title: Deep ACS Imaging of the Halo of NGC 5128: Reaching the Horizontal Branch

abstract:
  Using the HST Wide Field Camera of the Advanced Camera for Surveys (ACS), we
have obtained deep (V,I) photometry of an outer-halo field in NGC 5128, to a
limiting magnitude of I~29. Our photometry directly reveals the core
helium-burning stellar population (the ``red clump'' or horizontal branch) in a
giant E/S0 galaxy for the first time.
  The color-magnitude diagram displays a very wide red giant branch (RGB), an
asymptotic giant branch (AGB) bump, and the red clump; no noticeable population
of blue HB stars is present, confirming previous suggestions that old, very
metal-poor population is not ubiquitous in the halo of this galaxy. From the
upper RGB we derive the metallicity distribution, which we find to be very
broad and moderately metal-rich, with average [M/H]=-0.64 and dispersion 0.49
dex. The MDF is virtually identical to that found in other halo fields observed
previously with the HST, but with an enhanced metal-rich population which was
partially missed in the previous surveys due to V-band incompleteness for these
very red stars. Combining the metallicity sensitive colors of the RGB stars
with the metallicity and age sensitive features of the AGB bump and the red
clump, we infer the average age of the halo stars to be 8^{+3}_{-3.5} Gy.
  As part of our study, we present an empirical calibration of the ACS F606W
and F814W filters to the standard V and I bands, achieved with ground-based
observations of the same field made from the EMMI camera of the New Technology
Telescope of the ESO La Silla Observatory.


title: Gamma-Ray Burst Jet Profiles And Their Signatures

abstract:
  HETE-II and BeppoSAX have produced a sample of GRBs and XRFs with known
redshifts and $E_{pk}$. This sample provides four important empirical
constraints on the nature of the source jets: Log $E_{iso}$ is approximately
uniformly distributed over several orders of magnitude; the inferred prompt
energy Log $E_{\gamma}$ is narrowly distributed; the Amati relation holds
between $E_{iso}$ and $E_{pk}$; and the Ghirlanda relation holds between
$E_{\gamma}$ and $E_{pk}$.
  We explore the implications of these constraints for GRB jet structure during
the prompt emission phase. We infer the underlying angular profiles from the
first two of the above constraints assuming all jets have the same profile and
total energy, and show that such ``universal jet'' models cannot satisfy both
constraints.
  We introduce a general and efficient method for calculating relativistic
emission distributions and $E_{pk}$ distributions from jets with arbitrary
(smooth) angular jet profiles. We also exhibit explicit analytical formulas for
emission from top-hat jets (which are not smooth). We use these methods to
exhibit $E_{pk}$ and $E_{iso}$ as a function of viewing angle, for several
interesting families of GRB jet profiles. We use the same methods to calculate
expected frequency distributions of $E_{iso}$ and $E_{\gamma}$ for the same
families of models.
  We then proceed to explore the behavior of universal jet models under a range
of profile shapes and parameters, to map the extent to which these models can
conform to the above four empirical constraints.


title:
Hubble Space Telescope Imaging of Globular Cluster Candidates in Low
  Surface Brightness Dwarf Galaxies

abstract:
  Fifty-seven nearby low surface brightness dwarf galaxies were searched for
globular cluster candidates (GCCs) using Hubble Space Telescope WFPC2 imaging
in V and I. The sample consists of 18 dwarf spheroidal (dSph), 36 irregular
(dIrr), and 3 "transition" type (dIrr/dSph) galaxies with angular sizes less
than 3.7 kpc situated at distances 2-6 Mpc in the field and in the nearby
groups: M81, Centaurus A, Sculptor, Canes Venatici I cloud. We find that ~50%
of dSph, dIrr/dSph, and dIrr galaxies contain GCCs. The fraction of GCCs
located near the center of dwarf spheroidal galaxies is >2 times higher than
that for dIrrs. The mean integral color of GCCs in dSphs, V-I = 1.04+/-0.16
mag, coincides with the corresponding value for Galactic globular clusters and
is similar to the blue globular cluster sub-populations in massive early-type
galaxies. The color distribution for GCCs in dIrrs shows a clear bimodality
with peaks near V-I = 0.5 and 1.0 mag. Blue GCCs are presumably young with ages
t < 1 Gyr, while the red GCC population is likely to be older. The detected
GCCs have absolute visual magnitudes between M_V = -10 and -5 mag. We find
indications for an excess population of faint GCCs with M_V > -6.5 mag in both
dSph and dIrr galaxies, reminiscent of excess populations of faint globular
clusters in nearby Local Group spiral galaxies. The measurement of structural
parameters using King-profile fitting reveals that most GCCs have structural
parameters similar to extended outer halo globular clusters in the Milky Way
and M31, as well as the recently discovered population of "faint fuzzy"
clusters in nearby lenticular galaxies.


title: Intra-night Optical Variability of Luminous Radio Quiet QSOs

abstract:
  In the present paper we report the detection of intra-night variability in
some of the RQQSOs and one LDQ. To study intra-night variability, we carried
out photometric monitoring of seven RQQSOs and one LDQ in Johnson V-passband
using 1.2 meter optical/IR telescope at Gurushikhar, Mount Abu, India.
Observations were made in nine nights during the first half of the year 2000;
seven RQQSOs: 0748+291, 0945+438, 1017+280, 1029+329, 1101+319, 1225+317,
1252+020 and one LDQ: 1103-006 were observed. RQQSOs 0748+291, 1225+317 and LDQ
1103-006 have shown existence of intra-night variations. In the case of
1017+280 (RQQSO) there is indication of intra-night variation in one night
where as the observations in another night do not show convincingly the
existence of intra-night variability. RQQSOs 0945+438, 1029+329, 1101+319 and
1252+020 have not shown any intra-night variations. We compiled intra-night
variability data for radio-loud and radio-quiet AGNs from the literature for
statistical analysis. It is found that a good fraction of radio-quiet AGNs show
intra-night variations with the maximum amplitude of variation being about 10%.
On the other hand blazars show at times intra-night flux variability up to
100%. In case of radio-loud AGNs (excluding blazars), maximum amplitude of
intra-night variation lies between the variability amplitude of radio-quiet
AGNs and blazars i.e. the flux variation is close to 50%. The results indicate
that the energy generation mechanism and the environment around the central
engine in different classes of AGNs may be similar, if not identical. The
standard model for radio-loud AGNs, where shocks are propagating down
relativistic jet or models based on disturbances in accretion disks can also
explain the micro-variability in RQQSOs.


title: Dark matter in the inner parts of barred galaxies: The data

abstract:
  This paper presents surface photometry (B,V, I, J, H, K) and H_alpha rotation
curves of 27 isolated spiral galaxies. The final goal is to obtain the mass
distribution of a sample of isolated spiral galaxies in order to model their
gas kinematics. This is then compared to the observed rotation curve, to
determine the necessity of a dark halo in the inner parts (Perez et al. 2004).
The azimuthally averaged radial surface brightness profiles and the integrated
magnitudes obtained from ellipse fitting are given for each of the sample
galaxies. The ellipse fitting technique applied to the light distribution also
allowed us to obtain the size of the bar, and the inclination and position
angle of the outer isophotes that allow the galaxy deprojection. Using these
profiles, 1-D disk-bulge decomposition was performed to obtain the disk
scale-length and the bulge effective radius for the different bands. Through
the fitting of a parametric function to the observed rotation curve, the
maximum rotational velocity and the corresponding radius was obtained. The
correlation between the bulge and disk parameters is in agreement with previous
studies (de Jong 1996a; Marquez & Moles 1999; Baggett et al. 1998). Regarding
the Kormendy relation (Kormendy 1977), in agreement with de Jong, no
correlation between the bulge effective radius and its surface brightness is
found, possibly due to the small range of bulge magnitudes covered. We find a
smaller scatter in the structural relations when compared to non-isolated
samples in agreement with Marquez & Moles (1999). Finally, a correlation
between the disk scale-length and the bar size is observed, possibly reflecting
the rapid growth of a bar.


title: Photon dominated regions in the spiral arms of M83 and M51

abstract:
  We present CI 3P1-3P0 spectra at four spiral arm positions and the nuclei of
the nearby galaxies M83 and M51 obtained at the JCMT. This data is complemented
with maps of CO 1-0, 2-1, and 3-2, and ISO/LWS far-infrared data of CII (158
micron), OI (63 micron), and NII (122 micron) allowing for the investigation of
a complete set of all major gas cooling lines. From the intensity of the NII
line, we estimate that between 15% and 30% of the observed CII emission
originate from the dense ionized phase of the ISM. The analysis indicates that
emission from the diffuse ionized medium is negligible. In combination with the
FIR dust continuum, we find gas heating efficiencies below ~0.21% in the
nuclei, and between 0.25 and 0.36% at the outer positions. Comparison with
models of photon-dominated regions (PDRs) of Kaufman et al. (1999) with the
standard ratios OI(63)/CII_PDR and (OI(63)+CII_PDR) vs. TIR, the total infrared
intensity, yields two solutions. The physically most plausible solution
exhibits slightly lower densities and higher FUV fields than found when using a
full set of line ratios, CII_PDR/CI(1-0), CI(1-0)/CO(3-2), CO(3-2)/CO(1-0),
CII/CO(3-2), and, OI(63)/CII_PDR. The best fits to the latter ratios yield
densities of 10^4 cm^-3 and FUV fields of ~G_0=20-30 times the average
interstellar field without much variation. At the outer positions, the observed
total infrared intensities are in perfect agreement with the derived best
fitting FUV intensities. The ratio of the two intensities lies at 4-5 at the
nuclei, indicating the presence of other mechanisms heating the dust.


title:
Polarized Cosmological Gravitational Waves from Primordial Helical
  Turbulence

abstract:
  We show that helical turbulence produced during a first-order phase
transition generates circularly polarized cosmological gravitational waves
(GWs). The characteristic frequency of these GWs for an extreme case of the
phase transition model is around $10^{-3}$ --- $10^{-2}$ Hz with an energy
density parameter as high as $10^{-12}$ --- $10^{-11}$. The possibility of
detection is briefly discussed.


title: OH 12.8-0.9: A New Water-Fountain Source

abstract:
  We present observational evidence that the OH/IR star OH 12.8-0.9 is the
fourth in a class of objects previously dubbed "water-fountain" sources. Using
the Very Long Baseline Array, we produced the first images of the water maser
emission associated with OH 12.8-0.9. We find that the masers are located in
two compact regions with an angular separation of ~109 mas on the sky. The axis
of separation between the two maser regions is at a position angle of 1.5 deg.
East of North with the blue-shifted (-80.5 to -85.5 km/s) masers located to the
North and the red-shifted (-32.0 to -35.5 km/s) masers to the South. In
addition, we find that the blue- and red-shifted masers are distributed along
arc-like structures ~10-12 mas across oriented roughly perpendicular to the
separation axis. The morphology exhibited by the water masers is suggestive of
an axisymmetric wind with the masers tracing bow shocks formed as the wind
impacts the ambient medium. This bipolar jet-like structure is typical of the
three other confirmed water-fountain sources. When combined with the previously
observed spectral characteristics of OH 12.8-0.9, the observed spatio-kinematic
structure of the water masers provides strong evidence that OH 12.8-0.9 is
indeed a member of the water-fountain class.


title:
A short gamma-ray burst apparently asssociated with an elliptical galaxy
  at redshift z=0.225

abstract:
  Gamma Ray Bursts (GRBs) are bright, brief flashes of high energy photons that
have fascinated scientists for 30 years. They come in two classes: long (>2 s),
softspectrum bursts and short, hard events. The major progress to date on
understanding GRBs has been for long bursts which are typically at high
redshift (z ~ 1) and are in sub-luminous star-forming host galaxies. They are
likely produced in core-collapse explosions of massive stars. Until the present
observation, no short GRB had been accurately (<10") and rapidly (minutes)
located. Here we report the detection of X-ray afterglow from and the
localization of short burst GRB050509b. Its position on the sky is near a
luminous, non-starforming elliptical galaxy at a redshift of 0.225, exactly the
type of location one would expect if the origin of this GRB is the
long-proposed fiery merger of neutron star (NS) or black hole (BH) binaries.
The X-ray afterglow is found to be weak and fading below detection within a few
hours and no optical afterglow is detected to stringent limits, explaining the
past difficulty in localizing short GRBs.


title:
Broad-band colors and overall photometric properties of template galaxy
  models from stellar population synthesis

abstract:
  We present here a new set of evolutionary population synthesis models for
template galaxies along the Hubble morphological sequence. The models, that
account for the individual evolution of the bulge, disk, and halo components,
provide basic morphological features, along with bolometric luminosity and
color evolution (including Johnson/Cousins "UBVRcIcJHK", Gunn "gri", and
Washington "CMT1T2" photometric systems) between 1 and 15 Gyr. Luminosity
contribution from residual gas is also evaluated, both in terms of nebular
continuum and Balmer-line enhancement.


title: Low-Mass Runaway Stars from the Orion Trapezium Cluster

abstract:
  In the course of a search for common proper motion binaries, in the Jones &
Walker (JW) catalogue of proper motions in the Orion Nebula Cluster, we came
across several faint stars with proper motions larger than one arcsecond per
century and probabilities of membership P larger than 0.90. Such stars are
interesting because they could be low-mass runaway stars recently accelerated
by n-body interactions in compact multiple systems. Of particular interest
among these stars is JW 451, which has a P = 0.98, the largest transverse
velocity among all the stars with P larger or equal than 0.5 (69 km/s), and a
proper motion vector which suggests that it was accelerated by the component C
of the Trapezium some 1000 years ago. A closer examination of those JW stars
with proper motion larger than one arcsec per century revealed that two other
stars, JW 349 and JW 355 (with transverse velocities of 38 and 90 km/s
respectively), in spite of being listed with P = 0 by JW, should also be
considered part of the cluster, because these objects are also externally
ionized proplyds. In fact, Hillenbrand (1997) assigns to them probabilities of
membership of 0.99. Moreover, the proper motion errors of these two stars are
relatively small, and so they are good candidates to be runaway stars recently
accelerated in the Orion Nebula Cluster.


title: H_2 Pure Rotational Lines in the Orion Bar

abstract:
  Using the Texas Echelon Cross Echelle Spectrograph (TEXES) we mapped emission
in the H_2 v = 0-0 S(1) and S(2) lines toward the Orion Bar PDR at 2"
resolution. We also observed H_2 v = 0-0 S(4) at selected points toward the
front of the PDR. Our maps cover a 12" by 40" region of the bar where H_2
ro-vibrational lines are bright. The distributions of H_2 0-0 S(1), 0-0 S(2),
and 1-0 S(1) line emission agree in remarkable detail.
  The high spatial resolution (0.002 pc) of our observations allows us to probe
the distribution of warm gas in the Orion Bar to a distance approaching the
scale length for FUV photon absorption. We use these new observational results
to set parameters for the PDR models described in a companion paper (Draine et
al. 2005, in prep). The best-fit model can account for the separation of the
H_2 emission from the ionization front and the intensities of the ground state
rotational lines as well as the 1-0 S(1) and 2-1 S(1) lines. This model
requires significant adjustments to the commonly used values for the dust UV
attenuation cross section and the photoelectric heating rate.


title: The high-velocity clouds and the Magellanic Clouds

abstract:
  From an analysis of the sky and velocity distributions of the high-velocity
clouds (HVCs) we show that the majority of the HVCs has a common origin. We
conclude that the HVCs surround the Galaxy, forming a metacloud of 300 kpc in
size and with a mass of 3 10^9 M_sun, and that they are the product of a
powerful ``superwind'' (about 10^58 ergs), which occurred in the Magellanic
Clouds about 570 Myr ago as a consequence of the interaction of the Large and
Small Magellanic Clouds. The HVCs might be magnetic bubbles of semi-ionized
gas, blown from the Magellanic Clouds around 570 Myr ago, that circulate
largely through the halo of the Galaxy as a stream or flow of gas.


title:
On the Steady Nature of Line-Driven Disk Winds: Application to
  Cataclysmic Variables

abstract:
  We apply the semi-analytical analysis of the steady nature of line-driven
winds presented in two earlier papers to disk winds driven by the flux
distribution of a standard Shakura & Sunyaev (1973) disk for typical
cataclysmic variable (CV) parameters. We find that the wind critical point
tends to be closer to the disk surface towards the inner disk regions. Our main
conclusion, however, is that a line-driven wind, arising from a steady disk
flux distribution of a standard Shakura-Sunyaev disk capable of locally
supplying the corresponding mass flow, is steady. These results confirm the
findings of an earlier paper that studied "simple" flux distributions that are
more readily analyzable than those presented here. These results are consistent
with the steady velocity nature of outflows observationally inferred for both
CVs and quasi-stellar objects (QSOs). We find good agreement with the 2.5D CV
disk wind models of Pereyra and collaborators. These results suggest that the
likely scenario to account for the wind outflows commonly observed in CVs is
the line-driven accretion disk wind scenario, as suggested early-on by Cordova
& Mason (1982). For QSOs, these results show that the line-driven accretion
disk wind continues to be a promising scenario to account for the outflows
detected in broad absorption line (BAL) QSOs, as suggested early-on by Turnshek
(1984), and analyzed in detail by Murray et al. (1995).


title:
Characteristic QSO Accretion Disk Temperatures from Spectroscopic
  Continuum Variability

abstract:
  Using Sloan Digital Sky Survey (SDSS) quasar spectra taken at multiple
epochs, we find that the composite flux density differences in the rest frame
wavelength range 1300-6000 AA can be fit by a standard thermal accretion disk
model where the accretion rate has changed from one epoch to the next (without
considering additional continuum emission components). The fit to the composite
residual has two free parameters: a normalizing constant and the average
characteristic temperature $\bar{T}^*$. In turn the characteristic temperature
is dependent on the ratio of the mass accretion rate to the square of the black
hole mass. We therefore conclude that most of the UV/optical variability may be
due to processes involving the disk, and thus that a significant fraction of
the UV/optical spectrum may come directly from the disk.


title:
Development of an Electronic Readout System for the Detection of Radio
  Emission from Extensive Cosmic Ray Air Showers

abstract: This paper has been withdrawn.


title: Microquasars and Jets

abstract:
  I present an overview of past, present and future research on microquasars
and jets, showing that microquasars, i.e. galactic jet sources, are among the
best laboratories for high energy phenomena. After remindind the analogy with
quasars, I focus on one of the best microquasar representatives, probably the
archetype, namely GRS 1915+105, and present accretion and ejection phenomena,
showing that only a multi-wavelength approach allows a better understanding of
phenomena occuring in these sources. Thereafter, I review jets at different
scales: compact jets, large-scale jets, and the interactions between ejections
and the surrounding medium. I finish by speaking about microblazars and
ultraluminous X-ray sources.


title:
Can the rotation of the dark matter halo of our galaxy be detected
  through its effect on the cosmic microwave background polarisation?

abstract:
  The proposition that dark matter halos possess angular momentum, though
widely accepted, is a theoretical prediction which has, till date, not been
observationally verified. The gravi-magnetic field produced by a rotating
gravitating object is possibly the only direct consequence of the angular
momentum of dark matter halos. The gravitational Faraday rotation produced by
the dark matter halo of our galaxy is present in all astronomical observations.
A detection of the imprint of this effect on the all-sky cosmic microwave
background radiation polarisation pattern would directly probe the angular
momentum of the dark matter halo of our Galaxy. We have calculated the expected
gravitational Faraday rotation which turns out to be a $(v_c/c)^3$ effect,
$v_c$ being the rotational speed of our halo. The predicted gravitational
Faraday effect rotation angles are less than $1^{''}$, implying that this
effect, though present, is too small to be detected.


title:
Optical and X-ray studies of chromospherically active stars : FR Cancri,
  HD 95559 and LO Pegasi

abstract:
  We present a multiwavelength study of three chromospherically active stars,
namely FR Cnc (= BD +16\degr 1753), HD 95559 and LO Peg (=BD +22\degr 4409),
including newly obtained optical photometry, low-resolution optical
spectroscopy for FR Cnc, as well as archival IR and X-ray observations. The BVR
photometry carried out during the years 2001 - 2004 has found significant
photometric variability to be present in all three stars. For FR Cnc, a
photometric period $0.8267 \pm 0.0004 \rm {d}$ has been established. The strong
variation in the phase and amplitude of the FR Cnc light curves when folded on
this period implies the presence of evolving and migrating spots or i spot
groups on its surface. Two independent spots with migration periods of 0.97 and
0.93 years respectively are inferred. The photometry of HD 95559 suggests the
formation of a spot (group) during the interval of our observations. We infer
the existence of two independent spots or groups in the photosphere of LO Peg,
one of which has a migration period of 1.12 years. The optical spectroscopy of
FR Cnc carried out during 2002-2003, reveals the presence of strong and
variable Ca II H and K, H$_\beta$ and $H_{\alpha}$ emission features indicative
of high level of chromospheric activity. The value of 5.3 for the ratio of the
excess emission in $H_{\alpha}$ to $H_{\beta}$, $E_{H_{\alpha}}/E_{H_{\beta}}$,
suggests that the chromospheric emission may arise from an extended off-limb
region. We have also analyzed archival X-ray observations of HD 95559 and LO
Peg carried out by with the ROSAT observatory. The best fit models to their
X-ray spectra imply the presence of two coronal plasma components of differing
temperatures and with sub-solar metal abundances.


title: Direct detection of exo-planets: GQ Lupi

abstract:
  We present a comparison of our VLT/NACO K-band spectrum of the GQ Lupi
companion with the new GAIA-dusty model atmosphere grid for T=2000 and 2900 K
and log g from 0 to 4. Then, we discuss the mass estimate for GQ Lup companion.


title:
The Canis Major dwarf galaxy as the progenitor of the Monoceros tidal
  stream

abstract:
  The Sloan Digital Sky Survey has recently discovered a coherent ring of stars
at low galactic latitude that is believed to be the tidal stream of a merging
dwarf galaxy in the Galactic plane (named the Monoceros tidal stream). The
existence and location of the core of its progenitor galaxy is still
controversial. The best candidate is the Canis Major dwarf galaxy, a distinct
overdensity of red stars discovered in the 2MASS survey, but also interpreted
as the signature of the Galactic warp viewed in projection. In this paper, we
report a variety of new observational evidence that supports the notion that
CMa is the remnant of a partially disrupted core of a dwarf satellite. The
comparison of the orbit derived from our theoretical model for the parent
galaxy of this ring-like structure with an accurate determination of CMa orbit
leads to the conclusion that this satellite is the best candidate for the
progenitor of the Monoceros tidal stream.


title: Determination of stellar shape in microlensing event MOA 2002-BLG-33

abstract:
  We report a measurement of the shape of the source star in microlensing event
MOA 2002-BLG-33. The lens for this event was a close binary whose
centre-of-mass passed almost directly in front of the source star. At this
time, the source star was closely bounded on all sides by a caustic of the
lens. This allowed the oblateness of the source star to be constrained. We
found that a/b = 1.02^{+0.04}_{-0.02} where a and b are its semi-major and
semi-minor axes respectively. The angular resolution of this measurement is
approximately 0.04 microarcsec. We also report HST images of the event that
confirm a previous identification of the source star as an F8-G2 turn-off
main-sequence star.


title: Encounters between spherical galaxies I: systems without dark halo

abstract:
  We report here on a survey of N-body simulations of encounters between
spherical galaxies. Initial systems are isotropic Jaffe models. Different sets
of mass ratios, impact parameters and orbital energies are studied. Both merger
remnants and systems perturbed after a non-merging encounter are analysed and
compared to real-life elliptical galaxies. The properties of merger remnants
show a large variety. Merger remnants resulting from head-on encounters are
mainly non-rotating prolate spheroids. Merger remnants from models with angular
momentum different from zero are triaxial or mildly oblate spheroids supported
in part by rotation. The velocity distributions are biased towards the radial
direction in the prolate case and the tangential direction in the oblate case.
Non-mergers are affected in various ways, depending on the orbital
characteristics. We conclude that many of the global properties of real-life
ellipticals can in principle be attributed to a merger of spherical
progenitors.


title: Encounters between spherical galaxies II: systems with dark halo

abstract:
  We performe N-body simulations of encounters between spherical systems
surrounded by a spherical halo. Following a preceding paper with a similar aim,
the initial systems include a spherical Jaffe model for the luminous matter and
a Hernquist model for the halo. The merger remnants from this sample are mainly
slowly rotating, prolate spheroids with a radially anisotropic velocity
distribution. The results are compared with real-life ellipticals and with the
models without halo in paper I. We argue that elliptical galaxies with evidence
of dark matter could be formed in the field via a merger of spheroids
surrounded by a dark matter halo, while ellipticals with no evidence of dark
matter might be formed via a merger of two spheroids in a cluster.


title:
On the stratorotational instability in the quasi-hydrostatic
  semi-geostrophic limit

abstract:
  The linear normal-mode stratorotational instability (SRI) is analytically
reexamined in the inviscid limit where the length scales of horizontal
disturbances are large compared their vertical and radial counterparts.
Boundary conditions different than channel walls are also considered. This
quasi-hydrostatic, semi-geostrophic (QHSG) approximation allows one to examine
the effect of a vertically varying Brunt-Vaisaila frequency, $N^2$. It is found
that the normal-mode instability persists when $N^2$ increases quadratically
with respect to the disc vertical coordinate. However we also find that the SRI
seems to exist in this inviscid QHSG extreme only for channel wall conditions:
when one or both of the reflecting walls are removed there is no instability in
the asymptotic limit explored here. It is also found that only exponential-type
SRI modes (as defined by Dubrulle et al. 2005) exist under these conditions.
These equations also admit non-normal mode behaviour. Fixed Lagrangian pressure
conditions on both radial boundaries predicts there to be no normal mode
behaviour in the QHSG limit. The mathematical relationship between the results
obtained here and that of the classic Eady (1949) problem for baroclinic
instability is drawn. We conjecture as to the mathematical/physical nature of
the SRI.
  The general linear problem, analyzed without approximation in the context of
the Boussinesq equations, admits a potential vorticity-like quantity that is
advectively conserved by the shear. Its existence means that a continuous
spectrum \emph{is a generic feature of this system}. It also implies that in
places where the Brunt-Vaisaila frequency becomes dominant the linearized flow
may two-dimensionalize by advectively conserving its vertical vorticity.


title: Low Luminosity Companions to White Dwarfs

abstract:
  This paper presents results of a near-infrared imaging survey for low mass
stellar and substellar companions to white dwarfs. A wide field proper motion
survey of 261 white dwarfs was capable of directly detecting companions at
orbital separations between $\sim100$ and 5000 AU with masses as low as 0.05
$M_{\odot}$, while a deep near field search of 86 white dwarfs was capable of
directly detecting companions at separations between $\sim50$ and 1100 AU with
masses as low as 0.02 $M_{\odot}$. Additionally, all white dwarf targets were
examined for near-infrared excess emission, a technique capable of detecting
companions at arbitrarily close separations down to masses of 0.05 $M_{\odot}$.
  No brown dwarf candidates were detected, which implies a brown dwarf
companion fraction of $<0.5$% for white dwarfs. In contrast, the stellar
companion fraction of white dwarfs as measured by this survey is 22%,
uncorrected for bias. Moreover, most of the known and suspected stellar
companions to white dwarfs are low mass stars whose masses are only slightly
greater than the masses of brown dwarfs. Twenty previously unknown stellar
companions were detected, five of which are confirmed or likely white dwarfs
themselves, while fifteen are confirmed or likely low mass stars.
  Similar to the distribution of cool field dwarfs as a function of spectral
type, the number of cool unevolved dwarf companions peaks at mid-M type. Based
on the present work, relative to this peak, field L dwarfs appear to be roughly
2-3 times more abundant than companion L dwarfs. Additionally, there is no
evidence that the initial companion masses have been altered by post main
sequence binary interactions.


title:
The Diffuse Emission and a Variable ULX in the Elliptical Galaxy NGC
  3379

abstract:
  A Chandra observation of the intermediate luminosity (M_B=-20) elliptical
galaxy NGC 3379 resolves 75% of the X-ray emission within the central 5kpc into
point sources. Spectral analysis of the remaining unresolved emission within
the central 770pc indicates that 90% of the emission probably arises from
undetected point sources, while 10% arises from thermal emission from kT=0.6keV
gas. Assuming a uniform density distribution in the central region of the
galaxy gives a gas mass of 5.0e5 Mo.Such a small amount of gas can be supplied
by stellar mass loss in only 1.0e7 years. Thus, the gas must be accreting into
the central supermassive black hole at a very low radiative efficiency as in
the ADAF or RIAF models, or is being expelled in a galactic wind driven by the
same AGN feedback mechanism as that observed in cluster cooling flows. If the
gas is being expelled in an AGN driven wind, then the ratio of mechanical to
radio power of the AGN must be 1.0e4, which is comparable to that measured in
cluster cooling flows which have recently been perturbed by radio outbursts.
The brightest point source in NGC 3379 is located 360pc from the central AGN
with a peak luminosity of 3.5e39 ergs/s, which places it in the class of
ultra-luminous X-ray point sources (ULX). Analysis of an archival ROSAT HRI
observation of NGC 3379 shows that this source was at a comparable luminosity 5
years prior to the Chandra observation. During the Chandra observation, the
source intensity smoothly varies by a factor of two with the suggestion of an
8-10 hour period.


title:
Boundary layer emission and Z-track in the color-color diagram of
  luminous LMXBs

abstract:
  We demonstrate that Fourier-frequency resolved spectra of atoll and Z-
sources are identical, despite significant difference in their average spectra
and luminosity (by a factor of ~10-20). This result fits in the picture we
suggested earlier, namely that the f> 1 Hz variability in luminous LMXBs is
primarily due to variations of the boundary layer luminosity. In this picture
the frequency resolved spectrum equals the boundary layer spectrum, which
therefore can be straightforwardly determnined from the data. The obtained so
boundary layer spectrum is well approximated by the saturated Comptonization
model, its high energy cut-off follows kT~2.4 keV black body. Its independence
on the global mass accretion rate lends support to the theoretical suggestion
by Inogamov &Sunyaev (1999) that the boundary layer is radiation pressure
supported. With this assumption we constrain the gravity on the neutron star
surface and its mass and radius. Equipped with the knowledge of the boundary
layer spectrum we attempt to relate the motion along the Z-track to changes of
physically meaningful parameters. Our results suggest that the contribution of
the boundary layer to the observed emission decreases along the Z-track from
conventional ~50% on the horizontal branch to a rather small number on the
normal branch. This decrease can be caused, for example, by obscuration of the
boundary layer by the geometrically thick accretion disk at Mdot ~ Mdot_Edd.
Alternatively, this can indicate significant change of the structure of the
accretion flow at Mdot ~ Mdot_ Edd and disappearance of the boundary layer as a
distinct region of the significant energy release associated with the neutron
star surface.


title: Global properties of X-ray afterglows of GRB

abstract:
  In this paper we review the general properties of X-ray afterglows. We
discuss in particular on the powerful diagnostics provided by X-ray afterglows
in constraining the environment and fireball in normal GRB, and the
implications on the origin of dark GRB and XRF. We also discuss on the observed
properties of the transition from the prompt to the afterglow phase, and
present a case study for a late X-ray outburst interpreted as the onset of the
afterglow stage.


title: ESTREMO: Extreme phySics in the TRansient and Evolving COsmos

abstract:
  We present a mission designed for the study of transient phenomena in the
high energy sky, through a wide field X-ray/hard X-ray monitor, and fast (< 1
min) follow up observations with Narrow Field Instrumentation. This is based on
an X-ray telescope with an area of 1000 cm2, equipped with high-resolution
spectroscopy microcalorimeters and X-ray polarimeter. The performances of the
mission on the physics of GRB and their use as cosmological probes are
presented and discussed.


title: The SDSS View of the Palomar-Green Bright Quasar Survey

abstract:
  We investigate the extent to which the Palomar-Green (PG) Bright Quasar
Survey (BQS) is complete and representative of the general quasar population by
comparing with imaging and spectroscopy from the Sloan Digital Sky Survey. A
comparison of SDSS and PG photometry of both stars and quasars reveals the need
to apply a color and magnitude recalibration to the PG data. Using the SDSS
photometric catalog, we define the PG's parent sample of objects that are not
main-sequence stars and simulate the selection of objects from this parent
sample using the PG photometric criteria and errors. This simulation shows that
the effective U-B cut in the PG survey is U-B < -0.71 (rather than the intended
U-B < -0.44), implying a color-related incompleteness. As the color
distribution of bright quasars peaks near U-B=-0.7 and the 2-sigma error in U-B
is comparable to the full width of the color distribution of quasars, the color
incompleteness of the BQS is approximately 50% and essentially random with
respect to U-B color for z<0.5. There is, however, a bias against bright
quasars at 0.5 < z < 1, which is induced by the color-redshift relation of
quasars (although quasars at z>0.5 are inherently rare in bright surveys in any
case). We find no evidence for any other systematic incompleteness when
comparing the distributions in color, redshift, and FIRST radio properties of
the BQS and a BQS-like subsample of the SDSS quasar sample. However, the
application of a bright magnitude limit biases the BQS toward the inclusion of
objects which are blue in g-i, in particular compared to the full range of g-i
colors found among the i-band limited SDSS quasars, and even at i-band
magnitudes comparable to those of the BQS objects.


title:
Discovery of X-Ray Emission from Supernova 1970G with Chandra: Filling
  the Void between Supernovae and Supernova Remnants

abstract:
  We report on the discovery of X-ray emission from SN 1970G in M101, 35 years
after its outburst, using deep X-ray imaging with the Chandra X-ray
observatory. The Chandra ACIS spectrum shows that the emission is soft (<2 keV)
and characteristic for the reverse shock region. The X-ray luminosity (1 x
10^37 ergs/s) is likely caused by the interaction of the supernova (SN) shock
with dense circumstellar matter. If the material was deposited by the stellar
wind from the progenitor, a mass-loss rate of (2.6+/-0.4) x 10^-5 M_sun/year is
inferred. Utilizing the high-resolution Chandra ACIS data of SN 1970G and its
environment, we reconstruct the X-ray lightcurve from previous ROSAT HRI, PSPC,
and XMM-Newton EPIC observations, and find a best-fit linear rate of decline of
L \propto t^-s with index s = 1.7+/-0.6 over a period of 12-35 years after the
outburst. As the oldest SN detected in X-rays, SN 1970G allows, for the first
time, direct observation of the transition from a SN to its supernova remnant
(SNR) phase.


title: Massive Star Outflows

abstract:
  Molecular outflows in the form of wide-angle winds and/or well-collimated
jets are associated with young stellar objects of all luminosities. Independent
studies have established that the mass outflow rate is proportional to
L_bol^0.6 for L_bol = 0.3 to 10^5 L_sun, suggesting that there is a strong link
between accretion and outflow for a wide range of source luminosity and there
is reasonable evidence that accretion-related processes are responsible for
generating massive molecular flows from protostars up to spectral type B0.
Beyond L_bol ~ 10^4 L_sun, O stars generate powerful wide-angle, ionized winds
that can dramatically affect outflow morphology and even call into question the
relationship between outflow and accretion.
  Recently Beuther & Shepherd (2005) proposed an evolutionary scenario in which
massive protostellar flows (up to early B spectral type) begin collimated. Once
the star reaches the Main Sequence, ionizing radiation may affect the balance
between magnetic and plasma pressure, inducing changes in the flow morphology
and energetics. Here I review the properties of outflows from young OB stars,
discuss implications and observational tests of this proposed evolutionary
scenario, and examine differences between low-mass and massive star formation.


title: Recovering Solar Toroidal Field Dynamics From Sunspot Location Patterns

abstract:
  We analyze both Kitt Peak magnetogram data and MDI continuum intensity
sunspot data to search for the following solar toroidal band properties: width
in latitude and the existence of a tipping instability (longitudinal m=1 mode)
for any time during the solar cycle. To determine the extent which we can
recover the toroidal field dynamics, we forward model artificially generated
sunspot distributions from subsurface toroidal fields we assigned certain
properties. We analyzed two sunspot distribution parameters using MDI and model
data: the average latitudinal separation of sunspot pairs as a function of
longitudinal separation, and the number of sunspot pairs creating a given angle
with respect to the E-W direction. A toroidal band of 10 degrees width with a
constant tipping of 5 degrees best fits MDI data early in the solar cycle. A
toroidal band of 20 degrees width with a tipping amplitude decreasing in time
from 5 to 0 degrees best fits MDI data late in the solar cycle. Model data
generated by untipped toroidal bands cannot fit MDI high latitude data and can
fit only one parameter at low latitudes. Tipped toroidal bands satisfy chi
squared criteria at both high and low latitudes. We conclude this is evidence
to reject the null hypothesis - that toroidal bands in the solar tachocline do
not experience a tipping instability - in favor of the hypothesis that the
toroidal band experiences an m=1 tipping instability. Our finding that the band
widens from ~10 degrees early in the solar cycle to ~20 degrees late in the
solar cycle may be explained in theory by magnetic drag spreading the toroidal
band due to altered flow along the tipped field lines.


title:
The all-sky distribution of 511 keV electron-positron annihilation
  emission

abstract:
  We present a map of 511 keV electron-positron annihilation emission, based on
data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray
observatory, that covers approximately 95% of the celestial sphere. 511 keV
line emission is significantly detected towards the galactic bulge region and,
at a very low level, from the galactic disk. The bulge emission is highly
symmetric and is centred on the galactic centre with an extension of 8 deg. The
emission is equally well described by models that represent the stellar bulge
or halo populations. The disk morphology is only weakly constrained by the
present data, being compatible with both the distribution of young and old
stellar populations. The 511 keV line flux from the bulge and disk components
is 1.05e-3 ph cm-2 s-1 and 0.7e-3 ph cm-2 s-1, respectively, corresponding to a
bulge-to-disk flux ratio in the range 1-3. Assuming a positronium fraction of
0.93 this translates into annihilation rates of 1.5e43 s-1 and 3e42 s-1,
respectively. The ratio of the bulge luminosity to that of the disk is in the
range 3-9. We find no evidence for a point-like source in addition to the
diffuse emission, down to a typical flux limit of 1e-4 ph cm-2 s-1. We also
find no evidence for the positive latitude enhancement that has been reported
from OSSE measurements; our 3 sigma upper flux limit for this feature is 1.5e-4
ph cm-2 s-1. The disk emission can be attributed to the beta+ decay of the
radioactive species 26Al and 44Ti. The bulge emission arises from a different
source which has only a weak or no disk component. We suggest that Type Ia
supernovae and/or low-mass X-ray binaries are the prime candidates for the
source of the galactic bulge positrons. Light dark matter annihilation could
also explain the observed 511 keV bulge emission characteristics.


title: Convective Dynamos and the Minimum X-ray Flux in Main Sequence Stars

abstract:
  The objective of this paper is to investigate whether a convective dynamo can
account quantitatively for the observed lower limit of X-ray surface flux in
solar-type main sequence stars. Our approach is to use 3D numerical simulations
of a turbulent dynamo driven by convection to characterize the dynamic
behavior, magnetic field strengths, and filling factors in a non-rotating
stratified medium, and to predict these magnetic properties at the surface of
cool stars. We use simple applications of stellar structure theory for the
convective envelopes of main-sequence stars to scale our simulations to the
outer layers of stars in the F0--M0 spectral range, which allows us to estimate
the unsigned magnetic flux on the surface of non-rotating reference stars. With
these estimates we use the recent results of \citet{Pevtsov03} to predict the
level of X-ray emission from such a turbulent dynamo, and find that our results
compare well with observed lower limits of surface X-ray flux. If we scale our
predicted X-ray fluxes to \ion{Mg}{2} fluxes we also find good agreement with
the observed lower limit of chromospheric emission in K dwarfs. This suggests
that dynamo action from a convecting, non-rotating plasma is a viable
alternative to acoustic heating models as an explanation for the basal emission
level seen in chromospheric, transition region, and coronal diagnostics from
late-type stars.


title:
Red giant branch stars as probes of stellar populations. II. Properties
  of the newly discovered globular cluster GLIMPSE-C01

abstract:
  Deep near infrared photometry of the newly discovered Galactic globular
Cluster GLIMPSE-C01 is reported. We derived for the first time the metal
abundance of this object from the slope of the RGB: [Fe/H]=-1.61+/-0.14 in the
scale of Zinn (as implemented in Harris 1996), [Fe/H]=-1.44+/-0.12 in the scale
of Caretta & Gratton (1997), and [Fe/H]=-1.12+/-0.12 in the scale of Ferraro et
al. (1999). The tip and the clump of the red giant branch were used to confirm
the estimates of Kobulnicky et al. (2005), placing the cluster at D~3.7+/-0.8
kpc, behind A_v~15 mag of visual extinction. The best fit to the radial surface
brightness profile with a single-mass King's model (1962) yielded core radius
r_c=0.78 arcmin, tidal radius r_t=27 arcmin, and central concentration c=1.54.
  Finally, we estimate the number of the "missing" globulars in the central
region of the Milky Way. Based on the spatial distribution of the known
clusters, and assuming radial symmetry around the Galactic center, we conclude
that the Milky Way contains at least 10+/-3 undiscovered objects. The
distribution of known clusters in the bulge seem to resemble the orientation of
the Milky Way bar.


title:
Ultraviolet, Optical, and X-Ray Observations of the Type Ia Supernova
  2005am with Swift

abstract:
  We present ultraviolet and optical light curves in six broadband filters and
grism spectra obtained by Swift's Ultraviolet/Optical Telescope for the Type Ia
supernova SN2005am. The data were collected beginning about four days before
the B-band maximum, with excellent coverage of the rapid decline phase and
later observations extending out to 69 days after the peak. The optical and
near UV light curve match well those of SN1992A. The other UV observations
constitute the first set of light curves shorter than 2500 Angstroms and allow
us to compare the light curve evolution in three UV bands. The UV behavior of
this and other low redshift supernovae can be used to constrain theories of
progenitor evolution or to interpret optical light curves of high redshift
supernovae. Using Swift's X-Ray Telescope, we also report the upper limit to
SN2005am's X-ray luminosity to be 1.77 x 10^40 erg s^-1 in the 0.3--10 keV
range from 58,117 s of exposure time.


title:
Systematic Errors in Future Weak Lensing Surveys: Requirements and
  Prospects for Self-Calibration

abstract:
  We study the impact of systematic errors on planned weak lensing surveys and
compute the requirements on their contributions so that they are not a dominant
source of the cosmological parameter error budget. The generic types of error
we consider are multiplicative and additive errors in measurements of shear, as
well as photometric redshift errors. In general, more powerful surveys have
stronger systematic requirements. For example, for a SNAP-type survey the
multiplicative error in shear needs to be smaller than 1%(fsky/0.025)^{-1/2} of
the mean shear in any given redshift bin, while the centroids of photometric
redshift bins need to be known to better than 0.003(fsky/0.025)^{-1/2}. With
about a factor of two degradation in cosmological parameter errors, future
surveys can enter a self-calibration regime, where the mean systematic biases
are self-consistently determined from the survey and only higher-order moments
of the systematics contribute. Interestingly, once the power spectrum
measurements are combined with the bispectrum, the self-calibration regime in
the variation of the equation of state of dark energy w_a is attained with only
a 20-30% error degradation.


title:
An X-ray Variable Millisecond Pulsar in the Globular Cluster 47 Tucanae:
  Closing the Link to Low Mass X-ray Binaries

abstract:
  We report the discovery of peculiar X-ray spectral variability in the binary
radio millisecond pulsar PSR J0024--7204W in the globular cluster 47 Tucanae.
The observed emission consists of a dominant non-thermal component, which is
eclipsed for a portion of the orbit, and a thermal component, which appears to
be persistent. We propose that the non-thermal X-rays originate in a
relativistic intrabinary shock, formed due to interaction between the
relativistic particle wind from the pulsar and matter from the main-sequence
companion star, while the thermal photons are from the heated magnetic polar
caps of the millisecond pulsar. At optical wavelengths, the emission exhibits
large-amplitude variations at the orbital period, which can be attributed to
heating of one side of the tidally-locked secondary star by the pulsar wind.
The observed X-ray and optical properties of PSR J0024--7204W are remarkably
similar to those of the low mass X-ray binary and X-ray millisecond pulsar SAX
J1808.4--3658 in quiescence. This supports the conjecture that the non-thermal
X-ray emission and optical modulations seen in the SAX J1808.4--3658 system in
a quiescent state are due to interaction between the wind from a reactivated
rotation-powered pulsar and matter from the companion star. The striking
similarities between the two systems provide support for the long-sought
connection between millisecond radio pulsars and accreting neutron star
systems.


title: Silicon Tetrafluoride on Io

abstract:
  Silicon tetrafluoride (SiF4) is observed in terrestrial volcanic gases and is
predicted to be the major F - bearing species in low temperature volcanic gases
on Io (Schaefer and Fegley, 2005b). SiF4 gas is also a potential indicator of
silica-rich crust on Io. We used F/S ratios in terrestrial and extraterrestrial
basalts, and gas/lava enrichment factors for F and S measured at terrestrial
volcanoes to calculate equilibrium SiF4/SO2 ratios in volcanic gases on Io. We
conclude that SiF4 can be produced at levels comparable to the observed
NaCl/SO2 gas ratio. We also considered potential loss processes for SiF4 in
volcanic plumes and in Io's atmosphere including ion-molecule reactions,
electron chemistry, photochemistry, reactions with the major atmospheric
constituents, and condensation. Photochemical destruction (tchem ~ 266 days)
and/or condensation as Na2SiF6 (s) appear to be the major sinks for SiF4. We
recommend searching for SiF4 with infrared spectroscopy using its 9.7 micron
band as done on Earth.


title:
Rates of Neutrino Absorption on Nucleons and the Reverse Processes in
  Strong Magnetic Fields

abstract:
  The rates of electron neutrino capture on neutron, electron anti-neutrino
capture on proton, and their reverse processes are important for understanding
the production of heavy elements in the supernova environment above the
protoneutron star. Observations and theoretical considerations suggest that
some protoneutron stars may be born with strong magnetic fields. We develop a
numerical method to calculate the above rates in supernova environments with
magnetic fields up to 10^16 G. This method is accurate to the order of one over
nucleon mass. We show that our results have the correct behavior in the limit
of high neutrino energy or small magnetic field. Based on comparison of our
results with various approximations, we recommend efficient estimates of the
above rates for use in models of supernova nucleosynthesis in the presence of
strong magnetic fields.


title:
Application of an Equilibrium Vaporization Model to the Ablation of
  Chondritic and Achondritic Meteoroids

abstract:
  We modeled equilibrium vaporization of chondritic and achondritic materials
using the MAGMA code. We calculated both instantaneous and integrated element
abundances of Na, Mg, Ca, Al, Fe, Si, Ti, and K in chondritic and achondritic
meteors. Our results are qualitatively consistent with observations of meteor
spectra.


title:
The effect of the Coriolis force on Kelvin-Helmholtz-driven mixing in
  protoplanetary disks

abstract:
  We study the stability of proto-planetary disks with vertical velocity
gradients in their equilibrium rotation rates; such gradients are expected to
develop when dust settles into the midplane. Using a linear stability analysis
of a simple three-layer model, we show that the onset of instability occurs at
a larger value of the Richardson number, and therefore for a thicker layer,
when the effects of Coriolis forces are included. This analysis also shows that
even-symmetry (midplane-crossing) modes develop faster than odd-symmetry ones.
These conclusions are corroborated by a large number of nonlinear numerical
simulations with two different parameterized prescriptions for the initial
(continuous) dust distributions. Based on these numerical experiments, the
Richardson number required for marginal stability is more than an order of
magnitude larger than the traditional 1/4 value. The dominant modes that grow
have horizontal wavelengths of several initial dust scale heights, and in
nonlinear stages mix solids fairly homogeneously over a comparable vertical
range. We conclude that gravitational instability may be more difficult to
achieve than previously thought, and that the vertical distribution of matter
within the dust layer is likely globally, rather than locally, determined.


title:
Considerations in optimizing CMB polarization experiments to constrain
  inflationary physics

abstract:
  We quantify the limiting factors in optimizing current-technology cosmic
microwave background (CMB) polarization experiments in order to learn about
inflationary physics. We consider space-based, balloon-borne and ground-based
experiments. We find that foreground contamination and residuals from
foreground subtraction are ultimately the limiting factors in detecting a
primordial gravity wave signal. For full-sky space-based experiments, these
factors hinder the detection of tensor-to-scalar ratios of r < 10^{-3} on large
scales, while for ground-based experiments these factors impede the ability to
apply delensing techniques. We consider ground-based/balloon-borne experiments
of currently planned or proposed designs and find that it is possible for a
value of r=0.01 to be measured at ~ 3-sigma level. A small space-based CMB
polarization experiment, with current detector technology and full sky
coverage, can detect r ~ 10^{-3} at the ~ 3-sigma level, but a markedly
improved knowledge of polarized foregrounds is needed. We advocate using as
wide a frequency coverage as possible in order to carry out foreground
subtraction at the percent level, which is necessary to measure such a small
primordial tensor amplitude. To produce a clearly detectable (>3-sigma) tensor
component in a realistic CMB experiment, inflation must either involve
large-field variations, \Delta\phi >~ 1 or multi-field/hybrid models. Hybrid
models can be easily distinguished from large-field models due to their blue
scalar spectral index. Therefore, an observation of a tensor/scalar ratio and n
< 1 in future experiments with the characteristics considered here may be an
indication that inflation is being driven by some physics in which the inflaton
cannot be described as a fundamental field.


title:
ISO observations of the Wolf-Rayet galaxies NGC 5430, NGC 6764, Mrk 309
  and VII Zw 19

abstract:
  Observations of four WR galaxies (NGC 5430, NGC 6764, Mrk 309 and VII Zw 19)
using the Infrared Space Observatory are presented here. ISOCAM maps of NGC
5430, Mrk 309 and NGC 6764 revealed the location of star formation regions in
each of these galaxies. ISOPHOT spectral observations from 4 to 12 microns
detected the ubiquitous PAH bands in the nuclei of the targets and several of
the disk star forming regions, while LWS spectroscopy detected [OI] and [CII]
emission lines from two galaxies, NGC 5430 and NGC 6764.
  Using a combination of ISO and IRAS flux densities, a dust model based on the
sum of modified blackbody components was successfully fitted to the available
data. These models were then used to calculate new values for the total IR
luminosities for each galaxy, the size of the various dust populations, and the
global SFR.
  The derived flux ratios, the SFRs, the high L(PAH)/L(40-120 microns) and
F(PAH 7.7 microns)/F(7.7 microns continuum) values suggest that most of these
galaxies are home to only a compact burst of star formation. The exception is
NGC 6764, whose F(PAH 7.7 microns)/F(7.7 microns continuum) value of 1.22 is
consistent with the presence of an AGN, yet the L(PAH)/L(40-120 microns) is
more in line with a starburst, a finding in line with a compact low-luminosity
AGN dominated by the starburst.


title: The Evolution of the M-sigma Relation

abstract:
  (Abridged) We examine the evolution of the black hole mass - stellar velocity
dispersion (M-sigma) relation over cosmic time using simulations of galaxy
mergers that include feedback from supermassive black hole growth. We consider
mergers of galaxies varying the properties of the progenitors to match those
expected at redshifts z=0-6. We find that the slope of the resulting M-sigma
relation is the same at all redshifts considered. For the same feedback
efficiency that reproduces the observed amplitude of the M-sigma relation at
z=0, there is a weak redshift-dependence to the normalization that results from
an increasing velocity dispersion for a given galactic stellar mass. We develop
a formalism to connect redshift evolution in the M-sigma relation to the
scatter in the local relation at z=0. We show that the scatter in the local
relation places severe constraints on the redshift evolution of both the
normalization and slope of the M-sigma relation. Furthermore, we demonstrate
that cosmic downsizing introduces a black hole mass-dependent dispersion in the
M-sigma relation and that the skewness of the distribution about the locally
observed M-sigma relation is sensitive to redshift evolution in the
normalization and slope. In principle, these various diagnostics provide a
method for differentiating between theories for producing the M-sigma relation.
In agreement with existing constraints, our simulations imply that hierarchical
structure formation should produce the relation with small intrinsic scatter.


title: Star Formation in HI Selected Galaxies. II. HII Region Properties

abstract:
  A sample of 69 galaxies with radial velocities less than 2500 km/s was
selected from the HI Parkes All Sky Survey (HIPASS) to deduce details about
star formation in nearby disk galaxies selected with no bias to optical surface
brightness selection effects. Broad (B and R) and narrow band (H-alpha) images
were obtained for all of these objects. More than half of the sample galaxies
are late-type, dwarf disks (mostly Sc and Sm galaxies). We have measured the
properties of the HII regions on H-alpha, continuum subtracted images, using
the HIIphot package developed by Thilker et al. 2000. All but one of the
galaxies contained at least one detectable HII region. Examination of the
properties of the HII regions in each galaxy revealed that the brightest
regions in higher surface brightness galaxies tend to be more luminous than
those in lower surface brightness galaxies. A higher fraction (referred to as
the diffuse fraction) of the H-alpha emission from lower surface brightness
galaxies comes from diffuse ionized gas (DIG). HII region luminosity functions
(LFs) co-added according to surface brightness show that the shapes of the LFs
for the lowest surface brightness galaxies are different from those for typical
spiral galaxies. This discrepancy could be caused by the lowest surface
brightness galaxies having somewhat episodic star formation or by them forming
a relatively larger fraction of their stars outside of dense, massive molecular
clouds. In general, the results imply that the conditions under which star
formation occurs in lower surface brightness galaxies are different than in
more typical, higher surface brightness spiral galaxies.


title: Rapid growth of high redshift black holes

abstract:
  We discuss a model for the early assembly of supermassive black holes (SMBHs)
at the center of galaxies that trace their hierarchical build-up far up in the
dark halo `merger tree'. Motivated by the observations of luminous quasars
around redshift z=6 with SMBH masses of billion solar masses, we assess the
possibility of an early phase of stable super-critical quasi-spherical
accretion in the BHs hosted by metal free halos with virial temperature larger
than 10000 K. We assume that the first `seed' black holes formed with
intermediate masses following the collapse of the first generation of stars, in
mini-halos collapsing at z=20-30 from high peaks of density fluctuations. In
high redshift halos with virial temperature larger than 10000 K, conditions
exist for the formation of a fat disc of gas at T_gas=5000-10000 K. Cooling via
hydrogen atomic lines is in fact effective in these comparatively massive
halos. The cooling and collapse of an initially spherical configuration of gas
leads to a rotationally supported disc at the center of the halo if baryons
preserve their specific angular momentum during collapse. The conditions for
the formation of the gas disc and accretion onto a central black holes out of
this supply of gas are investigated, as well as the feedback of the emission
onto the host and onto the intergalactic medium. We find that even a short
phase of supercritical accretion eases the requirements set by the z=6 quasars.


title:
The DEEP2 Galaxy Redshift Survey: The Galaxy Luminosity Function to z ~
  1

abstract:
  The evolution of the B-band galaxy luminosity function is measured using a
sample of more than 11,000 galaxies with spectroscopic redshifts from the DEEP2
Redshift Survey. The rest-frame M_B versus U-B color-magnitude diagram of DEEP2
galaxies shows that the color-magnitude bi-modality seen in galaxies locally is
still present at redshifts z > 1. Dividing the sample at the trough of this
color bimodality into predominantly red and blue galaxies, we find that the
luminosity function of each galaxy color type evolves differently. Blue counts
tend to shift to brighter magnitudes at constant number density, while the red
counts remain largely constant at a fixed absolute magnitude. Using Schechter
functions with fixed faint-end slopes we find that M*_B for blue galaxies
brightens by ~ 1.3 magnitudes per unit redshift, with no significant evolution
in number density. For red galaxies M*_B brightens somewhat less with redshift,
while the formal value of phi* declines. When the population of blue galaxies
is subdivided into two halves using the rest-frame color as the criterion, the
measured evolution of both blue subpopulations is very similar.


title: A fresh view on Henize 2-10 with VLT/NAOS-CONICA

abstract:
  We present high-resolution observations of Henize 2-10 in Ks (2.2um), L'
(3.8um), M' (4.8um) bands. These allow for the first time to track accurately
the structures at the heart of the galaxy from the optical to the radio. All
radio knots previously observed can now be associated with L' and Ks emitting
regions. This implies a revision of their physical nature. Instead of highly
extinguished ultra-dense HII regions, we propose that two of the 5 radio knots
are either supernova remnants or "normal" HII regions, while the remaining
three are bona fide ultra-dense HII regions, although less obscured than was
previously thought.


title: Number counts in homogeneous and inhomogeneous dark energy models

abstract:
  In the simple case of a constant equation of state, redshift distribution of
collapsed structures may constrain dark energy models. Different dark energy
models having the same energy density today but different equations of state
give quite different number counts. Moreover, we show that introducing the
possibility that dark energy collapses with dark matter (``inhomogeneous'' dark
energy) significantly complicates the picture. We illustrate our results by
comparing four dark energy models to the standard $\Lambda$-model. We
investigate a model with a constant equation of state equal to -0.8, a phantom
energy model and two scalar potentials (built out of a combination of two
exponential terms). Although their equations of state at present are almost
indistinguishable from a $\Lambda$-model, both scalar potentials undergo quite
different evolutions at higher redshifts and give different number counts. We
show that phantom dark energy induces opposite departures from the
$\Lambda$-model as compared with the other models considered here. Finally, we
find that inhomogeneous dark energy enhances departures from the
$\Lambda$-model with maximum deviations of about 15% for both number counts and
integrated number counts. Larger departures from the $\Lambda$-model are
obtained for massive structures which are rare objects making it difficult to
statistically distinguish between models.


title:
Galaxy Luminosity Functions to z~1: DEEP2 vs. COMBO-17 and Implications
  for Red Galaxy Formation

abstract:
  The DEEP2 and COMBO-17 surveys are used to study the evolution of the
luminosity function of red and blue galaxies to $z \sim 1$. Schechter function
fits show that, since $z = 1$, $M^*_B$ dims by $\sim$ 1.3 mag per unit redshift
for both color classes, $\phi^*$ of blue galaxies shows little change, while
$\phi^*$ for red galaxies has formally nearly quadrupled. At face value, the
number density of blue galaxies has remained roughly constant since $ z = 1$,
whereas that of red galaxies has been rising. Luminosity densities support both
conclusions, but we note that most red-galaxy evolution occurs between our data
and local surveys and in our highest redshift bin, where the data are weakest.
We discuss the implications of having most red galaxies emerge after $z = 1$
from precursors among the blue population, taking into account the properties
of local and distant E/S0s. We suggest a ``mixed'' scenario in which some blue
galaxies have their star-formation quenched in gas-rich mergers, migrate to the
red sequence with a variety of masses, and merge further on the red sequence in
one or more purely stellar mergers. E/S0s of a given mass today will have
formed via different routes, in a manner that may help to explain the
fundamental plane and other local scaling laws.


title: Prospects for Redshifted 21-cm observations of quasar HII regions

abstract:
  The introduction of low-frequency radio arrays over the coming decade is
expected to revolutionize the study of the reionization epoch. Observation of
the contrast in redshifted 21cm emission between a large HII region and the
surrounding neutral IGM will be the simplest and most easily interpreted
signature. We find that an instrument like the planned Mileura Widefield Array
Low-Frequency Demonstrator (LFD) will be able to obtain good signal to noise on
HII regions around the most luminous quasars, and determine some gross
geometric properties, e.g. whether the HII region is spherical or conical. A
hypothetical follow-up instrument with 10 times the collecting area of the LFD
(MWA-5000) will be capable of mapping the detailed geometry of HII regions,
while SKA will be capable of detecting very narrow spectral features as well as
the sharpness of the HII region boundary. The MWA-5000 will discover
serendipitous HII regions in widefield observations. We estimate the number of
HII regions which are expected to be generated by quasars. Assuming a late
reionization at z~6 we find that there should be several tens of quasar HII
regions larger than 4Mpc at z~6-8 per field of view. Identification of HII
regions in forthcoming 21cm surveys can guide a search for bright galaxies in
the middle of these regions. Most of the discovered galaxies would be the
massive hosts of dormant quasars that left behind fossil HII cavities that
persisted long after the quasar emission ended, owing to the long recombination
time of intergalactic hydrogen. A snap-shot survey of candidate HII regions
selected in redshifted 21cm image cubes may prove to be the most efficient
method for finding very high redshift quasars and galaxies.


title:
Limits on Turbulent HI Fluctuations Towards PSR B0329+54 On Scales
  Between 0.0025 and 12.5 AU

abstract:
  We have measured the HI absorption towards pulsar B0329+54 using the Green
Bank Telescope during 18 epochs between 2002 June 30 and 2003 October 10. Three
observing epochs consisted of a continuous period of 20 hours each, while
fifteen epochs were 1-2 hours each. We calculate the structure function of HI
absorption variations toward the pulsar on time scales of 10 minutes to 16
months which, using the proper motion of 95 km/s and the parallactic distance
of 1.03 kpc measured towards B0329+54 (Brisken et al. 2002), corresponds to
angular scales of 0.37 micro-arcseconds to 23.8 milli-arseconds and samples
structures between 0.0025-12.5 AU assuming HI gas half way to the pulsar and
ignoring scintillation effects. We find no evidence for any turbulent HI
absorption fluctuations towards B0329+54, with the following upper limits on
the change in opacity for various absorption features: 0.026 at -31, -21, -18,
and +4 km/s, 0.12 at -11 km/s, and 0.055 at -1 km/s.


title:
Radio Observations of the Hubble Deep Field South Region II: The 1.4 GHz
  Catalogue and Source Counts

abstract:
  This paper is part of a series describing the results from the Australia
Telescope Hubble Deep Field South (ATHDFS) survey obtained with the Australia
Telescope Compact Array (ATCA). This survey consists of observations at 1.4,
2.5, 5.2 and 8.7 GHz, all centred on the Hubble Deep Field South.
  Here we present the first results from the extended observing campaign at 1.4
GHz. A total of 466 sources have been catalogued to a local sensitivity of 5
sigma (11 microJy rms). A source extraction technique is developed which: 1)
successfully excludes spurious sources from the final source catalogues, and 2)
accounts for the non-uniform noise in our image. A source catalogue is
presented and the general properties of the 1.4 GHz image are discussed. We
also present source counts derived from our ATHDFS 1.4 GHz catalogue.
Particular attention is made to ensure the counts are corrected for survey
incompleteness and systematic effects. Our counts are consistent with other
surveys (e.g. ATESP, VIRMOS, and Phoenix Deep Field), and we find, in common
with these surveys, that the HDFN counts are systematically lower.


title:
VLA Imaging of the Intriguing HI Cloud HIJASS J1021+6842 in the M81
  Group

abstract:
  We present VLA HI 21cm observations of HIJASS J1021+6842 which has been
discovered in the direction of the M81 group. Our synthesis imaging reveals
that the HI is distributed over a larger angular extent and velocity range than
the single dish discovery observations. Assuming that HIJASS J1021+6842 is at
the distance of the M81 group, we detect 1.5 x 10^8 M_sun of HI distributed
over as much as 30 kpc, i.e., substantially larger than the biggest dwarf
galaxies in the same group. At the depth of our imaging, the HI appears to be
confined to at least 7 clouds. Peak HI column densities are ~1.8 x 10^20 atoms
cm^-2 which is well below the canonical star formation threshold of ~10^21
atoms cm^-2 and therefore consistent with the fact that no optical counterpart
has as yet been identified. A gradient in velocity is observed across the
extent of the detected HI; assuming that the object is gravitationally bound we
derive a dynamical mass of 7 x 10^9 M_sun and a dark-to-luminous mass ratio of
>10. Alternatively, a tidal origin may also result in the observed velocity
gradient which would lead to a considerably lower dynamical mass. Given the
above properties and the absence of evidence of a stellar population, HIJASS
J1021+6842 is unique amongst the other systems in the M81 group.


title: X-ray emission from young brown dwarfs in the Orion Nebula Cluster

abstract:
  We use the sensitive X-ray data from the Chandra Orion Ultradeep Project
(COUP) to study the X-ray properties of 34 spectroscopically-identified brown
dwarfs with near-infrared spectral types between M6 and M9 in the core of the
Orion Nebula Cluster. Nine of the 34 objects are clearly detected as X-ray
sources. The apparently low detection rate is in many cases related to the
substantial extinction of these brown dwarfs; considering only the BDs with
$A_V \leq 5$ mag, nearly half of the objects (7 out of 16) are detected in
X-rays. Our 10-day long X-ray lightcurves of these objects exhibit strong
variability, including numerous flares. While one of the objects was only
detected during a short flare, a statistical analysis of the lightcurves
provides evidence for continuous (`quiescent') emission in addition to flares
for all other objects. Of these, the $\sim$ M9 brown dwarf COUP 1255 = HC 212
is one of the coolest known objects with a clear detection of quiescent X-ray
emission. The X-ray properties (spectra, fractional X-ray luminosities, flare
rates) of these young brown dwarfs are similar to those of the low-mass stars
in the ONC, and thus there is no evidence for changes in the magnetic activity
around the stellar/substellar boundary, which lies at $\sim$ M6 for ONC
sources. Since the X-ray properties of the young brown dwarfs are also similar
to those of M6--M9 field stars, the key to the magnetic activity in very cool
objects seems to be the effective temperature, which determines the degree of
ionization in the atmosphere.


title:
Comments on the structure and dynamics of magnetic fields in stellar
  convection zones

abstract:
  This paper is a ``Habilitationsschrift'', a second thesis required until
recently by universities in Germany and in a few other countries to obtain the
right to lecture. It was accepted by the University of Goettingen in 1990 after
review by a number of german and international experts. Although the
introduction and the references represent the state of research in 1990, most
of the remaining content is still relevant and has never been published
elsewhere. The most important part is the derivation of a linear stability
formalism for thin magnetic flux tubes following an arbitrary path in a
gravitationally stratified medium with a stationary velocity. It was found
later (Ferriz-Mas & Schuessler, Geophys. Astrophys. Fluid Dyn. vol. 72, 209;
1995) that, for consistency, the inertial term in the equation of motion for
the external medium should be included in Eq. (3.24), which leads to an
additional term in the stability equations in the case of a spatially varying
external velocity. This term is missing in the present text, but can be easily
introduced into the formalism. The full abstract can be found at the beginning
of the paper.


title:
The First Detailed Abundances for M giants in Baade's Window from
  Infrared Spectroscopy

abstract:
  We report the first abundance analysis of 14 M giant stars in the Galactic
bulge, based on R=25,000 infrared spectroscopy (1.5-1.8um) using NIRSPEC at the
Keck II telescope. Because some of the bulge M giants reach high luminosities
and have very late spectral type, it has been suggested that they are the
progeny of only the most metal rich bulge stars, or possibly members of a
younger bulge population. We find the iron abundance and composition of the M
giants are similar to those of the K giants that have abundances determined
from optical high resolution spectroscopy: <[Fe/H]>=-0.190 +/- 0.020 with a
1-sigma dispersion of 0.08 +/- 0.015. Comparing our bulge M giants to a control
sample of local disk M giants in the Solar vicinity, we find the bulge stars
are enhanced in alpha elements at the level of +0.3 dex relative to the Solar
composition stars, consistent with other studies of bulge globular clusters and
field stars. This small sample shows no dependence of spectral type on
metallicity, nor is there any indication that the M giants are the evolved
members of a subset of the bulge population endowed with special
characteristics such as relative youth or high metallicity. We also find low
12C/13C < 10, confirming the prsence of extra-mixing processes during the red
gaint phase of evolution


title: The evolution of X-ray emission in young stars

abstract:
  We study the relation between age and magnetic activity in late-type pre-main
sequence (PMS) stars, for the first time using mass-stratified subsamples. The
effort is based on the Chandra Orion Ultradeep Project (COUP) which provides
very sensitive and homogenous X-ray data on a uniquely large sample of 481
optically well-characterized low-extinction low-mass members of the Orion
Nebula Cluster, for which individual stellar masses and ages could be
determined. More than 98 percent of the stars in this sample are detected as
X-ray sources. Within the PMS phase for stellar ages in the range $\sim 0.1-10$
Myr, we establish a mild decay in activity with stellar age $\tau$ roughly as
$L_{\rm X} \propto \tau^{-1/3}$. On longer timescales, when the Orion stars are
compared to main sequence stars, the X-ray luminosity decay law for stars in
the $0.5 < M < 1.2$ M$_\odot$ mass range is more rapid with $L_{\rm X} \propto
\tau^{-0.75}$ over the wide range of ages $5 < \log \tau < 9.5$ yr. The
magnetic activity history for M stars with masses $0.1 < M < 0.4 M_\odot$ is
distinctly different. Only a mild decrease in X-ray luminosity, and even a mild
increase in $L_{\rm X}/L_{\rm bol}$ and $F_{\rm X}$, is seen over the 1-100 Myr
range, though the X-ray emission does decay over long timescales on the main
sequence. Together with COUP results on the absence of a rotation-activity
relation in Orion stars, we find that the activity-age decay is strong across
the entire history of solar-type stars but is not attributable to rotational
deceleration during the early epochs. A combination of tachocline and
distributed convective dynamos may be operative in young solar-type stars. The
results for the lowest mass stars are most easily understood by the dominance
of convective dynamos during both the PMS and main sequence phases.


title: Rotation in Gravitational Lenses

abstract:
  Gravitational lensing deflects light. A single lens deflector can only shear
images, but cannot induce rotations. Multiple lens planes can induce rotations.
Such rotations can be observed in quadruply imaged sources, and can be used to
distinguish between two proposed solutions of the flux anomaly problem:
substructures in lensing galaxies vs large scale structure. We predict the
expected amount of rotation due to large scale structure in strong lensing
systems, and show how this effect can be measured using ~ mas VLBI astrometry
of quadruple lenses with extended source structures. The magnitude of rotation
is around one degree. The biggest theoretical uncertainty is the power spectrum
of dark matter on very small scales. This procedure can potentially be turned
around to measure the dark matter power spectrum on very small scales. We list
the predicted RMS rotation angles for several quadruple lenses with known lens
and source redshifts.


title: VLA 3.5 cm continuum sources in the Serpens cloud core

abstract:
  We present VLA 3.5 cm continuum observations of the Serpens cloud core. 22
radio continuum sources are detected. 16 out of the 22 cm sources are suggested
to be associated with young stellar objects (Class 0, Class I, flat-spectrum,
and Class II) of the young Serpens cluster. The rest of the VLA sources
plausibly are background objects. Most of the Serpens cm sources likely
represent thermal radio jets; on the other hand, the radio continuum emission
of some sources could be due to a gyrosynchroton mechanism arising from
coronally active young stars. The Serpens VLA sources are spatially distributed
into two groups; one of them located towards the NW clump of the Serpens core,
where only Class 0 and Class I protostars are found to present cm emission, and
a second group located towards the SE clump, where radio continuum sources are
associated with objects in evolutionary classes from Class 0 to Class II. This
subgrouping is similar to that found in the near IR, mid-IR and mm wavelength
regimes.


title: HS 0943+1404, a true intermediate polar

abstract:
  We have identified a new intermediate polar, HS 0943+1404, as part of our
ongoing search for cataclysmic variables in the Hamburg Quasar Survey. The
orbital and white dwarf spin periods determined from time-resolved photometry
and spectroscopy are Porb ~= 250 min and Pspin = 69.171 +- 0.001 min,
respectively. The combination of a large ratio Pspin/Porb ~= 0.3 and a long
orbital period is very unusual compared to the other known intermediate polars.
The magnetic moment of the white dwarf is estimated to be mu1 ~ 10^{34} G cm^3,
which is in the typical range of polars. Our extensive photometry shows that HS
0943+1404 enters into deep (~ 3 mag) low states, which are also a
characteristic feature of polars. We therefore suggest that the system is a
true ``intermediate'' polar that will eventually synchronise, that is, a
transitional object between intermediate polars and polars. The optical
spectrum of HS 0943+1404 also exhibits a number of unusual emission lines, most
noticeably NII 5680, which is likely to reflect enhanced nitrogen abundances in
the envelope of the secondary.


title: Primordial non-gaussianities from multiple-field inflation

abstract:
  We calculate the three-point correlation function evaluated at horizon
crossing for a set of interacting scalar fields coupled to gravity during
inflation. This provides the initial condition for the three-point function of
the curvature perturbation in the Sasaki--Stewart \delta N formulation. We find
that the effect is small, of the order of a slow-roll parameter, and that the
non-gaussianity can be determined on large scales once the unperturbed
background evolution is known. As an example of the use of our formalism, we
calculate the primordial non-gaussianity arising in a model of assisted
inflation.


title: The Molecular Accretion Flow in G10.6-0.4

abstract:
  We have observed the ultracompact HII region G10.6-0.4 with the VLA in 23 GHz
continuum and the NH3(3,3) inversion line. By analyzing the optical depth of
the line as well as the kinematics, we have detected a flattened, rotating,
molecular accretion flow. We detect the fact that the highest column density
gas is more flattened, that is, distributed more narrowly, than the lower
column density gas, and that there is some inclination of the rotation axis.
The rotation is sub-Keplerian, and the molecular gas is not in a rotationally
supported disk. We do not find a single massive (proto)star forming in a scaled
up version of low mass star formation. Instead, our observations suggest a
different mode of clustered massive star formation, in which the accretion flow
flattens but does not form an accretion disk. Also in this mode of star
formation the central object can be a group of massive stars rather than a
single massive star.


title:
Statistical characteristics of observed Ly-$\alpha$ forest and the shape
  of linear power spectrum

abstract:
  Properties of $\sim$ 6 000 Ly-$\alpha$ absorbers observed in 19 high
resolution spectra of QSOs are investigated using the model of formation and
evolution of DM structure elements based on the Zel'dovich theory. This model
asserts that absorbers are formed in the course of both linear and nonlinear
adiabatic or shock compression of dark matter (DM) and gaseous matter. It
allows us to link the column density and overdensity of DM and gaseous
components with the observed column density of neutral hydrogen, redshifts and
Doppler parameters of absorbers and demonstrates that at high redshifts we
observe a self similar period of structure evolution with the Gaussian initial
perturbations. We show that the colder absorbers are associated with rapidly
expanded regions of a galactic scale which represent large amplitude negative
density perturbations.
  We extend and improve the method of measuring the power spectrum of initial
perturbations proposed in Demia\'nski & Doroshkevich (2003b). Our method links
the observed separations and the DM column density of absorbers with the
correlation function of the initial velocity field. We recover the cold dark
matter (CDM) like power spectrum at scales 10> D > 0.15Mpc/h with a precision
of ~15%. However at scales $\sim 3 - 150 h^{-1}$kpc the measured and CDM--like
spectra are different. This result suggests a possible complex inflation with
generation of excess power at small scales.


title:
An Infalling Torus of Molecular Gas Around the Ultra-Compact HII Region
  G28.20-0.05

abstract:
  We present new observations of the ultra-compact HII region G28.20-0.05 in 23
GHz continuum, and the NH3(1,1), NH3(2.2), and NH3(3,3) lines. To explain the
complicated kinematics of the molecular gas, we propose a model consisting of
two components. One component is an infalling, equatorial torus of molecular
gas, whose dense central region has been ionized to form the ultra-compact HII
region. The second component is a larger expanding molecular shell driven by
some type of wide-angle outflow or wind. We estimate that the infall component
includes more than 18 Msun of molecular gas. We calculate the central mass to
be 79 Msun, probably comprising more than one star. The arrangement of the
molecular material suggests a connection to the other disk-like structures seen
around massive young stars. The central star in this case is more massive, and
the whole region may be more evolved than other similar objects such as IRAS
20126+4104, IRAS 18089-1732, G192.16-3.84, and AFGL5142.


title: Modelling the chromosphere and transition region of Epsilon Eri (K2 V)

abstract:
  Measurements of ultraviolet line fluxes from Space Telescope Imaging
Spectrograph and Far-Ultraviolet Spectroscopic Explorer spectra of the K2-dwarf
Epsilon Eri are reported. These are used to develop new emission measure
distributions and semi-empirical atmospheric models for the chromosphere and
lower transition region of the star. These models are the most detailed
constructed to date for a main-sequence star other than the Sun. New ionisation
balance calculations, which account for the effect of finite density on
dielectronic recombination rates, are presented for carbon, nitrogen, oxygen
and silicon. The results of these calculations are significantly different from
the standard Arnaud & Rothenflug ion balance, particularly for alkali-like
ions. The new atmospheric models are used to place constraints on possible
First Ionisation Potential (FIP) related abundance variations in the lower
atmosphere and to discuss limitations of single-component models for the
interpretation of certain optically thick line fluxes.


title: Probing dark matter caustics with weak lensing

abstract:
  Caustics are high-density structures that form frequently in collisionless
media. Under self-gravity, cold dark matter flows focus onto caustics which are
yet to be resolved in numerical simulations and or observed in the real world.
If detected, caustics would provide a strong evidence for dark matter and would
rule out alternative models such as those with modified dynamics. Here, we
demonstrate how they might be observed in the weak lensing data. We evaluate
the shear distortion and show that its radial profile is marked by a
characteristic sawtooth pattern due to the caustics in dark matter haloes that
form by selfsimilar accretion. We discuss the observational complications,
mainly due to the poor knowledge of the virial radii of the haloes and
demonstrate that a superposition of about 300 cluster-size haloes would give a
signal-to-noise ratio which is sufficiently large for the detection of caustics
with ground-based observations. This number is reduced to 100 for space-based
observations. These bounds can be easily achieved by the ongoing wide field
optical surveys such as CFHTLS and the future space-based projects SNAP and
DUNE which have to be accompanied by a X-ray follow-up of the selected clusters
for a precise determination of their virial radii.


title: The Dust Depletion and Extinction of the GRB 020813 Afterglow

abstract:
  The Keck optical spectrum of the GRB 020813 afterglow is the best ever
obtained for GRBs. Its large spectral range and very high S/N ratio allowed for
the first time the detection of a vast variety of absorption lines, associated
with the circumburst medium or interstellar medium of the host. The remarkable
similarity of the relative abundances of 8 elements with the dust depletion
pattern seen in the Galactic ISM suggests the presence of dust. The derived
visual dust extinction A_V=0.40+/-0.06 contradicts the featureless UV spectrum
of the afterglow, very well described by a unreddened power law. The
forthcoming Swift era will open exciting opportunities to explain similar
phenomena in other GRB afterglows.


title:
Numerical 3+1 general relativistic magnetohydrodynamics: a local
  characteristic approach

abstract:
  We present a general procedure to solve numerically the general relativistic
magnetohydrodynamics (GRMHD) equations within the framework of the 3+1
formalism. The work reported here extends our previous investigation in general
relativistic hydrodynamics (Banyuls et al. 1997) where magnetic fields were not
considered. The GRMHD equations are written in conservative form to exploit
their hyperbolic character in the solution procedure. All theoretical
ingredients necessary to build up high-resolution shock-capturing schemes based
on the solution of local Riemann problems (i.e. Godunov-type schemes) are
described. In particular, we use a renormalized set of regular eigenvectors of
the flux Jacobians of the relativistic magnetohydrodynamics equations. In
addition, the paper describes a procedure based on the equivalence principle of
general relativity that allows the use of Riemann solvers designed for special
relativistic magnetohydrodynamics in GRMHD. Our formulation and numerical
methodology are assessed by performing various test simulations recently
considered by different authors. These include magnetized shock tubes,
spherical accretion onto a Schwarzschild black hole, equatorial accretion onto
a Kerr black hole, and magnetized thick accretion disks around a black hole
prone to the magnetorotational instability.


title: Sh2-188: a model for a speedy PN

abstract:
  Sh2-188 is thought to be an ancient planetary nebula in the galactic disk. It
appears to be one-sided with recent observations revealing structure behind the
filamentary limb. We postulate that Sh2-188 is interacting with the ISM and
simulate it in terms of a ``triple-wind'' model comprising of the usual
``fast'' and ``slow'' interacting stellar winds plus the wind due to motion
through the ISM. We have run simulations at various velocities of the central
star relative to the ISM and find that a high velocity of 125 km/s best
approximates the observed structure. We also suggest that Sh2-188 is younger
than previously thought and that much of the mass lost on the AGB has been
swept downstream.


title:
Cluster Baryon Fraction and Structure from the Convergence/SZ Effect
  Diagram

abstract:
  The cross-correlation of Sunyaev-Zel'dovich effect (SZ) and weak-lensing
imaging surveys can be used to test how well hot baryons trace dark matter in
clusters of galaxies. We examine this concept using mock SZ and weak-lensing
surveys based on the forthcoming AMiBA experiment and generated from a
pre-heated cosmological N-body/hydrodynamic simulation. A cross-correlation
diagram between matched lensing convergence and Compton y maps exhibits
butterfly-wing-like structures, corresponding to individual clusters, that
encode rich information about the distributions of hot gas and dark matter.
When the cluster redshift and temperature are available the slope of a wing
reveals the cluster gas fraction and the width of the wing indicates how badly
the hot gas traces dark matter. On the basis of simulated data we discuss
systematic errors in the projected gas fraction estimates that would be
obtained from such survey comparisons.


title:
The Star Cluster Population of M51: III. Cluster disruption and
  formation history

abstract:
  In this work we concentrate on the evolution of the cluster population of the
interacting galaxy M51 (NGC 5194), namely the timescale of cluster disruption
and possible variations in the cluster formation rate. We present a method to
compare observed age vs. mass number density diagrams with predicted
populations including various physical input parameters like the cluster
initial mass function, cluster disruption, cluster formation rate and star
bursts. If we assume that the cluster formation rate increases at the moments
of the encounters with NGC 5195, we find an increase in the cluster formation
rate of a factor of 3, combined with a disruption timescale which is slightly
higher then when assuming a constant formation rate (t_4 = 200 Myr vs. 100
Myr). The measured cluster disruption time is a factor of 5 shorter than
expected on theoretical grounds. This implies that the disk of M51 is not a
preferred location for survival of young globular clusters, since even clusters
with masses of the order of 10^6 M_sun will be destroyed within a few Gyr.


title:
H-alpha Imaging of Early-type (Sa-Sab) Spiral Galaxies II. Global
  Properties

abstract:
  New results, based on one of the most comprehensive H-alpha imaging surveys
of nearby Sa-Sab spirals completed to date, reveals early-type spirals to be a
diverse group of galaxies that span a wide range in massive star formation
rates. While the majority of Sa-Sab galaxies in our sample are forming stars at
a modest rate, a significant fraction (~29%) exhibit star formation rates
greater than 1 M(solar/yr), rivaling the most prolifically star forming
late-type spirals. A similar diversity is apparent in the star formation
history of Sa-Sab spirals as measured by their H-alpha equivalent widths.
Consistent with our preliminary results presented in the first paper in this
series, we find giant HII regions (L(H-alpha)>10^{39}erg/s) in the disks of 37%
of early-type spirals. We suspect that recent minor mergers or past
interactions are responsible for the elevated levels of H-alpha emission and
perhaps, for the presence of giant HII regions in these galaxies.


title: A Spectroscopic Study of HL Canis Majoris

abstract:
  We present optical spectroscopy of the dwarf nova HL Canis Majoris over a
span of four years. The observations were made during standstill, outburst, and
quiescence. We determine an orbital period of 0.2167867 +/- 0.0000017 days,
based on radial velocities determined from H-alpha, H-beta, and He I 5876
emission. We also present equivalent widths of the spectral features in
outburst and in quiescence.


title:
The Absence of Extra-Tidal Structure in the Sculptor Dwarf Spheroidal
  Galaxy

abstract:
  The results of a wide-field survey of the Sculptor dwarf spheroidal galaxy
are presented. Our aims were to obtain an accurate map of the outer structure
of Sculptor, and to determine the level of interaction between this system and
the Galaxy. Photometry was obtained in two colours down to the magnitude limits
of V=20 and I=19, covering a 3.1 times 3.1 square deg area centred on Sculptor.
The resulting colour-magnitude data were used as a mask to select candidate
horizontal branch and red giant branch stars for this system. Previous work has
shown that the red horizontal branch (HB) stars are more concentrated than the
blue HB stars. We have determined the radial distributions of these two
populations and show that the overall Sculptor density profile is well
described by a two component model based on a combination of these radial
distributions. Additionally, spectra of the Ca ii triplet region were obtained
for over 700 candidate red giant stars over the 10 square deg region using the
2dF instrument on the Anglo-Australian Telescope. These spectra were used to
remove foreground Galactic stars based on radial velocity and Ca ii triplet
strength. The final list of Sculptor members contained 148 stars, seven of
which are located beyond the nominal tidal radius. Both the photometric and
spectroscopic datasets indicate no significant extra-tidal structure. These
results support at most a mild level of interaction between this system and the
Galaxy, and we have measured an upper mass limit for extra-tidal material to be
2.3 +/- 0.6% of the Sculptor luminous mass. This lack of tidal interaction
indicates that previous velocity dispersion measurements (and hence the amount
of dark matter detected) in this system are not strongly influenced by the
Galactic tidal field.


title:
Co-existence of Gravity and Antigravity: The Unification of Dark Matter
  and Dark Energy

abstract:
  Massive gravity with second and fourth derivatives is shown to give both
attractive and repulsive gravities. In contrast to the attractive gravity
correlated with the energy-momentum tensor, the repulsive gravity is related to
a fixed mass $m_x$, which equals a spin-dependent factor $f_\sigma$ times the
graviton mass. Therefore, particles with energy below $m_x$ are both dark
matter and dark energy: Their overall gravity is attractive with normal matter
but repulsive among themselves. Detailed analyses reveal that this unified dark
scenario can properly account for the observed dark matter/energy phenomena:
galaxy rotation curves, transition from early cosmic deceleration to recent
acceleration; and naturally overcome other dark scenarios' difficulties: the
substructure and cuspy core problems, the difference of dark halo distributions
in galaxies and clusters, and the cosmic coincidence. Very interestingly, Dirac
particles have $f_\sigma=1/\sqrt 2$, all bosonic matter particles have
$f_\sigma=0$, and the only exceptional boson is the graviton itself, which may
have $f_\sigma>1$.