title: Discovering internal symmetry in cosmology

abstract:
  Internal (non-geometric) symmetry is recognized and studied as a new
phenomenon in cosmology. Symmetry relates cosmic vacuum to non-vacuum forms of
cosmic energies, which are dark matter, baryons, and radiation. It is argued
that the origin and physical nature of cosmic internal symmetry are due to the
interplay between gravity and electroweak scale physics in the early universe.
The time-independent characteristic number associated with this symmetry is
found in terms of the Planck energy and the electroweak energy scale. Cosmic
internal symmetry provides a framework which suggests a consistent solution to
both the `cosmic coincidence problem' and the `naturalness problem' that have
been considered as the most severe challenge to current concepts in cosmology
and fundamental physics.


title: The Zeta Herculis binary system revisited. Calibration and seismology

abstract:
  We have revisited the calibration of the visual binary system Zeta Herculis
with the goal to give the seismological properties of the G0 IV sub-giant Zeta
Her A. We have used the most recent physical and observational data. For the
age we have obtained 3387 Myr, for the masses respectively 1.45 and 0.98 solar
mass, for the initial helium mass fraction 0.243, for the initial mass ratio of
heavy elements to hydrogen 0.0269 and for the mixing-length parameters
respectively 0.92 and 0.90 using the Canuto & Mazitelli (1991, 1992) convection
theory. Our results do not exclude that Zeta Her A is itself a binary
sub-system; the mass of the hypothetical unseen companion would be smaller than
0.05 solar mass. The adiabatic oscillation spectrum of Zeta Her A is found to
be a complicated superposition of acoustic and gravity modes; some of them have
a dual character. This greatly complicates the classification of the non-radial
modes. The echelle diagram used by the observers to extract the frequencies
will work for ell=0, 2, 3. The large difference is found to be of the order of
42 mu Hz, in agreement with the Martic et al. (2001) seismic observations.


title:
Determination of the Distance to M33 Based on Single Epoch I-band HST
  Observations of Cepheids

abstract:
  We have determined the distance to M33 using single epoch I-band observations
of Cepheids based on HST/WFPC2 images of five fields in M33. Combining the HST
I-band photometry and the periods determined from the ground-based observations
(DIRECT) for 21 Cepheids with log P>0.8 in the sample of 32 Cepheids, we derive
a distance modulus of (m-M)_0=24.52+/-0.14(random)+/-0.13(systematic) for an
adopted total reddening of M33, E(B-V)=0.20+/-0.04 (E(V-I)=0.27+/-0.05) given
by Freedmand et al.(2001), the reddening to the LMC, E(B-V)=0.10, and the
distance to the LMC, (m-M)_0=18.50. If the total reddening to M33 of
E(B-V)=0.10+/-0.09 given by Freedman, Wilson, and Madore(1991) is used, the
Cepheid distance modulus based on the I-band photometry will be increased by
0.20. Metallicity effect on the Cepheid distance to M33 is estimated to be
small, delta(m-M)_Z=0.01 to 0.06, which leads to (m-M)_0=24.53 to 24.58 after
this metallicity effect correction. Using the Wesenheit W_I, an extinction-free
parameter, we derive a similar value,
(m-M)_0=24.52+/-0.15(random)+/-0.11(systematic). These results are in
reasonable agreement with those based on the ground-based multi-epoch BVRI
observations of brighter Cepheids in M33, and are ~0.3 smaller than those based
on the tip of the red giant branch and the red clump. It is needed to estimate
better the reddening to Cepheids in M33.


title:
Determination of the Distance to M33 Based on the Tip of the Red Giant
  Branch and the Red Clump

abstract:
  We have determined the distance to M33 using the tip of the red giant branch
(TRGB) and the red clump (RC), from the VI photometry of stars in ten regions
of M33 based on HST/WFPC2 images. The regions used in this study are located at
R=2.6 - 17.8 arcmin from the center of M33. The distance modulus to M33
obtained in this study, for an adopted foreground reddening of E(B-V)=0.04, is
(m-M)_{0,TRGB}=24.81+/-0.04(random)+0.15/-0.11(systematic) from the TRGB, and
(m-M)_{0,RC}=24.80+/-0.04(random)+/-0.05(systematic) from the RC, showing an
excellent agreement between the two (corresponding to a distance of
916+/-17(random) kpc and 912+/-17(random) kpc, respectively). These results are
\~0.3 mag larger than the Cepheid distances based on the same HST/WFPC2 data
and ground-based data. This difference is considered partially due to the
uncertainty in the estimates of the total reddening for Cepheids in M33.


title:
Strategies for prompt searches for GRB afterglows: the discovery of the
  GRB 001011 optical/near-infrared counterpart using colour-colour selection

abstract:
  We report the discovery of the optical and near-infrared counterparts to GRB
001011. The GRB 001011 error box determined by Beppo-SAX was simultaneously
imaged in the near-infrared by the 3.58-m New Technology Telescope and in the
optical by the 1.54-m Danish Telescope ~8 hr after the gamma-ray event. Here we
implement the colour-colour discrimination technique proposed by Rhoads (2001)
and extend it using near-IR data as well. We present the results provided by an
automatic colour-colour discrimination pipe-line developed to discern the
different populations of objects present in the GRB 001011 error box. Our
software revealed three candidates based on single-epoch images. Second-epoch
observations carried out ~3.2 days after the burst revealed that the most
likely candidate had faded, thus identifying it with the counterpart to the
GRB. In deep R-band images obtained 7 months after the burst a faint
(R=25.38+/-0.25) elongated object, presumably the host galaxy of GRB 001011,
was detected at the position of the afterglow. The GRB 001011 afterglow is the
first discovered with the assistance of colour-colour diagram techniques. We
discuss the advantages of using this method and its application to error boxes
determined by future missions.


title: The Origin of Blue Cores in Hubble Deep Fields E/S0 galaxies

abstract:
  In this letter we address the problem of the origin of blue cores and inverse
color gradients in early-type galaxies reported in the Hubble Deep Field North
and South (HDFs) by Menanteau, Abraham & Ellis 2001. We use a multi-zone single
collapse model. This model accounts for the observed blue cores by adopting a
broad spread in formation redshifts for ellipticals, allowing some of these
galaxies begin forming no more than ~1 Gyr before the redshift of observation.
The single-zone collapse model then produces cores that are bluer than the
outer regions because of the increase of the local potential well toward the
center which makes star-formation more extended in the central region of the
galaxy. We compare the predicted V-I(r) color gradients with the observed ones
using the redshift of formation ($z_F$) of the elliptical as the only free
parameter. We find that the model can account with relatively good agreement
for the blue cores and inverse color gradients found in many spheroidals and at
the same time for the red and smooth colors profiles reported. Based on the
model our analysis suggests two populations of field ellipticals, one formed
recently, within $\lesssim1$Gyr and another much older formed $\gtrsim4$Gyr
since the redshift of observation.


title:
Constraints on the optical afterglow emission of the short/hard burst
  GRB 010119

abstract:
  We report optical observations of the short/hard burst GRB 010119 error box,
one of the smallest error boxes reported to date for short/hard GRBs. Limits of
R > 22.3 and I > 21.2 are imposed by observations carried out 20.31 and 20.58
hours after the gamma-ray event, respectively. They represent the most
constraining limits imposed to date on the optical emission from a short/hard
gamma-ray burst afterglow.


title: Are Starburst Galaxies the Hosts of Gamma-Ray Bursts ?

abstract:
  We present deep 2.2 micron imaging of twelve gamma-ray burst host galaxies.
Template spectral energy distributions are fit to the multiband photometry
between visible and near-infrared wavelengths to derive a better constraint on
the stellar mass of these galaxies. The internal extinction in the host
galaxies is estimated using the rest-frame ultraviolet (UV) slope. We find that
the extinction corrected star-formation rates (SFRs) of the galaxies are
significantly larger than rates derived from emission lines in the visible or
the UV continuum. The ratio between the extinction corrected SFRs and stellar
mass for 7 of the host galaxies is high compared to local starbursts and 3 of
the hosts have derived far-infrared luminosities comparable to infrared
luminous galaxies. In addition, existing observational data reveal that at
least 6 of the 11 putative hosts seem to be disturbed or have companion
galaxies within a projected angular separation of about 2.5 arcsec. If we
assume that the host and the companion are at similar redshifts, this
corresponds to a physical separation of less than 20 kpc, providing some
evidence for an ongoing/recent tidal encounter. We conclude that
tidally-induced starbursts such as those found in infrared luminous galaxies
might be popular birthplaces for gamma-ray bursts. The age of the stellar
population in 4 out of 6 galaxies is rather young, of order 10 Myr. This favors
models where gamma-ray bursts are due to the core-collapse of isolated, massive
stars and explosion of the resultant black hole-accretion disk system.


title: Unusual diffuse X-ray source in the Galactic center region

abstract:
  We report the ASCA and Chandra discovery of a diffuse X-ray source in the
Galactic center region. The X-ray spectrum is fitted with a non-equilibrium
ionization (NEI) plasma model of about 6-keV temperature. The model requires
higher than solar metal abundances, a young plasma age of $\simeq$ 100 years
and a large N_H value of about 10^{23} cm^{-2}. The N_H value constrains the
source position to be in the Galactic center region at about 8.5 kpc distance.
The high resolution X-ray image with the Chandra ACIS shows a ring of 10''
radius which corresponds to 0.4 pc at the Galactic center, and a tail-like
structure. Although the morphology is peculiar, the other X-ray features are
likely to be a very young supernova remnant, possibly in a free expansion
phase.


title: Turbulence and mixing in the early universe

abstract:
  The role of turbulence and turbulent mixing in the formation and evolution of
the early universe is examined. A new quantum-gravitational-dynamics model
suggests that the mechanism of the hot big bang is functionally equivalent to
the mechanism of turbulence, where an inertial-vortex force at Planck scales
matches the Planck gravitational force and drives the formation of
space-time-energy and the formation of more Planck particles, more spinning
Planck-Kerr particles, and a big bang turbulence cascade to larger scales
before cooling to the strong force freeze out temperature. Temperature
fluctuations between the Planck temperature and strong force temperature are
mixed by turbulence to give a Corrsin-Obukhov spectral form. Inflation
fossilizes the turbulent temperature fluctuations by stretching them beyond the
horizon scale of causal connection ct, where c is light speed and t is time.
Fossil temperature turbulence fluctuations seed anisotropies in the
nucleosynthesis of light elements, causing density fluctuations that seed the
first formation of gravitational structure in the matter dominated
hydrogen-helium plasma: proto-voids at galaxy supercluster scales. Evidence of
the proposed big bang turbulence event and first gravitational structure
formation is provided by the spectral form of the cosmic microwave temperature
fluctuations, which have been misinterpreted as sonic.


title:
High Resolution Observations of the Elliptical Galaxy NGC 4636 with the
  Reflection Grating Spectrometer On-Board XMM-Newton

abstract:
  We present the first high spectral resolution X-ray observation of the giant
elliptical galaxy NGC 4636, obtained with the Reflection Grating Spectrometer
on-board the XMM-Newton Observatory. The resulting spectrum contains a wealth
of emission lines from various charge states of oxygen, neon, magnesium, and
iron. Examination of the cross-dispersion profiles of several of these lines
provides clear, unambiguous evidence of resonance scattering by the highest
oscillator strength lines, as well as a weak temperature gradient in the inner
regions of the interstellar medium. We invoke a sophisticated new Monte Carlo
technique which allows us to properly account for these effects in performing
quantitative fits to the spectrum. Our spectral fits are not subject to many of
the systematics that have plagued earlier investigations. The derived metal
abundances are higher than have been inferred from prior, lower spectral
resolution observations of this source (Awaki et al. 1994), but are still
incompatible with conventional chemical enrichment models of elliptical
galaxies. In addition, our data are incompatible with standard cooling flow
models for this system - our derived upper limit to the mass deposition rate is
below the predicted value by a factor of 3--5.


title: Element Diffusion During Cosmological Structure Formation

abstract:
  We consider element diffusion during the linear growth of structure in the
intergalactic medium (IGM) before the redshift of reionization. The elements
produced during big bang nucleosynthesis (such as D, He-4 or Li-7) condensed in
collapsing regions more readily than hydrogen. Diffusion was most effective
when the IGM was neutral since the collisional cross-section between neutral
species is smaller than the corresponding Coulomb cross-section in an ionized
gas. We find that diffusion led to small deviations in element abundances of up
to 0.1%. Abundance measurements to this level of precision in low-metallicity
environments could provide information about the thermal and ionization history
of the primordial gas during the early formation of structure in the IGM.


title:
Massive Star Evolution: Nucleosynthesis and Nuclear Reaction Rate
  Uncertainties

abstract:
  We present a nucleosynthesis calculation of a 25 solar mass star of solar
composition that includes all relevant isotopes up to polonium. In particular,
all stable isotopes and necessary nuclear reaction rates are covered. We follow
the stellar evolution from hydrogen burning till iron core collapse and
simulate the explosion using a ``piston'' approach. We discuss the influence of
two key nuclear reaction rates, C12(a,g) and Ne22(a,n), on stellar evolution
and nucleosynthesis. The former significantly influences the resulting core
sizes (iron, silicon, oxygen) and the overall presupernova structure of the
star. It thus has significant consequences for the supernova explosion itself
and the compact remnant formed. The later rate considerably affects the
s-process in massive stars and we demonstrate the changes that different
currently suggested values for this rate cause.


title: Gravitational Radiation from Black Hole Binaries in Globular Clusters

abstract:
  A populations of stellar mass black hole binaries may exist in globular
clusters. The dynamics of globular cluster evolution imply that there may be at
most one black hole binary is a globular cluster. The population of binaries
are expected to have orbital periods greater than a few hours and to have a
thermal distribution of eccentricities. In the LISA band, the gravitational
wave signal from these binaries will consist of several of the higher harmonics
of the orbital frequency. A Monte Carlo simulation of the galactic globular
cluster system indicates that LISA will detect binaries in 10 % of the clusters
with an angular resolution sufficient to identify the host cluster of the
binary.


title: Probing Dust in the Atmosphere of Brown Dwarfs Through Polarization

abstract:
  Theoretical analysis and observational evidences indicate that a brown dwarf
with effective temperature greater than 1400 K would have dust cloud in its
atmosphere. In this letter, we show that dust scattering should yield polarized
continuum radiation from the relatively warm brown dwarfs and the polarized
flux profile could be a potential diagnosis tool for the optical and the
physical properties of dust grains. The degree of polarization due to multiple
scattering will be more in the optical region if the particle size is small
while significant polarization should be detected in the infra-red region if
the particle size is large. It is pointed out that the departure from
sphericity in the shape of the object due to rapid rotation and due to tidal
effect by the companion in a binary system ensures the disc integrated
polarization to be non-zero.


title:
Effect of Fractional Kinetic Helicity on Turbulent Magnetic Dynamo
  Spectra

abstract:
  Magnetic field amplification in astrophysics ultimately requires an
understanding of magnetohydrodynamic turbulence. Kinetic helicity has long been
known to be important for large scale field growth in forced MHD turbulence,
and has been recently demonstrated numerically to be asymptotically consistent
with slow mean field dynamo action in a periodic box. Here we show numerically
that the magnetic spectrum at and below the forcing scale is also strongly
influenced by kinetic helicity. We identify a critical value, $f_{h,crit}$
above which the magnetic spectrum develops maxima at wavenumber $= 1$ scale
{\it and} at the forcing scale, For $f< f_{h,crit}$ the field peaks only at the
resistive scale. Kinetic helicity may thus be important not only for generating
a large scale field, but also for establishing observed peaks in magnetic
spectra at the forcing scale. The turbulent Galactic disk provides an example
where both large scale ($>$ supernova forcing scale) fields and small scale
($\le$ forcing scale, with peak at forcing scale) fields are observed. We
discuss this, and the potential application to the protogalaxy, but also
emphasize the limitations in applying our results to these systems.


title: Coupling Chemical Evolution with SPH

abstract:
  We present a new statistical algorithm of Chemical Evolution implemented into
the Tree-SPH code developed by Lia & Carraro (2000 MNRAS 314, 145).


title: ULTRACAM - an ultra-fast, triple-beam CCD camera

abstract:
  ULTRACAM is an ultra-fast, triple-beam CCD camera which has been designed to
study one of the few remaining unexplored regions of observational parameter
space - high temporal resolution. The camera will see first light in Spring
2002, at a total cost of GBP 300 k, and will be used on 2-m, 4-m and 8-m class
telescopes to study astrophysics on the fastest timescales.


title: Two collaborative experiments in star cluster evolution

abstract:
  We summarise the specification and some previously unpublished results of the
collaborative experiment (``KyotoI'') that was carried out at the time of the
Kyoto General Assembly of the IAU. As the subject has advanced considerably
since then, and codes have become more elaborate, we describe an agreed
proposal for a new experiment (``KyotoII'').


title: Stochastic spin evolution of neutron stars

abstract:
  In this paper we present calculations of period distribution for old
accreting isolated neutron stars (INSs).
  At the age about a few billions years low velocity INSs come to the stage of
accretion. At that stage their period evolution is governed by magnetic
breaking and accreted angular momentum. Due to turbulence of the interstellar
medium (ISM) accreted momentum can both accelerate and decelerate rotation of
an INS and spin evolution has chaotic character.
  Calculations show that for constant magnetic fields INSs have relatively long
spin periods, $\ge 10^4$--$10^5$ s, depending on parameters of INSs and an ISM.
Due to long periods INSs have high spin up/spin down rates, which should
fluctuate on a time scale about a few years.


title: Orbital variability of the PSR J2051-0827 Binary System

abstract:
  We have carried out high-precision timing measurements of the binary
millisecond pulsar PSR J2051$-$0827 with the Effelsberg 100-m radio telescope
of the Max-Planck-Institut f\"ur Radioastronomie and with the Lovell 76-m radio
telescope at Jodrell Bank. The 6.5-yrs radio timing measurements have revealed
a significant secular variation of the projected semi-major axis of the pulsar
at a rate of $\dot x\equiv d(a_{\rm 1} \sin i)/dt = (-0.23\pm 0.03)\times
10^{-12}$, which is probably caused by the Newtonian spin-orbit coupling in
this binary system leading to a precession of the orbital plane. The required
misalignment of the spin and orbital angular momenta of the companion are
evidence for an asymmetric supernova explosion. We have also confirmed that the
orbital period is currently decreasing at a rate of $\dot P_{\rm b}=(-15.5 \pm
0.8)\times 10^{-12}$s s$^{-1}$ and have measured second and third orbital
period derivatives $d^2P_{\rm b}/dt^2=(+2.1 \pm 0.3)\times 10^{-20} {\rm
s^{-1}}$ and $d^3P_{\rm b}/dt^3 =(3.6 \pm 0.6)\times 10^{-28} {\rm s^{-2}}$,
which indicate a quasi-cyclic orbital period variation similar to those found
in another eclipsing pulsar system, PSR B1957+20. The observed variation of the
orbital parameters constrains the maximal value of the companion radius to
$R_{\rm c max} \sim 0.06 R_{\odot}$ and implies that the companion is
underfilling its Roche lobe by 50 %. The derived variation in the quadrupole
moment of the companion is probably caused by tidal dissipation similar to the
mechanism proposed for PSR B1957+20. We conclude that the companion is at least
partially non-degenerate, convective and magnetically active.


title:
The Galactic disk mass-budget : II. Brown dwarf mass-function and
  density

abstract:
  In this paper, we extend the calculations conducted previously in the stellar
regime to determine the brown dwarf IMF in the Galactic disk. We perform Monte
Carlo calculations taking into account the brown dwarf formation rate, spatial
distribution and binary fraction. Comparison with existing surveys seems to
exclude a power-law MF as steep as the one determined in the stellar regime
below 1 $\msol$ and tends to favor a more flatish behaviour. Comparison with
methane-dwarf detections tends to favor an eventually decreasing form like the
lognormal or the more general exponential distributions determined in the
previous paper. We calculate predicting brown dwarf counts in near-infrared
color diagrams and brown dwarf discovery functions. These calculations yield
the presently most accurate determination of the brown dwarf census in the
Galactic disk. The brown dwarf number density is comparable to the stellar one,
$n_{BD}\simeq n_\star\simeq 0.1$ pc$^{-3}$. The corresponding brown dwarf mass
density, however, represents only about 10% of the stellar contribution, i.e.
$\rho_{BD}\simle 5.0\times 10^{-3} \mvol$. Adding up the local stellar density
determined previously yields the density of star-like objects, stars and brown
dwarfs, in the solar neighborhood $\rho_\odot \approx 5.0\times 10^{-2} \mvol$.


title:
Magnetic properties of photospheric regions having very low magnetic
  flux

abstract:
  The magnetic properties of the quiet Sun are investigated using a novel
inversion code, FATIMA, based on the Principal Component Analysis of the
observed Stokes profiles. The stability and relatively low noise sensitivity of
this inversion procedure allows for the systematic inversion of large data sets
with very weak polarization signal. Its application to quiet Sun observations
of network and internetwork regions reveals that a significant fraction of the
quiet Sun contains kilogauss fields (usually with very small filling factors)
and confirms that the pixels with weak polarization account for most of the
magnetic flux. Mixed polarities in the resolution element are also found to
occur more likely as the polarization weakens.


title: The extent of NGC 6822 revealed by its C stars population

abstract:
  Using the CFH12K camera, we apply the four band photometric technique to
identify 904 carbon stars in an area 28' x 42' centered on NGC 6822. A few C
stars, outside of this area were also discovered with the Las Campanas Swope
Telescope. The NGC 6822 C star population has an average I of 19.26 mag leading
to an average absolute I magnitude of
  -4.70 mag, a value essentially identical to the mean magnitude obtained for
the C stars in IC 1613. Contrary to stars highlighting the optical image of NGC
6822, C stars are seen at large radial distances and trace a huge slightly
elliptical halo which do not coincide with the huge HI cloud surrounding
NGC6822. The previously unknown stellar component of NGC 6822 has a exponential
scale length of 3.0' +/- 0.1' and can be traced to five scale lengths. The C/M
ratio of NGC 6822 is evaluated to br 1.0 +/- 0.2.


title: HST imaging of hyperluminous infrared galaxies

abstract:
  We present HST WFPC2 I band imaging for a sample of 9 Hyperluminous Infrared
Galaxies spanning a redshift range 0.45 < z < 1.34. Three of the sample have
morphologies showing evidence for interactions, six are QSOs. Host galaxies in
the QSOs are reliably detected out to z ~ 0.8. The detected QSO host galaxies
have an elliptical morphology with scalelengths spanning 6.5 < r_{e}(Kpc) < 88
and absolute k corrected magnitudes spanning -24.5 < M_{I} < -25.2. There is no
clear correlation between the IR power source and the optical morphology. None
of the sources in the sample, including F15307+3252, show any evidence for
gravitational lensing. We infer that the IR luminosities are thus real. Based
on these results, and previous studies of HLIRGs, we conclude that this class
of object is broadly consistent with being a simple extrapolation of the ULIRG
population to higher luminosities; ULIRGs being mainly violently interacting
systems powered by starbursts and/or AGN. Only a small number of sources whose
infrared luminosities exceed 10^{13}Lsun are intrinsically less luminous
objects which have been boosted by gravitational lensing.


title: A variable efficiency for thin disk black hole accretion

abstract:
  We explore the presence of torques at the inner edges of geometrically-thin
black hole accretion disks using 3-dimensional magnetohydrodynamic (MHD)
simulations in a pseudo-Newtonian potential. By varying the saturation level of
the magnetorotational instability that leads to angular momentum transport, we
show that the dynamics of gas inside the radius of marginal stability varies
depending upon the magnetic field strength just outside that radius. Weak
fields are unable to causally connect material within the plunging region to
the rest of the disk, and zero torque is an approximately correct boundary
condition at the radius of marginal stability. Stronger fields, which we obtain
artificially but which may occur physically within more complete disk models,
are able to couple at least some parts of the plunging region to the rest of
the disk. In this case, angular momentum (and implicitly energy) is extracted
from the material in the plunging region. Furthermore, the magnetic coupling to
the plunging region can be highly time dependent with large fluctuations in the
torque at the radius of marginal stability. This implies varying accretion
efficiencies, both across systems and within a given system at different times.
The results suggest a possible link between changes in X-ray and outflow
activity, with both being driven by transitions between weak and strong field
states.


title: The Butcher-Oemler Effect in High Redshift X-ray Selected Clusters

abstract:
  We are engaged in a wide-field, multi-colour imaging survey of X-ray selected
clusters at intermediate and high redshift. We present blue fractions for the
first 8 out of 29 clusters, covering almost a factor of 100 in X-ray
luminosity. We find no correlation of blue fraction with redshift or X-ray
luminosity. The lack of a correlation with L$_{X}$, places strong constraints
on the importance of ram-pressure stripping as a driver of the Butcher-Oemler
effect.


title: Super-massive stars: Dense star-gas systems

abstract:
  We use a gaseous model and a semi-analytical approach to study the evolution
of a super-massive central gaseous object (a super-massive star, (SMS from now
on) in an AGN and its evolution by interactions with the surrounding stellar
system. Our future work in this field is outlined, which aims at a more
detailed study of energy flows in the interstellar medium, stellar evolution
and the relation between QSOs and galaxy formation.


title: Constraints in the coupling Star-Life

abstract:
  If life is sustained by a process of photosynthesis, not necessarily the same
existing on Earth, the surface temperature of the star and the orbit of the
host planet cannot be whatsoever. In fact the global life cycle, no matter how
complicated, must contain in general an upper photochemical branch and a lower
dark branch, characterized by a higher and a lower temperature. These two
temperatures are star-orbit related. The velocity along the cycle or, in other
words, the power of the life machine, depends in general on several other
parameters. First of all the Gibbs photon availability, which is a star-orbit
parameter and is the input for the upper branch. Then follows the energy
cascade that develops along the organic web with a large number of interactions
and typical times that must match the typical times generated by the
combination of spin value and orientation, eccentricity and precession.
Finally, the capacity of the web to keep the global life cycle running along
the life span of the star, comes from some inner form of self-endurance and
self-balance. The property of not being transient could be the right way of
introducing the concept of intelligent life.


title: X-ray temperature and morphology of z>0.8 clusters of galaxies

abstract:
  We discuss our current progress in studying a sample of z>0.8 clusters of
galaxies from the ROSAT Distant Cluster Survey. To date, we have Chandra
observations for four of the ten clusters. We find that the morphology of two
of these four are quite regular, with deviations from circular of less than 5%,
while two are strikingly elliptical. When the temperatures and luminosities of
our sample are grouped with six other high-redshift measurements, there is no
measured evolution in the luminosity-temperature relation. We identify a number
of X-ray emitting point sources that are potential cluster members. These could
be sources of intracluster medium heating, adding the entropy necessary to
explain the cluster luminosity-temperature relation.


title: Wavelet Imaging Cleaning Method for Atmospheric Cherenkov Telescopes

abstract:
  We present a new method of image cleaning for imaging atmospheric Cherenkov
telescopes. The method is based on the utilization of wavelets to identify
noise pixels in images of gamma-ray and hadronic induced air showers. This
method selects more signal pixels with Cherenkov photons than traditional image
processing techniques. In addition, the method is equally efficient at
rejecting pixels with noise alone. The inclusion of more signal pixels in an
image of an air shower allows for a more accurate reconstruction, especially at
lower gamma-ray energies that produce low levels of light. We present the
results of Monte Carlo simulations of gamma-ray and hadronic air showers which
show improved angular resolution using this cleaning procedure. Data from the
Whipple Observatory's 10-m telescope are utilized to show the efficacy of the
method for extracting a gamma-ray signal from the background of hadronic
generated images.


title: Neutron star blackbody contraction during flaring in X1624-490

abstract:
  We present results of an investigation of the physical changes taking place
in the emission regions of the LMXB X1624-490 during strong flaring in RXTE
observations. Based on the detailed light curve, we propose that the flaring
consists of a superposition of X-ray bursts. It is shown that major changes
take place in the blackbody emission component, the temperature kT_BB
increasing to ~2.2 keV in flaring. Remarkably, the blackbody area decreases by
a factor of ~5 in flaring. During flare evolution, the blackbody luminosity
remains approximately constant, constituting a previously unknown Eddington
limiting effect which we propose is due to radiation pressure of the blackbody
as kT_BB increases affecting the inner disk or accretion flow resulting in a
decreased emitting area on the star. We argue that the large decrease in area
cannot be explained in terms of modification of the blackbody spectrum by
electron scattering in the atmosphere of the neutron star. The height of the
emitting region on the non-flaring neutron star is shown to agree with the
height of the inner radiatively-supported disk as found for sources in the ASCA
survey of LMXB of Church & Balucinska-Church (2001). The decrease in height
during flaring is discussed in terms of possible models, including radial
accretion flow onto the stellar surface and the theory of accretion flow
spreading on the neutron star surface of Inogamov & Sunyaev (1999). We
demonstrate that the intensity of the broad iron line at 6.4 keV is strongly
correlated with the luminosity of the blackbody emission from the neutron star,
and discuss the probable origin of this line in the ADC. Finally, possible
reasons for non-detection of a reflection component in this source, and LMXB in
general, are discussed.


title: X-Ray Plasma Diagnostics of Stellar Winds in Young Massive Stars

abstract:
  High resolution X-ray spectra of very young massive stars opened a new
chapter in the diagnostics and understanding of the properties of stellar wind
plasmas. Observations of several very young early type stars in the Orion
Trapezium demonstrated that the conventional model of shock heated plasmas in
stellar winds is not sufficient to explain the observed X-ray spectra. Detailed
X-ray line diagnostics revealed extreme temperatures in some of the candidates
as well as evidence for high plasma densities. It is also evident from high
resolution spectra of more conventional early type stars, that not all show
such extreme characteristics. However, the fact that some of the stars show hot
and dense components and some do not requires more understanding of the
physical processes involved in stellar wind emissions. The Orion Trapezium
stars distinguish themselves from all the others by their extreme youth. By
comparing the diverse spectral properties of theta Ori A and theta Ori E with
those of theta Ori C, we further demonstrate that X-ray spectral properties of
very young massive stars are far from understood.


title: A white dwarf with a low magnetic field in the IP RXJ0028.8+5917/V709Cas

abstract:
  We report the first detailed spectroscopic observations of the recently
identified intermediate polar RXJ0028.8+5917/V709 Cas. We discovered that the
system shows significant EW ~ (2-4)A broad absorptions, affecting the Balmer
lines from Hdelta to Hbeta. These broad absorptions are interpreted as the
contribution of an underlying DA logg=8 white dwarf at a temperature of ~ 23
000 K, contributing ~ 17 % (at 4500 A) to the overall flux. This is the first
direct detection of a white dwarf in an intermediate polar system. The absence
of significant Zeeman splitting indicates a magnetic field lower than 10 MG,
confirming that, at least in some cases, intermediate polars have weaker fields
than polars.


title: Optical/near-IR observations of Gamma-Ray Bursts in the Afterglow Era

abstract:
  An overview of the optical and near-IR observations of GRBs in the Afterglow
Era is presented, covering the period 1997-2000. They have allowed to a better
understanding of the underlying GRB physics as well as to constraint the
progenitor models.


title: Cosmological Simulations with Adaptive Smoothed Particles Hydrodynamics

abstract:
  We summarize the ideas that led to the Adaptive Smoothed Particle
Hydrodynamics (ASPH) algorithm, with anisotropic smoothing and shock-tracking.
We then identify a serious new problem for SPH simulations with shocks and
radiative cooling --- false cooling --- and discuss a possible solution based
on the shock-tracking ability of ASPH.


title: Long-term X-ray variability and state transition of GX 339-4

abstract:
  With extensive monitoring data spanning over 30 years from Vela 5B, Ariel 5,
Ginga, Compton Gamma Ray Observatory, Rossi X-ray Timing Explorer and BeppoSAX,
we find evidence for long-term X-ray variability on timescales ~190-240 d from
the black hole low-mass X-ray binary system GX 339-4. Such variability
resembles the outburst cycle of Z Cam-type dwarf novae, in which the standard
disc instability model plays a crucial role. If such a model is applicable to
GX 339-4, then the observed variability might be due to the irradiation of an
unstable accretion disc. We show that within the framework of the X-ray
irradiation model, when the accretion rate exceeds a critical value, GX 339-4
enters a `flat-topped' high/soft state, such as seen in 1998, which we suggest
corresponds to the `standstill' state of Z Cam systems.


title: Optical & NIR Surface Photometry of I Zw 18

abstract:
  Using HST and ground-based optical and NIR data, we investigate whether the
blue compact dwarf (BCD) galaxy I Zw 18 has an extended low-surface-brightness
(LSB) older stellar population underlying the star-forming regions, as is the
case in evolved iE/nE BCDs. Subtraction of narrow band H_alpha and [O III]
exposures from R and V images shows that the filamentary LSB envelope extending
out to ~2 kpc away from the starburst region, and hence the optical broad-band
colors observed therein, are due mainly to ionized gas emission. Ionized gas
accounts already at a galactocentric distance of 0.7 kpc for more than 80% of
the R band line-of-sight intensity and contributes more than 40% of the
integrated R band light of I Zw 18. The structural properties (such as the
exponential scale length) of the stellar LSB component underlying the extended
ionized gas emission place I Zw 18 among the most compact BCDs studied so far.
Contrary to evolved nE/iE BCDs, the stellar component in I Zw 18 shows no
appreciable color gradients over a range of ~8 mag in surface brightness.


title:
Gamma-ray Emission from an Outer-Gap Accelerator: Constraints on
  Magnetospheric Current, Magnetic Inclination, and Distance for PSR B1055-52

abstract:
  We investigate a stationary pair production cascade in the outer
magnetosphere of a spinning neutron star. The charge depletion due to global
flows of charged particles, causes a large electric field along the magnetic
field lines. Migratory electrons and/or positrons are accelerated by this field
to radiate curvature gamma-rays, some of which collide with the X-rays to
materialize as pairs in the gap. The replenished charges partially screen the
electric field, which is self-consistently solved, together with the
distribution functions of particles and gamma-rays. By solving the Vlasov
equations describing this pair production cascade, we demonstrate the existence
of a stationary gap in the outer magnetosphere of PSR B1055-52 for a wide range
of current densities flowing in the accelerator: From sub to super
Goldreich-Julian values. However, we find that the expected GeV spectrum
becomes very soft if the current density exceeds the Goldreich-Julian value. We
also demonstrate that the GeV spectrum softens with decreasing magnetic
inclination and with increasing distance to this pulsar. We thus conclude that
a sub-Goldreich-Julian current, a large magnetic inclination, and a small
distance (500 pc, say) are plausible to account for EGRET observations.
Furthermore, it is found that the TeV flux due to inverse Compton scatterings
of infrared photons whose spectrum is inferred from the Rayleigh-Jeans side of
the soft blackbody spectrum is much less than the observational upper limit.


title:
Outbursts of Classical Symbiotics: Multi-Wavelength Observations of the
  2000-2001 Outburst of Z Andromedae

abstract:
  We describe the first results from a program of multi-wavelength monitoring
of symbiotic binary stars in outburst. The prototypical symbiotic star Z
Andromedae was observed extensively at radio, optical, far-UV, and X-ray
wavelengths during its current (ongoing) outburst. These observations provide
evidence for an initial obscuration or the source of ionizing radiation by an
optically thick shell of material, outflow with velocities of 100s of km/s,
plus collisional excitation and shock heating of the red-giant wind. In
addition, the optical light curve reveals variability on time scales as short
as days on both the rise to and decline from optical maximum.


title: The Galactic Halo UV Field, Magellanic Stream and High Velocity Clouds

abstract:
  Significant numbers of high-velocity HI clouds (HVCs) have now been detected
in H-alpha, with a subset seen in low ionization lines (e.g. [NII]). It was
originally hoped that the observed H-alpha strength would provide a distance
constraint to individual clouds. This idea requires that a useful fraction
(f_esc > 1%) of ionizing photons escape the Galaxy, and that the halo ionizing
field is relatively smooth, as we discuss. Most HVCs which are known to be
close to the Sun are H-alpha; the brightest clouds also show enhanced [NII]
emission, in contrast to the Magellanic Stream where the low ionization
emission lines are always weak compared to H-alpha. But an acute complication
for H-alpha distances is the apparent H-alpha brightness of the Magellanic
Stream along several sight lines. To account for this, we present three
possible configurations for the Magellanic Stream and propose a follow-up
experiment. If we normalize the distances to local HVCs, some HVCs appear to be
scattered throughout the Galactic halo on scales of tens of kiloparsecs.


title:
H-alpha Distance Constraints for High-Velocity Clouds in the Galactic
  Halo

abstract:
  We present some developments in determining H-alpha distances to
high-velocity clouds (HVCs) in the Galactic halo. Until recently, it was
difficult to assess the nature and origin of HVCs because so little was known
about them. But now several HVCs have reliable distance bounds derived from the
stellar absorption technique, and more than a dozen have abundance
measurements. In addition, twenty or more HVCs have been detected in H-alpha
(and a few in optical forbidden lines). Over the past five years, we have been
developing a model of the halo radiation field which includes contributions
from the stellar disk, the stellar bulge, the hot corona, and the Magellanic
Clouds. In certain instances, the H-alpha flux from an opaque HI cloud can be
used to derive a crude distance constraint to the cloud. For a UV escape
fraction of f_esc ~ 6% perpendicular to the disk (f_esc ~ 1-2% when averaged
over solid angle), the HVCs appear to be broadly consistent with the spiral arm
model. We caution that a larger database with full sky coverage is required
before the usefulness of H-alpha distances can be fully assessed. We present a
number of detailed predictions from our distance frame to encourage independent
assessments from future observations. If the model is valid, we find that most
HVCs detected to date are scattered throughout the halo up to distances of 50
kpc from the Sun. Most of this material is likely to be debris from recent
galaxy interactions, or even debris dislodged from the outer Galaxy disk. We
propose some future tests of the H-alpha distance model and briefly discuss
recent H-alpha detections along the Magellanic Bridge and Magellanic Stream.


title: On the Global Anisotropy of Cosmic Ray Data above $4 \times 10^{19}eV$

abstract:
  The distribution of arrival directions of ultra-high energy cosmic rays may
yield clues to their mysterious origin. We introduce a method of {\it invariant
statistics} to analyze cosmic ray data which eliminates coordinate-dependent
artifacts. When combined with maximum likelihood analysis, the method is
capable of quantifying deviations of the distribution from isotropy with high
reliability. We test our method against published AGASA events with energies
above $4 \times 10^{19}$ eV. Angular cuts from observational limitations are
taken into account. A model based on the Fisher distribution reveals the
rotation of the Earth with the axis $\hat n$ along the direction ($5^h 53.36^m,
85.78^{\circ}$) in $(RA,DEC)$ coordinates, which is within $5^{\circ}$ of the
equatorial north pole. Global anisotropy of the data, if any, hinges on finer
understanding of detector acceptance than what is available from the published
literature.


title: The L_x-sigma Relation For Poor Groups of Galaxies

abstract:
  We use a sample of 20 poor groups of galaxies to study the low L_x tail of
the L_x-sigma relationship. We have obtained redshifts for fainter members and
deep X-ray imaging of these groups. We find that the L_x-sigma relationship
derived for the rich clusters in the sample of Mushotzky & Scharf (1997) is
consistent with the data for our 20 poor groups. However, it is not possible to
reach strong conclusions about differences in the L_x-sigma relationship for
groups and clusters in general at the present time because of significant
differences between various cluster samples.


title:
Discovery of a New Companion and Evidence of a Circumprimary Disk:
  Adaptive Optics Imaging of the Young Multiple System VW Cha

abstract:
  Since a majority of young low-mass stars are members of multiple systems, the
study of their stellar and disk configurations is crucial to our understanding
of both star and planet formation processes. Here we present near-infrared
adaptive optics observations of the young multiple star system VW Cha. The
previously known 0.7 arcsec binary is clearly resolved already in our raw J and
K band images. We report the discovery of a new, faint companion to the
secondary, at an apparent separation of only 0.1 arcsec or 16 AU. Our
high-resolution photometric observations also make it possible to measure the
J-K colors of each of the three components individually. We detect an infrared
excess in the primary, consistent with theoretical models of a circumprimary
disk. Analytical and numerical calculations of orbital stability show that VW
Cha may be a stable triple system. Using models for the age and total mass of
the secondary pair, we estimate the orbital period to be 74 years. Thus,
follow-up astrometric observations might yield direct dynamical masses within a
few years, and constrain evolutionary models of low-mass stars. Our results
demonstrate that adaptive optics imaging in conjunction with deconvolution
techniques is a powerful tool for probing close multiple systems.


title: The new cataclysmic variable RX J1554.2+2721 in the period gap

abstract:
  We report on the results of a spectroscopic and photometric study of a new
cataclysmic variable, identified as optical counterpart of the X-ray source RX
J1554.2+2721 detected by ROSAT. The spectroscopic observations of the
relatively bright (~16.5mag) object show systematic radial velocity variations
with a semi-amplitude of ~140 km/sec. Besides the clear presence of distinct
low and high states there are periodic photometric light variations with an
amplitude of about 0.15 magnitude in the R band. The orbital period is 2.753h
thus being within the period gap, at its upper border. The flux distribution in
the spectrum of the object shows a substantial contribution of a M4V secondary,
and also bears clear signs of cyclotron emission. Thus, we classify the
discovered object as a new member of the AM Her class of magnetic cataclysmic
variables. This classification is further supported by the soft X-ray spectrum,
the characteristic profiles of the emission lines, the tomography map and the
shape of the orbital light curve. A simple fitting of the spectrum in the low
and high states suggests a reduced mass transfer rate in RX J1554.2+2721,
compared to similar objects outside the period gap.


title: The bright optical afterglow of the long GRB 001007

abstract:
  We present optical follow up observations of the long GRB 001007 between 6.14
hours and ~468 days after the event. An unusually bright optical afterglow (OA)
was seen to decline following a steep power law decay with index alpha = -2.03
+/- 0.11, possibly indicating a break in the light curve at t - to < 3.5 days,
as found in other bursts. Upper limits imposed by the LOTIS alerting system
6.14 hours after the gamma ray event provide tentative (1.2 sigma) evidence for
a break in the optical light curve. The spectral index beta of the OA yields
-1.24 +/- 0.57. These values may be explained both by several fireball jet
models and by the cannonball model. Fireball spherical expansion models are not
favoured. Late epoch deep imaging revealed the presence of a complex host
galaxy system, composed of at least two objects located 1.2" (1.7 sigma) and
1.9" (2.7 sigma) from the afterglow position.


title: The New AM Her System RX J0704.2+6203. Northern Twin of BL Hyi

abstract:
  We report here on the identification and study of the optical counterpart of
the ROSAT source RX J0704.2+6203. Extensive spectral and photometric
observation showed that the object belongs to the class of magnetic Cataclysmic
Variables. We determined the orbital period of the system to be 97.27m and
estimated the strength of its magnetic field to be on the order of 20 MG. The
system was observed in both high and low states, common for its class. Other
parameters of the magnetic close binary system were estimated. The spectral and
photometric behavior of the object is similar to that of the well studied polar
BL Hyi.


title: Optical Observations of Afterglows

abstract:
  Optical, infrared and ultraviolet observations of GRB fields have allowed
detection of counterparts and host galaxies of the high energy transients, thus
crucially contributing to our present knowledge of the GRB phenomenon.
Measurements of afterglow variable emission, polarized light, redshifted
absorption and emission line spectra, as well as host galaxies brightnesses and
colors have clarified many fundamental issues related to the radiation
mechanisms and environments of GRBs, setting the background towards disclosing
the nature of their progenitors.


title: Star Formation Signatures in the Condensation Downstream of HH 80N

abstract:
  HH80N is one of the Herbig-Haro objects that have associated quiescent dense
clumps. We report CO and CS BIMA observations that reveal star formation within
the HH80N dense clump. The CO emission reveals clearly a bipolar molecular
outflow centered on the dense clump. The CS emission traces a ring-like
structure of radius ~0.24 pc. The CS kinematics shows that the ring is
collapsing with an infall speed of ~0.6 km/s. The required mass to produce the
collapse is in agreement with previous ammonia observations of the 20 solar
mass core, which is embedded within the CS structure. However, we cannot
discard that the ring structure is expanding driven by protostellar winds, if
the CS abundance if unusually high and the CO momentum rate is much higher than
that measured, due to inclination and optical depth effects. The properties of
the molecular outflow and of the dense core suggest that it harbors a Class 0
object. There are also signatures of interaction of the HH 80/81/80N outflow
with the dense gas. In particular it is possible that the HH 80/81/80N outflow
has triggered or at least speed up the star formation in this region.


title: Tracing the Cluster Internal Dynamics with Member Galaxies

abstract:
  The analysis of the spatial distribution and kinematics of galaxies in
clusters allows one to determine the cluster internal dynamics. In this paper,
I review the state of the art of this topic. In particular, I summarize what we
have learned so far about galaxy orbits in clusters, and about the cluster mass
distribution. I then compare four methods that have recently been used in the
literature, by applying them to the same data-set. The results stress the
importance of reducing systematic besides random errors, for a reliable
determination of cluster mass profiles.


title: Infrared Magnitude-Redshift Relations for Luminous Radio Galaxies

abstract:
  Infrared magnitude-redshift relations for the 3CR and 6C samples of radio
galaxies are presented for a wide range of plausible cosmological models,
including those with non-zero cosmological constant OmegaLambda. Variations in
the galaxy formation redshift, metallicity and star formation history are also
considered. The results of the modelling are displayed in terms of magnitude
differences between the models and no-evolution tracks, illustrating the amount
of K-band evolution necessary to account for the observational data. Given a
number of plausible assumptions, the results of these analyses suggest that:
(i) cosmologies which predict T_0xH_0>1 (where T_0 denotes the current age of
the universe) can be excluded; (ii) the star formation redshift should lie in
the redshift interval 5<z<20, values towards the lower end of the range being
preferred in cosmologies with larger values of T_0xH_0; (iii) the Einstein-de
Sitter model provides a reasonable fit to the data; (iv) models with finite
values of OmegaLambda can provide good agreement with the observations only if
appropriate adjustments of other parameters such as the galaxy metallicities
and star-formation histories are made. Without such modifications, even after
accounting for stellar evolution, the high redshift radio galaxies are more
luminous (ie. more massive) than those nearby in models with finite
OmegaLambda, including the favoured model with Omega=0.3, OmegaLambda=0.7. For
cosmological models with larger values of T_0xH_0, the conclusions are the same
regardless of whether any adjustments are made or not. The implications of
these results for cosmology and models of galaxy formation are discussed.


title: Models for the UV-X emission in AGN : influence of different parameters

abstract:
  We present the results of computations performed with a new
photoionisation-transfer code designed for hot Compton thick media. Presently
the code solves the transfer of the continuum with the Accelerated Lambda
Iteration method (ALI) and that of the lines in a two stream Eddington
approximation, without using the local escape probability formalism to
approximate the line transfer. We show the influence that the approximations
made in the treatment of the transfer and of the atomic data can have on the
broad band UV-X spectrum and on the detailed spectral features (X-ray lines and
ionization edges) emitted/absorbed by an X-ray irradiated medium. This transfer
code is coupled with a Monte Carlo code which allows to take into account
direct and inverse Compton diffusions, and to compute the spectrum emitted up
to hundreds of keV energies. The influence of a few physical parameters is
shown, and the importance of the density and pressure distribution (constant
density, pressure equilibrium) is discussed.


title: A powerful local shear instability in stratified disks

abstract:
  In this paper, we show that astrophysical accretion disks are dynamically
unstable to non-axisymmetric disturbances. This instability is present in any
stably stratified anticyclonically sheared flow as soon as the angular velocity
decreases outwards. In the large Froude number limit, the maximal growth rate
is proportional to the angular rotation velocity, and is independent of the
stratification. In the low Froude number limit, it decreases like the inverse
of the Froude number, thereby vanishing for unstratified, centrigugally stable
flows. The instability is not sensitive to disk boundaries. We discuss the
possible significance of our result, and its implications on the turbulent
state achieved by the disks. We conclude that this linear instability is one of
the best candidates for the source of turbulence in geometrically thin disks,
and that magnetic fields can be safely ignored when studying their turbulent
state. The relevance of the instability for thick disks or nearly neutrally
stratified disks remains to be explored.


title:
The dark side of star formation in galaxy clusters: spectroscopic
  follow-up of clusters observed with ISOCAM

abstract:
  The evolution of galaxies in cluster environments can be studied using mid-IR
observations which trace star forming regions hidden by dust. The optical
follow-up of A1689 (z=0.2), observed at 6.7 and 15um by ISOCAM, have revealed a
systematic excess of the B-[15um] galaxy color distribution with respect that
of Coma and Virgo clusters. This result suggests the existence of a dark side
of the Butcher-Oemler effect measured in the optical. We present an analysis of
the optical/mid-IR properties of the mid-IR emitters in A1689, comparing in
particular the star formation rates based on mid-IR and optical data. Morover,
we present preliminary result for J1888, a cluster at z=0.56 deeply observed
with ISOCAM, based on recent VLT/FORS and NTT/SOFI observations.


title: Visualising Interacting Binaries in 3D

abstract:
  I have developed a code which allows images to be produced of a variety of
interacting binaries for any system parameters. The resulting images are not
only helpful in visualising the geometry of a given system but are also helpful
in talks and educational work.


title: Spectrally resolved flares in the quiescent black hole V404 Cyg

abstract:
  We present a spectrophotometric study of short-term optical variability in
the quiescent black hole X-ray transient V404 Cyg focusing on two nights of
Halpha spectroscopy. We find significant variability, with both the Halpha line
and the continuum varying in a correlated way. This includes both dramatic
flares lasting a few hours in which the line flux nearly doubles and
lower-level flickering. The strongest flares involve development of asymmetry
in the line profile, with the red wing usually strongest independent of orbital
phase. Based on the line profile changes during the flares, we conclude that
the most likely origin for the variability is variable photoionisation by the
central source.


title: Supernova Interaction with a Circumstellar Medium

abstract:
  The explosion of a core collapse supernova drives a powerful shock front into
the wind from the progenitor star. A layer of shocked circumstellar gas and
ejecta develops that is subject to hydrodynamic instabilities. The hot gas can
be observed directly by its X-ray emission, some of which is absorbed and
re-radiated at lower frequencies by the ejecta and the circumstellar gas.
Synchrotron radiation from relativistic electrons accelerated at the shock
fronts provides information on the mass loss density if free-free absorption
dominates at early times or the size of the emitting region if synchrotron
self-absorption dominates. Analysis of the interaction leads to information on
the density and structure of the ejecta and the circumstellar medium, and the
abundances in these media. The emphasis here is on the physical processes
related to the interaction.


title:
Clustering of dark matter halos on the light-cone: scale-, time- and
  mass-dependence of the halo biasing in the Hubble volume simulations

abstract:
  We develop a phenomenological model to predict the clustering of dark matter
halos on the light-cone by combining several existing theoretical models.
Assuming that the velocity field of halos on large scales is approximated by
linear theory, we propose an empirical prescription of a scale-, mass-, and
time-dependence of halo biasing. We test our model against the Hubble Volume
$N$-body simulation and examine its validity and limitations. We find a good
agreement in two-point correlation functions of dark matter halos between the
phenomenological model predictions and measurements from the simulation for
$R>5h^{-1}$Mpc both in the real and redshift spaces. Although calibrated on the
mass scale of groups and clusters and for redshifts up to $z\sim2$, the model
is quite general and can be applied to a wider range of astrophysical objects,
such as galaxies and quasars, if the relation between dark halos and visible
objects is specified.


title: The Distance to Supernova 1998aq in NGC3982

abstract:
  The distance to NGC3982, host galaxy to the Type Ia supernova SN1998aq, is
derived using 32 Cepheids discovered in archival multi-epoch Hubble Space
Telescope observations. Employing recent Large Magellanic Cloud Cepheid
period-luminosity relations and absolute zero point, we find a distance to
NGC3982 of 20.5+/-0.8(r)+/-1.7(s) Mpc, including both random (r) and systematic
(s) uncertainties, and ignoring any metallicity dependency in the Cepheid
period-luminosity relation. Still unpublished light curve photometry promises
to make SN1998aq one of the most important calibrators for the Type Ia
supernova decline rate-peak luminosity relationship.


title: The Large-Scale Environment of Dynamical Young Clusters of Galaxies

abstract:
  We investigate whether the dynamical status of clusters is related to the
large-scale structure of the Universe. We find that cluster substructure is
strongly correlated with the tendency of clusters to be aligned with their
nearest neighbour and in general with the nearby clusters that belong to the
same supercluster. Furthermore, dynamically young clusters are more clustered
than the overall cluster population. These are strong indications that clusters
develop in a hierarchical fashion by merging along the large-scale filamentary
structures within which they are embedded.


title:
First results from multi-wavelength observations during the 2001
  outburst of WZ Sge

abstract:
  WZ Sge has shown superoutbursts in 1913, 1946 and 1978. On 2001 July 23 a new
outburst was announced, about 10 years `too early'. Target of opportunity
satellite observations with Chandra, FUSE, HST and RXTE were performed
throughout the outburst. From the ground WZ Sge was monitored by numerous
professional and amateur astronomers, in the optical, IR and radio. We give an
account of the first exciting results from these multi-wavelength observations.


title: An unusual H-alpha nebula around RX J1856.5-3754

abstract:
  We present spectroscopy and H alpha imaging of a faint nebula surrounding the
X-ray bright, nearby neutron star RX J1856.5-3754. The nebula shows no strong
lines other than the Hydrogen Balmer lines and has a cometary-like morphology,
with the apex being approximately 1 arcsec ahead of the neutron star, and the
tail extending up to at least 25 arcsec behind it. We find that the current
observations can be satisfactorily accounted for by two different models. In
the first, the nebula is similar to ``Balmer-dominated'' cometary nebulae seen
around several radio pulsars, and is due to a bow shock in the ambient gas
arising from the supersonic motion of a neutron star with a relativistic wind.
In the second model, the nebula is an ionisation nebula, but of a type not
observed before (though expected to exist), in which the ionisation and heating
are very rapid compared to recombination and cooling. We use a detailed
hydrodynamical simulation to confirm that a shape like that observed can be
reproduced. Independent of the model, we find that RX J1856.5-3754 is not kept
hot by accretion. If it is young and cooling, the lack of pulsations at X-ray
wavelengths is puzzling. Using phenomenological arguments, we suggest that RX
J1856.5-3754 may have a relatively weak, few 10^11 G, magnetic field. If so, it
would be ironic that the two brightest nearby neutron stars, RX J1856.5-3754
and RX J0720.4-3125, may well represent the extreme ends of the neutron star
magnetic field distribution, one a weak field neutron star and another a
magnetar. [Abridged]


title:
Chromospheric activity, lithium and radial velocities of single
  late-type stars possible members of young moving groups

abstract:
  We present here high resolution echelle spectra taken during three observing
runs of 14 single late-type stars identified in our previous studies (Montes et
al. 2001b, hereafter Paper I) as possible members of different young stellar
kinematic groups (Local Association (20 - 150 Myr), Ursa Major group (300 Myr),
  Hyades supercluster (600 Myr), and IC 2391 supercluster (35 Myr)). Radial
velocities have been determined by cross correlation with radial velocity
standard stars and used together with precise measurements of proper motions
and parallaxes taken from Hipparcos and Tycho-2 Catalogues, to calculate
Galactic space motions (U, V, W) and to apply Eggen's kinematic criteria. The
chromospheric activity level of these stars have been analysed using the
information provided for several optical spectroscopic features (from the Ca II
H & K to Ca II IRT lines) that are formed at different heights in the
chromosphere. The Li I 6707.8 AA line equivalent width (EW) has been determined
and compared in the EW(Li I) versus spectral type diagram with the EW(Li I) of
stars members of well known young open clusters of different ages, in order to
obtain an age estimation. All these data allow us to analyse in more detail the
membership of these stars in the different young stellar kinematic groups.
Using both kinematic and spectroscopic criteria we have confirmed PW And, V368
Cep, V383 Lac, EP Eri, DX Leo, HD 77407, and EK Dra as members of the Local
Association and V834 Tau, pi^{1} UMa, and GJ 503.2 as members of the Ursa Major
group. A clear rotation-activity dependence has been found in these stars.


title: Superquintessence

abstract:
  There is marginal evidence that the quintessential form of matter responsible
for the acceleration of the universe observed today has ratio between pressure
and energy density $w<-1$. Such a regime, called superacceleration, cannot be
achieved with conventional scalar field models. The simplest non-exotic model
achieving superacceleration is that of a scalar field nonminimally coupled to
the Ricci curvature. This model is studied for general potentials and an exact
superaccelerating solution is presented. In quintessential inflation, the model
can have blue gravitational wave spectra, improving the prospects for the
detection of cosmological gravitational waves.


title: Microlens Mass Measurement using Triple-Peak Events

abstract:
  We show that one can measure the effects of microlens parallax for binary
microlensing events with three well-measured peaks -- two caustic crossings
plus a cusp approach, and hence derive the projected Einstein radius. Since the
angular Einstein radius is measurable from finite source effects for almost any
well-observed caustic crossing, triple-peak events can yield the determination
of the lens mass. We note that, to a certain extent, rotation of the binary can
mimic the effects of parallax, but it should often be possible to disentangle
parallax from rotation by making use of the late-time light curve.


title: Comment on "Can there be a quark-matter core in a magnetar?"

abstract:
  We comment on the paper by Tanusri Ghosh and Somenath Chakrabarty, Phys. Rev.
D63, 043006 (2001). In that paper it was argued that a first-order transition
to quark matter in the core of a magnetar is absolutely forbidden if its
magnetic field strength exceeds $10^{15}$ G. However, we show in this comment
that if the quark anomalous magnetic moment and the population of higher Landau
levels is taken into account, it may still be possible for a first-order phase
transition from nuclear matter to quark matter to occur in the core of a
magnetar. These effects may also obscure the question of whether beta
equilibrium favors strange quark matter in the core of a magnetar.


title: Chandra Analysis of Abell 496

abstract:
  We present preliminary results of imaging and spectral analysis of the
cluster A496 with the S3 chip on-board the Chandra satellite. We confirm the
presence of a cooling flow and radial gradients in elemental abundances. The
cluster's core has clear signs of substructures (sharp edges, cavities),
similar to those recently found in other cooling flow clusters. The O/Fe ratio
distribution indicates that the gas in the core of the cluster is significantly
enriched by SN Ia ejecta.


title: Automated classification of variable stars for ASAS data

abstract:
  With the advent of surveys generating multi-epoch photometry and their
discoveries of large numbers of variable stars, the classification of the
obtained times series has to be automated. We have developed a classification
algorithm for the periodic variable stars using a Bayesian classifier on a
Fourier decomposition of the light curve. This algorithm is applied to ASAS
(All Sky Automated Survey, Pojmanski 2000). In the case of ASAS, 85% of
variable objects are red giants. A remarkable relation between their period and
amplitude is found for a large fraction of those stars.


title: History of mass assembly and star formation in clusters

abstract:
  We present deep, panoramic multi-color imaging of the distant rich cluster
A851 (z=0.41) using Suprime-Cam on Subaru. These images cover a 27' field of
view (~11 h_{50}^{-1}Mpc), and by exploiting photometric redshifts, we can
isolate galaxies in a narrow redshift slice at the cluster redshift. Using a
sample of ~2700 probable cluster members (<M*+4), we trace the network of
filaments and subclumps around the cluster core. The depth of our observations,
combined with the identification of filamentary structure, gives us an
unprecedented opportunity to test the influence of the environment on the
properties of low luminosity galaxies. We find an abrupt change in the colors
of faint galaxies (>M*+1) at a local density of 100 gal. Mpc^{-2}. The
transition in the color-local density behavior occurs at densities
corresponding to subclumps within the filaments surrounding the cluster.
Identifying the sites where the transition occurs brings us much closer to
understanding the mechanisms which are responsible for establishing the
present-day relationship between environment and galaxy characteristics.


title: Clustering of Dark Matter Halos on the Light-cone

abstract:
  A phenomenological model for the clustering of dark matter halos on the
light-cone is presented. In particular, an empirical prescription for the
scale-, mass-, and time-dependence of halo biasing is described in detail. A
comparison of the model predictions against the light-cone output from the
Hubble Volume $N$-body simulation indicates that the present model is fairly
accurate for scale above $\sim 5h^{-1}$Mpc. Then I argue that the practical
limitation in applying this model comes from the fact that we have not yet
fully understood what are clusters of galaxies, especially at high redshifts.
This point of view may turn out to be too pessimistic after all, but should be
kept in mind in attempting {\it precision cosmology} with clusters of galaxies.


title:
Balloon Flight Background Measurement with Actively-Shielded Planar and
  Imaging CZT Detectors

abstract:
  We present results from the flight of two prototype CZT detectors on a
scientific balloon payload in September 2000. The first detector, referred to
as ``CZT1,'' consisted of a 10 mm x 10 mm x 2 mm CZT crystal with a single gold
planar electrode readout. This detector was shielded by a combination of a
passive collimator surrounded by plastic scintillator and a thick BGO crystal
in the rear. The second detector, ``CZT2,'' comprised two 10 mm x 10 mm x 5 mm
CZT crystals, one made of eV Products high pressure Bridgman material and the
other of IMARAD horizontal Bridgman material, each fashioned with a 4 x 4 array
of gold pixels on a 2.5 mm pitch. The pixellated detectors were
flip-chip-mounted side by side and read out by a 32-channel ASIC. This detector
was also shielded by a passive/plastic collimator in the front, but used only
additional passive/plastic shielding in the rear. Both experiments were flown
from Ft. Sumner, NM on September 19, 2000 on a 24 hour balloon flight. CZT1
recorded a non-vetoed background level at 100 keV of ~1e-3 cts/cm2/s/keV.
Raising the BGO threshold from 50 keV to ~1 MeV produced only an 18% increase
in this level. CZT2 recorded a background at 100 keV of ~4e-3 cts/cm2/s/keV in
the eV Products detector and ~6e-3 cts/cm2/s/keV in the IMARAD detector. Both
CZT1 and CZT2 spectra were in basic agreement with Monte Carlo simulations,
though both recorded systematically higher count rates at high energy than
predicted. No lines were observed, indicating that neutron capture reactions,
at least those producing decay lines at a few 100 keV, are not significant
components of the CZT background. Comparison of the CZT1 and CZT2 spectra
indicates that passive/plastic shielding may provide adequately low background
levels for many applications.


title: Quasar Spectral Slope Variability in the Optical Band

abstract:
  We performed a new analysis of B and R light curves of a sample of PG
quasars. We confirm the variability-redshift correlation and its explanation in
terms of spectral variability, coupled with the increase of rest-frame
observing frequency for quasars at high redshift. The analysis of the
instantaneous spectral slope for the whole quasar samples indicates both an
inter-QSO and intra-QSO variability-luminosity correlation. Numerical
simulations show that the latter correlation cannot be entirely due to the
addition of the host galaxy emission to a nuclear spectrum of variable
luminosity but constant shape, implying a spectral variability of the nuclear
component. Changes of accretion rate are also insufficient to explain the
amount of spectral variation, while hot spots possibly caused by local disk
instabilities can explain the observations.


title: Nonlinear Beat Cepheid and RR Lyrae Models

abstract:
  The numerical hydrodynamic modelling of beat Cepheid behavior has been a long
standing quest in which purely radiative models had failed consistently. We
find that beat pulsations occur naturally when {\it turbulent convection} is
accounted for in our hydrodynamics code. The development of a relaxation code
and of a Floquet stability analysis greatly facilitates the search for and the
analysis of beat Cepheid models. The conditions for the occurrence of beat
behavior can be understood easily and at a fundamental level with the help of
amplitude equations.


title:
Can stellar winds account for temperature fluctuations in H II regions?
  The case of NGC 2363

abstract:
  We compare the rate of kinetic energy injected by stellar winds into the
extragalactic H II region NGC 2363 to the luminosity needed to feed the
observed temperature fluctuations. The kinetic luminosity associated to the
winds is estimated by means of two different evolutionary synthesis codes, one
of which takes into account the statistical fluctuations expected in the
Initial Mass Function. We find that, even in the most favorable conditions
considered by our model, such luminosity is much smaller than the luminosity
needed to account for the observed temperature fluctuations. The assumptions
underlying our study are emphasized as possible sources of uncertainty
affecting our results.


title:
Optical & NIR photometry of the interacting Dwarf Galaxies II Zw 70/II
  Zw 71

abstract:
  We obtained deep optical and NIR images of the pair of blue compact dwarf
(BCD) galaxies II Zw 70 and II Zw 71 in order to study the effects of
interaction on the structural properties of their stellar
low-surface-brightness (LSB) component. We find that within their Holmberg
radius the interacting BCDs under study do not differ significantly in terms of
the central surface brightness and exponential scale length of their LSB hosts
from typical iE/nE systems. In the faint outskirts (26.2 < mu_B [mag
arcsec^-2^] < 28.5) of both systems, however, the present data reveal
conspicuous morphological distortions, most notably an extended feature
protruding as far as ~9 kpc from the starburst region of II Zw 70 in the
direction of II Zw 71. The relatively blue colors of this stellar extension,
together with its apparent spatial coincidence with the massive HI streamer
connecting the dwarf galaxies, are consistent with the hypothesis that it
originates from recent star formation within the gaseous halo of II Zw 70,
rather than from stellar matter torn out of the LSB host of the BCD during the
interaction.The results presented here support the view that important
signatures of the dynamical response and secular evolution of the stellar LSB
component in interacting dwarf galaxies can be found in their very faint
outskirts.


title: Gamma-Ray Signatures of Supernovae and Hypernovae

abstract:
  We review the characteristics of nucleosynthesis and radioactivities in
'Hypernovae', i.e., supernovae with very large explosion energies ($ \gsim
10^{52} $ ergs) and their $\gamma$-ray line signatures. We also discuss the
$^{44}$Ti line $\gamma$-rays from SN1987A and the detectability with INTEGRAL.
Signatures of hypernova nucleosynthesis are seen in the large [(Ti, Zn)/Fe]
ratios in very metal poor stars. Radioactivities in hypernovae compared to
those of ordinary core-collapse supernovae show the following characteristics:
1) The complete Si burning region is more extended, so that the ejected mass of
$^{56}$Ni can be much larger. 2) Si-burning takes place in higher entropy and
more $\alpha$-rich environment. Thus the $^{44}$Ti abundance relative to
$^{56}$Ni is much larger. In aspherical explosions, $^{44}$Ti is even more
abundant and ejected with velocities as high as $\sim$ 15,000 km s$^{-1}$,
which could be observed in $\gamma$-ray line profiles. 3) The abundance of
$^{26}$Al is not so sensitive to the explosion energy, while the $^{60}$Fe
abundance is enhanced by a factor of $\sim$ 3.


title: Luminosity and Variability of Collimated Gamma-ray Bursts

abstract:
  Within the framework of the internal shock model, we study the luminosity and
the variability in gamma-ray bursts from collimated fireballs. In particular we
pay attention to the role of the photosphere due to $e^\pm$ pairs produced by
internal shock synchrotron photons. It is shown that the observed Cepheid-like
relationship between the luminosity and the variability can be interpreted as a
correlation between the opening angle of the fireball jet and the mass included
at the explosion with a standard energy output. We also show that such a
correlation can be a natural consequence of the collapsar model. Using a
multiple-shell model, we numerically calculate the temporal profiles of
gamma-ray bursts. Collimated jets, in which the typical Lorentz factors are
higher than in wide jets, can produce more variable temporal profiles due to
smaller angular spreading time scales at the photosphere radius. Our
simulations quantitatively reproduce the observed correlation.


title: Magnetized Turbulent Dynamo in Protogalaxies

abstract:
  The prevailing theory for the origin of cosmic magnetic fields is that they
have been amplified to their present values by the turbulent dynamo inductive
action in the protogalactic and galactic medium. Up to now, in calculation of
the turbulent dynamo, it has been customary to assume that there is no the back
reaction of the magnetic field on the turbulence, as long as the magnetic
energy is less than the turbulent kinetic energy. This assumption leads to the
kinematic dynamo theory. However, the applicability of the kinematic dynamo
theory to protogalaxies is rather limited. The reason is that in protogalaxies
the temperature is very high, and the viscosity is dominated by ions. As the
magnetic field strength grows in time, the ion cyclotron time becomes shorter
than the ion collision time, and the plasma becomes strongly magnetized. As a
result, the ion viscosity becomes the Braginskii viscosity. Thus, in
protogalaxies the back reaction sets in much earlier, at field strengths much
lower than the energy equipartition field strengths, and the turbulent dynamo
becomes what we call the magnetized turbulent dynamo. The purpose of this
thesis is to lay the theoretical groundwork for the magnetized turbulent
dynamo. In particular, we predict that the magnetic energy growth rate in the
magnetized dynamo theory is up to ten time larger than that in the kinematic
dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the
development of the inverse cascade of magnetic energy after the energy
equipartition time.


title:
Faint companions in the close environment of star-forming dwarf
  galaxies: possible overlooked starburst triggers?

abstract:
  Using the NASA Extragalactic Database, we have searched the close environment
of 98 star-forming dwarf galaxies (SFDGs) from field- and low density
environments for companion galaxies. Most of the found companions are dwarf
galaxies, previously disregarded in environmental studies of SFDGs. Using a
subsample at low redshifts, cz < 2000 km/s, i.e. less biased against dwarf
companions, we find that 30% of the SFDGs have close companions within a
projected linear separation s_p < 100 kpc and a redshift difference of (Delta
cz) < 500 km/s. This fraction must be considered a lower limit, given the
incompleteness of the available data sets and the non-negligible frequency of
HI clouds in the vicinity of SFDGs, so that the majority of SFDGs should not be
considered isolated. The redshift differences between companion candidates and
sample SFDGs are typically smaller than ~250 km/s and concentrated towards
lower values. This is similarly observed for dwarf satellites of spiral
galaxies and suggests a physical association between the companion candidates
and the sample SFDGs. SFDGs with a close companion do not show significant
differences in their H(beta) equivalent widths and B-V colours as compared to
isolated ones. However, the available data do not allow to rule out close dwarf
companions as an influencing factor for star formation activity.


title: Wide Field HR diagrams of Local Group Dwarf Galaxies

abstract:
  We present new observations of Sextans and Leo I dwarf galaxies, that provide
new insight on their stellar populations. The large sample of stars measured in
Sextans allowed us to obtain a reliable estimate of the metal content of this
galaxy, to study the population spatial gradients, and to investigate the
nature of the large number of blue stragglers. In Leo I, we discovered a
significant population of RR Lyrae variables. The analysis of the pulsational
properties of the detected variables suggests that this galaxy is an Oosterhoff
intermediate object, similar to the LMC and to other dwarf galaxies in the
Local Group.


title:
Serendipitous Detections of XTE J1906+09 with the Rossi X-ray Timing
  Explorer

abstract:
  In 1996 during Rossi X-ray Timing Explorer (RXTE) observations of SGR
1900+14, the 89-s X-ray pulsar XTE J1906+09 was discovered. As a result of
monitoring campaigns of SGR 1900+14, XTE J1906+09 was also monitored regularly
in 1996 September, 1998 May-June, 1998 August-1999 July, and 2000 March-2001
January. A search for pulsations in these observations resulted in detections
of only the two previously reported outbursts in 1996 September and 1998
August- September. Pulsed flux upper limits for the remaining observations
indicate that XTE J1906+09 is a transient X-ray pulsar and therefore likely has
a Be star companion. XTE J1906+09 was not detected with the RXTE All Sky
Monitor. Pulse timing analysis of the second outburst revealed a sinusoidal
signature in the pulse frequencies that is likely produced by periastron
passage in an orbit. Fits to pulse phases using an orbital model and quadratic
phase model have chi^2 minima at orbital periods of 26-30 days for fixed mass
functions of 5, 10, 15, and 20 M_sun. The pulse shape showed intensity and
energy dependent variations. Pulse phase spectroscopy was used to quantify the
energy dependent variations. The phase averaged spectrum, using the pulse
minimum spectrum as the background spectrum to eliminate effects from SGR
1900+14 and the galactic ridge, was well fitted by an absorbed power law with a
high energy cutoff. Estimated 2-10 keV peak fluxes, corrected for contributions
from the galactic ridge and SGR 1900+14, are 6E-12 ergs/cm^2/s and 1.1E-10
ergs/cm^2/s for the 1996 and 1998 outbursts, respectively. XTE J1906+09 may be
a member of an unusual class of Be/X-ray binaries that do not lie on the
general spin period versus orbital period correlation with the majority of
Be/X-ray binaries.


title: Locating the starburst in the SCUBA galaxy, SMM J14011+0252

abstract:
  We present new, multi-wavelength, high-resolution imaging of the luminous,
submillimeter galaxy, SMM J14011+0252, an interacting starburst at z = 2.56.
Our observations comprise optical imaging from the HST, sensitive radio mapping
from the VLA and CO observations from OVRO and BIMA. Aided by well-constrained
gravitational amplification, we use these new data to map the distribution of
gas and both obscured and unobscured starlight. The maps show that the gas and
star formation are extended on scales of >= 10 kpc, much larger than starbursts
seen in local ultraluminous galaxies, and larger than the rest-frame UV-bright
components of SMM J14011+0252, J1/J2. The most vigorous star formation is
marked by peaks in both the molecular gas and radio emission, ~1'' north of
J1/J2, in the vicinity of J1n, an apparent faint extension of J1. Using new
sub-0.5'' K-band imaging from UKIRT, we identify J1n as an extremely red object
(ERO). We suggest that while J1 and J2 are clearly associated with the submm
source, they are merely windows through the dust, or unobscured companions to a
large and otherwise opaque star-forming system. Hence, their rest-frame UV
properties are unlikely to be relevant for understanding the detailed internal
physics of the starburst.


title: Photon Folding for Imaging in Non-Focusing Telescopes

abstract:
  We present a new technique - photon folding - for imaging in non-focusing
telescopes. Motivated by the epoch-folding method in timing analysis, the
photon folding technique directly provides the statistical significance of
signals in images, using projection matrices. The technique is very robust
against common imaging problems such as aspect errors and non-uniform
background. The technique provides a deterministic recursive algorithm for
improving images, which can be implemented on-line. Higher-order photon folding
technique allows a systematic correction for coding noises, which is suitable
for studying weak sources in the presence of highly variable strong sources.
The technique can be applied to various types of non-focusing telescopes such
as coded-aperture optics, rotational collimators or Fourier grid telescopes.


title: New Results from Chandra

abstract:
  We discuss two themes from Chandra observations of galaxies and clusters.
First, we describe the effects of radio-emitting plasmas or ``bubbles'',
inflated by active galactic nuclei, on the hot X-ray emitting gaseous
atmospheres in galaxies and clusters. We describe the interaction of the
``bubbles'' and the X-ray emitting gas as the buoyant bubbles rise through the
hot gas. Second, we describe sharp, edge-like surface brightness structures in
clusters. Chandra observations show that these features are not shock fronts as
was originally thought, but ``cold fronts'', most likely the boundaries of the
remaining cores of merger components. Finally, we present recent observations
of M86 and NGC507 which show similar sharp features around galaxies. For M86,
the sharp edge is the boundary between the galaxy's X-ray corona and the Virgo
cluster gas. The structures around NGC507, the central galaxy in a group, could
be relics of galaxy formation or may reflect the motion of NGC507 in the larger
potential of the group.


title: Orbits of Four Very Massive Binaries in the R136 Cluster

abstract:
  We present radial velocity and photometry for four early-type, massive
double-lined spectroscopic binaries in the R136 cluster. Three of these systems
are eclipsing, allowing orbital inclinations to be determined. One of these
systems, R136-38 (O3 V + O6 V), has one of the highest masses ever measured, 57
Mo, for the primary. Comparison of our masses with those derived from standard
evolutionary tracks shows excellent agreement. We also identify five other
light variables in the R136 cluster which are worthy of follow-up study.


title:
Periodicities in ASCA X-ray observations of Non-Magnetic Cataclysmic
  Variables

abstract:
  We have carried out a thorough analysis of non-magnetic cataclysmic variables
observed with ASCA, and have discovered possible periods in three targets: WW
Cet, EI UMa and IX Vel. These may be caused by the rotation of the white dwarf
at the centre of the disk, or by the progression of a density wave in the inner
accretion disk.


title: An Intergalactic Magnetic Field from Quasar Outflows

abstract:
  Outflows from quasars inevitably pollute the intergalactic medium (IGM) with
magnetic fields. The short-lived activity of a quasar leaves behind an
expanding magnetized bubble in the IGM. We model the expansion of the remnant
quasar bubbles and calculate their distribution as a function magnetic field
strength at different redshifts. We find that by a redshift z ~ 3, about 5-80%
of the IGM volume is filled by magnetic fields with an energy density > 10% of
the mean thermal energy density of a photo-ionized IGM (at ~ 10^4 K). As
massive galaxies and X-ray clusters condense out of the magnetized IGM, the
adiabatic compression of the magnetic field could result in the fields observed
in these systems without a need for further dynamo amplification.


title:
Sungrazing comets: Properties of nuclei and in-situ detectability of
  cometary ions at 1 AU

abstract:
  A one dimensional sublimation model for cometary nuclei is used to derive
size limits for the nuclei of sungrazing comets, and to estimate oxygen ion
fluxes at 1 AU from their evaporation. Given that none of the ~300 sungrazers
detected by the SOlar and Heliospheric Observatory (SOHO) was observed after
disappearing behind the sun, and that small nuclei with a radius of ~3.5m could
be observed, it is assumed that all SOHO sungrazers were completely destroyed.
For the case that sublimation alone is sufficient for destruction, the model
yields an upper size limit as a function of nuclear density, albedo and
perihelion distance. If the density of the nuclei is that typical of porous ice
(600kg/m^3), the maximum size is 63m. These results confirm similar model
calculations by Weissman (1983). An analytical expression is derived that
approximates the model results well. We discuss possible modifications of our
results by different disruption mechanisms. While disruption by thermal stress
does not change the upper size limits significantly, they may be somewhat
increased by tidal disruption (up to 100m for a density of 600kg/m^3) dependent
on the isotropy of the sublimation process and the tensile strength of the
comet. Implications for the Kreutz family of sungrazers are discussed.
  Oxygen ions from the sublimation of sungrazing comets form a tail. Fluxes
from this tail are sufficiently high to be measured at 1 AU by particle
detectors on spacecraft, but the duration of a tail crossing is only about half
an hour. Therefore the probability of a spacecraft actually encountering a tail
of an evaporating sungrazer is only of the order of two percent per year.


title:
Genetic Connections of Anomalous X-ray Pulsars and Soft Gamma Repeaters
  with Supernova Remnants

abstract:
  Genetic connections between anomalous X-ray pulsars (AXPs) or soft gamma ray
repeaters (SGRs)and supernova remnants (SNRs) can hold important clues to the
nature of these objects through the properties of the associated SNRs. We
examine various criteria jointly to assess the reliability of possible
connections. 3 AXPs and 2 SGRs are most probably genetically connected with
SNRs. Distances and ages are discussed and their likely ranges are indicated.


title: Strong Gravitational Lensing and Dark Energy

abstract:
  We investigate the statistics of gravitational lenses in flat, low-density
cosmological models with different cosmic equations of state w. We compute the
lensing probabilities as a function of image separation \theta using a lens
population described by the mass function of Jenkins et al. and modeled as
singular isothermal spheres on galactic scales and as Navarro, Frenk & White
halos on cluster scales. It is found that COBE-normalized models with w > - 0.4
produce too few arcsecond-scale lenses in comparison with the JVAS/CLASS radio
survey, a result that is consistent with other observational constraints on w.
The wide-separation (\theta > 4'') lensing rate is a particularly sensitive
probe of both w and the halo mass concentration. The absence of these systems
in the current JVAS/CLASS data excludes highly concentrated halos in w < -0.7
models. The constraints can be improved by ongoing and future lensing surveys
of > 10^5 sources.


title:
The Chandra Deep Field North Survey. VIII. X-ray Constraints on Spiral
  Galaxies from 0.4 < z < 1.5

abstract:
  We present a statistical X-ray study of spiral galaxies in the Hubble Deep
Field-North and its Flanking Fields using the Chandra Deep Field North 1 Ms
dataset. We find that approximately L_star galaxies with 0.4 < z < 1.5 have
ratios of X-ray to B-band luminosity similar to those in the local Universe,
although the data indicate a likely increase in this ratio by a factor of
approximately 2-3. We have also determined that typical spiral galaxies at 0.4
< z < 1.5 should be detected in the 0.5--2 keV band in the flux range 3-6 X
10^-18 erg cm^-2 s^-1.


title: First microlens mass measurement: PLANET photometry of EROS BLG-2000-5

abstract:
  We analyze PLANET photometric observations of the caustic-crossing
binary-lens microlensing event, EROS BLG-2000-5, and find that modeling the
observed light curve requires incorporation of the microlens parallax and the
binary orbital motion. The projected Einstein radius (~r_E = 3.61 +/- 0.11 AU)
is derived from the measurement of the microlens parallax, and we are also able
to infer the angular Einstein radius (theta_E = 1.38 +/- 0.12 mas) from the
finite source effect on the light curve, combined with an estimate of the
angular size of the source given by the source position in a color-magnitude
diagram. The lens mass, M = 0.612 +/- 0.057 M_sun, is found by combining these
two quantities. This is the first time that parallax effects are detected for a
caustic-crossing event and also the first time that the lens mass degeneracy
has been completely broken through photometric monitoring alone. The
combination of the projected Einstein radius and the angular Einstein radius
also allows us to conclude that the lens lies in the near side of the disk,
within 2.6 kpc of the Sun, while the radial velocity measurement indicates that
the source is a Galactic bulge giant.


title: HST/NICMOS Imaging Survey of the Ophiuchus (Lynds 1688) Cluster

abstract:
  We present a catalogue of near-infrared photometry of young stars associated
with the Ophiuchus molecular cloud, based on observations made with the Hubble
Space Telescope NICMOS-3 camera at 1.1 $\mu$m and 1.6 $\mu$m. Our survey covers
0.02 square degrees centered on the dense molecular cores in Lynds 1688. We
detect 165 sources at 1.6 $\mu$m and 65 sources at 1.1 $\mu$m, within our
estimated completeness limits of 21.0 mag and 21.5 mag, respectively. An
analysis of the cloud extinction, based on existing molecular line maps,
suggests that most of the sources lying within the 40 $\rm{A_V}$ extinction
contour of the cloud are probable cloud members. Approximately half (58/108) of
these sources are previously unpublished. The faint embedded sources revealed
by these observations are spatially concentrated in three regions of high
stellar space density (N$> 10^4$ stars pc$^{-3}$). While the spatial
distribution of these sources reflects that of the brighter, well--known
population of young stars in Ophiuchus, it is distinctly different from the
distribution of cool concentrations seen in the submillimeter. Seven new brown
dwarf candidates are identified, based on their infrared colors and their
projected locations on high column-density regions of the molecular cloud.
Eight new candidate binary and five new candidate triple systems, having
separations between 0\farcs2 to 10\arcsec (29 to 1450 AU) are reported. The
spatial resolution and sensitivity of these observations reveal five apparent
disk/envelope systems seen via scattered light, and four nebulous objects with
complex morphologies.


title: Modeling Star Formation from Turbulent Fragmentation

abstract:
  Star formation is intimately linked to the dynamical evolution of molecular
clouds. Turbulent fragmentation determines where and when protostellar cores
form, and how they contract and grow in mass via accretion from the surrounding
cloud material. Using numerical models of self-gravitating supersonic
turbulence, efficiency, spatial distribution and timescale of star formation in
turbulent interstellar clouds are estimated. Turbulence that is not
continuously replenished or that is driven on large scales leads to a rapid
formation of stars in a clustered mode, whereas interstellar turbulence that
carries most energy on small scales results in isolated star formation with low
efficiency. The clump mass spectrum for models of pure hydrodynamic turbulence
is steeper than the observed one, but gets close to it when gravity is
included. The mass spectrum of dense cores is log-normal for decaying and
large-wavelength turbulence, similar to the IMF, but is too flat in the case of
small-scale turbulence. The three-dimensional models of molecular cloud
fragmentation can be combined with dynamical pre-main sequence stellar
evolution calculations to obtain a consistent description of all phases of the
star formation process. First results are reported for a one solar mass
protostar.


title: Gamma-Rays as Probes for the Multi-Dimensionality of Type Ia Supernovae

abstract:
  We present $\gamma $-ray spectra for a set of Type Ia supernovae models. Our
study is based on a detailed Monte Carlo transport scheme for both spherical
and full 3-D geometries. Classical and new challenges of the $\gamma $ ray
astronomy are addressed. We find that $\gamma $-rays are very suitable to
reveal the structure of the envelope and, thus, they allow to probe properties
of the nuclear burning front and the progenitor, namely its central density and
global asphericities. The potential problems are discussed for the quantitative
comparison between theoretical and observed line fluxes during the first few
months after the explosion.