title: Using galaxy redshift surveys to detect gravitationally-lensed quasars

abstract:
  Gravitationally-lensed quasars can be discovered as a by-product of galaxy
redshift surveys. Lenses discovered spectroscopically in this way should
require less observational effort per event than those found in dedicated lens
surveys. Further, the lens galaxies should be relatively nearby, facilitating a
number of detailed observations that are impossible for the more common
high-redshift lenses. This is epitomised by the wide range of results that have
been obtained from Q 2237+0305, which was discovered as part of the Center for
Astrophysics redshift survey, and remains the only quasar lens discovered in
this way. The likelihood of this survey yielding a lens is calculated to be
about 0.03, which is an order of magnitude larger than previous estimates due
to two effects. Firstly, the quasar images themselves increase the observed
flux of the lens, so that lens galaxies up to a magnitude fainter than the
nominal survey limit must be included in the calculation. Secondly, it is
possible for lensed quasars with extremely faint deflectors to enter the survey
due to the extended morphology of the multiple images. Extrapolating these
results to future surveys, the 2 degree Field galaxy redshift survey should
contain between 10 and 50 lenses and the Sloan Digital Sky Survey should yield
between 50 and 300 lenses, depending on the cosmological model and the
observing conditions.


title: Analysis of cosmic microwave background data on an incomplete sky

abstract:
  Measurement of the angular power spectrum of the cosmic microwave background
is most often based on a spherical harmonic analysis of the observed
temperature anisotropies. Even if all-sky maps are obtained, however, it is
likely that the region around the Galactic plane will have to be removed due to
its strong microwave emissions. The spherical harmonics are not orthogonal on
the cut sky, but an orthonormal basis set can be constructed from a linear
combination of the original functions. Previous implementations of this
technique, based on Gram-Schmidt orthogonalisation, were limited to maximum
Legendre multipoles of l_max < 50 as they required all the modes have
appreciable support on the cut sky, whereas for large l_max the fraction of
modes supported is equal to the fractional area of the region retained. This
problem is solved by using a singular value decomposition to remove the
poorly-supported basis functions, although the treatment of the
non-cosmological monopole and dipole modes necessarily becomes more
complicated. A further difficulty is posed by computational limitations --
orthogonalisation for a general cut requires O(l_max^6) operations and
O(l_max^4) storage and so is impractical for l_max > 200 at present. These
problems are circumvented for the special case of constant (Galactic) latitude
cuts, for which the storage requirements scale as O(l_max) and the operations
count scales as O(l_max^4). Less clear, however, is the stage of the data
analysis at which the cut is best applied. As convolution is ill-defined on the
incomplete sphere, beam-deconvolution should not be performed after the cut,
and, if all-sky component separation is as successful as simulations indicate,
the Galactic plane should probably be removed immediately prior to power
spectrum estimation.


title:
The Magnetohydrodynamic Kelvin-Helmholtz Instability: A
  Three-Dimensional Study of Nonlinear Evolution

abstract:
  We investigate through high resolution 3D simulations the nonlinear evolution
of compressible magnetohydrodynamic flows subject to the Kelvin-Helmholtz
instability. We confirm in 3D flows the conclusion from our 2D work that even
apparently weak magnetic fields embedded in Kelvin-Helmholtz unstable plasma
flows can be fundamentally important to nonlinear evolution of the instability.
In fact, that statement is strengthened in 3D by this work, because it shows
how field line bundles can be stretched and twisted in 3D as the quasi-2D Cat's
Eye vortex forms out of the hydrodynamical motions. In our simulations twisting
of the field may increase the maximum field strength by more than a factor of
two over the 2D effect. If, by these developments, the Alfv\'en Mach number of
flows around the Cat's Eye drops to unity or less, our simulations suggest
magnetic stresses will eventually destroy the Cat's Eye and cause the plasma
flow to self-organize into a relatively smooth and apparently stable flow that
retains memory of the original shear. For our flow configurations the regime in
3D for such reorganization is $4\lesssim M_{Ax} \lesssim 50$, expressed in
terms of the Alfv\'en Mach number of the original velocity transition and the
initial Alfv\'en speed projected to the flow plan. For weaker fields the
instability remains essentially hydrodynamic in early stages, and the Cat's Eye
is destroyed by the hydrodynamic secondary instabilities of a 3D nature. Then,
the flows evolve into chaotic structures that approach decaying isotropic
turbulence. In this stage, there is considerable enhancement to the magnetic
energy due to stretching, twisting, and turbulent amplification, which is
retained long afterwards. The magnetic energy eventually catches up to the
kinetic energy, and the nature of flows become magnetohydrodynamic.


title: Gas metallicities and early evolution of distant radiogalaxies

abstract:
  By modeling the rich emission line spectra of a sample of high redshift
(HzRG, z\sim 2.5) radio galaxies we find that solar and supersolar
metallicities are common in the extended gas of these objects. Our models and
the comparison with high redshift quasars suggest that HzRG at z\sim 2.5 are
associated with intense star formation activity. This is consistent with
chemical evolution models for giant ellipticals and it supports the idea that
distant powerful radio galaxies are progenitors of giant ellipticals. We might
be witnessing different evolutive status in different objects.


title: Halo streams as relicts from the formation of the Milky Way

abstract:
  In this contribution we discuss the expected properties of our halo if our
Galaxy had been built from mergers of smaller systems. Using both analytic
arguments and high-resolution simulations, we find that the Galactic halo in
the Solar neighbourhood should have a smooth spatial distribution and that its
stellar velocity ellipsoid should consist of several hundred kinematically cold
streams, relicts from the different merging events. We also discuss
observational evidence which supports this hierarchical picture: two stellar
streams originating in the same system that probably fell onto the Milky Way
about ten Gyr ago. Finally we address what future astrometric missions like
FAME or GAIA may reveal by observing the motions of nearby halo stars.


title: Comparison Between Extrasolar Planets and Low-Mass Secondaries

abstract:
  This paper compares the statistical features of the sample of discovered
extrasolar planets with those of the secondaries in nearby spectroscopic
binaries, in order to enable us to distinguish between the two populations.
Based on 32 planet candidates discovered until March 2000, we find that their
eccentricity and period distribution are surprisingly similar to those of the
binary population, while their mass distribution is remarkably different. The
mass distributions definitely support the idea of two distinct populations,
suggesting the planet candidates are indeed extrasolar planets. The transition
between the two populations probably occurs at 10--30 Jupiter masses. We point
out a possible negative correlation between the orbital period of the planets
and the metallicity of their parent stars, which holds only for periods less
than about 100 days. These short-period systems are characterized by circular
or almost circular orbits.


title: Molecular gas and star formation in BIMA SONG bars

abstract:
  Using a sample of 7 barred spirals from the BIMA Survey of Nearby Galaxies
(SONG), we compare the molecular gas distribution in the bar, to recent massive
star formation activity. In all 7 galaxies, Halpha is offset azimuthally from
the CO on the downstream side. The maximum offset, at the bar ends, ranges from
170-570 pc, with an average of 320 +/- 120 pc. We discuss whether the observed
offsets are consistent with the description of gas flows in bars provided by
the two main classes of models: n-body models and hydrodynamic models. This
work is supported by NSF grants AST 9981289, AST 9981308.


title:
On the Observational Characteristics of Inhomogeneous Cosmologies:
  Undermining the Cosmological Principle

abstract:
  This thesis concerns the compatibility of inhomogeneous cosmologies with our
present understanding of the universe. It is a problem of some interest to find
the class of all relativistic cosmological models which are capable of
providing a reasonable `fit' to the universe. This thesis, in some respects, is
part of this process. We consider Stephani models, which are a generalisation
of the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) models, which can be
thought of as FLRW models with acceleration and pressure gradients. Thus these
models generalise the `dust' assumption of standard cosmology.
  The crucial aspect of this work is the retention of the Copernican principle
-- an assumption regarded by many as crucial to cosmology. It states that we
are not at a special location in the universe. This is a vital aspect of the
original work in this thesis: consideration of an inhomogeneous model, while
retaining the Copernican principle has, as far as the author is aware, not been
considered in detail before.
  We start by generalising the Ehlers-Geren-Sachs Theorem to identify the class
of inhomogeneous spacetimes which allow an isotropic radiation field for all
observers in the spacetime. We then investigate observational and physical
aspects of these models from all observer locations. We conclude that there
exist spacetimes which conform to present observational constraints (especially
anisotropy constraints) for any location in the spacetime, while at the same
time being significantly inhomogeneous; ie, not `almost-FLRW'.


title:
On the peculiar X-ray properties of the bright nearby radio-quiet quasar
  PDS456

abstract:
  BeppoSAX and ASCA observations of the nearby (z=0.184), high-luminosity,
radio-quiet quasar PDS456 are presented. The X-ray spectrum is characterized by
a prominent ionized edge at 8-9 keV (originally discovered by RXTE, Reeves et
al. 2000) and by a soft excess below 1.5 keV. The lack of any significant iron
K alpha emission line suggests for the edge an origin from line-of-sight
material rather than from reflection from a highly ionized accretion disc. The
hard X-ray continuum is indeed well modelled by transmission through a
highly-ionized medium with a large column density (N_H warm = 4.5 x 10^24
cm^-2) plus an additional cold absorber with a lower column density (N_H cold =
2.7 x 10^22 cm^-2).


title: An X-ray Binary Model for the Galactic Center Source IRS 13E

abstract:
  We present several models for IRS 13E, an infrared, mm and X-ray source in
the Galactic Center. Our favored interpretation is that of an early-type binary
with strong colliding winds emission. This naturally explains the observed
X-ray count rate and the strong infrared emission lines, and has a distinct
advantage over competing hypotheses based upon a single star or black-hole
system.


title:
Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3--4 Micron
  Spectra

abstract:
  The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed
based on their ground-based 3--4 $\mu$m spectra. Both the equivalent width of
the 3.3 $\mu$m polycyclic aromatic hydrocarbon (PAH) emission feature and the
3.3 $\mu$m PAH to far-infrared luminosity ratio ($L_{3.3}/L_{\rm FIR}$) are
analyzed. Assuming nuclear compact starburst activity in these sources produces
the 3.3 $\mu$m PAH emission as strongly as that in starburst galaxies with
lower far-infrared luminosities, the followings results are found: For six
IRLGs, both the observed equivalent widths and the $L_{3.3}/L_{\rm FIR}$ ratios
are too small to explain the bulk of their far-infrared luminosities by compact
starburst activity, indicating that active galactic nucleus (AGN) activity is a
dominant energy source. For the other three IRLGs, while the 3.3 $\mu$m PAH
equivalent widths are within the range of starburst galaxies, the
$L_{3.3}/L_{\rm FIR}$ ratios after correction for screen dust extinction are a
factor of $\sim$3 smaller. The uncertainty in the dust extinction correction
factor and in the scatter of the intrinsic $L_{3.3}/L_{\rm FIR}$ ratios for
starburst galaxies do not allow a determination of the ultimate energy sources
for these three IRLGs.


title:
The 3.4 micron absorption feature towards three obscured active galactic
  nuclei

abstract:
  The results of 3-4 $\mu$m spectroscopy towards the nuclei of NGC 3094, NGC
7172, and NGC 7479 are reported. In ground-based 8-13 $\mu$m spectra, all the
sources have strong absorption-like features at $\sim$10 $\mu$m, but they do
not have detectable polycyclic aromatic hydrocarbon (PAH) emission features.
The 3.4 $\mu$m carbonaceous dust absorption features are detected towards all
nuclei. NGC 3094 shows a detectable 3.3 $\mu$m PAH emission feature, while NGC
7172 and NGC 7479 do not. Nuclear emission whose spectrum shows dust absorption
features but no PAH emission features is thought to dominated by highly
obscured active galactic nuclei (AGNs) activity. For NGC 7172, NGC 7479, and
three other such nuclei in the literature, we investigate the optical depth
ratios between the 3.4 $\mu$m carbonaceous dust and 9.7 $\mu$m silicate dust
absorption ($\tau_{3.4}$/$\tau_{9.7}$). The $\tau_{3.4}$/$\tau_{9.7}$ ratios
towards three highly obscured AGNs with face-on host galaxies are
systematically larger than the ratios in the Galactic diffuse interstellar
medium or the ratios for two highly obscured AGNs with edge-on host galaxies.
We suggest that the larger ratios can be explained if the obscuring dust is so
close to the central AGNs that a temperature gradient occurs in it. If this
idea is correct, our results may provide spectroscopic evidence for the
presence of the putative ``dusty tori'' in the close vicinity of AGNs.


title:
Observation of Optical Flashes of the Night Star Sky on the Atmospheric
  Cherenkov Installation Tunka-13

abstract:
  Experiment on the study of fluctuation of night glow is conducted on the base
of 13 module atmospheric Cherenkov telescope TUNKA-13.Basic task of TUNKA-13 is
registration of light from Extended Air Shower (EAS) initiated by primary
cosmic particles. Observation of light flashes radiating in nigght atmosphere
is one more experiment which is run for TUNKA-13 to study the background
condition for EAS registration. At a period from December 1997 on a May 1998
was registered 149 light flashes of radiwting night atmosphere with duration
from 16 ms to 190 seconds. General time of night observing has formed 237
hours. Coincidence of optical flashes with the gamma-bursts from the catalogue
of BATSE experiment of observatories "Compton" was analysed.


title:
Search for young stars among ROSAT All-Sky Survey X-ray sources in and
  around the R CrA dark cloud

abstract:
  We present the ROSAT All-Sky Survey data in a 126 deg^2 area in and around
the CrA star forming region. With low-resolution spectroscopy of unidentified
ROSAT sources we could find 19 new pre-main sequence stars, two of which are
classical T Tauri stars, the others being weak-lined. The spectral types of
these new T Tauri stars range from F7 to M6. The two new classical T Tauri
stars are located towards two small cloud-lets outside of the main CrA cloud.
They appear to be ~10 Myrs old, by comparing their location in the H-R diagram
with isochrones for an assumed distance of 130 pc, the distance of the main CrA
dark cloud. The new off-cloud weak-line T Tauri stars may have formed in
similar cloud-lets, which have dispersed recently. High-resolution spectra of
our new T Tauri stars show that they have significantly more lithium absorption
than zero-age main-sequence stars of the same spectral type, so that they are
indeed young. From those spectra we also obtained rotational and radial
velocities. For some stars we found the proper motion in published catalogs.
The direction and velocity of the 3D space motion - south relative to the
galatic plane - of the CrA T Tauri stars is consistent with the dark cloud
being formed originally by a high-velocity cloud impact onto the galactic
plane, which triggered the star formation in CrA. We also present VRIJHK
photometry for most of the new T Tauri stars to derive their luminosities,
ages, and masses.


title:
Quasi-periodic oscillations and noise in neutron star and black-hole
  X-ray binaries

abstract:
  Before the launch of the Rossi X-ray Timing Explorer (RXTE) satellite, the
differences in the rapid X-ray variability between the two main types of
neutron star binaries (i.e., the Z and atoll sources) could be explained by
invoking different mass accretion rates and magnetic field strengths. However,
the results obtained with RXTE now show that these systems are more similar
than previously thought and although differences in mass accretion rate are
still likely, the differences in the magnetic field strength have become
questionable. The great similarities between the neutron star systems and the
black-hole candidates at low mass accretion rates also point towards a similar
origin of their timing phenomena indicating that the presence or absence of a
solid surface, a magnetic field, or an event horizon do not play a significant
role in the production mechanisms for the rapid X-ray variability.


title: A 700 year-old Pulsar in the Supernova Remnant Kes 75

abstract:
  Since their discovery 30 years ago, pulsars have been understood to be
neutron stars (NSs) born rotating rapidly (~ 10-100 ms). These neutron stars
are thought to be created in supernova explosions involving massive stars,
which give rise to expanding supernova remnants (SNRs). With over 220 Galactic
SNRs known (Green 1998) and over 1200 radio pulsars detected (Camilo et al.
2000), it is quite surprising that few associations between the two populations
have been identified with any certainty. Here we report the discovery of a
remarkable 0.3 sec X-ray pulsar, PSR J1846-0258, associated with the supernova
remnant Kes 75. With a characteristic age of only 723 yr, consistent with the
age of Kes 75, PSR J1846-0258 is the youngest pulsar yet discovered and is
being rapidly spun down by torques from a large magnetic dipole of strength ~
5E13 G, just above the so-called quantum critical field. PSR J1846-0258 resides
in this transitional regime where the magnetic field is hypothesized to
separate the regular pulsars from the so-called magnetars. PSR J1846-0258 is
evidently a Crab-like pulsar, however, its period, spin-down rate, spin-down
conversion efficiency, are each an order-of-magnitude greater, likely the
result of its extreme magnetic field.


title:
Modelling the spectral energy distribution of galaxies. I. Radiation
  fields and grain heating in the edge-on spiral NGC891

abstract:
  We describe a new tool for the analysis of the UV to the sub-millimeter
(sub-mm) spectral energy distribution (SED) of spiral galaxies. We use a
consistent treatment of grain heating and emission, solve the radiation
transfer problem for a finite disk and bulge, and self-consistently calculate
the stochastic heating of grains placed in the resulting radiation field.
  We use this tool to analyse the well-studied nearby edge-on spiral galaxy
NGC891. First we investigate whether the old stellar population in NGC891,
along with a reasonable assumption about the young stellar population, can
account for the heating of the dust and the observed far-infrared (FIR) and
sub-mm emission. The dust distribution is taken from the model of Xilouris et
al. (1999), who used only optical and near-IR observations to determine it. We
have found that such a simple model cannot reproduce the SED of NGC891,
especially in the sub-mm range. It underestimates by a factor of 2-4 the
observed sub-mm flux.
  A number of possible explanations exist for the missing sub-mm flux. We
investigate a few of them and demonstrate that one can reproduce the observed
SED in the FIR and the sub-mm quite well, as well as the observed radial
profile at 850 microns. For the models calculated we give the relative
proportion of the dust radiation powered by the old and young stellar
populations as a function of FIR/sub-mm wavelength. In all models we find that
the dust is predominantly heated by the young stellar population.


title: Evolution of highly buoyant thermals in a stratified layer

abstract:
  The buoyant rise of thermals (i.e. bubbles of enhanced entropy, but initially
in pressure equilibrium) is investigated numerically in three dimensions for
the case of an adiabatically stratified layer covering 6-9 pressure scale
heights. It is found that these bubbles can travel to large heights before
being braked by the excess pressure that builds up in order to drive the gas
sideways in the head of the bubble. Until this happens, the momentum of the
bubble grows as described by the time-integrated buoyancy force. This validates
the simple theory of bubble dynamics whereby the mass entrainment of the bubble
provides an effective braking force well before the bubble stops ascending.
This is quantified by an entrainment parameter alpha which is calculated from
the simulations and is found to be in good agreement with the experimental
measurements. This work is discussed in the context of contact binaries whose
secondaries could be subject to dissipative heating in the outermost layers.


title:
ISO observations of the planetary nebula Lindsay 305 in the Small
  Magellanic Cloud

abstract:
  We present ISO (Infrared Space Observatory) observations of the planetary
nebula Lindsay 305 (L 305) in the Small Magellanic Cloud. L 305 is very
prominent in the ISOCAM frames at 6.75 and 11.5 $\mu$m, although it is under
the detection limit at 4.5 $\mu$m. The obtained spectral energy distribution
shows a strong mid-IR excess, which, depending on the amount of energy radiated
at wavelengths longer than 11.5 $\mu$m, may be as large as $\sim 1500
L_{\odot}$. However, since an accurate estimate of the total nebular luminosity
is not available up to date, the evolutionary status of L 305 can not yet be
constrained precisely.


title:
Mid-infrared studies of the AGB star populations in the Local Group
  galaxies : the Magellanic Clouds

abstract:
  We present a brief summary of the ISO survey of AGB stars in 8 populous
intermediate age clusters of the Magellanic Clouds. Totally, more than 100 AGB
and RGB stars were observed at 4.5, 6.7 and 12 $\mu$m. We introduce a new
method to estimate effective temperatures of oxygen-rich AGB stars, and derive
precise bolometric magnitudes and effective temperatures for a large population
of AGB objects in both LMC and SMC. The derived stellar parameters are used to
construct observed HR diagrams which are employed further to estimate cluster
ages using the isochrone fitting. We show that proposed method gives a powerful
tool to study AGB star populations within the Local Group galaxies, especially,
when backed up with the observations from forthcoming mid-IR astronomical space
facilities (IRIS, SIRTF) and large ground-based telescopes (SUBARU, VLT, etc.).


title: Updated AGASA event list above 4x10^19eV

abstract:
  After our Ap.J. publication of the Akeno Giant Air Shower Array (AGASA)
results in 1999 (Takeda et al., 1999), we observed nine events with energies
above 4 $\times$ 10$^{19}$eV until May 2000. This short report lists the
coordinates of these events, and shows the updated energy spectrum and arrival
direction map. The analysis was carried out with the same procedure employed in
the Ap.J. publication.


title:
Blob ejection from advection-dominated accretion flow: observational
  consequences

abstract:
  There is increasing evidence for the presence of an optically thin
advection-dominated accretion flow (ADAF) in low luminosity active galactic
nuclei and radio-loud quasars. The present paper is devoted to explore the fate
of a blob ejected from an ADAF, and to discuss its observational consequences.
It is inevitable for the ejected blob to drastically expand into its
surroundings. Consequently, it is expected that a group of relativistic
electrons should be accelerated, which may lead to nonthermal flares, since a
strong shock will be formed by the interaction between the blob and its
surroundings. Then the blob cools down efficiently, leading to the appearance
of recombination lines about $10^5$s after its ejection from an ADAF. We apply
this model to NGC 4258 for some observational prediction, and to PKS 2149--306
for the explanation of observational evidence. Future simultaneous observations
of recombination X-ray lines and continuum emission are highly desired to test
the present model.


title: Structure of Dark Matter Halos From Hierarchical Clustering

abstract:
  We investigate the structure of the dark matter halo formed in the cold dark
matter scenario using $N$-body simulations. We simulated 12 halos with the mass
of $6.6\times 10^{11}M_{\odot}$ to $8.0\times 10^{14}M_{\odot}$. In almost all
runs, the halos have density cusps proportional to $r^{-1.5}$ developed at the
center, which is consistent with the results of recent high-resolution
calculations. The density structure evolves in a self-similar way, and is
universal in the sense that it is independent of the halo mass and initial
random realization of density fluctuation. The density profile is in good
agreement with the profile proposed by Moore et al. (1999), which has central
slope proportional to $r^{-1.5}$ and outer slope proportional to $r^{-3}$. The
halo grows through repeated accretion of diffuse smaller halos. We argue that
the cusp is understood as a convergence slope for the accretion of tidally
disrupted matter.


title:
Black hole to bulge mass correlation in Active Galactic Nuclei: A test
  for the simple unified formation scheme

abstract:
  A mass correlation of central black holes and their spheroids ~0.002(within a
factor of three) is suggested by Hubble Space Telescope (HST) and various
ground-based CCD photometries of early type galaxies. The near-IR images of
quasar hosts and the emission line measurements of Broad Line Region for bright
QSOs present a similar correlation, which supports the speculation of an
evolutionary linkage between the early active QSO phase and the central black
holes in normal galaxies. On the other hand, recent reverberation mapping of a
sample of Seyferts shows a broad distribution of black hole to bulge mass ratio
with a mean of ~10^{-3.5}, about one magnitude lower than the value in early
type galaxies and bright QSOs. Adopting a simple unified formation scheme for
QSOs and Seyferts, we will discuss in this letter the dependence of the black
hole to bulge mass ratio in Active Galactic Nuclei (AGNs) on the environmental
parameters of the host galaxies. We show a broad distribution of the mass
correlation could be due to different velocity dispersion of the accreting gas
from different formation mechanism, and the mass ratio in normal galaxies and
bright QSOs is probably a limit case of black hole evolution by merger enhanced
accretion close to Eddington limit.


title: On physical foundations and observational effects of cosmic rotation

abstract:
  An overview of the cosmological models with expansion, shear and rotation is
presented. Problems of the rotating models are discussed, their general
kinematic properties and dynamical realizations are described. A particular
attention is paid to the discussion of possible observational effects which
could be used to estimate or to put limits on the cosmic rotation.


title:
Planck-scale deformation of Lorentz symmetry as a solution to the UHECR
  and the TeV-$\gamma$ paradoxes

abstract:
  One of the most puzzling current experimental physics paradoxes is the
arrival on Earth of Ultra High Energy Cosmic Rays with energies above the GZK
threshold. The recent observation of 20TeV photons from Mk 501 is another
somewhat similar paradox. Several models have been proposed for the UHECR
paradox. No solution has yet been proposed for the TeV-$\gamma$ paradox.
Remarkably, the drastic assumption of a violation of ordinary Lorentz
invariance would resolve both paradoxes. We present a formalism for the
description of the type of Lorentz-invariance deformation (LID) that could be
induced by non-trivial short-distance structure of space-time, and we show that
this formalism is well suited for comparison of experimental data with LID
predictions. We use the UHECR and TeV-$\gamma$ data, as well as bounds on
time-of-flight differences between photons of different energies, to constrain
the LID parameter space. A model with only two parameters, an energy scale and
a dimensionless parameter characterizing the functional dependence on the
energy scale, is shown to be sufficient to solve both the UHECR and the
TeV-$\gamma$ threshold anomalies while satisfying the time-of-flight bounds.
The allowed region of the two-parameter space is relatively small, but,
remarkably, it fits perfectly the expectations of the quantum-gravity-motivated
space-time models known to support such deformations of Lorentz invariance:
integer value of the dimensionless parameter and characteristic energy scale
constrained to a narrow interval in the neighborhood of the Planck scale.


title:
Effects of Neutrino Trapping on Thermodynamic Properties of Nuclear
  ``Pasta''

abstract:
  Geometrical structure of matter at subnuclear densities is investigated in
the presence of a degenerate gas of neutrinos as encountered in stellar
collapse. The crystalline phases with spherical, cylindrical and planar nuclei
as well as with spherical and cylindrical nuclear bubbles are considered by
using a compressible liquid-drop model. This model allows for uncertainties in
the lepton fraction $Y_{\rm L}$ in addition to those in the nuclear surface
tension $E_{\rm surf}$ and in the proton chemical potential in bulk neutron
matter $\mu_{\rm p}^{(0)}$. The phase diagrams obtained at zero temperature
show that only the phases with rod-like and slab-like nuclei occur at typical
values of $Y_{\rm L}$, $E_{\rm surf}$ and $\mu_{\rm p}^{(0)}$, whereas the
bubble phases, especially with spherical bubbles, are at best expected at
hypothetically low values of $Y_{\rm L}$ and/or $E_{\rm surf}$. For the
rod-like and slab-like nuclei, thermally induced displacements are calculated
from their respective elastic constants. It is found that at temperatures
appropriate to supernova cores, thermal fluctuations would destroy the layered
lattice of slab-like nuclei almost independently of the nuclear models and of
the degree of the neutrino degeneracy.


title: Ca II activity and rotation in F-K evolved stars

abstract:
  (Abridged) Ca II H and K high resolution observations for 60 evolved stars in
the field and in 5 open clusters are presented. From these spectra
chromospheric fluxes are derived, and a homogeneous sample of more than 100
giants is built adding data from the literature. In addition, for most stars,
rotational velocities were derived from CORAVEL observations. By comparing
chromospheric emission in the cluster stars we confirm that chromospheric
activity depends on T_eff, and mass, when intermediate mass stars (M~4 Msun)
are considered. The Hyades and Praesepe clump giants show the same level of
activity, as expected from stars with similar masses and T_effs. A difference
of up to 0.4 dex in the chromospheric fluxes among the Hyades giants is
recorded and this sets a clear limit to the intrinsic spread of stellar
activity in evolved giants. Among the field stars none of the giants with
(V-R)<0.4 and Ia supergiants observed shows a signature of Ca II activity. We
find that chromospheric activity scales linearly with stellar rotational
velocity and a high power of stellar effective temperature: F'_k propto
T_eff^7.7 Vsini^0.9. This result can be interpreted as the effect of two
chromospheric components of different nature: one mechanical and one magnetic.
For each range of masses activity can simply be expressed as a function of only
one parameter: either the T_eff or the angular rotation Omega. For the 1.6-3
solar mass stars the data are consistent with I Omega=const, while lower and
higher masses follow a law similar to I Omega^2=const. We find it intriguing
that Vsini remains almost constant for 1Msun stars along their evolution; if a
similar behavior is shared by Pop II stars, this could explain the relatively
high degree of activity observed in Pop II giants.


title: Optimizing ISOCAM data processing using spatial redundancy

abstract:
  We present new data processing techniques that allow to correct the main
instrumental effects that degrade the images obtained by ISOCAM, the camera on
board the Infrared Space Observatory (ISO). Our techniques take advantage of
the fact that a position on the sky has been observed by several pixels at
different times. We use this information (1) to correct the long term variation
of the detector response, (2) to correct memory effects after glitches and
point sources, and (3) to refine the deglitching process. Our new method allows
the detection of faint extended emission with contrast smaller than 1% of the
zodiacal background. The data reduction corrects instrumental effects to the
point where the noise in the final map is dominated by the readout and the
photon noises. All raster ISOCAM observations can benefit from the data
processing described here. These techniques could also be applied to other
raster type observations (e.g. ISOPHOT or IRAC on SIRTF).


title:
The Pseudo-$C_l$ method: Cosmic microwave background anisotropy power
  spectrum statistics for high precision cosmology

abstract:
  As the era of high precision cosmology approaches, the empirically determined
power spectrum of the microwave background anisotropy $C_l$ will provide a
crucial test for cosmological theories. We present an exact semi-analytic
framework for the study of the ampling statistics of the $C_l$ resulting from
observations with partial sky coverage and anisotropic noise distributions.
This includes space-borne, air-borne and ground-based experiments. We apply
this theory to demonstrate its power for constructing fast but unbiased
approximate methods for the joint estimation of cosmological parameters.
Further applications, such as a test for possible non-Gaussianity of the
underlying theory and a ``poor man's power spectrum estimator'' are suggested.
An appendix derives recursion relations for the efficient computation of the
couplings between spherical harmonics on the cut sky.


title:
CO in Stephan's Quintet: First Evidence of Molecular Gas in the
  Intragroup Starburst

abstract:
  We present the first interferometric evidence of CO(1-0) emission in the
intragroup starburst (IGS) region of HCG~92 (Stephan's Quintet). BIMA's large
primary beam covers fully both the IGS region and the dominant group member
galaxy Seyfert NGC 7319, as well as partially the intruder galaxy NGC 7318B. CO
emission of $\approxgt 4\sigma$ is detected in all of them. The detection of
the CO emission associated with the IGS is further supported by comparisons
with observations in other wavebands (e.g., HI, mid-IR, \ha). Assuming the
standard conversion factor, 3.6--8.0$\times 10^8~\Msun$ molecular gas is found
to be associated with the IGS. Confining to the region of the CO emission peak,
a relatively high star-formation efficiency of 8.6$\Lsun/\Msun$ is derived for
the IGS, which is nearly comparable to that of local starburst galaxies (e.g.,
M82).


title: The non-thermal radiation - Cluster merger connection

abstract:
  There is compelling evidence that at least some clusters of galaxies are
powerful sources of non-thermal radiation. In all cases where this radiation
has been detected, a general trend is that high energy densities of cosmic rays
and correspondingly low values of the average magnetic field are required in
order to have a self-consistent picture of the multiwavelength observations.
Mergers of clusters of galaxies might provide large enough cosmic ray injection
rates and at the same time provide the mechanism for the heating of the
intracluster medium to the observed temperatures. In this paper we analyze
critically all the components that play a role in the non-thermal emission of
clusters during a merger, with special attention to mergers occurred in the
past of the cluster. We outline the consequences of this model for high energy
gamma ray observations and for Faraday rotation measurements of the
intracluster magnetic field.


title: Molecular Gas Concentrations Outside the Merging Disks

abstract:
  We present our preliminary BIMA CO(1-0) images of II~Zw~96 which show huge
molecular gas concentrations outside the merging disks. The dominant extra-disk
CO concentrations in II~Zw~96 correspond to the two star-forming ``knots''
hidden by dust, whereas the others are associated with the two spiral disks.
The unique huge CO concentrations, $\approxgt 5$ kpc away from the merging
nuclei, account for $\approxgt 50 %$ of the total CO emission, yet only at a
moderate gas surface density as compared with that of ultraluminous infrared
galaxies (ULIGs). We tentatively conclude that the huge extra-disk gas
concentrations are most likely the overlap region of the gas disks, not
necessarily coinciding with the stellar disks overlap region. The gas disks
overlap region could be formed prior to the merging of the stellar disks and
become the overlap regions found between the disks like that in Arp~244 (the
``Antennae'' galaxies). These overlap regions would eventually nurture the {\it
extreme starbursts} and evolve into the extended gas disk surrounding the
double nuclei in final merging in most ULIGs.


title: Prospects for Indirect Detection of Neutralino Dark Matter

abstract:
  Dark matter candidates arising in models of particle physics incorporating
weak scale supersymmetry may produce detectable signals through their
annihilation into neutrinos, photons, or positrons. A large number of relevant
experiments are planned or underway. The `logically possible' parameter space
is unwieldy. By working in the framework of minimal supergravity, we can survey
the implications of the experiments for each other, as well as for direct
searches, collider searches, low-energy experiments, and naturalness in a
transparent fashion. We find that a wide variety of experiments provide
interesting probes. Particularly promising signals arise in the mixed
gaugino-Higgsino region. This region is favored by low-energy particle physics
constraints and arises naturally from minimal supergravity due to the focus
point mechanism. Indirect dark matter searches and traditional particle
searches are highly complementary. In cosmologically preferred models, if there
are charged superpartners with masses below 250 GeV, then some signature of
supersymmetry must appear before the LHC begins operation.


title:
Optical Observations of the Black Hole Candidate XTE J1550-564 During
  Re-Flare and Quiescence

abstract:
  We report optical monitoring of the soft X-ray transient XTE J1550-564 during
the 1999 season (4 January 1999 to 24 August 1999). The first optical
observations available in 1999 show that the peak ``re-flare'' brightness had
exceeded the peak brightness of the initial optical flare in September 1998 by
over half a magnitude. We compare the optical re-flare light curves with the
total X-ray flux, the power-law flux and disk flux light curves constructed
from the spectral fits to RXTE/PCA data made by Sobczak et al. (1999, 2000).
During the first 60 days of the observed optical re-flare, we find no
correspondence between the thermal component of the X-rays often associated
with a disk and the optical flux -- the former remains essentially flat whereas
the latter declines exponentially and exhibits three substantial dips. However,
the power law flux is anti-correlated with the optical dips, suggesting that
the optical flux may by up-scattered into the X-ray by the hot corona. Periodic
modulations were discovered during the final stage of the outburst (May to
June), with P=1.546+/-0.038 days, and during quiescence (July and August), with
P=1.540+/-0.008 days. The analysis of the combined data set reveals a strong
signal for a unique period at P=1.541+/-0.009 days, which we believe to be the
orbital period.


title: Polarization Sweeps in Rotation Powered Pulsars

abstract:
  We re-examine the characteristic polarization angle sweep of rotation-powered
pulsars and calculate the expected deviations from this sweep caused by
aberrational effects and by polar-cap current flow. We find that in addition to
the previously known phase shift of the entire sweep by $\Delta \Phi = -4
r/R_L$, aberration shifts the polarization angle itself by $\Delta \Psi =
-(10/3) (r/R_L) \cos \alpha$. Similarly, current flow above the polar cap
shifts the polarization sweep by $\Delta \Psi = (10/3) (r/R_L) (J/J_{GJ}) \cos
\alpha$, potentially providing a method of directly measuring the magnitude of
the current. The competition between these two effects produces a potentially
observable signature in the polarization angle sweep. Although these effects
may appear similar to orthogonal mode shifts, they are an independent
phenomenon with distinct observational characteristics.


title:
Relativistic Iron Emission and Disk Reflection in Galactic Microquasar
  XTE J1748-288

abstract:
  We report evidence for an Fe K-alpha fluorescence line feature and disk
reflection in the Very High, High, and Low State X-ray spectra of the galactic
microquasar XTE J1748-288 during its June~1998 outburst. Spectral analyses are
made on data gathered throughout the outburst by the Rossi X-ray Timing
Explorer Proportional Counter Array. Gaussian line, relativistic disk emission
line, and ionized disk reflection models are fit to the data. In the Very High
State the line profile appears strongly redshifted, consistent with disk
emission from the innermost stable orbits around a maximally rotating Kerr
black hole. In the High State the line profile is less redshifted and
increasingly prominent. The Low State line profile is very strong (~0.5 keV
equivalent width) and centered at 6.7 +/- 0.10 keV; disk line emission model
fits indicate that the inner edge of the disk fluctuates between ~20 and ~100
gravitational radii in this state. The disk reflection fraction is traced
through the outburst; reflection from an ionized disk is preferred in the VHS
and HS, and reflection from a relatively neutral disk is preferred in the LS.
We discuss the implications of our findings for the binary system dynamics and
accretion flow geometry in XTE J1748-288.


title:
The Nuclear Star Cluster of the Milky Way: Star Formation, Dynamics and
  Central Black Hole

abstract:
  High spatial resolution, near-infrared imaging and spectroscopy of the
nuclear star cluster have given key new insights about the dynamics, evolution
and mass distribution in the Milky Way Center. The central parsec is powered by
a cluster of hot, massive stars which must have formed a few million years ago.
Either star formation was triggered in the central parsec by the infall of a
very dense cloud, or a dense, young star cluster formed outside of the central
parsec sank rapidly into the nuclear region through dynamical friction. The
presence of luminous asymptotic giant branch (AGB) stars suggests that there
were earlier such star formation episodes. Measurements of radial and proper
motions for more than 200 stars delineate the stellar dynamics to a scale of a
few light days from the dynamic center which is coincident with the compact
radio source (SgrA*) within ~0.1" (800 AU). The stellar velocities increase
toward SgrA* with a Kepler law (to >1000 km/s for the innermost stars),
implying the presence of a three million solar mass central (dark) mass. The
observations make a compelling case that this mass concentration is a black
hole which is currently accreting at a low rate or radiating at low efficiency.
With the exception of the young, massive stars the velocity field of the
central stellar cluster is close to isotropic. The young stars are
characterized by a turbulent rotation pattern that still carries the imprint of
the angular momentum distribution in the original cloud or star cluster.


title: The Polar Stellar Ring and Dark Halo of NGC 5907

abstract:
  Numerical simulations of the disruption of a dwarf companion moving in the
polar plane of a massive galaxy are presented. The constructed model is
compared with observational data on the recently discovered
low-surface-brightness stellar ring around galaxy NGC 5907. Constraints on the
ring lifetime (<=1.5 gyr after the first approach of the galaxies), on the
structure of companion -- the ring presecursor, and on mass of dark halo of the
main galaxy in whose gravitational field the companion moves are provided. The
dark halo mass within 50 kpc of NGC 5907 center cannot exceed 3 or 4 "visible"
masses.


title: The mass distribution in the innermost regions of Spiral Galaxies

abstract:
  We use high-spatial resolution ($\sim 100 pc$) rotation curves of 83 spiral
galaxies to investigate the mass distribution of their innermost kpc. We show
that, {\it in this region}, the luminous matter completely accounts for the
gravitational potential and no dark component is required. The derived I-band
disk mass-to-light ratios agree well with those obtained from population
synthesis models and correlate with color in a similar way. We find strict
upper limits of $\sim 10^7 M_\odot$ for the masses of compact bodies at the
center of spirals, ruling out that these systems host the remnants of the
quasar activity.


title:
High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning
  Data III: A Color Selected Sample at i^*<20 in the Fall Equatorial Stripe

abstract:
  This is the third paper in a series aimed at finding high-redshift quasars
from five-color (u'g'r'i'z') imaging data taken along the Celestial Equator by
the SDSS during its commissioning phase. In this paper, we first present the
observations of 14 bright high-redshift quasars (3.66<z<4.77, i^*<20)
discovered in the SDSS Fall Equatorial Stripe, and the SDSS photometry of two
previously known high-redshift quasars in the same region of the sky. Combined
with the quasars presented in previous papers, we define a color-selected
flux-limited sample of 39 quasars at 3.6 < z < 5.0 and i^*<20, covering a total
effective area of 182 deg^2. From this sample, we estimate the average spectral
power law slope in the rest-frame ultraviolet for quasars at z~4 to be -0.79
with a standard deviation of 0.34, and the average rest-frame equivalent width
of the Ly alpha+N V emission line to be 69 A with a standard deviation of 18 A.
The selection completeness of this multicolor sample is determined from the
model colors of high-redshift quasars, taking into account the distributions of
emission line strengths, intrinsic continuum slope, the line and continuum
absorption from intervening material, and the effects of photometric errors.
The average completeness of this sample is about 75%. The selection function
calculated in this paper will be used to correct the incompleteness of this
color-selected sample and to derive the high-redshift quasar luminosity
function in a subsequent paper. In the Appendix, we present the observations of
an additional 18 faint quasars (3.57<z<4.80, 20.1<i^*<20.8) discovered in the
region on the sky that has been imaged twice. Several quasars presented in this
paper exhibit interesting properties, including a radio-loud quasar at z=4.77,
and a narrow-line quasar (FWHM = 1500 km s^-1) at z=3.57.


title:
High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning
  Data IV: Luminosity Function from the Fall Equatorial Stripe Sampl

abstract:
  This is the fourth paper in a series aimed at finding high-redshift quasars
from five-color imaging data taken along the Celestial Equator by the SDSS.
during its commissioning phase. In this paper, we use the color-selected sample
of 39 luminous high-redshift quasars presented in Paper III to derive the
evolution of the quasar luminosity function over the range of 3.6<z<5.0, and
-27.5<M_1450<-25.5 (Omega=1, H_0=50 km s^-1 Mpc^-1). We use the selection
function derived in Paper III to correct for sample incompleteness. The
luminosity function is estimated using three different methods: (1) the 1/V_a
estimator; (2) a maximum likelihood solution, assuming that the density of
quasars depends exponentially on redshift and as a power law in luminosity and
(3) Lynden-Bell's non-parametric C^- estimator. All three methods give
consistent results. The luminous quasar density decreases by a factor of ~ 6
from z=3.5 to z=5.0, consistent with the decline seen from several previous
optical surveys at z<4.5. The luminosity function follows psi(L) ~ L^{-2.5} for
z~4 at the bright end, significantly flatter than the bright end luminosity
function psi(L) \propto L^{-3.5} found in previous studies for z<3, suggesting
that the shape of the quasar luminosity function evolves with redshift as well,
and that the quasar evolution from z=2 to 5 cannot be described as pure
luminosity evolution. Possible selection biases and the effect of dust
extinction on the redshift evolution of the quasar density are also discussed.


title:
Multi-Frequency Analysis of the New Wide-Separation Gravitational Lens
  Candidate RX J0921+4529

abstract:
  We report the discovery of a new two-image gravitational lens candidate. The
system RX J0921+4529 contains two z_s=1.66 quasars separated by 6."93 with an H
band magnitude difference of $\Delta m=1.39$. The HST NIC2 H band images reveal
an H=18.2 spiral galaxy between the quasar images, which is probably a member
of a z_l=0.32 X-ray cluster centered on the field. We detect an extended source
near the fainter quasar image but not in the brighter image. If this extended
source is the host galaxy of the fainter quasar, then the system is a binary
quasar rather than a gravitational lens. VLA observations at 3.6 cm reveal
emission from the lens galaxy at the flux level of 1 mJy and a marginal
detection of the brighter quasar.


title: The distribution of shock waves in driven supersonic turbulence

abstract:
  Supersonic turbulence generates distributions of shock waves. Here, we
analyse the shock waves in three-dimensional numerical simulations of uniformly
driven supersonic turbulence, with and without magnetohydrodynamics and
self-gravity. We can identify the nature of the turbulence by measuring the
distribution of the shock strengths.
  We find that uniformly driven turbulence possesses a power law distribution
of fast shocks with the number of shocks inversely proportional to the square
root of the shock jump speed. A tail of high speed shocks steeper than Gaussian
results from the random superposition of driving waves which decay rapidly. The
energy is dissipated by a small range of fast shocks. These results contrast
with the exponential distribution and slow shock dissipation associated with
decaying turbulence.
  A strong magnetic field enhances the shock number transverse to the field
direction at the expense of parallel shocks. A simulation with self-gravity
demonstrates the development of a number of highly dissipative accretion
shocks. Finally, we examine the dynamics to demonstrate how the power-law
behaviour arises.


title: Arp 119: A High Speed Galaxy Collision with Episodic Star Formation

abstract:
  Colliding galaxies are excellent laboratories for studying galactic evolution
and global star formation. Computer simulations of galaxy collisions, in which
at least one galaxy has a significant gaseous component, show the production of
density enhancements and shock waves in the interstellar medium. These
high-density regions coincide with the locations of recent, large-scale star
formation in observations of some real colliding galaxies. Thus, combined
n-body/hydrodynamic computer simulations can be used to explore the history and
conditions of star forming regions in colliding galaxies. The galaxy system Arp
119 (CPG 29) contains a southern member, Arp 119S (Mrk 984), that has an
extremely disturbed appearance, and a northern member, Arp 119N, a gas-poor
elliptical. The morphology of both members can be fit well by a simulation in
which a gas-rich disk galaxy has been impacted by an equal mass elliptical that
had a trajectory approximately perpendicular to the plane of the disk and
passed through the disk slightly off-center. We compare multi-wavelength
observations of the Arp 119 system with a combined n-body/SPH simulation of
colliding galaxies. We find that the progression of recent, large-scale star
formation in this galaxy can be accounted for by a single, outwardly
propagating collision-induced density wave in the gas.


title: Neutralinos and the Origin of Radio Halos in Clusters of Galaxies

abstract:
  We assume that the supersymmetric lightest neutralino is a good candidate for
the CDM and explore the possibility to produce diffuse radio emission from
high-energy electrons arising from the neutralino annihilation in galaxy
clusters whose intracluster medium is filled with a large-scale magnetic field.
We show that these electrons fit the population of seed relativistic electrons
postulated in many models for the origin of cluster radio halos. For magnetic
fields with central values $3 \div 30$ $\mu$G (depending on the DM profile),
the population of seed relativistic electrons from neutralino annihilation can
fit the radio halo spectra of Coma and 1E0657-56. The shape and the frequency
extension of the radio halo spectra are connected with the mass and physical
composition of the neutralino. A pure-gaugino neutralino with mass $M_{\chi}
\geq 80$ GeV can reasonably fit the spectra of both Coma and 1E0657-56. This
model provides a number of extra predictions that make it definitely testable.
On the one hand, it agrees with the observations that {\it (i)} the radio halo
is centered on the cluster dynamical center, usually coincident with the X-ray
center, {\it (ii)} the radio halo surface brightness is similar to the X-ray
one, and {\it (iii)} the monochromatic radio luminosity at 1.4 GHz correlates
strongly with the IC gas temperature. On the other hand, the model predicts
that radio halos should be present in every cluster, which is not actually
observed, although the predicted radio halo luminosities can change by a large
amount ($\sim 10^2 \div 10^6$), depending on the amplitude and the structure of
the IC magnetic field. Also, neutral pions arising from neutralino annihilation
should give rise to substantial gamma-ray emission that could be tested by the
next generation gamma-ray experiments.


title:
High resolution images at 11 and 20 microns of the Active Galactic
  Nucleus in NGC 1068

abstract:
  We present diffraction-limited IR images at 11.2 and 20.5 microns of the
central 6''x6'' region in NGC 1068, collected with the CAMIRAS instrument
mounted at the f/36 IR focus of the CFHT/Hawaii 3.6m telescope and at the f/35
IR focus of the ESO/La Silla 3.6m telescope, respectively. After deconvolution,
the achieved resolution (0.6'') reveals a prominent central core emitting about
95 % of the total flux at these wavelengths, as well as extended emission, to
the South-West and to the North-East, broken into patchy components which are
particularly conspicuous at 20.5 microns and can be isolated as individual
clouds. The central core shows an East-West FWHM of 0.6'' (hence unresolved)
and a North-South FWHM of 0.9'' corresponding to a resolved full size extension
of abound 100 pc. Such an elongated shape is in agreement with model
predictions of a dusty/molecular torus surrounding the central engine in NGC
1068, observed under an inclination angle around 65 degrees.


title: Disk Formation by AGB Winds in Dipole Magnetic Fields

abstract:
  We present a simple, robust mechanism by which an isolated star can produce
an equatorial disk. The mechanism requires that the star have a simple dipole
magnetic field on the surface and an isotropic wind acceleration mechanism. The
wind couples to the field, stretching it until the field lines become mostly
radial and oppositely directed above and below the magnetic equator, as occurs
in the solar wind. The interaction between the wind plasma and magnetic field
near the star produces a steady outflow in which magnetic forces direct plasma
toward the equator, constructing a disk. In the context of a slow (10 km/s)
outflow (10^{-5} M_sun/yr) from an AGB star, MHD simulations demonstrate that a
dense equatorial disk will be produced for dipole field strengths of only a few
Gauss on the surface of the star. A disk formed by this model can be
dynamically important for the shaping of Planetary Nebulae.


title: HST Spectroscopy of Spot 1 on the Circumstellar Ring of SN 1987A

abstract:
  We present ultraviolet and optical spectra of the first bright spot (PA = 29
degrees) on Supernova 1987A's equatorial circumstellar ring taken with the
Space Telescope Imaging Spectrograph. We interpret this spot as the emission
produced by radiative shocks that occur where the supernova blast wave strikes
an inward protrusion of the ring. The observed line widths and intensity ratios
indicate the presence of radiative shocks with velocities ranging from 100 to
250 km s^-1 entering dense (> 10^4 cm^-3) gas. These observations, and future
observations of the development of the spectra and line profiles, provide a
unique opportunity to study the hydrodynamics of radiative shocks.


title: Observational Constraints on Higher Order Clustering up to $z\simeq 1

abstract:
  Constraints on the validity of the hierarchical gravitational instability
theory and the evolution of biasing are presented based upon measurements of
higher order clustering statistics in the Deeprange Survey, a catalog of
$\sim710,000$ galaxies with $I_{AB} \le 24$ derived from a KPNO 4m CCD imaging
survey of a contiguous $4^{\circ} \times 4^{\circ}$ region. We compute the
3-point and 4-point angular correlation functions using a direct estimation for
the former and the counts-in-cells technique for both. The skewness $s_3$
decreases by a factor of $\simeq 3-4$ as galaxy magnitude increases over the
range $17 \le I \le 22.5$ ($0.1 \lesssim z \lesssim 0.8$). This decrease is
consistent with a small {\it increase} of the bias with increasing redshift,
but not by more than a factor of 2 for the highest redshifts probed. Our
results are strongly inconsistent, at about the $3.5-4 \sigma$ level, with
typical cosmic string models in which the initial perturbations follow a
non-Gaussian distribution - such models generally predict an opposite trend in
the degree of bias as a function of redshift. We also find that the scaling
relation between the 3-point and 4-point correlation functions remains
approximately invariant over the above magnitude range. The simplest model that
is consistent with these constraints is a universe in which an initially
Gaussian perturbation spectrum evolves under the influence of gravity combined
with a low level of bias between the matter and the galaxies that decreases
slightly from $z \sim 0.8$ to the current epoch.


title:
Correcting Parameters of Events Based on the Entropy of Microlensing
  Ensemble

abstract:
  We entertain the idea that robust theoretical expectations can become a tool
in removing hidden observational or data-reduction biases. We illustrate this
approach for a specific problem associated with gravitational microlensing.
Using the fact that a group is more than just a collection of individuals, we
derive formulae for correcting the distribution of the dimensionless impact
parameters of events, u_min. We refer to the case when undetected biases in the
u_min distribution can be alleviated by multiplication of impact parameters of
all events by a common constant factor. We show that in this case the general
maximum likelihood problem of solving an infinite number of equations reduces
to two constraints, and we find an analytic solution. Under the above
assumptions, this solution represents a state in which the ``entropy'' of a
microlensing ensemble is at its maximum, that is, the distribution of u_min
resembles a specific, theoretically expected, box-like distribution to the
highest possible extent. We also show that this technique does not allow one to
correct the parameters of individual events on the event by event basis
independently from each other.


title: Hydrodynamic Simulations of the Sunyaev-Zel'dovich effect(s)

abstract:
  We have performed a sequence of high resolution hydrodynamic simulations of
structure formation in a LCDM model to study the thermal and kinetic
Sunyaev-Zel'dovich (SZ) effects. Including only adiabatic gas physics, we
demonstrate that our simulations for the thermal effect are converged down to
sub-arcminute scales. In this model, the angular power spectrum of CMB
anisotropies induced by the thermal effect peaks at l~10^4, and reaches an
amplitude just below current observational upper limits. Fluctuations due to
the kinetic effect are a factor of ~30 lower in power and peak at slightly
smaller angular scales. We identify individual SZ sources and compute their
counts as a function of source strength and angular size. We present a
preliminary investigation of the consequences of an early epoch of energy
injection which tends to suppress power on small angular scales, while giving
rise to additional power on largescales from the reheated IGM at high redshift.


title:
Cosmic Microwave Background constraint on residual annihilations of
  relic particles

abstract:
  Energy injected into the Cosmic Microwave Background at redshifts z<10^6 will
distort its spectrum permanently. In this paper we discuss the distortion
caused by annihilations of relic particles. We use the observational bounds on
deviations from a Planck spectrum to constrain a combination of annihilation
cross section, mass, and abundance. For particles with (s-wave) annihilation
cross section, <\sigma|v|>=\sigma_0, the bound is
f[(\sigma_0/6e-27cm^3/s)(\Omega_{X\bar{X}}h^2)^2]/(m_X/MeV)<0.2, where m_X is
the particle mass, \Omega_{X\bar{X}} is the fraction of the critical density
the particle and its antiparticle contribute if they survive to the present
time, h=H_0/(100km/s/Mpc), H_0 is the Hubble constant, and f is the fraction of
the annihilation energy that interacts electromagnetically. We also compute the
less stringent limits for p-wave annihilation. We update other bounds on
residual annihilations and compare them to our CMB bound.


title: Galaxy Spin Statistics and Spin-Density Correlation

abstract:
  We present a theoretical study of galaxy spin correlation statistics, with
detailed technical derivations. We also find an expression for the spin-density
cross-correlation, and apply that to the Tully galaxy catalog. The
observational results appear qualitatively consistent with the theoretical
predictions, yet the error bars are still large. However, we expect that
currently ongoing large surveys such as the Sloan Digital Sky survey (SDSS)
will enable us to make a precision measurement of these correlation statistics
in the near future. These intrinsic galaxy alignments are expected to dominate
over the weak lensing signal in SDSS, and we present the detailed algorithms
for the density reconstruction for this case.
  These observables are tracers of the galaxy-gravity interaction, which may
provide us deeper insights into the galaxy formation and large scale matter
distribution as well.


title: Cosmic Strings Lens Phenomenology Revisited

abstract:
  We present investigations of lens phenomenological properties of cosmic
strings for deep galaxy surveys. General results that have obtained for lineic
energy distribution are presented first. We stress that generically the local
convergence always vanishes in presence of strings although there might be some
significant distortions. We then propose a simplified model of strings, we call
``Poisson strings'', for which exhaustive investigations can be done either
numerically or analytically.


title: ADONIS observations of the HD 100546 circumstellar dust disk

abstract:
  We report here the first resolved images of the circumstellar dust disk
around the Pre-Main-Sequence star HD 100546. These near-infrared images were
obtained in J and short K bands with the adaptive optics system ADONIS at the
ESO observatory. A bright disk extending 2 arcsec (200 AU) far from the star
and viewed with an inclination with respect to the line of sight around 50
degrees is revealed by the observations. Using a simplified model of light
scattering, we find that the dust disk density peaks at a distance of 40 AU
from the star, and the FWHM of this dense ring is typically 20 AU. This type of
disk is believed to be a denser precursor of beta Pictoris-like main-sequence
disks. The structure of the disk is compared with the best known example of the
class of ``debris disks'', the disk surrounding beta Pictoris.


title: Molecular line study of evolution in protostellar cloud cores

abstract:
  Two dense dark cloud cores representing different stages of dynamical
evolution were observed in a number of molecular spectral lines. One of the
cores, Cha- MMS1 in the Chamaeleon cloud I contains a Class 0 protostar,
whereas the other, CrA C in the R Coronae Australis cloud, is pre-stellar. We
find that the cores have very different chemical compositions. Cha-MMS1
exhibits characteristics of so-called `early-type' chemistry with high abundan-
ces of carbon-chain molecules such as HC3N, but it also has a large N2H+
abundance, which is expected only to build up at later stages. In contrast,
none of the carbon-chain molecules were detected in CrA C. CrA C has a higher
SO abundance than Cha-MMS1, which implies that it is chemically `older' than
Cha- MMS1. The most striking difference between the two cores is seen in the
HC3N/SO abundance ratio, which is at least three orders of magnitude higher in
Cha-MMS than in CrA C. This result is surprising since starless cores are
usually thought to be chemically younger than star-forming cores. Because of
the high N2H+ abundance, we suggest that Cha-MMS1 represents the `late-time
cyanopolyyne peak'. This would also be a more natural explanation for the
carbon-chain molecules than the `early-time' picture in view of the fact that
the core is presently collapsing to form a star. Thus, the dynamical evolution
in CrA C seems to have been very slow compared with that of Cha-MMS1, and we
discuss possible reasons for this.


title:
Testing the Hypothesis of the Morphological Transformation from Field
  Spiral to Cluster S0

abstract:
  Hubble Space Telescope observations of distant clusters have suggested a
steep increase in the proportion of S0 galaxies between clusters at high
redshifts and similar systems the present-day. It has been proposed that this
increase results from the transformation of the morphologies of accreted field
galaxies from spirals to S0s. We have simulated the evolution of the
morphological mix in clusters based on a simple phenomenological model where
the clusters accrete a mix of galaxies from the surrounding field, the spiral
galaxies are transformed to S0s (through an unspecified process) and are added
to the existing cluster population. We find that in order to reproduce the
apparently rapid increase in the ratio of S0 galaxies to ellipticals in the
clusters, our model requires that: (1) galaxy accretion rate has to be high
(typically, more than half of the present-day cluster population must have been
accreted since z~0.5), and (2) most of the accreted spirals, with morphological
types as late as Scdm, must have transformed to S0's. Although the latter
requirement may be difficult to meet, it is possible that such bulge-weak
spirals have already been `pre-processed' into the bulge-strong galaxies prior
to entering the cluster core and are eventually transformed into S0's in the
cluster environment. On the basis of the evolution of the general morphological
mix in clusters our model suggests that the process responsible for the
morphological transformation takes a relatively long time (1-3Gyr) after the
galaxy has entered the cluster environment.


title: A Deep ROSAT HRI Observation of NGC 1313

abstract:
  We describe a series of observations of NGC 1313 using the ROSAT HRI with a
combined exposure time of 183.5 ksec. The observations span an interval between
1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray
flux of SN1978K, one of several luminous sources in the galaxy. No diffuse
emission is detected in the galaxy to a level of ~1-2x10^37 ergs/s/arcmin^-2. A
total of eight sources are detected in the summed image within the D_25
diameter of the galaxy. The luminosities of five of the eight range from
\~6x10^37 to ~6x10^38 erg/s; these sources are most likely accreting X-ray
binaries, similar to sources obseved in M31 and M33. The remaining three
sources all emit above 10^39 erg/s. We present light curves of the five
brightest sources. Variability is detected at the 99.9% level from four of
these. We identify one of the sources as an NGC 1313 counterpart of a Galactic
X-ray source. The light curve, though crudely sampled, most closely resembles
that of a Galactic black hole candidate such as GX339-4, but with considerably
higher peak X-ray luminosity. An additional seven sources lie outside of the
D_25 diameter and are either foreground stars or background AGN.


title:
Detection of a broad iron emission line and sub-millisecond
  quasiperiodic oscillations from the type I X-ray burster 4U1728-34 in a high
  state

abstract:
  We report results from simultaneous RossiXTE and BeppoSAX observations of the
neutron-star x-ray binary and type I X-ray burster 4U1728-34. The source was
found in a high luminosity state, L_X near 0.1 L_Edd, and quasiperiodic
oscillations were detected at 1284 +/- 6 Hz, the highest frequency ever
observed from this source. The x-ray spectrum shows a broad, FWHM = 0.8 keV,
iron K-alpha fluorescence line. We discuss interpretations of the broad line
and the quasiperiodic oscillations and how future simultaneous spectral and
timing observations can be used to test these interpretations and, potentially,
to estimate the mass of the compact object.


title: What Kind of Obscured AGN Make the Cosmic X-ray Background?

abstract:
  While it is understood that the origin of the Cosmic X-ray Background (CXRB)
can be explained in terms of a combination of obscured and unobscured AGN, the
identity of these obscured AGN showing up in large numbers at faint fluxes
remains unclear. Deep surveys are showing up increasingly large numbers of AGN
at the faintest fluxes which have broad optical lines but flat X-ray spectra.
It is commonly assumed that there must a new population of sources making a
substantial contribution to the CXRB. We show that we need not look further
than our own backyard to find familiar examples of such sources and there is no
compelling reason to invoke a mysterious, new population.


title:
A search for clusters at high redshift - II. A proto cluster around a
  radio galaxy at z=2.16

abstract:
  VLT spectroscopic observations of Ly alpha--excess objects in the field of
the clumpy radio galaxy 1138-262 at z=2.16 have led to the discovery of 14
galaxies and one QSO at approximately the same distance as the radio galaxy.
All galaxies have redshifts in the range 2.16 \pm 0.02, centered around the
redshift of the radio galaxy, and are within a projected physical distance of
1.5 Mpc from it. The velocity distribution suggests that there are two galaxy
subgroups having velocity dispersions of ~500 km/s and ~300 km/s and a relative
velocity of 1800 km/s. If these are virialized structures, the estimated
dynamical masses for the subgroups are ~9 and ~3x10E13 solar masses
respectively, implying a total mass for the structure of more than 10E14 solar
masses. The new observations, together with previous results, suggest that the
structure of galaxies around 1138-262 is likely to be a forming cluster.


title: HST Observations of Black Hole X-ray Transient Outbursts

abstract:
  The Hubble Space Telescope has now observed four black hole X-ray transients
in outburst under an ongoing Target-of-Opportunity program: GRO J0422+32
(1994), GRO J1655-40 (1996), XTE J1859+226 (1999-2000) and XTE J1118+480
(2000). We summarise the highlights of this program to date, including a
diversity of spectral energy distributions, correlated X-ray/UV/optical rapid
variability and detailed UV spectroscopy.


title: Doppler Tomography of XTE J2123-058 and Other Neutron Star LMXBs

abstract:
  We describe Doppler tomography obtained in the 1998 outburst of the neutron
star low mass X-ray binary (LMXB) XTE J2123-058. This analysis, and other
aspects of phase-resolved spectroscopy, indicate similarities to SW Sex
systems, except that anomalous emission kinematics are seen in HeII, whilst
phase 0.5 absorption is confined to H alpha. This separation of these effects
may provide tighter constraints on models in the LMXB case than is possible for
SW Sex systems. We will compare results for other LMXBs which appear to show
similar kinematics and discuss how models for the SW Sex phenomenon can be
adapted to these systems. Finally we will summarise the limited Doppler
tomography performed on the class of neutron star LMXBs as a whole, and discuss
whether any common patterns can yet be identified.


title:
Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and
  SMC

abstract:
  We construct size distributions for carbonaceous and silicate grain
populations in different regions of the Milky Way, LMC, and SMC. The size
distributions include sufficient very small carbonaceous grains (including
polycyclic aromatic hydrocarbon molecules) to account for the observed infrared
and microwave emission from the diffuse interstellar medium. Our distributions
reproduce the observed extinction of starlight, which varies depending upon the
interstellar environment through which the light travels. As shown by Cardelli,
Clayton & Mathis in 1989, these variations can be roughly parameterized by the
ratio of visual extinction to reddening, R_V. We adopt a fairly simple
functional form for the size distribution, characterized by several parameters.
We tabulate these parameters for various combinations of values for R_V and
b_C, the C abundance in very small grains. We also find size distributions for
the line of sight to HD 210121, and for sightlines in the LMC and SMC. For
several size distributions, we evaluate the albedo and scattering asymmetry
parameter, and present model extinction curves extending beyond the Lyman
limit.


title: On the magnetism of stars and planets

abstract:
  A self-consistent statistical approach to the problem of planetary and
stellar magnetism is suggested. The mechanism of magnetic field generation in
the astronomical objects, where the existence of fields is associated with the
axial rotation of objects, is discussed. In the general case different forces
produce partial R-separation of the charges. As a result of the system
rotation, the magnetic fields of the currents of these charges are not
compensated. The influence of various factors on the magnetic field of some
object is analysed.


title: A weak turbulence theory for incompressible MHD

abstract:
  We derive a weak turbulence formalism for incompressible MHD. Three-wave
interactions lead to a system of kinetic equations for the spectral densities
of energy and helicity. We find energy spectra solution of the kinetic
equations. The constants of the spectra are computed exactly and found to
depend on the amount of correlation between the velocity and the magnetic
field. Comparison with several numerical simulations and models is also made.


title: Theoretical Models of Photodissociation Fronts

abstract:
  Observations of H2 line emission have revealed higher-than-expected gas
temperatures in a number of photodissociation fronts. We discuss the heating
and cooling processes in photodissociation regions. Observations of NGC 2023
are compared to a theoretical model in which there is substantial gas at
temperatures T = 500-1000K heated by photoelectric emission and collisional
deexcitation of H2. In general the model successfully reproduces the observed
H2 line emission from a wide range of energy levels. The observed [SiII]34.8um
emission appears to indicate substantial depletion of Si in NGC 2023.


title: Interstellar Grains

abstract:
  Our current understanding of interstellar dust is summarized at an
introductory level. Submicron-sized interstellar dust grains absorb and scatter
light, and reradiate the absorbed energy in the infrared. The grain population
spans a range of sizes, from molecules containing only tens of atoms, to
particles containing 10^{10} atoms. Most of the grain mass appears to be due to
two types of solid, in approximately equal amounts: amorphous silicate mineral,
and carbonaceous material. Approximately 2/3 of the interstellar carbon in
diffuse clouds is in solid form.
  Interstellar grains are important for many reasons: they obscure our view (in
a wavelength-dependent manner); the infrared emission from dust provides a
valuable probe of dense regions; and because dust grains play a central role in
interstellar chemistry, gas dynamics, and heating and cooling of interstellar
gas.


title:
User Guide for the Discrete Dipole Approximation Code DDSCAT (Version
  5a10)

abstract:
  DDSCAT.5a is a freely available software package which applies the "discrete
dipole approximation" (DDA) to calculate scattering and absorption of
electromagnetic waves by targets with arbitrary geometries and complex
refractive index. The DDA approximates the target by an array of polarizable
points. DDSCAT.5a requires that these polarizable points be located on a cubic
lattice. DDSCAT.5a10 allows accurate calculations of electromagnetic scattering
from targets with "size parameters" 2 pi a/lambda < 15 provided the refractive
index m is not large compared to unity (|m-1| < 1).
  The DDSCAT package is written in Fortran and is highly portable. The program
supports calculations for a variety of target geometries (e.g., ellipsoids,
regular tetrahedra, rectangular solids, finite cylinders, hexagonal prisms,
etc.). Target materials may be both inhomogeneous and anisotropic. It is
straightforward for the user to import arbitrary target geometries into the
code, and relatively straightforward to add new target generation capability to
the package. DDSCAT automatically calculates total cross sections for
absorption and scattering and selected elements of the Mueller scattering
intensity matrix for specified orientation of the target relative to the
incident wave, and for specified scattering directions.
  This User Guide explains how to use DDSCAT.5a10 to carry out EM scattering
calculations. CPU and memory requirements are described.


title:
Contemporaneous Observations of Direct and Raman Scattered O VI in
  Symbiotic Stars

abstract:
  Symbiotic stars are binary systems consisting of a hot star, typically a
white dwarf, and a cool giant companion. The wind from the cool star is ionized
by the radiation from the hot star, resulting in the characteristic combination
of sharp nebular emission lines and stellar molecular absorption lines in the
optical spectrum. Most of the emission lines are readily identifiable with
common ions. However, two strong, broad emission lines at $\lambda\lambda$
6825, 7082 defied identification with known atoms and ions. In 1989 Schmid made
the case that these long unidentified emission lines resulted from the Raman
scattering of the O VI resonance photons at $\lambda\lambda$ 1032, 1038 by
neutral hydrogen.
  We present contemporaneous far-UV and optical observations of direct and
Raman scattered O VI lines for nine symbiotic stars obtained with the Hopkins
Ultraviolet Telescope (Astro-2) and various ground-based telescopes. The O VI
emission lines are present in every instance in which the $\lambda\lambda$
6825, 7082 lines are present in support of the Schmid Raman scattering model.
We calculate scattering efficiencies and interpret the results in terms of the
Raman models. Additionally, we measure the flux of the Fe II fluorescence line
at $\lambda$1776, which is excited by the O VI line at $\lambda$1032, and
calculate the first estimates of the conversion efficiencies of this process.


title: Gas/Star Offsets in Tidal Tails

abstract:
  We use numerical simulations to study the development of gas/star offsets in
the tidal tails of merging galaxies. These offsets are shown to be a natural
consequence of the radially extended HI spatial distribution in disk galaxies,
coupled with internal dissipation in the gaseous component driven by the
interaction. This mechanism explains the observed gas/star offsets in
interacting galaxies without invoking interactions with a hot (unseen) gaseous
component.


title:
Comptonization of Infrared Radiation from Hot Dust by Relativistic Jets
  in Quasars

abstract:
  We demonstrate the importance of near-infrared radiation from hot dust for
Compton cooling of electrons/positrons in quasar jets. In our model, we assume
that the non-thermal radiation spectra observed in OVV quasars are produced by
relativistic electrons/positrons accelerated in thin shells which propagate
down the jet with relativistic speeds. We show that the Comptonization of the
near-IR flux is likely to dominate the radiative output of OVV quasars in the
energy range from tens of keV up to hundreds of MeV, where it exceeds that
produced by Comptonization of the UV radiation reprocessed and rescattered in
the Broad Emission Line region. The main reason for this lies in the fact that
the jet encounters the ambient IR radiation over a relatively large distance as
compared to the distance where the energy density of the broad emission line
light peaks. In the soft - to mid energy X-ray band, the spectral component
resulting from Comptonization of the near-IR radiation joins smoothly with the
synchrotron-self-Compton component, which may be responsible for the soft X-ray
flux. At the highest observed gamma-ray energies, in the GeV range,
Comptonization of broad emission lines dominates over other components.


title: Dynamical Mass Estimates for the Halo of M31 from Keck Spectroscopy

abstract:
  The last few months have seen the measurements of the radial velocities of
all of the dwarf spheroidal companions to the Andromeda galaxy (M31) using the
spectrographs (HIRES and LRIS) on the Keck Telescope. This paper summarises the
data on the radial velocities and distances for all the companion galaxies and
presents new dynamical modelling to estimate the mass of extended halo of M31.
The best fit values for the total mass of M31 are between 7 and 10 x 10^{11}
solar masses, depending on the details of the modelling. The mass estimate is
accompanied by considerable uncertainty caused by the smallness of the dataset;
for example, the upper bound on the total mass is roughly 24 x 10^{11} solar
masses, while the lower bound is about 3 x 10^{11} solar masses. These values
are less than the most recent estimates of the most likely mass of the Milky
Way halo. Bearing in mind all the uncertainties, a fair conclusion is that the
M31 halo is roughly as massive as that of the Milky Way halo. There is no
dynamical evidence for the widely held belief that M31 is more massive -- it
may even be less massive.


title: Triaxial Haloes and Particle Dark Matter Detection

abstract:
  This paper presents the properties of a family of scale-free triaxial haloes.
We adduce arguments to suggest that the velocity ellipsoids of such models are
aligned in conical coordinates. We provide an algorithm to find the set of
conically aligned velocity second moments that support a given density against
the gravity field of the halo. The case of the logarithmic ellipsoidal model --
the simplest triaxial generalisation of the familiar isothermal sphere -- is
examined in detail. The velocity dispersions required to hold up the
self-consistent model are analytic. The velocity distribution of the dark
matter can be approximated as a triaxial Gaussian with semiaxes equal to the
velocity dispersions. There are roughly twenty experiments worldwide that are
searching for evidence of scarce interactions between weakly-interacting
massive-particle dark matter (WIMPs) and detector nuclei. The annual modulation
signal, caused by the Earth's rotation around the Sun, is a crucial
discriminant between WIMP events and the background. The greatest rate is in
June, the least in December. We compute the differential detection rate for
energy deposited by the rare WIMP-nucleus interactions in our logarithmic
ellipsoidal halo models. Triaxiality and velocity anisotropy change the total
rate by up to 40 %, and have a substantial effect on the amplitude of the
annual modulation signal. The overall rate is greatest, but the amplitude of
the modulation is weakest, in our radially anisotropic halo models. Even the
sign of the signal can be changed. Restricting attention to low energy events,
the models predict that the maximum rate occurs in December, and not in June.


title: The Orbital Structure of Dark Matter Halos with Gas

abstract:
  With the success of the Chandra and XMM missions and the maturation of
gravitational lensing techniques, powerful constraints on the orbital structure
of cluster dark matter halos are possible. I show that the X-ray emissivity and
mass of a galaxy cluster uniquely specify the anisotropy and velocity
dispersion profiles of its dark matter halo. I consider hydrostatic as well as
cooling flow scenarios, and apply the formalism to the lensing cluster
CL0024+16 and the cooling flow cluster Abell 2199. In both cases, the model
predicts a parameter-free velocity dispersion profile that is consistent with
independent optical redshift surveys of the clusters.


title: Searching for MACHOs in Galaxy Clusters

abstract:
  If cluster dark matter is in the form of compact objects it will introduce
fluctuations into the light curves of distant sources. Current searches for
MACHOs in clusters of galaxies focus on monitoring quasars behind nearby
systems. This paper considers the effect of such a compact population on the
surface brightness distribution of giant gravitationally lensed arcs. As the
microlensing optical depth is significant in these clusters, the expected
fluctuations are substantial and are observable. Focusing on the giant arc seen
in Abell 370, we demonstrate that several `extreme' events would be visible in
a comparison of HST observations at two epochs. Utilizing NGST, long term
monitoring should reveal a ubiquitous twinkling of brightness over the surface
of the arcs.


title:
A study of the shadowing of galactic cosmic rays by the sun in a quiet
  phase of solar activity with the Tibet air shower array

abstract:
  We have shown that the Sun's shadow by high energy cosmic rays moves year by
year and its behavior is correlated with a time variation of the large-scale
structure of the solar and interplanetary magnetic fields. The solar activity
was near minimum in the period from 1996 through 1997. Using the data obtained
with the Tibet air shower array, we examined the shadowing of cosmic rays by
the Sun in this quiet phase of solar cycle, and found that the Sun's shadow was
just in the apparent direction of the Sun, though it was observed at the
position considerably away from the Sun to the south-west in the period between
1990 and 1993. It is known that the magnetic pole of equivalent solar dipole
was reversed during the previous active phase, and near solar minimum the
dipole was aligned with the rotating axis, preserving its N-pole on the north
pole side of the Sun. This causes the solar magnetic field to shift the Sun's
shadow to the east. Thus, the observed results suggest that the shift of the
Sun's shadow due to the solar magnetic field was pushed back by the effect of
the geomagnetic field, since the geomagnetic field always make the shadow shift
to the west. We discuss the Sun's shadow observed during the period near solar
minimum in 1996-1997 and compare it with the simulation results.


title:
A Photometric Study of the Ages and Metallicities of Early-type Galaxies
  in A2218

abstract:
  We present deep optical and near-infrared imaging of the rich cluster A2218
at z=0.17. Our optical imaging comes from new multicolour Hubble Space
Telescope WFPC2 observations in the F450W (B), F606W (V) and F814W (I)
passbands. These observations are complemented by deep near-infrared, Ks-band,
imaging from the new INGRID imager on the 4.2-m William Herschel Telescope.
This combination provides unique high-precision multicolour optical-infrared
photometry and morphological information for a large sample of galaxies in the
core of this rich cluster at a lookback time of ~3Gyrs. We analyse the (B-I),
(V-I) and (I-Ks) colours of galaxies spanning a range of a factor of 100 in
K-band luminosity in this region and compare these with grids of stellar
population models. We find that the locus of the colours of the stellar
populations in the luminous (>0.5L*) early-type galaxies, both ellipticals and
S0s, traces a sequence of varying metallicity at a single age. At fainter
luminosities (<0.1L*), this sequence is extended to lower metallicities by the
morphologically-classified ellipticals. However, the faintest S0s exhibit very
different behaviour, showing a wide range in colours, including a large
fraction (30%) with relatively blue colours which appear to have younger
luminosity-weighted ages for their stellar populations, 2-5Gyrs. We show that
the proportion of these young S0s in the cluster population is consistent with
the observed decrease in the S0 population seen in distant clusters when
interpreted within the framework of a two-step spectroscopic and morphological
transformation of accreted spiral field galaxies into cluster S0s.


title: Superfluidity in relativistic neutron stars

abstract:
  The purpose of these notes is to give a brief review of superfluidity in
neutron stars. After a short presentation explaining why and how superfluidity
is expected in the crust and core of neutron stars, consequences on thermal
evolution and rotational dynamics are discussed. The second part summarizes a
formalism that has been recently developped to describe the hydrodynamics of
superfluids or superconductors in the framework of general relativity. As an
application, one can compute the oscillations of a two-component relativistic
neutron star.


title: Stromgren Photometry from z=0 to z~1. The Method

abstract:
  We use rest-frame Stromgren photometry to observe clusters of galaxies in a
self-consistent manner from z=0 to z=0.8. Stromgren photometry of galaxies is
an efficient compromise between standard broad-band photometry and
spectroscopy, in the sense that it is more sensitive to subtle variations in
spectral energy distributions than the former, yet much less time-consuming
than the latter. Principal Component Analysis (PCA) is used to extract maximum
information from the Stromgren data. By calibrating the Principal Components
using well-studied galaxies (and stellar population models), we develop a
purely empirical method to detect, and subsequently classify, cluster galaxies
at all redshifts smaller than 0.8. Interlopers are discarded with unprecedented
efficiency (up to 100%). The first Principal Component essentially reproduces
the Hubble Sequence, and can thus be used to determine the global star
formation history of cluster members. The (PC2, PC3) plane allows us to
identify Seyfert galaxies (and distinguish them from starbursts) based on
photometric colors alone. In the case of E/S0 galaxies with known redshift, we
are able to resolve the age-dust- metallicity degeneracy, albeit at the
accuracy limit of our present observations. This technique will allow us to
probe galaxy clusters well beyond their cores and to fainter magnitudes than
spectroscopy can achieve. We are able to directly compare these data over the
entire redshift range without a priori assumptions because our observations do
not require k-corrections. The compilation of such data for different cluster
types over a wide redshift range is likely to set important constraints on the
evolution of galaxies and on the clustering process.


title:
The ING Instrumentation Conference Discussion, Options for a Competitive
  Observatory

abstract:
  An expert panel initiated discussion on a number of key questions facing the
role of 4-m and small telescopes in the new era of 8-m telescopes. The panel
and audience agreed that the 4-m class telescope role would necessarily evolve,
but would still be important in the coming years. The need for an active
development programme of competitive instrumentation for 4-m class telescopes,
and in particular the William Herschel Telescope (WHT) was stressed. In
conjunction with this, the need to de-commission instrumentation made redundant
by 8-m class telescopes was noted. New operational modes, including greater
emphasis on survey programmes, and possibly queue scheduling, coupled with
changes to the procedures for allocating time were seen as desirable. The panel
and audience supported the Isaac Newton Group's emphasis on the development of
instrumentation to exploit its imminent deployment of the WHT's facility
Adaptive Optics system.


title: The Globular Cluster Omega Centauri and the Oosterhoff Dichotomy

abstract:
  CCD observations obtained by the OGLE team for 128 RR Lyrae variables in
Omega Cen have been analysed. The P-L and P-A plots indicate that, in addition
to fundamental (RRab) and first overtone (RRc) pulsators, the Omega Cen RR
Lyrae population seems to include second overtone (RRe) and possibly third
overtone pulsators. The mean periods derived for the RRab and RRc stars are
typical values for an Oosterhoff type II (OoII) cluster. Nevertheless, the P-A
plot plot also shows that some of the RR Lyrae variables have `Oosterhoff type
I' (OoI) characteristics. Relative luminosities derived for the RRc variables
from Fourier coefficients correlate with the observed apparent magnitudes.
Masses for the RRc stars have been calculated from Fourier coefficients. A
comparison of the derived masses for RRc stars in the four OoII clusters Omega
Cen, M15, M55 and M68 indicates that the masses of the RRc stars in M15 and M68
are almost 0.2 solar masses greater than those in the other two. Since M15 and
M68 have a high frequency of RRd stars among their first overtone pulsators,
while none have been identified in Omega Cen or M55, this suggests that the
double-mode pulsation phenomenon may be associated with mass. Among the RRc
variables in Omega Cen, the OoII variables have lower derived masses and higher
luminosities than the OoI variables. An application of the period-density law
to pairs of OoI and OoII RRab stars selected according to their position in the
P-A plot also indicates that the OoII variables in general have lower masses
and higher luminosities. These findings support the hypothesis that RR Lyrae
variables in OoII systems are evolved HB stars that spend their ZAHB phase on
the blue side of the instability strip.


title:
Global fits for the spectral index of the cosmological curvature
  perturbation

abstract:
  Best-fit values of the spectral index of the curvature perturbation are
presented, assuming the $\Lambda$CDM cosmology. Apart from the spectral index,
the parameters are the Hubble parameter, the total matter density and the
baryon density. The data points are intended to represent all measurements
which are likely to significantly affect the result. The cosmic microwave
anisotropy is represented by the COBE normalization, and heights of the first
and second peaks given by the latest Boomerang and Maxima data. The slope of
the galaxy correlation function and the matter density contrast on the
$8h^{-1}\Mpc$ scale are each represented by a data point, as are the expected
values of the Hubble parameter and matter density.
  The `low-deuterium' nucleosynthesis value of the baryon density provides a
final data point, the fit giving a value about one standard deviation higher.
The reionization epoch is calculated from the model by assuming that it
corresponds to the collapse of a fraction $f\gsim 10^{-4}$ of matter.
  We consider the case of a scale-independent spectral index, and also the
scale-dependent spectral index predicted by running mass models of inflation.
In the former case, the result is compared with the prediction of models of
inflation based on effective field theory, in which the field value is small on
the Planck scale. Detailed comparison is made with other fits, and other
approaches to the comparison with theory.


title: Putting The Together A Cyclical Baryonic Universe

abstract:
  There are multiple examples of gravitational losses in neutron stars and
black holes. Protons and neutrons have been found to have enormous repulsive
pressures that highly squeezed collapsing matter cannot overcome. The case
against singularities follows. Galactic black hole gravitational losses can
supply the missing dark energy. With highly squeezed nucleons, the big bang
could begin as a hot core and a cold dark matter shell. The 21 cm. radiation
data has identified baryon sized particles as cold dark matter. Highly squeezed
nucleons will not decompose to produce antimatter. The flatness of the Universe
is due to a baryonic bounce. The highly correlated galaxies originated from
primordial black holes capturing hot core gasses.There is evidence that
galaxies have not grown nor merged significantly since formation.