title: Global accretion disk simulations of magneto-rotational instability

abstract:
  We perform global three-dimensional simulations of accretion disks
integrating the compressible, non-viscous, but diffusive MHD equations. The
disk is supposed to be isothermal. We make use of the ZEUS-3D code integrating
the MHD equations and added magnetic diffusivity. We measure the efficiency of
the angular-momentum transport. Various model simulations delivered transport
parameters of alpha_SS=0.01 to 0.05 which are consistent with several local
numerical investigations. Two of the models reach a highly turbulent state at
which alpha_SS is of the order of 0.1. After a certain stage of saturating of
the turbulence, Reynolds stress is found to be negative (inward transport) in
many of the models, whereas Maxwell stresses dominate and deliver a positive
(outward) total transport. Several of the models yield strongly fluctuating
Reynolds stresses, while Maxwell stresses are smooth and always transport
outwards.
  Dynamo action is found in the accretion disk simulations. A positive
dynamo-alpha is indicated in the northern hemisphere of the most prominent run,
coming along with negative kinetic and current helicities (all having the
opposite sign on the southern side). The dipolar structure of the magnetic
field is maintained throughout the simulations, although indication for a decay
of antisymmetry is found. The simulations covered relatively thick disks, and
results of thin-disk dynamo models showing quadrupolar fields may not be
compatible with the results presented here.


title: Origin and possible birthplace of the extreme runaway star HIP 60350

abstract:
  Using the recently determined spatial velocity components of the extreme
runaway star HIP 60350 and a gravitation potential model of the Galaxy, we
integrate the orbit of HIP 60350 back to the plane of the Galaxy. In this way,
a possible location of the formation of the star is determined. We estimate the
uncertainty of the result due to the uncertainties of the gravitational
potential model and the errors in the spatial velocity components. The place of
birth lies (within the errors) near the position of the open cluster NGC 3603.
However, the ejection event which occured about 20 Myr ago is in contradiction
with the cluster mean age of 3-4 Myr. We suggest that it occured at an earlier
phase in sequential star formation in that region. We discuss also ejection
mechanisms. Due to the rather high mass of the star (about $5 \Msol$), the most
probable model is that of dynamical ejection.


title: Cosmological History of Stars and Metals

abstract:
  We study the evolution of stellar content and the chemical enrichment of the
universe averaged over the whole population of galaxies by means of a series of
chemo-spectrophotometric models that take into account the metallicity and dust
obscuration effects. We investigate various classes of cosmic star formation
rates (CSFR) histories consistent with current estimations. We are able to
reproduce a variety of observational constraints such as the emissivities at
rest-frame 0.44, 25, 60 and 100 $\mu$m of the local universe and also the
overall shape of the extragalactic background light from UV/NIR galaxy counts
and the cosmic infrared background (CIB) from DIRBE/FIRAS measurements. We find
that the CIB at 140 $\mu$m is crucial for discriminating between the CSFR
histories. The best-fit model to this constraint seems to favour mid-infrared
derived CSFR at low-$z$ and a flat CSFR at higher $z$ consistent with the most
recent estimations, although the shape of the CSFR at high redshifts has little
impact on the FIR/submm part of extragalactic background. We suggest that the
bulk of the CIB energy is produced by a population of moderately obscured
normal galaxies lying at $0\le z \le 1$. We then derive the global chemical
enrichment and stellar content of the universe and find that this model
predicts metallicities in good agreement with the metallicity in DLAs given
that some outflow of metal-enriched gas from galaxies is assumed, but it
overproduces the current present-day stellar mass density and NIR luminosity
density.


title: Does the Sun Shrink with Increasing Magnetic Activity?

abstract:
  We have analyzed the full set of SOHO/MDI f- and p-mode oscillation
frequencies from 1996 to date in a search for evidence of solar radius
evolution during the rising phase of the current activity cycle. Like Antia et
al. (2000), we find that a significant fraction of the f-mode frequency changes
scale with frequency; and that if these are interpreted in terms of a radius
change, it implies a shrinking sun. Our inferred rate of shrinkage is about 1.5
km/y, which is somewhat smaller than found by Antia et al. We argue that this
rate does not refer to the surface, but rather to a layer extending roughly
from 4 to 8 Mm beneath the visible surface. The rate of shrinking may be
accounted for by an increasing radial component of the rms random magnetic
field at a rate that depends on its radial distribution. If it were uniform,
the required field would be ~7 kG. However, if it were inwardly increasing,
then a 1 kG field at 8 Mm would suffice.
  To assess contribution to the solar radius change arising above 4Mm, we
analyzed the p-mode data. The evolution of the p-mode frequencies may be
explained by a magnetic^M field growing with activity. The implications of the
near-surface magnetic field changes depend on the anisotropy of the random
magnetic field. If the field change is predominantly radial, then we infer an
additional shrinking at a rate between 1.1-1.3 km/y at the photosphere. If on
the other hand the increase is isotropic, we find a competing expansion at a
rate of 2.3 km/y. In any case, variations in the sun's radius in the activity
cycle are at the level of 10^{-5} or less, hence have a negligible contribution
to the irradiance variations.


title:
Simultaneous Measurements of the Fried Parameter r_0 and the Isoplanatic
  Angle theta_0 using SCIDAR and Adaptive Optics - First Results

abstract:
  We present first results of a simultaneous atmospheric turbulence measurement
campaign at the Calar Alto (Spain) 1.23m and 3.5m telescopes. A SCIDAR
instrument and the Calar Alto Adaptive Optics system ALFA were used at the
1.23m and 3.5m telescopes respectively to determine essential turbulence
parameters like the Fried parameter r_0, the isoplanatic angle theta_0, and, in
the case of SCIDAR, the C_n^2 profile of the atmosphere. Both closed-loop and
open-loop data were obtained with ALFA. The desired parameters were then
calculated from this. This paper shows a comparison of the results obtained
from the two different systems for several times during a period of three
nights.


title: Do LINER 2 galaxies harbour low-luminosity Active Galactic Nuclei?

abstract:
  We use ROSAT HRI spatial data and ASCA spectral measurements for a sample of
seven nearby, early type spiral galaxies, to address the question of whether a
low-luminosity Active Galactic Nucleus (LLAGN) is present in galaxies that have
a LINER 2 classification. The brightest discrete X-ray source in the ROAST HRI
observations is invariably found to be positionally coincident with the optical
galactic nucleus, and in most cases its flux dominates the X-ray emission from
the central region of the galaxy. All seven galaxies have X-ray spectra
consistent with a two-component, soft thermal plus hard power-law, spectral
form. If we exclude the two galaxies with relatively hard X-ray spectra, NGC
3628 and NGC 4594, for which there is supporting evidence for a LLAGN (or
alternatively in the case of NGC 3628 a dominant ultra-luminous X-ray binary),
then the remaining galaxies show surprisingly similar X-ray spectral
properties. Specifically the flux ratio F_x(0.5-1)/F_x(2-5), which measures the
relative strengths of the thermal and non-thermal emission components, shows
little scatter about a mean of 0.66, a value very similar to that measured in
the classic starburst galaxy NGC 253. Since there is no obvious reason why the
luminosity of the hard power-law continuum emanating from a putative LLAGN
should be very closely correlated with the thermal emission of the surrounding
region, this suggests that that the broad-band (0.5-5 keV) X-ray emission from
these LINER 2 galaxies may originate in a common set of processes probably
associated with the starburst phenomenon. Conversely, it appears that in many,
perhaps the majority, of LINER 2 galaxies, the nuclear X-ray luminosity does
not derive directly from the presence of a LLAGN.


title: Element Synthesis in Stars

abstract:
  Except for 1H, 2H, 3He, 4He, and 7Li, originating from the Big Bang, all
heavier elements are made in stellar evolution and stellar explosions. Nuclear
physics, and in many cases nuclear structure far from stability, enters in a
crucial way. Therefore, we examine in this review the role of nuclear physics
in astrophysics in general and in particular how it affects stellar events and
the resulting nucleosynthesis. Stellar modeling addresses four major aspects:
1. energy generation and nucleosynthesis, 2. energy transport via conduction,
radiation or possibly convection, 3. hydrodynamics/hydrostatics, and finally 4.
thermodynamic properties of the matter involved. Nuclear Physics enters via
nuclear reaction cross sections and nuclear structure (affecting the
composition changes and nuclear energy generation), neutrino-nucleon and
neutrino-nucleus cross sections (affecting neutrino opacities and transport),
and e.g. the equation of state at and beyond nuclear densities which creates a
relation between the nuclear many-body problem and the hydrodynamic response
like pressure and entropy. In the following we review these four topics by
highlighting the role and impact of nuclear physics in each of these aspects of
stellar modeling. The main emphasis is put on the connection to element
synthesis.


title:
Models of circumstellar molecular radio line emission: Mass loss rates
  for a sample of bright carbon stars

abstract:
  Using a detailed radiative transfer analysis, combined with an energy balance
equation for the gas, we have performed extensive modelling of circumstellar CO
radio line emission from a large sample of optically bright carbon stars. We
determine some of the basic parameters that characterize circumstellar
envelopes (CSEs), e.g., the stellar mass loss rate, the gas expansion velocity,
and the kinetic temperature structure of the gas.
  The derived mass loss rates span almost four orders of magnitude, from 5E-9
up to 2E-5 solar masses per year, with the median mass loss rate being 3E-7
solar masses per year. We estimate that the estimated mass loss rates are
typically accurate to 50% within the adopted circumstellar model. The physical
conditions prevailing in the CSEs vary considerably over such a large range of
mass loss rates. Among other things, it appears that the dust-to-gas mass ratio
and/or the dust properties change with the mass loss rate. We find that the
mass loss rate and the gas expansion velocity are well correlated, and that
both of them clearly depend on the pulsational period and (with larger scatter)
the stellar luminosity. Moreover, the mass loss rate correlates weakly with the
stellar effective temperature, in the sense that the cooler stars tend to have
higher mass loss rates, but there seems to be no correlation with the stellar
C/O-ratio. We conclude that the mass loss rate increases with increased regular
pulsation and/or luminosity, and that the expansion velocity increases as an
effect of increasing mass loss rate (for low mass loss rates) and luminosity.


title: Chandra detection of the intracluster medium around 3C294 at z=1.786

abstract:
  We present a Chandra observation of the powerful radio galaxy 3C294 showing
clear evidence for a surrounding intracluster medium. At a redshift of 1.786
this is the most distant cluster of galaxies yet detected in X-rays. The radio
core is detected as a point source, which has a spectrum consistent with a
heavily-absorbed power law implying an intrinsic 2-10 keV luminosity of ~10^45
erg/s. A small excess of emission is associated with the southern radio
hotspots. The soft, diffuse emission from the intracluster medium is centred on
the radio source. It has an hour-glass shape in the N-S direction, extending to
radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of
this extended component is fit by a thermal model with temperature ~5 keV, or
by gas cooling from above 7 keV at rates of ~400-700 Msolar/yr. The rest-frame
0.3-10 keV luminosity of the cluster is ~4.5x10^44 erg/s. The existence of such
a cluster is consistent with a low density universe.


title: How to Correct for Dust Absorption in Starbursts

abstract:
  We review new and published results to examine how well the bolometric flux
of starbursts can be recovered from ultraviolet (UV) and optical observations.
We show that the effective absorption of starbursts can be substantial, up to
\~10 mag in the far UV, and ~5 mag in H-alpha, but apparently not as high as
some claims in the literature (several tens to a thousand mag). The bolometric
fluxes of an IUE sample of starbursts can be recovered to 0.14 dex accuracy
using the UV flux and spectral slope. However, this relationship breaks down
for Ultra Luminous Infrared Galaxies (ULIGs). The H-alpha flux combined with
the Balmer decrement can be used to predict the bolometric flux to 0.5 dex
accuracy for starbursts including most ULIGs. These results imply a foreground
screen component to the dust distribution.


title: Starbursts, Dark Matter and Dwarf Galaxy Evolution

abstract:
  Optical and HI imaging of both dwarf irregular (dI) and Blue Compact Dwarf
(BCD) galaxies reveal important clues on how dwarf galaxies evolve and their
star formation is regulated. Both usually show evidence for stellar and gaseous
disks. However, their total mass is dominated by dark matter. Gas rich dwarfs
form with a range of disk structural properties. These have been arbitrarily
separated them into two classes on the basis of central surface brightness.
Dwarfs with mu_{0}(B) > ~22 mag arcsec^{-2} are usually classified as BCDs,
while those fainter than limit are usually classified as dIs. Both classes
experience bursts of star formation, but with an absolute intensity correlated
with the disk surface brightness. Even in BCDs the bursts typically represent
only a modest < ~1 mag enhancement to the B luminosity of the disk. While
starbursts are observed to power significant galactic winds, the fractional ISM
loss remains modest. Dark matter halos play an important role in determining
dwarf galaxy morphology by setting the equilibrium surface brightness of the
disk.


title: A Dark-Matter Spike at the Galactic Center?

abstract:
  The past growth of the central black hole (BH) might have enhanced the
density of cold dark matter halo particles at the Galactic center. We compute
this effect in realistic growth models of the present (2-3)*10**6 solar mass BH
from a low-mass seed BH, with special attention to dynamical modeling in a
realistic galaxy environment with merger and orbital decay of a seed BH formed
generally outside the exact center of the halo. An intriguing ``very-dense
spike'' of dark matter has been claimed in models of Gondolo and Silk with
density high enough to contradict with experimental upper bounds of neutralino
annihilation radiation. This ``spike'' disappears completely or is greatly
weakened when we include important dynamical processes neglected in their
idealized/restrictive picture with cold particles surrounding an at-the-center
zero-seed adiabaticly-growing BH. For the seed BH to spiral in and settle to
the center within a Hubble time by dynamical friction, the seed mass must be at
least a significant fraction of the present BH. Any subsequent at-the-center
growth of the BH and steepening of the central Keplerian potential well can
squeeze the halo density distribution only mildly, whether the squeezing
happens adiabatically or instantaneously.


title: Extreme Starbursts and Molecular Clouds in Galaxies

abstract:
  The extraordinary starbursts found in ultraluminous IR galaxies occur in
molecular gas concentrated in compact very massive "clouds" which we call
"Extreme Starbursts". They have one thousand times the mass but are only a few
times larger than GMCs. High-mass star formation in sufficiently dense and
massive structures does not disrupt further star formation; it is a runaway
process. Star formation remains embedded in the molecular gas and there is
little or virtually no optical-UV radiation. In the early universe extreme
starbursts may be more frequent and they may be the mode of star formation in
high redshift submillimeter sources.


title: Polarimetric VLBI observations of 0735+178

abstract:
  We present a new centimeter polarimetric VLBI image of the BL Lac object
0735+178. This source exhibits one of the most pronounced curvatures observed
in jets of AGNs, with two sharp apparent bends of 90 degrees within the inner 2
milliarcseconds from the core. Through the analysis of the data gathered over
the past decades we study whether this curvature is produced by precession of
the jet with ejection of ballistic components, or a precession in such a way
that components' velocity vector are always parallel to the jet axis. These
possibilities are also studied by comparison with 3D hydrodynamic relativistic
simulations of precessing jets.


title: How dominant is the vacuum?

abstract:
  It would be hard to find a cosmologist today who does not believe that the
vast bulk of the Universe (ninety-five percent or more) is hidden from our
eyes. We review the evidence for this remarkable consensus, and for the latest
proposal, that the mysterious dark matter consists of as many as {\em four
separate ingredients}: baryons, massive neutrinos, ``exotic'' dark matter
particles, and vacuum energy, also known as the cosmological constant (Lambda).
Of these, only baryons fit within standard theoretical physics; the others, if
their existence is confirmed, will mean rewriting textbooks. New experimental
evidence has recently appeared for and against all four components, so that the
subject is in a state of turmoil and excitement. The past three years in
particular have seen the fourth (vacuum) component come into new prominence,
largely at the expense of the third (exotic dark matter). We conclude our
review by exploring the possibility that the energy density of the vacuum is in
fact so dominant as to leave little room for significant amounts of exotic dark
matter.


title: The White Dwarf Distance to the Globular Cluster 47 Tucanae and its Age

abstract:
  We present a new determination of the distance (and age) of the Galactic
globular cluster 47 Tucanae (NGC 104) based on the fit of its white dwarf (WD)
cooling sequence with the empirical fiducial sequence of local WD with known
trigonometric parallax, following the method described in Renzini et al.
(1996). Both the cluster and the local WDs were imaged with HST+WFPC2 using the
same instrument setup. We obtained an apparent distance modulus of
$(m-M)_V=13.27\pm0.14$ consistent with previous ground-based determinations and
shorter than that found using HIPPARCOS subdwarfs. Coupling our distance
determination with a new measure of the apparent magnitude of the main sequence
turnoff, based on our HST data, we derive an age of $13\pm2.5$ Gyr.


title: Circumstellar Disks in the IC 348 Cluster

abstract:
  We report the results of the first sensitive L-band (3.4 micron) imaging
survey of the young IC 348 cluster in Perseus. In conjunction with previously
acquired JHK (1.25, 1.65, 2.2 micron) observations, we use L-band data to
obtain a census of the circumstellar disk population to m_K=m_L<=12.0 in the
central 110 square arcmin region of the cluster. An analysis of the JHKL colors
of 107 sources indicates that 65% +/- 8% of the cluster membership possesses
(inner) disks. This fraction is lower than those (86% +/- 8% and 80% +/- 7%)
obtained from similar JHKL surveys of the younger NGC 2024 and Trapezium
clusters, suggesting that the disk fraction in clusters decreases with cluster
age. Sources with circumstellar disks in IC 348 have a median age of 0.9 Myr,
while the diskless sources have a median age of 1.4 Myr, for a cluster distance
of 320 pc. Although the difference in the median ages between the two
populations is only marginally significant, our results suggest that over a
timescale of 2 - 3 Myr, more than a third of the disks in the IC 348 cluster
disappear. Moreover, we find that at a very high confidence level, the disk
fraction is a function of spectral type. All stars earlier than G appear
diskless, while stars with spectral types G and later have a disk fraction
ranging between 50% - 67%, with the latest type stars having the higher disk
fraction. This suggests that the disks around stars with spectral types G and
earlier have evolved more rapidly than those with later spectral types. The
L-band disk fraction for sources with similar ages in both IC 348 and Taurus is
the same, within the errors, suggesting that, at least in clusters with no O
stars, the disk lifetime is independent of environment.


title:
Detection of [N II] 5755 Emission from Low Density Ionized Interstellar
  Gas

abstract:
  The extremely faint, temperature sensitive ``auroral'' emission line [N II]
5755 has been detected from the low density ionized gas along the sight line
toward l = 130.0, b = -7.5 using the Wisconsin H-Alpha Mapper (WHAM). The
intensity of this emission line, relative to the red nebular line [N II] 6584,
is found to be twice that observed in bright, classical H II regions
surrounding O stars. This implies that the electron temperature of the ionized
gas along this sight line is about 2000 K higher than the H II regions, and
that the enhanced [N II] 6584/H-Alpha and [S II] 6716/H-Alpha intensity ratios
in this low density gas are due at least in part to an elevated temperature.


title:
Limits on the cosmological abundance of supermassive compact objects
  from a millilensing search in gamma-ray burst data

abstract:
  A new search for the gravitational lens effects of a significant cosmological
density of supermassive compact objects (SCOs) on gamma-ray bursts has yielded
a null result. We inspected the timing data of 774 BATSE-triggered GRBs for
evidence of millilensing: repeated peaks similar in light-curve shape and
spectra. Our null detection leads us to conclude that, in all candidate
universes simulated, $\Omega_{SCO} < 0.1$ is favored for $10^5 <
M_{SCO}/M_{\odot} < 10^9$, while in some universes and mass ranges the density
limits are as much as 10 times lower. Therefore, a cosmologically significant
population of SCOs near globular cluster mass neither came out of the
primordial universe, nor condensed at recombination.


title:
Properties of Galaxy Disks in Hierarchical Hydrodynamical Simulations:
  Comparison with Observational Data

abstract:
  We analyze the structural and dynamical properties of disk-like objects
formed in fully consistent cosmological simulations with an inefficient star
formation algorithm. Comparison with data of similar observable properties of
spiral galaxies gives satisfactory agreement.


title:
Comparison between Disk-like Objects Formed in Hierarchical
  Hydrodynamical Simulations and Observations of Spiral Galaxies

abstract:
  We analyze the structural and dynamical properties of disk-like objects
formed in fully consistent cosmological simulations which include inefficient
star formation. Comparison with data of similar observable properties of spiral
galaxies gives satisfactory agreement, in contrast with previous findings using
other codes. This suggests that the stellar formation implementation used has
allowed the formation of disks as well as guaranteed their stability.


title: The FORS Deep Field

abstract:
  Dedicating a major fraction of its guaranteed time, the FORS consortium
established a FORS Deep Field which contains a known QSO at z = 3.36. It was
imaged in UBgRIz with FORS at the VLT as well as in J and Ks with the NTT.
Covering an area 6-8 times larger as the HDFs but with similar depth in the
optical it is one of the largest deep fields up to date to investigate i)
galaxy evolution in the field from present up to z $\sim$ 5, ii) the galaxy
distribution in the line of sight to the QSO, iii) the high-z QSO environment
and iv) the galaxy-galaxy lensing signal in such a large field. In this
presentation a status report of the FORS Deep Field project is given. In
particular, the field selection, the imaging results (number counts,
photometric redshifts etc.) and the first spectroscopic results are presented.


title:
Dynamos in Asymptotic-Giant-Branch Stars As the Origin of Magnetic
  Fields Shaping Planetary Nebulale

abstract:
  Planetary nebulae are thought to be formed when a slow wind from the
progenitor giant star is overtaken by a subsequent fast wind generated as the
star enters its white dwarf stage$^{1}$. A shock forms near the boundary
between the winds, which creates a relatively dense shell that provides the
characteristic appearance of a planetary nebula. A spherically symmetric wind
will produce a spherically symmetric shell, yet over half of known planetary
nebulae are not spherical; rather, they are elliptical or bipolar in
shape$^{2}$. While a magnetic field could launch and collimate a bipolar
outflow, the origin of such a field has hitherto been unclear, as previous work
suggested that a field could not be generated${^3}$. Here we show that an
asymptotic-giant-branch (AGB) star can indeed generate a strong magnetic field,
in a dynamo at the interface between a rapidly rotating core and the more
slowly rotating envelope of the star. The field is strong enough to shape the
bipolar outflows that produce the observed bipolar planetary nebulae. Magnetic
braking of the stellar core during this process may also explain the
puzzlingly$^{4}$ slow rotation of most white dwarf stars.


title:
Multicolor Photometry of the Uranus Irregular Satellites Sycorax and
  Caliban

abstract:
  We report on accurate BVRI photometry for the two Uranus irregular satellites
Sycorax and Caliban. We derive colours, showing that
  Sycorax is bluer than Caliban. Our data allows us to detect a significant
variability in the Caliban's light-curve, which suggests an estimated period of
about 3 hours. Despite it is the brighter of the two bodies, Sycorax does not
display a strong statistically significant variability. However our data seem
to suggest a period of about 4 hours


title:
The Chandra Deep Survey of the Hubble Deep Field North Area. II. Results
  from the Caltech Faint Field Galaxy Redshift Survey Area

abstract:
  We present results from a 221.9 ks Chandra exposure of the HDF-N and its
vicinity, concentrating on the 8.6' X 8.7' area covered by the Caltech Faint
Field Galaxy Redshift Survey (the `Caltech area'). The minimum detectable
fluxes in the 0.5-2 keV and 2-8 keV bands are 1.3e-16 cgs and 6.5e-16 cgs,
respectively and a total of 82 sources are detected. More than 80% of the
extragalactic X-ray background in the 2-8 keV band is resolved. Redshifts are
available for 96% of the sources with R<23; the redshift range is 0.1-3.5 with
most sources having z < 1.5. Eight of the X-ray sources are located in the
HDF-N itself, including two not previously reported. A population of X-ray
faint, optically bright, nearby galaxies emerges at soft-band fluxes of ~<
3e-16 cgs.
  We set the tightest constraints to date on the X-ray emission properties of
microJy radio sources, mid-infrared sources detected by ISO, and very red
(R-K_s > 5.0) objects. Where both the infrared and the X-ray coverage are
deepest, 75% of the X-ray sources are detected by ISO; the high X-ray to
infrared matching rate bodes well for future sensitive infrared observations of
faint X-ray sources. Four of the 33 very red objects that have been identified
in the Caltech area by Hogg et al. (2000) are detected in X-rays; these four
are among our hardest Chandra sources, and we argue that they contain
moderately luminous obscured AGN. Overall, however, the small Chandra detection
fraction suggests a relatively small AGN content in the optically selected very
red object population. (Abridged)


title:
X-Ray Observations of Low-Mass X-Ray Binaries: Accretion Instabilities
  on Long and Short Time-Scales

abstract:
  X-rays trace accretion onto compact objects in binaries with low mass
companions at rates ranging up to near Eddington. Accretion at high rates onto
neutron stars goes through cycles with time-scales of days to months. At lower
average rates the sources are recurrent transients; after months to years of
quiescence, during a few weeks some part of a disk dumps onto the neutron star.
Quasiperiodic oscillations near 1 kHz in the persistent X-ray flux attest to
circular motion close to the surface of the neutron star. The neutron stars are
probably inside their innermost stable circular orbits and the x-ray
oscillations reflect the structure of that region. The long term variations
show us the phenomena for a range of accretion rates. For black hole compact
objects in the binary, the disk flow tends to be in the transient regime.
Again, at high rates of flow from the disk to the black hole there are
quasiperiodic oscillations in the frequency range expected for the innermost
part of an accretion disk. There are differences between the neutron star and
black hole systems, such as two oscillation frequencies versus one. For both
types of compact object there are strong oscillations below 100 Hz.
Interpretations differ on the role of the nature of the compact object.


title:
A first EGRET-UNID-related agenda for the next-generation Cherenkov
  telescopes

abstract:
  The next generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) will
open the regime between approx. 30 GeV and 200 GeV to ground-based gamma
observations with unprecedented point source sensitivity and source location
accuracy. I examine the prospects of observing the unidentified objects (UNIDs)
of the Third EGRET Catalog using the IACT observatories currently under
construction by the CANGAROO, HESS, MAGIC and VERITAS collaborations. Assuming
a modest spectral steepening similar to that observed in the inverse Compton
component of the Crab Nebula spectrum and taking into account the sensitivity
of the instruments and its zenith angle dependence, a detailed list of 78
observable objects is derived which is then further constrained to 38 prime
candidates. The characteristics of this agenda are discussed.


title:
Infrared Line Emission in the Interacting Region of Arp 244 (the
  Antennae): Colliding Molecular Cloud Complexes ?

abstract:
  We report velocity-resolved spectroscopy of infrared hydrogen recombination
lines in the interacting region of the Antennae galaxies (NGC 4038/4039). It
generally has been assumed that the active star formation found there is due to
the interaction of the disks of the two galaxies and indeed two molecular cloud
complexes, separated in velocity by $\sim$100 km s$^{-1}$, have been observed
in the southern part of this region. Our measurements imply that the two cloud
complexes are moving away from each other. This result poses interesting
questions about the physical mechanisms leading to starbursts in Arp 244 and
other interacting galaxies.


title:
Electrodynamic Structure of an Outer Gap Accelerator: Location of the
  Gap and the Gamma-ray Emission from the Crab Pulsar

abstract:
  We investigate a stationary pair production cascade in the outer
magnetosphere of a spinning neutron star. The charge depletion due to global
flows of charged particles, causes a large electric field along the magnetic
field lines. Migratory electrons and/or positrons are accelerated by this field
to radiate curvature gamma-rays, some of which collide with the X-rays to
materialize as pairs in the gap. The replenished charges partially screen the
electric field, which is self-consistently solved together with the
distribution functions of particles and gamma-rays. If no current is injected
at neither of the boundaries of the accelerator, the gap is located around the
conventional null surface, where the local Goldreich-Julian charge density
vanishes. However, we first find that the gap position shifts outwards (or
inwards) when particles are injected at the inner (or outer) boundary. Applying
the theory to the Crab pulsar, we demonstrate that the pulsed TeV flux does not
exceed the observational upper limit for moderate infrared photon density and
that the gap should be located near to or outside of the conventional null
surface so that the observed spectrum of pulsed GeV fluxes may be emitted via a
curvature process. Some implications of the existence of a solution for a super
Goldreich-Julian current are discussed.


title: Nonlinear Peculiar-Velocity Analysis and PCA

abstract:
  We allow for nonlinear effects in the likelihood analysis of peculiar
velocities, and obtain ~35%-lower values for the cosmological density parameter
and for the amplitude of mass-density fluctuations. The power spectrum in the
linear regime is assumed to be of the flat LCDM model (h=0.65, n=1) with only
Om_m free. Since the likelihood is driven by the nonlinear regime, we "break"
the power spectrum at k_b=0.2 h/Mpc and fit a two-parameter power-law at k>k_b.
This allows for an unbiased fit in the linear regime. Tests using improved mock
catalogs demonstrate a reduced bias and a better fit. We find for the Mark III
and SFI data Om_m=0.35+-0.09$ with sigma_8*Om_m^0.6=0.55+-0.10 (90% errors).
When allowing deviations from \lcdm, we find an indication for a wiggle in the
power spectrum in the form of an excess near k~0.05 and a deficiency at k~0.1
h/Mpc --- a "cold flow" which may be related to a feature indicated from
redshift surveys and the second peak in the CMB anisotropy. A chi^2 test
applied to principal modes demonstrates that the nonlinear procedure improves
the goodness of fit. The Principal Component Analysis (PCA) helps identifying
spatial features of the data and fine-tuning the theoretical and error models.
We address the potential for optimal data compression using PCA.


title: Linear perturbations in a universe with a cosmological constant

abstract:
  There are now evidences that the cosmological constant $\Lambda$ has a
non-zero positive value. Alternative scenarios to a pure cosmological constant
model are provided by quintessence, an effective negative pressure fluid
permeating the universe. Recent results indicate that the energy density $\rho$
and the pressure $p$ of this fluid are constrained by $-\rho\leq p
\buildrel<\over\sim-0.6 \rho$. Since $p=-\rho$ is equivalent to the pure
cosmological constant model, it is appropriate to analyze this particular, but
important, case further. We study the linear theory of perturbations in a
Friedmann-Robertson-Walker universe with a cosmological constant. We obtain the
equations for the evolution of the perturbations in the fully relativistic
case, for which we analyze the single-fluid and the two-fluid cases. We obtain
solutions to these equations in appropriate limits. We also study the Newtonian
approximation. We find that for a positive cosmological constant universe (i)
the perturbations will grow slower in the relativistic regime for a two-fluid
composed of dark matter and radiation, and (ii) in the Newtonian regime, the
perturbations stop growing.


title: Nonlinear Outcome of Gravitational Instability in Cooling, Gaseous Disks

abstract:
  Thin, Keplerian accretion disks generically become gravitationally unstable
at large radius. I investigate the nonlinear outcome of such instability in
cool disks using razor-thin, local, numerical models. Cooling, characterized by
a constant cooling time t_c, drives the instability. I show analytically that,
if the disk can reach a steady state in which heating by dissipation of
turbulence balances cooling, then the dimensionless angular momentum flux
density \alpha = ((9/4) \gamma (\gamma-1) \Omega t_c)^{-1}. Numerical
experiments show that: (1) if t_c \gtrsim 3\Omega^{-1} then the disk reaches a
steady, gravito-turbulent state in which Q \sim 1 and cooling is balanced by
heating due to dissipation of turbulence; (2) if t_c \lesssim 3\Omega^{-1},
then the disk fragments, possibly forming planets or stars; (3) in a steady,
gravito-turbulent state, surface density structures have a characteristic
physical scale \sim 64 G \Sigma/\Omega^2 that is independent of the size of the
computational domain.


title: Red synchrotron jets in Parkes quasars

abstract:
  We present model fits to spectral energy distributions in the optical and NIR
of >100 flat-spectrum radio quasars from the Parkes Half-Jansky Flat-spectrum
Sample. We find that approximately 40% of the sources have power-law SEDs,
while a similar number show evidence for two primary components: a blue power
law and optical synchrotron emission. The blue power law is similar to the
dominant component observed in the spectra of optically-selected QSOs. There is
strong evidence that the synchrotron component has a turnover in the UV-optical
rest frame of the spectrum. In the remaining sources it is likely that the
synchrotron peaks at longer wavelengths. This mixture of two components is
supported by optical polarisation measurements in a subgroup of the sources.
The sources with power law SEDs show evidence for an excess number of red power
law slopes compared to optically-selected quasars. There are additional
spectral components in some of the sources, such as dust and the underlying
galaxy, which have not been considered here.


title: Correlation and clustering

abstract:
  In this lecture we clarify the basic difference between the correlation
properties for systems characterized by small or large fluctuations. The
concepts of correlation length, homogeneity scale, scale invariance and
criticality are discussed as well. We relate these concepts to the
interpretation of galaxy clsutering.


title: Radial Oscillations of Neutron Stars in Strong Magnetic Fields

abstract:
  The eigen frequencies of radial pulsations of neutron stars are calculated in
a strong magnetic field. At low densities we use the magnetic BPS equation of
state(EOS) similar to that obtained by Lai and Shapiro while at high densities
the EOS obtained from the relativistic nuclear mean field theory is taken and
extended to include strong magnetic field. It is found that magnetised neutron
stars support higher maximum mass where as the effect of magnetic field on
radial stability for observed neutron star masses is minimal.


title: Spectral Properties of a Sample of Low Luminosity Type I X-ray Bursters

abstract:
  I report on a sample of new type I X-ray bursters, firstly detected with the
Wide Field Cameras on board BeppoSAX and then studied with the Narrow Field
Instruments on a broad spectral range (0.1-200 keV). Properties of the
transient/persistent emission are summarized and the broad band X-ray spectra
discussed in detail for a few sources.


title:
Radio jets and diffuse X-ray emission around the peculiar galaxy pair
  ESO 295-IG022

abstract:
  We report Australia Telescope Compact Array (ATCA) radio-continuum and ROSAT
PSPC X-ray observations of the region surrounding the peculiar galaxy pair ESO
295-IG022, lying at the centre of the poor cluster Abell S0102. We identify a
radio galaxy coincident with the galaxy pair, with bipolar, bent radio jets
appearing centred on the southern galaxy, and extending both to the south, for
about 95 arcseconds (approximately 100 kpc at the distance of ESO 295-IG022),
and to the north, for approximately 80 arcseconds, encompassing the northern
galaxy. We discuss also the idea of an additional single jet structure from the
northern galaxy contributing to the emission. We estimate lower limit jet
velocities of at least 1000 km/s, and a relative proper velocity for the
southern galaxy through the cluster of around 200 km/s. Diffuse (kT=2.2 keV)
X-ray emission consistent with group or poor cluster emission is seen centred
on the southern galaxy surrounding the galaxy pair and the associated radio
jets. Structure within the radio jets and the X-ray emission is very suggestive
of there being some channeling of the radio emission with the surrounding
intragroup medium. Another bipolar jet radio galaxy, discovered close by, is
likely to be a background object, the optical counterpart having a magnitude
greater than m=22.


title: Eternal Inflation

abstract:
  The basic workings of inflationary models are summarized, along with the
arguments that strongly suggest that our universe is the product of inflation.
It is argued that essentially all inflationary models lead to (future-)eternal
inflation, which implies that an infinite number of pocket universes are
produced. Although the other pocket universes are unobservable, their existence
nonetheless has consequences for the way that we evaluate theories and extract
consequences from them. The question of whether the universe had a beginning is
discussed but not definitively answered. It appears likely, however, that
eternally inflating universes do require a beginning.


title: The Structure of Prestellar Cores as derived from ISO Observations

abstract:
  Observations of dark cloud cores have been carried out in the mid-infrared
using ISOCAM and in the far-infrared using ISOPHOT, both aboard the Infrared
Space Observatory. The cores are in most cases detected in emission at 200 and
170 micron, remain undetected at 90 micron and are seen in absorption against
the diffuse mid-infrared background at 7 micron. The observations are
consistent with the cores being pre-stellar and not having a central heating
source, and yield core temperatures of ~ 11-13 K. We were able to determine the
density structure of the cores up to radii that extend beyond the sensitivity
limit of previous submillimetre studies. The column density profiles of the
cores studied here flatten out in the centre, as shown by previous
submillimetre continuum results, and interestingly, in a few cases, the
profiles steepen with radius beyond ~ 5000-10000 AU and present sharp edges.
This could indicate that these cores are decoupled from their parent molecular
cloud and represent finite reservoirs of mass for subsequent accretion.


title: Mass-loss predictions for O and B stars as a function of metallicity

abstract:
  We have calculated a grid of massive star wind models and mass-loss rates for
a wide range of metal abundances between 1/100 and 10 Z/Zsun.
  The calculation of this grid completes the Vink et al. (2000) mass-loss
recipe with an additional parameter Z. We have found that the exponent of the
power law dependence of mass loss vs. metallicity is constant in the range
between 1/30 and 3 Z/Zsun. The mass-loss rate scales as Mdot \propto Z^0.85
Vinf^p with p = -1.23 for stars with Teff \ga 25000 K, and p = -1.60 for the B
supergiants with Teff \la 25000 K. Taking also into account the metallicity
dependence of Vinf, using the power law dependence Vinf \propto Z^0.13 from
Leitherer et al. (1992), the overall result of mass loss as a function of
metallicity can be represented by Mdot \propto Z^0.69 for stars with Teff \ga
25000 K, and Mdot \propto Z^0.64 for B supergiants with Teff \la 25000 K.
  Our mass-loss predictions are successful in explaining the observed mass-loss
rates for Galactic and Small Magellanic Cloud O-type stars, as well as in
predicting the observed Galactic bi-stability jump. Hence, we believe that our
predictions are reliable and suggest that our mass-loss recipe be used in
future evolutionary calculations of massive stars at different metal abundance.
A computer routine to calculate mass loss is publicly available.


title:
A Useful Approximation for Computing the Continuum Polarization of Be
  Stars

abstract:
  This paper describes a practical model for the polarization of Be stars which
can be used to estimate roughly the physical parameters for optically thin
circumstellar envelopes from broadband UBVRI photopolarimetry data. Analysis of
long-term variability in terms of these parameters is a promising approach
toward understanding the Be phenomenon. An interesting result from fitting the
model to observations of eight Be stars is that all of them may have
geometrically thin disks, with opening half-angles on the order of ten degrees
or less. This contributes to the growing evidence that most Be disks are
geometrically thin.


title: Cosmic Shear Statistics and Cosmology

abstract:
  We report a measurement of cosmic shear correlations using an effective area
of 6.5 sq. deg. of the VIRMOS deep imaging survey in progress at the
Canada-France-Hawaii Telescope. We measured various shear correlation
functions, the aperture mass statistic and the top-hat smoothed variance of the
shear with a detection significance exceeding 12 sigma for each of them. We
present results on angular scales from 3 arc-seconds to half a degree. The
consistency of different statistical measures is demonstrated and confirms the
lensing origin of the signal through tests that rely on the scalar nature of
the gravitational potential. For Cold Dark Matter models we find $\sigma_8
\Omega_0^{0.6}=0.43^{+0.04}_{-0.05}$ at the 95% confidence level. The
measurement over almost three decades of scale allows to discuss the effect of
the shape of the power spectrum on the cosmological parameter estimation. The
degeneracy on sigma_8-Omega_0 can be broken if priors on the shape of the
linear power spectrum (that can be parameterized by Gamma) are assumed. For
instance, with Gamma=0.21 and at the 95% confidence level, we obtain
0.6<sigma_8<1.1 and 0.2<Omega_0<0.5 for open models, and sigma_8>0.65 and
Omega_0<0.4 for flat (Lambda-CDM) models. From the tangential/radial modes
decomposition we can set an upper limit on the intrinsic shape alignment, which
was recently suggested as a possible contribution to the lensing signal. Within
the error bars, there is no detection of intrinsic shape alignment for scales
larger than 1'.


title: Generating non-Gaussian maps with a given power spectrum and bispectrum

abstract:
  We propose two methods for generating non-Gaussian maps with fixed power
spectrum and bispectrum. The first makes use of a recently proposed rigorous,
non-perturbative, Bayesian framework for generating non-Gaussian distributions.
The second uses a simple superposition of Gaussian distributions. The former is
best suited for generating mildly non-Gaussian maps, and we discuss in detail
the limitations of this method. The latter is better suited for the opposite
situation, i.e. generating strongly non-Gaussian maps. The ensembles produced
are isotropic and the power spectrum can be jointly fixed; however we cannot
set to zero all other higher order cumulants (an unavoidable mathematical
obstruction). We briefly quantify the leakage into higher order moments present
in our method. We finally present an implementation of our code within the
HEALPIX package


title: Roche tomography of cataclysmic variables: I. artefacts and techniques

abstract:
  Roche tomography is a technique used for imaging the Roche-lobe filling
secondary stars in cataclysmic variables (CVs). In order to interpret Roche
tomograms correctly, one must determine whether features in the reconstruction
are real, or due to statistical or systematic errors. We explore the effects of
systematic errors using reconstructions of simulated datasets and show that
systematic errors result in characteristic distortions of the final
reconstructions that can be identified and corrected. In addition, we present a
new method of estimating statistical errors on tomographic reconstructions
using a Monte-Carlo bootstrapping algorithm and show this method to be much
more reliable than Monte-Carlo methods which `jiggle' the data points in
accordance with the size of their error bars.


title: Neutrino Cooling of Neutron Stars. Medium effects

abstract:
  This review demonstrates that neutrino emission from dense hadronic component
in neutron stars is subject of strong modifications due to collective effects
in the nuclear matter. With the most important in-medium processes incorporated
in the cooling code an overall agreement with available soft X ray data can be
easily achieved. With these findings so called "standard" and "non-standard"
cooling scenarios are replaced by one general "nuclear medium cooling scenario"
which relates slow and rapid neutron star coolings to the star masses (interior
densities). In-medium effects take important part also at early hot stage of
neutron star evolution decreasing the neutrino opacity for less massive and
increasing for more massive neutron stars. A formalism for calculation of
neutrino radiation from nuclear matter is presented that treats on equal
footing one-nucleon and multiple-nucleon processes as well as reactions with
resonance bosons and condensates. Cooling history of neutron stars with quark
cores is also discussed.


title: Primordial Black Holes and Hot Matter

abstract:
  Microscopic black holes explode with their temperature varying inversely as
their mass. Such explosions would lead to the highest temperatures in the
present universe, all the way to the Planck energy. The possibility that a
quasi-stationary shell of hot matter surrounds these black holes has recently
been proposed and studied with relativistic Boltzmann transport equations and
with relativistic viscous fluid dynamics. For example, a black hole with a mass
of 10$^{10}$ g has a Hawking temperature of 1 TeV, a Schwarszchild radius of
1.6$\times10^{-5}$ fm, a luminosity of 7$\times10^{27}$ erg/s, and has less
than 8 minutes to live. It is an outstanding theoretical challenge to describe
the conditions exterior to such microscopic black holes and a great challenge
to finally detect them in the new millennium.


title: Quark-Gluon Plasma in the Early Universe

abstract:
  A QCD phase transition in the early universe could have left inhomogeneities
in the baryon to photon ratio and in isospin that might have affected
nucleosynthesis later on. At very high temperature QCD plasma can be described
by perturbation theory because of asymptotic freedom, but a possible phase
transition requires a nonperturbative approach like lattice gauge theory.
Assuming that a first order transition did occur, a dynamical set of equations
can be solved to evolve the universe through it and to quantify the scale of
inhomogeneity. Unfortunately this scale appears to be too small by two orders
of magnitude to affect nucleosynthesis.


title:
Entropy Evolution in Galaxy Groups and Clusters; A Comparison of
  External and Internal Heating

abstract:
  X-ray observations of hot gas in galaxy groups indicate higher entropies than
can be achieved in the accretion shocks as it fell into the dark halos. It has
been proposed that this entropy excess results from some universal external
heating process in the early universe - AGN, population III stars, etc. - that
occurred before most of the gas entered the dark halos. Alternatively, the hot
gas in groups may be heated internally by Type II supernovae when the galactic
stars formed. We investigate here the gas-dynamical consequences of various
amounts of external, high redshift heating and compare with internal supernova
heating. Radiative losses and distributed mass dropout are included. We find
that externally heated flows are unsatisfactory; when the heating is high
enough to bring the X-ray luminosities into agreement with observations, the
gas entropy is too high. Flows internally heated by Type II supernovae are
preferred. Our results are insensitive to the epoch and spatial distribution of
the supernova heating process. However, with a Salpeter IMF a large fraction of
the energy produced by supernovae must heat the hot gas. Alternatively, only
about 20 percent of the Type II supernova energy would be required to heat the
gas if the initial mass function is flatter than Salpeter, as suggested by
stellar mass to light ratios.


title: Abundance analyses of cool extreme helium stars

abstract:
  Extreme helium stars (EHe) with effective temperatures from 8000K to 13000K
are among the coolest EHe stars and overlap the hotter R CrB stars in effective
temperature. The cool EHes may represent an evolutionary link between the hot
EHes and the R CrBs. Abundance analyses of four cool EHes are presented. To
test for an evolutionary connection, the chemical compositions of cool EHes are
compared with those of hot EHes and R CrBs. Relative to Fe, the N abundance of
these stars is intermediate between those of hot EHes and R CrBs. For the R
CrBs, the metallicity M derived from the mean of Si and S appears to be more
consistent with the kinematics than that derived from Fe. When metallicity M
derived from Si and S replaces Fe, the observed N abundances of EHes and R CrBs
fall at or below the upper limit corresponding to thorough conversion of
initial C and O to N. There is an apparent difference between the composition
of R CrBs and EHes; the former having systematically higher [N/M] ratios. The
material present in the atmospheres of many R CrBs is heavily CN- and
ON-cycled. Most of the EHes have only CN-cycled material in their atmospheres.
There is an indication that the CN- and ON-cycled N in EHes was partially
converted to Ne by $\alpha$-captures. If EHes are to evolve to R CrBs, fresh C
in EHes has to be converted to N. If Ne is found to be normal in R CrBs, the
proposal that EHes evolve to R CrBs fails. The idea that R CrBs evolve to EHes
is ruled out; the N abundance in R CrBs has to be reduced to the level of EHes,
as the C/He which is observed to be uniform across EHes, has to be maintained.
Hence, the inferred [N/M], C/He, [Ne/M], and the H-abundances of these two
groups indicate that the EHes and the R CrBs may not be on the same
evolutionary path.


title:
Improved constraints on possible variation of physical constants from H
  I 21cm and molecular QSO absorption lines

abstract:
  QSO absorption spectra provide an extremely useful probe of possible
cosmological variation in various physical constants. Comparison of H I 21cm
absorption with corresponding molecular (rotational) absorption spectra allows
us to constrain variation in y=alpha^2*g_p where alpha is the fine structure
constant and g_p is the proton g-factor. We analyse spectra of two QSOs, PKS
1413+135 and TXS 0218+357, and derive values of dy/y at absorption redshifts of
z=0.2467 and 0.6847 by simultaneous fitting of the H I 21cm and molecular
lines. We find dy/y=(-0.20 +/- 0.44)*10^{-5} and dy/y=(-0.16 +/- 0.54)*10^{-5}
respectively, indicating an insignificantly smaller y in the past. We compare
our results with other recent constraints from the same two QSOs (Drinkwater et
al. 1998; Carilli et al. 2000) and with our recent optical constraints which
indicated a smaller alpha at higher redshifts.


title:
Evidence for Asphericity in a Subluminous Type Ia Supernova:
  Spectropolarimetry of SN 1999by

abstract:
  We present polarization spectra near maximum light for the strongly
subluminous Type Ia supernova 1999by that show that the supernova is
intrinsically polarized. SN 1999by has an observed, overall level of
polarization of ~0.3 to 0.8%, a rise of the polarization P redward of 6500 A,
and a change in polarization across the Si II 6150 A feature of about 0.4%. The
distribution of points with wavelength using an empirical Q-U plane method
reveals that SN 1999by has a well-defined axis of symmetry and suggests an
interstellar polarization (ISP) vector with P(ISP)=0.3% and position angle
Theta = 150 deg with an error circle in the Q-U plane of radius about 0.1%.
Synthetic NLTE-spectra for axisymmetric configurations based on delayed
detonation models have been computed assuming ellipsoidal geometry. Both flux
and polarization spectra can be reasonably well reproduced by models with an
asphericity of ~20 % observed equator-on. The general properties of the
polarization can be understood as a consequence of the structure of subluminous
models. The low upper limits for polarization determined for many normal events
in contrast to the high polarization in SN 1999by may suggest a relation
between the asymmetry we observed and the mechanism that produces a subluminous
Type Ia. Among various mechanisms, rapid rotation of the progenitor white
dwarf, or an explosion during a binary white dwarf merger process are likely
candidates to explain the asphericity in SN 1999by.


title: Testing Cosmic Acceleration with Type Ia Supernovae

abstract:
  We discuss recent evidence for an accelerating Universe from measurements of
type Ia supernovae at high redshift, and describe tests of various systematic
effects such as extinction and evolution that could be biasing the cosmological
result. Continued observations of these objects, both over a wider wavelength
region and at higher redshift, should provide strong evidence in favor or
against the accelerating Universe hypothesis.


title: Inflationary scenarios with scale-invariant spectral tensorial index

abstract:
  Next-to-leading order expressions related to Stewart-Lyth inverse problem are
used to determine the inflationary models with a tensorial power spectrum
described by a scale-invariant spectral index. Beyond power-law inflation,
solutions are characterized by scale dependent scalar indices. These models can
be used as assumption on the generation of primordial perturbations to test for
scale dependence of the scalar index at large angular scales. If such a
dependence is detected, a nonzero contribution of gravitational waves to the
CMB spectrum must be expected.


title:
Galactic planetary nebulae with Wolf-Rayet nuclei. II. A consistent
  observational data set

abstract:
  We present high resolution spectrophotometric data for 34 galactic planetary
nebulae with [WC] nuclei (WRPNe).The sample includes PNe with early and late
[WC] stars and some WELS. Physical conditions and chemical abundances have been
derived and expansion velocities were estimated for most objects of the sample.
A statistical study was developed to find fundamental relationships between the
nebular and central star parameters.We found evidence for a strong unexpected
electron temperature gradient in WRPNe which is related to nebular excitation.
Abundance ratios indicate that there seems to be no preferential stellar mass
for the WR phenomenon to occur in the nucleus of a planetary nebula. The PNe M
1-25 and M 1-32 were found to have very small Ne/O ratios.Our data confirm the
trend of the electron density decreasing with decreasing spectral type, which
was interpreted as evidence that [WC] stars evolve from late to early [WC]
types. On the other hand, the expansion velocities do not show the increase
with decreasing spectral type, that one might expect in such a scenario. Two
objects with very late [WC] central stars, K 2-16 and PM 1-188, do not follow
the general density sequence, being of very low density for their spectral
types. We suggest that the stars either underwent a late helium flash (the
``born again'' scenario) or that they have had a particularly slow evolution
from the AGB. The 6 WELS of our sample follow the same density vs. [WC]-type
relation as the bona fide WRPNe, but they tend to have smaller expansion
velocities. The comparison between the WRPNe in the Magellanic Clouds and in
the Galaxy indicates that metallicity affects the [WR] phenomenon in central
stars of planetary nebulae.


title: Sterile Neutrino Hot, Warm, and Cold Dark Matter

abstract:
  We calculate the incoherent resonant and non-resonant scattering production
of sterile neutrinos in the early universe. We find ranges of sterile neutrino
masses, vacuum mixing angles, and initial lepton numbers which allow these
species to constitute viable hot, warm, and cold dark matter (HDM, WDM, CDM)
candidates which meet observational constraints. The constraints considered
here include energy loss in core collapse supernovae, energy density limits at
big bang nucleosynthesis, and those stemming from sterile neutrino decay:
limits from observed cosmic microwave background anisotropies, diffuse
extragalactic background radiation, and Li-6/D overproduction. Our calculations
explicitly include matter effects, both effective mixing angle suppression and
enhancement (MSW resonance), as well as quantum damping. We for the first time
properly include all finite temperature effects, dilution resulting from the
annihilation or disappearance of relativistic degrees of freedom, and the
scattering-rate-enhancing effects of particle-antiparticle pairs (muons,
tauons, quarks) at high temperature in the early universe.


title:
Bipolar hypershell models of the extended hot interstellar medium in
  spiral galaxies

abstract:
  We simulated the million degree interstellar medium and its soft X-ray images
in the disk and halo of spiral galaxies using the bipolar hypershell (BHS)
model. In this model hourglass-shaped expanding shells of several kpc radii are
produced by a sudden energy release in the central region. We then applied our
model to a mini-sample of starburst galaxies seen under different inclinations
suhc as the nearly edge-on galaxies NGC 253. Our results reproduce the X-ray
characteristics observed in the 0.1--2.4 keV ROSAT energy band: The bipolar
hypershell morphology, the spectral energy distribution of the diffuse disk and
halo emission as well as absorption gaps in the diffuse X-ray emission caused
by a shadowing of soft X-rays due to cold intervening gas in the disks of the
galaxies. The required total energy for the starburst is estimated to be of the
order of $10^{55}$ ergs, corresponding to the overall kinetic energy generated
in $\sim 10^4$ type-II supernova explosions. The expansion velocity of the
shells is estimated to be $\sim 200$ \kms, which is necessary to heat the gas
to $\sim 0.2$ keV (2.3 million K), and the age to be of the order of $3 \times
10^7$ years. In the case of the very nearby galaxy NGC 253 all characteristics
of the BHS model can be studied with high spatial resolution. Using the
property that the shell morphology is sensitive to the ambient density
distribution, we propose using soft X-ray data to probe the gas distributions
in the disk, halo and intergalactic space. The application of our model to
images at higher spatial and spectral resolution, as provided by Chandra and
XMM, will help us to further disentangle the ISM density distributions and will
lead to a better understanding of the disk halo interface.


title:
On the radio spectrum of CI Cygni: a test of popular models for
  symbiotic stars

abstract:
  We have determined the spectral energy distribution at wavelengths between 6
cm and 0.85 mm for the proto-typical S(stellar)-type symbiotic star, CI Cygni,
during quiescence. Data were obtained simultaneously with the Very Large Array
and the SCUBA sub-millimetre (sub-mm) camera on the James Clerk Maxwell
Telescope. The data have allowed us to determine the free-free turnover
frequency of the ionised component, facilitating a model-dependent estimate of
the binary separation to compare with the known orbital parameters of CI Cug
and to critically test the known models for radio emission from symbiotic
stars. In particular, our data rule out the two most popular models: ionization
of the giant wind by Lyman continuum photons from its hot companion and
emission resulting from the interaction of winds from the two binary
components.


title:
The tensor virial method and its applications to self-gravitating
  superfluids

abstract:
  This review starts with a discussion of the hierarchy of scales, relevant to
the description of superfluids in neutron stars, which motivates a subsequent
elementary exposition of the Newtonian superfluid hydrodynamics. Starting from
the Euler equations for a superfluid and a normal fluid we apply the tensor
virial method to obtain the virial equations of the first, second, and third
order and to compute their Eulerian perturbations. Special emphasis is put on
the computation of perturbations of the new terms due to mutual gravitational
attraction and mutual friction between the two fluids. The oscillation modes of
superfluid Maclaurin spheroids are derived from the first and second order
perturbed virial equations. We discuss two generic classes of oscillation modes
which correspond to the co-moving and relative oscillations of two fluids.
These modes decouple if the normal fluid is inviscid. We also discuss the
mixing of these modes (when the normal fluid is viscous) and its effect on the
dynamical and secular instabilities of the co-moving modes and their damping.


title: Constraints on the warm dark matter model from gravitational lensing

abstract:
  Formation of sub-galactic halos is suppressed in warm dark matter (WDM) model
due to thermal motion of WDM particles. This may provide a natural resolution
to some puzzles in standard cold dark matter (CDM) theory such as the cusped
density profiles of virialized dark halos and the overabundance of low mass
satellites. One of the observational tests of the WDM model is to measure the
gravitationally lensed images of distant quasars below sub-arcsecond scales. In
this Letter, we report a comparison of the lensing probabilities of multiple
images between CDM and WDM models using a singular isothermal sphere model for
the mass density profiles of dark halos and the Press-Schechter mass function
for their distribution and cosmic evolution. It is shown that the differential
probability of multiple images with small angular separations down to 10
milliarcseconds should allow one to set useful constraints on the WDM particle
mass. We discuss briefly the feasibility and uncertainties of this method in
future radio surveys (e.g. VLBI) for gravitational lensing.


title:
Expectations for SZ cluster counts: mass function versus X-ray
  luminosity function

abstract:
  We present a comparison of the SZ cluster counts predicted by the
Press-Schechter (PS) mass function (MF) and the X-ray luminosity function (XLF)
of clusters. The employment of the cluster XLF, together with the
observationally determined X-ray luminosity(Lx)-temperature(T) relation, may
allow us to estimate the SZ cluster counts in a more realistic manner, although
such an empirical approach depends sensitively on our current knowledge of the
dynamical properties of intracluster gas and its cosmic evolution. Using both
the non-evolving and evolving XLFs of clusters suggested by X-ray observations,
we calculate the expectations for SZ surveys of clusters with X-ray luminosity
Lx>3X10^{44} erg/s and Lx>1X10^{43} erg/s in the 0.5 - 2.0 band, respectively.
The non-evolving XLF results in a significant excess of SZ cluster counts at
high redshifts as compared with the evolving XLF, while a slightly steeper Lx-T
relation than the observed one is needed to reproduce the distributions of SZ
clusters predicted by the standard PS formalism. It is pointed out that
uncertainties in the cosmological application of future SZ cluster surveys via
the standard PS formalism should be carefully studied.


title:
On the Binding Energy Parameter of Common Envelope Evolution. Dependency
  on the Definition of the Stellar Core Boundary during Spiral-in

abstract:
  According to the standard picture for binary interactions, the outcome of
binaries surviving the evolution through a common envelope (CE) and spiral-in
phase is determined by the internal structure of the donor star at the onset of
the mass transfer, as well as the poorly-known efficiency parameter, eta_CE},
for the ejection of the H-envelope of the donor. In this Research Note we
discuss the bifurcation point which separates the ejected, unprocessed H-rich
material from the inner core region of the donor (the central part of the star
which will later contract to form a compact object). We demonstrate that the
exact location of this point is very important for evaluating the binding
energy parameter, lambda, which is used to determine the post-CE orbital
separation. Here we compare various methods to define the bifurcation point
(core/envelope boundary) of evolved stars with masses 4, 7, 10 and 20 M_sun. We
consider the specific nuclear energy production rate profile, the change in the
mass-density gradient (Bisscheroux 1998), the inner region containing less than
10% hydrogen, the method suggested by Han et al. (1994) and the entropy
profile. We also calculated effective polytropic index profiles. The entropy
profile method measures the convective boundary (at the onset of flatness in
the specific entropy) which is not equivalent to the core boundary for RGB
stars. Hence, this method is not applicable for RGB stars, unless the actual
bifurcation point of a CE is located at the bottom of the outer convection zone
(resulting in larger values of lambda and larger post-CE orbital separations).
On the AGB, where highly degenerate and condensed cores are formed, we find
good agreement between the various methods, except for massive (20 M_sun)
stars.


title:
Torque Decay in the Pulsar (P,P_dot) Diagram. Effects of Crustal Ohmic
  Dissipation and Alignment

abstract:
  We investigate the evolution of pulsars in the (P,P-dot) diagram. We first
present analytical formulae to follow the evolution of a pulsar using simple
exponential models for magnetic field decay and alignment. We then compare
these evolutionary tracks with detailed model calculations using ohmic decay of
crustal neutron star magnetic fields. We find that, after an initial phase with
a small braking index, n, pulsars evolve with enhanced torque decay (n >> 3)
for about 1 Myr. The long term evolution depends on the impurity parameter of
the crust. If impurities are negligible in older isolated pulsars we expect
their true age to be approximately equal to their observed characteristic age,
tau = P/(2*P-dot). It is not possible from data to constrain model parameters
of the neutron star crust.


title: New appearance of cosmic coincidence problem

abstract:
  The integrals of the Friedmann cosmology equations are identified as constant
physical characteristics for both vacuum and non-vacuum cosmic energies. The
integrals are found to be numerically coincident. A model shows that the
coincidence can naturally originate in the electroweak scale physics at TeV
temperatures. The coincidence seems to reflect a new type of symmetry that
relates vacuum and non-vacuum energies.


title: Imaging Atmospheric Cerenkov Telescopes: Techniques and Results

abstract:
  The hunt for cosmic TeV particle accelerators is prospering through Imaging
Atmospheric Cerenkov Telescopes. We face challenges such as low light levels
and MHz trigger rates, and the need to distinguish between particle air showers
stemming from primary gamma rays and those due to the hadronic cosmic ray
background. Our test beam is provided by the Crab Nebula, a steady accelerator
of particles to energies beyond 20 TeV. Highly variable gamma-ray emission,
coincident with flares at longer wavelengths, is revealing the particle
acceleration mechanisms at work in the relativistic jets of Active Galaxies.
These 200 GeV to 20 TeV photons propagating over cosmological distances allow
us to place a limit on the infra-red background linked to galaxy formation and,
some speculate, to the decay of massive relic neutrinos. Gamma rays produced in
neutralino annihilation or the evaporation of primordial black holes may also
be detectable. These phenomena and a zoo of astrophysical objects will be the
targets of the next generation multi-national telescope facilities.


title:
Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation
  History

abstract:
  We model the star formation history (SFH) and the chemical evolution of the
Galactic disk by combining an infall model and a limit-cycle model of the
interstellar medium (ISM). Recent observations have shown that the SFH of the
Galactic disk violently variates or oscillates. We model the oscillatory SFH
based on the limit-cycle behavior of the fractional masses of three components
of the ISM. The observed period of the oscillation ($\sim 1$ Gyr) is reproduced
within the natural parameter range. This means that we can interpret the
oscillatory SFH as the limit-cycle behavior of the ISM. We then test the
chemical evolution of stars and gas in the framework of the limit-cycle model,
since the oscillatory behavior of the SFH may cause an oscillatory evolution of
the metallicity. We find however that the oscillatory behavior of metallicity
is not prominent because the metallicity reflects the past integrated SFH. This
indicates that the metallicity cannot be used to distinguish an oscillatory SFH
from one without oscillations.


title: Formation of Compact Binaries in Globular Clusters

abstract:
  We report here on two complementary population synthesis studies which relate
directly to the formation and evolution of neutron star binaries in globular
clusters. In the first, we compute the probability of retaining neutron stars
in globular clusters, and quantitatively confirm the idea that the retention
fraction for neutron stars born in binary systems is greatly enhanced over
those born in isolated stars. However, the retention fraction may well be
insufficient to explain the current population of neutron star binaries. In the
second study, we follow a large population of primordial binaries and neutron
stars throughout the lifetime of a globular cluster whose properties may be
similar to 47 Tuc. We directly compute all 3-body interactions among binary
systems, neutron stars, and isolated field stars throughout the history of the
cluster. The evolution of certain types of neutron star binaries is followed up
to the current epoch. The numbers of close, recycled, binary radio pulsars are
evaluated and compared with the results of radio observations.


title:
Confidence limits of SN, Kinetic Energy and chemical yields in
  evolutionary synthesis models

abstract:
  When evolutionary synthesis models take into account the stochastic nature of
the IMF together with the discrete number of stars in real stellar clusters,
typical output turns to dispersion band (where real data can be placed) instead
of narrow lines. We present here a qualitative analysis of such dispersion in
the SN rate, the kinetic energy and the 14N/12C ratio for different amounts of
mass transformed into stars.


title:
Self-Similar Equilibria of Self-Gravitating, Magnetized, Rotating,
  Isothermal Systems

abstract:
  The self-similar equilibrium models of self-gravitating, rotating, isothermal
systems are investigated analytically. In these models the rotation velocity is
constant and the density varies as $\frac{f(\theta, \phi)}{r^2}$, where $r$ and
$\theta$ are the spherical radius and the co-latitude, respectively. The
nonaxisymmetric solutions contain three free parameters, one of the parameters
depends on the rotation velocity. These parameters determine the overall shape
of the density distribution. By assuming that the dominant component of the
magnetic field is purely toroidal and the ratio of the purely toroidal magnetic
pressure to the gas pressure, $\alpha$, is spatially constant, the axisymmetric
solutions generalized so as the effect of magnetic field could be studied. We
find that the equilibria of axially symmetric systems yield ellipsoids or
spheres only when the ratio of rotation velocity to the sound speed is taken to
be $\sqrt{2\alpha}$.


title: X-ray Emitting QSOs Ejected from Arp 220

abstract:
  Four compact ROSAT X-ray sources very close to the nearby ultraluminous
infrared galaxy Arp 220 (IC 4553) have been identified as medium-redshift QSOs.
The closest pair lying symmetrically across the galaxy have almost identical
redshifts z = 1.25, 1.26. All of the evidence suggests that these QSOs have
been ejected from Arp 220 and have large intrinsic redshifts.


title: High latitude Galactic dust emission in the BOOMERanG maps

abstract:
  We present mm-wave observations obtained by the BOOMERanG experiment of
Galactic emission at intermediate and high (b < -20 deg) Galactic latitudes. We
find that this emission is well correlated with extrapolation of the IRAS-DIRBE
maps, and is spectrally consistent with thermal emission from interstellar dust
(ISD). The ISD brightness in the 410 GHz map has an angular power spectrum c_l
= A l^{-beta} with 2 < beta < 3. At 150 GHz and at multipoles ell \sim 200 the
angular power spectrum of the IRAS-correlated dust signal is estimated to be
l(l+1)c_l/2 pi = (3.7 \pm 2.9) uK^2. This is negligible with respect to the CMB
signal measured by the same experiment l(l+1)c_l/2 pi = (4700 \pm 540) uK^2.
For the uncorrelated dust signal we set an upper limit to the contribution to
the CMB power at 150GHz and l \sim 200 of l(l+1)c_l/2 pi < 3 uK^2 at 95% C.L. .


title:
High-Resolution X-ray Spectroscopy and Modeling of the Absorbing and
  Emitting Outflow in NGC 3783

abstract:
  (abridged) The high-resolution X-ray spectrum of NGC 3783 shows several dozen
absorption lines and a few emission lines from the H-like and He-like ions of
O, Ne, Mg, Si, and S as well as from Fe XVII - Fe XXIII L-shell transitions. We
have reanalyzed the Chandra HETGS spectrum using better flux and wavelength
calibrations along with more robust methods. Combining several lines from each
element, we clearly demonstrate the existence of the absorption lines and
determine they are blueshifted relative to the systemic velocity by -610+/-130
km/s. We find the Ne absorption lines in the High Energy Grating spectrum to be
resolved with FWHM=840{+490}{-360} km/s. We have used regions in the spectrum
where no lines are expected to determine the X-ray continuum, and we model the
absorption and emission lines using photoionized-plasma calculations. The model
consists of two absorption components which have an order of magnitude
difference in their ionization parameters. The two components are spherically
outflowing from the AGN and thus contribute to both the absorption and the
emission via P Cygni profiles. The model also clearly requires O VII and O VIII
absorption edges. The low-ionization component of our model can plausibly
produce UV absorption lines with equivalent widths consistent with those
observed from NGC 3783. However, we note that this result is highly sensitive
to the unobservable UV-to-X-ray continuum, and the available UV and X-ray
observations cannot firmly establish the relationship between the UV and X-ray
absorbers. We find good agreement between the Chandra spectrum and simultaneous
ASCA and RXTE observations. We set an upper limit on the FWHM of the narrow Fe
K\alpha emission line of 3250 km/s. This is consistent with this line
originating outside the broad line region, possibly from a torus.


title:
Photometric and kinematic studies of open star clusters. III. NGC 4103,
  NGC 5281, and NGC 4755

abstract:
  We present CCD photometry and proper motion studies of the three open star
clusters NGC 4103, NGC 5281, and NGC 4755 (kappa Cru). By fitting isochrones to
the colour magnitude diagrams, we found that all three objects are young open
star clusters with ages of at most t=45 Myr. They are located at distances from
approx. 1600 pc to 2200 pc, derived from distance moduli (m-M)_0 ranging from
11 mag to 12 mag. We combined membership determinations based on proper motions
and statistical field star subtraction to derive the initial mass function
(IMF) of the clusters. The shape of the IMFs could be represented by power laws
with exponents of Gamma=-1.46 +/- 0.22 for NGC 4103, Gamma=-1.60 +/- 0.50 for
NGC 5281, and Gamma=-1.68 +/- 0.14 for NGC 4755, when - as a reference -
Salpeter's (1955) value would be Gamma=-1.35. These results agree well with
other IMF studies of open star clusters.


title: X-ray Power Density Spectrum of the Narrow Line Seyfert 1 Galaxy Akn 564

abstract:
  Beginning in 1999 January, the bright, strongly variable Narrow-Line Seyfert
1 (NLS1) galaxy Akn 564 has been observed by RXTE once every ~4.3 days. It was
also monitored every ~3.2 hr throughout 2000 July. These evenly-sampled
observations have allowed the first quantitative comparison of long and short
time-scale X-ray variability in an NLS1 and the derivation of an X-ray Power
Density Spectrum (PDS). The variability amplitude in the short time-scale light
curve is very similar to that in the long time-scale light curve, in marked
contrast to the stronger variability on longer time-scales which is
characteristic of "normal" broad-line Seyfert 1s (BLS1s). Furthermore, the Akn
564 PDS power law cuts off at a frequency of 8.7x10^-7 Hz corresponding to a
timescale of ~13 d, significantly shorter than that seen in the PDS of NGC
3516, a BLS1 of comparable luminosity.
  This result is consistent with NLS1s showing faster (as opposed to larger
amplitude) variations than BLS1s, providing further evidence that NLS1s harbour
lower mass black holes than BLS1s of similar luminosity, accreting at a
correspondingly higher relative rate.


title: Interpreting Debris from Satellite Disruption In External Galaxies

abstract:
  We examine the detectability and interpretation of debris trails caused by
satellite disruption in external galaxies using semi-analytic approximations
for the dependence of streamer length, width and surface brightness on
satellite and primary galaxy characteristics. The semi-analytic method is
tested successfully against N-body simulations and then applied to three
representative astronomical applications. First, we show how streamer
properties can be used to estimate mass-to-light ratios $\Upsilon$ and streamer
ages of totally disrupted satellites, and apply the method to the stellar arc
in NGC 5907. Second, we discuss how the lack of observed tidal debris around a
satellite can provide an upper limit on its mass-loss rate, and, as an example,
derive the implied limits on mass-loss rates for M32 and NGC 205 around
Andromeda. Finally, we point out that a statistical analysis of streamer
properties might be applied to test and refine cosmological models of
hierarchical galaxy formation, and use the predicted debris from a standard
$\Lambda$CDM realization to test the feasibility of such a study. Using the
Local Group satellites and the few known examples of debris trails in the
Galaxy and in external systems, we estimate that the best current techniques
could characterize the brightest ($R < 29$ mag/ arcsec$^{2}$) portions of the
youngest (3 dynamical periods) debris streamers. If systematics can be
controlled, planned large-aperture telescopes such as CELT and OWL may allow
fainter trails to be detected routinely and thus used for statistical studies
such as those required for tests of galaxy formation.


title: Dark energy and the epoch of galaxy formation

abstract:
  The influence of a dark component on the first epoch of galaxy formation is
analysed by using the ages of the three oldest high-redshift galaxies known in
the literature. Our results, based on a spatially flat accelerated Universe
driven by a "quintessence" component ($p_x = \omega\rho_x$), show that if the
inferred ages of these objects are correct the first formation era is pushed
back to extremely high redshifts. For the present best-fit quintessence model
($\Omega_{x}= 0.7$, $\omega < -0.6$), we find a lower bound of $z_f \geq 7.7$,
whereas in the extreme case of $\Lambda$CDM model ($\omega = -1$) the limit is
slightly smaller ($z_f \geq 5.8$). The case for open cold dark matter models
(OCDM) has also been discussed. For $\Omega_m \simeq 0.3$, the formation
redshift is restricted by $z_f \geq 18$. As a general result, if $\Omega_m \geq
0.37$, these galaxies are not formed in FRW cosmologies with no dark energy
since for all these cases $z_f \to \infty$.


title:
Spatial Diffusion of X-ray Emission Lines in the M87 Cooling Flow;
  Evidence for Absorption

abstract:
  Recent XMM-Newton observations of the cooling flow gas in M87 indicate
sharply decreasing oxygen, iron and silicon abundances within $\sim 5$ kpc of
the galactic center. This result is unexpected since stellar mass loss and Type
Ia supernovae are expected to produce pronounced central abundance maxima for
all three elements. However, it has been suggested that many of the strong
X-ray lines are optically thick and diffuse to larger radii in the cooling flow
before escaping, falsifying the central abundances. We verify with radiation
transfer calculations that this effect does indeed occur in the M87 cooling
flow, but that it is insufficient to account for the M87 observations. We
suggest that some source of continuous opacity is required to reduce the
central X-ray line emission, perhaps by warm gas at $T \sim 10^5 - 10^6$ K. The
radial surface brightness profiles of X-ray resonance lines are also sensitive
to turbulence in cooling flows which reduces the line center optical depths
considerably. Turbulence may provide sufficient energy to continuously heat the
warm absorbing gas.


title:
The European Large Area ISO Survey V: a BeppoSAX hard X-ray survey of
  the S1 region

abstract:
  We present BeppoSAX observations of the Southern S1 region in the European
Large Area ISO Survey (ELAIS). These observations cover an area of ~1.7 sq.
deg. and reach an on-axis (~0.7 sq. deg) 2-10 keV (HX) sensitivity of ~10E-13
cgs. This is the first HX analysis of an ISOCAM survey. We detect 9 sources
with a signal to noise ratio SNR_HX>3, 4 additional sources with a 1.3 to 10
keV (T) SNR_T>3 and 2 additional sources which appear to be associated with
QSOs with SNR_T>2.9. The number densities of the SNR_HX>3 sources are
consistent with the ASCA and BeppoSAX logN-logS functions. Six BeppoSAX sources
have reliable ISOCAM 15 micron counterparts within ~60 arcsec. All these ISOCAM
sources have optical counterparts of R<20 mags. Five of these sources have been
previously optically classified giving 4 QSOs and 1 BALQSO at z=2.2. The
remaining unclassified source has X-ray and photometric properties consistent
with that of a nearby Seyfert galaxy. One further HX source has a 2.6sigma
ISOCAM counterpart associated with a galaxy at z=0.325. If this ISOCAM source
is real, the HX/MIR properties suggest either an unusual QSO or a cD cluster
galaxy. We have constructed MIR and HX spectral energy distributions to compute
the expected HX/MIR ratios for these classes of objects up to z=3.2 and assess
the HX/MIR survey depth.
  The BALQSO has an observed X-ray softness ratio and HX/MIR flux ratio similar
to QSOs but different to those found for low redshift BALQSOs. This difference
can be explained in terms of absorption, and suggests that high redshift
BALQSOs should be comparatively easy to detect in the HX band, allowing their
true fraction in the high redshift QSO population to be determined (ABRIDGED).


title: Recent results from the Alpha Magnetic Spectrometer (AMS) on the STS-91

abstract:
  The Alpha Magnetic Spectrometer (AMS) is a state of the art detector for the
extraterrestrial study of matter, antimatter and missing matter. During the ten
days long STS-91 precursor flight in may 1998 AMS collected nearly 100 millions
of Cosmic Rays on Low Earth Orbit, measuring with high accuracy their
composition. We present results on the flux of proton, electron, positron and
helium particles in the rigidity region 0.1 to 200 GV . Analysis of the under
cutoff spectra indicates the existence of a new type of belts containing high
energy particles and characterized by a dominance of positrons versus
electrons.


title: Observations of the interstellar medium in the Magellanic Bridge

abstract:
  We present ultraviolet and optical spectra of DI 1388, a young star in the
Magellanic Bridge, a region of gas between the Small and Large Magellanic
Clouds. The data have signal-to-noise ratios of 20 to 45 and a spectral
resolution of 6.5 km/s. Interstellar absorption by the Magellanic Bridge at
v_LSR = 200 km/s is visible in the lines of C I, C II,C II*, C IV, N I, O I, Al
II, Si II, Si III, Si IV, S II, Ca II, Fe II, and Ni II. The relative gas-phase
abundances of C II, N I, O I, Al II, Si II, Fe II, and Ni II with respect to S
II are similar to those found in Galactic halo clouds, despite a significantly
lower metallicity in the Magellanic Bridge. The higher ionization species in
the cloud have a column density ratio N(C IV)/N(Si IV) about 1.9, similar to
that inferred for collisionally ionized Galactic cloud interfaces at
temperatures 10^5 K.We identify sub-structure in the stronger interstellar
lines, with a broad component (FWHM = 20 km/s) at 179 km/s and a sharp
component (FWHM = 11 km/s) at 198 km/s. The abundance analysis for these clouds
indicates that the feature at 198 km/s consists of a low electron density,
mainly neutral gas that may be associated with an interface responsible for the
highly ionized gas. The 179 km/s cloud consists of warmer, lower density gas
that is partially ionized.


title: Quintessence dissipative superattractor cosmology

abstract:
  We investigate the simplest quintessence dissipative dark matter attractor
cosmology characterized by a constant quintessence baryotropic index and a
power--law expansion. We show a class of accelerated coincidence--solving
attractor solutions converging to this asymptotic behavior. Despite its
simplicity, such a ``superattractor'' regime provides a model of the recent
universe that also exhibits an excellent fit to supernovae luminosity
observations and no age conflict. Our best fit gives $\alpha=1.71\pm 0.29$ for
the power-law exponent. We calculate for this regime the evolution of density
and entropy perturbations.


title: Magnetically Accreting Isolated Old Neutron Stars

abstract:
  Previous work on the emission from isolated old neutron stars (IONS)
accreting the inter-stellar medium (ISM) focussed on gravitational capture -
Bondi accretion. We propose a new class of sources which accrete via magnetic
interaction with the ISM. While for the Bondi mechanism, the accretion rate
decreases with increasing NS velocity, in magnetic accretors (MAGACs="magics")
the accretion rate increases with increasing NS velocity. MAGACs will be
produced among high velocity (~> 100 km s-1) high magnetic field (B> 1e14 G)
radio pulsars - the ``magnetars'' - after they have evolved first through
magnetic dipole spin-down, followed by a ``propeller'' phase (when the object
sheds angular momentum on a timescale ~< 1e10 yr). The properties of MAGACS may
be summarized thus: dipole magnetic fields of B~>1e14 G; minimum velocities
relative to the ISM of >25-100 km s-1, depending on B, well below the median in
the observed radio-pulsar population; spin-periods of >days to years; accretion
luminosities of 1e28- 1e31 ergs s-1 ; and effective temperatures kT=0.3 - 2.5
keV if they accrete onto the magnetic polar cap. We find no examples of MAGACs
among previously observed source classes (anomalous X-ray pulsars,
soft-gamma-ray repeaters or known IONS). However, MAGACs may be more prevelant
in flux-limited X-ray catalogs than their gravitationally accreting
counterparts.


title:
Small Scale Fluctuations of the Microwave Background in the Quasi-Steady
  State Cosmology

abstract:
  In this paper we show that, within the framework of the QSSC, the small scale
deviations on angular scales $\lesssim 1^{0}$ expected in the MBR are due to
inhomogeneities in the distribution of galaxies and clusters. It is shown how
these can be estimated on the galaxy-cluster-supercluster scale at the epoch of
redshift $\sim 5$ when the universe was last passing through the minimum phase
of the scale factor. Rich clusters on the scale of 5-10 Mpc generate the kind
of peak in the fluctuation power spectrum observed by the Boomrang and Maxima
projects. Weaker inhomogeneities on smaller scales with $l~\sim 10^3$ are
expected to arise from individual galaxies and small groups.


title: Storage ring measurement of the C IV recombination rate coefficient

abstract:
  The low energy C IV dielectronic recombination (DR) rate coefficient
associated with 2s-2p Delta n=0 excitations of this lithiumlike ion has been
measured with high energy-resolution at the heavy-ion storage-ring TSR of the
Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany. The experimental
procedure and especially the experimental detection probabilities for the high
Rydberg states produced by the recombination of this ion are discussed in
detail. From the experimental data a Maxwellian plasma rate coefficient is
derived with 15% systematic uncertainty and parameterized for ready use in
plasma modeling codes. Our experimental result especially benchmarks the plasma
rate coefficient below 10000 K where DR occurs predominantly via C III (1s2 2p
4l) intermediate states and where existing theories differ by orders of
magnitude. Furthermore, we find that the total dielectronic and radiative C IV
recombination can be represented by the incoherent sum of our DR rate
coefficient and the RR rate coefficient of Pequignot et al. (1991, Astron.
Astrophys., 251, 680).


title: Evidence for Large Stellar Disks in Elliptical Galaxies

abstract:
  High-resolution numerical simulations of galaxy mergers are analysed. The
global structure and isophotal shapes of the merger remnants are in good
agreement with the observations. Whereas equal-mass mergers lead to
anisotropic, boxy ellipticals, unequal-mass mergers result in disky and
isotropic systems. The line-of-sight velocity distributions show small
deviations from a Gaussian distribution. In all cases we find that the
retrograde wings are steeper and that the prograde wings are broader than a
Gaussian distribution. This is in contradiction with the observations which
show broader retrograde and steeper prograde wings in all ellipticals. This
fundamental difference between observation and theory can be explained if all
ellipticals, even anistropic boxy ones, contain extended stellar disk
components with luminosities of order 10 to 20 percent the total luminosity and
scale radii of order the effective radii of the spheroids.


title: Chacaltaya: towards a solution of the knee ....?

abstract:
  Cosmic rays physics is currently being studied with rather sophisticated
detectors running in a variety of experimental conditions and atmospheric
depths around the world. In this paper we describe the reasons why cosmic ray
physics experiments at high altitudes like Chacaltaya are so important for
resolving some of the open problems in cosmic physics. A discussion on the
future prospects of the high altitude mountain laboratories such as Chacaltaya
for cosmic ray physics is presented.


title:
Impact of Future Submillimeter and Millimeter Large Facilities on the
  Studies of Galaxy Formation and Evolution

abstract:
  We investigate what we can learn about galaxy formation and evolution from
the data which will be obtained by the forthcoming large
submillimeter/millimeter facilities, mainly by the Atacama Submillimeter
Telescope Experiment (ASTE) and the Atacama Large Millimeter Array/Large
Millimeter and Submillimeter Array (ALMA/LMSA). We first calculate the source
counts from 350 um to 3 mm using the empirical infrared galaxy number count
model of Takeuchi et al. (2001). Based on the number counts, we evaluate the
source confusion and determine the confusion limit at various wavebands as a
function of the characteristic beam size. At submillimeter wavelengths, source
confusion with the 10-15-m class facilities becomes severe at 0.1 to 1 mJy
level, and astrometry and flux measurements will be difficult. However, we show
that very a large-area survey of submillimeter sources brighter than 10-50 mJy
can provide a unique constraint on infrared galaxy evolution at z = 1-2. We
also find that the 5\sigma-confusion limit of the LMSA is fainter than 1 \mu
Jy. The source counts at such faint flux levels give important information of
the epoch of galaxy formation. We then show that multiband photometry from the
infrared (by ASTRO-F) to the millimeter can be utilized as a redshift
estimator. In addition, we compare the observed 1.4, 5, and 8-GHz source counts
with our model counts to examine the contribution of star forming galaxies to
the faint radio galaxies.


title:
The AGB phase-transition outside the Local Group: K-band observations of
  young star clusters in NGC 7252

abstract:
  We have extended the study of the young star clusters observed in the merger
remnant galaxy NGC 7252 by obtaining K band photometry for these clusters. Our
K band data significantly complement the optical photometry and spectroscopy in
the literature: K band data are fundamental to study the Asymptotic Giant
Branch (AGB) population of these clusters, since the AGB phase transition
(occuring between the age of 200 Myr and 1 Gyr) causes abrupt changes in the
near-infrared luminosity of the clusters while producing only small changes in
the optical. Therefore, the e.g. V-K colour is ideal to study this evolutionary
phase of stellar populations. For the present analysis we present models for
Simple Stellar Populations which include the contribution of the AGB stellar
phase, calibrated with the young and intermediate age star clusters of the
Magellanic Clouds. The comparison with the colour distribution of the NGC 7252
star clusters shows that they are indeed intermediate age clusters undergoing
the AGB phase transition. The AGB phase transition is observed for the first
time outside the Local Group. Most of the studied clusters span the very narrow
age range 300-500 Myr, and likely have metallicities 0.5-1 Z_{\odot}. A very
important exception is the cluster W32, which has already completed its AGB
epoch, its colours being consistent with an age of 1-2 Gyr. This impacts on the
duration of the merger-induced starburst. The strengths of the magnesium and
iron lines in the spectrum of the best observed cluster W3, and in the spectrum
of the diffuse central light of NGC 7252, do not show an overabundance in
alpha-elements, in contrast to the bulk stellar population of elliptical
galaxies.