title:
The Importance of Nonlinear H2 Photoexcitiation in Strongly Irradiated
  PDRs

abstract:
  It is shown that, under sufficiently intense OB-star illumination of a
stationary photoexcitation front (PDR), nonlinear H2 photoexcitation processes
comprising driven resonant two-photon transitions between X-state quantum
levels, with VUV continuum light from the star supplying both driving fields,
largely determine the photonic pathways of H2 molecules in the PDR close to the
ionization front. Specifically, for a PDR irradiated by a 0.1-pc-distant B0 III
star, the total rate at which an H2 molecule is nonlinearly photoexcited out of
any X-state quantum level is calculated to be roughly 100 times greater than
the total rate at which it is linearly photoexcited out of the same level. In
strongly excited PDRs, the populations in almost all of the ~300 bound quantum
levels of the X state will be maintained approximately equal via a few myriads
of interconnecting two-photon steps. The remarkable importance of two-photon
transitions in H2 photoexcitation in strongly irradiated PDRs derives from the
exceptionally narrow Raman linewidth that characterizes all two-photon
transitions between bound H2 X-state quantum levels.


title:
A Measurement of the Three-Dimensional Clustering of C IV
  Absorption-Line Systems on Scales of 5 to 300 Mpc

abstract:
  We examine the three-dimensional clustering of C IV absorption-line systems,
using an extensive catalog of QSO heavy-element absorbers drawn from the
literature. We measure clustering by a volume-weighted integral of the
correlation function called the reduced second-moment measure, and include
information from both along and across QSO lines of sight, thus enabling a full
determination of the three-dimensional clustering of absorbers, as well as a
comparison of line- and cross-line-of-sight clustering properties. Here we
present the three-dimensional reduced second-moment estimator for a
three-dimensional point process probed by one-dimensional lines of sight, and
apply our algorithm to a sample of 345 C IV absorbers with median redshift of
2.2, drawn from the spectra of 276 QSOs. We confirm the existence of
significant clustering on comoving scales up to 100 Mpc, and find that the
additional cross-line-of-sight information strengthens the evidence for
clustering on scales from 100 Mpc to 150 Mpc. There is no evidence of absorber
clustering along or across lines of sight for scales from 150 Mpc to 300 Mpc.
We show that with a 300-times larger catalog, such as that to be compiled by
the Sloan Digital Sky Survey (100,000 QSOs), use of the full three-dimensional
estimator and cross-line-of-sight information will substantially increase
clustering sensitivity. We find that standard errors are reduced by an
additional factor of 2 to 20 on scales of 30 to 200 Mpc, effectively increasing
the sample size by an extra factor of 4 to 400 at large distances.


title:
On the APM power spectrum and the CMB anisotropy: Evidence for a phase
  transition during inflation?

abstract:
  Adams et al. (1997b) have noted that according to our current understanding
of the unification of fundamental interactions, there should have been phase
transitions associated with spontaneous symmetry breaking {\em during} the
inflationary era. This may have resulted in the breaking of scale-invariance of
the primordial density perturbation for brief periods. A possible such feature
was identified in the power spectrum of galaxy clustering in the APM survey at
the scale $k \sim 0.1 h$ Mpc^{-1} and it was shown that the secondary acoustic
peaks in the power spectrum of the CMB anisotropy should consequently be
suppressed. We demonstrate that this prediction is confirmed by the recent
Boomerang and Maxima observations, which favour a step-like spectral feature in
the range $k \sim (0.06-0.6)h$ Mpc^{-1}, independently of the similar previous
indication from the APM data. Such a spectral break enables an excellent fit to
both APM and CMB data with a baryon density consistent with the BBN value. It
also allows the possibility of a matter-dominated universe with zero
cosmological constant, which we show can now account for even the evolution of
the abundance of rich clusters.


title: HI gas disks in elliptical galaxies

abstract:
  We discuss a class of low-luminosity E/S0 galaxies which have both HI disks
and (in contrast to more luminous E/S0s with HI) ongoing star formation. We
suggest that such objects are common, but that only a few are known at present
because optical magnitude-limited galaxy catalogues are biased against them.
The HI Parkes All-Sky Survey (HIPASS) should eventually detect many more. We
suggest that `boxy' and `disky' ellipticals are distinct not only in their
structure and kinematics, but in their star-formation history.


title: Evidence for Galaxy Formation at High Redshift

abstract:
  We have shown previously that galaxy counts from the UV to the near-IR are
well-fitted by simple evolutionary models where the space density of galaxies
remains constant with look-back time while the star-formation rate rises
exponentially. We now extend these results, first by using data from the
Herschel Deep Field to show that these same models give detailed fits to the
faint galaxy r-i:b-r colour-colour diagram. We then use these models to predict
the number counts of high redshift galaxies detected by the Lyman break
technique. At z~3 there is almost exact agreement between ou r prediction and
the data, suggesting that the space density of galaxies at z~3 may be close to
its local value. At z~4 the space density of bright galaxies remains unchanged;
however, the space density of dwarf galaxies is significantly lower than it is
locally, suggesting that we have detected an epoch of dwarf galaxy formation at
z~4. Finally, significant numbers of Lyman-break galaxy candidates are also
detected at z~6 in the Hubble and Herschel Deep Fields; taking this observation
together with a number of recent detections of spectroscopically confirmed z~6
galaxies suggests that the space density of bright galaxies at z~6 remains
comparable to the local space density and thus that the epoch of formation of
bright galaxies may lie at yet higher redshift.


title: OAO1657-415 : A `Missing Link' in High Mass X-ray Binaries?

abstract:
  OAO1657-415 is only the seventh eclipsing X-ray pulsar known and therefore
has the potential to yield only the seventh mass of a neutron star in an X-ray
binary. Here we report photometric and spectroscopic observations of candidates
for the optical counterpart to the system and identify a B6V or B5III star as a
possible companion to the neutron star. We measure the observational parameters
of the star and suggest reasons why OAO1657-415 may be unlike other high mass
X-ray binaries.


title:
Synthetic Doppler maps of gaseous flows in semidetached binaries based
  on the results of 3D gas dynamical simulations

abstract:
  We present synthetic Doppler maps of gaseous flows in semidetached binaries
based on the results of 3D gas dynamical simulations. Using of gas dynamical
calculations alongside with Doppler tomography technique permits to identify
main features of the flow on the Doppler maps without solution of ill-posed
inverse problem. Comparison of synthetic tomograms with observations makes
possible both to refine the gas dynamical model and to interpret the
observational data.


title:
X Ray Precursors in GRBs and SGRs: outer X tails around a Precessing
  Gamma Jet

abstract:
  Weak isolated X-ray precursor events before the main Gamma Ray Burst, GRB,
and also rare Soft Gamma Repeaters, SGR, events are in disagreement with any
Fireball, or Magnetar, scenarios.
  These models are originated by an unique explosive event leading, by
internal-external shock waves, to softer secondary trains following a main
gamma signals. Indeed the earliest GRB980519,GRB981226 events as well as the
latest and most distant identified one as GRB000131 are showing rare but well
identified and distinct X Ray precursor, occurring tens of seconds or even a
minute before the main GRB eruption. These weak X precursors bursts correspond
to non-negligible energy powers, up to million Supernova ones.
  They are rare, about (3-6)% of all GRBs, but not unique.
  Similar huge explosive precursor are in total disagreement with a successive
main Fireball GRB outburst.
  Comparable brief X-ray precursor flashes are found also in rarest and most
detailed SGRs events as those observed on 27 and 29 August 1999 from SGR
1900+14.
  They are inconsistent with a Magnetar Fireball explosion.
  We interpret them as earlier marginal blazing of outlying X conical Jet tails
surrounding a narrower gamma precessing,spinning beamed Jet in blazing mode
toward the Earth; later re-crossing and better hitting of the target -the
satellite detectors- is source of the main GRB (and SGR) observed structured
event.
  The X Ray precursor existence is an additional remarkable evidence of the
Precessing relativistic Jet Nature of both GRBs and SGRs.


title: The Steady Spin Down Rate of 4U 1907+09

abstract:
  Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we report the
pulse timing results of the accretion powered high mass X-ray binary (HMXRB)
pulsar 4U 1907+09 covering a time span of almost two years. We measured three
new pulse periods in addition to the previously measured four pulse periods. We
are able to connect pulse arrival times in phase for more than a year. The
source has been spinning down almost at a constant rate with a spin down rate
of
  \dot \nu = (-3.54 \pm 0.02) \times 10^{-14} Hz s ^{-1} for more than
  15 years. Residuals of pulse arrival times yield a very low level of random
walk noise strengths
  \sim 2 \times 10^{-20} rad ^{2} sec ^{-3} on a time scale of 383 days, which
is four decades lower than that of the HMXRB pulsar Vela X-1. The noise
strength is only a factor of 5 greater than that of the low mass X-ray binary
pulsar (LMXRB) 4U 1626-67. The low level of the timing noise and the very
stable spin down rate of 4U 1907+09 makes this source unique among the HMXRBs,
providing another example, in addition to 4U 1626-67, of long term quiet spin
down from an accreting source. These examples show that the extended quiet spin
down episodes observed in the anomalous X-ray pulsars (AXPs) pulsars 1RXS
J170849.0-400910 and 1E 2259+586 do not necessarly imply that these sources are
not accreting pulsars.


title:
Giant cluster arcs as a constraint on the scattering cross-section of
  dark matter

abstract:
  We carry out ray tracing through five high resolution simulations of a galaxy
cluster to study how its ability to produce giant gravitationally lensed arcs
is influenced by the collision cross-section of its dark matter. In three cases
typical dark matter particles in the cluster core undergo between 1 and 100
collisions per Hubble time; two more explore the long (``collisionless'') and
short (``fluid'') mean free path limits. We study the size and shape
distributions of arcs and compute the cross-section for producing ``extreme''
arcs of various sizes. Even a few collisions per particle modify the core
structure enough to destroy the cluster's ability to produce long, thin arcs.
For larger collision frequencies the cluster must be scaled up to
unrealistically large masses before it regains the ability to produce giant
arcs. None of our models with self-interacting dark matter (except the
``fluid'' limit) is able to produce radial arcs; even the case with the
smallest scattering cross-section must be scaled to the upper limit of observed
cluster masses before it produces radial arcs. Apparently the elastic collision
cross-section of dark matter in clusters must be very small, below 0.1 cm^2
g^-1, to be compatible with the observed ability of clusters to produce both
radial arcs and giant arcs.


title: The X-ray outbursts of Be/X-ray transients

abstract:
  We present a new scenario for the behaviour of Be/X-ray binaries based on
long-term multiwavelength monitoring and the decretion disc model. The
circumstellar discs of the primaries are truncated because of the tidal and
resonant effect of the neutron star. The geometry of the systems and the value
of viscosity determine the presence or absence of Type I X-ray outbursts. The
interaction of a strongly disturbed disc with the neutron star originates Type
II X-ray and optical outbursts.


title: The Be/X-ray transient 4U 0115+63/V635 Cas I. A consistent model

abstract:
  We present photometry and high SNR spectroscopy in the classification region
of V635 Cas, the optical counterpart to the transient X-ray pulsator 4U
0115+63, taken at a time when the circumstellar envelope had disappeared. V635
Cas is classified as a B0.2Ve star at a distance of 7-8 kpc. We use the
physical parameters derived from these observations and the orbit derived from
X-ray observations to elaborate a model of the system based on the theory of
decretion discs around Be stars. We show that the disc surrounding the Be star
must be truncated by the tidal/resonant interaction with the neutron star and
cannot be in a steady state. This explains many of the observed properties of
4U 0115+63. In particular, because of this effect, under normal circumstances,
the neutron star cannot accrete from the disc, which explains the lack of
regular Type I outbursts from the source.


title:
On the spin-up of neutron stars to millisecond pulsars in long-period
  binaries

abstract:
  We study the accretion efficiency of neutron stars in long-period binaries,
i.e. with periods longer than about 200d, which accrete from a giant companion.
Using alpha-disc models and taking into account the effect of irradiation of
the accretion disc by the central accretion light source we derive explicit
expressions for the duty cycle and the accretion efficiency in terms of the
parameters of the binary system and the disc instability limit cycle. We show
that the absence of millisecond pulsars in wide binaries with circular orbits
and periods longer than about 200d can be understood as a consequence of the
disc instability if the duration of the quiescent phase between two subsequent
outbursts is at least a few decades.


title: Finding Signatures of the Youngest Starbursts

abstract:
  Embedded massive starclusters have recently been identified in several nearby
galaxies by means of the radio-wave thermal bremsstrahlung emission from their
surrounding HII regions. Energy requirements imply that these
optically-obscured starclusters contain 500-1000 O-type stars, making them
similar to the ``super starclusters'' observed in many dwarf starbursts and
mergers. Based on their high free-free optical depth and visual extinctions of
A_V>>10 mag., these massive ``ultra-dense'' HII regions (UDHIIs) are distinct
signatures of the youngest, most compact super starclusters. UDHII regions may
represent the earliest stages of globular cluster formation. We review the
properties of presently-known UDHIIs, and we outline a pictoral evolutionary
taxonomy for massive cluster formation which is analogous to the more familiar
evolutionary sequence for individual stars.


title: LOWL p-mode frequencies and their variation with solar activity

abstract:
  We present an analysis of the frequency shift and the even terms of the
frequency splitting coefficients carried out using six years of LOWL data,
starting in 1994. The temporal variations, and their dependences with the
frequency and degree are addressed. The results are consistent with previous
analysis.


title: Signature of the solar cycle in the low degree p-modes using Mark-I

abstract:
  High quality observations of the low degree p-modes exist for almost two
complete solar cycles using the solar spectrophotometer Mark-I, located and
operating at the Observatorio del Teide (Tenerife, Spain). In this work, the
observations available have been re-analyzed over a much wider time interval
than before. We analyze the time variation of the yearly frequency shift and
its frequency dependence. This information will be used in order to average
annual power spectra by removing the effect of the solar cycle. Using this
average power spectrum, a new estimate of the rotational splittings is
attempted.


title:
A New Radio Continuum Survey of the Sky at 1465 MHz between declinations
  -52 degrees and +68 degrees

abstract:
  We have mapped the total sky brightness at 1465 MHz in two adjacent 60-degree
declination bands with the portable 5.5-m parabolic reflector of the Galactic
Emission Mapping (GEM) project, an on-going international collaboration to
survey the radio continuum of the sky in decimeter and centimeter wavelengths.
The observations were conducted from two locations, one in the USA and the
other in Brazil, using a novel instrumental approach to overcome the well-known
shortcomings of survey experiments. Our strategy consists of a 1-rpm rotating
dish to circularly scan the sky at 30 degrees from zenith. The dish uses a
rim-halo to re-direct the spillover sidelobes of its backfire helical feed
toward the sky and the entire assembly has been enclosed inside a wire mesh
ground shield in order to minimize and level out the contamination from the
ground. The diffraction characteristics of this set-up have been succesfully
modelled and undesired systematic striping across the observed bands has been
carefully removed by a baseline propagation method which exploits the
time-forward and time-backward intersections of the circular scans. The map
displays nearly 300 hours of our best quality data taken with a HPBW of 5.4
degrees at a sensitivity of 20 mK.


title: A high-resolution multi-wavelength study of the jet in 3C 273

abstract:
  We present HST images at 622 nm and 300 nm of the optical jet in 3C273 and
determine the run of the optical spectral index at 0.2" along the jet. We find
no evidence for localized acceleration or loss sites, and support for a
little-changing spectral shape throughout the jet. We consider this further
evidence in favour of a distributed acceleration process.


title: Summary: ZeV Air Showers. Where do we Stand?

abstract:
  Here an attempt is made at summarizing the presentations, most of which were
about the highest energy particles observed in nature. Particular attention is
paid to the solutions to the Ultra High Energy Cosmic Ray particles, to the new
and forthcoming data, to the new proposals for experiments and to the role of
primary composition, that were amongst the most discussed subtopics.


title: The Galaxy Environment of a Quasar at z=1.226: A Possible Cluster Merger

abstract:
  We have conducted ultra-deep optical and deep near-infrared observations of a
field around the z=1.226 radio-quiet quasar 104420.8+055739 from the
Clowes-Campusano LQG of 18 quasars at z~1.3 in search of associated galaxy
clustering. Galaxies at these redshifts are distinguished by their
extremely-red colours, with I-K>3.75, and we find a factor ~11 overdensity of
such galaxies in a 2.25'x2.25' field centred on the quasar. In particular, we
find 15-18 galaxies with colours consistent with being a population of
passively-evolving massive ellipticals at the quasar redshift. They form
`fingers' in the V-K/K, I-K/K colour-magnitude plots at V-K~6.9, I-K~4.3
comparable to the red sequences observed in other z~1.2 clusters. We find
suggestive evidence for substructure among the red sequence galaxies in the K
image, in the form of two compact groups, 40 arcsec to the north, and 60 arcsec
to the south-east of the quasar. An examination of the wider optical images
indicates that this substructure is significant, and that the clustering
extends to form a large-scale structure 2-3 Mpc across. We find evidence for a
high (>50%) fraction of blue galaxies in this system, in the form of 15-20
`red-outlier' galaxies with I-K>3.75 and V-I<2.00, which we suggest are dusty,
star-forming galaxies at the quasar redshift. Within 30 arcsec of the quasar we
find a concentration of blue (V-I<1) galaxies in a band that bisects the two
groups of red sequence galaxies. This band of blue galaxies is presumed to
correspond to a region of enhanced star-formation. We explain this distribution
of galaxies as the early-stages of a cluster merger which has triggered both
the star-formation and the quasar.


title: A New Approach to Mass Measurements of UHECR: Horizontal Air Showers

abstract:
  The role of Horizontal Showers induced by cosmic rays is discussed in detail.
A new approach to the calculation of the muon component in horizontal air
showers induced by protons, heavier nuclei or photons is presented which allows
a simple analytical evaluation of the muon density profiles at ground level.
The results of the first application of these results to horizontal air showers
detected at the Haverah Park Array by the recently started {\sl Leeds-Santiago
collaboration}, leading to important restrictions on composition at ultra high
energies, are reported.


title: Supernovae in the nuclear regions of starburst galaxies

abstract:
  The feasibility of using near-infrared observations to discover supernovae in
the nuclear and circumnuclear regions of nearby starburst galaxies is
investigated. We provide updated estimates of the intrinsic core-collapse
supernova rates in these regions. We discuss the problem of extinction, and
present new estimates of the extinction towards 33 supernova remnants in the
starburst galaxy M 82. This is done using H I and H_2 column density
measurements. We estimate the molecular to atomic hydrogen mass ratio to be 7.4
+- 1.0 in M 82. We have assembled near-infrared photometric data for a total of
13 core-collapse supernovae, some unpublished hitherto. This constitutes the
largest database of IR light curves for such events. We show that the IR light
curves fall into two classes, ``ordinary'' and ``slow-declining''. Template
JHKL light curves are derived for both classes. For ordinary core-collapse
supernovae, the average peak JHKL absolute magnitudes are -18.4, -18.6, -18.6,
and -19.0 respectively. The slow-declining core-collapse SNe are found to be
significantly more luminous than the ordinary events, even at early times,
having average peak JHKL absolute magnitudes of -19.9, -20.0, -20.0, and -20.4
respectively. We investigate the efficiency of a computerised image subtraction
method in supernova detection. We then carry out a Monte Carlo simulation of a
supernova search using K-band images of NGC 5962. The effects of extinction and
observing strategy are discussed. We conclude that a modest observational
programme will be able to discover a number of nuclear supernovae.


title:
The Discovery of an Outburst and Pulsed X-ray Flux from SMC X-2 from
  RXTE Observations

abstract:
  Rossi X-ray Timing Explorer All Sky Monitor observations of SMC X-2 show that
the source experienced an outburst in January to April 2000 reaching a peak
luminosity of greater than ~10^38 ergs s^-1. RXTE Proportional Counter Array
observations during this outburst reveal the presence of pulsations with a
2.37s period. However, optical photometry of the optical counterpart showed the
source to be still significantly fainter than it was more than half a year
after the outburst in the 1970s when SMC X-2 was discovered.


title: Seyfert Galaxies with Circumnuclear/Nuclear Starbursts

abstract:
  In this paper, we present our preliminary results on Seyfert galaxies with
circumnuclear/nuclear starburst(SB) activity. We have searched the recent
available literature and found 76 active galaxies with clear evidence of
nuclear SB activity, among which 16 are Seyfert 1s, 51 Seyfert 2s, and 9
LINERs. After studying the 51 Seyfert 2s, we find that those Seyfert 2s with
hidden Seyfert 1 nuclei, have similar Infrared-Radio properties as Seyfert 1
galaxies, and are different from "real" Seyfert 2s without a hidden Seyfert 1
nucleus. The later are similar to starburst galaxies.


title: Nuclear obscuration and scattering in Seyfert 2 galaxies

abstract:
  We study the relation between gaseous absorbing column density (N$_{\rm H}$),
infrared colors and detectability of the broad lines in a large sample of
Seyfert 2 galaxies(Sy2s). We confirm that Sy2s without polarized broad lines
tend to have cooler 60$\mu$m/25$\mu$m colors; this correlation was previously
ascribed to the effect of obscuration towards the nuclear region.
  We find some evidence that Sy2s without polarized broad lines have larger
absorbing column density (N$_{\rm H}$) and that a fraction of them are
characterized by dust lanes crossing their nuclei.
  However, we find that the IR colors do not correlate with N$_{\rm H}$, in
disagreement with the obscuration scenario.
  Also, Sy2s without polarized broad lines follow the same radio-FIR relation
as normal and starburst galaxies, at variance with Sy2s with polarized broad
lines. These results indicate that the lack of broad lines in the polarized
spectrum of Sy2s is mostly due to the contribution/dilution from the host
galaxy or from a circumnuclear starburst, though at a lower extent the
obscuration toward the nuclear region also plays a role.


title: Near-Infrared Integral Field Spectroscopy of Damped Lyman-alpha Systems

abstract:
  We assess the feasibility of detecting star formation in damped Lyman-alpha
systems (DLAs) at z>1 through near-infrared spectroscopy using the forthcoming
integral field units on 8m-class telescopes. Although their relation to
galaxies is not well established, high-z DLAs contain most of the neutral gas
in the Universe, and this reservoir is depleted with time - presumably through
star formation. Line emission should be an indicator of star formation
activity, but searches based on Lyman-alpha are unreliable because of the
selective extinction of this resonant UV line. Using more robust lines such as
H-alpha forces a move to the near-infrared at z>1. For line emission searches,
spectroscopy is more sensitive than imaging, but previous long-slit
spectroscopic searches have been hampered by the likelihood that any star
forming region in the DLA galaxy disk would fall outside the narrow slit. The
new integral field units such as CIRPASS on Gemini will cover sufficient solid
angles to intercept these, even in the extreme case of large galactic disks at
high redshift. On an 8m-class telescope, star formation rates of <1M_sun/yr
will be reached at z~1.4 with H-alpha in the H-band. Such star formation rates
are well below L* for the high-z Lyman-break population, and are comparable
locally to the luminous giant HII complexes in M101. It appears that
instruments such as CIRPASS on Gemini will have both the sensitivity and the
survey area to measure star formation rates in z>1 DLAs. These observations
will probe the nature of damped Lyman-alpha systems and address their relation
to galaxies.


title: The Initial Mass Function in the Galactic Center

abstract:
  The Galactic Center contains the most massive young clusters in the Galaxy
and serves as the closest example of a massive starburst region. Our recent
results suggest that the Galactic Center environment produces massive clusters
with relatively flat initial mass functions, as might be expected on
theoretical grounds. I will discuss these recent results, along with evidence
for star formation in the immediate vicinity of the super massive black hole at
the Galactic Center. The results of this work might be useful in extrapolating
to other galactic centers with similar conditions, as well as other starburst
regions.


title: Globular Clusters as Probes of the Virgo gE NGC 4472

abstract:
  We present radial velocities for 144 globular clusters around the Virgo gE
NGC 4472 (M49), and ages and metallicities from co-added spectra of 131
clusters. We confirm our earlier finding that the metal-poor clusters have a
significantly higher velocity dispersion than the metal-rich clusters, and we
find little or no rotation in the metal-rich clusters. The velocity dispersion
profile is consistent with isotropic orbits for the clusters and the NGC 4472
mass distribution inferred from X-ray data. Our sample of clusters spans a
metallicity range of -1.6 < [Fe/H] < 0 dex. The metal-poor and metal-rich
cluster populations are coeval within the errors, and all clusters are older
than 6 Gyr at 95% confidence. Our findings are consistent with a merger origin
for NGC 4472, but other elliptical formation models cannot be ruled out.


title: Stellar Collisions and Mergers in the Galactic Center

abstract:
  Stars are most likely to merge or collide in regions of the highest stellar
densities, and our own Galactic Center contains many stars packed into a
relatively small volume -- even the ambient stellar number density in the
central 50 pc is quite high, ~10^3 stars pc^{-3}. More striking, the three
compact young clusters in this region have central densities as high as 10^6
stars pc^{-3}. We discuss these extreme environments and the possibility that
stellar mergers and collisions have recently occured there. In particular, we
predict that at least one massive star in the Arches cluster has already
experienced a stellar merger in its short lifetime. Further, the Pistol Star,
in the nearby Quintuplet cluster, might owe its apparent relative youth to a
rejuvinating stellar merger. Finally, the apparently young stars in the central
arcsecond could be products of either collisions, inducing atmospheric
stripping, or mergers.


title:
On the thermal conduction in tangled magnetic fields in clusters of
  galaxies

abstract:
  Thermal conduction in tangled magnetic fields is reduced because heat
conducting electrons must travel along the field lines longer distances between
hot and cold regions of space than if there were no fields. We consider the
case when the tangled magnetic field has a weak homogeneous component. We
examine two simple models for temperature in clusters of galaxies: a
time-independent model and a time-dependent one. We find that the actual value
of the effective thermal conductivity in tangled magnetic fields depends on how
it is defined for a particular astrophysical problem. Our final conclusion is
that the heat conduction never totally suppressed but is usually important in
the central regions of galaxy clusters, and therefore, it should not be
neglected.


title:
Isodensity Statistics on Clustering of High-z Objects in Cosmological
  Redshift-spaces

abstract:
  We discuss the systematic effects arising from the cosmological
redshift-space (geometric) distortion on the statistical analysis of isodensity
contour using high-redshift catalogs. Especially, we present a simple
theoretical model for isodensity statistics in cosmological redshift-space, as
a generalization of the work by Matsubara (1996). The statistical quantities
considered here are the two- and three-dimensional genus of isodensity contour,
the area of surface, the length of contour intersecting with a plane and the
number of the crossing points of isodensity contour on a line. We give useful
analytic formulae for the isodensity statistics, which take into account the
corrections from the geometric distortion, the nonlinear clustering and the
nonlinear velocity distortion phenomenologically. We then demonstrate how the
geometric distortion and the nonlinear corrections alter shapes of the
statistical quantities on the basis of plausible cosmological models. Our
results show that the nonlinear correction can be sensitive to a choice of the
redshift-space coordinate as increasing the redshift. The low-dimensional
quantities such as two-dimensional genus systematically yield anisotropy due to
the geometric and velocity distortions and their angle-dependence shows the
$10\sim20%$ difference of amplitude. Sensitivity for typical high-redshift
samples are estimated in an analytic manner, and the influence of the
light-cone effect for the isodensity statistics is also discussed.


title: The Abundance and Emission of H2O and O2 in Clumpy Molecular Clouds

abstract:
  Recent observations with the Submillimeter Wave Astronomy Satellite indicate
abundances of gaseous H2O and O2 in dense molecular clouds which are
significantly lower than found in standard homogeneous chemistry models. We
present here results for the thermal and chemical balance of inhomogeneous
molecular clouds exposed to ultraviolet radiation in which the abundances of
H2O and O2 are computed for various density distributions, radiation field
strengths and geometries. It is found that an inhomogeneous density
distribution lowers the column densities of H2O and O2 compared to the
homogeneous case by more than an order of magnitude at the same A_V. O2 is
particularly sensitive to the penetrating ultraviolet radiation, more so than
H2O. The S140 and rho Oph clouds are studied as relevant test cases of
star-forming and quiescent regions. The SWAS results of S140 can be
accommodated naturally in a clumpy model with mean density of 2x10^3 cm-3 and
enhancement I_UV=140 compared with the average interstellar radiation field, in
agreement with observations of [CI] and 13CO of this cloud. Additional
radiative transfer computations suggest that this diffuse H2O component is
warm, ~60-90 K, and can account for the bulk of the 1_10-1_01 line emission
observed by SWAS. The rho Oph model yields consistent O2 abundances but too
much H2O, even for [C]/[O]=0.94, if I_UV<10 respectively <40 for a mean density
of 10^3 respectively 10^4 cm-3. It is concluded that enhanced photodissociation
in clumpy regions can explain the low H2O and O2 abundances and emissivities
found in the large SWAS beam for extended molecular clouds, but that additional
freeze-out of oxygen onto grains is needed in dense cold cores.


title:
Near-infrared line imaging of the starburst galaxies NGC 520, NGC 1614
  and NGC 7714

abstract:
  We present high spatial resolution (0.6 arcsec) near-infrared broad-band JHK
images and Br_gamma 2.1661 micron and H_2 1-0 S(1) 2.122 micron emission line
images of the nuclear regions in the interacting starburst galaxies NGC 520,
NGC 1614 and NGC 7714. The near-infrared emission line and radio morphologies
are in general agreement, although there are differences in details. In NGC
1614, we detect a nuclear double structure in Br_gamma, in agreement with the
radio double structure. We derive average extinctions of A(K) = 0.41 and A(K) =
0.18 toward the nuclear regions of NGC 1614 and NGC 7714, respectively. For NGC
520, the extinction is much higher, A(K) = 1.2 - 1.6. The observed H_2/Br_gamma
ratios indicate that the main excitation mechanism of the molecular gas is
fluorescence by intense UV radiation from clusters of hot young stars, while
shock excitation can be ruled out.
  The starburst regions in all galaxies exhibit small Br_gamma equivalent
widths. Assuming a constant star formation model, even with a lowered upper
mass cutoff of M_u = 30 M_o, results in rather old ages (10 - 40 Myr), in
disagreement with the clumpy near-infrared morphologies. We prefer a model of
an instantaneous burst of star formation with M_u = 100 M_o, occurring 6 - 7
Myr ago, in agreement with previous determinations and with the detection of
W-R features in NGC 1614 and NGC 7714. Finally, we note a possible systematic
difference in the amount of hot molecular gas between starburst and Seyfert
galaxies.


title: Models of Polarized and Variable Radio Emission for IDV Source 0917+624

abstract:
  We examine the power spectra of IDV and show the information, which is to be
gained by wavelet analysis of light curves of the quasar 0917+624. Results for
total and polarized flux at 11cm are shown. Both interstellar scattering and
intrinsic models have difficulties in explaining the 1 day period variations. A
theoretical model for the time averaged emission is presented, which provides
the basis for the analysis of possible variations.


title: Optical Spectra of Dusty Starbursts

abstract:
  This contribution presents the optical spectral properties of FIR-luminous
galaxies, whose distinctive feature is often the simultaneous presence in the
spectra of a strong $\rm H\delta$ line in absorption and of emission lines
(e(a) spectra). A discrepancy between the star formation rate estimated from
the FIR luminosity and that derived from the $\rm H\alpha$ luminosity persists
even after having corrected the $\rm H\alpha$ flux for dust according to the
observed Balmer decrement. It is shown that the e(a) spectrum can be reproduced
assuming a current starburst and dust extinction affecting the youngest stellar
populations much more than the older stars.


title:
AGN in the XMM-Newton first-light image as probes for the interstellar
  medium in the LMC

abstract:
  The XMM-Newton first-light image revealed X-ray point sources which show
heavily absorbed power-law spectra. The spectral indices and the probable
identification of a radio counterpart for the brightest source suggest AGN
shining through the interstellar gas of the Large Magellanic Cloud (LMC). The
column densities derived from the X-ray spectra in combination with HI
measurements will allow to draw conclusions on HI to H_2 ratios in the LMC and
compare these with values found for the galactic plane.


title:
On the Stability of Quasi-Equilibrium Self-Gravitating Configurations in
  a Tidal Field

abstract:
  The possibility that quasi-equilibrium self-gravitating galaxy-like
configurations exist in a tidal field is analyzed in this paper. More
specifically, we address the question of how to predict initial configurations
modeling galaxies that are able to survive environmental effects in a dense
environment for a Hubble time or so, provided thay dynamical friction is
neglected. The initial quasi-equilibrium configurations have been built up
taking into account the external tidal field produced by the halo. It modifies
the escape velocity field of the configuration, compared with isolated
configurations. The survival of the configurations as they orbit inside the
halos has been studied through N-body simulations. As a general result, it has
been found out that the bulk of the models is conserved along 12.5 Gyears of
evolution, and that the low rates of mass losses they experience are consistent
with those expected when the adiabatic protection hypothesis is at work. So,
solutions for galaxy configurations in tidal quasi-equilibrium have been found,
showing that tidal stripping in quiescent phases does not seem to be very
important, unless that the density of the galaxy environment at its formation
had been much lower than that of the galaxy environment at the point of its
orbit where the tidal perturbation is maximum. (Abridged)


title: Search for Microflaring Activity in the Magnetic Network

abstract:
  We analyze the temporal behavior of Network Bright Points (NBPs) searching
for low-atmosphere signatures of flares occuring on the magnetic network. We
make use of a set of data acquired during coordinated observations between
ground based observatories (NSO/Sacramento Peak) and the MDI instrument onboard
SOHO. Light curves in chromospheric spectral lines show only small amplitude
temporal variations, without any sudden intensity enhancement that could
suggest the presence of a transient phenomenon such as a (micro) flare. Only
one NBP shows spikes of downward velocity, of the order of 2 - 4 Km/s,
considered as signals of compression associated to a (micro) flare occurrence.
For this same NBP, we also find a peculiar relationship between the magnetic
and velocity fields fluctuations, as measured by MDI. Only for this point the B
- V fluctuations are well correlated, suggesting the presence of magneto
acoustic waves propagating along the magnetic structure. This correlation is
lost during the compression episodes and resumes afterward. An A6 GOES soft
X-ray burst is temporally associated with the downward velocity episodes,
suggesting that this NBP is the footpoint of the flaring loop. This event has a
total thermal energy content of about $10^{28}$ erg, and hence belongs to the
microflare class.


title: Slim Disk Model for Ultra-Luminous X-Ray Sources

abstract:
  The Ultra Luminous X-ray Sources (ULXs) are unique in exhibiting moderately
bright X-ray luminosities, $L_{\rm x} \sim 10^{38-40} {\rm erg~s^{-1}}$, and
relatively high blackbody temperatures, $\Tin \sim 1.0-2.0 {\rm keV}$.
  From the constraint that $L_{\rm x}$ cannot exceed the Eddington luminosity,
$L_{\rm E}$, we require relatively high black-hole masses, $M\sim 10-100
M_\odot$, however, for such large masses the standard disk theory predicts
lower blackbody temperatures, $\Tin < 1.0$ keV. To understand a cause of this
puzzling fact, we carefully calculate the accretion flow structure shining at
$\sim L_{\rm E}$, fully taking into account the advective energy transport in
the optically thick regime and the transonic nature of the flow. Our
calculations show that at high accretion rate ($\dot M \ga 30~L_{\rm E}/c^2$)
an apparently compact region with a size of $\Rin \simeq (1-3)\rg$ (with $\rg$
being Schwarzschild radius) is shining with a blackbody temperature of $\Tin
\simeq 1.8 (M/10M_\odot)^{-1/4}$ keV even for the case of a non-rotating black
hole. Further, $\Rin$ decreases as $\dot M$ increases, on the contrary to the
canonical belief that the inner edge of the disk is fixed at the radius of the
marginally stable last circular orbit. Accordingly, the loci of a constant
black-hole mass on the "H-R diagram" (representing the relation between $L_{\rm
x}$ and $\Tin$ both on the logarithmic scales) are not straight but bent
towards the lower $M$ direction in the frame of the standard-disk relation.


title: Cosmochemistry in the early Universe

abstract:
  At early times the Universe was filled up with an extremely dense and hot
gas. Due to the expansion it cooled below the binding energies of atoms which
led to the formation of the first nuclei. In the physical environment of the
post-recombination period of hydrogen, molecules such as $H_2$, $HD$ and $LiH$
can be formed. The proto-object formation, resulting from the growth of linear
density fluctuations in the early Universe, can have an important impact on the
chemical state of the Universe. Hence it can be enriched with metals, and thus
lead to the formation of the first pre-biotic molecules. In this contribution,
I will present some scheme for the formation of primordial molecules and
discuss the consequence of the formation of first stars on the existence of
possible primordial pre-biotic.


title: Search for Discrete Refractive Scattering Events

abstract:
  We have searched for discrete refractive scattering events (including effects
due to possible non-multiple diffractive scattering) at meter wavelengths in
the direction of two close by pulsars B0950+08 and B1929+10, where we looked
for spectral signatures associated with the multiple imaging of pulsars due to
scattering in the interstellar medium. We do not find any signatures of such
events in the direction of either source over a spectral periodicity range of
50 KHz to 5 MHz. Our analysis puts strong upper limits on the column density
contrast associated with a range of spatial scales of the interstellar electron
density irregularities along these lines of sight.


title: Molecular hydrogen and the nature of damped Lyman-alpha systems

abstract:
  We report results from our mini-survey for molecular hydrogen in eight high
redshift damped Lyman-alpha (DLA) systems using the ESO Ultra-violet and
Visible Spectrograph on the VLT. In addition, we investigate two systems using
ESO public data. We include in the sample the only system where H2 was
previously detected and studied at high-spectral resolution. Altogether our
sample consists of eleven absorbers with 1.85<z_abs<3.4. We confirm the
presence of H2 in the z_abs = 2.3377, metal-poor ([Si/H] = -1.20) system toward
PKS 1232+082. The derived molecular fraction, f = 2N(H2)/(2N(H2)+N(HI)) = 4
10-4, is two orders of magnitude less than what has been claimed previously
from low-resolution data. The physical conditions within the cloud can be
constrained directly from observation. The kinetic temperature and particle
density are in the ranges, respectively, 100<T<300 K and 30<nH<50 cm-3. In
addition, UV pumping is of the same order of magnitude than in our Galaxy. The
upper limits on the molecular fraction derived in nine of the systems are in
the range 1.2 10-7 - 1.6 10-5. The molecular abundance in a few DLA systems
(and in particular in the two systems where H2 is detected) is consistent with
what is seen in the Magellanic clouds. But most of the DLA measurements are
well below these values. This is probably partly due to small amounts of dust
and/or high UV flux. We argue however that the lack of molecules is a direct
consequence of high kinetic temperature (T>3000 K) implying a low formation
rate of H2 onto dust grains. Therefore, most of the DLA systems arise in warm
and diffuse neutral gas. (Abridged)


title:
The first broad-band X-ray images and spectra of the 30 Doradus region
  in the LMC

abstract:
  We present the XMM-Newton first light image, taken in January 2000 with the
EPIC pn camera during the instrument's commissioning phase, when XMM-Newton was
pointing towards the Large Magellanic Cloud (LMC). The field is rich in
different kinds of X-ray sources: point sources, supernova remnants (SNRs) and
diffuse X-ray emission from LMC interstellar gas. The observations are of
unprecedented sensitivity, reaching a few 10^32 erg/s for point sources in the
LMC. We describe how these data sets were analysed and discuss some of the
spectroscopic results. For the SNR N157B the power law spectrum is clearly
steeper than previously determined from ROSAT and ASCA data. The existence of a
significant thermal component is evident and suggests that N157B is not a
Crab-like but a composite SNR. Most puzzling is the spectrum of the LMC hot
interstellar medium, which indicates a significant overabundance of Ne and Mg
of a few times solar.


title: The formation of cosmic structure with modified Newtonian dynamics

abstract:
  I consider the growth of inhomogeneities in a low-density baryonic, vacuum
energy-dominated universe in the context of modified Newtonian dynamics (MOND).
I first write down a two-field Langrangian-based theory of MOND
(non-relativistic), which embodies several assumptions such as constancy of the
MOND acceleration parameter, association of a MOND force with peculiar
accelerations only, and the deceleration of the Hubble flow as a background
field which influences the dynamics of a finite size region. In the context of
this theory, the equation for the evolution of spherically symmetric
over-densities is non-linear and implies very rapid growth even in a
low-density background, particularly at the epoch when the putative
cosmological constant begins to dominate the Hubble expansion. Small comoving
scales enter the MOND regime earlier than larger scales and therefore evolve to
large over-densities sooner. Taking the initial COBE-normalized power spectrum
provided by CMBFAST (Seljak & Zeldarriaga 1996), I find that the final
power-spectrum resembles that of the standard LCDM universe and thus retains
the empirical successes of that model.


title:
The brightness of SN 1991T and the uniformity of decline-rate and colour
  corrected absolute magnitudes of supernovae Ia

abstract:
  We present a distance to NGC 4527, the host galaxy of the type Ia SN 1991T,
measured by surface brightness fluctuations. This supernova has been labelled
``peculiar'' both on the grounds of its spectroscopic behaviour and its
apparent overluminosity with respect to other supernovae. The distance modulus
to NGC 4527 and thus to SN 1991T is 30.26+-0.09. This relatively short distance
largely removes the discrepancy with other Ia supernovae having similar
light-curve characteristics and also removes the motivation for interpreting SN
1991T as a super-Chandrasekhar explosion. However, the reddening uncertainty
results in significant uncertainty of the absolute magnitudes.


title: X-ray Luminosity Functions of Young Stars in Taurus-Auriga-Perseus

abstract:
  X-ray luminosity functions (XLF) are frequently used to assess the properties
of the X-ray emission from a given sample of stars, and particularly important
for a comparison of different groups of stars. I present the results from a
detailed analysis of the XLF of pre-main sequence T Tauri Stars in
Taurus-Auriga and young main-sequence objects (represented by the Pleiades and
Hyades cluster). The study is based on the ROSAT public archive. Various
possible biases related to the sample selection are described, and their
influence on the luminosity distributions is discussed.


title: Petersen diagram for RRd stars in the Magellanic Clouds

abstract:
  RRd stars from the Magellanic Clouds form a well-defined band in the Petersen
diagram. We explain this observed band with our evolutionary and pulsation
calculations with assumed metallicity [Fe/H]=(-2,-1.3). Vast majority of RRd
stars from LMC is confined to a narrower range of (-1.7,-1.3). The width of the
band, at specified fundamental mode period, may be explained by mass spread at
given metallicity. The shape of the band reflects the path of RRd stars within
the RR Lyrae instability strip. We regard the success in explaining the
Petersen diagram a support for our evolutionary models, which yield, mean
absolute magnitude in the mid of the instability strip, <M_V>, in the range 0.4
to 0.65 mag implying distance modulus to LMC of 18.4 mag.


title:
On the role of extinction in failed gamma-ray burst optical/IR
  afterglows

abstract:
  While all but one Gamma-Ray Bursts observed in the X-ray band showed an X-ray
afterglow, about 60 per cent of them have not been detected in the optical
band. We demonstrate that in many cases this is not due to adverse observing
conditions, or delay in performing the observations. We also show that the
optically non-detected afterglows are not affected by particularly large
Galactic absorbing columns, since its distribution is similar for both the
detected and non-detected burst subclasses. We then investigate the hypothesis
that the failure of detecting the optical afterglow is due to absorption at the
source location. We find that this is a marginally viable interpretation, but
only if the X-ray burst and afterglow emission and the possible optical/UV
flash do not destroy the dust responsible for absorption in the optical band.
If dust is efficiently destroyed, we are led to conclude that bursts with no
detected optical afterglow are intrinsically different. Prompt infrared
observations are the key to solve this issue.


title: Issues and methods for CMB anisotropy data reduction

abstract:
  Major issues and existing methods for the reduction of CMB anisotropy data
are reviewed. An emphasis is put on the proper modelling of the data. It is
suggested that the robustness of methods could be improved by taking into
account the uncertainty of the model for finding optimal solutions.


title:
Particle modeling of disk-shaped galaxies of stars on nowadays
  concurrent supercomputers

abstract:
  The time evolution of initially balanced, rapidly rotating models for an
isolated disk of highly flattened galaxies of stars is calculated. The method
of direct integration of the Newtonian equations of motion of stars over a time
span of many galactic rotations is applied. Use of modern concurrent
supercomputers has enabled us to make long simulation runs using a sufficiently
large number of particles N=30,000. One of the goals of the present simulation
is to test the validities of a modified local criterion for stability of
Jeans-type gravity perturbations (e.g. those produced by a barlike structure, a
spontaneous perturbation and/or a companion galaxy) in a self-gravitating,
infinitesimally thin and collisionless disk. In addition to the local criterion
we are interested in how model particles diffuse in velocity. This is of
considerable interest in the kinetic theory of stellar disks. Certain
astronomical implications of the simulations to actual disk-shaped (i.e.
rapidly rotating) galaxies are explored. The weakly nonlinear, or quasi-linear
kinetic theory of the Jeans instability in disk galaxies of stars is described
as well.


title: Primordial Star Formation under Far-ultraviolet radiation

abstract:
  Thermal and chemical evolution of primordial gas clouds irradiated with
far-ultraviolet (FUV; < 13.6 eV) radiation is investigated. In clouds
irradiated by intense FUV radiation, sufficient hydrogen molecules to be
important for cooling are never formed. However, even without molecular
hydrogen, if the clouds are massive enough, they start collapsing via atomic
hydrogen line cooling. Such clouds continue to collapse almost isothermally
owing to successive cooling by H^{-} free-bound emission up to the number
density of 10^{16} cm^{-3}. Inside the clouds, the Jeans mass eventually falls
well below a solar mass. This indicates that hydrogen molecules are dispensable
for low-mass primordial star formation, provided fragmentation of the clouds
occurs at sufficiently high density.


title:
Photon Scattering by Relativistic Flows in Schwarzschild Spacetimes. I.
  The Generation of Power-Law Spectra

abstract:
  We study the spectra generated as a result of bulk Comptonization by
relativistic electrons in radial flows onto compact objects. We solve
numerically the general-relativistic radiative transfer equation in the
Schwarzschild spacetime, in steady-state and under minimal assumptions. We show
that power-law spectra result from multiple scatterings, in a way similar to
thermal Comptonization. We also find that photon-electron interactions taking
place near the black-hole event horizon affect very little the emerging
spectra. We, therefore, argue that bulk Comptonization spectra do not carry
distinguishing signatures of the compact object around which they are produced.
We examine the dependence of the spectra on simplifications often employed
regarding the spacetime geometry, the distribution of photon sources, and the
boundary conditions. We show that the existence of trapped characteristics
around a black hole reduces the efficiency of Comptonization and that general
relativistic effects identically cancel bulk Comptonization effects for a
free-falling flow and in the limit of infinitesimal mean-free path. As a
result, we find that neglecting the curved spacetime geometry leads to
overestimating the high-energy flux by up to an order of magnitude. Finally, we
demonstrate that the spectrum from accretion onto a neutron star depends
sensitively on the imposed boundary conditions, while that from a black hole is
immune to such choices.


title: Comparative CMBology: Putting Things Together

abstract:
  I present a series of diagrams which illustrate why the cosmic microwave
background (CMB) data favor certain values for the cosmological parameters.
Various methods to extract these parameters from CMB and non-CMB observations
are forming an ever-tightening network of interlocking constraints. I review
the increasingly precise constraints in the Omega_m - Omega_Lambda plane and
show why more cosmologists now prefer Lambda-CDM cosmologies to any other
leading model.


title: Lithium-Beryllium-Boron and Oxygen in the early Galaxy

abstract:
  Oxygen is a much better evolutionary index than iron to follow the history of
Lithium-Beryllium-Boron (LiBeB) since it is the main producer of these light
elements at least in the early Galaxy. The O-Fe relation is crucial to the
determination of the exact physical process responsible for the LiBeB
production. Calculated nucleosynthetic yields of massive stars, estimates of
the energy cost of Be production, and above all recent observations reported in
this meeting seem to favor a mechanism in which fast nuclei enriched into He, C
and O arising from supernovae are accelerated in superbubbles and fragment on H
and He in the interstellar medium.


title: The Star Formation History of the Milky Way

abstract:
  Quantification of the Galaxy's star formation history involves both the
duration and the rate of formation, with these parameters being known with
different precision for different populations. The early rate of star formation
is knowable from modelling chemical element data, the recent rate directly from
isochrone analyses of colour-magnitude data. The field halo and globular
clusters are almost exclusively old, and formed in at most a few Gyr. The outer
bulge probably formed in a short period long ago -- extant data is
inconsistent, while the inner bulge/disk is forming today, and has continued to
form over time. Only very limited data is available on the inner disk. The
outer disk near the Sun seems as old as the halo. The earliest extended disk,
which forms the thick disk today, seems to have been in place very early, an
observation which is not simply consistent with some galaxy formation models.


title:
Weakly nonlinear theory of the Jeans instability in disk galaxies of
  stars

abstract:
  The reaction of collective oscillations excited in the interaction between
aperiodically growing Jeans-type gravity perturbations and stars of a rapidly
rotating disk of flat galaxies is considered. An equation is derived which
describes the change in the main body of equilibrium distribution of stars in
the framework of the nonresonant weakly nonlinear theory. Certain applications
of the theory to the problem of relaxation of the Milky Way at radii where
two-body relaxation is not effective are explored. The theory, as applied to
the Solar neighborhood, accounts for observed features, such as the shape for
the velocity ellipsoid of stars and the increase in star random velocities with
age.


title:
Determining the Geometry and the Cosmological Parameters of the Universe
  through SZE Cluster Counts

abstract:
  We study Sunyaev-Zeldovich Effect (SZE) cluster counts in different
cosmologies. It is found that even without the full knowledge of the redshift
distribution of SZE clusters, one can still readily distinguish a flat universe
with a cosmological constant from an open universe. We divide clusters into a
low redshift group (with redshift z<0.5) and a high redshift group (with z>1),
and compute the relation r=N(z<0.5)/N(z>1), where N is the number of
flux-limited (S_lim) SZE clusters. With about the same total number of SZE
clusters N(z>0), the r-value for a flat universe with a consmological constant
and that for an open universe occupy different regions in the S_lim -- r plot
for the most likely cosmological parameters 0.25<\Omega_0<0.35 and
0.2<\Gamma<0.3, where \Gamma is the shape parameter of the initial power
spectrum of density fluctuations. Thus, with a deep SZE cluster survey, the
ratio r can reveal, independent of the normalization of the power spectrum,
whether we are living in a low-density flat universe or an open universe.
  Within the flat universe scenario, the SZE cluster-normalized \sigma_8 has
also been investigated in this work, where sigma_8 is the r.m.s. density
fluctuations within the top-hat scale of 8 h^{-1} Mpc. A functional relation
sigma_8 \sim \Omega_0^{-0.13} is found. Combining it with the X-ray
cluster-normalized \sigma_8\sim\Omega_0^{-0.52+0.13\Omega_0}, one can put tight
constraints on both \Omega_0 and \sigma_8 simulataneously.


title:
The stellar content of the Hamburg/ESO survey. I. Automated selection of
  DA white dwarfs

abstract:
  We describe automatic procedures for the selection of DA white dwarfs in the
Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection
of other stellar objects (e.g., metal-poor stars and carbon stars), a flexible,
robust algorithm for detection of stellar absorption and emission lines in the
digital spectra of the HES was developed. Broad band (U-B, B-V) and narrow band
(Str\"omgren c_1) colours can be derived directly from HES spectra, with
precisions of sigma(U-B)=0.092mag; sigma(B-V)=0.095mag; sigma(c_1)=0.15mag.
  We describe simulation techniques that allow to convert model or slit spectra
to HES spectra. These simulated objective-prism spectra are used to determine
quantitative selection criteria, and for the study of selection functions. We
present an atlas of simulated HES spectra of DA and DB white dwarfs.
  Our current selection algorithm is tuned to yield maximum efficiency of the
candidate sample (minimum contamination with non-DAs). DA candidates are
selected in the B-V versus U-B and c_1 versus W_\lambda(Hbeta+Hgamma+Hdelta)
parameter spaces. The contamination of the resulting sample with hot subdwarfs
is expected to be as low as ~8%, while there is essentially no contamination
with main sequence or horizontal branch stars. We estimate that with the
present set of criteria, ~80% of DAs present in the HES database are recovered.
A yet higher degree of internal completeness could be reached at the expense of
higher contamination. However, the external completeness is limited by
additional losses caused by proper motion effects and the epoch differences
between direct and spectral plates used in the HES.


title:
Isotropization of Ultra-High Energy Cosmic Ray Arrival Directions by
  Radio Ghosts

abstract:
  The isotropy in the ultra high energy cosmic ray (UHECR) flux observed by
Yakutsk and AGASA experiments, is a very strong constraint to production and
propagation models alike. Most of the scenarios proposed in the literature
should produce a sizable anisotropy as either extragalactic luminous or dark
matter is normally associated with the invoked particle sources. We explore the
possibility that the magnetic fields in fossil cocoons of former radio galaxies
-- so called {\it radio ghosts} -- are able to scatter UHECR in the
intergalactic medium giving rise to the observed isotropy. We show, through
numerical simulations, under which conditions this process can be operative and
the magnitude of the effect. We further demonstrate, that if radio ghosts mix
with the ambient medium, they might be able to produce the observed magnetic
fields in clusters of galaxies. In the case of mixing, the UHECR isotropization
would be even stronger than in our conservative estimates.


title: BeppoSAX observation of Hercules A and MRC 0625-536

abstract:
  We present BeppoSAX observations of the two FR I type radio galaxies Hercules
A (3C 348) and MRC 0625-536 in the energy range $0.2 - 200$ keV. Data analysis
shows that the X-ray flux from Hercules A is consistent with a diffuse thermal
plasma emitting at $T \approx 4-5$ keV with a possible, but somewhat uncertain,
contribution of a softer component at $T \approx 3 $ keV. The non thermal
emission from the active nucleus must be significantly smaller than the thermal
one, and no indication of relevant core obscuration by a surrounding torus was
detected. The flux from MRC 0625-536 originates form an extended region and has
been fitted to a thermal law with $T \approx 5.7$ keV and with a column density
consistent with the galactic absorption. A spatially resolved spectral analysis
does not show a relevant variation of the temperature and the metallicity
across the diffuse emission zone. A non thermal spectral component, related to
the nuclear activity, may be present in the innermost region with some possible
amount of local obscuration, contributing $\lapp 10%$ to the total luminosity.
Hard X-ray emission from MRC 0625-536 has been detected in the PDS (15 - 200
keV) that may be related either to its galactic core or to the intracluster
region.


title: The K-Band Galaxy Luminosity Function

abstract:
  We measured the K-band luminosity function using a complete sample of 4192
morphologically-typed 2MASS galaxies with 7 < K < 11.25 mag spread over 2.12
str. Early-type (T < -0.5) and late-type (T > -0.5) galaxies have similarly
shaped luminosity functions, alpha_e=-0.92+/-0.10 and alpha_l=-0.87+/-0.09. The
early-type galaxies are brighter, M_*e=-23.53+/-0.06 mag compared to
M_*l=-22.98\pm0.06 mag, but less numerous, n_*e=(0.0045+/-0.0006)h^3/Mpc^3
compared to n_*l=(0.0101+/-0.0013)h^3/Mpc^3 for H_0=100h km/s Mpc, such that
the late-type galaxies slightly dominate the K-band luminosity density,
j_late/j_early=1.17+/-0.12. Our morphological classifications are internally
consistent, consistent with previous classifications and lead to luminosity
functions unaffected by the estimated uncertainties in the classifications.
These luminosity functions accurately predict the K-band number counts and
redshift distributions for K < 18 mag, beyond which the results depend on
galaxy evolution and merger histories.


title: The X-ray evolution of clusters of galaxies to z=0.9

abstract:
  The evolution of the X-ray luminosity function of clusters of galaxies has
been measured to z=0.9 using over 150 X-ray selected clusters discovered in the
WARPS survey. We find no evidence for evolution of the luminosity function at
any luminosity or redshift. The observations constrain the evolution of the
space density of moderate luminosity clusters to be very small, and much less
than predicted by most models of the growth of structure with Omega_m=1. All
the current X-ray surveys agree on this result. Several notable luminous
clusters at z>0.8 have been found, including one cluster which is more luminous
(and is probably more massive) than the well known MS1054 cluster.


title:
Evidence for Inconsistencies in Galaxy Luminosity Functions Defined by
  Spectral Type

abstract:
  Galaxy morphological and spectroscopic types should be nearly independent of
apparent magnitude in a local, magnitude-limited sample. Recent luminosity
function surveys based on morphological classification of galaxies are
substantially more successful at passing this test than surveys based on
spectroscopic classifications. Among spectroscopic classifiers, those defined
by small aperture fibers (ESP, LCRS) show far stronger systematic
classification biases than those defined by large apertures (APM). This effect
can be easily explained as an aperture bias, whereby galaxies with globally
late-type spectra are assigned earlier spectral types which depend on the
redshift and luminosity of the galaxy. The effect is demonstrated by extracting
successively larger aperture spectra from long-slit spectroscopy of nearby
galaxies. This systematic classification bias is generic, and the 2dFGRS and
SDSS surveys will show similar systematic biases in their spectral types. We
suggest several methods for correcting the problem or avoiding it altogether.
If not corrected, this aperture bias can mimic galaxy evolutionary effects and
distort estimates of the luminosity function.


title: XMM-Newton observations of M87 and Its X-Ray Halo

abstract:
  We report performance verification observations of the giant elliptical
galaxy M87 in the Virgo Cluster with the MOS, pn, and optical monitor
instruments on board of XMM-Newton. With the energy sensitive imaging
instruments MOS and pn we obtain the first spatially constrained X-ray spectra
of the nucleus and the jet of the galaxy. The good photon statistics of the pn
and MOS allow a detailed analysis of the radial temperature and abundance
distribution of 6 elements. The data provide no indication of a
multi-temperature structure for radii less than 2 arcmin. An apparent sharp
metal abundance drop deduced for the regions inside this radius is probably due
to resonant line scattering.


title: The Structure of the Cold Neutral ISM on 10-100 Astronomical Unit Scales

abstract:
  We have used the Very Long Baseline Array (VLBA) and the Very Large Array
(VLA) to image Galactic neutral hydrogen in absorption towards four compact
extragalactic radio sources with 10 milliarcsecond resolution. Previous VLBA
data by Faison et al (1998) have shown the existence of prominent structures in
the direction of the extragalactic source 3C~138 with scale sizes of 10-20 AU
with changes in HI optical depth in excess of 0.8 $\pm$ 0.1. In this paper we
confirm the small scale \hi optical depth variations toward 3C~147 suggested
earlier at a level up to 20 % $\pm$ 5% . The sources 3C~119, 2352+495 and
0831+557 show no significant change in \hi optical depth across the sources
with one sigma limits of 30%, 50%, and 100%. Of the seven sources recently
investigated with the VLBA and VLA, only 3C~138 and 3C~147 show statistically
significant variations in HI opacities.
  Deshpande (2000) have attempted to explain the observed small-scale structure
as an extension of the observed power spectrum of structure on parsec size
scales. The predictions of Deshpande (2000) are consistent with the VLBA HI
data observed in the directions of a number of sources, including 3C~147, but
are not consistent with our previous observations of the HI opacity structure
toward 3C~138.


title: Searching for X-ray Galaxy Clusters in the Zone of Avoidance

abstract:
  Based on the ROSAT All-Sky Survey we are constructing a sample of the X-ray
brightest galaxy clusters for cosmological studies. We have already completed
the compilation of a sample of about 1000 clusters in the sky excluding a 40
degree wide band around the galactic plane. We have demonstrated with the
southern sample, which is the so far most complete, that we can get reliable
statistical measures of the large-scale structure of the Universe to scales in
excess of 400 Mpc (for Ho=100). With the experience gained in these projects we
are extending the search for X-ray galaxy clusters into the Zone-of-Avoidance.
We have compiled a sample of 181 good cluster candidates with a well defined
completeness of about 70% down to a flux limit of 3 10e-12 erg/s/cm**2 in the
zone with an absorption depth less than Av = 2.25. The candidates are
definitely identified and redshifts are obtained in an ongoing optical
follow-up program.


title: COBE Constraints on a Compact Toroidal Low-density Universe

abstract:
  In this paper, the cosmic microwave background (CMB) anisotropy in a
multiply-connected compact flat 3-torus model with the cosmological constant is
investigated. Using the COBE-DMR 4-year data, a full Bayesian analysis revealed
that the constraint on the topology of the flat 3-torus model with
low-matter-density is less stringent. As in compact hyperbolic models, the
large-angle temperature fluctuations can be produced as the gravitational
potential decays at the $\Lambda$-dominant epoch well after the last
scattering. The maximum allowed number $N$ of images of the cell (fundamental
domain) within the observable region at present is approximately 49 for
$\Omega_m=0.1$ and $\Omega_\Lambda=0.9$ whereas $N\sim8$ for $\Omega_m=1.0$ and
$\Omega_\Lambda=0$.


title:
The XMM-Newton Serendipitous Survey I. The role of XMM-Newton Survey
  Science Centre

abstract:
  This paper describes the performance of XMM-Newton for serendipitous surveys
and summarises the scope and potential of the XMM-Newton Serendipitous Survey.
The role of the Survey Science Centre (SSC) in the XMM-Newton project is
outlined. The SSC's follow-up and identification programme for the XMM-Newton
serendipitous survey is described together with the presentation of some of the
first results.


title: OPTICON and the Virtual Observatory

abstract:
  The challenges of multi-wavelength astrophysics require new outlooks from
those appropriate to traditional astronomy. The next generation of research
scientists must be trained to exploit the potentiality now being provided for
the first time. Just as importantly, the full range of available information
must be indexed and made available, to avoid wasteful repeat observations, or
incomplete analyses. Perhaps the greatest challenge in the immediate future is
to ensure the wealth of multi-wavelength data already available, and being
accumulated, is available for efficient scientific exploitation. The difference
between observations in a depositary and a fully-operational data archive is
the difference between waste and cutting-edge science. The EU Optical Infrared
Coordination Network for Astronomy (OPTICON) provides a forum to coordinate and
develop the many national and international efforts and desires leading towards
an operational virtial observatory.


title: The Stellar IMF from Turbulent Fragmentation

abstract:
  The morphology and kinematics of molecular clouds (MCs) are best explained as
the consequence of super--sonic turbulence. Super--sonic turbulence fragments
MCs into dense sheets, filaments and cores and large low density ``voids'', via
the action of highly radiative shocks. We refer to this process as "turbulent
fragmentation". In this work we derive the mass distribution of gravitationally
unstable cores generated by the process of turbulent fragmentation. The mass
distribution above one solar mass depends primarily on the power spectrum of
the turbulent flow and on the jump conditions for isothermal shocks in a
magnetized gas. For a power spectrum index \beta=-1.74, consistent with
Larson's velocity dispersion--size relation as well as with new numerical and
analytic results on super--sonic turbulence, we obtain a power law mass
distribution of dense cores with a slope equal to 3/(4-\beta) = 1.33,
consistent with the slope of the stellar IMF. Below one solar mass, the mass
distribution flattens and turns around at a fraction of a solar mass, as
observed for the stellar IMF in a number of stellar clusters, because only the
densest cores are gravitationally unstable. The mass distribution at low masses
is determined by the probability distribution of the gas density, which is
known to be approximately Log--Normal for an isothermal turbulent gas. The
intermittent nature of the turbulent density distribution is thus responsible
for the existence of a significant number of small collapsing cores, even of
sub--stellar mass. Since turbulent fragmentation is unavoidable in
super--sonically turbulent molecular clouds, and given the success of the
present model in predicting the observed shape of the stellar IMF, we conclude
that turbulent fragmentation is essential to the origin of the stellar IMF.


title:
Simulation of a Space-Based Microlensing Survey for Terrestrial
  Extra-Solar Planets

abstract:
  We show that a space-based gravitational microlensing survey for terrestrial
extra-solar planets is feasible in the near future, and could provide a nearly
complete picture of the properties of planetary systems in our Galaxy. We
present simulations of such a survey using a 1-2m aperture space telescope with
a ~2 square degree field-of-view which is used to continuously monitor ~10^8
Galactic bulge main sequence stars. The microlensing techniques allows the
discovery of low mass planets with high signal-to-noise, and the space mission
that we have studied are sensitive to planets with masses as low as that of
Mars. By targeting main sequence source stars, which can only be resolved from
space, the space-based microlensing survey is able to detect enough light from
the lens stars to determine the spectral type of one third of the lens stars
with detected planets, including virtually all of the F, G, and K stars which
comprise one quarter of the event sample. This enables the determination of the
planetary masses and separations in physical units, as well as the abundance of
planets as a function of stellar type and distance from the Galactic center. We
show that a space-based microlensing planet search program has its highest
sensitivity to planets at orbital separations of 0.7-10 AU, but it will also
have significant sensitivity at larger separations and will be able to detect
free-floating planets in significant numbers. This complements the planned
terrestrial planet transit missions which are sensitive to terrestrial planets
at separations of =< 1 AU. Such a mission also detect ~50,000 giant planets via
transits, and it is, therefore, the only proposed planet detection method that
is sensitive to planets at all orbital radii.


title: On the Hidden Nuclear Starburst in Arp 220

abstract:
  We construct a starburst model for the hidden starbursts in Arp 220 based on
the new Starburst99 models of Leitherer et al. Comparing these stellar
population synthesis models with observations, we show that the hidden power
source must be due to star formation (as opposed to an AGN) at the 50% level or
more in order to avoid an ionizing photon excess problem, and this starburst
must be young ($< 7 \times 10^7$ yr). We derive a current star formation rate
of $270 M_{\odot}$ yr$^{-1}$, and an extinction $A_V > 30$ mag for our line of
sight to this hidden starburst.


title:
Detection of anisotropy in the Cosmic Microwave Background at horizon
  and sub-horizon scales with the BOOMERanG experiment

abstract:
  BOOMERanG has recently resolved structures on the last scattering surface at
redshift $\sim$ 1100 with high signal to noise ratio. We review the technical
advances which made this possible, and we focus on the current results for maps
and power spectra, with special attention to the determination of the total
mass-energy density in the Universe and of other cosmological parameters.


title: First results from the BOOMERanG experiment

abstract:
  We report the first results from the BOOMERanG experiment, which mapped at
90, 150, 240 and 410 GHz a wide (3%) region of the microwave sky with minimal
local contamination. From the data of the best 150 GHz detector we find
evidence for a well defined peak in the power spectrum of temperature
fluctuations of the Cosmic Microwave Background, localized at $\ell = 197 \pm
6$, with an amplitude of $(68 \pm 8) \mu K_{CMB}$. The location, width and
amplitude of the peak is suggestive of acoustic oscillations in the primeval
plasma. In the framework of inflationary adiabatic cosmological models the
measured spectrum allows a Bayesian estimate of the curvature of the Universe
and of other cosmological parameters. With reasonable priors we find $\Omega =
(1.07 \pm 0.06)$ and $n_s = (1.00 \pm 0.08)$ (68%C.L.) in excellent agreement
with the expectations from the simplest inflationary theories. We also discuss
the limits on the density of baryons, of cold dark matter and on the
cosmological constant.


title:
Molecular hydrogen abundance in the dust-free damped Ly-alpha galaxy at
  z = 3.4

abstract:
  New results from the search for H2 absorption in the damped Ly-alpha galaxy
at redshift z = 3.4 toward QSO 0000-2620 (z_em = 4.1) are reported. The
high-resolution (lambda/Delta lambda = 48,000) spectra of Q0000-2620 were
obtained using the Ultraviolet - Visual Echelle Spectrograph (UVES) on the 8.2m
ESO Kueyen telescope. The ortho-H2 column density is found to be N(J=1) = (5.55
+/- 1.35) 10^{13} cm^{-2} (2sigma C.L.). The combination of N(J=1) with the
limits available for other low rotational levels restricts the excitation
temperature T_ex in the range (290-540) K. This gives the total H2 column
density of N(H2) = (8.75 +/- 1.25) 10^{13} cm^{-2} and the corresponding
fraction of hydrogen atoms bound in molecules of f(H2) = (6.8 +/- 2.0) 10^{-8}.


title: Foregrounds in the BOOMERANG-LDB data: a preliminary rms analysis

abstract:
  We present a preliminary analysis of the BOOMERanG LDB maps, focused on
foregrounds. BOOMERanG detects dust emission at moderately low galactic
latitudes ($b > -20^o$) in bands centered at 90, 150, 240, 410 GHz. At higher
Galactic latitudes, we use the BOOMERanG data to set conservative upper limits
on the level of contamination at 90 and 150 GHz. We find that the mean square
signal correlated with the IRAS/DIRBE dust template is less than 3% of the mean
square signal due to CMB anisotropy.


title:
Star Formation History and Stellar Metallicity Distribution in a Cold
  Dark Matter Universe

abstract:
  We study star formation history and stellar metallicity distribution in
galaxies in a Lambda cold dark matter universe using a hydrodynamic
cosmological simulation. Our model predicts star formation rate declining in
time exponentially from an early epoch to the present with the time-scale of 6
Gyr, which is consistent with the empirical Madau plot with modest dust
obscuration. Star formation in L^* galaxies continues intermittently to the
present also with an exponentially declining rate of a similar time-scale,
whereas in small galaxies star formation ceases at an early epoch. The mean age
of the extant stars decreases only slowly with increasing redshift, and exceeds
1 Gyr at z=3. Normal galaxies contain stars with a wide range of metallicity
and age: stars formed at z<1 have metallicity of 0.1-1.0 Zsun, while old stars
take a wide range of values from 10^{-6} Zsun to 3.0 Zsun. The mean metallicity
of normal galaxies is in the range 0.1-1.0 Zsun. Dwarf galaxies that contain
only old stars have a wide range of mean metallicity (10^{-4}-1.0 Zsun), but on
average they are metal deficient compared with normal galaxies.


title: The Metallicity Evolution of Damped Lyman-alpha Systems

abstract:
  According to Pei, Fall & Hauser (1999), the global metallicity evolution of
the Universe can be represented by the ratio of the total metal content to the
total gas content measured in Damped Lyman-alpha (DLA) systems (the ``column
density weighted metallicity'' `a la Pettini). To minimize dust obscuration
effects, a DLA sample with negligible dust content is considered, namely, 50
DLAs with log N(HI) < 20.8. The global metallicity found shows clear evidence
of redshift evolution that goes from \sim1/30 solar at z\sim4.1 to solar at z
\sim 0.4. More generally, DLAs with measured heavy elements probe the ISM of
high redshift galaxies. The whole sample collected from the literature contains
75 DLAs. The metallicity is calculated adopting for the dust correction the
most general method used so far, based on models of the ISM dust depletions in
the Galaxy. The intrinsic metallicity evolution of DLA galaxies is dlog
Z(DLA)/dz \propto -0.33 +/- 0.06.


title: PSCz vs. 1.2 Jy velocity fields: a Spherical Harmonics Comparison

abstract:
  We perform a detailed comparison of the IRAS PSCz and 1.2-Jy spherical
harmonic coefficients of the predicted velocity fields in redshift space. The
monopole terms predicted from the two surveys show some differences. Faint
galaxies are responsible for this mismatch that disappears when extracting a
PSCz subsample of galaxies with fluxes larger than 1.2 Jy. The analysis of PSCz
dipole components confirms the same inconsistencies found by Davis, Nusser and
Willick (1996) between the IRAS 1.2-Jy gravity field and MARKIII peculiar
velocities.
  Shot-noise, which is greatly reduced in our PSCz gravity field, cannot be
responsible for the observed mismatch.


title: Probing Galaxy Formation with High Energy Gamma-Rays

abstract:
  We discuss how measurements of the absorption of $\gamma$-rays from GeV to
TeV energies via pair production on the extragalactic background light (EBL)
can probe important issues in galaxy formation. We use semi-analytic models
(SAMs) of galaxy formation, set within the hierarchical structure formation
scenario, to obtain predictions of the EBL for 0.1-1000$\mu$m. SAMs incorporate
simplified physical treatments of the key processes of galaxy formation ---
including gravitational collapse and merging of dark matter halos, gas cooling
and dissipation, star formation, supernova feedback and metal production ---
and have been shown to reproduce key observations at low and high redshift.
Here we also introduce improved modelling of the spectral energy distributions
in the mid-to-far-IR arising from emission by dust grains. Assuming a flat
\lcdm cosmology with $\Omega_m=0.3$ and Hubble parameter $h=0.65$, we
investigate the consequences of variations in input assumptions such as the
stellar initial mass function (IMF) and the efficiency of converting cold gas
into stars. We conclude that observational studies of the absorption of
$\gamma$-rays with energies from 10s of Gev to 10s of TeV will help to
determine the EBL, and also help to explain its origin by constraining some of
the most uncertain features of galaxy formation theory, including the IMF, the
history of star formation, and the reprocessing of light by dust.


title: CMBR in G\"{o}del Universe:A possible test to Einstein-Cartan gravity?

abstract:
  A rotating universe represented by the G\"{o}del metric in spacetimes with
Cartan torsion is investigated where the Cosmic Microwave Background Radiation
(CMBR) is computed from the G\"{o}del rotation of the universe and the spin
density of the spinning fluid in Einstein-Cartan gravity.The autoparallel
equation in Riemann-Cartan spacetime is shown to lead to the evolution equation
of the cosmological perturbation where the spin-rotation coupling is the source
of the growth of inhomogeneities.It is shown that temperature anisotropy is
within the limits of COBE constraint yielding a value of
$\frac{{\delta}T}{T}=10^{-7}$.This result opens the possibility of testing
Einstein-Cartan gravity from a cosmological experiment such as PLANCK or MAP.


title: Supernova 1991T and the Value of the Hubble Constant

abstract:
  Based upon multi-epoch Hubble Space Telescope observations, we present the
discovery of sixteen high-quality Cepheid candidates in NGC 4527. Corrected for
metallicity effects in the Cepheid period-luminosity relation, we derive a
distance, including both random (r) and systematic (s) uncertainties, of
13.0+/-0.5(r)+/-1.2(s) Mpc. Our result is then used to provide a calibration of
the peak B-, V-, and I-band luminosities of the peculiar Type Ia supernova SN
1991T, a resident of NGC 4527. Despite its documented spectroscopic
peculiarities, after correction for the decline rate-luminosity correlation the
corrected peak luminosity is indistinguishable from those of so-called
``normal'' Type Ia SNe. With now nine local calibrators at our disposal, we
determine a robust value for the Hubble Constant of H_0=73+/-2(r)+/-7(s)
km/s/Mpc.


title: SCUBA deep fields and source confusion

abstract:
  Deep submillimetre(submm)-wave surveys made over the last three years using
the SCUBA camera at the 15-m James Clerk Maxwell Telescope (JCMT) have revealed
a new population of very luminous high-redshift galaxies. The properties of
this population, and their contribution to the intensity of the extragalactic
background radiation field are described briefly, especially in the context of
the SCUBA lens survey (carried out since 1997 by Ian Smail, Rob Ivison,
Jean-Paul Kneib and the author: a full description of the survey and references
to supporting work can be found in the recent catalogue paper). The potential
problems caused by source confusion in the large 15-arcsec SCUBA observing beam
for the identification and follow up of the results are discussed. The effects
of confusion are not important for the study of 850-micron SCUBA sources
brighter than about 2 mJy.


title:
An Apparent Gap in Stellar Mass Distributions around 0.7 Solar Masses
  and a Possible Explanation

abstract:
  Mass functions for samples of white dwarf stars and for a large heterogeneous
sample of nearby stars appear to have unexplained deficits in the range of 0.70
to 0.75 Solar Masses. The existence, or non-existence, of this anomaly
constitutes a definitive test of a fractal cosmological model that inherently
predicts a gap in stellar mass functions at about 0.73 Solar Masses.


title: Stellar Kinematics of the Spiral Structure in the Solar Neighborhood

abstract:
  We present a method, based on the kinematic analysis of the Galactic disk
stars, to clarify whether the internal motions of the stellar system in spiral
arms follow those expected in the density wave theory. The method relies on the
comparison with the linear relation between the phases of spatial positions and
epicyclic motions of stars, as drawn from the theory. The application of the
method to the 78 Galactic Cepheids near the Sun, for which accurate proper
motions are available from the {\it Hipparcos} Catalogue, has revealed that
these Cepheids hold no correlation between both phases, thereby implying that
their motions are in contradiction with the theoretical predictions. Possible
reasons for this discrepancy are discussed and future prospects are outlined.


title: Enhanced black hole formation by multiple winding cosmic strings

abstract:
  Primordial black hole formation by cosmic string collapse is reconsidered
when the winding number of the string is larger than the unity. The line energy
density of the multiple winding string becomes greater than that of the single
winding string so that the probability of the black hole formation by the
string collapse during the loop oscillation would be strongly enhanced.
Although the production of the multiple winding defect is suppressed and its
number density should be small, the enhancement of the black hole formation by
the increased energy density may provide a large number of evaporating black
holes in the present universe which gives more stringent constraint on the
string model compared to the ordinary string scenario.


title:
Reanalysis of the high energy cutoff of the 1997 Mkn 501 TeV energy
  spectrum

abstract:
  Data taken with the HEGRA system of imaging atmospheric Cherenkov telescopes
during the 1997 flares of Mkn 501 are reanalyzed using an algorithm providing
improved energy resolution. A resolution of 10% to 12% is obtained by
accounting for the variation of the Cherenkov light yield with the height of
the shower maximum in the atmosphere. The improved energy resolution is
particularly relevant for the study of the high-energy cutoff in the spectrum,
which might be caused by interactions with the intergalactic infrared
background radiation. The reanalysis presented here confirms the results
obtained in the previous analysis, but hints a steeper slope of the spectrum in
the region around 20 TeV.


title: A Local Void and the Accelerating Universe

abstract:
  Corresponding to the recent observational claims that we are in a local void
(an underdense region) on scales of 200 - 300 Mpc, the magnitude-redshift
relation in a cosmological model with a local void is investigated. It is
already evident that the accelerating behavior of high-z supernovae can be
explained in this model, because the local void plays a role similar to the
positive cosmological constant. In this paper the dependence of the behavior on
the gaps of cosmological parameters in the inner (low-density) region and the
outer (high-density) region, the radius of the local void, and the clumpiness
parameter is studied and its implication is discussed.


title: Evidence for compact structuring in the corona of active stars

abstract:
  The ``current wisdom'' regarding the structuring of the X-ray emitting corona
in active stars (i.e. a corona dominated by extended coronal structures) is
briefly reviewed, followed by a review of a new approach to flare analysis and
the analysis of a significant number of newly observed and previously published
large flares, all leading to a much more compactly structured corona. Recent
observations showing the polar location of the flaring plasma are then
discussed, showing how the current evidence points toward a (flaring) corona
composed of rather low-lying polar structures, also in agreement with some
recent radio VLBI observational results and with starspot Doppler images. The
resulting picture is significantly different from the solar case.


title:
Effects of the X-ray emission from young stars on the ionization level
  of a fractal star forming cloud

abstract:
  We present the initial results of a study aimed at computing the global
effects of the X-ray ionization due to young stars within a molecular cloud
that forms stars with a standard IMF at a rate accelerating with time. We model
the gas distribution of the cloud as a fractal of dimension 2.3. We introduce
the concept of a "Roentgen sphere" as the region around each PMS star where the
ionization rate due to stellar X-rays exceeds that due to interstellar cosmic
rays. Using values of the X-ray luminosity typical of T Tauri stars, we find
that within the Roentgen radius the average ionization rate is increased by a
factor 4 to 20 with respect to the value obtained from cosmic-rays.


title:
Detection of X-ray line emission from the shell of SNR B0540-69.3 with
  XMM-Newton RGS

abstract:
  We present X-ray observations of PSR 0540-69.3 with the XMM-Newton
observatory. The spectra obtained with the Reflection Grating Spectrometer
reveal, for the first time, emission from ionized species of O, Ne and Fe
originating from the SNR shell. Analysis of the emission line spectrum allows
us to derive estimates of the temperature, ionization timescale, abundances,
location, and velocity of the emitting gas.


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

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


title: Emission line oscillations in the dwarf nova V2051 Ophiuchi

abstract:
  We have detected coherent oscillations, at multiple frequencies, in the line
and continuum emission of the eclipsing dwarf nova V2051 Ophiuchi using the 10m
Keck II telescope. Our own novel data acquisition system allowed us to obtain
very fast spectroscopy using a continuous readout of the CCD on the LRIS
spectrograph. This is the first time that dwarf nova oscillations are detected
and resolved in the emission lines. The accretion disc is highly asymmetric
with a stronger contribution from the blue-shifted side of the disc during our
observations. The disc extends from close to the white dwarf out to the outer
regions of the primary Roche lobe.
  Continuum oscillations at 56.12s and its first harmonic at 28.06 s are most
likely to originate on the surface of a spinning white dwarf with the
fundamental period corresponding to the spin period. Balmer and Helium emission
lines oscillate with a period of 29.77s at a mean amplitude of 1.9%. The line
kinematics as well as the eclipse constraints indicate an origin in the
accretion disc at a radius of 12 R_wd. The amplitude of the emission line
oscillation modulates (0-4%) at a period of 488s, corresponding to the Kepler
period at R=12 R_wd. This modulation is due to the beating between the white
dwarf spin and the orbital motion in the disc.
  The observed emission line oscillations cannot be explained by a truncated
disc as in the intermediate polars. The observations suggest a non-axisymmetric
bulge in the disc, orbiting at 12R_wd, is required. The close correspondence
between the location of the oscillations and the circularisation radius of the
system suggests that stream overflow effects may be of relevance


title: Modelling Horizontal Air Showers Induced by Cosmic Rays

abstract:
  We present a framework for the study of muon density patterns on the ground
due to showers produced in the atmosphere by cosmic rays incident at high
zenith angles. As a checking procedure predictions of a model based on such a
framework are compared to simulation results.


title:
Metallicity estimates for A-, F-, and G-type stars from the
  Edinburgh-Cape blue object survey

abstract:
  The Edinburgh-Cape Blue Object Survey is an ongoing project to identify and
analyse a large sample of hot stars selected initially on the basis of
photographic colours (down to a magnitude limit B~18.0) over the entire
high-Galactic-latitude southern sky, then studied with broadband UBV photometry
and medium-resolution spectroscopy. Due to unavoidable errors in the initial
candidate selection, stars that are likely metal-deficient dwarfs and giants of
the halo and thick-disk populations are inadvertently included, yet are of
interest in their own right. In this paper we discuss a total of 206 candidate
metal-deficient dwarfs, subgiants, giants, and horizontal-branch stars with
photoelectric colours redder than (B-V)o = 0.3, and with available
spectroscopy. Radial velocities, accurate to ~10-15 km/s, are presented for all
of these stars. Spectroscopic metallicity estimates for these stars are
obtained using a recently re-calibrated relation between Ca II K-line strength
and (B-V)o colour. The identification of metal-poor stars from this
colour-selection technique is remarkably efficient, and competitive with
previous survey methods. An additional sample of 186 EC stars with
photoelectric colours in the range -0.4 < (B-V)o < 0.3, comprised primarily of
field horizontal-branch stars and other, higher-gravity, A- and B-type stars,
is also analysed. Estimates of the physical parameters Teff, log g, and [Fe/H]
are obtained for cooler members of this subsample, and a number of candidate RR
Lyrae variables are identified.


title: Very Low Mass Stars and Brown Dwarfs of the Young Open Cluster IC2391

abstract:
  We have identified a large sample of probable low mass members of the young
open cluster IC2391 based on optical (VRIZ) and Infrared (JHK$_s$) photometry.
Our sample includes 50 probable members and 82 possible members, both very low
mass stars and brown dwarfs. We also provide accurate positions for these stars
and brown dwarf candidates derived from red UK Schmidt plates measured using
the microdensitometer SuperCOSMOS. Assuming an age of 53 Myr, we estimate that
we have reached a mass of 0.025 M$_\odot$, if the identified objects are indeed
members of IC2391.