title: GRBs in the Cannonball model: an overview

abstract:
  The cannonball model of GRBs is very overt (and, thus, falsifiable) in its
hypothesis and results: all the considerations I review are based on explicit
analytical expressions derived, in fair approximations, from first principles.
The model provides a good description of all the data on all GRBs of known
redshift, has made correct predictions, and is unprecedentedly self-consintent,
simple and successful.


title: Searching for low mass objects around nearby dMe radio stars

abstract:
  Nearby M-dwarfs are best suited for searches of low mass companions. VLBI
phase-referencing observations with sensitive telescopes are able to detect
radio star flux-densities of tenths of mJy as well as to position the star on
the sky with submilliarcsecond precision. We have initiated a long-term
observational program, using EVN telescopes in combination with NASA DSN
dishes, to revisit the kinematics of nearby, single M dwarfs. The precision of
the astrometry allows us to search for possible companions with masses down to
1 Jupiter mass. In this contribution we report preliminary results of the first
observation epochs, in which we could detect some of the radio stars included
in our program.


title: Molecular hydrogen formation in the interstellar medium

abstract:
  We have developed a model for molecular hydrogen formation under
astrophysically relevant conditions. This model takes fully into account the
presence of both physisorbed and chemisorbed sites on the surface, allows
quantum mechanical diffusion as well as thermal hopping for absorbed H-atoms,
and has been benchmarked versus recent laboratory experiments on H2 formation
on silicate surfaces. The results show that H2 formation on grain surface is
efficient in the interstellar medium up to some 300K. At low temperatures
(<100K), H2 formation is governed by the reaction of a physisorbed H with a
chemisorbed H. At higher temperatures, H2 formation proceeds through reaction
between two chemisorbed H atoms. We present simple analytical expressions for
H2 formation which can be adopted to a wide variety of surfaces once their
surfaces characteristics have been determined experimentally.


title:
A Finite Difference Representation of Neutrino Radiation Hydrodynamics
  in Spherically Symmetric General Relativistic Space-Time

abstract:
  We present an implicit finite difference representation for general
relativistic radiation hydrodynamics in spherical symmetry. Our code,
Agile-Boltztran, solves the Boltzmann transport equation for the angular and
spectral neutrino distribution functions in self-consistent simulations of
stellar core collapse and postbounce evolution. It implements a dynamically
adaptive grid in comoving coordinates. Most macroscopically interesting
physical quantities are defined by expectation values of the distribution
function. We optimize the finite differencing of the microscopic transport
equation for a consistent evolution of important expectation values. We test
our code in simulations launched from progenitor stars with 13 solar masses and
40 solar masses. ~0.5 s after core collapse and bounce, the protoneutron star
in the latter case reaches its maximum mass and collapses further to form a
black hole. When the hydrostatic gravitational contraction sets in, we find a
transient increase in electron flavor neutrino luminosities due to a change in
the accretion rate. The muon- and tauon-neutrino luminosities and rms energies,
however, continue to rise because previously shock-heated material with a
non-degenerate electron gas starts to replace the cool degenerate material at
their production site. We demonstrate this by supplementing the concept of
neutrinospheres with a more detailed statistical description of the origin of
escaping neutrinos. We compare the evolution of the 13 solar mass progenitor
star to simulations with the MGFLD approximation, based on a recently developed
flux limiter. We find similar results in the postbounce phase and validate this
MGFLD approach for the spherically symmetric case with standard input physics.


title: Hot Horizontal Branch Stars: Predictions for Mass Loss

abstract:
  We predict mass-loss rates for the late evolutionary phases of low-mass
stars, with special emphasis on the consequences for the morphology of the
Horizontal Branch (HB). We show that the computed rates, as predicted by the
most plausible mechanism of radiation pressure on spectral lines, are too low
to produce EHB/sdB stars. This invalidates the scenario recently outlined by
Yong et al. (2000) to create these objects by mass loss on the HB. We argue,
however, that mass loss plays a role in the distribution of rotational
velocities of hot HB stars, and may -- together with the enhancement of heavy
element abundances due to radiative levitation -- provide an explanation for
the so-called ``low gravivity problem. The mass loss recipe derived for hot HB
(and extreme HB, sdB, sdOB) stars may also be applied to post-HB (AGB-manque,
UV-bright) stars over a range in effective temperatures between 12500 -- 40000
K.


title: Multi-frequency Study of Intraday Variable Sources

abstract:
  Intraday variability (IDV) of compact extragalactic radio sources is a
complex phenomenon and shows a wavelength dependent mixture of refractive
interstellar scintillation (RISS) (dominant at long cm-wavelengths) and
source-intrinsic effects (dominant at shorter wavelengths). Detailed
investigations of individual sources and new high frequency observations
suggest a source-intrinsic contribution to the IDV pattern at least in some
sources. However, the sizes of intraday variable sources at cm-wavelength are
typically smaller than the scattering size set by the ISM in our galaxy and
scintillation must be present, too. We present new IDV observations in
different regimes (from cm to sub-mm wavelengths) and show how such
multi-frequency study can be used as powerful instrument to describe different
aspects of IDV.


title:
Multiwavelength evidence for a 15-year periodic activity in the
  symbiotic nova V1016 Cygni

abstract:
  The ~15.1 years period found in the long-term UBV photoelectric and
photographic photometry of the symbiotic nova V1016 Cyg is detected also in the
(J-K) colour index and in the UV continuum and emission line fluxes from IUE
and HUT spectra. It could be interpreted either as the effect of recurrent
enhanced mass loss episodes from the Mira type variable companion to a hot
component along its ultra-wide orbit (proposed from recent HST observations) or
the true orbital period of the inner, unresolved binary of a triple system. A
410-day delay of the maximum of UV emission lines fluxes with respect to the
maximum of continuum was found. The pulsation period of the Mira type variable
was improved to 474+/-6 days.


title:
Atomic Hydrogen Gas in Dark-Matter Minihalos and the Compact High
  Velocity Clouds

abstract:
  We calculate the coupled hydrostatic and ionization structures of
pressure-supported gas clouds that are confined by gravitationally dominant
dark-matter (DM) mini-halos and by an external bounding pressure provided by a
hot medium. We focus on clouds that are photoionized and heated by the
present-day background metagalactic field and determine the conditions for the
formation of warm (WNM), and multi-phased (CNM/WNM) neutral atomic hydrogen
(HI) cores in the DM-dominated clouds. We consider LCDM dark-matter halos, and
we compute models for a wide range of halo masses, total cloud gas masses, and
external bounding pressures. We present models for the pressure-supported HI
structures observed in the Local Group dwarf galaxies Leo A and Sag DIG. We
then construct minihalo models for the multi-phased (and low-metallicity)
compact high-velocity HI clouds (CHVCs). If the CHVCs are drawn from the same
family of halos that successfully reproduce the dwarf galaxy observations, then
the CHVCs must be "circumgalactic objects" with characteristic distances of 150
kpc. For such systems we find that multi-phased behavior occurs for peak WNM HI
column densities between 2e19 and 1e20 cm^-2, consistent with observations. If
the large population of CHVCs represent "missing low-mass satellites" of the
Galaxy, then these clouds must be pressure-confined to keep the gas neutral.
For an implied CHVC minihalo scale velocity of v_s=12 km s^-1, the confining
pressure must exceed ~50 cm^-3 K. A hot (2e6 K) Galactic corona could provide
the required pressure at 150 kpc.


title: Discovery of a Group of Star-Forming Dwarf Galaxies in Abell 1367

abstract:
  We describe the properties of a remarkable group of actively star-forming
dwarf galaxies and HII galaxies in the Abell 1367 cluster, which were
discovered in a large-scale H-alpha imaging survey of the cluster.
Approximately 30 H-alpha-emitting knots were identified in a region
approximately 150 kpc across, in the vicinity of the spiral galaxies NGC 3860,
CGCG 97-125 and CGCG 97-114. Follow-up imaging and spectroscopy reveals that
some of the knots are associated with previously uncataloged dwarf galaxies
(M_B = -15.8 to -16.5), while others appear to be isolated HII galaxies or
intergalactic HII regions. Radial velocities obtained for several of the knots
show that they are physically associated with a small group or subcluster
including CGCG 97-114 and CGCG 97-125. No comparable concentration of
emission-line objects has been found elsewhere in any of the eight northern
Abell clusters surveyed to date. The strong H-alpha emission in the objects and
their high spatial density argue against this being a group of normal,
unperturbed dwarf galaxies. Emission-line spectra of several of the knots also
show some to be anomalously metal-rich relative to their luminosities. The
results suggest that many of these objects were formed or triggered by tidal
interactions or mergers involving CGCG 97-125 and other members of the group. A
Westerbork Synthesis Radio Telescope HI map of the region shows direct evidence
for tidal interactions in the group. These objects may be related to the tidal
dwarf galaxies found in some interacting galaxy pairs, merger remnants, and
compact groups. They could also represent evolutionary precursors to the class
of isolated ultracompact dwarf galaxies that have been identified in the Fornax
cluster.


title: The Molecular Continuum Opacity of MgH in Cool Stellar Atmospheres

abstract:
  The opacity due to photodissociation of 24MgH is investigated in the
atmospheres of cool stars. The lowest two electronic transitions A 2Pi -- X
2Sigma+ and B' 2Sigma+ -- X 2 Sigma+ are considered where the cross sections
for the latter were published previously (Weck, Stancil, & Kirby 2002) while
the former are presented in this work. Model atmospheres calculated with the
PHOENIX code are used to investigate the effect of the photodissociation
opacity on spectra of cool stars. The A -- X photodissociation cross sections
are obtained using a combination of ab initio and experimentally derived
potential curves and dipole transition moments. Partial cross sections have
been evaluated over the accessible wavelength range 1770-4560 Angstrom for all
rotational transitions from the vibrational levels v''=0-11. Assuming a
Boltzmann distribution of the rovibrational levels of the X 2Sigma+ state, LTE
photodissociation cross sections are presented for temperatures between 1000
and 5000 K. Shape resonances, arising from rotational predissociation of
quasi-bound levels of the A 2Pi state near threshold, characterize the LTE
photodissociation cross sections. A sum rule is proposed as a check on the
accuracy of the photodissociation calculations.


title: Parallelization Strategies for ALI Radiative Transfer in Moving Media

abstract:
  We describe the method we have used to parallelize our spherically symmetric
special relativistic short characteristics general radiative transfer code
PHOENIX. We describe some possible parallelization strategies and show why they
would be inefficient. We discuss the multiple parallelization strategy
techniques that we have adopted. We briefly discuss generalizing these
strategies to full 3-D (spatial) radiation transfer codes.


title: The Formation of a Realistic Disk Galaxy in Lambda Dominated Cosmologies

abstract:
  We simulate the formation of a realistic disk galaxy within the hierarchical
scenario of structure formation and study its internal properties to the
present epoch. We compare results from a LambdaCDM simulation with a LambdaWDM
(2keV) simulation that forms significantly less small scale structure. We show
how high mass and force resolution in both the gas and dark matter components
play an important role in solving the angular momentum catastrophe claimed from
previous simulations of galaxy formation within the hierarchical framework. The
stellar material in the disk component has a final specific angular momentum
equal to 40% and 90% of that of the dark halo in the LambdaCDM and LambdaWDM
models respectively. The LambdaWDM galaxy has a drastically reduced satellite
population and a negligible stellar spheroidal component. Encounters with
satellites play only a minor role in disturbing the disk. Satellites possess a
variety of star formation histories linked to mergers and pericentric passages
along their orbit around the primary galaxy. In both cosmologies, the galactic
halo retains most of the baryons accreted and builds up a hot gas phase with a
substantial X-ray emission. Therefore, while we have been successful in
creating a realistic stellar disk in a massive galaxy within the LambdaCDM
scenario, energy injection emerges as necessary ingredient to reduce the baryon
fraction in galactic halos, independent of the cosmology adopted. (abridged)


title:
Constraints on the Collisional Nature of the Dark Matter from
  Gravitational Lensing in the Cluster A2218

abstract:
  The detailed distribution of mass within clusters of galaxies can be used to
probe the nature of dark matter. We show that constraints on the extent of the
mass distribution around galaxies in the rich cluster Abell 2218 obtained from
combining strong and weak lensing observations are consistent with the
predictions which assume that the dominant mass component (dark matter) in
these halos is collisionless. A strongly interacting (fluid-like) dark matter
is ruled-out at a confidence level of more than 5-sigma.


title: The possible origin of the faint fuzzy star clusters in NGC 1023

abstract:
  In the lenticular galaxy NGC 1023 a new population of star clusters (``faint
fuzzies'') was recently discovered by Larsen & Brodie. These clusters are found
inside the disc and are faint (23 < V < 24 mag) and extended with effective
radii of r_eff approx. 7 to 15 pc. We present here N-body calculations of a
likely formation-scenario through merging star clusters in clusters of star
clusters (super-clusters). Such super-clusters are observed to form in
interacting galaxies. The resulting merger objects have masses comparable to
the ``faint fuzzies'' and show large effective radii (r_eff > 7 pc). Even
though these objects are suffering from strong tidal forces they are able to
survive and reach the estimated ages of the extended star clusters in NGC 1023.


title:
Separating the Early Universe from the Late Universe: cosmological
  parameter estimation beyond the black box

abstract:
  We present a method for measuring the cosmic matter budget without
assumptions about speculative Early Universe physics, and for measuring the
primordial power spectrum P*(k) non-parametrically, either by combining CMB and
LSS information or by using CMB polarization. Our method complements currently
fashionable ``black box'' cosmological parameter analysis, constraining
cosmological models in a more physically intuitive fashion by mapping
measurements of CMB, weak lensing and cluster abundance into k-space, where
they can be directly compared with each other and with galaxy and Lyman alpha
forest clustering. Including the new CBI results, we find that CMB measurements
of P(k) overlap with those from 2dF galaxy clustering by over an order of
magnitude in scale, and even overlap with weak lensing measurements. We
describe how our approach can be used to raise the ambition level beyond
cosmological parameter fitting as data improves, testing rather than assuming
the underlying physics.


title:
The dark matter density profile of the lensing cluster MS2137-23: a test
  of the cold dark matter paradigm

abstract:
  We present new spectroscopic observations of the gravitational arcs and the
brightest cluster galaxy (BCG) in the cluster MS2137-23 (z=0.313) obtained with
the Echelle Spectrograph and Imager on the Keck II telescope. We find that the
tangential and radial arcs arise from sources at almost identical redshifts
(z=1.501,1.502). We combine the measured stellar velocity dispersion profile of
the BCG with a lensing analysis to constrain the distribution of dark and
stellar matter in the central 100 kpc of the cluster. Our data indicate a
remarkably flat inner slope for the dark matter profile, rho_d propto r^-beta,
with beta<0.9 at 99% CL. Steep inner slopes obtained in cold dark matter
cosmological simulations -- such as Navarro Frenk & White (beta=1) or Moore
(1.5) universal dark matter profiles -- are ruled out at better than 99% CL. As
baryon collapse is likely to have steepened the dark matter profile from its
original form, our data provides a powerful test of the cold dark matter
paradigm at the cluster mass scale.


title:
Evidence for tidal stripping of dark matter halos in massive
  cluster-lenses

abstract:
  In this letter, we present the results of our study of galaxy-galaxy lensing
in massive cluster-lenses spanning $z = 0.17$ to 0.58, utilizing high-quality
archival {\it Hubble Space Telescope} ({\it HST}) data. Local anisotropies in
the shear maps are assumed to arise from dark matter substructure within these
clusters. Associating the substructure with bright early-type cluster galaxies,
we quantify the properties of typical $L^*$ cluster members in a statistical
fashion. The fraction of total mass associated with individual galaxies within
the inner regions of these clusters ranges from 10--20% implying that the bulk
of the dark matter in massive lensing clusters is smoothly distributed. Looking
at the properties of the cluster galaxies, we find strong evidence
($>3$-$\sigma$ significance) that a fiducial early-type $L^\ast$ galaxy in
these clusters has a mass distribution that is tidally truncated compared to
equivalent luminosity galaxies in the field. In fact, we exclude field galaxy
scale dark halos for these cluster early-types at $>10$-$\sigma$ significance.
We compare the tidal radii obtained from this lensing analysis with the central
density of the cluster potentials and find a correlation which is in excellent
agreement with theoretical expectations of tidal truncation: $\log [r_t*]
\propto (-0.6\pm 0.2) \log [\rho_0]$.


title: Supermassive Black Hole Research in the Post-HST Era

abstract:
  Thanks to its unprecedented spatial resolution, the Hubble Space Telescope
has ended a 20-year long stalemate by detecting the dynamical signature of
nuclear supermassive black holes (SBHs) in a sizeable number of nearby
galaxies. These detections have revealed the existence of a symbiotic
relationship between SBHs and their hosts, changing the way we view SBH and
galaxy formation. In this contribution I review which are the most pressing
outstanding issues in SBH research, and what are the technological requirements
needed to address them.


title:
Cosmological Constraints from Compact Radio Source Angular Size versus
  Redshift Data

abstract:
  We use the Gurvits, Kellermann, & Frey compact radio source angular size
versus redshift data to place constraints on cosmological model parameters in
models with and without a constant or time-variable cosmological constant. The
resulting constraints are consistent with but weaker than those determined
using current supernova apparent magnitude versus redshift data.


title: The Connection Between Spectral Evolution and GRB Lag

abstract:
  The observed delay in the arrival times between high and low energy photons
in gamma-ray bursts (GRBs) has been shown by Norris et al. to be correlated to
the absolute luminosity of a GRB. Despite the apparent importance of this
spectral lag, there has yet to be a full explanation of its origin. We put
forth that the lag is directly due to the evolution of the GRB spectra. In
particular, as the energy at which the GRB's $\nu F_{\nu}$ spectra is a maximum
($E_{pk}$) decays through the four BATSE channels, the photon flux peak in each
individual channel will inevitably be offset producing what we measure as lag.
We test this hypothesis by measuring the rate of $E_{pk}$ decay ($\Phi_{o}$)
for a sample of clean single peaked bursts with measured lag. We find a direct
correlation between the decay timescale and the spectral lag, demonstrating the
relationship between time delay of the low energy photons and the decay of
$E_{pk}$. This implies that the luminosity of a GRB is directly related to the
burst's rate of spectral evolution, which we believe begins to reveal the
underlying physics behind the lag-luminosity correlation. We discuss several
possible mechanisms that could cause the observed evolution and its connection
to the luminosity of the burst.


title: Nuclear and High-Energy Astrophysics

abstract:
  There has never been a more exciting time in the overlapping areas of nuclear
physics, particle physics and relativistic astrophysics than today. Orbiting
observatories such as the Hubble Space Telescope, Rossi X-ray Timing Explorer
(RXTE), Chandra X-ray satellite, and the X-ray Multi Mirror Mission (XMM) have
extended our vision tremendously, allowing us to see vistas with an
unprecedented clarity and angular resolution that previously were only
imagined, enabling astrophysicists for the first time ever to perform detailed
studies of large samples of galactic and extragalactic objects. On the Earth,
radio telescopes (e.g., Arecibo, Green Bank, Parkes, VLA) and instruments using
adaptive optics and other revolutionary techniques have exceeded previous
expectations of what can be accomplished from the ground. The gravitational
wave detectors LIGO, LISA VIRGO, and Geo-600 are opening up a window for the
detection of gravitational waves emitted from compact stellar objects such as
neutron stars and black holes. Together with new experimental forefront
facilities like ISAC, ORLaND and RIA, these detectors provide direct,
quantitative physical insight into nucleosynthesis, supernova dynamics,
accreting compact objects, cosmic-ray acceleration, and pair-production in high
energy sources which reinforce the urgent need for a strong and continuous
feedback from nuclear and particle theory and theoretical astrophysics. In my
lectures, I shall concentrate on three selected topics, which range from the
behavior of superdense stellar matter, to general relativistic stellar models,
to strange quark stars and possible signals of quark matter in neutron stars.


title: An Improved uvby-Metallicity Calibration for Metal-Rich Stars

abstract:
  We present an improved uvby-metallicity relation calibrated for F, G, and
early K dwarfs, and an analogous uvby-T(eff) relation, both derived using a
Levenberg-Marquardt minimization scheme. Our calibrations are based on 1533
stars which appear in both the Cayrel de Strobel (2001) metallicity
compilation, and in the Hauck-Mermilliod (1998) catalog of uvby photometry. We
also examine the speculative possibility of using uvby photometry to produce a
uvby-planeticity calibration. We conclude that while there is likely no strong
photometric indicator of the presence or absence of short-period planets, the
possibility of a spectroscopic indicator of planeticity is well worth
examining.


title: Large-Scale Asymmetry of Rotation Curves in Lopsided Spiral Galaxies

abstract:
  Many spiral galaxies show a large-scale asymmetry with a cos\phi dependence
in their rotation curves as well as in their morphology, such as M101 and NGC
628. We show that both these features can be explained by the response of a
galactic disk to an imposed lopsided halo potential. A perturbation potential
of 5 % is deduced for the morphologically lopsided galaxies in the Rix &
Zaritsky (1995) sample. This is shown to result in a difference of 10 % or
about 20-30 kms^{-1} in the rotation velocity on the two sides of the major
axis. Interestingly, the observed isophotal asymmetry in a typical spiral
galaxy is not much smaller and it results in a velocity asymmetry of 7 % or
about 14-21 kms^{-1} . Hence, we predict that most galaxies show a fairly
significant rotational asymmetry. The rotation velocity is shown to be maximum
along the elongated isophote - in agreement with the observations along the SW
in M101, while it is minimum along the opposite direction. This result leads to
the distinctive asymmetric shape of the rotation curve which rises more steeply
in one half of the galaxy than the other, as observed by Swaters et al. (1999).
This shape is shown to be a robust feature and would result for any centrally
concentrated disk. The net disk lopsidedness and hence the asymmetry in the
rotation curve is predicted to increase with radius and hence can be best
studied using HI gas as the tracer.


title: On the Final State of Spherical Gravitational Collapse

abstract:
  In a recent paper (FPL 13(6), 543, 2000, astro-ph/9910408), from several
independent considerations we showed that GTR does not allow formation of
trapped surfaces and finite mass BHs. We rediscuss here several subtle issues
involved in this work. So far only the scientific critique to this work was due
to Tereno (astro-ph/9905144, astro-ph/9905298) and which was answered in Mitra
(astro-ph/9905175, astro-ph/9905175, astro-ph/9905329). Now Tereno
(gr-qc/0111073) has also admitted that the local 3-speed of a free particle as
conventionally defined by all previous authors and as measured in any
coordinate system, is indeed c at the EH. Further since the acceleration SCALAR
BLOWS UP at the EH, our result that there cannot be any EH at a finite R is
reconfirmed. We explicitly show here that the final state of spherical collapse
of very massive stars corresponds to a zero mass BH with 2M/R ->0. But at any
finite epoch there would be a Eternally Collapsing Objects (ECO) of finite
mass. However, if quantum back reaction in the strong gravity regime would
cause a phase transition p ~ rho, there could be static ultracompact objects
(UCO) of ~ 10 M (solar). Further, if the phase transition goes proceeds to p=
-rho, there could be UCOs of arbitrary high mass (Mazur & Mottola,
astro-ph/0109035). Both ECOs and UCOs are expected to possess strong internal
magnetic field whereas the the same for a BH is zero. Robertson & Leiter (ApJ
565, 447, 2002, astro-ph/0102381) have shown that the BH candiadates may indeed
possess such strong intrinsic mag field. Thus the BHCs are likely to ECOs/UCOs
rather than BHs. We also discuss that there is no real evidence for detection
of EH.


title: Understanding Scintillation of Intraday Variables

abstract:
  Intraday Variability of compact extragalactic radio sources can be
interpreted as quenched scintillation due to turbulent density fluctuations of
the nearby ionized interstellar medium. We demonstrate that the statistical
analysis of IDV time series contains both information about sub-structure of
the source on the scale of several 10 micro-arcsec and about the turbulent
state of the ISM. The source structure and ISM properties cannot be
disentangled using IDV observations alone. A comparison with the known
morphology of the `local bubble' and the turbulent ISM from pulsar observations
constrains possible source models. We further argue that earth orbit synthesis
fails for non-stationary relativistic sources and no reliable 2D-Fourier
reconstruction is possible.


title:
Young massive stars in the ISOGAL survey II. The catalogue of bright YSO
  candidates

abstract:
  The 7 and 15 um observations of selected fields in the Galactic Plane
obtained with ISOCAM during the ISOGAL program offer an unique possibility to
search for previously unknown YSOs, undetected by IRAS because of lower
sensitivity or confusion problems. In a previous paper (Felli et al. 2000) we
established criteria of general validity to select YSOs from the much larger
population of Post Main Sequence (Post-MS) stars present in the ISOGAL fields
by comparing radio and IR observations of five fields located at l +45 deg. The
selection was based primarily on the position of the point sources in the [15]
- [7]--[15] diagram, which involves only ISOGAL data and allows to find
possible YSOs using the survey data alone. In the present work we revise the
adopted criteria by comparing radio-identified UC HII regions and ISOGAL
observations over a much larger region. The main indications of the previous
analysis are confirmed, but the criteria for selecting YSO candidates had to be
revised to select only bright objects, in order to limit the contamination of
the sample by Post-MS stars. The revised criteria ([15]<=4.5, [7]--[15]>=1.8)
are then used to extract YSO candidates from the ISOGAL Point Source Catalogue
in preparation. We select a total of 715 YSO candidates, corresponding to ~2%
of the sources with good detections at 7 and 15 um. The results are presented
in a table form that provides an unique input list of small diameter, <=6",
Galactic YSO candidates. The global properties of the sample of YSO candidates
are briefly discussed.


title: Anomalous RR Lyrae stars(?). III. CM Leonis

abstract:
  Time series of B,V,I CCD photometry and radial velocity measurements from
high resolution spectroscopy (R=30,000) covering the full pulsation cycle are
presented for the field RR Lyrae star CM Leonis. The photometric data span a 6
year interval from 1994 to 1999, and allow us to firmly establish the pulsation
mode and periodicity of the variable. The derived period P=0.361699 days (+/-
0.000001) is very close to the value published in the Fourth Edition of the
General Catalogue of Variable Stars (P=0.361732 days). However, contrary to
what was previously found, the amplitude and shape of the light curve qualify
CM Leo as a very regular first overtone pulsator with a prominent hump on the
rising branch of its multicolour light curves. According to an abundace
analysis performed on three spectra taken near minimum light (0.42 < phase <
0.61), CM Leo is a metal-poor star with metal abundance [Fe/H]=-1.93 +/- 0.20.
The photometric and radial velocity curves of CM Leo have been compared with
the predictions of suitable pulsational models to infer tight constraints on
the stellar mass, effective temperature, and distance modulus of the star. We
derive a true distance modulus of CM Leo of (m-M)0=13.11 +/- 0.02 mag and a
corresponding absolute magnitude of Mv=0.47 +/- 0.04. This absolute magnitude,
once corrected for evolutionary and metallicity effects, leads to a true
distance modulus of the Large Magellanic Cloud of (m-M)0=18.43 +/- 0.06 mag, in
better agreement with the long astronomical distance scale.


title: A Far-Ultraviolet Survey of 47 Tucanae. I. Imaging

abstract:
  We present results from the imaging portion of a far-ultraviolet (FUV) survey
of the core of 47 Tucanae. We have detected 767 FUV sources, 527 of which have
optical counterparts in archival HST/WFPC2 images of the same field.
  Most of our FUV sources are main-sequence (MS) turn-off stars near the
detection limit of our survey. However, the FUV/optical color-magnitude diagram
(CMD) also reveals 19 blue stragglers (BSs), 17 white dwarfs (WDs) and 16
cataclysmic variable (CV) candidates. The BSs lie on the extended cluster MS,
and four of them are variable in the FUV data. The WDs occupy the top of the
cluster cooling sequence, down to an effective temperature of T_{eff} \simeq
20,000 K. Our FUV source catalog probably contains many additional, cooler WDs
without optical counterparts. Finally, the CV candidates are objects between
the WD cooling track and the extended cluster MS.
  Four of the CV candidates are previously known or suspected cataclysmics. All
of these are bright and variable in the FUV. Another CV candidate is associated
with the semi-detached binary system V36 that was recently found by Albrow et
al. (2001). V36 has an orbital period of 0.4 or 0.8 days, blue optical colors
and is located within 1 arcsec of a Chandra x-ray source. A few of the
remaining CV candidates may represent chance superpositions or SMC interlopers,
but at least half are expected to be real cluster members with peculiar colors.
However, only a few of these CV candidates are possible counterparts to Chandra
x-ray sources. Thus it is not yet clear which, if any, of them are true CVs,
rather than non-interacting MS/WD binaries or Helium WDs.


title: The Equatorial Outflow of SS433

abstract:
  We present VLBI imaging results for SS433 from the period 1995-2000. An
equatorial emission region is detected and confirmed in 7 experiments at 1.6
and 5 GHz. The structure of the region changes with time on scales of weeks to
months. The nature of emission is unknown, but it is certainly non-thermal,
maybe optically thin synchrotron. The spectrum however might be attenuated by a
thermal population of electrons. There were previous indications for an
equatorial outflow from the system. We do detect outward motion of a radio
component, and estimate a speed of 1200/sin(i) km/s. Theoretical work and IR
observations suggest that the mass-loss rate in SS433 is much higher in this
region than in the jets. We suggest that the high-mass microquasars might all
have equatorial outflows; in fact, it is the dominant form of mass-loss in
these systems.


title: HE 0435-1223: a wide separation quadruple QSO and gravitational lens

abstract:
  We report the discovery of a new gravitationally lensed QSO, at a redshift z
= 1.689, with four QSO components in a cross-shaped arrangement around a bright
galaxy. The maximum separation between images is 2.6 arcsec, enabling a
reliable decomposition of the system. Three of the QSO components have g =
19.6, while component A is about 0.6 mag brighter. The four components have
nearly identical colours, suggesting little if any dust extinction in the
foreground galaxy. The lensing galaxy is prominent in the i band, weaker in r
and not detected in g. Its spatial profile is that of an elliptical galaxy with
a scale length of $\sim$ 12 kpc. Combining the measured colours and a mass
model for the lens, we estimate a most likely redshift range of 0.3 < z < 0.4.
Predicted time delays between the components are $\la$ 10 days. The QSO shows
evidence for variability, with total g band magnitudes of 17.89 and 17.71 for
two epochs separated by $\sim 2$ months. However, the relative fluxes of the
components did not change, indicating that the variations are intrinsic to the
QSO rather than induced by microlensing.


title: Chandra Observations of the A3266 Galaxy Cluster Merger

abstract:
  Analysis of a 30,000 s X-ray observation of the Abell 3266 galaxy cluster
with the ACIS on board the Chandra Observatory has produced several new
insights into the cluster merger. The intracluster medium has a
non-monotonically decreasing radial abundance profile. We argue that the most
plausible origin for the abundance enhancement is unmixed, high abundance
subcluster gas from the merger. The enrichment consists of two stages:
off-center deposition of a higher abundance material during a subcluster merger
followed by a strong, localized intracluster wind that acts to drive out the
light elements, producing the observed abundance enhancement. The wind is
needed to account for both an increase in the heavy element abundance and the
lack of an enhancement in the gas density. Dynamical evidence for the wind
includes: (1) a large scale, low surface brightness feature perpendicular to
the merger axis that appears to be an asymmetric pattern of gas flow to the
northwest, away from the center of the main cluster, (2) compressed gas in the
opposite direction (toward the cluster center), and (3), the hottest regions
visible in the temperature map coincide with the proposed merger geometry and
the resultant gas flow. The Chandra data for the central region of the main
cluster shows a slightly cooler, filamentary region that is centered on the
central cD galaxy and is aligned with the merger axis directly linking the
dynamical state of the cD to the merger. Overall, the high spectral/spatial
resolution Chandra observations support our earlier hypothesis (Henriksen,
Donnelly, & Davis 1999) that we are viewing a minor merger in the plane of the
sky.


title: A Magic Electromagnetic Field

abstract:
  An electromagnetic field of simple algebraic structure is simply derived. It
turns out to be the G=0 limit of the charged rotating Kerr-Newman metrics.
These all have gyromagnetic ratio 2, the same as the Dirac electron. The charge
and current distributions giving this high gyromagnetic ratio have charges of
both signs rotating at close to the velocity of light.
  It is conjectured that something similar may occur in the quantum
electrodynamic charge distribution surrounding the point electron.


title:
Non--linear magnetic field decay in neutron stars -- Theory and
  observations

abstract:
  There exists both theoretical and observational evidence that the magnetic
field decay in neutron stars may proceed in a pronounced non--linear way during
a certain episode of the neutron star's life. In the presence of a strong
magnetic field the Hall--drift dominates the field evolution in the crust
and/or the superfluid core of neutron stars. Analysing observations of $P$ and
$\dot{P}$ for sufficiently old isolated pulsars we gain strong hints for a
significantly non--linear magnetic field decay. Under certain conditions with
respect to the geometry and strength of a large--scale magnetic background
field an instability is shown to occur which rapidly raises small--scale
magnetic field modes. Their growth rates increase with the background field
strength and may reach $\sim 10^4$ times the ohmic decay rate. Consequences for
the rotational and thermal evolution as well as for the cracking of the crust
of neutron stars are discussed.


title:
Conversion of relativistic pair energy into radiation in the jets of
  active galactic nuclei

abstract:
  It is generally accepted that relativistic jet outflows power the nonthermal
emission from active galactic nuclei (AGN). The composition of these jets --
leptonic versus hadronic -- is still under debate. We investigate the
microphysical details of the conversion process of the kinetic energy in
collimated relativistic pair outflows into radiation through interactions with
the ambient interstellar medium. Viewed from the coordinate system comoving
with the pair outflow, the interstellar protons and electrons represent a
proton-electron beam propagating with relativistic speed in the pair plasma. We
demonstrate that the beam excites both electrostatic and low-frequency
magnetohydrodynamic Alfven-type waves via a two-stream instability in the pair
background plasma, and we calculate the time evolution of the distribution
functions of the beam particles and the generated plasma wave turbulence power
spectra. For standard AGN jet outflow and environment parameters we show that
the initial beam distributions of interstellar protons and electrons quickly
relax to plateau-distributions in parallel momentum, transferring thereby
one-half of the initial energy density of the beam particles to electric field
fluctuations of the generated electrostatic turbulence. On considerably longer
time scales, the plateaued interstellar electrons and protons will isotropise
by their self-generated transverse turbulence and thus be picked-up in the
outflow pair plasma. These longer time scales are also characteristic for the
development of transverse hydromagnetic turbulence from the plateaued electrons
and protons. This hydromagnetic turbulence upstream and downstream is crucial
for diffusive shock acceleration to operate at external or internal shocks
associated with pair outflows.


title:
Peculiar Chemical Abundances in the Starburst Galaxy M82 and Hypernova
  Nucleosynthesis

abstract:
  X-ray observations have shown that the chemical abundance in the starburst
galaxy M82 is quite rich in Si and S compared with oxygen. Such an abundance
pattern cannot be explained with any combination of conventional Type I and II
supernova yields. Also the energy to heavy element mass ratio of the observed
hot plasma is much higher than the value resulted from normal supernovae. We
calculate explosive nucleosynthesis in core-collapse hypernovae and show that
the abundance pattern and the large ratio between the energy and the heavy
element mass can be explained with the hypernova nucleosynthesis. Such
hypernova explosions are expected to occur for stars more massive than >~ 20-25
Msun, and likely dominating the starburst, because the age after the starburst
in M82 is estimated to be as short as ~ 10^6 - 10^7 yr. We also investigate
pair-instability supernovae (~ 150-300 Msun) and conclude that the energy to
heavy element mass ratio in these supernovae is too small to explain the
observation.


title:
Kinetic theory of interstellar density and magnetic field fluctuations.
  Relations between interstellar density and magnetic field fluctuations

abstract:
  Using linear kinetic plasma theory the relation between electron density and
magnetic field fluctuations for low-frequency plasma waves for Maxwellian
background distribution functions of arbitrary temperatures in an uniform
magnetic field is derived. By taking the non-relativistic temperature limit
this relation is calculated for the diffuse intercloud medium in our Galaxy.
The diffuse intercloud medium is the dominant phase of the interstellar medium
with respect to radio wave propagation, dispersion and rotation measure
studies. The differences between the relation of electron density and magnetic
field fluctuations from the linear kinetic theory as compared to the classical
MHD theory are established and discussed.


title: Chandra Observations of the Nucleus of M33

abstract:
  The nearby galaxy M33 hosts the most luminous steady X-ray source in the
Local Group. The high spatial resolution of Chandra allows us to confirm that
this ultra-luminous X-ray source is within the nucleus and rule out at the 4.6
sigma level a previously proposed possible counterpart located 1" away. The
X-ray spectrum is well fitted by a disc blackbody with kT=1.18+-0.02 keV and R
cos(theta)^(0.5}=57+-3 km, consistent with earlier results from ASCA and
BeppoSAX. The source flux is steady between 1 and 1e4 s (<3% rms variability,
0.5-10 keV) with a 0.5-10 keV luminosity of 1.5e39 erg/s. The X-ray properties
and an association with a radio source are reminiscent of the galactic
microquasar GRS 1915+105.


title: Non-equilibrium chemistry in the atmospheres of brown dwarfs

abstract:
  Carbon monoxide and ammonia have been detected in the spectrum of Gl 229B at
abundances that differ substantially from those obtained from chemical
equilibrium. Vertical mixing in the atmosphere is a mechanism that can drive
slowly reacting species out of chemical equilibrium. We explore the effects of
vertical mixing as a function of mixing efficiency and effective temperature on
the chemical abundances in the atmospheres of brown dwarfs and on their
spectra. The models compare favorably with the observational evidence and
indicate that vertical mixing plays an important role in brown dwarf
atmospheres.


title:
On the Determination of the Mean Cosmic Matter Density and the Amplitude
  of Density Fluctuations

abstract:
  The cosmological implications from a new estimate of the local X-ray galaxy
cluster abundance are summarized. The results are then compared to independent
observations. It is suggested that `low' values for the mean cosmic matter
density and the amplitude of mass density fluctuations currently do not appear
unreasonable observationally.


title: 2mm Wavelength VLBI of SiO Masers and AGN

abstract:
  In April 2002 an array of antennas operating at 129GHz successfully detected
VLBI fringes on both continuum AGN and SiO maser sources. The 129GHz fringes on
maser sources represent the highest frequency spectral line VLBI detections to
date. The AGN 3C279 was detected on long baselines at both 129GHz (and at
147GHz, see Krichbaum et al in these proceedings) yielding fringe spacings of
50-56 micro arc seconds, an angular resolution record. The array consisted of
the University of Arizona Kittpeak 12m antenna, the Heinrich Hertz 10m
Telescope (HHT), and the IRAM 30m dish on Pico Veleta.
  At 129GHz, a number of evolved stars and several young stellar objects
exhibit strong SiO maser emission in the v=1 J=3-2 transition. Preliminary
cross power spectra of SiO masers around the red hypergiant VYCMa on the
HHT-KittPeak baseline ~190km are consistent with multiple spatially separate
maser spots associated with the star. Future observations will include
continuum observations of the radio source at the Galactic Center, SgrA*, and
higher frequency maser lines including HCN and methanol.


title:
Observational evidence for gravitationally trapped massive axion(-like)
  particles

abstract:
  Unexpected astrophysical observations can be explained by gravitationally
captured massive particles, which are produced inside the Sun or other Stars
and are accumulated over cosmic times. Their radiative decay in solar outer
space would give rise to a `self-irradiation' of the whole star, providing the
time-independent component of the corona heating source. In analogy with the
Sun-irradiated Earth atmosphere, the temperature and density gradient in the
corona - chromosphere transition region is suggestive for an omnipresent
irradiation of the Sun. The same scenario fits other astrophysical X-ray
observations. The radiative decay of a population of such elusive particles
mimics a hot gas. X-ray observatories, with an unrivalled sensitivity below ~10
keV, can search for such particles. The elongation angle relative to the Sun is
the relevant new parameter.


title: Rayleigh Laser Guide Star Systems: Application to UnISIS

abstract:
  Laser guide stars created by Rayleigh scattering provide a reasonable means
to monitor atmospheric wavefront distortions for real-time correction by
adaptive optics systems. Because of the $\lambda^{-4}$ wavelength dependence of
Rayleigh scattering, short wavelength lasers are a logical first choice for
astronomical laser guide star systems, and in this paper we describe the
results from a sustained experimental effort to integrated into an adaptive
optics system a 351 nm Rayleigh laser guide star created at an altitude of 20
km (above MSL) at the Mt. Wilson 2.5-m telescope. In addition to providing
obvious scientific benefits, the 351 nm laser guide star projected by UnISIS is
"Stealth qualified: in terms of the FAA and airplane avoidance. Due to the
excellent return signal at the wavefront sensor, there is no doubt that future
applications will be found for short-wavelength Rayleigh scattered laser guide
stars.


title: The classification of BL Lacertae objects: the Ca H&K break

abstract:
  We investigate why BL Lacertae objects (BL Lacs) have values of the Ca H&K
break (a stellar absorption feature) lower than low-power radio galaxies and if
its use is justified to separate the two classes. For this purpose we relate
this parameter to the radio and optical core emissions, as well as to the X-ray
powers, for a sample of ~90 radio sources. We find that the Ca H&K break value
decreases with increasing jet powers, and that it also anti-correlates with the
radio core dominance parameter but not with extended radio emission. Based on
this we conclude that the Ca H&K break value of BL Lacs and radio galaxies is a
suitable indicator of orientation. From the luminosity ratios between objects
with low and high Ca H&K break values we constrain the average Lorentz factors
for BL Lacs and low-power radio galaxies in the radio and X-ray band to Gamma ~
2 -- 4 and derive average viewing angles for the galaxies. Our values are in
agreement with results from independent methods. We find that the correlations
between Ca H&K break and radio core and X-ray luminosity hold independently for
low- (LBL) and high-energy peaked BL Lacs (HBL). We derive average viewing
angles for their parent populations, which turn out to be similar to the ones
for our entire sample, and compare for the first time the luminosities of LBL
and HBL at different orientations.


title: Unveiling the Behavior of the Ionized Gas in Irregular Galaxies

abstract:
  We present the results of a detailed kinematical and dynamical analysis
performed in two highly interesting gas-rich Irregular galaxies (Irrs): IC 1613
and NGC 4449. The analysis has been accomplished by means of optical
Fabry-Perot interferometry mapping the Halpha and [SII] lines. The question we
addressed in this study is: how does the ionized gas behave -kinematically and
dynamically speaking- on global and local scales in gas-rich Irr galaxies?


title: A Warp in the LMC Disk?

abstract:
  We present a study of the shape of the Large Magellanic Cloud disk. We use
the brightnesses of core helium-burning red clump stars identified in V-I,I
color-magnitude diagrams of 50 randomly selected LMC fields, observed with the
CTIO 0.9-m telescope, to measure relative distances to the fields. Random
photometric errors and errors in the calibration are controlled to <1%.
Following correction for reddening measured through the color of the red clump,
we solve for the inclination and position angle of the line of nodes of the
tilted plane of the LMC, finding i=35.8 +/- 2.4 degrees and theta=145 +/- 4
degrees. Our solution requires that we exclude 15 fields in the southwest of
the LMC which have red clump magnitudes ~0.1 magnitudes brighter than the
fitted plane. On the basis of these fields, we argue that the LMC disk is
warped and twisted, containing features that extend up to 2.5 kpc out of the
plane. We argue that alternative ways of producing red clump stars brighter
than expected, such as variations in age and metallicity of the stars, are
unlikely to explain our observations.


title: SACY - Present Status

abstract:
  The scientific goal of the SACY (Search for Associations Containing
Young-stars) project is to identify eventual associations of stars younger than
the Local Association, spread among the optical counterparts of the ROSAT X-ray
bright sources. High-resolution spectra for possible optical counterpart later
than G0 belonging to HIPPARCOS and/or TYCHO-2 catalogues were obtained in order
to assess both the youth and the spatial motion of each target. The newly
identified young stars present a patchy distribution in UVW space and in the
sky as well revealing the existence of huge nearby young associations. Here we
present the associations identified in the present sample.


title: A note on the discovery of absorption features in 1E 1207.4-5209

abstract:
  In a paper by Sanwal et al. (2002), it is supposed to be very difficult to
interpret the absorption features in term of cyclotron lines. However, we would
like to address here that the possibility of the absorption being cyclotron
resonance can not be ruled out.We propose that the isolate neutron star, 1E
1207.4-5209 in the center of supernova remnant PKS 1209-51/52, has a debris
disk and is in a propeller phase, with an accretion rate 6x10^{-11}
M_solar/year.


title: Gravitational instability of isothermal and polytropic spheres

abstract:
  We complete previous investigations on the thermodynamics of self-gravitating
systems by studying the grand canonical, grand microcanonical and isobaric
ensembles. We also discuss the stability of polytropic spheres in the light of
a generalized thermodynamics proposed by Tsallis. We determine in each case the
onset of gravitational instability by analytical methods and graphical
constructions in the Milne plane. We also discuss the relation between
dynamical and thermodynamical stability of stellar systems and gaseous spheres.
Our study provides an aesthetic and simple approach to this otherwise
complicated subject.


title: Higher Resolution VLBI Imaging with Fast Frequency Switching

abstract:
  Millimetre-VLBI is an important tool in AGN astrophysics, but it is limited
by short atmospheric coherence times and poor receiver and antenna performance.
We demonstrate a new kind of phase referencing for the VLBA, enabling us to
increase the sensitivity in mm-VLBI by an order of magnitude. If a source is
observed in short cycles between the target frequency, nu_t, and a reference
frequency, nu_ref, the nu_t data can be calibrated using scaled-up phase
solutions from self-calibration at nu_ref. We have demonstrated the phase
transfer on 3C 279, where we were able to make an 86 GHz image with 90 %
coherence compared to self-calibration at nu_t. We have detected M81, our
science target in this project, at 86 GHz using the same technique. We describe
scheduling strategy and data reduction. The main impacts of fast frequency
switching are the ability to image some of the nearest, but relatively weak AGN
cores with unprecedented high angular resolution and to phase-reference the
nu_t data to the nu_ref core position, enabling the detection of possible core
shifts in jets due to optical depth effects. This ability will yield important
constraints on jet properties and might be able to discriminate between the two
competing emission models of Blandford-Konigl jets and spherical
advection-dominated accretion flows (ADAFs) in low-luminosity AGNs.


title: Proper motion in Cygnus A

abstract:
  Our recent VLBI observations of the prominent FR II radio galaxy Cygnus A
with the EVN and the VLBA reveal a pronounced two-sided jet structure. At 5
GHz, we now have 4 epochs from 1986, 1991 (Carilli et al., 1991 & 1994), 1996
and 2002 from which we could derive the kinematics of the jet and counter-jet.
On the jet side and on mas scales, the jet seems to accelerate from $\beta_{\rm
app}\approx 0.1-0.2$ (Krichbaum et al. 1998) at core-separations near 1 mas to
$\beta_{\rm app}\approx 0.4-0.6$ at $r \geq 4$ mas ($H_0=100$ km s$^{-1}$
Mpc$^{-1}$, $q_0=0.5$). For the first time we also measure significant
structural variability on the counter-jet side. For this, we derive a motion of
$\beta_{\rm app}=0.35\pm0.2$ at $r=9.5$ mas. The flat spectrum of the inner
region of the counter-jet (free-free absorption) and the frequency dependence
of the jet to counter-jet ratio support strong evidence for an obscuring torus
in front of the counter-jet (Bach et al. in prep, Krichbaum et al. 1998).


title: Is 0716+714 a superluminal blazar?

abstract:
  We present an analysis of new and old high frequency VLBI data collected
during the last 10 years at 5--22 GHz. For the jet components in the mas-VLBI
jet, two component identifications are possible. One of them with
quasi-stationary components oscillating about their mean positions. Another
identification scheme, which formally gives the better expansion fit, yields
motion with $\sim 9$ $c$ for $H_0=65$ km s$^{-1}$ Mpc$^{-1}$ and $q_0=0.5$.
This model would be in better agreement with the observed rapid IDV and the
expected high Lorentz-factor, deduced from IDV.


title: VY Sculptoris stars as magnetic CVs

abstract:
  We show that the absence of outbursts during low states of VY Scl stars is
easily explained if white dwarfs in these systems are weakly magnetized ($\mu
\gta 5 10^{30}$ G cm$^{3}$). However, some of the VY Scl stars are observed to
have very slow declines to minimum and similarly slow rises to maximum. The
absence of outbursts during such intermediate (as opposed to low) states, which
last much longer than typical disc's viscous times, can be explained only if
accretion discs are absent when their temperatures would correspond to an
unstable state. This requires magnetic fields stronger than those explaining
outburst absence during low states, since white dwarfs in this sub-class of VY
Scl stars should have magnetic moments $\mu \gta 1.5 10^{33}$ G cm$^{3}$ i.e.
similar to those of Intermediate Polars. Since at maximum brightness several VY
Scl stars are SW Sex stars, this conclusion is in agreement with recent claims
about the magnetic nature of these systems.


title: ROSAT Blank Field Sources I: Sample Selection and Archival Data

abstract:
  We have identified a population of blank field sources (or `blanks') among
the ROSAT bright unidentified X-ray sources with faint optical counterparts.
The extreme X-ray over optical flux ratio of blanks is not compatible with the
main classes of X-ray emitters except for extreme BL Lacertae objects. From the
analysis of ROSAT archival data we found no indication of variability and
evidence for only three sources, out of 16, needing absorption in excess of the
Galactic value. We also found evidence for an extended nature for only one of
the 5 blanks with a serendipitous HRI detection; this source (1WGAJ1226.9+3332)
was confirmed as a z=0.89 cluster of galaxies. Palomar images reveal the
presence of a red (O-E~2) counterpart in the X-ray error circle for 6 blanks.
The identification process brought to the discovery of another high z cluster
of galaxies, one (possibly extreme) BL Lac, two ultraluminous X-ray sources in
nearby galaxies and two apparently normal type1 AGNs. These AGNs, together with
4 more AGN-like objects seem to form a well defined group: they present
unabsorbed X-ray spectra but red Palomar counterparts. We discuss the possible
explanations for the discrepancy between the X-ray and optical data, among
which: a suppressed big blue bump emission, an extreme dust to gas (~40-60 the
Galactic ratio), a high redshift (z>3.5) QSO nature, an atypical dust grain
size distribution and a dusty warm absorber. These AGN-like blanks seem to be
the bright (and easier to study) analogs of the sources which are found in deep
Chandra observations. Three more blanks have a still unknown nature.


title:
Constraints on Jupiters from observations of Galactic Bulge microlensing
  events during 2000

abstract:
  We present observations of 8 Galactic Bulge microlensing events taken with
the 1.0m JKT on La Palma during 2000 June and July. The JKT observing schedule
was optimized using a prioritizing algorithm to automatically update the target
list. For most of these events we have sampled the lightcurves at times where
no information was available from the OGLE alert team. We assume a point-source
point-lens (PSPL) model and perform a maximum likelihood fit to both our data
and the OGLE data to constrain the event parameters of the fit. We then refit
the data assuming a binary lens and proceed to calculate the probability of
detecting planets with mass ratio $q=10^{-3}$. We have seen no clear signatures
of planetary deviations on any of the 8 events and we quantify constraints on
the presence of planetary companions to the lensing stars. For two well
observed events, 2000BUL31 and 2000BUL33, our detection probabilities peak at
$\sim$30% and $\sim$20% respectively for $q=10^{-3}$ and $a \sim R_{E}$ for a
$\Delta\chi^2$ threshold value of 60.


title: An Optical Velocity for the Phoenix Dwarf Galaxy

abstract:
  We present the results of a VLT observing program carried out in service mode
using FORS1 on ANTU in Long Slit mode to determine the optical velocities of
nearby low surface brightness galaxies. As part of our program of service
observations we obtained long-slit spectra of several members of the Phoenix
dwarf galaxy from which we derive an optical helio-centric radial velocity of
-13 +/- 9km/s. This agrees very well with the velocity of the most promising of
the HI clouds seen around Phoenix, which has a helio-centric velocity of -23
km/s, but is significantly different to the recently published optical
heliocentric velocity of Phoenix of -52 +/- 6 km/s of Gallart et al. (2001).


title:
V838 Mon and the new class of stars erupting into cool supergiants
  (SECS)

abstract:
  V838 Mon has undergone one of the most mysterious stellar outbursts on
record. The spectrum at maximum closely resembled a cool AGB star, evolving
toward cooler temperatures with time, never reaching optically thin conditions
or a nebular stage. The latest spectral type recorded is M8-9. The amplitude
peaked at DeltaV=9 mag, with the outburst evolution being characterized by a
fast rise, three maxima over four months, and a fast decay (possibly driven by
dust condensation in the ejecta). BaII, LiI and s-element lines were prominent
in the outburst spectra. Strong and wide (500 km/sec) P-Cyg profiles affected
low ionization species, while Balmer lines emerged to modest emission only
during the central phase of the outburst. A light-echo discovered expanding
around the object constrains its distance to 790+/-30 pc, providing M_V=+4.45
in quiescence and M_V=-4.35 at optical maximum (dependent on the still
uncertain E(B-V)=0.5 reddening). The visible progenitor resembled a somewhat
under-luminous F0 main sequence star, that did not show detectable variability
over the last half century. V838 Mon together with M31-RedVar and V4332 Sgr
seems to define a new class of astronomical objects: stars that erupt into cool
supergiants (SECS). They do not develop optically thin or nebular phases, and
deep P-Cyg profiles denounce large mass loss at least in the early outburst
phases. Their visible progenitors are located close to the Main Sequence, away
from the post-AGB region. After the outburst, the remnants still closely
resemble the precursors (same brightness, same spectral type). Many more
similar objects could be buried among poorly studied novae that have been
classified as Miras on the base of a single spectrum at maximum brightness.


title: Synthetic Spectra from 3D Models of Supernovae

abstract:
  We describe Brute, a code for generating synthetic spectra from 3D supernova
models. It is based on a Monte Carlo implementation of the Sobolev
approximation. The current version is highly parameterized, but in the future
it will be extended for full NLTE spectrum modelling of supernovae.


title: Smooth potential chaos and N-body simulations

abstract:
  Integrations in fixed N-body realisations of smooth density distributions
corresponding to a chaotic galactic potential can be used to derive reliable
estimates of the largest (finite time) Lyapunov exponent X_S associated with an
orbit in the smooth potential generated from the same initial condition, even
though the N-body orbit is typically characterised by an N-body exponent X_N >>
X_S. This can be accomplished either by comparing initially nearby orbits in a
single N-body system or by tracking orbits with the same initial condition
evolved in two different N-body realisations of the same smooth density.


title:
Detection of a Super Star Cluster as the Ionizing Source in the Low
  Luminosity AGN NGC 4303

abstract:
  HST UV STIS imaging and spectroscopy of the low luminosity AGN (LLAGN) NGC
4303 have identified the previously detected UV-bright nucleus of this galaxy,
as a compact, massive and luminous stellar cluster. The cluster with a size
(FWHM) of 3.1 pc, and an ultraviolet luminosity log L (1500 A}(erg/s/A)= 38.33
is identified as a nuclear super star cluster (SSC) like those detected in the
circumnuclear regions of spirals and starburst galaxies. The UV spectrum
showing the characteristic broad P Cygni lines produced by the winds of massive
young stars, is best fitted by the spectral energy distribution of a massive
cluster of 1e5 Msol generated in an instantaneous burst 4 Myr ago. No evidence
for an additional non-thermal ionizing source associated with an accreting
black hole is detected in the ultraviolet. We hypothesize that at least some
LLAGNs in spirals could be understood as the result of the combined ionizing
radiation emitted by an evolving SSC and a black hole (BH) accreting with low
radiative efficiency, coexisting in the inner few parsecs region.


title:
The X-ray Structure and Spectrum of the Pulsar Wind Nebula Surrounding
  PSR B1853+01 in W44

abstract:
  We present the result of a Chandra ACIS observation of the pulsar PSR
B1853+01 and its associated pulsar wind nebula (PWN), embedded within the
supernova remnant W44. A hard band ACIS map cleanly distinguishes the PWN from
the thermal emission of W44. The nebula is extended in the north-south
direction, with an extent about half that of the radio emission. Morphological
differences between the X-ray and radio images are apparent. Spectral fitting
reveals a clear difference in spectral index between the hard emission from PSR
B1853+01 (Gamma ~ 1.4) and the extended nebula (Gamma ~ 2.2). The more accurate
values for the X-ray flux and spectral index are used refine estimates for PWN
parameters, including magnetic field strength, the average Lorentz factor,
gamma, of the particles in the wind, the magnetization parameter, sigma, and
the ratio k of electrons to other particles.


title: Spectral Observations of Stars in Late Stages of Stellar Evolution

abstract:
  Interferometric observations of stars in late stages of stellar evolution and
the impact of VLTI observations are discussed. Special attention is paid to the
spectral information that can be derived from these observations and on the
corresponding astrophysical interpretation of the data by radiative transfer
modelling. It is emphasized that for the robust and non-ambiguous construction
of dust-shell models it is essential to take diverse and independent
observational constraints into account. Apart from matching the spectral energy
distribution, the use of spatially resolved information plays a crucial role
for obtaining reliable models. The combination of long-baseline interferometry
data with high-resolution single-dish data (short baselines), as obtained, for
example, by bispectrum speckle interferometry, provides complementary
information and will improve modelling and interpretation.


title:
A Chandra observation of the neutron star X-ray transient and eclipsing
  binary MXB 1659-29 in quiescence

abstract:
  After almost 2.5 years of actively accreting, the neutron star X-ray
transient and eclipsing binary MXB 1659-29 returned to quiescence in 2001
September. We report on a Chandra observation of this source taken a little
over a month after this transition. The source was detected at an unabsorbed
0.5-10 keV flux of only (2.7 - 3.6) x 10^{-13} ergs/s/cm/cm, which implies a
0.5-10 keV X-ray luminosity of approximately (3.2 - 4.3) x 10^{33} (d/10 kpc)^2
erg/s, with d the distance to the source in kpc. Its spectrum had a thermal
shape and could be well fitted by either a blackbody with a temperature kT of
0.3 keV or a neutron star atmosphere model with a kT of ~0.1 keV. The
luminosity and spectral shape of MXB 1659-29 are very similar to those observed
of the other neutron star X-ray transients when they are in their quiescent
state. The source was variable during our observation, exhibiting a complete
eclipse of the inner part of the system by the companion star. Dipping behavior
was observed before the eclipse, likely due to obscuration by an extended
feature in the outer part of a residual accretion disk. We discuss our
observation in the context of the cooling neutron star model proposed to
explain the quiescent properties of neutron star X-ray transients.


title: A Universal Temperature Profile for Galaxy Clusters

abstract:
  We investigate the predicted present-day temperature profiles of the hot,
X-ray emitting gas in galaxy clusters for two cosmological models - a current
best-guess LCDM model and standard cold dark matter (SCDM). Our
numerically-simulated "catalogs" of clusters are derived from high-resolution
(15/h kpc) simulations which make use of a sophisticated, Eulerian-based,
Adaptive Mesh-Refinement (AMR) code that faithfully captures the shocks which
are essential for correctly modelling cluster temperatures. We show that the
temperature structure on Mpc-scales is highly complex and non-isothermal.
However, the temperature profiles of the simulated LCDM and SCDM clusters are
remarkably similar and drop-off as $T +AFw-propto (1+-r/a_x)^{-+AFw-delta}$
where $a_x +AFw-sim r_{vir}/1.5$ and $+AFw-delta +AFw-sim 1.6$. This decrease
is in good agreement with the observational results of Markevitch et al.(1998)
but diverges, primarily in the innermost regions, from their fit which assumes
a polytropic equation of state. Our result is also in good agreement with a
recent sample of clusters observed by BeppoSAX though there is some indication
of missing physics at small radii ($r<0.2 r_{vir}$). We discuss the
interpretation of our results and make predictions for new x-ray observations
that will extend to larger radii than previously possible. Finally, we show
that, for $r>0.2 r_{vir}$, our universal temperature profile is consistent with
our most recent simulations which include both radiative cooling and supernovae
feedback.


title: Radio Galaxy Redshift-Angular Size Data Constraints on Dark Energy

abstract:
  We use FRIIb radio galaxy redshift-angular size data to constrain
cosmological parameters in a dark energy scalar field model. The derived
constraints are consistent with but weaker than those determined using Type Ia
supernova redshift-magnitude data.


title: The magnification of SN 1997ff, the farthest known Supernova

abstract:
  With a redshift of z~1.7, SN 1997ff is the most distant type Ia supernova
discovered so far. This SN is close to several bright, z=0.6-0.9 galaxies, and
we consider the effects of lensing by those objects on the magnitude of SN
1997ff. We estimate their velocity dispersions using the Tully-Fisher and
Faber-Jackson relations corrected for evolution effects,and calculate, applying
the multiple-plane lensing formalism, that SN 1997ff is magnified by 0.34+-0.12
mag. Due to the spatial configuration of the foreground galaxies, the shear
from individual lenses partially cancels out,and the total distortion induced
on the host galaxy is considerable smaller than that produced by a single lens
having the same magnification. After correction for lensing, the revised
distance to SN 1997ff is m-M=45.5 mag, which improves the agreement with the
Omega_M=0.35, Omega_Lambda = 0.65 cosmology expected from lower-redshift SNe
Ia, and is inconsistent at the ~3 sigma confidence level with a uniform gray
dust model or a simple evolution model.


title: The Neutral Atomic Phases of the ISM in the Galaxy

abstract:
  Much of the interstellar medium in disk galaxies is in the form of neutral
atomic hydrogen, H I. This gas can be in thermal equilibrium at relatively low
temperatures, T < 300 K (the cold neutral medium, or CNM) or at temperatures
somewhat less than 10^4 K (the warm neutral medium, or WNM). These two phases
can coexist over a narrow range of pressures, P_min < P < P_max. We determine
P_min and P_max in the plane of the Galaxy as a function of Galactocentric
radius R using recent determinations of the gas heating rate and the gas phase
abundances of interstellar gas. We provide an analytic approximation for P_min
as a function of metallicity, far-ultraviolet radiation field, and the
ionization rate of atomic hydrogen. Over most of the disk of the Galaxy, the H
I must be in two phases: the weight of the H I in the gravitational potential
of the Galaxy is large enough to generate thermal pressures exceeding P_min, so
that turbulent pressure fluctuations can produce cold gas that is thermally
stable; and the mean density of the H I is too low for the gas to be all CNM.
Our models predict the presence of CNM gas to R = 16-18 kpc, somewhat farther
than previous estimates. We also examine the potential impact of turbulent
heating on our results and provide expressions for the heating rate as a
function of Galactic radius.


title: A Near-Infrared Imaging Survey of Coalsack Globule 2

abstract:
  We describe a near-infrared imaging survey of Globule 2 in the Coalsack. This
Bok globule is the highest density region of this southern hemisphere molecular
cloud and is the most likely location for young stars in this complex. The
survey is complete for K < 14.0, H < 14.5, and J < 15.5, several magnitudes
more sensitive than previous observations of this globule. From the large
number of background stars, we derive an accurate near-infrared extinction law
for the cloud. Our result, E_{J-H}/E_{H-K} = 2.08 \pm 0.03, is significantly
steeper than results for other southern clouds. We use the J-H/H-K color-color
diagram to identify two potential young stars with K < 14.0 in the region. We
apply H-band star counts to derive the density profile of the Coalsack Globule
2 and use a polytropic model to describe the internal structure of this small
cloud. For a gas temperature T \sim 15 K, this globule is moderately unstable.


title:
What Fraction of the Young Clusters in the Antennae Galaxies are
  "Missing"?

abstract:
  A reexamination of the correspondence between 6 cm radio continuum sources
and young star clusters in the Antennae galaxies indicates that 85 % of the
strong thermal sources have optical counterparts, once the optical image is
shifted 1.2 arcsec to the southwest. A sample of 37 radio-optical matches are
studied in detail showing correlations between radio properties and a variety
of optical characteristics. There is a strong correlation between the radio
flux and the intrinsic optical brightness. In particular, the brightest radio
source is also the intrinsically brightest optical cluster (WS80). It is also
the most extincted cluster in the sample, the strongest CO source and the
strongest 15 micron source . Furthermore, the brightest ten radio sources are
all amongst the youngest clusters with ages in the range 0 - 4 Myr and
extinctions from A_V = 0.5 to 7.6 mag (with a median value of 2.6 mag). Only a
few of the very red clusters originally discovered by Whitmore & Schweizer are
radio sources, contrary to earlier suggestions. Finally, a new hybrid method of
determining cluster ages has been developed using both UBVI colors and H_alpha
equivalent widths to break the age-reddening degeneracy.


title:
Discovery of Radio-loud Quasars with Redshifts above 4 from the PMN
  sample

abstract:
  We present results of a new, large survey for high-redshift radio-loud
quasars, which targets quasars with z>4. The survey is based on the PMN and
NVSS radio surveys, optically identified using digitised UKST B, R and I
plates. Six new z>4 flat-spectrum QSOs have been discovered, and one previously
known z>4 QSO rediscovered, based on their red optical colours. The QSOs
discovered in this survey are bright in both radio and optical bands; in
particular PMN J1451-1512 (z=4.763, I=17.3, R=19.1) and PMN J0324-2918
(z=4.630, R=18.7) are very luminous. PMN J1451-1512 at z=4.763 is also now the
most distant radio-selected quasar. In addition, 9 new quasars with 3.5<z<4.0
were discovered during the survey. We present spectra and finding charts for
the new quasars. We also derive a surface density of 1.0+/-0.4 x 10^-3 /sq deg
for flat-spectrum z>4 QSOs with S>= 72mJy and R< 21mag.


title: A XMM-Newton observation during the 2000 outburst of SAX J1808.4-3658

abstract:
  I present a XMM-Newton observation of the accretion driven millisecond X-ray
pulsar SAX J1808.4-3658 during its 2000 outburst. The source was conclusively
detected, albeit at a level of only ~2 x 10^{32} erg/s. The source spectrum
could be fitted with a power-law model (with a photon index of ~2.2), a neutron
star atmosphere model (with a temperature of ~0.2 keV), or with a combination
of a thermal (either a black-body or an atmosphere model) and a power-law
component. During a XMM-Newton observation taken approximately one year later,
the source was in quiescence and its luminosity was a factor of ~4 lower. It is
possible that the source spectrum during the 2000 outburst was softer than its
quiescent 2001 spectrum, however, the statistics of the data do not allow to
make a firm conclusion. The results obtained are discussed in the context of
the 2000 outburst of SAX J1808.4-3658 and the quiescent properties of the
source.


title: Accelerated Lambda Iteration in Rapidly Expanding Envelopes

abstract:
  We discuss the current implementation of the ALI method into our
HYDrodynamical RAdiation(HYDRA) code for rapidly expanding, low density
envelopes commonly found in core collapse and thermonuclear supernovae, novae
and WR stars. Due to the low densities, non-thermal excitation by high energy
photons (e.g. by radioactive decays) and the time dependence of the problem,
large departures from LTE are common throughout the envelope even at large
optical depths. ALI is instrumental for both the coupling of the statistical
equations and the hydrodynamical equations with the radiation transport (RT).
We employ several concepts to improve the stability, and convergence
rate/control including the concept of leading elements, the use of net rates,
level locking, reconstruction of global photon redistribution functions,
equivalent-2-level approach, and predictive corrector methods. For appropriate
conditions, the solution of the time-dependent rate equations can be reduced to
the time-independent problem plus an analytic solution of an ODE For the 3-D
problem, we solve the radiation transport via the moment equations. To
construct the Eddington tensor elements, we use a Monte Carlo scheme to
determine the deviation of the solution of the RT equation from the diffusion
approximation (ALI of second kind). At the example of a thermonuclear supernova
(SN99by),we show an analysis of light light curves, flux and polarization
spectra and discuss the limitations of our approach.


title:
The Millennium Arecibo 21-cm Absorption Line Survey. I. Techniques and
  Gaussian Fits

abstract:
  We review the theory of measuring spectral lines in emission/absorption
observations and apply it to a new survey of the 21-cm line against 79
continuum sources. We develop an observing technique and least-squares
procedure to determine the opacity profile, the expected emission profile, and
their uncertainty profiles. We discuss the radiative transfer for the
two-component interstellar HI gas and use Gaussian components, separate ones
for the Warm and Cold neutral media (WNM and CNM), as a practical
implementation of a simple but physically correct model that successfully
treats both simple and complicated profiles. Our Gaussians provide CNM spin
temperatures, upper limits on kinetic temperatures for both CNM and WNM from
the line widths, column densities, and velocities; we discuss these
astrophysical aspects in Paper II.


title:
The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of
  the Warm and Cold Neutral Media

abstract:
  We use the Gaussian-fit results of Paper I to investigate the properties of
interstellar HI in the Solar neighborhood. The Warm and Cold Neutral Media (WNM
and CNM) are physically distinct components. The CNM spin temperature histogram
peaks at about 40 K. About 60% of all HI is WNM. At z=0, we derive a volume
filling fraction of about 0.50 for the WNM; this value is very rough. The
upper-limit WNM temperatures determined from line width range upward from about
500 K; a minimum of about 48% of the WNM lies in the thermally unstable region
500 to 5000 K. The WNM is a prominent constituent of the interstellar medium
and its properties depend on many factors, requiring global models that include
all relevant energy sources, of which there are many. We use Principal
Components Analysis, together with a form of least squares fitting that
accounts for errors in both the independent and dependent parameters, to
discuss the relationships among the four CNM Gaussian parameters. The spin
temperature T_s and column density N(HI) are, approximately, the two most
important eigenvectors; as such, they are sufficient, convenient, and
physically meaningful primary parameters for describing CNM clouds. The Mach
number of internal macroscopic motions for CNM clouds is typically 2.5, but
there are wide variations. We discuss the historical tau-T_s relationship in
some detail and show that it has little physical meaning. We discuss CNM
morphology using the CNM pressure known from UV stellar absorption lines.
Knowing the pressure allows us to show that CNM structures cannot be isotropic
but instead are sheetlike, with length-to-thickness aspect ratios ranging up to
about 280. We present large-scale maps of two regions where CNM lies in very
large ``blobby sheets''.


title: Deciphering The Last Major Invasion of the Milky Way Galaxy

abstract:
  We present first results from a spectroscopic survey of 2000 F/G stars
0.5--5kpc from the Galactic plane, obtained with the 2dF facility on the AAT.
These data show the mean rotation velocity of the thick disk about the Galactic
center a few kpc from the plane is very different than expectation, being about
100km/s, rather than the predicted ~180km/s. We propose that our sample is
dominated by stars from a disrupted satellite which merged with the disk of the
Milky Way Galaxy some 10-12Gyr ago. We do not find evidence for the many
substantial mergers expected in hierarchical clustering theories. We find yet
more evidence that the stellar halo retains kinematic substructure, indicative
of minor mergers


title:
Dynamical limits on galactic winds, halo machos and intergalactic
  globular clusters

abstract:
  We argue that any violent galactic winds following early epoch of star bursts
would significantly weaken the potentials of galaxies, and leave lasting
signatures such as a lowered dark halo density and preferentially
radial/escaping orbits for halo tracers such as globular clusters. A galaxy is
disintegrated if more than half of its dynamical mass is blown off. The
presence of dense halos in galaxies and the absence of intergalactic/escaping
globulars should imply an upper limit on the amount of baryons lost in galactic
winds around 4% of the total mass of the galaxy. This translates to limits on
the baryons participating the early star bursts and baryons locked in stellar
remnents, such as white dwarfs. The amount of halo white dwarfs claimed in
recent proper motion searches and microlensing observations in the Galactic
halo are too high to be consistent with our dynamical upper limits. Similar
arguments also imply upper limits for the amount of neutron stars and stellar
black holes, in galaxy halos. Nevertheless, a milder outflow is desirable,
especially in dwarf galaxies, both for lowering their cold dark matter central
density and for injecting metals to the intergalactic medium.


title: HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars

abstract:
  We derive age-metallicity relations (AMRs) and orbital parameters for the
1658 solar neighbourhood stars to which accurate distances are measured by the
HIPPARCOS satellite. The sample stars comprise 1382 thin disc stars, 229 thick
disc stars, and 47 halo stars according to their orbital parameters. We find a
considerable scatter for thin disc AMR along the one-zone Galactic chemical
evolution (GCE) model. Orbits and metallicities of thin disc stars show now
clear relation each other. The scatter along the AMR exists even if the stars
with the same orbits are selected. We examine simple extension of one-zone GCE
models which account for inhomogeneity in the effective yield and inhomogeneous
star formation rate in the Galaxy. Both extensions of one-zone GCE model cannot
account for the scatter in age - [Fe/H] - [Ca/Fe] relation simultaneously. We
conclude, therefore, that the scatter along the thin disc AMR is an essential
feature in the formation and evolution of the Galaxy. The AMR for thick disc
stars shows that the star formation terminated 8 Gyr ago in thick disc. As
already reported by Gratton et.al. (2000) and Prochaska et.al. (2000), thick
disc stars are more Ca-rich than thin disc stars with the same [Fe/H]. We find
that thick disc stars show a vertical abundance gradient. These three facts,
the AMR, vertical gradient, and [Ca/Fe]-[Fe/H] relation, support monolithic
collapse and/or accretion of satellite dwarf galaxy as thick disc formation
scenario.


title:
Outflow from and asymmetries in the nebula around the LBV candidate
  Sk-69 279

abstract:
  We present and discuss new long-slit Echelle spectra of the LMC LBV candidate
Sk-69 279 and put them in context with previous images and spectra. While at
first glance a simple spherically expanding symmetric shell, we find a
considerably more complex morphology and kinematics. The spectra indicate that
morphologically identified deviations from sphericity are outflows of faster
material out of the main body of Sk-69 279. The morphological as well as the
kinematic similarity with other LBV nebulae makes it likely that Sk-69 279 is
an LBV candidate, indeed, and poses the question in how far outflows out of
expanding LBV nebulae are a general property of such nebulae--at least during
some phases of their evolutions.


title: Simulations of dual morphology in spiral galaxies

abstract:
  Gas and stars in spiral galaxies are modelled with the DUAL code, using
hydrodynamic and N-body techniques. The simulations reveal morphological
differences mirroring the dual morphologies seen in B and K' band observations
of many spiral galaxies. In particular, the gaseous images are more flocculent
with lower pitch angles than the stellar images, and the stellar arm-interarm
contrast correlates with the degree of morphological decoupling.


title: Simple models of cooling flows

abstract:
  A semi-analytic model of cluster cooling flows is presented. The model
assumes that episodic nuclear activity followed by radiative cooling without
mass-dropout cycles the cluster gas between a relatively homogeneous, nearly
isothermal post-outburst state and a cuspy configuration in which a cooling
catastrophe initiates the next nuclear outburst. Fitting the model to Chandra
data for the Hydra cluster, a lower limit of $284\Myr$ until the next outburst
of Hydra A is derived. Density, temperature and emission-measure profiles at
several times prior to the cooling catastrophe are presented. It proves
possible to fit the mass $M(\sigma)$ with entropy index $P\rho^{-\gamma}$ less
than $\sigma$ to a simple power-law form, which is almost invariant as the
cluster cools. We show that radiative cooling automatically establishes this
power-law form if the entropy index was constant throughout the cluster gas at
some early epoch or after an AGN activity cycle. To high precision, the central
value of $\sigma$ decreases linearly in time. The fraction of clusters in a
magnitude-limited sample that have gas cooler than $T$ is calculated, and is
shown to be small for $T=2\keV$. Similarly, only 1 percent of clusters in such
a sample contain gas with $P\rho^{-\gamma} < 2\keV\cm^2$. Entropy production in
shocks is shown to be small. The entropy that is radiated from the cluster can
be replaced if a few percent of the cluster gas passes through bubbles heated
during an outburst of the AGN.


title:
Neutral Hydrogen and Optical Observations of Edge-on Galaxies: Hunting
  for Warps

abstract:
  We present 21-cm HI line and optical R-band observations for a sample of 26
edge-on galaxies. The HI observations were obtained with the Westerbork
Synthesis Radio Telescope, and are part of the WHISP database (Westerbork HI
Survey of Spiral and Irregular Galaxies). We present HI maps, optical images,
and radial HI density profiles. We have also derived the rotation curves and
studied the warping and lopsidedness of the HI disks.
  20 out of the 26 galaxies of our sample are warped, confirming that warping
of the HI disks is a very common phenomenon in disk galaxies. Indeed, we find
that all galaxies that have an extended HI disk with respect to the optical are
warped.
  The warping usually starts around the edge of the optical disk. The degree of
warping varies considerably from galaxy to galaxy. Furthermore, many warps are
asymmetric, as they show up in only one side of the disk or exhibit large
differences in amplitude in the approaching and receding sides of the galaxy.
These asymmetries are more pronounced in rich environments, which may indicate
that tidal interactions are a source of warp asymmetry. A rich environment
tends to produce larger warps as well. The presence of lopsidedness seems to be
related to the presence of nearby companions.


title: High proper motion white dwarfs and halo dark matter

abstract:
  The interpretation of the old, cool white dwarfs recently found by
Oppenheimer et al. (2001) is still controversial. Whereas these authors claim
that they have finally found the elusive ancient halo white dwarf population
that contributes significantly to the mass budget of the galactic halo, there
have been several other contributions that argue that these white dwarfs are
not genuine halo members but, instead, thick disk stars. We show here that the
interpretation of this sample is based on the adopted distances, which are
obtained from a color--magnitude calibration, and we demonstrate that when the
correct distances are used a sizeable fraction of these putative halo white
dwarfs belong indeed to the disk population. We also perform a maximum
likelihood analysis of the remaining set of white dwarfs and we find that they
most likely belong to the thick disk population. However, another possible
explanation is that this sample of white dwarfs has been drawn from a 1:1
mixture of the halo and disk white dwarf populations.


title: Star Formation from Galaxies to Globules

abstract:
  The empirical laws of star formation suggest that galactic-scale gravity is
involved, but they do not identify the actual triggering mechanisms for
clusters in the final stages. Many other triggering processes satisfy the
empirical laws too, including turbulence compression and expanding shell
collapse. The self-similar nature of the gas and associated young stars
suggests that turbulence is more directly involved, but the small scale
morphology of gas around most embedded clusters does not look like a random
turbulent flow. Most clusters look triggered by other nearby stars. Such a
prominent local influence makes it difficult to understand the universality of
the Kennicutt and Schmidt laws on galactic scales. A unified view of
multi-scale star formation avoids most of these problems. Ambient self-gravity
produces spiral arms and drives much of the turbulence that leads to
self-similar structures, while localized energy input from existing clusters
and field supernovae triggers new clusters in pre-existing clouds. The
hierarchical structure in the gas made by turbulence ensures that the
triggering time scales with size, giving the Schmidt law over a wide range of
scales and the size-duration correlation for young star fields. The efficiency
of star formation is determined by the fraction of the gas above a critical
density of around 10^5 m(H2)/cc. Star formation is saturated to its largest
possible value given the fractal nature of the interstellar medium.


title:
On the Potential of the Imaging Atmospheric Cherenkov Technique for
  Study of the Mass Composition of Primary Cosmic Radiation in the Energy
  Region above 30 TeV

abstract:
  We suggest a new approach to study the cosmis ray (CR) mass composition in
the energy region from 30 TeV/nucleus up to the "knee" region, i.e. up to a few
PeV/nucleus, using an array of imaging atmospheric Cherenkov telescopes (IACTs)
of a special architecture. This array consists of telescopes with a relatively
small mirror size (~10 square meters) separated from each other by large
distances (~500 meters) and equipped by multichannel cameras with a modest
pixel size (0.3-0.5 degree) and a sufficiently large viewing angle (6-7
degree).
  Compared to traditional IACT systems (like HEGRA, HESS or VERITAS) the IACT
array considered here could provide a very large detection area (several square
kilometers or more). At the same time, it allows an accurate measurement of the
energy of CR induced air showers (the energy resolution ranges within 25-35%)
and an effective separation of air showers created by different nuclei.
Particularly, it is possible to enrich air showers belonging to the nucleus
group assigned for selection up to ~90% purity at a detection efficiency of
15-20% of such showers.


title:
HST/WFPC2 proper motions in two bulge fields: kinematics and stellar
  population of the Galactic bulge

abstract:
  We report proper motion dispersions for stars in the direction of two fields
of the Galactic bulge, using HST/WFPC2 images taken six years apart.
  Our two fields are Baade's Window (l,b)=(1.13,-3.77) and Sgr I (l,b)=(1.25
,-2.65). Our proper motion dispersions are in good agreement with prior ground-
and space-based proper motion studies in bulge fields, but in contrast to some
prior studies, we do not exclude any subset of stars from our studies. In
Baade's Window, we find the $l$ and $b$ proper motion dispersions are 2.9 and
2.5 mas/yr, while in Sgr I, they are 3.3 and 2.7 mas/yr, respectively.
  For the first time, we can clearly separate the foreground disk stars out
from the bulge because of their large mean apparent proper motion. The
population with non-disk kinematics (which we conclude to be the bulge) has an
old main sequence turnoff point, similar to those found in old, metal rich
bulge globular clusters while those stars selected to have disk kinematics lie
on a fully populated main sequence. Separating main sequence stars by
luminosity, we find strong evidence that the bulge population is rotating,
largely explaining observations of proper motion anisotropy in bulge fields.
Because we have isolated such a pure sample of stars in the bulge, we have one
of the clearest demonstrations that the old stellar population of the inner
bulge/bar is in fact rotating.


title:
Optical monitoring of the gravitationally lensed quasar Q2237+0305 from
  APO between June 1995 and January 1998

abstract:
  We present a data set of images of the gravitationally lensed quasar
Q2237+0305, that was obtained at the Apache Point Observatory (APO) between
June 1995 and January 1998. Although the images were taken under variable,
often poor seeing conditions and with coarse pixel sampling, photometry is
possible for the two brighter quasar images A and B with the help of exact
quasar image positions from HST observations. We obtain a light curve with 73
data points for each of the images A and B. There is evidence for a long (>~
100 day) brightness peak in image A in 1996 with an amplitude of about 0.4 to
0.5 mag (relative to 1995), which indicates that microlensing has been taking
place in the lensing galaxy. Image B does not vary much over the course of the
observation period. The long, smooth variation of the light curve is similar to
the results from the OGLE monitoring of the system (Wozniak et al. 2000a).


title:
Gravitational radiation from highly magnetized nascent neutron stars in
  supernova remnants

abstract:
  We consider the spin evolution of highly magnetized neutron stars in a
hypercritical inflow just after their birth in supernovae. Presence of a strong
magnetic field could deform the star and if the symmetry axis of the field is
misaligned with that of stellar rotation, the star will be an emitter of
gravitational wave. Here we investigate the possibility of gravitational
radiation from such a star when there is a hypercritical inflow onto it. The
stellar configuration is slightly deformed away from spherical by the intense
magnetic field; the rotational angular frequency of the star is determined by
the balance between the accretion torque and the magnetic dipole radiation. An
estimation of the characteristic amplitude of the gravitational radiation from
such systems is given. (abridged abstract)


title:
Metallicity of the Intergalactic Medium Using Pixel Statistics: I.
  Method

abstract:
  Studies of absorption spectra of high-z QSOs have revealed that the
intergalactic medium at z ~ 2-3 is enriched to ~ 0.1%-1% solar for gas
densities more than a few times the mean cosmic density, but have not yet
produced an accurate metallicity estimate, nor constrained variations in the
metallicity with density, redshift, or spatial location. This paper discusses
the ``pixel optical depth'' (POD) method of QSO spectrum analysis, using
realistic simulated spectra from cosmological simulations. In this method,
absorption in Ly-alpha is compared to corresponding metal absorption on a
pixel-by-pixel basis, yielding for each analyzed spectrum a single statistical
correlation encoding metal enrichment information. Our simulations allow
testing and optimization of each step of the technique's implementation. Tests
show that previous studies have probably been limited by C IV
self-contamination and O VI contamination by HI lines; we have developed and
tested an effective method of correcting for both contaminants. We summarize
these and other findings, and provide a useful recipe for the POD technique's
application to observed spectra. Our tests reveal that the POD technique
applied to spectra of presently available quality is effective in recovering
useful metallicity information even in underdense gas. We present an extension
of the POD technique to directly recover the intergalactic metallicity as a
function of gas density. For a given ionizing background, both the oxygen and
carbon abundance can be measured with errors of at most a factor of a few over
at least an order of magnitude in density, using a single high-quality
spectrum.


title:
The M31 Dwarf Spheroidal Companion And V: g', r', and i' Imaging with
  GMOS on Gemini North

abstract:
  g', r', and i' images obtained with the Gemini Multi-Object Spectrograph
(GMOS) on Gemini North are used to investigate the metallicity and stellar
content of the M31 dwarf spheroidal companion galaxy And V. Red giant branch
(RGB) stars are traced out to radii in excess of 126 arcsec from the galaxy
center, indicating that And V extends over a diameter approaching 1 kpc. The
mean g'-i' color of the RGB does not change with radius. Based on the slope of
the RGB in the (i', g'-i') color-magnitude diagram we conclude that [Fe/H] =
-2.2 +/- 0.1. This metallicity is lower than earlier estimates, and places And
V squarely on the relation between metallicity and integrated brightness
defined by other dwarf spheroidal and dwarf elliptical galaxies. We also fail
to find a statistically significant population of luminous asymptotic giant
branch stars near the center of the galaxy.