title: Signals of primordial phase transitions on CMB maps

abstract:
  The analysis of the CMB anisotropies is a rich source of cosmological
informations. In our study, we simulated the signals produced by the relics of
a first order phase transition occured during an inflationary epoch in the
early Universe. These relics are bubbles of true vacuum that leave a
characteristic non-Gaussian imprint on the CMB. We use different statistical
estimators in order to evaluate this non-Gaussianity. We obtain some limits on
the allowed values of the bubble parameters comparing our results with the
experimental data.
  We also predict the possibility to detect this signal with the next high
resolution experiments.


title: Atomic T Tauri disk winds heated by ambipolar diffusion

abstract:
  We summarize results on the thermal and ionization structure of self-similar,
magnetically-driven, atomic disk winds heated by ambipolar diffusion. We
improve upon earlier work by Safier by considering (1) new MHD solutions
consistent with underlying cold keplerian disk equilibrium, (2) a more accurate
treatment of the micro-physics, and (3) predictions for spatially resolved
forbidden line emission (maps, long-slit spectra). The temperature plateau
$\simeq 10^4$ K found earlier is recovered, but ionization fractions are
revised downward by a factor of 10, due to previous omission of thermal speeds
in ion-neutral momentum-exchange rates. The physical origin of the temperature
plateau is outlined. Predictions are then compared with T~Tauri star
observations, with emphasis on the necessity of suitable beam convolution. Jet
widths and variations in line profiles with distance and line tracer are well
reproduced. However, predicted maximum velocities are too high, total densities
too low, and the low-velocity [OI] component is too weak. Denser, slower MHD
winds from warm disks might resolve these discrepancies.


title: Constraining the Properties of Dark Energy

abstract:
  The presence of dark energy in the Universe is inferred directly from the
accelerated expansion of the Universe, and indirectly, from measurements of
cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3
of the critical density, is very smoothly distributed, and has large negative
pressure. Its nature is very much unknown. Most of its discernible consequences
follow from its effect on evolution of the expansion rate of the Universe,
which in turn affects the growth of density perturbations and the age of the
Universe, and can be probed by the classical kinematic cosmological tests.
Absent a compelling theoretical model (or even a class of models), we describe
dark energy by an effective equation of state w=p_X/rho_X which is allowed to
vary with time. We describe and compare different approaches for determining
w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies
and clusters, and CMB anisotropy, focusing particular attention on the use of a
sample of several thousand type Ia supernova with redshifts z < 1.7, as might
be gathered by the proposed SNAP satellite. Among other things, we derive
optimal strategies for constraining cosmological parameters using type Ia
supernovae. While in the near term CMB anisotropy will provide the first
measurements of w, supernovae and number counts appear to have the most
potential to probe dark energy.


title: High Sensitivity, High Spectral Resolution, Mid-infrared Spectroscopy

abstract:
  We broadly discuss mid-infrared spectroscopy and detail our new high spectral
resolution instrument, the Texas Echelon-cross-Echelle Spectrograph (TEXES).


title: Probing the Early Universe with the S-Z Effect

abstract:
  The cosmic microwave background radiation (CMBR) is providing important clues
into the evolution of the early universe. In this Science Perspective, Joy and
Carlstrom discuss one feature of the CMBR, the Sunyaev-Zel'dovich effect, which
can be used to determine the abundance and evolution of clusters of galaxies,
thereby constraining key cosmological parameters such as the matter density of
the universe and its expansion rate.


title:
Relativistic close coupling calculations for photoionization and
  recombination of Ne-like Fe XVII

abstract:
  Relativistic and channel coupling effects in photoionization and unified
electronic recombination of Fe XVII are demonstrated with an extensive 60-level
close coupling calculation using the Breit-Pauli R-matrix method.
Photoionization and (e + ion) recombination calculations are carried out for
the total and the level-specific cross sections, including the ground and
several hundred excited bound levels of Fe XVII (up to fine structure levels
with n = 10). The unified (e + ion) recombination calculations for (e + Fe
XVIII --> Fe XVII) include both the non-resonant and resonant recombination
(`radiative' and `dielectronic recombination' -- RR and DR). The low-energy and
the high energy cross sections are compared from: (i) a 3-level calculation
with 2s^2p^5 (^2P^o_{1/2,3/2}) and 2s2p^6 (^2S_{1/2}), and (ii) the first
60-level calculation with \Delta n > 0 coupled channels with spectroscopic
2s^2p^5, 2s2p^6, 2s^22p^4 3s, 3p, 3d, configurations, and a number of
correlation configurations. Strong channel coupling effects are demonstrated
throughout the energy ranges considered, in particular via giant
photoexcitation-of-core (PEC) resonances due to L-M shell dipole transition
arrays 2p^5 --> 2p^4 3s, 3d in Fe XIII that enhance effective cross sections by
orders of magnitude. Comparison is made with previous theoretical and
experimental works on photoionization and recombination that considered the
relatively small low-energy region (i), and the weaker \Delta n = 0 couplings.
While the 3-level results are inadequate, the present 60-level results should
provide reasonably complete and accurate datasets for both photoionization and
(e + ion) recombination of Fe~XVII in laboratory and astrophysical plasmas.


title:
HST Observations of SGR 0526-66: New Constraints on Accretion and
  Magnetar Models

abstract:
  Soft Gamma-ray Repeaters (SGRs) are among the most enigmatic sources known
today. Exhibiting huge X- and Gamma-ray bursts and flares, as well as soft
quiescent X-ray emission, their energy source remains a mystery. Just as
mysterious are the Anomalous X-ray pulsars (AXPs), which share many of the same
characteristics. Thanks to recent Chandra observations, SGR 0526-66, the first
SGR, now appears to be a transition object bridging the two classes, and
therefore observations of it have implications for both SGRs and AXPs. The two
most popular current models for their persistent emission are accretion of a
fossil disk or decay of an enormous (~10^15 G) magnetic field in a magnetar. We
show how deep optical observations of SGR 0526-66, the only SGR with small
enough optical extinction for meaningful observations, show no evidence of an
optical counterpart. These observation place strong new constraints on both
accretion disk and magnetar models, and suggest that the spectral energy
distribution may peak in the hard-UV. Almost all accretion disks are excluded
by the optical data, and a magnetar would require a ~10^15-10^16 G field.


title: Time Variable Faraday Rotation Measures of 3C-273 and 3C-279

abstract:
  Multifrequency polarimetry with the VLBA confirms the previously reported
time-varying Faraday rotation measure (RM) in the quasar 3C-279. Variability in
the RM and electric vector position angle (EVPA) of the jet component (C4) is
seen making it an unreliable absolute EVPA calibrator. 3C-273 is also shown to
vary its RM structure on 1.5 year time-scales. Variation in the RM properties
of quasars may result from a Faraday screen which changes on time-scales of a
few years, or from the motion of jet components which sample spatial variations
in the screen. A new component emerging from the core of 3C-279 appears to be
starting to sample such a spatial variation. Future monitoring of this
component and its RM properties is suggested as a diagnostic of the narrow line
region in 3C-279. We also present a new method of EVPA calibration using the
VLA Monitoring Program.


title: Star Formation Thresholds in Galactic Disks

abstract:
  We report the first results of a detailed study of the star formation law in
a sample of 32 nearby spiral galaxies with well-measured rotation curves, HI
and H$_2$ (as traced by CO) surface density profiles, and new \Ha CCD
photometry. Our results strongly support the view that the formation of
gravitationally bound interstellar clouds regulates the onset of widespread
star formation -- at least in the outer regions of galactic disks.


title: On the two types of steady hard X-ray states of GRS 1915+105

abstract:
  Using the data of 5 years of RXTE observations we investigate the X-ray
spectral and timing properties of GRS 1915+105 during the hard steady states.
According to the results of our simultaneous X-ray spectral and timing analysis
the behavior the source during the hard steady states can be reduced to a
couple of major distinct types. i) Type I states: The dominant hard component
of the energy spectrum has characteristic quasi- exponential cut-off at 50-120
keV. The broad-band power density spectrum of the source shows significant high
frequency noise component with a cut-off at 60-80 Hz. ii) Type II states: The
hard spectral component has a break in its slope at ~12-20 keV. The high
frequency part of the power density spectrum fades quickly lacking significant
variability at frequencies higher than ~30 Hz. These two types of the X-ray
hard states are also clearly distinguished by their properties in the radio
band: while during the type I observations the source tends to be
'radio-quiet', the type II observations are characterized by high level of
radio flux ('plateau' radio states). In this work we demonstrate aforementioned
differences using the data of 12 representative hard steady state observations.
We conclude that the difference between these two types can be probably
explained in terms of different structure of the accretion flow in the
immediate vicinity of the compact object due to presence of relativistic
outflow of matter.


title: Soft X-ray Properties of ULIRGs Based on a Large and Complete Sample

abstract:
  We report on the results of the cross-correlation of a sample of 903
Ultraluminous IRAS galaxies (ULIRGs) with the ROSAT-All Sky Survey Bright
Source Catalogue and the ROSAT archived pointing observations. The sample of
ULIRGs has been compiled from the PSCz redshift survey. In total, 35 ULIRGs are
securely detected by the ROSAT All-Sky Survey and pointing observations, five
of which are blazars. The statistical properties of these sources in the soft
X-ray band are determined and compared with their properties in other
wavebands. We find that the ratio of the soft X-ray to the far-infrared flux
spans about 5 orders of magnitude and reaches values of about unity. This ratio
is a good indicator of the main energy source of ULIRGs. Those with soft X-ray
to far-infrared flux exceeding 0.01 are probably powered by accretion onto
central supermassive black holes while those with ratios smaller than 0.001 are
probably caused by starbursts or other heating processes, or are Compton thick
sources. Some ULIRGs have energy contributions from both. This ratio is low for
most ULIRGs and hyperluminous infrared galaxies, which explains their low
detection rate by ROSAT and ASCA. We also find that some ULIRGs have a similar
soft X-ray luminosity vs. temperature relation to that for groups of galaxies
and elliptical galaxies, suggesting a common origin of these systems. Our study
also reveals a correlation between the hardness ratio and the soft X-ray
luminosity for Seyfert 1s/QSOs.


title: Radio and Infrared Properties of Dust-Enshrouded Wolf-Rayet Stars

abstract:
  This paper discusses our ongoing efforts to characterize dust-enshrouded
Wolf-Rayet (WR) stars in the radio and infrared. We have used the Very Large
Array to measure the broadband radio spectrum of WR stars in suspected binary
systems and discovered non-thermal emission, which is usually attributed to
colliding winds. In addition, infrared imaging using aperture masking
interferometry on the Keck-I telescope has resolved the dust shells around a
number of WR stars with K-magnitudes brighter than ~6. Although this admittedly
small study suffers from selection bias, we note that all the dust-enshrouded
WR stars with radio detections show evidence for colliding winds, supporting
the theory that wind compression in a binary system is necessary for efficient
dust production. A consequence of this hypothesis is that virtually all WC8-10
stars must be in binaries, since most are dusty. Single-star and binary stellar
evolution models will have to be modified to accommodate this observational
result if confirmed.


title: Dusty Debris Around Solar-Type Stars: Temporal Disk Evolution

abstract:
  Using ISO-ISOPHOT we carried out a survey of almost 150 stars to search for
evidence of emission from dust orbiting young main sequence stars, both in
clusters and isolated systems. Over half of the detections are new examples of
dusty stellar systems, and demonstrate that such dust can be detected around
numerous stars older than a few x 10^6 years. Fluxes at 60 microns and either
90 or 100 microns for the new excess sources together with improved fluxes for
a number of IRAS-identified sources are presented. Analysis of the excess
luminosity relative to the stellar photosphere shows a systematic decline of
this excess with stellar age consistent with a power law index of -2.


title: High energy particles from gamma-ray bursts

abstract:
  A review is presented of the fireball model of gamma-ray bursts (GRBs), and
of the production in GRB fireballs of high energy protons and neutrinos.
Constraints imposed on the model by recent afterglow observations, which
support the association of GRB and ultra-high energy cosmic-ray (UHECR)
sources, are discussed. Predictions of the GRB model for UHECR production,
which can be tested with planned large area UHECR detectors and with planned
high energy neutrino telescopes, are reviewed.


title:
Infrared Observations and Modeling of one of the Coolest T Dwarfs, Gl
  570D

abstract:
  We have obtained a good quality R$\sim$400 0.8-2.5 $\mu$m spectrum and
accurate photometry of Gl 570D, one of the coolest and least luminous brown
dwarfs currently known. The spectrum shows that Gl 570D has deeper absorptions
in the strong water and methane bands at 1.12-1.17 $\mu$m, 1.33-1.45 $\mu$m,
1.62-1.88 $\mu$m, and 2.20-2.45 $\mu$m and is both bluer at J-K and redder at
$K-L^{\prime}$ than previously observed T dwarfs. Data analysis using model
spectra coupled with knowledge of the well-understood primary implies that for
the same surface gravity, Gl 570D is about 160 K cooler than Gl 229B. For an
age range of 2-5 Gyr Gl 570D has an effective temperature in the range 784-824
K, a log gravity in the range 5.00-5.27 cm s$^{-2}$, and a luminosity in the
range 2.88-2.98 $\times$ 10$^{-6}$ L$_\odot$.


title: Empirical relations for cluster RR Lyrae stars revisited

abstract:
  Our former study on the empirical relations between the Fourier parameters of
the light curves of the fundamental mode RR Lyrae stars and their basic stellar
parameters has been extended to considerably larger data sets. The most
significant contribution to the absolute magnitude M_v comes from the period P
and from the first Fourier amplitude A_1, but there are statistically
significant contributions also from additional higher order components, most
importantly from A_3 and in a lesser degree from the Fourier phase phi_51. When
different colors are combined in reddening-free quantities, we obtain basically
period-luminosity-color relations. Due to the log T_eff (B-V, log g, [Fe/H])
relation from stellar atmosphere models, we would expect some dependence also
on phi_31. Unfortunately, the data are still not extensive and accurate enough
to decipher clearly the small effect of this Fourier phase. However, with the
aid of more accurate multicolor data on field variables, we show that this
Fourier phase should be present either in V-I or in B-V or in both. From the
standard deviations of the various regressions, an upper limit can be obtained
on the overall inhomogeneity of the reddening in the individual clusters. This
yields sigma_E(B-V)}< 0.012 mag, which also implies an average minimum
observational error of sigma_V > 0.018 mag.


title: Why Canonical Disks Cannot Produce Advection Dominated Flows

abstract:
  Using simple arguments we show that the canonical thin keplerian accretion
disks cannot smoothly match any plain advection dominated flow (ADAF) model. By
'plain' ADAF model we mean the ones with zero cooling. The existence of sonic
points in exact solutions is critical and imposes constraints that cannot be
surpassed adopting 'reasonable' physical conditions at the hypothetical match
point. Only the occurrence of new critical physical phenomena may produce a
transition. We propose that exact advection models are a class of solutions
which don't necessarily involve the standard thin cool disks and suggest a
different scenario in which good ADAF solutions could eventually occur.


title: Sub-arcsecond imaging of SiO in the HH 211 protostellar jet

abstract:
  We present images of the HH 211 molecular jet in the SiO v=0, J=1-0 line at
43 GHz made with the Very Large Array at approximately 0.5 arcsec resolution.
The SiO emission appears to trace primarily internal bowshocks in the outflow,
suggesting that the dust and molecular gas are accelerated via prompt
entrainment at internal working surfaces in the jet. There is also some
evidence for limb-brightening of the SiO emission, indicating that SiO emission
may also arise from entrainment in the jet's boundary layer. Excitation
temperatures of >~150-200 K are inferred from the SiO emission. Enhancements in
the SiO abundance of ~10^6 over interstellar values are observed, and the
possible origin of the SiO is discussed.


title:
Evolution of magnetic field curvature in the Kulsrud-Anderson dynamo
  theory

abstract:
  We find that in the kinematic limit the ensemble averaged square of the
curvature of magnetic field lines is exponentially amplified in time by the
turbulent motions in a highly conductive plasma. At the same time, the ensemble
averaged curvature vector exponentially decays to zero. Thus, independently of
the initial conditions, the fluctuation field becomes very curved, and the
curvature vector becomes highly isotropic.
  Keywords: ISM: magnetic fields, MHD, turbulence, methods: analytical


title: Temporal properties of short GRBs

abstract:
  We analyze a sample of bright short bursts from the BATSE 4B-catalog and find
that many short bursts are highly variable ($\delta t_{min}/T\ll 1$, where
$\delta t_{min}$ is the shortest pulse duration and T is the burst duration).
This indicates that it is unlikely that short bursts are produced by external
shocks. We also analyze the available (first 1-2 seconds) high resolution (TTE)
data of some of the long bursts. We find that variability on a 10ms time-scale
is common in long bursts. This result shows that some long bursts are even more
variable than it was thought before ($\delta t_{min}/T\approx 10^{-4}-10^{-3}$
)


title: The Measurement of Disk Ellipticity in Nearby Spiral Galaxies

abstract:
  We have measured the intrinsic disk ellipticity for 7 nearby, nearly face-on
spiral galaxies by combining Densepak integral-field spectroscopy with I-band
imaging from the WIYN telescope. Initially assuming an axisymmetric model, we
determine kinematic inclinations and position angles from H-alpha velocity
fields, and photometric axis ratios and position angles from imaging data. We
interpret the observed disparities between kinematic and photometric disk
parameters in terms of an intrinsic non-zero ellipticity. The mean ellipticity
of our sample is 0.05. If the majority of disk galaxies have such intrinsic
axis ratios, this would account for roughly 50% of the scatter in the
Tully-Fisher relation. This result, in turn, places tighter constraints on
other sources of scatter in this relation, the most astrophysically compelling
of which is galaxy mass-to-light ratios.


title: Quintessence and the first Doppler peak

abstract:
  By using a tracking quintessence model we obtain that the position of the
first Doppler peak in the spectrum of CMB anisotropies only depends on the
topology of the universe, $\Omega_k$, for any value of the ratio
$\Omega_{\Lambda}/\Omega_M$, so that such a dependence is perfectly valid in
the range suggested by supernova observations.


title: High Energy Neutrino Astronomy: Towards Kilometer-Scale Detectors

abstract:
  Of all high-energy particles, only neutrinos can directly convey astronomical
information from the edge of the universe---and from deep inside the most
cataclysmic high-energy processes. Copiously produced in high-energy
collisions, travelling at the velocity of light, and not deflected by magnetic
fields, neutrinos meet the basic requirements for astronomy. Their unique
advantage arises from a fundamental property: they are affected only by the
weakest of nature's forces (but for gravity) and are therefore essentially
unabsorbed as they travel cosmological distances between their origin and us.
Many of the outstanding mysteries of astrophysics may be hidden from our sight
at all wavelengths of the electromagnetic spectrum because of absorption by
matter and radiation between us and the source. For example, the hot dense
regions that form the central engines of stars and galaxies are opaque to
photons. In other cases, such as supernova remnants, gamma ray bursters, and
active galaxies, all of which may involve compact objects or black holes at
their cores, the precise origin of the high-energy photons emerging from their
surface regions is uncertain. Therefore, data obtained through a variety of
observational windows---and especially through direct observations with
neutrinos---may be of cardinal importance. In this talk, the scientific goals
of high energy neutrino astronomy and the technical aspects of water and ice
Cherenkov detectors are examined, and future experimental possibilities,
including a kilometer-square deep ice neutrino telescope, are explored.


title:
X-ray, Optical, and Radio Observations of the Type II Supernovae 1999em
  and 1998S

abstract:
  Observations of the Type II-P (plateau) Supernova (SN) 1999em and Type IIn
(narrow emission line) SN 1998S have enabled estimation of the profile of the
SN ejecta, the structure of the circumstellar medium (CSM) established by the
pre-SN stellar wind, and the nature of the shock interaction. SN 1999em is the
first Type II-P detected at both X-ray and radio wavelengths. The Chandra X-ray
data indicate non-radiative interaction of SN ejecta with a power-law density
profile (rho \propto r^{-n} with n ~ 7) with a pre-SN wind with a low mass-loss
rate of ~2 \times 10^{-6} M_sun/yr for a wind velocity of 10 km/sec, in
agreement with radio mass-loss rate estimates. The Chandra data show an
unexpected, temporary rise in the 0.4--2.0 keV X-ray flux at ~100 days after
explosion. SN 1998S, at an age of >3 years, is still bright in X-rays and is
increasing in flux density at cm radio wavelengths. Spectral fits to the
Chandra data show that many heavy elements (Ne, Al, Si, S, Ar, and Fe) are
overabundant with respect to solar values. We compare the observed elemental
abundances and abundance ratios to theoretical calculations and find that our
data are consistent with a progenitor mass of approximately 15-20 M_sun if the
heavy element ejecta are radially mixed out to a high velocity. If the X-ray
emission is from the reverse shock wave region, the supernova density profile
must be moderately flat at a velocity ~10^4 km/sec, the shock front is
non-radiative at the time of the observations, and the mass-loss rate is 1-2
\times 10^{-4} M_sun/yr for a pre-supernova wind velocity of 10 km/sec. This
result is also supported by modeling of the radio emission which implies that
SN 1998S is surrounded by a clumpy or filamentary CSM established by a high
mass-loss rate, ~2 \times 10^{-4} M_sun/yr, from the pre-supernova star.


title: A Molecular Gas of z<0.2 Infrared-Excess, Optical QSOs

abstract:
  Millimeter-wave (CO) observations of optically-selected QSOs are potentially
a powerful tool for studying the properties of both the QSOs and their host
galaxies. We summarize here a recent molecular gas survey of z<0.17 optical
QSOs with infrared (IR) excess, L_IR (8-1000 um) / L_bbb (0.1-1.0 um) > 0.36.
Eight of these QSOs have been detected to date in CO(1-0), and the derived
molecular gas masses are in the range 1.7-35x10^9 M_sun. The high L_IR / L'_CO
of QSOs relative to the bulk of the local (z<0.2) IR luminous galaxy merger
population is indicative of significant heating of dust (L_IR) by the QSO
nucleus and/or by massive stars created in the host galaxy with high efficiency
(i.e., per unit molecular gas, L'_CO).


title: A Classic Type 2 QSO

abstract:
  In the Chandra Deep Field South 1Msec exposure we have found, at redshift
3.700 +- 0.005, the most distant Type 2 AGN ever detected. It is the source
with the hardest X-ray spectrum with redshift z>3. The optical spectrum has no
detected continuum emission to a 3sigma detection limit of ~3 10^{-19}
ergs/s/cm^2/AA and shows narrow lines of Ly_alpha, CIV, NV, HeII, OVI, [OIII],
and CIII]. Their FWHM line widths have a range of ~700-2300 km/s with an
average of approximately ~1500 km/s. The emitting gas is metal rich (Z ~2.5-3
Z_solar). In the X-ray spectrum of 130 counts in the 0.5-7 keV band there is
evidence for intrinsic absorption with N_H > 10^{24} cm^{-2}. An iron K_alpha
line with rest frame energy and equivalent width of ~6.4 keV and ~1 keV,
respectively, in agreement with the obscuration scenario, is detected at a
2sigma level. If confirmed by our forthcoming XMM observations this would be
the highest redshift detection of FeK_alpha. Depending on the assumed cosmology
and the X-ray transfer model, the 2-10 keV rest frame luminosity corrected for
absorption is ~10^{45 +- 0.5} ergs/s, which makes our source a classic example
of the long sought Type 2 QSOs. From standard population synthesis models,
these sources are expected to account for a relevant fraction of the
black-hole-powered QSO distribution at high redshift.


title:
The Probability Distribution Function of Column Density in Molecular
  Clouds

abstract:
  (Abridged) We discuss the probability distribution function (PDF) of column
density resulting from density fields with lognormal PDFs, applicable to
isothermal gas (e.g., probably molecular clouds). We suggest that a
``decorrelation length'' can be defined as the distance over which the density
auto-correlation function has decayed to, for example, 10% of its zero-lag
value, so that the density ``events'' along a line of sight can be assumed to
be independent over distances larger than this, and the Central Limit Theorem
should be applicable. However, using random realizations of lognormal fields,
we show that the convergence to a Gaussian is extremely slow in the high-
density tail. Thus, the column density PDF is not expected to exhibit a unique
functional shape, but to transit instead from a lognormal to a Gaussian form as
the ratio $\eta$ of the column length to the decorrelation length increases.
Simultaneously, the PDF's variance decreases. For intermediate values of
$\eta$, the column density PDF assumes a nearly exponential decay. We then
discuss the density power spectrum and the expected value of $\eta$ in actual
molecular clouds. Observationally, our results suggest that $\eta$ may be
inferred from the shape and width of the column density PDF in
optically-thin-line or extinction studies. Our results should also hold for gas
with finite-extent power-law underlying density PDFs, which should be
characteristic of the diffuse, non-isothermal neutral medium (temperatures
ranging from a few hundred to a few thousand degrees). Finally, we note that
for $\eta \gtrsim 100$, the dynamic range in column density is small
($\lesssim$ a factor of 10), but this is only an averaging effect, with no
implication on the dynamic range of the underlying density distribution.


title: Gamma-Ray Emission from Active Galactic Nuclei - an Overview

abstract:
  Gamma-ray emission from AGN provides us with unprecedented insights into the
physics of extragalactic jets. The emission from these jets fits naturally into
the existing theoretical framework of relativistic jets as inferred from parsec
scale and kiloparsec scale observations. Models of the $\gamma$-ray fluxes give
us important knowledge of jet parameters, in particular magnetic fields and the
size of the emitting region. For example, in the case of Markarian~501, the jet
plasma is subequipartiion and the energy flux is particle dominated. Discussion
of the physics of jets on the sub-parsec scale leads naturally to questions of
jet composition. The dynamics of jets are consistent with conventional
electron-proton composition if the minimum Lorentz factors, $\gamma_{\rm min} >
100$. Jets can be electron-positron if $\gamma_{\rm min} \approx 100$.


title: Search for low-mass PMS companions around X-ray selected late B stars

abstract:
  We have observed 49 X-ray detected bright late B-type dwarfs to search for
close low-mass pre-main sequence (PMS) companions using the European Southern
Observatory's ADONIS (Adaptive Optics Near Infrared System) instrument. We
announce the discovery of 21 new companions in 9 binaries, 5 triple, 4
quadruple system and 1 system consisting of five stars. The detected new
companions have K magnitudes between 6.5 mag and 17.3 mag. and angular
separations ranging from 0.2 and 14.1 arcsec (18-2358 AU).


title: The North Ecliptic Pole Supercluster

abstract:
  We have used the ROSAT All-Sky Survey to detect a known supercluster at
z=0.087 in the North Ecliptic Pole region. The X-ray data greatly improve our
understanding of this supercluster's characteristics, approximately doubling
our knowledge of the structure's spatial extent and tripling the cluster/group
membership compared to the optical discovery data. The supercluster is a rich
structure consisting of at least 21 galaxy clusters and groups, 12 AGN, 61 IRAS
galaxies, and various other objects. A majority of these components were
discovered with the X-ray data, but the supercluster is also robustly detected
in optical, IR, and UV wavebands. Extending 129 x 102 x 67 (1/h50 Mpc)^3, the
North Ecliptic Pole Supercluster has a flattened shape oriented nearly edge-on
to our line-of-sight. Owing to the softness of the ROSAT X-ray passband and the
deep exposure over a large solid angle, we have detected for the first time a
significant population of X-ray emitting galaxy groups in a supercluster. These
results demonstrate the effectiveness of X-ray observations with contiguous
coverage for studying structure in the Universe.


title: The X-ray Spectrum of the Rapid Burster using the Chandra HETGS

abstract:
  We present observations of the Rapid Burster (RB, also known as MXB 1730-335)
using the Chandra High Energy Transmission Grating Spectrometer. The average
interval between type II (accretion) bursts was about 40 s. There was one type
I (thermonuclear flash) burst and about 20 "mini-bursts" which are probably
type II bursts whose peak flux is 10-40% of the average peak flux of the other
type II bursts. The time averaged spectra of the type II bursts are well fit by
a blackbody with a temperature of kT = 1.6 keV, a radius of 8.9 km for a
distance of 8.6 kpc, and an interstellar column density of 1.7e22 per sq. cm.
No narrow emission or absorption lines were clearly detected. The 3 sigma upper
limits to the equivalent widths of any features are < 10 eV in the 1.1-7.0 keV
band and as small as 1.5 eV near 1.7 keV. We suggest that Comptonization
destroys absorption features such as the resonance line of Fe XXVI.


title: GRB and Environment Interaction

abstract:
  We discuss three aspects of the interaction between GRB and their
surroundings. The illumination of the progenitor remnant and/or the
surroundings by the X-ray afterglow continuum can produce substantial Fe
K-alpha line and edge emission, with implications for the progenitor model. The
presence of large dust column densities, capable of obscuring the GRB optical
afterglow, will lead to characteristic delayed X-ray and far-IR light curve
signatures. Pair production induced by the initial gamma-rays in the nearby
environment will modify the initial spectrum and the afterglow light curve, and
the magnitude of these changes provides a diagnostic for the external density.


title: The Evolution of Stellar Exponential Discs

abstract:
  Models of disc galaxies which invoke viscosity-driven radial flows have long
been known to provide a natural explanation for the origin of stellar
exponential discs, under the assumption that the star formation and viscous
timescales are comparable. We present models which invoke simultaneous star
formation, viscous redistribution of gas and cosmologically-motivated gaseous
infall and explore the predictions such models make for the scale length
evolution and radial star formation history of galactic stellar discs. While
the inclusion of viscous flows is essential for ensuring that the stellar disc
is always exponential over a significant range in radius, we find that such
flows play essentially no role in determining the evolution of the disc scale
length. In models in which the main infall phase precedes the onset of star
formation and viscous evolution, we find the exponential scale length to be
rather invariant with time. On the other hand, models in which star
formation/viscous evolution and infall occur concurrently result in a smoothly
increasing scale length with time, reflecting the mean angular momentum of
material which has fallen in at any given epoch. The disc stellar populations
in these models are predominantly young (ie. ages < 5 Gyr) beyond a few scale
lengths. In both cases, viscous flows are entirely responsible for transporting
material to very large radii. We discuss existing observational constraints on
these models from studies of both local and moderate redshift disc galaxies. In
particular, a good agreement is found between the solar neighbourhood star
formation history predicted by our infall model and the recent observational
determination of this quantity by Rocha-Pinto et al (2000).


title:
Using the 6dF galaxy redshift survey to detect gravitationally-lensed
  quasars

abstract:
  It is possible to detect gravitationally-lensed quasars spectroscopically if
the spectra obtained during galaxy surveys are searched for the presence of
quasar emission lines. The up-coming 6 degree Field (6dF) redshift survey on
the United Kingdom Schmidt Telescope (UKST) will involve obtaining 10^5 spectra
of near-infrared selected galaxies to a magnitude limit of K = 13. Applying
previously developed techniques implies that at least one lens should be
discovered in the 6dF survey, but that as many as ten could be found if quasars
typically have B_J - K = 8. In this model there could be up to fifty lensed
quasars in the sample, but most of them could only be detected by infrared
spectroscopy.


title: The 2dF gravitational lens survey

abstract:
  The 2 degree Field (2dF) galaxy redshift survey will involve obtaining
approximately 2.5 x 10^5 spectra of objects previously identified as galaxy
candidates on morphological grounds. Included in these spectra should be about
ten gravitationally-lensed quasars, all with low-redshift galaxies as
deflectors (as the more common lenses with high-redshift deflectors will be
rejected from the survey as multiple point-sources). The lenses will appear as
superpositions of galaxy and quasar spectra, and both cross-correlation
techniques and principal components analysis should be able to identify
candidates systematically. With the 2dF survey approximately half-completed it
is now viable to begin a systematic search for these spectroscopic lenses, and
the first steps of this project are described here.


title: Gravitational lensing and modified Newtonian dynamics

abstract:
  Gravitational lensing is most often used as a tool to investigate the
distribution of (dark) matter in the universe, but, if the mass distribution is
known a priori, it becomes, at least in principle, a powerful probe of gravity
itself. Lensing observations are a more powerful tool than dynamical
measurements because they allow measurements of the gravitational field far
away from visible matter. For example, modified Newtonian dynamics (MOND) has
no relativistic extension, and so makes no firm lensing predictions, but
galaxy-galaxy lensing data can be used to empirically the deflection law of a
point-mass. MONDian lensing is consistent with general relativity, in so far as
the deflection experienced by a photon is twice that experienced by a massive
particle moving at the speed of light. With the deflection law in place and no
invisible matter, MOND can be tested wherever lensing is observed. The
implications are that either MONDian lensing is completely non-linear or that
MOND is not an accurate description of the universe.


title: Hydrodynamic simulations of the triaxial bulge of M31

abstract:
  The interstellar gas flow in the inner disk of M31 is modelled using a new,
two dimensional, grid based, hydrodynamics code. The potential of the stellar
bulge is derived from its surface brightness profile. The bulge is assumed to
be triaxial and rotating in the same plane as the disk in order to explain the
twisted nature of M31's central isophotes and the non circular gas velocities
in the inner disk. Results are compared with CO observations and the bulge is
found to be a fast rotator with a B-band mass-to-light ratio, Y = 6.5 +/- 0.8,
and a ratio of co-rotation radius to bulge semi-major axis, R = 1.2 +/- 0.1,
implying that any dark halo must have a low density core in contradiction to
the predictions of CDM. These conclusions would be strengthened by further
observations confirming the model's off axis CO velocity predictions.


title: Time Scales in Long GRBs

abstract:
  We analyze a sample of bright long bursts and find that the pulses duration
have a lognormal distribution while the intervals between pulses have an excess
of long intervals (relative to lognormal distribution). This excess can be
explained by the existence of quiescent times, long periods with no signal
above the background. The lognormal distribution of the intervals (excluding
the quiescent times) is similar to the distribution of the pulses width. This
result suggests that the quiescent times are made by a different mechanism than
the rest of the intervals. It also suggests that the intervals (excluding the
quiescent times) and the pulse width are connected to the same parameters of
the source. We find that there is a correlation between a pulse width and the
duration of the interval preceding it. There is a weaker, but still a
significant, correlation between a pulse width and the interval following it.
The significance of the correlation drops substantially when the intervals
considered are not adjacent to the pulse.


title: On the Surface Waves in the Solar Photosphere

abstract:
  The regular structures similar to the chains and clusters on the Solar
Photosphere are investigated and mechanism these origin are proposed.


title: Kinematics of young stars. II. Galactic spiral structure

abstract:
  The young star velocity field is analysed by means of a galactic model which
takes into account solar motion, differential galactic rotation and spiral arm
kinematics. We use two samples of Hipparcos data, one containing O- and B-type
stars and another one composed of Cepheid variable stars. The robustness of our
method is tested through careful kinematic simulations. Our results show a
galactic rotation curve with a classical value of $A$ Oort constant for the O
and B star sample ($A^{\mathrm{OB}} =$ 13.7-13.8 km s$^{-1}$ kpc $^{-1}$) and a
higher value for Cepheids ($A^{\mathrm{Cep}} =$ 14.9-16.9 km s$^{-1}$ kpc
$^{-1}$, depending on the cosmic distance scale chosen). The second-order term
is found to be small, compatible with a zero value. The study of the residuals
shows the need for a $K$-term up to a heliocentric distance of 4 kpc, obtaining
a value $K = -$(1-3) km s$^{-1}$ kpc$^{-1}$. The results obtained for the
spiral structure from O and B stars and Cepheids show good agreement. The Sun
is located relatively near the minimum of the spiral perturbation potential
($\psi_\odot =$ 284-20$\degr$) and very near the corotation circle. The angular
rotation velocity of the spiral pattern was found to be $\Omega_{\mathrm{p}}
\approx 30$ km s$^{-1}$ kpc $^{-1}$.


title:
An Ultraviolet through Infrared Look at Star Formation and Super Star
  Clusters in Two Circumnuclear Starburst Rings

abstract:
  We present broad-band (U, V, I,and H) and narrow-band(H-alpha+[N II] and
Paschen-alpha) images of the circumnuclear starburst rings in two nearby spiral
galaxies, NGC 1512 and NGC 5248, obtained with WFPC2 and NICMOS on HST.
Combined with HST images at 2300 Ang, these data provide a particularly wide
wavelength range with which to study the properties of the stellar populations,
the gas, and the dust in the rings. Some large (50-pc scale) line emitting
regions have little associated continuum emission, but a Pa equivalent width
indicating a few-Myr-old embedded stellar population. The Ha/Pa intensity
ratios suggest the gas is mixed with dust, making it effective at obscuring
some of the young clusters. We identify about 1000 compact continuum sources
(super star clusters and individual stars) and analyze their spectral energy
distributions (SEDs) from 0.2 to 1.6 micron by fitting them with a grid of
spectral synthesis models with a range of ages and extinctions. Most of the
visible clusters are only mildly reddened, with A_V=0 to 1 mag, suggesting that
the processes that clear out the gas and dust of the stellar birth clouds are
efficient and fast. The patchiness of the dust distribution makes it difficult
to estimate reliably the star formation rate, based on UV continuum slope or
hydrogen emission-line ratios. The cluster SEDs are consistent with a range in
ages, from 1 Myr to 300 Myr, but with only a minority older than a few tens of
Myr. However, after accounting for an age bias, the fraction of old clusters is
consistent with continuous star formation in the rings over the past ~300 Myr.
Some of the brightest young clusters have excess emission in the IR that may be
radiation by circumstellar dust. The cluster mass functions follow an m^-2
power-law distribution, distinct from those of old globular clusters.


title: A Complete Relativistic Ionized Accretion Disc in Cygnus X-1

abstract:
  The galactic black hole candidate Cygnus X-1 is observed to be in one of two
X-ray spectral states; either the low/hard (low soft X-ray flux and a flat
power law tail) or high/soft (high blackbody-like soft X-ray flux and a steep
power law tail) state. The physical origin of these two states is unclear. We
present here a model of an ionized accretion disc, the spectrum of which is
blurred by relativistic effects, and fit it to the ASCA, Ginga and EXOSAT data
of Cygnus X-1 in both spectral states. We confirm that relativistic blurring
provides a much better fit to the low/hard state data and, contrary to some
previous results, find the data of both states to be consistent with an ionized
thin accretion disc with a reflected fraction of unity extending to the
innermost stable circular orbit around the black hole. Our model is an
alternative to those which, in the low/hard state, require the accretion disc
to be truncated at a few tens of Schwarzschild radii, within which there is a
Thomson-thin, hot accretion flow. We suggest a mechanism that may cause the
changes in spectral state.


title:
Chandra and RXTE Spectroscopy of the Galactic Microquasar XTE J1550-564
  in Outburst

abstract:
  On two occasions, we obtained nearly simultaneous ~ 4 kilosecond snapshot
observations of the Galactic black hole and microquasar XTE J1550-564 with
Chandra and RXTE near the peak of its May, 2000 outburst. The low-energy
sensitivity of Chandra and the resolution of the High Energy Transmission
Grating Spectrometer (HETGS), coupled with the broad energy range and large
collecting area of RXTE, have allowed us to place constraints on the outburst
accretion flow geometry of this source in the ``intermediate'' X-ray state. The
0.65-25.0 keV continuum spectra are well-described by relatively hot (kT ~ 0.8
keV) accretion disk and hard (Gamma ~ 2.3) coronal power-law components. Broad,
relatively strong Fe K-alpha emission line (EW ~170 eV) and smeared absorption
edge components consistent with Fe XXV are strongly required in joint spectral
fits. The resolution of the Chandra/HETGS reveals that the broad Fe K-alpha
emission lines seen clearly in the individual RXTE spectra are not due to an
intrinsically narrow line.


title: The Evolution of Relativistic Binary Progenitor Systems

abstract:
  Relativistic binary pulsars, such as B1534+12 and B1913+16 are characterized
by having close orbits with a binary separation of ~ 3 R_\sun. The progenitor
of such a system is a neutron star, helium star binary. The helium star, with a
strong stellar wind, is able to spin up its compact companion via accretion.
The neutron star's magnetic field is then lowered to observed values of about
10^{10} Gauss. As the pulsar lifetime is inversely proportional to its magnetic
field, the possibility of observing such a system is, thus, enhanced by this
type of evolution. We will show that a nascent (Crab-like) pulsar in such a
system can, through accretion-braking torques (i.e. the "propeller effect") and
wind-induced spin-up rates, reach equilibrium periods that are close to
observed values. Such processes occur within the relatively short helium star
lifetimes. Additionally, we find that the final outcome of such evolutionary
scenarios depends strongly on initial parameters, particularly the initial
binary separation and helium star mass. It is, indeed, determined that the
majority of such systems end up in the pulsar "graveyard", and only a small
fraction are strongly recycled. This fact might help to reconcile theoretically
expected birth rates with limited observations of relativistic binary pulsars.


title: Structure in the Velocity Space of Globular Clusters

abstract:
  We present an analysis of the velocity space of a sample of globular clusters
(GC) with absolute proper motions. The vertical component of the velocity is
found to be correlated with luminosity and galactocentric radius. We divided
the sample into two luminosity groups above and below the peak of the
luminosity function (LF), MV=-7.5, for Galactic GCs. The two groups display
different kinematic behaviour according to the first and second statitical
moments of the velocity distribution as well as distinct velocity ellipsoids.
The velocity ellipsoid of the high luminosity clusters is aligned with the
symmetry axes of the Galaxy, whereas the minor axis of the Low Luminosity group
is strongly inclined relative to the Galactic rotation axis.


title: Brown Dwarf Companions to G-type Stars. I: Gliese 417B and Gliese 584C

abstract:
  We present astrometric and spectroscopic observations confirming that two
nearby G dwarf systems (Gliese 417 = BD+36 2162 and Gliese 584AB = eta CrB AB)
have a widely separated, L dwarf, substellar companion. Using age estimates of
the G dwarf primaries, we estimate masses for these L dwarfs from theoretical
evolutionary tracks. For the L4.5 dwarf Gl 417B we estimate an age of 0.08-0.3
Gyr and a mass of 0.035+/-0.015 M_sun. For the L8 dwarf Gl 584C we estimate an
age of 1.0-2.5 Gyr and a mass of 0.060+/-0.015 M_sun. This latter object also
shows evidence of spectrum variability, which may be due to surface
inhomogeneities rotating into and out of view. These new companions are also
compared to six other L dwarf and T dwarf companions previously recognized. For
the L dwarf companions, ages implied by the presence or absence of lithium are
consistent with ages inferred from the primaries alone.


title:
Substellar Companions to Main Sequence Stars: No Brown Dwarf Desert at
  Wide Separations

abstract:
  We use three field L and T dwarfs which were discovered to be wide companions
to known stars by the Two Micron All-Sky Survey (2MASS) to derive a preliminary
brown dwarf companion frequency. Observed L and T dwarfs indicate that brown
dwarfs are not unusually rare as wide (Delta >1000 A.U.) systems to F-M0
main-sequence stars (M>0.5M_sun, M_V<9.5), even though they are rare at close
separation (Delta <3 A.U.), the ``brown dwarf desert.'' Stellar companions in
these separation ranges are equally frequent, but brown dwarfs are >~ 10 times
as frequent for wide than close separations. A brown dwarf wide-companion
frequency as low as the 0.5% seen in the brown dwarf desert is ruled out by
currently-available observations.


title:
Atomic Physics with the Goddard High Resolution Spectrograph on the
  Hubble Space Telescope. V. Oscillator Strengths for Neutral Carbon Lines
  below 1200 Angstrom

abstract:
  We analyzed high resolution spectra of interstellar neutral carbon absorption
toward $\lambda$ Ori, 1 Sco, and $\delta$ Sco that were obtained with the
Goddard High Resolution Spectrograph on the Hubble Space Telescope. Several
multiplets were detected within the wavelength interval 1150 to 1200 A, where
most neutral carbon lines have ill-defined oscillator strength; multiplets at
longer wavelengths with well-defined atomic parameters were also seen. We
extracted accurate column densities and Doppler parameters from lines with
precise laboratory-based f-values. These column densities and b-values were
used to obtain a self-consistent set of f-values for all the observed neutral
carbon lines. For many of the lines with wavelength below 1200 A, the derived
f-values differ appreciably from the values quoted in the compilation by Morton
(1991). The present set of f-values extends and in some cases supersedes those
given in Zsargo et al. (1997), which were based on lower resolution data.


title: The Evolution of Stellar Populations

abstract:
  We summarize the discussion section on ``Evolution of Stellar Populations''
we led on May 27, 2000 in Granada, Spain, as part of the Euroconference on The
Evolution of Galaxies. I- Observational Clues. We also provide a partial
comparison between the present knowledge of these topics and that which existed
at the time of the Crete Conference of 1995.


title:
The Early Formation, Evolution and Age of the Neutron-Capture Elements
  in the Early Galaxy

abstract:
  Abundance observations indicate the presence of rapid-neutron capture (i.e.,
r-process) elements in old Galactic halo and globular cluster stars. These
observations demonstrate that the earliest generations of stars in the Galaxy,
responsible for neutron-capture synthesis and the progenitors of the halo
stars, were rapidly evolving. Abundance comparisons among several halo stars
show that the heaviest neutron-capture elements (including Ba and heavier) are
consistent with a scaled solar system r-process abundance distribution, while
the lighter such elements do not conform to the solar pattern. These
comparisons suggest two r-process sites or at least two different sets of
astrophysical conditions. The large star-to-star scatter observed in the
neutron-capture/iron ratios at low metallicities -- which disappears with
increasing [Fe/H] -- suggests an early, chemically unmixed and inhomogeneous
Galaxy. The stellar abundances indicate a change from the r-process to the slow
neutron capture (i.e., s-) process at higher metallicities in the Galaxy. The
detection of thorium in halo and globular cluster stars offers a promising,
independent age-dating technique that can put lower limits on the age of the
Galaxy.


title:
A molecular-line study of clumps with embedded high-mass protostar
  candidates

abstract:
  We present molecular line observations made with the IRAM 30-m telescope of
the immediate surroundings of a sample of 11 candidate high-mass protostars.
These observations are part of an effort to clarify the evolutionary status of
a set of objects which we consider to be precursors of UC HII regions. We find
that the present data are consistent with such an interpretation. The sources
have FIR luminosities indicating the presence of B2.5 to O8.5V0 stars, are
associated with dense gas and dust, have (sub-)mm continuum spectra indicating
temperatures of ca. 30K, and have no detectable radio continuum emission. All
observed sources are associated with well-defined molecular clumps. Masses,
sizes, and other parameters depend on the tracer used, but typically the cores
have average diameters of ca. 0.5-1 pc, and masses of a few tens to a few
thousand solar masses. Compared to a similar analysis of sources which are
mostly identifyable with UC HII regions, the present sample has molecular
clumps that are more massive, larger, cooler, and less turbulent. They also
tend to have a smaller ratio of virial-to-luminous mass, indicating they are
less dynamically stable than their counterparts embedded in the UC HII-like
sources. The large sizes suggest these clumps should still undergo substantial
contraction. The lower temperatures and small linewidths are also expected in
objects in an earlier evolutionary state. We find that the masses of the
molecular clumps associated with our objects increase with Lfir [M(clump)
propto Lfir^(1.17)], and that there is a (weak) relation between the clump mass
and the mass of the embedded protostellar object M(proto) propto
M(clump)^(0.30).


title: Relativistic Jet Response to Precession and Wave-Wave Interactions

abstract:
  Three dimensional numerical simulations of the response of a Lorentz factor
2.5 relativistic jet to precession at three different frequencies have been
performed. Low, moderate and high precession frequencies have been chosen
relative to the maximally unstable frequency predicted by a Kelvin-Helmholtz
stability analysis. Transverse motion and velocity decreases as the precession
frequency increases. Although helical displacement of the jet decreases in
amplitude as the precession frequency increases, a helical shock is generated
in the medium external to the jet at all precession frequencies. Complex
pressure and velocity structure inside the jet is shown to be produced by a
combination of the helical surface and first body modes predicted by a normal
mode analysis of the relativistic hydrodynamic equations. The surface and first
body mode have different wave speed and wavelength, are launched in phase by
the periodic precession, and exhibit beat patterns in synthetic emission
images. Wave (pattern) speeds range from $0.41c$ to $0.86c$ but beat patterns
remain stationary. Thus, we find a mechanism that can produce differentially
moving and stationary features in the jet.


title: Perturbation spectrum in inflation with cutoff

abstract:
  It has been pointed out that the perturbation spectrum predicted by inflation
may be sensitive to a natural ultraviolet cutoff, thus potentially providing an
experimentally accessible window to aspects of Planck scale physics. A priori,
a natural ultraviolet cutoff could take any form, but a fairly general
classification of possible Planck scale cutoffs has been given. One of those
categorized cutoffs, also appearing in various studies of quantum gravity and
string theory, has recently been implemented into the standard inflationary
scenario. Here, we continue this approach by investigating its effects on the
predicted perturbation spectrum. We find that the size of the effect depends
sensitively on the scale separation between cutoff and horizon during
inflation.


title: Magnetorotational Instability in a Rotating Liquid Metal Annulus

abstract:
  Although the magnetorotational instability (MRI) has been widely accepted as
a powerful accretion mechanism in magnetized accretion disks, it has not been
realized in the laboratory. The possibility of studying MRI in a rotating
liquid-metal annulus (Couette flow) is explored by local and global stability
analysis and magnetohydrodynamic (MHD) simulations. Stability diagrams are
drawn in dimensionless parameters, and also in terms of the angular velocities
at the inner and outer cylinders. It is shown that MRI can be triggered in a
moderately rapidly rotating table-top apparatus, using easy-to-handle metals
such as gallium. Practical issues of this proposed experiment are discussed.


title: Surface Emission Properties of Strongly Magnetic Neutron Stars

abstract:
  We construct radiative equilibrium models for strongly magnetized (B > 10^13
G) neutron-star atmospheres taking into account magnetic free-free absorption
and scattering processes computed for two polarization modes. We include the
effects of vacuum polarization in our calculations. We present temperature
profiles and the angle-, photon energy-, and polarization-dependent emerging
intensity for a range of magnetic field strengths and effective temperatures of
the atmospheres. We find that for B < 10^14 G, the emerging spectra are bluer
than the blackbody corresponding to the effective temperature, T_eff, with
modified Planckian shapes due to the photon-energy dependence of the magnetic
opacities. However, vacuum polarization significantly modifies the spectra for
B~10^15 G, giving rise to power-law tails at high photon energies. The
angle-dependence (beaming) of the emerging intensity has two maxima: a narrow
(pencil) peak at small angles (<5 degrees) with respect to the normal and a
broad maximum (fan beam) at intermediate angles (~20-60 degrees). The relative
importance and the opening angle of the radial beam decreases strongly with
increasing magnetic field strength and decreasing photon energy. We finally
compute a T_eff-T_c relation for our models, where T_c is the local color
temperature of the spectrum emerging from the neutron star surface, and find
that T_c/T_eff ranges between 1.1-1.8. We discuss the implications of our
results for various thermally emitting neutron star models.


title:
High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning
  Data VI. Sloan Digital Sky Survey Spectrograph Observations

abstract:
  We present results on over 100 high-redshift quasars found in the Sloan
Digital Sky Survey (SDSS), using automated selection algorithms applied to SDSS
imaging data and with spectroscopic confirmation obtained during routine
spectroscopic operations of the Sloan 2.5-m telescope. The SDSS spectra cover
the wavelength range 3900--9200 Angstroms at a spectral resolution of 1800, and
have been obtained for 116 quasars with redshifts greater than 3.94; 92 of
these objects were previously uncataloged, significantly increasing the current
tally of published z>4 quasars. The paper also reports observations of five
additional new z>4.6 quasars; all were found from the SDSS imaging survey and
spectroscopically confirmed with data from the Apache Point Observatory's 3.5-m
telescope. The i' magnitudes of the quasars range from 18.03 to 20.56. Of the
97 new objects in this paper, 13 are Broad Absorption Line quasars. Five
quasars, including one object at a redshift of 5.11, have 20 cm peak flux
densities greater than 1 mJy. Two of the quasars, both at z=4.5, have very weak
emission lines; one of these objects is a radio source. Nineteen of the
newly-discovered objects have redshifts above 4.6, and the maximum redshift is
z=5.41; among objects reported to date, the latter is the third highest
redshift AGN, and penultimate in redshift among luminous quasars.


title: High Energy Spectral Components in Gamma-Ray Burst Afterglows

abstract:
  We investigate two high energy radiation mechanisms, the proton synchrotron
and the electron inverse Compton emission, and explore their possible
signatures in the broad-band spectra and in the keV to GeV light curves of
gamma-ray burst afterglows. We develop a simple analytical approach, allowing
also for the effects of photon-photon pair production, and explore the
conditions under which one or the other of these components dominates. We
identify three parameter space regions where different spectral components
dominate: (I) a region where the proton synchrotron and other hadron-related
emission components dominate, which is small; (II) a region where the electron
inverse Compton component dominates, which is substantial; (III) a third
substantial region where electron synchrotron dominates. We discuss the
prospects and astrophysical implications of directly detecting the inverse
Compton and the proton high energy components in various bands, in particular
in the GeV band with future missions such as GLAST, and in the X-ray band with
Chandra. We find that regime II parameter space is the most favorable regime
for high energy emission. The inverse Compton component is detectable by GLAST
within hours for bursts at typical cosmological distances, and by Chandra in
days if the ambient density is high.


title: Stability of Accretion Disks in Presence of Nucleosynthesis

abstract:
  We study the effect of nuclear reaction on a thin, axisymmetric,
differentially rotating, inviscid, steady accretion flow around a black hole
from an analytical point of view. We find that for most of the reasonable disk
parameters, when $p-p$-reaction, dissociation of deuterium and helium are taken
into account, the transonic region of the disk continues to have the inner
sonic point and if the temperature of the flow at the injection sonic point
could be raised (by say, some heating processes) the flow would to pass through
this inner sonic point. Otherwise, the flow may be unstable. We use the sonic
point analysis to study the solution. In the rest of the disk parameters the
inner sonic point is absent altogether and the flow will definitely be
unstable.


title:
Effect of Dust Extinction on Estimating Star Formation Rate of Galaxies:
  Lyman Continuum Extinction

abstract:
  We re-examine the effect of Lyman continuum ($\lambda \leq 912$ \AA)
extinction (LCE) by dust in H {\sc ii} regions in detail and discuss how it
affects the estimation of the global star formation rate (SFR) of galaxies. To
clarify the first issue, we establish two independent methods for estimating a
parameter of LCE ($f$), which is defined as the fraction of Lyman continuum
photons contributing to hydrogen ionization in an H {\sc ii} region. One of
those methods determines $f$ from the set of Lyman continuum flux, electron
density and metallicity. In the framework of this method, as the metallicity
and/or the Lyman photon flux increase, $f$ is found to decrease. The other
method determines $f$ from the ratio of infrared flux to Lyman continuum flux.
Importantly, we show that $f \la 0.5$ via both methods in many H {\sc ii}
regions of the Galaxy. Thus, it establishes that dust in such H {\sc ii}
regions absorbs significant amount of Lyman continuum photons directly. To
examine the second issue, we approximate $f$ to a function of only the
dust-to-gas mass ratio (i.e., metallicity), assuming a parameter fit for the
Galactic H {\sc ii} regions. We find that a characteristic $\hat{f}$, which is
defined as $f$ averaged over a galaxy-wide scale, is 0.3 for the nearby spiral
galaxies. This relatively small $\hat{f}$ indicates that a typical increment
factor due to LCE for estimating the global SFR ($1/\hat{f}$) is large ($\sim
3$) for the nearby spiral galaxies. Therefore, we conclude that the effect of
LCE is not negligible relative to other uncertainties of estimating the SFR of
galaxies.


title: Adaptive optics imaging of low and intermediate redshift quasars

abstract:
  We present the results of adaptive-optics imaging in the H and K bands of 12
low and intermediate redshift (z<0.6) quasars using the PUEO system mounted on
the Canada-France-Hawaii telescope. Five quasars are radio-quiet and seven are
radio-loud. The images, obtained under poor seeing conditions, and with the
QSOs (mV>15.0) themselves as reference for the correction, have typical spatial
resolution of FWHM~0.3 arcsec before deconvolution. The deconvolved H-band
image of PG1700+514 has a spatial resolution of 0.16 arcsec and reveals a
wealth of details on the companion and the host-galaxy. Four out of the twelve
quasars have close companions and obvious signs of interactions. The
two-dimensional images of three of the host-galaxies unambiguously reveal bars
and spiral arms. The morphology of the other objects are difficult to determine
from one dimensional surface brightness profile and deeper images are needed.
Analysis of mocked data shows that elliptical galaxies are always recognized as
such, whereas disk hosts can be missed for small disk scale lengths and large
QSO contributions.


title: The angular power spectrum of radio emission at 2.3 GHz

abstract:
  We have analysed the Rhodes/HartRAO survey at 2326 MHz and derived the global
angular power spectrum of Galactic continuum emission. In order to measure the
angular power spectrum of the diffuse component, point sources were removed
from the map by median filtering. A least-square fit to the angular power
spectrum of the entire survey with a power law spectrum C_l proportional to
l^{-alpha}, gives alpha = 2.43 +/- 0.01 for l = 2-100. The angular power
spectrum of radio emission appears to steepen at high Galactic latitudes and
for observed regions with |b| > 20 deg, the fitted spectral index is alpha =
2.92 +/- 0.07. We have extrapolated this result to 30 GHz (the lowest frequency
channel of Planck) and estimate that no significant contribution to the sky
temperature fluctuation is likely to come from synchrotron at degree-angular
scales


title:
An astrophysical oscillator strength for the SII 94.7 nm resonance line
  and S abundances in DLAs

abstract:
  By using UV spectra for the O star HD 93521 taken with the ORFEUS II echelle
spectrograph, we determine an ``astrophysical'' f value for the SII 94.7 nm
line: f = 0.00498 (+0.00172)(-0.00138), error at 1 sigma level.This is almost a
factor of 30 smaller than the guessed value found in the Kurucz database
(f=0.1472), which was up to now the only one available for this transition. We
use our ``astrophysical'' f to investigate the S abundance in two Damped
Ly-alpha absorption systems (DLAs) observed with UVES at the ESO 8.2m Kueyen
telescope. In the case of the absorber at zabs=3.02486 towards QSO 0347-3819 we
find a sulphur column density which is consistent, within errors, with that
determined by Centurion et al by means of the 125.9 nm line, thus providing an
external check on the accuracy of our f value. For the damped absorber at
zabs=4.4680 towards BR J0307-4945 we determine a high value of the S abundance,
which, however, is probably the result of blending with Ly-alpha forest lines.


title: Gamma-Ray Bursts from Extragalactic Magnetar Flares

abstract:
  The prototype for events that we call MFs - "March Fifth" events or "Magnetar
Flares" - was observed on March 5, 1979. There is evidence that MFs are powered
by catastrophic magnetic instabilities in ultramagnetized neutron stars. These
events begin with brief (~ 0.1 - 1 s), intense, hard spikes of gamma rays
followed by long (~ 100 s) softer tails of hard X-rays, modulated on the
stellar rotation period. Prototypical MFs could have been detected by BATSE out
to ~ 13 Mpc, nearly reaching the Virgo cluster. The likely number of isotropic,
standard-candle MFs detected by the BATSE experiment is ~ 12. Bayes' Theorem
implies that there is a 99% chance for at least 1 MF in the BATSE catalog, and
a 16% chance for more than 20. These short-duration, fast-rising gamma-ray
bursts could in principle be identified by their positional coincidences with
nearby galaxies. The ensuing soft tail emission would not have been detected by
BATSE for sources more distant than M31.
  It is possible that MFs also emit an intense, hard, BEAMED component during
the intial spike phase. If this beamed component has opening angle ~ 8 degrees
and peak luminosity comparable to the power of the isotropic component, then
BATSE would detect such beamed sources out to redshift z ~ 0.1, at a full-sky
rate of ~ 100 yr^-1. We speculate that such beamed MFs could account for the
short, hard Class II gamma-ray bursts in the BATSE catalog, or some significant
subset of them. If true, then Class II GRBs positions would correlate with the
positions of galaxies and galaxy clusters within ~ 350 Mpc.


title:
BMW: a ROSAT-HRI source catalogue obtained with a wavelet transform
  detection algorithm

abstract:
  In collaboration with the Observatories of Palermo and Rome and the SAX-SDC
we are constructing a multi-site interactive archive system featuring specific
analysis tools. In this context we developed a detection algorithm based on the
Wavelet Transform (WT) and performed a systematic analysis of all ROSAT-HRI
public data (~3100 observations +1000 to come). The WT is specifically suited
to detect and characterize extended sources while properly detecting point
sources in very crowded fields. Moreover, the good angular resolution of HRI
images allows the source extension and position to be accurately determined.
This effort has produced the BMW (Brera Multiscale Wavelet) catalogue, with
more than 19,000 sources detected at the ~4.2sigma level. For each source
detection we have information on the position, X-ray flux and extension. This
allows for instance to select complete samples of extended X-ray sources such
as candidate clusters of galaxies or SNR's. Details about the detection
algorithm and the catalogue can be found in Lazzati et al. (1999), Campana et
al. (1999) and Panzera et al. (2001). Here we shall present an overview of
first results from several undergoing projects which make use of the BMW
catalogue.


title: The Late-time Expansion of the Ejecta of SN 1987A

abstract:
  The evolution of the shape and size of the ejecta of SN 1987A is analyzed
over a period of ~ 8 years based on HST images and spectra taken between 1278
and 4336 days after the supernova outburst. We combine both proprietary and
archival HST data obtained with the FOC, WFPC2 and STIS. The low resolution
near-UV prism FOC spectrum obtained at day 3043 has not been described
previously. Although the FWHM of the ejecta grew linearly over the time span
studied, the appearance of the SN envelope also changed markedly with
wavelength. At visible wavelengths (lambda ~ 5000 Angstrom) the ejecta became
progressively more elongated, reaching an ellipticity epsilon ~ 0.25 by day
4000. In the near-UV (lambda ~ 2500 AA), the ejecta remained closely circular
(epsilon <= 0.1) and ~ 50% larger in angular extent than in the visible. The
FOC prism observations show that the large extent of the SN envelope is
confined to a grouping of resonance lines spanning Mg I 2852, Mg II 2795,2802
and several Fe II multiplets -- thereby confirming that the larger size of the
debris in the near-UV is due to scattering in these optically thick transitions
compared to the optically thin forbidden and semi-forbidden transitions that
dominate the visible spectrum. The available data are not of sufficient quality
to detect the slight deviation from linear expansion expected for the outermost
regions of the near-UV images as predicted by Chugai et al. (1997).


title: The Host Galaxies of Radio-Loud and Radio-Quiet Quasars

abstract:
  I review our knowledge of the properties of the host galaxies of radio-loud
and radio-quiet quasars, both in comparison to each other and in the context of
the general galaxy population. It is now clear that the hosts of radio-loud and
radio-quiet quasars with M_V < -23.5 are virtually all massive elliptical
galaxies. The masses of these spheroids are as expected given the relationship
between black-hole and spheroid mass found for nearby quiescent galaxies, as is
the growing prevalence of disc components in the hosts of progressively fainter
AGN. There is also now compelling evidence that quasar hosts are practically
indistinguishable from normal ellipticals, both in their basic structural
parameters and in the old age of their dominant stellar populations; at low z
the nuclear activity is not associated with the formation of a significant
fraction of the host galaxy. While the long-held view that quasar radio power
might be a simple function of host morphology is now dead and buried, I argue
that host-galaxy studies may yet play a crucial role in resolving the
long-standing problem of the origin of radio loudness. Specifically there is
growing evidence that radio-loud objects are powered by more massive black
holes accreting at lower efficiency than their radio-quiet couterparts of
comparable optical output. A black-hole mass > 10^9 solar masses appears to be
a necessary (although perhaps not sufficient) condition for the production of
radio jets of sufficient power to produce an FRII radio source within a massive
galaxy halo.


title:
Extinction of gamma-ray burst afterglows as a diagnostic of the location
  of cosmic star formation

abstract:
  The properties of gamma-ray bursts (GRBs) and their afterglows are used to
investigate the location of star formation activity through the history of the
Universe. This approach is motivated by the following: (i) GRBs are thought to
be associated with the deaths of massive stars and so the GRB rate ought to
follow the massive star formation rate, (ii) GRBs are the final evolutionary
phase of these short-lived stars, which do not travel far from their
birthplace, and so should be located where the stars formed, and (iii) The
differential effects of dust extinction on GRB afterglows between the X-ray and
optical wavebands can reveal whether or not large amounts of gas and dust are
present in GRB host galaxies. From recent evidence, we estimate that a
significant fraction (about 75%) of stars in the Universe formed in galaxies
that are brightest at rest-frame far-infrared (IR) wavelengths. This value is
marginally consistent with observations: 60 +/- 15% of GRBs have no detected
optical afterglow, whereas almost all have an X-ray afterglow. If the X-ray
afterglows of a large number of GRBs disappear at soft X-ray wavelengths (<2
keV), then this would provide strong evidence for dominant heavily obscured
star-formation activity. Far-IR and submillimetre studies of GRB hosts would
also test this idea: about 20% of hosts should be detectable using SCUBA.


title: Variability in the extreme helium star LSS 5121

abstract:
  We report a photometric and spectroscopic study of the hot extreme helium
star LSS 5121. We found photometric variability, but no period was evident in
its periodogram. This is consistent with the previous proposal, based on
spectral line variations, that LSS 5121 is a non-radial pulsator similar to
other hot extreme helium stars.


title:
Nucleosynthesis of Zinc and Iron-Peak Elements in Pop III Type II
  Supernovae : Comparison with abundances of Very Metal-Poor Halo Stars

abstract:
  We calculate nucleosynthesis in core-collapse explosions of massive Pop III
stars, and compare the results with abundances of metal-poor halo stars to
constrain the parameters of Pop III supernovae. We focus on iron-peak elements
and, in particular, we try to reproduce the large [Zn/Fe] observed in extremely
metal-poor stars. The interesting trends of the observed ratios [Zn, Co, Mn,
Cr, V/Fe] can be related to the variation of the relative mass of the complete
and incomplete Si-burning regions in supernova ejecta. We find that [Zn/Fe] is
larger for deeper mass-cuts, smaller neutron excess, and larger explosion
energies. The large [Zn/Fe] and [O/Fe] observed in the very metal-poor halo
stars suggest deep mixing of complete Si-burning material and a significant
amount of fall-back in Type II supernovae. Furthermore, large explosion
energies (E_51 >~ 2 for M ~ 13 Msun and E_51 >~ 20 for M >~ 20 Msun) are
required to reproduce [Zn/Fe] ~ 0.5. The observed trends of the abundance
ratios among the iron-peak elements are better explained with this high energy
(``Hypernova'') models rather than the simple ``deep'' mass-cut effect, because
the overabundance of Ni can be avoided in the hypernova models. We also present
the yields of pair-instability supernova explosions of M = 130 - 300 Msun
stars, and discuss that the abundance features of very metal-poor stars cannot
be explained by pair-instability supernovae.


title: The milliJansky 12 micron Population: First Followup

abstract:
  We present the first results of our followup programme of optical imaging and
spectroscopy of a deep 12 micron survey conducted with the ISO satellite
(Clements et al. 1999). We find that the objects are typically of fairly low
redshift (z ~ 0.1-0.2), but with a tail that extends to high redshifts. The
highest redshift object is a previously unknown quasar at z=1.2. The sample of
objects for which spectroscopy has been obtained forms a complete subsample of
the original survey with an R band magnitude limit of 19.6. We are thus able to
use accessible volume methods to determine the luminosity function. We find
that the luminosity function is close to the low redshift 12 micron luminosity
function determined by IRAS (Fang et al., 1998; Rush et al., 1993), but with a
possible excess at the highest luminosities, which also correspond to the
highest redshifts. This excess is compatible with the rapid luminosity
evolution of L ~ (1+z)^{4.5} claimed by Xu (2000) and suggested by Elbaz (1999)
on the basis of number counts. These conclusions remain tentative because of
small number statistics at the highest redshifts. Almost all of the galaxies in
this survey are emission line objects. We use the spectra to determine emission
line diagnostics for the underlying ionisation source. We find that the
majority of objects have HII region-like spectra (roughly 2/3) but there is a
significant fraction (about 1/3) that contain an AGN. This confirms suspicions
that deep mid-IR surveys will be a powerful way to find obscured AGN. Part of
the survey area has been imaged deeply by the INT Wide Field Camera. Nearly all
12 micron sources in this area have good optical identifications. The prospects
are thus good for obtaining complete spectroscopy.


title: UBVRI photometric comparison sequences for symbiotic stars. II

abstract:
  We present accurate and deep UBVRI photometric sequences for an additional 20
symbiotic stars. As for the 20 targets of Paper I, the sequences extend over
wide brightness and color ranges, and are suited to cover both quiescence and
outburst phases. The sequences are intended to assist both present time
photometry as well as measurement of photographic plates from historical
archives.


title: Cosmological Perturbations with Multiple Fluids and Fields

abstract:
  We consider the evolution of perturbed cosmological spacetime with multiple
fluids and fields in Einstein gravity. Equations are presented in gauge-ready
forms, and are presented in various forms using the curvature (\Phi or
\phi_\chi) and isocurvature (S_{(ij)} or \delta \phi_{(ij)}) perturbation
variables in the general background with K and \Lambda. We clarify the
conditions for conserved curvature and isocurvature perturbations in the
large-scale limit. Evolutions of curvature perturbations in many different
gauge conditions are analysed extensively. In the multi-field system we present
a general solution to the linear order in slow-roll parameters.


title:
UBV stellar photometry of bright stars in GC M5. I. UV colour-magnitude
  and colour-colour diagrams and some peculiarities in the HB stellar
  distribution

abstract:
  We present stellar photometry in the UBV passbands for the globular cluster
M5 = NGC5904. The observations, short-exposured photographic plates and CCD
frames, were obtained in the RC-focus of the 2m telescope of the Natl. Astron.
Obs. 'Rozhen'. All stars in an annulus with radius 1 < r < 5.5 arcmin were
measured. We show that the UV CMDs describe different evolutionary stages in a
better manner than the 'classical' (V, B-V) diagram. We use HB stars, with
known spectroscopic Teff, to check the validity of the colour zero-point. A
review of all known UV-bright star candidates in M5 is made and some of their
parameters are catalogued. Six new stars of this kind are suspected on the
basis of their position on the CMD. New assessment of the cluster reddening and
metallicity is done using the (U-B, B-V) diagram. We find [Fe/H]= -1.38, which
confirms the Zinn & West (1984) value contrasting with recent spectroscopic
estimates. In an effort to clarify the question of the gap in the BHB stellar
distribution and to investigate some other peculiarities, we use the relatively
long-base colour index U-V. A comparison of the unreddened (V, U-V)
distribution of HB stars with a canonical ZAHB model (Dorman et al. 1993)
reveals that the hottest stars rise above the model line. We find this similar
to the 'u-jump' found in the Stroemgren photometry (Grundahl et al. 1998,
1999). (U-B)o indeces of 18 BHB stars with (B-V)o in [-0.02, 0.18] were used to
estimate their ultraviolet deficiency. It is shown that low gravity log g < 2
Kurucz's atmospheric models fit well the observed distribution of these stars
along the two-colour diagram.


title: The Spin Temperature of Warm Interstellar H I

abstract:
  Collisional excitation of the 21cm HI hyperfine transition is not strong
enough to thermalize it in warm neutral (``intercloud'') interstellar gas,
which we show by simultaneously solving the equations of ionization and
collisional equilibrium under typical conditions. Coupling of the 21cm
excitation temperature and local gas motions may be established by the Ly-alpha
radiation field, but only if strong Galactic Ly-alpha radiation permeates the
gas in question. The Ly-alpha radiation tends to impart to the gas its own
characteristic temperature, which is determined by the range of gas motions
that occur on the spatial scale of the Ly-alpha scattering. In general, the
calculation of H I spin temperatures is a more difficult and interesting
problem than might have been expected, as is any interpretation of H I spin
temperature measurements.


title: Comparative Chemistry of Diffuse Clouds II: CN, HCN, HNC, CH3CN & N2H+

abstract:
  Using the Plateau de Bure interferometer, we observed the 3mm absorption
lines of CN, HCN and HNC from some of the diffuse clouds which lie toward our
well-studied sample of compact extragalactic mm-wave continuum sources. The
column densities of these species all vary by a factor of about fifty and are
prominent in only a limited subset of the clouds seen in the most ubiquitous
species such as OH, HCO+, C2H and C3H2. The CN, HCN, and HNC column densities
vary in fixed proportion to each other, with <N(HNC)/N(HCN)> = 0.21+/-0.05 and
<N(CN)/N(HCN)> = 6.8+/-1. We searched unsuccessfully for CH3CN and N2H+, which
are underabundant compared to dark clouds, by factors of at least 10 and 100,
respectively.


title:
Heating of gas inside radio sources to mildly relativistic temperatures
  via induced Compton scattering

abstract:
  Measured values of the brightness temperature of low-frequency synchrotron
radiation emitted by powerful extragalactic sources reach 10^11--10^12 K. If
some amount of nonrelativistic ionized gas is present within such sources, it
should be heated as a result of induced Compton scattering of the radiation. If
this heating is counteracted by cooling due to inverse Compton scattering of
the same radio radiation, then the plasma can be heated up to mildly
relativistic temperatures kT~10--100 keV. The stationary electron velocity
distribution can be either relativistic Maxwellian or quasi-Maxwellian (with
the high-velocity tail suppressed), depending on the efficiency of Coulomb
collisions and other relaxation processes. We derive several easy-to-use
approximate expressions for the induced Compton heating rate of mildly
relativistic electrons in an isotropic radiation field, as well as for the
stationary distribution function and temperature of electrons. We also give
analytic expressions for the kernel of the integral kinetic equation (one as a
function of the scattering angle and another for the case of an isotropic
radiation field), which describes the redistribution of photons in frequency
caused by induced Compton scattering in thermal plasma. These expressions can
be used in the parameter range hnu<< kT<~ 0.1mc^2 (the formulae earlier
published in Sazonov, Sunyaev, 2000 are less accurate).


title:
Radiative Equilibrium and Temperature Correction in Monte Carlo
  Radiation Transfer

abstract:
  We describe a general radiative equilibrium and temperature correction
procedure for use in Monte Carlo radiation transfer codes with sources of
temperature-independent opacity, such as astrophysical dust. The technique
utilizes the fact that Monte Carlo simulations track individual photon packets,
so we may easily determine where their energy is absorbed. When a packet is
absorbed, it heats a particular cell within the envelope, raising its
temperature. To enforce radiative equilibrium, the absorbed packet is
immediately re-emitted. To correct the cell temperature, the frequency of the
re-emitted packet is chosen so that it corrects the temperature of the spectrum
previously emitted by the cell. The re-emitted packet then continues being
scattered, absorbed, and re-emitted until it finally escapes from the envelope.
As the simulation runs, the envelope heats up, and the emergent spectral energy
distribution (SED) relaxes to its equilibrium value, without iteration. This
implies that the equilibrium temperature calculation requires no more
computation time than the SED calculation of an equivalent pure scattering
model with fixed temperature. In addition to avoiding iteration, our method
conserves energy exactly, because all injected photon packets eventually
escape. Furthermore, individual packets transport energy across the entire
system because they are never destroyed. This long-range communication, coupled
with the lack of iteration, implies that our method does not suffer the
convergence problems commonly associated with lambda-iteration. To verify our
temperature correction procedure, we compare our results to standard benchmark
tests, and finally we present the results of simulations for two-dimensional
axisymmetric density structures.


title:
The Ultra-luminous M81 X-9 source: 20 years variability and spectral
  states

abstract:
  The source X-9 was discovered with the {\it Einstein Observatory} in the
field of M81, and is located in the dwarf galaxy Holmberg IX. X-9 has a 0.2-4.0
keV luminosity of $\sim 5.5\times 10^{39}$ ergs~s$^{-1}$, if it is at the same
distance as Holmberg IX (3.4 Mpc). This luminosity is above the Eddington
luminosity of a 1~$M_{\odot}$ compact accreting object. Past hypotheses on the
nature of this Super-Eddington source included a SNR or supershell, an
accreting compact object and a background QSO. To shed light on the nature of
this source, we have obtained and analyzed archival data, including the {\it
Einstein} data, 23 ROSAT observations, Beppo-SAX and ASCA pointings. Our
analysis reveals that most of the emission of X-9 arises from a point-like
highly-variable source, and that lower luminosity extended emission may be
associated with it. The spectrum of this source changes between low and high
intensity states, in a way reminiscent of the spectra of galactic Black Hole
candidates. Our result strongly suggest that X-9 is not a background QSO, but a
bonafide `Super-Eddington' source in Ho IX, a dwarf companion of M81.


title: A New Method to Measure and Map the Gas Scale-Height of Disk Galaxies

abstract:
  We propose a new method to measure and map the gas scale height of nearby
disk galaxies. This method is applied successfully to the Australia Telescope
Compact Array interferometric HI survey of the Large Magellanic Cloud (LMC); it
could also be applied to a significant number of nearby disk galaxies, thanks
to the next generation of interferometric facilities, such as the extended VLA
and CARMA.
  The method consists of computing the Spectral Correlation Function (SCF) for
a spectral-line map of a face-on galaxy. The SCF quantifies the correlation
between spectra at different map positions as a function of their separation,
and is sensitive to the properties of both the gas mass distribution and the
gas velocity field. It is likely that spatial correlation properties of the gas
density and velocity fields in a galactic disk are sensitive to the value of
the scale height of the gas disk. A scale-free turbulent cascade is unlikely to
extend to scales much larger than the disk scale height, as the disk dynamics
on those larger scales should be dominated by two dimensional motions.
  We find a clear feature in the SCF of the LMC HI disk, on the scale of
approximately 180 pc, which we identify as the disk scale height. We are also
tentatively able to map variations of the scale height over the disk.


title: A 250 GHz Survey of High Redshift QSOs from the Sloan Digital Sky Survey

abstract:
  We present observations at 250 GHz (1.2 mm), 43 GHz, and 1.4 GHz of a sample
of 41 QSOs at z > 3.7 found in the Sloan Digital Sky Survey. We detect 16
sources with a 250 GHz flux density greater than 1.4 mJy. The combination of
centimeter and millimeter wavelength observations indicates that the 250 GHz
emission is most likely thermal dust emission. Assuming a dust temperature of
50 K, the implied dust masses for the 16 detected sources are in the range
1.5e8 to 5.9e8 Msun, and the dust emitting regions are likely to be larger than
1 kpc in extent. The radio-through-optical spectral energy distributions for
these sources are within the broad range defined by lower redshift, lower
optical luminosity QSOs. We consider possible dust heating mechanisms,
including UV emission from the active nucleus (AGN) and a starburst concurrent
with the AGN, with implied star formation rates between 500 and 2000 Msun/year.


title:
Towards a resolution of the discrepancy between different estimators of
  star formation rate

abstract:
  Different wavelength regimes and methods for estimating the space density of
the star-formation rate (SFR) result in discrepant values. While it is
recognised that ultra-violet (UV) and H-alpha emission line data must be
corrected for the effects of extinction, the magnitude of the required
correction is uncertain. Even when these corrections are made there remains a
significant discrepancy between SFRs derived from UV and H-alpha measurements
compared with those derived from far-infrared (FIR) and radio luminosities.
Since the FIR/radio derived SFRs are not affected by extinction, and simple
corrections to reconcile the UV and H-alpha measurement with these do not fully
account for the discrepancies, a more sophisticated correction may be required.
Recent results suggest that at least part of the solution may be a form of
extinction which increases with increasing SFR (or luminosity, given the common
assumption that SFR is proportional to luminosity). We present an analysis of
the effects of a dust reddening dependent on star formation rate applied to
estimators of SFR. We show (1) that the discrepancies between H-alpha and
FIR/radio SFR estimates may be explained by such an effect, and we present an
iterative method for applying the correction; and (2) UV-based estimates of SFR
are harder to reconcile with FIR/radio estimates using this method, although
the extent of the remaining discrepancy is less than for a non-SFR-dependent
correction. Particularly at high redshift, our understanding of extinction at
UV wavelengths may require a still more complex explanation.


title: Construction of the Variability -> Luminosity Estimator

abstract:
  We present a possible Cepheid-like luminosity estimator for the long-duration
gamma-ray bursts based on the variability of their light curves.


title:
Construction and Preliminary Application of the Variability ->
  Luminosity Estimator

abstract:
  We present a possible Cepheid-like luminosity estimator for the long-duration
gamma-ray bursts based on the variability of their light curves. We also
present a preliminary application of this luminosity estimator to 907
long-duration bursts from the BATSE catalog.


title: Cosmological Evolution of Supergiant Star-Forming Clouds

abstract:
  In an exploration of the birthplaces of globular clusters, we present a
careful examination of the formation of self-gravitating gas clouds within
assembling dark matter haloes in a hierarchical cosmological model. Our
high-resolution smoothed particle hydrodynamical simulations are designed to
determine whether or not hypothesized supergiant molecular clouds (SGMCs) form
and, if they do, to determine their physical properties and mass spectra. It
was suggested in earlier work that clouds with a median mass of several 10^8
M_sun are expected to assemble during the formation of a galaxy, and that
globular clusters form within these SGMCs. Our simulations show that clouds
with the predicted properties are indeed produced as smaller clouds collide and
agglomerate within the merging dark matter haloes of our cosmological model. We
find that the mass spectrum of these clouds obeys the same power-law form
observed for globular clusters, molecular clouds, and their internal clumps in
galaxies, and predicted for the supergiant clouds in which globular clusters
may form. We follow the evolution and physical properties of gas clouds within
small dark matter haloes up to z = 1, after which prolific star formation is
expected to occur. Finally, we discuss how our results may lead to more
physically motivated "rules" for star formation in cosmological simulations of
galaxy formation.


title:
Atmospheric Abundances in Post-AGB candidates of Intermediate
  Temperature

abstract:
  Detailed atmospheric abundances have been calculated for a sample of A-G
supergiant stars with IR fluxes and/or high galactic latitudes. HD 172481 and
HD 158616 show clear indications of being post-AGB stars that have experienced
third dredge-up. HD 158616 is carbon-rich while the abundance pattern of HD
172481 and its large Li enhancement gives support to the hot bottom burning
scenario that explains paucity of carbon-rich stars among AGB stars. HD 172324
is very likely a hot post-AGB star that shows a strong carbon deficiency. HD
725, HD 218753 and HD 331319 also appear to be evolved objects between the red
giant and the AGB. HD 9167, HD 173638 with a few exceptions, reflect solar
abundances and no signs of post red giant evolution. They are most likely young
massive disk supergiants. Further analysis of proto-Planetary Nebula HDE 341617
reveals that He lines show signs of velocity stratification. The emission lines
have weakened considerably since 1993. The envelope expands at 19 km s$^{-1}$
relative to the star. Atmospheric abundances, evolutionary tracks and
isochrones are used to estimate masses and ages of all stars in the sample.


title: Energetics of Gamma Ray Bursts

abstract:
  We determine the distribution of total energy emitted by gamma-ray bursts for
bursts with fluences and distance information. Our core sample consists of
eight bursts with BATSE spectra and spectroscopic redshifts. We extend this
sample by adding four bursts with BATSE spectra and host galaxy R magnitudes.
  From these R magnitudes we calculate a redshift probability distribution;
this method requires a model of the host galaxy population. From a sample of
ten bursts with both spectroscopic redshifts and host galaxy R magnitudes (some
do not have BATSE spectra) we find that the burst rate is proportional to the
galaxy luminosity at the epoch of the burst. Assuming that the total energy
emitted has a log-normal distribution, we find that the average emitted energy
(assumed to be radiated isotropically) is $<E_{\gamma iso} > =
1.3^{+1.2}_{-1.0} \times 10^{53}$ ergs (for H$_0$ = 65 km s$^{-1}$ Mpc$^{-1}$,
$\Omega_m=0.3$ and $\Omega_\Lambda=0.7$); the distribution has a logarithmic
width of $\sigma_\gamma=1.7^{+0.7}_{-0.3}$. The corresponding distribution of
X-ray afterglow energy (for seven bursts) has $<E_{X iso} > = 4.0^{+1.6}_{-1.8}
\times 10^{51}$ergs and $\sigma_X = 1.3^{+0.4}_{-0.3}$. For completeness, we
also provide spectral fits for all bursts with BATSE spectra for which there
were afterglow searches.


title: A representative sample of Be stars III: H band spectroscopy

abstract:
  We present H band (1.53 - 1.69 micron) spectra of 57 isolated Be stars of
spectral types O9-B9 and luminosity classes III,IV & V. The HI Brackett (n-4)
series is seen in emission from Br 11-18, and FeII emission is also apparent
for a subset of those stars with HI emission. No emission from species with a
higher excitation temperature, such as He II or CIII is seen, and no forbidden
line emission is present. A subset of 12 stars show no evidence for emission
from any species; these stars appear indistinguishable from normal B stars of a
comparable spectral type. In general the line ratios constructed from the
transitions in the range Br 11-18 do not fit case B recombination theory
particularly well. Strong correlations between the line ratios with Br-gamma
and spectral type are found. These results most likely represent systematic
variations in the temperature and ionization of the circumstellar disc with
spectral type. Weak correlations between the line widths and projected
rotational velocity of the stars are observed; however no systematic trend for
increasing line width through the Brackett series is observed.