title:
Effects of Grain Morphology and Impurities on the Infrared Spectra of
  Silicon Carbide Particles

abstract:
  In this paper we demonstrate that distinguishing between the polytypes of
silicon carbide by means of infrared features in small-grain spectra is
impossible. Therefore, the infrared spectra of carbon stars, unfortunately, do
not provide a means for drawing comparisons between the crystal structures of
grains condensed in these environments and found in meteorites.
  This is proven first by comparing theoretical band profiles calculated for
ellipsoidal particles, which show clearly a strong dependence on the axis ratio
of the ellipsoids but negligible differences for the two most common polytypes.
Second, spectra measured on submicron particle samples in the laboratory do not
show any obvious correlation of band position or shape to the polytype.
However, we demonstrate by measurements on SiC whiskers that grain shape is
able to determine the spectrum completely. A further strong systematic
influence on the band profile can be exerted by plasmon-phonon coupling due to
conductivity of the SiC material. The latter fact probably is responsible for
the confusion in the astronomical literature about spectral properties of SiC
grains. We show that, although the conductivity seems to be a common property
of many SiC laboratory samples, it is, however, independent of the polytype.


title: Circular Polarization in AGN

abstract:
  We discuss the constraints that recent observations place on circular
polarization in AGN. In many sources the circular polarization is variable on
short timescales, indicating that it originates in compact regions of the
sources. The best prospects for gleaning further information about circular
polarization are high resolution VLBI and scintillation `imaging' which probe
source structure on milliarcsecond and microarcsecond scales respectively.


title:
Temperature Isotropization in Solar Flare Plasmas due to the Electron
  Firehose Instability

abstract:
  The isotropization process of a collisionless plasma with an electron
temperature anisotropy along an external magnetic field ($T_\| ^e\gg
T_\perp^e$, $\|$ and $\perp$ with respect to the background magnetic field) and
isotropic protons is investigated using a particle-in-cell(PIC) code.
Restricting wave growth mainly parallel to the external magnetic field, the
isotropization mechanism is identified to be the Electron Firehose Instability
(EFI). The free energy in the electrons is first transformed into left-hand
circularly polarized transverse low-frequency waves by a non-resonant
interaction. Fast electrons can then be scattered towards higher perpendicular
velocities by gyroresonance, leading finally to a complete isotropization of
the velocity distribution. During this phase of the instability, Langmuir waves
are generated which may lead to the emission of radio waves. A large fraction
of the protons is resonant with the left-hand polarized electromagnetic waves,
creating a proton temperature anisotropy $T_\|^p < T_\perp^p$. The parameters
of the simulated plasma are chosen compatible to solar flare conditions. The
results indicate the significance of this mechanism in the particle
acceleration context: The EFI limits the anisotropy of the electron velocity
distribution, and thus provides the necessary condition for further
acceleration. It enhances the pitch-angle of the electrons and heats the ions.


title:
The Anomalous X-ray Pulsar 1E 1048.1-5937: Phase resolved spectroscopy
  with the XMM-Newton satellite

abstract:
  We report on an observation of the Anomalous X-ray Pulsar 1E 1048.1-5937
performed with the XMM-Newton satellite. The phase averaged spectrum of 1E
1048.1-5937 is well described by the sum of a power law with photon index ~2.9
and a blackbody with temperature ~0.6 keV, without evidence for significant
absorption or emission lines. The above spectral parameters do not vary during
the phases corresponding to the broad pulse, while the off pulse emission shows
a different spectrum characterized by a soft excess at energies below ~1.5 keV.
The XMM-Newton observation and a re-analysis of archival BeppoSAX data, show
that the spectral parameters and flux of 1E 1048.1-5937 did not change
significantly during observations spanning the last four years. All the data
are consistent with a 2-10 keV luminosity varying in the range ~(5-7) 10^33
erg/s (for a distance of 3 kpc).


title:
Tracing protons through the Galactic magnetic field: a clue for charge
  composition of ultra-high energy cosmic rays

abstract:
  We reconstruct the trajectories of ultra-high energy cosmic rays (UHECR) -
observed by the AGASA experiment - in the Galactic magnetic field assuming that
all particles have the same charge. We then study correlations between the
reconstructed events and BL Lacs. The correlations have significance below
10^{-3} in the case of particles with charge +1. In the case of charge -1 the
correlations are absent. We interpret this as evidence that protons are present
in the flux of UHECR. Observed correlation provides an independent evidence
that BL Lacs emit UHECR.


title: Cosmological contraction of the atomic space-time scale

abstract:
  Quantum mechanical effects related to the recently developed projective
theory of relativity are considered. It is shown that at cosmological time
intervals the light velocity increases and the atomic units of length and time
are shrinking. A new derivation of the Hubble Law is presented.


title:
HST observations of the cometary blue compact dwarf galaxy UGC 4483: a
  relatively young galaxy?

abstract:
  We present V and I photometry of the resolved stars in the cometary blue
compact dwarf galaxy UGC 4483 using Hubble Space Telescope Wide Field Planetary
Camera 2 (WFPC2) images. The resulting I vs. (V-I) color-magnitude diagram
(CMD) reaches limiting magnitudes V = 27.5 mag and I = 26.5 mag for photometric
errors less than 0.2 mag. It reveals not only a young stellar population of
blue main-sequence stars and blue and red supergiants, but also an older
evolved population of red giant and asymptotic giant branch stars. The measured
magnitude I = 23.65 +/- 0.10 mag of the red giant branch tip results in a
distance modulus (m-M) = 27.63 +/- 0.12, corresponding to a distance of 3.4 +/-
0.2 Mpc. The youngest stars are associated with the bright H II region at the
northern tip of the galaxy. The population of older stars is found throughout
the low-surface-brightness body of the galaxy and is considerably more spread
out than the young stellar population, suggesting stellar diffusion. The most
striking characteristics of the CMD of UGC 4483 are the very blue colors of the
red giant stars and the high luminosity of the asymptotic giant branch stars.
Both of these characteristics are consistent with either: 1) a very low
metallicity ([Fe/H] = -2.4 like the most metal-deficient globular clusters) and
an old age of 10 Gyr, or 2) a higher metallicity ([Fe/H] = -1.4 as derived from
the ionized gas emission lines) and a relatively young age of the oldest
stellar population in UGC 4483, not exceeding ~ 2 Gyr. Thus our data do not
exclude the possibility that UGC 4483 is a relatively young galaxy having
formed its first stars only ~ 2 Gyr ago.


title: The formation of stars in groups

abstract:
  Observations of the dust and gas around embedded stellar clusters reveal some
of the processes involved in their formation and evolution. Large scale mass
infall with rates dM/dt=4e-4 solar masses/year is found to be disrupted on
small scales by protostellar outflows. Observations of the size and velocity
dispersion of clusters suggest that protostellar migration from their
birthplace begins at very early times and is a potentially useful evolutionary
indicator.


title: Large-Scale Structure and X-ray Clusters of Galaxies

abstract:
  I review recent progress in the study of the large-scale structure of the
Universe through the distribution of clusters of galaxies, concentrating on new
results using X-ray selected samples. After discussing the importance of
understanding the properties of the tracers used to map structure and their
relation to the underlying mass, I elaborate on the advantages and
disadvantages of clusters of galaxies to this end. I then present the most
recent estimates of the power spectrum and correlation function of X-ray
clusters in the local (z~0.2) Universe, and their implications for cosmological
models. Finally, I briefly summarize most recent results from deep X-ray
surveys as probes of the evolution of structure and highlight current ongoing
observational efforts in this field.


title:
Phase-resolved X-ray spectroscopy of the millisecond pulsar SAX
  J1808.4-3658

abstract:
  We present new results based on RXTE observations of SAX J1808.4-3658. The
X-ray spectrum can be fitted by a two-component model. We interpret the soft
component as blackbody emission from a heated spot on the neutron star, and the
hard component as coming from Comptonization in plasma heated by the accretion
shock as the material collimated by the magnetic field impacts onto the neutron
star surface. The hotspot is probably the source of seed photons for
Comptonization. The hard component illuminates the disc, giving rise to a
reflected spectrum. The inferred evolution of the inner radius is not
consistent with the magnetic field truncating the disc. Instead it seems more
likely that the inner disc radius is set by some much longer time-scale
process, most probably connected to the overall evolution of the accretion
disc. This disc truncation mechanism would then have to be generic in all low
mass accretion rate flows both in disc accreting neutron stars and black hole
systems. The phase resolved spectra show clearly that the blackbody and hard
Comptonized spectra pulse independently. This obviously gives an energy
dependent phase lag. Full general relativistic effects are not required to
explain this. We do not detect Compton reflection from the neutron star
surface, though we predict that it should be present in the X-ray spectrum.
This would give an unambiguous observational measure of M/R if there is any
iron on the neutron star surface which is not completely ionized.


title:
Mass segregation in young compact star clusters in the Large Magellanic
  Cloud: I. Data and Luminosity Functions

abstract:
  We have undertaken a detailed analysis of HST/WFPC2 and STIS imaging
observations, and of supplementary wide-field ground-based observations
obtained with the NTT of two young ~10-25 Myr) compact star clusters in the
LMC, NGC 1805 and NGC 1818. The ultimate goal of our work is to improve our
understanding of the degree of primordial mass segregation in star clusters.
This is crucial for the interpretation of observational luminosity functions
(LFs) in terms of the initial mass function (IMF), and for constraining the
universality of the IMF.
  We present evidence for strong luminosity segregation in both clusters. The
LF slopes steepen with cluster radius; in both NGC 1805 and NGC 1818 the LF
slopes reach a stable level well beyond the clusters' core or half-light radii.
In addition, the brightest cluster stars are strongly concentrated within the
inner ~4 R_hl.
  The global cluster LF, although strongly nonlinear, is fairly well
approximated by the core or half-light LF; the (annular) LFs at these radii are
dominated by the segregated high-luminosity stars, however.
  We present tentative evidence for the presence of an excess number of bright
stars surrounding NGC 1818, for which we argue that they are most likely
massive stars that have been collisionally ejected from the cluster core. We
therefore suggest that the cores of massive young stars clusters undergo
significant dynamical evolution, even on time-scales as short as ~25 Myr.


title:
Mass segregation in young compact star clusters in the Large Magellanic
  Cloud: II. Mass Functions

abstract:
  We review the complications involved in the conversion of stellar
luminosities into masses and apply a range of mass-to-luminosity relations to
our Hubble Space Telescope observations of the young LMC star clusters NGC 1805
and NGC 1818.
  Both the radial dependence of the mass function (MF) and the dependence of
the cluster core radii on mass indicate clear mass segregation in both clusters
at radii r <= 20-30'', for masses in excess of ~1.6-2.5 Msun. This result does
not depend on the mass range used to fit the slopes or the metallicity assumed.
It is clear that the cluster MFs, at any radius, are not simple power laws.
  The global and the annular MFs near the core radii appear to be characterised
by similar slopes in the mass range (-0.15 <= log m/Msun <= 0.85), the MFs
beyond r >= 30'' have significantly steeper slopes.
  We estimate that while the NGC 1818 cluster core is between ~5 and ~30
crossing times old, the core of NGC 1805 is likely $\lesssim 3-4$ crossing
times old. However, since strong mass segregation is observed out to ~6 Rcore
and ~3 Rcore in NGC 1805 and NGC 1818, respectively, it is most likely that
significant primordial mass segregation was present in both clusters,
particularly in NGC 1805.


title: Nonaxisymmetric stability in the shearing sheet approximation

abstract:
  Aims: To quantify the transient growth of nonaxisymmetric perturbations in
unstratified magnetized and stratified non-magnetized rotating linear shear
flows in the shearing sheet approximation of accretion disc flows. Method: The
Rayleigh quotient in modal approaches for the linearized equations (with
time-dependent wavenumber) and the amplitudes from direct shearing sheet
simulations using a finite difference code are compared. Results: Both
approaches agree in their predicted growth behavior. The magneto-rotational
instability for axisymmetric and non-axisymmetric perturbations is shown to
have the same dependence of the (instantaneous) growth rate on the wavenumber
along the magnetic field, but in the nonaxisymmetric case the growth is only
transient. However, a meaningful dependence of the Rayleigh quotient on the
radial wavenumber is obtained. While in the magnetized case the total
amplification factor can be several orders of magnitude, it is only of order
ten or less in the nonmagnetic case. Stratification is shown to have a
stabilizing effect. In the present case of shearing-periodic boundaries the
(local) strato-rotational instability seems to be absent.


title: The Energy of Gamma-Ray Bursts

abstract:
  The energy of a Gamma-Ray Burst is one of the most interesting factors that
can help determining the origin of these mysterious explosions. After the
discovery that GRBs are cosmological it was thought, for a while that they are
standard candles releasing $\sim 10^{51}$ergs. Redshift measurements that
followed the discovery of GRB afterglow revealed that GRBs are (i) further than
what was initially believed and (ii) have a very wide luminosity function. Some
bursts revealed an enormous energy release with a record estimate of $ 1.4
\times 10^{54}$ergs for GRB990123. The energy budget was stretched even further
when it was suggested that the conversion efficiency of producing gamma-rays is
low. The realization that GRBs are beamed changed this perspective and brought
the energy budget of GRBs down back to a "modest" $\sim 5 \times 10^{50}$ergs.
I discuss here various estimates showing that GRB energy is narrowly
distributed and discuss the implications of this conclusion to GRB models.


title: Millions of Single Cloud Weak MgII Systems

abstract:
  We report on a population of absorption systems selected by the presence of
very weak Mg II doublets. A sub-population of these systems are iron enriched
and have near solar metallicities. This would indicated advanced stages (i.e.
few Gyr) of in situ star formation within the absorbing structures. From
photoionization modeling, we infer low ionization fractions of f(HI/H)~0.01,
and gas densities of ~0.1 cm^-3. Since the maximum HI column densities are
\~10^17 cm^-2, the inferred cloud sizes are ~10 pc. From their redshift number
densities, this implies that their co-moving spatial density outnumbers normal
bright galaxies by a factor of a few million.


title:
Astrophysical Polarimetric Signature Against TeV Fundamental Planck
  Scale

abstract:
  I present the analysis of data of astrophysical polarimetric observations
that gives the signature of the fundamental extra dimension Planck scale
magnitude essentially higher than $~1TeV$. Magnetic conversion of photons into
the fundamental particles (scalars, gravitons) is the probable mechanism that
can produce noticeable amount of polarization of optical radiation of
astrophysical objects, especially, of distant extragalactic sources. The
results of magnetic conversion process of optical light of extragalactic
sources are presented for a number of situations including: (a) intergalactic
magnetic field, (b) galaxy cluster magnetic field, (c) magnetic conversion in
the typical galaxy magnetic field, (d) magnetic conversion of CMB radiation.


title:
Flaring Up All Over -- Radio Activity in Rapidly-Rotating Late-Type M
  and L Dwarfs

abstract:
  We present Very Large Array observations of twelve late M and L dwarfs in the
Solar neighborhood. The observed sources were chosen to cover a wide range of
physical characteristics - spectral type, rotation, age, binarity, and X-ray
and H\alpha activity - to determine the role of these properties in the
production of radio emission, and hence magnetic fields. Three of the twelve
sources, TVLM513-46546, 2MASS J0036159+182110, and BRI0021-0214, were observed
to flare and also exhibit persistent emission, indicating that magnetic
activity is not quenched at the bottom of the main sequence. The radio emission
extends to spectral type L3.5, and there is no apparent decrease in the ratio
of flaring luminosities to bolometric luminosities between M8-L3.5. Moreover,
contrary to the significant drop in persistent H\alpha activity beyond spectral
type M7, the persistent radio activity appears to steadily increase between
M3-L3.5. Similarly, the radio emission from BRI0021-0214 violates the
phenomenological relations between the radio and X-ray luminosities of
coronally active stars, hinting that radio and X-ray activity are also
uncorrelated at the bottom of the main sequence. The radio active sources that
have measured rotational velocities are rapid rotators, Vsin(i)>30 km/sec,
while the upper limits on radio activity in slowly-rotating late M dwarfs
(Vsin(i)<10 km/sec) are lower than these detections. These observations provide
tantalizing evidence that rapidly-rotating late M and L dwarfs are more likely
to be radio active. This possible correlation is puzzling given that the
observed radio emission requires sustained magnetic fields of 10-1000 G and
densities of 10^12 cm^-3, indicating that the active sources should have slowed
down considerably due to magnetic braking.


title: Photodissociation regions and star formation in the Carina Nebula

abstract:
  We have obtained wide-field thermal infrared (IR) images of the Carina
Nebula, using the SPIREX/Abu telescope at the South Pole. Emission from
poly-cyclic aromatic hydrocarbons (PAHs) at 3.29um, a tracer of
photodissociation regions (PDRs), reveals many interesting well defined clumps
and diffuse regions throughout the complex. Near-IR images (1--2um), along with
images from the Midcourse Space Experiment (MSX) satellite (8--21um) were
incorporated to study the interactions between the young stars and the
surrounding molecular cloud in more detail. Two new PAH emission clumps have
been identified in the Keyhole Nebula and were mapped in 12CO(2--1) and (1--0)
using the SEST. Analysis of their physical properties reveals they are dense
molecular clumps, externally heated with PDRs on their surfaces and supported
by external pressure in a similar manner to the other clumps in the region. A
previously identified externally heated globule containing IRAS 10430-5931 in
the southern molecular cloud, shows strong 3.29-, 8- and 21-um emission, the
spectral energy distribution (SED) revealing the location of an ultra-compact
(UC) HII region. The northern part of the nebula is complicated, with PAH
emission inter-mixed with mid-IR dust continuum emission. Several point sources
are located here and through a two-component black-body fit to their SEDs, we
have identified 3 possible UC HII regions as well as a young star surrounded by
a circumstellar disc. This implies that star formation in this region is
on-going and not halted by the intense radiation from the surrounding young
massive stars.


title: Magnetospheric Structure and Non-Thermal Emission of AXPs and SGRs

abstract:
  In the framework of the magnetar model for the Soft Gamma Repeaters and
Anomalous X-ray Pulsars, we consider the structure of neutron star
magnetospheres threaded by large-scale electrical currents. We construct
self-similar, force-free equilibria under the assumption of axisymmetry and a
power law dependence of magnetic field on radius, ${\bf B} \propto r^{-(2+p)}$.
A large-scale twist of the field lines softens the radial dependence to $p <
1$, thereby accelerating the spindown torque with respect to a vacuum dipole. A
magnetosphere with a strong twist ($B_\phi/B_\theta = O(1)$ at the equator) has
an optical depth $\sim 1$ to resonant cyclotron scattering, independent of
frequency (radius), surface magnetic field strength, or the charge/mass ratio
of the scattering charge. We investigate the effects of the resonant Compton
scattering by the charge carriers (both electrons and ions) on the emergent
X-ray spectra and pulse profiles.


title: A Spectroscopic Reconnaissance of UV-Bright Stars

abstract:
  We have carried out spectroscopic observations and made preliminary
classifications of 62 UV-bright stars identified by Lanning on plates taken by
A. Sandage. The goal was to search for "interesting" objects, such as
emission-line stars, hot sub-dwarfs, and high-gravity stars. Our targets were
grouped into two samples, a bright, B < 13, sample of 35 stars observed with
the Kitt Peak 2.1m telescope and a faint, 13< B < 16, sample of 27 stars
observed with the Hobby-Eberly Telescope. We find 39% fairly normal O-mid B
stars, 15% late ~B-late A stars and 32% F-G stars, with 13% of the stars being
high gravity objects, composite, or otherwise peculiar. Included are four
emission-line stars, three composite systems. Thus one out of every ten Lanning
stars is "interesting" and may deserve individual study. Stars in the bright
sample are often found to be late F or early G stars, although this sample does
include interesting stars as well. No such large contamination occurs among the
fainter stars, however, owing to "deselection" of these stars by interstellar
reddening in the low-latitude fields of the survey.


title: Strong Relativistic Collisionless Shock

abstract:
  A direct numerical simulation of a strong relativistic collisionless shock
propagating into an unmagnetized medium has been performed in two spatial
dimensions. It is found that: (i) collisionless shock exists, (ii) particle
acceleration is insignificant, (iii) the shock does not generate
``quasi-static'' magnetic fields, contrary to recent claims by other authors.
All our results agree with a simple plasma-physical model of collisionless
shocks. On the other hand, astrophysical evidence indicates that shocks do
accelerate charged particles, and GRB phenomenology indicates that shocks do
generate strong magnetic fields. The conflict between the simplest
plasma-physical model and astronomical observations of collisionless shocks is
discussed.


title: The Substructure-Alignment Connection

abstract:
  Using a sample of 903 APM clusters we investigate whether their dynamical
status, as evidenced by the presence of significant substructures, is related
to the large-scale structure of the Universe. We find that the cluster
dynamical activity is strongly correlated with the tendency of clusters to be
aligned with their nearest neighbour and in general with the nearby clusters
that belong to the same supercluster. Furthermore, dynamically active clusters
are more clustered than the overall cluster population. These are strong
indications that clusters develop in a hierarchical fashion by anisotropic
merging along the large-scale filaments within which they are embedded.


title: CN and HNC Line Emission in IR Luminous Galaxies

abstract:
  We have observed HNC 1-0, CN 1-0 and 2-1 line emission in a sample of 13 IR
luminous (LIRGs, L_IR > 10E11 Lo) starburst and Seyfert galaxies. HNC 1-0 is
detected in 9, CN 1-0 is detected in 10 and CN 2-1 in 7 of the galaxies. We
also report the first detection of HC3N (10-9) emission in Arp220. The
excitation of HNC and CN emission requires densities n > 10E4 cm-3. We compare
their intensities to that of the usual high density tracer HCN. The
I(HCN)/I(HNC}) and I(HCN)/I(CN) 1-0 line intensity ratios vary significantly,
from 0.5 to >6, among the galaxies. This implies that the actual properties of
the dense gas is varying among galaxies who otherwise have similar I(CO)/I(HCN)
line intensity ratios. We suggest that the HNC emission is not a reliable
tracer of cold (10 K) gas at the center of LIRGs, as it often is in the disk of
the Milky Way. Instead, the HNC abundance may remain substantial, despite high
gas temperatures, because the emission is emerging from regions where the HCN
and HNC formation and destruction processes are dominated by ion-neutral
reactions which are not strongly dependent on kinetic temperature. We find five
galaxies (four AGNs and one starburst) where the I(HCN)/I(HNC) intensity ratio
is close to unity. In other AGNs, however, I(HCN)/I(HNC}) is >4. The CN
emission is on average a factor of two fainter than HCN, but the variation is
large and there seems to be a trend of reduced relative CN luminosity with
increasing IR luminosity. One galaxy, NGC3690, has a CN luminosity twice that
of HCN and its ISM is thus strongly affected by UV radiation. We discuss the
I(HCN)/I(HNC) and I(HCN)/I(CN) line ratios as indicators of starburst
evolution.


title: Density profiles in a spherical infall model with non-radial motions

abstract:
  A generalized version of the Spherical Infall Model (SIM) is used to study
the effect of angular momentum on the final density profile of a spherical
structure. The numerical method presented is able to handle a variety of
initial density profiles (scale or not scale free) and no assumption of
self-similar evolution is required. The realistic initial overdensity profiles
used are derived by a CDM power spectrum. We show that the amount of angular
momentum and the initial overdensity profile affect the slope of the final
density profile at the inner regions. Thus, a larger amount of angular momentum
or shallower initial overdensity profiles lead to shallower final density
profiles at the inner regions. On the other hand, the slope at the outer
regions is not affected by the amount of angular momentum and has an almost
constant value equal to that predicted in the radial collapse case.


title:
Unification of Dark Matter and Dark Energy: the Inhomogeneous Chaplygin
  Gas

abstract:
  We extend the world model of Kamenshchik et al. to large perturbations by
formulating a Zeldovich-like approximation. We sketch how this model unifies
dark matter with dark energy in a geometric setting reminiscent of M-theory.


title: The Short Period Supersoft Source in M31

abstract:
  We show that the recently discovered short period supersoft source in M31 is
probably a progenitor of a magnetic CV. The white dwarf spins asynchronously
because of the current high accretion rate. However its fieldstrength is
typical of an AM Herculis system, which is what it will ultimately become. We
discuss the relevance of this system to CV evolution, and its relation to some
particular CVs with special characteristics.


title: Dynamics of Walls: Fermion Scattering in Magnetic Field

abstract:
  We investigate the scattering of fermions off walls in the presence of a
magnetic field. We consider both the bubble wall and the kink domain wall. By
solving the Dirac equation for fermions in the presence of a domain wall in an
external magnetic field, we investigate the dependence on the magnetic field of
the transmission and reflection coefficients. In the case of kink domain wall,
we also consider the solutions localized on the wall. The possibile role of the
ferromagnetic domain walls in the dynamics of the early Universe is also
discussed.


title:
Measurement of the angular correlation function of radio galaxies from
  the NRAO VLA Sky Survey

abstract:
  We quantify the angular distribution of radio sources in the NVSS by
measuring the two-point angular correlation function. By careful consideration
of the resolution of radio galaxies into multiple components, we are able to
determine both the galaxy angular clustering and the size distribution of giant
radio galaxies. The slope of the correlation function for radio galaxies agrees
with that for other classes of galaxy, gamma = 1.8, with a 3D correlation
length r_0 = 6 h^-1 Mpc (under certain assumptions). Calibration problems in
the survey prevent clustering analysis below 10 mJy. About 7 per cent of radio
galaxies are resolved by NVSS into multiple components, with a power-law size
distribution. Our work calls into question previous analyses and
interpretations of the angular correlation function from radio surveys.


title:
First Clear Signature of an Extended Dark Matter Halo in the Draco Dwarf
  Spheroidal

abstract:
  We present the first clear evidence for an extended dark matter halo in the
Draco dwarf spheroidal galaxy based on a sample of new radial velocities for
159 giant stars out to large projected radii. Using a two parameter family of
halo models spanning a range of density profiles and velocity anisotropies, we
are able to rule out (at about the 2.5 sigma confidence level) haloes in which
mass follows light. The data strongly favor models in which the dark matter is
significantly more extended than the visible dwarf. However, haloes with
harmonic cores larger than the light distribution are also excluded. When
combined with existing measurements of the proper motion of Draco, our data
strongly suggest that Draco has not been tidally truncated within ~1 kpc. We
also show that the rising velocity dispersion at large radii represents a
serious problem for modified gravity (MOND).


title: Global spiral modes in multi-component disks

abstract:
  We performed two-dimensional non-linear hydrodynamical simulations of
two-component gravitating disks aimed at studying stability properties of these
systems. In agreement with previous analytical and numerical simulations, we
find that the cold gas component strongly affects the growth rates of the
unstable global spiral modes in the disk. Already a five percent admixture of
cold gas increases approximately two-fold the growth rate of the most unstable
global mode while a twenty percent gas admixture enhances the modal growth rate
by a factor of four. The local stability properties of a two-component disk
coupled by self-gravity are governed by a stability criterion similar to
Toomre's Q-parameter derived for one-component systems. Using numerical
simulations, we analyse the applicability of a two-component local stability
criterion for the analysis of the stability properties of global modes. The
comparison of non-linear simulations with the analytical stability criterion
shows that the two-component disks can be globally unstable while being stable
to the local perturbations. The minimum value of the local stability criterion
provides, however, a rough estimate of the global stability properties of
two-component systems. We find that two-component systems with a content of
cold gas of ten percent or less are globally stable, if the minimum value of
the stability parameter exceeds about 2.5.


title: Host galaxies of AGN

abstract:
  The relationship of an AGN to its host galaxy is a crucial question in the
study of galaxy evolution. We perform stellar population synthesis in the
central regions of galaxies of different activity levels. A large number of
stellar features are measured both in the optical and near-infrared. We find
the nuclear stellar population to be related to the level of activity. These
differences are no more conspicuous further away in the bulge of the galaxy.


title:
Deuterium and Oxygen Toward Feige 110: Results from the Far Ultraviolet
  Spectroscopic Explorer (FUSE) Mission

abstract:
  We present measurements of the column densities of interstellar DI and OI
made with the Far Ultraviolet Spectroscopic Explorer (FUSE), and of HI made
with the International Ultraviolet Explorer (IUE) toward the sdOB star Feige
110 [(l,b) = (74.09, -59.07); d = 179 +265 -67 pc; z = -154 +57 -227 pc]. Our
determination of the DI column density made use of curve of growth fitting and
profile fitting analyses, while our OI column density determination used only
curve of growth techniques. The HI column density was estimated by fitting the
damping wings of the interstellar Ly alpha profile. We find log N(DI) = 15.47
+/- 0.06, log N(OI) = 16.73 +/- 0.10, and log N(HI) = 20.14 +0.13 -0.20 (all
errors 2 sigma). This implies D/H = (2.14 +/- 0.82) x 10^-5, D/O = (5.50 +1.64
-1.33) x 10^-2, and O/H = (3.89 +/- 1.67) x 10^-4. Taken with the FUSE results
reported in companion papers (Moos et al. 2001) and previous measurements of
the local interstellar medium, this suggests the possibility of spatial
variability in D/H for sight lines exceeding ~100 pc. This result may constrain
models which characterize the mixing time and length scales of material in the
local interstellar medium.


title:
The Evolving Accretion Disc in the Black Hole X-ray Transient XTE
  J1859+226

abstract:
  We present HST, RXTE, and UKIRT observations of the broad band spectra of the
black hole X-ray transient XTE J1859+226 during the decline from its 1999-2000
outburst. Our UV spectra define the 2175A interstellar absorption feature very
well and based on its strength we estimate E(B-V)=0.58+/-0.12. Hence we
deredden our spectra and follow the evolution of the spectral energy
distribution on the decline from outburst. We find that the UV and optical
data, and the X-ray thermal component when detectable, can be fit with a simple
blackbody model of an accretion disc heated by internal viscosity and X-ray
irradiation, and extending to close to the last stable orbit around the black
hole, although the actual inner radius cannot be well constrained. During the
decline we see the disc apparently evolving from a model with the edge
dominated by irradiative heating towards one where viscous heating is dominant
everywhere. The outer disc radius also appears to decrease during the decline;
we interpret this as evidence of a cooling wave moving inwards and discuss its
implications for the disc instability model. Based on the normalisation of our
spectral fits we estimate a likely distance range of 4.6-8.0kpc, although a
value outside of this range cannot securely be ruled out.


title:
What have we learnt about the Sun from the measurement of the $^8$B
  neutrino flux?

abstract:
  By combining the results of SNO and Super-Kamiokande one can derive - in the
absence of sterile neutrinos - the total neutrino flux produced from $^8$B
decay in the Sun. We use this information to check the accuracy of several
input parameters of solar model calculations. Opacity and p-p fusion cross
section are constrained by the $^8$B flux measurement to the level of few per
cent. The central solar temperature is determined to the one-percent level. We
also find an upper limit for the flux on Earth of sterile neutrinos. We discuss
the role of nuclear physics uncertainties on these determinations.


title: Frequency Analysis of Delta Scuti and RR Lyrae Stars in OGLE-1 Database

abstract:
  We discuss the results of a systematic search for multiperiodic pulsations in
Galactic Bulge Delta Scuti and RR Lyrae stars. Six "normal" double-mode
variables pulsating in two radial modes have been identified (5 Delta
Scuti-type and 1 RR Lyrae-type). In 37 RR Lyrae stars secondary periodicities
very close to the primary pulsation frequency have been detected. These
periodicities correspond to nonradial modes of oscillation. They are found in
\~23% of RRab and in ~3% of RRc variables of our sample.


title:
Deuterium toward the WD0621-376 sight line: Results from the Far
  Ultraviolet Spectroscopic Explorer (FUSE) Mission

abstract:
  Far Ultraviolet Spectroscopic Explorer observations are presented for
WD0621-376, a DA white dwarf star in the local interstellar medium (LISM) at a
distance of about 78 pc. The data have a signal-to-noise ratio of about 20-40
per 20 km/s resolution element and cover the wavelength range 905-1187 \AA.
LISM absorption is detected in the lines of D I, C II, C II*, C III, N I, N II,
N III, O I, Ar I, and Fe II. This sight line is partially ionized, with an
ionized nitrogen fraction of > 0.23. We determine the ratio $D/O = (3.9 \pm
^{1.3}_{1.0})\times 10^{-2}$ (2$\sigma$). Assuming a standard interstellar
oxygen abundance, we derive ${\rm D/H} \approx 1. 3 \times 10^{-5}$. Using the
value of N(H I) derived from EUVE data gives a similar D/H ratio. The D I/N I
ratio is $(3.3 \pm ^{1.0}_{0.8})\times 10^{-1}$ (2$\sigma$).


title:
A Chandra observation of the globular cluster Terzan 1: the neutron-star
  X-ray transient X 1732-304 in quiescence

abstract:
  We present a short (~3.6 ks) Chandra/HRC-I observation of the globular
cluster Terzan 1. This cluster is known to contain the bright neutron star
low-mass X-ray binary X 1732-304 which was active during the 1980's and most of
the 1990's. But a BeppoSAX observation performed in 1999 only showed a very
weak source indicating that the source had become quiescent. During our Chandra
observation, we detect one source with a 0.5-10 keV luminosity of approximately
1 - 2 x 10^{33} erg/s (for an assumed distance of 5.2 kpc). However, its
position is not consistent with that of X 1732-304. We do not conclusively
detect X 1732-304 with a 0.5-10 keV luminosity upper limit of 0.5 - 1 x 10^{33}
erg/s. This limit is consistent with the luminosities observed for several
neutron-star X-ray transients in our Galaxy when they are quiescent, strongly
suggesting that X 1732-304 was still quiescent during our Chandra observation.
If the quiescent emission in neutron star X-ray transients is due to the
thermal emission from the neutron star, then it is expected that the quiescent
luminosity depends on the time-averaged accretion rate of the source. However,
the upper limit on the quiescent luminosity of X 1732-304, combined with its
very long accretion episode prior to the current quiescent episode, indicates
that the quiescent episodes of the source have to be longer than ~200 years.
This would be the second system after KS 1731-260 for which quiescent episodes
longer than several hundreds of years have been inferred. We discuss this
possibility and alternative quiescent models to explain our results.


title: Discover of the "missing" mode in HR 1217 by the Whole Earth Telescope

abstract:
  HR 1217 is a prototypical rapidly oscillating Ap star that has presented a
test to the theory of nonradial stellar pulsation. Prior observations showed a
clear pattern of five modes with alternating frequency spacings of 33.3 microHz
and 34.6 microHz, with a sixth mode at a problematic spacing of 50.0 microHz
(which equals 1.5 times 33.3 microHz) to the high-frequency side. Asymptotic
pulsation theory allowed for a frequency spacing of 34 microHz, but Hipparcos
observations rule out such a spacing. Theoretical calculations of
magnetoacoustic modes in Ap stars by Cunha (2001) predicted that there should
be a previously undetected mode 34 microHz higher than the main group, with a
smaller spacing between it and the highest one. In this Letter, we present
preliminary results from a multi-site photometric campaign on the rapidly
oscillating Ap star HR 1217 using the "Whole Earth Telescope". While a complete
analysis of the data will appear in a later paper, one outstanding result from
this run is the discovery of a newly detected frequency in the pulsation
spectrum of this star, at the frequency predicted by Cunha (2001).


title:
A Deep Search for Pulsations from the Nearby Isolated Neutron Star RX
  J1856.5-3754

abstract:
  We present the results of a deep search for pulsations from the nearby
isolated neutron star RX J1856.5-3754 using the 450 ks Director's Discretionary
Time Chandra observation completed on 2001 Oct 15. No pulsations were detected.
We find a 99% confidence upper limit on the pulsed fraction of ~4.5% for
worst-case sinusoidal pulsations with frequency <~50 Hz and frequency
derivatives -5x10^-10 <= f-dot <= 0 Hz/s. The non-detection of pulsations is
most likely due to an unfavorable viewing angle or emitting geometry. Such
emitting geometries are much more likely to occur for more ``compact'' neutron
stars which show increased gravitational light-bending effects. In this case,
the non-detection implies a radius/mass ratio for RX J1856.5-3754 of R/M <~10
km/Msun.


title: Chandra Observations of the X-ray Jet in Centaurus A

abstract:
  We present high angular resolution X-ray images and spectra from two {\em
Chandra} ACIS-I observations of the X-ray jet in the nearby radio galaxy
Centaurus A. We find that the X-ray emission from the jet is composed of a low
surface brightness diffuse component extending continuously from within at
least 60 pc of the active nucleus into the NE radio lobe 4 kpc from the
nucleus, along with 31 discrete compact knots, most of which are extended at
the resolution of our observation. We find that there are small but significant
differences between the X-ray and radio morphologies of the inner jet at the
arcsecond level, making it unlikely that a single, spatially coincident
population of ultrarelativistic electrons is responsible for the emission in
both energy regimes. We suggest that the X-ray knots of the inner jet are
indeed the sites of particle acceleration and shocks, and the X-ray and radio
knot offsets are caused by a combination of particle diffusion and energy loss.
These offsets may be a common feature of all jets in radio galaxies, or at
least jets in FR I type galaxies, and may be fundamental to the physics of such
jets. The X-ray spectra of several regions of the jet are well fit by absorbed
power-law models with photon indices $\sim$2.2-2.5, although the spectrum of
one bright knot located $\sim$1 kpc from the nucleus (knot B) is harder (photon
index = 2.0).


title: First stars, very massive black holes and metals

abstract:
  Recent studies suggest that the initial mass function (IMF) of the first
stars was likely to be extremely top-heavy, unlike what is observed at present.
We propose a scenario to generate fragmentation to lower masses once the first
massive stars have formed and derive constraints on the primordial IMF. We
estimate the mass fraction of pair-unstable supernovae, shown to be the
dominant sources of the first heavy elements. These metals enrich the gas up to
about $10^{-5}$ solar metallicity, when a transition to efficient
cooling-driven fragmentation occurs producing 1 solar mass clumps. We argue
that the remaining fraction of the first stars ends up in 100 solar mass VMBHs
(Very Massive Black Holes). We obtain constraints on the fraction of first
stars that contribute to the initial metal enrichment and the transition
redshift for primordial IMF away from a top-heavy one, by making various
assumptions about the fate of these VMBHs at late times. We conclude with a
discussion of several hitherto unexplored implications of a high-mass dominated
star formation mode in the early Universe.


title: Precursors and electron-positron pair loading from erupting fireballs

abstract:
  Recent observations suggest that long-duration gamma-ray bursts and their
afterglows are produced by highly relativistic jets emitted in core-collapse
explosions. As the jet makes its way out of the stellar mantle, a bow shock
runs ahead and a strong thermal precursor is produced as the shock breaks out.
Such erupting fireballs produce a very bright gamma-ray precursor as they
interact with the thermal break-out emission. The prompt gamma-ray emission
propagates ahead of the fireball before it becomes optically thin, leading to
electron-positron pair loading and radiative acceleration of the external
medium. The detection of such precursors would offer the possibility of
diagnosing not only the radius of the stellar progenitor and the initial
Lorentz factor of the collimated fireball, but also the density of the external
environment.


title: Theoretical Limb Darkening for Pulsating Cepheids

abstract:
  This work presents a new method to compute time and wavelength dependent
center-to-limb brightness distributions for Classical Cepheids. Our model
atmospheres are based on second-order accurate 1-D hydrodynamic calculations,
performed in spherical geometry. The brightness intensity distributions, and
the resulting limb darkening, are computed through the dynamic atmospheres by
using a full set of atomic and molecular opacities. Our results confirm
important differences with respect to equivalent hydrostatic models. The amount
of limb darkening, and the shape of the limb profiles, show a strong dependence
on the pulsational phase of the Cepheid, which cannot be reproduced by static
models. Non-linear effects in our hydrodynamic equations add a new level of
complexity in the wavelength dependence of our limb profiles, which are
affected by the presence of shock-waves traveling through the atmosphere. These
effects, already detectable by present-day interferometers, should be taken
into consideration when deriving limb darkened diameters for nearby Cepheids
with the accuracy required to measure their radial pulsations.


title: Relativistic Self-similar Disks

abstract:
  We formulate and solve by semi-analytic means the axisymmetric equilibria of
relativistic self-similar disks of infinitesimal vertical thickness. These
disks are supported in the horizontal directions against their self-gravity by
a combination of isothermal (two-dimensional) pressure and a flat rotation
curve. The dragging of inertial frames restricts possible solutions to rotation
speeds that are always less than 0.438 times the speed of light, a result first
obtained by Lynden-Bell and Pineault in 1978 for a cold disk. We show that
prograde circular orbits of massive test particles exist and are stable for all
of our model disks, but retrograde circular orbits cannot be maintained with
particle velocities less than the speed of light once the disk develops an
ergoregion. We also compute photon trajectories, planar and non-planar, in the
resulting spacetime, for disks with and without ergoregions. We find that all
photon orbits, except for a set of measure zero, tend to be focused by the
gravity of the flattened mass-energy distribution toward the plane of the disk.
This result suggests that strongly relativistic, rapidly rotating, compact
objects may have difficulty ejecting collimated beams of matter or light along
the rotation axes until the flows get well beyond the flattened parts of the
relativistic mass distribution (which cannot happen in the self-similar models
considered in this paper).


title:
Scaling relations of supersonic turbulence in star-forming molecular
  clouds

abstract:
  We present a direct numerical and analytical study of driven supersonic MHD
turbulence that is believed to govern the dynamics of star-forming molecular
clouds. We describe statistical properties of the turbulence by measuring the
velocity difference structure functions up to the fifth order. In particular,
the velocity power spectrum in the inertial range is found to be close to E(k)
\~ k^{-1.74}, and the velocity difference scales as <|\Delta u|>~ L^{0.42}. The
results agree well with the Kolmogorov--Burgers analytical model suggested for
supersonic turbulence in [astro-ph/0108300]. We then generalize the model to
more realistic, fractal structure of molecular clouds, and show that depending
on the fractal dimension of a given molecular cloud, the theoretical value for
the velocity spectrum spans the interval [-1.74 ... -1.89], while the
corresponding window for the velocity difference scaling exponent is [0.42 ...
0.78].


title: How Neutral is the Intergalactic Medium at z ~ 6?

abstract:
  Recent observations of high redshift quasar spectra reveal long gaps with
little flux. A small or no detectable flux does not by itself imply the
intergalactic medium (IGM) is neutral. Inferring the average neutral fraction
from the observed absorption requires assumptions about clustering of the IGM,
which the gravitational instability model supplies. Our most stringent
constraint on the neutral fraction at z ~ 6 is derived from the mean Lyman-beta
transmission measured from the z=6.28 SDSS quasar of Becker et al. -- the
neutral hydrogen fraction at mean density has to be larger than 4.7 times
10^{-4}. This is substantially higher than the neutral fraction of ~ 3-5 times
10^{-5} at z = 4.5 - 5.7, suggesting that dramatic changes take place around or
just before z ~ 6, even though current constraints are still consistent with a
fairly ionized IGM at z ~ 6. An interesting alternative method to constrain the
neutral fraction is to consider the probability of having many consecutive
pixels with little flux, which is small unless the neutral fraction is high.
This constraint is slightly weaker than the one obtained from the mean
transmission. We show that while the derived neutral fraction at a given
redshift is sensitive to the power spectrum normalization, the size of the jump
around z ~ 6 is not. We caution that systematic uncertainties include spatial
fluctuations in the ionizing background, and the continuum placement. Tests are
proposed. In particular, the sightline to sightline dispersion in mean
transmission might provide a useful diagnostic. We express the dispersion in
terms of the transmission power spectrum, and develop a method to calculate the
dispersion for spectra that are longer than the typical simulation box.


title:
X-ray emission from a merger remnant, NGC 7252,the "Atoms-for-Peace"
  galaxy

abstract:
  We observed a nearby merger remnant NGC 7252 with the X-ray satellite ASCA,
and detected X-ray emission with the X-ray flux of (1.8+/-0.3)E-13 ergs/s/cm/cm
in the 0.5 - 10 keV band. This corresponds to the X-ray luminosity of 8.1E40
ergs/s. The X-ray emission is well described with a two-component model: a soft
component with kT =0.72+/-0.13 keV and a hard component with kT > 5.1 keV.
Although NGC 7252 is referred to as a dynamically young protoelliptical, the
0.5 - 4 keV luminosity of the soft component is about 2E40 ergs/s, which is low
for an early-type galaxy. The ratio of L_X/L_FIR suggests that the soft
component originated from the hot gas due to star formation. Its low luminosity
can be explained by the gas ejection from the galaxy as galaxy winds. Our
observation reveals the existence of hard X-ray emission with the 2 - 10 keV
luminosity of 5.6E40 ergs/s. This may indicate the existence of nuclear
activity or intermediate-mass black hole in NGC 7252.


title:
Detection of HI 21 cm-line absorption in the Warm Neutral Medium and in
  the Outer Arm of the Galaxy

abstract:
  Using the Westerbork Synthesis Radio Telescope, we have detected HI 21
cm-line absorption in the Warm Neutral Medium of the Galaxy toward the
extragalactic source 3C147. This absorption, at an LSR velocity of -29+/-4 km/s
with a full width at half maximum of 53+/-6 km/s, is associated with the
Perseus Arm of the Galaxy. The observed optical depth is (1.9+/-0.2)*10**(-3).
The estimated spin temperature of the gas is 3600+/-360 K. The volume density
is 0.4 per cc assuming pressure equilibrium. Toward two other sources, 3C273
and 3C295, no wide HI 21 cm-line absorption was detected. The highest of the
3sigma lower limits on the spin temperature of the Warm Neutral Medium is 2600
K. In addition, we have also detected HI 21 cm-line absorption from high
velocity clouds in the Outer Arm toward 3C147 and 3C380 at LSR velocities of
-117.3, -124.5 and -113.7 km/s respectively. We find two distinct temperature
components in the high velocity clouds with spin temperatures of greater than
1000 K and less than 200 K, respectively.


title: Chemodynamical evolution of interacting galaxies

abstract:
  We have undertaken numerical simulations of galaxy interactions and mergers,
coupling the dynamics with the star formation history and the chemical
evolution. The self-gravity of stars and gas is taken into account through a
tree-code algorithm, the gas hydrodynamics through SPH, and an empirical law
such as a local Schmidt law is used to compute star formation. The gas and
stellar metallicity is computed at each position, according to assumed yields,
and the dust amount is monitored. At each step the spectra of galaxies are
computed, according to simple radiative transfer and dust models. Initial
conditions for these simulations will be taken from a large-scale cosmological
frame-work. The aim is to build a statistically significant library of merger
histories. The first results of the project will be discussed, in particular on
predictions about galaxy surveys at high redshift.


title: Spontaneous CPT asymmetry of the Universe

abstract:
  The extended QED with renormalizable interactions breaking the Lorentz and
CPT symmetry is considered and the phenomenological consequences of such a
symmetry breaking are illuminated in view of recent discussion of large scale
anisotropy of the Universe. Other physical effects in QED with CPT violation
are examined, in particular, mass splitting between electrons of different
helicities and decay of very high energetic electrons into lower energy
electrons and positrons.


title: Ultracompact HII Regions

abstract:
  We review some recent observational results on the properties of ultracompact
HII regions, in particular the presence of extended continuum emission
surrounding ultracompact sources and the discovery of a new class of so-called
``Hypercompact'' HII regions. In addition, we discuss recent attempts to probe
the density structure within UC HII regions using the technique of spectral
index analysis.


title: Five-Dimensional Brane World Theory

abstract:
  We present a five-dimensional gravitational theory in a space-time-velocity
Riemannian manifold. The equations of motion of a star moving around a galaxy
are shown to be the Tully-Fisher law. The problem of the cosmological constant
is discussed, and a new formula for the cosmological redshift is derived.


title:
Nuclear and global X-ray properties of LINER galaxies: Chandra and
  BeppoSAX results for Sombrero and NGC 4736

abstract:
  We report on the 0.1--100 keV BeppoSAX observations of two nearby LINER
galaxies, Sombrero and NGC 4736. Chandra ACIS-S observations supplement this
broad-beam spectral study with a high resolution look into the nuclear region,
and show a dominating central point source in Sombrero and a complex X-ray
binary dominated/starburst region in NGC 4736. A compact non-thermal radio
source, present in the nucleus of both galaxies, coincides with the central
source in Sombrero, while in NGC 4736 its X-ray counterpart is a much fainter
point source, not the brightest of the central region. On the basis of these
and other results, we conclude that the LINER activity is linked to the
presence of a low luminosity AGN in Sombrero and to a recent starburst in NGC
4736, and that Chandra's spectroscopic capabilities coupled to high resolution
imaging are essential to establish the origin of the nuclear activity.


title: On the association of G343.1-2.3 and PSR 1706-44

abstract:
  The observations of the supernova remnant G343.1-2.3 with the Mauritius Radio
Telescope, the Australia Compact Array, and the Hobart Single dish are
presented. With these more sensitive measurements the association with the
pulsar PSR1706-44 becomes much more likely. The major points from the
observations are presented.


title:
Study of variable stars in the MOA data base: long-period red variables
  in the Large Magellanic Cloud

abstract:
  One hundred and forty six long-period red variable stars in the Large
Magellanic Cloud (LMC) from the three year MOA project database were analysed.
A careful periodic analysis was performed on these stars and a catalogue of
their magnitudes, colours, periods and amplitudes is presented. We convert our
blue and red magnitudes to $K$ band values using 19 oxygen-rich stars. A group
of red short-period stars separated from the Mira sequence has been found on a
(log P, K) diagram. They are located at the short period side of the Mira
sequence consistent with the work of Wood and Sebo (1996). There are two
interpretations for such stars; a difference in pulsation mode or a difference
in chemical composition. We investigated the properties of these stars together
with their colour, amplitude and periodicity. We conclude that they have small
amplitudes and less regular variability. They are likely to be higher mode
pulsators. A large scatter has been also found on the long period side of the
(log P, K) diagram. This is possibly a systematic spread given that the blue
band of our photometric system covers both standard B and V bands and affects
carbon-rich stars.


title: The Power of Jets: New Clues from Radio Circular Polarization and X-rays

abstract:
  Jets are ubiquitous in accreting black holes. Often ignored, they may be a
major contributor to the emitted spectral energy distribution for sub-Eddington
black holes. For example, recent observations of radio-to-X-ray correlations
and broad band spectra of X-ray binaries in the low/hard state can be explained
by a significant synchrotron contribution from jets also to their IR-to-X-ray
spectrum as proposed by Markoff, Falcke, Fender 2001. This model can also
explain state-transitions from low/hard to high/soft states. Relativistic
beaming of the jet X-ray emission could lead to the appearance of seemingly
Super-Eddington X-rays sources in other galaxies. We show that a simple
population synthesis model of X-ray binaries with relativistic beaming can well
explain the currently found distribution of off-nucleus X-ray point sources in
nearby galaxies. Specifically we suggest that the so-called ultra-luminous
X-ray sources (ULXs, also IXOs) could well be relativistically beamed
microblazars. The same model that can be used to explain X-ray binaries also
fits Low-Luminosity AGN (LLAGN) and especially Sgr A* in the Galactic Center.
The recent detection of significant circular polarization in AGN radio cores,
ranging from bright quasars down to low-luminosity AGN like M81*, Sgr A* and
even X-ray binaries, now places additional new constraints on the matter
contents of such jets. The emerging picture are powerful jets with a mix of hot
and cold matter, a net magnetic flux, and a stable magnetic north pole.


title: The X-ray Source at the Center of the Cassiopeia A Supernova Remnant

abstract:
  We present the first results of an XMM-Newton observation of the central
X-ray source in the Cas A supernova remnant. The spectrum can be fit equally
well with an absorbed steep power law (alpha~3, N_H~1.5x10^22 cm^-2) or with a
bremsstrahlung with temperature kT~2.4 keV and N_H~10^22 cm^-2. A blackbody
model (kT~0.7 keV) gives a slightly worse fit and requires a column density
N_H~5x10^21 cm^-2 and an emitting area with radius ~0.3 km (for d=3.4 kpc). A
search for pulsations for periods longer than 150 ms gave negative results. The
3 sigma upper limits on the pulsed fraction are ~13% for P>0.3 s and ~7% for
P>3 s. The overall properties of the central X-ray source in Cas A are
difficult to explain in terms of a rapidly spinning neutron star with a
canonical magnetic field of ~10^12 G, and are more similar to those of slowly
rotating neutron stars such as the Anomalous X-ray Pulsars.


title: An electrically powered binary star?

abstract:
  We propose a model for stellar binary systems consisting of a magnetic and a
non-magnetic white-dwarf pair which is powered principally by electrical
energy. In our model the luminosity is caused by resistive heating of the
stellar atmospheres due to induced currents driven within the binary. This
process is reminiscent of the Jupiter-Io system, but greatly increased in power
because of the larger companion and stronger magnetic field of the primary.
Electrical power is an alternative stellar luminosity source, following on from
nuclear fusion and accretion. We find that this source of heating is sufficient
to account for the observed X-ray luminosity of the 9.5-min binary RX J1914+24,
and provides an explanation for its puzzling characteristics.


title: New clues to the evolution of dwarf early-type galaxies

abstract:
  Surface photometry of 18 Virgo cluster dwarf elliptical (dE) and dwarf
lenticular (dS0) galaxies, made by Gavazzi et al. (2001) in the H-band (1.65
micron) and in the B-band (0.44 micron), shows that the ratio of the effective
radii of these stellar systems in the B- and H-band, r_{e B}/r_{e H}, ranges
between 0.7 and 2.2. In particular, dwarf ellipticals and lenticulars with a
red total color index B-H (i.e. with 3.2 < B-H < 4) have equal effective radii
in these two pass-bands. By contrast, blue (i.e. with 2.5 < B-H < 3.1) dEs and
dS0s have B-band effective radii about 50% longer than the H-band ones, on
average. Consistently, strong negative gradients in B-H along the
galactocentric radius are found to be associated with blue total colors. This
trend is not found in a sample of 29 giant E and S0 galaxies of the Coma
cluster with analogous data available in the literature. These early-type
giants span a broad range in r_{e B}/r_{e H} (0.2--2.2), with a mean r_{e
B}/r_{e H} of about 1.1, but a narrow range in (red) color (3.3 < B-H < 4.2).
In these stellar systems, color gradients are usually interpreted as due either
to age/metallicity gradients along the radial coordinate or to dust
attenuation, whatever the total color of the system is. Assuming each of these
three distinct interpretations of the origin of color gradients, we discuss the
origin of the association of strong negative color gradients with blue colors
found in the early-type dwarfs under study, in relation with current scenarios
of formation and evolution of dE and dS0 galaxies.


title: Coherent Scalar Field Oscillations and the Epoch of Deceleration

abstract:
  The discovery of supernova SN 1997ff at z~1.7 has confirmed the expected
switch from cosmological acceleration to deceleration, as predicted by the
concordance Lambda/CDM model. However, its position in the SN Ia Hubble diagram
suggestes that the switch is too pronounced, which here is taken to mean that a
cosmological constant is not an adequate description of the state of the
vacuum. An 'oscillessence' model is invoked, with a scalar field phi governed
by a simple quadratic potential, which gives a better fit to the new data
point. The field is undergoing coherent oscillations, and a key feature of the
proposal is that we are towards the end of the second period of acceleration; a
Lambda/phi mix replaces Lambda/CDM, with Omega_Lambda~0.4 and Omega_phi~0.6.


title:
Asteroseismology from space: the Delta Scuti star Theta2 Tauri monitored
  by the WIRE satellite

abstract:
  The first intensive photometric time-series of a Delta Scuti star was
obtained from space. Theta2 Tau was monitored with the star camera on the
Wide-Field Infrared Explorer (WIRE) satellite. Twelve independent frequencies
were detected down to the 0.5 mmag amplitude level. Their reality was
investigated by searching for them using two different algorithms and by some
internal checks. All the frequencies are in the range 10.8-14.6 c\d. The
histogram of the frequency spacings shows that 81% are below 1.8 c\d; rotation
may thus play a role in the mode excitation. The fundamental radial mode is not
observed, although it is expected to occur in a region where the noise level is
very low (55 micromag). The rms residual is about two times lower than that
usually obtained from successful ground--based multisite campaigns. The
comparison of the results of previous campaigns with the new ones establishes
the amplitude variability of some modes.


title: Cluster abundance normalization from observed mass-temperature relation

abstract:
  Abundance of rich clusters in local universe is currently believed to provide
the most robust normalization of power spectrum at a scale of 10 Mpc. This
normalization depends very sensitively on the calibration between virial mass M
and temperature T, which is usually taken from simulations. Uncertainties in
the modelling, such as gas cooling and heating, can lead to a factor of two
variations in the normalization and are thus not very reliable. Here we use
instead an empirical M_{500}-T relation derived from X-ray mass determinations
to calibrate the method. We use results from dark matter simulations to relate
the virial mass function to the mass function at observed M_{500}. We find that
the best fitted value in flat models is sigma_8=(0.7 \pm 0.06)
(\Omega_m/0.35)^{-0.44}(\Gamma/0.2)^{0.08}, where only the statistical error is
quoted. This is significantly lower than previously obtained values from the
local cluster abundance. This lower value for sigma_8 is in a better agreement
with cosmic microwave background and large scale structure constraints and
helps alleviate small scale problems of CDM models. Presently the systematic
uncertainties in the mass determination are still large, but ultimately this
method should provide a more reliable way to normalize the M-T relation. This
can be achieved by obtaining a larger sample of well measured cluster masses
out to a significant fraction of virial radius with BeppoSAX, Chandra and
XMM-Newton.


title: The Low-Energy Spectral Response of the ACIS CCDs

abstract:
  The flight calibration of the spectral response of the Advanced CCD Imaging
Spectrometer (ACIS) below 1.5 keV is difficult because of the lack of strong
lines in the calibration source on-board the Chandra X-ray Observatory. We have
been using 1E0102.2-7219 (the brightest supernova remnant in the SMC) to
evaluate the ACIS response matrices, since this remnant has strong lines of O,
Ne and Mg below 1.5 keV. The spectrum of 1E0102.2-7219 has been
well-characterized using the gratings on Chandra and XMM. We have used the
high-resolution spectral data from both gratings instruments to develop a
spectral model for the CCD spectra. Fits with this model are sensitive to any
problems with the gain calibration and the spectral redistribution model. We
have fit the data with the latest response matrix for the S3 device released in
August 2001 (available in CALDB 2.7 or higher). We have also applied the
charge-transfer inefficiency (CTI) correction software (version 1.37) developed
at Penn State to both the Backside-illuminated (BI) and Front-side illuminated
(FI) data and fit the data with the associated CTI-corrected response matrices.
All fits show a significant improvement in the low energy response with the new
matrices. The fits to the FI CCDs demonstrate the utility of the FI CCDs for
spectral analysis, in spite of the radiation damage the devices suffered early
in the mission.


title: Evolution of Brightest Cluster Galaxies in X-Ray Clusters

abstract:
  A recent paper (Burke, Collins & Mann 2000) presents the analysis of the
K-band Hubble diagram of 76 brightest cluster galaxies (BCGs) in X-ray clusters
and shows that the properties of BCGs depend on the X-ray luminosity (Lx) of
their host clusters. Unfortunately, the low numbers of nearby clusters in this
sample makes it difficult to constrain evolutionary trends. In this letter we
extend the Hubble diagram of Burke et al. (2000) to a total of 155 clusters
using new data on 79 BCGs at z<0.1 from the 2MASS extended source catalogue. We
show that the major division between BCGs in high and low-Lx clusters
disappears at z<0.1, with BCGs having similar absolute magnitudes independent
of the X-ray luminosity of their host clusters. At larger redshifts the K-band
light of BCGs in high-Lx systems is consistent with little or no merging back
to z~0.8, whereas BCGs in the low-Lx systems have a different evolutionary
history, with many increasing their mass by a factor >4 since z~1. This
provides direct evidence of hierarchical merging in a galaxy population.


title: The Stellar Populations of the Cetus Dwarf Spheroidal Galaxy

abstract:
  We present Hubble Space Telescope Wide Field Planetary Camera 2 photometry in
the V and I passbands of the recently discovered Local Group dwarf spheroidal
galaxy in Cetus. Our color-magnitude diagram extends from above the first
ascent red giant branch (RGB) tip to approximately half a magnitude below the
horizontal branch (HB). Adopting a reddening of E(B-V) = 0.03, the magnitude of
the RGB tip yields a distance modulus of (m-M)o = 24.46 +/- 0.14. After
applying the reddening and distance modulus, we have utilized the color
distribution of RGB stars to determine a mean metal abundance of [Fe/H] = -1.7
on the Zinn & West scale with an intrinsic internal abundance dispersion of
+/-0.2 dex. An indirect calculation of the HB morphology of Cetus based on the
mean dereddened HB color yields (B-R)/(B+V+R) = -0.91 +/- 0.09, which
represents an HB that is redder than what can be attributed solely to Cetus'
metal abundance. As such, Cetus suffers from the `second parameter effect' in
which another parameter besides metallicity is controlling the HB morphology.
If we adopt the conventional `age hypothesis' explanation for the second
parameter effect, then this implies that Cetus is 2-3 Gyr younger than Galactic
globular clusters at its metallicity.


title:
Unified description of dark matter at the center and in the halo of the
  Galaxy

abstract:
  We consider a self-gravitating ideal fermion gas at nonzero temperature as a
model for the Galactic halo. The Galactic halo of mass ~ 2 x 10^12 Msol
enclosed within a radius of ~ 200 kpc implies the existence of a supermassive
compact dark object at the Galactic center that is in hydrostatic and thermal
equilibrium with the halo. The central object has a maximal mass of ~ 2.3 x
10^6 Msol within a minimal radius of ~ 18 mpc for fermin masses ~ 15 keV.


title:
Cosmological Hydrodynamics with Adaptive Mesh Refinement: a new high
  resolution code called RAMSES

abstract:
  A new N-body and hydrodynamical code, called RAMSES, is presented. It has
been designed to study structure formation in the universe with high spatial
resolution. The code is based on Adaptive Mesh Refinement (AMR) technique, with
a tree based data structure allowing recursive grid refinements on a
cell-by-cell basis. The N-body solver is very similar to the one developed for
the ART code (Kravtsov et al. 97), with minor differences in the exact
implementation. The hydrodynamical solver is based on a second-order Godunov
method, a modern shock-capturing scheme known to compute accurately the thermal
history of the fluid component. The accuracy of the code is carefully estimated
using various test cases, from pure gas dynamical tests to cosmological ones.
The specific refinement strategy used in cosmological simulations is described,
and potential spurious effects associated to shock waves propagation in the
resulting AMR grid are discussed and found to be negligible. Results obtained
in a large N-body and hydrodynamical simulation of structure formation in a low
density LCDM universe are finally reported, with 256^3 particles and 4.1 10^7
cells in the AMR grid, reaching a formal resolution of 8192^3. A convergence
analysis of different quantities, such as dark matter density power spectrum,
gas pressure power spectrum and individual haloes temperature profiles, shows
that numerical results are converging down to the actual resolution limit of
the code, and are well reproduced by recent analytical predictions in the
framework of the halo model.


title:
Chandra observations of RXJ1347.5-1145: the distribution of mass in the
  most X-ray luminous galaxy cluster known

abstract:
  We present Chandra observations of RXJ1347.5-1145, the most X-ray luminous
cluster of galaxies known. We report the discovery of a region of relatively
hot, bright X-ray emission, located approximately 20 arcsec to the southeast of
the main X-ray peak, at a position consistent with the region of enhanced
Sunyaev-Zeldovich effect reported by Komatsu et al. (2001). We suggest that
this region contains shocked gas resulting from a recent subcluster merger
event. Excluding the data for the southeast quadrant, the cluster appears
relatively relaxed. The X-ray gas temperature rises from kT~6 keV within the
central 25 h_50^{-1} kpc radius to a mean value of ~16 keV between 0.1-0.5
h_50^{-1} Mpc. The mass profile for the relaxed regions of the cluster,
determined under the assumption of hydrostatic equilibrium, can be
parameterized by a Navarro, Frenk & White (1997) model with a scale radius
r_s~0.4 h_50^{-1} Mpc and a concentration parameter c~6. The best-fit Chandra
mass model is in good agreement with independent measurements from weak
gravitational lensing studies. Strong lensing data for the central regions of
the cluster can be also explained by the introduction of an additional mass
clump centred on the second brightest galaxy. We argue that this galaxy is
likely to have been the dominant galaxy of the recently merged subcluster.


title:
Does the plasma composition affect the long term evolution of
  relativistic jets?

abstract:
  We study the influence of the matter content of extragalactic jets on their
morphology, dynamics and emission properties. For this purpose we consider jets
of extremely different compositions including pure leptonic and baryonic
plasmas. Our work is based on two-dimensional relativistic hydrodynamic
simulations of the long-term evolution of powerful extragalactic jets
propagating into a homogeneous environment. The equation of state used in the
simulations accounts for an arbitrary mixture of electrons, protons and
electron-positron pairs. Using the hydrodynamic models we have also computed
synthetic radio maps and the thermal Bremsstrahlung X-ray emission from their
cavities.
  Although there is a difference of about three orders of magnitude in the
temperatures of the cavities inflated by the simulated jets, we find that both
the morphology and the dynamic behaviour are almost independent on the assumed
composition of the jets. Their evolution proceeds in two distinct epochs.
During the first one multidimensional effects are unimportant and the jets
propagate ballistically. The second epoch starts when the first larger vortices
are produced near the jet head causing the beam cross section to increase and
the jet to decelerate. The evolution of the cocoon and cavity is in agreement
with a simple theoretical model. The beam velocities are relativistic ($\Gamma
\simeq 4$) at kiloparsec scales supporting the idea that the X-ray emission of
several extragalactic jets may be due to relativistically boosted CMB photons.
The radio emission of all models is dominated by the contribution of the hot
spots. All models exhibit a depression in the X-rays surface brightness of the
cavity interior in agreement with recent observations.


title: How Do Z and Atoll X-ray Binaries Differ?

abstract:
  Low-mass X-ray binaries containing weakly magnetized neutron stars may be
divided into two classes, Z and atoll sources, based in large part upon the
patterns which they trace in plots of two X-ray colors. In this paper, we
examine color-color diagrams of nine atoll sources and five Z sources using
data from the Rossi X-ray Timing Explorer. The five-year span of data we have
examined is significantly longer than those of previous studies. We find that
the previous clear distinction between atoll and Z sources may be an artifact
of incomplete sampling, as those atoll sources which are sampled over a wide
dynamic range in intensity (greater than a factor of 80) trace three-branched
color-color patterns similar to the tracks for which Z sources are named. This
suggests that the two classes are more intimately related than previously
realized, which also has been suggested based upon recent timing studies.
However, detailed differences in the spectral behavior of the two classes argue
against any simple unification.


title:
Keck Spectroscopy and Imaging of Faint Galaxies Identified as
  MicroJansky Radio Sources

abstract:
  We investigate the nature of the faintest radio sources detected in 3 VLA
surveys, to faint limits 8 microJy at 8.5 GHz. Using the Keck Low Resolution
Imaging Spectrograph in BRI and the Near Infra Red Camera in K, we image 51
radio sources, and identify probable optical counterparts for 50. With LRIS
spectroscopy, we successfully acquire new redshifts for 17 sources, and 9 have
redshifts from previous data. Of this sample of 26, about 60 per cent are disk
galaxies with high radio to optical ratios, indicating ongoing or very recent
starbursts, at redshifts z=0-1. Others are normal, non-interacting galaxies at
z<0.4, QSOs and radioluminous giant ellipticals (obscured AGN?). All of the 14
non-QSO galaxies with spectra show emission lines, but with luminosities
corresponding to star-formation rates about an order of magnitude lower than
estimated from the high radio luminosities (dust extinction?). Three have
strong H-delta absorption (`e+a galaxies'). The Keck spectra also provide
approximate emission line widths and rotation curves. Most (12/14) have
kinematics implying large dynamical masses, and moderate excitation ratios
consistent with L* spirals. The other two, which have sub-L* optical
luminosities, appear to be low-mass galaxies with much higher excitations and
may be more similar to HII galaxies.


title: Tip of the Red Giant Branch Distances to NGC 4214, UGC 685, and UGC 5456

abstract:
  We have used WFPC2 VRI observations to calculate the distances to three
nearby galaxies, NGC 4214, UGC 685, and UGC 5456 using the tip of the red giant
branch method. Our values for NGC 4214 (2.94 +/- 0.18 Mpc) and UGC 685 (4.79
+/- 0.30 Mpc) are the most precise measurementes of the distances to these
objects ever made. For UGC 5456 the data do not allow us to reach a decisive
conclusion since there are two possible solutions, one leading towards a short
distance around 3.8 Mpc and another one towards a long distance of 5.6 Mpc or
more.


title: Bullets in a Core Collapse Supernova Remnant: The Vela Remnant

abstract:
  We use two-dimensional hydrodynamical simulations to investigate the
properties of dense ejecta clumps (bullets) in a core collapse supernova
remnant, motivated by the observation of protrusions probably caused by clumps
in the Vela supernova remnant. The ejecta, with an inner flat and an outer
steep power law density distribution, were assumed to freely expand into an
ambient medium with a constant density, $\sim 0.1$ H atoms cm$^{-3}$ for the
case of Vela. At an age of $10^4$ yr, the reverse shock front is expected to
have moved back to the center of the remnant. Ejecta clumps with an initial
density contrast $\chi \sim 100$ relative to their surroundings are found to be
rapidly fragmented and decelerated. In order to cause a pronounced protrusion
on the blast wave, as observed in the Vela remnant, $\chi \sim 1000$ may be
required. In this case, the clump should be near the inflection point in the
ejecta density profile, at an ejecta velocity $\sim 3000 \kms $. These results
apply to moderately large clumps; smaller clumps would require an even larger
density contrast. Clumps can create ring structure in the shell of the Vela
remnant and we investigate the possibility that RX J0852--4622, an apparent
supernova remnant superposed on Vela, is actually part of the Vela shell. Radio
observations support this picture, but the possible presence of a compact
object argues against it. The Ni bubble effect or compression in a pulsar wind
nebula are possible mechanisms to produce the clumping.


title: Neutron star composition in strong magnetic fields

abstract:
  We study the problem of neutron star composition in the presence of a strong
magnetic field. The effects of the anomalous magnetic moments of both nucleons
and electrons are investigated in relativistic mean field calculations for a
$\beta$-equilibrium system. Since neutrons are fully spin polarized in a large
field, generally speaking, the proton fraction can never exceed the field free
case. An extremely strong magnetic field may lead to a pure neutron matter
instead of a proton-rich matter.


title: Properties of a spectroscopically selected CV sample

abstract:
  We have initiated a dedicated search for new CVs, selecting candidates on the
base of their spectroscopic properties in the Hamburg Quasar Survey (HQS),
which lead up to now to the identification of 50 new CVs and a dozen good
candidates. Using the HQS data of the previously known CVs for extensive tests
of our selection scheme, we demonstrate that our survey should be very
efficient in finding short period systems as long as they have emission lines
with equivalent widths >=10 A. So far, orbital periods have been measured for
15 of the new CVs, with the surprising result that only two systems lie at or
below the lower boundary of the period gap. This - somewhat preliminary -
result is in uncomfortable disagreement with the predictions of the standard
scenario of CV evolution.


title: Comparison of bar strengths in active and non-active galaxies

abstract:
  Bar strengths are compared between active and non-active galaxies for a
sample of 43 barred galaxies. The relative bar torques are determined using a
new technique (Buta and Block 2001), where maximum tangential forces are
calculated in the bar region, normalized to the axisymmetric radial force
field. We use JHK images of the 2 Micron All Sky Survey. We show a first clear
empirical indication that the ellipticies of bars are correlated with the
non-axisymmetric forces in the bar regions. We found that nuclear activity
appears preferentially in those early type galaxies in which the maximum bar
torques are weak and appear at quite large distances from the galactic center.
Most suprisingly the galaxies with the strongest bars are non-active. Our
results imply that the bulges may be important for the onset of nuclear
activity, but that the correlation between the nuclear activity and the early
type galaxies is not straightforward.


title: Parallel Science with Astero-seismology missions

abstract:
  Eddington, COROT, MONS, KEPLER, and the other asteroseismology and planet
finding missions, obtain extremely high photometric quality time-series data as
their primary purpose. Similar quality data are potentially, and in some
designs actually, being obtained for very many other sources in the telescope
field of view, in addition to the primary mission targets. These parallel data,
of exceptional quality and broad scientific interest, can be made available for
scientific analysis with small system impact. This paper lists some of the most
obvious of the serendipitous research and discovery opportunities which these
parallel data will allow. The scientific potential is both large and unique,
encouraging efforts to provide these data to the community.


title: A comment on the colour-colour diagrams of Low Mass X-ray Binaries

abstract:
  Disc accreting neutron stars come in two distinct varieties, atolls and Z
sources, named after their differently shaped tracks on a colour-colour diagram
as the source luminosity changes. Here we present analysis of three transient
atoll sources showing that there is an additional branch in the colour-colour
diagram of atoll sources which appears at very low luminosities. This new
branch connects to the top of previously known C-shaped (atoll) path, forming a
horizontal track where the average source flux decrease from right to left.
This turns the C-shape into a Z. Thus both atolls and Z sources share the same
topology on the colour-colour diagram, and evolve in similar way as a function
of increasing averaged mass accretion rate. This strongly favours models in
which the underlying geometry of these sources changes in similar ways. A
possible scenario is one where the truncated disc approaches the neutron star
when the accretion rate increases, but that in the atolls the disc is truncated
by evaporation (similarly to black holes) whereas in the Z sources it is
truncated by the magnetic field.


title:
A study of the spectral evolution during dipping in XB 1323-619 with
  Rossi-XTE and BeppoSAX

abstract:
  We report results from analysis of the observations of the dipping low mass
X-ray binary XB 1323-619 made with BeppoSAX} and Rossi-XTE. The dust-scattered
halo contributes significantly in this source, and the observation made with
BeppoSAX on 1997 August was used to provide MECS radial intensity profiles at
several energies. From these, the halo fractions were obtained and thus an
optical depth to dust scattering of 1.8 +/- 0.4 derived. In the Rossi-XTE
observation of April 25-28, 1997, seven X-rays dips were observed together with
7 bursts repeating approximately periodically. Non-dip and dip PCA spectra can
be well-described by assuming the emission consists of point-like blackbody
emission identified with the neutron star, plus Comptonized emission from an
extended ADC. The blackbody temperature is 1.79 +/- 0.21 keV and the cut-off
power law photon index 1.61 +/- 0.04. Spectral evolution in dipping is well
described by progressive covering of the extended Comptonizing region by
absorber plus more rapid removal of the point-like blackbody. The effects of
dust scattering and of the X-ray pulsar 1SAX J1324.4-6200 also in the field of
view are included in the fitting. We detect an iron line at ~6.4 keV and its
probable origin in the ADC is discussed.


title: Resolved shocks in clumpy media

abstract:
  We study the structure of shocks in clumpy media, using a multifluid
formalism. As expected, shocks broaden as they weaken: for sufficiently weak
shocks, no viscous subshock appears in the structure. This has significant
implications for the survival of dense clouds in regions overrun by shocks in a
wide range of astrophysical circumstances, from planetary nebulae to the nuclei
of starburst galaxies.


title:
Parsec-scale structure in the warm ISM from polarized galactic radio
  background observations

abstract:
  We present multi-frequency polarization observations of the diffuse radio
synchrotron background modulated by Faraday rotation, in two directions of
positive latitude. No extended total intensity I is observed, which implies
that total intensity has no structure on scales smaller than approximately a
degree. Polarized intensity and polarization angle, however, show abundant
small-scale structure on scales from arcminutes to degrees. Rotation Measure
(RM) maps show coherent structure over many synthesized beams, but also abrupt
large changes over one beam. RM's from polarized extragalactic point sources
are correlated over the field in each of the two fields, indicating a galactic
component to the RM, but show no correlation with the RM map of the diffuse
radiation. The upper limit in structure in I puts constraints on the random and
regular components of the magnetic field in the galactic interstellar medium
and halo. The emission is partly depolarized so that the observed polarization
mostly originates from a nearby part of the medium. This explains the lack of
correlation between RM from diffuse emission and from extragalactic point
sources as the latter is built up over the entire path length through the
medium.


title: A change in the outburst recurrence time of the Rapid Burster

abstract:
  An apparent sudden change in the outburst recurrence time displayed by the
Rapid Burster occurred around the end of 1999. The time between consecutive
outbursts shrinked from ~200 to ~100 days somewhere between November 1999 and
March 2000. In parallel, the average peak intensity also decreased of a factor
about 2 in all outbursts occurred after November 1999 with respect to those
occurred before this date. I discuss these results by comparing them with
similar cases of changes in the recurrence time of other transient X-ray
binaries and with the behaviour of Dwarf Novae. A viable explanation is
connected with changes in the value of the quiescence mass transfer rate from
the secondary, although the detailed origin of these changes remains at best
speculative. Further, this result has important implications for programming
time-constrained observations of the Rapid Burster both in outburst and in
quiescence.


title: ISOPHOT - Photometric Calibration of Point Sources

abstract:
  All observations by the aperture photometer (PHT-P) and the far-infrared
(FIR) camera section (PHT-C) of ISOPHOT included reference measurements against
stable internal fine calibration sources (FCS) to correct for temporal drifts
in detector responsivities. The FCSs were absolutely calibrated in-orbit
against stars, asteroids and planets, covering wavelengths from 3.2 to 240
micron. We present the calibration concept for point sources within a
flux-range from 60 mJy up to 4500 Jy for staring and raster observations in
standard configurations and discuss the requisite measurements and the
uncertainties involved. In this process we correct for instrumental effects
like nonlinearities, signal transients, time variable dark current,
misalignments and diffraction effects. A set of formulae is developed that
describes the calibration from signal-level to flux densities. The scatter of
10 to 20 % of the individual data points around the derived calibration
relations is a measure of the consistency and typical accuracy of the
calibration. The reproducibility over longer periods of time is better than 10
%. The calibration tables and algorithms have been implemented in the final
versions of the software for offline processing and interactive analysis.


title: Collisional Cascades in Planetesimal Disks I. Stellar Flybys

abstract:
  We use a new multiannulus planetesimal accretion code to investigate the
evolution of a planetesimal disk following a moderately close encounter with a
passing star. The calculations include fragmentation, gas and
Poynting-Robertson drag, and velocity evolution from dynamical friction and
viscous stirring. We assume that the stellar encounter increases planetesimal
velocities to the shattering velocity, initiating a collisional cascade in the
disk. During the early stages of our calculations, erosive collisions damp
particle velocities and produce substantial amounts of dust. For a wide range
of initial conditions and input parameters, the time evolution of the dust
luminosity follows a simple relation, L_d/L_{\star} = L_0 / [alpha +
(t/t_d)^{beta}]. The maximum dust luminosity L_0 and the damping time t_d
depend on the disk mass, with L_0 proportional to M_d and t_d proportional to
M_d^{-1}. For disks with dust masses of 1% to 100% of the `minimum mass solar
nebula' (1--100 earth masses at 30--150 AU), our calculations yield t_d approx
1--10 Myr, alpha approx 1--2, beta = 1, and dust luminosities similar to the
range observed in known `debris disk' systems, L_0 approx 10^{-3} to 10^{-5}.
Less massive disks produce smaller dust luminosities and damp on longer
timescales. Because encounters with field stars are rare, these results imply
that moderately close stellar flybys cannot explain collisional cascades in
debris disk systems with stellar ages of 100 Myr or longer.


title:
Evolutionary models for low-mass stars and brown dwarfs: uncertainties
  and limits at very young ages

abstract:
  We analyse pre-Main Sequence evolutionary tracks for low mass stars with
masses $m \le 1.4 \msol$ based on the Baraffe et al. (1998) input physics. We
also extend the recent Chabrier et al. (2000) evolutionary models based on
dusty atmosphere to young brown dwarfs down to one mass of Jupiter. We analyse
current theoretical uncertainties due to molecular line lists, convection and
initial conditions. Simple tests on initial conditions show the high
uncertainties of models at ages $\simle$ 1 Myr. We find a significant
sensitivity of atmosphere profiles to the treatment of convection at low
gravity and $\te < 4000$ K, whereas it vanishes as gravity increases. This
effect adds another source of uncertainty on evolutionary tracks at very early
phases. We show that at low surface gravity ($\log g \simle 3.5$,) the common
picture of vertical Hayashi lines with constant $\te$ is oversimplified. The
effect of a variation of initial deuterium abundance is studied. We compare our
models with evolutionary tracks available in the literature and discuss the
main differences. We finally analyse to which extent current observations of
young systems provide a good test for pre-Main Sequence tracks.


title: The X-ray R Aquarii: A Two-sided Jet and Central Source

abstract:
  We report Chandra ACIS-S3 x-ray imaging and spectroscopy of the R Aquarii
binary system that show a spatially resolved two-sided jet and an unresolved
central source. This is the first published report of such an x-ray jet seen in
an evolved stellar system comprised of ~2-3 solar masses. At E < 1 keV, the
x-ray jet extends both to the northeast and southwest relative to the central
binary system. At 1 < E < 7.1 keV, R Aqr is a point-like source centered on the
star system. While both 3.5-cm radio continuum emission and x-ray emission
appear coincident in projection and have maximum intensities at ~7.5" northeast
of the central binary system, the next strongest x-ray component is located
\~30" southwest of the central binary system and has no radio continuum
counterpart. The x-ray jets are likely shock heated in the recent past, and are
not in thermal equilibrium. The strongest southwest x-ray jet component may
have been shocked recently since there is no relic radio emission as expected
from an older shock. At the position of the central binary, we detect x-ray
emission below 1.6 keV consistent with blackbody emission at T ~2 x 10^6 K. At
the central star there is also a prominent 6.4 keV feature, a possible
fluorescence or collisionally excited Fe K-alpha line from an accretion disk or
from the wind of the giant star. For this excitation to occur, there must be an
unseen hard source of x-rays or particles in the immediate vicinity of the hot
star. Such a source would be hidden from view by the surrounding edge-on
accretion disk.


title: Detection of a Quiescent Low Mass X-Ray Binary Companion in 47 Tucanae

abstract:
  We present the results of a search for optical counterparts to the two
quiescent low mass X-ray binaries (X5 and X7) in the globular cluster 47
Tucanae, using high quality Chandra and HST images. A faint blue (V=21.7;
U-V=0.9) star within 0.03" of the eclipsing system X5 shows variability on both
short and long timescales, and is the counterpart of the X-ray source. The
colors and variability of this object are consistent with the combination of
light from an accretion disk and a red main sequence star (possibly somewhat
larger than a normal MS star with similar luminosity). No evidence is found for
a star showing either variability or unusual colors near the position of X7,
but a probable chance superposition of a star with V=20.25 limits the depth of
our search.


title:
Globular Cluster Systems and the Missing Satellite Problem: Implications
  for Cold Dark Matter Models

abstract:
  We analyze the metallicity distributions of globular clusters belonging to 28
early-type galaxies in the survey of Kundu & Whitmore (2001). A Monte Carlo
algorithm which simulates the chemical evolution of galaxies that grow
hierarchically via dissipationless mergers is used to determine the most
probable protogalactic mass function for each galaxy. Contrary to the claims of
Kundu & Whitmore, we find that the observed metallicity distributions are in
close agreement with the predictions of such hierarchical formation models. The
mass spectrum of protogalactic fragments for the galaxies in our sample has a
power-law behavior, with an exponent of roughly -2. This spectrum is
indistinguishable from the mass spectrum of dark matter halos predicted by cold
dark matter models for structure formation. We argue that these protogalactic
fragments, the likely sites of globular cluster formation in the early
universe, are the disrupted remains of the "missing" satellite galaxies
predicted by cold dark matter models. Our findings suggest that the solution to
the missing satellite problem is through the suppression of gas accretion in
low-mass halos after reionization, or via self-interacting dark matter, and
argue against models with suppressed small-scale power or warm dark matter.


title:
A Sensitive Targeted Search Campaign at Parkes to Find Young Radio
  Pulsars at 20 cm

abstract:
  We describe a sensitive targeted search campaign at Parkes to find faint
young radio pulsars using the center beam of the 20-cm multibeam receiver. The
high frequency of the receiver mitigates scattering effects which can dominate
profiles of distant pulsars at low frequencies and prevent detection. The
targets included several composite supernova remnants (SNRs), two fast X-ray
pulsars, long-period anomalous X-ray pulsars, and a soft gamma repeater. The
sensitivity limits in this search are significantly better than those
previously reported for these objects. We have discovered three new radio
pulsars, two of which are not associated with the target objects. The third
pulsar, PSR J1713-3949, is possibly associated with SNR G347.3-0.5; the
estimated ages and distances of the two objects are consistent, but a more
significant positional coincidence must be established with the central X-ray
source in the SNR through pulsar timing to confirm or refute the association.