title: Rapid Formation of Molecular Clouds and Stars in the Solar Neighborhood

abstract:
  Observations of both star-forming regions and young, gas-free stellar
associations indicate that most nearby molecular clouds form stars only over a
short time span before dispersal; large-scale flows in the diffuse interstellar
medium have the potential for forming clouds sufficiently rapidly, and for
producing stellar populations with ages much less than the lateral crossing
times of their host molecular clouds. We identify four important factors for
understanding rapid star formation and short cloud lifetimes. First, much of
the accumulation and dispersal of clouds near the solar circle might occur in
the atomic phase; only the high-density portion of a cloud's lifecycle is spent
in the molecular phase, thus helping to limit molecular cloud ``lifetimes''.
Second, once a cloud achieves a high enough column density to form $\h2$ and
CO, gravitational forces become larger than typical interstellar pressure
forces; thus star formation can follow rapidly upon molecular gas formation and
turbulent dissipation in limited areas of each cloud complex. Third, typical
magnetic fields are not strong enough to prevent rapid cloud formation and
gravitational collapse. Fourth, rapid dispersal of gas by newly-formed stars,
and reduction of shielding by a small expansion of the cloud after the first
events of star formation, might limit the length of the star formation epoch
and the lifetime of a cloud in its molecular state. This picture emphasizes the
importance of large-scale boundary conditions for understanding molecular cloud
formation, and implies that star formation is a highly dynamic, rather than
quasi-static, process.


title: Variable Stars in Galactic Globular Clusters

abstract:
  Based on a search of the literature up to May 2001, the number of known
variable stars in Galactic globular clusters is approximately 3000. Of these,
more than 2200 have known periods and the majority (approximately 1800) are of
the RR Lyrae type. In addition to the RR Lyrae population, there are
approximately 100 eclipsing binaries, 120 SX Phe variables, 60 Cepheids
(including population II Cepheids, anomalous Cepheids and RV Tauri) and 120
SR/red variables. The mean period of the fundamental mode RR Lyrae variables is
0.585, for the overtone variables it is 0.342 (0.349 for the first-overtone
pulsators and 0.296 for the second-overtone pulsators) and approximately 30%
are overtone pulsators. These numbers indicate that about 65% of RR Lyrae
variables in Galactic globular clusters belong to Oosterhoff type I systems.
The mean period of the RR Lyrae variables in the Oosterhoff type I clusters
seems to be correlated with metal abundance in the sense that the periods are
longer in the more metal poor clusters. Such a correlation does not exist for
the Oosterhoff type II clusters. Most of the Cepheids are in clusters with blue
horizontal branches.


title: Weighing nearby stars with GAIA ?

abstract:
  Microlensing consists in two major effects: (1) variation in the apparent
position of the background sources (astrometric component) and (2) flux
variations of the background sources (photometric component). While the latter
has been extensively used in the search for dark objects in the Galactic disk
and halo (projects like MACHO (Alcock et al, 1997), EROS (Derue et al, 1999),
OGLE (Paczynski et al, 1994)), the first effect has not yet been part of a
systematic observational program, simply because the observations of very
slight displacements in the positions of background sources requires an
astrometric accuracy which current telecopes do not yet provide. We investigate
here whether the astrometric accuracy of GAIA could enable such measurements
and, as a consequence, enable new, direct and original measurements of the mass
of nearby stars.


title:
Uncertainties in Dielectronic Recombination Rate Coefficients: Effects
  on Solar and Stellar Upper Atmosphere Abundance Determinations

abstract:
  We have investigated how the relative elemental abundances inferred from the
solar upper atmosphere are affected by uncertainties in the dielectronic
recombination (DR) rate coefficients used to analyze the spectra. We find that
the inferred relative abundances can be up to a factor of ~5 smaller or ~1.6
times larger than those inferred using the currently recommended DR rate
coefficients. We have also found a plausible set of variations to the DR rate
coefficients which improve the inferred (and expected) isothermal nature of
solar coronal observations at heights of >~ 50 arcsec off the solar limb. Our
results can be used to help prioritize the enormous amount of DR data needed
for modeling solar and stellar upper atmospheres. Based on the work here, our
list of needed rate coefficients for DR onto specific isoelectronic sequences
reads, in decreasing order of importance, as follows: O-like, C-like, Be-like,
N-like, B-like, F-like, Li-like, He-like, and Ne-like. It is our hope that this
work will help to motivate and prioritize future experimental and theoretical
studies of DR.


title: The Shape of Spectral Breaks in GRB Afterglows

abstract:
  Gamma-Ray Burst (GRB) afterglows are well described by synchrotron emission
from relativistic blast waves expanding into an external medium. The blast wave
is believed to amplify the magnetic field and accelerate the electrons into a
power law distribution of energies promptly behind the shock. These electrons
then cool both adiabatically and by emitting synchrotron and inverse Compton
radiation. The resulting spectra is known to consist several power law
segments, which smoothly join at certain break frequencies. Here, we give a
complete description of all possible spectra under those assumptions, and find
that there are 5 possible regimes, depending on the ordering of the break
frequencies. The flux density is calculated by integrating over the
contributions from all the shocked region, using the Blandford McKee solution.
This allows us to calculate more accurate expressions for the value of these
break frequencies, and describe the shape of the spectral breaks around them.
This also provides the shape of breaks in the light curves caused by the
passage of a break frequency through the observed band. These new, more exact,
estimates are different from more simple calculations by up to a factor of
about 70, and describe some new regimes which where previously ignored.


title: A Practical Theorem on Gravitational Wave Backgrounds

abstract:
  There is an extremely simple relationship between the spectrum of the
gravitational wave background produced by a cosmological distribution of
discrete gravitational wave sources, the total time-integrated energy spectrum
of an individual source, and the present-day comoving number density of
remnants. Stated in this way, the background is entirely independent of the
cosmology, and only weakly dependent on the evolutionary history of the
sources. This relationship allows one easily to compute the amplitude and
spectrum of cosmic gravitational wave backgrounds from a broad range of
astrophysical sources, and to evaluate the uncertainties therein.


title: Nested and Single Bars in Seyfert and Non-Seyfert Galaxies

abstract:
  We analyze the observed properties of nested and single stellar bar systems
in disk galaxies. The 112 galaxies in our sample comprise the largest matched
Seyfert vs. non-Seyfert sample of nearby galaxies with complete near-infrared
or optical imaging sensitive to lengthscales ranging from tens of pc to tens of
kpc. We find that a significant fraction of the sample galaxies, 17% +/- 4%,
has more than one bar, and that 28% +/- 5% of barred galaxies have nested bars.
The bar fractions appear to be stable according to reasonable changes in our
adopted bar criteria. For these nested bars, we detect a clear division in
length between the large-scale (primary) bars and small-scale (secondary) bars,
both in absolute and normalized (to the size of the galaxy) length. We argue
that this bimodal distribution can be understood within the framework of the
inner Lindblad resonances (ILRs), which are located where the gravitational
potential of the innermost galaxy switches effectively from 3D to 2D. While
primary bars are found to correlate with the host galaxy sizes, no such
correlation is observed for the secondary bars. Moreover, we find that
secondary bars differ morphologically from single bars. Overall, our matched
Seyfert and non-Seyfert samples show a statistically significant excess of bars
among the Seyfert galaxies at practically all lengthscales. We confirm our
previous result that Seyfert galaxies always show a preponderance of "thick"
bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is
observed between the presence of a bar and that of companion galaxies, even
relatively bright ones.


title:
The QMAP and MAT/TOCO Experiments for Measuring Anisotropy in the Cosmic
  Microwave Background

abstract:
  We describe two related experiments that measured the anisotropy in the
cosmic microwave background (CMB). QMAP was a balloon-borne telescope that flew
twice in 1996, collecting data on degree angular scales with an array of six
high electron mobility transistor-based amplifiers (HEMTs). QMAP was the first
experiment to use an interlocking scan strategy to directly produce high
signal-to-noise CMB maps. The QMAP gondola was then refit for ground based work
as the MAT/TOCO experiment. Observations were made from 5200 m on Cerro Toco in
Northern Chile in 1997 and 1998 using time-domain beam synthesis. MAT/TOCO was
the first experiment to see both the rise and fall of the CMB angular spectrum,
thereby localizing the position of the first peak to l_{peak}=216 +/- 14. In
addition to describing the instruments, we discuss the data selection methods,
checks for systematic errors, and we compare the MAT/TOCO results to those from
recent experiments. We also correct the data to account for an updated
calibration and a small contribution from foreground emission. We find the
amplitude of the first peak for l between 160 and 240 to be T_{peak}=80.9 +/-
3.4 +/- 5.1 uK, where the first error is statistical and the second is from
calibration.


title: Study of the TeV gamma-ray spectrum of SN 1006 around the NE Rim

abstract:
  The differential spectrum of TeV gamma rays between 1.5 TeV and 20 TeV from
the north-east rim of SN1006 was obtained from the data observed in 1996 and
1997 using the 3.8m CANGAROO \v{C}erenkov telescope. This spectrum matches the
model calculated using the Inverse Compton (IC) process with 2.7k Cosmic
Microwave Background (CMB). This enables us to estimate the absolute strength
of the magnetic field around the shock and the maximum energy of accelerated
electrons with the considerable accuracy: the obtained field strength and
maximum electron energy are $4\pm1$ $\mu$G and 50 TeV respectively.
  Also we have detected again the TeV gamma-ray emission from the same position
using the 10m CANGAROO-II telescope in 2000, and the preliminary spectrum
around 1 TeV region is presented in this conference. The two spectra agree well
in the overlapped energy region.


title: The Future of Fe-K Line Diagnostics for Probing Strong Gravity

abstract:
  We review what we have learnt with ASCA from studying the Fe-K lines in AGN
and describe a program to deconvolve the narrow, non-disk components of the
lines with Chandra. This is necessary to derive the correct profiles of the
broad, relativistic lines obtained using data from XMM and other
high-throughput instruments. Since reverberation techniques are now not looking
promising, we present Constellation-X simulations showing an alternative way we
might be able to measure black-hole mass and spin.


title: The Energy Distribution of Long Duration GRBS

abstract:
  The energy release in gamma-ray bursts is one of the most interesting clues
on the nature of their "inner engines". We show here that the total energy
release in GRBs varies by less than one order of magnitude from one burst to
another while the energy emitted in $\gamma$-ray photons varies by more than an
order of magnitude. This result indicates that the central engine of long
duration GRB has a remarkably constant energy output which provides very
important constraint on the nature of these enigmatic explosions. The broader
distribution of the observed $\gamma$-ray flux, about three orders of magnitude
in width, can be attributed, in part, to a variation in the opening angle of
the collimated explosion, and in part to the variation of Lorentz factor across
the jet as well as a variable efficiency for converting the kinetic energy of
explosion to $\gamma$-rays.


title: Do globular clusters time the Universe?

abstract:
  Estimating the age of the Universe is an old problem. Rapid progress in
observational cosmology in recent years has led to more accurate values of the
fundamental parameters. The current most popular model is a flat Universe, with
about 30% of the critical density in the form of matter (baryonic and
non-baryonic) and 70% in the form of `dark energy'. These two densities,
together with the Hubble constant (estimated to be about 70 km/s/Mpc),
constrain the age of the Universe to be approximately 13 Gyr. This expansion
age is uncomfortably close to the age of the oldest globular clusters
(approximately 12.5 Gyr), in particular if they formed relatively recently. We
review here proposed models of globular cluster formation and point out
possible conflicts with cosmology.


title: MHD Instability in cylindric Taylor-Couette flow

abstract:
  The linear marginal instability of an axisymmetric MHD Taylor-Couette flow of
infinite vertical extension is considered. For flows with a resting outer
cylinder there is a well-known characteristic Reynolds number even without
magnetic field but for sufficiently weak magnetic fields there are solutions
with smaller Reynolds numbers so that a characteristic minimum exists. The
minimum only exists, however, for not too small magnetic Prandtl numbers. For
small magnetic Prandtl numbers one only finds the typical magnetic suppression
of the instability.
  We are here particularly interested in the case where the outer cylinder
rotates so fast that the Rayleigh criterion for hydrodynamic stability is
fulfilled. We find that for given magnetic Prandtl number now always a magnetic
field amplitude exists where the characteristic Reynolds number is minimal.
These critical values are computed for different magnetic Prandtl numbers. In
all cases the Reynolds numbers are running with 1/Pm so that for the small
magnetic Prandtl numbers of sodium (10^-5) or gallium (10^-6) the critical
Reynolds numbers exceed values of 10^6 or 10^, resp.


title: NGC 4151: an intrinsically average Seyfert 1

abstract:
  We present a detailed analysis of a long, 100 ksec, observation of NGC 4151
by ASCA, contemporaneous with an observation by the CGRO/OSSE. We fit the data
with physical models including an Fe K line and Compton reflection both
relativistically broadened and coupled according to theoretical results. The
model also includes a narrow Fe K component, which is emitted by both an
extended plasma region and the X-ray absorber. Our study of the absorber shows
strong evidence for the presence of more than one partial-covering cloud in the
line of sight. Taking these points into account, our best intrinsic model
includes a Comptonization continuum with an X-ray slope of Gamma=1.9 from a
thermal plasma with an electron kT=70 keV or so and a disk line with an
equivalent width of about 70 eV. The broadening of the line and reflection
indicate their origin from innermost parts of an accretion disk. Our results
indicate that NGC 4151 has an intrinsic X-ray spectrum and variability
properties similar to those of average Seyfert 1s.


title: A natural explanation for periodic X-ray outbursts in Be/X-ray binaries

abstract:
  When applied to Be/X-ray binaries, the viscous decretion disc model for Be
stars naturally predicts the truncation of the circumstellar disc. The distance
at which the circumstellar disc is truncated depends mainly on the orbital
parameters and the viscosity. In systems with low eccentricity, the disc is
expected to be truncated at the 3:1 resonance radius, for which the gap between
the disc outer radius and the critical lobe radius of the Be star is so wide
that, under normal conditions, the neutron star cannot accrete enough gas at
periastron passage to show Type I X-ray outbursts. These systems will display
only Type II X-ray outbursts. On the other hand, in systems with high orbital
eccentricity, the disc truncation occurs at a much higher resonance radius,
which is very close to or slightly beyond the critical lobe radius at
periastron unless the viscosity is very low. In these systems, disc truncation
cannot be efficient, allowing the neutron star to capture gas from the disc at
every periastron passage and display Type I outbursts regularly. In contrast to
the rather robust results for systems with low eccentricity and high
eccentricity, the result for systems with moderate eccentricity depends on
rather subtle details. Systems in which the disc is truncated in the vicinity
of the critical lobe will regularly display Type I outbursts, whereas those
with the disc significantly smaller than the critical lobe will show only Type
II outbursts under normal conditions and temporary Type I outbursts when the
disc is strongly disturbed.


title:
Chaos, ergodicity, and the thermodynamics of lower-dimensional
  Hamiltonian systems

abstract:
  This paper uses the assumptions of ergodicity and a microcanonical
distribution to compute estimates of the largest Lyapunov exponents in
lower-dimensional Hamiltonian systems. That the resulting estimates are in
reasonable agreement with the actual values computed numerically corroborates
the intuition that chaos in such systems can be understood as arising
generically from a parametric instability and that this instability can be
modeled by a stochastic-oscillator equation (cf. Casetti, Clementi, and
Pettini, Phys. Rev. E 54, 5969 (1996)), linearised perturbations of a chaotic
orbit satisfying a harmonic-oscillator equation with a randomly varying
frequency.


title: Near-infrared Spectroscopy and HST Imaging of a Dusty Starburst ERO

abstract:
  We present near-IR spectroscopy and HST imaging of EROJ164023, an Extremely
Red Object (ERO) with R-K=5.9 at z=1.05. EROJ164023 is a disk galaxy, with an
optical/IR spectral energy distribution which is strongly reddened by dust
(L_FIR/L_B<~200; A_V~5). The narrow emission lines (~300km/s) and the high
[NII]/Halpha line ratio indicate that this is a ``composite'' starburst-Seyfert
galaxy. Assuming that star formation dominates, we constrain the SFR to be
10-700Mo/yr from a variety of indicators. We compare EROJ164023 with the only
other spectroscopically identified dusty EROs: HR10 (z=1.44) and ISOJ1324-2016
(z=1.50). EROJ164023 and HR10 have similar disk-like morphologies, and both
exhibit a variation in the apparent dust obscuration depending upon the
diagnostic used, suggesting that there is a complex spatial mix of stellar
populations and dust in these galaxies. In contrast, the compact morphology and
spectral properties of ISOJ1324-2016 indicate that it is a dusty quasar. Our
results demonstrate that dusty galaxies identified using photometric ERO
criteria include pure starbursts, composite systems such as EROJ164023 and
dusty quasars. We suggest that the classification of EROs into these
sub-classes cannot be reliably achieved from optical/near-IR photometry and
instead requires mid/far-IR or sub-mm photometry and near-IR spectroscopy. The
advent of efficient multi-object spectrographs working in the near-IR as well
as the imminent launch of SIRTF therefore promise the opportunity of rapid
progress in our understanding of the elusive ERO population. [Abridged]


title:
Flash Mixing on the White Dwarf Cooling Curve: Understanding Hot
  Horizontal Branch Anomalies in NGC 2808

abstract:
  We present a UV CMD spanning the hot horizontal branch (HB), blue straggler,
and white dwarf populations of the globular cluster NGC 2808. These data were
obtained with the Space Telescope Imaging Spectrograph (STIS). Although
previous optical CMDs of NGC 2808 show a high temperature gap within the hot HB
population, no such gap is evident in our UV CMD. Instead, we find a population
of hot subluminous HB stars, an anomaly only previously reported for the
globular cluster omega Cen. Our modeling indicates that the location of these
subluminous stars in the UV CMD, as well as the high temperature gap along the
HB in optical CMDs, can be explained if these stars underwent a late He-core
flash while descending the white dwarf cooling curve. We show that the
convection zone produced by such a late He flash will penetrate into the H
envelope, thereby mixing H into the hot He-burning interior, where it is
rapidly consumed. This phenomenon is analogous to the "born again" scenario for
producing H-deficient stars following a late He-shell flash. The flash mixing
of the envelope greatly enhances the envelope He and C abundances, and leads,
in turn, to a discontinuous increase in the HB effective temperatures at the
transition between canonical and flash-mixed stars. We argue that the hot HB
gap is associated with this theoretically predicted dichotomy in the HB
properties. Moreover, the changes in the emergent spectral energy distribution
caused by these abundance changes are primarily responsible for explaining the
hot subluminous HB stars. Although further evidence is needed to confirm that a
late He-core flash can account for the subluminous HB stars and the hot HB gap,
we demonstrate that an understanding of these stars requires the use of
appropriate theoretical models for their evolution, atmospheres, and spectra.


title: Influence of irradiation on the space-time structure of shock waves

abstract:
  The long-range energy deposition by heavy-ion beams makes new types of shock
wave experiments possible in the laboratory. We have investigated a situation
that is of relevance to supernova dynamics in astrophysics, where a shock wave
is irradiated by a flux of neutrinos depositing energy throughout the shock
wave and surrounding matter, thus changing the behaviour of the running shock.
We have carried out fluid-dynamical simulations to study generic features of
stimulated shock waves. First we consider an idealized case assuming uniform
energy deposition into a planar shock wave propagating through an ideal gas.
Then we investigate more realistic situations realizable in laboratory
experiments with heavy-ion beams. We have found that energy deposition leads to
two important effects: acceleration of the shock front and decay of the shock
strength. The possibility of laboratory experiments is briefly discussed.


title:
Stability and chaos around multipolar deformed bodies: A general
  relativistic approach

abstract:
  The exact solution to the Einstein equations that represents a static axially
symmetric source deformed by an internal quadrupole is considered. By using the
Poincare section method we numerically study the geodesic motion of test
particles. For the prolate quadrupolar deformations we found chaotic motions
contrary to the oblate case where only regular motion is found. We also study
the metric that represents a rotating black hole deformed by a quadrupolar
term. This metric is obtained as a two soliton solution in the context of
Belinsky--Zakharov inverse scattering method. The stability of geodesics
depends strongly on the relative direction of the spin of the center of
attraction and the test particle angular momentum. The rotation does not alter
the regularity of geodesic motions in the oblate case, i.e., the orbits in this
case remain regular. We also employ the method of Lyapounov characteristic
numbers to examine the stability of orbits evolving around deformed nonrotating
centers of attraction. The typical time to observe instability of orbits is
analyzed.


title:
Initial magnetic field configurations for 3-dimensional simulations of
  astrophysical jets

abstract:
  We solve, and provide analytical expressions, for current-free magnetic
configurations in the context of initial setups of 3-dimensional simulations of
astrophysical jets involving an accretion disk corona in hydrostatic balance
around a central object. These configurations which thread through the
accretion disk and its corona preserve the initial hydrostatic state. This work
sets stage for future 3-dimensional jet simulations (including disk rotation
and mass-load) where launching, acceleration and collimation mechanisms can be
investigated.


title: Recent Chandra Results on AGNs & Future Prospects

abstract:
  I review Chandra's achievements in the last two years in AGN research. I
concentrate on some topics of my interest; some others are reviewed in an
accompanying article by K. Nandra. I comment briefly on the need to allow for
the discovery space to ensure rapid progress in the field.


title: Fundamental Physical Parameters of Collimated Gamma-Ray Burst Afterglows

abstract:
  We determine the basic physical characteristics of eight Gamma-Ray Bursts --
980519, 990123, 990510, 991028, 991216, 000301c, 000926 and 010222 -- by
modelling the broadband emission of their afterglows. We find that the burst
kinetic energies after the GRB phase are well clustered around a mean value of
3E50 ergs. In contrast, the energy release in gamma-rays, after correcting for
collimated explosion, varies among bursts by more than an order of magnitude.
  The jet initial apertures are the 2-14 degree range, mildly correlated with
the energy, half of the jets being narrower than ~3 deg. This implies that,
within 100 Mpc, there are about 10 GRB remnants (expanding at ~0.1c) which can
be resolved with VLBA.
  For all eight afterglows the total energy in the shock-accelerated electrons
is close to equipartition with protons. However the slope of the power-law
electron distribution is not universal, varying between 1.4 and 2.8.
  In at least half of the cases, the density structure of the medium is
inconsistent with an r^{-2} profile. A homogeneous medium with density in the
0.1-50 per cc range can accommodate the broadband emission of all afterglows,
with the exception of 990123, for which we find the density to be less than
0.01 per cc. If GRBs arise from the core collapse of massive stars, then such
low densities indicate the existence of superbubbles created by the supernovae
and winds within a cluster of massive stars.


title:
Detection of a Large Arc of Ionized Hydrogen Far Above the Cas OB6
  Association: A Superbubble Blowout into the Galactic Halo?

abstract:
  The Wisconsin H-Alpha Mapper (WHAM) Northern Sky Survey has revealed a loop
of H II reaching 1300 pc from the Galactic midplane above the Cas OB6
association in the Perseus sprial arm. This enormous feature surrounds and
extends far above the "W4 Chimney" identified by Normandeau et al. and appears
to be associated with the star formation activity near the W3/W4/W5 H II region
complex. The existence of this ionized structure suggests that past episodes of
massive star formation have cleared the H I from an enormous volume above the
Perseus arm, allowing Lyman continuum photons from O stars near the Galactic
midplane to reach into the halo.


title:
Far Ultraviolet Spectroscopy of the Intergalactic and Interstellar
  Absorption Toward 3C 273

abstract:
  We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the
molecular, neutral atomic, weakly ionized, and highly ionized components of the
interstellar and intergalactic material toward the quasar 3C 273. We identify
Ly-beta absorption in 8 of the known intergalactic Ly-alpha absorbers along the
sight line with rest-frame equivalent widths greater than 50 mA. Refined
estimates of the H I column densities and Doppler parameters (b) of the clouds
are presented. We find a range of b = 16-46 km/s. We detect multiple H I lines
(Ly-beta - Ly-theta) in the 1590 km/s Virgo absorber and estimate log N(H I) =
15.85, ten times more H I than in all of the other absorbers along the sight
line combined. The Doppler width of this absorber, b ~ 16 km/s, implies T <
15,000 K. We detect O VI absorption at 1015 km/s at the 2-3 sigma level that
may be associated with hot, X-ray emitting gas in the Virgo Cluster. We detect
weak C III and O VI absorption in the IGM at z=0.12007; this absorber is
predominantly ionized and has N(H+)/N(H I) > 4000/Z, where Z is the
metallicity. Strong Galactic interstellar O VI is present between -100 and +100
km/s, with an additional high-velocity wing containing about 13% of the total O
VI between +100 and +240 km/s. The broad O VI absorption wing likely traces the
expulsion of hot gas out of the Galactic disk into the halo. A limit on the
amount of diffuse O VI emission present 3.5 arc minutes off the sight line
combined with the observed O VI column density toward 3C 273, implies n_e <
0.02 cm^-3 and P/k < 11,500 cm^-3 K for an assumed temperature of 3x10^5 K.
(abbreviated version)


title:
Dielectronic Recombination (via N=2 --> N'=2 Core Excitations) and
  Radiative Recombination of Fe XX: Laboratory Measurements and Theoretical
  Calculations

abstract:
  We have measured the resonance strengths and energies for dielectronic
recombination (DR) of Fe XX forming Fe XIX via N=2 --> N'=2 (Delta_N=0) core
excitations. We have also calculated the DR resonance strengths and energies
using AUTOSTRUCTURE, HULLAC, MCDF, and R-matrix methods, four different
state-of-the-art theoretical techniques. On average the theoretical resonance
strengths agree to within <~10% with experiment. However, the 1 sigma standard
deviation for the ratios of the theoretical-to-experimental resonance strengths
is >~30% which is significantly larger than the estimated relative experimental
uncertainty of <~10%. This suggests that similar errors exist in the calculated
level populations and line emission spectrum of the recombined ion. We confirm
that theoretical methods based on inverse-photoionization calculations (e.g.,
undamped R-matrix methods) will severely overestimate the strength of the DR
process unless they include the effects of radiation damping. We also find that
the coupling between the DR and radiative recombination (RR) channels is small.
We have used our experimental and theoretical results to produce
Maxwellian-averaged rate coefficients for Delta_N=0 DR of Fe XX. For kT>~1 eV,
which includes the predicted formation temperatures for Fe XX in an optically
thin, low-density photoionized plasma with cosmic abundances, our experimental
and theoretical results are in good agreement. We have also used our R-matrix
results, topped off using AUTOSTRUCTURE for RR into J>=25 levels, to calculate
the rate coefficient for RR of Fe XX. Our RR results are in good agreement with
previously published calculations.


title:
Far Ultraviolet Spectroscopic Explorer Observations of a Supernova
  Remnant in the Line of Sight to HD 5980 in the Small Magellanic Cloud

abstract:
  We report a detection of far ultraviolet absorption from the supernova
remnant SNR 0057 - 7226 in the Small Magellanic Cloud (SMC). The absorption is
seen in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the
LBV/WR star HD 5980. Absorption from O VI 1032 and C III 977 is seen at a
velocity of +300 km/s with respect to the Galactic absorption lines, +170 km/s
with respect to the SMC absorption. The O VI 1038 line is contaminated by H_2
absorption, but is present. These lines are not seen in the FUSE spectrum of
Sk80, only ~1' (~17 pc) away from HD 5980. No blue-shifted O VI 1032 absorption
from the SNR is seen in the FUSE spectrum. The O VI 1032 line in the SNR is
well described by a Gaussian with FWHM=75 km/s. We find log N(O
VI)=14.33-14.43, which is roughly 50% of the rest of the O VI column in the SMC
(excluding the SNR) and greater than the O VI column in the Milky Way halo
along this sight line. The N(C IV)/N(O VI) ratio for the SNR absorption is in
the range of 0.12-0.17, similar to the value seen in the Milky Way disk, and
lower than the halo value, supporting models in which SNRs produce the highly
ionized gas close to the plane of the Galaxy, while other mechanisms occur in
the halo. The N(C IV)/N(O VI) ratio is also lower than the SMC ratio along this
sight line, suggesting that other mechanisms contribute to the creation of the
global hot ionized medium in the SMC. The O VI, C IV, and Si IV apparent column
density profiles suggest the presence of a multi-phase shell followed by a
region of higher temperature gas.


title: The Density Profile of the Dark Matter Halo of NGC 4605

abstract:
  We have obtained ~100 pc resolution CO and ~60 pc resolution Halpha
observations of the dwarf spiral galaxy NGC 4605. We use them to derive a high
resolution rotation curve and study the central density profile of NGC 4605's
dark matter halo. We find that these observations do not agree with the
predictions of most high resolution Cold Dark Matter calculations. We
investigate two extreme cases: 1) NGC 4605 has a maximal exponential disk, that
we model using K-band observations and remove to study the structure of its
dark matter halo, and 2) NGC 4605 is dark matter dominated and its disk is
dynamically negligible. Because the mass-to-light ratio of the maximal disk is
already very low we favor the first solution, which indicates the halo has one
component with a density profile rho ~ r^{-0.6} out to R~2.8 kpc. In the second
case, the rotation curve requires the presence of two components: a small (~600
pc) core surrounded by a much steeper rho ~ r^{-1.1} halo. Removal of
intermediate (submaximal) disks does not ameliorate the discrepancy between the
predictions and the observations.


title: Quasi-Steady State Cosmology

abstract:
  A brief historical account of modern cosmology shows that the standard big
bang (BB) model, believed by so many, does not have the strong observational
foundations that are frequently claimed for it. The theory of the Quasi-Steady
State Cosmology (QSSC) and explosive cosmogony is outlined. Comparisons are
made between the two theories in explaining the observed properties of the
universe, namely, the expansion, chemical composition, CMB, QSO redshifts and
explosive events, galaxy formation, and the m-z and theta-z relations. Only two
of the observed properties have ever been predicted from the theories (a) the
expansion predicted from Einstein's theory by Friedmann and Lemaitre, and (b)
the acceleration predicted by the classical steady state theory and the QSSC.


title: The first world atlas of the artificial night sky brightness

abstract:
  We present the first World Atlas of the zenith artificial night sky
brightness at sea level. Based on radiance calibrated high resolution DMSP
satellite data and on accurate modelling of light propagation in the
atmosphere, it provides a nearly global picture of how mankind is proceeding to
envelope itself in a luminous fog. Comparing the Atlas with the U.S. Department
of Energy (DOE) population density database we determined the fraction of
population who are living under a sky of given brightness. About two thirds of
the World population and 99% of the population in US (excluding Alaska and
Hawaii) and EU live in areas where the night sky is above the threshold set for
polluted status. Assuming average eye functionality, about one fifth of the
World population, more than two thirds of the US population and more than one
half of the EU population have already lost naked eye visibility of the Milky
Way. Finally, about one tenth of the World population, more than 40% of the US
population and one sixth of the EU population no longer view the heavens with
the eye adapted to night vision because the sky brightness.


title: High-Energy Neutrinos from Photomeson Processes in Blazars

abstract:
  An important radiation field for photomeson neutrino production in blazars is
shown to be the radiation field external to the jet. Assuming that protons are
accelerated with the same power as electrons and injected with a -2 number
spectrum, we predict that km^2 neutrino telescopes will detect about
1-to-several neutrinos per year from flat spectrum radio quasars (FSRQs) such
as 3C 279. The escaping high-energy neutron and photon beams transport inner
jet energy far from the black-hole engine, and could power synchrotron X-ray
jets and FR II hot spots and lobes.


title: Symmetry properties of the large-scale solar magnetic field

abstract:
  We investigate symmetry properties of the solar magnetic field in the
framework of the linear Parker's migratory dynamo model. We show that the
problem can be mapped onto the well-known quantum-mechanical double-well
problem. Using the WKB approximation, we construct analytical solutions for the
dipole and quadrupole configurations of the generated magnetic field. Our
asymptotic analysis within the equatorial region indicates the existence of an
additional weak dynamo wave which violates the Hale's polarity law. We estimate
the spatial decay decrement of this wave. We also calculate explicitly the
splitting of the eigenvalues corresponding to the dipole and quadrupole modes.
The real part of the dipole eigenvalue is shown to exceed the quadrupole one. A
sufficiently long time after generation the dipole mode should dominate the
quadrupole one. The relevant observational evidences of the properties obtained
are discussed.


title: X-ray Desorption of Molecules from Grains in Protoplanetary Disks

abstract:
  We examine the ability of stellar X-rays to desorb molecules from grains in
outer protoplanetary disks. In particular, we consider the possibility of spot
heating by X-rays and examine its effectiveness, compared to whole grain
heating by X-rays, in sustaining a gas phase abundance of CO. As found in
previous studies, whole grain heating is effective only for small grains (< 500
A). As a result, large grains are a permanent sink of CO and whole grain
heating cannot sustain an equilibrium gas phase abundance of CO. Spot heating,
in which the incident X-ray deposits energy in only a restricted region of the
grain volume and which may occur as a consequence of the aggregate nature of
grains, proves to be more promising. Assuming that grains are comprised of many
thermal subunits that are poorly connected thermally, we find that spot heating
is efficient at all grain sizes if large grains are effectively ``coated'' with
small grains < 100 A in size. We discuss the implications of X-ray spot heating
for the interpretation of millimeter emission line studies of outer
protoplanetary disks.


title: Large-scale star formation in the Magellanic Clouds

abstract:
  In this contribution I will present the current status of our project of
stellar population analyses and spatial information of both Magellanic Clouds
(MCs). The Magellanic Clouds - especially the LMC with its large size and small
depth (<300pc) - are suitable laboratories and testing ground for theoretical
models of star formation. With distance moduli of 18.5 and 18.9mag for the LMC
and SMC, respectively, and small galactic extinction, their stellar content can
be studied in detail from the most massive stars of the youngest populations
(<25Myr) connected to H-alpha emission down to the low mass end of about 1/10
of a solar mass. Based on broad-band photometry (U,B,V) I present results for
the supergiant shell (SGS) SMC1, some regions at the LMC east side incl. LMC2
showing different overlapping young populations and the region around N171 with
its large and varying colour excess, and LMC4. This best studied SGS shows a
coeval population aged about 12Myr with little age spread and no correlation to
distance from LMC4's centre. I will show that the available data are not
compatible with many of the proposed scenarios like SSPSF or a central trigger
(like a cluster or GRB), while a large-scale trigger like the bow-shock of the
rotating LMC can do the job.


title:
The central region of M31 observed with XMM-Newton. II. Variability of
  the individual sources

abstract:
  We present the results of a study of the variability of X-ray sources in the
central 30' of the nearby Andromeda Galaxy (M31) based on XMM Performance
Verification observations. Two observations of this field, with a total
exposure time of about 50 ks, were performed in June and December of 2000. We
found 116 sources brighter than a limiting luminosity of 6 x 10(35) erg/s
(0.3--12 keV, d=760 kpc). For the ~60 brightest sources, we searched for
periodic and non-periodic variability; at least 15% of these sources appear to
be variable on a time scale of several months. We discovered a new bright
transient source ~2.9' from the nucleus in the June observation; this source
faded significantly and was no longer detected in December. The behaviour of
the object is similar to a handful of Galactic LMXB transients, most of which
are supposed to harbor black holes. We detected pulsations with a period of
\~865 s from a source with a supersoft spectrum. The flux of this source
decreased significantly between the two XMM observations. The detected period
is unusually short and points to a rapidly spinning magnetized white dwarf. The
high luminosity and transient nature of the source suggest its possible
identification with classical or symbiotic nova, some of which were observed
earlier as supersoft sources.


title: Atomic Data Needs for Modeling Photoionized Plasmas

abstract:
  Many of the fundamental questions in astrophysics can be addressed using
spectroscopic observations of photoionized cosmic plasmas. However, the
reliability of the inferred astrophysics depends on the accuracy of the
underlying atomic data used to interpret the collected spectra. In this paper,
we review some of the most glaring atomic data needs for better understanding
photoionized plasmas.


title:
First Simultaneous Optical and EUV Observations of the Quasi-Coherent
  Oscillations of SS Cygni

abstract:
  Using EUV photometry obtained with the Extreme Ultraviolet Explorer (EUVE)
satellite and UBVR optical photometry obtained with the 2.7-m telescope at
McDonald Observatory, we have detected quasi-coherent oscillations (so-called
``dwarf nova oscillations'') in the EUV and optical flux of the dwarf nova SS
Cygni during its 1996 October outburst. There are two new results from these
observations. First, we have for the first time observed ``frequency
doubling:'' during the rising branch of the outburst, the period of the EUV
oscillation was observed to jump from 6.59 s to 2.91 s. Second, we have for the
first time observed quasi-coherent oscillations simultaneously in the optical
and EUV. We find that the period and phase of the oscillations are the same in
the two wavebands, finally confirming the long-held assumption that the periods
of the optical and EUV/soft X-ray oscillations of dwarf novae are equal. The
UBV oscillations can be simply the Rayleigh-Jeans tail of the EUV oscillations
if the boundary layer temperature kT_bb <~ 15 eV and hence the luminosity L_bb
>~ 1.2e34 (d/75 pc)^2 erg/s (comparable to that of the accretion disk).
Otherwise, the lack of a phase delay between the EUV and optical oscillations
requires that the optical reprocessing site lies within the inner third of the
accretion disk. This is strikingly different from other cataclysmic variables,
where much or all of the disk contributes to the optical oscillations.


title: WIMPS Are Stronger When They Stick Together

abstract:
  Weakly interacting massive particles (WIMPs) remain the strongest candidates
for the dark matter in the Universe. If WIMPs are the dark matter, they will
form galactic halos according to the hierarchical clustering observed in N-body
simulations. Cold dark matter (CDM) simulations show that large dark matter
structures such as galactic and cluster halos are formed by the merging of many
smaller clumps of dark matter. Each clump or halo is characterized by a
centrally cusped density profile that can enhance the rate of WIMP annihilation
and make the annihilation products more easily detectable. Electrons and
positrons generated as decay products of WIMP annihilation emit synchrotron
radiation in the Galactic magnetic field. We study the synchrotron signature
from the clumps of dark matter in our Galactic halo. We find that the emission
in the radio and microwave region of the electromagnetic spectrum can be above
the CMB anisotropy level and should be detectable by CMB anisotropy
experiments. Depending on the density profile of dark matter clumps, hundreds
of clumps can have detectable fluxes and angular sizes.


title:
The 2MASS Color-Magnitude Diagram of the Center of the Sagittarius Dwarf
  Galaxy: Photometric Measurements of a Surprisingly High Mean Metallicity

abstract:
  We present the Two Micron All Sky Survey (2MASS) (J-K, K) color-magnitude
diagram for the region within 1 degree of the center of the Sagittarius dwarf
spheroidal galaxy. Using the slope of the red giant branch (RGB), we determine
a mean metallicity for the main stellar population of [Fe/H] = -0.5 +/-0.2. The
Sagittarius RGB possesses a blue tail that overlaps with the foreground Milky
Way giant branch, and suggests that approximately 1/3 of the RGB is more
metal-poor than [Fe/H] = -1. Direct comparison to the Large Magellanic Cloud
confirms the metal-rich nature of the bulk of the Sagittarius population. Our
result is marginally consistent with the even higher metallicities determined
from high-resolution spectroscopy.


title:
High-Redshift Superwinds as the Source of the Strongest Mg II Absorbers:
  A Feasibility Analysis

abstract:
  We present HIRES/Keck profiles of four extremely strong (W_r > 1.8 A) Mg II
absorbers at 1 < z < 2. The profiles display a common kinematic structure,
having a sharp drop in optical depth near the center of the profile and strong,
black-bottomed absorption on either side. This ``symmetric-inverted''
structure, with a velocity spread of several hundred kilometers per second, is
suggestive of superwinds arising in actively star-forming galaxies.
Low-ionization absorption of similar strength has been observed in local
star-forming galaxies.
  The Mg II absorbers with W_r > 1.8 A evolve away from z = 2 to the present.
We propose that a substantial fraction of these very strong absorbers are due
to superwinds and that their evolution is related to the redshift evolution of
star-forming galaxies. Based on the observed redshift number density of W_r >
1.8 A Mg II absorbers at 1 < z < 2, we explore whether it is realistic that
superwinds from starbursting galaxies could give rise to these absorbers.
Finally, we do an analysis of the superwind connection to damped Lya absorbers
(DLAs). DLAs and superwinds evolve differently and usually have different
kinematic structure, indicating that superwinds probably do not give rise to
the majority of DLAs.


title:
A Survey of z>5.8 Quasars in the Sloan Digital Sky Survey I: Discovery
  of Three New Quasars and the Spatial Density of Luminous Quasars at z~6

abstract:
  We present the results from a survey of i-dropout objects selected from ~1550
deg^2 of multicolor imaging data from the Sloan Digital Sky Survey, to search
for luminous quasars at z>5.8. Objects with i*-z*>2.2 and z*<20.2 are selected,
and follow-up J band photometry is used to separate L and T type cool dwarfs
from high-redshift quasars. We describe the discovery of three new quasars, at
z=5.82, 5.99 and 6.28, respectively. Their spectra show strong and broad Ly
alpha+NV emission lines, and very strong Ly alpha absorption, with a mean
continuum decrement D_A > 0.90. The ARC 3.5m spectrum of the z=6.28 quasar
shows that over a range of 300 A immediately blueward of the Ly alpha emission,
the average transmitted flux is only 0.003 +/-0.020 times that of the continuum
level, consistent with zero flux, and suggesting a tentative detection of the
complete Gunn-Peterson trough. The existence of strong metal lines suggests
early chemical enrichment in the quasar enviornment. The three new objects,
together with the previously published z=5.8 quasar form a complete
color-selected flux-limited sample at z>5.8. We estimate that at $z=6$, the
comoving density of luminous quasars at M_1450 < -26.89 (h=0.5, Omega=1)is
1.1x10^-9 Mpc^-3. This is a factor of ~2 lower than that at z~5, and is
consistent with an extrapolation of the observed quasar evolution at low-z. We
discuss the contribution of quasars to the ionizing background at z~6. The
luminous quasars discussed in the paper have central black hole masses of
several times 10^9 M_sun by the Eddington argument. Their observed space
density provides a sensitive test of models of quasar and galaxy formation at
high redshift. (Abridged)


title:
Toward a Measurement of the Cosmological Geometry at z~2: Predicting
  Lyman-alpha Forest Correlation in Three Dimensions, and the Potential of
  Future Data Sets

abstract:
  The correlation between Lyman-alpha absorption in the spectra of quasar pairs
can be used to measure the transverse distance scale at z~2, which is sensitive
to the cosmological constant (Omega_Lambda) or other forms of vacuum energy.
Using Hydro-PM simulations, I compute the three-dimensional power spectrum of
the Lyman-alpha forest flux, P_F(k,mu), from which the redshift-space
anisotropy of the correlation can be obtained. I find that box size ~40 Mpc/h
and resolution ~40 Kpc/h are necessary for convergence of the calculations to
<5% on all relevant scales, although somewhat poorer resolution can be used for
large scales. I compute directly the linear theory bias parameters of the
Lyman-alpha forest, potentially allowing simulation results to be extended to
arbitrarily large scales. I investigate the dependence of P_F(k,mu) on the
primordial power spectrum, the temperature-density relation of the gas, and the
mean flux decrement, finding that the redshift-space anisotropy is relatively
insensitive to these parameters. A table of results is provided for different
parameter variations. I investigate the constraint that can be obtained on
Omega_Lambda using quasars from a large survey. Assuming 13 (theta/1')^2 pairs
at separation <theta, and including separations <10', a measurement to <5% can
be made if simulations can predict the redshift-space anisotropy with <5%
accuracy, or to <10% if the anisotropy must be measured from the data. The
Sloan Digital Sky Survey (SDSS) will obtain spectra for a factor ~5 fewer pairs
than this, so followup observations of fainter pair candidates will be
necessary. I discuss the requirements on spectral resolution and
signal-to-noise ratio (SDSS-quality spectra are sufficient).


title: Observations of O (1S) and O (1D) in Spectra of C/1999 S4 (LINEAR)

abstract:
  We report on high spectral resolution observations of comet C/1999 S4
(LINEAR) obtained at McDonald Observatory in June and July 2000. We report
unequivocal detections of the O (1S) and O (1D) metastable lines in emission in
the cometary spectrum. These lines are well separated from any telluric or
cometary emission features. We have derived the ratio of the two red doublet
lines and show they are consistent with the predictions of the branching ratio.
We also derived a ratio of 0.06+/-0.01 for the green line flux to the sum of
the red line fluxes. This ratio is consistent with H2O as the dominant parent
for atomic oxygen. We have measured the widths of the lines and show that the
widths imply that there must be some parent of atomic oxygen in addition to the
H2O.


title:
Keck NIRC Observations of Planetary-mass Candidate Members in the sigma
  Orionis Open Cluster

abstract:
  We present K-band photometry and low-resolution near-infrared spectroscopy
from 1.44 to 2.45 micron of isolated planetary-mass candidate members in the
sigma Orionis cluster found by Zapatero Osorio et al. The new data have been
obtained with NIRC at the Keck I telescope. All of our targets, except for one,
are confirmed as likely cluster members. Hence, we also confirm that the
planetary-mass domain in the cluster is well populated. Using our deep K-band
images we searched for companions to the targets in the separation range 0.3"
to 10" up to a maximum faint limit of K=19.5 mag. One suspected companion seems
to be an extremely red galaxy. The near-infrared colors of the sigma Orionis
substellar members indicate that dust grains condense and settle in their
atmospheres. We estimate that the surface temperatures range from 2500 K down
to 1500 K. The spectroscopic sequence covers the full range of L subclasses,
and the faintest object is tentatively classified as T0. These targets provide
a sequence of substellar objects of known age, distance and metallicity, which
can be used as benchmark for understanding the spectral properties of ultracool
dwarfs.


title:
Laboratory Astrophysics and Collimated Stellar Outflows: The Production
  of Radiatively Cooled Hypersonic Plasma Jets

abstract:
  We present first results of astrophysically relevant experiments where highly
supersonic plasma jets are generated via conically convergent flows. The
convergent flows are created by electrodynamic acceleration of plasma in a
conical array of fine metallic wires (a modification of the wire array
Z-pinch). Stagnation of plasma flow on the axis of symmetry forms a standing
conical shock effectively collimating the flow in the axial direction. This
scenario is essentially similar to that discussed by Canto\' ~and collaborators
as a purely hydrodynamic mechanism for jet formation in astrophysical systems.
Experiments using different materials (Al, Fe and W) show that a highly
supersonic ($M\sim 20$), well-collimated jet is generated when the radiative
cooling rate of the plasma is significant. We discuss scaling issues for the
experiments and their potential use for numerical code verification. The
experiments also may allow direct exploration of astrophysically relevant
issues such as collimation, stability and jet-cloud interactions.


title:
Properties of a Chemically Enriched Lya Absorption System at z=0.167 and
  Implications for the Total Baryons in Extended Gaseous Envelopes Around
  Galaxies

abstract:
  We present a detailed analysis of the chemical abundances, ionization state,
and origin of a partial Lyman limit system (N(HI) ~ 10^{16} cm^{-2}) at low
redshift (z=0.167 towards PKS0405-1219). We also present the first estimate of
the total baryons in extended gaseous envelopes around galaxies based on a
simple photoionization model for the Lya absorbers. We find that extended
gaseous envelopes can explain between 5--20% of the total baryons predicted by
the big bang nucleosynthesis model.


title: On the Threshold of the Reionization Epoch

abstract:
  Discovery of the cosmic reionization epoch would represent a significant
milestone in cosmology. We present Keck spectroscopy of the quasar SDSS
1044-0125, at z = 5.73. The spectrum shows a dramatic increase in the optical
depth at observed wavelengths lambda >~7550 A, corresponding to z_abs >~ 5.2.
Only a few small, narrow transmission regions are present in the spectrum
beyond that point, and out to the redshifts where the quasar signal begins. We
interpret this result as a signature of the trailing edge of the cosmic
reionization epoch, which we estimate to occur around <z> ~ 6 (as indeed
confirmed by subsequent observations by Becker et al.), and extending down to z
\~ 5.2. This behavior is expected in the modern theoretical models of the
reionization era, which predict a patchy and gradual onset of reionization. The
remaining transmission windows we see may correspond to the individual
reionization bubbles (Stromgren spheres) embedded in a still largely neutral
intergalactic medium, intersected by the line of sight to the quasar. Future
spectroscopic observations of quasars at comparable or larger redshifts will
provide a more detailed insight into the structure and extent of the
reionization era.


title: Million solar mass black holes at high redshift

abstract:
  The existence of quasars at redshift z > 5 indicates that supermassive black
holes were present since the very early times. If they grew by accretion, the
seeds of mass ~ 10^5 Msun must have formed at z ~ 9. These seed black holes may
result from the collapse and dissipation of primordial gas during the early
stages of galaxy formation. I discuss the effects of magnetic fields on the
fragmentation of cold gas clouds embedded into a hot diffuse phase and a
virialized dark matter halo. The field of 10^-4 G ejected by supernova remnants
can halt cloud break-up at 10^4 Msun. High star formation rates keep the clouds
partially ionized, making ambipolar diffusion inefficient. The
magnetically-supported clouds collapse into black holes, which later spiral via
dynamical friction into a central cluster with the total mass Mbh ~ 6 10^6
Msun. As the cluster collapses, the black holes merge emitting gravitational
radiation that should be detectable by LISA.


title:
Second-Generation Objects in the Universe: Radiative Cooling and
  Collapse of Halos with Virial Temperatures Above 10^4 Kelvin

abstract:
  The first generation of protogalaxies likely formed out of primordial gas via
H2-cooling in cosmological minihalos with virial temperatures of a few 1000K.
However, their abundance is likely to have been severely limited by feedback
processes which suppressed H2 formation. The formation of the protogalaxies
responsible for reionization and metal-enrichment of the intergalactic medium,
then had to await the collapse of larger halos. Here we investigate the
radiative cooling and collapse of gas in halos with virial temperatures Tvir >
10^4K. In these halos, efficient atomic line radiation allows rapid cooling of
the gas to 8000 K; subsequently the gas can contract nearly isothermally at
this temperature. Without an additional coolant, the gas would likely settle
into a locally gravitationally stable disk; only disks with unusually low spin
would be unstable. However, we find that the initial atomic line cooling leaves
a large, out-of-equilibrium residual free electron fraction. This allows the
molecular fraction to build up to a universal value of about x(H2) = 10^-3,
almost independently of initial density and temperature. We show that this is a
non--equilibrium freezeout value that can be understood in terms of timescale
arguments. Furthermore, unlike in less massive halos, H2 formation is largely
impervious to feedback from external UV fields, due to the high initial
densities achieved by atomic cooling. The H2 molecules cool the gas further to
about 100K, and allow the gas to fragment on scales of a few 100 Msun. We
investigate the importance of various feedback effects such as
H2-photodissociation from internal UV fields and radiation pressure due to
Ly-alpha photon trapping, which are likely to regulate the efficiency of star
formation.


title: HI Shells Behind the Coalsack

abstract:
  We report the discovery of two new large HI shells in the direction of the
Coalsack nebula. Both shells were observed with the Parkes Radio Telescope as
part of the Southern Galactic Plane Survey. The largest shell, GSH 304-00-12,
is at a distance of ~1.2 kpc and has derived physical dimensions of 280 x 200
pc. The second shell, GSH 305+01-24, is at a distance of ~2.2 kpc and has
derived dimensions of 280 x 440 pc. We present a simple numerical model to show
that GSH 305+01-24 most likely formed from stellar winds in the Centaurus OB1
stellar association. There is associated radio, infrared and H-alpha continuum
emission. Both shells are situated in the Sagittarius-Carina arm, with GSH
305+01-24 more distant. The far edge of GSH 304-00-12 is at the near side of
the arm and opens into the interarm region. We find no evidence for closure at
the near side of the shell and therefore describe the geometry as conical.
Emission from the near side of the shell may be lost in absorption by the
Coalsack Nebula.


title: Planetary-Mass Dark Matter?

abstract:
  Sahu et al. recently reported tentative evidence for a large population of
"free-floating" planetary-mass objects in a nearby globular cluster. If
verified, this discovery is consistent with a prediction that the galactic dark
matter has a substantial planetary-mass component.


title:
Propagation of thermonuclear flames on rapidly rotating neutron stars:
  extreme weather during type I X-ray bursts

abstract:
  We analyze the global hydrodynamic flow in the ocean of an accreting, rapidly
rotating, non-magnetic neutron star in an LMXB during a type I X-ray burst. Our
analysis takes into account the rapid rotation of the star and the lift-up of
the burning ocean during the burst. We find a new regime for spreading of a
nuclear burning front, where the flame is carried along a coherent shear flow
across the front. If turbulent viscosity is weak, the speed of flame
propagation is ~20 km/s, while, if turbulent viscosity is dynamically
important, the flame speed increases, and reaches the maximum value, ~300 km/s,
when the eddy overturn frequency is comparable to the Coriolis parameter. We
show that, due to rotationally reduced gravity, the thermonuclear runaway is
likely to begin on the equator. The equatorial belt is ignited first, and the
flame then propagates from the equator to the poles. Inhomogeneous cooling
(equator first, poles second) drives strong zonal currents which may be
unstable to formation of Jupiter-type vortices; we conjecture that these
vortices are responsible for modulation of X-ray flux in the tails of some
bursts. We consider the effect of strong zonal currents on the frequency of
modulation of the X-ray flux and show that the large values of the frequency
drifts observed in some bursts can be accounted for within our model combined
with the model of homogeneous radial expansion. Also, if inhomogeneities are
trapped in the forward zonal flows around the propagating burning front, chirps
with large frequency ranges (~25-500 Hz) may be detectable during the burst
rise. We argue that an MHD dynamo within the burning front can generate a
small-scale magnetic field, which may enforce vertically rigid flow in the
front's wake and can explain the coherence of oscillations in the burst tail.


title: Far-infrared mapping of the starburst galaxy NGC 253 with ISOPHOT

abstract:
  A 180 micron map and strip maps at 120 and 180 microns were obtained for the
edge-on starburst galaxy NGC 253 with ISOPHOT, the photometer on board the
Infrared Space Observatory. We compare these observations with those obtained
by IRAS at 60 micron and 100 micron and derive the far--infrared spectral
energy distribution at different locations in the galaxy. There is evidence for
the presence of cold dust (T < 20 K) both in the nucleus and in the disk.
Extended emission dominated by cold dust is detected up to 15 arcmin (~ 10 kpc)
along the major and minor axis; its spatial distribution is similar to that
seen in the IRAS and ROSAT PSPC images. The emission along the minor axis is
probably related to large-scale outflows of gas (superwinds) which originate in
the nuclear starburst and maybe to star formation in the halo. The radial
dependence of the dust temperature along the major axis is found using a
radiative transfer code: we show that the dust scale length in the disk is ~
40% larger than that of stars.


title:
Evolution of active galactic nuclei broad-line region clouds: low- and
  high-ionization lines

abstract:
  The formation of quasar broad-line region (BLR) clouds via thermal
instability in the presence of Alfven heating has been discussed by Goncalves
et al. (1993a, 1996). In particular, these studies showed the relevance of
Alfven heating in establishing the stability of BLR clouds in the intercloud
medium. The present paper shows the results of time-dependent calculations (we
use a time-dependent hydrodynamic code) following the evolution of BLR clouds,
since their formation from the 10^7 K intercloud medium. We also calculate the
UV and optical line emission associated with the clouds in order to compare
with observations. Our results are compared with those of UV and optical
monitoring of well-studied AGN, which suggest that the BLR is most probably
composed of at least two different regions, each one giving rise to a kind of
line variability, since low- and high-ionization lines present different
patterns of variability. We discuss the alternative scenario in which lines of
different ionization could be formed at the same place but heated/excited by
distinct mechanisms, considering as a non-radiative mechanism the Alfven
heating.


title: A chemical evolution model for galaxy clusters

abstract:
  We develop a toy-model for the chemical evolution of the intracluster medium,
polluted by the galactic winds from elliptical galaxies. The model follows the
"galaxy formation history" of cluster galaxies, constrained by the observed
luminosity function.


title:
X-ray Detection from Bona-fide and Candidate Brown Dwarfs in the Rho
  Ophiuchi Cloud with Chandra

abstract:
  We present results of an X-ray search from bona-fide and candidate brown
dwarfs in the Rho Ophiuchi cloud cores with the Chandra X-ray Observatory. The
selected areas are two fields near the cloud center and are observed with the
ACIS-I array of a 17'x17' size and a ~100 ks exposure. Among 18 bona-fide and
candidate brown dwarfs listed by the infrared spectroscopy, we find X-ray
emission from 7 sources above 99.9% confidence level. Therefore ~40% of the
infrared-selected brown dwarfs in this cloud emit X-rays. For the brightest 4
sources, the X-ray spectra are made and are fitted with a thin-thermal plasma
model of a temperature 1-2.5 keV. The X-rays are also time variable with rapid
flares from 2 of the brown dwarfs. Assuming 2 keV temperature and using the
empirical relation of Av vs. NH, we estimate the X-ray luminosity or its upper
limit of the other faint or non-X-ray sources. The X-ray luminosity (Lx) of the
X-ray-detected sources is in the range of 0.3-90x10^28 ergs s^-1, while the
luminosity ratio of X-ray to bolometric (Lx/Lbol) is 10^-3 - 10^-5, similar to
those of low-mass pre-main-sequence and dMe stars. All these results suggest
that the X-ray origin of brown dwarfs is the same as low-mass stars; strong
magnetic activity at the stellar surface.


title:
$\beta$--Radioactive Cosmic Rays in a diffusion model: test for a local
  bubble?

abstract:
  In the present paper, we extend the analysis of Maurin et al. (2001) and
Donato et al. (2001) to the $\beta$-radioactive nuclei $^{10}$Be, $^{26}$Al and
$^{36}$Cl. These species are be shown to be particularly sensitive to the
properties of the local interstellar medium (LISM). As studies of the LISM
suggest that we live in an underdense bubble of extent $r_{hole} \sim 50 - 200
\unit{pc}$, this local feature must be taken into account. We present a
modified version of our diffusion model which describes the underdensity as a
hole in the galactic disc. It is found that the presence of the bubble leads to
a decrease in the radioactive fluxes which can be approximated by a simple
factor $\exp(-r_{hole}/l_{rad})$ where $l_{rad}=\sqrt{K \gamma \tau_0}$ is the
typical distance travelled by a radioactive nucleus before it decays. We find
that each of the radioactive nuclei independently point towards a bubble radius
$\lesssim 100 \unit{pc}$. If these nuclei are considered simultaneously, only
models with a bubble radius $r_{hole} \sim 60 - 100 \unit{pc}$ are marginally
consistent with data. In particular, the standard case $r_{hole}=0 \unit{pc}$
is disfavoured. Our main concern is about the consistency of the currently
available data, especially $^{26}$Al/$^{27}$Al.


title: Ellipsoidal collapse and previrialization

abstract:
  We study the non-linear evolution of a dust ellipsoid,embedded in a Friedmann
flat background universe, in order to determine the evolution of the density of
the ellipsoid as the perturbation to it related detaches from general expansion
and begins to collapse. We show that while the growth rate of the density
contrast of a mass element is enhanced by the shear in agreement with Hoffman
(1986a), the angular momentum acquired by the ellipsoid has the right magnitude
to counterbalance the effect of the shear. The result confirms the
previrialization conjecture (Peebles & Groth 1976; Davis & Peebles 1977;
Peebles 1990) by showing that initial asphericities and tidal interactions
begin to slow down the collapse after the system has broken away from the
general expansion.


title: Isocurvature Fluctuations in Tracker Quintessence Models

abstract:
  We consider effects of the isocurvature perturbation in the framework of the
tracker-type quintessence models. During the inflation, fluctuations in the
amplitude of the quintessence field are generated, which provide isocurvature
component of the cosmic density perturbation. Contrary to the conventional
notion, it is shown that effects of the isocurvature fluctuation may become
sizable in some cases, and in particular, the cosmic microwave background
angular power spectrum may be significantly enhanced due to the effect of the
isocurvature mode. Such an enhancement may be detectable in on-going and future
experiments.


title: Superbursts and long bursts as surface phenomenon of compact objects

abstract:
  X-ray bursts from compact stars is believed to be due to type I thermonuclear
processes which are short lived, typically ~ 10 to 100 s. There are some low
mass X-ray binaries (LMXB) like 4U 1820-30, 4U 1636-53, KS 1731-260 and Serpens
X-1, known as Super Bursters (SB) which emit X-rays close to the Eddington
luminosity limit for long periods of several hours. Recently there are reports
of some long bursters (LB), which have bursts lasting 6-25 minutes, whereas the
4U 1735-44 has a burst period of 86 minutes. We suggest that these bursts from
SB and LB may be due to breaking and re-formation of diquark pairs, on the
surface of realistic strange quark stars. We use the beta equilibrated u, d and
s quark model of Dey et al. (1998) and Li et al. (1999a and 1999b) and allow
for spin dependent hyperfine interaction between quarks. The interaction
produces pairing of specific colour-spin diquarks, leading to further lowering
of energy by several MeV-s for each pair, on the average. Diquarks are expected
to break up due to the explosion and shock of the TN process. The subsequent
production of copious diquark pairing may produce sufficient energy to produce
the very long bursts seen in SB or LB. The estimated total energy liberated,
10^{42} ergs, can be explained in our model with the calculated pair density ~
0.275/fm^3 and a surface thickness of only half a micron, if the entire surface
is involved. The depth of the surface involved in the process may be only few
microns if the process is restricted to small part of the surface near the
equator as suggested by Bildsten.


title: Gas properties in the Medusa minor merger - comparing with ULIRGs

abstract:
  High resolution observations of CO and 13CO 1--0 in the Medusa (NGC4194)
minor merger show the CO/13CO 1--0 intensity ratio (R) increasing from normal
values (5-10) in the outer parts of the galaxy to high (>20) values in the
central, extended starburst region. Ratios >20 are otherwise typical of more
luminous mergers. The Medusa L_FIR/L_CO ratio rivals that of ultraluminous
galaxies (ULIRGs), despite the comparatively modest luminosity, indicating an
exceptionally high star formation efficiency (SFE). We present models of the
high pressure ISM in a ULIRG and the relatively low pressure ISM of the Medusa.
We discuss how these models may explain large R in both types of distributions.
Since the HCN emission is faint towards the Medusa, we suggest that the SFE is
not primarily controlled by the mass fraction of dense (n > 10^4 cm-3) gas, but
is probably strongly dependent on dynamics. The bright HCN emission towards
ULIRGs is not necessarily evidence that the IR emission there is always powered
by starbursts.


title:
Low and High Angular Momentum Accretion Flows in BHCs: Case Study of XTE
  J1550-564

abstract:
  The 1998 outburst of XTE J1550-564 started with a hard X-ray spike, rising in
less than a day and declining after 3-4 days; at the same time, the soft X-ray
flux was rising with a longer timescale (~ 10 days). We suggest that the soft
and the initial hard X-ray emission are produced by two different components of
the accretion flow: a higher angular momentum flow, which forms the disk, and a
lower angular momentum flow feeding the hot inner region. Thus, we argue that
the onset of the outburst is determined by an increased mass transfer rate from
the companion star, but the outburst morphology is also determined by the
distribution of specific angular momentum in the accreting matter. In XTE
J1550-564, we attribute the initial, impulsive low angular momentum accretion
to the breaking down of magnetic confinement by the magnetically active
secondary star. We show that a hard X-ray spike is seen at the onset of an
outburst in other BHCs.


title:
Large zenith angle observations with the high-resolution GRANITE III
  camera

abstract:
  The GRANITE III camera of the Whipple Cherenkov Telescope at the Fred
Lawrence Whipple Observatory on Mount Hopkins, Arizona (2300 m a.s.l.) has the
highest angular resolution of all cameras used on this telescope so far. The
central region of the camera has 379 pixels with an individual angular diameter
of 0.12 degrees. This makes the instrument especially suitable for observations
of gamma-induced air-showers at large zenith angles since the increase in
average distance to the shower maximum leads to smaller shower images in the
focal plane of the telescope. We examine the performance of the telescope for
observations of gamma-induced air-showers at zenith angles up to 63 degrees
based on observations of Mkn 421 and using Monte Carlo Simulations. An
improvement to the standard data analysis is suggested.


title:
Equilibrium sequences of synchronized and irrotational binary systems
  composed of different mass stars in Newtonian gravity

abstract:
  We study equilibrium sequences of close binary systems on circular orbits and
composed of different mass stars with polytropic equation of state in Newtonian
gravity. The solving method is a multidomain spectral method which we have
recently developed. The computations are performed for both cases of
synchronized and irrotational binary systems with adiabatic indices $\gamma =
3, 2.5, 2.25, 2$ and 1.8, and for three mass ratios: $M_1/M_2 =0.5, 0.2$ and
0.1. It is found that the equilibrium sequences always terminate at a mass
shedding limit (appearance of a cusp on the surface of the less massive star).
For synchronized binaries, this contrasts with the equal mass case, where the
sequences terminate instead by a contact configuration. Regarding the turning
point of the total angular momentum (or total energy) along a sequence, we find
that it is difficult to get it for small mass ratios. Indeed, we do not find
any turning points for $M_1/M_2 \le 0.5$ in the irrotational case. However, in
the synchronized case, it becomes easier again to find one for mass ratios much
smaller than $M_1/M_2 \sim 0.2$.


title:
Far infrared mapping of three Galactic star forming regions : W3(OH), S
  209 & S 187

abstract:
  Three Galactic star forming regions associated with W3(OH), S209 and S187
have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands
centered at ~ 140 and 200 micron using the TIFR 100 cm balloon borne FIR
telescope. These maps show extended FIR emission with structures. The HIRES
processed IRAS maps of these regions at 12, 25, 60 & 100 micron have also been
presented for comparison. Point-like sources have been extracted from the
longest waveband TIFR maps and searched for associations in the other five
bands. The diffuse emission from these regions have been quantified, which
turns out to be a significant fraction of the total emission. The spatial
distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209),
has been determined reliably from the maps in TIFR bands. The dust temperature
and optical depth maps show complex morphology. In general the dust around S209
has been found to be warmer than that in W3(OH) region.


title: O VI High Velocity Clouds: Where and What are They?

abstract:
  Our view of the high velocity cloud (HVC) system is changing dramatically
with new observations from the Far Ultraviolet Spectroscopic Explorer mission
and the Space Telescope Imaging Spectrograph onboard the Hubble Space
Telescope. In particular, the detection of O VI absorption indicates that many
HVCs have a hot, collisionally-ionized component in addition to the neutral gas
detected in H I 21cm emission. A better understanding of the ionization of this
gas will help to determine the distances of some HVCs, as well as constrain the
properties of a hot Galactic corona or Local Group medium. In this article, I
briefly summarize some recent observations of O VI HVCs.


title:
Multicomponent radiatively driven stellar winds II. Gayley-Owocki
  heating in multitemperature winds of OB stars

abstract:
  We show that the so-called Gayley-Owocki (Doppler) heating is important for
the temperature structure of the wind of main sequence stars cooler than the
spectral type O6. The formula for Gayley-Owocki heating is derived directly
from the Boltzmann equation as a direct consequence of the dependence of the
driving force on the velocity gradient. Since Gayley-Owocki heating deposits
heat directly to the absorbing ions, we also investigated the possibility that
individual components of the radiatively driven stellar wind have different
temperatures. This effect is negligible in the wind of O stars, whereas a
significant temperature difference takes place in the winds of main sequence B
stars for stars cooler than B2. Typical temperature difference between
absorbing ions and other flow components for such stars is of the order 10^3 K.
However, in the case when passive component falls back onto the star the
absorbing component reaches temperatures of order 10^6 K, which allows for
emission of X-rays.
  Moreover, we compare our computed terminal velocities with the observed ones.
We found quite good agreement between predicted and observed terminal
velocities. The systematic difference coming from the using of the so called
"cooking formula" has been removed.


title: Dark Synergy: Gravitational Lensing and the CMB

abstract:
  Power spectra and cross-correlation measurements from the weak gravitational
lensing of the cosmic microwave background (CMB) and the cosmic shearing of
faint galaxies images will help shed light on quantities hidden from the CMB
temperature anisotropies: the dark energy, the end of the dark ages, and the
inflationary gravitational wave amplitude. Even with modest surveys, both types
of lensing power spectra break CMB degeneracies and they can ultimately improve
constraints on the dark energy equation of state w by over an order of
magnitude. In its cross correlation with the integrated Sachs-Wolfe effect, CMB
lensing offers a unique opportunity for a more direct detection of the dark
energy and enables study of its clustering properties. By obtaining source
redshifts and cross-correlations with CMB lensing, cosmic shear surveys provide
tomographic handles on the evolution of clustering correspondingly better
precision on the dark energy equation of state and density. Both can indirectly
provide detections of the reionization optical depth and modest improvements in
gravitational wave constraints which we compare to more direct constraints.
Conversely, polarization B-mode contamination from CMB lensing, like any other
residual foreground, darkens the prospects for ultra-high precision on
gravitational waves through CMB polarization requiring large areas of sky for
statistical subtraction. To evaluate these effects we provide fitting formula
for the evolution and transfer function of the Newtonian gravitational
potential.


title: Inhomogeneous Metallicities and Cluster Cooling Flows

abstract:
  The theme of this contribution is the idea that the metals in the
intracluster medium (ICM) may be inhomogeneously distributed on small scales.
We focus on the possible interplay between this and the cooling flow process.
We begin with a brief review of some evidence for a patchy distribution of
metals in the ICM. Next we outline a simple numerical model for this within the
framework of the cooling flow hypothesis. Finally we present some of our recent
results on the presence of gradients in the observed abundance profiles.


title:
Very high-energy observations of the Crab nebula with the GRAAL
  experiment

abstract:
  The ``Gamma Ray Astronomy at ALmeria'' (GRAAL) experiment uses 63
heliostat-mirrors with a total mirror area of ~ 2500 m2 from the CESA-1 field
to collect Cherenkov light from airshowers. The detector is located in a
central solar tower and detects photon-induced showers with an energy threshold
of 250 +- 110 GeV and an asymptotic effective detection area of about 15000 m2.
Data sets taken in the period September 1999 - September 2000 in the direction
of the Crab pulsar were analysed for high energy gamma-ray emission. Evidence
for gamma-ray flux from the Crab pulsar with an integral flux of 2.2 +- 0.4
(stat) $^{+1.9}_{-1.5}$ (syst) x 10$^{-9}$ cm$^{-2}$ s$^{-1}$ above threshold
and a significance of 4.5 sigma in a total (usable) observing time of 7 hours
and 10 minutes on source was found. No evidence for emission from the other
sources was seen. The effect of field-of-view restricted to the central part of
a detected airshower on the lateral distribution and timing properties of
Cherenkov light and their effect on an efficient gamma-hadron separation are
discussed.


title: Natural Magnetogenesis from Inflation

abstract:
  We consider the gravitational generation of the massive Z-boson field of the
standard model, due to the natural breaking of its conformal invariance during
inflation. The electroweak symmetry restoration at the end of inflation turns
the almost scale-invariant superhorizon Z-spectrum into a hypermagnetic field,
which transforms into a regular magnetic field at the electroweak phase
transition. The mechanism is generic and is shown to generate a superhorizon
spectrum of the form B~1/L on a length-scale L regardless of the choice of
inflationary model. Scaled to the epoch of galaxy formation such a field
suffices to trigger the galactic dynamo and explain the observed galactic
magnetic fields in the case of a spatially flat, dark energy dominated Universe
with GUT-scale inflation. The possibility of further amplification of the
generated field by preheating is also investigated. To this end we study a
model of Supersymmetric Hybrid Inflation with a Flipped SU(5) grand unified
symmetry group.


title:
A Multi-Wavelength, Multi-Epoch Study of the Soft X-Ray Transient
  Prototype, V616 Mon (A0620-00)

abstract:
  We have obtained optical and infrared photometry of the soft x-ray transient
prototype V616 Mon (A0620-00). From this photometry, we find a spectral type of
K4 for the secondary star in the system, which is consistent with spectroscopic
observations. We present J-, H-, and K-band light curves modeled with WD98 and
ELC. Combining detailed, independently run models for ellipsoidal variations
due to a spotted, non-spherical secondary star, and the observed ultraviolet to
infrared spectral energy distribution of the system, we show that the most
likely value for the orbital inclination is 40.75 +/- 3 deg. This inclination
angle implies a primary black hole mass of 11.0 +/- 1.9 solar masses.


title: A Simple Family of Models for Eccentric Keplerian Fluid Disks

abstract:
  In order to be in a long-lived configuration, the density in a fluid disk
should be constant along streamlines to prevent compressional (PdV) work from
being done cyclically around every orbit. In a pure Kepler potential, flow
along aligned, elliptical streamlines of constant eccentricity will satisfy
this condition. For most density profiles, differential precession driven by
the pressure gradient will destroy the alignment; however, in the razor-thin
approximation there is a family of simple equilibria in which the precession
frequency is the same at all radii. These disks may therefore be long-lived at
significant eccentricities. The density can be made axisymmetric as r goes to
0, while maintaining the precession rate, by relaxing the requirement of
constancy along streamlines in an arbitrarily small transition region near the
center. In the limit of small eccentricity, the models can be seen as
acoustically perturbed axisymmetric disks, and the precession rate is shown to
agree with linear theory. The perturbation is a traveling wave similar to an
ocean wave, with the fluid rising and falling epicyclically in the
gravitational field of the central mass. The expected emission line profiles
from the eccentric disks are shown to be strongly asymmetric in general, and,
in extreme cases, prone to misinterpretation as single narrow lines with
significant velocity offsets.


title:
A 12-day ASCA Observation of the Narrow-Line Seyfert 1 Galaxy Ton S180:
  Time-Selected Spectroscopy

abstract:
  We present an analysis of the X-ray variability properties of the NLS1 galaxy
Ton S180, based upon a 12-day continuous ASCA observation. We observe flux
variations of a factor of 3.5 in the 0.7-1.3 keV band and 3.9 in the 2-10 keV
band.Time-resolved spectroscopy (~1d sampling) reveals that the broad `soft
hump' component at energies <2 keV shows flux variations on timescales down to
1 day that are well correlated with the photon index and the 2-10 keV band
flux. A broad Fe K$\alpha$ emission is detected. There is a evidence for a
narrow Fe K$\alpha$ line at ~6.8 keV, indicating an origin in ionized material.
We do not detect significant variations of the line flux or EW on ~1 day-1 week
timescales. The softness ratio reveals spectral variability on timescales down
to ~1000 s, indicating that the power-law continuum and soft hump fluxes are
not well correlated on this timescale. It also shows a slow decline across the
observation, due to a combination of the different time-variability of the
power-law continuum and soft hump flux on timescales of ~1 week. The X-ray
emission originates within 12 Schwarzschild radii, and the amplitudes and
timescales of the rapid variations we observed are consistent with those
expected within disk-corona models. The soft hump variability timescale rules
out an origin in large scale components (circumnuclear starburst). The
$\Gamma$-soft hump correlation is consistent with the soft hump being produced
by up-scattering of the accretion disk radiation within a flaring disk corona.


title:
Evidence for Reionization at z ~ 6: Detection of a Gunn-Peterson Trough
  in a z=6.28 Quasar

abstract:
  We present moderate resolution Keck spectroscopy of quasars at z=5.82, 5.99
and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the
Ly Alpha absorption in the spectra of these quasars evolves strongly with
redshift. To z~5.7, the Ly Alpha absorption evolves as expected from an
extrapolation from lower redshifts. However, in the highest redshift object,
SDSSp J103027.10+052455.0 (z=6.28), the average transmitted flux is
0.0038+-0.0026 times that of the continuum level over 8450 A < lambda < 8710 A
(5.95<z(abs)<6.16), consistent with zero flux. Thus the flux level drops by a
factor of >150, and is consistent with zero flux in the Ly Alpha forest region
immediately blueward of the Ly Alpha emission line, compared with a drop by a
factor of ~10 at z(abs)~5.3. A similar break is seen at Ly Beta; because of the
decreased oscillator strength of this transition, this allows us to put a
considerably stronger limit, tau(eff) > 20, on the optical depth to Ly Alpha
absorption at z=6.
  This is a clear detection of a complete Gunn-Peterson trough, caused by
neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen
fraction in the intergalactic medium would result in an undetectable flux in
the Ly Alpha forest region. Therefore, the existence of the Gunn-Peterson
trough by itself does not indicate that the quasar is observed prior to the
reionization epoch. However, the fast evolution of the mean absorption in these
high-redshift quasars suggests that the mean ionizing background along the line
of sight to this quasar has declined significantly from z~5 to 6, and the
universe is approaching the reionization epoch at z~6.


title: Metallicity gradients in the Sagittarius dwarf spheroidal Galaxy

abstract:
  Metallicity gradients in the Sagittarius dwarf Galaxy (Sgr) are investigated
by using infrared photometric data from the 2MASS survey. To search for
metallicity effects, the giant branch in a field situated near the Center of
the Sgr is compared to the giant branch in a field situated near its southern
edge. The contamination of Sgr giant branch by foreground Galactic stars is
canceled by statistical subtraction of diagrams symmetrical in Galactic
latitude. After subtraction it is possible to reconstruct the Sgr giant branch
with excellent accuracy. The giant branch in the two fields have similar slopes
but are shifted in color. Even after correction for the differential reddening
between the fields, the shift in color between the branch remains, and is very
significant. This variation in the color of the giant branch corresponds to a
metallicity variation of about -0.25 Dex. The existence of a metallicity
gradient in Sgr may indicate that there are two different stellar population in
Sgr. One has low metallicity, and another one of higher metallicity has a
smaller spatial extension.


title: Gamma-Ray Bursts as a Probe of Cosmology

abstract:
  We show that, if the long GRBs are produced by the collapse of massive stars,
GRBs and their afterglows may provide a powerful probe of cosmology and the
early universe.


title:
New insights on the Draco dwarf spheroidal galaxy from SDSS: a larger
  radius and no tidal tails

abstract:
  We have investigated the spatial extent and structure of the Draco dwarf
spheroidal galaxy using deep wide-field multicolor CCD photometry from the
Sloan Digital Sky Survey (SDSS). Our study covers an area of 27 square degrees
around the center of the Draco dwarf. We show that the spatial distribution of
Draco's red giants, red horizontal branch stars and subgiants down to i=21.7
mag does not provide evidence for the existence of tidally induced tails or a
halo of unbound stars. The radial profile can be fit by King models as well as
by a generalized exponential. The core radius and the limiting (or tidal)
radius along the major axis are 7.7' and 40.1', respectively, making Draco 40%
larger than previously measured. Down to our magnitude limit tidal effects can
only exist at a level of 10^-3 of the central surface density of Draco or
below. The regular structure of Draco found from the new data argues against it
being a portion of an unbound tidal stream and lends support to the assumption
of dynamical equilibrium. We estimate Draco's total mass to be 2.2 - 3.5 times
10^7 solar masses. We obtain an overall mass-to-light ratio of 146+-42 or
92+-28 solar masses depending on the details of the mass and luminosity
estimates. In summary, our results strengthen the case for a strongly dark
matter dominated, bound stellar system. (Abstract strongly abridged).


title:
On the relation between high-redshift starburst galaxies and damped
  Ly-alpha systems

abstract:
  Essentially all high-redshift galaxies show evidence for strong large-scale
outflows that should have a profound effect on the structure and kinematics of
both the galaxies themselves and their environment. The interstellar absorption
spectra of both Lyman break galaxies (LBGs) and local starburst galaxies are
remarkably similar to those of damped Ly-alpha (DLA) systems in QSO spectra.
Their rest-frame UV spectra typically show broad, blueshifted Ly-alpha
absorption accompanied by low-ionization metallic absorption lines with complex
profiles. Hydrodynamical simulations of galactic winds suggest that the
absorption arises in a collection of dense clouds entrained in the hot wind
and/or in shells swept up by the outflow. It seems likely that outflows would
also give rise to DLA absorption when seen in absorption against a background
QSO. It is emphasized that some differences are expected between the properties
of DLA systems in the emission weighted galaxy spectra, which always probe the
centers of star formation, and those in random sight lines through the outflow.
The observed LBGs alone can account for all DLA absorption at z ~ 3 if the
cross section for DLA absorption is pi*r^2 with r = 19 h^{-1} kpc. If the cross
section is smaller than this, then the fraction of DLA systems arising in
outflows could still be significant if there are many wind-driving galaxies
below the current detection limits. This is certainly possible since the z=3
luminosity function is still rising down to the detection limit of 0.1 L_star
and observations and simulations of local dwarf galaxies indicate that many of
these fainter galaxies drive winds as well.


title: Ultracompact X-Ray Binaries with Neon-Rich Degenerate Donors

abstract:
  There are three low-mass X-ray binaries (4U 0614+091, 2S 0918-549, and 4U
1543-624) for which broad line emission near 0.7 keV was previously reported. A
recent high-resolution observation of 4U 0614+091 with the Chandra/LETGS found
evidence for an unusually high Ne/O abundance ratio along the line of sight but
failed to detect the previously reported 0.7 keV feature. We have made a search
of archival ASCA spectra and identified a fourth source with the 0.7 keV
feature, the 20-min ultracompact binary 4U 1850-087. In all four of these
sources, the 0.7 keV residual is eliminated from the ASCA spectra by allowing
excess photoelectric absorption due to a non-solar relative abundance of neon,
just as in the LETGS spectrum of 4U 0614+091. The optical properties of these
systems suggest that all four are ultracompact (P_orb<80 min) binaries. We
propose that there is excess neon local to each of these sources, as also found
in the ultracompact binary pulsar 4U 1626-67. We suggest that the mass donor in
these systems is a low-mass, neon-rich degenerate dwarf and that the binaries
are all ultracompact.


title: Dark Energy and the New Cosmology

abstract:
  A successor to the standard hot big-bang cosmology is emerging. It greatly
extends the highly successful hot big-bang model. A key element of the New
Standard Cosmology is dark energy, the causative agent for accelerated
expansion. Dark energy is just possibly the most important problem in all of
physics. The only laboratory up to the task of studying dark energy is the
Universe itself.


title: Dynamics and Origin of the 2:1 Orbital Resonances of the GJ 876 Planets

abstract:
  (Abridged) A dynamical fit has placed the two planets about the star GJ 876
in coplanar orbits deep in 3 resonances at the 2:1 mean-motion commensurability
with small libration amplitudes. The libration of both lowest order mean-motion
resonance variables, theta_1 and theta_2, and the secular resonance variable,
theta_3, about 0 deg. differs from the familiar geometry of the Io-Europa pair,
where theta_2 and theta_3 librate about 180 deg. By considering a condition for
stable simultaneous librations of theta_1 and theta_2, we show that the GJ 876
geometry results because of the large orbital eccentricities e_i, whereas the
very small e_i in the Io-Europa system lead to the latter's geometry.
Surprisingly, the GJ 876 resonance configuration remains stable for e_1 up to
0.86 and for amplitude of libration of theta_1 approaching 45 deg. with the
current e_i. We find that inward migration of the outer planet of the GJ 876
system results in certain capture into the observed resonances if initially e_1
<0.06 and e_2<0.03 and the migration rate |(da_2/dt)/a_2| < 0.03(a_2/AU)^{-3/2}
yr^{-1}. The bound on the migration rate is easily satisfied by migration due
to planet-nebula interaction. If there is no eccentricity damping, eccentricity
growth is rapid with continued migration within the resonance, with e_i
exceeding the observed values after a further reduction in the semi-major axes
a_i of only 7%. With eccentricity damping (de_i/dt)/e_i = -K|(da_i/dt)/a_i|,
the e_i reach equilibrium values that remain constant for arbitrarily long
migration within the resonances. The equilibrium e_i are close to the observed
e_i for K=100 (K=10) if there is migration and damping of the outer planet only
(of both planets). It is as yet unclear that planet-nebula interaction can
produce the large value of K required to obtain the observed eccentricities.


title: Hot Outflowing Gas from the X-ray Binary Hercules X-1

abstract:
  We present a unified picture of outflowing gas from the X-ray binary system
Hercules X-1/HZ Herculis. We suggest that the outflowing gas (a wind) causes UV
emission seen in mid-eclipse, narrow UV absorption lines, and broad UV P Cygni
lines. Observations with the FOS and STIS spectrographs on the Hubble Space
Telescope (HST) show UV emission lines in the middle of X-ray eclipse, when the
X-ray heated atmosphere of the normal star and accretion disk should be
entirely hidden from view. Narrow absorption lines (FWHM~50 km/s) blueshifted
by 500 km/s during observations in 1998 and by 400 km/s during observations in
1999 were seen from phi=0.0-0.3. The line velocity was constant to within 20
km/s. The P Cygni profiles from Hercules~X-1 have optical depths tau<1 with a
maximum expansion velocity of 600 km/s, and are seen in the resonance lines N V
1238.8,1242.8, Si IV 1393.7,1402.8, and C IV 1548.2, 1550.8. We discuss whether
this wind originates in the accretion disk or on the companion star, and how
the relevant ions can survive X-ray ionization by the neutron star.


title: Multi-Conjugate Adaptive Optics with Laser Guide Stars

abstract:
  The Laser Guide Star Facility for the VLT will be commissioned during 2003.
This, of course, can only be the first step towards enhancing the scientific
output of the VLT through adaptive optics. So in this contribution we propose
the development of a laser guide star multi-conjugate adaptive optics system.
We consider geometries for the adaptive optics system, and discuss the
technology needed to project up to 5 laser beacons. The rationale for such a
project is provided by an outline of two primary science drivers.


title: The Age of the Galactic Bulge

abstract:
  The dominant stellar population of the central bulge of the Milky Way is old,
with roughly solar metallicity. The age is very similar to that of the old
metal rich bulge globular clusters and to 47 Tucanae, which has an age of 13
Gyr. Stellar composition measurements from Keck/HIRES confirm that the bulge
stars are enhanced in Mg and Ti. New HST/NICMOS data are consistent with an old
stellar population dominating the central 100 pc of the Milky Way.
  New infrared photometry has been reported for the bulge of M31. Although
bright asymptotic asymptotic giant branch stars are observed in the infrared,
the data are most consistent with an old stellar population.