title:
Emission and absorption lines of gamma-ray bursts affected by the
  relativistic motion of fireball ejecta

abstract:
  We display by numerical calculation how rest frame spectral lines appear in
the observed spectrum of gamma-ray bursts due to the Doppler effect in the
fireball framework. The analysis shows that: a) in the spectrum of a
relativistically expanding fireball, all rest frame lines would shift to higher
energy bands and would be significantly smoothed; b) rest frame weak narrow
emission lines as well as narrow absorption lines and absorption line forests
would be smoothed and would hardly be detectable; c) the features of rest frame
broad emission lines as well as both strong and weak broad absorption lines
would remain almost unchanged and therefore would be easier to detect; d) deep
gaps caused by rest frame broad absorption lines would be significantly filled;
e) a rest frame emission line forest would form a single broad line feature; f)
the observed relative width of the rest frame very narrow line would approach $
0.162$; g) when the Lorentz factor $\Gamma $ is large enough, the observed line
frequency $\nu_{line}$ and the rest frame line frequency $\nu_{0,line} $ would
be related by $\nu_{line}\approx 2\Gamma \nu_{0,line}$. We also investigate the
effect of time dependence of the line intensity and the effect of variation of
$\Gamma $. We find that the feature of rest frame dimming narrow emission lines
would disappear when $\Gamma $ is very large. The form of emission lines would
be sharp on both edges when $\Gamma $ varies with time. This phenomenon depends
not only on the initial Lorentz factor but also on the observation time.


title:
Characteristics of profiles of gamma-ray burst pulses associated with
  the Doppler effect of fireballs

abstract:
  In this paper, we derive in a much detail the formula of count rates, in
terms of the integral of time, of gamma-ray bursts in the framework of
fireballs, where the Doppler effect of the expanding fireball surface is the
key factor to be concerned. Effects arising from the limit of the time delay
due to the limited regions of the emitting areas in the fireball surface and
other factors are investigated. Our analysis shows that the formula of the
count rate of fireballs can be expressed as a function of $\tau $ which is the
observation time scale relative to the dynamical time scale of the fireball.
The profile of light curves of fireballs depends only on the relative time
scale, entirely independent of the real time scale and the real size of the
objects. It displays in detail how a cutoff tail, or a turn over, feature
(called a cutoff tail problem) in the decay phase of a light curve can be
formed. This feature is a consequence of a hot spot in the fireball surface,
moving towards the observer, and was observed in a few cases previously. By
performing fits to the count rate light curves of six sample sources, we show
how to obtain some physical parameters from the observed profile of the count
rate of GRBs. In addition, the analysis reveals that the Doppler effect of
fireballs could lead to a power law relationship between the $FWHM$ of pulses
and energy, which were observed previously by many authors.


title:
Radiatively driven electron-positron jets from two component accretion
  flows

abstract:
  Matter accreting onto black holes has long been known to have standing or
oscillating shock waves. The post-shock matter puffs up in the form of a torus,
which intercepts soft photons from the outer Keplerian disc and inverse
Comptonizes to produce hard photons. The post-shock region also produces jets.
We study the interaction of both hard photons and soft photons, with on-axis
electron-positron jets. We show that the radiation from post-shock torus
accelerates the flow to relativistic velocities, while that from the Keplerian
disc has marginal effect. We also show that, the velocity at infinity or
terminal velocity ${\vartheta}$, depends on the shock location in the disc.


title: Search for Southern-Hemisphere Giant Radio Galaxies with SALT

abstract:
  An extensive search for distant Giant radio galaxies on the southern
hemisphere is justified. We emphasize the crucial role of optical spectroscopy
in determination of their basic physical parameters, i.e. the distance,
projected linear size, volume of their lobes or cocoon, luminosity, etc., and
argue that SALT will be the best instrument for such a task.


title: Rapid Variations in V2275 Cyg (Nova Cyg 2001 #2)

abstract:
  We present time-resolved CCD photometry of V2275 Cyg 790 days after the nova
outburst. The data show a 20% peak-to-peak oscillation with a period of 24
minutes. The period appears stable over the two nights of observation, but QPO
can not be ruled out.


title: Chandra Observations of the X-ray Environs of SN 1998bw/GRB 980425

abstract:
  (Abrigded) We report X-ray studies of the environs of SN 1998bw and GRB
980425 using the Chandra X-Ray Observatory 1281 days after the GRB. Combining
our observation of the supernova with others of the GRB afterglow, a smooth
X-ray light curve, spanning ~1300 days, is obtained by assuming the burst and
supernova were coincident at 35.6 Mpc. When this X-ray light curve is compared
with those of the X-ray ``afterglows'' of ordinary GRBs, X-ray Flashes, and
ordinary supernovae, evidence emerges for at least two classes of lightcurves,
perhaps bounding a continuum. By three to ten years, all these phenomena seem
to converge on a common X-ray luminosity, possibly indicative of the supernova
underlying them all. This convergence strengthens the conclusion that SN 1998bw
and GRB 980425 took place in the same object. One possible explanation for the
two classes is a (nearly) standard GRB observed at different angles, in which
case X-ray afterglows with intermediate luminosities should eventually be
discovered. Finally, we comment on the contribution of GRB afterglows to the
ULX source population.


title: Dark Matter in the Local Galactic Disk

abstract:
  The existence of dark matter in the Galactic disk has been a topic of
significant debate, especially over the past two decades. Evidence for dark
matter in the disk, a component in addition to the now well-proven dark matter
halo, has been meticulously explored by analyzing the local disk density in the
solar neighborhood. Due to the extensiveness of this particular subfield of
astrophysics, the goal of this investigation is to gain a broad understanding
of the initial debates as well as general insight into some of the more recent
advances. The analysis of the most prominent participants in the debate
includes comparing and contrasting the methods, data, assumptions, as well as
the ultimate conclusions of each study. In particular, this discussion
introduces the significant and varied issues, such as systematic errors,
uncertainties, and selection effects in the data populations, relating to each
method of investigating the density and local structure in the solar
neighborhood of the Galactic disk. Furthermore, recent studies involved in the
determination of the ultimate conclusion to this quandary are also explored.


title: Molecular Gas & Star Formation in Nearby Galaxies

abstract:
  We review recent observations of molecular gas in nearby galaxies and their
implications for the star formation law on large (>1 kpc) scales.
High-resolution data provided by millimetre interferometers are now adding to
the basic understanding that has been provided by single-dish telescopes. In
particular, they confirm the good correlation between star formation rate (SFR)
and molecular gas surface densities, while at the same time revealing a greater
degree of heterogeneity in the CO distribution. Galaxies classified as SAB or
SB tend to show radial CO profiles that peak sharply in the inner ~20 arcsec,
indicative of bar-driven inflow. The observed Schmidt law index of ~1.5 may
result from a nearly linear relation between SFR and H_2 mass coupled with a
modest dependence of the molecular gas fraction on the total gas density. The
normalisation of the Schmidt law, giving the characteristic timescale for star
formation, may stem from the generic nature of interstellar turbulence.


title: A Search for Kinematic Evidence of Radial Gas Flows in Spiral Galaxies

abstract:
  CO and HI velocity fields of seven nearby spiral galaxies, derived from
radio-interferometric observations, are decomposed into Fourier components
whose radial variation is used to search for evidence of radial gas flows.
Additional information provided by optical or near-infrared isophotes is also
considered, including the relationship between the morphological and kinematic
position angles. To assist in interpreting the data, we present detailed
modeling that demonstrates the effects of bar streaming, inflow, and a warp on
the observed Fourier components. We find in all of the galaxies evidence for
either elliptical streaming or a warped disk over some range in radius, with
deviations from pure circular rotation at the level of ~20-60 km/s. Evidence
for kinematic warps is observed in several cases well inside R_{25}. No
unambiguous evidence for radial inflows is seen in any of the seven galaxies,
and we are able to place an upper limit of ~5-10 km/s (3-5% of the circular
speed) on the magnitude of any radial inflow in the inner regions of NGC 4414,
5033 and 5055. We conclude that the inherent non-axisymmetry of spiral galaxies
is the greatest limitation to the direct detection of radial inflows.


title:
Cosmic Hydrogen Was Significantly Neutral a Billion Years After the Big
  Bang

abstract:
  The ionization fraction of cosmic hydrogen, left over from the big bang,
provides crucial fossil evidence for when the first stars and quasar black
holes formed in the infant universe. Spectra of the two most distant quasars
known show nearly complete absorption of photons with wavelengths shorter than
the Ly-alpha transition of neutral hydrogen, indicating that hydrogen in the
intergalactic medium (IGM) had not been completely ionized at a redshift z~6.3,
about a billion years after the big bang. Here we show that the radii of
influence of ionizing radiation from these quasars imply that the surrounding
IGM had a neutral hydrogen fraction of tens of percent prior to the quasar
activity, much higher than previous lower limits of ~0.1%. When combined with
the recent inference of a large cumulative optical depth to electron scattering
after cosmological recombination from the WMAP data, our result suggests the
existence of a second peak in the mean ionization history, potentially due to
an early formation episode of the first stars.


title: The Evolution of Accreting Black Holes in Outburst

abstract:
  Black hole binaries exhibit dramatic changes in their X-ray spectral and
timing properties over time, providing important clues about the physical
processes that occur in these systems. Black holes and black hole candidates
are prime targets for RXTE with observational goals including the study of
extreme gravitational fields and jet formation mechanisms. The great wealth of
data from RXTE has helped us to learn about these systems as well as raising
new questions about accreting black holes. RXTE observations have allowed us to
study a wide range of black hole science topics including the connection
between the accretion disk and jets, the geometry of the inner accretion flow,
and the physical changes that occur between spectral states. In this
presentation, I discuss significant results on these topics that have been
obtained for persistent and transient black holes over the past several years,
and I present results from our program of X-ray and radio observations during
the decays of black hole transient outbursts.


title:
3C 345: The Historical Light Curve (1966-1991) from the digitized plates
  of the Asiago Observatory

abstract:
  In the frame of a large project to digitize the plate archives of the Italian
and Vatican Astronomical Observatory, we have already performed the
digitization of all available plates of the field of 3C345. The plates,
approximately 100, were taken with the three telescopes of the Asiago
Observatory (122 cm, 180 cm, 67/90 Schmidt Telescope) in the period from 1966
to 1991. Many of them were not analyzed till now, so we present here
essentially new data about the variability of 3C 345 and also of other six
quasars in the same field, in that period.


title: The Sunyaev-Zeldovich effect as a probe of the galaxy formation process

abstract:
  The Sunyaev-Zeldovich (SZ) effect has proven to be an extremely powerful tool
to study the physical and evolutionary properties of rich clusters of galaxies.
Upcoming SZ experiments, with their much improved sensitivity and angular
resolution, will provide unique information also on phases of galaxy evolution
characterized by the presence of large amounts of hot proto-galactic gas. We
present a preliminary analysis of the SZ signals that can be expected at the
collapse of the proto-galaxy when, according to the standard scenario, the gas
is heated at its virial temperature, and during episodes of strong energy
injections from the active nucleus. The contributions of such signals to excess
power on arc-minute scales recently found by CBI and BIMA experiments are
briefly discussed.


title: Discovery of an Ultracool White Dwarf Companion

abstract:
  The discovery of a low luminosity common proper motion companion to the white
dwarf GD392 at a wide separation of $46''$ is reported. $BVRI$ photometry
suggests a low temperature ($T_{\rm eff}\sim4000$ K) while $JHK$ data strongly
indicate suppressed flux at all near infrared wavelengths. Thus, GD392B is one
of the few white dwarfs to show significant collision induced absorption due to
the presence of photospheric ${\rm {H_2}}$ and the first ultracool white dwarf
detected as a companion to another star. Models fail to explain GD392B as a
normal mass white dwarf. If correct, the cool companion may be explained as a
low mass white dwarf or unresolved double degenerate. The similarities of
GD392B to known ultracool degenerates are discussed, including some possible
implications for the faint end of the white dwarf luminosity function.


title: The Sky Polarization Observatory

abstract:
  SPOrt is an ASI-funded experiment specifically designed to measure the sky
polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be
flown on the International Space Station. Starting in 2006 and for at least 18
months, it will be taking direct and simultaneous measurements of the Stokes
parameters Q and U at 660 sky pixels, with FWHM=7 degrees. Due to development
efforts over the past few years, the design specifications have been
significantly improved with respect to the first proposal. Here we present an
up-to-date description of the instrument, which now warrants a pixel
sensitivity of 1.7 microK for the polarization of the cosmic background
radiation, assuming two years of observations. We discuss SPOrt scientific
goals in the light of WMAP results, in particular in connection with the
emerging double-reionization cosmological scenario.


title:
NLTE models of line-driven stellar winds I. Method of calculation and
  first results for O stars

abstract:
  New numerical models of line-driven stellar winds of late O stars are
presented. Statistical equilibrium (NLTE) equations of the most abundant
elements are solved. Properly obtained occupation numbers are used to calculate
consistent radiative force and radiative heating terms. Wind density, velocity
and temperature are calculated as a solution of model hydrodynamical equations.
Contrary to other published models we account for a multicomponent wind nature
and do not simplify the calculation of the radiative force (e.g. using force
multipliers). We discuss the convergence behaviour of our models. The ability
of our models to predict correct values of mass-loss rates and terminal
velocities of selected late O stars (mainly giants and supergiants) is
demonstrated. The systematic difference between predicted and observed terminal
velocities reported in the literature has been removed. Moreover, we found good
agreement between the theoretical wind momentum-luminosity relationship and the
observed one for Cyg OB2 supergiants.


title: Likelihood analysis of the Local Group acceleration revisited

abstract:
  We reexamine likelihood analyzes of the Local Group (LG) acceleration, paying
particular attention to nonlinear effects. Under the approximation that the
joint distribution of the LG acceleration and velocity is Gaussian, two
quantities describing nonlinear effects enter these analyzes. The first one is
the coherence function, i.e. the cross-correlation coefficient of the Fourier
modes of gravity and velocity fields. The second one is the ratio of velocity
power spectrum to gravity power spectrum. To date, in all analyzes of the LG
acceleration the second quantity was not accounted for. Extending our previous
work, we study both the coherence function and the ratio of the power spectra.
With the aid of numerical simulations we obtain expressions for the two as
functions of wavevector and \sigma_8. Adopting WMAP's best determination of
\sigma_8, we estimate the most likely value of the parameter \beta and its
errors. As the observed values of the LG velocity and gravity, we adopt
respectively a CMB-based estimate of the LG velocity, and Schmoldt et al.'s
(1999) estimate of the LG acceleration from the PSCz catalog. We obtain \beta =
0.66^{+0.21}_{-0.07}; thus our errorbars are significantly smaller than those
of Schmoldt et al. This is not surprising, because the coherence function they
used greatly overestimates actual decoherence between nonlinear gravity and
velocity.


title:
The X-ray and radio emission from SN 2002ap: The importance of Compton
  scattering

abstract:
  The radio and X-ray observations of the Type Ic supernova SN 2002ap are
modeled. We find that inverse Compton cooling by photospheric photons explains
the observed steep radio spectrum, and also the X-ray flux observed by XMM.
Thermal emission from the shock is insufficient to explain the X-ray flux. The
radio emitting region expands with a velocity of, roughly, 70,000 km/s. From
the ratio of X-ray to radio emission we find that the energy densities of
magnetic fields and relativistic electrons are close to equipartion.


title:
Parameter properties and stellar population of the old open cluster NGC
  3960

abstract:
  We present a $BVI$ photometric and astrometric catalogue of the open cluster
NGC 3960, down to limiting magnitude $V\sim22$, obtained from observations
taken with the Wide Field Imager camera at the MPG/ESO 2.2 m Telescope at La
Silla. The photometry of all the stars detected in our field of view has been
used to estimate a map of the strong differential reddening affecting this
area. Our results indicate that, within the region where the cluster dominates,
the $E(V-I)$ values range from 0.21 up to 0.78, with $E(V-I)=0.36$
($E(B-V)=0.29$) at the nominal cluster centroid position; color excesses
$E(V-I)$ up to 1 mag have been measured in the external regions of the field of
view where field stars dominate. The reddening corrected color-magnitude
diagram (CMD) allows us to conclude that the cluster has an age between 0.9 and
1.4 Gyr and a distance modulus of $(V-M_V)_0=11.35$.
  In order to minimize field star contamination, their number has been
statistically subtracted based on the surface density map. The empirical
cluster main sequence has been recovered in the $V$ vs. $V-I$ and in the $J$
vs. $J-K_S$ planes, using optical and infrared data, respectively. From these
empirical cluster main sequences, two samples of candidate cluster members were
derived in order to obtain the luminosity distributions as a function of the
$V$ and $J$ magnitudes. The Luminosity Functions have been transformed into the
corresponding Mass Functions; for $M>1 M_\odot$, the two distributions have
been fitted with a power law of index $\alpha_V=2.95\pm0.53$ and
$\alpha_J=2.81\pm0.84$ in $V$ and in $J$, respectively, while the Salpeter Mass
Function in this notation has index $\alpha=2.35$.


title: How many cosmological parameters?

abstract:
  Constraints on cosmological parameters depend on the set of parameters chosen
to define the model which is compared with observational data. I use the Akaike
and Bayesian information criteria to carry out cosmological model selection, in
order to determine the parameter set providing the preferred fit to the data.
Applying the information criteria to the current cosmological data sets
indicates, for example, that spatially-flat models are statistically preferred
to closed models, and that possible running of the spectral index has lower
significance than inferred from its confidence limits. I also discuss some
problems of statistical assessment arising from there being a large number of
`candidate' cosmological parameters that can be investigated for possible
cosmological implications, and argue that 95% confidence is too low a threshold
to robustly identify the need for new parameters in model fitting. The best
present description of cosmological data uses a scale-invariant (n=1) spectrum
of gaussian adiabatic perturbations in a spatially-flat Universe, with the
cosmological model requiring only five fundamental parameters to fully specify
it.


title: Confusion noise at far-IR to millimeter wavelengths

abstract:
  We present detailed predictions for the confusion noise due to extragalactic
sources in the far-IR/(sub)-millimeter channels of ESA/ISO, NASA/Spitzer,
ESA/Herschel and ESA/Planck satellites, including the contribution from
clustering of unresolved SCUBA galaxies. Clustering is found to increase the
confusion noise, compared to the case of purely Poisson fluctuations, by 10-15%
for the lowest frequency (i.e. lowest angular resolution) Spitzer and Herschel
channels, by 25-35% for the 175 micron ISOPHOT channel, and to dominate in the
case of Planck/HFI channels at nu>143GHz. Although our calculations make use of
a specific evolutionary model (Granato et al. 2004), the results are strongly
constrained by the observed counts and by data on the redshift distribution of
SCUBA sources, and therefore are not expected to be heavily model dependent.
The main uncertainty arises from the poor observational definition of the
source clustering properties. Two models have been used for the latter: a
power-law with constant slope and a redshift-independent comoving correlation
length,r_0, and the standard theoretical model for clustering evolution in a
LambdaCDM universe, with a redshift-dependent bias factor. In both cases, the
clustering amplitude has been normalized to yield a unit angular correlation
function at theta_0=1-2 arcsec for 850 micron sources fainter than 2 mJy,
consistent with the results by Peacock et al. (2000). This normalization
yields, for the first model, r_0=8.3$ Mpc/h, and, for the second model, an
effective mass of dark matter haloes in which these sources reside of
M_halo=1.8*10^{13} M_sun/h. These results are consistent with independent
estimates for SCUBA galaxies and for other, likely related, sources.


title:
Digitatio and Scientific Exploitation of the Italian and Vatican
  Astronomical Plate Archives

abstract:
  There is a widespread interest to digitize the precious information contained
in the astronomical plate archives, both for the preservation of their content
and for its fast distribution to all interested researchers in order to achieve
their better scientific exploitation. This paper presents the first results of
our large-scale project to digitize the archive of plates of the Italian
Astronomical Observatories and of the Specola Vaticana. Similar systems,
composed by commercial flat-bed retro-illuminated scanners plus dedicated
personal computers and acquisition and analysis software, have been installed
in all participating Institutes. Ad-hoc codes have been developed to acquire
the data, to test the suitability of the machines to our scientific needs, and
to reduce the digital data in order to extract the astrometric, photometric and
spectroscopic content. Two more elements complete the overall project: the
provision of high quality BVRI CCD sequences in selected fields with the Campo
Imperatore telescopes, and the distribution of the digitized information to all
interested researchers via the Web. The methods we have derived in the course
of this project have been already applied successfully to plates taken by other
Observatories, for instance at Byurakan and at Hamburg.


title: Close binary EHB stars from SPY

abstract:
  We present the results of a radial velocity (RV) survey of 46 subdwarf B
(sdB) and 23 helium-rich subdwarf O (He-sdO) stars. We detected 18 (39%) new
sdB binary systems, but only one (4%) He-sdO binary. Orbital parameters of nine
sdB and sdO binaries, derived from follow-up spectroscopy, are presented. Our
results are compared with evolutionary scenarios and previous observational
investigations.


title: Detections of Warm-Hot Intergalactic Medium

abstract:
  Several popular cosmological models predict that most of the baryonic mass in
the local universe is located in filamentary and sheet-like structures
associated with groups and clusters of galaxies. This gas is expected to be
gravitationally heated to ~10^6 K and therefore emitting in the soft X-rays. We
have investigated three fields with large scale structures of galaxies at
redshifts 0.1, 0.45, 0.79 and found signatures of warm-hot thermal emission
(kT< 1 keV) correlated with the distribution of galaxies for the first two. The
correlation and the properties of both X-ray and galaxy distribution strongly
suggest that the diffuse X-ray flux is due to extragalactic emission by the
Warm-Hot Intergalactic Medium (WHIM) predicted by cosmological models.


title:
GaBoDS: The Garching-Bonn Deep Survey -- II. Confirmation of EIS cluster
  candidates by weak gravitational lensing

abstract:
  We report the first confirmation of colour-selected galaxy cluster candidates
by means of weak gravitational lensing. Significant lensing signals were
identified in the course of the shear-selection programme of dark matter haloes
in the Garching-Bonn Deep Survey, which currently covers 20 square degrees of
deep, high-quality imaging data on the southern sky. The detection was made in
a field that was previously covered by the ESO Imaging Survey (EIS) in 1997. A
highly significant shear-selected mass-concentration perfectly coincides with
the richest EIS cluster candidate at z~0.2, thus confirming its cluster nature.
Several other shear patterns in the field can also be identified with cluster
candidates, one of which could possibly be part of a filament at z~0.45.


title: Complexity in cosmic structures

abstract:
  We discuss correlation properties of a general mass density field introducing
a classification of structures based on their complexity. Standard cosmological
models for primordial mass fluctuations are characterized by a sort of
large-scale stochastic order, that we call super-homogeneity to highlight the
fact that mass fluctuations increase as a function of scale in the slowest
possible way for any stochastic mass field. On the other hand the galaxy
spatial distribution show complex structures with a high degree of
inhomogeneity and fractal-like spatial correlations up to some relevant
cosmological scale. The theoretical problem of cosmological structure formation
should then explain the growth of strongly correlated and non-linear structures
from the very uniform field of density fluctuations given as standard initial
condition.


title:
Diagnostics of Neutron Star and Black Hole X-Ray Binaries with X-Ray
  Shot Widths

abstract:
  A statistic w, the differential coefficient of the mean absolute difference
of an observed lightcurve, is proposed for timescale analysis of shot widths.
The shortest width of random shots can be measured by the position of the lower
cut-off in the timescale spectrum of w. We use the statistic to analyze X-ray
lightcurves from a sample of neutron star and black hole binaries and the
results show that the timescale analysis can help us distinguish between
neutron star binaries and black hole binaries. The analysis can further reveal
the structure and dynamics of accretion disks around black holes.


title: The CMBR fluctuations from HI perturbations prior to reionization

abstract:
  Loeb and Zaldarriaga (2003) have recently proposed that observations of the
CMBR brightness temperature fluctuations produced by the HI inhomogeneities
prior to reionization hold the promise of probing the primordial power spectrum
to a hitherto unprecedented level of accuracy. This requires a precise
quantification of the relation between density perturbations and brightness
temperature fluctuations. Brightness temperature fluctuations arise from two
sources (1.) fluctuations in the spin temperature, and (2.) fluctuations in the
HI optical depth, both of which are caused by density perturbations. For the
spin temperature, we investigate in detail its evolution in the presence of HI
fluctuations. For the optical depth, we find that it is affected by density
perturbations both directly and through peculiar velocities which move the
absorption features around in frequency. The latter effect, which has not been
included in earlier studies, is similar to the redshift space distortion seen
in galaxy surveys and this can cause changes of 50% or more in the birghtness
temperature fluctuations.


title: Observational constraints on dark energy model

abstract:
  The recent observations support that our universe is flat and expanding with
acceleration. A quintessence model with a general relation between the
quintessence potential and the quintessence kinetic energy was proposed to
explain the phenomenon. The dark energy potential includes both the hyperbolic
and the double exponential potentials. We analyze this model in detail by using
the recent supernova and the first year Wilkinson Microwave Anisotropy Probe
(WMAP) observations. For a flat universe dominated by a dark energy with
constant $\omega$ which is a special case of the general model, we find that
$\Omega_{\rm m0}=0.30^{+0.06}_{-0.08}$ and $\omega_{\rm Q}\le -0.82$, and the
turnaround redshift $z_{\rm T}$ when the universe switched from the
deceleration phase to the acceleration phase is $z_{\rm T}=0.65$. For the
general model, we find that $\Omega_{\rm m0}\sim 0.3$, $\omega_{\rm Q0}\sim
-1.0$, $\beta\sim 0.5$ and $z_{\rm T}\sim 0.67$. A model independent polynomial
parameterization is also considered, the best fit model gives $\Omega_{\rm
m0}=0.40\pm 0.14$, $\omega_{\rm Q0}=-1.4$ and $z_{\rm T}=0.37$.


title:
Ultrafast studies on the photophysics of matrix-isolated radical cations
  of polycyclic aromatic hydrocarbons: implications for the Diffuse
  Interstellar Bands (DIB) problem

abstract:
  Rapid, efficient deactivation of the photoexcited PAH cations accounts for
their remarkable photostability and have important implications for
astrochemistry, as these cations are the leading candidates for the species
responsible for the diffuse interstellar bands (DIB) observed throughout the
Galaxy.Ultrafast relaxation dynamics for photoexcited PAH cations isolated in
boric acid glass have been studied using femtosecond and picosecond transient
grating spectroscopy. With the exception of perylene+, the recovery kinetics
for the ground doublet (D0) states of these radical cations are biexponential,
containing a fast (< 200 fs) and a slow (3-20 ps) components. No temperature
dependence or isotope effect was observed for the fast component, whereas the
slow component exhibits both the H/D isotope effect (1.1-1.3) and strong
temperature dependence (15 to 300 K). We suggest that the fast component is due
to internal Dn to D0 conversion and the slow component is due to vibrational
energy transfer (VET) from a hot D0 state to the glass matrix.


title: The Physics of X-ray Emission from Accreting Millisecond Pulsars

abstract:
  By analyzing the Rossi X-ray Timing Explorer data on SAX J1808.4-3658 we show
that the X-ray emission in accretion powered millisecond pulsars can be
produced by Comptonization in a hot slab (radiative shock) of Thomson optical
depth tau~1 at the neutron star surface. The escaping radiation consists of two
components: a black body and a hard Comptonized tail. These components have
very different angular distribution: the black body peaks along the slab normal
(a ``pencil''--like emission pattern), while the tail has a broader angular
distribution (a ``fan''--like pattern). This results in very different
variability properties. We construct a detailed model of the X-ray production
accounting for the Doppler boosting, relativistic aberration and gravitational
light bending. We are able to reproduce the pulse profiles at different
energies, corresponding phase lags, as well as the time-averaged spectrum. We
obtain constraints on the neutron star radius: R~11 km if its mass M=1.6 Msun,
and R~8.5 km if M=1.4 M_sun. We present simple analytical formulae for
computing the light curves and oscillation amplitudes expected from hot spots
in X-ray bursters and accretion powered millisecond pulsars. We also propose an
analytical expression that can be used to determine the size of the black body
emission region from the observed properties.


title: Water masers in dusty environments

abstract:
  We study in details a pumping mechanism for the lambda=1.35 cm maser
transition 6_16 -> 5_23 in ortho-water based on the difference between gas and
dust temperatures. The upper maser level is populated radiatively through 4_14
-> 5_05 and 5_05 -> 6_16 transitions. The heat sink is realized by absorbing
the 45 mum photons, corresponding to the 5_23 -> 4_14 transition, by cold dust.
We compute the inversion of maser level populations in the optically thick
medium as a function of the hydrogen concentration, the gas-to-dust mass ratio,
and the difference between the gas and the dust temperatures. The main results
of numerical simulations are interpreted in terms of a simplified four-level
model. We show that the maser strength depends mostly on the product of
hydrogen concentration and the dust-to-water mass ratio but not on the size
distribution of the dust particles or their type. We also suggest approximate
formulae that describe accurately the inversion and can be used for fast
calculations of the maser luminosity. Depending on the gas temperature, the
maximum maser luminosity is reached when the water concentration N_water ~
10^6-10^7 cm^-3 times the dust-to-hydrogen mass ratio, and the inversion
completely disappears at density just an order of magnitude larger. For the
dust temperature of 130 K, the 6_16 -> 5_23 transition becomes inverted already
at the temperature difference of Delta T ~1 K, while other possible masing
transitions require a larger Delta T > 30 K. We identify the region of the
parameter space where other ortho- and para-water masing transitions can
appear.


title:
The effect of metallicity on the Cepheid Period-Luminosity relation from
  a Baade-Wesselink analysis of Cepheids in the Galaxy and in the Small
  Magellanic Cloud

abstract:
  (ABRIDGED) We have applied the near-IR Barnes-Evans realization of the
Baade-Wesselink method as calibrated by Fouque & Gieren (1997) to five
metal-poor Cepheids with periods between 13 and 17 days in the Small Magellanic
Cloud as well as to a sample of 34 Galactic Cepheids to determine the effect of
metallicity on the period-luminosity (P-L) relation. For ten of the Galactic
Cepheids we present new accurate and well sampled radial-velocity curves. The
Baade-Wesselink analysis provides accurate individual distances and
luminosities to the Cepheids in the two samples, allowing us to constrain
directly, in a purely differential way, the metallicity effect on the Cepheid
P-L relation. For the Galactic Cepheids we provide a new set of P-L relations
which have zero-points in excellent agreement with astrometric and
interferometric determinations. These relations can be used directly for the
determination of distances to solar-metallicity samples of Cepheids in distant
galaxies, circumventing any corrections for metallicity effects on the
zero-point and slope of the P-L relation. We find evidence for both such
metallicity effects in our data. Comparing our two samples of Cepheids at a
mean period of about 15 days, we find a weak effect of metallicity on the
luminosity similar to that adopted by the HST Key Project on the Extragalactic
Distance Scale.


title: Evolution of Spectral States of Aql X-1 during the 2000 Outburst

abstract:
  We present the results of detailed analysis of X-ray data in 3-20 keV range
from a ~70 day outburst of the neutron star transient Aquila X-1 during
September-November 2000. Optical monitoring with the YALO 1m telescope was used
to trigger X-ray observations with Rossi X-ray Timing Explorer (RXTE) in order
to follow the outburst from a very early stage. In this paper we discuss the
correlated evolution in time of features in the spectral and temporal domains,
for the entire outburst. The state transition from low/hard state to high/soft
state during the rise of the outburst occurs at higher luminosity than the
transition back to low/hard state during the decay, as has also been observed
in other outbursts. Fourier power spectra at low frequencies show a broken
power law continuum during the rising phase, with the break frequency
increasing with time. During the decline from maximum the source evolves to a
position in the hardness-intensity plane as well as in the color-color diagram
which is similar to, but distinct from, the canonical high/soft state. High
frequency quasi-periodic oscillations from 636-870 Hz were seen only during
this transitional state.


title: What We Know and What We Don't Know About the Universe

abstract:
  I present a non-technical and necessarily biased and incomplete overview of
our present understanding of the physical universe and its constituents,
emphasizing what we have learned from the explosive growth in cosmological and
astrophysical data acquisition and some of the key open questions that remain.
The topics are organized under the labels space, time, and matter. Most
bibliographical references are for the non-expert.


title: Pacman (I): A new Algorithm to calculate Faraday Rotation Maps

abstract:
  We propose a new method to calculate Faraday rotation measure maps from
multi-frequency polarisation angle data. In order to solve the so called n-pi
ambiguity problem which arises from the observationally ambiguity of the
polarisation angle which is only determined up to additions of +-n*pi, where n
is an integer, we suggest using a global scheme. Instead of solving the n-pi
ambiguity for each data point independently, our algorithm, which we chose to
call "Pacman" (Polarisation Angle Correcting rotation Measure ANalysis), solves
the n-pi ambiguity for a high signal-to-noise region ``democratically'' and
uses this information to assist computations in adjacent low signal-to-noise
areas.


title: Tracing the formation of massive spheroids from high-z galaxy clustering

abstract:
  The high-z progenitors of local massive early-type galaxies should be
characterized by a strong level of clustering, larger than that measured for
z=3 Lyman Break Galaxies and comparable to that of z~1 EROs. First possible
evidences for such strongly clustered objects at z~2 were found by the FIRES
and K20 surveys, that have identified new classes of faint high-z K-selected
galaxies. Some details are given here for the new population of massive
star-forming galaxies at z~2, found by the K20 survey in the GOODS-South area.
Because of their much redder UV continuum, most of these galaxies would not be
selected by the Lyman Break criterion. Such objects are good candidates for the
precursors of local ellipticals caught in their formation phase. We have
calibrated a two color criterion to allow the identification of these highest
redshift galaxies in bright K-limited samples.


title:
Pacman (II): Application and Statistical Characterisation of Improved RM
  Maps

abstract:
  We proposed a new method -- "Pacman" -- to calculate Faraday rotation measure
(RM) maps from multi-frequency polarisation angle data (Dolag et al.) in order
to avoid the so-called n-pi ambiguity. Here, we apply our "Pacman" algorithm to
two polarisation data sets of extended radio sources in the Abell 2255 and the
Hydra A cluster, and compare the RM maps obtained using "Pacman" to RM maps
obtained employing already existing methods. Thereby, we provide a new high
quality RM map of the Hydra north lobe which is in a good agreement with the
existing one but find significant differences in the case of the south lobe of
Hydra A. We demonstrate the reliability and the robustness of "Pacman". In
order to study the influence of map making artefacts, which are imprinted by
wrong solutions to the n-pi ambiguities, and of the error treatment of the
data, we calculated and compared magnetic field power spectra from various RM
maps. The power spectra were derived using the method recently proposed by
Ensslin & Vogt (2003). We demonstrate the sensitivity of statistical analysis
to artefacts and noise in the RM maps and thus, we demonstrate the importance
of an unambiguous determination of RM maps and an understanding of the nature
of the noise in the data. We introduce and perform statistical tests to
estimate the quality of the derived RM maps, which demonstrate the quality
improvements due to "Pacman".


title: Northern Sky Variability Survey (NSVS): Public data release

abstract:
  The Northern Sky Variability Survey (NSVS) is a temporal record of the sky
over the optical magnitude range from 8 to 15.5. It was conducted in the course
of the first generation Robotic Optical Transient Search Experiment (ROTSE-I)
using a robotic system of four co-mounted unfiltered telephoto lenses equipped
with CCD cameras. The survey was conducted from Los Alamos, NM, and primarily
covers the entire northern sky. Some data in southern fields between
declinations 0 and -38 deg is also available, although with fewer epochs and
noticeably lesser quality. The NSVS contains light curves for approximately 14
million objects. With a one year baseline and typically 100-500 measurements
per object, the NSVS is the most extensive record of stellar variability across
the bright sky available today. In a median field, bright unsaturated stars
attain a point to point photometric scatter of ~0.02 mag and position errors
within 2 arcsec. At Galactic latitudes |b| < 20 deg the data quality is limited
by severe blending due to ~14 arcsec pixel size. We present basic
characteristics of the data set and describe data collection, analysis, and
distribution. All NSVS photometric measurements are available for on-line
public access from the Sky Database for Objects in Time-Domain (SkyDOT;
http://skydot.lanl.gov) at LANL. Copies of the full survey photometry may also
be requested on tape.


title:
The Globular Cluster System of NGC 1399: III. VLT Spectroscopy and
  Database

abstract:
  Radial velocities of 468 globular clusters around NGC 1399, the central
galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask
Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest sample
of globular cluster velocities around any galaxy obtained so far. The mean
velocity uncertainty is 50 km/sec. This data sample is accurate and large
enough to be used in studies of the mass distribution of NGC 1399 and the
properties of its globular cluster system. Here we describe the observations,
the reduction procedure, and discuss the uncertainties of the resulting
velocities. The complete sample of cluster velocities which is used in a
dynamical study of NGC 1399 is tabulated. A subsample is compared with
previously published values.


title:
Wide-field millimagnitude photometry with HAT: A Tool for Extra-solar
  Planet Detection

abstract:
  We discuss the system requirements for obtaining millimagnitude photometric
precision over a wide field using small aperture short focal length telescope
systems, such as are being developed by a number of research groups to search
for transiting extra-solar planets. We describe the Hungarian-made Automated
Telescope (HAT) system which attempts to meet these requirements. The
attainable precision of HAT has been significantly improved by a technique in
which the telescope is made to execute small pointing steps during each
exposure so as to broaden the effective point spread function of the system to
a value more compatible with the pixel size of our CCD detector. Experiments
during a preliminary survey (Spring 2003) of two star fields with the HAT-5
instrument allowed us to optimize the HAT photometric precision using this
method of PSF broadening; in this way have been able to achieve a precision as
good as 2 millimagnitudes on brighter stars. We briefly describe development of
a network of HAT telescopes (HATnet) spaced in longitude.


title: KELT: The Kilodegree Extremely Little Telescope

abstract:
  Transits of bright stars offer a unique opportunity to study detailed
properties of extrasolar planets that cannot be determined through
radial-velocity observations. We propose a technique to find such systems using
all-sky small-aperture transit surveys. The optimal telescope design for
finding transits of bright stars is a 5 cm ``telescope'' with a 4k x 4k camera.
We are currently building such a system and expect to detect ~10 bright star
transits after one year of operation.


title:
The Link between Warm Molecular Disks in Maser Nuclei and Star Formation
  near the Black Hole at the Galactic Center

abstract:
  The discovery of hundreds of young, bright stars within a parsec from the
massive black hole at the center of the Galaxy presents a challenge to star
formation theories. The requisite Roche densities for the gravitational
collapse of gas clouds are most naturally achieved in accretion disks. The
water maser sources in Keplerian rotation in the nuclei of NGC4258, NGC1068,
and the Circinus galaxy indicate the presence of warm, extended, molecular
accretion disks around black holes similar in mass to the one at the Galactic
center. Here we argue that the current conditions in the maser nuclei, and
those near the Galactic center, represent two consecutive, recurrent phases in
the life cycle of the nucleus of a typical gas-rich spiral bulge. The warm
molecular disks that give rise to the observed maser emission fragment into
stellar-size objects. The stellar masses, their orbital geometry, and the total
number of stars thus formed are consistent with the values identified at the
Galactic center. The stars tend to form in compact groups resembling the IRS 13
complex that dominates the stellar light in the neighborhood of the black hole.


title: X-ray Flaring Activity of Mrk 421

abstract:
  We report results from a systematic search for X-ray flares from Mrk 421,
using archival data from the Rossi X-ray Timing Explorer (RXTE) satellite. The
flares are clearly seen over a wide range of timescales. The quasi-continuous
coverage of the source with the All-Sky Monitor (ASM) reveals frequent
occurrence of major flares that last for months. On a few occasions, the source
was intensively monitored with the more sensitive pointing instruments aboard
RXTE. The data from these observations shows the presence of X-ray flares of
much shorter durations, ranging from weeks down to less than an hour. For the
first time, we clearly resolved the sub-hour flares from Mrk 421. Moreover,
Fourier analyses reveal variability on even shorter timescales, up to about
0.01 Hz. The source appears to behave differently in its spectral properties
during different flares, large or small, which is intriguing. While significant
hysteresis is observed to be associated with spectral evolution in some cases,
little is seen in other cases. Sometimes, the shape of the X-ray spectrum
hardly varies across a flare. Therefore, the phenomenology is complex. The
observed hierarchical structure of the X-ray flares seems to imply the
scale-invariant nature of the phenomenon, perhaps similar to solar flares or
rapid X-ray flares observed of stellar-mass black holes in this regard.
Combined with other results, the observed flaring timescales seriously
constrain the physical properties of X-ray emitting regions in the jets of Mrk
421.


title:
A transition to a low/soft state in the ultra-luminous compact X-ray
  source Holmberg II X-1

abstract:
  We present three XMM-Newton observations of the ultra-luminous compact X-ray
source Holmberg II X-1 in its historical brightest and faintest states. The
source was in its brightest state in April 2002 with an isotropic X-ray
luminosity of 2e40 erg/s but changed to a peculiar low/soft state in September
2002 in which the X-ray flux dropped by a factor of four and the spectrum
softened. In all cases, a soft excess component, which can be described by a
simple or multicolor disk blackbody (MCD; kT = 120-170 eV), is statistically
required in addition to a power-law continuum (Gamma = 2.4 - 2.9). Both the
spectral components became weaker and softer in the low/soft state, however,
the dramatic variability is seen in the power-law component. This spectral
transition is opposite to the `canonical' high/soft -- low/hard transitions
seen in many Galactic black hole binaries. There is possible contribution from
an optically thin thermal plasma. When this component is taken into account,
the spectral transition appears to be normal -- a drop of the power-law flux
and slightly softer blackbody component in the low state.


title: The Formation of Cataclysmic Variables with Brown Dwarf Secondaries

abstract:
  The present-day formation of cataclysmic variables (CVs) with brown dwarf
(BD) secondaries (0.013 M_sun < M_sec < 0.075 M_sun) is investigated using a
population synthesis technique. Results from the latest, detailed models for
BDs have been incorporated into the population synthesis code. For our models,
we find that ZACVs with BD secondaries have orbital periods in the range 46 min
to 2.5 hrs. We also find that ZACVs with BD secondaries comprise 18% of the
total, present-day ZACV population. In addition, we find that 80% of ZACVs with
BD secondaries have orbital periods < 78 minutes. This implies that 15% of the
present-day ZACV population should have orbital periods shorter than the
observed orbital period minimum for CVs. We also investigate the dependence of
the present-day formation rate of CVs with BD secondaries on the assumed value
of the common envelope efficiency parameter, alpha_CE, for three different
assumed mass ratio distributions in ZAMS binaries. Surprisingly, we find that
the common envelope process must be extremely inefficient (alpha_CE < 0.1) in
order for CVs with BD secondaries not to be formed. Finally, we find that the
progenitor binaries of ZACVs with BD secondaries have ZAMS orbital separations
< 3 AU and ZAMS primary masses between ~1-10 M_sun, with ~75% of the primary
masses less than ~1.6 M_sun. Interestingly, these ranges in orbital separation
and primary mass place the majority of the progenitor binaries within the
so-called ``brown dwarf desert.''


title: A very low luminosity X-ray flash: XMM-Newton observations of GRB 031203

abstract:
  GRB031203 was observed by XMM-Newton twice, first with an observation
beginning 6 hours after the burst, and again after 3 days. The afterglow had
average 0.2-10.0keV fluxes for the first and second observations of
4.2+/-0.1x10^-13 and 1.8+/-0.1x10^-13 erg/cm^2/s respectively, decaying very
slowly according to a power-law with an index of -0.55+/-0.05. The prompt soft
X-ray flux, inferred from a detection of the dust echo of the prompt emission,
strongly implies that this burst is very soft and should be classified as an
X-ray flash (XRF) and further, implies a steep temporal slope (<~-1.7) between
the prompt and afterglow phases or in the early afterglow, very different from
the later afterglow decay slope. A power-law (Gamma=1.90+/-0.05) with
absorption at a level consistent with the Galactic foreground absorption fits
the afterglow spectrum well. A bright, low-redshift (z=0.105) galaxy lies
within 0.5 arcsec of the X-ray position and is likely to be the GRB host. At
this redshift, GRB031203 is the closest GRB or XRF known after GRB980425. It
has a very low equivalent isotropic gamma-ray energy in the burst (~3x10^49
erg) and X-ray luminosity in the afterglow (9x10^42 erg/s at 10 hours), 3-4
orders of magnitude less than typical bursts, though higher than either the
faint XRF020903 or GRB980425. The rapid initial decline and subsequent very
slow fading of the X-ray afterglow is also similar to that observed in
GRB980425, indicating that GRB031203 may be representative of low luminosity
bursts.


title:
Intrinsic Absorption in the Spectrum of Mrk 279: Simultaneous Chandra,
  FUSE, and STIS Observations

abstract:
  We present a study of the intrinsic X-ray and far-ultraviolet absorption in
the Seyfert 1.5 galaxy Markarian 279 using simultaneous observations from the
Chandra X-ray Observatory, the Space Telescope Imaging Spectrograph aboard the
Hubble Space Telescope, and the Far Ultraviolet Spectroscopic Explorer (FUSE).
We also present FUSE observations made at three additional epochs. We detect
the Fe K-alpha emission line in the Chandra spectrum, and its flux is
consistent with the low X-ray continuum flux level of Mrk 279 at the time of
the observation. Due to low signal-to-noise ratios in the Chandra spectrum, no
O VII or O VIII absorption features are observable in the Chandra data, but the
UV spectra reveal strong and complex absorption from HI and high-ionization
species such as O VI, N V, and C IV, as well as from low-ionization species
such as C III, N III, C II, and N II in some velocity components. The far-UV
spectral coverage of the FUSE data provides information on high-order Lyman
series absorption, which we use to calculate the optical depths and line and
continuum covering fractions in the intrinsic HI absorbing gas in a
self-consistent fashion. The UV continuum flux of Mrk 279 decreases by a factor
of ~7.5 over the time spanning these observations and we discuss the
implications of the response of the absorption features to this change. From
arguments based on the velocities, profile shapes, covering fractions and
variability of the UV absorption, we conclude that some of the absorption
components, particularly those showing prominent low-ionization lines, are
likely associated with the host galaxy of Mrk 279, and possibly with its
interaction with a close companion galaxy, while the remainder arises in a
nuclear outflow.


title:
XMM-Newton observations of the M31 northern disk: Properties of selected
  X-ray sources and diffuse emission

abstract:
  We present the results of XMM-Newton survey of the northern part of the disk
of M31. The results of a spectral and timing analysis of the thirty seven
brightest sources are presented. Combining the results of X-ray analysis with
available data at other wavelengths, we were able to classify ~50%, or 19 out
of 37 sources. Two sources in our sample were previously unknown: the hard
X-ray source XMMU J004415.8+413057 and a transient supersoft source
XMMUJ004414.1+412206. We report the discovery of possible X-ray pulsations from
the source XMMUJ004415.8+413057 with a period of 197 s. The spectral and timing
properties of XMMU J004415.8+413057 make it first accreting X-ray pulsar
candidate detected in M31. We report on the first unambiguous detection of the
soft unresolved X-ray emission from the disk of M31. The unresolved emission
follows the pattern of the spiral arms and can be traced up to distance of ~0.5
deg (~7 kpc at 760 kpc) from the center of the galaxy. The spectrum of the
unresolved emission shows dominant soft thermal component which can be fitted
with a ~0.3 keV optically thin thermal plasma emission models. We suggest that
significant part of this diffuse soft X-ray component may represent hot diffuse
gas in the spiral arms of M31 and emission from normal stars in the disk of
M31.


title: Impact of astronomical research from different countries

abstract:
  The impact of astronomical research carried out by different countries has
been compared by analysing the 1000 most-cited astronomy papers published
1991-8 (125 from each year). 61% of the citations are to papers with first
authors at institutions in the USA, 11% in the UK, 5% in Germany, 4% in Canada,
3% in Italy and 3% in France. 17% are to papers with first authors in ESO
countries. The number of citations is approximately proportional to the number
of IAU members in a given country. The number of citations per IAU astronomer
is highest in the USA, Switzerland and the UK. Within continental Europe, the
number of citations per IAU astronomer varies little from country to country,
but is slightly higher in the north than in the south. The sample of 1000
papers maps regional subject preferences. 62% of the extragalactic papers in
the sample were published from the USA, 15% from the UK, 23% from other
countries (mainly in continental Europe). 62% of the papers on stars were also
published from the USA, but the fractions from the UK and from other countries
are 2% and 36% respectively.


title:
Formation of giant globular cluster G1 and the origin of the M31 stellar
  halo

abstract:
  We first demonstrate that globular cluster G1 could have been formed by tidal
interaction between M31 and a nucleated dwarf galaxy (dE,N). Our fully
self-consistent numerical simulations show that during tidal interaction
between M31 and G1's progenitor dE,N with $M_{\rm B}$ $\sim$ -15 mag and its
nucleus mass of $\sim$ $10^7$ $M_{\odot}$, the dark matter and the outer
stellar envelope of the dE,N are nearly completely stripped whereas the nucleus
can survive the tidal stripping because of its initially compact nature. The
naked nucleus (i.e., G1) has orbital properties similar to those of its
progenitor dE,N. The stripped stars form a metal-poor ([Fe/H] $\sim$ -1)
stellar halo around M31 and its structure and kinematics depend strongly on the
initial orbit of G1's progenitor dE,N. We suggest that the observed large
projected distance of G1 from M31 ($\sim$ 40 kpc) can give some strong
constraints on the central density of the dark matter halo of dE,N. We discuss
these results in the context of substructures of M31's stellar halo recently
revealed by Ferguson et al. (2002).


title:
Explosion models for thermonuclear supernovae resulting from different
  ignition conditions

abstract:
  We have explored in three dimensions the fate of a massive white dwarf as a
function of different initial locations of carbon ignition, with the aid of a
SPH code. The calculated models cover a variety of possibilities ranging from
the simultaneous ignition of the central volume of the star to the off-center
ignition in multiple scattered spots. In the former case, there are discussed
the possibility of a transition to a detonation when the mean density of the
nuclear flame decreases below 2x10**7 g cm**-3, and its consequences. In the
last case, the dependence of the results on the number of initial igniting
spots and the chance of some of these models to evolve to the pulsating delayed
detonation scenario are also outlined.


title: Phantom Inflation and Primordial Perturbation Spectrum

abstract:
  In this paper we study the inflation model driven by the phantom field. We
propose a possible exit from phantom inflation to our observational cosmology
by introducing an additional normal scalar field, similar to hybrid inflation
model. Then we discuss the primordial perturbation spectra from various phantom
inflation models and give an interesting compare with those of normal scalar
field inflation models.


title:
The Chemo-Dynamical Evolution of Elliptical Galaxies: Pre-heating and
  AGN heating

abstract:
  We study the chemodynamical evolution of elliptical galaxies and their X-ray
and optical properties using high-resolution cosmological simulations. Our Tree
N-body/SPH code includes a self-consistent treatment of radiative cooling, star
formation, supernovae feedback, and chemical enrichment. We present a series of
LCDM cosmological simulations which trace the spatial and temporal evolution of
abundances of heavy elements in both the stellar and gas components of
galaxies. A giant elliptical galaxy formed in one of the simulations is
quantitatively compared with the observational data in both the X-ray and
optical regime. We implement a treatment of both pre-heating and AGN heating in
this simulation, and examine the effect of these processes on elliptical galaxy
formation. We find that the adopted pre-heating (T=10^7 K at z=4) is not strong
enough to explain the observed X-ray or optical properties. On the other hand,
our AGN heating model in which the gas inflow induces the AGN heating is
consistent with both the X-ray and optical properties.


title:
Multifrequency radio continuum observations of NGC 1569: Evidence for a
  convective wind

abstract:
  We present high-sensitivity radio continuum observations with the VLA and
Ryle Telescope at 1.5, 4.9, 8.4 and 15.4 GHz of the dwarf irregular galaxy NGC
1569. The radio data show an extended, irregularly-shaped halo with filamentary
structure around the galaxy. The spectral index maps reveal an unusually patchy
distribution with regions of flat spectral index extending into the halo. The
data allow us to perform a spatially-resolved spectral fitting analysis of the
continuum emission from which we derive maps of the thermal and synchrotron
emission. The thermal radio emission is concentrated towards the brightest \hii
region west of the super star clusters A and B whereas the distribution of the
synchrotron emission peaks in a bar-like structure in the disk extending
between the two clusters. The total flux density of the thermal radio emission
allows us to derive the integrated synchrotron spectrum and we confirm the
break in the spectrum that was found by \citet{isr-deb88}. We discuss various
possibilities that could produce such a break and conclude that the only
mechanism able to fit the radio data and being consistent with data at other
wavelengths is a convective wind allowing cosmic ray electrons to escape from
the halo.


title:
On the correlation of elemental abundances with kinematics among
  galactic disk stars

abstract:
  We have performed the detailed analysis of 174 high-resolution spectra of FGK
dwarfs obtained with the ELODIE echelle spectrograph at the Observatoire de
Haute-Provence. Abundances of Fe, Si and Ni have been determined from
equivalent widths under LTE approximation, whereas abundances of Mg have been
determined under NLTE approximation using equivalent widths of 4 lines and
profiles of 5 lines. Spatial velocities with an accuracy better than 1 km/s, as
well as orbits, have been computed for all stars. They have been used to define
2 subsamples kinematically representative of the thin disk and the thick disk
in order to highlight their respective properties. A transition occurs at
[Fe/H]=-0.3. Stars more metal-rich than this value have a flat distribution
with Zmax<1 kpc and sigma_W<20 km/s, and a narrow distribution of [alpha/Fe].
There exist stars in this metallicity regime which cannot belong to the thin
disk because of their excentric orbits, neither to the thick disk because of
their low scale height. Several thin disk stars are identified down to
[Fe/H]=-0.80. Their Mg enrichment is lower than thick disk stars with the same
metallicity. We confirm from a larger sample the results of Feltzing et al
(2003) and Bensby et al (2003) showing a decrease of [alpha/Fe] with [Fe/H] in
the thick disk interpreted as the signature of the SNIa which have
progressively enriched the ISM with iron. However our data suggest that the
star formation in the thick disk stopped when the enrichment was [Fe/H]=-0.30,
[Mg/Fe]=+0.20, [Si/Fe]=+0.17. A vertical gradient in [alpha/Fe] may exist in
the thick disk but should be confirmed with a larger sample. Finally we have
identified 2 new candidates of the HR1614 moving group.


title:
Detection of a red supergiant progenitor star of a type II-plateau
  supernova

abstract:
  We present the discovery of a red supergiant star that exploded as supernova
2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and
the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova
explosion and subsequent HST images confirm the positional coincidence of the
supernova with a single,resolved star which is an 8 +4/-2 solar mass red
supergiant. This confirms both stellar evolution models and supernova theories
which predict that type II-Plateau supernovae have cool red supergiants as
their immediate progenitor stars.


title:
The Future of Far-Infrared / Submillimeter Astrophysics with Single-Dish
  Telescopes

abstract:
  Although far-IR -- mm-wave astronomy has now been developing for several
decades, access to this portion of the spectrum remains difficult and limited.
Relative to their optical-wavelength counterparts, the submillimeter
observatories are both small in units of wavelength and hot in units of photon
energy, which imposes limits on their angular resolution and sensitivity.
Nevertheless, even the modest far-IR and submillimeter observations obtained in
the last two decades have revolutionized our understanding the physics and
chemistry of the ISM, the formation of stars, and the cosmic history of these
processes. The demonstration by COBE that about half of the radiant energy
released in the universe since decoupling comes to us in the submm/far--IR has
further underscored the scientific necessity of observations in this wavelength
regime. The next decade promises even greater discoveries, as new observatories
and detectors are still pushing toward fundamental limits. The paper briefly
outlines some of the exciting capabilities and scientific roles of new
single-dish far--IR -- mm-wave telescopes and their instruments.


title: The distance to IC4499 from K-band photometry of 32 RR Lyrae stars

abstract:
  Single epoch K-band photometry of 32 RR Lyrae stars in the young galactic
globular cluster IC4499 is presented. The mean magnitudes have been estimated
using the K-band template light-curves of Jones, Carney and Fulbright (1996).
We derive an independent estimate of the distance and reddening for the cluster
based on the new <Mk>-logP-[Fe/H] relation from Bono et al.(2003) which has a
zero-point in agreement with the canonical LMC distance of (m-M)0 = 18.5. For
an assumed metallicity of [Fe/H]=-1.65+-0.1 we find (m-M)0 = 16.47+-0.04+-0.06
(random and systematic errors respectively) and E(B-V)=0.24+-0.03 in good
agreement with the findings of Walker and Nemec (1996) based on optical data.
The distance estimate is very robust to uncertainties in the reddening estimate
but naturally depends directly on the adopted zero-point of the
<Mk>-logP-[Fe/H] relation.


title: Growth of correlations in gravitational N-body simulations

abstract:
  In the gravitational evolution of a cold infinite particle distribution,
two-body interactions can be predominant at early times: we show that, by
treating the simple case of a Poisson particle distribution in a static
universe as an ensemble of isolated two-body systems, one may capture the
origin of the first non-linear correlated structures. The developed power-law
like behavior of the two-point correlation function is then simply related to
the functional form of the time evolved nearest-neighbor probability
distribution, whose time dependence can be computed by using Liouville theorem
for the gravitational two-body problem. We then show that a similar dynamical
evolution is also found in a large-scale ordered distribution, which has
striking similarities to the case of a cosmological CDM simulation which we
also consider.


title:
Missing Massive Stars in Starbursts: Stellar Temperature Diagnostics and
  the IMF

abstract:
  Determining the properties of starbursts requires spectral diagnostics of
their ultraviolet radiation fields, to test whether very massive stars are
present. We test several such diagnostics, using new models of line ratio
behavior combining Cloudy, Starburst99 and up-to-date spectral atlases. For six
galaxies we obtain new measurements of HeI 1.7 um / Brackett 10, a difficult to
measure but physically simple (and therefore reliable) diagnostic. We obtain
new measurements of HeI 2.06 um / Brackett gamma in five galaxies, and find
that it and [OIII]/Hbeta are generally unreliable diagnostics in starbursts.
The heteronuclear and homonuclear mid--infrared line ratios (notably [NeIII]
15.6 um / [NeII] 12.8 um) consistently agree with each other and with HeI 1.7
um / Br10; this argues that the mid-infrared line ratios are reliable
diagnostics of spectral hardness. In a sample of 27 starbursts, [NeIII]/[NeII]
ratios are significantly less excited than model predictions for a Salpeter IMF
extending to 100 solar masses. Plausible model alterations strengthen this
conclusion. By contrast, the low-mass and low-metallicity galaxies II Zw 40 and
NGC 5253 show relatively high neon line ratios, compatible with a Salpeter
slope extending to at least 40--60 Msol. One solution for the low neon line
ratios in the high--metallicity starbursts would be that they are deficient in
>40 Msol stars compared to a Salpeter IMF. An alternative explanation, which we
prefer, is that massive stars in high--metallicity starbursts spend much of
their lives embedded within ultra--compact HII regions that prevent the near-
and mid-infrared nebular lines from forming and escaping. This hypothesis has
important consequences for starburst modelling and interpretation.


title:
Chandra Observations of the Cloverleaf Quasar H 1413+117: A Unique
  Laboratory for Microlensing Studies of a Lobal Quasar

abstract:
  We present new results uncovered by a re-analysis of a Chandra observation of
the gravitationally lensed, low-ionization broad absorption line (LoBAL) quasar
H 1413+117. Previous analyses of the same Chandra observation led to the
detection of a strong, redshifted Fe Kalpha line from the combined spectrum of
all images. We show that the redshifted Fe Kalpha line is only significant in
the brighter image A. The X-ray flux fraction of image A is larger by a factor
of 1.55 +/- 0.17 than the optical R-band flux fraction, indicating that image A
is significantly enhanced in the X-ray band. We also find that the Fe Kalpha
line and the continuum are enhanced by different factors. A microlensing event
could explain both the energy-dependent magnification and the significant
detection of Fe Kalpha line emission in the spectrum of image A only. In the
context of this interpretation we provide constraints on the spatial extent of
the inferred scattered continuum and reprocessed Fe Kalpha line emission
regions in a LoBAL quasar.


title: X-raying Chemical Evolution and Galaxy Formation in The Antennae

abstract:
  We present the integrated 411 ks {\it Chandra} ACIS-S exposure of the
Antennae galaxies (NGC 4038/39). Besides a rich population of point-like
sources, this spectacular image reveals a spatially and spectrally complex hot
diffuse gaseous component. For the first time we detect intense line emission
from Fe, Ne, Mg and Si in The Antennae, and obtain a detailed picture of
spatially varied metal abundances in the hot interstellar medium (ISM) of a
galaxy. In certain regions, the abundances of $\alpha$-elements may be many
times solar, while the Fe abundance is sub-solar or near-solar. The differences
in the local metal enrichment of the hot ISM may be related to the local star
formation rates and to the degree of confinement of the enriched hot ISM. We
also report large-scale gaseous features, including two gigantic,
$\sim$10-kpc-scale `loops' extending to the South of the merging disks, and a
low-surface-brightness hot halo, extending out to $\sim$18 kpc. These features
may be related to superwinds from the starburst in The Antennae or result from
the merger hydrodynamics. Their long cooling times suggest that they may
persist to form the hot X-ray halo of the emerging elliptical galaxy.


title: Radio Emission from the Milky Way

abstract:
  In the last 5-10 years, wide-field imaging capabilities and effective
mosaicing algorithms have made possible a variety of ambitious interferometric
surveys of the Galaxy, resulting in images of unprecedented sensitivity and
resolution. Here I discuss some of the highlights from these new surveys.
Amongst the new results are the identification of many new supernova remnants
in confused regions, spectacular low frequency images of the inner Galaxy with
the VLA, and some remarkable new insights into the structure of the Galactic
magnetic field from linear polarization.


title: Kelvin-Helmholtz Instability in a Weakly Ionized Medium

abstract:
  Ambient interstellar material may become entrained in outflows from massive
stars as a result of shear flow instabilities. We study the linear theory of
the Kelvin - Helmholtz instability, the simplest example of shear flow
instability, in a partially ionized medium. We model the interaction as a two
fluid system (charged and neutral) in a planar geometry. Our principal result
is that for much of the relevant parameter space, neutrals and ions are
sufficiently decoupled that the neutrals are unstable while the ions are held
in place by the magnetic field. Thus, we predict that there should be a
detectably narrower line profile in ionized species tracing the outflow
compared with neutral species since ionized species are not participating in
the turbulent interface with the ambient ISM. Since the magnetic field is
frozen to the plasma, it is not tangled by the turbulence in the boundary
layer.


title: Probing cosmological parameters with GRBs

abstract:
  In light of the recent finding of the narrow clustering of the
geometrically-corrected gamma-ray energies emitted by Gamma Ray Bursts (GRBs),
we investigate the possibility to use these sources as standard candles to
probe cosmological parameters such as the matter density Omega_m and the
cosmological constant energy density Omega_Lambda. By simulating different
samples of gamma-ray bursts, based on recent observational results, we find
that Omega_m (with the prior Omega_m + Omega_Lambda = 1) can be determined with
accuracy ~7% with data from 300 GRBs, provided a local calibration of the
standard candles be achieved.


title: Testing Pulsar Thermal Evolution Theories with Observation

abstract:
  With the successful launch of Chandra and XMM/Newton X-ray space missions
combined with the lower-energy band observations, time has arrived when careful
comparison of thermal evolution theories of isolated neutron stars with
observations will offer a better hope for distinguishing among various
competing neutron star cooling theories. For instance, the latest theoretical
and observational developments may already exclude both nucleon and kaon direct
Urca cooling. In this way we can now have a realistic hope for determining
various important properties, such as the composition, superfluidity, the
equation of state and stellar radius. These developments should help us obtain
deeper insight into the properties of dense matter.


title: Galaxy formation and evolution since z=1

abstract:
  Determination of the star formation rate can be done using mid-IR photometry
or Balmer line luminosity after a proper correction for extinction effects.
Both methods show convergent results while those based on UV or on [OII]3727
luminosities underestimate the SFR by factors ranging from 5 to 40 for
starbursts and for luminous IR galaxies, respectively. Most of the evolution of
the cosmic star formation density is related to the evolution of luminous
compact galaxies and to luminous IR galaxies. Because they were metal deficient
and were forming stars at very high rates (40 to 100 solar mass per year), it
is probable that these (massive) galaxies were actively forming the bulk of
their stellar/metal content at z < 1.


title:
Direct Numerical Simulations of Type Ia Supernovae Flames II: The
  Rayleigh-Taylor Instability

abstract:
  A Type Ia supernova explosion likely begins as a nuclear runaway near the
center of a carbon-oxygen white dwarf. The outward propagating flame is
unstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtz
instabilities, which serve to accelerate it to a large fraction of the speed of
sound. We investigate the Rayleigh-Taylor unstable flame at the transition from
the flamelet regime to the distributed-burning regime, around densities of
$10^7$ g/cc, through detailed, fully resolved simulations. A low Mach number,
adaptive mesh hydrodynamics code is used to achieve the necessary resolution
and long time scales. As the density is varied, we see a fundamental change in
the character of the burning--at the low end of the density range the
Rayleigh-Taylor instability dominates the burning, whereas at the high end the
burning suppresses the instability. In all cases, significant acceleration of
the flame is observed, limited only by the size of the domain we are able to
study. We discuss the implications of these results on the potential for a
deflagration to detonation transition.


title:
1420 MHz Continuum Absorption Towards Extragalactic Sources in the
  Galactic Plane

abstract:
  We present a 21-cm emission-absorption study towards extragalactic sources in
the Canadian Galactic Plane Survey (CGPS). We have analyzed HI spectra towards
437 sources with S > 150 mJy, giving us a source density of 0.6 sources per
square degree at arcminute resolution. We present the results of a first
analysis of the HI temperatures, densities, and feature statistics. Particular
emphasis is placed on 5 features with observed spin temperatures below 40 K. We
find most spin temperatures in the range from 40 K to 300 K. A simple HI
two-component model constrains the bulk of the cold component to temperatures
(T_c) between 40 K and 100 K. T_c peaks in the Perseus arm region and clearly
drops off with Galactocentric radius, R, beyond that. The HI density follows
this trend, ranging from a local value of 0.4 cm^{-3} to less than 0.1 cm^{-3}
at R = 20 kpc. We find that HI emission alone on average traces about 75% of
the total HI column density, as compared to the total inferred by the emission
and absorption. Comparing the neutral hydrogen absorption to CO emission no
correlation is found in general, but all strong CO emission is accompanied by a
visible HI spectral feature. Finally, the number of spectral HI absorption
features per kpc drop off exponentially with increasing R.


title:
Cosmological Parameters from Eigenmode Analysis of Sloan Digital Sky
  Survey Galaxy Redshifts

abstract:
  We present estimates of cosmological parameters from the application of the
Karhunen-Loeve transform to the analysis of the 3D power spectrum of density
fluctuations using Sloan Digital Sky Survey galaxy redshifts. We use Omega_m*h
and f_b = Omega_b/Omega_m to describe the shape of the power spectrum, sigma8
for the (linearly extrapolated) normalization, and beta to parametrize linear
theory redshift space distortions. On scales k < 0.16 h/Mpc, our maximum
likelihood values are Omega_m*h = 0.264 +/-0.043, f_b = 0.286 +/- 0.065, sigma8
= 0.966 +/- 0.048, and beta = 0.45 +/- 0.12. When we take a prior on Omega_b
from WMAP, we find Omega_m*h = 0.207 +/- 0.030, which is in excellent agreement
with WMAP and 2dF. This indicates that we have reasonably measured the gross
shape of the power spectrum but we have difficulty breaking the degeneracy
between Omega_m*h and f_b because the baryon oscillations are not resolved in
the current spectroscopic survey window function.


title: MOA 2003-BLG-37: A Bulge Jerk-Parallax Microlens Degeneracy

abstract:
  We analyze the Galactic bulge microlensing event MOA-2003-BLG-37. Although
the Einstein timescale is relatively short, t_e=43 days, the lightcurve
displays deviations consistent with parallax effects due to the Earth's
accelerated motion. We show that the chi^2 surface has four distinct local
minima that are induced by the ``jerk-parallax'' degeneracy, with pairs of
solutions having projected Einstein radii, \tilde r_e = 1.76 AU and 1.28 AU,
respectively. This is the second event displaying such a degeneracy and the
first toward the Galactic bulge. For both events, the jerk-parallax formalism
accurately describes the offsets between the different solutions, giving hope
that when extra solutions exist in future events, they can easily be found.
However, the morphologies of the chi^2 surfaces for the two events are quite
different, implying that much remains to be understood about this degeneracy.


title: Eigenmode Analysis of Galaxy Distributions in Redshift Space

abstract:
  Eigenmode analysis is one of the most promising methods of analyzing large
data sets in ongoing and near-future galaxy surveys. In such analyses, a fast
evaluation of the correlation matrix in arbitrary cosmological models is
crucial. The observational effects, including peculiar velocity distortions in
redshift space, light-cone effects, selection effects, and effects of the
complex shape of the survey geometry, should be taken into account in the
analysis. In the framework of the linear theory of gravitational instability,
we provide the methodology to quickly compute the correlation matrix. Our
methods are not restricted to shallow redshift surveys, arbitrarily deep
samples can be dealt with as well. Therefore, our methods are useful in
constraining the geometry of the universe and the dark energy component, as
well as the power spectrum of galaxies, since ongoing and near-future galaxy
surveys probe the universe at intermediate to deep redshifts, z ~ 0.2--5. In
addition to the detailed methods to compute the correlation matrix in
3-dimensional redshift surveys, methods to calculate the matrix in
2-dimensional projected samples are also provided. Prospects of applying our
methods to likelihood estimation of the cosmological parameters are discussed.


title: Disk Galaxy Formation in a LambdaCDM Universe

abstract:
  We describe hydrodynamical simulations of galaxy formation in a Lambda cold
dark matter (CDM) cosmology performed using a subresolution model for star
formation and feedback in a multiphase interstellar medium (ISM). In
particular, we demonstrate the formation of a well-resolved disk galaxy. The
surface brightness profile of the galaxy is exponential, with a B-band central
surface brightness of 21.0 mag arcsec^-2 and a scale-length of R_d = 2.0 h^-1
kpc. We find no evidence for a significant bulge component. The simulated
galaxy falls within the I-band Tully-Fisher relation, with an absolute
magnitude of I = -21.2 and a peak stellar rotation velocity of V_rot=121.3 km
s^-1. While the total specific angular momentum of the stars in the galaxy
agrees with observations, the angular momentum in the inner regions appears to
be low by a factor of ~2. The star formation rate of the galaxy peaks at ~7
M_sun yr^-1 between redshifts z=2-4, with the mean stellar age decreasing from
\~10 Gyrs in the outer regions of the disk to ~7.5 Gyrs in the center,
indicating that the disk did not simply form inside-out. The stars exhibit a
metallicity gradient from 0.7 Z_sun at the edge of the disk to 1.3 Z_sun in the
center. Using a suite of idealized galaxy formation simulations with different
models for the ISM, we show that the effective pressure support provided by
star formation and feedback in our multiphase model is instrumental in allowing
the formation of large, stable disk galaxies. If ISM gas is instead modeled
with an isothermal equation of state, or if star formation is suppressed
entirely, growing gaseous disks quickly violate the Toomre stability criterion
and undergo catastrophic fragmentation.


title:
Are Supershells Powered by Multiple Supernovae? Modeling the Radio
  Pulsar Population Produced by OB Associations

abstract:
  Traditional searches for radio pulsars have targeted individual small regions
such as supernova remnants or globular clusters, or have covered large
contiguous regions of the sky. None of these searches has been specifically
directed towards giant supershells, some of which are likely to have been
produced by multiple supernova (SN) explosions from an OB association. Here we
perform a Montecarlo simulation of the pulsar population associated with
supershells powered by multiple SNe. We predict that several tens of radio
pulsars could be detected with current instruments associated with the largest
Galactic supershells (with kinetic energies >~ 10^{53} ergs), and a few pulsars
with the smaller ones. We test these predictions for some of the supershells
which lie in regions covered by past pulsar surveys. For the smaller
supershells, our results are consistent with the few detected pulsars per
bubble. For the giant supershell GSH 242-03+37, we find the multiple SN
hypothesis inconsistent with current data at the 95% level. We stress the
importance of undertaking deep pulsar surveys in correlation with supershells.
Failure to detect any pulsar enhancement in the largest of them would put
serious constraints on the multiple SN origin for them. Conversely, the
discovery of the pulsar population associated with a supershell would allow a
different/independent approach to the study of pulsar properties.


title:
Eta Carinae's Brightness Variations Since 1998: HST Observations of the
  Central Star

abstract:
  We have measured the brightness variations in Eta Carinae for the past six
years using the Hubble Space Telescope Space Telescope Imaging Spectrograph and
Advanced Camera for Surveys. Unlike ground-based data, observations by the HST
allow direct measurement of the brightness of the central star by resolving it
from the surrounding bright ejecta. We find interesting behavior during 2003 in
the continuum and H$\alpha$ emission. The data show that the established long
term brightening trend of Eta Car continues, including regular events which
coincide with the 5.5 year spectroscopic cycle and other more rapid and
unexpected variations. In addition to the HST data, we also present
ground-based data obtained from the AAVSO which show many of the same features.
The dip in the apparent brightness of the central star at the time of the
2003.5 event is wavelength dependent with no decrease in the continuum. These
observations cast doubt on asimple eclipse or occultation as the explanation
for the dip and place constraints on the models for the event.


title: Relativistic effects and polarization in three high-energy pulsar models

abstract:
  We present the influence of the special relativistic effects of aberration
and light travel time delay on pulsar high-energy lightcurves and polarization
characteristics predicted by three models: the two-pole caustic model, the
outer gap model, and the polar cap model. Position angle curves and degree of
polarization are calculated for the models and compared with the optical data
on the Crab pulsar. The relative positions of peaks in gamma-ray and radio
lightcurves are discussed in detail for the models. We find that the two-pole
caustic model can reproduce qualitatively the optical polarization
characteristics of the Crab pulsar - fast swings of the position angle and
minima in polarization degree associated with both peaks. The anticorrelation
between the observed flux and the polarization degree (observed in the optical
band also for B0656+14) naturally results from the caustic nature of the peaks
which are produced in the model due to the superposition of radiation from many
different altitudes, ie. polarized at different angles. The two-pole caustic
model also provides an acceptable interpretation of the main features in the
Crab's radio profile. Neither the outer gap model nor the polar cap model are
able to reproduce the optical polarization data on the Crab. Although the outer
gap model is very successful in reproducing the relative positions of gamma-ray
and radio peaks in pulse profiles, it can reproduce the high-energy lightcurves
only when photon emission from regions very close to the light cylinder is
included.


title: A Unified View of Coronagraph Image Masks

abstract:
  The last few years have seen a variety of new image mask designs for
diffraction-limited coronagraphy. Could there still be useful designs as yet
undiscovered? To begin to answer this question, I survey and unify the
Fraunhofer theory of coronagraph image masks in the context of a
one-dimensional classical coronagraph. I display a complete solution to the
problem of removing on-axis light assuming an unapodized entrance aperture and
I introduce the attenuation function, a measure of a generic coronagraph's
off-axis performance. With these tools, I demonstrate that the masks proposed
so far form a nearly complete library of image masks that are useful for
detecting faint extrasolar planets.


title: Low-Metallicity Gas Clouds in a Galaxy Proto-Cluster at Redshift 2.38

abstract:
  We present high resolution spectroscopy of a QSO whose sight-line passes
through the halo of a pair of elliptical galaxies at redshift 2.38. This pair
of galaxies probably lies at the center of a galaxy proto-cluster, and is
embedded in a luminous extended Ly-alpha nebula.
  The QSO sight-line intersects two small gas clouds within this halo. These
clouds have properties similar to those of high velocity clouds (HVCs) seen in
the halo of the Milky Way. The gas is in a cool (< 2 x 10^4 K) and at least 20%
neutral phase, with metallicities in the range -3.0 < [Fe/H] < -1.1 and neutral
hydrogen column densities of ~10^19.5 /cm^2.
  The origin of these clouds is unclear. The presence of low metallicity gas
within this possible proto-cluster implies either that the intra-cluster medium
has not been enriched with metals at this redshift, or the clouds are embedded
within a hot, ionized, metal-rich gas phase.


title: Radio Observations of the Afterglow of GRB 030329

abstract:
  We present the results of the radio observations of the afterglow of GRB
030329 with the Nobeyama 45-m telescope. The observations were made at 23.5
GHz, 43 GHz, and 90 GHz. The light curves show steep decline after constant
phase. The start time of the decline depends on frequency. Namely, the decline
started earlier at higher frequency. The spectrum has a peak at mm wavelength
range. The peak frequency and the peak flux decreased with time. These results
are consistent with the expectation from fireball model.


title: Lithium Abundances of the Local Thin Disk Stars

abstract:
  Lithium abundances are presented for a sample of 181 nearby F and G dwarfs
with accurate {\it Hipparcos} parallaxes. The stars are on circular orbits
about the Galactic centre and, hence, are identified as belonging to the thin
disk.
  This sample is combined with two published surveys to provide a catalogue of
lithium abundances, metallicities ([Fe/H]), masses, and ages for 451 F-G
dwarfs, almost all belonging to the thin disk. The lithium abundances are
compared and contrasted with published lithium abundances for F and G stars in
local open clusters. The field stars span a larger range in [Fe/H] than the
clusters for which [Fe/H] $\simeq 0.0\pm0.2$. The initial (i.e., interstellar)
lithium abundance of the solar neighborhood, as derived from stars for which
astration of lithium is believed to be unimportant, is traced from
$\log\epsilon$(Li) = 2.2 at [Fe/H] = -1 to $\log\epsilon$(Li) = 3.2 at $+0.1$.
This form for the evolution is dependent on the assumption that astration of
lit hium is negligible for the stars defining the relation. An argument is
advanced that this latter assumption may not be entirely correct, and, the
evolution of lithium with [Fe/H] may be flatter than previously supposed. A
sharp Hyades-like Li-dip is not seen among the field stars and appears to be
replaced by a large spread among lithium abundances of stars more massive than
the lower mass limit of the dip. Astration of lithium by stars of masses too
low to participate in the Li-dip is discussed. These stars show little to no
spread in lithium abundance at a given [Fe/H] and mass.


title: A numerical model for the gamma-ray emission of the microquasar LS 5039

abstract:
  The possible association between the microquasar LS 5039 and the EGRET source
3EG J1824-1514 suggests that microquasars could also be sources of high energy
gamma-rays. In this paper, we explore, with a detailed numerical model, if this
system can produce the emission detected by EGRET (>100 MeV) through inverse
Compton (IC) scattering. Our numerical approach considers a population of
relativistic electrons entrained in a cylindrical inhomogeneous jet,
interacting with both the radiation and the magnetic fields, taking into
account the Thomson and Klein-Nishina regimes of interaction. The computed
spectrum reproduces the observed spectral characteristics at very high energy.


title:
X-Ray Evolution of Active Galactic Nuclei and Hierarchical Galaxy
  Formation

abstract:
  We have incorporated the description of the X-ray properties of Active
Galactic Nuclei (AGNs) into a semi-analytic model of galaxy formation, adopting
physically motivated scaling laws for accretion triggered by galaxy encounters.
Our model reproduces the level of the cosmic X-ray background at 30 keV; we
predict that the largest contribution (around 2/3) comes from sources with
intermediate X-ray luminosity 10^{43.5}< L_X/erg/s <10^{44.5}, with 50 % of the
total specific intensity produced at z<2. The predicted number density of
luminous X-ray AGNs (L_X>10^{44.5} erg/s in the 2-10 keV band) peaks at z
around 2 with a decline of around 3 dex to z=0; for the low luminosity sources
(10^{43}<L_X/erg/s <10^{44}) it has a broaderand less pronounced maximum around
z 1.5. The comparison with the data shows a generally good agreement. The model
predictions slightly exceed the observed number of low-luminosity AGNs at z
around 1.5, with the discrepancy progressively extending to
intermediate-luminosity objects at higher redshifts; we discuss possible
origins for the mismatch. Finally, we predict the source counts and the flux
distribution at different redshifts in the hard (20-100 keV) X-ray band for the
sources contributing to the X- ray background.


title:
86 GHz SiO maser survey of late-type stars in the Inner Galaxy II.
  Infrared photometry of the SiO Target Stars

abstract:
  We present a compilation and study of DENIS, 2MASS, ISOGAL, MSX and IRAS
1--25 micron photometry for a sample of 441 late-type stars in the inner
Galaxy, which we previously searched for 86 GHz SiO maser emission (Messineo et
al.2002). The comparison of the DENIS and 2MASS J and Ks magnitudes shows that
most of the SiO targets are indeed variable stars. The MSX colours and the IRAS
[12]-[25] colour of our SiO targets are consistent with those of Mira type
stars with dust silicate feature at 9.7 micron feature in emission, indicating
only a moderate mass-loss rate.


title:
Abundances of neutron-capture elements in the Hot Extreme-Helium Stars
  V1920 Cygni and HD 124448

abstract:
  Analysis of HST STIS ultraviolet spectra of two hot extreme helium stars
(EHes): V1920 Cyg and HD 124448 provide the first measurements of abundances of
neutron-capture elements for EHes. Although the two stars have similar
abundances for elements up through the iron-group, they differ strikingly in
their abundances of heavier elements: V1920 Cyg is enriched by a factor of 30
in light neutron-capture elements (Y/Fe, Zr/Fe) relative to HD 124448. These
differences in abundances of neutron-capture elements among EHes mirrors that
exhibited by the RCrB stars, and is evidence supporting the view that there is
an evolutionary connection between these two groups of hydrogen-deficient
stars. Also, the abundances of Y and Zr in V1920 Cyg provide evidence that at
least one EHe star went through a s-process synthesis episode in its earlier
evolution.


title: Chandra observations of five X-ray transient galactic nuclei

abstract:
  We report on exploratory Chandra observations of five galactic nuclei that
were found to be X-ray bright during the ROSAT all-sky survey (with L_X > 10^43
erg s^-1) but subsequently exhibited a dramatic decline in X-ray luminosity.
Very little is known about the post-outburst X-ray properties of these
enigmatic sources. In all five cases Chandra detects an X-ray source
positionally coincident with the nucleus of the host galaxy. The spectrum of
the brightest source (IC 3599) appears consistent with a steep power-law
(Gamma~3.6). The other sources have too few counts to extract individual,
well-determined spectra, but their X-ray spectra appear flatter (Gamma~2) on
average. The Chandra fluxes are ~10^2-10^3 fainter than was observed during the
outburst (up to 12 years previously). That all post-outburst X-ray observations
showed similarly low X-ray luminosities is consistent with these sources having
`switched' to a persistent low-luminosity state. Unfortunately the relative
dearth of long-term monitoring and other data mean that the physical mechanism
responsible for this spectacular behaviour is still highly unconstrained.


title: A study of RXTE and BeppoSAX observations of Cyg X-3

abstract:
  We present an analysis of Cyg X-3 data from RXTE/PCA,HEXTE and ASM,
supplemented by a selected spectrum from BeppoSAX. We fit the PCA/HEXTE spectra
from 1996-2000 by a model including hybrid Comptonization, reflection and
absorption, and classify them into hard, intermediate and soft states. Apart
from the very strong absorption in Cyg X-3, the spectra resemble those of GRS
1915+105. The soft and intermediate state spectra require the presence of
nonthermal Comptonizing electrons. We then study the radiative processes at
soft X-rays with a hard-state spectrum from BeppoSAX modeled including emission
from a photoionized plasma.


title:
Synthetic X-ray light curves of BL Lacs from relativistic hydrodynamic
  simulations

abstract:
  We present the results of relativistic hydrodynamic simulations of the
collision of two dense shells in a uniform external medium, as envisaged in the
internal shock model for BL Lac jets. The non-thermal radiation produced by
highly energetic electrons injected at the relativistic shocks is computed
following their temporal and spatial evolution. The acceleration of electrons
at the relativistic shocks is parametrized using two different models and the
corresponding X-ray light curves are computed. We find that the interaction
time scale of the two shells is influenced by an interaction with the external
medium. For the chosen parameter sets, the efficiency of the collision in
converting dissipated kinetic energy into the observed X-ray radiation is of
the order of one percent.