title: Cosmic Equation of State and Advanced LIGO Type Gravity Wave Experiments

abstract:
  Future generation of interferometric gravitational wave detectors is hoped to
provide accurate measurements of the final stages of binary inspirals. The
sources probed by such experiments are of extragalactic origin and the observed
chirp mass is the intrinsic chirp mass multiplied by $(1+z)$ where $z$ is the
redshift of the source. Moreover the luminosity distance is a direct observable
is such experiments. This creates the possibility to establish a new kind of
cosmological tests, supplementary to more standard ones.
  Recent observations of distant type Ia supernovae light-curves suggest that
the expansion of the universe has recently begun to accelerate. A popular
explanation of present accelerating expansion of the universe is to assume that
some part $\Omega_Q$ of the matter-energy density is in the form of dark
component called ``the quintessence'' with the equation of state $p_Q = w
\rho_Q$ with $w \geq -1.$ In this paper we consider the predictions concerning
observations of binary inspirals in future LIGO type interferometric
experiments assuming a ``quintessence cosmology''. In particular we compute the
expected redshift distributions of observed events in the a priori admissible
range of parameters describing the equation of state for the quintessence. We
find that this distribution has a robust dependence on the cosmic equation of
state.


title: A model for the optical high state light curve of AM Herculis

abstract:
  We present a simple quantitative model that can describe the photometric B
and V band light curves of AM Herculis obtained during a high state. The
double-humped shape of the V band light curve is dominated by cyclotron
emission from a region at the main accreting pole with an area of ~5x10e16 cm^2
and sustaining an inflow of ~0.06 g/cm^2/s. The almost unmodulated B band is
dominated by emission from the accretion stream. The contribution of the heated
white dwarf to the optical emission is small in the B band, but comparable to
that of the accretion stream in the V band. The emission of the secondary star
is negligible both in B and in V.


title: HST observations of the LMC compact HII region N11A

abstract:
  We present a study of the LMC compact HII region N11A using Hubble Space
Telescope imaging observations which resolve N11A and reveal its unknown
nebular and stellar features. The presence of a sharp ionization front
extending over more than 4'' (1 pc) and fine structure filaments as well as
larger loops indicate an environment typical of massive star formation regions,
in agreement with high [OIII]/Hb line ratios. N11A is a young region, as
deduced from its morphology, reddening, and especially high local concentration
of dust, as indicated by the Balmer decrement map. Our observations also reveal
a cluster of stars lying towards the central part of N11A. Five of the stars
are packed in an area less than 2'' (0.5 pc), with the most luminous one being
a mid O type star. N11A appears to be the most evolved compact HII region in
the Magellanic Clouds so far studied.


title:
The visibility of gamma-ray burst afterglows in dusty star-forming
  regions

abstract:
  Recent observations of the environments of gamma-ray bursts (GRBs) favour
massive stars as their progenitors, which are likely to be surrounded by gas
and dust. The visibility of the optical and UV emission of a GRB are expected
to depend on the characteristics of both the dust and the GRB emission itself.
A reasonable distribution of surrounding dust is capable of absorbing all the
optical and UV emission of the optical flash and afterglow of a GRB, unless the
optical flash has a peak isotropic luminosity L_peak > 10^49 erg/s. This means
that dark bursts should exist and these bursts will have to be studied at
infrared rather than optical wavelengths. In this paper details will be given
about the infrared GRB dust emission. The reprocessed dust emission peaks at a
rest-frame wavelength of about 8 micron. Forthcoming space telescopes, in
particular the IRAC camera aboard the Space Infrared Telescope Facility could
detect this emission out to a redshift of about 2. However, an accurate
position of the GRB afterglow must be provided for this emission to be
identified, because the light curve of the reprocessed dust emission does not
vary on time-scales less than several years.


title: Where Have All the Submillisecond Pulsars Gone?

abstract:
  The existence of pulsars with spin period below one millisecond is expected,
though they have not been detected up to now. Their formation depends on the
quantity of matter accreted from the companion which, in turn, is limited by
the mechanism of mass ejection from the binary. Mass ejection must be
efficient, at least in some cases, in order to produce the observed population
of moderately fast spinning millisecond pulsars. First we demonstrate, in the
framework of the widely accepted recycling scenario, using a population
synthesis approach, that a significant number of pulsars with spin period below
one millisecond is expected. Then we propose that significant variations in the
mass-transfer rate may cause, in systems with orbital periods larger than 1 hr,
the switch-on of a radio pulsar whose radiation pressure is capable of ejecting
out of the system most of the matter transferred by the companion and prevent
any further accretion. We show how this mechanism could dramatically alter the
binary evolution since the mechanism that drives mass overflow from the inner
Lagrangian point is still active while the accretion is inhibited. Moreover we
demonstrate that the persistency of this ``radio ejection'' phase depends on
the binary orbital period, demonstrating that close systems (orbital periods
lower than 1 hr) are the only possible hosts for ultra fast spinning neutron
stars. This could explain why submillisecond pulsars have not been detected so
far, as current radio surveys are hampered by computational limitations with
respect to the detection of very short spin period pulsars in short orbital
period binaries.


title:
Partially Absorbed Comptonization Spectrum from the Nearly Edge-on
  Source X 1822-371

abstract:
  We report the results of a spectral analysis over the range 0.1-200 keV
performed on the dipping source X 1822-371 observed by BeppoSAX. We find the
best fit to the continuum using a partially covered Comptonization model, due
to scattering off soft seed photons by electrons at a temperature of ~4.8 keV,
without the presence of any soft blackbody emission. The equivalent hydrogen
column obtained for the absorbed component is ~4.5 10^{22} cm^{-2}, an order of
magnitude larger than the Galactic absorption for this source, and the covering
fraction is ~71%. Because the inclination angle of X 1822-371 to the line of
sight is ~85^\circ, this model gives a reasonable scenario for the source: the
Comptonized spectrum could come from an extended accretion disk corona (ADC),
probably the only region that can be directly observed due to the high
inclination. The excess of matter producing the partial covering could be close
to the equatorial plane of the system, above the outer disk, occulting the
emission from the inner disk and the inner part of the ADC. An iron emission
line is also present at ~6.5 keV with an equivalent width of ~150 eV. We argue
that this strong iron line cannot be explained as reflection of the Comptonized
spectrum by the accretion disk. It is probably produced in the ADC. An emission
line at ~1.9 keV (with an equivalent width of ~54 eV) and an absorption edge at
\~8.7 keV (with an optical depth of ~0.1) are also required to fit this
spectrum. These features are probably produced by highly ionized iron (Fe XXIV)
present in the outer part of the ADC, where the plasma density is
\~10^{11}-10^{12} cm^{-3} and ionized plasma is present.


title: R-process pattern in the Very-Metal-Poor Halo Star CS31082-001

abstract:
  The very-metal-poor halo star CS31082-001 was discovered to be very strongly
r-process-enhanced during the course of a VLT+UVES high-resolution follow-up of
metal-poor stars identified in the HK survey of Beers and colleagues. Both the
strong n-capture element enhancement and the low carbon and nitrogen content of
the star (reducing the CN molecular band contamination) led to the first
$^{238}$U abundance measurement in a stellar spectrum (Cayrel et al. 2001), and
the opportunity to use both radioactive species $^{238}$U and $^{232}$Th for
dating the progenitor to this star. However, age computations all rely on the
hypothesis that the r-process pattern is solar, as this was indeed observed in
the other famous r-process-enhanced very metal poor stars CS22892-052 (Sneden
et al. 1996, 2000) and in HD115444 (Westin et al. 2000). Here, we investigate
whether this hypothesis is verified also for CS31082-001, using a preliminary
analysis of over 20 abundances of n-capture elements in the range Z=38 to Z=92.


title: Damping scales of neutralino cold dark matter

abstract:
  The lightest supersymmetric particle, most likely the neutralino, might
account for a large fraction of dark matter in the Universe. We show that the
primordial spectrum of density fluctuations in neutralino cold dark matter
(CDM) has a sharp cut-off due to two damping mechanisms: collisional damping
during the kinetic decoupling of the neutralinos at about 30 MeV (for typical
neutralino and sfermion masses) and free streaming after last scattering of
neutralinos. The last scattering temperature is lower than the kinetic
decoupling temperature by one order of magnitude. The cut-off in the primordial
spectrum defines a minimal mass for CDM objects in hierarchical structure
formation. For typical neutralino and sfermion masses the first gravitationally
bound neutralino clouds have to have masses above 10^(-7) solar masses.


title: The Jet and the Supernova in GRB990712

abstract:
  The optical light curve of the afterglow following the gamma-ray burst
GRB990712 is re-examined. Recently published polarization measurements of that
source require a collimated outflow geometry that in turn predicts a break in
the light curve. We show that the V-band light curve is consistent with such a
break and that the post-break light curve evolution is dominated by a supernova
contribution.


title: Nuclear obscuration in the high-ionization Seyfert 2 galaxy Tol 0109-383

abstract:
  We report the BeppoSAX detection of a hard X-ray excess in the X-ray spectrum
of the classical high-ionization Seyfert 2 galaxy Tol0109-383. The X-ray
emission of this source observed below 7 keV is dominated by reflection from
both cold and ionized gas, as seen in the ASCA data. The excess hard X-ray
emission is presumably due to the central source absorbed by an optically thick
obscuring torus with N(H)~2e24 cm-2. The strong cold X-ray reflection, if it is
produced at the inner surface of the torus, is consistent with the picture
where much of the inner nucleus of Tol0109-383 is exposed to direct view, as
indicated by optical and infrared properties. However, the X-ray absorption
must occur at small radii in order to hide the central X-ray source but leave
the optical high-ionization emission line region unobscured. This may also be
the case for objects like the Seyfert 1 galaxy Mrk231.


title: Predicting the Second Caustic Crossing in Binary Microlensing Events

abstract:
  We fit binary lens models to the data covering the initial part of real
microlensing events in an attempt to predict the time of the second caustic
crossing. We use approximations during the initial search through the parameter
space for light curves that roughly match the observed ones. Exact methods for
calculating the lens magnification of an extended source are used when we
refine our best initial models. Our calculations show that the reliable
prediction of the second crossing can only be made very late, when the light
curve has risen appreciably after the minimum between the two
caustic-crossings. The best observational strategy is therefore to sample as
frequently as possible once the light curve starts to rise after the minimum.


title:
The properties of field elliptical galaxies at intermediate redshift.
  II: photometry and spectroscopy of an HST selected sample

abstract:
  A sample of field early-type galaxies (E/S0) at intermediate redshift
($z\sim0.1-0.6$) is selected, based on morphology and colours from HST-WFPC2
parallel images. Photometric structural parameters (effective radius
$R_{\tx{e}}$ and effective surface brightness $SB_{\tx{e}}$) are derived
through the F606W and F814W filters, using luminosity profile fitting and
two-dimensional fitting techniques. The combined parameter that enters the
Fundamental Plane ($\log R_{\tx{e}}-\beta SB_{\tx{e}}$, with
$\beta\approx0.32$) is shown to suffer from significantly smaller uncertainties
(r.m.s. 0.03) than the individual structural parameters (e.g. $\sim 15$ per
cent r.m.s. on the effective radius).
  High signal-to-noise intermediate resolution spectra, taken at the ESO-3.6m,
yield redshifts for 35 galaxies and central velocity dispersions for 22
galaxies. Central velocity dispersions are derived using a library of stellar
templates covering a wide range of spectral types, in order to study the
effects of templates mismatches. The average random error on the central
velocity dispersion is found to be 8 per cent and the average systematic error
due to template mismatch is found to be 5 per cent. The errors on velocity
dispersion measurement and the effects of template mismatches are studied by
means of extensive Montecarlo simulations. In addition, we investigate whether
the determination of the velocity dispersion is sensitive to the spectral range
used, finding that the value of velocity dispersion is unchanged when the
spectral regions that include the absorption features Ca HK and NaD are masked
out during the fit.


title: SX Phoenicis Stars in the Core of 47 Tucanae

abstract:
  We present new results on five of six known SX Phoenicis stars in the core of
the globular cluster 47 Tucanae. We give interpretations of the light curves in
the V and I bands from 8.3 days of observations with the Hubble Space Telescope
near the core of 47 Tuc. The most evolved SX Phe star in the cluster is a
double-mode pulsator (V2) and we determine its mass to be 1.54+/-0.05 solar
masses from its position in the Hertzsprung-Russell diagram and by comparing
observed periods with current theoretical pulsation models. For V14 we do not
detect any pulsation signal. For the double-mode pulsators V3, V15, and V16 we
cannot give a safe identification of the modes. We also describe the
photometric techniques we have used to extract the light curves of stars in the
crowded core. Some of the SX Phoenicis are saturated and we demonstrate that
even for stars that show signs of a bleeding signal we can obtain a
point-to-point accuracy of 1-3%.


title: UBVI and Ha Photometry of the h & chi Persei cluster

abstract:
  UBVI and Ha photometry is presented for 17319 stars in vicinity of the young
double cluster h & chi Persei. Our photometry extends over a 37arcmin x 1arcdeg
field centered on the association. We construct reddening contours within the
imaged field. We find that the two clusters share a common distance modulus of
11.75$\pm$0.05 and ages of log age(yr) = 7.1$\pm$0.1. From the V-Ha colour, a
measure of the Ha emission strength, we conduct a survey for emission line
objects within the association. We detect a sample of 33 Be stars, 8 of which
are new detections. We present a scenario of evolutionary enhancement of the Be
phenomenon to account for the peak in Be fraction towards the top of the
main-sequence in the population of h & chi Persei and similar young clusters.


title: High Redshift Quasars and Star Formation History

abstract:
  Quasars are among the most luminous objects in the universe, and they can be
studied in detail up to the highest known redshift. Assuming that the gas
associated with quasars is closely related to the interstellar medium of the
host galaxy, quasars can be used as tracer of the star formation history in the
early universe. We have observed a small sample of quasars at redshifts 3<z<5
and present results using NV/CIV and NV/HeII as well as MgII/FeII to estimate
the date of the first major star formation epoch. These line ratios indicate
solar and supersolar metallicities of the gas close to the quasars. Assuming
times of tau_{evol} = 1 Gyr the first star formation epoch can be dated to z_f
>= 10, corresponding to an age of the universe of less than 5*10^8 yrs (H_o =
65 km/s/Mpc, Omega_M = 0.3, Omega_Lambda = 0.7).


title:
The Apparent Fractal Conjecture: Scaling Features in Standard
  Cosmologies

abstract:
  This paper presents an analysis of the smoothness problem in cosmology by
focussing on the ambiguities originated in the simplifying hypotheses aimed at
observationally verifying if the large-scale distribution of galaxies is
homogeneous, and conjecturing that this distribution should follow a fractal
pattern in perturbed standard cosmologies. This is due to a geometrical effect,
appearing when certain types of average densities are calculated along the past
light cone. The paper starts reviewing the argument concerning the possibility
that the galaxy distribution follows such a scaling pattern, and the premises
behind the assumption that the spatial homogeneity of standard cosmology can be
observable. Next, it is argued that to discuss observable homogeneity one needs
to make a clear distinction between local and average relativistic densities,
and showing how the different distance definitions strongly affect them,
leading the various average densities to display asymptotically opposite
behaviours. Then the paper revisits Ribeiro's (1995: astro-ph/9910145) results,
showing that in a fully relativistic treatment some observational average
densities of the flat Friedmann model are not well defined at z ~ 0.1, implying
that at this range average densities behave in a fundamentally different manner
as compared to the linearity of the Hubble law, well valid for z < 1. This
conclusion brings into question the widespread assumption that relativistic
corrections can always be neglected at low z. It is also shown how some key
features of fractal cosmologies can be found in the Friedmann models. In view
of those findings, it is suggested that the so-called contradiction between the
cosmological principle, and the galaxy distribution forming an unlimited
fractal structure, may not exist.


title: The Distance to the Magellanic Clouds

abstract:
  The distance to LMC and SMC is a subject of controversy, with the difference
between the extreme values in distance moduli exceeding 0.5 mag. While
currently the best calibrated method is based on red clump giants, and the near
future improvement is most likely to come from detached eclipsing binaries, the
ultimate goal is to have a purely geometrical determination. The best prospect
will be to use relatively wide binary stars, for which spectroscopic orbits
will be obtained with large ground based telescopes, and astrometric orbits
will be obtained either with SIM, or with future ground based interferometers.
A preliminary list of 25 candidate systems is presented. It is based on OGLE
catalogs of BVI photometry.


title: On The Parent Population of Radio Galaxies and the FRI - FRII Dichotomy

abstract:
  We test the hypothesis that radio galaxies are a random subset of otherwise
normal elliptical galaxies. Starting with the observed optical luminosity
functions for elliptical galaxies, we show that the probability of an
elliptical forming a radio source is a continuous, increasing function of
optical luminosity, proportional to L squared. With this probability function
and the luminosity function of normal elliptical galaxies as input to Monte
Carlo simulations, we reproduce the observed distribution of radio galaxies in
the radio-optical luminosity plane. Our results show that radio galaxies are a
luminosity-biased but otherwise random sample of elliptical galaxies. This
unified view of radio-loud and radio-quiet ellipticals also explains the well
known difference of ~0.5 mag in average optical luminosity between FRI and FRII
radio galaxies as a simple selection effect. Specifically, FRII appear
preferentially in smaller galaxies because both radio and optical luminosity
functions are steep, so there is a negligible probability of observing a
powerful radio source associated with a bright galaxy; no intrinsic physical
differences between FRI and FRII host galaxies are required.


title:
Oxygen Abundances in Metal-Poor Stars (-2.2 < [Fe/H] < -1.2) from
  Infrared OH lines

abstract:
  Infrared OH lines at 1.55 - 1.56 um in the H-band were obtained with the
Phoenix high-resolution spectrograph at the 2.1m telescope of the Kitt Peak
National Observatory for a sample of 14 metal-poor stars. Detailed analyses of
the sample stars have been carried out, deriving stellar parameters based on
two methods: (a) spectroscopic parameters; (b) IRFM effective temperatures,
trigonometric gravities and metallicities from Fe II lines. The Fe I lines
present in the H-band region observed showed to be well fitted by the stellar
parameters within $\Delta$[Fe/H] < 0.15 dex. The oxygen abundances were derived
from fits of spectrum synthesis calculations to the infrared OH lines. CO lines
in the H- and K-bands were obtained for a subsample in order to determine their
carbon abundances. Adopting the spectroscopic parameters a mean oxygen-to-iron
ratio of [O/Fe] ~ +0.52 is obtained, whereas using the IRFM temperatures,
Hipparcos gravities and [FeII/H], [O/Fe] ~ +0.25 is found. A mean of the two
methods gives a final value of [O/Fe] ~ +0.4 for the metallicity range -2.2 <
[Fe/H] < -1.2 of the sample metal-poor stars.


title: Late Light Curves of Type Ia Supernovae

abstract:
  We extend earlier efforts to determine whether the late (t$\geq$60d)
light-curves of type Ia SNe are better explained by the escape of positrons
from the ejecta or by the complete deposition of positron kinetic energy in a
trapping magnetic field We find that applying a filter efficiency correction,
derived from measured spectra, to B, V, R, and I light-curves after day 50 can
produce a consistent bolometric light-curve. The V band is an accurate
indicator of total emission in the 3500$\AA$ - 9700$\AA$ range, with a constant
fraction ($\sim$25%) appearing in the V band after day 50. This suggests that
the V band scales with the bolometric luminosity, and that the deposited energy
is instantaneously recycled into optical emission during this epoch. Varying
bolometric corrections for the other bands are derived. We see significant
evolution of the colors of SNe Ia between day 50 and day 170. We suggest that
this may be due to the transition from spectra dominated by emission lines from
the radioactive nucleus, $^{56}$Co, to those from the stable daughter nucleus,
$^{56}$Fe. We show that the B, V, R, and I band light-curves of SNe Ia after
t$\geq$60d can be completely explained with energy deposition from $^{56}$Co
decay photons and positrons if substantial positron escape occurs.


title: Empirical diagnostics of the starburst-AGN connection

abstract:
  We examine a representative sample of 35 Seyfert 2 nuclei. Previous work has
shown that nearly 1/2 of these nuclei show the direct (but difficult-to-detect)
spectroscopic signatures at optical-UV wavelengths of the hot massive stars
that power circum-nuclear starbursts. In this paper we examine a variety of
more-easily-measured quantities for this sample, such as the equivalent widths
of strong absorption features, continuum colors, emission line equivalent
widths, ratios and profiles, far-IR luminosities and near-UV surface
brightness. We compare the composite starburst+Seyfert 2 nuclei to ``pure''
Seyfert 2's, Starburst galaxies and normal galactic nuclei. Our goals are to
verify whether these properties in composite nuclei are consistent with the
expected impact of a starburst, and to investigate alternative less-demanding
methods to infer the presence of starbursts in Seyfert 2's, applicable to
larger or more distant samples. We show that starbursts do indeed leave clear
and easily quantifiable imprints on the near-UV to optical continuum range.
Composite starburst+Seyfert 2 systems can be recognized by: (1) a strong
``Featureless Continuum'' which dilutes the CaII K line from the host's bulge
to W_K < 10 A; (2) emission lines whose equivalent widths are intermediate
between Starburst galaxies and ``pure'' Seyfert 2's; (3) relatively low
excitation line-ratios, which indicate that part of the gas ionization in these
Seyfert 2's (typically \sim 50% of Hbeta) is due to photoionization by OB
stars; (4) large far IR luminosities (> 10^10 Lsun); (5) High near-UV surface
brightness (~10^3 Lsun/pc^2). These characteristics are all consistent with the
expected impact of circum-nuclear starbursts on the observed properties of
Seyfert 2's. (abridged)


title:
Diverse Supernova Sources for the r-Process and Abundances in Metal-Poor
  Stars

abstract:
  The dispersion and mean trends of r-process abundances in metal-poor stars
are discussed based on a model of diverse supernova sources for the r-process.
This model is unique in that its key parameters are inferred from solar system
data independent of stellar observations at low metallicities. It is shown that
this model provides a good explanation for the observed dispersion and mean
trend of Eu abundances over -3 < [Fe/H] < -1. It is also shown that this model
provides a means to discuss r-abundances in general. For example, the Ag
abundance in any metal-poor star with observed Eu and Fe abundances can be
calculated from the model. This approach is demonstrated with success for two
stars and can be further tested by future Ag data. The dispersion and mean
trend of Ag abundances in metal-poor stars are also calculated for comparison
with future observations.


title:
The Expansion Center and Dynamical Age of the Galactic Supernova Remnant
  Cassiopeia A

abstract:
  We present proper motions for 21 bright main shell and 17 faint,
higher-velocity, outer ejecta knots in the Cas A supernova remnant and use them
to derive new estimates for the remnant's expansion center and age. Our study
included 1951 - 1976 Palomar 5 m prime focus plates, 1988 - 1999 CCD images
from the KPNO 4 m and MDM 2.4 m telescopes, and 1999 HST WFPC2 images.
Measurable positions covered a 23 to 41 yr time span for most knots, with a few
outer knots followed for almost 48 yr. We derive an expansion center of alpha =
23h 23m 27s.77 +- 0s.05, delta = 58d 48' 49".4 +- 0".4 (ICRS), with little
difference between centers derived using outer or main shell knots. This
position is 3.0 arcsec due north of that estimated by van den Bergh and Kamper
(1983). It also lies 6.6 +- 1.5 arcsec almost due north (PA = 354 deg) of the
remnant's recently-detected central X-ray point source, implying a transverse
velocity for the X-ray point source of about 330 km/s at a distance of 3.4 kpc.
Using the knots which lie out ahead of the remnant's forward blast wave, we
estimate a knot convergent date of A.D. 1671.3 +- 0.9, assuming no
deceleration. However, a deceleration of just approximately 1.6 km/(s yr) over
a 300 yr time span would produce an explosion date A.D. 1680, consistent with
the suspected sighting of the Cas A supernova by J. Flamsteed.


title: Scintillation as a Probe of the Intergalactic Medium

abstract:
  Most of the baryons in the low-redshift universe reside in a warm/hot
component which is difficult to detect with standard absorption/emission line
techniques. We propose to use quasar refractive scintillation as an useful,
complementary probe of such ionized, intergalactic gas. In particular, an
application to the case of the intracluster medium is presented. We show that
clusters located at z approx 0.02 should produce a source rms intensity
fluctuation at 50-100 GHz of several tens of percent and on time scales ranging
from days to months, depending on the projected location of the source on the
foreground cluster. However, in order to produce such a signal, the source
needs to be very compact. This effect, if observed, can be used as an
independent test of the baryonic mass fraction in clusters.


title: Chandra Observation of the Rho Oph Cloud

abstract:
  We observed a 17$'\times17'$ region of the $\rho$ Oph molecular cloud, using
the ACIS-I array onboard the {\it Chandra X-ray Observatory} (CXO). A 100-ks
exposure observation revealed $\sim$ hundred X-ray sources above the detection
limit of $\sim$ 10$^{28}$ ergs s$^{-1}$. About 2/3 of the X-ray sources are
identified to an optical and/or infrared counterpart, including significant
numbers of class I, II and III sources and a few brown dwarfs. The X-ray
detection rate of class I sources is surprisingly high of 70 %. Many X-ray
flares, possibly due to the magnetic activity, are found from all of the
classes. We make systematic spectral studies on the quiescent and flare X-rays
for all the X-ray sources. The X-ray temperatures and absorptions of class I
sources are generally larger than those of class II and III sources. Also X-ray
flares from class I sources show a hint of higher duty ratio, temperature and
luminosity, than those from more evolved classes. We further give brief results
on brown dwarfs, younger phase than class I, unclassified and unidentified
sources. Details for several selected young stellar objects, including the
first detection of a neutral iron line (6.4 keV) from a class I source YLW 16A,
are separately addressed.


title: The Oldest Stellar Populations at z ~ 1.5

abstract:
  There are at least three reasons for being interested in galaxies at high
redshifts that formed most of their stars quite quickly early in the history of
the Universe: (1) the ages of their stellar populations can potentially place
interesting constraints on cosmological parameters and on the epoch of the
earliest major episodes of star formation, (2) their morphologies may provide
important clues to the history and mechanisms of spheroid formation, and (3)
they are likely to identify the regions of highest overdensity at a given
redshift.
  We describe a systematic search for galaxies at z ~ 1.5 having essentially
pure old stellar populations, with little or no recent star formation. Our
approach is to apply a "photometric sieve" to the fields of quasars near this
redshift, looking for companion objects with the expected spectral-energy
distributions. Follow-up observations on two of the fields having candidates
discovered by this technique are described.


title: Dark Matter Search in the EDELWEISS experiment

abstract:
  The EDELWEISS Dark Matter Search uses low-temperature Ge detectors with heat
and ionisation read-out to identify nuclear recoils induced by elastic
collisions with WIMPs from the galactic halo. Preliminary results obtained with
320g bolometers are described. After a few weeks of data taking, data
accumulated with one of these detectors already allow to reach the upper part
of the DAMA region. Prospects for the present run and the second stage of the
experiment, EDELWEISS-II, using an innovative reversed cryostat allowing data
taking with 100 detectors, are briefly described.


title: On the accretion flow geometry in A0535+26

abstract:
  The geometry of accretion flow in the Be/X-ray transient A0535+26 is
explored. It is shown that neither moderate nor giant X-ray flaring events
observed in the system can be interpreted within the spherically symmetrical
accretion model and hence the formation of an accretion disk around the neutron
star magnetosphere during the both types of flares is required. The accretion
disk can be formed at the periastron if (i) the expansion velocity of the Be
star envelope in the equatorial plane is V_wr < 150 km/s and (ii) the parameter
accounting for the accretion flow inhomogeneities, xi, satisfies the following
condition: xi > 0.16 (Mdot_17)^-1/7, where (Mdot_17)^-1/7 is the rate of mass
capture by the neutron star expressed in units of 1017 g/s. We suggest that the
`missing' outburst phenomenon can be associated with the spherically
symmetrical accretion onto the interchange-stable magnetosphere of the neutron
star. The average spin up rate of the neutron star during moderate flares < 3.5
x 10^-12 Hz/s is predicted.


title: Evolution of Lithium-Beryllium-Boron and Oxygen in the early Galaxy

abstract:
  Oxygen is a much better evolutionary index than iron to describe the history
of Lithium-Beryllium-Boron (LiBeB) since it is the main producer of these light
elements at least in the early Galaxy. The O-Fe relation is crucial to the
determination of the exact physical process responsible for the LiBeB
production. At low metallicity, if [O/Fe] vs [Fe/H] is flat, then the
production mode is independent of the interstellar metallicity, BeB is
proportional to oxygen, i.e. is of primary nature. If not, the production mode
is function of the progressive enrichment in O of the interstellar medium, BeB
varies rather as the square of O, i.e. is of secondary nature. In the first
case, fast nuclei enriched into He, C and O injected by supernovae and
accelerated in surrounding superbubbles would explain the primary trend.
  In the second case, the main spallative agent would be the standard galactic
cosmic rays. Calculated nucleosynthetic yields of massive stars, estimates of
the energy cost of production of beryllium nuclei, and above all recent
observations reported in this meeting seem to favor the primary mechanism, at
least in the early Galaxy.


title:
Star clusterings in the Carina complex: UBVRI photometry of Bochum 9, 10
  and 11

abstract:
  We report on the first UBVRI CCD photometry of three poorly known star
clusterings in the region of Eta Carinae: Bochum9, Bochum10 and Bochum11. We
found that they are young, rather poor and loose open clusters. We argue that
Bochum9 is probably a small and loose cluster with about 30 probable members
having E(B-V)=0.63, located 4.6 kpc far from the Sun, beyond the Carina spiral
arm. Similarly, Bochum10 is a sparse aggregate with 14 probable members having
E(B-V)=0.47 and at a distance of 2.7 kpc from the Sun. Finally, Bochum11 is a
less than 4x10^6 yrs old cluster for which we identify 24 members. It has a
reddening E(B-V)=0.58, and lies between Bochum10 and 9, at 3.5 kpc from the
Sun. We propose that in the field of the cluster some stars might be pre Main
Sequence (MS) candidates.


title: CI and CO in the Spiral Galaxies NGC 6946 and M 83

abstract:
  Multitransition 12CO, 13CO and 492 GHz [CI] measurements of the late-type
spiral galaxies NGC 6946 and M 83 (NGC 5236) show pronounced molecular gas
concentrations in rapid solid-body rotation within a few hundred parsec from
both nuclei. Their 12CO, 13CO and [CI] relative intensities are nearly
identical. However, the very different [CII] intensities imply that the
physical conditions are not. The slow decrease of 12CO intensities with
increasing rotational level marks the presence of significant amounts of warm
and dense molecular gas in both galaxy centers. Detailed modelling indicates
that both galaxiy centers contain at least two distinct molecular components: a
warm and dense component with T(kin) = 30-60 K, n(H2) = 3000-10 000 cc, and a
more tenuous hotter component with T(kin) = 100-150 K, n(H2) < 1000 cc). Atomic
carbon column densities exceed CO column densities by a factor of about 1.5 in
NGC 6946 and about 4 in M 83. Unlike NGC 6946, M 83 contains a significant
amount of molecular hydrogen associated with ionized carbon rather than CO. The
centers of NGC 6946 and M 83 contain nearly identical total (atomic and
molecular) gas masses of about 3 x 10**7 M(sun). Despite their prominence, the
central gas concentrations in these galaxies represent only a few per cent of
the stellar mass in the same volume. The peak face-on gas mass density is much
higher in M 83 (120 M(sun)/pc**2) than in NGC 6946 (45 M(sun)/pc**2). The more
intense starburst in M 83 is associated with a more compact and somewhat hotter
PDR zone than the milder starburst in NGC 6946.


title:
Integral Field Near-IR Spectroscopy of a Sample of Seyfert and LINER
  Galaxies I: The Data

abstract:
  We present near-IR integral field spectroscopy of a sample of 31 Seyfert and
LINER galaxies which were selected both to span a wide range of nuclear
magnitudes and to possess roughly equal numbers of Seyfert type 1 and 2 nuclei.
Moderate resolution (R~1000; R~2000 for 3 cases) integral field K-band spectra
were obtained for all 31 galaxies in our sample and for 18 galaxies (R~1000;
R~2000 for 4 cases) H-band integral field spectra were also obtained. In each
case, we present nuclear, larger aperture, and difference spectra with
corresponding information about emission line wavelengths, fluxes, and widths.
Line-free H- and K-band continuum images as well as [FeII] 1.644 micron,
Brackett-gamma, and H_2 1-0 S(1) emission lines are also presented. In
addition, we provide extensive information about each galaxy obtained from the
literature that will be useful subsequently for characterizing the sample and
for comparison with our near-IR data.


title:
Far Infrared Spectroscopy of star-forming galaxies: Expectations for the
  Herschel Space Observatory

abstract:
  ISO has enabled far-infrared spectroscopy of a variety of galaxies. Using the
[CII] (158 micron) and [OI](63 micron) lines, we can characterize the physical
conditions in the star-forming ISM. These observations also form the basis of
our expectations for what the Herschel Space Observatory will observe for high
redshift galaxies. While [CII] is suppressed in ULIRGs and normal galaxies with
high dust temperatures, it is stronger than expected in metal poor galaxies by
factors of a few. Young galaxies at high redshifts might be expected to be both
metal poor and actively star-forming, leading to contrary expectations for the
[CII] line strength. The best prediction for [CII] detection is derived by
using the observed proportionality between [CII] and mid-IR emission from PAHs.
Using the observed [CII]/7 micron ratio and number counts from ISO deep surveys
we predict that HSO will be able to detect 100 sources/square-degree in the
[CII] line.


title: Atmospheres and Spectra of Strongly Magnetized Neutron Stars

abstract:
  We construct atmosphere models for strongly magnetized neutron stars with
surface fields $B\sim 10^{12}-10^{15}$ G and effective temperatures $T_{\rm
eff}\sim 10^6-10^7$ K. The atmospheres directly determine the characteristics
of thermal emission from isolated neutron stars, including radio pulsars, soft
gamma-ray repeaters, and anomalous X-ray pulsars. In our models, the atmosphere
is composed of pure hydrogen or helium and is assumed to be fully ionized. The
radiative opacities include free-free absorption and scattering by both
electrons and ions computed for the two photon polarization modes in the
magnetized electron-ion plasma. Since the radiation emerges from deep layers in
the atmosphere with $\rho\ga 10^2$ g/cm$^3$, plasma effects can significantly
modify the photon opacities by changing the properties of the polarization
modes. In the case where the magnetic field and the surface normal are
parallel, we solve the full, angle-dependent, coupled radiative transfer
equations for both polarization modes. We also construct atmosphere models for
general field orientations based on the diffusion approximation of the
transport equations and compare the results with models based on full radiative
transport. In general, the emergent thermal radiation exhibits significant
deviation from blackbody, with harder spectra at high energies. The spectra
also show a broad feature ($\Delta E/\Ebi\sim 1$) around the ion cyclotron
resonance $\Ebi=0.63 (Z/A)(B/10^{14}{G})$ keV, where $Z$ and $A$ are the atomic
charge and atomic mass of the ion, respectively; this feature is particularly
pronounced when $\Ebi\ga 3k\Teff$. Detection of the resonance feature would
provide a direct measurement of the surface magnetic fields on magnetars.


title: Experimental Constraints on the Axion Dark Matter Halo Density

abstract:
  Most of the mass of the Milky Way galaxy is contributed by its halo,
presumably in the form of non-interacting cold dark matter. The axion is a
compelling cold dark matter candidate. We report results from a search which
probes the local galactic halo axion density using the Sikivie RF cavity
technique. Candidates over the frequency range 550$$ $\le$ f $\le$$$ 810 MHz
(2.3$$ $\mu$eV $\le$$$ m$_{a}$ $\le$ 3.4 $\mu$eV) were investigated. The
absence of a signal suggests that KSVZ axions contribute no more than 0.45
GeV/cm$^3$ of mass density to the local dark matter halo over this mass range.


title: Sloan Digital Sky Survey Multicolor Observations of GRB010222

abstract:
  The discovery of an optical counterpart to GRB010222 (detected by BeppoSAX;
Piro 2001) was announced 4.4 hrs after the burst by Henden (2001a). The Sloan
Digital Sky Survey's 0.5m photometric telescope (PT) and 2.5m survey telescope
were used to observe the afterglow of GRB010222 starting 4.8 hours after the
GRB. The 0.5m PT observed the afterglow in five, 300 sec g' band exposures over
the course of half an hour, measuring a temporal decay rate in this short
period of F_nu \propto t^{-1.0+/-0.5}. The 2.5m camera imaged the counterpart
nearly simultaneously in five filters (u' g' r' i' z'), with r' = 18.74+/-0.02
at 12:10 UT. These multicolor observations, corrected for reddening and the
afterglow's temporal decay, are well fit by the power-law F_nu \propto
nu^{-0.90+/-0.03} with the exception of the u' band UV flux which is 20% below
this slope. We examine possible interpretations of this spectral shape,
including source extinction in a star forming region.


title:
A Method for Determining the Star Formation History of a Mixed Stellar
  Population

abstract:
  We present a method to determine the star formation history of a mixed
stellar population from its photometry. We perform a chi-squared minimization
between the observed photometric distribution and a model photometric
distribution, based on theoretical isochrones. The initial mass function,
distance modulus, interstellar reddening, binary fraction and photometric
errors are incorporated into the model, making it directly comparable to the
data. The model is a linear combination of individual synthetic color-magnitude
diagrams (CMDs), each of which represents the predicted photometric
distribution of a stellar population of a given age and metallicity. We present
extensive tests of the algorithm, using both simulated and actual photometric
data. From a preliminary application of the algorithm to a subregion of the
Large Magellanic Cloud (LMC), we find that the that the lull in star formation
observed among the LMC's cluster population between 3 and 8 Gyr ago is also
present in the field population. The method was designed with flexibility and
generality in mind, and we make the code available for use by the astronomical
community.


title:
Optical and X-ray characteristics of a newly discovered narrow-line QSO
  : RX J1334.2+3759

abstract:
  We report the discovery of a narrow-line QSO (NLQSO) RX J1334.2+3759 with a
steep soft X-ray spectrum. Soft X-ray emission from the NLQSO is highly
variable. Changes in the intensity by a factor of about 2 have been detected in
the ROSAT PSPC observations of RX J1334.2+3759 on time scales of 20000-40000s.
Rapid variability events have also been observed from RX J1334.2+3759. The most
extreme variable event has Delta L/Delta t = (1.95+/-1.02)E42 erg/s/s
corresponding to a change in intensity by a factor of about 4 within 400s. The
PSPC spectra of the NLQSO can be well represented by a power-law of photon
index 3.8, modified by an absorbing column local to the source over and above
that due to our own Galaxy. The intrinsic soft X-ray luminosity of RX
J1334.2+3759 is estimated to be 2.2E44 erg/s in the energy band of 0.1-2.0 keV.
The optical spectrum of RX J1334.2+3759 is typical of the NLS1 galaxies showing
strong Balmer Hbeta, Halpha, and forbidden line [O III]5007. Fe II multiplets,
usually present in the optical spectra of NLS1 galaxies, are also detected from
RX J1334.2+3759. Decomposition of the Hbeta and Halpha line profiles shows the
presence of narrow (FWHM = 880 km/s) and broad (FWHM = 2850 km/s) components in
the spectrum of RX J1334.2+3759. The narrow-line region of RX J1334.2+3759
appears to be significantly different from those of normal Seyfert galaxies. A
possible explanation for the observed properties of the narrow line region and
the broad line region is suggested in terms of density enhancements.


title:
Testing Comptonisation models using BeppoSAX observations of Seyfert 1
  galaxies

abstract:
  We have used realistic Comptonization models to fit high quality BeppoSAX
data of 6 Seyfert galaxies. Our main effort was to adopt a Comptonization model
taking into account the anisotropy of the soft photon field. The most important
consequence is a reduction of the first scattering order, which produces a
break (the so-called anisotropy break) in the outgoing spectra. The physical
parameters of the hot corona (i.e. the temperature and optical depth) obtained
fitting this class of models to broad band X-ray spectra are substantially
different from those derived fitting the same data with the power law + cut-off
model commonly used in the literature. In particular, our best fits with
Comptonization models in slab geometry give a temperature generally much larger
and an optical depth much smaller than derived from the power law + cut-off
fits, using standard Comptonization formulae. The estimate of the reflection
normalization is also larger with the slab corona model. For most objects of
our sample, both models give Compton parameter values larger than expected in a
slab corona geometry, suggesting a more ``photon starved'' X-ray source
configuration. Finally, the two models provide different trends and correlation
between the physical parameters which has major consequences for the physical
interpretation of the data.


title:
Preliminary Constraints on 12C(alpha,gamma)16O from White Dwarf
  Seismology

abstract:
  For many years, astronomers have promised that the study of pulsating white
dwarfs would ultimately lead to useful information about the physics of matter
under extreme conditions of temperature and pressure. In this paper we finally
make good on that promise. Using observational data from the Whole Earth
Telescope and a new analysis method employing a genetic algorithm, we
empirically determine that the central oxygen abundance in the
helium-atmosphere variable white dwarf GD 358 is 84+/-3 percent. We use this
value to place preliminary constraints on the 12C(alpha,gamma)16O nuclear
reaction cross-section. More precise constraints will be possible with
additional detailed simulations. We also show that the pulsation modes of our
best-fit model probe down to the inner few percent of the stellar mass. We
demonstrate the feasibility of reconstructing the internal chemical profiles of
white dwarfs from asteroseismological data, and find an oxygen profile for GD
358 that is qualitatively similar to recent theoretical calculations.


title: Magnetorotational instability of dissipative Couette flow

abstract:
  Global axisymmetric stability of viscous, resistive, magnetized Couette flow
is re-examined, with the emphasis on flows that would be hydrodynamically
stable according to Rayleigh's criterion: opposing gradients of angular
velocity and specific angular momentum. In this regime, magnetorotational
instabilities [MRI] may occur. Previous work has focused on the
Rayleigh-unstable regime. To prepare for an experimental study of MRI, which
are of intense astrophysical interest, we solve for global linear modes in a
wide gap with realistic dissipation coefficients. Exchange of stability appears
to occur through marginal modes. Velocity eigenfunctions of marginal modes are
nearly singular at conducting boundaries, but magnetic eigenfunctions are
smooth and obey a fourth-order differential equation in the inviscid limit. The
viscous marginal system is of tenth order; an eighth-order approximation
previously used for Rayleigh-unstable modes does not permit MRI. Peak growth
rates are insensitive to boundary conditions. They are predicted with
surprising accuracy by WKB methods even for the largest-scale mode. We conclude
that MRI is achievable under plausible experimental conditions using
easy-to-handle liquid metals such as gallium.


title:
A Spectroscopic and Photometric Study of Short-Timescale Variability in
  NGC5548

abstract:
  Results of a ground-based optical monitoring campaign on NGC5548 in June 1998
are presented. The broad-band fluxes (U,B,V), and the spectrophotometric
optical continuum flux F_lambda(5100 A) monotonically decreased in flux while
the broad-band R and I fluxes and the integrated emission-line fluxes of Halpha
and Hbeta remained constant to within 5%. On June 22, a short continuum flare
was detected in the broad band fluxes. It had an amplitude of about ~18% and it
lasted only ~90 min. The broad band fluxes and the optical continuum
F_lambda(5100 A) appear to vary simultaneously with the EUV variations. No
reliable delay was detected for the broad optical emission lines in response to
the EUVE variations. Narrow Hbeta emission features predicted as a signature of
an accretion disk were not detected during this campaign. However, there is
marginal evidence for a faint feature at lambda = 4962 A with FWHM=~6 A
redshifted by Delta v = 1100 km/s with respect to Hbeta_narrow.


title:
A Search for Early Optical Emission from Short and Long Duration
  Gamma-ray Bursts

abstract:
  Gamma-ray bursts of short duration may harbor vital clues to the range of
phenomena producing bursts. However, recent progress from the observation of
optical counterparts has not benefitted the study of short bursts. We have
searched for early optical emission from six gamma-ray bursts using the ROTSE-I
telephoto array. Three of these events were of short duration, including GRB
980527 which is among the brightest short bursts yet observed. The data consist
of unfiltered CCD optical images taken in response to BATSE triggers delivered
via the GCN. For the first time, we have analyzed the entire 16 degree by 16
degree field covered for five of these bursts. In addition, we discuss a search
for the optical counterpart to GRB 000201, a well-localized long burst. Single
image sensitivities range from 13th to 14th magnitude around 10 s after the
initial burst detection, and 14 - 15.8 one hour later. No new optical
counterparts were discovered in this analysis suggesting short burst optical
and gamma-ray fluxes are uncorrelated.


title: Intermittent Jolts of Galactic UV Radiation: Mutagenetic Effects

abstract:
  We estimate the frequency of intermittent hypermutation events and
disruptions of planetary/satellite photochemistry due to ultraviolet radiation
from core collapse supernova explosions. Calculations are presented for
planetary systems in the local Milky Way, including the important moderating
effects of vertical Galactic structure and UV absorption by interstellar dust.
The events are particularly frequent for satellites of giant gas planets at
\gtrsim 5-10 AU distance from solar-type parent stars, or in the conventional
habitable zones for planets orbiting spectral type K and M parent stars, with
rates of significant jolts about 10^3 - 10^4 per Gyr. The steep source spectra
and existing data on UVA and longer-wavelength radiation damage in terrestrial
organisms suggest that the mutational effects may operate even on planets with
ozone shields. We argue that the mutation doubling dose for UV radiation should
be much smaller than the mean lethal dose, using terrestrial prokaryotic
organisms as our model, and that jolts may lead to important real-time
evolutionary episodes if the jolt durations are longer than about a week,
corresponding to several hundred generation times, or much less if the
equivalent of mutator genes exist in extraterrestrial organisms. Longer-term
phylogenetic effects are likely if atmospheric photochemical disturbances lead
to niche creation or destruction in relevant habitats.


title:
Disk Contamination in a sample of proper motion selected halo stars: A
  Comment on "Direct Detection of Galactic Halo Dark Matter", B.A. Oppenheimer
  et al., Science

abstract:
  Based on a proper motion survey, Oppenheimer et al. claim the detection of a
white dwarf component of the dark matter of the halo. I show that most of the
white dwarfs in their sample are likely disk white dwarfs which have been
previously detected, and represent no new population.


title: On The Origin of Radio Halos in Galaxy Clusters

abstract:
  Previously it has been recognized that radio halos in galaxy clusters are
preferentially associated with merging systems as indicated by substructure in
the X-ray images and temperature maps. Since, however, many clusters without
radio halos also possess substructure, the role of mergers in the formation of
radio halos has remained unclear. By using power ratios to relate gravitational
potential fluctuations to substructure in X-ray images, we provide the first
quantitative comparison of the dynamical states of clusters possessing radio
halos. A correlation between the 1.4 GHz power (P_{1.4}) of the radio halo (or
relic) and the magnitude of the dipole power ratio (P_1/P_0) is discovered such
that approximately P_{1.4} ~ P_1/P_0; i.e., the strongest radio halos appear
only in those clusters currently experiencing the largest departures from a
virialized state. From additional consideration of a small number of highly
disturbed clusters without radio halos detected at 1.4 GHz, and recalling that
radio halos are more common in clusters with high X-ray luminosity (Giovannini,
Tordi, & Feretti), we argue that radio halos form preferentially in massive
(L_x >~ 0.5 x 10^{45} erg/s) clusters experiencing violent mergers (P_1/P_0 >~
0.5 x 10^{-4}) that have seriously disrupted the cluster core. The association
of radio halos with massive, large-P_1/P_0, core-disrupted clusters is able to
account for both the vital role of mergers in accelerating the relativistic
particles responsible for the radio emission as well as the rare occurrence of
radio halos in cluster samples.


title:
X-Rays from Superbubbles in the Large Magellanic Cloud. VI. A Sample of
  Thirteen Superbubbles

abstract:
  We present ROSAT observations and analysis of thirteen superbubbles in the
Large Magellanic Cloud. Eleven of these observations have not been previously
reported. We have studied the X-ray morphology of the superbubbles, and have
extracted and analyzed their X-ray spectra. Diffuse X-ray emission is detected
from each of these superbubbles, and X-ray emission is brighter than is
theoretically expected for a wind-blown bubble, suggesting that the X-ray
emission from the superbubbles has been enhanced by interactions between the
superbubble shell and interior SNRs. We have also found significant positive
correlations between the X-ray luminosity of a superbubble and its H-alpha
luminosity, expansion velocity, and OB star count. Further, we have found that
a large fraction of the superbubbles in the sample show evidence of
``breakout'' regions, where hot X-ray emitting gas extends beyond the H-alpha
shell.


title: Large Scale Diffuse X-ray Emission from the Large Magellanic Cloud

abstract:
  X-ray mosaics of the Large Magellanic Cloud (LMC) taken with the ROSAT
Position Sensitive Proportional Counter (PSPC) have revealed extensive diffuse
X-ray emission, indicative of hot >= 10^6 K gas associated with this irregular
galaxy on scales from ~10 pc to >= 1000 pc. We have selected regions of
large-scale (d >= 600 pc) diffuse X-ray emission, such as supergiant shells,
the LMC Spur, and the LMC Bar, and examined the physical conditions of the hot
gas associated with them. We find that for these objects the plasma
temperatures range from kT ~0.15 - 0.60 keV and the derived electron densities
range from n_e ~0.005 - 0.03 cm^-3. Furthermore, we have examined the fraction
of diffuse X-ray emission from the LMC and compared it to the total X-ray
emission. We find that discrete sources such as X-ray binaries and supernova
remnants (SNRs) account for ~41% and ~21% of the X-ray emission from the LMC,
respectively. In contrast, diffuse X-ray emission from the field and from
supergiant shells account for ~30% and ~6% of the total X-ray emission,
respectively.


title: LBV Nebulae: The Mass Lost from the Most Massive Stars

abstract:
  The most massive stars, with initial masses above ~50M_sun, encounter a phase
of extreme mass loss - sometimes accompanied by so-called giant eruptions - in
which the stars' evolution is reversed from a redward to a blueward motion in
the HRD. In this phase the stars are known as Luminous Blue Variable
(LBVs).Neither the reason for the onset of the strong mass loss nor the cause
for the giant eruptions is really understood, nor is their implications for the
evolution of these most massive stars. I will present a study of the LBV
nebulae which are formed in this phase as a consequence of the strong mass loss
and draw conclusions from the morphology and kinematics of these nebulae on
possible eruption mechanisms and stellar parameters of the LBV stars. The
analysis contains a large collection of LBV nebulae which form an evolutionary
sequence of LBV nebulae. A special concern will be the frequently observed
bipolar nature of the LBV nebulae which seems to be a general feature and
presents strong constraints on further models of the LBV phase and especially
on the formation mechanism of the nebulae.


title: Rates of Observable Black Hole Emergence in Supernovae

abstract:
  A newly formed black hole may be directly identified if late-time accretion
of material from the base of the ejected envelope generates a luminosity that
is observable in the tail of the supernova light curve. In this work we
estimate the rate at which events where the black hole ``emerges'' in the
supernova light curve can be detected with present capabilities. Our
investigation is based on an analytical model of the accretion luminosity at
emergence as a function of progenitor mass, coupled to the inferred rate of
observed Type II supernovae in nearby galaxies. We find through a parameter
survey that under optimistic assumptions the potential rate of observable
events can be as high as several per year. However, supernovae which produce
black holes are also likely to be low energy explosions and therefore
subluminous, as was the case for the best candidate to date, SN1997D. If black
hole-forming supernovae are underdetected owing to lower luminosities, the rate
of observing black hole emergence is probably not larger than once every few
years. We therefore emphasize the importance of dedicated searches for nearby
supernovae as well as faint supernovae projects for improving the prospects of
observationally certifying the supernova--black hole connection.


title:
Small Scale Structure at High Redshift: II. Physical Properties of the
  CIV Absorbing Clouds

abstract:
  Keck HIRES spectra were obtained of the separate images of three
gravitationally lensed QSOs (UM 673, Q1104-1804, and Q1422+2309). We studied
the velocity and column density differences in CIV doublets in each QSO. Unlike
the low ionization gas clouds typical of the interstellar gas in the Galaxy or
damped Ly alpha galaxies, the spatial density distribution of CIV absorbing gas
clouds turns out to be mostly featureless on scales up to a few hundred
parsecs, with column density differences rising to 50 percent or more over
separations beyond a few kpc. Similarly, velocity shear becomes detectable only
over distances larger than a few hundred pc, rising to 70 km/s at a few kpc.
The energy transmitted to the gas is substantially less than in present day
star-forming regions, and the gas is less turbulent on a given spatial scale
than, e.g., local HII regions. The quiescence of CIV clouds, taken with their
probable low density, imply that these objects are not internal to galaxies.
The CIV absorbers could be gas expelled recently to large radii and raining
back onto its parent galaxy, or pre-enriched gas from an earlier (population
III) episode of star formation, falling into the nearest mass concentration.
However, while the metals in the gas may have been formed at higher redshifts,
the residual turbulence in the clouds and the minimum coherence length measured
here imply that the gas was stirred more recently, possibly by star formation
events recurring on a timescale on the order of 10-100 Million years (abstract
abbreviated).


title:
A joint fit to the cosmological Model and the T-M and L_x-T relations
  using cluster data

abstract:
  In this work we show how well can the cosmological parameters be constrained
using galaxy cluster data. We also show how in the process of fitting the model
which attempts to describe the data it is possible to get some information
about the cluster scaling relations T-M and L_x-T. Among other conclusions we
found that only low density universes (Omega approx. 0.3 with or without
cosmological constant) are compatible with recent data sets. These constraints
will be improved with future SZ data.


title: A nanoflare heating model for the quiet solar corona

abstract:
  The energy input into the lower solar corona by flare evaporation events has
been modeled according to the available observations for quiet regions. The
question is addressed whether such heating events can provide the observed
average level of the coronal emission measure and thus of the observed flux of
extreme ultraviolet (EUV) and X-ray emission without contradicting the observed
average power spectrum of the emission measure, the typical emission measure
variations observed for individual pixels and the observed flare energy
distribution. As the assumed flare height influences the derived flare energy,
the mathematical foundations of nanoflare distributions and their conversion to
different height assumptions are studied first. This also allows a comparison
with various published energy distributions differing in height assumptions and
to relate the observations to the input parameters of the heating model. An
analytic evaluation of the power spectrum yields the relationship between the
average time profile of nanoflares (or microflares), assumed to be self-similar
in energy, and the power spectrum. We find that the power spectrum is very
sensitive to the chosen time profile of the flares. Models are found by
numerical simulation that fit all available observations. They are not unique
but severely constrained. We concentrate on a model with a flare height
proportional to the square root of the flare area. The existence of a fitting
model demonstrates that nanoflare heating of the corona is a viable and
attractive mechanism.


title: X-ray emission from classical and recurrent-novae observed with ROSAT

abstract:
  We have analysed 350 pointed and serendipitous observations of 108 different
classical and recurrent novae in outburst and in quiescence, contained in the
ROSAT archive. One aim was to search for super-soft X-ray sources and we found
only 3 of them among post-novae. Thus, the super-soft X-ray phase of novae is
relatively short lived (up to 10 years) and is observed only for up to 20% of
novae.
  Most classical and recurrent novae instead emit hard X-rays (in the ROSAT
band) in the first months after the outburst, with peak X-ray luminosity of a
few times 10(33) erg/s. The emission, which we attribute to shocks in the nova
ejecta, lasts at least 2 years and even much longer under special circumstances
(like preexisting circumstellar material, or a prolonged wind phase).
  We also investigate X-ray emission due to accretion in quiescent novae. Only
11 out of 81 Galactic classical and recurrent novae were detected. The average
X-ray uminosity is not higher than for dwarf novae, and some novae are variable
in X-rays on time scales of years.


title: Spectroscopic evidence for the binary nature of AM CVn

abstract:
  We analysed archival spectroscopic data of AM CVn taken with the William
Herschel Telescope in 1996. In the literature two orbital periods for AM CVn
are proposed. A clear S-wave in the HeI 4471, 4387 and 4143 \AA lines is
revealed when the spectra are folded on the 1029 s period. No signature of this
S-wave is seen when folded on 1051 s. Doppler tomography of the line profiles
shows a clear signature of the hotspot. Using this we can constrain the value
of K_2 to lie between 210 and 280 km/s. Our work confirms the binary nature of
AM CVn beyond any doubt, establishes 1028.73 s as the true orbital period and
supports the interpretation of AM CVn as a permanent superhump system.


title: Testing dark matter with high-redshift supernovae

abstract:
  Dark matter in the Universe consisting of macroscopic objects such as
primordial black holes may cause gravitational lensing of distant objects. The
magnification associated with lensing will lead to additional scatter in the
received flux from standard candles, and too small an observed scatter could
rule out compact dark matter entirely. In this letter, we show how the scatter
in fluxes of distant Type 1a supernovae could be used to distinguish between
models with and without lensing by macroscopic dark matter. The proposed SNAP
project, with $\sim 2400$ supernovae in the range $0.1\ls z\ls 1.7$, should be
able to identify models at 99.9% confidence, if systematic errors are
controlled. Note that this test is independent of any evolution of the mean
supernova luminosity with redshift. The variances of the current Supernova
Cosmology Project sample do not rule out compact lenses as dark matter:
formally they favour such a population, but the significance is low, and
removal of a single faint supernova from the sample reverses the conclusion.


title:
SBS 1150+599A: an extremely oxygen-poor planetary nebula in the Galactic
  halo?

abstract:
  We report results of a spectrophotometric study of SBS 1150+599A and discuss
the nature of this object based upon our data. Our study shows that SBS
1150+599A is most probably a planetary nebula located in the Galactic halo and
not a cataclysmic variable as originally proposed by the authors of the Second
Byurakan Survey from low resolution spectroscopy. We have further elaborated on
the properties of SBS 1150+599A (now becoming PN G135.9+55.9) with tools used
for planetary nebula analysis. Our photoionization models show that, in order
to match the observational constraints, the oxygen abundance in the nebula is
probably extremely low, around 1/500 solar, which is one order of magnitude
lower than the most oxygen-poor planetary nebulae known so far. This finding
has strong implications on our understanding of the formation of planetary
nebulae and of the evolution of the Galactic halo.


title: Magnetic Fields in the 3C 129 Cluster

abstract:
  We present multi-frequency VLA observations of the two radio galaxies 3C 129
and 3C 129.1 embedded in a luminous X-ray cluster. These radio observations
reveal a substantial difference in the Faraday Rotation Measures (RMs) toward
3C 129.1 at the cluster center and 3C 129 at the cluster periphery. After
deriving the density profile from available X-ray data, we find that the RM
structure of both radio galaxies can be fit by a tangled cluster magnetic field
with strength 6 microGauss extending at least 3 core radii (450 kpc) from the
cluster center. The magnetic field makes up a small contribution to the total
pressure (5%) in the central regions of the cluster. The radio morphology of 3C
129.1 appears disturbed on the southern side, perhaps by the higher pressure
environment. In contrast with earlier claims for the presence of a moderately
strong cooling flow in the 3C 129 cluster, our analysis of the X-ray data
places a limit on the mass deposition rate from any such flow of <1.2 Msun/yr.


title: Does the galaxy correlation length increase with the sample depth?

abstract:
  We have analyzed the behavior of the correlation length, $r_0$, as a function
of the sample depth by extracting from the CfA2 redshift survey volume--limited
samples out to increasing distances. For a fractal distribution, the value of
$r_0$ would increase with the volume occupied by the sample. We find no linear
increase for the CfA2 samples of the sort that would be expected if the
Universe preserved its small scale fractal character out to the distances
considered (60--100$\hmpc$). The results instead show a roughly constant value
for $r_0$ as a function of the size of the sample, with small fluctuations due
to local inhomogeneities and luminosity segregation. Thus the fractal picture
can safely be discarded.


title: NLTE Synthetic Spectral Fits to the Type Ia Supernova 1994D in NGC 4526

abstract:
  We have fit the normal, well observed, Type Ia Supernova (SN Ia) SN 1994D
with non-LTE spectra of the deflagration model W7. We find that well before
maximum luminosity W7 fits the optical spectra of SN 1994D. After maximum
brightness the quality of the fits weakens as the spectrum forms in a core rich
in iron peak elements. We show the basic structure of W7 is likely to be
representative of the typical SN Ia. We have shown that like W7, the typical SN
Ia has a layer of unburned C+O composition at v > 15000 \kmps, followed by
layers of C-burned and O-burned material with a density structure similar to
W7. We present UVOIR (UBVRIJKH) synthetic photometry and colors and compare
with observation. We have computed the distance to the host galaxy, NGC 4526,
obtaining a distance modulus of \mu = 30.8 \pm 0.3. We discuss further
application of this direct measurement of SNe Ia distances. We also discuss
some simple modifications to W7 that could improve the quality of the fits to
the observations.


title: On the Thermonuclear Runaway in Type Ia Supernovae: How to run away?

abstract:
  Type Ia Supernovae are thought to be thermonuclear explosions of massive
white dwarfs (WD). We present the first study of multi-dimensional effects
during the final hours prior to the thermonuclear runaway which leads to the
explosion. The calculations utilize an implicit, 2-D hydro code.Mixing and the
ignition process are studied in detail. We find that the initial chemical
structure of the WD is changed but the material is not fully homogenized. The
exploding WD sustains a central region with a low C/O ratio. This implies that
the explosive nuclear burning will begin in a partially C-depleted environment.
The thermonuclear runaway happens in a well defined region close to the center.
It is induced by compressional heat when matter is brought inwards by
convective flows. We find no evidence for multiple spot or strong off-center
ignition. Convective velocities are of the order of 100 km/sec which is well
above the effective burning speeds in SNe Ia previously expected right after
the runaway. For about 0.5 to 1 sec, the speed of the burning front will
neither be determined by the laminar speed nor the Rayleigh-Taylor
instabilities but by convective flows produced prior to the runaway. The
consequences are discussed for our under- standing of the detailed physics of
the flame propagation, the deflagration detonation transition, and the
nucleosynthesis in the central layers. Our results strongly suggest the
pre-conditioning of the progenitor as a key-factor for our understanding of the
diversity in SNeIa.


title:
The Line-of-Sight Depth of Populous Clusters in the Small Magellanic
  Cloud

abstract:
  We present an analysis of age, metal abundance, and positional data on
populous clusters in the Small Magellanic Cloud (SMC) with the ultimate aim of
determining the line-of-sight (LOS) depth of the SMC using these clusters as
proxies. Our dataset contains 12 objects and is limited to clusters with the
highest quality data for which the ages and abundances are best known and can
be placed on an internally consistent scale. We have analyzed the variation of
the clusters' properties with position on the sky and with line-of-sight depth.
Based on this analysis, we draw the following conclusions. 1) The observational
data indicates that the eastern side of the SMC (facing the LMC) contains
younger and more metal-rich clusters as compared with the western side. This is
not a strong correlation because our dataset of clusters is necessarily
limited, but it is suggestive and warrants further study. 2) Depending on how
the reddening is computed to our clusters, we find a mean distance modulus that
ranges from (m-M)_0 = 18.71 +/- 0.06 to (m-M)_0 = 18.82 +/- 0.05. 3) The
intrinsic +/- 1-sigma line-of-sight depth of the SMC populous clusters in our
study is between ~6 kpc and ~12 kpc depending primarily on whether we adopt the
Burstein & Heiles reddenings or those from Schlegel et al. 4) Viewing the SMC
as a triaxial galaxy with the Declination, Right Ascension, and LOS depth as
the three axes, we find axial ratios of approximately 1:2:4. Taken together,
these conclusions largely agree with those of previous investigators and serve
to underscore the utility of populous star clusters as probes of the structure
of the Small Magellanic Cloud.


title:
Anomalous X-ray Pulsars and Soft Gamma-Ray Repeaters in supernova
  remnants

abstract:
  Important constraints on the properties of the Anomalous X-ray Pulsars (AXPs)
and Soft Gamma-Ray Repeaters (SGRs) can be provided by their associations with
supernova remnants (SNRs). We have made a radio search for SNRs towards the
AXPs RX J170849-400910 and 4U 0142+61 - we find that the former lies near a
possible new SNR with which it is unlikely to be physically associated, but see
no SNR in the vicinity of the latter. We review all claimed pairings between
AXPs and SNRs; the three convincing associations imply that AXPs are young (<
10 000 yr) neutron stars with low projected space velocities (< 500 km/s).
Contrary to previous claims, we find no evidence that the density of the
ambient medium around AXPs is higher than that in the vicinity of radio
pulsars. Furthermore, the non-detection of radio emission from AXPs does not
imply that these sources are radio-silent. We also review claimed associations
between SGRs and SNRs. We find none of these associations to be convincing,
consistent with a scenario in which SGRs and AXPs are both populations of
high-field neutron stars ("magnetars") but in which the SGRs are an older or
longer-lived group of objects than are the AXPs. If the SGR/SNR associations
are shown to be valid, then SGRs must be high-velocity objects and most likely
represent a different class of source to the AXPs.


title: Physics Results From Alpha Magnetic Spectrometer 1998 Shuttle Flight

abstract:
  The Alpha Magnetic Spectrometer (AMS) is a particle detector designed to
detect antimatter. During the 10-day test flight on the space shuttle in June
1998, AMS detected $10^8$ events. Upon analysis, no antimatter was found and
the antimatter limit was reduced to $1.1\times10^{-6}$. The proton spectrum
shows some differences with the cosmic ray flux used in atmospheric neutrino
simulation. A large amount of protons, positrons, and electrons were found
below the geomagnetic rigidity cutoff. The energy of these particles are as
high as several GeV, one order of magnitude higher than any previously measured
energy in radiation belts. These particles also exhibit many interesting
features. This paper reviews the results in the four published papers of the
AMS collaboration and provides explanation for some features of the albedo
particles.


title: A 168-s X-Ray Pulsar in the SMC Observed with ASCA

abstract: This paper has been withdrawn because the class file must not be uploaded.


title: Theoretical Models of Polarized Dust Emission from Protostellar Cores

abstract:
  We model the polarized thermal dust emission from protostellar cores that are
assembled by super-sonic turbulent flows in molecular clouds. Self-gravitating
cores are selected from a three dimensional simulation of super-sonic and
super-Alfvenic magneto-hydrodynamic (MHD) turbulence. The polarization is
computed in two ways. In model A it is assumed that dust properties and grain
alignment efficiency are uniform; in model B it is assumed that grains are not
aligned at visual extinction larger than 3 mag. The main results of this work
are: i) Values of the degree of polarization P between 1 and 10% are typical,
despite the super-Alfvenic nature of the turbulence; ii) A steep decrease of P
with increasing values of the sub-mm dust continuum intensity I is always found
in self--gravitating cores selected from the MHD simulations, if grains are not
aligned above a certain value of visual extinction (model B); iii) The same
behavior is hard to reproduce if grains are aligned independently of visual
extinction (model A); iv) The Chandrasekhar-Fermi formula, corrected by a
factor f=0.4, provides an approximate estimate of the average magnetic field
strength in the cores. Sub-mm dust continuum polarization maps of quiescent
protostellar cores and Bok globules always show a decrease in P with increasing
value of I consistent with the predictions of our model B. We therefore
conclude that sub-mm polarization maps of quiescent cores do not map the
magnetic field inside the cores at visual extinction larger than approximately
3 mag. There is no inconsistency between the results from optical and near-IR
polarized absorption of background stars, and the observed polarization of
sub-mm dust continuum from quiescent cores. In both cases, grains at large
visual extinction appear to be virtually unaligned.


title: On the Power Spectrum Density of Gamma Ray Bursts

abstract:
  Gamma ray bursts (GRBs) are known to have short-time variability and
power-law behavior with the index -1.67 in the power spectrum density.
Reanalyzing the expanded data, we have found a) the power-law comes from the
global profile of the burst and not from the self-similar shots nor rapid
fluctuations in the luminosity profile. b) The power indices vary from burst to
burst and the value -1.67 is given simply as the mean value of the
distribution; there is no systematic correlation among GRBs to yield the power
law.


title: On the Formation of Cluster Radio Relics

abstract:
  (abridged) We present detailed 3-dimensional magneto-hydrodynamical
simulations of the passage of a radio plasma cocoon filled with turbulent
magnetic fields through a shock wave. Taking into account synchrotron, inverse
Compton and adiabatic energy losses and gains we evolved the relativistic
electron population to produce synthetic polarisation radio maps. On contact
with the shock wave the radio cocoons are first compressed and finally torn
into filamentary structures, as is observed in several cluster radio relics. In
the synthetic radio maps the electric polarisation vectors are mostly
perpendicular to the filamentary radio structures. If the magnetic field inside
the cocoon is not too strong, the initially spherical radio cocoon is
transformed into a torus after the passage of the shock wave. Very recent,
high-resolution radio maps of cluster radio relics seem to exhibit such
toroidal geometries in some cases. This supports the hypothesis that cluster
radio relics are fossil radio cocoons that have been revived by a shock wave.
For a late-stage relic the ratio of its global diameter to the filament
diameter should correlate with the shock strength. Finally, we argue that the
total radio polarisation of radio relic should be well correlated with the
3-dimensional orientation of the shock wave that produced the relic.


title: The Ionization of Nearby Interstellar Gas

abstract:
  We present new calculations of the photoionization of interstellar matter
within ~5 pc of the Sun (which we refer to as the Complex of Local Interstellar
Clouds or CLIC) by directly observed radiation sources including nearby hot
stars and the diffuse emission of the Soft X-ray Background (SXRB). In
addition, we model the important, unobserved EUV emission both from the hot gas
responsible for the SXRB and from a possible evaporative boundary between the
CLIC and the hot gas. We carry out radiative transfer calculations and show
that these radiation sources can provide the ionization and heating of the
cloud required to match a variety of observations. The ionization predicted in
our models shows good agreement with pickup ion results, interstellar
absorption line data towards epsilon CMa, and EUV opacity measurements of
nearby white dwarf stars. Including the radiation from the conductive boundary
improves agreement with data on the temperature and electron density in the
cloud. The presence of dust in the cloud, or at least depleted abundances, is
necessary to maintain the heating/cooling balance and reach the observed
temperature. Using the column density observations as inputs, we derive the gas
phase abundances of C, N, O, Mg, Si, S and Fe. Based on these inferred
depletions, it appears that silicate and iron dust exists in the CLIC, while
carbonaceous dust has been destroyed.


title:
The Fading Radio Emission from SN 1961V: Evidence for a Type II Peculiar
  Supernova?

abstract:
  Using the Very Large Array (VLA), we have detected radio emission from the
site of SN 1961V in the Sc galaxy NGC 1058. With a peak flux density of 0.063
+/- 0.008 mJy/beam at 6 cm and 0.147 +/- 0.026 mJy/beam at 18 cm, the source is
non-thermal, with a spectral index of -0.79 +/- 0.23. Within errors, this
spectral index is the same value reported for previous VLA observations taken
in 1984 and 1986. The radio emission at both wavelengths has decayed since the
mid 1980's observations with power-law indices of beta(20cm) = -0.69 +/- 0.23
and beta(6cm) = -1.75 +/- 0.16. We discuss the radio properties of this source
and compare them with those of Type II radio supernovae and luminous blue
variables.


title: Discovery of a 2 Kpc Binary Quasar

abstract:
  LBQS 0103$-$2753 is a binary quasar with a separation of only 0.3 arcsec. The
projected spacing of 2.3 kpc at the distance of the source (z = 0.848) is much
smaller than that of any other known binary QSO. The binary nature is
demonstrated by the very different spectra of the two components and the low
probability of a chance pairing. LBQS 0103$-$2753 presumably is a galaxy merger
with a small physical separation between the two supermassive black holes. Such
objects may provide important constraints on the evolution of binary black
holes and the fueling of AGN.


title: Chemical Evolution of Galaxies

abstract:
  Chemical abundances provide important clues to the evolution of galaxies.
Ionized nebulae are one of the main sources of chemical abundance measurements,
especially in external galaxies. Studies of H II regions have shown that the
overall metallicity of galaxies increases with galactic luminosity, and that
spiral galaxies characteristically have radial gradients in chemical
composition. There are indications of environmental influences on chemical
abundances. Planetary nebulae provide another measure of abundances in the
Milky Way and other galaxies. Space facilities have allowed measurements for
elements that are inaccessible at optical wavelengths. Large telescopes make
possible the study of individual stars in external galaxies and the study of
interstellar abundances in galaxies at intermediate and high redshifts. These
advances promise exciting times as astrophysicists strive to paint a complete
picture of galactic evolution from the Big Bang to the present.


title:
Tracing the Mass during Low-Mass Star Formation. II. Modelling the
  Submillimeter Emission from Pre-Protostellar Cores

abstract:
  We have modeled the emission from dust in pre-protostellar cores, including a
self-consistent calculation of the temperature distribution for each input
density distribution. Model density distributions include Bonnor-Ebert spheres
and power laws. The Bonnor-Ebert spheres fit the data well for all three cores
we have modeled. The dust temperatures decline to very low values ($\Td \sim 7$
K) in the centers of these cores, strongly affecting the dust emission.
Compared to earlier models that assume constant dust temperatures, our models
indicate higher central densities and smaller regions of relatively constant
density. Indeed, for L1544, a power-law density distribution, similar to that
of a singular, isothermal sphere, cannot be ruled out. For the three sources
modeled herein, there seems to be a sequence of increasing central
condensation, from L1512 to L1689B to L1544. The two denser cores, L1689B and
L1544, have spectroscopic evidence for contraction, suggesting an evolutionary
sequence for pre-protostellar cores.


title: Density Contrast-Peculiar Velocity Relation in the Newtonian Gauge

abstract:
  In general relativistic framework of the large scale structure formation
theory in the universe, we investigate the relation between density contrast
and peculiar velocity in the Newtonian gauge. According to the gauge-invariant
property of the energy-momentum tensor in the Newtonian gauge, we consider the
perturbation of velocity in the energy-momentum tensor behaves as the Newtonian
peculiar velocity. It is shown that in the relativistic framework, the relation
between peculiar velocity and density contrast has an extra correction term
with respect to the Newtonian Peebles formula which in small scales, can be
ignorable . The relativistic correction of peculiar velocity for the structures
with the extension of few hundred mega parsec is about few percent which is
smaller than the accuracy of the recent observations for measuring peculiar
velocity. The peculiar velocity in the general relativistic framework also
changes the contribution of Doppler effect on the anisotropy of CMB.


title:
A backwards approach to the formation of disk galaxies I. Stellar and
  gas content

abstract:
  A simple chemical enrichment code is described where the two basic mechanisms
driving the evolution of the ages and metallicities of the stellar populations
are the star formation efficiency and the fraction of gas ejected from the
galaxy. Using the observed Tully-Fisher relation in different passbands as a
constraint, it is found that a steep correlation between the maximum disk
rotational velocity and star formation efficiency must exist either for a
linear or a quadratic Schmidt law. Outflows do not play a major role. The
redshift evolution of disk galaxies is explored, showing that a significant
change in the slope of the Tully-Fisher relation is expected because of the
different age distributions of the stellar components in high and low-mass disk
galaxies. The slope measured in the rest frame B,K bands is found to change
from 3(B); 4(K) at z=0 up to 4.5(B); 5(K) at z~1, with a slight dependence on
formation redshift.


title: Quiet Sun coronal heating: statistical model

abstract:
  Recent observations of Krucker & Benz (1998) give strong support to Parker's
hypothesis (Parker 1988) that small scale dissipative events make the main
contribution to quiet Sun coronal heating. They also showed that these small
scale events are associated not only with the magnetic network, but also with
the cell interiors (Benz & Krucker, 1998). Taking into account in addition the
results of the analysis performed by Priest with co-authors (Priest et al.
2000) who demonstrated that the heating is quasi-homogeneous along the arcs we
come to the conclusion that the sources driving these dissipative events are
also small scale sources. Typically they are of the order of or smaller than
the linear scale of the events observed, that is smaller than 2000 km. To
describe statistical properties of quiet Sun corona heating by microflares,
nanoflares, and even smaller events, we consider a cellular automata model
subject to uniform small scale driving and dissipation. The model consists of
two elements, the magnetic field source supposed to be associated with the
small scale hydrodynamic turbulence convected from the photosphere and local
dissipation of small scale currents. The dissipation is assumed to be provided
by either anomalous resistivity, when the current density exceeds a certain
threshold value, or by the magnetic reconnection. The main problem considered
is how the statistical characteristics of dissipated energy flow depend upon
characteristics of the magnetic field source and on physical mechanism
responsible for the magnetic field dissipation. As the threshold value of
current is increased, we observe the transition from Gaussian statistics to
power-law type. In addition, we find that the dissipation provided by
reconnection results in stronger deviations from Gaussian distribution.


title: The Thick Disk-Halo Interface

abstract:
  The star formation history of a galaxy, explicitely here our Milky Way
Galaxy, where the most detailed information is attainable, is the convolution
of two functions. One function describes the rate of formation of the stars
which are today in the Galaxy. The second describes the assembly of those stars
into the present Galactic potential well. There is direct evidence that this
assembly continues today, with both stars and gas being assembled into, or at
least rearranged in, the Galactic potential. But is this recent accretion
significant? Was the last significant accretion the formation of the thick
disk, some 10Gyr ago?. Recent spectroscopic studies support this unexpected
result, while dynamical studies find increasing numbers of specific examples of
smaller scale more recent accretion. We present early results for one specific
such survey, the Anglo Australian Old Stellar populations Survey, to illustrate
current studies.


title: A Detailed Analysis of a Cygnus Loop Shock-Cloud Interaction

abstract:
  The XA region of the Cygnus Loop is a complex zone of radiative and
nonradiative shocks interacting with interstellar clouds. We combine five far
ultraviolet spectral observations from the Hopkins Ultraviolet Telescope (HUT),
a grid of 24 IUE spectra and a high-resolution longslit Halpha spectrum to
study the spatial emission line variations across the region. These spectral
data are placed in context using ground-based, optical emission line images of
the region and a far-UV image obtained by the Ultraviolet Imaging Telescope
(UIT). The presence of high-ionization ions (OVI, NV, CIV) indicates a shock
velocity near 170 km/s while other diagnostics indicate v_shock=140 km/s. It is
likely that a large range of shock velocities may exist at a spatial scale
smaller than we are able to resolve. By comparing CIV 1550, CIII 977 and CIII]
1909, we explore resonance scattering across the region. We find that a
significant column depth is present at all positions, including those not near
bright optical/UV filaments. Analysis of the OVI doublet ratio suggests an
average optical depth of about unity in that ion while flux measurements of
[SiVIII] 1443 suggest a hot component in the region at just below 10^6K. Given
the brightness of the OVI emission and the age of the interaction, we rule out
the mixing layer interpretation of the UV emission. Furthermore, we formulate a
picture of the XA region as the encounter of the blast wave with a finger of
dense gas protruding inward from the pre-SN cavity.


title: Lensing magnification effects on the cosmic shear statistics

abstract:
  Gravitational lensing causes a correlation between a population of foreground
large-scale structures and the observed number density of the background
distant galaxies as a consequence of the flux magnification and the lensing
area distortion. This correlation has not been taken into account in
calculations of the theoretical predictions of the cosmic shear statistics but
may cause a systematic error in a cosmic shear measurement. We examine its
impact on the cosmic shear statistics using the semi-analytic approach. We find
that the lensing magnification has no practical influence on the cosmic shear
variance. Exploring possible shapes of redshift distribution of source
galaxies, we find that the relative amplitude of the effect on the convergence
skewness is 3% at most


title: Cluster abundance and large-scale structure

abstract:
  We use the presently observed number density of large X-ray clusters and
linear mass power spectra to constrain the shape parameter ($\Gamma$), the
spectral index ($n$), the amplitude of matter density perturbations on the
scale of $8 h^{-1}$Mpc ($\sigma_8$), and the redshift distortion parameter
($\beta$). The non-spherical-collapse model as an improvement to the
Press-Schechter formula is used and yields significantly lower $\sigma_8$ and
$\beta$. An analytical formalism for the formation redshift of halos is also
derived.


title: New method of extracting non-Gaussian signals in the CMB

abstract:
  Searching for and charactering the non-Gaussianity (NG) of a given field has
been a vital task in many fields of science, because we expect the consequences
of different physical processes to carry different statistical properties. Here
we propose a new general method of extracting non-Gaussian features in a given
field, and then use simulated cosmic microwave background (CMB) as an example
to demonstrate its power. In particular, we show its capability of detecting
cosmic strings.


title: Cosmological matter perturbations with causal seeds

abstract:
  We investigate linear matter density perturbations in models of structure
formation with causal seeds. Under the fluid approximation, we obtain the
analytic solutions using Green-function technique. Some incorrect solutions in
the literature are corrected here. Based on this, we analytically prove that
the matter density perturbations today are independent of the way the causal
seeds were compensated into the background contents of the universe when they
were first formed. We also find that the compensation scale depends not only on
the dynamics of the universe, but also on the properties of the seeds near the
horizon scale. It can be accurately located by employing our Green-function
solutions.


title: Tests for Gaussianity of the MAXIMA-1 CMB Map

abstract:
  Gaussianity of the cosmological perturbations in the universe is one of the
key predictions of standard inflation, but it is violated by other models of
structure formation such as topological defects. We present the first test of
the Gaussianity of the cosmic microwave background (CMB) on sub-degree angular
scales, where deviations from Gaussianity are most likely to occur. We apply
the methods of moments, cumulants, the Kolmogorov test, the $\chi^2$ test, and
Minkowski functionals in eigen, real, Wiener-filtered and signal-whitened
spaces, to the MAXIMA-1 CMB anisotropy data. We conclude that the data, which
probe angular scales between 10 arcminutes and 5 degrees, are consistent with
Gaussianity.


title:
Optical and Radio observations of the bright GRB010222 afterglow:
  evidence for rapid synchrotron cooling?

abstract:
  We report photometric observations of the optical afterglow of GRB010222 in
V,R and I passbands carried out at UPSO, Naini Tal between 22-27 Feb 2001. We
determine CCD Johnson BV and Cousins RI photometric magnitudes for 31 stars in
the field of GRB010222 and use them to calibrate our measurements as well as
other published BVRI photometric magnitudes of GRB010222 afterglow. We
construct the light curve in V,R,I passbands and from a broken power-law fit
determine the decay indices of 0.74+/-0.05 and 1.35+/-0.04 before and after the
break at 0.7 days. Using reported X-ray flux measurements at 0.35 and 9.13 days
after the burst we determine X-ray to opt/IR spectral index of 0.61+/-0.02 and
0.75+/-0.02 on these two days. We also report upper limits to the radio flux
obtained from the RATAN-600 telescope and the GMRT, and millimeter-wave upper
limits obtained from the Plateau de Bure Millimeter interferometer. We argue
that the synchrotron cooling frequency is below the optical band for most of
the observing period. We also estimate an initial jet opening angle of about
2.0n^(1/8) degrees, where n is the number density of the ambient medium.


title: Flat Spectrum Gamma Ray Burst Afterglows

abstract:
  Temporal behaviour of GRB afterglow light curve is derived for the case where
the electron energy distribution is relatively flat, with the power-law index p
lying between 1.0 and 2.0. It is shown that the expected behaviour will be the
same as that for p>2.0 if the upper cutoff in the electron energy distribution
evolves in direct proportion to the bulk Lorentz factor of the blast wave.


title: Do mirror planets exist in our solar system?

abstract:
  Mirror matter is predicted to exist if parity is an unbroken symmetry of
nature. Currently, there is a large amount of evidence that mirror matter
actually exists coming from astrophysics and particle physics. One of the most
fascinating (but speculative) possibilities is that there is a significant
abundance of mirror matter within our solar system. If the mirror matter
condensed to form a large body of planatary or stellar mass then there could be
interesting observable effects. Indeed studies of long period comets suggest
the existence of a solar companion which has escaped direct detection and is
therefore a candidate for a mirror body. Nemesis, hypothetical "death star"
companion of the Sun, proposed to explain biological mass extinctions, may
potentially be a mirror star. We examine the prospects for detecting these
objects if they do indeed exist and are made of mirror matter.


title: A Chandra Observation of the Circinus Galaxy

abstract:
  We report on a recent Chandra ACIS-S observation of the Circinus galaxy.
These observations confirm that the nuclear spectrum results from reflection of
a hard X-ray continuum by ``neutral'' matter. The nuclear X-ray emission is
extended by \sim 60 pc in the general direction of the optical ``ionization
cone''. An image in the Fe K\alpha line has been made and shows that this
emission extends up to 200 pc from the nucleus. There is also large-scale X-ray
emission both along and perpendicular to the galaxy disk. Thermal plasma models
for this extended gas indicate temperatures kT \sim 0.6 keV, though cooler
photoionized gas is also possible. The X-ray emission from gas in the disk is
probably associated with the starburst ring of radius 150--250 pc. The gas
extending \sim 600 pc perpendicular to the disk is closely correlated with the
high-excitation optical-line emission. In addition to its soft X-ray emission,
we tentatively detect a hard component from the gas above the plane; this hard
emission may represent nuclear X-rays scattered into our line of sight by
electrons in the outflowing wind. Ten compact sources are found in the central
kpc of the galaxy. The most luminous has an X-ray luminosity of \simeq 10^{40}
erg s^{-1} and seems to be an X-ray binary in the Circinus galaxy with a
black-hole mass exceeding 80 M_{\odot}.