title: Stellar mass-to-light ratios and the Tully-Fisher relation

abstract:
  We have used a suite of simplified spectrophotometric spiral galaxy evolution
models to argue that there are substantial variations in stellar mass-to-light
ratios (M/Ls) within and among galaxies, amounting to factors of between 3 and
7 in the optical, and factors of 2 in the near-infrared. Under the assumption
of a universal spiral galaxy IMF, our models show a strong and robust
correlation between stellar M/L and the optical colors of the integrated
stellar populations. Using observed maximum disk M/Ls we conclude that a
Salpeter Initial Mass Function (IMF) has too many low-mass stars per unit
luminosity, but that an IMF similar to the Salpeter IMF at the high-mass end
with less low-mass stars (giving stellar M/Ls 30% or more lower than the
Salpeter value) is consistent with the maximum disk constraints. We apply the
model trends in stellar M/L with color to the Tully-Fisher (TF) relation. We
find that the stellar mass TF relation is relatively steep and has modest
scatter, and is independent of the passband and color used to derive the
stellar masses. The difference in slope between the optical (especially blue)
and near-infrared TF relations is due to the combined effects of dust
attenuation and stellar M/L variations with galaxy mass. We find that the
baryonic TF relation has a slope of 3.5 (with random and systematic errors of
+/- 0.2 each). Since we have normalized the stellar M/L to be as high as can
possibly be allowed by maximum disk constraints, the slope of the baryonic TF
relation will be somewhat shallower than 3.5 if all disks are substantially
sub-maximal. [Abridged]


title: A Review of Disk-Corona Oscillations

abstract:
  Low frequency (approximately 0.1-35 Hz) quasi-periodic oscillations (QPO) of
the X-ray flux characterize many of the black hole candidates, in particular
those which have radio evidence for jets. These QPO have amplitudes of up to 20
per cent in the states of black hole novae which are called very high and
intermediate. The frequencies are correlated with the break frequency of the
band-limited low frequency white noise. With transition to the state called the
soft high state, both the QPO and the noise disappear. While the noise is
strong in the low hard states like that of Cyg X-1, the QPO, when present, are
weak and broad. In their strong manifestations, these QPO have the curious
property of appearing to have the spectrum of the power-law component which
dominates in the low state, while correlations between their frequency and the
disk component in the spectrum imply control by the disk. The correlations, the
harmonic structure of the QPO, and the phase lags have complex behavior in the
same source (GRS 1915+105, XTE J1550-564). The phenomena point to interaction
between the disk and the corona, for which there are several interesting ideas.


title: The mass of a halo

abstract:
  We discuss the different definitions of the mass of a halo in common use and
how one may convert between them. Using N-body simulations we show that mass
estimates based on spherical averages are much more tightly correlated with
each other than with masses based on the number of particles in a halo. The
mass functions pertaining to some different mass definitions are estimated and
compared to the `universal form' of Jenkins et al. (2000). Using a different
simulation pipeline and a different cosmological model we show that the mass
function is well fit by the Jenkins et al. (2000) fitting function,
strengthening the claim to universality made by those authors. We show that
care must be taken to match the definitions of mass when using large N-body
simulations to bootstrap scaling relations from smaller hydrodynamical runs to
avoid observationally significant bias in the predictions for abundances of
objects.


title: Cosmological thermal decoupling and primordial molecules

abstract:
  Primordial chemistry began, at the recombination epoch, when the adiabatic
expansion caused the temperature of the radiation to fall below 4000K. The
chemistry of the early Universe involves the elements hydrogen, its isotope
deuterium, helium with its isotopic forms and lithium. In this contribution I
will discuss the influence of the primordial molecules on the cosmological
decoupling. In the framework of the gravitational instability theory, each
protostructure started as a tiny local overdensity. As long as these
inhomogeneities are small, their evolution can be studied by the classical
linear perturbation theory. Once the deviations become large, the linear theory
is no more valid. we present the role played by these molecules on the
transition between the linear regime and the non-linear regime, and show that
the molecules can lead to a thermal change at the turn-around point between
these two regimes.


title:
Database of Geneva stellar evolution tracks and isochrones for
  UBVRIJHKLL'M, HST-WFPC2, Geneva and Washington photometric systems

abstract:
  We have used an updated version of the empirically and semi-empirically
calibrated BaSeL library of synthetic stellar spectra of Lejeune et al. (1997,
1998) and Westera et al. (1999) to calculate synthetic photometry in the
UBVRIJHKLL'M, HST-WFPC2, Geneva, and Washington systems for the entire set of
non-rotating Geneva stellar evolution models covering masses from 0.4-0.8 to
120-150 Msun and metallicities Z=0.0004 (1/50 Zsun) to 0.1 (5 Zsun). The
results are provided in a database which includes all individual stellar tracks
and the corresponding isochrones covering ages from 10^3 yr to 16--20 Gyr in
time steps of Delta(log t)= 0.05 dex. The database also includes a new grid of
stellar tracks of very metal-poor stars (Z=0.0004) from 0.8 - 150 Msun
calculated with the Geneva stellar evolution code.
  The full database will be available in electronic form at the CDS
(http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/(vol)/(page)) and at
http://webast.ast.obs-mip.fr/stellar/.


title: The European Photon Imaging Camera on XMM-Newton: The MOS Cameras

abstract:
  The EPIC focal plane imaging spectrometers on XMM-Newton use CCDs to record
the images and spectra of celestial X-ray sources focused by the three X-ray
mirrors. There is one camera at the focus of each mirror; two of the cameras
contain seven MOS CCDs, while the third uses twelve PN CCDs, defining a
circular field of view of 30 arcmin diameter in each case. The CCDs were
specially developed for EPIC, and combine high quality imaging with spectral
resolution close to the Fano limit. A filter wheel carrying three kinds of
X-ray transparent light blocking filter, a fully closed, and a fully open
position, is fitted to each EPIC instrument. The CCDs are cooled passively and
are under full closed loop thermal control. A radio-active source is fitted for
internal calibration. Data are processed on-board to save telemetry by removing
cosmic ray tracks, and generating X-ray event files; a variety of different
instrument modes are available to increase the dynamic range of the instrument
and to enable fast timing. The instruments were calibrated using laboratory
X-ray beams, and synchrotron generated monochromatic X-ray beams before launch;
in-orbit calibration makes use of a variety of celestial X-ray targets. The
current calibration is better than 10% over the entire energy range of 0.2 to
10 keV. All three instruments survived launch and are performing nominally in
orbit. In particular full field-of-view coverage is available, all electronic
modes work, and the energy resolution is close to pre-launch values. Radiation
damage is well within pre-launch predictions and does not yet impact on the
energy resolution. The scientific results from EPIC amply fulfil pre-launch
expectations.


title: Clustering of Very Red Galaxies in the Las Campanas IR Survey

abstract:
  We report results from the first 1000 square arc-minutes of the Las Campanas
IR survey. We have imaged 1 square degree of high latitude sky in six distinct
fields to a 5-sigma H-band depth of 20.5 (Vega). Optical imaging in the
V,R,I,and z' bands allow us to select color subsets and
photometric-redshift-defined shells. We show that the angular clustering of
faint red galaxies (18 < H < 20.5, I - H > 3) is an order of magnitude stronger
than that of the complete H-selected field sample. We employ three approaches
to estimate $n(z)$ in order to invert w(theta) to derive r_0. We find that our
n(z) is well described by a Gaussian with <z> = 1.2, sigma(z) = 0.15. From this
we derive a value for r_0 of 7 (+2,-1) co-moving H^{-1} Mpc at <z> = 1.2. This
is a factor of ~ 2 larger than the clustering length for Lyman break galaxies
and is similar to the expectation for early type galaxies at this epoch.


title: Adaptive binning of X-ray galaxy cluster images

abstract:
  We present a simple method for adaptively binning the pixels in an image. The
algorithm groups pixels into bins of size such that the fractional error on the
photon count in a bin is less than or equal to a threshold value, and the size
of the bin is as small as possible. The process is particularly useful for
generating surface brightness and colour maps, with clearly defined error maps,
from images with a large dynamic range of counts, for example X-ray images of
galaxy clusters. We demonstrate the method in application to data from Chandra
ACIS-S and ACIS-I observations of the Perseus cluster of galaxies. We use the
algorithm to create intensity maps, and colour images which show the relative
X-ray intensities in different bands. The colour maps can later be converted,
through spectral models, into maps of physical parameters, such as temperature,
column density, etc. The adaptive binning algorithm is applicable to a wide
range of data, from observations or numerical simulations, and is not limited
to two-dimensional data.


title: Global MHD Simulations of Cylindrical Keplerian Disks

abstract:
  This paper presents a series of global three dimensional accretion disk
simulations carried out in the cylindrical limit in which the vertical
component of the gravitational field is neglected. The simulations use a
cylindrical pseudo-Newtonian potential to model the main dynamical properties
of the Schwarzschild metric. The disks are initially constant density with a
Keplerian angular momentum distribution and contain a weak toroidal or vertical
field. These simulations reaffirm many of the conclusions of previous local
simulations. The magnetorotational instability grows rapidly and produces MHD
turbulence with a significant Maxwell stress which drives accretion.
Tightly-wrapped low-$m$ spiral waves are prominent. In some simulations radial
variations in Maxwell stress concentrate gas into rings, creating substantial
spatial inhomogeneities. There is a nonzero stress at the marginally stable
orbit which produces a small decline in specific angular momentum inside the
last stable orbit. Detailed comparisons between simulations are used to examine
the effects of computational domain and equation of state. Simulations that
begin with vertical fields have greater field amplification and higher ratios
of stress to magnetic pressure compared with those beginning with toroidal
fields. In contrast to MHD, hydrodynamics alone neither creates nor sustains
turbulence.


title: Large-Scale Simulations of Clusters of Galaxies

abstract:
  We discuss some of the computational challenges encountered in simulating the
evolution of clusters of galaxies. Eulerian adaptive mesh refinement (AMR)
techniques can successfully address these challenges but are currently being
used by only a few groups. We describe our publicly available AMR code, FLASH,
which uses an object-oriented framework to manage its AMR library, physics
modules, and automated verification. We outline the development of the FLASH
framework to include collisionless particles, permitting it to be used for
cluster simulation.


title: Hydrodynamical winds from two-temperature plasma in X-ray binaries

abstract:
  Hydrodynamical winds from a spherical two-temperature plasma surrounding a
compact object are constructed. The mass-loss rate is computed as a function of
electron temperature, optical depth and luminosity of the sphere, the values of
which can be constrained by the fitting of the spectral energy distributions
for known X-ray binary systems. The sensitive dependence of the mass loss rate
with these parameters leads to the identification of two distinct regions in
the parameter space separating wind-dominated from non wind dominated systems.
A critical optical depth, tau_c, as a function of luminosity and electron
temperature, is defined which differentiates these two regions. Systems with
optical depths significantly smaller than tau_c are wind-dominated.
  The results are applied to black hole candidate X-ray binary systems in the
hard spectral state (Cyg X-1, GX 339-4 and Nova Muscae), and it is found that
the inferred optical depth (tau) is similar to tau_c suggesting that they are
wind regulated systems. On the other hand, for X-ray binary systems containing
a neutron star (e.g., Cyg X-2) tau is much larger than tau_c indicating the
absence of significant hydrodynamical winds.


title: Models of Cuspy Triaxial Galaxies

abstract:
  We construct numerical models of mildly triaxial elliptical galaxies with
central density cusps. Using a technique we call ``adiabatic squeezing'', we
begin with a spherical gamma=1 Hernquist model and apply a drag to the
velocities of the particles along each principle axis. The final models are
stable in isolation, preserving their density structure and figure shape over
many dynamical timescales. The density profile and axial ratios compare well to
the observed properties of elliptical galaxies. The orbital structure of these
models show a mixture of tubes, boxes, and boxlets, as expected for triaxial
systems, with very few chaotic orbits. These N-body realizations of cuspy
triaxial galaxies provide a basis for the study of the dynamical evolution of
elliptical galaxies.


title: B1359+154: A Six Image Lens Produced by a z=1 Compact Group of Galaxies

abstract:
  HST V and I-band observations show that the gravitational lens B1359+154
consists of six images of a single z_s=3.235 radio source and its star-forming
host galaxy, produced by a compact group of galaxies at z_l = 1. VLBA
observations at 1.7 GHz strongly support this conclusion, showing six compact
cores with similar low-frequency radio spectra. B1359+154 is the first example
of galaxy-scale gravitational lensing in which more than four images are
observed of the same background source. The configuration is due to the unique
lensing mass distribution: three primary lens galaxies lying on the vertices of
a triangle separated by 0.7 arcsec (4/h kpc), inside the 1.7 arcsec diameter
Einstein ring defined by the radio images. The gravitational potential has
additional extrema within this triangle, creating a pair of central images that
supplement the ``standard'' four-image geometry of the outer components. Simple
mass models consisting of three lens galaxies constrained by HST and VLBA
astrometry naturally reproduce the observed image positions but must be
finely-tuned to fit the flux densities.


title:
MACHO Project Limits on Black Hole Dark Matter in the 1-30 Solar Mass
  Range

abstract:
  We report on a search for long duration microlensing events towards the Large
Magellanic Cloud. We find none, and therefore put limits on the contribution of
high mass objects to the Galactic dark matter. At 95% confidence level we
exclude objects in the mass range 0.3 solar masses to 30.0 solar masses from
contributing more than 4 times 10^11 solar masses to the Galactic halo.
Combined with earlier results, this means that objects with masses under 30
solar masses cannot make up the entire dark matter halo if the halo is of
typical size. For a typical dark halo, objects with masses under 10 solar
masses contribute less than 40% of the dark matter.


title: Presupernova Evolution with Improved Rates for Weak Interactions

abstract:
  Recent shell-model calculations of weak-interaction rates for nuclei in the
mass range A = 45 - 65 have resulted in substantial revisions to the hitherto
standard set of Fuller, Fowler, & Newman (FFN). In particular, key
electron-capture rates, such as that for Co60 are much smaller. We consider
here the effects of these revised rates on the presupernova (post-oxygen
burning) evolution of massive stars in the mass range 11 to 40 M_sun. Moreover,
we include, for the first time in models by our group, the effects of modern
rates for beta-decay in addition to electron capture and positron emission.
Values for the central electron mole number at the time of iron core collapse
in the new models are typically larger, by delta Y_e = 0.005 to 0.015, than
those of Woosley & Weaver 1995, with a tendency for the more massive models to
display larger differences. About half of this change is a consequence of
including beta-decay; the other half, result of the smaller rates for electron
capture. Unlike what might be expected solely on basis of the larger Y_e's, the
new iron core masses are systematically smaller owing to a decrease in the
entropy in the outer iron core. The changes in iron core mass range from zero
to 0.1 M_sun. We also observe, as predicted by Aufderheide et al. (1994), a
tendency towards beta-equilibrium just prior to the collapse of the core, and
the subsequent loss of that equilibrium as core collapse proceeds. We discuss
the key weak reaction rates, both beta-decay and electron-capture, responsible
for the evolution of Y_e and make suggestions for future measurements.


title: Lower Limits on Lorentz Factors in Gamma Ray Bursts

abstract:
  As is well-known, the requirement that gamma ray bursts (GRB's) be optically
thin to high energy photons yields a lower limit on the Lorentz factor (\gamma)
of the expansion. In this paper, we provide a simple derivation of the lower
limit on \gamma due to the annihilation of photon pairs, and correct the errors
in some of the previous calculations of this limit. We also derive a second
limit on \gamma due to scattering of photons by pair-created electrons and
positrons. For some bursts, this limit is the more stringent. In addition, we
show that a third limit on \gamma, which is obtained by considering the
scattering of photons by electrons which accompany baryons, is nearly always
less important than the second limit. Finally, we evaluate these limits for a
number of bursts.


title:
Lyman alpha line formation in starbursting galaxies I. Moderately thick,
  dustless, and static HI media

abstract:
  We investigate the Lyman alpha line transfer in nearby and high redshift
starbursting galaxies, where the effect of high optical depths and the role of
dust in the scattering medium are expected to be conspicuous and should be
treated in a very careful manner. We present our first results in dustless,
static, and uniform HI media with moderate Lyman alpha line center optical
depths \tau_0=10^{3-6}. We assume that the temperatures of media to be
T=10^{1-4}K, and use a Monte Carlo technique. We investigate the basic
processes of the line transfer and confirm the criterion of a\tau_0>10^3 for
the validity of diffusion approximation suggested by Neufeld in 1990, where $a$
is the Voigt parameter. Adopting the model suggested by Tenorio-Tagle et al.,
we performed calculations on the Lyman alpha line formation for each
evolutionary stage of an expanding supershell. The emergent Lyman alpha
profiles are characterized by the double peaks and the absorption trough at the
line center. We found that the absorption troughs expected in most of the
evolutionary stages are not wide enough to be observed with current
instruments. However, the absorption trough in the Lyman alpha emission profile
from an expanding recombining supershell can be marginally detected.


title: The red stellar population in NGC 1569

abstract:
  We present HST NICMOS photometry of the resolved stellar population in NGC
1569. The CMD in the F110W and F160W photometric bands contains ~2400 stars
with a formal photometric error < 0.1 mag down to J~23.5 and H~22.5. We
describe the data processing which is required to calibrate the instrumental
peculiarities of NICMOS. Two different packages for PSF-fitting photometry are
used to strengthen the photometric results in the crowded stellar field of NGC
1569. The resulting CMD is discussed in terms of the major evolutionary
properties of the resolved stellar populations. For a distance modulus of 26.71
and a reddening E(B-V)=0.56, our CMD samples stars down to ~0.8 Mo,
corresponding to look-back times > 15 Gyr. This is clear indication of SF
activity spanning an entire Hubble time. The metallicity of the reddest RGB
stars is in better agreement with Z=0.004 as measured in HII regions, than with
Z=0.0004 as expected from the stellar ages. The presence of - yet undetected -
very metal-poor stars embedded in the stellar distribution around J=22.75 and
J-H=1.15 is, however, not ruled out. The youngest stars (< 50 Myr) are
preferentially found around the two central super star clusters, whereas the
oldest population has a more uniform spatial distribution. A SFR per unit area
of 1 Mo yr*(-1) kpc*(-2) and a mass formed in stars of ~ 1.4x10*6 Mo in the
last 50 Myr are derived from the CMD. The NIR CMD places strong constraints on
the lower limit of the onset of SF in NGC 1569. The exceptionally high crowding
in the NICMOS images of NGC 1569 is a challenge for the photometric analysis.
As a result, optical and NIR images of NGC 1569 sample different populations
and cannot be cross-correlated. Nevertheless, we demonstrate the consistency of
the SF histories derived from the optical and NIR CMDs.


title:
Star Formation-Regulated Growth of Black Holes in Protogalactic
  Spheroids

abstract:
  The observed relation between central black hole mass and spheroid velocity
dispersion is interpreted in terms of a self-regulation model that incorporates
a viscous Keplerian accretion disk to feed the black hole, embedded in a
massive, self-gravitating star forming disk that eventually populates the
spheroid. The model leads to a constant ratio between black hole mass and
spheroid mass which is equal to the inverse of the critical Reynolds number for
the onset of turbulence in the accretion disk surrounding the central black
hole. Applying the fundamental plane correlation for spheroids, we find that
the black hole mass has a power-law dependence on the spheroid velocity
dispersion with a slope in the range of 4-5. We explain the larger scatter in
the Magorrian relation with respect to the black hole mass-spheroid velocity
dispersion relationship as a result of secular evolution of the spheroid that
primarily affects its luminosity and to a much lesser extent its velocity
dispersion.


title: Large scale grain mantle disruption in the Galactic Center

abstract:
  We present observations of C2H5OH toward molecular clouds in Sgr A, Sgr B2
and associated with thermal and non-thermal features in the Galactic center.
C2H5OH emission in Sgr A and Sgr B2 is widespread, but not uniform. C2H5OH
emission is much weaker or it is not detected in some molecular clouds in both
complexes, in particular those with radial velocities between 70 and 120 km/s.
While most of the clouds associated with the thermal features do not show
C2H5OH emission, that associated with the Non-Thermal Radio Arc shows emission.
The fractional abundance of C2H5OH in most of the clouds with radial velocities
between 0 and 70 km/s in Sgr A and Sgr B2 is relatively high, of few 1e-8. The
C2H5OH abundance decreases by more than one order of magnitude (aprox. 1e-9) in
the clouds associated with the thermal features. The large abundance of C2H5OH
in the gas-phase indicates that C2H5OH has formed in grains and released to
gas-phase by shocks in the last aprox. 1e5 years.


title: Argon and Silicon abundances in the damped Ly-alpha system I Zw 18

abstract:
  We show that the difference between the Ar and Si relative abundance ratio
derived from FUSE absorption spectra and from the HII regions of I Zw 18 is a
consequence of the microturbulent analysis applied to the absorption spectra.
FUSE observations were performed with a large entrance aperture which fully
covered the galaxy. This means that the observed profiles are averaged over the
full body of I Zw 18, implying that large-scale velocity fields influence the
absorption - line profiles. Taking this into account, we show that the
absorption spectra are consistent with the same metal abundances as those
derived from the HII regions. It follows that no significant ionization
correction as suggested by Izotov and collaborators to describe metal contents
in damped Ly-alpha systems (DLA) is required to model abundances in the neutral
gas of I Zw 18 (a local DLA system). Using a mesoturbulent approach and
applying the generalized radiative transfer equation to the ArI1048 and
SiII1020 lines observed by Vidal-Madjar et al., we found that the profiles may
be reproduced with log (Ar/Si) ~= - 0.8 and N(SiII) ~= 4 10^{15} cm^{-2}.


title: The Formation and Evolution of Multiple Star Systems

abstract:
  Multiple systems play an important role in the evolution of star clusters.
First we discuss several formation mechanisms which depend on the presence of
binaries, either primordial or of dynamical origin. Hierarchical configurations
are often stable over long times and yet may experience evolution of the
internal orbital parameters. We describe an attempt to model the eccentricity
change induced by the outer component using an averaging method, together with
the effects due to tidal dissipation and apsidal motion acting on the inner
binary. This treatment is adopted for systems with high induced eccentricity
which gives rise to some interesting outcomes of significant period shrinkage.


title: The Nature of Jets: Evidence from Circular Polarization Observations

abstract:
  We review recent observations of circularly polarized radiation from AGN made
with the VLBA and with the ATCA. We also discuss briefly the detections of the
Galactic sources Sag A* and SS433. The origin of the circular polarization is
still an open question in most cases, and we discuss four possible mechanisms.
Detectable circular polarization is a common property of quasars, but not of
radio galaxies, and is always associated with the compact core. There is
growing evidence that the sign of the circular polarization stays the same over
at least two or three decades in time, suggesting it is a fundamental property
of the jet.


title:
Properties and nature of Be stars. XX. Binary nature and orbital
  elements of gamma Cas

abstract:
  An analysis of accurate radial velocities (RVs) of the Be star gamma Cas from
295 Reticon spectrograms secured between October 1993 and May 2000 allowed us
to prewhiten the RVs for the long-term changes and to obtain the first orbital
RV curve of this star. The orbital period is 203d59 and the orbit has an
eccentricity of 0.26. The orbital motion is detectable even in the published
velocities, based on photographic spectra. This implies that gamma Cas is a
primary component of a spectroscopic binary. The secondary has a mass of about
1 solar mass, appropriate for a white dwarf or a neutron star, but it could
also be a normal late-type dwarf. The ultimate solution of the dispute whether
the observed X-ray emission is associated with the secondary or with the
primary will need further dedicated studies.


title: Quark stars in Low-Mass X-ray Binaries: for and against

abstract:
  It has been suggested that both X-ray bursters and millisecond radio pulsars
may be strange (quark) stars, rather than neutron stars. Confirming (or
rejecting) this suggestion may require knowing what role strong-field effects
of general relativity play in the accretion flow of the compact X-ray source in
low-mass X-ray binaries (LMXBs). We discuss the range of rotational and orbital
frequencies, and of masses expected in various models of strange stars, and
compare them with observational constraints, suggested by the observed
frequencies of kHz QPOs. We explain why future observations of transients (such
as SAX J~1808.4-3658) may be crucial to understanding the precise nature of the
accreting source. For flattened (e.g., rapidly rotating) distributions of
matter, an innermost (marginally) stable orbit may be present even if
relativistic effects are negligible. Depending on the stellar rotation rate,
the same value of orbital frequency in the innermost stable orbit (say, 0.9
kHz) can correspond to a star of mass equal to $2.4M_\odot$, $1.4M_\odot$,
$0.1M_\odot$, $0.01M_\odot$, or less.


title:
Chandra detection of reflected X-ray emission from the type 2 QSO in
  IRAS 09104+4109

abstract:
  We present X-ray imaging spectroscopy of the extremely luminous infrared
galaxy IRAS 09104+4109 (z=0.442) obtained with the Chandra X-ray Observatory.
With the arcsec resolution of Chandra, an unresolved source at the nucleus is
separated from the surrounding cluster emission. A strong iron K line at 6.4
keV on a very hard continuum is detected from the nuclear source, rendering
IRAS 09104+4109 the most distant reflection-dominated X-ray source known.
Combined with the BeppoSAX detection of the excess hard X-ray emission, it
provides further strong support to the presence of a hidden X-ray source of
quasar luminosity in this infrared galaxy. Also seen is a faint linear
structure to the North, which coincides with the main radio jet. An X-ray
deficit in the corresponding region suggests an interaction between the cluster
medium and the jet driven by the active nucleus.


title:
General relativistic spectra of accretion disks around rotating neutron
  stars

abstract:
  General relativistic spectra from accretion disks around rotating neutron
stars in the appropriate space-time geometry for several different equation of
state, spin rates and mass of the compact object have been computed. The
analysis involves the computation of the relativistically corrected radial
temperature profiles and the effect of Doppler and gravitational red-shifts on
the spectra. Light bending effects have been omitted for simplicity. The
relativistic spectrum is compared with the Newtonian one and it is shown that
the difference between the two is primarily due to the different radial
temperature profile for the relativistic and Newtonian disk solutions.
  To facilitate direct comparison with observations, a simple empirical
function has been presented which describes the numerically computed
relativistic spectra well. This empirical function (which has three parameters
including normalization) also describes the Newtonian spectrum adequately. Thus
the function can in principle be used to distinguish between the two. In
particular, the best fit value of one of the parameters ($\beta$-parameter)
$\approx 0.4$ for the Newtonian case, while it ranges from 0.1 to 0.35 for
relativistic case depending upon the inclination angle, EOS, spin rate and mass
of the neutron star. Constraining this parameter by fits to future
observational data of X-ray binaries will indicate the effect of strong gravity
in the observed spectrum.


title:
Molecular Gas in the Powerful Radio Galaxies 3C~31 and 3C~264: Major or
  Minor Mergers?

abstract:
  We report the detection of $^{12}$CO~($1 \to 0$) and $^{12}$CO~($2 \to 1$)
emission from the central regions ($\lesssim 5$--$10 {\rm kpc}$) of the two
powerful radio galaxies 3C~31 and 3C~264. Their individual CO emission exhibits
a double-horned line profile that is characteristic of an inclined rotating
disk with a central depression at the rising part of its rotation curve. The
inferred disk or ring distributions of the molecular gas is consistent with the
observed presence of dust disks or rings detected optically in the cores of
both galaxies. For a CO to H$_2$ conversion factor similar to that of our
Galaxy, the corresponding total mass in molecular hydrogen gas is $(1.3 \pm
0.2) \times 10^9 {\rm M_{\odot}}$ in 3C~31 and $(0.31 \pm 0.06) \times 10^9
{\rm M_{\odot}}$ in 3C~264. Despite their relatively large molecular-gas masses
and other peculiarities, both 3C~31 and 3C~264, as well as many other powerful
radio galaxies in the (revised) 3C catalog, are known to lie within the
fundamental plane of normal elliptical galaxies. We reason that if their gas
originates from the mergers of two gas-rich disk galaxies, as has been invoked
to explain the molecular gas in other radio galaxies, then both 3C~31 and
3C~264 must have merged a long time (a few billion years or more) ago but their
remnant elliptical galaxies only recently (last tens of millions of years or
less) become active in radio. Instead, we argue that the cannibalism of
gas-rich galaxies provides a simpler explanation for the origin of molecular
gas in the elliptical hosts of radio galaxies. Given the transient nature of
their observed disturbances, these galaxies probably become active in radio
soon after the accretion event when sufficient molecular gas agglomerates in
their nuclei.


title:
Peculiarities of anisotropy and polarization as an indicator of noises
  in the CMB maps

abstract:
  We discuss some new problems of the modern cosmology which arose after the
BOOMERANG and MAXIMA-1 successful missions. Statistics of high peaks of the CMB
anisotropy is analyzed and we discuss possible inner structure of such peaks in
the observational data of future MAP and PLANCK missions. We have investigated
geometrical and statistical properties of the CMB polarization around such high
isolated peaks of anisotropy in the presence of a polarized pixel noise and
point sources. The structure of polarization fields in the vicinity of singular
points with zero polarization is very sensitive to the level of pixel noises
and point sources in the CMB maps.


title: The M31 Globular Cluster Luminosity Function

abstract:
  We combine our compilation of photometry of M31 globular cluster and probable
cluster candidates with new near-infrared photometry for 30 objects. Using
these data we determine the globular cluster luminosity function (GCLF) in
multiple filters for the M31 halo clusters. We find a GCLF peak and dispersion
of V_0^0=16.84 +/-0.11, sigma_t=0.93 +/- 0.13 (Gaussian sigma = 1.20 +/- 0.14),
consistent with previous results. The halo GCLF peak colors (e.g., B^0_0 -
V^0_0) are consistent with the average cluster colors. We also measure V-band
GCLF parameters for several other subsamples of the M31 globular cluster
population. The inner third of the clusters have a GCLF peak significantly
brigher than that of the outer clusters (delta V =~ 0.5mag). Dividing the
sample by both galacticentric distance and metallicity, we find that the GCLF
also varies with metallicity, as the metal-poor clusters are on average 0.36
mag fainter than the metal-rich clusters. Our modeling of the catalog selection
effects suggests that they are not the cause of the measured differences, but a
more complete, less-contaminated M31 cluster catalog is required for
confirmation. Our results imply that dynamical destruction is not the only
factor causing variation in the M31 GCLF: metallicity, age, and cluster initial
mass function may also be important.


title:
Off-Beam Gamma-Ray Pulsars and Unidentified EGRET Sources in the Gould
  Belt

abstract:
  We investigate whether gamma-ray pulsars viewed at a large angle to the
neutron star magnetic pole could contribute to the new population of galactic
unidentified EGRET sources associated with the Gould Belt. The faint, soft
nature of these sources is distinctly different from both the properties of
unidentified EGRET sources along the galactic plane and of the known gamma-ray
pulsars. We explore the possibility, within the polar cap model, that some of
these sources are emission from pulsars seen at lines of sight that miss both
the bright gamma-ray cone beams and the radio beam. The off-beam gamma-rays
come from high-altitude curvature emission of primary particles, are radiated
over a large solid angle and have a much softer spectrum than that of the main
beams. We estimate that the detectability of such off-beam emission is about a
factor of 4-5 higher than that of the on-beam emission. At least some of the
radio-quiet Gould Belt sources detected by EGRET could therefore be such
off-beam gamma-ray pulsars. GLAST should be able to detect pulsations in most
of these sources.


title: Origin of Cosmic Radiation

abstract:
  I give a brief overview of cosmic ray physics, highlighting some key
questions and how they will be addressed by new experiments.


title: High Energy Neutrino Astronomy - the cosmic-ray connection

abstract:
  Several of the models for origin of the highest energy cosmic rays also
predict significant neutrino fluxes. A common factor of the models is that they
must provide sufficient power to supply the observed energy in the
extragalactic component of the cosmic radiation. The assumption that a
comparable amount of energy goes into high-energy neutrinos allows a
model-independent estimate of the neutrino signal that may be expected.


title: Heavy sterile neutrinos - what they can be and what they can't

abstract:
  We review current astrophysical bounds on MeV sterile neutrinos, and then we
discuss why a sterile keV neutrino is a natural warm dark matter candidate.


title: Discovery of the Bright Trans-Neptunian Object 2000 EB173

abstract:
  We describe the discovery circumstances and photometric properties of 2000
EB173, now one of the brightest trans-Neptunian objects (TNOs) with opposition
magnitude m_R=18.9 and also one of the largest Plutinos, found with the
drift-scanning camera of the QUEST Collaboration, attached to the 1-m Schmidt
telescope of the National Observatory of Venezuela. We measure B-V = 0.99 +/-
0.14 and V-R = 0.57 +/- 0.05, a red color observed for many fainter TNOs. At
our magnitude limit m_R = 20.1 +/- 0.20, our single detection reveals a sky
density of 0.015 (+0.034, -0.012) TNOs per deg^2 (the error bars are 68%
confidence limits), consistent with fainter surveys showing a cumulative number
proportional to 10^0.5m_R. Assuming an inclination distribution of TNOs with
FWHM exceeding 30 deg, it is likely that one hundred to several hundred objects
brighter than m_R=20.1 remain to be discovered.


title: The local Hubble flow: a manifestation of dark energy

abstract:
  Our local environment at $r<10$ Mpc expands linearly and smoothly, as if
ruled by a uniform matter distribution, while observations show the very clumpy
local universe. This is a long standing enigma in cosmology. We argue that the
recently discovered vacuum or quintessence (dark energy (DE) component with the
equation of state $p_Q = w \rho_Q c^2$, $w \in [-1,0)$) from observations of
the high-redshift universe may also manifest itself in the properties of the
very local Hubble flow. We introduce the concept of the critical distance $r_Q$
where the repulsive force of dark energy starts to dominate over the gravity of
a mass concentration. For the Local Group $r_Q$ is about 1.5 Mpc. Intriguingly,
at the same distance 1.5 Mpc the linear and very "cold" Hubble flow emerges,
with about the global Hubble constant. We also consider the critical epoch
$t_Q$, when the DE antigravity began to dominate over the local matter gravity
for a galaxy which at the present epoch is in the local DE dominated region.
Our main result is that the homogeneous dark energy component, revealed by SNIa
observations, resolves the old confrontation between the local Hubble flow and
local highly non-uniform, fractal matter distribution. It explains why the
Hubble law starts on the outskirts of the Local Group, with the same Hubble
constant as globally and with a remarkably small velocity dispersion.


title: What is the Highest Plausible Redshift of Luminous Quasars?

abstract:
  The recent discoveries of luminous quasars at high redshifts imply that black
holes more massive than a few billion solar masses have been assembled already
when the universe was less than a billion years old. We show that the existence
of these black holes is not surprising in popular hierarchical models of
structure formation. For example, the black hole needed to power the quasar
SDSS 1044-0125 at redshift z=5.8 can arise naturally from the growth of stellar
mass seeds forming at z>10, when typical values are assumed for the radiative
accretion efficiency and the bolometric accretion luminosity in Eddington
units. Nevertheless, SDSS 1044-0125 yields a non-trivial constraint on a
combination of these parameters. Extrapolating our model to future surveys, we
derive the highest plausible redshift for quasars which are not lensed or
beamed, as a function of their apparent magnitude. We find that at a limiting
magnitude of K(AB)=20, quasar surveys can yield strong constraints on the
growth of supermassive black holes out to z=10.


title: Stellar Pollution in the Solar Neighborhood

abstract:
  We study spectroscopically determined iron abundances of 642 solar-type stars
to search for the signature of accreted iron-rich material. We find that the
metallicity [Fe/H] of a subset of 466 main sequence stars, when plotted as a
function of stellar mass, mimics the pattern seen in lithium abundances in open
clusters. Using Monte Carlo models we find that, on average, these stars have
accreted about 0.4 Earth masses of iron while on the main sequence. A much
smaller sample of 19 stars in the Hertzsprung gap, which are slightly evolved
and whose convection zones are significantly more massive, have lower average
[Fe/H], and their metallicity shows no clear variation with stellar mass. These
findings suggest that terrestrial-type material is common around solar type
stars.


title: Extended quintessence and the primordial helium abundance

abstract:
  In extended quintessence models, a scalar field which couples to the
curvature scalar R provides most of the energy density of the universe. We
point out that such models can also lead naturally to a decrease in the
primordial abundance of helium-4, relieving the tension which currently exists
between the primordial helium-4 abundance inferred from observations and the
amount predicted by Standard Big Bang Nucleosynthesis (SBBN) corresponding to
the observed deuterium abundance. Using negative power-law potentials for the
quintessence field, we determine the range of model parameters which can lead
to an interesting reduction in the helium-4 abundance, and we show that it
overlaps with the region allowed by other constraints on extended quintessence
models.


title: How to get less helium and more neutrinos from BBN

abstract:
  We discuss BBN in the presence of a non-minimally coupled quintessence model.
In some of these models, the gravitational constant and cosmic expansion rate
are smaller than standard model predicts. The Helium abundance is then smaller,
possibly resolve the marginal disagreement between theory and observation.
Furthermore, the constraint on neutrino species may also be relaxed.


title: The Helium abundance problem and non-minimally coupled quintessence

abstract:
  There is a tension between observed Helium abundance and the prediction of
the standard Big Bang Nucleosynthesis. We show that non-minimally quintessence
model may help to reduce this tension between theory and observation.


title:
Compton Scattering in Static and Moving Media. II. System-Frame
  Solutions for Spherically Symmetric Flows

abstract:
  I study the formation of Comptonization spectra in spherically symmetric,
fast moving media in a flat spacetime. I analyze the mathematical character of
the moments of the transfer equation in the system-frame and describe a
numerical method that provides fast solutions of the time-independent radiative
transfer problem that are accurate in both the diffusion and free-streaming
regimes. I show that even if the flows are mildly relativistic (V~0.1, where V
is the electron bulk velocity in units of the speed of light), terms that are
second-order in V alter the emerging spectrum both quantitatively and
qualitatively. In particular, terms that are second-order in V produce
power-law spectral tails, which are the dominant feature at high energies, and
therefore cannot be neglected. I further show that photons from a static source
are upscattered by the bulk motion of the medium even if the velocity field
does not converge. Finally, I discuss these results in the context of radial
accretion onto and outflows from compact objects.


title: On the Nature of AX J2049.6+2939 and AX J2050.0+2914

abstract:
  AX J2049.6+2939 is a compact X-ray source in the vicinity of the southern
blow-up region of the Cygnus Loop supernova remnant (Miyata et al. 1998a). This
source was the brightest X-ray source inside the
  Cygnus Loop observed during the ASCA survey project. The X-ray spectrum was
well fitted by a power-law function with a photon index of $-2.1
  \pm 0.1$. Short-term timing analysis was performed and no coherent pulsation
was found. Follow-up observations with ASCA have revealed a large variation in
X-ray intensity by a factor of $\simeq$ 50, whereas the spectral shape did not
change within the statistical uncertainties. In the second ASCA observation, we
found another X-ray source, AX J2050.0+2941, at the north east of AX
  J2049.6+2939. During the three ASCA observations, the X-ray intensity of AX
J2050.0+2941 varied by a factor of $\simeq$4. No coherent pulsations could be
found for AX J2050.0+2941.
  We have performed optical photometric and spectroscopic observations in the
vicinity of AX J2049.6+2939 at the Kitt Peak National Observatory
  (KPNO). As a result, all objects brighter than $B$-band magnitude of 22 in
the error box can be identified with normal stars. Combined with the
  X-ray results and the fact that there are no radio counterparts, AX
  J2049.6+2939 is not likely to be either an ordinary rotation-powered pulsar
or an AGN. The nature of AX J2049.6+2939 is still unclear and further
observations over a wide energy band are strongly required.
  As to AX J2050.0+2941, the long-term X-ray variability and the radio
counterpart suggests that it is an AGN.


title: Optical and infrared interferometry

abstract:
  Interferometric techniques are at the forefront of modern astronomical
instrumentation. A new generation of instruments are either operating or
nearing completion, including arrays of small telescopes as well as the ``big
guns'' (VLTI and Keck). A number of space interferometers for the detection of
extra-solar planets are also being planned. I review the current state of play
and describe the latest developments in the field.


title:
Multi-wavelength observations of the red giant R Doradus with the MAPPIT
  interferometer

abstract:
  We present visibility measurements of the nearby Mira-like star R Doradus
taken over a wide range of wavelengths (650-990 nm). The observations were made
using MAPPIT (Masked APerture-Plane Interference Telescope), an interferometer
operating at the 3.9-m Anglo-Australian Telescope. We used a slit to mask the
telescope aperture and prism to disperse the interference pattern in
wavelength. We observed in R Dor strong decreases in visibility within the TiO
absorption bands. The results are in general agreement with theory but differ
in detail, suggesting that further work is needed to refine the theoretical
models.


title: Time Evolution of Cosmic-Ray Modified Plane Shocks

abstract:
  We have developed a novel computer code designed to follow the evolution of
cosmic-ray modified shocks, including the full momentum dependence of the
particles for a realistic diffusion coefficient model. In this form the problem
is technically very difficult, because one needs to cover a wide range of
diffusive scales, beginning with those slightly larger than the physical shock
thickness. With most finite difference schemes for Euler's equations the
numerical shock thickness is at least one zone across, so this provides a lower
bound on the physical scale for diffusive transport computation. Our code uses
sub-zone shock tracking and multi-level adaptive mesh refinement to provide
enhanced spatial resolution around shocks at modest cost compared to the coarse
grid and vastly improved cost effectiveness compared to a uniform, highly
refined grid. We present and discuss the implications from our initial results.


title: Cosmic Microwave Background in Closed Multiply Connected Universes

abstract:
  We have investigated the cosmic microwave background (CMB) anisotropy in
closed multiply connected universes
  (flat and hyperbolic) with low matter density. We show that the COBE
constraints on these low matter density models with non-trivial topology are
less stringent since a large amount of CMB anisotropy on large angular scales
can be produced due to the decay of the gravitational potential at late time.


title: Implications of 21cm observations for damped Ly-$\alpha$ systems

abstract:
  We present Giant Metrewave Radio Telescope HI 21cm absorption observations,
of candidate and confirmed damped Lyman-$\alpha$ systems (DLAS). The derived
spin temperatures (T_s) are in all cases $\sim 1000$ K or higher. We have also
collated from the literature a list of DLAS for which 21cm observations exist,
and discuss their implications for the nature of the absorbers.
  A cross-comparison of the 21cm profiles with low ionization metal profiles
shows that the 21cm absorption coincides in velocity with the deepest metal
line feature. This is consistent with models in which the deep metal line
features arise from discrete clouds but not with models where the deepest
features are the result of velocity crowding.
  We also find that the typical derived spin temperatures of DLAS are
considerably higher than those in the Galaxy or nearby spirals. The only
exceptions are DLAS which are known to be associated with the disks of spirals;
these do, in fact, show low spin temperatures. In a multi-phase medium,the
derived T_s is a weighted average of the temperatures of the individual phases.
High derived T_s values are hence to be expected from small, low metallicity
objects, since these objects should have a lower fraction of the cold phase in
their ISM as compared to large galaxies. The high T_s in DLAS is hence
consistent with their observed low metallicities as well as with recent
observations that DLAS are also associated with dwarf/LSB galaxies. Finally, we
suggest that the following trend may be identified: at low redshift, damped
absorption arises from a range of systems, including spiral galaxy disks,
while, at high redshift, absorption occurs predominantly in smaller systems.
(Abridged)


title:
Magnetocentrifugal acceleration of plasma in a nonaxisymmetric
  magnetosphere

abstract:
  Violation of the axial synnetry of a magnetic field essentially modifies the
physics of the plasma outflow in the magnetosphere of rotating objects. In
comparison to the axisymmetric outflow, two new affects appear: more efficient
magnetocentrifugal acceleration of the plasma along particular field lines and
generation of MHD waves. Here, we use an ideal MHD approximation to study the
dynamics of a cold wind in the nonaxisymmetric magnetosphere. We obtain a
self-consistent analytical solution of the problem of cold plasma outflow from
a slowly rotating star with a slightly nonaxisymmetric magnetic field using
perturbation theory. In the axisymmetric (monopole-like) magnetic field, the
first term in the expansion of the terminating energy of the plasama in powers
of $\Omega$ is proportional to $\Omega^4$, where $\Omega$ is the angular
velocity of the central source. Violation of the axial symmetry of the magnetic
field crucially changes this dependence. The first correction to the energy of
the plasma becomes proportional to $\Omega$. Efficient magnetocentrifugal
acceleration occurs along the field lines curved initially in the direction of
the rotation. I argue that all necessary conditions for the efficient
magnetocentrifugal acceleration of the plasma exist in the radio pulsar
megnetosphere. We calculated the first correction of the rotational losses due
to the generation of the MHD waves and analysed the plasma acceleration by
these waves.


title: Variable X-ray Absorption in the Seyfert 2 Galaxy Mrk 348

abstract:
  We present RXTE monitoring observations of the Seyfert 2 galaxy Mrk 348
spanning a 6 month period. The time-averaged spectrum in the 3-20 keV band
shows many features characteristic of a Compton-thin Seyfert 2 galaxy, namely a
hard underlying power-law continuum (photon index = 1.8) with heavy soft X-ray
absorption (N_h ~ 10^23 cm^-2) plus measureable iron line emission (equivalent
width ~ 100 eV) and, at high energy, evidence for a reflection component (R <
1). During the first half of the monitoring period the X-ray continuum flux
from Mrk 348 remained relatively steady. However this was followed by a
significant brightening of the source (by roughly a factor of 4) with the
fastest change corresponding to a doubling of its X-ray flux on a timescale of
about 20 days. The flux increase was accompanied by a marked softening of X-ray
spectrum most likely attributable to a factor 3 decline in the intrinsic
line-of-sight column density. In contrast the iron line and the reflection
components showed no evidence of variability. These observations suggest a
scenario in which the central X-ray source is surrounded by a patchy
distribution of absorbing material located within about a light-week of the
nucleus of Mrk 348. The random movement of individual clouds within the
absorbing screen, across our line of sight, produces substantial temporal
variations in the measured column density on timescales of weeks to months and
gives rise to the observed X-ray spectral variability. However, as viewed from
the nucleus the global coverage and typical thickness of the cloud layer
remains relatively constant.


title: The broad-band spectrum of 3C 120 observed by BeppoSAX

abstract:
  We study a broad-band X-ray observation by BeppoSAX of the broad-line radio
galaxy 3C 120. The primary X-ray continuum is well described by a power law
with the photon index of Gamma=1.85+-0.05 and a high-energy break or a cutoff.
The obtained e-folding energy of about100-300 keV corresponds to kT of about 50
keV in thermal-Compton models. A soft X-ray excess is found at a statistical
significance of >98%$ Our physical best-fit model of the excess is
optically-thin emission from an extended plasma (with a luminosity of 2% of the
total X-ray luminosity), which interpretation is supported by an independent
finding of an extended soft X-ray halo in 3C 120. We find a moderate Compton
reflection component together with a moderately broad Fe K alpha line with an
equivalent width fully consistent with the strength of reflection, indicating
their origin in an optically-thick accretion disk extending relatively close to
the central black hole. We observe strong spectral variability during our 2-day
observation with Gamma varying from 1.7 to 2.0 and correlated with the soft
X-ray flux. The variability is very well modeled by thermal Comptonization in a
hot plasma irradiated by a variable UV flux. Both a hot patchy corona
outflowing with a mildly relativistic velocity away from a cold disk and a hot
inner accretion flow overlapping with the cold disk are viable geometries. The
presence of an outflow in the first case and an overlap between the hot and
cold phases in the second case are required by energy balance and the observed
strength of Compton reflection.


title:
Inhomogeneous Big Bang Nucleosynthesis and the High Baryon Density
  Suggested by Boomerang and MAXIMA

abstract:
  The recent Boomerang and MAXIMA data on the cosmic microwave background
suggest a large value for the baryonic matter density of the universe, omega_b
= 0.03. This density is larger than allowed by standard big bang
nucleosynthesis theory and observations on the abundances of the light
elements. We explore here the possibility of accommodating this high density in
inhomogeneous big bang nucleosynthesis (IBBN). It turns out that in IBBN the
observed D and Y_p values are quite consistent with this high density. However,
IBBN is not able to reduce the 7Li yield by more than about a factor of two.
For IBBN to be the solution, one has to accept that the 7Li plateau in
population II halo stars is depleted from the primordial abundance by at least
a factor of two.


title: The effects of vertical outflows on disk dynamos

abstract:
  We consider the effect of vertical outflows on the mean-field dynamo in a
thin disk. These outflows could be due to winds or magnetic buoyancy. We
analyse both two-dimensional finite-difference numerical solutions of the
axisymmetric dynamo equations and a free-decay mode expansion using the
thin-disk approximation. Contrary to expectations, a vertical velocity can
enhance dynamo action, provided it is not too strong. In the nonlinear regime
this can lead to super-exponential growth of the magnetic field.


title:
The First Complete and Fully Sampled HI Survey of the Tidal Arms of the
  Magellanic System

abstract:
  The LMC, SMC, and the Milky Way are a spectacular set of interacting
galaxies. The prominent tidal arms which protrude from the Magellanic Clouds
extend for tens of kiloparsecs and cover a large part of the southern sky.
These arms, and the Magellanic Clouds themselves, are therefore a highly
suitable subject for the detailed investigation of an interacting galaxy
system. We present the first results of the Parkes narrow-band HI survey of the
tidal arms of the Magellanic System. It is the first fully sampled, spatially
complete survey of this system. The data provide information on the column
density distribution and the variation of the shape of the line profiles over
the extent of the tidal features. We present a cloud catalogue of the tidal
features of the Magellanic System and discuss the distribution relative to the
observational parameters longitude, latitude and radial velocity (v_LSR and
v_GSR). We find a new stream-like feature that is most likely related to the
Leading Arm. Detailed investigation reveals a number of clouds showing a
cometary appearance in the position-velocity representation (so-called
head-tail structures). These head-tail structures are interpreted as clouds
that are currently interacting with an ambient medium.


title: Chandra imaging of the X-ray core of Abell 1795

abstract:
  We report the discovery of a 40 arcsec long X-ray filament in the core of the
cluster of galaxies A1795. The feature coincides with an Halpha+NII filament
found by Cowie et al in the early 1980s and resolved into at least 2 U-band
filaments by McNamara et al in the mid 1990s. The (emission-weighted)
temperature of the X-ray emitting gas along the filament is 2.5-3 keV, as
revealed by X-ray colour ratios. The deprojected temperature will be less. A
detailed temperature map of the core of the cluster presented. The cD galaxy at
the head of the filament is probably moving through or oscillating in the
cluster core. The radiative cooling time of the X-ray emitting gas in the
filament is about 3x10^8 yr which is similar to the age of the filament
obtained from its length and velocity. This suggests that the filament is
produced by cooling of the gas from the intracluster medium. The filament, much
of which is well separated from the body of the cD galaxy and its radio source,
is potentially of great importance in helping to understand the energy and
ionization source of the optical nebulosity common in cooling flows.


title:
Conservation of Magnetic Helicity and Its Constraint on $\alpha$-Effect
  of Dynamo Theory

abstract:
  Dynamical studies of MHD turbulence on the one hand, and arguments based upon
magnetic helicity on the other, have yielded seemingly contradictory estimates
for the $\alpha$ parameter in turbulent dynamo theory. Here we show, with
direct numerical simulation of three-dimensional magnetohydrodynamic turbulence
with a mean magnetic field, $\OB$, that the constraint on the dynamo
$\alpha$-effect set by the magnetic helicity is time-dependent. A time-scale
$t_c$ is introduced such that for $t<t_c$, the $\alpha$-coefficient calculated
from the simulation is close to the result of Pouquet et al and Field et al,
$-\frac{\tau_{cor}}{3}(< \v \cdot \nabla \times \v > - < \b \cdot \nabla \times
\b >)$; for $t>t_c$, the classical result of the $\alpha$-coefficient given by
the Mean-Field Electrodynamics is reduced by a factor of $1/({R_m
|\OB|^2/v_{rms}^2})$, as argued by Gruzinov & Diamond, Seehafer and Cattaneo &
Hughes. Here, $R_m$ is the magnetic Reynolds number, $v_{rms}$ the rms velocity
of the turbulence, $\tau_{cor}$ the correlation time of the turbulence, and
$\overline B$ is in velocity unit. The applicability of and connection between
different models of dynamo theory are also discussed.


title: On Dynamical Models for Radio Galaxies

abstract:
  The tailed radio galaxies that have been called ``Type I'' are not a uniform
set. To study their dynamics, we have used the Ledlow-Owen data set, which
provides a new sample of 250 radio galaxies in nearby Abell clusters. These
sources divide into two clear categories based on their radio morphology. Type
A sources (``straight'') contain nearly straight jets which are embedded in
outer radio lobe. Type B sources (``tailed'') have a well-collimated jet flow
which undergoes a sudden transition, at an inner hot spot, to a less collimated
flow which continues on and forms a radio tail. We have not found any
separation of these classes in terms of radio power, radio flux size, galaxy
power or external gas density. We propose the difference is due to the
development, or not, of a disruptive flow instability, such as
Kelvin-Helmholtz, and the saturation of the instability when it develops.


title: Two Types of Radio Galaxies: A New Approach

abstract:
  We do not fully understand the dynamics and evolution of a radio galaxy.
Models of classical double (Type II) sources are in a reasonable state, but
these objects are rare. Non-type II sources (generically called Type I) are far
more common, but much less well understood. In this paper I use the data to
suggest possible new models for Type I sources, and discuss the physical
questions which these new models raise.


title: The effect of 3-He diffusion on the pulsational spectra of DBV models

abstract:
  We consider envelopes of DB white dwarfs which are not composed of pure 4-He,
but rather a mixture of 3-He and 4-He. Given this assumption, the same
diffusive processes which produce a relatively pure H layer overlying a He
layer in the DA's should work to produce a 3-He layer overlying a 4-He layer in
the DB's. We examine the relevant timescales for diffusion in these objects,
and compare them to the relevant evolutionary timescales in the context of the
DBV white dwarfs. We then explore the consequences which 3-He separation has on
the pulsational spectra of DBV models. Since GD 358 is the best-studied member
of this class of variables, we examine fits to its observed pulsation spectrum.
We find that the inclusion of a 3-He layer results in a modest improvement in a
direct fit to the periods, while a fit to the period spacings is significantly
improved.


title: X-Ray Constraints on the Warm_hot Intergalactic Medium

abstract:
  Three observational constraints can be placed on a warm-hot intergalactic
medium (WHIM) using \rosat PSPC pointed and survey data, the emission strength,
the energy spectrum, and the fluctuation spectrum. The upper limit to the
emission strength of the WHIM is 7.5 +/- 1.0 keV s^-1 cm^-2 sr^-1 keV^-1 in the
3/4 keV band, an unknown portion of which value may be due to our own Galactic
halo. The spectral shape of the WHIM emission can be described as thermal
emission with log T=6.42, although the true spectrum is more likely to come
from a range of temperatures. The values of emission strength and spectral
shape are in reasonable agreement with hydrodynamical cosmological models. The
autocorrelation function in the 0.44 keV < E < 1.21 keV band range, w(theta),
for the extragalactic soft X-ray background (SXRB) which includes both the WHIM
and contributions due to point sources, is less than about 0.002 for 10
arcminutes < theta < 20 arcminutes in the 3/4 keV band. This value is lower
than the Croft et al. (2000) cosmological model by a factor of about 5, but is
still not inconsistent with cosmological models. It is also found that the
normalization of the extragalactic power law component of the soft X-ray
background spectrum must be 9.5 +/- 0.9 keV s^-1 cm^-2 sr^-1 keV^-1 to be
consistent with the ROSAT All-Sky Survey.


title: Annihilations from the Galactic Centre

abstract:
  A massive black hole is present at the centre of our galaxy and inevitably
accretes dark matter particles, creating a region of very high particle
density. The annihilation rate is enhanced with a large number of e+e- pairs
produced either directly or by successive decays of mesons. We evaluate the
synchrotron emission (and self-absorption) associated with the propagation of
these particles through the galactic magnetic field and give constraints on the
values of mass and cross section of the dark matter particles.


title: The X-ray sources at the center of the supernova remnant RXJ0852.0-4622

abstract:
  We present a BeppoSAX observation of the X-ray source AX J0851.9-4617.4 that
has been proposed as the neutron star associated to the shell like-supernova
remnant RX J0852.0-4622. The image at E>5 keV shows the presence of a new
source, SAX J0852.0-4615, not resolved from AX J0851.9-4617.4 in previous
observations. The improved positional accuracy obtained for AX J0851.9-4617.4
confirms its possible identification with an early type star, also consistent
with its soft thermal spectrum (kT~1.3 keV). SAX J0852.0-4615, with a harder
X-ray spectrum and a higher X-ray to optical flux ratio, is a more likely
candidate for the neutron star associated to the supernova remnant.


title: Data Analysis for the Microwave Anisotropy Probe (MAP) Mission

abstract:
  We present an overview of the upcoming Microwave Anisotropy Probe (MAP)
mission, with an emphasis on those aspects of the mission that simplify the
data analysis. The method used to make sky maps from the differential
temperature data is reviewed and we present some of the noise properties
expected from these maps. An overview of the method we plan to use to mine the
angular power spectrum from the mega-pixel sky maps closes the paper.


title:
Ionization Sources and Physical Conditions in the Diffuse Ionized Gas
  Halos of Four Edge-On Galaxies

abstract:
  Deep long-slit spectra of the diffuse ionized gas halos of the edge-on spiral
galaxies NGC 4302 and UGC 10288 are presented. These data, along with
previously presented data for NGC 5775 and NGC 891, are used to address the
issue of how DIG halos are energized. Composite photo-ionization/shock models
are generally better at explaining runs of line ratios in these galaxies than
photo-ionization models alone. Models of line ratios in NGC 5775 require a
greater contribution from shocks for filamentary regions than for
non-filamentary regions to explain the run of [OIII]/Halpha. In either case,
the [SII]/[NII] ratio is not well fit by the models. Composite models for UGC
10288 are successful at reproducing the run of [SII]/[NII] for all but the the
highest values of [NII]/Halpha; however, the run of [OIII]/Halpha vs.
[NII]/Halpha does not show any discernible trend, making it difficult to
determine whether or not shocks make a contribution.
  We also examine whether the data can be explained simply by an increase in
temperature with z in a pure photo-ionization model. Runs of [SII]/Halpha,
[NII]/Halpha, and [SII]/[NII] in each of the four galaxies are consistent with
such an increase. However, the runs of [OIII]/Halpha vs. z in NGC 5775 and UGC
10288 require unusually high ionization fractions of O^{++} that can not be
explained without invoking a secondary ionization source or at the very least a
much higher temperature for the [OIII]-emitting component than for the [SII]-
and [NII]-emitting component. An increase in temperature with z is generally
more successful at explaining the [OIII]/Halpha run in NGC 891.


title: SDSS-RASS: Next Generation of Cluster-Finding Algorithms

abstract:
  We outline here the next generation of cluster-finding algorithms. We show
how advances in Computer Science and Statistics have helped develop robust,
fast algorithms for finding clusters of galaxies in large multi-dimensional
astronomical databases like the Sloan Digital Sky Survey (SDSS). Specifically,
this paper presents four new advances: (1) A new semi-parametric algorithm -
nicknamed ``C4'' - for jointly finding clusters of galaxies in the SDSS and
ROSAT All-Sky Survey databases; (2) The introduction of the False Discovery
Rate into Astronomy; (3) The role of kernel shape in optimizing cluster
detection; (4) A new determination of the X-ray Cluster Luminosity Function
which has bearing on the existence of a ``deficit'' of high redshift, high
luminosity clusters. This research is part of our ``Computational
AstroStatistics'' collaboration (see Nichol et al. 2000) and the algorithms and
techniques discussed herein will form part of the ``Virtual Observatory''
analysis toolkit.


title:
The Unusual Spectral Energy Distribution of a Galaxy Previously Reported
  to be at Redshift 6.68

abstract:
  Observations of distant galaxies are important both for understanding how
galaxies form and for probing the physical conditions of the universe at the
earliest epochs. It is, however, extremely difficult to identify galaxies at
redshift z>5, because these galaxies are faint and exhibit few spectral
features. In a previous work, we presented observations that supported the
identification of a galaxy at redshift z = 6.68 in a deep STIS field. Here we
present new ground-based photometry of the galaxy. We find that the galaxy
exhibits moderate detections of flux in the optical B and V images that are
inconsistent with the expected absence of flux at wavelength shortward of the
redshifted Lyman-alpha emission line of a galaxy at redshift z>5. In addition,
the new broad-band imaging data not only show flux measurements of this galaxy
that are incompatible with the previous STIS measurement, but also suggest a
peculiar spectral energy distribution that cannot be fit with any galaxy
spectral template at any redshift. We therefore conclude that the redshift
identification of this galaxy remains undetermined.


title: Constraints from the Lyman alpha forest power spectrum

abstract:
  We use published measurements of the transmission power spectrum of the Lyman
alpha forest to constrain several parameters that describe cosmology and
thermal properties of the intergalactic medium (IGM). A 6 parameter grid is
constructed using Particle-Mesh dark matter simulations together with scaling
relations to make predictions for the gas properties. We fit for all parameters
simultaneously and identify several degeneracies. We find that the temperature
of the IGM can be well determined from the fall-off of the power spectrum at
small scales. We find a temperature around 20.000 K, dependent on the slope of
the gas equation of state. We see no evidence for evolution in the IGM
temperature. We place constraints on the amplitude of the dark matter
fluctuations. However, contrary to previous results, the slope of the dark
matter power spectrum is poorly constrained. This is due to uncertainty in the
effective Jeans smoothing scale, which depends on the temperature as well as
the thermal history of the gas.


title:
An Extinction Map and Color Magnitude Diagram for the Globular Cluster
  NGC 3201

abstract:
  Differential $E_{V-I}$ variations of up to $\sim 0.2$ mag on a scale of
arcminutes across NGC 3201 are presented in the form of an extinction map. This
map, created by calculating average $E_{V-I}$ values for stars in small
subregions of the field with respect to a fiducial region, greatly improves the
appearance of the CMD of the cluster. We describe how we implemented this
technique in detail with our data for NGC 3201. A comparison between our map
and that of the same region extracted from the COBE/DIRBE reddening maps
published by Schlegel, Finkbeiner, & Davis (1998) (SFD) displays larger-scale
similarities between the two maps as well as smaller-scale features which show
up in our map but not in the SFD map. Several methods of determining an
$E_{V-I}$ zeropoint to add to our differential extinction map are presented.
Isochrone fitting proved to be the most successful one, but it produces an
average $E_{V-I}$ for the cluster which is smaller than previously published
values by $\sim 1.5\sigma$. Finally, our results seem to support the statement
by Arce & Goodman (1999) that the SFD maps overestimate the reddening in
regions of high extinction.


title: An Optical Counterpart to the Anomalous X-ray Pulsar 4U 0142+61

abstract:
  The energy source of the anomalous X-ray pulsars is not well understood,
hence their designation as anomalous. Unlike binary X-ray pulsars, no
companions are seen, so the energy cannot be supplied by accretion of matter
from a companion star. The loss of rotational energy, which powers radio
pulsars, is insufficient to power AXPs. Two models are generally considered:
accretion from a large disk left over from the birth process, or decay of a
very strong magnetic field (10^15 G) associated with a 'magnetar'. The lack of
counterparts at other wavelengths has hampered progress in our understanding of
these objects. Here, we present deep optical observations of the field around
4U 0142+61, which is the brightest AXP in X-rays. We find an object with
peculiar optical colours at the position of the X-ray source, and argue that it
is the optical counterpart. The optical emission is too faint to admit the
presence of a large accretion disk, but may be consistent with magnetospheric
emission from a magnetar.


title:
High resolution spectroscopy of symbiotic stars. VI. Orbital and stellar
  parameters for AR Pav

abstract:
  We present new dynamical parameters of the AR Pav binary system.
Ourobservations consist of a series of high resolution optical/NIR spectra from
which we derive the radial velocity curve of the red giant as well as its
rotation velocity. Assuming co-rotation, we determine the stellar radius (130
R_solar) of the red giant. Based on this we derive the red giant's luminosity
and mass (2.0 M_solar) as well as the distance of the system (4.9 kpc). The
binary mass function finally yields the companion's mass (0.75 M_solar) and the
binary separation (1.95 AU). We find that the red giant does not fill its Roche
lobe. We review the radial velocity data of Thackeray and Hutchings (1974), and
compare it with our red giant's orbit. We find that their RV curves of the blue
absorption system and the permitted emission lines are in anti-phase with the
red giant, and that the forbidden emission lines are shifted by a quarter of a
period. The blue absorptions and the permitted emission lines are associated
with the hot companion but not in a straightforward way. The blue absorption
system only tracks the hot component's orbital motion whilst it is in front of
the red giant, whereas at other phases line blanketing by interbinary material
leads to perturbations. We finally present UV light curves based on IUE archive
spectra. We clearly detect eclipses in the continuum at all wavelengths. The
eclipse light curves are unusual in that they show a slow and gradual decline
prior to eclipse which is followed by a sharp increase after eclipse.


abstract:
  Astrophysical implications of gravitational microlensing of gravitational
waves emitted by rotating neutron stars (NSs) are investigated. In particular,
attention is focused on the following situations: i) NSs in the galactic bulge
lensed by a central black hole of $2.6\times 10^6 M_{\odot}$ or by stars and
MACHOs distributed in the galactic bulge, disk and halo between Earth and the
sources; ii) NSs in globular clusters lensed by a central black hole of $\sim
10^3 M_{\odot}$ or by stars and MACHOs distributed throughout the Galaxy. The
detection of such kind of microlensing events will give a unique opportunity
for the unambiguous mapping of the central region of the Galaxy and of globular
clusters. In addition, the detection of such events will provide a new test of
the General Theory of Relativity. Gravitational microlensing will, moreover,
increase the challenge of detecting gravitational waves from NSs.


title: The Magnificent Seven: Close-by Cooling Neutron Stars?

abstract:
  We model Galactic populations of accreting and cooling isolated neutron stars
in the attempt to explore their link with a new class of dim soft X-ray sources
revealed by ROSAT. For accretors we follow the magneto-rotational and dynamical
evolution in the Galactic potential and a realistic large scale distribution of
the interstellar medium is used. Under standard assumptions old neutron stars
enter the accretor stage only if their magnetic field exceeds $\approx
10^{11}$--$10^{12}$ G. We predict about 1 source per square degree for fluxes
$\approx 10^{-15}$--$10^{-16}$ erg cm$^{-2}$s$^{-1}$ in the energy range 0.5-2
keV.
  Cooling neutron stars are explored within a simpler model of local sources,
including however interstellar absorption. They are found to be significantly
less abundant at low fluxes, $<0.1$ sources per square degree, but dominate
over accretors at higher flux levels ($\approx 10^{-12}$--$10^{-11}$ erg
cm$^{-2}$s$^{-1}$). We suggest that the faint sources observed by ROSAT may be
young cooling neutron stars with typical age $\la 10^6$ yrs, if the total
number of young neutron stars in the Solar proximity is $\sim 10$ times higher
than inferred from radiopulsars statistics.


title:
A Hipparcos study of the Hyades open cluster: Improved colour-absolute
  magnitude and Hertzsprung-Russell diagrams

abstract:
  Hipparcos parallaxes fix distances to individual stars in the Hyades cluster
with an accuracy of 6%. We use the Hipparcos (and Tycho-2) proper motions,
which have a larger relative precision than the trigonometric parallaxes, to
derive ~3 times more precise distance estimates, by assuming that all members
share the same space motion. The improved parallaxes as a set are statistically
consistent with the Hipparcos parallaxes. The new parallaxes confirm that the
Hipparcos measurements are correlated on small angular scales, consistent with
the limits specified in the Hipparcos Catalogue, though with significantly
smaller `amplitudes' than claimed by Narayanan & Gould.
  The colour-absolute magnitude diagram of the cluster based on the new paral-
laxes shows a well-defined main sequence with two gaps/turn-offs. These
features provide the first direct observational support of Boehm-Vitense's
prediction that (the onset of) surface convection in stars affects their B-V
colours. We present and discuss the theoretical HRD for an objectively defined
set of 88 high-fidelity members of the cluster as well as the delta Scuti star
theta^2 Tau, the giants delta^1, theta^1, epsilon, and gamma Tau, and the white
dwarfs V471 Tau and HD 27483 (all of which are also members). The precision
with which the new parallaxes place individual Hyades members in the Hertz-
sprung-Russell diagram is limited by (systematic) uncertainties related to the
transformations from observed colours and absolute magnitudes to effective
temperatures and luminosities. The new parallaxes provide stringent constraints
on the calibration of such transformations when combined with theoretical
stellar evolutionary modelling, tailored to the chemical composition and age of
the Hyades, over the large stellar mass range probed by Hipparcos.


title: PMN J0525-3343: soft X-ray spectral flattening in a blazar at z=4.4

abstract:
  We report optical, radio and X-ray observations of a new distant blazar, PMN
J0525-3343, at a redshift of 4.4. The X-ray spectrum measured from ASCA and
BeppoSAX flattens below a few keV, in a manner similar to the spectra of two
other z>4 blazars, GB 1428+4217 (z=4.72) reported by Boller et al and RXJ
1028.6-0844 (z=4.28) by Yuan et al. The spectrum is well fitted by a power-law
continuum which is either absorbed or breaks at a few keV. An intrinsic column
density corresponding to 2 x 10^23 H-atoms cm-2 at solar abundance is required
by the absorption model. This is however a million times greater than the
neutral hydrogen, or dust, column density implied by the optical spectrum,
which covers the rest-frame UV emission of the blazar nucleus. We discuss the
problems raised and suggest that, unless there is intrinsic flattening in the
spectral distribution of the particles/seed photons producing X-rays via
inverse Compton scattering, the most plausible solution is a warm absorber
close to the active nucleus.


title: Type Ia Supernovae and the Value of the Hubble Constant

abstract:
  The methodology involved in deriving the Hubble Constant via the calibration
of the corrected peak luminosities of Type Ia supernovae (SNe) is reviewed. We
first present a re-analysis of the Calan-Tololo (C-T) and Center for
Astrophysics (CfA) Type Ia SN surveys. Bivariate linear least squares and
quadratic boot-strapped fits in peak apparent magnitude and light curve shape
are employed to correct this heterogeneous sample of peak apparent magnitudes,
resulting in an homogeneous (and excellent) secondary distance indicator: the
so-called corrected peak luminosity. We next provide an empirical calibration
for this corrected luminosity, using Cepheid-based distances for seven nearby
spiral galaxies host to Type Ia SNe. Included in this sample is the
spectroscopically peculiar SN 1991T (in NGC 4527), whose corrected peak
luminosity is shown to be indistinguishable from that of so-called ``normal''
SNe. A robust value of the Hubble Constant is derived and shown to be
H0=73+/-2(r)+/-7(s) km/s/Mpc.


title:
Towards optimal softening in 3D N-body codes: I. Minimizing the force
  error

abstract:
  In N-body simulations of collisionless stellar systems, the forces are
softened to reduce the shot noise. Softening modifies gravity at r=|x-y|
smaller than softening length epsilon and the softened forces are increasingly
biased for ever larger epsilon. There is, thus, some optimum between reducing
the fluctuations and introducing a bias. Here, analytical relations are derived
for the amplitudes of the bias and the fluctuations in the limit of small
epsilon and large N. It is shown that the fluctuations of the force are
generated locally, in contrast to the variations of the potential, which
originate from noise in the whole system. Based on the asymptotic relations and
using numerical experiments, I study the dependence of the resulting force
error on N, epsilon, and on the functional form by which Newtonian gravity is
replaced. The Plummer softening, where each body is replaced by a Plummer
sphere of scale radius epsilon, yields significantly larger force errors than
do methods in which the bodies are replaced by density kernels of finite
extent. I also give special kernels, which reduce the errors even further.
These kernels largely compensate the errors made with too small inter-particle
forces at r<epsilon by exceeding Newtonian forces at r epsilon. Additionally,
the possibilities of locally adapting epsilon and of using unequal weights for
the bodies are investigated. These various techniques allow, without increasing
N, to reduce the rms force error by a factor 2 compared to Plummer softening
with constant epsilon. The results of this study are directly relevant to
N-body simulations using direct summation techniques or the tree code.
(abridged)


title:
An observational constraint on gravitational lensing by objects of mass
  10^(9.5) - 10^(10.9) Mo

abstract:
  A radio-based search for strong gravitational lensing, with image separations
in the range 160-300 milliarcsec (mas), has yielded a null result for a sample
of 1665 sources (Augusto, Wilkinson & Browne 1998) whose mean redshift is
estimated to be ~1.3. The lensing rate for this previously-unexplored
separation range, <1:555 at the 95% confidence level, is less than on
arcsecond-scales - as expected from models of lensing galaxy populations.
Lensing on 160-300 mas scales is expected to arise predominantly from spiral
galaxies at a rate dependent on the disk-halo mass ratio and the evolving
number density of the population with redshift. While the present sample is too
small for there to be a high probability of finding spiral galaxy lenses, our
work is a pilot survey for a much larger search based on the full CLASS
database which would provide useful information on galactic structure at z~0.5.
We examine other possible lens populations relevant to our present search, in
particular dwarf galaxies and supermassive black holes in galactic nuclei, and
conclude that none of them are likely to be detected. Our null result enables
us formally to rule out a cosmologically significant population of
uniformly-distributed compact objects: Omega (CO)<0.1 (95% confidence) in the
mass range 10^(9.5) - 10^(10.9) Mo.


title: Neutrino Astrophysics

abstract:
  A general overview of neutrino physics and astrophysics is given, starting
with a historical account of the development of our understanding of neutrinos
and how they helped to unravel the structure of the Standard Model. We discuss
why it is so important to establish if neutrinos are massive and introduce the
main scenarios to provide them a mass. The present bounds and the positive
indications in favor of non-zero neutrino masses are discussed, including the
recent results on atmospheric and solar neutrinos. The major role that
neutrinos play in astrophysics and cosmology is illustrated.


title: Slow modes in Keplerian disks

abstract:
  Low-mass disks orbiting a massive body can support "slow" normal modes, in
which the eigenfrequency is much less than the orbital frequency. Slow modes
are lopsided, i.e., the azimuthal wavenumber m=1. We investigate the properties
of slow modes, using softened self-gravity as a simple model for collective
effects in the disk. We employ both the WKB approximation and numerical
solutions of the linear eigenvalue equation. We find that all slow modes are
stable. Discrete slow modes can be divided into two types, which we label
g-modes and p-modes. The g-modes involve long leading and long trailing waves,
have properties determined by the self-gravity of the disk, and are only
present in narrow rings or in disks where the precession rate is dominated by
an external potential. In contrast, the properties of p-modes are determined by
the interplay of self-gravity and other collective effects. P-modes involve
both long and short waves, and in the WKB approximation appear in degenerate
leading/trailing pairs. Disks support a finite number---sometimes zero---of
discrete slow modes, and a continuum of singular modes.


title:
AD Leo from X-Rays to Radio: Are Flares Responsible for the Heating of
  Stellar Coronae?

abstract:
  In spring 1999, a long coordinated observing campaign was performed on the
flare star AD Leo, including {\it EUVE}, {\it BeppoSAX}, the {\it VLA}, and
optical telescopes. The campaign covered a total of 44 days. We obtained
high-quality light curves displaying ongoing variability on various timescales,
raising interesting questions on the role of flare-like events for coronal
heating. We performed Kolmogorov-Smirnov tests to compare the observations with
a large set of simulated light curves composed of statistical flares that are
distributed in energy as a power law of the form ${\rm d}N/{\rm d}E \propto
E^{-\alpha}$ with selectable index $\alpha$. We find best-fit $\alpha$ values
slightly above a value of 2, indicating that the extension of the flare
population toward small energies could be important for the generation of the
overall X-ray emission.


title: Stellar Coronae with \textit{XMM-Newton} RGS. I. Coronal Structure

abstract:
  First results from high-resolution coronal spectroscopy with the {\it
XMM-Newton} Reflection Grating Spectrometers (RGS) are reviewed. Five stellar
systems (HR 1099, Capella, Procyon, YY Gem, AB Dor) have been observed. The
emphasis of the present paper is on overall coronal structure. Elemental
abundances in {\it active stars} are found to be `anomalous' in the sense that
they tend to increase with increasing First Ionization Potential (FIP - i.e.,
signifying an inverse FIP effect). Coronal densities are measured at levels of
a few times $10^{10}$ cm$^{-3}$ for cooler plasma, although there are
indications for very high densities in the hotter plasma components.


title: Stellar Coronae with \textit{XMM-Newton} RGS. II. X-ray Variability

abstract:
  First results from high-resolution coronal spectroscopy of flares with the
Reflection Grating Spectrometers on board the \textit{XMM-Newton} satellite are
reviewed. Rotational modulation in the X-ray light curve of HR 1099 is
discussed. Results from time-dependent spectroscopy of flares in the active
stars HR 1099, AB Dor, YY Gem are also presented. Variations in the shape of
the emission measure distributions, in the abundances and in the average
density of the cool plasma are discussed.


title: The DIRTY Model. I. Monte Carlo Radiative Transfer Through Dust

abstract:
  We present the DIRTY radiative transfer model in this paper and a companion
paper. This model computes the polarized radiative transfer of photons from
arbitrary distributions of stars through arbitrary distributions of dust using
Monte Carlo techniques. The dust re-emission is done self-consistently with the
dust absorption and scattering and includes all three important emission paths:
equilibrium thermal emission, non-equilibrium thermal emission, and the
aromatic features emission. The algorithm used for the radiative transfer
allows for the efficient computation of the appearance of a model system as
seen from any viewing direction. We present a simple method for computing an
upper limit on the output quantity uncertainties for Monte Carlo radiative
transfer models which use the weighted photon approach.


title:
The DIRTY Model II: Self-Consistent Treatment of Dust Heating and
  Emission in a 3-D Radiative Transfer Code

abstract:
  In this paper and a companion paper we present the DIRTY model, a Monte Carlo
radiative transfer code, self-consistently including dust heating and emission,
and accounting for the effects of the transient heating of small grains. The
code is completely general; the density structure of the dust, the number and
type of heating sources, and their geometric configurations can be specified
arbitrarily within the model space. Source photons are tracked through the
scattering and absorbing medium using Monte Carlo techniques and the effects of
multiple scattering are included. The dust scattering, absorbing, and emitting
properties are calculated from realistic dust models derived by fitting
observed extinction curves in Local Group galaxies including the Magellanic
Clouds and the Milky Way. The dust temperature and the emitted dust spectrum
are calculated self consistently from the absorbed energy including the effects
of temperature fluctuations in small grains. Dust self-absorption is also
accounted for, allowing the treatment of high optical depths, by treating
photons emitted by the dust as an additional heating source and adopting an
iterative radiative transfer scheme. As an illustrative case, we apply the
DIRTY radiative transfer code to starburst galaxies wherein the heating sources
are derived from stellar evolutionary synthesis models. Within the context of
the starburst model, we examine the dependence of the UV to FIR SED, dust
temperatures, and dust masses predicted by DIRTY on variations of the input
parameters.


title: Galaxies: From Kinematics to Dynamics

abstract:
  These lectures are intended to provide an introduction to the rich interplay
between N-body simulations and stellar-kinematic observations of galaxies. The
first section describes the kinematic properties of galaxies that are
accessible to observation, and gives a brief introduction to the stellar
dynamics that one might wish to infer from such observations. In the next
section, the use of N-body simulations in the study of galaxy dynamics is
placed in its historical context. The next two sections provide case studies of
the stellar-dynamical properties of elliptical and disk galaxies where N-body
simulations have been used to explain kinematic data, to test new analysis
techniques, and to motivate further observations. The final section contains
some speculation as to how the symbiotic relation between observations and
N-body simulations may develop in future studies of galaxy dynamics.


title:
Detecting X-ray Synchrotron Emission in Supernova Remnants: Implications
  for Abundances and Cosmic Rays

abstract:
  The 10^51 ergs released in a supernova have far reaching consequences in the
galaxy, determining elemental abundances, accelerating cosmic rays, and
affecting the makeup of the interstellar medium. Recently the spectra of
several supernova remnants have been found to be dominated by nonthermal
emission. Separating the thermal and nonthermal components is important not
only for the understanding of cosmic-ray acceleration and shock microphysics
properties but for accurate assessment of the temperatures and line strengths.
New models designed to model spatially resolved synchrotron X-rays from type Ia
supernovae can contribute to the understanding of both the thermal physics
(dynamics, abundances) and nonthermal physics (shock acceleration,
magnetic-field amplification) of supernova remnants. I will describe model fits
to SN 1006, emphasizing the physical constraints that can be placed on SNRs,
abundances, and the cosmic-ray acceleration process.


title: The solar dynamo: old, recent, and new problems

abstract:
  A number of problems of solar and stellar dynamo theory are briefly reviewed
and the current status of possible solutions is discussed. Results of direct
numerical simulations are described in view of mean-field dynamo theory and the
relation between the alpha-effect and the inverse cascade of magnetic helicity
is highlighted. The possibility of `catastrophic' quenching of the alpha-effect
is explained in terms of the constraint placed by the conservation of magnetic
helicity.


title: Illuminated, and enlightened, by GRB 991216

abstract:
  We consider models for the generation of the emission line recently
discovered in the X-ray afterglow spectrum of several bursts, and especially of
GRB 991216 observed by Chandra. These observations suggest the presence of
0.1-1 solar masses of iron in the vicinity of the bursts. We show that there
are strong geometrical and kinematical constraints on the line emitting
material. We discuss several classes of models, favoring one where the line
photons are produced by reflection off the walls of a wide funnel of
semi-opening angle 45 degrees, excavated in a young (a few months old)
supernova remnant made of ~10 solar masses with radius 6x10^15 cm, and ~1 solar
mass of iron, providing strong support for the SupraNova model.


title: VLA HI Zeeman Observations Toward the W49 Complex

abstract:
  We report VLA HI Zeeman observations toward the W49A star-forming region and
the SNR W49B. Line of sight magnetic fields (Blos) of 60 to 300 muG at 25"
resolution were detected toward W49A at velocities of ~4 and ~7 km/s. The Blos
values measured toward W49A show a significant increase in field strength with
higher resolution especially for the ~4 km/s HI gas. The HI gas in the velocity
range -5 to 25 km/s toward W49A shows good agreement both kinematically and
spatially with molecular emission intrinsically associated with W49A. Based on
comparisons with molecular data toward W49A, we suggest that the 4 km/s HI gas
is directly associated with the northern part of the HII region ring, while the
7 km/s HI gas seems to originate in a lower density halo surrounding W49A. We
estimate that the W49A North core is significantly subvirial, and that the
total kinetic +magnetic energies amount to less than 1/3 of the total W49A
North gravitational energy. These magnetic field results suggest that W49A
North is unstable to overall gravitational collapse in agreement with evidence
that the halo is collapsing onto the W49A North ring of HII regions.
  The majority of the HI column density toward W49B comes from Sagittarius Arm
clouds along the line of sight at ~40 km/s and ~60 km/s. No significant
magnetic fields were detected toward W49B. Comparison of the spectral
distribution of HI gas toward W49A and W49B suggests that evidence placing W49B
3 kpc closer to the sun (i.e. at 8 kpc) than W49A is quite weak.


title: Warm Molecular Gas in Dwarf Starburst Galaxies: CO(3-2) Observations

abstract:
  Eight dwarf starburst galaxies have been observed with the Caltech
Submillimeter Observatory (CSO) telescope in the CO J= 3 - 2 transition. The
galaxies observed are He 2-10, NGC 5253, NGC 1569, NGC 3077, Haro 2, Haro 3, II
Zw 40 and Mrk 86; all but the last two are detected. The central regions of He
2-10 and NGC 5253 were mapped and a CO(2-1) spectrum of NGC 5253 was obtained.
The error weighted mean CO(3-2)/CO(1-0) ratio of the detected galaxies is
0.60$\pm$0.06, which is virtually identical to what is found for starbursts in
the nuclei of nearby spirals, and suggests that the molecular gas is optically
thick, warm (T$_{k}>$20 K), and moderately dense ($n_{H_{2}}\sim 10^{3-4}
cm^{-3}$). The CO(3-2)/CO(1-0) ratio peaks at or close to the starburst in all
cases. CO emission does not appear to be optically thin in these dwarfs,
despite the low metallicity and intense radiation fields, which is probably
because in order for CO to exist in detectable amounts it must be
self-shielding and hence optically thick. Physical properties of the molecular
clouds in these dwarf starbursts appear to be essentially the same as nearby
spiral nuclei, with the possible exception that CO is more confined to the
cloud cores.


title: Mining Gamma-Ray Burst Data

abstract:
  Gamma-ray bursts provide what is probably one of the messiest of all
astrophysical data sets. Burst class properties are indistinct, as overlapping
characteristics of individual bursts are convolved with effects of instrumental
and sampling biases. Despite these complexities, data mining techniques have
allowed new insights to be made about gamma-ray burst data. We demonstrate how
data mining techniques have simultaneously allowed us to learn about gamma-ray
burst detectors and data collection, cosmological effects in burst data, and
properties of burst subclasses. We discuss the exciting future of this field,
and the web-based tool we are developing (with support from the NASA AISR
Program). We invite others to join us in AI-guided gamma-ray burst
classification (http://grb.mnsu.edu/grb/).