title: An Observational Test of Two-field Inflation

abstract:
  We study adiabatic and isocurvature perturbation spectra produced by a period
of cosmological inflation driven by two scalar fields. We show that there
exists a model-independent consistency condition for all two-field models of
slow-roll inflation, despite allowing for model-dependent linear processing of
curvature and isocurvature perturbations during and after inflation on
super-horizon scales. The scale-dependence of all spectra are determined solely
in terms of slow-roll parameters during inflation and the dimensionless
cross-correlation between curvature and isocurvature perturbations. We present
additional model-dependent consistency relations that may be derived in
specific two-field models, such as the curvaton scenario.


title: The stellar content, metallicity and ionization structure of HII regions

abstract:
  Observations of infrared fine-structure lines provide direct information on
the metallicity and ionization structure of HII regions and indirectly on the
hardness of the radiation field ionizing these nebulae. We have analyzed a
sample of Galactic and Magellanic Cloud HII regions observed by the Infrared
Space Observatory (ISO) to examine the interplay between stellar content,
metallicity and the ionization structure of HII regions. The observed
[SIV]10.5/[SIII]18.7 mum and [NeIII]15.5/[NeII]12.8 mum line ratios are shown
to be highly correlated over more than two orders of magnitude. We have
compared the observed line ratios to the results of photoionization models
using different stellar energy distributions. The derived characteristics of
the ionizing star depend critically on the adopted stellar model as well as the
(stellar) metallicity. We have compared the stellar effective temperatures
derived from these model studies for a few well-studied HII regions with
published direct spectroscopic determinations of the spectral type of the
ionizing stars. This comparison supports our interpretation that stellar and
nebular metallicity influences the observed infrared ionic line ratios. We can
explain the observed increase in degree of ionization, as traced by the
[SIV]\[SIII] and [NeIII]\[NeII] line ratios, by the hardening of the radiation
field due to the decrease of metallicity. The implications of our results for
the determination of the ages of starbursts in starburst galaxies are assessed.


title:
Rotational velocities of A-type stars II. Measurement of vsini in the
  northern hemisphere

abstract:
  This work is the second part of the set of measurements of vsini for A-type
stars, begun by Royer et al. (2002). Spectra of 249 B8 to F2-type stars
brighter than V=7 have been collected at Observatoire de Haute-Provence (OHP).
Fourier transforms of several line profiles in the range 4200--4600 A are used
to derive vsini from the frequency of the first zero. Statistical analysis of
the sample indicates that measurement error mainly depends on vsini and this
relative error of the rotational velocity is found to be about 5% on average.
The systematic shift with respect to standard values from Slettebak et al.
(1975), previously found in the first paper, is here confirmed. Comparisons
with data from the literature agree with our findings: vsini values from
Slettebak et al. are underestimated and the relation between both scales
follows a linear law: vsini(new) = 1.03 vsini(old) + 7.7. Finally, these data
are combined with those from the previous paper (Royer et al. 2002), together
with the catalogue of Abt & Morrell (1995). The resulting sample includes some
2150 stars with homogenized rotational velocities.


title:
No evidence yet for hadronic TeV gamma-ray emission from SNR RX
  J1713.7-3946

abstract:
  Recent TeV-scale gamma-ray observations with the CANGAROO II telescope have
led to the claim that the multi-band spectrum of RX J1713.7-3946 cannot be
explained as the composite of a synchrotron and an inverse Compton component
emitted by a population of relativistic electrons. It was argued that the
spectrum of the high-energy emission is a good match to that predicted by pion
decay, thus providing observational evidence that protons are accelerated in
SNR to at least TeV energies. In this Letter we discuss the multi-band spectrum
of RX J1713.7-3946 under the constraint that the GeV-scale emission observed
from the closely associated EGRET source 3EG J1714-3857 is either associated
with the SNR or an upper limit to the gamma-ray emission of the SNR. We find
that the pion-decay model adopted by Enomoto et al. is in conflict with the
existing GeV data. We have examined the possibility of a modified proton
spectrum to explain the data, and find that we cannot do so within any existing
theoretical framework of shock acceleration models.


title: A simple model for magnetic reconnection heated corona

abstract:
  We construct a simple model for a magnetic reconnection heated corona above a
thin accretion disk in AGNs and Galactic black hole candidates(GBHCs). The
basic assumptions are that (1) the magnetic reconnection heat is cooled down
overwhelmingly by Compton scattering in the corona and that (2) thermal
conduction is dominantly cooled by evaporation of the chromospheric plasma in
the disk-corona interface before Compton cooling sets in. With these two basic
equations as well as equi-partition of magnetic energy with gas energy in the
disk, we can consistently determine the fraction of accretion energy dissipated
in the corona without free parameters, and thus determine the temperature and
all other quantities in both the corona and disk for given black hole mass and
accretion rate. Then, we calculate the luminosity contributed from the disk and
corona and the coronal flux weighted Compton $y$ parameter. It is found that,
at a low luminosity (less than 0.1 Eddington luminosity) the spectrum is hard
with energy spectral index of around 1, while at a high luminosity (larger than
0.1 Eddington luminosity) the spectrum can be either soft or hard. We also find
that the situation is almost same for supermassive and stellar-mass black
holes. These features are consistent with observations of AGNs and GBHCs.


title: A Statistical Strategy for the Sunyaev-Zel'dovich Effect's Cluster Data

abstract:
  We present a statistical strategy for the efficient determination of the
cluster luminosity function from the Sunyaev-Zel'dovich (SZ) effects survey. To
determine the cluster luminosity function from the noise contaminated SZ map,
we first define the zeroth-order cluster luminosity function as a discrepancy
between the measured peak number density of the SZ map and the mean number
density of noise. Then we demonstrate that the noise contamination effects can
be removed by the stabilized deconvolution of the zeroth-order cluster
luminosity function with the one-dimensional Gaussian distribution. We test
this analysis technique against Monte-Carlo simulations, and find that it works
quite well especially in the medium amplitude range where the conventional
cluster identification method based on the threshold cut-off usually fails.


title:
The Clustering, Number Counts and Morphology of Extremely Red (R-K>5)
  Galaxies to K=21

abstract:
  We investigate the number counts, clustering, morphology and radio/X-ray
emission of extremely red objects (EROs), defined as galaxies with R-K>5.0.
This criterion will select old, passive ellipticals at z>0.9. To K=21 we
identify a total of 158 EROs in 81.5 sq. arcmin. The ERO number counts are
lower than predicted by a pure luminosity evolution model, but higher than
predicted by current CDM-based hierarchical models. They can be fitted by a
combination of moderate merging with a decrease with redshift in the comoving
number density of passive galaxies. We investigate the angular correlation
function and find that the EROs have a much higher correlation amplitude than
full K-limited samples of galaxies. This implies that the intrinsic clustering
of EROs is stronger than that of present-day E/S0 galaxies. We estimate the
comoving correlation radius as 10-13 Mpc. We estimate seeing-corrected angular
sizes and morphological types for a K<19.5 subsample (31 galaxies), and find a
3:2 mixture of bulge and disk profiles. 1/4 appear to be interacting, disturbed
or irregular. The angular sizes of the bulge-profile EROs are consistent with
passively evolving ellipticals at 0.9<z<2. Seven of the bright EROs are
detected as 1.4 GHz radio sources. The strongest, at 5 mJy, is also a Chandra
X-ray detection, and lies at the centre of a possible cluster of EROs. Another
source is elongated and aligned with the optical axis and may be a ULIRG-type
starburst.


title: Nonlinear analysis of EAS clusters

abstract:
  We apply certain methods of nonlinear time series analysis to the extensive
air shower clusters found earlier in the data set obtained with the EAS-1000
Prototype array. In particular, we use the Grassberger-Procaccia algorithm to
compute the correlation dimension of samples in the vicinity of the clusters.
The validity of the results is checked by surrogate data tests and some
additional quantities. We compare our conclusions with the results of similar
investigations performed by the EAS-TOP and LAAS groups.


title: On the nature of the compact condensations at the centre of galaxies

abstract:
  There are many observational evidences for the existence of massive compact
condensations in the range $10^6 -10^{10} M_\odot$ at the core of various
galaxies. At present such condensations are commonly interpreted as Black Holes
(BHs). However, we point out that while such Black Hole Candidates (BHCs) must
be similar to BHs in many respects they, actually, can not be BHs because
existence of Black Holes would violate the basic tenet of the General Theory of
Relativity (GTR) that the worldline of a material particle must be timelike at
any regular region of spacetime. On the other hand general relativistic
collapse of very massive bodies should lead to Eternally Collapsing
Configurations (ECOs) or Ultra Compact Objects (UCOs). While ECOs/UCOs may
practically be as compact as corresponding BHs, they will have a physical
surface. Also while BHs do not have any intrinsic magnetic field ECOs may have
strong intrinsic magnetic field. We point out that despite many claims actually
there is no real evidence for the ``Event Horizon'' (EH) of supposed BHs and on
the other hand, there are tentative evidence for the existence of strong
magnetic field in several BHCs (or ECOs). The presence of such intrinsic
magnetic field may render the task of explaining high energy radiation
phenomenon in many Active Galactic Nuclei easier.


title: Measuring CMB Polarization with ESA PLANCK SubMM-Wave Telescope

abstract:
  We analyze the polarization properties of the tilted off-axis dual-reflector
submillimeter-wave telescope on the ESA PLANCK Surveyor designed for measuring
the temperature anisotropies and polarization characteristics of the cosmic
microwave background.


title:
The association between water kilomasers and compact radio sources in
  the starburst galaxy NGC2146

abstract:
  We report the detection of 22 GHz water vapor emission toward the starburst
galaxy NGC2146, made using the Effelsberg 100-m telescope. Interferometric
observations with the Very Large Array (VLA) show that a part of the emission
originates from two prominent sites of star formation that are associated with
compact radio continuum sources, likely ultra-compact HII regions. It is
concluded that the emission arises from the most luminous and distant water
`kilomasers' detected so far. Our data increase the number of water maser
detections in northern galaxies (Dec > -30 deg) with 100 micron IRAS point
source fluxes > 50 Jy to 18%.


title:
The Relative Performance of Filled and Feedhorn-Coupled Focal-plane
  Architectures

abstract:
  Modern far infrared and submillimeter instruments require large format
arrays. We consider the relative performance of filled array (bare pixel) and
feedhorn-coupled architectures for bolometer focal planes. Based on typical
array parameters, we quantify the relative observing speeds and comment on the
merits of the different architectures. Filled arrays can provide higher mapping
speed (by a factor of up to 3.5) and simpler observing modes at the expense of
reduced sensitivity for pointed observations, increased detector numbers, and
greater vulnerability to stray light and electromagnetic interference. Taking
advantage of the filled array architecture requires strongly background limited
detectors. At millimeter wavelengths, filled arrays must be surrounded by a
sufficiently cold enclosure to minimize the background power from the
instrument itself.


title: Radio Studies of Young Core Collapse Supernovae

abstract:
  Multi-frequency observations of two radio bright SNe (SN1993J, SN1979C)
carried out over a year with GMRT are presented. Their radio light curves trace
the evolution of the mass loss in the stellar wind before the pre-supernova
star exploded. Their spectra at low frequencies distinguish between the
synchrotron self-absorption and free-free absorption based models. Two very
similar type IIp SN1999gi and SN1999em were also observed and we comment on
their progenitor mass. These observations of different subclasses of
core-collapse supernovae will aid in defining their progenitors.


title:
Helicity Balance and Steady-State Strength of the Dynamo Generated
  Galactic Magnetic Field

abstract:
  We demonstrate that the inclusion of the helicity flux in the magnetic
helicity balance in the nonlinear stage of galactic dynamo action results in a
radical change in the magnetic field dynamics. The equilibrium value of the
large-scale magnetic field is then approximately the equipartition level. This
is in contrast to the situation without the flux of helicity, when the magnetic
helicity is conserved locally, which leads to substantially subequipartition
values for the equilibrium large-scale magnetic field.


title: Quintessence and the cosmological constant

abstract:
  Quintessence -- the energy density of a slowly evolving scalar field -- may
constitute a dynamical form of the homogeneous dark energy in the universe. We
review the basic idea in the light of the cosmological constant problem.
Cosmological observations or a time variation of fundamental `constants' can
distinguish quintessence from a cosmological constant.


title: A Search for $^{6}$Li in Stars with Planets

abstract:
  Using very high-resolution (R$\sim$ 125,000) and high quality (S/N $\geq$
350) spectra, we have searched for $^{6}$Li in stars hosting extra-solar
planets. From detailed profile-fitting of the Li {\sc i} resonance line at
6707.7 \AA, we find no significant amount of $^{6}$Li relative to the $^{7}$Li
for any of 8 planet bearing stars ($^{6}$Li/$^{7}$Li $\leq$ 0.0 - 0.03) with a
strong Li {\sc i} lines. In particular, we do not confirm the presence of
$^{6}$Li with $^{6}$Li/$^{7}$Li = 0.13 reported by Israelian et al.(2001) for
HD 82943, a star with two known planets. Several of the 8 stars plus HD 219542
A, the planet-less primary of a binary, have been identified in the literature
as possible recipients of accreted terrestrial material. For all of the
planet-hosting stars and an additional 5 planet-less stars, we find no
$^{6}$Li.


title:
Optimization of the Coupling of High-Frequency Horn Antenna Array to the
  ESA PLANCK Submillimeter-Wave Telescope

abstract:
  We study the electromagnetic coupling of the array of Gaussian and
multi-moded horn antennas to the dual-reflector submillimeter-wave telescope on
the ESA PLANCK Surveyor designed for measuring the temperature anisotropies and
polarization characteristics of the cosmic microwave background. In this paper,
we present the results of our analysis concerning the measurement of
polarization with tilted off-axis dual-reflector Gregorian telescope and the
propagation of multi-moded beams through such a system.


title: Anomalous Scalings and Dynamics of Magnetic Helicity

abstract:
  It is demonstrated that the two-point correlation function of the magnetic
helicity in the case of zero mean magnetic field has anomalous scalings for
both, compressible and incompressible turbulent helical fluid flow. The
magnetic helicity in the limit of very high electrical conductivity is
conserved. This implies that the two-point correlation function of the
conserved property does not necessarily have normal scaling. The reason for the
anomalous scalings of the magnetic helicity correlation function is that the
magnetic field in the equation for the two-point correlation function of the
magnetic helicity plays a role of a pumping with anomalous scalings. It is
shown also that when magnetic fluctuations with zero mean magnetic field are
generated the magnetic helicity is very small even if the hydrodynamic helicity
is large. Astrophysical applications of the obtained results are discussed.


title: Space Time Fluctuations and Ultra High Energy Cosmic Ray Interactions

abstract:
  The intimate geometry of space-time is expected to suffer stochastic
fluctuations as a result of quantum gravitational effects. These fluctuations
may induce observable consequences on the propagation of high energy particles
over large distances, so that the strength and the characteristics of these
fluctuations may be constrained, mainly in the range of energies of interest
for cosmic ray physics. While invoked as a possible explanation for the
detection of the puzzling cosmic rays with energies in excess of the threshold
for photopion production (the so-called super-GZK particles), we demonstrate
here that lower energy observations may provide strong constraints on the role
of a fluctuating space-time structure.


title: Galactic Constraints on the Sources of Ultra-High Energy Cosmic Rays

abstract:
  We show that if the sources of ultra-high energy cosmic rays (UHECRs) with
energies E>10^{19}eV are associated with galaxies, then the production of
UHECRs must occur in transient events. Our galaxy is currently at a dim state
in between transients. The time interval between transients is >3x10^4 years if
the minimum Lorentz factor to which protons are accelerated in the transients
is between 10^3 and 10^7. This constraint is satisfied by gamma-ray bursts.


title:
Eccentricity Excitation and Apsidal Resonance Capture in the Planetary
  System Upsilon Andromedae

abstract:
  The orbits of the outer two known planets orbiting Upsilon Andromedae are
remarkably eccentric. Planet C possesses an orbital eccentricity of e1 = 0.253.
For the more distant planet D, e2 = 0.308. Previous dynamical analyses strongly
suggest that the two orbits are nearly co-planar and are trapped in an apsidal
resonance in which the difference between their longitudes of periastron
undergoes a bounded oscillation about 0 degrees. Here we elucidate the origin
of these large eccentricities and of the apsidal alignment. Resonant
interactions between a remnant circumstellar disk of gas lying exterior to the
orbits of both planets can smoothly grow e2. Secular interactions between
planets D and C can siphon off the eccentricity of the former to grow that of
the latter. Externally amplifying e2 during the phase of the apsidal
oscillation when e2/e1 is smallest drives the oscillation amplitude towards
zero. Thus, the substantial eccentricity of planet C and the locking of orbital
apsides are both consequences of externally pumping the eccentricity of planet
D over timescales exceeding apsidal precession periods of order 1e4 yr. We
explain why the recently detected stellar companion to Upsilon Andromedae is
largely dynamically decoupled from the planetary system.


title: Chondrules and Nebular Shocks

abstract:
  Beneath the fusion-encrusted surfaces of the most primitive stony meteorites
lies not homogeneous rock, but a profusion of millimeter-sized igneous spheres.
These chondrules, and their centimeter-sized counterparts, the
calcium-aluminum-rich inclusions, comprise more than half of the volume
fraction of chondritic meteorites. They are the oldest creations of the solar
system. Their chemical composition matches that of the solar photosphere in all
but the most volatile of elements, reflecting their condensation from the same
pristine gas that formed the sun. In this invited editorial, we review the
nebular shock wave model of Desch and Connolly (Meteoritics and Planetary
Science 2002, 37, 183) that seeks to explain their origin. While the model
succeeds in reproducing the unique petrological signatures of chondrules, the
origin of the required shock waves in protoplanetary disks remains a mystery.
Outstanding questions are summarized, with attention paid briefly to competing
models.


title: A Collisional Family in the Classical Kuiper Belt

abstract:
  The dynamical evolution of Classical Kuiper Belt Objects (CKBOs) divides into
two parts, according to the secular theory of test particle orbits. The first
part is a forced oscillation driven by the planets, while the second part is a
free oscillation whose amplitude is determined by the initial orbit of the test
particle. We extract the free orbital inclinations and free orbital
eccentricities from the osculating elements of 125 known CKBOs. The free
inclinations of 32 CKBOs strongly cluster about 2 degrees at orbital semi-major
axes between 44 and 45 AU. We propose that these objects comprise a collisional
family, the first so identified in the Kuiper Belt. Members of this family are
plausibly the fragments of an ancient parent body having a minimum diameter of
\~800 km. This body was disrupted upon colliding with a comparably sized
object, and generated ejecta having similar free inclinations. Our candidate
family is dynamically akin to a sub-family of Koronis asteroids located at
semi-major axes less than 2.91 AU; both families exhibit a wider range in free
eccentricity than in free inclination, implying that the relative velocity
between parent and projectile prior to impact lay mostly in the invariable
plane of the solar system. We urge more discoveries of new CKBOs to test the
reality of our candidate family and physical studies of candidate family
members to probe the heretofore unseen interior of a massive, primitive
planetesimal.


title: An Analytical Approach to Inhomogeneous Structure Formation

abstract:
  We develop an analytical formalism that is suitable for studying
inhomogeneous structure formation, by studying the joint statistics of dark
matter halos forming at two points. Extending the Bond et al. (1991) derivation
of the mass function of virialized halos, based on excursion sets, we derive an
approximate analytical expression for the ``bivariate'' mass function of halos
forming at two redshifts and separated by a fixed comoving Lagrangian distance.
Our approach also leads to a self-consistent expression for the nonlinear
biasing and correlation function of halos, generalizing a number of previous
results including those by Kaiser (1984) and Mo & White (1996). We compare our
approximate solutions to exact numerical results within the excursion-set
framework and find them to be consistent to within 2% over a wide range of
parameters. Our formalism can be used to study various feedback effects during
galaxy formation analytically, as well as to simply construct observable
quantities dependent on the spatial distribution of objects. A code that
implements our method is publicly available at
http://www.arcetri.astro.it/~evan/Gemini


title: A Distant Stellar Companion in the Upsilon Andromedae System

abstract:
  Upsilon Andromedae is an F8V star known to have an extrasolar system of at
least 3 planets in orbit around it. Here we report the discovery of a low-mass
stellar companion to this system. The companion shares common proper motion,
lies at a projected separation of ~750 AU, and has a spectral type of M4.5V.
The effect of this star on the radial velocity of the brighter primary is
negligible, but this system provides an interesting testbed for stellar
planetary formation theory and understanding dynamical stability since it is
the first multiple planetary system known in a multiple stellar system.


title: X-ray and Optical Variations in the Classical Be Star gamma Cas

abstract:
  gamma Cas (B0.5e) is known to be a unique X-ray source because ot its
moderate L_x, hard X-ray spectrum, and light curve punctuated by ubiquitous
flares and slow undulations. Its X-ray peculiarities have led to a controversy
concerning their origin: either from wind infall onto a putative degenerate
companion, as for typical Be/X-ray binaries, or from the Be star per se. Recent
progress has been made to address this: (1) the discovery that gamma Cas is an
eccentric binary system (P = 203.59 d) with unknown secondary type, (2) the
accumulation of RXTE data at 9 epochs in 1996-2000, and (3) the collation of
robotic telescope B, V-band photometric observations over 4 seasons. The latter
show a 3%, cyclical flux variation with cycle lengths 55-93 days. We find that
X-ray fluxes at all 9 epochs show random variations with orbital phase. This
contradicts the binary accretion model, which predicts a substantial
modulation. However,these fluxes correlate well with the cyclical optical
variations. Also, the 6 flux measurements in 2000 closely track the
interpolated optical variations between the 2000 and 2001 observing seasons.
Since the optical variations represent a far greater energy than that emitted
as X-rays, the optical variability cannot arise from X-ray reprocessing.
However, the strong correlation between the two suggests that they are driven
by a common mechanism. We propose that this mechanism is a cyclical magnetic
dynamo excited by a Balbus-Hawley instability located within the inner part of
the circumstellar disk. In our model, variations in the field strength directly
produce the changes in the magnetically related X-ray activity. Turbulence
associated with the dynamo results in changes to the density distribution
within the disk and creates the observed optical variations.


title: The Ultimate Fate of Life in an Accelerating Universe

abstract:
  The ultimate fate of life in a universe with accelerated expansion is
considered. Previous work showed that life cannot go on indefinitely in a
universe dominated by a cosmological constant. In this paper we consider
instead other models of acceleration (including quintessence and Cardassian
expansion). We find that it is possible in these cosmologies for life to
persist indefinitely. As an example we study potentials of the form $V \propto
\phi^n$ and find the requirement $n < -2$.


title:
General Relativistic Geodetic Spin Precession in Binary Pulsar B1913+16:
  Mapping the Emission Beam in Two Dimensions

abstract:
  We have carefully measured the pulse profile of the binary pulsar PSR
B1913+16 at 21 cm wavelength for twenty years, in order to search for
variations that result from general relativistic geodetic precession of the
spin axis. The profile width is found to decrease with time in its inner
regions, while staying essentially constant on its outer skirts. We fit these
data to a model of the beam shape and precession geometry. Four equivalent
solutions are found, but evolutionary considerations and polarization data
select a single preferred model. While the current data sample only a limited
range of latitudes owing to the long precessional cycle, the preferred model
shows a beam elongated in the latitude direction and hourglass--shaped.


title:
The Structure and Dynamics of Luminous and Dark Matter in the Early-Type
  Lens Galaxy of 0047-281 at z=0.485

abstract:
  We have measured the kinematic profile of the early-type (E/S0) lens galaxy
in the system 0047-281 (z=0.485) with the {\sl Echelle Spectrograph and Imager}
(ESI) on the W.M. Keck--II Telescope, as part of the {\sl Lenses Structure and
Dynamics (LSD) Survey}. The central velocity dispersion is \sigma=229\pm 15
\kms, and the dispersion profile is nearly flat to beyond one effective radius
(R_e). Surface photometry of the lens galaxy is measured from {\sl Hubble Space
Telescope} images. From the offset from the local Fundamental Plane (FP), we
measure an evolution of the effective mass-to-light ratio of \Delta \log
M/L_B=-0.37\pm0.06 between z=0 and z=0.485, consistent with the observed
evolution of field E/S0 galaxies. (We assume h_{65}=1,\Omega_{\rm m}=0.3 and
\Omega_\Lambda=0.7 throughout.) Gravitational lens models provide a mass of
M_{\rmE}=(4.06\pm0.20)\times 10^{11} h_{65}^{-1}M_\odot inside the Einstein
radius of R_{\rm E}=(8.70\pm0.07) h_{65}^{-1} kpc. This allows us to break the
degeneracy between velocity anisotropy and density profile, typical of
dynamical models for E/S0 galaxies. We find that constant M/L model, even with
strongly tangential anisotropy of the stellar velocity ellipsoid, are excluded
at >99.9%CL. The total mass distribution inside R_{\rm E} can be described by a
single power-law density profile, \rho_t\propto r^{-\gamma'}, with an effective
slope \gamma'=1.90^{+0.05}_{-0.23} (68%CL; \pm0.1 systematic error).
Two-component models yield an upper limit (68% CL) of \gamma\le 1.55(1.12) on
the power-law slope of the dark-matter density profile and a projected
dark-matter mass fraction of 0.41(0.54)^{+0.15}_{-0.05}(^{+0.09}_{-0.06}) (68%
CL) inside R_{\rm E}, for Osipkov--Merritt models with anisotropy radius
r_i=\infty(R_e).


title: Compressible Sub-Alfvenic MHD turbulence in Low-beta Plasmas

abstract:
  We present a model for compressible sub-Alfvenic isothermal
magnetohydrodynamic (MHD) turbulence in low-beta plasmas and numerically test
it. We separate MHD fluctuations into 3 distinct families - Alfven, slow, and
fast modes. We find that, production of slow and fast modes by Alfvenic
turbulence is suppressed. As a result, Alfven modes in compressible regime
exhibit scalings and anisotropy similar to those in incompressible regime. Slow
modes passively mimic Alfven modes. However, fast modes show isotropy and a
scaling similar to acoustic turbulence.

categories: astro-ph physics.flu-dyn physics.geo-ph physics.plasm-ph physics.space-ph


title: Dust Motions Driven by MHD Turbulence

abstract:
  We discuss the relative grain motions due to MHD turbulence in interstellar
medium. It has been known for decades that turbulent drag is an efficient way
to induce grain relative motions. However, earlier treatments disregarded
magnetic field and used Kolmogorov turbulence. Unlike hydro turbulence, MHD
turbulence is anisotropic on small scales. Moreover, compressible modes are
important for MHD and magnetic perturbations can directly interact with grains.
We provide calculations of grain relative motion for realistic interstellar
turbulence driving that is consistent with the velocity dispersions observed in
diffuse gas and for realistic grain charging. We account for the turbulence
cutoff arising from abmipolar drag. Our results on grain shattering are
consistent with the customary accepted cutoff size. We obtain grain velocities
for turbulence with parameters consistent with those in HI and dark clouds.
These velocities are smaller than those in earlier papers, where MHD effects
were disregarded. Finally, we consider grain velocities arising from
photoelectric emission, radiation pressure and the thrust due to molecular
hydrogen formation. These are lower than relative velocities induced by
turbulence. We conclude that turbulence should prevent these mechanisms from
segregating grains by size.


title: MHD Turbulence as a Foreground for CMB Studies

abstract:
  Measurements of intensity and polarization of diffuse Galactic synchrotron
emission as well as starlight polarization reveal power law spectra of
fluctuations. We show that these fluctuations can arise from
magnetohydrodynamic (MHD) turbulence in the Galactic disk and halo. To do so we
take into account the converging geometry of lines of sight for the
observations when the observer is within the turbulent volume. Assuming that
the intensity of turbulence changes along the line of sight, we get a
reasonable fit to the observed synchrotron data. As for the spectra of
polarized starlight we get a good fit to the observations taking into account
the fact that the observational sample is biased toward nearby stars.


title: Scattering of Cosmic Rays by Magnetohydrodynamic Interstellar Turbulence

abstract:
  Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for substantial revisions in our understanding of cosmic ray transport. In this
paper we use gyroresonance recently obtained scaling laws for MHD modes to
calculate the scattering frequency for cosmic rays in the ISM. We consider
gyroresonance with MHD modes (Alfvenic, slow and fast) and transit-time damping
(TTD) by fast modes. We conclude that the gyroresonance with fast modes is the
dominant contribution to cosmic ray scattering for the typical interstellar
conditions. In contrast to earlier studies, we find that Alfvenic and slow
modes are inefficient because they are far from isotropy usually assumed.


title: MHD Turbulence: Scaling Laws and Astrophysical Implications

abstract:
  Turbulence is the most common state of astrophysical flows. In typical
astrophysical fluids, turbulence is accompanied by strong magnetic fields,
which has a large impact on the dynamics of the turbulent cascade. Recently,
there has been a significant breakthrough on the theory of magnetohydrodynamic
(MHD) turbulence. For the first time we have a scaling model that is supported
by both observations and numerical simulations. We review recent progress in
studies of both incompressible and compressible turbulence. We compare
Iroshnikov-Kraichnan and Goldreich-Sridhar models, and discuss scalings of
Alfv\'en, slow, and fast waves. We also discuss the completely new regime of
MHD turbulence that happens below the scale at which hydrodynamic turbulent
motions are damped by viscosity. In the case of the partially ionized diffuse
interstellar gas the viscosity is due to neutrals and truncates the turbulent
cascade at $\sim$parsec scales. We show that below this scale magnetic
fluctuations with a shallow spectrum persist and discuss the possibility of a
resumption of the MHD cascade after ions and neutrals decouple. We discuss the
implications of this new insight into MHD turbulence for cosmic ray transport,
grain dynamics, etc., and how to test theoretical predictions against
observations.

categories: astro-ph physics.ao-ph physics.flu-dyn physics.geo-ph physics.plasm-ph physics.space-ph


title: Plasma Wakefield Acceleration for Ultrahigh Energy Cosmic Rays

abstract:
  A cosmic acceleration mechanism is introduced which is based on the
wakefields excited by the Alfven shocks in a relativistically flowing plasma,
where the energy gain per distance of a test particle is Lorentz invariant. We
show that there exists a threshold condition for transparency below which the
accelerating particle is collision-free and suffers little energy loss in the
plasma medium. The stochastic encounters of the random
accelerating-decelerating phases results in a power-law energy spectrum: f(e)
1/e^2. The environment suitable for such plasma wakefield acceleration can be
cosmically abundant. As an example, we discuss the possible production of
super-GZK ultra high energy cosmic rays (UHECR) through this mechanism in the
atmosphere of gamma ray bursts. We show that the acceleration gradient can be
as high as G ~ 10^16 eV/cm. The estimated event rate in our model agrees with
that from UHECR observations.


title: The mysterious eruption of V838 Mon

abstract:
  V838 Mon is marking one of the most mysterious stellar outbursts on record.
The spectral energy distribution of the progenitor resembles an under-luminous
F main sequence star (at V=15.6 mag), that erupted into a cool supergiant
following a complex and multi-maxima lightcurve (peaking at V=6.7 mag). The
outburst spectrum show BaII, LiI and lines of several s-elements, with wide
P-Cyg profiles and a moderate and retracing emission in the Balmer lines. A
light-echo discovered expanding around the object helped to constrain the
distance (d=790+/-30 pc), providing M_V=+4.45 in quiescence and M_V=-4.35 at
optical maximum (somewhat dependent on the still uncertain E(B-V)=0.5
reddening). The general outburst trend is toward lower temperatures and larger
luminosities, and continuing so at the time of writing. The object properties
conflict with a classification within already existing categories: the
progenitor was not on a post-AGB track and thus the similarities with the
born-again AGB stars FG Sge, V605 Aql and Sakurai's object are limited to the
cool giant spectrum at maximum; the cool spectrum, the moderate wind velocity
(500 km/sec and progressively reducing) and the monotonic decreasing of the low
ionization condition argues against a classical nova scenario. The closest
similarity is with a star that erupted into an M-type supergiant discovered in
M31 by Rich et al. (1989), that became however much brighter by peaking at
M_V=-9.95, and with V4332 Sgr that too erupted into an M-type giant (Martini et
al. 1999) and that attained a lower luminosity, closer to that of V838 Mon.
M31-RedVar, V4332 Sgr and V838 Mon could be manifestations of the same and new
class of astronomical objects.


title:
The Optical Gravitational Lensing Experiment. Catalog of high proper
  motion stars towards the Magellanic Clouds

abstract:
  We present a Catalog of high proper motion (HPM) stars detected in the
foreground of central parts of the Magellanic Clouds. The Catalog contains 2161
objects in the 4.5 square degree area towards the LMC, and 892 HPM stars in the
2.4 square degree area towards the SMC. The Catalog is based on observations
collected during four years of the OGLE-II microlensing survey. The Difference
Image Analysis (DIA) of the images provided candidate HPM stars with proper
motion as small as 4 mas/yr. These appeared as pseudo-variables, and were all
measured astrometrically on all CCD images, providing typically about 400 data
points per star. The reference frame was defined by the majority of background
stars, most of them members of the Magellanic Clouds. The reflex motion due to
solar velocity with respect to the local standards of rest is clearly seen. The
largest proper motion in our sample is 363 mas/yr. Parallaxes were measured
with errors smaller than 20% for several stars.


title:
An efficient shock-capturing central-type scheme for multidimensional
  relativistic flows. I. Hydrodynamics

abstract:
  Multidimensional shock-capturing numerical schemes for special relativistic
hydrodynamics (RHD) are computationally more expensive than their correspondent
Euler versions, due to the nonlinear relations between conservative and
primitive variables and to the consequent complexity of the Jacobian matrices
(needed for the spectral decomposition in most of the approximate Riemann
solvers of common use). Here an efficient and easy-to-implement
three-dimensional (3-D) shock-capturing scheme for ideal RHD is presented.
Based on the algorithms developed by P. Londrillo and L. Del Zanna ({\em
Astrophys. J.} 530, 508-524, 2000) for the non-relativistic magnetohydrodynamic
(MHD) case, and having in mind its relativistic MHD extension (to appear in a
forthcoming paper), the scheme uses high order (third) Convex Essentially
Non-Oscillatory (CENO) finite difference interpolation routines and
central-type averaged Riemann solvers, which do not make use of time-consuming
characteristic decomposition. The scheme is very efficient and robust, and it
gives results comparable to those obtained with more sophisticated algorithms,
even in ultrarelativistic multidimensional test problems.


title:
A Correlation between Light Concentration and Cluster Local Density for
  Elliptical Galaxies

abstract:
  Using photometric and redshift data for the Virgo and Coma clusters, we
present evidence for a correlation between the light concentration of
elliptical galaxies (including dwarf ellipticals) and the local 3-D (i.e.
non-projected) density of the clusters: more concentrated ellipticals are
located in denser regions. The null hypothesis (i.e. the absence of any
relation) is rejected at a significance level better than 99.9%. In order to
explain the observed relation, a power law relating the galaxy light
concentration and the cluster 3-D density is proposed. We study how the
projection effects affect the form and dispersion of the data-points in the
light concentration-projected density diagram. The agreement between our model
and the observed data suggests that there is a paucity of dwarf elliptical
galaxies in the cluster central regions.


title:
Chemistry as a probe of the structures and evolution of massive star
  forming regions

abstract:
  We present detailed thermal and gas-phase chemical models for the envelope of
the massive star-forming region AFGL 2591. Time- and space-dependent chemistry
are used to study the physical structure proposed by van der Tak et al. (1999;
2000), and the chemical evolution of this region. The model is compared with
observations for 29 species covering a wide range of conditions within the
source. Taking appropriate care when comparing models with both emission and
absorption measurements, we find that the majority of the chemical structure
can be well-explained. In particular, we find that the nitrogen and hydrocarbon
chemistry can be significantly affected by temperature, with the possibility of
high-temperature pathways to HCN. While we cannot determine the sulphur
reservoir, the observations can be explained by models with the majority of the
sulphur in CS in the cold gas, SO$_{2}$ in the warm gas, and atomic sulphur in
the warmest gas. The observed abundances of ions such as HCO$^+$ and N$_2$H$^+$
and the cold gas-phase production of HCN constrain the cosmic-ray ionization
rate to $\sim 5.6 \times 10^{-17}$ s$^{-1}$, to within a factor of three.
Finally, we find that the model and observations can simultaneously agree at a
reasonable level and often to within a factor of three for $7 \times 10^{3}
\leq t(\mathrm{yrs}) \leq 5 \times 10^{4}$, with a strong preference for $t
\sim 3 \times 10^{4}$ yrs since the collapse and formation of the central
luminosity source.


title:
Visible-IR Colors and Lightcurve Analysis of Two Bright TNOs: 1999 TC36
  and 1998 SN165

abstract:
  We report on observations of two bright Trans-Neptunian Objects (TNOs) - 1999
TC36 and 1998 SN165}- during two observational campaigns, as part of the Meudon
Multicolor Survey of Outer Solar System Objects. V-J color was measured for
1999 TC36 (V-J=2.34+/-0.18), which combined with previous measured colors in
the visible, indicate a red reflectivity spectrum at all wavelengths.
Photometric V-band lightcurves were taken for both objects over a time span of
around 8 hours. We have determined a possible rotational period of P=10.1+/-0.8
h for 1998 SN165, making it the seventh TNO with an estimated period. From its
lightcurve variation of Dm=0.151(+0.022/-0.030), we have inferred an asymmetry
ratio of a/b >=1.148(+0.024/-0.031). For 1999 TC36, we did not detect any
rotational period or periodic signal variation within the uncertainties, but
the analysis of its lightcurve hints to a slight systematic magnitude decrease.


title:
Zeeman tomography of magnetic white dwarfs, I. Reconstruction of the
  field geometry from synthetic spectra

abstract:
  We have computed optical Zeeman spectra of magnetic white dwarfs for field
strengths between 10 and 200MG and effective temperatures between 8000 and
40000K. They form a database containing 20628 sets of flux and circular
polarization spectra. A least-squares optimization code based on an
evolutionary strategy can recover relatively complex magnetic field topologies
from phase-resolved synthetic Zeeman spectra of rotating magnetic white dwarfs.
We consider dipole and quadrupole components which are non-aligned and shifted
off-centre. The model geometries include stars with a single high-field spot
and with two spots separated by approx. 90 degrees. The accuracy of the
recovered field structure increases with the signal-to-noise ratio of the input
spectra and is significantly improved if circular polarization spectra are
included in addition to flux spectra. We discuss the strategies proposed so far
to unravel the field geometries of magnetic white dwarfs.


title:
First measurement of cluster temperature using the thermal
  Sunyaev-Zeldovich effect

abstract:
  We discuss a new method of finding the cluster temperatures which is
independent of distance and therefore very useful for distant clusters. The hot
gas of electrons in clusters of galaxies scatters and distorts the cosmic
microwave background radiation in a well determined way. This
Sunyaev-Zel'dovich (SZ) effect is a useful tool for extracting information
about clusters such as their peculiar radial velocity and optical depth. Here
we show how the temperature of the cluster can be inferred from the SZ effect,
in principle without use of X-ray data. We use recent millimetre observation of
Abell 2163 to determine for the first time a cluster temperature using SZ
observations only. The result T_e = 26^+34_-19 keV at 68% confidence level (at
95% c.l. we find T>1.5 keV) is in reasonable agreement with the X-ray results,
T_e =12.4^+2.8_-1.9 keV.


title:
A differential method of search for the CMBR spectral-spatial
  fluctuations

abstract:
  The CMBR spectral-spatial fluctuations (SSF) formed in early Universe during
the Dark Ages are considered. Main attention is focused on the narrow-band
spectral properties of the SSF. Based on these properties we propose to use a
differential method in order to search for these fluctuations. Description of
the method is given.


title:
Multiple Weak Deflections and the Detection of Flattened Halos with
  Galaxy-Galaxy Lensing

abstract:
  We investigate the occurrence of multiple weak deflections in deep data sets
which are used to detect galaxy-galaxy lensing. Using the galaxies in the HDF
(North) for which both redshifts and rest-frame blue luminosities are known, we
show that the probability for a given source galaxy to be lensed by two or more
foreground galaxies exceeds 50% for z_s > 1, and for which the separate,
individual deflections yield gamma > 0.005. Neglecting multiple deflections
when obtaining best-fitting halo parameters for the lens galaxies can lead to
an overestimate by a factor of order 2 for the halo mass interior to a radius
of 100 kpc/h. We also show that multiple weak deflections create systematic
effects which may hinder observational efforts to use weak lensing to constrain
the projected shapes of the halos of field galaxies. For a data set in which
the galaxies have magnitudes in the rage 19 < I < 23, multiple deflections
result in strong correlations between the post-lensing image shapes of most
foreground-background pairs of galaxies. Imposing a simple redshift cut during
the data anaysis is sufficient to reduce the correlation between the final
images of lenses and sources to the point that the expected anisotropy in the
weak lensing signal can be detected via a straightforward average. We conclude
that previous theoretical calculations of weak lensing due to flattened halos
have considerably underestimated the sizes of the observational data sets which
would be required to detect this effect. [Abridged]


title:
Astrophysics of isolated neutron stars: radioquiet neutron stars and
  magnetars

abstract:
  In this paper we review present state of theoretical and observational
exploration of isolated neutron stars. We mainly discuss objects which do not
show usual radiopulsar activity. We include into our review the following types
of objects: dim X-ray sources in the Galactic disk and in globular clusters;
compact X-ray sources in supernova remnants; anomalous X-ray pulsars; soft
gamma repeaters; Geminga. Also we briefly discuss related types of objects:
isolated black holes, quark stars and supernovae.
  We review basic physical processes connected with evolution of isolated
neutron stars: cooling; magnetic field decay; period evolution; magnetospheric
processes, accretion. We discuss populational synthesis of isolated neutron
stars of different types.


title:
High matter density peaks from UVES observations of QSO pairs:
  correlation properties and chemical abundances

abstract:
  We study the transverse clustering properties of high matter density peaks as
traced by high column density absorption systems (either Lyman limit systems
characterized by N(HI)> 2 x 10^{17} cm^{-2} or CIV systems with W_{r}> 0.5 A)
at redshifts between 2 and 3 with UVES spectra of two QSO pairs (UM680/UM681 at
56 arcsec angular separation and Q2344+1228/Q2343+1232 at 5 arcmin angular
separation) and a QSO triplet (Q2139-4433/Q2139-4434/Q2138-4427 at 1, 7 and 8
arcmin angular separation). We find 3 damped Ly-alpha systems (N(HI)> 2 x
10^{20} cm^{-2}): 2 coinciding with strong metal systems in the nearby line of
sight and 1 matching the emission redshift of the paired QSO; plus 7 Lyman
limit systems: 4 forming two matching couples and 3 without a corresponding
metal system within ~3000 km/s in the coupled line of sight. In summary, we
detect five out of ten matching systems within 1000 km/s, indicating a highly
significant overdensity of strong absorption systems over separation lengths
from ~1 to 8 h^{-1} Mpc. The observed coincidences could arise in gas due to
starburst-driven superwinds associated with a quasar or a galaxy, or gas
belonging to large scale structures like filaments or sheets. We also determine
chemical abundance ratios for three damped Ly-alpha systems. In particular, for
the damped system at z ~ 2.53788 in the spectrum of Q2344+1228, new estimates
of the ratios O/Fe, C/Fe are obtained: [C/Fe]<0.06, [O/Fe]<0.2. They indicate
that O and C are not over-solar in this system.


title: Rotation and activity in the solar-metallicity open cluster NGC2516

abstract:
  We report new measures of radial velocities and rotation rates (v sin i) for
51 F and early-G stars in the open cluster NGC2516, and combine these with
previously published data. From high signal-to-noise spectra of two stars, we
show that NGC2516 has a relative iron abundance with respect to the Pleiades of
delta([Fe/H])= +0.04 +/- 0.07 at the canonical reddening of E(B - V) = 0.12, in
contrast to previous photometric studies that placed the cluster 0.2 to 0.4 dex
below solar. We construct a color-magnitude diagram based on radial velocity
members, and explore the sensitivity of photometric determinations of the
metallicity and distance to assumed values of the reddening. For a metal
abundance near solar, the Hipparcos distance to NGC2516 is probably
underestimated. Finally, we show that the distribution of rotation rates and
X-ray emission does not differ greatly from that of the Pleiades, when
allowance is made for the somewhat older age of NGC2516.


title: Looking for Pure Rotational H_2 Emission from Protoplanetary Disks

abstract:
  We report on a limited search for pure-rotational molecular hydrogen emission
associated with young, pre-main-sequence stars. We looked for H_2 v=0 J = 3->1
and J = 4->2 emission in the mid-infrared using the Texas Echelon-Cross-Echelle
Spectrograph (TEXES) at NASA's 3m Infrared Telescope Facility. The high
spectral and spatial resolution of our observations lead to more stringent
limits on narrow line emission close to the source than previously achieved.
One star, AB Aur, shows a possible (2sigma) H_2 detection, but further
observations are required to make a confident statement. Our non-detections
suggest that a significant fraction, perhaps all, of previously reported H_2
emission towards these objects could be extended on scales of 5" or more.


title: Hybrid simulations of extensive air showers

abstract:
  We present a fast one dimensional hybrid method to efficiently simulate
extensive air showers up to the highest observed energies. Based on
precalculated pion showers and a bootstrap technique, our method predicts the
average shower profile, the number of muons at detector level above several
energy thresholds as well as the fluctuations of the electromagnetic and
hadronic components of the shower. We study the main characteristics of
proton-induced air showers up to ultra-high energy, comparing the predictions
of three different hadronic interaction models: SIBYLL 1.7, SIBYLL 2.1 and
QGSjet98. The influence of the hadronic interaction models on the shower
evolution, in particular the elongation rate, is discussed and the
applicability of analytical approximations is investigated.


title:
An Exploratory Chandra survey of Large Bright Quasar Survey broad
  absorption line QSOs

abstract:
  We are in the process of obtaining a complete sample of exploratory X-ray
observations of broad absorption line (BAL) QSOs from the Large Bright Quasar
Survey (LBQS). This survey is composed of short (5-7 ks) Chandra ACIS-S3
observations designed to significantly constrain X-ray fluxes and hardness
ratios. Our sample avoids the selection biases of some previous surveys while
providing X-ray data of similar quality. Of 17 BAL QSOs observed to date, 13
are detected. In general, our results are consistent with absorption as the
primary cause of X-ray weakness in BAL QSOs. As found by Green et al. (2001),
those BAL QSOs with low-ionization absorption lines are found to be notably
X-ray weaker than BAL QSOs with only high ionization lines.


title: Search for neutrinos from Gamma-Ray Bursts using Super-Kamiokande

abstract:
  Using the Super-Kamiokande neutrino observatory, a search was conducted for
neutrinos produced in coincidence with gamma-ray bursts observed by the BATSE
detector. Super-Kamiokande data in the neutrino energy range of 7 MeV ~ 100 TeV
were analyzed. For gamma-ray bursts that occurred between 1996 April and 2000
May, no statistically significant signal in excess of the background levels was
detected. Implied upper limits on associated GRB neutrino production are
presented.


title: L-dwarf variability: I-band observations

abstract:
  We report on the results of an I-band photometric variability survey of
eighteen L dwarfs. We find that seven exhibit statistically significant
variations above the 95.4% confidence level with root-mean-square scatter
(including photometric errors) between 0.010 and 0.083 mag. Another five
targets have variability probabilities ~80%, suggesting that these are likely
variable objects. Three of the variable objects display significant peaks in a
CLEAN periodogram that are several times higher than the noise. The period for
2MASS 0345+25 is clearly not intrinsic to the object and can be dismissed. The
periods found for 2MASS 0746+20AB and 2MASS 1300+19 are unique but longer than
those periods likely from rotation velocity measurements and they do not
represent periodic behavior in the light curve that persists through the entire
data set. These observations suggest that we are not observing the rotation
modulation of a long-lived albedo feature. Instead, rapid evolution of
atmospheric features is likely causing the non-periodic variability. The
remaining variable objects show no prominent features in their light curves,
suggesting even more rapid evolution of atmospheric features. We argue against
the existence of magnetic spots in these atmospheres and favor the idea that
non-uniform condensate coverage is responsible for these variations. The
magnetic Reynolds number in the atmosphere of L dwarfs is too small to support
the formation of magnetic spots. In contrast, silicate and iron clouds are
expected to form in the photospheres of L dwarfs. Inhomogeneities in such cloud
decks and the evolution of the inhomogeneities can plausibly produce the
observed photometric variations.


title:
A Lensing Reconstruction of Primordial Cosmic Microwave Background
  Polarization

abstract:
  We discuss a possibility to directly reconstruct the CMB polarization field
at the last scattering surface by accounting for modifications imposed by the
gravitational lensing effect. The suggested method requires a tracer field of
the large scale structure lensing potentials that deflected propagating CMB
photons from the last scattering surface. This required information can come
from a variety of observations on the large scale structure matter
distribution, including convergence reconstructed from lensing shear studies
involving galaxy shapes. In the case of so-called curl, or B,-modes of CMB
polarization, the reconstruction allows one to identify the distinct signature
of inflationary gravitational waves.


title: Formation and Migration of Trans-Neptunian Objects

abstract:
  We suppose that some large trans-Neptunian objects could be formed directly
by the compression of rarefied dust condensations of the protoplanetary disk,
but not by the accretion of smaller planetesimals. About 0.0015 of former
Jupiter-crossing objects can get orbits with aphelia inside Jupiter's orbit
(mainly less than 4.7 AU) during more than 1 Myr. A considerable portion of
near-Earth objects could have come from the trans-Neptunian belt.


title: Radiative feedback from an early X-ray background

abstract:
  The first generation of stars (commonly known as population III) are expected
to form in low-mass protogalaxies in which molecular hydrogen is the dominant
coolant. Radiation from these stars will rapidly build up an extragalactic
ultraviolet background capable of photodissociating H2, and it is widely
believed that this background will suppress further star formation in low-mass
systems.
  However, star formation will also produce an extragalactic X-ray background.
This X-ray background, by increasing the fractional ionization of protogalactic
gas, promotes H2 formation and reduces the effectiveness of ultraviolet
feedback.
  In this paper, we examine which of these backgrounds has the dominant effect.
Using a simple model for the growth of the UV and X-ray backgrounds, together
with a detailed one-dimensional model of protogalactic chemical evolution, we
examine the effects of the X-ray backgrounds produced by a number of likely
source models. We show that in several cases, the resulting X-ray background is
strong enough to offset UV photodissociation in large H2-cooled protogalaxies.
On the other hand, small protogalaxies (those with virial temperatures T_vir <
2000K) remain dominated by the UV background in all of the models we examine.
  We also briefly investigate the effects of the X-ray background upon the
thermal and chemical evolution of the diffuse IGM.


title:
Migration of asteroids from the 3/1 and 5/2 resonances with Jupiter to
  the Earth

abstract:
  The orbital evolution of asteroids from the 3:1 and 5:2 resonances with
Jupiter under the gravitational influence of planets was investigated both by
the Bulirsh-Stoer method and by a symplectic method. The probabilities of
collisions of asteroids with the terrestrial planets were calculated for
orbital elements obtained with a step of 500 yr. The ratio of asteroids from
the 3:1 resonance that were ejected into hyperbolic orbits to those collided
the Sun was by an order of magnitude larger for direct integrations than for a
symplectic method. The probability of a collision of an asteroid with the Earth
for the 3:1 resonance was by a factor of 4 larger than that for the 5:2
resonance. The ratio of the probability of a collision of a body with a planet
to the mass of the planet for Mars was by a factor of 2 larger than that for
Earth and Venus.


title:
Discovery of a Possible Anomalous X-ray Pulsar in the Small Magellanic
  Cloud

abstract:
  We report the serendipitous detection of a previously unreported pulsar from
the direction of the Small Magellanic Cloud using data from the CHANDRA X-Ray
Observatory. Because of the luminosity of about 1.5x10^35 ergs/s, its near lack
of variability for more than 20 years, and its soft spectrum we propose that it
is an anomalous X-ray pulsar (AXP). Data from the ROSAT PSPC in conjunction
with the CHANDRA data give a period, P, of 5.44 s and a spin down time, Pdot/P,
of 11 ky. If this is a correct identification it will be the first
extragalactic AXP and the fastest yet discovered.


title: Optical microvariability of EGRET blazars

abstract:
  We present results of a photometric CCD study of the incidence of
microvariability in the optical emission of a sample of 20 blazars detected at
gamma-ray energies by the EGRET instrument of the Compton Gamma-Ray
Observatory. We have observed strong outbursts in some sources, but many others
displayed no significant variability on timescales of hours. The typical
minimum timescale results to be of ~ several hours, not tens of minutes as
claimed by some authors. The duty cycle for optical intranight microvariations
of gamma-ray blazars, as estimated from our observations, seems to be ~50%,
lower than what is usually assumed. For night-to-night variations, instead, the
duty cycle approaches to what is observed in radio-selected BL Lacs and
flat-spectrum radio quasars (i.e. ~70%).


title:
Small-scale microwave background anisotropies due to tangled primordial
  magnetic fields

abstract:
  An inhomogeneous cosmological magnetic field creates vortical perturbations
that survive Silk damping on much smaller scales than compressional modes. This
ensures that there is no sharp cut-off in anisotropy on arc-minute scales. As
we had pointed out earlier, tangled magnetic fields, if they exist, will then
be a potentially important contributor to small-angular scale CMBR
anisotropies. Several ongoing and new experiments, are expected to probe the
very small angular scales, corresponding to multipoles with l>1000. In view of
this observational focus, we revisit the predicted signals due to primordial
tangled magnetic fields, for different spectra and different cosmological
parameters. We also identify a new regime, where the photon mean-free path
exceeds the scale of the perturbation, which dominates the predicted signal at
very high l. A scale-invariant spectrum of tangled fields which redshifts to a
present value B_{0}=3\times 10^{-9} Gauss, produces temperature anisotropies at
the 10 micro Kelvin level between l ~ 1000-3000. Larger signals result if the
univese is lambda dominated, if the baryon density is larger, or if the
spectral index of magnetic tangles is steeper, n > -3. The signal will also
have non-Gaussian statistics. We predict the distinctive form of the increased
power expected in the microwave background at high l in the presence of
significant tangled magnetic fields. We may be on the verge of detecting or
ruling out the presence of tangled magnetic fields which are strong enough to
influence the formation of large-scale structure in the Universe.


title:
Breaking the "Redshift Deadlock" -- II: The redshift distribution for
  the submillimetre population of galaxies

abstract:
  In this paper we apply our Monte-Carlo photometric-redshift technique,
introduced in paper I (Hughes et al. 2002), to the multi-wavelength data
available for 77 galaxies selected at 850um and 1.25mm. We calculate a
probability distribution for the redshift of each galaxy, which includes a
detailed treatment of the observational errors and uncertainties in the
evolutionary model. The cumulative redshift distribution of the submillimetre
galaxy population that we present in this paper, based on 50 galaxies found in
wide-area SCUBA surveys, is asymmetric, and broader than those published
elsewhere, with a significant high-z tail for some of the evolutionary models
considered. Approximately 40 to 90 per cent of the sub-mm population is
expected to have redshifts in the interval 2 < z < 4. Whilst this result is
completely consistent with earlier estimates for the sub-mm galaxy population,
we also show that the colours of many (< 50 per cent) individual sub-mm
sources, detected only at 850um with non-detections at other wavelengths, are
consistent with those of starburst galaxies that lie at extreme redshifts, z >
4. Spectroscopic confirmation of the redshifts, through the detection of
rest-frame FIR--mm wavelength molecular transition-lines, will ultimately
calibrate the accuracy of this technique. We use the redshift probability
distribution of HDF850.1 to illustrate the ability of the method to guide the
choice of possible frequency tunings on the broad-band spectroscopic receivers
that equip the large aperture single-dish mm and cm-wavelength telescopes.


title: Magnetic Helicity Tensor for an Anisotropic Turbulence

abstract:
  The evolution of the magnetic helicity tensor for a nonzero mean magnetic
field and for large magnetic Reynolds numbers in an anisotropic turbulence is
studied. It is shown that the isotropic and anisotropic parts of the magnetic
helicity tensor have different characteristic times of evolution. The time of
variation of the isotropic part of the magnetic helicity tensor is much larger
than the correlation time of the turbulent velocity field. The anisotropic part
of the magnetic helicity tensor changes for the correlation time of the
turbulent velocity field. The mean turbulent flux of the magnetic helicity is
calculated as well. It is shown that even a small anisotropy of turbulence
strongly modifies the flux of the magnetic helicity. It is demonstrated that
the tensor of the magnetic part of the alpha-effect for weakly inhomogeneous
turbulence is determined only by the isotropic part of the magnetic helicity
tensor. Astrophysical applications of the obtained results are discussed.


title: Quantitative Stellar Spectral Classification. II. Early Type Stars

abstract:
  The method developed by Stock and Stock (1999) for stars of spectral types A
to K to derive absolute magnitudes and intrinsic colors from the equivalent
widths of absorption lines in stellar spectra is extended to B-type stars.
Spectra of this type of stars for which the Hipparcos Catalogue gives
parallaxes with an error of less than 20% were observed with the CIDA 1-meter
reflector equipped with a Richardson spectrograph with a Thompson 576x384 CCD
detector. The dispersion is 1.753 A/pixel using a 600 lines/mm grating in the
first order. In order to cover the spectral range 3850 A to 5750 A the grating
had to be used in two different positions, with an overlap in the region from
4800 A to 4900 A. A total of 116 stars was oberved, but not all with both
grating positions. A total of 12 measureable absorption lines was identified in
the spectra and their equivalent widths were measured. These were related to
the absolute magnitudes derived from the Hipparcos Catalogue and to the
intrinsic colors (deduced from the MK spectral types) using linear and second
order polynomials and two or three lines as independent variables. The best
solutions were obtained with polynomials of three lines, reproducing the
absolute magnitudes with an average residual of about 0.40 magnitudes and the
intrinsic colors with an average residual of 0.016 magnitudes.


title:
Determination of the Dark Matter Profile of Abell 2199 from Integrated
  Starlight

abstract:
  We have obtained deep, long-slit spectroscopy along the major axis of NGC
6166, the cD galaxy in the cluster Abell 2199, in order to measure the
kinematics of intracluster starlight at large radii. The velocity dispersion
rises beyond a few kpc, and steadily rises to 660 km/s at a radius of 60 kpc,
nearly reaching the velocity dispersion of the cluster (775+-50 km/s). These
data suggest that the stars in the halo of the cD trace the potential of the
cluster and that the kinematics of these intracluster stars can be used to
constrain the mass profile of the cluster. In addition, we find evidence for
systematic rotation in the intracluster stars beyond 20 kpc. The surface
brightness and velocity dispersion profiles can be fit using a single component
mass model only by making unphysical assumptions about the level of anisotropy
for both the stars in the cD galaxy and for the kinematics of the galaxies in
the cluster. Two-component mass models for the cD and its halo are explored
using the kinematics of known cluster members as an additional constraint
beyond the extent of the stellar kinematics. Assuming isotropy, the observed
kinematics can be reproduced only if the halo has a soft core, i.e., Alpha < 1
(Alpha=1 is excluded due to low implied stellar mass-to-light ratios). This
result is inconsistent with the predictions of current N-body simulations with
CDM. Assuming that our best-fit mass models for the Abell 2199 were placed at
cosmological redshifts between 0.2 <= z <= 0.5, the derived tangential critical
radii range from 5'' to 40'' consistent with the strong lensing observed in
intermediate redshift clusters. We also present Monte Carlo simulations that
test the reliability of velocity dispersions when the S/N is low.


title: Lambda-inflation versus observations

abstract:
  Lambda-inflation is tested against CMB and LSS observational data. The
constraints for inflationary parameters are considered.


title: Spectroscopic Survey of Field stars: A search for Metal-Poor stars

abstract:
  We have undertaken a spectroscopic survey of field stars to find metal-poor
objects among them. Observations are carried out using OMR spectrograph
attached to 2.3m telescope at VBO Kavalur, India.
  The sample of candidate stars are chosen from prismatic survey of Beers and
his collaborators covering a large part of the Galaxy. At the first phase of
this project, the analysis is completed for a set of 19 relatively hot stars
(Teff in 6000 to 8000K range). The metallicities of the program stars are
derived by synthesizing the spectrum in the wavelength range 4900 to 5400A for
different metallicities and matching them with the observed spectra. More than
half of the candidate stars were found to show [Fe/H] in -0.7 to -1.2 range.
Two most metal-poor stars have [Fe/H] values of -1.3 and -1.8. It appears that
metal-poor candidates suggested by Beers et al. from their prismatic survey has
a very significant fraction of metal-poor stars. The significantly metal-poor
stars found so far would be studied in detail using high resolution spectra to
understand nucleosynthesis processes that might have occurred in early Galaxy.


title: What Do Gravitational Lens Time Delays Measure?

abstract:
  Gravitational lens time delays depend on the Hubble constant, the observed
image positions, and the surface mass density of the lens in the annulus
between the images. Simple time delay lenses like PG1115+080, SBS1520+530,
B1600+434, PKS1830-211 and HE2149-2745 have H0 = A(1-<k>)+B<k>(e-1) where the
two coefficients A ~ 90km/s Mpc and B ~ 10km/s Mpc depend on the measured
delays and the observed image positions, <k> is the mean surface density in the
annulus between the images, and there is a small correction from the
logarithmic slope e ~ 2 of the surface density profile, k ~ R^(1-e), in the
annulus. These 5 systems are very homogeneous, since for fixed H0=100h km/s Mpc
they must have the same surface density, <k>=1.11-1.22 h +/- 0.04, with an
upper bound of 0.07 on any dispersion in <k> beyond those due to the
measurement errors. If the lenses have their expected dark halos, <k> ~ 0.5 and
H0=51+/-5 km/s Mpc, while if they have constant mass-to-light ratios, <k> ~
0.1-0.2 and H0=73+/-8 km/s Mpc. More complicated lenses with multiple
components or strong perturbations from nearby clusters, like RXJ0911+0551 and
Q0957+561, are easily recognized because they have significantly different
coefficients.


title: Metal enrichment of the high-z intergalactic medium

abstract:
  Recent observations show the presence of metals in low-density Ly$\alpha$
forest absorbers at high redshift ($z\sim 3$). It remains still far from being
clearly understood what mechanisms spread metals over Mpc scales from the
parent galaxies, whether metals are homogeneously distributed in the
intergalactic medium (IGM), how metallicity of the IGM does evolve. These
questions are briefly addressed in this review.


title: Delayed Nickel Decay in Gamma Ray Bursts

abstract:
  Recently observed emission lines in the X-ray afterglow of gamma ray bursts
suggest that iron group elements are either produced in the gamma ray burst, or
are present nearby. If this material is the product of a thermonuclear burn,
then such material would be expected to be rich in Nickel-56. If the nickel
remains partially ionized, this prevents the electron capture reaction normally
associated with the decay of Nickel-56, dramatically increasing the decay
timescale. Here we examine the consequences of rapid ejection of a fraction of
a solar mass of iron group material from the center of a collapsar/hypernova.
The exact rate of decay then depends on the details of the ionization and
therefore the ejection process. Future observations of iron, nickel and cobalt
lines can be used to diagnose the origin of these elements and to better
understand the astrophysical site of gamma ray bursts. In this model, the X-ray
lines of these iron-group elements could be detected in suspected hypernovae
that did not produce an observable gamma ray burst due to beaming.


title:
Structure and Subhalo Population of Halos in a Self-Interacting Dark
  Matter Cosmology

abstract:
  We study the structure of Milky Way (MW)- and cluster-sized halos in a Lambda
Cold Dark Matter (CDM) cosmology with self-interacting (SI) dark particles. The
cross section per unit of particle mass has the form sigma =
sig_0(1/v_100)^alpha, where sig_0 is a constant in units of cm^2/gr and v_100
is the relative velocity in units of 100 km/s. Different values for sigma with
alpha= 0 or 1 were used. For small values of sigma = const. (sig_0<0.5), the
core density of the halos at z=0 is typically higher at a given mass for lower
values of sig_0 or, at a given sig_0, for lower masses. For values of sig_0 as
high as 3.0, the halos may undergo the gravothermal catastrophe before z=0.
When alpha = 1, the core density of cluster- and MW-sized halos is similar.
Using sigma = 0.5-1.0x(1/v_100), our predictions agree with the central
densities and the core scaling laws of halos both inferred from the
observations of dwarf and LSB galaxies and clusters of galaxies. The cumulative
Vmax-functions of subhalos in MW-sized halos with (sig_0,alpha) = (0.1,0.0),
(0.5,0.0) and (0.5,1.0) agree roughly with observations (luminous satellites)
for Vmax > 30 km/s, while at Vmax = 20 km/s the functions are a factor 5-8
higher, similar to the CDM predictions. The halos with SI have slightly more
specific angular momentum at a given mass shell and are rounder than their CDM
counterparts. We conclude that the introduction of SI particles with sigma
\propto 1/v_100 may remedy the cuspy core problem of the CDM cosmogony, while
the subhalo population number remains similar to that of the CDM halos.


title: Proposed Next Generation GRB Mission: EXIST

abstract:
  A next generation Gamma Ray Burst (GRB) mission to follow the upcoming Swift
mission is described. The proposed Energetic X-ray Imaging Survey Telescope,
EXIST, would yield the limiting (practical) GRB trigger sensitivity, broad-band
spectral and temporal response, and spatial resolution over a wide field. It
would provide high resolution spectra and locations for GRBs detected at GeV
energies with GLAST. Together with the next generation missions
Constellation-X, NGST and LISA and optical-survey (LSST) telescopes, EXIST
would enable GRBs to be used as probes of the early universe and the first
generation of stars. EXIST alone would give ~10-50" positions (long or short
GRBs), approximate redshifts from lags, and constrain physics of jets, orphan
afterglows, neutrinos and SGRs.


title:
Images of very high energy cosmic ray sources in the Galaxy: I. A source
  towards the Galactic Centre

abstract:
  Recent analyses of the anisotropy of cosmic rays at $10^{18}$ eV (the AGASA
and SUGAR data) show significant excesses from regions close to the Galactic
Centre and Cygnus. Our aim is to check whether such anisotropies can be caused
by single sources of charged particles. We investigate propagation of protons
in two models of the Galactic regular magnetic field (with the irregular
component included) assuming that the particles are injected by a short lived
discrete source lying in the direction of the Galactic Centre. We show that
apart from a prompt image of the source, the regular magnetic field may cause
delayed images at quite large angular distances from the actual source
direction. The image is strongly dependent on the time elapsed after ejection
of particles and it is also very sensitive to their energy. For the most
favourable conditions for particle acceleration by a young pulsar the predicted
fluxes are two to four order of magnitudes higher than that observed. The
particular numbers depend strongly on the Galactic magnetic field model adopted
but it looks that a single pulsar in the Galactic Centre could be responsible
for the observed excess.


title: UHE and EHE neutrino induced taus inside the Earth

abstract:
  Tau neutrinos interacting inside the Earth produce $\tau$ leptons which
thereafter can decay inside the atmosphere. The propagation of extremely
energetic \nut's and $\tau$'s through the Earth is studied by means of a
detailed Monte Carlo simulation, taking into account all major mechanisms of
\nut interactions and $\tau$ energy loss as well as decay modes. The rates of
$\tau$'s emerging from the Earth are determined as a function of $\tau$'s
energy for several cosmic neutrino models.


title:
The surface carbon and nitrogen abundances in models of ultra metal-poor
  stars

abstract:
  We investigate whether the observed high number of carbon- and
nitrogen-enhanced extremely metal-poor stars could be explained by peculiar
evolutionary properties during the core He flash at the tip of the red giant
branch. For this purpose we compute a series of detailed stellar models
expanding upon our previous work; in particular, we investigate if during the
major He flash the penetration of the helium convective zone into the overlying
hydrogen-rich layers can produce carbon- and nitrogen-rich abundances in
agreement with current spectroscopic observations. The dependence of this
phenomenon on selected model input parameters, such as initial metallicity and
treatment of convection is examined in detail.


title: The small-scale structure of the Magellanic Stream

abstract:
  We have mapped two regions at the northern tip of the Magellanic Stream in
neutral hydrogen 21-cm emission using the Arecibo telescope. The new data are
used to study the morphology and properties of the Stream far away from the
Magellanic Clouds, as well as to provide indirect constraints on the properties
of the Galactic Halo. We investigate confinement mechanisms for the Stream
clouds and conclude that these clouds cannot be gravitationally confined or in
free expansion. The most likely mechanism for cloud confinement is pressure
support from the hot Galactic Halo gas. This allows us to place an upper limit
on the Halo density: n(15 kpc) = 10^-3 cm^-3 and/or n(45 kpc) = 3 x 10^-4 cm^-3
depending on the distance. These values are significantly higher than predicted
for an isothermal stratified Halo.


title:
Magnetic Fields in Star-Forming Molecular Clouds. V. Submillimeter
  Polarization of the Barnard 1 Dark Cloud

abstract:
  We present 850 micron polarimetry from the James Clerk Maxwell Telescope
toward several dense cores within the dark cloud Barnard 1 in Perseus.
Significant polarized emission is detected from across the mapped area and is
not confined to the locations of bright cores. This indicates the presence of
aligned grains and hence a component of the magnetic field in the plane of the
sky. Polarization vectors detected away from bright cores are strongly aligned
at a position angle of ~ 90 degrees (east of north), while vectors associated
with bright cores show alignments of varying orientations. There is no direct
correlation between the polarization angles measured in earlier optical
polarimetry toward Perseus and the polarized submillimeter thermal emission.
Depolarization toward high intensities is exhibited, but toward the brightest
core reaches a threshold beyond which no further decrease in polarization
percentage is measured. The polarized emission data from the interior envelope
are compared with previously published OH Zeeman data to estimate the total
field strength and orientation under the assumption of a uniform and
non-uniform field component in the region. These results are rough estimates
only due to the single independent detection of Zeeman splitting toward Barnard
1. The uniform field component is thus calculated to be B(0) = 31 microGauss
[+/- (0.52 (north) - 0.01 (east)) - 0.86 (l.o.s.)] in the case where we have
assumed the ratio of the dispersion of the line-of-sight field to the field
strength to be 0.2.


title: Short-Spacings Correction from the Single-Dish Perspective

abstract:
  While, in general, interferometers provide high spatial resolution for
imaging small-scale structure (corresponding to high spatial frequencies in the
Fourier plane), single-dishes can be used to image the largest spatial scales
(corresponding to the lowest spatial frequencies), including the total power
(corresponding to zero spatial frequency). For many astrophysical studies, it
is essential to bring `both worlds' together by combining information over a
wide range of spatial frequencies. This article demonstrates the effects of
missing short-spacings, and discusses two main issues: (a) how to provide
missing short-spacings to interferometric data, and (b) how to combine
short-spacing single-dish data with those from an interferometer.


title: Chaotic Motions of F-Ring Shepherds

abstract:
  Recent HST images of the Saturnian satellites Prometheus and Pandora show
that their longitudes deviate from predictions of ephemerides based on Voyager
images. Currently Prometheus is lagging and Pandora leading these predictions
by somewhat more than 20 degrees. We show that these discrepancies are fully
accounted for by gravitational interactions between the two satellites. These
peak every 24.8 days at conjunctions and excite chaotic perturbations. The
Lyapunov exponent for the Prometheus-Pandora system is of order 0.35 inverse
years for satellite masses based on a nominal density of 1.3 gm/cm^3.
Interactions are strongest when the orbits come closest together. This happens
at intervals of 6.2 years when their apses are anti-aligned. In this context we
note the sudden changes of opposite signs in the mean motions of Prometheus and
Pandora at the end of 2000 occured shortly after their apsidal lines were
anti-aligned.


title: Photon mass from inflation

abstract:
  We consider vacuum polarization from massless scalar electrodynamics in de
Sitter inflation. The theory exhibits a 3+1 dimensional analogue of the
Schwinger mechanism in which a photon mass is dynamically generated. The
mechanism is generic for light scalar fields that couple minimally to gravity.
The non-vanishing of the photon mass during inflation may result in magnetic
fields on cosmological scales.


title: The UV Spectrum of the Ultra-compact X-ray Binary- 4U 1627-673

abstract:
  We have obtained Hubble Space Telescope/STIS low-resolution ultraviolet
spectra of the X-ray pulsar 4U 1626-67 (=KZ TrA); 4U 1626-67 is unusual even
among X-ray pulsars due to its ultra-short binary period (P=41.4 min) and
remarkably low mass-function (<1.3e-6 Msun). The far-UV spectrum was exposed
for a total of 32ks and has sufficient signal-to-noise to reveal numerous broad
emission and prominent narrower absorption lines. Most of the absorption lines
are consistent in strength with a purely interstellar origin. However, there is
evidence that both CI and CIV require additional absorbing gas local to the
system. In emission, the usual prominent lines of NV and HeII are absent,
whilst both OIV and OV are relatively strong. We further identify a rarely seen
feature at ~1660A as the OIII] multiplet. Our ultraviolet spectra therefore
provide independent support for the recent suggestion that the mass donor is
the chemically fractionated core of either a C-O-Ne or O-Ne-Mg white dwarf;
this was put forward to explain the results of Chandra high-resolution X-ray
spectroscopy. The velocity profiles of the ultraviolet lines are in all cases
broad and/or flat-topped, or perhaps even double-peaked for the highest
ionization cases of O; in either case the ultraviolet line profiles are in
broad agreement with the Doppler pairs found in the X-ray spectra. Both the
X-ray and far-UV lines are plausibly formed in (or in an corona just above) a
Keplerian accretion disc; the combination of ultraviolet and X-ray spectral
data may provide a rich data set for follow-on detailed models of the disk
dynamics and ionization structure in this highly unusual low-mass X-ray pulsar
system.


title:
On the discrepancy between Chandra and XMM temperature profiles for
  A1835

abstract:
  This short technical note addresses a large discrepancy between the
temperature profiles for the galaxy cluster A1835 derived by Schmidt et al.
(2001) using Chandra and by Majerowicz et al. (2002) using XMM. The causes of
this discrepancy may be instructive for the Chandra and XMM cluster analyses in
general. The observation used by Schmidt et al. was affected by a mild
background flare that could not be identified by the usual technique. This
flare biased upwards the measured temperatures at large radii. The remaining
discrepancy appears to be due to the XMM PSF scattering that was not taken into
account in the published analyses. While the XMM PSF is narrow, the surface
brightness of a typical cluster also declines very steeply with radius. For the
moderately distant, cooling flow cluster A1835, about 1/3 of the observed XMM
brightness at any radius is due to the PSF scattering from the smaller radii.
As a result, the contamination from the bright cool cluster center biases low
the measured temperatures near the core, and in general, any temperature
gradients are underestimated.


title:
Period-doubling events in the light curve of R Cygni: evidence for
  chaotic behaviour

abstract:
  A detailed analysis of the century long visual light curve of the long-period
Mira star R Cygni is presented and discussed. The data were collected from the
publicly available databases of the AFOEV, the BAAVSS and the VSOLJ. The full
light curve consists of 26655 individual points obtained between 1901 and 2001.
The light curve and its periodicity were analysed with help of the O-C diagram,
Fourier analysis and time-frequency analysis. The results demonstrate the
limitations of these linear methods. The next step was to investigate the
possible presence of low-dimensional chaos in the light curve. For this, a
smoothed and noise-filtered signal was created from the averaged data and with
help of time delay embedding, we have tried to reconstruct the attractor of the
system. The main result is that R Cygni shows such period-doubling events that
can be interpreted as caused by a repetitive bifurcation of the chaotic
attractor between a period 2T orbit and chaos. The switch between these two
states occurs in a certain compact region of the phase space, where the light
curve is characterized by ~1500-days long transients. The Lyapunov spectrum was
computed for various embedding parameters confirming the chaotic attractor,
although the exponents suffer from quite high uncertainty because of the
applied approximation. Finally, the light curve is compared with a simple one
zone model generated by a third-order differential equation which exhibits
well-expressed period-doubling bifurcation. The strong resemblance is another
argument for chaotic behaviour. Further studies should address the problem of
global flow reconstruction, including the determination of the accurate
Lyapunov exponents and dimension.


title:
Probing dark matter distribution with gravitational lensing and stellar
  dynamics

abstract:
  The Lenses Structure and Dynamics (LSD) Survey aims at measuring the luminous
and dark matter distribution of high redshift early-type galaxies by combining
gravitational lens analysis with newly determined velocity dispersion profiles.
Here we describe the first results from the LSD survey, a measurement of the
internal structure of the lens galaxy in MG2016+112 (z=1.004). The relevance of
this measurement to the cosmological model is briefly discussed, in particular
in the context of E/S0 galaxy formation and evolution, the existence and shape
of universal dark matter profiles, and the measurement of the Hubble constant
from gravitational time delay.


title: AGN-selected clusters as revealed by weak lensing

abstract:
  As a pilot study to investigate the distribution of matter in the fields of
powerful AGN, we present weak lensing observations of deep fields centered on
the radio-quiet quasar E1821 + 643, the radio galaxy 3C295, and the two
radio-loud quasars, 3C334 and 3C254. The host clusters of E1821 + 643 and 3C295
are comfortably detected via their weak lensing signal, and we report the
detection of a cluster-sized mass concentration in the field of the z=0.734
quasar 3C254. The data for the 3C334 field are so far inconclusive. We find
that the clusters are massive and have smooth mass distributions, although one
shows some evidence of past merger activity. The mass-to-light ratios are found
to be moderately high. We discuss the results in light of the cooling flow and
the merger/interaction scenarios for triggering and fuelling AGN in clusters,
but find that the data do not point unambiguously to neither of the two.
Instead, we speculate that sub-cluster mergers may be responsible for
generating close encounters or mergers of galaxies with the central cluster
member, which could trigger the AGN.


title: The Axially Symmetric Ejecta of Supernova 1987A

abstract:
  Extensive early observations proved that the ejecta of supernova 1987A (SN
1987A) are aspherical. Fifteen years after the supernova explosion, the Hubble
Space Telescope has resolved the rapidly expanding ejecta. The late-time images
and spectroscopy provide a geometrical picture that is consistent with early
observations and suggests a highly structured, axially symmetric geometry. We
present here a new synthesis of the old and new data. We show that the Bochum
event, presumably a clump of $^{56}$Ni, and the late-time image, the locus of
excitation by $^{44}$Ti, are most naturally accounted for by sharing a common
position angle of about 14\degree, the same as the mystery spot and early
speckle data on the ejecta, and that they are both oriented along the axis of
the inner circumstellar ring at 45\degree to the plane of the sky. We also
demonstrate that the polarization represents a prolate geometry with the same
position angle and axis as the early speckle data and the late-time image and
hence that the geometry has been fixed in time and throughout the ejecta. The
Bochum event and the Doppler kinematics of the [Ca II]/[O II] emission in
spatially resolved HST spectra of the ejecta can be consistently integrated
into this geometry. The radioactive clump is deduced to fall approximately
along the axis of the inner circumstellar ring and therefore to be redshifted
in the North whereas the [Ca II]/[O II] 7300 \AA emission is redshifted in the
South. We present a jet-induced model for the explosion and argue that such a
model can account for many of the observed asymmetries. In the jet models, the
oxygen and calcium are not expected to be distributed along the jet, but
primarily in an expanding torus that shares the plane and northern blue shift
of the inner circumstellar ring.


title: An EUV Study of the Intermediate Polar EX Hydrae

abstract:
  On 2000 May 5, we began a large multi-wavelength campaign to study the
intermediate polar, EX Hydrae. The simultaneous observations from six
satellites and four telescopes were centered around a one million second
observation with EUVE. Although EX Hydrae has been studied previously with
EUVE, our higher signal-to-noise observations present new results and challenge
the current IP models. Previously unseen dips in the light curve are
reminiscent of the stream dips seen in polar light curves. Also of interest is
the temporal extent of the bulge dip; approximately 0.5 in phase, implying that
the bulge extends over half of the accretion disk. We propose that the magnetic
field in EX Hydrae is strong enough (a few MG) to begin pulling material
directly from the outer edge of the disk, thereby forming a large accretion
curtain which would produce a very broad bulge dip. This would also result in
magnetically controlled accretion streams originating from the outer edge of
the disk. We also present a period analysis of the photometric data which shows
numerous beat frequencies with strong power and also intermittent and wandering
frequencies, an indication that physical conditions within EX Hya changed over
the course of the observation. Iron spectral line ratios give a temperature of
log T=6.5-6.9 K for all spin phases and a poorly constrained density of
n_e=10^10-10^11 cm^-3 for the emitting plasma. This paper is the first in a
series detailing our results from this multi-wavelength observational campaign.


title: The nature of the X-ray transient SAX J1711.6-3808

abstract:
  SAX J1711.6-3808 is an X-ray transient in the Galactic bulge that was active
from January through May of 2001 and whose maximum 1-200 keV luminosity was
measured to be 5X10-9 erg/s/cm2 which is less than ~25% of the Eddington limit,
if placed at a distance equal to that of the galactic center. We study the
X-ray data that were taken of this moderately bright transient with instruments
on BeppoSAX and RXTE. The spectrum shows two interesting features on top of a
Comptonized continuum commonly observed in low-state X-ray binaries: a broad
emission feature peaking at 7 keV and extending from 4 to 9 keV, and a soft
excess with a color temperature below 1 keV which reveals itself only during
one week of data. High time-resolution analysis of 412 ksec worth of data fails
to show bursts, coherent or high-frequency quasi-periodic oscillations. Given
the dynamic range of the flux measurements, this would be unusual if a neutron
star were present. SAX J1711.6-3808 appears likely to contain a black hole. No
quiescent optical counterpart could be identified in archival data within the
5"-radius XMM error circle, but the limits are not very constraining because of
heavy extinction (Av=16).


title: Three-integral models for axisymmetric galactic discs

abstract:
  We present new equilibrium component distribution functions that depend on
three analytic integrals in a Stackel potential, and that can be used to model
stellar discs of galaxies. These components are generalizations of two-integral
ones and can thus provide thin discs in the two-integral approximation. Their
most important properties are the partly analytical expression for their
moments, the disc-like features of their configuration space densities
(exponential decline in the galactic plane and finite extent in the vertical
direction) and the anisotropy of their velocity dispersions. We further show
that a linear combination of such components can fit a van der Kruit disc.


title: RXTE observations of XTE J1550-564 during its 2000 outburst

abstract:
  We report on timing and spectral observations of the microquasar XTE
J1550-564 during its 2000 outburst made by the Rossi X-ray Timing Experiment
(RXTE). We study the spectral properties of the source during both the rise to
the outburst and its decline. We observe transitions from a low hard state to
an intermediate state, and vice versa, before the source returns to quiescence.
We show that the first transition likely reflects a change in the relative
importance of the emitting media, instead of a change in the total accretion
rate, contrary to the second transition.
  We investigate the temporal properties of the source, and follow the
evolution of a low frequency Quasi Periodic Oscillations (QPO).


title:
The ROSAT-ESO Flux-Limited X-Ray (REFLEX) Galaxy Cluster Survey VI:
  Constraints on the cosmic matter density from the KL power spectrum

abstract:
  The Karhunen-Lo\'{e}ve (KL) eigenvectors and eigenvalues of the sample
correlation matrix are used to analyse the spatial fluctuations of the REFLEX
clusters of galaxies. The method avoids the disturbing effects of correlated
power spectral densities which affects all previous cluster measurements on Gpc
scales. Comprehensive tests use a large set of independent REFLEX-like mock
cluster samples extracted from the Hubble Volume Simulation. It is found that
unbiased measurements on Gpc scales are possible with the REFLEX data. The
distribution of the KL eigenvalues are consistent with a Gaussian random field
on the 93.4% confidence level. Assuming spatially flat cold dark matter models,
the marginalization of the likelihood contours over different sample volumes,
fiducial cosmologies, mass/X-ray luminosity relations and baryon densities,
yields the 95.4% confidence interval for the matter density of
$0.03<\Omega_mh^2<0.19$. The N-body simulations show that cosmic variance,
although difficult to estimate, is expected to increase the confidence
intervals by about 50%.


title: `Strange Stars' - have they been discovered ?

abstract:
  Recently there is a suggestion about the star RXJ1856.5$-$3754, being a
possible candidate for quark star. While from the estimates of the radiation
radius, given by the authors, it does not seem to fit with any of the known
models for such stars, the mass radius diagram admits the possibility of this
being a quark star of mass ${\rm M_\odot<M<1.4M_\odot}$, provided the radius
mentioned is the actual radius of the star.


title:
Precise Measurements of Atmospheric Muon Fluxes with the BESS
  Spectrometer

abstract:
  The vertical absolute fluxes of atmospheric muons and muon charge ratio have
been measured precisely at different geomagnetic locations by using the BESS
spectrometer. The observations had been performed at sea level (30 m above sea
level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada.
The vertical cutoff rigidities in Tsukuba (36.2 N, 140.1 E) and in Lynn Lake
(56.5 N, 101.0 W) are 11.4 GV and 0.4 GV, respectively. We have obtained
vertical fluxes of positive and negative muons in a momentum range from 0.6 to
20 GeV/c with systematic errors less than 3 % in both measurements. By
comparing the data collected at two different geomagnetic latitudes, we have
seen an effect of cutoff rigidity. The dependence on the atmospheric pressure
and temperature, and the solar modulation effect have been also clearly
observed. We also clearly observed the decrease of charge ratio of muons at low
momentum side with at higher cutoff rigidity region.