title: Weak Lensing as a Calibrator of the Cluster Mass-Temperature Relation

abstract:
  The abundance of clusters at the present epoch and weak gravitational lensing
shear both constrain roughly the same combination of the power spectrum
normalization sigma_8 and matter energy density Omega_M. The cluster constraint
further depends on the normalization of the mass-temperature relation.
Therefore, combining the weak lensing and cluster abundance data can be used to
accurately calibrate the mass-temperature relation. We discuss this approach
and illustrate it using data from recent surveys.


title:
A feature at z ~ 3.2 in the evolution of the Ly-alpha forest optical
  depth

abstract:
  The effective optical depth in the Ly-alpha forest region of 1061
low-resolution QSO spectra drawn from the SDSS database decreases with
decreasing redshift over the range 2.5 < z < 4. Although the evolution is
relatively smooth, tau_eff ~ (1+z)^{3.8 pm 0.2}, at z ~ 3.2 the effective
optical depth decreases suddenly, by about ten percent with respect to this
smoother evolution. It climbs back to the original smooth scaling again by z ~
2.9. We describe two techniques, one of which is new, for quantifying this
evolution which give consistent results. A variety of tests show that the
feature is not likely to be a consequence of how the QSO sample was selected,
nor the result of flux calibration or other systematic effects. Other authors
have argued that, at this same epoch, the temperature of the IGM also shows a
departure from an otherwise smooth decrease with time. These features in the
evolution of the temperature and the optical depth are signatures of the
reionization of He II.


title: Temporal properties of short and long gamma-ray bursts

abstract:
  A temporal analysis was performed on a sample of 100 bright short GRBs with
T90 < 2s from the BATSE Current Catalog along with a similar analysis on 319
long bright GRBs with T90 > 2s from the same catalog. The short GRBs were
denoised using a median filter and the long GRBs were denoised using a wavelet
method. Both samples were subjected to an automated pulse selection algorithm
to objectively determine the effects of neighbouring pulses. The rise times,
fall times, FWHM, pulse amplitudes and areas were measured and their frequency
distributions are presented. The time intervals between pulses were also
measured. The frequency distributions of the pulse properties were found to be
similar and consistent with lognormal distributions for both the short and long
GRBs. The time intervals between the pulses and the pulse amplitudes of
neighbouring pulses were found to be correlated with each other. The same
emission mechanism can account for the two sub-classes of GRBs.


title: The Luminosity Function of Star Clusters in Spiral Galaxies

abstract:
  Star clusters in 6 nearby spiral galaxies are examined using archive images
from HST/WFPC2. The galaxies have previously been studied from the ground and
some of them are known to possess rich populations of "young massive clusters"
(YMCs). Comparison with the HST images indicates a success-rate of about 75%
for the ground-based cluster detections, with typical contaminants being blends
or loose groupings of several stars in crowded regions. The luminosity
functions (LFs) of cluster candidates identified on the HST images are analyzed
and compared with existing data for the Milky Way and the LMC. The LFs are well
approximated by power-laws of the form dN(L)/dL ~ L^alpha, with slopes in the
range -2.4<alpha<-2.0. The steeper slopes tend to be found among fits covering
brighter magnitude intervals, although direct hints of a variation in the LF
slope with magnitude are seen only at low significance in two galaxies. The
surface density of star clusters at a reference magnitude of M(V)=-8 scales
with the mean star formation rate per unit area, Sigma(SFR). Assuming that the
LF can be generally expressed as a power-law with normalization proportional to
the galaxy area (A) and Sigma(SFR), the maximum cluster luminosity expected in
a galaxy from random sampling of the LF is estimated as a function of
Sigma(SFR) and A. The predictions agree well with existing observations of
galaxies spanning a wide range of Sigma(SFR) values, suggesting that sampling
statistics play an important role in determining the maximum observed
luminosities of young star clusters in galaxies.


title:
The UCSD HIRES/KECK I Damped Lya Abundance Database: IV. Probing
  Galactic Enrichment Histories with Nitrogen

abstract:
  We present 14 N^0 measurements from our HIRES/Keck database of damped Lya
abundances. These data are combined with measurements from the recent and past
literature to build an homogeneous, uniform set of observations. We examine
photoionization diagnostics like Fe^++ and Ar^0 in the majority of the complete
sample and assess the impact of ionization corrections on N/alpha and alpha/H
values derived from observed ionic column densities of N^0, Si^+, H^0, and S^+.
Our final sample of 19 N/alpha, alpha/H pairs appears bimodal; the majority of
systems show N/alpha values consistent with metal-poor emission regions in the
local universe but a small sub-sample exhibit significantly lower N/alpha
ratios. Contrary to previous studies of N/alpha in the damped systems, our
sample shows little scatter within each sub-sample. We consider various
scenarios to explain the presence of the low N/alpha sightlines and account for
the apparent bimodality. We favor a model where at least some galaxies undergo
an initial burst of star formation with suppressed formation of
intermediate-mass stars. We found a power-law IMF with slope 0.10 or a mass cut
of ~5-8 Msolar would successfully reproduce the observed LN-DLA values. If the
bimodal distribution is confirmed by a larger sample of measurements, this may
present the first observational evidence for a top heavy initial mass function
in some early stellar populations.


title: FUSE Observations of the Narrow-Line Seyfert 1 Galaxy Arakelian 564

abstract:
  We present a 63 ks FUSE observation of the Narrow-Line Seyfert 1 galaxy
Arakelian 564. The spectrum is dominated by the strong emission in the O VI
\lambda\lambda1032, 1038 resonance doublet. Strong, heavily saturated
absorption troughs due to Lyman series of Hydrogen, O VI and C III \lambda 977
at velocities near the systemic redshift of Arakelian564 are also observed. We
used the column densities of O VI and C III in conjunction with the published
column densities of species observed in the UV and X-ray bands to derive
constraints on the physical parameters of the absorber through photoionization
modeling. The available data suggest that the UV and X-ray absorbers in
Arakelian~564 are physically related, and possibly identical. The combination
of constraints indicates that the absorber is characterized by a narrow range
in total column density N_H and U, centered at log N_H ~ 21 and log U ~ -1.5,
and may be spatially extended along the line of sight.


title: Tracking K-essence

abstract:
  We derive a condition for converging a common evolutionary track for
k-essence (a scalar field dark energy with non-canonical kinetic terms). For
the Lagrangian density V(phi)W(X) with X=dot{phi}^2/2, we find tracker
solutions with w_{phi} < w_B exist if Gamma equivalent V''V/(V')^2 > 3/2. Here
w_{phi}(w_B) is the equation-of-state of the scalar field (background
radiation/matter).
  Our condition may be useful for examining the existence of the attractor-like
behavior in cosmology with k-essence.


title: Star Formation in the ISO Atlas of Spiral Galaxies

abstract:
  We investigate star formation along the Hubble sequence using the ISO Atlas
of Spiral Galaxies. Using mid-infrared and far-infrared flux densities
normalized by K-band flux densities as indicators of recent star formation, we
find several trends. First, star formation activity is stronger in late-type
(Sc - Scd) spirals than in early-type (Sa - Sab) spirals. This trend is seen
both in nuclear and disk activity. These results confirm several previous
optical studies of star formation along the Hubble sequence but conflict with
the conclusions of most of the previous studies using IRAS data, and we discuss
why this might be so. Second, star formation is significantly more extended in
later-type spirals than in early-type spirals. We suggest that these trends in
star formation are a result of differences in the gas content and its
distribution along the Hubble sequence, and it is these differences that
promote star formation in late-type spiral galaxies. We also search for trends
in nuclear star formation related to the presence of a bar or nuclear activity.
The nuclear star formation activity is not significantly different between
barred and unbarred galaxies. We do find that star formation activity appears
to be inhibited in LINERs and transition objects compared to HII galaxies. The
mean star formation rate in the sample is 1.4 Msun/yr based on global
far-infrared fluxes. Combining these data with CO data gives a mean gas
consumption time of 6.4 x 10^8 yr, which is ~5 times lower than the values
found in other studies. Finally, we find excellent support for the Schmidt Law
in the correlation between molecular gas masses and recent star formation in
this sample of spiral galaxies.


title:
Fractal dust model of the Universe based on Mandelbrot's Conditional
  Cosmological Principle and General Theory of Relativity

abstract:
  We present a fractal dust model of the Universe based on Mandelbrot's
proposal to replace the standard Cosmological Principle by his Conditional
Cosmological Principle within the framework of General Theory of Relativity.
This model turns out to be free from the de-Vaucouleurs paradox and is
consistent with the SNe1a observations. The expected galaxy count as a function
of red-shift is obtained for this model. An interesting variation is a steady
state version, which can account for an accelerating scale factor without any
cosmological constant in the model.


title: Large Scale Structure in the SDSS Galaxy Survey

abstract:
  The Large Scale Structure (LSS) in the galaxy distribution is investigated
using the Sloan Digital Sky Survey Early Data Release (SDSS EDR). Using the
Minimal Spanning Tree technique we have extracted sets of filaments, of
wall-like structures, of galaxy groups, and of rich clusters from this unique
sample. The physical properties of these structures were then measured and
compared with the expectations from Zel'dovich' theory.
  The measured characteristics of galaxy walls were found to be consistent with
those for a spatially flat $\Lambda$CDM cosmological model with
$\Omega_m\approx$ 0.3 and $\Omega_\Lambda \approx$ 0.7, and for Gaussian
initial perturbations with a Harrison -- Zel'dovich power spectrum.
Furthermore, we found that the mass functions of groups and of unrelaxed
structure elements generally fit well with the expectations from Zel'dovich'
theory, although there was some discrepancy for lower mass groups which may be
due to incompleteness in the selected sample of groups. We also note that both
groups and rich clusters tend to prefer the environments of walls, which tend
to be of higher density, rather than the environments of filaments, which tend
to be of lower density.
  Finally, we note evidence of systematic differences in the properties of the
LSS between the Northern Galactic Cap stripe and the Southern Galactic Cap
stripe -- in particular, in the physical properties of the walls, their spatial
distribution, and the relative numbers of clusters embedded in walls. Because
the mean separation of walls is $\approx$ 60 -- 70$h^{-1}$ Mpc, each stripe
only intersects a few tens of walls. Thus, small number statistics and cosmic
variance are the likely drivers of these systematic differences.


title:
The Magnetospheric Flare on Compact Magnetized Object (Neutron Star or
  White Dwarf) - Model for Cosmological Gamma-Ray Burst (GRB)

abstract:
  The SN explosion in the closed binary can give the magnetospheric flare
possessing the properties of GRB. The SN shock, flowing around the
magnetosphere of a magnetized neutron star or a white dwarf, produces a narrow
magnetic tail 10^9 cm long, 10^8 cm wide and a magnetic field of 10^6 Gauss.
Fast particles (Lorentz factor of 10^4), generated in the tail by reconnection
processes, radaite gamma rays of the 100 KeV - 1 MeV energies. The duration of
radiation T<1 sec corresponds to a short GRB. Apart, the powerful shock can
tear and accelerate part of the tail. That is the relativistic, strongly
magnetized jet, producing gamma radiation and also X-rays and optic afterglow.
That is long (T> 10 sec) GRB. The duration of the afterglow is inversly
proportional to the photon energy and is several months for optic.


title: On the Orbital Period of the Intermediate Polar 1WGA J1958.2+3232

abstract:
  Recently, Norton et al. 2002, on the basis of multiwavelength photometry of
1WGA J1958.2+3232, argued that the -1 day alias of the strongest peak in the
power spectrum is the true orbital period of the system, casting doubts on the
period estimated by Zharikov et al. 2001. We re-analyzed this system using our
photometric and spectroscopic data along with the data kindly provided by Andy
Norton and confirm our previous finding. After refining our analysis we find
that the true orbital period of this binary system is 4.35h.


title:
The Distribution of Dark Matter in Galaxies: a Constant-Density Halo
  around DDO 47

abstract:
  In this paper we present strong evidence for a core in the density
distribution of the dark halo around a (dwarf) galaxy. DDO 47 has a rotation
curve that increases linearly from the first data point, at 300 pc, up to to
the last one, at 5 kpc. This profile cannot be reproduced unless we consider a
dark halo with a flat density core. The optical region of this galaxy is
dominated by a homogeneous halo of costant density of ~ 10^{-24} g/cm^3 and a
size of ~3 kpc, about twice that of the stellar disk. This result is a
formidable case of the inability of standard Lambda Cold Dark Matter scenario
to account for the dark mass distribution around galaxies, and points toward
the existence of an intriguing halo scale-length. With respect to the recent
claim that the "status of CDM on galactic scales" is satisfactorily in
agreement with observations (Primack, 2002), this paper adds up to the results
of Blais-Ouellette et al. (2002), Trott & Webster (2002), Binney & Evans
(2002), de Blok & Bosma (2002), Bottema (2002) in providing evidence that,
"succesfull CDM" is instead obliged to implement the "soft core" feature as a
general property of the distribution of galactic dark matter.


title:
The role of photon scattering in shaping the lightcurves and spectra of
  gamma-ray bursts

abstract:
  We analyze the power spectra of the lightcurves of long gamma-ray bursts,
dividing the sample in bins of luminosity, using the recently discovered
variability-luminosity correlation. We find that the value of the variability
parameter strongly correlates with the frequency that contains most of the
power in the burst comoving frame. We compute the average power spectra in
luminosity bins. The average power spectrum is well described by a broken
power-low and the break frequency is a function of the variability parameter,
while the two slopes are roughly constant. This allow us to conclude that
scattering processes do not play a relevant role in modelling the lightcurves.
We finally discuss in which conditions scattering may still play a relevant
role in shaping the spectra of GRBs.


title: An all-sky study of compact, isolated high-velocity clouds

abstract:
  We combine the catalogs of compact high-velocity HI clouds extracted from the
LDS and HIPASS surveys and analyze the all-sky properties of the ensemble. Five
principal observables are defined for the CHVC population: (1) the spatial
deployment of the objects on the sky, (2) the kinematic distribution, (3) the
number distribution of observed HI column densities, (4) the number
distribution of angular sizes, and (5) the number distribution of HI linewidth.
Two classes of models are considered to reproduce the observed properties. The
agreement of models with the data is judged by extracting these same
observables from simulations, in a manner consistent with the sensitivities of
the observations and explicitly taking account of Galactic obscuration. We show
that models in which the CHVCs are the HI counterparts of dark-matter halos
evolving in the Local Group potential provide a good match to the observables.
The best-fitting populations have a maximum HI mass of 10^7 M_Sun a power-law
slope of the HI mass distribution in the range -1.7 to -1.8, and a Gaussian
dispersion for their spatial distributions of between 150 and 200 kpc centered
on both the Milky Way and M31. Given its greater mean distance, only a small
fraction of the M31 sub-population is predicted to have been detected in
present surveys. An empirical model for an extended Galactic halo distribution
for the CHVCs is also considered. While reproducing some aspects of the
population, this class of models does not account for some key systematic
features of the population.


title:
The vertical structure of T Tauri accretion discs III. Consistent
  interpretation of spectra and visibilities with a two-layer model

abstract:
  We present a two-layer accretion disc model developed to simultaneously fit
optical long baseline visibilities and spectral energy distributions of T Tauri
accretion discs.
  Our model includes viscous heating and absorption of stellar radiation. It
analytically expresses the vertical structure of the disc using a two-layer
approach: the outer layer is heated by the star and by the inner layer, and the
inner layer by visous dissipation and by the outer layer. We compare three
prescriptions for the flaring of the irradiated surface, and conclude that a
smooth profile with r ~ r^1/8->1/7 has predictions close to those of comparable
numerical models. The observables (spectra, images and visibilities) are
numerically determined.
  We study the influence of disc parameters on the structure and observables.
Then we apply it to three stars observed in IR interferometry. For T Tau and SU
Aur we find a model fit consistent with both visibilities and spectrum but we
could not in the case of T Tau North, which might come from caveats in the flux
correction from the close South companion.
  We find that even a single interferometric measurement at one wavelength can
bring a very strong constraint on disc models. We predict that future massive
interferometric observations will provide a breakthrough in the understanding
of accretion disc physics.


title:
The 21 cm Forest: Radio Absorption Spectra as Probes of Minihalos Before
  Reionization

abstract:
  We study the absorption along lines of sight toward high-z radio sources
caused by the 21 cm transition of neutral hydrogen in the intergalactic medium
(IGM) before reionization. Using semi-analytic methods, we compute the number
density of observable features caused by both ``minihalos'' (bound objects that
are unable to cool efficiently because of their small virial temperatures) and
protogalactic disks. We show that both sets of features should be observable by
the next generation of low-frequency radio telescopes, including the Low
Frequency Array and the Square Kilometer Array, provided that sufficiently
bright background sources exist. The statistics of minihalo absorption features
seen along lines of sight to radio-loud quasars offer a way to measure the
evolution of the radiation background and the IGM temperature with cosmic time.
Intersections with disks are much less common, but also cause much deeper
absorption features that would be visible in the spectra of both radio-loud
quasars and gamma-ray bursts (GRBs). The absorption feature caused by HI in the
host galaxy of a GRB should be observable, offering a route to determine
spectroscopically the burst redshift.


title:
Bispectrum speckle interferometry of IRC+10216: the dynamic evolution of
  the innermost circumstellar environment from 1995 to 2001

abstract:
  We present new near-infrared (JHK) bispectrum speckle-interferometry
monitoring of the carbon star IRC+10216 obtained between 1999 and 2001 with the
SAO 6m telescope. The J-, H-, and K-band resolutions are 50mas, 56mas, and
73mas, resp. The total sequence of K-band observations covers now 8 epochs from
1995 to 2001 and shows the dynamic evolution of the inner dust shell. The
present observations show that the appearance of the dust shell has
considerably changed compared to the epochs of 1995 to 1998. Four main
components within a 0.2" radius can be identified in the K-band images. The
apparent separation of the two initially brightest components A and B increased
from ~191mas in 1995 to ~351mas in 2001. Simultaneously, component B has been
fading and almost disappeared in 2000 whereas the initially faint components C
and D became brighter (relative to peak intensity). These changes can be
related to changes of the optical depth caused, e.g., by mass-loss variations
or new dust condensation in the wind. Our 2D radiative transfer model suggests
that the observed relative motion of A and B is not consistent with the known
terminal wind velocity of 15 km/s. The apparent motion with a deprojected
velocity of 19 km/s on average and of recently 27 km/s appears to be caused by
adisplacement of the dust density peak due to dust evaporation in the optically
thicker and hotter environment. Our monitoring, covering more than 3 pulsation
periods, shows that the structural variations are not related to the stellar
pulsation cycle in a simple way. This is consistent with the predictions of
hydrodynamical models that enhanced dust formation takes place on a timescale
of several pulsation periods. The timescale of the fading of component B can
well be explained by the formation of new dust in the circumstellar envelope.


title: Relativistic Particles in Clusters of Galaxies

abstract:
  A brief overview on the theory and observations of relativistic particle
populations in clusters of galaxies is given. The following topics are
addressed: (i) the diffuse relativistic electron population within the
intra-cluster medium (ICM) as seen in the cluster wide radio halos and possibly
also seen in the high energy X-ray and extreme ultraviolet excess emissions of
some clusters, (ii) the observed confined relativistic electrons within fresh
and old radio plasma and their connection to cluster radio relics at cluster
merger shock waves, (iii) the relativistic proton population within the ICM,
and its observable consequences (if it exists), and (iv) the confined
relativistic proton population (if it exists) within radio plasma. The
importance of upcoming, sensitive gamma-ray telescopes for this research area
is highlighted.


title:
Shapes of Molecular Cloud Cores and the Filamentary Mode of Star
  Formation

abstract:
  Using recent dust continuum data, we generate the intrinsic ellipticity
distribution of dense, starless molecular cloud cores. Under the hypothesis
that the cores are all either oblate or prolate randomly-oriented spheroids, we
show that a satisfactory fit to observations can be obtained with a gaussian
prolate distribution having a mean intrinsic axis ratio of 0.54. Further, we
show that correlations exist between the apparent axis ratio and both the peak
intensity and total flux density of emission from the cores, the sign of which
again favours the prolate hypothesis. The latter result shows that the mass of
a given core depends on its intrinsic ellipticity. Monte Carlo simulations are
performed to find the best-fit power law of this dependence. Finally, we show
how these results are consistent with an evolutionary scenario leading from
filamentary parent clouds to increasingly massive, condensed, and roughly
spherical embedded cores.


title:
Diffuse X-ray emission from the spiral galaxy NGC 2403 discovered with
  Chandra

abstract:
  We have detected diffuse soft X-ray emission (0.4-1 keV) from the disk of the
spiral galaxy NGC 2403 with Chandra. This diffuse emission (with a total
luminosity of 2.1 x 10^38 erg/s and a gas temperature of 2-8 x 10^6 K) is well
separated from the numerous bright point sources. NGC 2403 is a luminous spiral
galaxy with a high rate of star formation. Recent HI observations have revealed
an extended HI halo with anomalous velocities and a general inflow towards the
central regions of the galaxy. This result and the present detection of a
diffuse, hot X-ray emitting gas point at a very active disk-halo connection and
galactic fountain types of phenomena.


title: The Embedded Super Star Cluster of SBS0335-052

abstract:
  We analyze the infrared (6-100 micron) spectral energy distribution of the
blue compact dwarf and metal-poor (Z=Z_solar/41) galaxy SBS0335-052. With the
help of DUSTY (Ivezic et al. 1999), a program that solves the radiation
transfer equations in a spherical environment, we evaluate that the infrared
(IR) emission of SBS0335-052 is produced by an embedded super-star cluster
(SSC) hidden under 10^5 M_solar of dust, causing 30 mag of visual extinction.
This implies that one cannot detect any stellar emission from the 2x10^6
M_solar stellar cluster even at near-infrared (NIR) wavelengths. The derived
grain size distribution departs markedly from the widely accepted size
distribution inferred for dust in our galaxy (the so-called MRN distribution,
Mathis et al. 1977), but resembles what is seen around AGNs, namely an absence
of PAH and smaller grains, and grains that grow to larger sizes (around 1
micron). The fact that a significant amount of dust is present in such a
low-metallicity galaxy, hiding from UV and optical view most of the star
formation activity in the galaxy, and that the dust size distribution cannot be
reproduced by a standard galactic law, should be borne in mind when
interpreting the spectrum of primeval galaxies.


title:
A test for the search for life on extrasolar planets: Looking for the
  terrestrial vegetation signature in the Earthshine spectrum

abstract:
  We report spectroscopic observations (400 to 800nm, R = approx 100) of
Earthshine in June, July and October 2001 from which normalised Earth albedo
spectra have been derived. The resulting spectra clearly show the blue colour
of the Earth due to Rayleigh diffusion in its atmosphere. They also show the
signatures of oxygen, ozone and water vapour. We tried to extract from these
spectra the signature of Earth vegetation. A variable signal (4 to 10 +/-3%)
around 700nm has been measured in the Earth albedo. It is interpreted as being
due to the vegetation red edge, expected to be between 2 to 10% of the Earth
albedo at 700nm, depending on models. We discuss the primary goal of the
present observations: their application to the detection of vegetation-like
biosignatures on extrasolar planets.


title:
A model of the Universe including Dark Energy accounted for by both a
  Quintessence Field and a (negative) Cosmological Constant

abstract:
  In this work we present a model of the universe in which dark energy is
modelled explicitely with both a dynamical quintessence field and a
cosmological constant. Our results confirm the possibility of a future
collapsing universe (for a given region of the parameter space), which is
necessary for a consistent formulation of string theory and quantum field
theory. We have also reproduced the measurements of modulus distance from
supernovae with good accuracy.


title: Multi-wavelength study of the Seyfert 1 galaxy NGC 3783 with XMM-Newton

abstract:
  We present the analysis of multi-wavelength XMM-Newton data from the Seyfert
galaxy NGC 3783, including UV imaging, X-ray and UV lightcurves, the 0.2-10 keV
X-ray continuum, the iron K-alpha emission line, and high-resolution
spectroscopy and modelling of the soft X-ray warm absorber. The 0.2-10 keV
spectral continuum can be well reproduced by a power-law at higher energies; we
detect a prominent Fe K-alpha emission line, with both broad and narrow
components, and a weaker emission line at 6.9 keV which is probably a
combination of Fe K-beta and Fe XXVI. We interpret the significant deficit of
counts in the soft X-ray region as being due to absorption by ionised gas in
the line of sight. This is demonstrated by the large number of narrow
absorption lines in the RGS spectrum from iron, oxygen, nitrogen, carbon, neon,
argon, magnesium, silicon and sulphur. The wide range of iron states present in
the spectrum enables us to deduce the ionisation structure of the absorbing
medium. We find that our spectrum contains evidence of absorption by at least
two phases of gas: a hotter phase containing plasma with a log ionisation
parameter xi (where xi is in erg cm/s) of 2.4 and greater, and a cooler phase
with log xi centred around 0.3. The gas in both phases is outflowing at speeds
of around 800 km/s. The main spectral signature of the cold phase is the
Unresolved Transition Array (UTA) of M-shell iron, which is the deepest yet
observed; its depth requires either that the abundance of iron, in the cold
phase, is several times that of oxygen, with respect to solar abundances, or
that the absorption lines associated with this phase are highly saturated. The
cold phase is associated with ionisation states that would also absorb in the
UV.


title: Can Deuterium Formation Be Measured?

abstract:
  The fundamental PP reaction has never been attempted in the laboratory as
theory states it cannot be measured within the human life span. This forms the
foundation of stellar nucleosynthesis and the standard solar model. Yet
numerous observations including the Sun's obvious variability argue the theory
is flawed and the reaction occurs in times many orders of magnitude shorter
than prediction. Considering the consequence to accepted models and controlled
fusion, testing is warranted.


title:
Improved Astrometry and Photometry for the Luyten Catalog. II. Faint
  Stars and the Revised Catalog

abstract:
  We complete construction of a catalog containing improved astrometry and new
optical/infrared photometry for the vast majority of NLTT stars lying in the
overlap of regions covered by POSS I and by the second incremental 2MASS
release, approximately 44% of the sky. The epoch 2000 positions are typically
accurate to 130 mas, the proper motions to 5.5 mas/yr, and the V-J colors to
0.25 mag. Relative proper motions of binary components are measured to 3
mas/yr. The false identification rate is ~1% for 11 < V < 18 and substantially
less at brighter magnitudes. These improvements permit the construction of a
reduced proper motion diagram that, for the first time, allows one to classify
NLTT stars into main-sequence (MS) stars, subdwarfs (SDs), and white dwarfs
(WDs). We in turn use this diagram to analyze the properties of both our
catalog and the NLTT catalog on which it is based. In sharp contrast to popular
belief, we find that NLTT incompleteness in the plane is almost completely
concentrated in MS stars, and that SDs and WDs are detected almost uniformly
over the sky DEC > -33 deg. Our catalog will therefore provide a powerful tool
to probe these populations statistically, as well as to reliably identify
individual SDs and WDs.


title: Detection of He II reionization in the SDSS quasar sample

abstract:
  The expansion of the Universe leads to a rapid drop in the mean hydrogen
Ly-alpha opacity tau of the intergalactic medium (IGM), tau (1+z)^{3.8},
between redshifts 4 and 3. Measurements of the temperature evolution of the IGM
and of the He II opacity both suggest that He II reionizes in this redshift
range. We use hydrodynamical simulations to show that the temperature increase
associated with He II reionization leads to a relatively sudden decrease in tau
around the reionization epoch of ~ 10 per cent. We find clear evidence for such
a feature in the evolution of tau determined from a sample of ~ 1100 quasars
obtained from the SDSS. He II reionization starts at redshift ~ 3.4, and lasts
for (Delta z) ~ 0.4. The increase in the IGM temperature also explains the
widths of hydrogen absorption lines as measured in high-resolution spectra.


title: Near-IR and Optical Morphology of Spiral Galaxies

abstract:
  We announce the initial release of data from the Ohio State University Bright
Spiral Galaxy Survey, a BVRJHK imaging survey of a well-defined sample of 205
bright, nearby spiral galaxies. We present H-band morphological classification
on the Hubble sequence for the OSU Survey sample. We compare the H-band
classification to B-band classification from our own images and from standard
galaxy catalogs. Our B-band classifications match well with those of the
standard catalogs. On average, galaxies with optical classifications from Sa
through Scd appear about one T-type earlier in the H-band than in the B-band,
but with large scatter. This result does not support recent claims made in the
literature that the optical and near-IR morphologies of spiral galaxies are
uncorrelated. We present detailed descriptions of the H-band morphologies of
our entire sample, as well as B- and H-band images for a set of 17 galaxies
chosen as type examples, and BRH color-composite images of six galaxies chosen
to demonstrate the range in morphological variation as a function of
wavelength. Data from the survey are accessible at
http://www.astronomy.ohio-state.edu/~survey/


title:
An Atlas of Galactic Spectra Observed with the Far Ultraviolet
  Spectroscopic Explorer

abstract:
  An atlas of far-ultraviolet spectra of 45 Galactic OB stars observed with the
Far Ultraviolet Spectroscopic Explorer is presented. The atlas covers the
wavelength region between 912 and 1185A with an effective spectral resolution
of 0.12A. Systematic trends in the morphology and strength of stellar features
are discussed. Particular attention is drawn to the variations of the
CIII$\lambda$1176, SIV$\lambda\lambda$1063, 1073, and PV$\lambda\lambda$1118,
1128 line profiles as a function of temperature and luminosity class; and the
lack of a luminosity dependence associated with OVI$\lambda\lambda$1032, 1038.
Numerous interstellar lines are also identified.


title:
R-Process Nucleosynthesis In Neutrino-Driven Winds From A Typical
  Neutron Star With M = 1.4 Msun

abstract:
  We study the effects of the outer boundary conditions in neutrino-driven
winds on the r-process nucleosynthesis. We perform numerical simulations of
hydrodynamics of neutrino-driven winds and nuclear reaction network
calculations of the r-process. As an outer boundary condition of hydrodynamic
calculations, we set a pressure upon the outermost layer of the wind, which is
approaching toward the shock wall. Varying the boundary pressure, we obtain
various asymptotic thermal temperature of expanding material in the
neutrino-driven winds for resulting nucleosynthesis. We find that the
asymptotic temperature slightly lower than those used in the previous studies
of the neutrino-driven winds can lead to a successful r-process abundance
pattern, which is in a reasonable agreement with the solar system r-process
abundance pattern even for the typical proto-neutron star mass Mns ~ 1.4 Msun.
A slightly lower asymptotic temperature reduces the charged particle reaction
rates and the resulting amount of seed elements and lead to a high
neutron-to-seed ratio for successful r-process. This is a new idea which is
different from the previous models of neutrino-driven winds from very massive
(Mns ~ 2.0 Msun) and compact (Rns ~ 10 km) neutron star to get a short
expansion time and a high entropy for a successful r-process abundance pattern.
Although such a large mass is sometimes criticized from observational facts on
a neutron star mass, we dissolve this criticism by reconsidering the boundary
condition of the wind. We also explore the relation between the boundary
condition and neutron star mass, which is related to the progenitor mass, for
successful r-process.


title: Starcounts Redivivus. IV. Density Laws Through Photometric Parallaxes

abstract:
  In an effort to more precisely define the spatial distribution of Galactic
field stars, we present an analysis of the photometric parallaxes of 70,000
stars covering nearly 15 square degrees in seven Kapteyn Selected Areas. We
address the affects of Malmquist Bias, subgiant/giant contamination,
metallicity and binary stars upon the derived density laws. The affect of
binary stars is the most significant. We find that while the disk-like
populations of the Milky Way are easily constrained in a simultaneous analysis
of all seven fields, no good simultaneous solution for the halo is found. We
have applied halo density laws taken from other studies and find that the
Besancon flattened power law halo model (c/a=0.6, r^-2.75) produces the best
fit to our data. With this halo, the thick disk has a scale height of 750 pc
with an 8.5% normalization to the old disk. The old disk scale height is
280-300 pc. Corrected for a binary fraction of 50%, these scale heights are 940
pc and 350-375 pc, respectively. Even with this model, there are systematic
discrepancies between the observed and predicted density distributions. Our
model produces density overpredictions in the inner Galaxy and density
underpredictions in the outer Galaxy. A possible solution is modeling the
stellar halo as a two-component system in which the halo has a flattened inner
distribution and a roughly spherical, but substructured outer distribution.
Further reconciliation could be provided by a flared thick disk, a structure
consistent with a merger origin for that population. (Abridged)


title: Multiband VLA Observations of the Faint Radio Core of 3CR 68.1

abstract:
  The large, powerful Fanaroff-Riley class II radio source 3CR 68.1 is an
optically red quasar with strong evidence for dust reddening, intrinsic
ultraviolet line absorption, and X-ray absorption. In the context of its large,
extended radio structure and the evidence for intrinsic material along the line
of sight, it is a good candidate for a quasar seen through the edge of an
obscuring torus proposed by unified schemes. The compact radio core coincident
with the optical position of the quasar is extremely weak compared to the very
bright and luminous radio lobes, suggesting that the radio core might also
suffer absorption. We observed 3CR 68.1 at six frequencies and show that the
radio core has a flat spectrum with no evidence for free-free absorption or
other strong absorption mechanisms. This result helps establish an empirical
intrinsic lower range for core-to-lobe radio flux in the most powerful radio
sources.


title:
Substellar Mass Function of Young Open Clusters as Determined through a
  Statistical Approach Using 2MASS and GSC Data

abstract:
  In this paper we present the mass functions in the substellar regime of three
young open clusters, IC 348, $\sigma$ Orionis and Pleiades, as derived using
the data from the 2 Micron All Sky Survey (2MASS) catalogue which has a
limiting magnitude of K_s ~ 15, and the latest version of the Guide Star
Catalogue (GSC) which has a limiting magnitude of F ~ 21 where F refers to the
POSS II IIIa-F passband. Based on recent evolutionary models for low mass
stars, we have formulated the selection criteria for stars with masses below
0.5 solar mass. Using a statistical approach to correct for the background
contamination, we derive the mass function of objects with masses ranging from
0.5 solar mass down to the substellar domain, well below the Hydrogen Burning
Mass Limit. The lowest mass bins in our analysis are 0.025, 0.045 and 0.055
solar masses for IC 348, sigma Orionis and Pleiades, respectively. The
resultant slopes of the mass functions are 0.8 +/- 0.2 for IC 348, 1.2 +/- 0.2
for sigma Orionis and 0.5 +/- 0.2 for Pleiades, which are consistent with the
previous results. The contribution of objects below 0.5 solar mass to the total
mass of the cluster is ~40%, and the contribution of objects below 0.08 solar
mass to the total mass is ~4%.


title:
The Relative Spatial Distribution of SiO Masers in AGB Stars at 43 and
  86 GHz

abstract:
  We present the first VLBI images of SiO masers in the circumstellar envelope
of an S-type star obtained with the newly developed capabilities of the Very
Long Baseline Array (VLBA) at 86 GHz. We combine these data with those obtained
quasy simultaneously at 43 GHz. These observations provide information on the
structure and dynamics of the innermost circumstellar shells, where the return
of large quantities of stellar material to the interstellar medium starts.
Despite of the fact that these are prelimininary results, we report that the
maser emission of the $v$=1 J=1--0 and J=2--1 present a very different emission
distribution, being not coincident in most case.


title: The N-point correlation functions of the COBE-DMR maps revisited

abstract:
  We calculate the two-, three- and (for the first time) four-point correlation
functions of the COBE-DMR 4-year sky maps, and search for evidence of
non-Gaussianity by comparing the data to Monte Carlo-simulations of the
functions. The analysis is performed for the 53 and 90 GHz channels, and five
linear combinations thereof. For each map, we simulate an ensemble of 10,000
Gaussian realisations based on an a priori best-fit scale-invariant
cosmological power spectrum, the DMR beam pattern and instrument-specific noise
properties. Each observed COBE-DMR map is compared to the ensemble using a
simple chi^2 statistic, itself calibrated by simulations. In addition, under
the assumption of Gaussian fluctuations, we find explicit expressions for the
expected values of the four-point functions in terms of combinations of
products of the two-point functions, then compare the observed four-point
statistics to those predicted by the observed two-point function, using a
redefined chi^2 statistic. Both tests accept the hypothesis that the DMR maps
are consistent with Gaussian initial perturbations.


title: Mixing and Accretion in lambda Bootis Stars

abstract:
  Strong evidence for deep mixing has been uncovered for slowly rotating F, and
A stars of the main sequence. As the accretion/diffusion model for the
formation of lboo stars is heavily dependent on mixing in superficial regions,
such deep mixing may have important repercussions on our understanding of these
stars. It is shown that deep mixing at a level similar to that of FmAm stars
increases the amount of matter that needs to be accreted by the stars with
respect with the standard models by some three orders of magnitude. It is also
shown that significantly larger accretion rates have to be maintained, as high
as $10^{-11}$~M$_\sun yr^{-1}$, to prevent meridional circulation from
canceling the effect of accretion. The existence of old ($\approx 1$~Gyr) is
not a likely outcome of the present models for accretion/diffusion with or
without deep mixing. It is argued that lboo stars are potentially very good
diagnostics of mixing mechanisms in moderately fast rotators.


title:
X-ray Emission near the Substellar Limit: The sigma Orionis and Taurus
  Star Forming Regions

abstract:
  We have carried out an extensive search for X-ray emission from young, very
low-mass objects near and beyond the substellar limit, making use of archived
ROSAT PSPC and HRI observations pointed at Brown Dwarfs and Brown Dwarf
candidates in the young sigma Orionis and Taurus-Auriga associations. In sigma
Ori we identify three Brown Dwarf candidates with X-ray sources; in
Taurus-Auriga we add one further X-ray detection of a Brown Dwarf to the list
published earlier. We combine this data with all previously X-ray detected
Brown Dwarfs and Brown Dwarf candidates in young stellar associations and star
forming regions to perform a study of stellar activity parameters on the as yet
largest sample of young, very low mass objects. A similar relation between
X-ray and bolometric luminosity, and H-alpha emission, respectively, as is
known for T Tauri stars seems to hold for young objects down to the substellar
limit, too. No signs for a change in X-ray activity are found on the transition
to substellar masses.


title:
On Period and Burst Histories of AXPs and SGRs and the Possible
  Evolution of these Objects on the P-Pdot Diagram

abstract:
  In this paper, timing data for all of the anomalous X-ray pulsars and soft
gamma repeaters are compiled. Timing properties of these objects are
investigated. The effect of bursts of soft gamma repeaters on their period
history is investigated. The P-Pdot diagram for pulsars, X-ray binaries,
anomalous X-ray pulsars, soft gamma repeaters and dim radio quiet netron stars
is constructed. The possible evolutionary tracks for anomalous X-ray pulsars,
soft gamma repeaters and dim radio quiet netron stars are examined.


title: Evolutionary synthesis models of starbursts IV. Soft X-ray emission

abstract:
  In this work we investigate the evolution of the X-ray emission of a cluster
of single young massive stars with different metallicities. We have considered
the X-ray contribution originated by the diffuse gas heated by the mechanical
energy released by stellar winds and SN explosions as well as the X-ray
contribution from SN remnants. The resulting ionizing spectrum (i.e. lambda <
912 A) has been used to compute the expected intensity of the nebular He II
4686 A. The observational ratio He II/Hbeta could be reproduced by the models
assuming that a fraction of the mechanical energy produced by the
star-formation episode is reprocessed by interaction with the ISM as soft X-ray
radiation, contributing to the He ionization. However, the discreteness of the
stellar populations affects the ionizing flux and may be responsible for the
observed dispersion of the ratio. We have finally used the synthesis models to
estimate the contribution of circumnuclear star-forming regions to the
multiwavelength energy distribution in Active Galactic Nuclei, finding that the
UV to soft X-ray continuum in many Seyfert 2 galaxies seems to be dominated by
star-formation processes.


title:
Ultraviolet images of Seyfert galaxies from the Optical Monitor on
  XMM-Newton

abstract:
  The Optical Monitor telescope (Mason et al. 2001) on XMM-Newton provides an
exciting multi-wavelength dimension to observations of Active Galactic Nuclei.
Here we present ultraviolet images, taken with the OM UVW2 filter (140-270 nm),
of various Seyfert galaxies, some of which have never been observed in this
waveband before. The images show UV emission from both the active nucleus and
the host galaxy. The distribution of UV emission in the galaxy shows where star
formation is occurring, thus giving us clues as to the evolution of the host
galaxy and perhaps its relationship to the Seyfert Nucleus.


title: High-resolution imaging of compact high-velocity clouds (II)

abstract:
  We have imaged five compact high-velocity clouds in HI with arcmin angular-
and km/s spectral-resolution using the WSRT. Supplementary total-power data,
which is fully sensitive to both the cool and warm components of HI, is
available for comparison for all the sources, albeit with angular resolutions
that vary from 3' to 36'. The fractional HI flux in compact CNM components
varies from 4% to 16% in our sample. All objects have at least one local peak
in the CNM column which exceeds about 10^19 cm^-2 when observed with arcmin
resolution. It is plausible that a peak column density of 1-2x10^19 cm^-2 is a
prerequisite for the long-term survival of these sources. One object in our
sample, CHVC120-20-443 (Davies' cloud), lies in close projected proximity to
the disk of M31. This object is characterized by exceptionally broad linewidths
in its CNM concentrations (more than 5 times greater than the median value).
These CNM concentrations lie in an arc on the edge of the source facing the M31
disk, while the diffuse HI component of this source has a position offset in
the direction of the disk. All of these attributes suggest that CHVC120-20-443
is in a different evolutionary state than most of the other CHVCs which have
been studied. Similarly broad CNM linewidths have only been detected in one
other object, CHVC111-07-466, which also lies in the Local Group barycenter
direction and has the most extreme radial velocity known. A distinct
possibility for Davies' cloud seems to be physical interaction of some type
with M31. The most likely form of this interaction might be the ram-pressure or
tidal- stripping by either one of M31's visible dwarf companions, M32 or
NGC205, or else by a dark companion with an associated HI condensation.


title: Size and Structure of the Narrow-Line Region of Quasars

abstract:
  We have observed the narrow-line regions (NLRs) of the seven brightest
radio-quiet PG (or BQS) quasars (z < 0.5) with the Wide Field and Planetary
Camera 2 on board the Hubble Space Telescope (HST). Linear-ramp filters were
used to image the [OIII] lambda 5007 line emission with 0.0455-0.1 arcsec pixel
resolution. We find that the NLRs are very compact with typical extents of 2-4
arcsec. Two quasars show compact filamentary structures similar to Seyfert
NLRs. They may be related to radio outflows. Most interestingly, when including
a sample of Seyfert galaxies observed with HST, we tentatively find that the
size of the NLR is proportional to the square root of the [OIII] luminosity.
This is comparable to the scaling found for the size of the broad-line region
with continuum luminosity, which has been interpreted in terms of a constant
photoionization parameter. The relation determined here connects the NLR of
radio-quiet quasars and Seyferts over three orders of magnitude in [OIII]
luminosity.


title: ROSAT PSPC view of the hot interstellar medium of the Magellanic Clouds

abstract:
  Diffuse X-ray emission from the Magellanic Clouds (MCs) is studied by using
all the archival data of pointed ROSAT Position Sensitive Proportional Counter
(PSPC) observations. For this purpose, contributions from the point and
point-like sources in the ROSAT High Resolution Imager (HRI) and PSPC source
catalogues are eliminated and periods of high solar activity are excluded. The
spectral analysis yielded characteristic temperatures of 10^6 - 10^7 K for the
hot thin plasma of the ISM which extends over the whole Large Magellanic Cloud
(LMC) and the Small Magellanic Cloud (SMC). The total unabsorbed luminosity in
the 0.1 - 2.4 keV band within the observed area amounts to 3.2 x 10^38 erg s^-1
in the LMC and 1.1 x 10^37 erg s^-1 in the SMC, each with an uncertainty of
-40%, +100%. The X-ray luminosity of the LMC is comparable to that of other
nearby galaxies with pronounced star formation. In the LMC, hot regions were
found especially around the supergiant shell (SGS) LMC 4 and in the field
covering SGS LMC 2 and LMC 3. Highest temperatures for the SMC were derived in
the southwestern part of the galaxy. The diffuse X-ray emission is most likely
a superposition of the emission from the hot gas in the interior of shells and
supershells as well as from the halo of these galaxies.


title:
Turbulent diffusion and drift in galactic magnetic fields and the
  explanation of the knee in the cosmic ray spectrum

abstract:
  We reconsider the scenario in which the knee in the cosmic ray spectrum is
explained as due to a change in the escape mechanism of cosmic rays from the
Galaxy from one dominated by transverse diffusion to one dominated by drifts.
We solve the diffusion equations adopting realistic galactic field models and
using diffusion coefficients appropriate for strong turbulence (with a
Kolmogorov spectrum of fluctuations) and consistent with the assumed magnetic
fields. We show that properly taking into account these effects leads to a
natural explanation of the knee in the spectrum, and a transition towards a
heavier composition above the knee is predicted.


title: Submillimeter dust emission of the M17 complex measured with PRONAOS

abstract:
  We map a 50' x 30' area in and around the M17 molecular complex with the
French submillimeter balloon-borne telescope PRONAOS, in order to better
understand the thermal emission of cosmic dust and the structure of the
interstellar medium. The PRONAOS-SPM instrument has an angular resolution of
about 3', corresponding to a size of 2 pc at the distance of this complex, and
a high sensitivity up to 0.8 MJy/sr. The observations are made in four wide
submillimeter bands corresponding to effective wavelengths of 200, 260, 360 and
580 um. Using an improved map-making method for PRONAOS data, we map the M17
complex and faint condensations near the dense warm core. We derive maps of
both the dust temperature and the spectral index, which vary over a wide range,
from about 10 K to 100 K for the temperature and from about 1 to 2.5 for the
spectral index. We show that these parameters are anticorrelated, the cold
areas (10-20 K) having a spectral index around 2, whereas the warm areas have a
spectral index between 1 and 1.5. We discuss possible causes of this effect,
and we propose an explanation involving intrinsic variations of the grain
properties. Indeed, to match the observed spectra with two dust components
having a spectral index equal to 2 leads to very large and unlikely amounts of
cold dust. We also give estimates of the column densities and masses of the
studied clumps. Three cold clumps (14-17 K) could be gravitationally unstable.


title: Interstellar Phase Transitions Stimulated by Time-dependent Heating

abstract:
  We use three-dimensional hydrodynamic numerical simulations to study phase
transformations occurring in a clumpy interstellar gas exposed to
time-dependent volumetric heating. To mimic conditions in the Galactic
interstellar medium, we take a numerical model of a turbulent multiphase medium
from Kritsuk & Norman (2002) computed in a periodic box with mean density
n_0=0.25 cm^-3 and mean pressure P_0/k~10^3.4 K cm^-3. A second model with
n_0=1 cm^-3 is also considered. Variations of the heating rate on a timescale
of 1-10 Myr applied thereafter cause pressure variations in the gas and
shifting of the thermal equilibrium curve in the phase plane. This stimulates
mass transfer between the gas phases via thermal instability, converting 5-10%
of the thermal energy into kinetic energy of gas motions. The experiments
demonstrate that recurrent substantial heating episodes can maintain turbulence
at this level. Possible applications to the interstellar gas heated by variable
far-ultraviolet background radiation produced by short-living massive stars are
discussed.


title: Corrective lenses for high redshift supernovae

abstract:
  Weak lensing of high-redshift Type Ia supernovae induces an external
dispersion in their observed standard candle brightnesses, comparable in
magnitude to the intrinsic dispersion for redshifts z>1. The same matter
fluctuations responsible for the magnification of distant supernovae also
generate shear in the images of background galaxies. We investigate the
possibility of using lensing shear maps constructed from galaxies surrounding
the supernovae as a means of correcting the lensing-induced magnification
dispersion. We find that a considerable fraction of the lensing dispersion
derives from sub-arcminute scales, which are not probed by shear maps smoothed
on arcminute scales. We thus find that weak lensing shear maps will be of only
limited value in reducing the weak lensing magnification fluctuations of
supernovae.


title: Spectroscopy of low energy solar neutrinos using CdTe detectors

abstract:
  The usage of a large amount of CdTe(CdZnTe) semiconductor detectors for solar
neutrino spectroscopy in the low energy region is investigated. Several
different coincidence signals can be formed on five different isotopes to
measure the Be-7 neutrino line at 862 keV in real-time. The most promising one
is the usage of Cd-116 resulting in 89 SNU. The presence of Te-125 permits even
the real-time detection of pp-neutrinos. A possible antineutrino flux above 713
keV might be detected by capture on Cd-106 .


title: GAIA survey of galactic eclipsing binaries

abstract:
  General importance and capabilities of observations of eclipsing binaries by
the forthcoming ESA mission GAIA are discussed. Availability of spectroscopic
observations and a large number of photometric bands on board will make it
possible to reliably determine physical parameters for $\sim 10^5$ binary
stars. It is stressed that current methods of object by object analysis will
have to be modified and included in an automatic analysis pipeline.


title:
Evidence for Post-Quiescent, High-Energy Emission from Gamma-Ray Burst
  990104

abstract:
  It is well known that high-energy emission (MeV-GeV) has been observed in a
number of gamma-ray bursts, and temporally-extended emission from lower energy
gamma rays through radio wavelengths is well established. An important observed
characteristic of some bursts at low energy is quiescence: an initial emission
followed by a quiet period before a second (postquiescent) emission. Evidence
for significant high-energy, postquiescent emission has been lacking. Here we
present evidence for high-energy emission, coincident with lower energy
emission, from the postquiescent emission episode of the very bright and long
burst, GRB 990104. We show light curves and spectra that confirm emission above
50 MeV, approximately 152 seconds after the BATSE trigger and initial emission
episode. Between the initial emission episode and the main peak, seen at both
low and high energy, there was a quiescent period of ~100 s during which the
burst was relatively quiet. This burst was found as part of an ongoing search
for high-energy emission in gamma-ray bursts using the EGRET fixed interval (32
s) accumulation spectra, which provide sensitivity to later, high-energy
emission that is otherwise missed by the standard EGRET BATSE-triggered burst
spectra.


title: A search for brown-dwarf like secondaries in cataclysmic variables

abstract:
  We present VTL/ISAAC infrared spectroscopy of a sample of short orbital
period cataclysmic variables which are candidates for harboring substellar
companions. We have detected the KI and NaI absorption lines of the companion
star in VY Aqr. The overall spectral distribution in this system is best fit
with a M9.5 type dwarf spectra, implying a distance of $100 \pm 10$ pc. VY Aqr
seems to fall far from the theoretical distribution of secondary star
temperatures around the orbital period minimum. Fitting of the IR spectral
energy distribution (SED) was performed by comparing the observed spectrum with
late-type templates. The application of such a spectral fitting procedure
suggests that the continuum shape in the 1.1-2.5 $\mu$m spectral region in
short orbital period cataclysmic variables may be an useful indicator of the
companion spectral type. The SED fitting for RZ Leo and CU Vel suggests M5 type
dwarf companions, and distances of 340 $\pm$ 110 and 150 $\pm$ 50 pc,
respectively. These systems may be placed in the upper evolution branch for
short period cataclysmic variables.


title: The Structure and Stellar Content of the Central Region of M33

abstract:
  Using Gemini QuickStart infrared observations of the central 22" of M33, we
analyze the stellar populations in this controversial region. Based on the
slope of the giant branch we estimate the mean metallicity to be -0.26+/-0.27,
and from the luminosities of the most luminous stars, we estimate that there
were two bursts of star formation ~2 and ~0.5 Gyr ago. We show that the stellar
luminosity function not only has a different bright end cutoff, but also a
significantly different slope than that of the Galactic bulge, and suggest that
this difference is due to the young stellar component in M33. We combine our
infrared Gemini data with optical HST-WFPC2 measurements revealing a CMD
populated with young, intermediate, and old age stellar populations. Using
surface brightness profiles from 0.1" to 18', we perform simple decompositions
and show that the data are best fit by a three-component, core + bulge + disk
model. Finally, we find no evidence for radial variations of the stellar
populations in the inner 3"-10" of M33 based on a spatial analysis of the
color-magnitude diagrams and luminosity functions.


title:
Very high-energy neutrinos from slowly decaying, massive dark matter, as
  a source of explosive energy for gamma-ray bursts

abstract:
  We consider a speculative model for gamma-ray bursts (GRB), which predicts
that the total kinetic energy in the ejected matter is less than the total
energy in the gamma rays. There is also secondary energy in X-rays, which are
emitted contemporaneously with the gamma rays. The model suggests that
bremsstrahlung and Compton up-scattering by very energetic electrons, are
important processes for producing the observed burst radiation. The dynamics
naturally allows for the possibility of a moderate degree of beaming of matter
and radiation in some gamma-ray bursts. GRB are predicted to have an
intrinsically wide distribution in total energies, in particular, on the low
side. They are predicted to occur out to large red-shifts, z~8, in local
regions of dense matter.


title: Filaments in Warm Dark Matter

abstract:
  Using Warm Dark Matter rather then Cold Dark Matter we are able to solve the
over-production of satellite galaxies orbiting in galactic haloes. Moreover, we
can show that this model leads to interesting new results in terms of the
history and large-scale distribution of low-mass objects as well as the
formation of filamentary structures when being compared to the standard CDM
scenario.


title: Globular Clusters and Galaxy Formation

abstract:
  Globular clusters provide a unique probe of galaxy formation and evolution.
Here I briefly summarize the known observational properties of globular cluster
systems. One re-occurring theme is that the globular cluster systems of spirals
and ellipticals are remarkably similar. Photometry, and the limited spectra
available, are consistent with metal-poor clusters forming before the main
spheroid component is established and the metal-rich ones forming at the same
time as the spheroid in a burst of star formation. These observations are
compared to a model for globular cluster formation in a LCDM hierarchical
universe. One model result reported here is that S_N is determined at early
times and little affected by late epoch mergers.


title: Gravitational mesolensing by King objects and quasar-galaxy associations

abstract:
  The probability of strong gravitational lensing of distant compact objects by
transparent lenses with King mass distributions is calculated. Examples of such
lenses are globular clusters, dwarf galaxies, and clusters of hidden mass. The
lens masses thus range from 10^3 to 10^9 Solar mass, intermediate between
stellar and galactic masses. Taking account of the conic caustic of King lenses
and the fractal large-scale distribution of matter along the line of sight, it
is possible to explain the correlation between quasars and galaxies as the
effect of strong gravitational lensing of the active nuclei of distant galaxies
by globular clusters in the halos of nearby galaxies. Observational tests for
verifing this mesolensing hypothesis are described.


title:
The Cosmic QCD Phase Transition, Quasi-baryonic Dark Matter and Massive
  Compact Halo Objects

abstract:
  We propose that the cold dark matter (CDM) is composed entirely of quark
matter, arising from a cosmic quark-hadron transition. We denote this phase as
"quasibaryonic", distinct from the usual baryons. We show that compact
gravitational lenses, with masses around 0.5 (M_{\odot}), could have evolved
out of the quasibaryonic CDM.


title: Construction of a Database of CMB Spectrum Observations

abstract:
  We present the complete set of the measures of the CMB absolute temperature
on the basis on the works published in the literature, recognize the main
causes of error with the aim of estimating separately the magnitude of the
systematic and statistical errors, by focussing in particular on the most
recent observations. The main purpose of this work is to create a complete and
reasoned database of CMB absolute temperatures. The simple database format
permits a reading of the data through any text editor or through programs for
data handling. This is the first step for a statistical analysis of CMB
spectrum data and their comparison with the theoretical predictions for the
distorted spectra in order to derive constraints on physical processes at very
high redshifts.


title:
BeppoSAX observations of the three Gamma-ray pulsars PSR B0656+14, PSR
  B1055-52 and PSR B1706-44

abstract:
  We report the results of the observations of the three gamma-ray pulsars PSR
B0656+14, PSR B1055-52 and PSR B1706-44 performed with BeppoSAX. We detected a
pulsed emission only for PSR B1055-52: in the range 0.1-6.5 keV the pulse
profile is sinusoidal and the statistical significance is 4.5 sigma. The pulsed
fraction was estimated 0.64+/-0.17. This pulsation was detected also at
energies greater than 2.5 keV suggesting either a non-thermal origin or a quite
high temperature region on the neutron star surface. Spectral analysis showed
that only the X-ray spectrum of PSR B1706-44 can be fitted by a single
power-law component, while that of PSR B1055-52 requires also a blackbody
component (kT = 0.075 keV) and that of PSR B0656+14 two blackbody components
(kT_1 = 0.059, kT_2 = 0.12 keV).


title:
Fragmentation of Magnetically Subcritical Clouds into Multiple
  Supercritical Cores and the Formation of Small Stellar Groups

abstract:
  Isolated low-mass stars are formed in dense cores of molecular clouds. In the
standard picture, the cores are envisioned to condense out of strongly
magnetized clouds through ambipolar diffusion. Most previous calculations based
on this scenario are limited to axisymmetric cloud evolution leading to a
single core, which collapses to form an isolated star or stellar system at the
center. These calculations are here extended to the nonaxisymmetric case under
thin-disk approximation, which allows for a detailed investigation into the
process of fragmentation, fundamental to binary, multiple system, and cluster
formation. We have shown previously that initially axisymmetric, magnetically
subcritical clouds with an $m=2$ density perturbation of modest fractional
amplitude ($\sim 5%$) can develop highly elongated bars, which facilitate
binary and multiple system formation. In this paper, we show that in the
presence of higher order ($m\ge 3$) perturbations of similar amplitude such
clouds are capable of breaking up into a set of discrete dense cores. These
multiple cores are magnetically supercritical. They are expected to collapse
into single stars or stellar systems individually and, collectively, to form a
small stellar group. Our calculations demonstrate that the standard scenario
for single star formation involving magnetically subcritical clouds and
ambipolar diffusion can readily produce more than one star, provided that the
cloud mass is well above the Jeans limit and relatively uniformly distributed.
The fragments develop in the central part of the cloud, after the region has
become magnetically supercritical but before rapid collapse sets in. It is
enhanced by the flattening of mass distribution along the field lines and by
the magnetic tension force.


title: A Methane Isolated Planetary Mass Object in Orion

abstract:
  We report on the discovery of a free-floating methane dwarf toward the
direction of the young star cluster sigma Orionis. Based on the object's
far-red optical and near-infrared photometry and spectroscopy, we conclude that
it is a possible member of this association. We have named it as S Ori
J053810.1-023626 (S Ori 70 is the abridged name). If it is a true member of
sigma Orionis, the comparison of the photometric and spectroscopic properties
of S Ori 70 with state-of-the-art evolutionary models yields a mass of 3
(+5/-1) Jupiter mass for ages between 1 Myr and 8 Myr. The presence of such a
low-mass object in our small search area (55.4 sq. arcmin) would indicate a
rising substellar initial mass function in the sigma Orionis cluster even for
planetary masses.


title:
On the reliability of the semiempirical RR Lyrae Period - Blue Amplitude
  - V-band Luminosity relation

abstract:
  We investigate the accuracy and reliability of the semiempirical period -
blue amplitude - V-band luminosity relationship for ab-type RR Lyrae stars
originally obtained by Castellani & De Santis (1994) and De Santis (1996). We
infer that the zero point of this relationship does depend on the metallicity,
by studying a sample of both field and cluster variables. We also show that the
use of this relationship can still be useful for those stellar systems showing
an intrinsic metallicity spread, since in this case the metallicity effect has
a negligible effect on the final distance modulus estimate. We compare the
adopted semiempirical relationship with the fully empirical one recently
provided by Kovacs & Walker (2001). When the zero point of the latter relation
is fixed consistently with the former one, the two equations are equivalent. By
appling the semiempirical period - blue amplitude - V-band luminosity relation,
as well as the technique proposed by Cassisi, De Santis & Piersimoni (2001), to
the globular cluster $\omega$ Cen, we show that the empirical slope of the
relationship between the mass of the fundamental RR Lyrae pulsators and their
metallicity, is in fair agreement with the one predicted by updated
evolutionary models for Horizontal-Branch stars.


title:
Erratum: Star formation and chemical evolution in SPH simulations: a
  statistical approach

abstract:
  Errata for MNRAS 330, 821 (2002, astro-ph/0111084). A notation error in Eq. 7
and some typos in Table 3 corrected.


title:
Chandra and RXTE studies of X-ray/gamma-ray millisecond pulsar PSR
  J0218+4232: A clue to unidentified gamma-ray sources?

abstract:
  Millisecond pulsar PSR J0218+4232 shows remarkable high-energy properties:
very hard pulsed X-ray emission up to ~10 keV and a likely detection of
high-energy gamma-rays (> 100 MeV) with a soft spectrum. The relative phasing
of the X-ray and gamma-ray profiles, however, was unknown. A recently performed
Chandra (0.08-10 keV) observation of PSR J0218+4232 settled the phasing down to
0.2 millisecond, and shows that the X-ray pulses are aligned with the gamma-ray
pulses providing supporting evidence for our first detection of high-energy
gamma-rays from this source. The preliminary results from a recent RXTE (2-250
keV) observation (27-12-2001 -- 7-01-2002) show significant pulsed emission, in
a complex profile, up to ~20 keV. The composite high-energy spectrum of this
millisecond pulsar is similar to the canonical spectrum of Unidentified
Gamma-ray Sources (UGS), making fast (<3-4 ms) millisecond pulsars with low
characteristic ages (<10^8 years) good candidates for an UGS association and
challenging targets for INTEGRAL observations.


title:
More concerning the anelastic and subseismic approximations for
  low-frequency modes in stars

abstract:
  Two approximations, namely the subseismic approximation and the anelastic
approximation, are presently used to filter out the acoustic modes when
computing low frequency modes of a star (gravity modes or inertial modes). In a
precedent paper (Dintrans & Rieutord 2001), we observed that the anelastic
approximation gave eigenfrequencies much closer to the exact ones than the
subseismic approximation. Here, we try to clarify this behaviour and show that
it is due to the different physical approach taken by each approximation: On
the one hand, the subseismic approximation considers the low frequency part of
the spectrum of (say) gravity modes and turns out to be valid only in the
central region of a star; on the other hand, the anelastic approximation
considers the Brunt-Vaisala frequency as asymptotically small and makes no
assumption on the order of the modes. Both approximations fail to describe the
modes in the surface layers but eigenmodes issued from the anelastic
approximation are closer to those including acoustic effects than their
subseismic equivalent.
  We conclude that, as far as stellar eigenvalue problems are concerned, the
anelastic approximation is better suited for simplifying the eigenvalue problem
when low-frequency modes of a star are considered, while the subseismic
approximation is a useful concept when analytic solutions of high order
low-frequency modes are needed in the central region of a star.


title: The Galactic Distribution of Large HI Shells

abstract:
  We report the discovery of nineteen new HI shells in the Southern Galactic
Plane Survey (SGPS). These shells, which range in radius from 40 pc to 1 kpc,
were found in the low resolution Parkes portion of the SGPS dataset, covering
Galactic longitudes l=253 deg to l=358 deg. Here we give the properties of
individual shells, including positions, physical dimensions, energetics,
masses, and possible associations. We also examine the distribution of these
shells in the Milky Way and find that several of the shells are located between
the spiral arms of the Galaxy. We offer possible explanations for this effect,
in particular that the density gradient away from spiral arms, combined with
the many generations of sequential star formation required to create large
shells, could lead to a preferential placement of shells on the trailing edges
of spiral arms. Spiral density wave theory is used in order to derive the
magnitude of the density gradient behind spiral arms. We find that the density
gradient away from spiral arms is comparable to that out of the Galactic plane
and therefore suggest that this may lead to exaggerated shell expansion away
from spiral arms and into interarm regions.


title: Compact, Isolated High-Velocity Clouds

abstract:
  We consider here the class of compact, isolated, high-velocity HI clouds,
CHVCs, which are sharply bounded in angular extent down to a limiting column
density of 1.5x10^18 cm^-2. We describe our automated search algorithm and it's
application to the LDS north of dec= -28 deg. and the HIPASS data south of
dec=0, resulting in an all--sky catalog numbering 246 CHVCs. We argue that
these objects are more likely to represent a single phenomenon in a similar
evolutionary state than would a sample which included any of the major HVC
complexes. Five principal observables are defined for the CHVC population: (1)
the spatial deployment of the objects on the sky, (2) the kinematic
distribution, (3) the number distribution of observed HI column densities, (4)
the number distribution of angular sizes, and (5) the number distribution of
line widths. We show that the spatial and kinematic deployments of the ensemble
of CHVCs contain various clues regarding their characteristic distance. These
clues are not compatible with a location of the ensemble within the Galaxy
proper. The deployments resemble in several regards those of the Local Group
galaxies. We describe a model testing the hypothesis that the CHVCs are a Local
Group population. The agreement of the model with the data is judged by
extracting the observables from simulations, in a manner consistent with the
sensitivities of the observations and explicitly taking account of Galactic
obscuration. We show that models in which the CHVCs are the HI counterparts of
dark-matter halos evolving in the Local Group potential provide a good match to
the observables, if account is taken of tidal and ram--pressure disruption, the
consequences of obscuration due to Galactic HI and of differing sensitivities
and selection effects pertaining to the surveys.


title: The Mass Function of the Arches Cluster from Gemini Adaptive Optics Data

abstract:
  We present the mass function (MF) of the Arches cluster obtained from
ground-based adaptive optics data in comparison with results derived from
HST/NICMOS data. A MF slope of Gamma = -0.8 +- 0.2 is obtained. Both datasets
reveal a strong radial variation in the MF, with a flat slope in the cluster
center, which increases with increasing radius.


title: Coherent Emission from Magnetars

abstract:
  It is proposed that magnetospheric currents above the surfaces of magnetars
radiate coherent emission in analogy to pulsars. Scaling the magnetospheric
parameters suggests that the coherent emission from magnetars would emerge in
the infra-red or optical.


title:
ASCA observations of groups at radii of low overdensity. Implications
  for the cosmic preheating

abstract:
  Through a 3d-modeling of ASCA observations, we performed a spatially resolved
X-ray spectroscopic study, extending to radii exceeding 150 kpc, for a sample
of 9 groups of galaxies. Combined with published ROSAT results, we conclude
that these systems generally exhibit a strong temperature decline at outer
radii. In our best case, NGC3268, this corresponds to a flattening of the
entropy profile at a level of ~400 keV cm^2. This value is high compared both
to the observed entropy floor of ~100 keV cm^2 and to the expected value from
gravitational heating. We suggest that the observed entropy profile in most
groups at densities exceeding 500 times the critical is purely driven by
non-gravitational heating processes. After comparison with a larger sample of
groups and clusters, we conclude that there is a variation in the level of
non-gravitational heating between ~100 keV cm^2 and ~400 keV cm^2 within every
system. Using models of cluster formation as a reference frame, we established
that the accreted gas reaches an entropy level of 400 keV cm^2 by redshift
2.0-2.5, while such high entropies where not present at redshifts higher than
2.8-3.5, favoring nearly instantaneous preheating. Adopting galactic winds as a
source of preheating, and scaling the released energy by the observed metal
abundance, the variation in the preheating could be ascribed mostly to
variation in the typical overdensity of the energy injection, ~30 for an
entropy floor (100 keV cm^2) and to ~5 for an entropy of 400 keV cm^2.


title:
Maximum orbital frequencies for rotating quark stars and neutron
  stars--implications for the resonance theory of kHz QPOs

abstract:
  The spin-up of a neutron star crucially depends on the maximum orbital
frequency around it, as do a host of other high energy accretion phenomena in
low mass X-ray binaries, including quasi-periodic oscillations (QPOs) in the
X-ray flux. We compare the maximum orbital frequencies for MIT-bag quark stars
and for neutron stars modeled with the FPS equation of state. The results are
based on relativistic calculations of constant baryon sequences of uniformly
rotating strange star models, and are presented as a function of the stellar
rotational frequency. The marginally stable orbit is present outside quark
stars for a wide range of parameters, but outside the neutron stars it is
present only for the highest values of mass. This allows a discrimination
between quark stars and neutron stars in the resonance theory of kHz QPOs.


title: A statistical study of binary and multiple clusters in the LMC

abstract:
  Based on the Bica et al. (1999) catalogue we studied the star cluster system
of the LMC and provide a new catalogue of all binary and multiple cluster
candidates found. We performed Monte Carlo simulations and produced artificial
cluster distributions that we compared with the real one in order to check how
many of the found cluster pairs and groups can be expected statistically due to
chance superposition on the plane of the sky. We found that, depending on the
cluster density, between 56% (bar region) and 12% (outer LMC) of the detected
pairs can be explained statistically. We studied in detail the properties of
the multiple cluster candidates. The binary cluster candidates seem to show a
tendency to form with components of similar size. When possible, we studied the
age structure of the cluster groups and found that the multiple clusters are
predominantly young with only a few cluster groups older than 300 Myr. The
spatial distribution of the cluster pairs and groups coincides with the
distribution of clusters in general; however, old groups or groups with large
internal age differences are mainly located in the densely populated bar
region. Thus, they can easily be explained as chance superpositions. Our
findings show that a formation scenario through tidal capture is not only
unlikely due to the low probability of close encounters of star clusters, and
thus the even lower probability of tidal capture, but the few groups with large
internal age differences can easily be explained with projection effects. We
favour a formation scenario as suggested by Fujimoto & Kumai (1997) in which
the components of a binary cluster formed together and thus should be coeval or
have small age differences compatible with cluster formation time scales.


title: The Formation Mechanism of Brown Dwarfs

abstract:
  We present results from the first hydrodynamical star formation calculation
to demonstrate that brown dwarfs are a natural and frequent product of the
collapse and fragmentation of a turbulent molecular cloud. The brown dwarfs
form via the fragmentation of dense molecular gas in unstable multiple systems
and are ejected from the dense gas before they have been able to accrete to
stellar masses. Thus, they can be viewed as `failed stars'. Approximately three
quarters of the brown dwarfs form in gravitationally-unstable circumstellar
discs while the remainder form in collapsing filaments of molecular gas. These
formation mechanisms are very efficient, producing roughly the same number of
brown dwarfs as stars, in agreement with recent observations. However, because
close dynamical interactions are involved in their formation, we find a very
low frequency of binary brown dwarf systems ($\lsim 5$%) and that those binary
brown dwarf systems that do exist must be close $\lsim 10$ AU. Similarly, we
find that young brown dwarfs with large circumstellar discs (radii $\gsim 10$
AU) are rare ($\approx 5$%).


title:
The Cosmic Foam: Stochastic Geometry and Spatial Clustering Across the
  Universe

abstract:
  We stress the importance of stochastic geometry as a branch of mathematical
statistics particularly suited to model and investigate nontrivial spatial
patterns. One of its key concepts, Voronoi tessellations, represents a
versatile and flexible mathematical model for foamlike patterns. Based on a
seemingly simple definition, Voronoi tessellations define a wealthy stochastic
network of interconnected anisotropic components, each of which can be
identified with the various structural elements of the cosmic galaxy
distribution. Here we describe results of an ongoing investigation of a variety
of aspects of cosmologically relevant spatial distributions and statistics
within the framework of Voronoi tessellations. Interesting is the recent
finding of a profound scaling of both clustering strength and clustering extent
for the distribution of tessellation nodes, representing galaxy clusters. It
suggests a hitherto unexpected fundamental and profound property of foamlike
geometries. In a sense, cellular networks may be the source of an intrinsic
``geometrically biased'' clustering.


title:
Membership, metallicity and lithium abundances for solar-type stars in
  NGC 6633

abstract:
  We present spectroscopic observations of candidate F, G and K type stars in
NGC 6633, an open cluster with a similar age to the Hyades. We identify 10 new
cluster members including one short period binary system. Combining this survey
with that of Jeffries (1997), we identify a total of 30 solar-type members. We
have used the F and early G stars to spectroscopically estimate
[Fe/H]=-0.096+/-0.081 for NGC 6633 and with more precision that NGC 6633 has
(0.074+/-0.041) dex less iron than the Pleiades and (0.206+/-0.040) dex less
iron than the Hyades. Lithium abundances have been estimated for the NGC 6633
members and compared with consistently determined Li abundances in other
clusters. Several mid F stars in NGC 6633 show strong Li depletion at
approximately the same effective temperature that this phenomenon is seen in
the Hyades. At cooler temperatures the Li abundance patterns in several open
clusters with similar ages (NGC 6633, Hyades, Praesepe and Coma Berenices) are
remarkably similar, despite their differing [Fe/H]. There is however evidence
that the late G and K stars of NGC 6633 have depleted less Li than their Hyades
counterparts. This qualitatively agrees with models for pre-main sequence Li
depletion that feature only convective mixing, but these models cannot
simultaneously explain why these stars have in turn depleted Li by more than 1
dex compared with their ZAMS counterparts in the Pleiades. Two explanations are
put forward. The first is that elemental abundance ratios, particularly [O/Fe],
may have non-solar values in NGC 6633 and would have to be higher than in
either the Hyades or Pleiades. The second is that additional non-convective
mixing, driven by angular momentum loss, causes additional photospheric Li
depletion during the first few hundred Myr of main sequence evolution.


title:
Photospheric-Phase Spectropolarimetry and Nebular-Phase Spectroscopy of
  the Peculiar Type Ic Supernova 2002ap

abstract:
  The early-time optical spectrum of the Type Ic supernova (SN) 2002ap was
characterized by unusually broad features, leading some authors to designate it
a "hypernova." We present optical spectropolarimetry of this object 16 and 37
days after the estimated date of explosion. After correcting for interstellar
polarization, we find evidence for a high level of intrinsic continuum
polarization at both epochs: p >~ 1.3% on day 16 and p >~ 1.0% on day 37.
Prominent line polarization is also seen, especially in the trough of the Ca II
near-infrared triplet during the second epoch. When interpreted in terms of the
oblate, electron-scattering model atmospheres of Hoeflich (1991), our results
imply an asymmetry of at least 20% (day 16) and 17% (day 37). The data suggest
a fair degree of axisymmetry, although the polarization angle of the dominant
polarization axes are different by about 55 deg. between the two epochs,
implying a complex morphology for the thinning ejecta. In particular, there
exists some spectropolarimetric evidence for a different distribution of Ca
relative to iron-group elements. We also present flux spectra of SN 2002ap
taken 131 and 140 days after the explosion. The spectra are characterized by a
very weak continuum and broad emission lines, indicating that SN 2002ap has
entered the nebular phase. The spectral features are substantially similar to
those of ``normal'' SNe Ic in the nebular phase, and the emission lines are not
significantly broader. However, some of the broad lines are very sharply
peaked, and may possess a narrow component (probably unresolved by our spectra,
FWHM <~ 400 km/s that is redshifted by ~ 580$ km/s with respect to the systemic
velocity of the host galaxy.


title: Chandra X-ray Observations of NGC 1316 (Fornax A)

abstract:
  We report the results of the Chandra ACIS sub-arcsecond resolution X-ray
observation of the archetypal merger radio galaxy NGC 1316 (Fornax A). We
confirm the presence of fine sub-structures in the hot Interstellar Medium
(ISM). Some of these are likely to result from interaction with the radio jets,
while others may be related to a complex intermingling of different phases of
the ISM. We detect a low-luminosity X-ray AGN with Lx = 5 x 1039 erg sec-1 (in
0.3-8 keV) and a G=1.7 power-law energy spectrum. We also detect 81 point
sources within the 25th magnitude isophotal ellipse of NGC 1316 (Lx in the
range of 2 x 1037 - 2 x 1039 erg sec-1), with hard (kT~5 keV) X-ray spectra,
typical of X-ray binaries, and a spatial radial distribution consistent with
that of the optical (i.e., stellar) surface brightness. We derive the X-ray
luminosity function (XLF) of these sources, correcting for the incompleteness
at the faint end caused by the presence of the diffuse emission from the hot
ISM in the central regions of NGC 1316 and by the widening of the Chandra PSFs
at increasing distance from the aim point. With these corrections, the XLF is
well reproduced by a single -unbroken- power law with a slope of -1.3 down to
our threshold luminosity of ~3 x 1037 erg sec-1. The hot ISM has temperatures
in the 0.5 - 0.6 keV range, its surface brightness distribution is more
centrally concentrated than that of the point sources, and its temperature
appears to decrease at larger radii. These properties suggest that the ISM may
be subject to partial winds. Taking into account the spectral complexity of the
ISM, and the presence of unresolved low luminosity X-ray sources (which can be
inferred from the spectra), we constrain the metal abundance of the hot ISM to
be Z = 0.25 - 1.3 solar (90% confidence).


title:
X-ray, Optical, and Infrared Imaging and Spectral Properties of the 1 Ms
  Chandra Deep Field North Sources

abstract:
  We present the optical, near-infrared, submillimeter, and radio follow-up
catalog of the X-ray selected sources from the 1 Ms Chandra observation of the
Hubble Deep Field North region. We have B, V, R, I, and z' magnitudes for the
370 X-ray point sources, HK' magnitudes for 276, and spectroscopic redshifts
for 182. We present high-quality spectra for 175 of these. The redshift
distribution shows indications of structures at z=0.843 and z=1.0175 (also
detected in optical surveys) which could account for a part of the
field-to-field variation seen in the X-ray number counts. The flux
contributions separated into unit bins of redshift show that the z<1
spectroscopically identified sources already contribute about one-third of the
total flux in both the hard and soft bands. We find from ratios of the X-ray
counts that the X-ray spectra are well-described by absorption of an intrinsic
Gamma=1.8 power-law, with log NH values ranging from 21 to 23.7. We estimate
that the Chandra sources that produce 87% of the HEAO-A X-ray background (XRB)
at 3 keV produce 57% at 20 keV, provided that at high energies the spectral
shape of the sources continues to be well-described by a Gamma=1.8 power-law.
However, when the Chandra contributions are renormalized to the BeppoSAX XRB at
3 keV, the shape matches fairly well the observed XRB at both energies. Thus,
whether a substantial population of as-yet undetected Compton-thick sources is
required to completely resolve the XRB above 10 keV depends critically on how
the currently discrepant XRB measurements in the 1-10 keV energy range tie
together with the higher energy XRB. (Abridged)


title:
Limits on the Ultra-High Energy Electron Neutrino Flux from the RICE
  Experiment

abstract:
  Upper limits are presented on the diffuse flux of ultra-high energy $\nu_e$,
based on analysis of data taken by the RICE experiment during August, 2000. The
RICE receiver array at South Pole monitors cold ice for radio-wavelength
Cherenkov radiation resulting from neutrino-induced in-ice showers. For
energies above 1 EeV, RICE is an effective detector of over 15 km$^3$ sr.
Potential signal events are separated from backgrounds using vertex location,
event reconstruction, and signal shape. These are the first terrestrial limits
exploiting the physics of radio Cherenkov emissions from charged-current
$\nu_e+N\to e+N'$ interactions.


title:
Sensitivity of the Cosmic Microwave Background Anisotropy to Initial
  Conditions in Quintessence Cosmology

abstract:
  We analyze the evolution of energy density fluctuations in cosmological
scenarios with a mixture of cold dark matter and quintessence, in which the
quintessence field is modeled by a constant equation of state. We obtain
analytic expressions for the time evolution of the quintessence perturbations
in models with light fields. The fluctuations behave analogously to a driven
harmonic oscillator, where the driving term arises from the inhomogeneities in
the surrounding cosmological fluid. We demonstrate that the homogeneous
solution, determined by the initial conditions, is completely sub-dominant to
the inhomogeneous solution for physically realistic scenarios. Thus we show
that the cosmic microwave background anisotropy predicted for such models is
highly insensitive to the initial conditions in the quintessence field.


title: Multiwavelength observations of the M15 intermediate velocity cloud

abstract:
  We present Westerbork Synthesis Radio Telescope HI images, Lovell Telescope
multibeam HI wide-field mapping, Wisconsin H-alpha Mapper facility images,
William Herschel Telescope longslit echelle CaII observations, and IRAS ISSA 60
and 100 micron coadded images towards the intermediate velocity cloud located
in the general direction of the M15 globular cluster. When combined with
previously-published Arecibo data, the HI gas in the IVC is found to be clumpy,
with peak HI column density of 1.5x10^(20) cm^(-2), inferred volume density
(assuming spherical symmetry) of 24 cm^(-3)/(D kpc), and maximum brightness
temperature at a resolution of 81x14 arcsec of 14 K. The HI gas in the cloud is
warm, with a minimum FWHM value of 5 km/s, corresponding to a kinetic
temperature, in the absence of turbulence, of 540 K. There are indications in
the HI data of 2-component velocity structure in the IVC, indicative of
cloudlets. This velocity structure is also tentatively seen in the CaK spectra,
although the SNR is low. The main IVC condensation is detected by WHAM in
H-alpha with intensities uncorrected for Galactic absorption of upto 1.3
Rayleigh, indicating that the cloud is partially ionised. The FWHM of the
ionised component, at a resolution of 1 degree, exceeds 30 km/s. The spatial
and velocity coincidence of the H-alpha and HI peaks in emission is
qualitatively good. Finally, the 100 and 60 micron IRAS images show spatial
coincidence over a 0.7 degree field, with low and intermediate-velocity gas,
respectively, indicating that the IVC may contain dust.


title:
A Chandra High-Resolution Camera Observation of X-Ray Point Sources in
  M31

abstract:
  We present results from a 47 ks observation of the Andromeda galaxy, M31,
using the High-Resolution Camera of the Chandra X-Ray Observatory. We detect
142 point sources spanning three orders of magnitude in luminosity, from $L_X =
2\times 10^{35} \rm erg s^{-1}$ to $L_X = 2\times 10^{38} \rm erg s^{-1}$ in
the 0.1-10 keV band. The X-ray source location accuracy is better than
$1\arcsec$ in the central regions of the galaxy. One source lies within
$1.3\arcsec$ of SN 1885 but does not coincide with the UV absorption feature
identified as the supernova remnant. However, there is an optical transient,
which is likely an optical nova, at the location of the X-ray source. There is
a weak source, $L_X \sim 4 \times 10^{36} \rm erg cm^{2} s^{-1}$, coincident
with the nucleus of M31, and 14 sources coincident with globular clusters.
  Our observation has very high efficiency down to luminosities of $1.5\times
10^{36} \rm erg s^{-1}$ for sources within $5\arcmin$ of the nucleus. Comparing
with a ROSAT observation made 11 years earlier, we find that $0.46 \pm 0.26$ of
the sources with $L_X > 5 \times 10^{36} \rm erg s^{-1}$ are variable. We find
no evidence for X-ray pulsars in this region, indicating that the population is
likely dominated by low-mass X-ray binaries. The source density radial profile
follows a powerlaw distribution with an exponent of $1.25 \pm 0.10$ and is
inconsistent with the optical surface brightness profile. The x-ray point
source luminosity function is well fitted by a differential broken powerlaw
with a break at a luminosity of $(4.5^{+1.1}_{-2.2}) \times 10^{37} \rm erg
s^{-1}$. The luminosity function is consistent with a model of an aging
population of X-ray binaries.


title: A review of x-ray spectral evolution in Crab pulsar

abstract:
  Pravdo et al (1997) claimed that the phase resolved x-ray spectrum in Crab
pulsar (PSR B0531+21) shows a spectral hardening at the leading edge of the
first peak of its integrated profile; this was a new and unexpected result.
This article reanalyzes their data, as well as some other related data, and
argues that the spectrum is as likely to be unvarying (i.e., neither hardening
nor softening).


title:
An XMM-Newton study of the 401 Hz accreting pulsar SAX J1808.4-3658 in
  quiescence

abstract:
  SAX J1808.4-3658 is a unique source being the first Low Mass X-ray Binary
showing coherent pulsations at a spin period comparable to that of millisecond
radio pulsars. Here we present an XMM-Newton observation of SAX J1808.4-3658 in
quiescence, the first which assessed its quiescent luminosity and spectrum with
good signal to noise. XMM-Newton did not reveal other sources in the vicinity
of SAX J1808.4-3658 likely indicating that the source was also detected by
previous BeppoSAX and ASCA observations, even if with large positional and flux
uncertainties. We derive a 0.5-10 keV unabsorbed luminosity of L_X=5x10^{31}
erg/s, a relatively low value compared with other neutron star soft X-ray
transient sources. At variance with other soft X-ray transients, the quiescent
spectrum of SAX J1808.4-3658 was dominated by a hard (Gamma~1.5) power law with
only a minor contribution (<10%) from a soft black body component. If the power
law originates in the shock between the wind of a turned-on radio pulsar and
matter outflowing from the companion, then a spin-down to X-ray luminosity
conversion efficiency of eta~10^{-3} is derived; this is in line with the value
estimated from the eclipsing radio pulsar PSR J1740-5340. Within the deep
crustal heating model, the faintness of the blackbody-like component indicates
that SAX J1808.4-3658 likely hosts a massive neutronstar (M>1.7 solar masses).


title: Time Resolved Spectral Analysis of Bright Gamma Ray Bursts

abstract:
  We present the time integrated and time resolved spectral analysis of a
sample of bright bursts selected with F_{peak}>20 phot cm^{-2} sec^{-1} from
the BATSE archive. We fitted four different spectral models to the pulse time
integrated and time resolved spectra. We compare the low energy slope of the
fitted spectra with the prediction of the synchrotron theory [predicting photon
spectra softer than E^{-2/3}], and test, through direct spectral fitting, the
synchrotron shock model. We point out that differences in the parameters
distribution can be ascribed to the different spectral shape of the models
employed and that in most cases the spectrum can be described by a smoothly
curved function. The synchrotron shock model does not give satisfactory fits to
the time averaged and time resolved spectra. Finally, we derive that the
synchrotron low energy limit is violated in a considerable number of spectra
both during the rise and decay phase around the peak.