title: Thermal Comptonization in GRS 1915+105

abstract:
  The Rossi X-ray Timing Explorer data of GRS 1915+105 from several observing
periods are modeled with a thermal Comptonization model. Best-fit models
indicate that there is a strong correlation between the inner disk temperature
and the disk luminosity. The hard Comptonized luminosity does not depend
significantly on the total luminosity. The spectral hardness of the Comptonized
radiation, the fraction of seed soft photons scattered by the Comptonizing
cloud, its Thomson optical depth, and the fraction of the total power
dissipated in the optically thin hot plasma, all strongly anticorrelate with
the luminosity. We find that the inner disk radius is almost constant and that
the hot Comptonizing corona shrinks at high luminosities. We note that the fits
using xspec diskbb + power law model underestimate the amplitude of the
blackbody component (and therefore the corresponding size of the emitting
region) and overestimate the absorption column density and the total, corrected
for absorption, luminosity.


title: Bipolar outflows in OH/IR stars

abstract:
  We investigate the development of bipolar outflows during the early post-AGB
evolution. A sample of ten OH/IR stars is observed at high angular resolution,
including bipolar nebulae (OH231.8+4.2), bright post-AGB stars (HD 101584) and
reflection nebulae (e.g. Roberts 22). The IRAS colour--colour diagram separates
the sample into different types of objects. One group may contain the
progenitors to the (few) extreme bipolar planetary nebulae. Two objects show
colours and chemistry very similar to the planetary nebulae with late IR-[WC]
stars. One object is a confirmed close binary.
  A model is presented consisting of an outer AGB wind which is swept up by a
faster post-AGB wind, with either wind being non-spherically symetric. The
interface of the two winds is shown to exhibit a linear relation between
velocity and distance from the star. The OH data confirms the predicted linear
velocity gradients, and reveals torus-like, uniformly expanding components. All
sources are discussed in detail using optical/HST images where available. ISO
data for Roberts 22 reveal a chemical dichotomy, with both crystalline
silicates and PAHs features being present. IRAS 16342-3814 shows a dense torus;
HST data shows four point-like sources located symmetrically around the nebula,
near the outer edge of the dense torus.
  Lifetimes for the bipolar OH/IR stars are shown to be in excess of 10^4 yr,
longer than normal post-AGB timescales. This suggests that the disks are
near-stationary. We suggest that accretion from such a disk slows down the
post-AGB evolution. Such a process could explain the link between the
long-lived bipolar nebular geometry and the retarded star.


title: Vacuum gaps in pulsars and PSR J2144-3933

abstract:
  In this paper we revisit the radio pulsar death line problem within the
framework of curvature radiation and/or inverse compton scattering induced
vacuum gap model above neutron star polar caps. Our special interest is in the
recently detected pulsar PSR J2144-3933 with extremal period 8.5 seconds, which
lies far beyond conventional death lines. We argue, that formation of vacuum
gaps requires a complicated multipolar surface magnetic field, with a strenght
$B_s$ much higher than the surface dipolar component $B_d$, and radii of
curvature ${\cal R}$ much smaller than the neutron star radius $R=10^6$ cm.
Such a multipolar surface field is also consistent with death lines including
the extremal pulsar PSR J2144-3933. Since vacuum gap models produce sparks, our
paper naturally supports the spark related models of subpulse drift phenomenon
as well as to the spark associated models of coherent pulsar radio emission.


title: Multi-color Classification in the Calar Alto Deep Imaging Survey

abstract:
  We use a multi-color classification method introduced by Wolf, Meisenheimer &
Roeser (2000) to reliably identify stars, galaxies and quasars in the up to
16-dimensional color space provided by the filter set of the Calar Alto Deep
Imaging Survey (CADIS). The samples of stars, galaxies and quasars obtained
this way have been used for dedicated studies published in separate papers. The
classification is good enough to detect quasars rather completely and
efficiently without confirmative spectroscopy. The multi-color redshifts are
accurate enough for most statistical applications, e.g. evolutionary studies of
the galaxy luminosity function. We characterize our current dataset on the
CADIS 1h-, 9h- and 16h-fields. Using Monte-Carlo simulations we model the
classification performance expected for CADIS. We present a summary of the
classification results and discuss unclassified objects. More than 99% of the
whole catalog sample at R<22 (more than 95% at R<23) are successfully
classified matching the expectations derived from the simulations. A small
number of peculiar objects challenging the classification are discussed in
detail. Spectroscopic observations are used to check the reliability of the
multi-color classification (6 mistakes among 151 objects with R<24). We also
determine the accuracy of the multi-color redshifts which are rather good for
galaxies (sigma_z = 0.03) and useful for quasars. We find the classification
performance derived from the simulations to compare well with results from the
real survey. Finally, we locate areas for potential improvement of the
classification.


title:
Can the gamma-ray source 3EG J2033+4118 be produced by the stellar
  system Cyg OB2 No.5?

abstract:
  We discuss the possibility that the stellar system Cyg OB2 No.5 can be a
gamma-ray source in the light of recent EGRET and radio data. This system is
formed by an O7 Ia + Ofpe/WN9 contact binary. A third star, probably a B0 V
star also associated with the system, is located at $\sim 1700$ AU from the
primary. We estimate the expected gamma-ray luminosity from the colliding winds
region, the terminal shock of the wind, and the unstable zone at the base of
the wind, and conclude that, under very reasonable assumptions, Cyg OB2 No.5
can generate about a half of the gamma-ray flux detected from the positionally
coincident source 3EG J2033+4118. We suggest, then, that other O stars
belonging to the association, also placed within the 95 % probability EGRET
location contour, could contribute to the observed gamma-ray flux.


title:
Cassiopeia A: on the origin of the hard X-ray continuum and the
  implication of the observed O VIII Ly-alpha/Ly-beta distribution

abstract:
  We present the first results on the hard X-ray continuum image (up to 15 keV)
of the supernova remnant Cas A measured with the EPIC cameras onboard
XMM-Newton. The data indicate that the hard X-ray tail, observed previously,
that extends to energies above 100 keV does not originate in localised regions,
like the bright X-ray knots and filaments or the primary blast wave, but is
spread over the whole remnant with a rather flat hardness ratio of the 8-10 and
10-15 keV energy bands. This result does not support an interpretation of the
hard X-radiation as synchrotron emission produced in the primary shock, in
which case a limb brightened shell of hard X-ray emission close to the primary
shock front is expected. In fact a weak rim of emission near the primary shock
front is discernable in the hardest X-ray image but it contains only a few
percent of the hard X-ray emissivity. The equivalent width of the Fe-K line
blend varies by more than an order of magnitude over the remnant, it is hard to
explain this as Fe-emission from the reverse shock heated ejecta given the
ejecta temperature and the age of the remnant. The uniquely high
wavelength-dispersive RGS-spectrometer has allowed, for the first time, to
extract monochromatic images in several highly ionised element species with
high spectral resolution. We present here a preliminary result on the
measurement of the O VIII Ly-alpha and Ly-beta brightness distribution and
brightness ratios. The large observed decrease of the Ly-alpha/Ly-beta ratio
going from the N to the SE can be explained by small-scale (10 arcsec)
variations in the N_H column over the remnant and the potential presence of
resonance scattering of the O VIII Ly-alpha photons in the limb brightened
shell.


title:
Long-term evolution of a dipole type magnetosphere interacting with an
  accretion disk. II. Transition into a quasi-stationary spherically radial
  outflow

abstract:
  The evolution of an initially stellar dipole type magnetosphere interacting
with an accretion disk is investigated numerically using the ideal MHD ZEUS-3D
code in the 2D-axisymmetry option. The simulations last several thousands of
Keplerian periods of the inner disk. A Keplerian disk is assumed as a boundary
condition prescribing a mass inflow into the corona. Additionally, a stellar
wind from a rotating central star is prescribed. Our major result is that the
initially dipole type field develops into a spherically radial outflow pattern
with two main components, a disk wind and a stellar wind component. These
components evolve into a quasi- stationary final state. The poloidal field
lines follow a conical distribution. As a consequence of the initial dipole,
the field direction in the stellar wind is opposite to that in the disk wind.
The maximum speed of the outflow is about the Keplerian speed at the inner disk
radius. With the chosen mass flow rates and field strength we see almost no
indication for a flow self-collimation.


title:
XMM-Newton observations of NGC 253: Resolving the emission components in
  the disk and nuclear area

abstract:
  The high XMM-Newton throughput allows a detailed investigation of the
spatial, spectral and variability properties of the extended and point source
emission of the starburst galaxy NGC 253 simultaneously. We characterize the
brightest sources by their hardness ratios, detect a bright X-ray transient,
and show the spectrum and light curve of the brightest point source, most
likely a black-hole X-ray binary. The unresolved emission of two disk regions
can be modeled by two thin thermal plasma components of 0.13 and 0.4 keV plus
residual harder emission, with the lower temperature component originating from
above the disk, the nuclear spectrum by a three temperature plasma (~0.6, 0.9,
and 6 keV) with the higher temperatures increasingly absorbed. The high
temperature component most likely originates from the starburst nucleus. No
non-thermal component, that would point at a significant contribution from an
active nucleus (AGN), is needed. Assuming that type IIa supernova remnants
(SNRs) are mostly responsible for the E>4 keV emission, the detection with EPIC
of the 6.7 keV line allows us to estimate a supernova rate within the nuclear
starburst of 0.2 yr^-1. RGS spectra and EPIC images reveal that the
limb-brightening of the plume is mostly seen in higher ionization emission
lines, while in the lower ionization lines, and below 0.5 keV, the plume is
more homogeneously structured. (abridged)


title:
Simultaneous BeppoSAX and RXTE observations of the X-ray burst sources
  GX 3+1 and Ser X-1

abstract:
  We have obtained spectral and timing data on GX 3+1 and Ser X-1. Both sources
were observed simultaneously with BeppoSAX and RXTE. The RXTE data is used to
provide power spectra and colour-colour diagrams in order to constrain the
state (and thus track $\dot M$) the sources are in. The BeppoSAX data provide
the broad-band spectra. The spectra of both sources are reasonably well-fit
using a model consisting of a disk-blackbody, a comptonized component and a Fe
line, absorbed by interstellar absorption. The electron temperature (kT$_{\rm
e}$) of the Comptonizing plasma is in both cases $\sim$2.5 keV. This implies
that no strong high-energy tail from the Comptonized component is present in
either of the sources. We discuss the similarities between these burst sources
and the luminous X-ray sources located in globular clusters. We find that the
spectral parameters of the comptonized component provide information about the
mass-accretion rate, which agrees well with estimates from the timing and
spectral variations.


title:
EUV and X-ray observations of Abell 2199: a three-phase intracluster
  medium with a massive warm component

abstract:
  Various independent ways of constraining key cosmological parameters yielded
a consensus range of values which indicates that at the present epoch the bulk
of the universe's baryons is in the form of a warm ($\sim$ 10$^6$ K) gas - a
temperature regime which renders them difficult to detect. The discovery of EUV
and soft X-ray excess emission from clusters of galaxies was originally
interpreted as the first direct evidence for the large scale presence of such a
warm component. We present results from an EUVE Deep Survey (DS) observation of
the rich cluster Abell 2199 in the Lex/B (69 - 190 eV) filter passband. The
soft excess radial trend (SERT), shown by a plot against cluster radius $r$ of
the percentage EUV emission $\eta$ observed above the level expected from the
hot intracluster medium (ICM), behaves as a simple function of $r$ which
decreases monotonically towards $r = 0$; it smoothly turns negative at $r \sim$
6 arcmin, inwards of this radius the EUV is absorbed by cold matter with a
line-of-sight column density of $\geq$ 2.7 $\times$ 10$^{19}$ cm$^{-2}$. The
centre of absorption is offset from that of the emission by $\sim$ 1 arcmin,
and the area involved is much larger than that of the cooling flow. These facts
together provide strong evidence for a centrally concentrated but cluster-wide
distribution of clumps of cold gas which co-exist with warm gas of similar
spatial properties. Further, the simultaneous modeling of EUV and X-ray data
requires a warm component even within the region of absorption. The phenomenon
demonstrates a three phase ICM, with the warm phase estimated to be $\sim$ 5-10
times more massive than the hot.


title: On the way to global phase-delay astrometry

abstract:
  The use of the phase-delay improves substantially the accuracy obtained in
VLBI astrometry with respect to the group-delay observable. Recently, Ros et
al. (1999) have extended the related phase-connection technique to a triangle
of radio sources with relative separations up to 6.8deg (the S5 sources
BL1803+784/ QSO1928+738/ BL2007+777). This technique has also been extended for
separations up to 15deg in the studies of the pair of S5 radio sources
QSO1150+812/ BL1803+784 (Perez-Torres et al. 2000). We are carrying out a
long-term astrometric programme at 8.4, 15, and 43 GHz to determine the
absolute kinematics of radio source components in the 13 members of the
complete S5 polar cap sample. For each epoch, all the radio sources are
observed at the same frequency for 24 hours in total. Bootstrapping techniques
are used to phase-connect the data jointly for the 13 objects throughout the
observations. An accurate registration of the maps of the radio sources at
different frequencies will allow a study of jet components with unprecedented
precision and provide spectral information. This observing scheme could be
extended in the future to other regions of the sky and eventually lead to
global phase-delay astrometry.


title: XMM-Newton First-Light Observations of the Hickson Galaxy Group 16

abstract:
  This paper presents the XMM-Newton first-light observations of the Hickson-16
compact group of galaxies. Groups are possibly the oldest large-scale
structures in the Universe, pre-dating clusters of galaxies, and are highly
evolved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) is
exceptional in the having the highest concentration of starburst or AGN
activity in the nearby Universe. So it is a veritable laboratory for the study
of the relationship between galaxy interactions and nuclear activity. Previous
optical emission line studies indicated a strong ionising continuum in the
galaxies, but its origin, whether from starbursts, or AGN, was unclear.
Combined imaging and spectroscopy with the EPIC X-ray CCDs unequivocally
reveals a heavily obscured AGN and a separately identified thermal (starburst)
plasma, in NGC 835, NGC 833 and NGC 839. NGC 838 shows only starburst thermal
emission. Starbursts and AGN can evidently coexist in members of this highly
evolved system of merged and merging galaxies, implying a high probability for
the formation of AGN as well as starbursts in post-merger galaxies.


title: Energetics of jets from X-ray binaries

abstract:
  I discuss the energetics of synchrotron-emitting outflows, increasingly found
to be present in many different classes of X-ray binary systems. It is shown
that the outflow is likely to be comparable in power to the integrated X-ray
luminosity, traditionally taken to be an indicator of the global mass-transfer
rate. This is especially found to be the case in the (low/)hard states of black
hole candidate systems. I conclude that jets are extremely important,
energetically and dynamically, for the accretion process in the majority of
known X-ray binary systems.


title: Preliminary Spectral Analysis of the Type II Supernova 1999em

abstract:
  We have calculated fast direct spectral model fits to two early-time spectra
of the Type-II plateau SN 1999em, using the SYNOW synthetic spectrum code. The
first is an extremely early blue optical spectrum and the second a combined HST
and optical spectrum obtained one week later. Spectroscopically this supernova
appears to be a normal Type II and these fits are in excellent agreement with
the observed spectra. Our direct analysis suggests the presence of enhanced
nitrogen. We have further studied these spectra with the full NLTE general
model atmosphere code PHOENIX. While we do not find confirmation for enhanced
nitrogen (nor do we rule it out), we do require enhanced helium. An even more
intriguing possible line identification is complicated Balmer and He I lines,
which we show falls naturally out of the detailed calculations with a shallow
density gradient. We also show that very early spectra such as those presented
here combined with sophisticated spectral modeling allows an independent
estimate of the total reddening to the supernova, since when the spectrum is
very blue, dereddening leads to changes in the blue flux that cannot be
reproduced by altering the ``temperature'' of the emitted radiation. These
results are extremely encouraging since they imply that detailed modeling of
early spectra can shed light on both the abundances and total extinction of SNe
II, the latter improving their utility and reliability as distance indicators.


title:
Analysis of the Type IIn Supernova 1998S: Effects of Circumstellar
  Interaction on Observed Spectra

abstract:
  We present spectral analysis of early observations of the Type IIn supernova
1998S using the general non-local thermodynamic equilibrium atmosphere code \tt
PHOENIX}. We model both the underlying supernova spectrum and the overlying
circumstellar interaction region and produce spectra in good agreement with
observations. The early spectra are well fit by lines produced primarily in the
circumstellar region itself, and later spectra are due primarily to the
supernova ejecta. Intermediate spectra are affected by both regions. A
mass-loss rate of order $\dot M \sim 0.0001-0.001$\msol yr$^{-1}$ is inferred
for a wind speed of 100-1000 \kmps. We discuss how future self-consistent
models will better clarify the underlying progenitor structure.


title: Self-Interacting Dark Matter with Flavor Mixing

abstract:
  The crisis of both cold and collisional dark matter (DM) models is resolved
by postulating flavor mixing of DM particles. Flavor-mixed particles segregate
in the gravitational field to form dark halos composed of heavy mass
eigenstates. Since these particles are mixed in the interaction basis, elastic
collisions convert some of heavy eigenstates into light ones which leave the
halo. This annihilation-like process will soften dense central cusps of halos.
The proposed model accumulates most of the attractive features of
self-interacting and annihilating DM models, but does not suffer from their
severe drawbacks. This model is natural does not require fine tuning.


title:
Introductory Remarks on The Extragalactic Infrared Background and its
  Cosmological Implications

abstract:
  I review the assumptions and observations that motivate the concept of the
extragalactic cosmic background radiation, and the issues of energy accounts
and star formation history as a function of galaxy morphological type that
figure in the interpretation of the measurements of the extragalactic infrared
background.


title:
Mapping the Galactic Free-Free Foreground via Interstellar H-Alpha
  Emission

abstract:
  Recently completed H-Alpha surveys of large portions of the sky can be used
to create maps of the free-free intensity distribution at high Galactic
latitude that are independent of the spectral fits to the CMB data. This
provides an opportunity to test the accuracy of the spectral fitting procedures
and to search for other sources of Galactic forground contamination that could
be confused spectrally with the free-free, such as spinning dust grains. The
Wisconsin H-Alpha Mapper (WHAM) survey has sampled the sky north of declination
-30 deg at about one degree angular resolution and has revealed that, except
for a few isolated regions of enhanced emission, \Delta T_{ff} (30 GHz) < 30
micro-K at Galactic latitudes near 15 deg, decreasing to \Delta T_{ff} (30 GHz)
< 4 mircro-K at latitudes above 50 deg. Also in progress are H-Alpha surveys
that sample the sky at higher angular resolution.


title: Exploring the Multi-Wavelength, Low Surface Brightness Universe

abstract:
  Our current understanding of the low surface brightness universe is quite
incomplete, not only in the optical, but also in other wavelength regimes. As a
demonstration of the type of science which is facilitated by a virtual
observatory, we have undertaken a project utilizing both images and catalogs to
explore the multi-wavelength, low surface brightness universe. Here, we present
some initial results of this project. Our techniques are complimentary to
normal data reduction pipeline techniques in that we focus on the diffuse
emission that is ignored or removed by more traditional algorithms. This
requires a spatial filtering which must account for objects of interest, in
addition to observational artifacts (e.g., bright stellar halos). With this
work we are exploring the intersection of the catalog and image domains in
order to maximize the scientific information we can extract from the federation
of large survey data.


title:
An Approximate Determination of the Gas-Phase Metal Abundance in
  Herbig-Haro Outflows and their Shocks

abstract:
  (modified for brevity) It is important to determine whether the observed bow
shocks in the working surfaces of Herbig-Haro outflows has lead to a
destruction of dust grains and consequently to a change in the gas phase metal
abundances (say of Fe) in the cooling regions of HH bow shocks. Detailed
studies are currently available for only 5 HH outflows (Beck-Winchatz et al.\
1996), due to the large observational and theoretical effort required to
determine metal abundances in HH objects.
  Information about metal abundances in more HH objects is badly needed. We
therefore use a very approximate method by introducing a "characteristic
number", A_me, whose definition is based only on often observed line fluxes. We
find a good correlation between A_me and the Fe abundance for the 5
well-studied HH objects. We use this correlation to determine approximate
values of the gas phase Fe abundance in 13 additional high excitation and in 3
additional low excitation HH objects.
  Of the 16 high excitation HH objects studied, there are 6 which approximately
agree with normal population I abundance (i.e., no depletion due to dust
formation). The remaining 10 show some Fe gas phase depletion which never gets
larger than by a factor of 2.5. This result is in agreement with our
qualitative expectations that fast shocks efficiently destroy dust grains. Of
the 5 low excitation HH objects studied, there are 4 which, unexpectedly, show
a normal population I abundance. In low excitation objects, one might expect
strong gas phase Fe depletion (showing the unchanged molecular cloud
composition), unless the matter has previously gone through shocks of much
higher shock velocities.


title: The Structure of Self-Gravitating Polytropic Systems with n around 5

abstract:
  We investigate the structure of self-gravitating polytropic stellar systems.
We present a method which allows to obtain approximate analytical solutions,
$\psi_{n+\epsilon}({\bf x})$, of the nonlinear Poisson equation with the
polytropic index $n+\epsilon$, given the solution $\psi_n({\bf x})$ with the
polytropic index n, for any positive or negative $\epsilon$ such that
$|\epsilon|\ll1$. Application of this method to the spherically symmetric
stellar polytropes with $n\simeq5$ yields the solutions which describe
spatially bound systems if n<5 and the formation of a second core if n>5. A
heuristic approximate expressions for the radial profiles are also presented.
Due to the duality between stellar and gas polytropes, our results are valid
for gaseous, self-gravitating polytropic systems (e.g., molecular clouds) with
the index $\gamma\simeq 6/5$. Stability of such systems and observational
consequences for both stellar and gaseous systems are discussed.


title: The Universe Traced by Clusters

abstract:
  I critically review a methodology of using clusters of galaxies as
cosmological probes. The understanding of the abundances and spatial
correlations of dark matter halos has been significantly advanced especially
for a last few years. Nevertheless such dark matter halos are not necessarily
identical to clusters of galaxies in the universe. This is a quite obvious
fact, but it seems that the resulting systematic errors, on the cosmological
parameter estimates for instance, are often neglected in the literature.


title: Hipparcos Luminosities and Asteroseismology

abstract:
  Asteroseismology involves using the resonant frequencies of a star to infer
details about its internal structure and evolutionary state. Oscillation
frequencies are most useful when accompanied by accurate measurements of the
more traditional stellar parameters such as luminosity and effective
temperature. The Hipparcos catalogue provides luminosities with precisions of a
few percent or better for many oscillating stars. I briefly discuss the
importance of Hipparcos measurements for interpreting asteroseismic data on
three types of oscillating stars: delta Scuti variables, rapidly oscillating Ap
stars and solar-like stars. I also retract the endorsement I made during my
talk of Trimble's (1995) suggestion to change the spelling of
"asteroseismology".


title: The Formation of Galaxy Disks

abstract:
  Galaxy disk formation must incorporate the multiphase nature of the
interstellar medium. The resulting two-phase structure is generated and
maintained by gravitational instability and supernova energy input, which yield
a source of turbulent viscosity that is able to effectively compete in the
protodisk phase with early angular momentum loss of the baryonic component via
dynamical friction in the dark halo. Provided that star formation occurs on the
viscous drag time-scale, this mechanism provides a means of accounting for disk
sizes and radial profiles.
  The star formation feedback is self-regulated by turbulent gas
pressure-limited percolation of the supernova remnant-heated hot phase, but can
run away in gas-rich protodisks to generate compact starbursts. A simple
analytic model is derived for a Schmidt-like global star formation law in terms
of the cold gas volume density.


title: Estimating jet power in proton blazar models

abstract:
  We discuss the various contributions to the jet luminosity in proton blazar
models of active galactic nuclei and describe a method of estimating the jet
luminosity from the observed spectral energy distribution (SED) and the fitted
model parameters. We apply this to a synchrotron proton blazar (SPB) model for
Markarian 501.


title: AMRA: An Adaptive Mesh Refinement Hydrodynamic Code for Astrophysics

abstract:
  Implementation details and test cases of a newly developed hydrodynamic code,
AMRA, are presented. The numerical scheme exploits the adaptive mesh refinement
technique coupled to modern high-resolution schemes which are suitable for
relativistic and non-relativistic flows. Various physical processes are
incorporated using the operator splitting approach, and include self-gravity,
nuclear burning, physical viscosity, implicit and explicit schemes for
conductive transport, simplified photoionization, and radiative losses from an
optically thin plasma. Several aspects related to the accuracy and stability of
the scheme are discussed in the context of hydrodynamic and astrophysical
flows.


title: The Orion Star-Forming Region

abstract:
  General properties of the Orion star-forming region are discussed, with a
focus on the dense Orion Nebula Cluster (ONC). This cluster contains between
2500 and 4500 objects located within a few parsecs of the eponymous Trapezium
stars. Its members are aged <1 to a few Myr and encompass the full spectrum of
stellar masses <50 Msun, as well as brown dwarfs detected with masses as low as
<0.02 Msun (20 Mjup) thusfar. Recent results from optical, near-infrared, and
x-ray studies of the stellar/sub-stellar population associated with this
cluster are summarized.


title: Preheating - cosmic magnetic dynamo ?

abstract:
  We study the amplification of large-scale magnetic fields during preheating
and inflation in several different models. Preheating can resonantly amplify
seed fields on cosmological scales. In the presence of conductivity, however,
the effect of resonance is typically weakened while the amplitude of produced
magnetic fields depends sensitively on the evolution of the conductivity during
the preheating and thermalisation phases. In addition we discuss geometric
magnetisation, where amplification of magnetic fields occurs through coupling
to curvature invariants. This can be efficient during inflation due to a
negative coupling instability. Finally we discuss the breaking of the conformal
flatness of the background metric whereby magnetic fields can be stimulated
through the growth of scalar metric perturbations during metric preheating.


title: Some Common Problems and Challenges that Emission-Line Stars Present

abstract:
  Four examples are given of problems that arise in the study of emission-line
stars, each of which deserves further quantitative study. (1) Archival slit
spectra of \eta Car show that epochs of low excitation have occurred regularly
in the 2020 day period of Damineli et al. since at least 1948. They last about
10 percent of the period. Earlier slit spectra (1899 -1919) suggest that the
the object was always in a low excitation state at that time. This result may
be connected with the gradual brightening of eta Car through most of the 20th
century. (2) FeII and [FeII] emission in Mira variables is probably
chromospheric. It would be important to understand how this is excited and its
relation to mass loss and dust formation in Miras. (3) Declines of RCB stars
are due to eclipses by dust clouds. At such times a rich emission line spectrum
from the outer atmosphere of the star is seen. The quantitative study of the
changes in this spectrum as more and more of the star is eclipsed should yield
important information on the extended atmosphere of these objects. (4) In deep
minima when the entire star is eclipsed, RCB stars show a broad-line emission
spectrum. The excitation of this spectrum, particularly HeI 3888A, constitutes
a puzzle. Two possible excitation mechanisms are discussed.


title: Cosmological thermodynamics and deflationary gas universe

abstract:
  We establish a general thermodynamic scheme for cosmic fluids with internal
self-interactions and discuss equilibrium and non-equilibrium aspects of such
systems in connection with (generalized) symmetry properties of the
cosmological dynamics. As an example we construct an exactly solvable gas
dynamical model of a ``deflationary'' transition from an initial de Sitter
phase to a subsequent Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) period.
We demonstrate that this dynamics represents a manifestation of a conformal
symmetry of an ``optical'' metric, characterized by a specific effective
refraction index of the cosmic medium.


title: An ionizing UV background dominated by massive stars

abstract:
  We discuss implications of a stellar-dominated UV background at high
redshifts. The composite spectrum of 29 LBGs evaluated by Steidel etal (2000)
at <z>=3.4 can be well fit by a stellar population with ongoing star formation,
a Salpeter initial mass function, modest or negligible dust reddening, and no
intrinsic HI photoelectric absorption. Fading starbursts in which star
formation has ceased for 10^7 yr or more cannot reproduce the observed flux
shortward of 1 Ryd.The escape fraction of H-ionizing photons must be close to
100 percent for the observed sample of LBGs. The spectrum of ionizing photons
produced by a stellar population with ongoing star formation is similar to that
of QSOs between 1 and 3 Ryd, becomes softer between 3 and 4 Ryd and drops
sharply shortward of 4 Ryd. A galaxy-dominated UV background appears
inconsistent with the observed HeII/HI opacity ratio at z=2.4, but might be
able to explain the SiIV/CIV abundances measured at z>3 in absorption spectra.
A scenario may be emerging where star-forming galaxies reionized intergalactic
hydrogen at $z>6$ and dominate the 1 Ryd metagalactic flux at z>3, with
quasi-stellar sources taking over at low redshifts. If the large amplitude of
the H-ionizing flux estimated by Steidel etal is correct, hydrodynamical
simulations of structure formation in the IGM require a baryon density (to
explain the observed Lyalpha opacity in absorption spectra) which is similar to
or larger than that favoured by recent CMB experiments, and is inconsistent
with standard nucleosynthesis values.


title: Future X-ray timing missions

abstract:
  Thanks to the Rossi X-ray Timing Explorer (RXTE), it is now widely recognized
that fast X-ray timing can be used to probe strong gravity fields around
collapsed objects and constrain the equation of state of dense matter in
neutron stars. We first discuss some of the outstanding issues which could be
solved with an X-ray timing mission building on the great successes of RXTE and
providing an order of magnitude better sensitivity. Then we briefly describe
the 'Experiment for X-ray timing and Relativistic Astrophysics' (EXTRA)
recently proposed to the European Space Agency as a follow-up to RXTE and the
related US mission 'Relativistic Astrophysics Explorer' (RAE).


title:
Reproducing the observed Cosmic microwave background anisotropies with
  causal scaling seeds

abstract:
  During the last years it has become clear that global O(N) defects and U(1)
cosmic strings do not lead to the pronounced first acoustic peak in the power
spectrum of anisotropies of the cosmic microwave background which has recently
been observed to high accuracy. Inflationary models cannot easily accommodate
the low second peak indicated by the data. Here we construct causal scaling
seed models which reproduce the first and second peak. Future, more precise CMB
anisotropy and polarization experiments will however be able to distinguish
them from the ordinary adiabatic models.


title: Supernova and Cosmology

abstract:
  These lecture notes intend to form a short pedagogical introduction to the
use of typical type Ia-Supernovae (hereafter SNIa) as standard candles to
determine the energy density of the universe. Problems of principle for taking
SNIa as cosmological probes are pointed out, and new attempts at solving them
are indicated including the empirical width-luminosity relation and its
possible explanations. Finally, the observations of SNIa at high redshift
carried out by two major teams are briefly reviewed and their interpretation as
evidence for an accelerating universe is also rapidly discussed.


title: The Accretion Ejection Instability : Observationnal Tests

abstract:
  The Accretion Ejection Instability (hereafter AEI), has been proposed to
explain, the energy and angular momentum transport from the innermost parts of
accretion disks in the X-Ray Binaries (XB), (permitting thus the accretion),
toward a coronal medium, which is thought to be the base of jets (Tagger &
Pellat, 1999; Tagger 1999, Varni\`ere et al., 2000; Corbel, phD Thesis, 1999).
The low frequency QPO often observed in the XB's, are theorically predicted
with the AEI; furthemore theorical calculations in a strong gravitationnal
field (Varni\`ere, Rodriguez & Tagger, 2000) lead to an unexpected behavior
when looking at the QPO frequency variations vs. the disk radius. We the
analysed a set of public observations of GRO J1655-40 and GRS 1915+105, in
order to verify the theorical predictions. We 'll see in particular that they
have different behavior, and will point out interesting differences between the
two sources when the model gives unrealistic low values of the disk radius.


title:
HI absorption in radio galaxies: effect of orientation or interstellar
  medium?

abstract:
  A search for HI absorption has been made in 23 radio galaxies using the ATCA,
the VLA and the WSRT. In five galaxies HI absorption was detected. We
investigate how the detection rate is distributed among galaxies with different
radio and optical properties. Among the Fanaroff-Riley (FR) type I radio
galaxies, only one object (10% of total) was detected. The HI absorption in
these objects is likely to come from a nuclear disk, as found for other
galaxies of this type. The low detection rate is consistent with the hypothesis
(as suggested by optical and X-ray data) that the ``standard'' pc scale,
geometrically thick torus is not required in low-luminosity radio galaxies. In
the case of FR type-II powerful radio galaxies, no HI absorption has been
detected in broad line radio galaxies, while three out of four narrow-line
radio galaxies have been detected (the one non-detection having quite a high
upper limit). All these are compact or small radio galaxies. To first order
this is consistent with the predictions of the unified schemes, assuming that
the HI absorption is due to an obscuring torus. However, the indications of
this being the only cause of the absorption are not very strong. In particular,
we find that in two of the three detected objects that the HI is blueshifted
compared to the systemic velocity. In the third galaxy (PKS 1549-79) two
redshift systems (from the optical lines) are found. The uncertainty in the
systemic velocity derived from optical lines is discussed. Finally, we find a
tendency for radio galaxies with a strong component of young stellar population
and far-IR emission to show HI absorption. The overall richer ISM that is
likely to be present in these galaxies may be a factor in producing the
absorption.


title:
Massive and luminous YSO IRAS 05361+3539 and its environment. A study of
  star formation in the parent cloud - I

abstract:
  Near-infrared photometry and narrow/broad-band imaging of the massive and
luminous young stellar object IRAS 05361+3539 are presented. Imaging
observations were made at Mt. Abu while the photometric data were taken from
the 2MASS. From the color-color and color-magnitude diagrams, we identified
several sources of faint Class II type and about six Class I type in the parent
molecular cloud complex. The IRAS 05361+3539 itself was seen to be a Class I
object and our images in Br$\gamma$ and H$_{2}$ lines show jets/outflows from
this object. The jet/outflow matches with the axis of CO outflow detected
earlier. The near-infrared and the IRAS far-infrared flux distribution suggests
a possible accretion disk with dust temperatures between 80 to 800K and extent
of several tens to hundreds of AU. A possible FU Orionis type of source was
detected in the cluster.


title:
Color Gradients and the Secular Evolutionary Scenario in Late-Type
  Spiral Galaxies

abstract:
  We have done a robust statistical study of the behaviour of color profiles
for 257 Sbc galaxies, having determined (B-V) and (U-B) color gradients, as
well as color indices of bulges and disks separately. Applying a bidimensional
decomposition technique to model the brightness profiles of bulges and disks,
we obtained characteristic structural parameters for 39 galaxies. Among the
main results obtained, we point out: 65% of the galaxies have negative color
gradients (reddish inward), 25% have no gradients, and 10% show positive
gradients; galaxies that show no color gradients tend to be barred; we confirm
the correlation between the color indices of bulges and disks; the absence of
correlation between color and metallicity gradients suggests that the excess of
barred galaxies with zero or positive color gradients reflects a difference in
the behaviour of the mean age of the stellar population along barred and
unbarred galaxies; galaxies with zero or positive color gradients show a slight
tendency of having larger bulges, with a greater central concentration of
light, and we confirm the correlation between the scale lengths of bulges and
disks. These results are compatible and favourable to the secular evolutionary
scenario, in which stellar bars induce radial mass fluxes to the central
regions of galaxies. (Abridged)


title: Super-horizon perturbations and preheating

abstract:
  We discuss the evolution of linear perturbations about a
Friedmann-Robertson-Walker background metric, using only the local conservation
of energy-momentum. We show that on sufficiently large scales the curvature
perturbation on spatial hypersurfaces of uniform-density is constant when the
non-adiabatic pressure perturbation is negligible. We clarify the conditions
under which super-horizon curvature perturbations may vary, using preheating as
an example.


title: Radio galaxies at z~2.5: results from Keck spectropolarimetry

abstract:
  In classifying the ensemble of powerful extragalactic radio sources,
considerable evidence has accumulated that radio galaxies and quasars are
orientation-dependent manifestations of the same parent population: massive
spheroidal galaxies containing correspondingly massive black holes. [...] In
this study, we exploit the opportunity to eliminate the quasar glare by
performing sensitive spectropolarimetry with the Keck II telescope of a sample
of radio galaxies with redshifts around 2.5. [...] We show that dust-reflected
quasar light generally dominates the restframe ultraviolet continuum of these
sources and that a highly clumped scattering medium results in almost grey
scattering of the active galactic nucleus photons. The observations, however,
do not exclude a substantial star formation rate averaged over a Gyr of
evolution. The sub-mm reradiation from the scattering dust is likely to
represent only a small fraction (~10%) of the total far infrared luminosity. An
analysis of the emission lines excited in the interstellar medium of the host
galaxy by the hard quasar radiation field reveals evidence of a dramatic
chemical evolution within the spheroid during this epoch. Secondary nitrogen
production in intermediate mass stars produces a characteristic signature in
the NV/CIV and NV/HeII line ratios which has been seen previously in the broad
line region of quasars at similar redshifts. We find intriguing correlations
between the strengths of the Ly alpha and NV emission lines and the degree of
ultraviolet continuum polarization which may represent the dispersal of dust
associated with the chemical enrichment of the spheroid.


title: Multicolour Observations, Inhomogeneity & Evolution

abstract:
  We propose a method of testing source evolution theories that is independent
of the effects of inhomogeneity, and thus complementary to other studies of
evolution. It is suitable for large scale sky surveys, and the new generation
of large telescopes.
  In an earlier paper it was shown that basic cosmological observations -
luminosity versus redshift, area distance versus redshift and number counts
versus redshift - cannot separate the effects of cosmic inhomogeneity, cosmic
evolution and source evolution. We here investigate multicolour observations,
and show that by comparing luminosity versus redshift in two or more colours,
contraints can be placed on source evolution even if unknown source evolution
is present, providing an important test of evolution theories that is
complementary to present methods. However, number counts in different colours
versus redshift are not useful in separating the effects of source evolution
and inhomogeneity.


title:
Modelling the spin pulse profile of the isolated neutron star RX
  J0720.4--3125 observed with XMM-Newton

abstract:
  We model the spin pulse intensity and hardness ratio profiles of the isolated
neutron star RXJ0720.4--3125 using XMM-Newton data. The observed variation is
approximately sinusoidal with a peak-to-peak amplitude of 15%, and the hardness
ratio is softest slightly before flux maximum. By using polar cap models we are
able to derive maximum polar cap sizes and acceptable viewing geometries. The
inferred sizes of the caps turn out to be more compatible with a scenario in
which the neutron star is heated by accretion, and place limits on the magnetic
field strength. The hardness ratio modulation can then be explained in terms of
energy-dependent beaming effects, and this constrains the acceptable models of
the emerging radiation to cases in which softer photons are more strongly
beamed than harder photons. An alternative explanation in terms of spatially
variable absorption co-rotating in the magnetosphere is also discussed.


title: On ionization effects and abundance ratios in damped Lyman alpha systems

abstract:
  The similarity between observed velocity structures of Al III and singly
ionized species in damped Lyman-alpha systems (DLAs) suggests the presence of
ionized gas in the regions where most metal absorption lines are formed. A
simplified model consisting of Region 1) a plane-parallel ionization bounded
region illuminated by an internal radiation field, and Region 2) a neutral
region with a negligible metal content is considered. We calculate
photoionization equilibrium models for region 1, and constrain the ionization
parameter by the observed N(Al III)/N(Si II) column density ratio. Under these
conditions we find that ionization effects are important. If these effects are
taken into account, the element abundance ratios in DLAs are quite consistent
with those observed in Milky Way stars and in H II regions of local
low-metallicity blue compact dwarf galaxies. In particular we cannot exclude
the same primary N origin in both DLAs and metal-poor galaxies. No depletion of
heavy elements on dust grains needs to be invoked, although our models do not
exclude the presence of little depletion. Although highly simplified and
relying on the strong assumption of a significantly lower metal content in
region 2, our model appears to be supported by recent data on a local DLA and
it is not in contradiction with the current knowledge on high redshift DLAs. If
correct, it offers a clear simplification in the understanding of heavy element
abundance ratios in DLAs and their comparison with the local Universe.


abstract:
  The equilibrium of dense plasma in a gravity field and problem of a
gravity-induced electric polarization in this matter are discussed. The
calculation for metals performed before shows that both - the gravity-induced
compressive strain and the gravity-induced electric field - are inversely
proportional to their Young moduli. The calculation for high dense plasma,
where Young modulus is equal to zero, shows that there is another effect: each
cell of this plasma inside a celestial body in own gravity field obtains the
small positive electric charge. It happens as heavy ions sag on to light
electron clouds. A celestial body stays electrically neutral as a whole,
because the negative electric charge concentrates on its surface. The
gravity-induced positive volume charge is very small, its order of magnitude
equals to $10^{-18}e$ per atom only. But it is sufficient for the complete
conterbalancing of the gravity force.


title: Resolving Sirius-like binaries with the Hubble Space Telescope

abstract:
  We present initial results from a Hubble Space Telescope ultraviolet imaging
survey of stars known to have hot white-dwarf companions which are unresolved
from the ground. The hot companions, discovered through their EUV or UV
emission, are hidden by the overwhelming brightnesses of the primary stars at
visible wavelengths. Out of 17 targets observed, we have resolved eight of them
with the Wide Field Planetary Camera~2, using various ultraviolet filters. Most
of the implied orbital periods for the resolved systems are hundreds to
thousands of years, but in at least three cases (56 Persei, zeta Cygni, and
REJ1925-566) it shouldbe possible to detect the orbital motions within the next
few years, and they may eventually yield new dynamically determined masses for
the white-dwarf components. The 56 Persei and 14 Aurigae systems are found to
be quadruple and quintuple, respectively, including the known optical
components as well as the newly resolved white-dwarf companions. The mild
barium star zeta Cygni, known to have an 18 year spectroscopic period, is
marginally resolved. All of these new resolved Sirius-type binaries will be
useful in determining gravitational redshifts and masses of the white-dwarf
components.


title:
Detection of an X-ray periodicity in the Narrow-line Seyfert 1 Galaxy
  Mrk 766 with XMM-Newton

abstract:
  We have analyzed the timing properties of the Narrow-line Seyfert 1 galaxy
Mrk 766 observed with XMM-Newton during the PV phase. The source intensity
changes by a factor of 1.3 over the 29,000 second observation. If the soft
excess is modeled by a black body component, as indicated by the EPIC pn data,
the luminosity of the black body component scales with its temperature
according to L ~ T^4. This requires a lower limit 'black body size` of about
1.3*10^25 cm^2. In addition, we report the detection of a strong periodic
signal with 2.4*10^-4 Hz. Simulations of light curves with the observed time
sequence and phase randomized for a red noise spectrum clearly indicate that
the periodicity peak is intrinsic to the distant AGN. Furthermore, its
existence is confirmed by the EPIC MOS and RGS data. The spectral fitting
results show that the black body temperature and the absorption by neutral
hydrogen remain constant during the periodic oscillations. This observational
fact tends to rule out models in which the intensity changes are due to hot
spots orbiting the central black hole. Precession according to the
Bardeen-Petterson effect or instabilities in the inner accretion disk may
provide explanations for the periodic signal.


title:
Energy relaxation in galaxies induced by an external environment and/or
  incoherent internal pulsations

abstract:
  This paper explores the phenomenon of energy relaxation for stars in a galaxy
embedded in a high density environment that is subjected continually to
perturbations reflecting the presence of other nearby galaxies and/or
incoherent internal pulsations. The analysis is similar to earlier analyses of
energy relaxation induced by binary encounters between nearby stars and between
stars and giant molecular clouds in that the perturbations are idealised as a
sum of near-random events which can be modeled as diffusion and dynamical
friction. However, the analysis differs in one important respect: because the
time scale associated with these perturbations need not be short compared with
the characteristic dynamical time t_D for stars in the original galaxy, the
diffusion process cannot be modeled as resulting from a sequence of
instantaneous kicks, i.e., white noise. Instead, the diffusion is modeled as
resulting from random kicks of finite duration, i.e., coloured noise
characterised by a nonzero autocorrelation time t_c. A detailed analysis of
coloured noise generated by sampling an Ornstein-Uhlenbeck process leads to a
simpling scaling in terms of t_c and an effective diffusion constant D.
Interpreting D and t_c following early work by Chandrasekhar (1941) (the
`nearest neighbour approximation') implies that, for realistic choices of
parameter values, energy relaxation associated with an external environment
and/or internal pulsations could be important on times short compared with the
age of the Universe.


title: Reconstruction of the Zone of Avoidance

abstract:
  The uncovering of the large-scale structure that is hidden in the Zone of
Avoidance is essential to our quest for the understanding of the dynamics of
the nearby universe. Dedicated and sophisticated observations of the Zone of
Avoidance have to be matched by equally sophisticated theoretical tools for the
reconstruction of the large-scale structure from sparse, noisy and very
incomplete data. A general approach for the estimation of cosmological
parameters and the reconstruction of the density and velocity fields is
presented here, based on maximum likelihood analysis, Wiener filtering and
constrained realizations. Radial velocity surveys and the IRAS 1.2 Jy redshift
survey are used to reconstruct the Zone of Avoidance.


title: XMM-Newton observations of the BL Lac MS 0737+7441

abstract:
  We report on the XMM-Newton observations of the BL Lac object MS 0737.9+7441
during the performance verification phase. A simple power-law fit provides an
adequate description of the integrated spectrum in the 0.2-10 keV energy band.
The photon index is slightly steeper in the EPIC pn data with 2.38+-0.01
compared to the EPIC MOS data (2.28+-0.01). The difference is most probably due
to the present uncertainties in the calibration of the EPIC MOS and EPIC pn
data sets. We report evidence for intrinsic absorption in the distant BL Lac
above the Galactic column N_H,Gal=3.2*10^20 cm^-2 which is N_H,fit(z=0.315)=
(2.70+-0.20)*10^20cm^-2 in the EPIC pn data and N_H,fit(z=0.315)=
(3.25+-0.25)*10^20cm^-2 in the EPIC MOS data assuming neutral gas and solar
abundances. The flux variations are found to be of the order of 10 %.


title: VLBI imaging of the gravitational lenses B1422+231 and MGJ0414+0534

abstract:
  We present wide-field images of the quadruple gravitational lenses B1422+231
and MGJ0414+0534 obtained from global Very Long Baseline Interferometry (VLBI)
observations at 8.4 GHz on 23 November 1997. We present also a lens model for
MGJ0414+0534, which reproduces the core positions and flux densities of the
VLBI images, combining a singular isothermal ellipsoid with external shear, and
a singular isothermal sphere to represent, respectively, the main lens galaxy
and its neighbor, a faint galaxy near one of the images.


title:
Anisotropic inverse Compton scattering in radio galaxies and particle
  energy distribution

abstract:
  In this talk we briefly review the inverse Compton (IC) scattering of nuclear
photons in the lobes of radio galaxies and quasars. We concentrate on the
possibility to test this model with the Chandra observatory and to constrain
the electron energy distribution by measuring the X-ray fluxes produced by this
effect. We also discuss the evidence for IC scattering of nuclear photons in
the powerful radio galaxies.


title:
Measurement of the Cosmic Ray Energy Spectrum and Composition from
  10^{17} to 10^{18.3} eV Using a Hybrid Fluorescence Technique

abstract:
  We study the spectrum and average mass composition of cosmic rays with
primary energies between 10^{17} eV and 10^{18} eV using a hybrid detector
consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon
array. Measurements have been made of the change in the depth of shower maximum
as a function of energy. A complete Monte Carlo simulation of the detector
response and comparisons with shower simulations leads to the conclusion that
the cosmic ray intensity is changing f rom a heavier to a lighter composition
in this energy range. The spectrum is consistent with earlier Fly's Eye
measurements and supports the previously found steepening near 4 \times 10^{17}
eV .


title: Non-Linear Evolution of the r-Modes in Neutron Stars

abstract:
  The evolution of a neutron-star r-mode driven unstable by gravitational
radiation (GR) is studied here using numerical solutions of the full non-linear
fluid equations. The amplitude of the mode grows to order unity before strong
shocks develop which quickly damp the mode. In this simulation the star loses
about 40% of its initial angular momentum and 50% of its rotational kinetic
energy before the mode is damped. The non-linear evolution causes the fluid to
develop strong differential rotation which is concentrated near the surface and
especially near the poles of the star.


title:
The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables
  Determined from Cluster Turn-offs. II. Results from 12 Galactic Clusters and
  OB Associations

abstract:
  Here we examine 12 Galactic clusters and OB associations containing
Wolf-Rayet stars (W-Rs) and/or Luminous Blue Variables (LBVs), in order to
assess the progentor masses of these evolved massive stars. We find that in the
Milky Way, early-type WN stars evolve from stars with masses as low as 20Mo.
Some early-type WN stars are found in clusters with very high turn-off masses,
supporting our earlier results that the "WNE" class of W-Rs is a common stage
in the evolution of stars with a wide range of mases. In contrast, the
late-type WNs (particularly those of WN7 class) and the LBVs are only found in
clusters with the very highest turn-off masses, suggesting that only the most
massive stars evolve to these objects. An examination of the environment of the
archetype LBV Eta Car reveals that this star is coeval with the rest of the
Tr14/16 association, suggesting that its LBV properties is a normal consequence
of evolution, and has little to do with the possibility that it is a binary.


title:
A Neutron-Star Identification for the High-Energy Gamma-ray Source 3EG
  J1835+5918 Detected in the ROSAT All-Sky Survey

abstract:
  In the error box of 3EG J1835+5918, the brightest as-yet unidentified EGRET
source at intermediate Galactic latitude, we find a weak, ultrasoft X-ray
source at energies E < 0.3 keV in the ROSAT All-Sky Survey. Deep optical
imaging at the location of this source, as pinpointed by an observation with
the ROSAT HRI, reveals a blank field to a limit of V > 25.2. The corresponding
lower limit on f_X/f_V is 300, which signifies that the X-ray source is
probably a thermally emitting neutron star. Considering our previous complete
multiwavelength survey of the 3EG J1835+5918 region which failed to find any
other notable candidate for identification with 3EG J1835+5918, we propose that
this X-ray source, RX J1836.2+5925, is a rotation-powered gamma-ray pulsar
which is either older or more distant than the prototype Geminga. We see
marginal evidence for variability between two ROSAT HRI observations. If real,
this would indicate that the X-ray emission has an external origin, perhaps due
to intermittent heating of the polar caps by a variable particle accelerator.
RX J1836.2+5925 could even be an old, recycled pulsar, which may nevertheless
have a high gamma-ray efficiency.


title: Metal Enrichment and Temperature of the Intergalactic Medium

abstract:
  Hydrodynamic simulations of Lyman alpha clouds based on ab inito cosmological
models have produced results that are in broad agreement with observations.
However, further analyses have revealed that, with progressively higher
numerical resolution, the median or cutoff line width of the simulated Lyman
alpha clouds (i.e. the Doppler parameter) appears to converge to a value
significantly below what is observed at z~3 (by about a factor of 1.5). These
convergence test simulations do not include feedback from star formation. Given
the observed metallicity in the Lyman alpha clouds we suggest that supernovae,
which presumably polluted the IGM with metals, may have deposited a sufficient
amount of energy in the IGM to reconcile the theory with observations. Simple
arguments immediately narrow the redshift range of pollution down to
4<z_{dep}<9. It seems quite certain that dwarf and sub-dwarf galaxies with
total masses in the range 10^{6.5-9.0}Msun have to be largely responsible for
the pollution. Furthermore, it is implied that either star formation is very
efficient or metal yield is very high for these early dwarf galaxies, if the
mean metallicity in the universe at z=3 is as high as <Z>=0.01Zsun. Finally,
assuming the specific supernova heating energy is proportional to the
metallicity of a gas, we note that the picture proposed here would be
consistent with supernovae being the apparently needed heating source for the
intra-cluster gas, if the required heating of the intra-cluster gas is no
greater than 1 keV per particle.


title:
A 10-micron Search for Inner-Truncated Disks Among Pre-Main-Sequence
  Stars With Photometric Rotation Periods

abstract:
  We use mid-IR (primarily 10 $\mu$m) photometry as a diagnostic for the
presence of disks with inner cavities among 32 pre-main sequence stars in Orion
and Taurus-Auriga for which rotation periods are known and which do not show
evidence for inner disks at near-IR wavelengths. Disks with inner cavities are
predicted by magnetic disk-locking models that seek to explain the regulation
of angular momentum in T Tauri stars. Only three stars in our sample show
evidence for excess mid-IR emission. While these three stars may possess
truncated disks consistent with magnetic disk-locking models, the remaining 29
stars in our sample do not. Apparently, stars lacking near-IR excesses in
general do not possess truncated disks to which they are magnetically coupled.
  We discuss the implications of this result for the hypothesis of
disk-regulated angular momentum. Evidently, young stars can exist as slow
rotators without the aid of present disk-locking, and there exist very young
stars already rotating near breakup velocity whose subsequent angular momentum
evolution will not be regulated by disks. Moreover, we question whether disks,
when present, truncate in the manner required by disk-locking scenarios.
Finally, we discuss the need for rotational evolution models to take full
account of the large dispersion of rotation rates present at 1 Myr, which may
allow the models to explain the rotational evolution of low-mass pre-main
sequence stars in a way that does not depend upon braking by disks.


title: X-ray Imaging Spectroscopy of Abell 1835

abstract:
  We present detailed spatially-resolved spectroscopy results of the
observation of Abell 1835 using the European Photon Imaging Cameras (EPIC) and
the Reflection Grating Spectrometers (RGS) on the XMM-Newton observatory. Abell
1835 is a luminous ($10^{46}$ ergs ${s}^{-1}$), medium redshift ($z=0.2523$),
  X-ray emitting cluster of galaxies. The observations support the
interpretation that large amounts of cool gas are present in a multi-phase
medium surrounded by a hot ($kT_{e}$=8.2 keV) outer envelope. We detect O VIII
Ly$\alpha$ and two Fe XXIV complexes in the RGS spectrum. The emission measure
of the cool gas below $kT_{e}$=2.7 keV is much lower than expected from
standard cooling-flow models, suggesting either a more complicated cooling
process than simple isobaric radiative cooling or differential cold absorption
of the cooler gas.


title: High-Resolution spectroscopy of the low-mass X-ray binary EXO 0748-67

abstract:
  We present initial results from observations of the low-mass X-ray binary EXO
0748-67 with the Reflection Grating Spectrometer on board the XMM-Newton
Observatory. The spectra exhibit discrete structure due to absorption and
emission from ionized neon, oxygen, and nitrogen. We use the quantitative
constraints imposed by the spectral features to develop an empirical model of
the circumsource material. This consists of a thickened accretion disk with
emission and absorption in the plasma orbiting high above the binary plane.
This model presents challenges to current theories of accretion in X-ray binary
systems.


title:
Complex resonance absorption structure in the X-ray spectrum of
  IRAS13349+2438

abstract:
  The luminous infrared-loud quasar IRAS 13349+2438 was observed with the
XMM-Newton Observatory as part of the Performance Verification program. The
spectrum obtained by the Reflection Grating Spectrometer (RGS) exhibits broad
(v ~ 1400 km/s FWHM) absorption lines from highly ionized elements including
hydrogen- and helium-like carbon, nitrogen, oxygen, and neon, and several iron
L-shell ions (Fe XVII - XX). Also shown in the spectrum is the first
astrophysical detection of a broad absorption feature around lambda = 16 - 17
Ang identified as an unresolved transition array (UTA) of 2p - 3d inner-shell
absorption by iron M-shell ions in a much cooler medium; a feature that might
be misidentified as an O VII edge when observed with moderate resolution
spectrometers. No absorption edges are clearly detected in the spectrum. We
demonstrate that the RGS spectrum of IRAS 13349+2438 exhibits absorption lines
from at least two distinct regions, one of which is tentatively associated with
the medium that produces the optical/UV reddening.


title: A universal angular momentum profile for galactic halos

abstract:
  [Abridged] We study the angular-momentum profiles of a statistical sample of
halos drawn from a high-resolution N-body simulation of the LCDM cosmology. We
find that the cumulative mass distribution of specific angular momentum, j, in
a halo of mass Mv is well fit by a universal function, M(<j) = Mv \mu
j/(j_0+j). This profile is defined by one shape parameter (\mu or j_0) in
addition to the global spin parameter \lambda. It follows a power-law over most
of the mass, and flattens at large j, with the flattening more pronounced for
small values of \mu. Compared to a uniform sphere in solid-body rotation, most
halos have a higher fraction of their mass in the low- and high-j tails of the
distribution. The spatial distribution of angular momentum in halos tends to be
cylindrical and is well-aligned within each halo for ~80% of the halos. We
investigate two ideas for the origin of this profile. The first is based on a
revised version of linear tidal-torque theory combined with extended
Press-Schechter mass accretion, and the second focuses on j transport in minor
mergers. Finally, we briefly explore implications of the M(<j) profile on the
formation of galactic disks assuming that j is conserved during an adiabatic
baryonic infall. The implied gas density profile deviates from an exponential
disk, with a higher density at small radii and a tail extending to large radii.
The steep central density profiles may imply disk scale lengths that are
smaller than observed. This is reminiscent of the "angular-momentum problem"
seen in hydrodynamic simulations, even though we have assumed perfect j
conservation. A possible solution is to associate the central excesses with
bulge components and the outer regions with extended gaseous disks.


title: Spin Profile of Galactic Halos and Disk Formation

abstract:
  We summarize recent developments in the study of the origin of halo spin
profiles and preliminary implications on disk formation. The specific
angular-momentum distributions within halos in N-body simulations match a
universal shape, M(<j) \propto j/(j_0+j). It is characterized by a power law
over most of the mass, and one shape parameter in addition to the spin
parameter \lambda. The angular momentum tends to be aligned throughout the halo
and of cylindrical symmetry. Even if angular momentum is conserved during
baryonic infall, the resultant disk density profile is predicted to deviate
from exponential, with a denser core and an extended tail. A slightly corrected
version of the scaling relation due to linear tidal-torque theory is used to
explain the origin of a typical power-law profile in shells, j(M) \propto M^s
with s \gsim 1. While linear theory crudely predicts the amplitudes of halo
spins, it is not a good predictor of their directions. Independently, mergers
of halos are found to produce a similar profile due to j transfer from the
orbit to the product halo via dynamical friction and tidal stripping. The halo
spin is correlated with having a recent major merger, though this correlation
is weakened by mass loss. These two effects are due to a correlation between
the spins of neighboring halos and their orbit, leading to prograde mergers.


title:
Explosive Nucleosynthesis in Aspherical Hypernova Explosions and Late
  Time Spectra of SN1998bw

abstract:
  Aspherical explosion models for the hypernova (hyper-energetic supernova) SN
1998bw are presented. Nucleosynthesis in aspherical explosions is examined with
a two-dimensional hydrodynamical code and a detailed nuclear reaction network.
Aspherical explosions lead to a strong $\alpha$-rich freezeout, thus enhancing
the abundance ratios [$^{44}$Ca, $^{48}$Ti, and $^{64}$Zn / Fe] in the ejecta.
The nebular line profiles of the Fe-dominated blend near 5200 \AA and of [\OI]
6300,6363 \AA are calculated and compared with the observed late time spectra
of SN 1998bw. Compared with the spherical model, the unusual features of the
observed nebular spectra can be better explained if SN 1998bw is a strongly
aspherical explosion with a kinetic energy of $\sim 10^{52}$ ergs viewed from
near the jet direction.


title:
The differential energy distribution of the universal density profile of
  dark halo

abstract:
  We study the differential energy distribution of dark matter halos, carrying
out cosmological N-body simulation.We give an analytical formula of the
differential energy distribution of dark matter in the halos obtained by the
numerical simulation.From the analytical formula we reconstruct the density
profile described by the Navarro,Frenk, & White (NFW) profile.The NFW profile
is consistent with the analytical formula of our fractional mass distribution.
We find that a parameter in our analytical formula of differential energy
distribution which is related with the slope of inner cusp of dark halo.We
obtain the distribution function for the NFW profile which has sharp cut off at
the high binding energy.We discuss physical reason of form of the analytical
formula.


title:
Optimising background-limited observing during bright-moon phases and
  twilight

abstract:
  For the majority of optical observing programs, the sky brightness provides
the fundamental limit to signal detection such that the scientific feasibility
is largely dictated by the moon phase. Since most observatories do not have the
resources to build expensive high-resolution or infrared instruments, they are
increasingly at a loss as to how to exploit bright time. We show that, with due
consideration of the field and moon position, it is possible to undertake `dark
time' observing programs under `bright time' conditions. Our recommendations
are particularly appropriate to all-sky survey programs.
  In certain instances, there are gains in observing efficiency with the use of
a polariser, which can significantly reduce the moonlight (or twilight)
sky-background flux relative to an extraterrestrial flux. These gains are
possible in background-limited cases because the sky background can be highly
polarised, due to scattering, around ninety degrees away from the moon (or
sun). To take advantage of this, only minor modifications to existing
instruments are needed.


title:
Stars of the Draco Dwarf Spheroidal Galaxy Beyond its Measured Tidal
  Boundary

abstract:
  We report R- and V-band photometry derived from CCD imaging for objects in
nine fields in and around the Draco dwarf spheroidal galaxy. The most distant
fields are about 1.3 degrees from the center. We use these data to search for
Draco stars outside of its measured tidal boundary. The search involves three
methods: 1) Plotting color-magnitude diagrams for individual fields, for
sections of fields, and for combined fields and sections. A color-magnitude
diagram can reveal a population of Draco stars by the presence of the expected
principal sequences. 2) Measuring field-to-field fluctuations and 3) measuring
intra-field fluctuations in the surface density of objects located near the
Draco principal sequences in the color-magnitude diagram. We find evidence for
the presence of Draco stars immediately beyond the measured tidal boundary of
Draco and place an upper limit on the number of such stars in more distant
fields that lie close to the extension of its major axis. The best evidence is
the presence of the Draco principal sequences in the color-magnitude diagram
for some combined fields and sections of fields. The measurements of the
field-to-field fluctuations in the stellar surface density confirm this result.


title:
Continuous Fields and Discrete Samples: Reconstruction through Delaunay
  Tessellations

abstract:
  Here we introduce the Delaunay Density Estimator Method. Its purpose is
rendering a fully volume-covering reconstruction of a density field from a set
of discrete data points sampling this field. Reconstructing density or
intensity fields from a set of irregularly sampled data is a recurring key
issue in operations on astronomical data sets, both in an observational context
as well as in the context of numerical simulations. Our technique is based upon
the stochastic geometric concept of the Delaunay tessellation generated by the
point set. We shortly describe the method, and illustrate its virtues by means
of an application to an N-body simulation of cosmic structure formation. The
presented technique is a fully adaptive method: automatically it probes high
density regions at maximum possible resolution, while low density regions are
recovered as moderately varying regions devoid of the often irritating
shot-noise effects. Of equal importance is its capability to sharply and
undilutedly recover anisotropic density features like filaments and walls. The
prominence of such features at a range of resolution levels within a
hierarchical clustering scenario as the example of the standard CDM scenario is
shown to be impressively recovered by our scheme.


title: The evolution of AGN in the Hard X-rays from HELLAS

abstract:
  We present optical spectroscopic identification of sources identified in the
BeppoSAX MECS fields of the High Energy LLarge Area Survey (HELLAS). In total
62 sources from a sample of 115 brighter than F_{5-10keV}>5x10^{-14} cgs have
been identified. We find a density of 13-21 sources/deg^2 at
F_{5-10keV}>5x10^{-14} cgs, which contribute to 20-30 % of the hard X-ray
background. Evidences are found for type 1 AGN being more absorbed with
increasing redshift or luminosity. The low redshift (z<0.2) ratio of type 2 to
type 1 AGN is 3+/-1.5, in agreement with the unified models for AGN. The
luminosity function of type 1 AGN in the 2-10 keV band is preliminary fitted by
a two-power law function evolving according to a pure luminosity evolution
model: L~(1+z)^{2.2}.


title: Trapped Disk Oscillations and Stable QPOs in Microquasars

abstract:
  The observed quasi-periodic oscillations (QPOs) in low-mass X-ray binaries
have been suggested to be probably related to the characteristic oscillation
modes in the inner part of a relativistic accretion disk. In this paper we
study the trapped feature of these oscillation modes by considering the radial
perturbations and viscosity effects. We find that the trapped oscillations are
amplified significantly when the viscosity parameter increases and the trapped
size varies when the radial wavenumber and Mach number change. Our results
support that the stable hundred-hertz QPOs and their low fractional rms
amplitudes found in two Galactic microquasars may be explained by some trapped
non-damping oscillation modes in the inner part of accretion disks around
rotating black holes.


title: Cosmic ray photodisintegration and the knee of the spectrum

abstract:
  We explore in some detail the scenario proposed to explain the observed knee
of the cosmic ray (CR) spectrum as due to the effects of photodisintegration of
the CR nuclei by interactions with optical and soft UV photons in the source
region. We show that the photon column densities needed to explain the
experimental data are significantly lower than those obtained in previous
estimations which neglected multinucleon emission in the photodisintegration
process. We also treat more accurately the photodisintegration thresholds, we
discuss the effects of photopion production processes and the neutron escape
mechanism, identifying the physical processes responsible for the qualitative
features of the results. This scenario would require the CR nuclei to traverse
column densities of $\sim 5 \times 10^{27}- 2 \times 10^{28}$ eV/cm$^2$ after
being accelerated in order to reproduce the observed knee, and predicts that
the CR composition should become lighter above $\sim 10^{16}$ eV.


title: The disc-jet connection in GRS 1915+105

abstract:
  We have compared simultaneous Ryle Telescope (RT) radio and Rossi X-Ray
Timing Explorer (RXTE) X-ray observations of the galactic microquasar GRS
1915+105. We find that radio emission, and therefore also the radio jet,
requires the presence of long (~100s), hard dips in the X-ray light curve which
seem to have a one-to-one relation with the radio events: each hard dip
produces a new radio "flare". We discuss the characteristic features of the
connection between the hard X-ray states and the radio emission.


title: Test particle acceleration by rotating jet magnetospheres

abstract:
  Centrifugal acceleration of charged test particles at the base of a rotating
jet magnetosphere is considered. Based on an analysis of forces we derive the
equation for the radial accelerated motion and present an analytical solution.
It is shown that for particles moving outwards along rotating magnetic field
lines, the energy gain is in particular limited by the breakdown of the
bead-on-the-wire approximation which occurs in the vicinity of the light
cylinder $r_{L}$. The corresponding upper limit for the maximum Lorentz factor
$\gamma_{max}$ for electrons scales $\propto B^{2/3} r_{L}^{2/3}$, with $B$ the
magnetic field strength at $r_{L}$, and is at most of the order of a
$10^2-10^3$ for the conditions regarded to be typical for BL Lac objects. Such
values suggest that this mechanism may provide pre-accelerated seed particles
which are required for efficient Fermi-type particle acceleration at larger
scales in radio jets.


title: Evolving Stellar Background Radiation and Gamma-Ray Optical Depth

abstract:
  We present a semi-empirical model for the evolving far-infrared to
ultraviolet diffuse background produced by stars in galaxies. The model is
designed to reproduce the results of deep galaxy surveys, and therefore may be
considered as a cosmology-independent lower limit to the extragalactic
background light. Using this model and recent HEGRA data, we infer the
intrinsic spectrum at multi-TeV gamma-ray energies for Mkn501 and find that it
is consistent with a power law of spectral index 2.49+-0.04. In turn, this
finding renders it rather unlikely that the present-day infrared background has
an intensity as high as claimed by Finkbeiner et al. (2000). Future 10GeV to
TeV observations could be used to either constrain the ultraviolet-to-infrared
background model at high redshifts or cosmological parameters.


title:
The Infrared Spectral Energy Distribution of Normal Star-Forming
  Galaxies

abstract:
  We present a new phenomenological model for the spectral energy distribution
of normal star-forming galaxies between 3 and 1100 microns. A sequence of
realistic galaxy spectra are constructed from a family of dust emission curves
assuming a power law distribution of dust mass over a wide range of
interstellar radiation fields. For each interstellar radiation field heating
intensity we combine emission curves for large and very small grains and
aromatic feature carriers. The model is constrained by IRAS and ISOCAM
broadband photometric and ISOPHOT spectrophotometric observations for our
sample of 69 normal galaxies; the model reproduces well the empirical spectra
and infrared color trends. These model spectra allow us to determine the
infrared energy budget for normal galaxies, and in particular to translate
far-infrared fluxes into total (bolometric) infrared fluxes. The 20 to 42
micron range appears to show the most significant growth in relative terms as
the activity level increases, suggesting that the 20-42 micron continuum may be
the best dust emission tracer of current star formation in galaxies. The
redshift dependence of infrared color-color diagrams and the far-infrared to
radio correlation for galaxies are also explored.


title: A possible black hole binary in Mkn 501

abstract:
  A simple binary model for Mkn~501 is considered under the assumption that the
TeV and X-ray periodicity of $\sim 23$ days, observed during the flaring state
in 1997, may be basically interpreted as a doppler-shifted flux modulation due
to the orbital motion of the relativistic jet. For the typical jet properties
inferred from emission models, we find an intrinsic orbital period of $(6-14)$
yrs and a centre-of-mass distance of $(2-3.5) \times 10^{16}$ cm, the binary
thus being a very close system. If the binary separation corresponds to that at
which gravitational radiation becomes dominant, one may obtain a maximum
allowed primary mass of $\sim 10^8 M_{\odot}$ and a corresponding maximum
allowed secondary mass in the range of $\sim (1-9)\times 10^7 M_{\odot}$
assuming that gas accretion occurs on around the salpeter time scale.
Interestingly such values agree with the black hole masses expected from merger
scenarios.


title:
1.65mic (H-band) surface photometry of galaxies. VI: The history of star
  formation in normal late-type galaxies

abstract:
  We have collected a large body of NIR (H band), UV (2000 A) and Halpha
measurements of late-type galaxies. These are used, jointly with spectral
evolutionary synthesis models, to study the initial mass function (IMF) in the
mass range m > 2 Mo. For spirals (Sa-Sd), Magellanic irregulars (Im) and blue
compact dwarfs (BCD), our determination is consistent with a Salpeter IMF with
an upper mass cutoff M_up = 80 Mo. The history of star formation and the amount
of total gas (per unit mass) of galaxies are found to depend primarily on their
total masses (as traced by the H band luminosities) and only secondarily on
morphological type. The present star formation activity of massive spirals is
up to 100 times smaller than that average over their lifetime, while in low
mass galaxies it is comparable to or higher than that at earlier epochs. Dwarf
galaxies have presently larger gas reservoirs per unit mass than massive
spirals. The efficiency in transforming gas into stars and the time scale for
gas depletion (10 Gyrs) are independent of the luminosity and/or of the
morphological type. These evidences are consistent with the idea that galaxies
are coeval systems,that they evolved as closed-boxes forming stars following a
simple, universal star formation law whose characteristic time scale is small
(1 Gyr) in massive spirals and large (10 Gyr) in low mass galaxies. A similar
conclusion was drawn by Gavazzi and Scodeggio (1996) to explain the
colour-magnitude relation of late-type galaxies. The consequences of this
interpretation on the evolution of the star formation rate and of the gas
density per comoving volume of the Universe with look-back time are discussed.


title: Gravitational Excitons as Dark Matter

abstract:
  In earlier work it was pointed out that for warped product spacetimes the
conformal (geometrical moduli) excitations of the internal compactified factor
spaces should be observable as massive scalar fields in the external spacetime.
Here we show that these scalar fields (gravitational excitons) describe weakly
interacting particles and can be considered as dark matter component. Masses of
the gravexcitons are defined by the form of the effective potential of the
theory and the stabilization scales of the internal space. This implies that
different stabilization scales result in different types of DM. An essential
role is played by the effective potential. On the one hand, its minima fix
possible stabilization scales of the internal spaces; on the other hand, they
provide possible values for the effective cosmological constant.


title:
First Light Measurements with the XMM-Newton Reflection Grating
  Spectrometers: Evidence for an Inverse First Ionisation Potential Effect and
  Anomalous Ne A bundance in the Coronae of HR 1099

abstract:
  The RS CVn binary system HR 1099 was extensively observed by the XMM-Newton
observatory in February 2000 as its first-light target. A total of 570 ks of
exposure time was accumulated with the Reflection Grating Spectrometers (RGS).
The integrated X-ray spectrum between 5-35 Angstrom is of unprecedented quality
and shows numerous features attributed to transitions of the elements C, N, O,
Ne, Mg, Si, S, Fe, and Ni. We perform an in-depth study of the elemental
composition of the average corona of this system, and find that the elemental
abundances strongly depend on the first ionisation potential (FIP) of the
elements. But different from the solar coronal case, we find an inverse FIP
effect, i.e., the abundances (relative to oxygen) increase with increasing FIP.
Possible scenarios, e.g., selective enrichment due to Ne-rich flare-like
events, are discussed.


title: Models for SNeIa and Evolutionary Effects with Redshift

abstract:
  Based on detailed models for the explosions, light curves and NLTE-spectra,
evolutionary effects of Type Ia Supernovae (SNe Ia) with redshift have been
studied to evaluate their size on cosmological time scales,how the effects can
be recognized and how one may be able to correct for them. We show that delayed
detonation models can account for the majority of observations of spectra and
LCs. IR observations are a new and powerful tools to constrain explosion
models, e.g. by a strong MgII line at propagation in the WD. A strong Mg II
line at 1.05 mu shows that nuclear burning takes place at the outer, low
density layers. This requires a transition from the deflagration to the
detonation regime of the nuclear burning front, or a very fast deflagration. We
put the models into context with the empirical brightness decline relation
which is widely applied to use SNe Ia as yardsticks on cosmological distance
scales. This relation can be well understood in the framework of M(Ch)-WDs as a
consequence of the opacity effects in combination with the amount of 56Ni which
determines the brightness. We show that evolution may produce an offset in the
brightness decline relation but it is restricted to a few tenth of a magnitude.
Effects reveal themself by changes in the U and UV fluxes, and in a change in
the maximum brightness/decline relation by DM is about 0.1Dt where Dt is the do
difference between local and distant SN-samples. According to new data by Alde-
ring et al.(2000), Dt<1day and, likely, evolution will not eliminate Lambda.


title: Doppler Tomography

abstract:
  I review the method of Doppler tomography which translates binary-star line
profiles taken at a series of orbital phases into a distribution of emission
over the binary. I begin with a discussion of the basic principles behind
Doppler tomography, including a comparison of the relative merits of maximum
entropy regularisation versus filtered back-projection for implementing the
inversion. Following this I discuss the issue of noise in Doppler images and
possible methods for coping with it. Then I move on to look at the results of
Doppler Tomography applied to cataclysmic variable stars. Outstanding successes
to date are the discovery of two-arm spiral shocks in cataclysmic variable
accretion discs and the probing of the stream/magnetospheric interaction in
magnetic cataclysmic variable stars. Doppler tomography has also told us much
about the stream/disc interaction in non-magnetic systems and the irradiation
of the secondary star in all systems. The latter indirectly reveals such
effects as shadowing by the accretion disc or stream. I discuss all of these
and finish with some musings on possible future directions for the method. At
the end I include a tabulation of Doppler maps published in refereed journals.


title:
The Importance of Fourier Phases for the Morphology of Gravitational
  Clustering

abstract:
  The phases of the Fourier modes appearing in a plane-wave expansion of
cosmological density fields play a vital role in determining the morphology of
gravitationally-developed clustering. We demonstrate this qualitatively and
quantitatively using simulations. In particular, we use cross-correlation and
rank-correlation techniques to quantify the agreement between a simulated
distribution and phase-only reconstructions. The phase-only reconstructions
exhibit a high degree of correlation with the original distributions, showing
how meaningful spatial reconstruction of cosmological density fields depends
more on phase accuracy than on amplitudes.


title:
The Tully-Fisher Relation as a Measure of Luminosity Evolution: A Low
  Redshift Baseline for Evolving Galaxies

abstract:
  We use optical rotation curves to investigate the R-band Tully-Fisher
properties of a sample of 90 spiral galaxies in close pairs. The galaxies
follow the Tully-Fisher relation remarkably well, with the exception of eight
distinct 3-sigma outliers. Although most of the outliers show signs of recent
star formation, gasdynamical effects are probably the dominant cause of their
anomalous Tully-Fisher properties. Four outliers with small emission line
widths have very centrally concentrated line emission and truncated rotation
curves; the central emission indicates recent gas infall after a close
galaxy-galaxy pass. These four galaxies may be local counterparts to compact,
blue galaxies at intermediate redshift. The remaining galaxies have a
negligible offset from the reference Tully-Fisher relation, but a shallower
slope (2.6-sigma significance) and a 25% larger scatter. We characterize the
non-outlier sample with measures of distortion and star formation to search for
third parameter dependence in the residuals of the TF relation. Severe
kinematic distortion is the only significant predictor of TF residuals; this
distortion is not, however, responsible for the slope difference from the
reference distribution.
  Because the outliers are easily removed by sigma clipping, we conclude that
even in the presence of some tidal distortion, detection of moderate luminosity
evolution should be possible with high-redshift samples the size of this
90-galaxy study. (Abridged.)


title: Jet Induced Supernovae-Hydrodynamics and Observational Consequences

abstract:
  Core collapse supernovae (SN) are the final stages of stellar evolution in
massive stars during which the central region collapses, forms a neutron star
(NS), and the outer layers are ejected. Recent explosion scenarios assumed that
the ejection is due to energy deposition by neutrinos into the envelope but
detailed models do not produce powerful explosions. There is mounting evidence
for an asphericity in the SN which is difficult to explain within this picture.
This evidence includes the observed high polarization, pulsar kicks, high
velocity iron-group and intermediate-mass elements material observed in
remnants, etc.
  The discovery of highly magnetars revived the idea that the basic mechanism
for the ejection of the envelope is related to a highly focused MHD-jet formed
at the NS. Our 3-D hydro simulations of the jet propagation through the star
confirmed that the mechanism can explain the asphericities.
  In this paper, detailed 3-D models for jet induced explosions of "classical"
core collapse supernovae are presented. We demonstrate the influence of the jet
properties and of the underlaying progenitor structure on the final density and
chemical structure. Finally, we discuss the observational consequences,
predictions and tests of this scenario.


title: A young stellar group associated with HD 199143 (d = 48 pc)

abstract:
  We present new optical and ultraviolet spectroscopy of the anomalous EUV
emitter HD 199143 (F8V). High resolution spectra in the Halpha and Na I D
wavelength regions show evidence for very rapid (a few hundred km/s) rotation
of the stellar photosphere. Using archive IRAS data we also show that the star
has excess emission above photospheric levels at 12 micron. IUE data of
HD199143 reveal the presence of emission lines of Mg II, C I, C II, C III, C
IV, Si IV, He II and N V and show a large variability, both in the continuum
and line fluxes. We propose that all available data of HD 199143 can be
explained by assuming that is has been spun up by accretion of material from a
close T Tauri like companion, responsible for the emission lines, the
ultraviolet variability and the excess infrared emission. The bursting or
flaring nature of this object, mostly in high energies, could be explained as
episodic mass transfer between the star and its close companion. We show that
HD 199143 and the Li-rich late-type dwarf BD-17 6128 form a physical pair and
suggest that both may be part of a new nearby (48 pc) young (approx. 10^7 yr)
stellar association in Capricornius.


title:
Primordial Isocurvature Perturbations: Testing the Adiabaticity of the
  CMB Anisotropy

abstract:
  Prospects for testing the adiabaticity of the primordial cosmological
perturbations using MAP and PLANCK are evaluated. The most general cosmological
perturbation in a universe with just baryons, photons, neutrinos, and a cold
dark matter (CDM) component is described. In addition to the familiar adiabatic
mode, there are four nonsingular isocurvature modes: a baryon isocurvature
mode, a CDM isocurvature mode, a neutrino density isocurvature mode, and a
neutrino velocity isocurvature mode. The most general perturbation is described
by a 5x5, positive-definite, symmetric, matrix-valued function of wave number
whose off-diagonal elements represent the correlations between the above
mentioned modes. We found that when three modes and their correlations are
admitted, the fractional uncertainties in the cosmological parameters and
amplitudes of the isocurvature modes and their correlations become of order
unity. These degeneracies, however, can be broken with the polarization
information provided by PLANCK, reducing the uncertainties to below the ten
percent level. Polarization is thus crucial to testing the adiabaticity of the
primordial fluctuations.


title:
High resolution X-Ray spectroscopy of Zeta Puppis with the XMM-Newton
  Reflection Grating Spectrometer

abstract:
  We present the first high resolution X-ray spectrum of the bright O4Ief
supergiant star Zeta Puppis, obtained with the Reflection Grating Spectrometer
on-board XMM-Newton. The spectrum exhibits bright emission lines of
hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and
silicon, as well as neon-like ions of iron. The lines are all significantly
resolved, with characteristic velocity widths of order 1000-1500 km s^{-1}. The
nitrogen lines are especially strong, and indicate that the shocked gas in the
wind is mixed with CNO-burned material, as has been previously inferred for the
atmosphere of this star from ultraviolet spectra. We find that the forbidden to
intercombination line ratios within the helium-like triplets are anomalously
low for N VI, O VII, and Ne IX. While this is sometimes indicative of high
electron density, we show that in this case, it is instead caused by the
intense ultraviolet radiation field of the star. We use this interpretation to
derive constraints on the location of the X-ray emitting shocks within the wind
that are consistent with current theoretical models for this system.


title: Extensive Serendipitous X-ray Coverage of a Flare Star with ROSAT

abstract:
  We report the serendipitous discovery of a flare star observed with the ROSAT
X-ray observatory. From optical spectra, which show strong and variable
emission lines of the hydrogen Balmer series and neutral helium, we classify
this object as a M3.0Ve star, and estimate a distance of 52 pc from published
photometry. Due to the star's close proximity (13.6') to the calibration source
and RS CVn binary AR Lacertae, long term X-ray coverage is available in the
ROSAT archive (~50 hours spanning 6.5 years). Two large flare events occurred
early in the mission (6-7/1990), and the end of a third flare was detected in
6/1996. One flare, observed with the Position Sensitive Proportional Counter
(PSPC), had a peak luminosity Lx=1.1x10^{30} erg/s, an e-folding rise time of
2.2 hours and a decay time of 7 hours. This decay time is one of the longest
detected on a dMe star, providing evidence for the possibility of additional
heating during the decay phase. A large HRI flare (peak Lx=2.9x10^{30} erg/s)
is also studied. The "background" X-ray emission is also variable - evidence
for low-level flaring or microflaring. We find that >=59% of the HRI counts and
>=68% of the PSPC counts are due to flares. At least 41% of the HRI exposure
time and 47% of the PSPC are affected by detectable flare enhancement.


title: Small strange stars and marginally stable orbit in Newtonian theory

abstract:
  It is shown that for very rapidly rotating low mass strange stars the
marginally stable orbit is located above the stellar surface. This effect is
explained by the very important role of the oblateness of the rotating strange
star. The comparison with some ``academic'' examples is presented. This feature
is purely Newtonian in its nature and has nothing to do with relativistic
marginally stable orbit. The effect is very large and cannot be treated in a
perturbative way. It seems that strange stars as a very dense self-bound
objects are the only possibility in Nature to represent these toy models.