title: Iron K Lines from Gamma Ray Bursts

abstract:
  We present models for reprocessing of an intense flux of X-rays and gamma
rays expected in the vicinity of gamma ray burst sources. We consider the
transfer and reprocessing of the energetic photons into observable features in
the X-ray band, notably the K lines of iron. Our models are based on the
assumption that the gas is sufficiently dense to allow the microphysical
processes to be in a steady state, thus allowing efficient line emission with
modest reprocessing mass and elemental abundances ranging from solar to
moderately enriched. We show that the reprocessing is enhanced by
down-Comptonization of photons whose energy would otherwise be too high to
absorb on iron, and that pair production can have an effect on enhancing the
line production. Both "distant" reprocessors such as supernova or wind remnants
and "nearby" reprocessors such as outer stellar envelopes can reproduce the
observed line fluxes with Fe abundances 30-100 times above solar, depending on
the incidence angle. The high incidence angles required arise naturally only in
nearby models, which for plausible values can reach Fe line to continuum ratios
close to the reported values.


title: Cluster Magnetic Fields

abstract:
  Magnetic fields in galaxy clusters have been measured using a variety of
techniques, including: studies of synchrotron relic and halo radio sources
within clusters, studies of inverse Compton X-ray emission from clusters,
surveys of Faraday rotation measures of polarized radio sources both within and
behind clusters, and studies of Cluster Cold Fronts in X-ray images. These
measurements imply that most cluster atmospheres are substantially magnetized,
with typical field strengths of order 1 microGauss with high areal filling
factors out to Mpc radii. There is likely, however, to be considerable
variation in field strengths and topologies both within and between clusters,
especially when comparing dynamically relaxed clusters to those that have
recently undergone a merger. In some locations, such as the cores of cooling
flow clusters, the magnetic fields reach levels of 10 - 40 microGauss, and may
be dynamically important. In all clusters the magnetic fields have a
significant effect on energy transport in the intracluster medium. We also
review current theories on the origin of cluster magnetic fields.


title:
XMM-Newton Observation of a Distant X-ray Selected Cluster of Galaxies
  at z=1.26 with Possible Cluster Interaction

abstract:
  We report on the XMM-Newton (XMM) observation of RXJ1053.7+5735, one of the
most distant (z = 1.26) X-ray selected clusters of galaxies, which also shows
an unusual double-lobed X-ray morphology, indicative of possible
cluster-cluster interaction. The cluster was discovered during our ROSAT deep
pointings in the direction of the Lockman Hole. The XMM observations were
performed with the European Photon Imaging Camera (EPIC) during the performance
verification phase. Total effective exposure time was ~ 100 ksec. The best fit
temperature based on a simultaneous fit of spectra from the all EPIC cameras is
4.9(+1.5/-0.9) keV. Metallicity is poorly constrained even using the joint fit
of all spectra, with an upper limit on the iron abundance of 0.62 solar. Using
the best fit model parameters, we derived a bolometric luminosity of L(bol) =
3.4x10^44 h_{50}^-2 erg /s. Despite the fact that it was observed at fairly
large off-axis angle, the temperature errors are much smaller compared with
those of typical measurements based on ASCA or Beppo-Sax observations of z >
0.6 clusters, demonstrating the power of the XMM for determining the X-ray
temperature for high-z clusters. The measured temperature and luminosity show
that one can easily reach the intrinsically X-ray faint and cool cluster regime
comparable with those of z ~ 0.4 clusters observed by past satellites. The new
cluster temperature and L(bol) we have measured for RXJ1053.7+5735 is
consistent with a weak/no evolution of the L(bol) - Tx relation out to z ~ 1.3,
which lends support to a low Omega universe, although more data-points of z > 1
clusters are required for a more definitive statement. The caution has to be
also exercised in interpreting the result, because of the uncertainty
associated with the dynamical status of this cluster.


title: First XMM-Newton Observations of the Globular Cluster M22

abstract:
  We have examined preliminary data of the globular cluster, M22, from the EPIC
MOS detectors on board XMM-Newton. We have detected 27 X-ray sources within the
centre of the field of view, 24 of which are new detections. Three sources were
found within the core of the cluster. From spectral analysis of the X-ray
sources, it is possible that the object at the centre of the core is a
quiescent X-ray transient and those lying further out are maybe cataclysmic
variables.


title: Low-extinction windows in the inner Galactic Bulge

abstract:
  We built K band extinction maps in the area of two candidate low-extinction
windows in the inner Bulge: W0.2-2.1 at (l,b) = (0.25o,-2.15o), and W359.4-3.1
at (l,b) = (359.40o,-3.10o). We employed JHKs photometry from the 2MASS Point
Source Catalog. Extinction values were determined by fitting the upper giant
branch found in the present 2MASS Ks x J-Ks diagrams to a de-reddened bulge
stellar population reference giant branch. We tested the method on the well
known Baade's and Sgr I windows: the 2MASS mean extinction values in these
fields agreed well with those of previous studies. We confirm the existence of
low-extinction windows in the regions studied, as local minima in the A_K maps
reaching A_K values about 2 standard deviations below the mean values found in
the neighbouring areas. Schlegel et al.'s (1998) FIR extinction maps, which
integrate dust contributions throughout the Galaxy, are structurally similar to
those derived with 2MASS photometry in the two studied windows. We thus
conclude that the dust clouds affecting the 2MASS and FIR maps in these
directions are basically the same and are located on foreground of the bulk of
bulge stars. However, the A_K absolute values differ significantly. In
particular, the FIR extinction values for W359.4-3.1 are a factor ~1.45 larger
than those derived from the 2MASS photometry. Possible explanations of this
effect are discussed. The lower Galactic latitudes of the low-extinction
windows W359.4-3.1 and W0.2-2.1, as compared to Baade's Window, make them
promising targets for detailed studies of more central bulge regions.


title: Probing the OVI forest

abstract:
  Recent FUSE and STIS observations of OVI absorption at low redshift along the
sightline to distant quasars have been interpreted as the signature of a
warm-hot diffuse component of the intergalactic medium (IGM). In these
proceedings we show that the predicted numbers of such absorbers in numerical
simulations agree with the observed characteristics, lending support to this
idea. We find that collisionally ionized lines tend to be stronger and wider,
while photo-ionized absorbers are weaker and narrower. We also find that a
comparison of the predicted distribution of line widths to that observed is
marginally too low.


title:
Baryon asymmetry of the Universe from evaporation of primordial black
  holes

abstract:
  The process of baryogenesis through the evaporation of black holes formed at
the end of inflation phase is considered. The increase of black hole mass due
to accretion from the surrounding radiation after the reheating is taken into
account. It is shown that the influence of the accretion on the baryogenesis is
important only in the case when the initial values of black hole mass are
larger than $\sim 10^{4}{g}$. The behavior of calculated baryon asymmetry, as a
function of model parameters, is studied.


title: The Ca II Triplet as an Abundance Indicator

abstract:
  How can we accurately determine the metallicity of faint red giant stars in
nearby galaxies? The equivalent widths of the broad absorption lines from Ca II
at 8498, 8542, and 8662 Angstrom (the calcium triplet) have shown a smooth
relationship to metallicity, [Fe/H], in Galactic globular clusters, i.e., old,
metal-poor stars. The exact relationship depends on the [Fe/H] scale assumed.
The sensitivity of the sum of the equivalent widths, sum{W_{Ca II}}, to [Fe/H]
has been well studied for metal-poor stars, but theory and observations show
that sum{W_{Ca II}} will become less sensitive to [Fe/H] for young or
metal-rich stars, but this needs to be calibrated. Built into the present
calibration of sum{W_{Ca II}} to [Fe/H] is also a dependence on the Galactic
[Ca/Fe] to [Fe/H] relationship, which is a function of the Galaxy's star
formation history and chemical evolution. Our goal is to remove uncertainties
in the [Fe/H] scale used in previous calibrations and remove the dependence on
galactic evolution. We are obtaining high dispersion spectra to
self-consistently calibrate the calcium triplet to give [Ca/H] abundances, and
extend the current calibration to near-solar metallicities and to ages as young
as 2 Gyr.


title:
Calculation of the Masses of the Binary Star HD 93205 by Application of
  the Theory of the Apsidal Motion

abstract:
  We present a method to calculate masses for components of both eclipsing and
non-eclipsing binary systems as long as their apsidal motion rates are
available. The method is based on the fact that the equation that gives the
rate of apsidal motion is a supplementary equation that allows the computation
of the masses of the components, if the radii and the internal structure
constants of them can be obtained from theoretical models. For this reason the
use of this equation makes the method presented here model dependent.
  We apply this method to calculate the mass of the components of the
non-eclipsing massive binary system HD 93205 (O3V+O8V), which is suspected to
be a very young system. To this end, we computed a grid of evolutionary models
covering the mass range of interest, and taking the mass of the primary (M_1)
as the only independent variable, we solve the equation of apsidal motion for
M_1 as a function of the age of the system. The mass of the primary we find
ranges from M_1= 60+-19 msun for ZAMS models, which sets an upper limit for
M_1, down to M_1= 40+-9 msun for an age of 2 Myr. Accordingly, the upper limit
derived for the mass of the secondary (M_2= Q M_1) is M_2= 25 msun is in very
good agreement with the masses derived for other O8V stars occurring in
eclipsing binaries.


title: Wide Field Imaging of the Sextans Dwarf Spheroidal Galaxy

abstract:
  We present wide field multiband photometry of the very low surface brightness
dwarf Spheroidal galaxy (dSph) Sextans. We have found convincing evidence for
the presence of multiple stellar populations in this galaxy. In particular we
discovered: (a) a Blue Horizontal Branch tail kinked over the instability
strip; (b) a clearly bimodal distribution in color of the Red Giant Branch
(RGB) stars and (c) a double RGB-bump. All these features suggest that (at
least) two components are present in the old stellar population that dominates
the galaxy: a main one with [Fe/H]~-1.8 and a minor component around
[Fe/H]~-2.5. Similar evidence has been recently found by Majewski et al. (1999)
for the Sculptor dwarf Spheroidal, suggesting that multiple star formation
episodes are common also in the most nearby dSphs that ceased their star
formation activity at very early epochs.


title: CMB anisotropy: deviations from Gaussianity due to non-linear gravity

abstract:
  Non-linear evolution of cosmological energy density fluctuations triggers
deviations from Gaussianity in the temperature distribution of the cosmic
microwave background. A method to estimate these deviations is proposed. N-body
simulations -- in a $\Lambda$CDM cosmology -- are used to simulate the strongly
non-linear evolution of cosmological structures. It is proved that these
simulations can be combined with the potential approximation to calculate the
statistical moments of the CMB anisotropies produced by non-linear gravity.
Some of these moments are computed and the resulting values are different from
those corresponding to Gaussianity.


title:
The Magellanic Clouds Photometric Survey: The Small Magellanic Cloud
  Stellar Catalog and Extinction Map

abstract:
  We present our catalog of U, B, V, and I stellar photometry of the central 18
sq. degree area of the Small Magellanic Cloud. We combine our data with the
2MASS and DENIS catalogs to provide, when available, U through K_S data for
stars. Internal and external astrometric and photometric tests using existing
optical photometry (U, B, and V from Massey's bright star catalog; B, V, and I
from the microlensing database of OGLE and I from the near-infrared sky survey
DENIS) are used to determine the observational uncertainties and identify
systematic errors. We fit stellar atmosphere models to the optical data to
check the consistency of the photometry for individual stars across the
passbands and to estimate the line-of-sight extinction. Finally, we use the
estimated line-of-sight extinctions to produce an extinction map across the
Small Magellanic Cloud and investigate the nature of extinction as a function
of stellar population.


title:
The Optical Counterpart of the Accreting Millisecond Pulsar SAX
  J1808.4-3658 in Outburst: Constraints on the Binary Inclination

abstract:
  We present multiband optical/infrared photometry of V4580 Sgr, the optical
counterpart of the accretion-powered millisecond pulsar SAX J1808.4-3658, taken
during the 1998 X-ray outburst of the system. The optical flux is consistent
with emission from an X-ray-heated accretion disk. Self-consistent modeling of
the X-ray and optical emission during the outburst yields best-fit extinction
Av=0.68 and inclination cos(i)=0.65, assuming a distance of 2.5 kpc. The
allowed inclination range requires that the pulsar's stellar companion has
extremely low mass, 0.05-0.10 Msun. Some of the infrared observations are not
consistent with disk emission and are too bright to be from either the disk or
the companion, even in the presence of X-ray heating.


title: An HI Rogues Gallery

abstract:
  We have begun a compilation of HI maps of peculiar galaxies kindly
contributed by individual investigators, many as part of the ``Gas & Galaxy
Evolution'' conference. In this gallery we present images of the first 181
objects, which includes over 400 individually cataloged galaxies. The images
consist of a greyscale representation of the optical morphology and an
accompanying optical image with HI contours superimposed. A web-based ``living
Gallery'' is being maintained on the NRAO homepage (presently at
http://www.nrao.edu/astrores/HIrogues/).


title:
A novel approach for extracting time-delays from lightcurves of lensed
  quasar images

abstract:
  We present a new method to estimate time delays from light curves of lensed
quasars. The method is based on chi^2 minimization between the data and a
numerical model light curve. A linear variation can be included in order to
correct for slow long-term microlensing effects in one of the lensed images. An
iterative version of the method can be applied in order to correct for higher
order microlensing effects. The method is tested on simulated light curves.
When higher order microlensing effects are present the time delay is best
constrained with the iterative method. Analysis of a published data set for the
lensed double Q0957+561 yields results in agreement with other published
estimates.


title:
Discovery of a 0.15" Binary Brown Dwarf 2MASSJ 1426316+155701 With
  Gemini/Hokupa'a Adaptive Optics

abstract:
  Use of the highly sensitive Hokupa'a curvature wavefront sensor has allowed
for the first time direct adaptive optics (AO) guiding on brown dwarfs and VLM
stars (SpT=M7-L2). An initial survey of 9 such objects discovered one 0.15"
binary (2MASSJ 1426316+155701). The companion is about half as bright as the
primary (Delta K = 0.61+/-0.05$, Delta H = 0.70+/-0.05) and has even redder
colors H-K=0.59+/-0.14 than the primary. The blended spectrum of the binary has
been previously determined to be M9.0. We modeled a blend of an M8.5 template
and a L1-L3 template reproducing a M9.0 spectrum in the case of Delta K =
0.61+/-0.05,Delta H = 0.70\pm0.05$. These spectral types also match the
observed H-K colors of each star. Based the previously observed low space
motion and $H_{\alpha}$ activity we assign an age of $0.8^{+6.7}_{-0.3} Gyr$.
Utilizing this age range and the latest DUSTY models of the Lyon group we
assign a photometric distance of $18.8^{+1.44}_{-1.02} pc$ and masses of
$M_{A}=0.074^{+0.005}_{-0.011} M_\odot$ and $M_{B}=0.066^{+0.006}_{-0.015}
M_\odot$. We therefore estimate a system separation of $2.92_{+0.22}^{-0.16}AU$
and a period of $13.3{+3.18}^{-1.51} yr$ respectively. Hence, 2M1426 is among
the smallest separation brown dwarf binaries resolved to date.


title: Magnetic activity in accretion disc boundary layers

abstract:
  We use three dimensional magnetohydrodynamic simulations to study the
structure of the boundary layer between an accretion disc and a non-rotating,
unmagnetized star. Under the assumption that cooling is efficient, we obtain a
narrow but highly variable transition region in which the radial velocity is
only a small fraction of the sound speed. A large fraction of the energy
dissipation occurs in high density gas adjacent to the hydrostatic stellar
envelope, and may therefore be reprocessed and largely hidden from view of the
observer. As suggested by Pringle (1989), the magnetic field energy in the
boundary layer is strongly amplified by shear, and exceeds that in the disc by
an order of magnitude. These fields may play a role in generating the magnetic
activity, X-ray emission, and outflows in disc systems where the accretion rate
is high enough to overwhelm the stellar magnetosphere.


title:
An Efficient Strategy to Select Targets for Gas-Dynamical Measurements
  of Black Hole Masses Using the Hubble Space Telescope

abstract:
  Gas-dynamical studies using the Hubble Space Telescope are an integral
component for future progress in the search for massive black holes in galactic
nuclei. Here we present an extensive set of gas rotation curves obtained with
the Space Telescope Imaging Spectrograph for the central regions of 23 disk
galaxies. We find that the bulges of randomly selected, nearby spiral and S0
galaxies generally do not contain well-defined gaseous disks. Only 15%-20% of
disk galaxies have regular, symmetric velocity fields useful for dynamical
analysis. Through comparison of the kinematics with Hubble Space Telescope
images of the nuclear regions, we show that the probability of success can be
significantly boosted by preselecting objects whose central dust lanes follow a
well-ordered, circularly symmetric pattern. The dust morphology can be
ascertained efficiently by visual inspection of unsharp-masked images.


title: Measuring Black Hole Masses Using Ionized Gas Kinematics

abstract:
  We describe techniques for measuring the central masses of galaxies using
emission-line kinematics observed with the Hubble Space Telescope. For accurate
results, it is necessary to model various instrumental effects, particularly
the blurring due to the telescope PSF and the width of the spectroscopic
aperture. Observations of nuclear gas disks often reveal substantial internal
velocity dispersions in the gas, suggesting that the disks may be partially
pressure-supported. We also describe a technique for fitting 2-dimensional
spectroscopic data directly in pixel space. This method may be useful for
objects such as M84 that show highly complex and asymmetric line profiles.


title: Limits on the Mass of the Central Black Hole in 16 Nearby Bulges

abstract:
  We report upper limits on the masses of black holes that can be present in
the centers of 16 nearby galaxy bulges. These limits for our statistically
complete sample were derived from the modeling of the central emission-line
widths ([N II] or [S II]), observed over a 0.25" X 0.2" (R < 9 pc) aperture.
The experiment has a mean detection sensitivity of 3.9 X 10^6 solar masses. For
three sample members with direct determinations of black hole masses our upper
limits agree within the uncertainties, while in general our upper limits are
found to be close to the masses measured in other bulges with global properties
similar to ours. Remarkably, our limits lie quite closely to the recently
derived relation between black hole mass and stellar velocity dispersion. These
results support a picture wherein the black hole mass and overall galaxy
structure are closely linked, as galaxies with exceptionally high black hole
masses at a given velocity dispersion apparently are rare.


title: Observations of H3+ in the Diffuse Interstellar Medium

abstract:
  Surprisingly large column densities of H3+ have been detected using infrared
absorption spectroscopy in seven diffuse cloud sightlines (Cygnus OB2 12,
Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating
that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard
model of diffuse cloud chemistry, our H3+ column densities imply unreasonably
long path lengths (~1 kpc) and low densities (~3 cm^-3). Complimentary
millimeter-wave, infrared, and visible observations of related species suggest
that the chemical model is incorrect and that the number density of H3+ must be
increased by one to two orders of magnitude. Possible solutions include a
reduced electron fraction, an enhanced rate of H2 ionization, and/or a smaller
value of the H3+ dissociative recombination rate constant than implied by
laboratory experiments.


title:
The Giant Flare of 1998 August 27 from SGR 1900+14: II. Radiative
  Mechanism and Physical Constraints on the Source

abstract:
  (ABBREVIATED) The extraordinary 1998 August 27 giant flare places strong
constraints on the physical properties of its source, SGR 1900+14. We make
detailed comparisons of the published data with the magnetar model. The giant
flare evolved through three stages, whose radiative mechanisms we address in
turn. A triggering mechanism is proposed, whereby a helical distortion of the
core magnetic field induces large-scale fracturing in the crust and a twisting
deformation of the crust and exterior magnetic field. The envelope of the
pulsating tail of the August 27 flare can be accurately fit, after ~40 s, by
the contracting surface of a relativistically hot, but inhomogeneous, trapped
fireball. We quantify the effects of direct neutrino-pair emission, thereby
deducing a lower bound ~ 10^{32} G-cm^3 to the magnetic moment of the confining
field. The radiative flux during the intermediate ~40 s of the burst appears to
exceed the trapped fireball fit. The spectrum and lightcurve of this smooth
tail are consistent with heating in an extended pair corona, possibly powered
by continuing seismic activity in the star. We consider in detail the critical
luminosity, below which a stable balance can be maintained between heating and
radiative cooling in a confined, magnetized pair plasma; but above which the
confined plasma runs away to local thermodynamic equilibrium. In the later
pulsating tail, the best fit temperature equilibrates at a value which agrees
well with the regulating effect of photon splitting. The remarkable four-peaked
substructure within each 5.16-s pulse provides strong evidence for the presence
of higher magnetic multipoles in SGR 1900+14. The corresponding collimation of
the X-ray flux is related to radiative transport in a super-QED magnetic field.


title:
The 2dF Galaxy Redshift Survey: constraints on cosmic star-formation
  history from the cosmic spectrum

abstract:
  We present the first results on the history of star formation in the Universe
based on the `cosmic spectrum', in particular, the volume-averaged,
luminosity-weighted, stellar absorption line spectrum of present day galaxies
from the 2dFGRS. This method is novel in that unlike previous studies it is not
an estimator based on total luminosity density. The cosmic spectrum is fitted
with models of population synthesis, tracing the history of star formation
prior to the epoch of the observed galaxies, using a method we have developed
which decouples continuum and spectral-line variations and is robust against
spectrophotometric uncertainties. The cosmic spectrum can only be fitted with
models incorporating chemical evolution and indicates there was a peak of
star-formation rate in the past of at least three times the current value and
that the increase back to z=1, assuming it scales as (1+z)^beta, has a strong
upper limit of beta<5. We find in the general case there is some model
degeneracy between star formation at low and high redshift. However, if we
incorporate previous work on star formation at z<1 we can put strong upper
limits on the SFR at z>1: e.g., if beta>2 then the SFR for 1<z<5 scales as
(1+z)^alpha with alpha<2. This is equivalent to stating that no more than 80%
of stars in the Universe formed at z>1. Our results are consistent with the
best-fit results from compilations of cosmic SFR estimates based on UV
luminosity density, which give 1.8<beta<2.9 and -1.0<alpha<0.7, and are also
consistent with estimates of Omega_stars based on the K-band luminosity
density.


title:
Electrodynamics of Magnetars: Implications for the Persistent X-ray
  Emission and Spindown of the Soft Gamma Repeaters and Anomalous X-ray Pulsars

abstract:
  (ABBREVIATED) We consider the structure of neutron star magnetospheres
threaded by large-scale electrical currents, and the effect of resonant Compton
scattering by the charge carriers (both electrons and ions) on the emergent
X-ray spectra and pulse profiles. In the magnetar model for the SGRs and AXPs,
these currents are maintained by magnetic stresses acting deep inside the star.
We construct self-similar, force-free equilibria of the current-carrying
magnetosphere with a power-law dependence of magnetic field on radius, B ~
r^(-2-p), and show that a large-scale twist softens the radial dependence to p
< 1. The spindown torque acting on the star is thereby increased in comparison
with a vacuum dipole. We comment on the strength of the surface magnetic field
in the SGR and AXP sources, and the implications of this model for the narrow
measured distribution of spin periods. A magnetosphere with a strong twist,
B_\phi/B_\theta = O(1) at the equator, has an optical depth ~ 1 to resonant
cyclotron scattering, independent of frequency (radius), surface magnetic field
strength, or charge/mass ratio of the scattering charge. When electrons and
ions supply the current, the stellar surface is also heated by the impacting
charges at a rate comparable to the observed X-ray output of the SGR and AXP
sources, if B_{dipole} ~ 10^{14} G. Redistribution of the emerging X-ray flux
at the ion and electron cyclotron resonances will significantly modify the
emerging pulse profile and, through the Doppler effect, generate a non-thermal
tail to the X-ray spectrum. The sudden change in the pulse profile of SGR
1900+14 after the 27 August 1998 giant flare is related to an enhanced optical
depth to electron cyclotron scattering, resulting from a sudden twist imparted
to the external magnetic field.


title:
Cluster Galaxy Populations from z=0.33 - 0.83: Characterizing Evolution
  with CL1358+62

abstract:
  We combine HST WFPC mosaics of clusters at multiple redshifts with Keck LRIS
spectroscopy to characterize different galaxy populations and how they evolve.
By combining quantitative measurements of structural parameters with velocity
dispersions, line indices, and morphological types, we attempt to establish
links between ellipticals, S0's, E+A's, and later type galaxies. Here we focus
on galaxies in CL1358+62, a massive cluster at z=0.33.


title: Nature of the Soft Gamma Repeaters and Anomalous X-ray Pulsars

abstract:
  I summarize recent developments in the magnetar model of the Soft Gamma
Repeaters and Anomalous X-ray Pulsars, give a critical inventory of alternative
models for the AXPs, and outline the improved diagnostics expected from present
observational efforts.


title: The Inner Structure of Cold Dark Matter Halos

abstract:
  I report on recent progress in our understanding of the structure of CDM
halos, and in particular of the inner mass profile of galaxy-sized systems.
Numerical simulations have consistently shown that the density profiles of CDM
halos steepen monotonically from the center outwards, with slopes shallower
than isothermal near the center and steeper than isothermal near the virial
radius. Ongoing debate centers on the precise radial dependence of the
logarithmic slope, as well as on whether it approaches a well defined
asymptotic central value. The latest high-resolution simulations suggest that
the circular velocity profile is well approximated by the model proposed by
Navarro, Frenk & White (NFW). On the other hand, the radial dependence of the
slope of the density profile differs modestly, but significantly, from the
model proposed by NFW. As a result, NFW fits tend to underestimate the density
at radii just inside the scale radius. Rather than implying a very steep (-1.5)
inner divergent slope, I argue that the data is actually best represented by a
model where the density profile becomes increasingly shallow with radius, with
little sign of approach to a well-defined asymptotic value. A model where the
{\it phase-space density profile} is a power law accounts well for these
results and suggests that the innermost slope may be as shallow as -0.75. These
conclusions are supported by a thorough numerical convergence study that
elucidates the effect of numerical parameters such as the timestep,
gravitational softening, and particle number, on the mass profile of simulated
dark matter halos.


title: Substructure in CDM Halos and the Heating of Stellar Disks

abstract:
  Numerical simulations have revealed the presence of long-lived substructure
in Cold Dark Matter (CDM) halos. These surviving cores of past merger and
accretion events vastly outnumber the known satellites of the Milky Way. This
finding has prompted suggestions that substructure in cold dark matter (CDM)
halos may be incompatible with observation and in conflict with the presence of
thin, dynamically fragile stellar disks. N-body simulations of a
disk/bulge/halo model of the Milky Way that includes several hundred dark
matter satellites with masses, densities and orbits derived from
high-resolution cosmological CDM simulations indicate that substructure plays
only a minor dynamical role in the heating of the disk. This is because the
orbits of satellites seldom take them near the disk, where their tidal effects
are greatest. We conclude that substructure might not preclude virialized CDM
halos from being acceptable hosts of thin stellar disks like that of the Milky
Way.


title:
Interferometric Mapping of Magnetic Fields in Star-forming Regions II.
  NGC2024 FIR5

abstract:
  We present the first interferometric polarization maps of the NGC2024 FIR5
molecular core obtained with the BIMA array at approximately 2 arcsec
resolution. We measure an average position angle of -60+-6 degrees in the main
core of FIR5 and 54+-9 degrees in the eastern wing of FIR5. The morphology of
the polarization angles in the main core of FIR5 suggests that the field lines
are parabolic with a symmetry axis approximately parallel to the major axis of
the putative disk in FIR5, which is consistent with the theoretical scenario
that the gravitational collapse pulled the field lines into an hour-glass
shape. The polarization percentage decreases toward regions with high intensity
and close to the center of the core, suggesting that the dust alignment
efficiency may decrease at high density. The plane-of-sky field strength can be
estimated with the modified Chandrasekhar-Fermi formula, and the small
dispersion of the polarization angles in FIR5 suggests that the magnetic field
is strong ($\gtrsim$ 2mG) and perhaps dominates the turbulent motions in the
core.


title:
Tomographic Separation of Composite Spectra. VIII. The Physical
  Properties of the Massive Compact Binary in the Triple Star System HD 36486
  (delta Orionis A)

abstract:
  Double-lined spectroscopic orbital elements have recently been found for the
central binary in the massive triple, delta Orionis A based on radial
velocities from cross-correlation techniques applied to IUE high dispersion
spectra and He I 6678 spectra obtained at Kitt Peak. The primary and secondary
velocity amplitudes were found to be 94.9 +/- 0.6 km/s and 186 +/- 9 km/s
respectively. Tomographic reconstructions of the primary and secondary stars'
spectra confirm the O9.5 II classification of the primary and indicate a B0.5
III type for the secondary. The widths of the UV cross-correlation functions
are used to estimate the projected rotational velocities, Vsin i = 157 +/- 6
km/s and 138 +/- 16 km/s for the primary and secondary, respectively implying
that both stars rotate faster than their orbital motion. We used the
spectroscopic results to make a constrained fit of the Hipparcos light curve of
this eclipsing binary, and the model fits limit the inclination to the range
between 67 and 77 degrees. The i = 67 degrees solution, which corresponds to a
near Roche-filling configuration, results in a primary mass of 11.2 solar
masses and a secondary mass of 5.6 solar masses, both of which are
substantially below the expected masses for stars of their luminosity. This
binary may have experienced a mass ratio reversal caused by Case A Roche lobe
overflow, or the system may have suffered extensive mass loss through a binary
interaction, perhaps during a common envelope phase, in which most of the
primary's mass was lost from the system rather than transferred to the
secondary.


title: On the C/O Enrichment of Novae Ejecta

abstract:
  Using the results of recent work in shear instabilities in stratified fluids,
we show that the resonant interaction between large-scale flows in the accreted
H/He envelope of white dwarf stars and interfacial gravity waves can mix with
the star's envelope with the white dwarf's surface material, leading to the
enhancement of the envelope's C/O abundance to levels required by extant models
for nova outbursts.


title:
Surface brightness fluctuation distances for nearby dwarf elliptical
  galaxies

abstract:
  We obtained B and R-band CCD images for the dwarf elliptical (dE) galaxies
DDO44, UGC4998, KK98_77, DDO71, DDO113, and UGC7356 at the NOT. Using Fourier
analysis technique we measure stellar R-band surface brightness fluctuations
(SBFs) and magnitudes in 29 different fields of the galaxies. Independent tip
of the red giant branch distances for DDO44, KK98_77, DDO71 are used to convert
their set of apparent into absolute SBF magnitudes. The results are combined
with the local (B-R) colours and compared with the (B-R)-\bar{M}_R relation for
mainly old, metal-poor stellar populations as predicted by Worthey's population
synthesis models using Padova isochrones. While the colour dependency of the
theoretical relation is confirmed by the empirical data, we find a systematic
zero point offset between observations and theory in the sense that models are
too faint by 0.13+-0.02 mag. Based on these findings we establish a new
semiempirical calibration of the SBF method as distance indicator for dE
galaxies with an estimated uncertainty of ~10 percent. Taking first advantage
of the improved calibration, we determine SBF distances for the other three
early-type dwarfs. Although found in the M81 group region, previous velocity
measurements suggested UGC4998 is in the background. This picture is confirmed
by our SBF distance of 10.5+-0.9 Mpc. We can further identify DDO113 as a faint
stellar system at the near side of the Canes Venatici I (CVn I) cloud at a
distance of 3.1+-0.3 Mpc. The second CVn I member in our sample, UGC7356, lies
at 6.7+-0.6 Mpc and spatially close to M106. We derive BR surface brightness
profiles and colour gradients for all dwarfs and determine photometric and
Sersic parameters. Finally, we discuss two objects in DDO71 and UGC7356 which
may resemble GCs.


title: On the shear instability of fluid interfaces

abstract:
  We examine the linear stability of fluid interfaces subjected to a shear
flow. Our main object is to generalize previous work to arbitrary Atwood
number, and to allow for surface tension and weak compressibility. The
motivation derives from instances in astrophysical systems where mixing across
material interfaces driven by shear flows may significantly affect the
dynamical evolution of these systems.


title:
Wide-field High-precision CCD Photometry of omega Centauri and Its RR
  Lyrae Stars

abstract:
  We present wide-field and high-precision BV and Ca & Stromgren by photometry
of omega Centauri and its RR Lyrae stars, which represents one of the most
extensive photometric surveys to date for this cluster. The member stars of
omega Cen are well discriminated from foreground Galactic disk stars from the
different distributions in the hk [=(Ca-b)-(b-y)] vs. b-y diagram. The
color-magnitude diagrams show the presence of several distinct red-giant
branches with a red, metal-rich, sequence clearly separated from other bluer
metal-poor ones. Comparison with our population models suggests the most
metal-rich population is few billion years younger than the most metal-poor
population. From our new BV photometry and hk metallicity measurements for RR
Lyrae stars in omega Cen, we also confirm that the luminosity of RR Lyrae stars
depends on evolutionary status as well as metallicity. From the presence of
several distinct populations and the internal age-metallicity relation, we
conclude omega Cen was once part of a more massive system that merged with the
Milky Way, as the Sagittarius dwarf galaxy is in the process of doing now.


title:
Omega Centauri as a Disrupted Dwarf Galaxy: Evidence from Multiple
  Stellar Populations

abstract:
  Our recent CCD photometry (Lee et al. 1999) has shown, for the first time,
that omega Cen has several distinct stellar populations, which is reminiscent
of the Sagittarius dwarf galaxy. Here we present more detailed analysis of the
data along with the population models. We confirm the presence of several
distinct red-giant-branches (RGBs) with a red metal-rich sequence well
separated from other bluer metal-poor ones. Our population models suggest the
red clump associated with the most metal-rich RGB is about 4 Gyr younger than
the dominant metal-poor component, indicating that omega Cen was enriched over
this timescale. These features, taken together with this cluster's other
unusual characteristics, provide good evidence that omega Cen was once part of
a more massive system that merged with the Milky Way, as the Sagittarius dwarf
galaxy is in the process of doing now. Mergers probably were much more frequent
in the early history of the Galaxy and omega Cen appears to be a relict of this
era.


title:
Synthetic Color-Magnitude Diagrams for omega Centauri and Other Massive
  Globular Clusters with Multiple Populations

abstract:
  We have constructed synthetic color-magnitude diagrams (CMDs) for omega Cen
and other massive globular clusters with apparently peculiar CMD morphology.
Our population models, which adopt the most up-to-date input physics and
parameters, show that the observed CMD of omega Cen can be reproduced by
adopting (1) multimodal metallicity distribution function as derived from the
observed color distribution of red-giant-branch (RGB) stars, and (2) an
internal age-metallicty relation among the populations therein. Similar results
were obtained for other massive globular clusters with bimodal
horizontal-branches (HBs). In particular, we found that the peculiar CMD
morphology (broad RGB, bimodal HB) and properties of RR Lyrae stars observed in
NGC 6388 and NGC 6441 can be reproduced by the composite of two distinct
populations with mild internal age-metallicity relations. This suggests that
these clusters, as well as omega Cen, may represent the relicts of disrupted
dwarf galaxies.


title: Uncovering CDM halo substructure with tidal streams

abstract:
  Models for the formation and growth of structure in a cold dark matter
dominated universe predict that galaxy halos should contain significant
substructure. Studies of the Milky Way, however, have yet to identify the
expected few hundred sub-halos with masses greater than about 10^6 Msun. Here
we propose a test for the presence of sub-halos in the halos of galaxies. We
show that the structure of the tidal tails of ancient globular clusters is very
sensitive to heating by repeated close encounters with the massive dark
sub-halos. We discuss the detection of such an effect in the context of the
next generation of astrometric missions, and conclude that it should be easily
detectable with the GAIA dataset. The finding of a single extended cold stellar
stream from a globular cluster would support alternative theories, such as
self-interacting dark matter, that give rise to smoother halos.


title:
Sub-structure of the outer Galactic Halo from the 2 Micron All Sky
  Survey

abstract:
  A pole-count analysis of the infrared 2MASS survey is presented, in order to
identify faint stream-like structures within the halo of the Milky Way.
Selecting stars with colours consistent with M-giant stars, we find a strong
over-density of sources on a stream with pole (l=95,b=13), which corresponds to
the pole of the orbit of the Sagittarius dwarf galaxy. This great-circle
feature of width ~12 degrees, contains 5% of the late M-giants in the Halo. No
other stream-like structures are detected in M-giants in the 2MASS Second
Incremental Data Release (2IDR), and in particular, we find no evidence for a
stellar component to the Magellanic Stream. This suggests that the present
accretion rate of low-mass satellites with a luminous component is very low,
and the formation of the luminous component of the Halo must have been
essentially complete before the accretion of the Sagittarius dwarf galaxy, more
than 3Gyr ago. We also search for great-circle streams using almost all
high-latitude (|b|>30) sources in the 2IDR dataset. No narrow great-circle
streams of width 0.5-2 degrees were found, though we were only sensitive to
relatively nearby (<17kpc) remnants of massive (10^6 Msun) globular clusters.
If the Galactic potential is close to being spherical, as some recent
observations suggest, the lack of observed great-circle streams is consistent
with the presence of dark matter substructures in the Halo. Although
alternative explanations cannot be ruled out from our analysis of the 2IDR
dataset, future experiments with better statistics have the potential to reveal
the heating effect of dark matter substructure on stellar streams.


title: Bending Instability of an Accretion Disc Around a Black Hole

abstract:
  We demonstrate that generically an accretion disk around a compact object
could have a new type of instability in that the accretion flow need not be
symmetric with respect to the equatorial plane even when matter is supplied
symmetrically farther out. We find that this behaviour is mainly due to
interaction of outgoing matter bounced off the centrifugal barrier and the
incoming accretion. We believe that X-ray variability could be developed by
this instability.


title: Evolution of the Radio Remnant of SN 1987A: 1990 -- 2001

abstract:
  The development of the radio remnant of SN 1987A has been followed using the
Australia Telescope Compact Array since its first detection in 1990 August. The
remnant has been observed at four frequencies, 1.4, 2.4, 4.8 and 8.6 GHz, at
intervals of 4 - 6 weeks since the first detection. These data are combined
with the 843 MHz data set of Ball et al. (2001) obtained at Molonglo
Observatory to study the spectral and temporal variations of the emission.
These observations show that the remnant continues to increase in brightness,
with a larger rate of increase at recent times. They also show that the radio
spectrum is becoming flatter, with the spectral index changing from -0.97 to
-0.88 over the 11 years. In addition, at roughly yearly intervals since 1992,
the remnant has been imaged at 9 GHz using super-resolution techniques to
obtain an effective synthesised beamwidth of about 0".5. The imaging
observations confirm the shell-morphology of the radio remnant and show that it
continues to expand at ~3000 km/s. The bright regions of radio emission seen on
the limb of the shell do not appear to be related to the optical hotspots which
have subsequently appeared in surrounding circumstellar material.


title: Ecosystems, from life, to the Earth, to the Galaxy

abstract:
  Ecosystems are systems where energy flows and material cycles are maintained
in an apparently stable, but non-equilibrium state through a process of
self-regulation. Such a definition does just apply to biological systems, it
can also apply to systems that involve entirely physical processes. We discuss
how four systems, each operating on very different spatial and temporal scales,
each exhibit these features of an ecosystem. These are, in order of increasing
magnitude, the cell, the forest, the Earth and the Galaxy. In particular, we
discuss how the process of star formation across the spiral arms of galaxies
works as an ecosystem. The carbon abundance plays a crucial role in both the
self-regulation and the evolution of the system. We suggest that spiral
galaxies may be the first ecosystems to form in the Universe after the Big
Bang.


title: Discovery of a 1247 s pulsar in the Be X-ray binary SAX J2239.3+6116

abstract:
  A search for pulsations from the Be X-ray binary SAX J2239.3+6116, through
observations with the Narrow Field Instruments on BeppoSAX and the Proportional
Counter Array on RXTE, yielded the clear presence of a 1247 s coherent
oscillation. Given the fairly high X-ray luminosity on previous occasions (up
to a few times 10^36 erg/s in 2 to 28 keV), the oscillation must be due to the
spin of a neutron star. Assuming that the 262 day recurrence time is the
orbital period, SAX J2239.3+6116 has both the longest orbital period and the
longest pulse period of 24 Be X-ray binaries with measured orbital periods.


title: Group analysis in the SSRS2 catalog

abstract:
  We present an automated method to detect populations of groups in galaxy
redshift catalogs. This method uses both analysis of the redshift distribution
along lines of sight in fixed cells to detect elementary structures and a
friend-of-friend algorithm to merge these elementary structures into physical
structures. We apply this method to the SSRS2 galaxy redshift catalog. The
groups detected with our method are similar to group catalogs detected with
pure friend-of-friend algorithms. They have similar mass distribution, similar
abundance versus redshift, similar 2-point correlation function and the same
redshift completeness limit, close to 5000 km/s. If instead of SSRS2, we use
catalogs of new generation, it would lead to a completeness limit of
z$\sim$0.7. We model the luminosity function for nearby galaxy groups by a
Schechter function with parameters M*=(-19.99+/-0.36)+5logh and alpha=-1.46 +/-
0.17 to compute the mass to light ratio. The median value of the mass to light
ratio is 360 h M/L and we deduce a relation between mass to light ratio and
velocity dispersion sigma (M/L=3.79 +/- 0.64)sigma -(294 +/- 570)). The more
massive the group, the higher the mass to light ratio, and therefore, the
larger the amount of dark matter inside the group. Another explanation is a
significant stripping of the gas of the galaxies in massive groups as opposed
to low mass groups. This extends to groups of galaxies the mild tendency
already detected for rich clusters of galaxies. Finally, we detect a barely
significant fundamental plane for these groups but much less narrow than for
clusters of galaxies.


title:
On the properties of massive Population III stars and metal-free stellar
  populations

abstract:
  We present realistic models for massive Population III stars and stellar
populations based on non-LTE model atmospheres, recent stellar evolution tracks
and up-to-date evolutionary synthesis models, to study their spectral
properties, including their dependence on age, star formation history, and IMF.
(..) The main results regarding integrated stellar populations are: * For young
bursts and the case of a constant SFR, nebular continuous emission - neglected
in previous studies - dominates the spectrum redward of Lyman-alpha (...).
Therefore predicted emission line equivalent widths are considerably smaller
than found in earlier studies, whereas the detection of the continuum is eased.
Nebular line and continuous emission strongly affect the broad band photometric
properties of Pop III objects. * Due to stellar evolution, the hardness of the
ionising spectrum decreases rapidly, leading to the disappearance of the
characteristic HeII 1640 recombination lines after ~ 3 Myr in instantaneous
bursts. * The relative efficiency of ionising photon energy to heavy element
rest mass production, eta, of metal-poor and metal-free populations is
increased by factors of ~ 4 to 18 with respect to solar metallicity and for
``standard'' IMFs. * The lowest values of eta ~ 1.6 - 2.2 % are obtained for
IMFs exclusively populated with high mass stars (M_low >~ 50 Msun). If correct,
the yields dominated by pair creation SNae then predict large overabundances of
O/C and Si/C compared to solar abundance ratios. Detailed results are given in
tabular form and as fit formulae for implementation in other calculations.
(abridged abstract)


title: Relic Black Holes and Type 2 Quasars

abstract:
  We follow the evolution of the Black Hole mass function in the assumption
that mass accretion onto a massive BH is the powering mechanism of AGN
activity. With reasonable assumptions suggested by current knowledge, it is
possible to reproduce the Black Hole mass function derived from local bulges.
In particular it is found that the majority of the mass in relic Black Holes
was produced during AGN activity and that the ratio between obscured and
unobscured quasars is between 1 and 2, much lower than required by synthesis
models of the X-ray background.


title: Environmental Effects in Galaxies: The Data

abstract:
  We present optical and millimetric data for 47 intermediate Hubble type
spiral galaxies located either in dense environments or in the field. We
compare correlations between global parameters, such as far-infrared
luminosity, blue luminosity, and total molecular gas content, with other
samples of galaxies, including normal galaxies, clusters and ultraluminous
infrared galaxies. We find that overall our sample is a well defined subset of
these other samples of galaxies.


title:
Investigating the long-term evolution of galaxies: Noise,cuspy halos and
  bars

abstract:
  I review the arguments for the importance of halo structure in driving galaxy
evolution and coupling a galaxy to its environment. We begin with a general
discussion of the key dynamics and examples of structure dominated by modes. We
find that simulations with large numbers of particles (N > 1e6) are required to
resolve the dynamics. Finally, I will describe some new results which
demonstrates that a disk bar can produce cores in a cuspy CDM dark-matter
profile within a gigayear. An inner Lindblad-like resonance couples the
rotating bar to halo orbits at all radii through the cusp, rapidly flattening
it. This resonance disappears for profiles with cores and is responsible for a
qualitative difference in bar-driven halo evolution with and without a cusp.
Although the bar gives up the angular momentum in its pattern to make the core,
the formation epoch is rich in accretion events to recreate or trigger a
classic stellar bar. The evolution of the cuspy inner halo by the
first-generation bar paves the way for a long-lived subsequent bar with low
torque and a stable pattern speed.


title:
Cometary molecular clouds around RNO6. On-going star formation near the
  double cluster h and chi Persei

abstract:
  We present molecular line observations of the star-forming cloud around RNO6
along with a newly discovered nearby molecular cloud that we name RNO6NW. Both
clouds display striking similarities in their cometary structures and overall
kinematics. By using 13CO line observations, we estimate that these clouds have
similar sizes (~4.5 pc) and masses (~200 solar masses). Both molecular clouds
RNO6 and RNO6NW are active in star formation. From new high resolution near-IR
narrowband images, we confirm that RNO6 hosts an embedded IR cluster that
includes a Herbig Be star. A conspicuous H2 filament is found to delineate the
dense cometary head of the globule. RNO6NW hosts at least two IR sources and a
bipolar molecular outflow of ~0.9 pc of length and ~0.5 solar masses. We show
that the cometary structure of both clouds has been created by the UV radiation
from numerous OB stars lying ~1.5 degree to the north. Such OB stars are
associated with the double cluster h and chi Persei, and are probably members
of the PerOB1 association. Thus star formation inside these clouds has been
very likely triggered by the Radiation Driven Implosion (RDI) mechanism. From
comparison to RDI theoretical models, we find that the similar kinematics and
morphology of both clouds is well explained if they are at a re-expansion
phase. Triggered sequential star formation also explains the observed spatial
distribution of the members of the near-IR cluster inside the RNO6 cloud, and
the morphology of the H2 filament. We conclude that the RNO6 and RNO6NW clouds
are high-mass counterparts to the cometary globules of smaller masses which
have been studied up to now. Thus our observations demonstrate that the RDI
mechanism can produce, not only low mass stars in small globules, but also
intermediate mass stars and clusters in massive clouds.


title:
Environmental effects in galaxies: Molecular Gas, Star Formation, and
  Activity

abstract:
  In order to study whether there is any correlation between nuclear
activities, gas content, and the environment where galaxies reside, we have
obtained optical and millimetric spectra for a well-defined sample of
intermediate Hubble type spirals in dense environments and in the field. We
found that these spirals in dense environments have on average: less molecular
gas per blue luminosity, higher atomic gas fraction, lower current star
formation rate, and the same star formation efficiency as field galaxies.
Although none of these results stand out as a single strong diagnostic, given
their statistical significance, taken together they indicate a trend for
diminished gas content and star formation activity in galaxies in high density
environments. Our results suggest that galaxies in dense environments have
either (i) consumed their molecular gas via star formation in the past or (ii)
that dense environments leads to an inhibition of molecular gas from atomic
phase. The similarities in star formation efficiency of the dense environments
and field galaxies suggest that the physical processes controling the formation
of stars from the molecular gas are local rather than global. We also found
that star formation rate per blue luminosity increases linearly as the total
amount of gas increases in LINERs. This result, based on a small sample,
suggests that LINERs are powered by star formation rather than an AGN.


title:
Tracing out the northern stream of the Sagittarius dwarf galaxy with
  color- magnitude diagram techniques

abstract:
  Standard cosmology predicts that dwarfs were the first galaxies to be formed
in the Universe and that many of them merge afterwards to form bigger galaxies
such as the Milky Way. This process would have left behind traces such as tidal
debris or tidal streams in the outer halo. We report here the detection of two
new tidal debris of the northern stream of the Sagittarius dwarf galaxy, based
in the analysis of wide field, deep color- magnitude diagrams. These detections
provide strong observational evidence that the stripped debris of Sagittarius
extends up to 60 degrees from its center, suggesting that the stream of this
galaxy completely wraps the Milky Way in an almost polar orbit. Our negative
detections also suggest the stream is narrow, supporting a nearly spherical
Milky Way dark matter halo potential.


title:
Image reduction pipeline for the detection of variable sources in highly
  crowded fields

abstract:
  We present a reduction pipeline for CCD (charge-coupled device) images which
was built to search for variable sources in highly crowded fields like the M31
bulge and to handle extensive databases due to large time series. We describe
all steps of the standard reduction in detail with emphasis on the realisation
of per pixel error propagation: Bias correction, treatment of bad pixels,
flatfielding, and filtering of cosmic rays. The problems of conservation of PSF
(point spread function) and error propagation in our image alignment procedure
as well as the detection algorithm for variable sources are discussed: We build
difference images via image convolution with a technique called OIS (Alard &
Lupton, 1998), proceed with an automatic detection of variable sources in noise
dominated images and finally apply a PSF-fitting, relative photometry to the
sources found. For the WeCAPP project (Riffeser et al., 2001) we achieve 3
sigma detections for variable sources with an apparent brightness of e.g. m =
24.9 mag at their minimum and a variation of dm = 2.4 mag (or m = 21.9 mag
brightness minimum and a variation of dm = 0.6 mag) on a background signal of
18.1 mag/arcsec^2 based on a 500 s exposure with 1.5 arcsec seeing at a 1.2 m
telescope. The complete per pixel error propagation allows us to give accurate
errors for each measurement.


title:
The nonlinear-electrodynamic bending of the x-ray and gamma-ray in the
  magnetic field of pulsars and magnetars

abstract:
  It was shown that according to the non-linear electrodynamics of vacuum
electromagnetic rays should bend in the field of magnetic dipole. The angles of
ray bending in the gravitational and magnetic fields of pulsars and magnetars
were obtained. In the case of pulsars with $b\sim R\sim $ 100 km, $B_0\sim
10^{13} G$ the value of the angle of non-linear electrodynamic bending of a ray
in the Heisenberg-Euler theory will reach the value of $\delta \psi_{NED}\sim
30'',$ and in the case of a magnetar with $B_0\sim 10^{15} G$ the angle $\delta
\psi_{NED}$ will increase to $\delta \psi_{NED}\sim 1 rad\sim 60^\circ .$ The
angle of gravitational bending of a ray at neutron star with $r_g$ = 3 km in
the same conditions will be equal to $\delta \psi_g\sim 0.06$ rad $\sim 4^\circ
>.$ Observations can only be made in X- rays and gamma-rays, for which the
agnetosphere is quite opaque. Because the distance from the Earth to the
well-known pulsars and magnetars is too large to observe the pure effect of a
ray bending. The non-linear electrodynamic bending of a ray as well as the
gravitational bending will be revealed in the effect of lensing.

categories: astro-ph gr-qc hep-ex hep-th physics.optics


title: Microlensing search towards M31

abstract:
  We present the first results of the analysis of data collected during the
1998-99 observational campaign at the 1.3 meter McGraw-Hill Telescope, towards
the Andromeda galaxy (M31), aimed to the detection of gravitational
microlensing effects as a probe of the presence of dark matter in our and in
M31 halo. The analysis is performed using the pixel lensing technique, which
consists in the study of flux variations of unresolved sources and has been
proposed and implemented by the AGAPE collaboration. We carry out a shape
analysis by demanding that the detected flux variations be achromatic and
compatible with a Paczynski light curve. We apply the Durbin-Watson hypothesis
test to the residuals. Furthermore, we consider the background of variables
sources. Finally five candidate microlensing events emerge from our selection.
Comparing with the predictions of a Monte Carlo simulation, assuming a standard
spherical model for the M31 and Galactic haloes, and typical values for the
MACHO mass, we find that our events are only marginally consistent with the
distribution of observable parameters predicted by the simulation.


title:
Variability in active galactic nuclei: confrontation of models with
  observations

abstract:
  The variability of active galactic nuclei (AGN) has long held the promise of
shedding light on their detailed structure, and possibly other astrophysical
phenonema. Different emission mechanisms lead to different patterns of
variability in flux which are in principle easily distinguishable. Recent
predictions for the expected spectrum of variations for various models are now
in such a form that they can be compared with the observed statistical
properties of AGN light curves from large scale monitoring programmes. In this
paper, we use the results of a long term monitoring programme of a large sample
of quasars and Seyfert galaxies, as well as individual light curves from the
literature, to distinguish between the various model predictions. The results
favour a model based on accretion disc instability over the starburst model
where the variation comes from a succession of supernova bursts, but it also
appears that much of the observed variation in quasars is due to gravitational
microlensing.


title: Variability of accretion flow in the core of the Seyfert galaxy NGC 4151

abstract:
  We analyze observations of the Seyfert galaxy NGC 4151 covering 90 years in
the optical band and 27 years in the 2-10 keV X-ray band. We compute the
Normalized Power Spectrum Density (NPSD), the Structure Function (SF) and the
Autocorrelation Function (ACF) for these data. The results show that the
optical and X-ray variability properties are significantly different. X-ray
variations are predominantly in the timescale range of 5 - 1000 days. The
optical variations have also a short timescale component which may be related
to X-ray variability but the dominant effect is the long timescale variability,
with timescales longer than $\sim$ 10 years. We compare our results with
observations of NGC 5548 and Cyg X-1. We conclude that the long timescale
variability may be caused by radiation pressure instability in the accretion
disk, although the observed timescale in NGC 4151 is by a factor of few longer
than expected. X-ray variability of this source is very similar to what is
observed in Cyg X-1 but scaled with the mass of the black hole, which suggests
that the radiation pressure instability does not affect considerably the X-ray
production.


title:
An X-ray Selected Galaxy Cluster at z=1.11 in the Rosat Deep Cluster
  Survey

abstract:
  We report the discovery of an X-ray luminous galaxy cluster at z =1.11. RDCS
J0910+5422 was selected as an X-ray cluster candidate in the ROSAT Deep Cluster
Survey on the basis of its spatial extent in a Rosat PSPC image. Deep optical
and near-IR imaging reveal a red galaxy overdensity around the peak of the
X-ray emission, with a significant excess of objects with J-K and I-K colors
typical of elliptical galaxies at z ~ 1.0. Spectroscopic observations at the
Keck II telescope secured 9 galaxy redshifts in the range 1.095<z<1.120
yielding a mean cluster redshift of <z>=1.106. Eight of these galaxies lie
within a 30 arcsec radius around the peak X-ray emission. A deep Chandra ACIS
exposure on this field shows extended X-ray morphology and allows the X-ray
spectrum of the intracluster medium to be measured. The cluster has a
bolometric luminosity L_x = 2.48^{+0.33}_{-0.26} x 10^44 ergs/s, a temperature
of kT = 7.2^{+2.2}_{-1.4} keV, and a mass within r = 1 Mpc of 7.0 x 10^14 M_sun
(H_0=65 km/s/Mpc, Omega_m = 0.3, and Lambda = 0.7). The spatial distribution of
the cluster members is elongated, which is not due to an observational
selection effect, and followed by the X-ray morphology. The X-ray surface
brightness profile and the spectrophotometric properties of the cluster members
suggest that this is an example of a massive cluster in an advanced stage of
formation with a hot ICM and an old galaxy population already in place at z >
1.


title:
From Correlations of Galaxy Properties to the Physics of Galaxy
  Formation: A Theoretical Framework

abstract:
  (Abridged) Motivated by forthcoming data from the Sloan Digital Sky Survey,
we present a theoretical framework that can be used to interpret Principal
Component Analysis (PCA) of disk galaxy properties. We use the formalism
introduced by Mo, Mao, & White to compute the observable properties of galaxies
in a number of model populations, varying assumptions about which physical
parameters determine structural quantities and star formation histories. We
then apply PCA to these model populations. Our baseline model assumes that halo
mass, spin parameter, and formation redshift are the governing input parameters
and that star formation is determined by surface density through a Schmidt law.
  In all cases, the first principal component is primarily a measure of the
shape of the spectral energy distribution (SED), and it is usually driven by
variations in the spin parameter, which influences star formation through the
disk surface density. The second and (in some cases) third principal components
consist mainly of ``scale'' parameters like luminosity, disk radius, and
circular velocity. However, the detailed division of these scale parameters,
the disk surface brightness, and the rotation curve slope among the principal
components changes significantly from model to model. Our calculations yield
predictions of principal component structure for the baseline model of disk
galaxy formation, and a physical interpretation of these predictions. They also
show that PCA can test the core assumptions of that model and reveal the
presence of additional physical parameters that may govern observable galaxy
properties.


title: The Metallicity of the Redshift 4.16 Quasar BR2248-1242

abstract:
  We estimate the metallicity in the broad emission-line region of the redshift
z=4.16 quasar, BR2248-1242, by comparing line ratios involving nitrogen to
theoretical predictions. BR2248-1242 has unusually narrow emission lines with
large equivalent widths, thus providing a rare opportunity to measure several
line-ratio abundance diagnostics. The combined diagnostics indicate a
metallicity of ~2 times solar. This result suggests that an episode of vigorous
star formation occurred near BR2248-1242 prior to the observed z=4.16 epoch.
The time available for this enrichment episode is only ~1.5 Gyr at z=4.16 (for
H_{0}=65 km s^-1 Mpc^-1, Omega_{m}=0.3 and Omega_Lambda ~< 1). This evidence
for high metallicities and rapid star formation is consistent with the expected
early-epoch evolution of dense galactic nuclei.


title: Simulating CCDs for the Chandra Advanced CCD Imaging Spectrometer

abstract:
  We have implemented a Monte Carlo algorithm to model and predict the response
of various kinds of CCDs to X-ray photons and minimally-ionizing particles and
have applied this model to the CCDs in the Chandra X-ray Observatory's Advanced
CCD Imaging Spectrometer. This algorithm draws on empirical results and
predicts the response of all basic types of X-ray CCD devices. It relies on new
solutions of the diffusion equation, including recombination, to predict the
radial charge cloud distribution in field-free regions of CCDs. By adjusting
the size of the charge clouds, we can reproduce the event grade distribution
seen in calibration data. Using a model of the channel stops developed here and
an insightful treatment of the insulating layer under the gate structure
developed at MIT, we are able to reproduce all notable features in ACIS
calibration spectra.
  The simulator is used to reproduce ground and flight calibration data from
ACIS, thus confirming its fidelity. It can then be used for a variety of
calibration tasks, such as generating spectral response matrices for spectral
fitting of astrophysical sources, quantum efficiency estimation, and modeling
of photon pile-up.


title: The Arecibo Dual-Beam Survey: The HI Mass Function of Galaxies

abstract:
  We use the HI-selected galaxy sample from the Arecibo Dual-Beam Survey
(Rosenberg & Schneider 2000) to determine the shape of the HI mass function of
galaxies in the local universe using both the step-wise maximum likelihood and
the 1/V_tot methods. Our survey region spanned all 24 hours of right ascension
at selected declinations between 8 and 29 degrees covering ~430 deg^2 of sky in
the main beam. The survey is not as deep as some previous Arecibo surveys, but
it has a larger total search volume and samples a much larger area of the sky.
We conducted extensive tests on all aspects of the galaxy detection process,
allowing us to empirically correct for our sensitivity limits, unlike the
previous surveys. The mass function for the entire sample is quite steep, with
a power-law slope of \alpha ~ -1.5. We find indications that the slope of the
HI mass function is flatter near the Virgo cluster, suggesting that
evolutionary effects in high density environments may alter the shape of the HI
mass function. These evolutionary effects may help to explain differences in
the HI mass function derived by different groups. We are sensitive to the most
massive sources (log M > 5x10^10 M\solar) over most of the declination range,
\~1 sr, and do not detect any massive low surface brightness galaxies. These
statistics restrict the population of Malin 1-like galaxies to <5.5x10^-6
Mpc^-3.


title: Tilted CDM versus WDM in the Subgalactic Scuffle

abstract:
  Although the currently favored cold dark matter plus cosmological constant
model (LCDM) has proven to be remarkably successful on large scales, on
subgalactic scales it faces some potentially fatal difficulties; these include
over-producing dwarf satellite galaxies and predicting excessive central
densities in dark halos. Among the most natural cosmological solutions to these
problems is to replace cold dark matter with a warm species (LWDM). The warm
component acts to reduce the small-scale power, resulting in fewer galactic
subhalos and lower halo central densities. An alternative model with a mild
``tilt'' in the inflationary power spectrum (TLCDM; n =0.9) similarly reduces
the central densities of dark halos, although the substructure abundance
remains relatively high. Here I argue that because dwarf galaxy formation
should be suppressed in the presence of a strong ionizing background, favored
LWDM models will generally under-predict the observed abundance of dwarf
galaxies. The satellite count for TLCDM fairs much better, as long as the
photoionization effect is taken into account. TLCDM provides a more successful
alternative to LWDM on subgalactic scales with the added attraction that it
relies on only a minor, natural adjustment to the standard framework of CDM.


title:
Pulsar Timing at Urumqi Astronomical Observatory: Observing System and
  Results

abstract:
  A pulsar timing system has been operating in the 18-cm band at the Urumqi
Astronomical Observatory 25-m telescope since mid-1999. Frequency resolution
allowing dedispersion of the pulsar signals is provided by a 2X128X2.5 MHz
filterbank/digitiser system. Observations of 74 pulsars over more than 12
months have resulted in updated pulsar periods and period derivatives, as well
as improved positions. Comparison with previous measurements showed that the
changes in period and period derivative tend to have the same sign and to be
correlated in amplitude. A model based on unseen glitches gives a good
explanation of the observed changes, suggesting that long-term fluctuations in
period and period derivatives are dominated by glitches. In 2000 July, we
detected a glitch of relative amplitude Delta_nu/nu~24X1e-9 in the Crab pulsar.
The post-glitch decay appears similar to other large Crab glitches.


title: The GAIA astrometric survey of extra-solar planets

abstract:
  The ESA Cornerstone Mission GAIA, to be launched prior to 2012 and with a
nominal lifetime of 5 years, will improve the accuracy of Hipparcos astrometry
by more than two orders of magnitude. GAIA high-precision global astrometric
measurements will provide deep insights on the science of extra-solar planets.
The GAIA contribution is primarily understood in terms of the number and
spectral type of targets available for investigation, and characteristics of
the planets to be searched for. Several hundreds of thousands of solar-type
stars (F-G-K) within a sphere of $\sim 200$ pc centered on our Sun will be
observed. GAIA will be particularly sensitive to giant planets
(M$_\mathrm{p}$$\sim$M$_\mathrm{J}$) on wide orbits, up to periods twice as
large as the mission duration, the potential signposts of the existence of
rocky planets in the Habitable Zone. Thousands of new planets might be
discovered, and a significant fraction of those which will be detected will
have orbital parameters measured to better than 30% accuracy. By measuring to a
few degrees the relative inclinations of planets in multiple systems with
favorable configurations, GAIA will also make measurements of unique value
towards a better understanding of the formation and evolution processes of
planetary systems.


title: The Nonlinear Turbulent Dynamo

abstract:
  We simulate the evolution of an initially weak magnetic field in forced
turbulence for a range of Prandtl numbers. The field grows exponentially with
the Kulsrud-Anderson $k^{3/2}$ spectrum until the magnetic energy approaches
the viscous-scale kinetic energy, where the magnetic forces then backreact on
the velocity. Further growth proceeds more slowly until a saturated state is
reached where the magnetic and kinetic energies are equal, and where the
magnetic energy exists primarily at the resistive scale. We discuss the
structure of this turbulence and the extrapolation of the results to
astrophysically-large Prandtl numbers.


title:
Discovery of Active Galactic Nuclei in Mid- and Far-Infrared Deep
  Surveys with ISO

abstract:
  We present a summary on the discovery of active galactic nuclei in mid- and
far-infrared deep surveys with use of the Infrared Space Observatory.


title:
Frequentist Estimation of Cosmological Parameters from the MAXIMA-1
  Cosmic Microwave Background Anisotropy Data

abstract:
  We use a frequentist statistical approach to set confidence intervals on the
values of cosmological parameters using the MAXIMA-1 and COBE measurements of
the angular power spectrum of the cosmic microwave background. We define a
$\Delta \chi^{2}$ statistic, simulate the measurements of MAXIMA-1 and COBE,
determine the probability distribution of the statistic, and use it and the
data to set confidence intervals on several cosmological parameters. We compare
the frequentist confidence intervals to Bayesian credible regions. The
frequentist and Bayesian approaches give best estimates for the parameters that
agree within 15%, and confidence interval-widths that agree within 30%. The
results also suggest that a frequentist analysis gives slightly broader
confidence intervals than a Bayesian analysis. The frequentist analysis gives
values of \Omega=0.89{+0.26\atop -0.19}, \Omega_{\rm B}h^2=0.026{+0.020\atop
-0.011} and n=1.02{+0.31\atop -0.10}, and the Bayesian analysis gives values of
\Omega=0.98{+0.14\atop -0.19}, \Omega_{\rm B}h^2=0.0.029{+0.015\atop-0.010},
and $n=1.18{+0.10\atop -0.23}$, all at the 95% confidence level.


title:
The 2dF Galaxy Redshift Survey: The b_J-band galaxy luminosity function
  and survey selection function

abstract:
  We use more than 110500 galaxies from the 2dF galaxy redshift survey (2dFGRS)
to estimate the b_J-band galaxy luminosity function at redshift z=0, taking
account of evolution, the distribution of magnitude measurement errors and
small corrections for incompletenessin the galaxy catalogue. Throughout the
interval -16.5>M- 5log h>-22, the luminosity function is accurately described
by a Schechter function with M* -5log h =-19.66+/-0.07, alpha=-1.21+/-0.03 and
phistar=(1.61+/-0.08) 10^{-2} h^3/Mpc^3, giving an integrated luminosity
density of rho_L=(1.82+/-0.17) 10^8 h L_sol/Mpc^3 (assuming an Omega_0=0.3,
Lambda_0=0.7 cosmology). The quoted errors have contributions from the accuracy
of the photometric zeropoint, large scale structure in the galaxy distribution
and, importantly, from the uncertainty in the appropriate evolutionary
corrections. Our luminosity function is in excellent agreement with, but has
much smaller statistical errors than an estimate from the Sloan Digital Sky
Survey (SDSS) data when the SDSS data are accurately translated to the b_J-band
and the luminosity functions are normalized in the same way. We use the
luminosity function, along with maps describing the redshift completeness of
the current 2dFGRS catalogue, and its weak dependence on apparent magnitude, to
define a complete description of the 2dFGRS selection function. Details and
tests of the calibration of the 2dFGRS photometric parent catalogue are also
presented.


title: Closed Universes from Cosmological Instantons

abstract:
  Current observational data is consistent with the universe being slightly
closed. We investigate families of singular and non-singular closed instantons
that could describe the beginning of a closed inflationary universe. We
calculate the scalar and tensor perturbations that would be generated from
singular instantons and compute the corresponding CMB power spectrum in a
universe with cosmological parameters like our own. We investigate spatially
homogeneous modes of the instantons, finding unstable modes which render the
instantons sub-dominant contributions in the path integral. We show that a
suitable condition may be imposed on singular closed instantons, constraining
their instabilities. With this constraint these instantons can provide a
suitable model of the early universe, and predict CMB power spectra in close
agreement with the predictions of slow-roll inflation.


title:
Lyman alpha line formation in starbursting galaxies II. Extremely Thick,
  Dustless, and Static HI Media

abstract:
  The Lya line transfer in an extremely thick medium of neutral hydrogen is
investigated by adopting an accelerating scheme in our Monte Carlo code to skip
a large number of core or resonant scatterings. This scheme reduces computing
time significantly with no sacrifice in the accuracy of the results. We applied
this numerical method to the Lya transfer in a static, uniform, dustless, and
plane-parallel medium. Two types of photon sources have been considered, the
midplane source and the uniformly distributed sources. The emergent profiles
show double peaks and absorption trough at the line-center. We compared our
results with the analytic solutions derived by previous researchers, and
confirmed that both solutions are in good agreement with each other. We
investigated the directionality of the emergent Lya photons and found that limb
brightening is observed in slightly thick media while limb darkening appears in
extremely thick media. The behavior of the directionality is noted to follow
that of the Thomson scattered radiation in electron clouds, because both Lya
wing scattering and Thomson scattering share the same Rayleigh scattering phase
function. The mean number of wing scatterings just before escape is in exact
agreement with the prediction of the diffusion approximation. The Lya photons
constituting the inner part of the emergent profiles follow the relationship
derived from the diffusion approximation. We present a brief discussion on the
application of our results to the formation of Lya broad absorption troughs and
P-Cygni type Lya profiles seen in the UV spectra of starburst galaxies.


title:
Cluster of Gamma-ray Bursts - Image of a Source. Catalog of Clusters
  (Sources) of Gamma-ray Bursts

abstract:
  The clusters of gamma-ray bursts are considered which are assumed to be
images of the repeated gamma-ray burst (GRB) sources. It is shown, that
localization of the cosmic gamma-ray burst sources (GBS) is determined by the
clusters of GRBs. About 100 candidates in sources are presented in the form of
the catalog, which is compiled relying on the base of the BATSE data up to
middle of 2000. Gamma-ray bursts (from 5 to 13) of a cluster that display a
source do not coincide in their position. The catalog table containing basic
information about the GRB sources yields the possibility to research the GBS
properties and their identification. The birth of GRBs in the clusters allows
predicting the appearance of GRBs both in time and space. Most general
properties of the supposed GRB sources are discussed. An attempt to compile the
first GRB source catalog is made.


title: Orbital Divergence and Relaxation in the Gravitational N-Body Problem

abstract:
  One of the fundamental aspects of statistical behaviour in many-body systems
is exponential divergence of neighbouring orbits, which is often discussed in
terms of Liapounov exponents. Here we study this topic for the classical
gravitational N-body problem. The application we have in mind is to old stellar
systems such as globular star clusters, where N~10^6, and so we concentrate on
spherical, centrally concentrated systems with total energy E<0. Hitherto no
connection has been made between the time scale for divergence (denoted here by
t_e) and the two-body relaxation time scale (t_r), even though both may be
calculated by consideration of two-body encounters.
  In this paper we give a simplified model showing that divergence in phase
space is initially roughly exponential, on a timescale proportional to the
crossing time (defined as a mean time for a star to cross from one side of the
system to another). In this phase t_e is much less than t_r, if N is not too
small (i.e. N is much more than about 30). After several e-folding times, the
model shows that the divergence slows down. Thereafter the divergence (measured
by the energies of the bodies) varies with time as t^{1/2}, on a timescale
nearly proportional to the familiar two-body relaxation timescale, i.e. t_e ~
t_r in this phase. These conclusions are illustrated by numerical results.


title: Cosmological SPH simulations: The entropy equation

abstract:
  We discuss differences in simulation results that arise between the use of
either the thermal energy or the entropy as an independent variable in smoothed
particle hydrodynamics (SPH). In this context, we derive a new version of SPH
that manifestly conserves both energy and entropy if smoothing lengths are
allowed to adapt freely to the local mass resolution. To test various formu-
lations of SPH, we consider point-like energy injection and find that powerful
explosions are well represented by SPH even when the energy is deposited into a
single particle, provided that the entropy equation is integrated. If the
thermal energy is instead used as an independent variable, unphysical solutions
can be obtained for this problem. We also examine the radiative cooling of gas
spheres that collapse and virialize in isolation and of halos that form in
cosmological simulations of structure formation. When applied to these
problems, the thermal energy version of SPH leads to substantial overcooling in
halos that are resolved with up to a few thousand particles, while the entropy
formulation is biased only moderately low for these halos. For objects resolved
with much larger particle numbers, the two approaches yield consistent results.
We trace the origin of the differences to systematic resolution effects in the
outer parts of cooling flows. The cumulative effect of this overcooling can be
significant. In cosmological simulations of moderate size, we find that the
fraction of baryons which cool and condense can be reduced by up to a factor ~2
if the entropy equation is employed rather than the thermal energy equation. We
also demonstrate that the entropy method leads to a greatly reduced scatter in
the density-temperature relation of the low-density Ly-alpha forest relative to
the thermal energy approach, in accord with theoretical expectations.(abridged)


title:
ASCA Observation of the Nearest Gravitational Lensing Cluster Candidate
  -- A 3408

abstract:
  We observed the nearest gravitational lensing cluster candidate, A 3408
(${\it z}=0.042$), with ASCA. The projected mass profile of A 3408 was
determined from the ICM temperature and the $\beta$-model parameters obtained
with ASCA, assuming that the hot gas is spherically symmetric and in
hydrostatic equilibrium. The projected mass within an arc radius, $r_{\rm
arc}$, of 110 kpc is $M(r_{\rm arc})=1.2^{+0.8}_{-0.4} \times10^{13} \MO$. This
is 18 -- 45% of the mass previously derived from a lensing analysis by
Campusano et al. (1998, AAA 069.160.189) without any X-ray information.
  The primary cause of this discrepancy is in their assumption that the center
of the cluster potential coincides with the position of the brightest cluster
galaxy (BCG), while we reveal the BCG position to be 60$''$ outside of the
X-ray center. We further calculated a model for the source galaxy position and
the gravitational potential that can reproduce both the X-ray data and the arc
image. In this model, the magnification factor of the lens for the source
galaxy was evaluated to be ${\Delta}m=$ 0.07$\pm$0.03 mag; i.e., the source
galaxy is slightly magnified by the lens cluster A 3408.


title: Periodic Acceleration of Electrons in the 1998 November 10 Solar Flare

abstract:
  We present an examination of the multi-wavelength observation of a C7.9 flare
which occurred on 1998 November 10. This is the first time of imaging
observation of the quasi-periodic pulsations (QPPs). Four bursts were observed
with the hard X-ray telescope aboard Yohkoh and the Nobeyama Radioheliograph
during the impulsive phase of the flare. In the second burst, the hard X-ray
and microwave time profiles clearly showed a QPP. We estimated the Alfven
transit time along the flare loop using the images of the soft X-ray telescope
aboard it Yohkoh and the photospheric magnetgrams, and found that the transit
time was almost equal to the period of the QPP. We therefore suggest, based on
a shock acceleration model, that variations of macroscopic magnetic structures,
such as oscillations of coronal loops, affect the efficiency of particle
injection/acceleration.


title: The Angular Clustering of Galaxy Pairs

abstract:
  We identify close pairs of galaxies from 278 deg^2 of Sloan Digital Sky
Survey commissioning imaging data. The pairs are drawn from a sample of 330,041
galaxies with 18 < r^* < 20. We determine the angular correlation function of
galaxy pairs, and find it to be stronger than the correlation function of
single galaxies by a factor of 2.9 +/- 0.4. The two correlation functions have
the same logarithmic slope of 0.77. We invert Limber's equation to estimate the
three-dimensional correlation functions; we find clustering lengths of r_0= 4.2
+/- 0.4 h^{-1} Mpc for galaxies and 7.8 +/- 0.7 h^{-1} Mpc for galaxy pairs.
These results agree well with the global richness dependence of the correlation
functions of galaxy systems.


title: Triaxial Black-Hole Nuclei

abstract:
  We demonstrate that the nuclei of galaxies containing supermassive black
holes can be triaxial in shape. Schwarzschild's method was first used to
construct self-consistent orbital superpositions representing nuclei with axis
ratios of 1:0.79:0.5 and containing a central point mass representing a black
hole. Two different density laws were considered, with power-law slopes of -1
and -2. We constructed two solutions for each power law: one containing only
regular orbits and the other containing both regular and chaotic orbits.
Monte-Carlo realizations of the models were then advanced in time using an
N-body code to verify their stability. All four models were found to retain
their triaxial shapes for many crossing times. The possibility that galactic
nuclei may be triaxial complicates the interpretation of stellar-kinematical
data from the centers of galaxies and may alter the inferred interaction rates
between stars and supermassive black holes.


title: Plasma Ejections from a Light Bridge in a Sunspot Umbra

abstract:
  We present conspicuous activities of plasma ejections along a light bridge of
a stable and mature sunspot in NOAA 8971 on 2000 May 02. We found the ejections
both in the H-alpha (10^4 K) images obtained with the Domeless Solar Telescope
(DST) at Hida Observatory, and in the 171 A (Fe IX/X, ~10^6 K) images obtained
with the Transition Region and Coronal Explorer (TRACE). Main characteristics
of the ejections are as follows: (1)Ejections occur intermittently and
recurrently, (2)The velocities and the timings of the 171 A-ejections are the
same as those of H-alpha ejections, (3)The appearance of ejections are
different from one another, i.e. the H-alpha ejections have jet-like
appearance, while that of 171 A-ejections is like a loop.


title: Seeing Measurements at Skinakas Observatory using the DIMM method

abstract:
  We present preliminary results from a study of the seeing at Skinakas
Observatory in Crete, Greece. The measurements have been made during the years
2000 and 2001 using a two-aperture Differential Image Motion Monitor (DIMM).
The results of both campaigns are extremely promising with the median seeing
value being 0.''64 and 0.''69, respectively.


title:
Pulsar "Drifting"-Subpulse Polarization: No Evidence for Systematic
  Polarization-Angle Rotations

abstract:
  Polarization-angle density displays are given for pulsars B0809+74 and
B2303+30, which exhibit no evidence of the systematic polarization-angle
rotation within individual subpulses previously reported for these two stars.
The ``drifting'' subpulses of both pulsars exhibit strikingly linear and
circular polarization which appears to reflect the characteristics of two
nearly orthogonally polarized emission ``modes''--along which the severe
average-profile depolarization that is characteristic of their admixture at
comparable overall intensities.


title:
The Optical, Infrared and Radio Properties of Extragalactic Sources
  Observed by SDSS, 2MASS and FIRST Surveys

abstract:
  We positionally match sources observed by the Sloan Digital Sky Survey
(SDSS), the Two Micron All Sky Survey (2MASS), and the Faint Images of the
Radio Sky at Twenty-cm (FIRST) survey. Practically all 2MASS sources are
matched to an SDSS source within 2 arcsec; ~11% of them are optically resolved
galaxies and the rest are dominated by stars. About 1/3 of FIRST sources are
matched to an SDSS source within 2 arcsec; ~80% of these are galaxies and the
rest are dominated by quasars. Based on these results, we project that by the
completion of these surveys the matched samples will include about 10^7 stars
and 10^6 galaxies observed by both SDSS and 2MASS, and about 250,000 galaxies
and 50,000 quasars observed by both SDSS and FIRST. Here we present a
preliminary analysis of the optical, infrared and radio properties for the
extragalactic sources from the matched samples. In particular, we find that the
fraction of quasars with stellar colors missed by the SDSS spectroscopic survey
is probably not larger than ~10%, and that the optical colors of radio-loud
quasars are ~0.05 mag. redder (with 4-sigma significance) than the colors of
radio-quiet quasars.


title:
An SDSS Survey For Resolved Milky Way Satellite Galaxies I: Detection
  Limits

abstract:
  We present the detection limits of a new survey for resolved low surface
brightness satellite galaxies to the Milky Way, based on the Sloan Digital Sky
Survey (SDSS). Our survey exploits SDSS's major strengths (multi-color
photometry, depth, large-scale, and uniformity) by combining filter smoothing
with limits in both magnitude and color space to search for low surface
brightness galaxies and stellar counterparts to the Compact High Velocity
Clouds out to the Milky Way's virial radius (350 kpc). Our calculated detection
limits for a purely old stellar population vary with galaxy size and distance
between mu_{V,0} = 26.7 and 30.1 mag/sq ''. These limits will allow us to
detect systems whose surface brightnesses are .5-3.9 mag/sq '' fainter than
Sextans, the lowest surface brightness Local Group member known. Our survey not
only is sensitive to lower surface brightness stellar populations than possible
with previous Local Group surveys, but will also allow us to make an unbiased
and well defined assessment of the completeness of the observed Local Group
galaxy luminosity function, so that we may compare the results with the
predictions of various structure formation scenarios.


title: A young protoplanetary disk in the Bok globule CB26?

abstract:
  We present sub-arcsecond resolution millimeter-wave images of a circumstellar
disk in the Bok globule CB26. The presence of an edge-on disk is confirmed by
the dust continuum morphology and the velocity field of 13CO emission, which
displays a Keplerian rotation pattern about an axis perpendicular to the long
axis of the dust emission. We deduce a mass ~0.3 Msun for the obscured central
star. The disk is optically thick at mm wavelengths inside 120 AU, has a
symmetric 20 degree warp beyond 120 AU, an outer radius of ~200 AU, and a mass
of at least 0.1 Msun. We suggest that the CB26 system is in an intermediate
stage between deeply embedded protostellar accretion disks and the more
evolved, perhaps protoplanetary, disks around T Tauri stars.


title:
Extremely Weak Reflection Features in the X-ray Spectrum of XTE
  J1118+480: Possible Evidence for X-ray-Emitting Jets?

abstract:
  We have simultaneously fit Chandra and RXTE spectra of the Galactic black
hole XTE J1118+480 with three models for X-ray reflection. We explored a range
of accretion disc ionizations (log(xi)=1-4; xi=L_X/nR^{2}) and iron abundances
(0.10-1.00). Our fits with the constant density ionized disc models of Ross &
Fabian indicate that less than 0.5 per cent (90 per cent confidence
upper-limit) of the observed flux is reflected. Fits with the "pexrav" of model
Magdziarz & Zdziarski indicate that the two-dimensional solid angle (Omega/2pi)
subtended by the disc relative to a central source of incident hard X-rays is
0.01 +0.06 -0.01. A combination of the high inclination (i=81 degrees),
Comptonization, and bulk velocities may each contribute to the low reflection
fractions we have measured. The results are also consistent with extended jets
being the source of the hard X-ray flux, as the disc would then represent a
small solid angle as seen from the emission region.


title:
SCUBA sub-millimeter observations of gamma-ray bursters: II. GRB 991208,
  991216, 000301C, 000630, 000911, 000926

abstract:
  We discuss our ongoing program of Target of Opportunity sub-millimeter
observations of gamma-ray bursts (GRBs) using the Sub-millimetre Common-User
Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT).
Sub-millimeter observations of the early afterglows are of interest because
this is where the emission peaks in some bursts in the days to weeks following
the burst. Of increasing interest is to look for underlying quiescent
sub-millimeter sources that may be dusty star-forming host galaxies. In this
paper, we present observations of GRB 991208, 991216, 000301C, 000630, 000911,
and 000926. For all these bursts, any sub-millimeter emission is consistent
with coming from the afterglow. This means that we did not conclusively detect
quiescent sub-millimeter counterparts to any of the bursts that were studied
from 1997 through 2000. The inferred star formation rates (M > 5 Msun) are
typically < 300 Msun/yr. If GRBs are due to the explosions of high-mass stars,
this may indicate that the relatively small population of extremely luminous
dusty galaxies does not dominate the total star formation in the universe at
early epochs. Instead, the GRBs may be predominantly tracing slightly lower
luminosity galaxies. The optical faintness of some host galaxies is unlikely to
be explained as due to dust absorption in the host.


title: The Evolution of Cuspy Triaxial Galaxies Harboring Central Black Holes

abstract:
  We use numerical simulations to study the evolution of triaxial elliptical
galaxies with central black holes. In contrast to earlier numerical studies
which used galaxy models with central density ``cores,'' our galaxies have
steep central cusps, like those observed in real ellipticals. As a black hole
grows in these cuspy triaxial galaxies, the inner regions become rounder owing
to chaos induced in the orbit families which populate the model. At larger
radii, however, the models maintain their triaxiality, and orbital analyses
show that centrophilic orbits there resist stochasticity over many dynamical
times. While black hole induced evolution is strong in the inner regions of
these galaxies, and reaches out beyond the nominal ``sphere of influence'' of a
black hole, our simulations do not show evidence for a rapid {\it global}
transformation of the host. The triaxiality of observed elliptical galaxies is
therefore not inconsistent with the presence of supermassive black holes at
their centers.


title: Gamma Ray Bursts as Probes of the First Stars

abstract:
  The redshift where the first stars formed is an important and unknown
milestone in cosmological structure formation. The evidence linking gamma ray
bursts (GRBs) with star formation activity implies that the first GRBs occurred
shortly after the first stars formed. Gamma ray bursts and their afterglows may
thus offer a unique probe of this epoch, because they are bright from gamma ray
to radio wavelengths and should be observable to very high redshift. Indeed,
our ongoing near-IR followup programs already have the potential to detect
bursts at redshift z ~ 10. In these proceedings, we discuss two distinct ways
of using GRBs to probe the earliest star formation. First, direct GRB counts
may be used as a proxy for star formation rate measurements. Second, high
energy cutoffs in the GeV spectra of gamma ray bursts due to pair production
with high redshift optical and ultraviolet background photons contain
information on early star formation history. The second method is
observationally more demanding, but also more rewarding, because each observed
pair creation cutoff in a high redshift GRB spectrum will tell us about the
integrated star formation history prior to the GRB redshift.