We
examine the different possible mechanisms to explain this dual Sgr A* L'
emission and conclude it is likely a flaring emission associated to energetic
events in the close environment of the black hole plus a quiescent emission
resulting from the collision of Sgr A*-f by a jet from Sgr A*.


title:
Are Passive Spiral Galaxies truly 'passive' and 'spiral'?: a
  Near-Infrared perspective

abstract:
  Passive spiral galaxies - unusual galaxies with spiral morphologies but
without any sign of on-going star formation - have recently been shown to exist
preferentially in cluster infalling regions. This discovery directly connects
passive spiral galaxies to cluster galaxy evolution studies, such as the
Butcher-Oemler effect or the morphology-density relation. Thus, detailed study
of passive spiral galaxies could potentially yield new insight on the
underlying physical mechanisms governing cluster galaxy evolution.
  However, in previous work, passive spiral galaxies were selected from
low-resolution optical images with $\sim$1.5 arcsec seeing. Passive spirals
could therefore be mis-identified as S0 galaxies, or as dusty-starburst
galaxies which are not passive at all. To address this issue we performed deep,
high-resolution, near-infrared imaging of 32 passive spiral galaxies with
UKIRT.


title:
Numerical Relativistic Hydrodynamics Based on the Total Variation
  Diminishing Scheme

abstract:
  This paper describes a multidimensional hydrodynamic code which can be used
for studies of relativistic astrophysical flows. The code solves the special
relativistic hydrodynamic equations as a hyperbolic system of conservation laws
based on the total variation diminishing (TVD) scheme. It uses a new set of
conserved quantities and employs an analytic formula for transformation from
the conserved quantities in the reference frame to the physical quantities in
the local rest frame. Several standard tests, including relativistic shock
tubes, a relativistic wall shock, and a relativistic blast wave, are presented
to demonstrate that the code captures discontinuities correctly and sharply in
ultrarelativistic regimes. The robustness and flexibility of the code are
demonstrated through test simulations of the relativistic Hawley-Zabusky shock
and a relativistic extragalactic jet.


title:
AGN Host Galaxies at z~0.4-1.3 : Bulge-dominated and Lacking Merger-AGN
  Connection

abstract:
  We investigate morphological structure parameters and local environments of
distant moderate-luminosity active galactic nucleus (AGN) host galaxies in the
overlap between the HST/ACS observations of the Great Observatories Origins
Deep Survey (GOODS) and the two Chandra Deep Fields. We compute near-neighbor
counts and BViz asymmetry (A) and concentration (C) indices for ~35,500
GOODS/ACS galaxies complete to z_850 ~ 26.6, including the resolved hosts of
322 X-ray-selected AGNs. Distributions of (1) z_850 asymmetry for 130 AGN hosts
at z_850 < 23 and (2) near-neighbor counts for 173 AGN hosts at z_850 < 24 are
both consistent with non-AGN control samples. This implies no close connection
between recent galaxy mergers and moderate-luminosity AGN activity out to
appreciable look-back times (z < 1.3), approaching the epoch of peak AGN
activity in the universe. The distribution of z_850 concentrations for the AGN
hosts is offset by +0.5 compared to the non-AGN, a 6.4-sigma discrepancy much
larger than can be explained by the possible influence of unresolved emission
from the AGN or a circumnuclear starburst. The local universe association
between AGN and bulge-dominated galaxies thus persists to substantial look-back
time. We discuss implications in the context of the low-redshift supermassive
central black hole mass correlation with host galaxy properties, including
concentration.


title:
Chandra sample of nearby relaxed galaxy clusters: mass, gas fraction,
  and mass-temperature relation

abstract:
  We present gas and total mass profiles for 13 low-redshift, relaxed clusters
spanning a temperature range 0.7-9 keV, derived from all available Chandra data
of sufficient quality. In all clusters, gas temperature profiles are measured
to large radii (Vikhlinin et al.) so that direct hydrostatic mass estimates are
possible to nearly r_500 or beyond. The gas density was accurately traced to
larger radii; its profile is not described well by a beta-model, showing
continuous steepening with radius. The derived rho_tot profiles and their
scaling with mass generally follow the Navarro-Frenk-White model with
concentration expected for dark matter halos in LambdaCDM cosmology. In the
inner region (r<0.1r_500), the gas density and temperature profiles exhibit
significant scatter and trends with mass, but they become nearly self-similar
at larger radii. Correspondingly, we find that the slope of the
mass-temperature relation for these relaxed clusters is in good agreement with
the simple self-similar behavior, M_500 ~ T^alpha, where alpha=(1.5-1.6)+-0.1,
if the gas temperatures are measured excluding the central cool cores. The
normalization of this M-T relation is significantly, by =~ 30%, higher than
most previous X-ray determinations. We derive accurate gas mass fraction
profiles, which show increase both with radius and cluster mass. The enclosed
f_gas profiles within r_2500 =~ 0.4 r_500 have not yet reached any asymptotic
value and are still far (by a factor of 1.5-2) from the Universal baryon
fraction according to the CMB observations. The f_gas trends become weaker and
its values closer to Universal at larger radii, in particular, in spherical
shells r_2500<r<r_500.


title:
A fast method for computing strong-lensing cross sections: Application
  to merging clusters

abstract:
  Strong gravitational lensing by irregular mass distributions, such as galaxy
clusters, is generally not well quantified by cross sections of analytic mass
models. Computationally expensive ray-tracing methods have so far been
necessary for accurate cross-section calculations. We describe a fast,
semi-analytic method here which is based on surface integrals over
high-magnification regions in the lens plane and demonstrate that it yields
reliable cross sections even for complex, asymmetric mass distributions. The
method is faster than ray-tracing simulations by factors of $\sim30$ and thus
suitable for large cosmological simulations, saving large amounts of computing
time. We apply this method to a sample of galaxy cluster-sized dark matter
haloes with simulated merger trees and show that cluster mergers approximately
double the strong-lensing optical depth for lens redshifts
$z_\mathrm{l}\gtrsim0.5$ and sources near $z_\mathrm{s} = 2$. We believe that
this result hints at one possibility for understanding the recently detected
high arcs abundance in clusters at moderate and high redshifts, and is thus
worth further studies.


title:
VLT Diffraction Limited Imaging and Spectroscopy in the NIR: Weighing
  the black hole in Centaurus A with NACO

abstract:
  We present high spatial resolution near-infrared spectra and images of the
nucleus of Centaurus A (NGC 5128) obtained with NAOS-CONICA at the VLT. The
adaptive optics corrected data have a spatial resolution of 0.06" (FWHM) in K-
and 0.11" in H-band, four times higher than previous studies. The observed gas
motions suggest a kinematically hot disk which is orbiting a central object and
is oriented nearly perpendicular to the nuclear jet. We model the central
rotation and velocity dispersion curves of the [FeII] gas orbiting in the
combined potential of the stellar mass and the (dominant) black hole. Our
physically most plausible model, a dynamically hot and geometrically thin gas
disk, yields a black hole mass of M_bh = (6.1 +0.6/-0.8) 10^7 M_sun. As the
physical state of the gas is not well understood, we also consider two limiting
cases: first a cold disk model, which completely neglects the velocity
dispersion; it yields an M_bh estimate that is almost two times lower. The
other extreme case is to model a spherical gas distribution in hydrostatic
equilibrium through Jeans equation. Compared to the hot disk model the best-fit
black hole mass increases by a factor of 1.5. This wide mass range spanned by
the limiting cases shows how important the gas physics is even for high
resolution data. Our overall best-fitting black hole mass is a factor of 2-4
lower than previous measurements. With our revised M_bh estimate, Cen A's
offset from the M_bh-sigma relation is significantly reduced; it falls above
this relation by a factor of ~2, which is close to the intrinsic scatter of
this relation. (Abridged)


title: Radial and 2D Colour Properties of E+A Galaxies

abstract:
  We investigated the radial colour gradient and two-dimensional (2D) colour
properties of 22 E+A galaxies with 5.5 < Hdelta equivalent width(EW) < 8.5\AA
and 49 normal early-type galaxies as a control sample at a redshift of <0.2 in
the Second Data Release of the Sloan Digital Sky Survey. We found that a
substantial number of E+A galaxies exhibit positive slopes of radial colour
gradient (bluer gradients toward the centre) which are seldom seen in normal
early-type galaxies. We found irregular 'colour morphologies'-- asymmetrical
and clumpy patterns -- at the centre of g-r and r-i 2D colour maps of E+A
galaxies with positive slopes of colour gradient. Kolomogorov-Smirnov
two-sample tests show that g-r and r-i colour gradient distributions of E+A
galaxies differ from those of early-type galaxies with a more than 99.99 per
cent significance level. We also found a tight correlation between radial
colour gradients and colours, and between radial colour gradients and the
4000-\AA break in the E+A sample; E+A galaxies which exhibit bluer colour or
weaker D4000 tend to have positive slopes of radial colour gradient. We
compared the GISSEL model and E+A observational quantities, Hdelta EW, D4000
and u-g colour, and found that almost all our E+A galaxies are situated along a
single evolutionary track. Therefore, these results are interpreted as E+A
galaxies evolving from Hdelta EW ~ 8 \AA to Hdelta EW ~ 5 \AA, with colour
gradients changing from positive to negative, and with the irregular 2D colour
map becoming smoother, during a time-scale of ~300 Myr. Our results favour the
hypothesis that E+A galaxies are post-starburst galaxies caused by
merger/interaction, having undergone a centralized violent starburst.


title:
Non-Gaussianity in the WMAP data using the peak-peak correlation
  function

abstract:
  We present a search for non-Gaussianity in the WMAP first-year data using the
two-point correlation function of maxima and minima in the temperature map. We
find evidence for non-Gaussianity on large scales, whose origin appears to be
associated with unsubstracted foregrounds, but which is not entirely clear. The
signal appears to be associated most strongly with cold spots, and is more
pronounced in the Southern galactic hemisphere. Removal of the region of sky
near the galactic plane, or filtering out large-scale modes removes the signal.
Analysis of individual frequency maps shows strongest signal in the 41GHz Q
band. A study of difference maps tests the hypothesis that the non-Gaussianity
is due to residual foregrounds and noise, but shows no significant detection.
We suggest that the detection is due to large-scale residual foregrounds
affecting more than one frequency band, but a primordial contribution from the
Cosmic Microwave Background cannot be excluded.


title: The Island state of the Atoll Source 4U 1820--30

abstract:
  We study the rapid X-ray time variability in all public data available from
the \textit{Rossi X-ray Timing Explorer's} Proportional Counter Array on the
atoll source 4U 1820--30 in the low-luminosity island state. A total of
$\sim46$ ks of data were used. We compare the frequencies of the variability
components of 4U 1820--30 with those in other atolls sources. These frequencies
were previously found to follow a universal scheme of correlations. We find
that 4U 1820--30 shows correlations that are shifted by factors of
$1.13\pm0.01$ and $1.21\pm0.02$ with respect to those in other atoll sources.
These shifts are similar to, but smaller than the shift factor $\sim1.45$
previously reported for some accreting millisecond pulsars. Therefore, 4U
1820--30 is the first atoll source which shows no significant pulsations but
has a significant shift in the frequency correlations compared with other 3
non-pulsating atoll sources.


title: Aligning spinning black holes and accretion discs

abstract:
  We consider the alignment torque between a spinning black hole and an
accretion disc whose angular momenta are misaligned. This situation must hold
initially in almost all gas accretion events on to supermassive black holes,
and may occur in binaries where the black hole receives a natal supernova kick.
We show that the torque always acts to align the hole's spin with the total
angular momentum without changing its magnitude. The torque acts dissipatively
on the disc, reducing its angular momentum, and aligning it with the hole if
and only if the angle theta between the angular momenta J_d of the disc and J_h
of the hole satisfies the inequality cos theta > -J_d / 2 J_h. If this
condition fails, which requires both theta > pi/2 and J_d < 2 J_h, the disc
counteraligns.


title:
Torus Formation in Neutron Star Mergers and Well-Localized Short
  Gamma-Ray Bursts

abstract:
  Merging neutron stars (NSs) are hot candidates for the still enigmatic
sources of short gamma-ray bursts (GRBs). If the central engines of the huge
energy release are accreting relic black holes (BHs) of such mergers, it is
important to understand how the properties of the BH-torus systems, in
particular disc masses and mass and rotation rate of the compact remnant, are
linked to the characterizing parameters of the NS binaries. For this purpose we
present relativistic smoothed particle hydrodynamics simulations with
conformally flat approximation of the Einstein field equations and a physical,
non-zero temperature equation of state. Thick disc formation is highlighted as
a dynamical process caused by angular momentum transfer through tidal torques
during the merging process of asymmetric systems or in the rapidly spinning
triaxial post-merger object. Our simulations support the possibility that the
first well-localized short and hard GRBs 050509b, 050709, 050724, 050813 have
originated from NS merger events and are powered by neutrino-antineutrino
annihilation around a relic BH-torus system. Using model parameters based on
this assumption, we show that the measured GRB energies and durations lead to
estimates for the accreted masses and BH mass accretion rates which are
compatible with theoretical expectations. In particular, the low energy output
and short duration of GRB 050509b set a very strict upper limit of less than
100 ms for the time interval after the merging until the merger remnant has
collapsed to a BH, leaving an accretion torus with a small mass of only about
0.01 solar masses. This favors a (nearly) symmetric NS+NS binary with a typical
mass as progenitor system.


title: Blue, Green, and Red Bumps in AGN

abstract:
  I show that the summed spectral energy distribution (SED) $L(\nu)$ of any
extended blackbody radiator will scale in a predictable way if all parts of the
body change in temperature by the same factor $X$, such that $ L^\prime(\nu) =
X^3L(\nu/X) $. This should for example apply to accretion disks around black
holes, where $X$ is relative accretion rate, or external heating rate, but will
not apply to changes in black hole mass. I summarise evidence that AGN
optical-UV SEDs become progressively redder with decreasing luminosity, and
show that the trend in colour versus luminosity shown by Mushotzky and Wandel
(1989) is matched extremely well by taking a template high-luminosity SED and
scaling it in the manner described above. This agreement is striking because it
involves {\em no adjustable parameters}. The agreement breaks down at low
luminosities because of stellar contamination and reddening. I then consider
the colour changes of an individual AGN (NGC 5548) during luminosity changes,
which according to the popular X-ray reprocessing model, should follow the
scaling law well. However the observed changes are clearly {\em not} consistent
with the simple scaling prediction. Instead, these colour changes are quite
well explained by the mixing of a constant red component and variable blue
component. Overall, there is then strong support for the ideas (i) that AGN
optical-UV SEDs arise from accretion discs, (ii) that accretion rate plays a
significant role in the very large range of luminosity seen in AGN, and (ii)
that the inner regions of AGN vary independently of the outer accretion disc.


title: Four new wide binaries among exoplanet host stars

abstract:
  In our ongoing survey for wide (sub)stellar companions of exoplanet host
stars we have found 4 new co-moving stellar companions of the stars HD114729,
HD16141, HD196050 and HD213240 with projected separations from 223 up to
3898AU. The companionship of HD114729B, HD196050B and HD213240C is confirmed by
photometry and spectroscopy, all being early M dwarfs. The masses of the
detected companions are derived from their infrared JHK magnitudes and range
between 0.146 and 0.363 Msun. Our first and second epoch observations can rule
out additional stellar companions around the primaries from ~200 up to ~2400 AU
(S/N=10). In our survey we have found so far 6 new binaries among the exoplanet
host stars. According to these new detections, the reported differences between
single-star and binary-star planets with orbital periods short than 40 days
remain significant in both the mass-period and eccentricity-period
distribution. In contrast, all exoplanets with orbital periods longer than 100
days tend to display similar distributions.


title:
Wouthuysen-Field coupling strength and application to high-redshift 21
  cm radiation

abstract:
  The first UV sources in the universe are expected to have coupled the HI spin
temperature to the gas kinetic temperature via scattering in the Lyman-alpha
resonance [the Wouthuysen-Field (WF) effect]. By establishing an HI spin
temperature different from the temperature of the CMB, the WF effect should
allow observations of HI during the reionization epoch in the redshifted 21 cm
line. This paper investigates four mechanisms that can affect the strength of
the WF effect that were not previously considered: (1) Photons redshifting into
the HI Lyman resonances may excite an H atom and result in a radiative cascade
terminating in two-photon 2s->1s emission, rather than always degrading to
Lyman-alpha as usually assumed. (2) The fine structure of the Lyman-alpha
resonance alters the photon frequency distribution and leads to a suppression
of the scattering rate. (3) The spin-flip scatterings change the frequency of
the photon and cause the photon spectrum to relax not to the kinetic
temperature of the gas but to a temperature between the kinetic and spin
temperatures, effectively reducing the strength of the Wouthuysen-Field
coupling. (4) Near line centre, a photon can change its frequency by several
times the line width in a single scattering event, thus potentially
invalidating the usual calculation of the Lyman-alpha spectral distortion based
on the diffusion approximation. It is shown that (1) suppresses the WF coupling
strength by a factor of up to ~2, while (2) and (3) are important only at low
kinetic temperatures. Effect (4) has a <=3% effect for kinetic temperatures
T_k>=2K. If the pre-reionization IGM was efficiently heated by X-rays, only
effect (1) is important. Fitting formulae are provided for the range of T_k>=2K
and Gunn-Peterson optical depth 10^5--10^7. [ABRIDGED]


title:
Fluorescence and Hybrid Detection Aperture of the Pierre Auger
  Observatory

abstract:
  The aperture of the Fluorescence Detector (FD) of the Pierre Auger
Observatory is evaluated from simulated events using different detector
configurations: mono, stereo, 3-FD and 4-FD. The trigger efficiency has been
modeled using shower profiles with ground impacts in the field of view of a
single telescope and studying the trigger response (at the different levels) by
that telescope and by its neighbours. In addition, analysis cuts imposed by
event reconstruction have been applied. The hybrid aperture is then derived for
the Auger final extension. Taking into account the actual Surface Detector (SD)
array configuration and its trigger response, the aperture is also calculated
for a typical configuration of the present phase.


title: The Impact of Hydrodynamic Mixing on Supernova Progenitors

abstract:
  Recent multidimensional hydrodynamic simulations have demonstrated the
importance of hydrodynamic motions in the convective boundary and radiative
regions of stars to transport of energy, momentum, and composition. The impact
of these processes increases with stellar mass. Stellar models which
approximate this physics have been tested on several classes of observational
problems. In this paper we examine the implications of the improved treatment
on supernova progenitors. The improved models predict substantially different
interior structures. We present pre-supernova conditions and simple explosion
calculations from stellar models with and without the improved mixing treatment
at 23 solar masses. The results differ substantially.


title: Measurement of the Sky Photon Background Flux at the Auger Observatory

abstract:
  The sky photon background flux has been measured at the southern Auger site
in Malargue, Argentina, using the observatory's fluorescence detectors (FD).
The analysis is based on ADC variances of pixels not triggered by the First
Level Trigger. Photon fluxes are calculated for each individual pixel at each
telescope. The statistics from each night of data taking allows a study of
local variations in the photon flux. Results show a clear dependence of the
flux on elevation angle. Time variations, possibly related to different
atmospheric conditions, do not mask this dependence. In particular the flux
excess above the horizon shows a rather stable and reproducible behaviour with
elevation. Correlation of this dependence with atmospheric parameters can be of
interest as it offers the promise of extracting those parameters directly from
FD data, thus allowing cross checks with independent methods based on different
monitoring devices.


title:
Ionizing radiation from hydrogen recombination strongly suppresses the
  lithium scattering signature in the CMB

abstract:
  It has been suggested that secondary CMB anisotropies generated by neutral
lithium could open a new observational window into the universe around the
redshift z ~ 400, and permit a determination of the primordial lithium
abundance. The effect is due to resonant scattering in the allowed LiI doublet
(2s ^2S_{1/2} - 2p ^2P_{1/2,3/2}), so its observability depends on the
formation history of neutral lithium. Here we show that the ultraviolet photons
produced during hydrogen recombination are sufficient to keep lithium in the
LiII ionization stage in the relevant redshift range and suppress the neutral
fraction by ~3 orders of magnitude from previous calculations, making the
lithium signature unobservable.


title: Thermal Particle Injection in Nonlinear Diffusive Shock Acceleration

abstract:
  Particle acceleration in collisionless astrophysical shocks, i.e., diffusive
shock acceleration (DSA), is the most likely mechanism for producing cosmic
rays, at least below 10^{15} eV. Despite the success of this theory, several
key elements, including the injection of thermal particles, remains poorly
understood. We investigate injection in strongly nonlinear shocks by comparing
a semi-analytic model of DSA with a Monte Carlo model. These two models treat
injection quite differently and we show, for a particular set of parameters,
how these differences influence the overall acceleration efficiency and the
shape of the broad-band distribution function.


title: Ellipticity of dark matter halos with galaxy-galaxy weak lensing

abstract:
  We present the results of attempts to detect the ellipticity of dark matter
halos using galaxy-galaxy weak lensing with SDSS data. We use 2,020,256
galaxies brighter than r=19 with photometric redshifts (divided into colour and
luminosity subsamples) as lenses and 31,697,869 source galaxies. We search for
and identify several signal contaminants, which if not removed lead to a
spurious detection. These include systematic shear that leads to a slight
spurious alignment of lens and source ellipticities, intrinsic alignments (due
to contamination of the source sample by physically-associated lens source
pairs), and anisotropic magnification bias. We develop methods that allow us to
remove these contaminants to the signal. We split the analysis into blue
(spiral) and red (elliptical) galaxies. Assuming Gaussian errors as in previous
work and a power-law profile, we find f_h=e_h/e_g=0.1+/-0.06 for red galaxies
and -0.8+/-0.4 for blue galaxies using 20-300 kpc/h, averaged over luminosity.
Inclusion of the more realistic non-Gaussian error distributions and of the NFW
density profile (which predicts much smaller ellipticity of the shear for
scales above the scale radius) yields 0.60+/-0.38 for ellipticals and
-1.4+1.7-2.0 for spirals. While there is no concrete detection of alignment in
either case, there is a suggestion in the data of a positive alignment in the
brightest lens sample of ellipticals. Our results appear to be mildly
inconsistent with a previously reported detection by Hoekstra et al. (2004),
but more data and further tests are needed to clarify whether the discrepancy
is real or a consequence of differences in the lens galaxy samples used and
analysis methods.


title: Test-Particle Diffusive Shock Acceleration in Relativistic Shocks

abstract:
  We present results from a fully relativistic Monte Carlo simulation of
diffusive shock acceleration (DSA) in unmodified (i.e., test-particle) shocks.
The computer code uses a single algorithmic sequence to smoothly span the range
from nonrelativistic speeds to fully relativistic shocks of arbitrary
obliquity, providing a powerful consistency check. We show the dependence of
the particle spectrum, which can differ strongly from the canonical f(p)
proportional to p^{-4.23} result, on the obliquity and on the strength and
``fineness'' of scattering for a range of shock Lorentz factors. The Monte
Carlo results are also shown to be consistent with a simple relation for the
spectral index given by Keshet and Waxman (2005) in parallel shocks when the
diffusion is ``fine'' and isotropic.


title: Dynamical dark energy or variable cosmological parameters?

abstract:
  One of the main aims in the next generation of precision cosmology
experiments will be an accurate determination of the equation of state (EOS)
for the dark energy (DE). If the latter is dynamical, the resulting barotropic
index \omega should exhibit a non-trivial evolution with the redshift. Usually
this is interpreted as a sign that the mechanism responsible for the DE is
related to some dynamical scalar field, and in some cases this field may behave
non-canonically (phantom field). Present observations seem to favor an evolving
DE with a potential phantom phase near our time. In the literature there is a
plethora of dynamical models trying to describe this behavior. Here we show
that the simplest option, namely a model with a variable cosmological term,
\Lambda=\Lambda(t), leads in general to a non-trivial effective EOS, with index
\omega_e, which may naturally account for these data features. We prove that in
this case there is always a ``crossing'' of the \omega_e=-1 barrier near our
time. We also show how this effect is modulated (or even completely controled)
by a variable Newton's constant G=G(t).


title: Efficient Cosmic Ray Ion Production in Young Supernova Remnants

abstract:
  The strong shocks in young supernova remnants (SNRs) should accelerate cosmic
rays (CRs) and no doubt exists that relativistic electrons are produced in
SNRs. However, direct evidence that SNRs produce CR nuclei depends on seeing an
unambiguous pion-decay feature and this has not yet been obtained.
Nevertheless, the lack of an observed pion-decay feature does not necessarily
mean that CR ions are not abundantly produced since ions do not radiate
efficiently. If CR ions are produced efficiently by diffusive shock
acceleration (DSA), their presence will modify the hydrodynamics of the SNR and
produce morphological effects which can be clearly seen in radiation produced
by electrons.


title:
Search for Very High Energy Emission from Satellite-triggered GRBs with
  the Milagro Observatory

abstract:
  The Milagro gamma-ray observatory employs a water Cherenkov detector to
observe extensive air showers produced by high energy particles interacting in
the Earth's atmosphere. Milagro has a wide field of view (2 sr) and high duty
cycle (> 90%) making it an ideal all-sky monitor of the northern hemisphere in
the 100 GeV to 100 TeV energy range. More than 45 satellite-triggered gamma-ray
bursts (GRBs) have occurred in the field of view of Milagro since January 2000,
with the rate of bursts increasing significantly with the launch of Swift. We
discuss the most recent results of a search for very high energy (VHE) emission
from these GRBs.


title: Clustered Massive Star Formation in Molecular Clouds

abstract:
  I review some important questions in the field of massive star formation:
What are the initial conditions for proto star clusters and how do they arise?
What are the initial conditions for individual massive star formation within
star clusters? How do massive protostars accumulate their mass? I compare the
Turbulent Core Model (McKee & Tan 2003) to several nearby regions, including
Orion KL. Here I also discuss the origin of BN's high proper motion.


title:
Chemical Abundance Distributions of Galactic Halos and their Satellite
  Systems in a Lambda CDM Universe

abstract:
  We present a cosmologically motivated model for the hierachical formation of
the stellar halo which includes a semi-analytic treatment of galactic chemical
enrichment coupled to numerical simulations that track the orbital evolution
and tidal disruption of satellites. A major motivating factor in this
investigation is the observed systematic difference between the chemical
abundances of stars in satellite galaxies and those in the Milky Way halo.
Specifically, for the same [Fe/H] values, stars in neighboring satellite
galaxies display significantly lower [alpha/Fe] ratios than stars in the halo.
  We find that the observed chemical abundance patterns are a natural outcome
of the process of hierarchical assembly of the Galaxy. This result follows
because the stellar halo in this context is built up from satellite galaxies
accreted early on (more than 8-9 Gyr ago) and enriched in alpha-elements
produced in Type II supernovae. In contrast, satellites which survive today are
typically accreted late (within the last 4-5 Gyr) with nearly solar [alpha/Fe]
values as a result of contributions from both Type II and Type Ia supernovae.
We use our model to investigate the abundance distribution functions (using
both [Fe/H] and [alpha/Fe] ratios) for stars in the halo and in surviving
satellites. Our results suggest that the shapes and peaks in the abundance
distribution functions provide a direct probe of the accretion histories of
galaxies.


title:
Astrometric Methods and Instrumentation to Identify and Characterize
  Extrasolar Planets: A Review

abstract:
  I present a review of astrometric techniques and instrumentation utilized to
search for, detect, and characterize extra-solar planets. First, I briefly
summarize the properties of the present-day sample of extrasolar planets, in
connection with predictions from theoretical models of planet formation and
evolution. Next, the generic approach to planet detection with astrometry is
described, with significant discussion of a variety of technical, statistical,
and astrophysical issues to be faced by future ground-based as well as
space-borne efforts in order to achieve the required degree of measurement
precision. After a brief summary of past and present efforts to detect planets
via milli-arcsecond astrometry, I then discuss the planet-finding capabilities
of future astrometric observatories aiming at micro-arcsecond precision.
Lastly, I outline a number experiments that can be conducted by means of
high-precision astrometry during the next decade, to illustrate its potential
for important contributions to planetary science, in comparison with other
indirect and direct methods for the detection and characterization of planetary
systems.


title:
Constraints from the Detection of Cosmic Topology on the Generalized
  Chaplygin Gas

abstract:
  Despite our present-day inability to predict the topology of the universe one
may expect that we should be able to detect it in the near future, given the
increasing accuracy in the astro-cosmological observations. Motivated by this,
we examine to what extent a possible detection of a non-trivial topology of a
low curvature (Omega_0 ~ 1) universe, suggested by a diverse set of current
observations, may be used to place constraints on the matter content of the
universe, focusing our attention on the generalized Chaplgygin gas (GCG) model,
which unifies dark matter and dark energy in a single matter component. We show
that besides constraining the GCG free parameters, the detection of a
nontrivial topology also allows to set bounds on the total density parameter
Omega_0. We also study the combination of the bounds from the topology
detection with the limits that arise from current data on 194 SNIa, and show
that the determination of a given nontrivial topology sets complementary bounds
on the GCG parameters (and on Omega_0) to those obtained from the SNIa data.


title: The free precession and libration of Mercury

abstract:
  An analysis based on the direct torque equations including tidal dissipation
and a viscous core-mantle coupling is used to determine the damping time scales
of O(10^5) years for free precession of the spin about the Cassini state and
free libration in longitude for Mercury. The core-mantle coupling dominates the
damping over the tides by one to two orders of magnitude for the plausible
parameters chosen. The short damping times compared with the age of the solar
system means we must find recent or on-going excitation mechanisms if such free
motions are found by the current radar experiments or the future measurement by
the MESSENGER and BepiColombo spacecraft that will orbit Mercury. We also show
that the average precession rate is increased by about 30% over that obtained
from the traditional precession constant because of a spin-orbit resonance
induced contribution by the C_{22} term in the expansion of the gravitational
field. The C_{22} contribution also causes the path of the spin during the
precession to be slightly elliptical with a variation in the precession rate
that is a maximum when the obliquity is a minimum. An observable free
precession will compromise the determination of obliquity of the Cassini state
and hence of C/MR^2 for Mercury, but a detected free libration will not
compromise the determination of the forced libration amplitude and thus the
verification of a liquid core


title: DM clumps as discrete sources of gamma-radiation

abstract:
  Massive objects (clumps) of Cold Dark Matter (CDM) in Galaxy can appear due
to its annihilation as discrete sources of gamma-radiation. Some number of
unidentified regular gamma-sources, observed by EGRET, can be accounted for by
massive CDM clumps. Future gamma-ray expreriment GLAST in combination with data
of EGRET will enable to probe a wide range of models of clumped annihilating
CDM.


title:
A new estimate of the Galactic interstellar radiation field between 0.1
  microns and 1000 microns

abstract:
  Cosmic-ray electrons and positrons propagating in the Galaxy produce diffuse
gamma-rays via the inverse Compton (IC) process. The low energy target photon
populations with which the cosmic-rays interact during propagation are produced
by stars, this stellar light being reprocessed by Galactic dust. Detailed
modelling of the Galactic stellar distribution, dust distribution, and
treatment of the absorption and scattering of light is therefore required to
obtain accurate models for the low energy Galactic photon distribution and
spectrum. Using a realistic Galactic stellar distribution model, and dust
distribution, we calculate the diffuse radiation field from stars in the Galaxy
(the `optical' radiation field), including absorption and scattering. Using a
dust heating code, we self-consistently calculate the infra-red radiation field
for the same dust model used for the optical calculation; both transient and
equilibrium heating are included. We present the calculated radiation field
spectra and distributions, and will use these to calculate the expected
Galactic diffuse IC gamma-ray spectrum.


title:
Search for Cross-Correlations of Ultra--High-Energy Cosmic Rays with BL
  Lacertae Objects

abstract:
  Data taken in stereo mode by the High Resolution Fly's Eye (HiRes) air
fluorescence experiment are analyzed to search for correlations between the
arrival directions of ultra--high-energy cosmic rays with the positions of BL
Lacertae objects. Several previous claims of significant correlations between
BL Lacs and cosmic rays observed by other experiments are tested. These claims
are not supported by the HiRes data. However, we verify a recent analysis of
correlations between HiRes events and a subset of confirmed BL Lacs from the
10th Veron Catalog, and we study this correlation in detail. Due to the a
posteriori nature of the search, the significance level cannot be reliably
estimated and the correlation must be tested independently before any claim can
be made. We identify the precise hypotheses that will be tested with
statistically independent data.


title:
Photodisintegration of cosmic ray nuclei in galaxies and galaxy cluster
  radiation fields

abstract:
  We present the results of a new calculation for the photodisintegration of
ultra-high energy cosmic ray nuclei on soft photon targets. We include all the
relevant photodisintegraton processes i.e giant dipole resonance,
quasi-deuteron, baryonic resonances and photofragmentation. In particular, for
the giant dipole process we use a recent calculation of the giant dipole cross
section. We calculate the mean free path for photodisintegration processes for
radiation fields that are likely to exist within galaxies and clusters of
galaxies.


title:
Whims of an Accreting Young Brown Dwarf: Exploring Emission Line
  Variability of 2MASSW J1207334-393254

abstract:
  We report the first comprehensive study of emission line variability in an
accreting young brown dwarf. We have collected 14 high-resolution optical
spectra of 2MASSW J1207334-393254 (M8), a likely member of the nearby
8-million-year-old TW Hydrae association. These spectra show a variety of
emission lines that are commonly seen in classical T Tauri stars. Halpha line
in particular shows dramatic changes in shape and intensity in our dataset,
both on timescales of several weeks and several hours. In spectra from
late-January, the line is relatively weak and only slightly asymmetric. Spectra
from mid- and late-March show intense, broad and asymmetric Halpha emission,
indicative of on-going disk accretion. We estimate that the accretion rate
could have changed by a factor of 5-10 over ~6 weeks in this brown dwarf. March
spectra also reveal significant `quasi-periodic' changes in the Halpha line
profile over the course of a night, from clearly double-peaked to nearly
symmetric. These nightly profile changes, roughly consistent with the brown
dwarf's rotation period, could be the result of a redshifted absorption feature
coming into and out of our line of sight; when the profile is double-peaked we
may be looking into an accretion column, flowing from the inner disk edge on to
the central object, indicating that the accretion is probably channelled along
the magnetic field lines. Our findings provide strong support for the
magnetospheric accretion scenario, and thus for the existence of large-scale
magnetic fields, in the sub-stellar regime (abridged).


title:
The stability of MHD Taylor-Couette flow with current-free spiral
  magnetic fields between conducting cylinders

abstract:
  We study the magnetorotational instability in cylindrical Taylor-Couette
flow, with the (vertically unbounded) cylinders taken to be perfect conductors,
and with externally imposed spiral magnetic fields. The azimuthal component of
this field is generated by an axial current inside the inner cylinder, and may
be slightly stronger than the axial field. We obtain an instability beyond the
Rayleigh line, for Reynolds numbers of order 1000 and Hartmann numbers of order
10, and independent of the (small) magnetic Prandtl number. For experiments
with R_out = 2 R_in = 10 cm and Omega_out = 0.27 Omega_in, the instability
appears for liquid sodium for axial fields of ~20 Gauss and axial currents of
\~1200 A. For gallium the numbers are ~50 Gauss and ~3200 A. The vertical cell
size is about twice the cell size known for nonmagnetic experiments.


title: On the detection of chemically peculiar stars using Delta a photometry

abstract:
  We have summarized all Delta a measurements for galactic field stars (1474
objects) from the literature published over more than two decades. These
measurements were, for the first time, compiled and homogeneously analyzed. The
Delta a intermediate band photometric system samples the depth of the 520nm
flux depression by comparing the flux at the center with the adjacent regions
with bandwidths of 11 to 23nm. Because it was slightly modified over the last
three decades, we checked for systematic trends for the different measurements
but found no correlations whatsoever. The Delta a photometric system is most
suitable to detecting magnetic chemically peculiar (CP) stars with high
efficiency, but is also capable of detecting a small percentage of non-magnetic
CP objects. Furthermore, the groups of (metal-weak) lambda Bootis, as well as
classical Be/shell stars, can be successfully investigated. In addition, we
also analyzed the behaviour of supergiants (luminosity class I and II). On the
basis of apparent normal type objects, the correlation of the three sigma
significance limit and the percentage of positive detection for all groups was
derived. We compared the capability of the Delta a photometric system with the
Delta (V1 - G) and Z indices of the Geneva 7-color system to detect peculiar
objects. Both photometric systems show the same efficiency for the detection of
CP and lambda Bootis stars, while the indices in the Geneva system are even
more efficient at detecting Be/shell objects. On the basis of this statistical
analysis it is possible to derive the incidence of CP stars in galactic open
cluster and extragalactic systems including the former unknown bias of
undetected objects.


title: Dust Properties in the FUV in Ophiuchus

abstract:
  We have derived the albedo ($a$) and phase function asymmetry factor ($g$) of
interstellar dust grains at 1100 \AA ~ using archival {\it Voyager}
observations of diffuse radiation in Ophiuchus. We have found that the grains
are highly forward scattering with $g =$ 0.55 $\pm$ 0.25 and $a =$ 0.40 $\pm$
0.10. Even though most of the gas in this direction is in the Ophiuchus
molecular cloud, the diffuse FUV radiation is almost entirely due to scattering
in a relatively thin foreground cloud. This suggests that one cannot assume
that the UV background is directly correlated with the total amount of gas in
any direction.


title: On the origin of bimodal duration distribution of Gamma Ray Bursts

abstract:
  The modified version of a bullet model for gamma ray bursts is studied. The
central engine of the source produces multiple sub-jets that are contained
within a cone. The emission of photons in the source frame of a sub-jet either
takes part in an infinitesimally thin shell, or during its expansion for a
finite time. The analysis of the observed profiles of GRBs taken by BATSE leads
us to the conclusion that the latter possibility is much more favored. We also
study the statistical distribution of GRBs, in the context of their bimodality
of durations, taking into account the detector's capability of observing the
signal above a certain flux limit. The model with shells emitting for a finite
time is able to reproduce only one class of bursts, short or long, depending on
the adopted physical parameters. Therefore we suggest that the GRB bimodality
is intrinsically connected with two separate classes of sources.


title:
Chiral Properties of QCD Vacuum in Magnetars- A Nambu-Jona-Lasinio Model
  with Semi-Classical Approximation

abstract:
  The breaking of chiral symmetry of light quarks at zero temperature in
presence of strong quantizing magnetic fiels is studied using
Nambu-Jona-Lasinio (NJL) model with Thomas-Fermi type semi-classical formalism.
It is found that the dynamically generated light quark mass can never become
zero if the Landau levels are populated and the mass increases with the
increase of magnetic field strength.