title: Measurements of atmospheric muon spectra at mountain altitude

abstract:
  We report new measurements of the atmospheric muons at mountain altitude. The
measurement was carried out with the BESS detector at the top of Mt. Norikura,
Japan. The altitude is 2,770 m above sea level. Comparing our results and
predictions given by some interaction models, a further appropriate model has
been investigated. These studies would improve accuracy of atmospheric neutrino
calculations.


title: A late-time transition in the equation of state versus Lambda-CDM

abstract:
  We study a model of the dark energy which exhibits a rapid change in its
equation of state w(z), such as occurs in vacuum metamorphosis. We compare the
model predictions with CMB, large scale structure and supernova data and show
that a late-time transition is marginally preferred over standard Lambda-CDM.


title:
Phase offsets between core and conal components of radio pulsars and
  their emission altitudes

abstract:
  We present a new method for investigating emission altitudes of radio pulsar
core and conal components by attributing them different altitudes and by
providing a framework to understand the resulting longitude offsets between
them which are frequently observed. By investigating the contributions to these
offsets due to aberration and the magnetic field line sweepback, we show that
they are always dominated by aberration for all emission altitudes and
inclination angles. This directly allows the conclusion that the core emission
does not necessarily come from the surface. Our results and the observational
trends imply that for a large number of pulsars the emission altitudes of core
and conal components are close when compared to the light cylinder radius but
not necessarily relative to the stellar radius. The core/cone altitude
differences that we find are typically larger than the individual altitudes
ascribed to them so far. Widely different core/cone altitudes for some pulsars
are also supported by data and suggest a novel explanation of the precursors in
the Crab and similar pulsars. We show that the question of emission altitudes
can not be divorced from considerations of the core/cone components' filling
factors of the polar flux tube. We propose an empirical '1/3 rule' to describe
the observed core/cone morphologies. With it core/cone phase offsets allow a
glimpse into the variation of the filling factors with altitude.


title: On the Phenomenology of Hydrodynamic Shear Turbulence

abstract:
  The question of a purely hydrodynamic origin of turbulence in accretion disks
is reexamined, on the basis of a large body of experimental and numerical
evidence on various subcritical (i.e., linearly stable) hydrodynamic flows.
  One of the main points of this paper is that the length scale and velocity
fluctuation amplitude which are characteristic of turbulent transport in these
flows scale like $Re_m^{-1/2}$, where $Re_m$ is the minimal Reynolds number for
the onset of fully developed turbulence. From this scaling, a simple
explanation of the dependence of $Re_m$ with relative gap width in subcritical
Couette-Taylor flows is developed. It is also argued that flows in the shearing
sheet limit should be turbulent, and that the lack of turbulence in all such
simulations performed to date is most likely due to a lack of resolution, as a
consequence of the effect of the Coriolis force on the large scale fluctuations
of turbulent flows.
  These results imply that accretion flows should be turbulent through
hydrodynamic processes. If this is the case, the Shakura-Sunyaev $\alpha$
parameter is constrained to lie in the range $10^{-3}-10^{-1}$ in accretion
disks, depending on unknown features of the mechanism which sustains
turbulence. Whether the hydrodynamic source of turbulence is more efficient
than the MHD one where present is an open question.


title: Correlated X-ray and optical variability in KV UMa

abstract:
  We present coordinated X-ray and optical observations of the X-ray transient
KV UMa (= XTE J1118+480) at high time resolution. The optical variation
associated with spikes in the X-rays consist of a dip preceding the spike by
0-5 s, and a peak following it. The cross-correlation function between X-rays
and optical has the same shape. It rises sharply, within 30ms of the peak of
the X-rays. The shape of the cross correlation shows significant intrinsic
variability on time scales as short as 30s. Analyzing this variability with
principal component analysis (calibrated with simulated data), we find two
statistically independent components. The first is similar to the average
cross-correlation. The second also consists of a dip followed by a peak, but on
a 3x shorter time scale. These properties of the optical light, together with
the high optical brightness of the transient, are not easily explained by
reprocessing of the X-rays.


title:
Probing the Initial Conditions of Clustered Star Formation -- Large
  Scale On-the-Fly Mapping of Orion B at FCRAO

abstract:
  In order to obtain a census of the pre-stellar and star-forming molecular
cores, we have begun an unbiased survey in CS and N2H+ of the L1630 and L1641
molecular clouds. The use of these two molecular species enables us to quantify
and disentangle the effects of depletion often seen in CS observations of dense
cores. The spectral line data will provide essential kinematical information
not present in similar studies of the sub-millimeter dust-continuum, enabling
us to examine the overall core to core velocity dispersion and study the
effects of infall and outflows around known sub-mm and infra-red sources. Here
we present our initial observations of part of L1630, taken during the
commissioning phase of the FCRAO On-the-Fly Mapping system in January 2002.


title:
Near-infrared properties of blue compact dwarf galaxies: the link
  between solar and low metallicity

abstract:
  We have obtained near-infrared images and spectra of three blue compact dwarf
galaxies of intermediate sub-solar metallicity Tol~35, Tol~3 and UM 462. This
work is part of a larger project aimed to study the star formation and the
stellar populations of low metallicity galaxies in the near-infrared. In this
frame work galaxies of intermediate metallicity represent an important step in
understanding the most extreme cases filling the gap between solar and very low
metallicity galaxies. We have observed HII region like spectra in all three
galaxies; in all cases the star formation episodes are only a few Myr old.
Consistently with a young age our spectra show no evidence for stellar
absorption features typical of supergiants, nor of [FeII] emission typical of
supernovae. The K-band gas fraction ranges from 20 to 40 % showing that gas
emission can significantly contaminate broadband near-infrared colors in young
metal-poor starbursts. We have detected molecular hydrogen in emission in all
three objects. All sources show bright knots superimposed on a lower surface
brighness envelope. The knots are identified with Super Star Clusters; six of
them are present in UM 462. In all galaxies we detect the presence of an old
stellar population.


title: Atomic diffusion in star models of type earlier than G

abstract:
  We find that the radiative diffusivity associated with the radiative
viscosity generates a mixing that diminishes the efficiency of the
gravitational settling in the external layers of stellar models corresponding
to types earlier than G. The surface abundances of chemical species predicted
by the models are successfully compared with the abundances determined in
members of the Hyades open cluster. Our modeling depends on an efficiency
parameter, which is evaluated to a value close to unity, that we calibrate in
this study.


title: Evidence for a Millisecond Pulsar in 4U 1636-53 During a Superburst

abstract:
  We report the discovery with the Proportional Counter Array on board the
Rossi X-ray Timing Explorer of highly coherent 582 Hz pulsations during the
February 22, 2001 (UT) ``superburst'' from 4U 1636-53. The pulsations are
detected during an 800 s interval spanning the flux maximum of the burst.
Within this interval the barycentric oscillation frequency increases in a
monotonic fashion from 581.89 to 581.93 Hz. The predicted orbital motion of the
neutron star during this interval is consistent with such an increase as long
as optical maximum corresponds roughly with superior conjunction of V801 Arae,
the optical companion to the neutron star in 4U 1636-53. We show that a range
of circular orbits with velocity 90 < v sin i < 175 km/s and fractional phase
0.336 > p > 0.277 for the neutron star can provide an excellent description of
the frequency and phase evolution. The average pulse profile is sinusoidal and
the time averaged pulsation amplitude, as inferred from the half amplitude of
the sinusoid is 1%, smaller than typical for burst oscillations observed in
normal thermonuclear bursts. We do not detect any higher harmonics nor the
putative subharmonic near 290 Hz. The 90% upper limits on signal amplitude at
the subharmonic and first harmonic are 0.1% and 0.06%, respectively. The
coherent pulsation provides compelling evidence for a rapidly rotating neutron
star in 4U 1636-53, and further supports the connection of burst oscillation
frequencies with the spin frequencies of neutron stars. Our results provide
further evidence that some millisecond pulsars are spun up via accretion in
LMXBs. We also discuss the implications of our orbital velocity constraint for
the masses of the components of 4U 1636-53.


title: Cosmological parameters from CMB and other data: a Monte-Carlo approach

abstract:
  We present a fast Markov Chain Monte-Carlo exploration of cosmological
parameter space. We perform a joint analysis of results from recent CMB
experiments and provide parameter constraints, including sigma_8, from the CMB
independent of other data. We next combine data from the CMB, HST Key Project,
2dF galaxy redshift survey, supernovae Ia and big-bang nucleosynthesis. The
Monte Carlo method allows the rapid investigation of a large number of
parameters, and we present results from 6 and 9 parameter analyses of flat
models, and an 11 parameter analysis of non-flat models. Our results include
constraints on the neutrino mass (m_nu < 0.3eV), equation of state of the dark
energy, and the tensor amplitude, as well as demonstrating the effect of
additional parameters on the base parameter constraints. In a series of
appendices we describe the many uses of importance sampling, including
computing results from new data and accuracy correction of results generated
from an approximate method. We also discuss the different ways of converting
parameter samples to parameter constraints, the effect of the prior, assess the
goodness of fit and consistency, and describe the use of analytic
marginalization over normalization parameters.


title:
Simulating the Sunyaev-Zel'dovich effect(s): including radiative cooling
  and energy injection by galactic winds

abstract:
  We present results on the thermal and kinetic Sunyaev-Zel'dovich (SZ) effects
from a sequence of high resolution hydrodynamic simulations of structure
formation, including cooling, feedback and metal injection. These simulations
represent a self-consistent thermal model which incorporates ideas from the
`pre-heating' scenario while preserving good agreement with the low density IGM
at z~3 probed by the Ly-a forest. Four simulations were performed, at two
different resolutions with and without radiative effects and star formation.
The long-wavelength modes in each simulation were the same, so that we can
compare the results on an object by object basis. We demonstrate that our
simulations are converged to the sub-arcminute level. The effect of the
additional physics is to suppress the mean Comptonization parameter by 20% and
to suppress the angular power spectrum of fluctuations by just under a factor
of two in this model while leaving the source counts and properties relatively
unchanged. We quantify how non-Gaussianity in the SZ maps increases the sample
variance over the standard result for Gaussian fluctuations. We identify a
large scatter in the Y-M relation which will be important in searches for
clusters using the SZ effect(s).


title:
Using Galaxy Cluster Peculiar Velocities to Constrain Cosmological
  Parameters

abstract:
  Galaxy cluster peculiar velocities can be inferred from high-sensitivity,
high-resolution multiple-frequency observations in the 30 to 400 GHz range.
While galaxy cluster counts and power spectra are sensitive to the growth
factor, peculiar velocities are sensitive to the time-derivative of the growth
factor and are hence complementary. Using linear perturbation theory, we
forecast constraints on Omega(matter), the Hubble constant today, and the
dark-energy equation of state parameter, given 820 densely sampled cluster
locations (near redshift 1) from a Lambda-CDM N-body simulation and 820
sparsely sampled cluster locations in a broader redshift range.


title:
Dust-Induced Systematic Errors in Ultraviolet-Derived Star Formation
  Rates

abstract:
  Rest-frame far-ultraviolet (FUV) luminosities form the `backbone' of our
understanding of star formation at all cosmic epochs. These luminosities are
typically corrected for dust by assuming that the tight relationship between
the UV spectral slopes and the FUV attenuations of starburst galaxies applies
for all star-forming galaxies. Data from seven independent UV experiments
demonstrates that quiescent, `normal' star-forming galaxies deviate
substantially from the starburst galaxy spectral slope-attenuation correlation,
in the sense that normal galaxies are redder than starbursts. Spatially
resolved data for the Large Magellanic Cloud suggests that dust geometry and
properties, coupled with a small contribution from older stellar populations,
cause deviations from the starburst galaxy spectral slope-attenuation
correlation. Folding in data for starbursts and ultra-luminous infrared
galaxies, it is clear that neither rest-frame UV-optical colors nor UV/H-alpha
significantly help in constraining the UV attenuation. These results argue that
the estimation of SF rates from rest-frame UV and optical data alone is subject
to large (factors of at least a few) systematic uncertainties because of dust,
which cannot be reliably corrected for using only UV/optical diagnostics.


title: A massive star-forming region in a very early stage of evolution

abstract:
  We present results from a study of two luminous IRAS sources thought to be
young massive star-forming regions and which have no previously detected radio
continuum emission: IRAS 15596-5301 and IRAS 16272-4837. Our study incorporates
sensitive ATCA radio continuum data, SEST 1.2-mm continuum (using the new SIMBA
bolometer) and line data, as well as data taken from the MSX database. The
results show that both sources are associated with dense molecular cores which
appear to host recently formed massive stars. We argue that IRAS16272 is in a
very early stage of evolution, prior to the formation of an ultra compact HII
region and that IRAS15596 is in a more advanced stage and hosts a cluster of
B-type stars.


title: Gravitational microlensing of gamma-ray blazars

abstract:
  We present a detailed study of the effects of gravitational microlensing on
compact and distant $\gamma$-ray blazars. These objects have $\gamma$-ray
emitting regions which are small enough as to be affected by microlensing
effects produced by stars lying in intermediate galaxies. We analyze the
temporal evolution of the gamma-ray magnification for sources moving in a
caustic pattern field, where the combined effects of thousands of stars are
taken into account using a numerical technique. We propose that some of the
unidentified $\gamma$-ray sources (particularly some of those lying at high
galactic latitude whose gamma-ray statistical properties are very similar to
detected $\gamma$-ray blazars) are indeed the result of gravitational lensing
magnification of background undetected Active Galactic Nuclei (AGNs).


title:
The Next Geminga: Deep Multiwavelength Observations of a Neutron Star
  Identified with 3EG J1835+5918

abstract:
  We describe Chandra, HST, and radio observations that reveal a radio-quiet
but magnetospherically active neutron star in the error circle of the
high-energy gamma-ray source 3EG J1835+5918, the brightest of the unidentified
EGRET sources at high Galactic latitude. A Chandra ACIS-S spectrum of the
ultrasoft X-ray source RX J1836.2+5925, suggested by Mirabal & Halpern as the
neutron star counterpart of 3EG J1835+5918, requires two components: a
blackbody of T~3x10^5 K and a hard tail that can be parameterized as a power
law of photon index Gamma~2. An upper limit of d < 800 pc can be derived from
the blackbody fit under an assumption of R = 10 km. Deep optical imaging with
the HST STIS CCD failed to detect this source to a limit of V > 28.5, thus
f_X/f_V > 6000 and d > 250 pc assuming the X-ray fitted temperature for the
full surface. Repeated observations with the 76 m Lovell telescope at Jodrell
Bank place an upper limit of < 0.1 mJy on the flux density at 1400 MHz for a
pulsar with P > 0.1 s, and < 0.25 mJy for a ~10 ms pulsar at the location of RX
J1836.2+5925. All of this evidence points to an older, possibly more distant
version of the highly efficient gamma-ray pulsar Geminga, as the origin of the
gamma-rays from 3EG J1835+5918.


title: Is the Cygnus Loop two supernova remnants?

abstract:
  The Cygnus Loop is classified as a middle-aged supernova remnant (SNR)
located below the Galactic equator (l=74, b=-8.6) and 770 pc away from us. Its
large size and little confusion with Galactic emission makes it an ideal test
ground for evolutionary and structural theories of SNRs. New radio continuum
mapping of the Cygnus Loop at 2695 MHz with the Effelsberg 100-m telescope
provides indications that the Cygnus Loop consists of two separate SNRs.
Combining this result with data from the literature we argue that a secondary
SNR exists in the south with a recently detected neutron star close to its
center. Two interacting SNRs seem to be the best explanation to account for the
Cygnus Loop observations at all wavelengths.


title: Radio Luminosities and Classificatory Criteria of BL Lacertae Objects

abstract:
  Using the sample of radio selected BL Lacertae objects (RBLs) and X-ray
selected BL Lacertae objects (XBLs) presented by Sambruna et al. (1996), we
calculated the luminosities of radio, optical and X-ray of each source and made
the statistical analysis among the luminosities at different wave-bands,
broad-band spectral indices from radio to X-ray ($\alpha_{\rm rx}$) and peak
frequencies ($\nu_p$). Our results are as follows: (i) there is a positive
correlation between radio luminosity $L_{\rm r}$ and $\alpha_{\rm rx}$ and a
negative correlation between $L_{\rm r}$ and $\nu_p$. High-energy peak BL Lacs
(HBLs) and low-energy peak BL Lacs (LBLs) can be distinguished very well, the
dividing lines are probably those of $\log {L_{\rm r}}=43.25$ (erg/sec) and
$\alpha_{\rm rx}>$(or $\leq $)0.75 for $L_{\rm r}$ - $\alpha_{\rm rx}$ plot and
those of $\log {L_{\rm r}}\leq 43.25$ (erg/sec) and $\log {\nu_p}>14.7$ for the
$L_{\rm r}$ - $\nu_p$ plot; (ii) there is a weak positive correlation between
optical luminosity $L_o$ and $\alpha_{\rm rx}$ and a negatively weak
correlation between $L_{\rm o}$ and $\nu_p$; (iii) there is no correlation
between X-ray luminosity $L_X$ and $\alpha_{\rm rx}$ or between $L_X$ and
$\nu_p$. From our analysis, we find that synchrotron radiation is the main
X-ray radiation mechanism for HBLs while inverse Compton scattering for LBLs.


title:
Impossibility of Spin Polarized States for Neutron Star / Proto-neutron
  Star Matter in $\beta$-Equilibrium Condition

abstract:
  It is shown explicitly that a ferromagnetic transition of neutron star (NS) /
proto-neutron star (PNS) matter in the $\beta$-equilibrium condition with
$\sigma-\omega-\rho$ exchange type of mean field approximation can actually
occur if and only if the neutrinos remain trapped within the system, and
perhaps it is also necessary for the neutrinos / anti-neutrinos to carry some
finite non-zero mass. It is further shown that the electrons also play a
significant role in this transition process. It is therefore, very much
unlikely that such a transition of spin polarization can really take place in
old neutron stars of very low temperature, whereas, the possibility of
spontaneous ferromagnetic transition cannot be ruled out in a newly born PNS.


title: Probing the dark ages with redshift distribution of GRBs

abstract:
  In this article, we explore the possibility of using the properties of gamma
ray bursts (GRBs) to probe the physical conditions in the epochs prior to
reionization. The redshift distribution of GRBs is modelled using the
Press-Schechter formalism with an assumption that they follow the cosmic star
formation history. We reproduce the observed star formation rate obtained from
galaxies in the redshift range 0 < z < 5, as well as the redshift distribution
of the GRBs inferred from the luminosity-variability correlation of the burst
light curve. We show that the fraction of GRBs at high redshifts, whose
afterglows cannot be observed in R and I band due to HI Gunn Peterson optical
depth can, at the most, account for one third of the dark GRBs. The observed
redshift distribution of GRBs, with much less scatter than the one available
today, can put stringent constraints on the epoch of reionization and the
nature of gas cooling in the epochs prior to reionization.


title: Future Pulsar Observations with H.E.S.S

abstract:
  Since their discovery at radio wavelengths pulsars have been persistent
targets for widespread multi-wave observations throughout optics, radio,
X-rays, and high-energy gamma-rays. Observations with the EGRET gamma-ray
telescope, on board Compton GRO satellite, confirmed the expectation of a
pulsed high-energy emission up to a few GeV. Presently, at least seven objects
are known as well established high-energy gamma-ray pulsars. A few of those
emit gamma-rays well above 1 GeV. Forthcoming ground-based Cherenkov telescopes
will enable observations of gamma-rays well below 100 GeV, finally reaching the
yet unexplored energy gap at tens of GeV. H.E.S.S. (High Energy Stereoscopic
System) is one of such instruments which is planned to be operational in 2004.
Here I summarize the basic scientific motivations, the H.E.S.S. sensitivity,
and the first targets for future pulsar observations at high energies from the
ground.


title: Dark-Halo Cusp: Asymptotic Convergence

abstract:
  We propose a model for how the buildup of dark halos by merging satellites
produces a characteristic inner cusp, of a density profile \rho \prop r^-a with
a -> a_as > 1, as seen in cosmological N-body simulations of hierarchical
clustering scenarios. Dekel, Devor & Hetzroni (2003) argue that a flat core of
a<1 exerts tidal compression which prevents local deposit of satellite
material; the satellite sinks intact into the halo center thus causing a rapid
steepening to a>1. Using merger N-body simulations, we learn that this cusp is
stable under a sequence of mergers, and derive a practical tidal mass-transfer
recipe in regions where the local slope of the halo profile is a>1. According
to this recipe, the ratio of mean densities of halo and initial satellite
within the tidal radius equals a given function psi(a), which is significantly
smaller than unity (compared to being 1 according to crude resonance criteria)
and is a decreasing function of a. This decrease makes the tidal mass transfer
relatively more efficient at larger a, which means steepening when a is small
and flattening when a is large, thus causing converges to a stable solution.
Given this mass-transfer recipe, linear perturbation analysis, supported by toy
simulations, shows that a sequence of cosmological mergers with homologous
satellites slowly leads to a fixed-point cusp with an asymptotic slope a_as>1.
The slope depends only weakly on the fluctuation power spectrum, in agreement
with cosmological simulations. During a long interim period the profile has an
NFW-like shape, with a cusp of 1<a<a_as. Thus, a cusp is enforced if enough
compact satellite remnants make it intact into the inner halo. In order to
maintain a flat core, satellites must be disrupted outside the core, possibly
as a result of a modest puffing up due to baryonic feedback.


title:
A theoretical study of the mass temperature relation for clusters of
  galaxies

abstract:
  I derive the mass-temperature relation and its time evolution for clusters of
galaxies in different cosmologies by means of two different models. The first
one is a modification and improvement of a model by Del Popolo & Gambera(1999),
namely based upon a modification of the top-hat model in order to take account
of angular momentum acquisition by protostructures and of an external pressure
term in the virial theorem. The second one is based on the merging-halo
formalism of Lacey & Cole (1993), accounting for the fact that massive clusters
accrete matter quasi-continuously, and is an improvement of a model proposed by
Voit (2000). The final result is that, in both models, the M-T relation shows a
break at T \sim 3-4 keV. The behavior of the M-T relation is as usual, M
\propto T^{3/2}, at the high mass end, and M \propto T^{\gamma}, with a value
of \gamma>3/2 depending on the chosen cosmology. The evolution of the M-T
relation, for a given M_{\rm vir}, is more modest both in flat and open
universes in comparison to previous estimate found in literature, even more
modest than what found by V2000. Moreover the time evolution is more rapid in
models with L=0 than in models in which the angular momentum acquisition by
protostructures is taken into account (L \neq 0). The effect of a non-zero
cosmological constant is that of slightly increasing the evolution of the M-T
relation with respect to open models with L \neq 0. The evolution is more rapid
for larger values (in absolute value) of the spectral index, n. The comparison
of the mass-temperature relation with the data by Finoguenov, Reiprich &
Bohringer (2001), shows that the FRB data is able to rule out very low Omega_0
models (<0.3), particularly in the open case, and that better fit are obtained
by LambdaCDM models and by CDM models with Omega_0>0.3.


title:
Automatic Observation Rendering (AMORE) I. On a synthetic stellar
  population's colour-magnitude diagram

abstract:
  A new method, AMORE - based on a genetic algorithm optimizer, is presented
for the automated study of colour-magnitude diagrams. The method combines
several stellar population synthesis tools developed in the last decade by or
in collaboration with the Padova group. Our method is able to recover, within
the uncertainties, the parameters -- distance, extinction, age, metallicity,
index of a power-law initial mass function and the index of an exponential star
formation rate -- from a reference synthetic stellar population. No a priori
information is inserted to recover the parameters, which is done simultaneously
and not one at a time. Examples are given to demonstrate and to better
understand biases in the results, if one of the input parameters is
deliberately set fixed to a non-optimum value.


title: The Appearance of Tau Neutrinos from a Gamma Ray Burst

abstract:
  The muon neutrinos from the Gamma Ray Bursts(GRBs) during their propagation
oscillate to tau neutrinos. The tau neutrinos can be identified by the
appearance of tau leptons which decay to muons below the detector. We examine
the prospect of detecting these tau neutrinos from individual GRBs in a large
area muon detector. We investigate for what range of values of the physical
parameters of the GRBs such as Lorentz factor, redshift(distance from the
observer) and total energy emitted in neutrino emissions the appearance of tau
neutrinos from individual GRBs will be observable in a ground based muon
detector of km^2 area. We find it will be possible to detect tau neutrino
signals from a single GRB in a ground based muon detector of km^2 area above a
muon threshold energy 30 PeV and at a zenith angle 180 degree if the energy
emitted in neutrinos is 10^53 erg and its redshift is below 0.01 or if the
energy emitted in neutrinos by the GRB is 10^54 erg and its redshift is below
0.03.


title: Protoplanetary disk in V645 Cyg as seen with H2O and methanol masers

abstract:
  Radio images of maser spots in the infrared source GL2789, connected with the
young stellar object V645 Cyg, have been obtained as a result of the radio
interferometric observations of H2O maser at 22 GHz and methanol maser at 6.7
GHz, with the VLBI arrays VLBA and EVN. It was shown that the position of the
masers coincide with the optical object within 0.2''. The maser spots are
located along the line North-South, and their position and radial velocity can
be described by a model of the Keplerian disk with a maximum radius of 40 AU
for H2O maser and 800 AU for methanol maser. The H2O and methanol maser spots
have not been resolved, and lower limits of the brightness temperature is
2x10^{13} K and 1.4x10^9 K, respectively. A model of the maser was suggested in
which the maser emission is generated in extended water and methanol envelopes
of icy planets orbiting the young star.


title: Exceptionally Bright Type Ib Supernova 1991D

abstract:
  Photometric and spectroscopic observations of the peculiar Type Ib Supernova
1991D are presented. SN 1991D was exceptionally bright for a Type Ib supernova.
The He I lines were rather weak and the velocity at the photosphere as a
function of time was unusually low. Comparison of the observed and synthetic
spectra indicates that either hydrogen was ejected with a minimum velocity of
12,000 km/s or the spectrum contained features caused by lines of Ne I. Light
curve modelling suggests that the progenitor probably had a very large radius
(~10^14 cm) and that a considerable amount of 56Ni was synthesized during the
explosion (~0.7 Msolar). We suggest a progenitor model of SN 1991D that
involves a binary system.


title: Radio Observations of Super Star Clusters in Dwarf Starburst Galaxies

abstract:
  We present new radio continuum observations of two dwarf starburst galaxies,
NGC3125 and NGC5408, with observations at 4.80GHz (6cm) and 8.64GHz (3cm),
taken with the Australia Telescope Compact Array (ATCA). Both galaxies show a
complex radio morphology with several emission regions, mostly coincident with
massive young star clusters. The radio spectral indices of these regions are
negative (with alpha ~ -0.5 - -0.7), indicating that the radio emission is
dominated by synchrotron emission associated with supernova activity from the
starburst. One emission region in NGC5408 has a flatter index (alpha ~ -0.1)
indicative of optically thin free-free emission, which could indicate it is a
younger cluster. Consequently, in these galaxies we do not see regions with the
characteristic positive spectral index indicative of optically obscured
star-formation regions, as seen in other dwarf starbursts such as Hen 2-10.


title: Edge-on boxy profiles in non-barred disc galaxies

abstract:
  Boxy edge-on profiles can be accounted for not only in models of barred
galaxies, but also in models of normal (non-barred) galaxies. Thus, the
presence of a bar is not a sine qua non condition for the appearance of this
feature, as often assumed. We show that a `boxy' or a `peanut' structure in the
central parts of a model is due to the presence of vertical resonances at which
stable families of periodic orbits bifurcate from the planar x1 family. The
orbits of these families reach in their projections on the equatorial plane a
maximum distance from the center, beyond which they increase their mean radii
by increasing only their deviations from the equatorial plane. The resulting
orbital profiles are `stair-type' and constitute the backbone for the observed
boxy structures in edge-on views of $N$-body models and, we believe, in edge-on
views of disc galaxies. Since the existence of vertical resonances is
independent of barred or spiral perturbations in the disc, `boxy' profiles may
appear also in almost axisymmetric cases.


title:
Current and Future Developments in Deep, Wide--field VLBI Continuum
  Surveys

abstract:
  I review the current status of deep, wide-field VLBI continuum surveys. I
also discuss anticipated short and long-term improvements in sensitivity (e.g.
the eEVN), and the science these developments will enable.


title:
Does IRAS 16293-2422 have a hot core? Chemical inventory and abundance
  changes in its protostellar environment

abstract:
  A detailed radiative transfer analysis of the observed continuum and
molecular line emission toward the deeply embedded young stellar object IRAS
16293-2422 is performed. The continuum modelling is used to constrain the
temperature and density distributions in the envelope, enabling quantitative
estimates of various molecular abundances. The molecular excitation analysis
reveals that the emission from some molecular species is well reproduced
assuming a constant fractional abundance throughout the envelope. The
abundances and isotope ratios are generally close to typical values found in
cold molecular clouds in these cases, and there is a high degree of deuterium
fractionation. There are, however, a number of notable exceptions. Lines
covering a wide range of excitation conditions indicate for some molecules,
e.g., H2CO, CH3OH, SO, SO2 and OCS, a drastic increase in their abundances in
the warm and dense inner region of the circumstellar envelope. The location at
which this increase occurs is consistent with the radius at which ices are
expected to thermally evaporate off the grains. In all, there is strong
evidence for the presence of a `hot core' close to the protostar, whose
physical properties are similar to those detected towards most high mass
protostars except for a scaling factor. However, the small scale of the hot gas
and the infalling nature of the envelope lead to very different chemical time
scales between low mass and high mass hot cores, such that only very rapidly
produced second-generation complex molecules can be formed in IRAS 16293-2422.
Alternatively, the ices may be liberated due to grain-grain collisions in
turbulent shear zones where the outflow interacts with the envelope.


title: Small-scale magnetic fields on late-type M-dwarfs

abstract:
  We performed kinematic studies of the evolution of small-scale magnetic
fields in the surface laters of M-dwarfs. We solved the induction equation for
a prescribed velocity field, magnetic Reynolds number, and boundary conditions
in a Cartesian box, representing a volume comprising the optically thin stellar
atmosphere and the uppermost part of the optically thick convective envelope.
The velocity field is spatially and temporally variable, and stems from
detailed radiation-hydrodynamics simulations of convectione flows in a
proto-typical late-type M-dwarf. We find dynamo action for large magnetic
Reynolds numbers. Growth time scales of the magnetic field is comparable to the
convective turn-over time scale (approximately 150 seconds). The convective
velocity field concentrates the magnetic field in sheets and tubular structures
in the inter-granular down-flows. Scaling from solar conditions suggests that
field strengths as high as 20 kG might be reached locally. Perhps surprisingly,
the magnetic Reynolds number is of the order unity in the surface layers of
cooler M-dwarfs, rendering the dynamo inoperative. In all studied cases we find
a rather low spatial filling factor of the magnetic field.


title:
The asteroseismological potential of the pulsating DB white dwarf stars
  CBS 114 and PG 1456+103

abstract:
  We have acquired 65 h of single-site time-resolved CCD photometry of the
pulsating DB white dwarf star CBS 114 and 62 h of two-site high-speed CCD
photometry of another DBV, PG 1456+103. The pulsation spectrum of PG 1456+103
is complicated and variable on time scales of about one week and could only
partly be deciphered with our measurements. The modes of CBS 114 are more
stable in time and we were able to arrive at a frequency solution somewhat
affected by aliasing, but still satisfactory, involving seven independent modes
and two combination frequencies. These frequencies also explain the discovery
data of the star, taken 13 years earlier. We find a mean period spacing of 37.1
+/- 0.7 s significant at the 98% level between the independent modes of CBS 114
and argue that they are due to nonradial g-mode pulsations of spherical degree
l=1. We performed a global search for asteroseismological models of CBS 114
using a genetic algorithm, and we examined the susceptibility of the results to
the uncertainties of the observational frequency determinations and mode
identifications (we could not provide m values). The families of possible
solutions are identified correctly even without knowledge of m. Our optimal
model suggests Teff = 21,000 K and M_* = 0.730 M_sun as well as log(M_He/M_*) =
-6.66, X_O = 0.61. This measurement of the central oxygen mass fraction implies
a rate for the ^12C(alpha,gamma)^16O nuclear reaction near S_300=180 keV b,
consistent with laboratory measurements.


title: XMM-Newton observations of the isolated neutron star RX J0806.4-4123

abstract:
  The isolated neutron star RX J0806.4-4123 was observed with XMM-Newton in
November 2000. The data from the three EPIC instruments allowed us (i) to
derive an improved X-ray position to an accuracy of 2-3'', (ii) to accumulate
the first medium-resolution soft X-ray spectra of high statistical quality and
(iii) to find a candidate for the neutron star rotation period. Although this
period of 11.3714 s is formally detected at a 3.5-\sigma level in the EPIC-pn
data, the similar pulse profiles deduced from all three EPIC instruments
increase the confidence that the period is real. The pulsed fraction of ~6%
would then be the weakest X-ray flux modulation detected from dim isolated
neutron stars. We fitted the X-ray spectra with blackbody and neutron star
atmosphere models and discuss the results with respect to the brightness limit
placed by optical images. The reduced size of the error circle on the X-ray
position should allow deeper searches for an optical counterpart.


title:
On The Wavy Symmetry of The Solar System Planetary and Satellites
  Distances Scales

abstract:
  The symmetry of the wavy undulating spacial distributions of the differences
of the mean inverse orbital velocities of the Solar system neighboring planets,
satellites and rings of the Jupiter and Saturn is discovered. The global
dependence of planetary distances scale and satellites and rings of the planets
distances scale on the sidereal period rotation and radius of the Sun has been
found.(250kb)


title: On the large-scale inhomogeneous Universe and the cosmological constant

abstract:
  We study the large-scale inhomogeneity of the Universe based on the averaging
procedure of Buchert and Ehlers. The generalized Dyer-Roeder equation for the
angular diameter distance of the inhomogeneous Universe is derived and solved
for different cosmological models. We make a comparison of certain cosmic
observables, such as the Hubble function, angular diameter
distance,cosmological correction factor of homogeneous and inhomogeneous
cosmological models, which are crucial ingredients in galaxy number counts and
gravitational lenses.


title: A mini-survey for variability in early L dwarfs

abstract:
  We report differential I-band photometry of four early L-dwarfs obtained to
study variability. We detect variability on the timescale of hours in two
objects, 2M0746425+200032 (at a level of 0.007 mag -- 6.5 sigma) and
2M1108307+683017 (0.012 mag -- 5 sigma). We also place upper limits of 0.02 mag
(1 sigma) on the variability of two others.


title: The Cold Dark Matter crisis on galactic and subgalactic scales

abstract:
  The Cold Dark Matter model describes successfully our Universe on large
scales, as has been verified by a wide range of observations. Nevertheless, in
the last years, and especially with the advances in numerical simulations, a
number of apparent inconsistencies arose between what is observed and what the
CDM model predicts on small scales. In this work, the current status of
observations on galactic and subgalactic scales is reviewed. Furthermore,
theory and observation are brought together in order to reveal the nature of
the inconsistencies and, consequently, to reveal their severity. Lastly, the
progress towards the resolution of each one of these conflicts is briefly
reviewed.


title:
Three-Dimensional Simulations of Jets from Keplerian Disks:
  Self--Regulatory Stability

abstract:
  We present the extension of previous two-dimensional simulations of the
time-dependent evolution of non-relativistic outflows from the surface of
Keplerian accretion disks, to three dimensions. The accretion disk itself is
taken to provide a set of fixed boundary conditions for the problem. The 3-D
results are consistent with the theory of steady, axisymmetric, centrifugally
driven disk winds up to the Alfv\'en surface of the outflow. Beyond the
Alfv\'en surface however, the jet in 3-D becomes unstable to non-axisymmetric,
Kelvin-Helmholtz instabilities. We show that jets maintain their long-term
stability through a self-limiting process wherein the average Alfv\'enic Mach
number within the jet is maintained to order unity. This is accomplished in at
least two ways. First, poloidal magnetic field is concentrated along the
central axis of the jet forming a ``backbone'' in which the Alfv\'en speed is
sufficiently high to reduce the average jet Alfv\'enic Mach number to unity.
Second, the onset of higher order Kelvin-Helmholtz ``flute'' modes (m \ge 2)
reduce the efficiency with which the jet material is accelerated, and transfer
kinetic energy of the outflow into the stretched, poloidal field lines of the
distorted jet. This too has the effect of increasing the Alfv\'en speed, and
thus reducing the Alfv\'enic Mach number. The jet is able to survive the onset
of the more destructive m=1 mode in this way. Our simulations also show that
jets can acquire corkscrew, or wobbling types of geometries in this relatively
stable end-state, depending on the nature of the perturbations upon them.
Finally, we suggest that jets go into alternating periods of low and high
activity as the disappearance of unstable modes in the sub-Alfv\'enic regime
enables another cycle of acceleration to super-Alfv\'enic speeds.


title: The Stellar Initial Mass Function and Beyond

abstract:
  A brief review is given of the basic observed features of the stellar IMF,
and also of some of the theoretical ideas and simulations that may help to
explain these features. The characteristic stellar mass of order one solar mass
may derive from the typical masses of the observed star-forming clumps in
molecular clouds, and the typical clump mass may in turn be determined mainly
by the Jeans mass, as is true in many numerical simulations of cloud collapse
and fragmentation. The Salpeter power law that approximates the IMF at higher
masses is less well understood, but it may result from the effects of
continuing gas accretion by the more massive forming stars together with the
effects of interactions and mergers in dense forming stellar systems. The mass
of the most massive star that forms in a cluster is observed to increase
systematically with the mass of the cluster, and the most massive clusters may
form stars that are massive enough to collapse completely to black holes.


title: Radio Point Sources and the Thermal SZ Power Spectrum

abstract:
  Radio point sources are strongly correlated with clusters of galaxies, so a
significant fraction of the thermal Sunyaev-Zel'dovich (SZ) effect signal could
be affected by point source contamination. Based on empirical estimates of the
radio galaxy population, it is shown that the rms temperature fluctuations of
the thermal SZ effect could be underestimated by as much as 30% at an observing
frequency of 30 GHz at l>1000. The effect is larger at higher multipoles. If
the recent report of excess power at small angular scales is to be explained by
the thermal SZ effect, then radio point sources at an observing frequency of 30
GHz must be a surprisingly weak contaminant of the SZ effect for low-mass
clusters.


title:
The Sunyaev-Zel'dovich angular power spectrum as a probe of cosmological
  parameters

abstract:
  The angular power spectrum of the SZ effect, C_l, is a powerful probe of
cosmology. It is easier to detect than individual clusters in the field, is
insensitive to observational selection effects and does not require a
calibration between cluster mass and flux, reducing the systematic errors which
dominate the cluster-counting constraints. It receives a dominant contribution
from cluster region between 20-40% of the virial radius and is thus insensitive
to the poorly known gas physics in the cluster centre, such as cooling or
(pre)heating. In this paper we derive a refined analytic prediction for C_l
using the universal gas-density and temperature profile and the dark-matter
halo mass function. The predicted C_l has no free parameters and fits all of
the published hydrodynamic simulation results to better than a factor of two
around l=3000. We find that C_l scales as (sigma_8)^7 times (Omega_b h)^2 and
is almost independent of all of the other cosmological parameters. This differs
from the local cluster abundance studies, which give a relation between sigma_8
and Omega_m. We also compute the covariance matrix of C_l using the halo model
and find a good agreement relative to the simulations. We estimate how well we
can determine sigma_8 with sampling-variance-limited observations and find that
for a several-square-degree survey with 1-2 arcminute resolution one should be
able to determine sigma_8 to within a few percent, with the remaining
uncertainty dominated by theoretical modelling. If the recent excess of the CMB
power on small scales reported by the CBI experiment is due to the SZ effect,
then we find sigma_8(Omega_b h/0.029)^0.3 = 1.04 +- 0.12 at the 95% confidence
level (statistical) and with a residual 10% systematic (theoretical)
uncertainty.


title:
Chandra Evidence for a Flattened, Triaxial Dark Matter Halo in the
  Elliptical Galaxy NGC 720

abstract:
  (Abridged) We present an analysis of a Chandra ACIS-S observation of the
elliptical galaxy NGC 720 to verify the existence of a dark matter (DM) halo
and to measure its ellipticity. The ACIS-S3 image reveals over 60 point
sources. For semi-major axes a<~150" (18.2h_{70}^{-1} kpc) the ellipticity of
the diffuse emission is ex ~0.15, which is less than the values 0.2-0.3
obtained from ROSAT because the point sources contaminated the ROSAT values.
The Chandra data confirm the ~20 deg position angle (PA) twist discovered by
ROSAT, but the Chandra twist is more gradual also because of the point sources
contaminating the ROSAT values. Overall the ex and PA values for a<~150" can be
explained by the triaxial model of NGC 720 published by Romanowsky & Kochanek.
Since the optical image displays no substantial isophote twisting, the X-ray PA
twist requires a massive DM halo if the hot gas is in hydrostatic equilibrium.
The mass-follows-light hypothesis is also inconsistent with the Chandra
ellipticities at the 96% (98%) level for oblate (prolate) symmetry. Thus, both
the PA twist and the ellipticities of the Chandra image imply a DM halo
independent of the gas T profile -- evidence that cannot be obviated by
alternative gravity theories such as MOND. The DM density model, rho ~a^{-2},
provides the best fit and gives ellipticities of 0.37 +/- 0.03 (0.36 +/- 0.02)
for oblate (prolate) models. These moderate ellipticities for the DM halo are
inconsistent with both the nearly spherical halos predicted if the DM is
self-interacting and with the highly flattened halos predicted if the DM is
cold molecular gas. These ellipticities may also be too large to be explained
by warm DM, but are consistent with galaxy-sized halos formed in the Lambda-CDM
paradigm.


title: X-ray temporal properties of XTE J1650-500 during outburst decay

abstract:
  We investigated the temporal behavior of the new black hole transient XTE
J1650-500 with the Rossi X-ray Timing Explorer (RXTE) as the source made a
transition to the low/hard state during the decay of the 2001 outburst. We find
QPOs in the 4 - 9 Hz range, enhanced time lags and reduced coherence during the
state transition. We also observe a shift in the peak frequency of the noise
component with energy during the transition. The evolution of the power
spectrum as well as the lag and coherence behavior during the state transition
are similar to the state transitions observed for other black hole sources,
especially Cyg X-1. The temporal properties during the transition to the low
state put constraints on the accretion geometry of XTE J1650-500 and may have
implications for all black hole binary systems. We suggest a possible geometry
and evolution of a jet+corona+disk system based on enhanced lags and peak
frequency shift during the transition.


title:
The effect of non--gravitational gas heating in groups and clusters of
  galaxies

abstract:
  We present a set of gas-dynamical simulations of galaxy groups and clusters
aimed at exploring the effect of non-gravitational heating. We use GASOLINE, a
parallel Tree+SPH code, to simulate the formation of four cosmic halos with
temperature 0.5<T<8 keV. Non-gravitational heating is implemented in two
different ways: (1) by imposing a minimum entropy floor at a given redshift,
1<z<5; (2) by gradually heating gas, proportionally to the SN rate expected
from semi-analytical modeling of galaxy formation. Our main results are the
following. (a) An extra heating energy of about 1 keV per gas particle is
required to reproduce the observed Lx-T relation, independent of whether it is
provided so as to create an entropy floor of 50-100 keV cm^2, or is modulated
in redshift; our SN feedback recipe provides only 1/3 keV/part. (b) The M-T
relation is almost unaffected by non-gravitational heating and follows the M
T^{3/2} scaling, with a normalization ~40% higher than observed, independent of
the heating scheme. The inclusion of cooling in a run of a small group has the
effects of increasing T_ew by ~30%, possibly reconciling simulated and observed
M-T relations, and of decreasing Lx by ~40%. In spite of the inclusion of SN
feedback energy, almost 40% of the gas becomes cold, in excess of current
observational estimates. (abridged)


title: The Abundances of Nitrogen and Oxygen in Damped Lyman Alpha Systems

abstract:
  We take a fresh look at the abundance of nitrogen in DLAs with oxygen
abundances between 1/10 and 1/100 of solar. This is a metallicity regime poorly
sampled in the local universe and where QSO absorbers may hold clues to both
the nucleosynthetic origin of N and the chemical evolution of high redshift
galaxies. We combine new VLT UVES observations with others from the literature
to form a sample of 10 DLAs in which the abundances of N and of one of the two
alpha-capture elements O or S have been measured. We confirm earlier reports
that the (N/O) ratio exhibits a larger range of values than other ratios of
heavy elements in DLAs; however, all 10 DLAs fall in the region of the (N/O)
vs. (O/H) plot delimited by the primary and secondary levels of nitrogen
production. Our results provide empirical evidence in support of the proposal
that intermediate mass stars (with masses less than 7 solar masses) are the
main source of primary nitrogen, so that its release into the ISM lags behind
that of oxygen, which is produced by Type II SNae. A high proportion (40%) of
the DLAs in our sample have apparently not yet attained the full primary level
of N enrichment; this finding may be an indication that the metallicity regime
we are studying preferentially picks out galaxies which have only recently
condensed out of the IGM and begun forming stars. Alternatively, the delay in
the release of N following an episode of star formation may increase with
decreasing metallicity, if stars of progressively lower masses than 4 solar
masses can synthesize N in their hotter interiors.


title:
The soft X-ray emission in a large sample of galaxy clusters with ROSAT
  PSPC

abstract:
  The study of soft X-ray emission of 38 X-ray selected galaxy clusters
observed by ROSAT PSPC indicates that the soft excess phenomenon may be a
common occurrence in galaxy clusters. Excess soft X-ray radiation, above the
contribution from the hot intra-cluster medium, is evident in a large fraction
of sources, and is clearly detected with large statistical significance in the
deepest observations. The investigation relies on new, high resolution 21 cm HI
observations. The sample selection also features analysis of infra-red images,
to further ensure reliability of results with respect to the characteristics of
Galactic absorption. The possibility of background or calibration effects as
cause of the excess emission is likewise investigated; a detailed analysis of
the distribution of the excess emission with respect to detector position and
Galactic HI column density shows that the excess emission is a genuine
celestial phenomenon. We find evidence for a preferential distribution of the
soft excess emission at distances larger than ~150-200 kpc from the centers of
clusters; this behavior may be naturally explained in the context of a
non-thermal Inverse-Compton scenario. Alternatively, we propose that the
phenomenon may be caused by thermal emission of very large-scale `warm'
filaments seen in recent hydrodynamic simulations. This new interpretation
relieves the very demanding requirements of either the traditional
intra-cluster `warm' gas and the non-thermal scenarios. We also investigate the
possibility of the soft excess originating from unresolved, X-ray faint cluster
galaxies.


title: Anisotropic Sunyaev-Zel'dovich Effect

abstract:
  The spectral distortion in the Cosmic Microwave Background Radiation (CMBR)
caused from the inverse Compton scattering of low energy CMB photons by
thermally distributed hot electrons in massive clusters of galaxies - better
known as the thermal Sunyaev-Zel'dovich effect is usually estimated by the
analytical or semi-analytical solutions of Kompaneets equation. These solutions
are based on the assumption that the scattering is isotropic, i.e., the
intensity of the CMBR remains angle-independent after scattering. In this
letter, I present the solution of the full radiative transfer equations by
incorporating anisotropic inverse Compton scattering of CMBR photons by
relativistic electrons and show that the thermal Sunyaev-Zel'dovich effect is
strongly angle-dependent. The spectral distortion in the CMBR alters
significantly in different angular directions. The amount of distortion
increases several times when the angle between the axis of symmetry and the
photon ray path is increased. It is pointed out that for anisotropic scattering
the Compton y parameter is angle dependent. Hence it is important to consider
the direction of the emergent radiation with respect to the axis of symmetry in
the electron rest frame while estimating any cosmological quantity from the
Sunyaev-Zel'dovich effect.
  ~


title:
Description of Pseudo-Newtonian Potential for the Relativistic Accretion
  Disk around Kerr Black Holes

abstract:
  We present a pseudo-Newtonian potential for accretion disk modeling around
the rotating black holes. This potential can describe the general relativistic
effects on accretion disk. As the inclusion of rotation in a proper way is very
important at an inner edge of disk the potential is derived from the Kerr
metric. This potential can reproduce all the essential properties of general
relativity within 10% error even for rapidly rotating black holes.


title: The distant Type Ia supernova rate

abstract:
  We present a measurement of the rate of distant Type Ia supernovae derived
using 4 large subsets of data from the Supernova Cosmology Project. Within this
fiducial sample, which surveyed about 12 square degrees, thirty-eight
supernovae were detected at redshifts 0.25--0.85. In a spatially-flat
cosmological model consistent with the results obtained by the Supernova
Cosmology Project, we derive a rest-frame Type Ia supernova rate at a mean
redshift $z\simeq0.55$ of $1.53 {^{+0.28}_{-0.25}} {^{+0.32}_{-0.31}} 10^{-4}
h^3 {\rm Mpc}^{-3} {\rm yr}^{-1}$ or $0.58 {^{+0.10}_{-0.09}}
{^{+0.10}_{-0.09}} h^2 {\rm SNu}$ (1 SNu = 1 supernova per century per
$10^{10}$\Lbsun), where the first uncertainty is statistical and the second
includes systematic effects. The dependence of the rate on the assumed
cosmological parameters is studied and the redshift dependence of the rate per
unit comoving volume is contrasted with local estimates in the context of
possible cosmic star formation histories and progenitor models.


title: A Steeper Stellar Mass Spectrum in the Outer Galaxy?

abstract:
  We discuss the results of high-resolution (~0.1-0.2 pc) BIMA CO observations
of the central regions of 3 molecular clouds in the far-outer Galaxy (FOG). We
identify clumps and investigate their stability by using the virial theorem,
including terms due to gravity, turbulence, magnetic field, and interclump gas
pressure, and make a comparison with clumps in local clouds (RMC and Orion B
South). While a reasonable combination of these forces can render most clumps
stable, an interesting difference between FOG and local clumps emerges when
comparing only gravity and turbulence. In the FOG these forces are in
equilibrium (virial parameter alpha ~ 1) for clumps down to the lowest masses
found (a few Msol), but for local clumps alpha ~ 1 only for clumps with masses
larger than a few tens of Msol. Thus it appears that in the FOG gravity is the
dominant force down to a much lower mass than in local clouds, implying that
gravitational collapse and star formation may occur more readily even in the
smallest clumps. This might explain the apparently steeper IMF found in the
outer Galaxy.


title: Dust en-route to Jupiter and the Galilean satellites

abstract:
  Spacecraft investigations during the last ten years have vastly improved our
knowledge about dust in the Jovian system. All Galilean satellites, and
probably all smaller satellites as well, are sources of dust in the Jovian
system. In-situ measurements with the dust detectors on board the Ulysses and
Galileo spacecraft have for the first time demonstrated the electromagnetic
interaction of charged dust grains with the interplanetary magnetic field and
with a planetary magnetosphere. Jupiter's magnetosphere acts as a giant
mass-velocity spectrometer for charged 10-nanometer dust grains. These dust
grains are released from Jupiter's moon Io with typical rate of 1 kg s^1. The
dust streams probe the plasma conditions in the Io plasma torus and can be used
as a potential monitor of Io's volcanic plume activity. The other Galilean
satellites are surrounded by tenuous impact-generated clouds of mostly
sub-micrometer ejecta grains. Galileo measurements have demonstrated that
impact-ejecta derived from hypervelocity impacts onto satellites are the major
-- if not the only -- constituent of dusty planetary rings. We review the
in-situ dust measurements at Jupiter and give an update of most recent results.


title: The WEBT BL Lac Campaign 2000

abstract:
  We present UBVRI light curves of BL Lacertae from May 2000 to January 2001,
obtained by 24 telescopes in 11 countries. More than 15000 observations were
performed in that period, which was the extension of the Whole Earth Blazar
Telescope (WEBT) campaign originally planned for July-August 2000. Rapid flux
oscillations are present all the time, involving variations up to a few tenths
of mag on hour time scales, and witnessing an intense intraday activity of this
source. Colour indexes have been derived by coupling the highest precision B
and R data taken by the same instrument within 20 min and after subtracting the
host galaxy contribution from the fluxes. The 620 indexes obtained show that
the optical spectrum is weakly sensitive to the long-term trend, while it
strictly follows the short-term flux behaviour, becoming bluer when the
brightness increases. Thus, spectral changes are not related to the host galaxy
contribution, but they are an intrinsic feature of fast flares. We suggest that
the achromatic mechanism causing the long-term flux base-level modulation can
be envisaged in a variation of the relativistic Doppler beaming factor, and
that this variation is likely due to a change of the viewing angle. Discrete
correlation function (DCF) analysis reveals the existence of a characteristic
time scale of variability of about 7 h in the light curve of the core WEBT
campaign, while no measurable time delay between variations in the B and R
bands is found.


title:
Discovery of the host galaxy of HDF850.1, the brightest sub-mm source in
  the Hubble Deep Field

abstract:
  Despite extensive observational efforts, the brightest sub--mm source in the
Hubble Deep Field, HDF850.1, has failed to yield a convincing optical/infrared
identification almost 4 years after its discovery. This failure is all the more
notable given the availability of supporting multi-frequency data of
unparalleled depth, and sub-arcsec positional accuracy for the sub-mm/mm
source. Consequently, HDF850.1 has become a test case of the possibility that
the most violently star-forming objects in the universe are too red and/or
distant to be seen in the deepest optical images. Here we report the discovery
of the host galaxy of HDF850.1. This object has been revealed by careful
analysis of a new, deep K-prime image of the HDF obtained with the Subaru 8.2-m
telescope. Its reality is confirmed by a similar analysis of the HST NICMOS
F160W image of the same region. This object is extremely faint (K=23.5), clumpy
(on sub-arcsec scales) and very red (I-K > 5.2; H-K = 1.4 +- 0.35). The
likelihood that it is the correct identification is strongly reinforced by a
reanalysis of the combined MERLIN+VLA 1.4-GHz map of the field which yields a
new radio detection of HDF850.1 only 0.1 arcsec from the new near-ir
counterpart, and with sufficient positional accuracy to exclude all previously
considered alternative optical candidates. We have calculated new confidence
limits on the estimated redshift of HDF850.1 and find z = 4.1 +- 0.5. We also
calculate that the flux density of HDF850.1 has been boosted by a factor of ~3
through lensing by the intervening elliptical 3-586.0, consistent with
predictions that a small but significant fraction of blank-field sub-mm sources
are lensed by foreground galaxies. We discuss the wider implications of these
results for the sub-mm population and cosmic star-formation history.


title: Particle Acceleration in Supernova Remnants and Pulsar Wind Nebulae

abstract:
  While supernova remnants (SNRs) have long been considered prime candidates
for the source of cosmic rays, at least to energies up to ~10^14 eV, it is only
over the past several years that direct evidence of such energetic particles in
SNRs has been uncovered. X-ray observations of several shell-type SNRs have now
revealed sites dominated by nonthermal emission, indicating an electron
population whose energy extends far beyond the thermal distribution typical of
such SNRs. In other remnants, discrepancies between the shock velocity and the
electron temperature points to a strong cosmic ray component that has
essentially thrived at the expense of the thermal component of the gas.
Modeling of the radio, X-ray, and gamma-ray emission provides strong
constraints on the acceleration mechanism as well as the properties of the
ambient medium in which the mechanism prospers. In the innermost regions of
some SNRs, particle acceleration is taking place over much different scales.
The formation of Crab-like pulsar wind nebulae (PWNe) is understood to require
the presence of a termination shock at which the relativistic pulsar wind is
forced to join the slow expansion of the outer nebula. While the acceleration
mechanism is necessarily different, these shocks also act as sites in which
particles are boosted to high energies. In the Crab Nebula, optical wisps mark
the location of this termination shock. Recent X-ray observations have begun to
reveal the termination shock zones in other PWNe, and are now allowing us to
constrain the nature of the pulsar wind as well as the flow conditions in the
outer nebula. Here I present a summary of the properties of shock acceleration
in these two distinct regions of SNRs, and review recent observational results
in which the properties of the shocks are finally being revealed.


title: The Supermassive Black Hole in the Gamma-ray Loud Blazar PKS 1510-089

abstract:
  We present the optical light curve for the gamma-ray blazar PKS 1510-089 with
a significant variability of 2.0 mag within about 41 minutes in the R band
which is the most violently rapid variability detected in our optical
monitoring campaign operating since 1982. In the framework of the relativistic
beaming model, the central supermassive black hole mass of PKS 1510-089 is of
$(1.16-1.98)\times10^8M_\odot$. This is larger than some previous estimates for
the central mass in blazars that have been based on models for nonthermal
emission, but is consistent with the estimated result of the
$M_\bullet-\sigma_\star$ correlation. Some other physical parameters, including
the emission region size, Doppler factor $\delta$, the efficiency $\eta$ for
conversion of accreted matter into energy and luminosity are calculated. The
value of $\eta$ = 62.2 strongly implies that the relativistic beaming is
responsible for the rapid variability of the gamma-ray loud blazar PKS
1510-089.


title: Deprojection of luminosity functions of galaxies in the Coma cluster

abstract:
  We use a simple analytic model to deproject 2-d luminosity functions (LF) of
galaxies in the Coma cluster measured by Beijersbergen et al. 2002. We
demonstrate that the shapes of the LFs change after deprojection. It is
therefore essential to correct LFs for projection effects. The deprojected LFs
of the central area have best-fitting Schechter parameters of
M^{*}_U=-18.31^{+0.08}_{-0.08} and \alpha_U=-1.27^{+0.018}_{-0.018},
M^{*}_B=-19.79^{+0.14}_{-0.15} and \alpha_B=-1.44^{+0.016}_{-0.016} and
M^{*}_r=-21.77^{+0.20}_{-0.28} and \alpha_r=-1.27^{+0.012}_{-0.012}. The
corrections are not significant enough to change the previously observed trend
of increasing faint end slopes with increasing distance to the cluster center.
The weighted U, B, and r band slopes of the deprojected LFs show a slightly
weaker steepening with increasing projected cluster radius.


title:
Astrophysical magnetic field reconstruction and spectroscopy with ultra
  high energy cosmic rays

abstract:
  The next generation of ultra high energy cosmic ray experiments will probably
detect several dozens of events clustered around the direction towards each of
the most powerful extragalactic sources. We develop a method which could make
possible to reconstruct, from the arrival directions and energies of the
clustered events, the strength and coherence properties of the magnetic field
along the line of sight towards the sources. The method exploits peculiar
signatures arising from magnetic lensing effects, such as the strong flux
magnification of multiple images around caustics. We also discuss how to obtain
information about the cosmic ray composition, and apply this method to samples
of simulated data.


title: Do Herbig Ae/Be Stars have Discs?

abstract:
  H_alpha spectropolarimetry on Herbig Ae/Be stars shows that the innermost
regions of intermediate mass (2 -- 15 M_sun) Pre-Main Sequence stars are
flattened. This may be the best evidence to date that the higher mass Herbig Be
stars are embedded in circumstellar discs.
  A second outcome of our study is that the spectropolarimetric signatures for
the lower mass Herbig Ae stars differ from those of the higher mass Herbig Be
stars. Depolarisations across H_alpha are observed in the Herbig Be group,
whereas line polarisations are common amongst the Herbig Ae stars in our
sample. These line polarisation effects can be understood in terms of a compact
H_alpha source that is polarised by a rotating disc-like configuration. The
difference we detect between the Herbig Be and Ae stars may be the first
indication that there is a transition in the Hertzsprung-Russell Diagram from
magnetic accretion at spectral type A to disc accretion at spectral type B.
However, it is also possible that the compact polarised line component, present
in the Herbig Ae stars, is masked in the Herbig Be stars due to their higher
levels of H_alpha emission.


title:
A Deep Optical Observation for an Enigmatic Unidentified Gamma-Ray
  Source 3EG J1835+5918

abstract:
  We report a deep optical imaging observation by the Subaru telescope for a
very soft X-ray source RX J1836.2+5925, which has been suspected to be an
isolated neutron star associated with the brightest as-yet unidentified EGRET
source outside the Galactic plane, 3EG J1835+5918. An extended source having a
complex, bipolar shape is found at B ~ 26, and this might be an extended pulsar
nebular whose flux is about 5-6 orders of magnitude lower than gamma-ray flux,
although finding a galaxy of this magnitude by chance in the error circle is of
order unity. We have found two even fainter, possibly point sources at B ~ 28,
although their detections are not firm because of low signal-to-noise. If the
extended object of B ~ 26 is a galaxy and not related to 3EG J1835+5918, a
lower limit on X-ray/optical flux ratio is set as f_X/f_B >~ 2700, giving a
further strong support of the neutron-star identification of 3EG J1835+5918.
Interestingly, if either of the two sources at B ~ 28 is the real counterpart
of RX J1836.2+5925 and thermal emission from the surface of an isolated neutron
star, the temperature and distance to the source become ~ 4 x 10^5K and ~300pc,
respectively, showing a striking similarity of its spectral energy distribution
to the proto-type radio-quiet gamma-ray pulsar Geminga. No detection of
nonthermal hard X-ray emission is consistent with the ASCA upper limit, if the
nonthermal flux of 3EG J1835+5918/RX J1836.2+5925 is at a similar level with
that of Gemiga.


title:
Spin-Induced Disk Precession in the Supermassive Black Hole at the
  Galactic Center

abstract:
  Sgr A* is a compact radio source at the Galactic Center, thought to be the
radiative manifestation of a $2.6\times 10^6 M_\odot$ supermassive black hole.
At least a portion of its spectrum--notably the mm/sub-mm ``bump''--appears to
be produced within the inner portion ($r< 10 r_S$) of a hot, magnetized
Keplerian flow, whose characteristics are also consistent with the $\sim 10%$
linear polarization detected from this source at mm wavelengths. (The
Schwarzschild radius, $r_S$, for an object of this mass $M$ is $2GM/c^2\approx
7.7\times 10^{11}$ cm, or roughly 1/20 A.U.) The recent detection of a 106-day
cycle in Sgr A*'s radio variability adds significant intrigue to this picture,
since it may signal a precession of the disk induced by the spin $a$ of the
black hole. The dynamical time scale near the marginally stable orbit around an
object with this mass is $\approx 20$ mins. Thus, since the physical conditions
associated with the disk around Sgr A* imply rigid-body rotation, a precession
period of 106 days may be indicative of a small black hole spin if the
circularized flow is confined to a region $\sim 30 r_S$, for which $a\approx
(M/10) (r_o/30 r_S)^{5/2}$. The precession of a larger structure would require
a bigger black hole spin. We note that a small value of $a/M$ ($< 0.1$) would
be favored if the non-thermal ($\sim 1-20$ cm) portion of Sgr A*'s spectrum is
powered with energy extracted via a Blandford-Znajek type of process, for which
the observed luminosity would correspond to an outer disk radius $r_o\sim 30
r_S$. Such a small disk size is also suggested by earlier hydrodynamical
simulations, and is implied by Sgr A*'s spectral and polarimetric
characteristics.


title: X-ray Lines From Gamma-ray Bursts

abstract:
  X-ray lines have been recently detected in the afterglows of a few gamma-ray
bursts. We derive constraints on the physical conditions in the line-emitting
gas, using as an example the multiple K$_\alpha$ lines detected by Reeves et
al. (2002) in GRB 011211. We argue that models previously discussed in the
literature require either a very extreme geometry or too much mass in the
line-emitting region. We propose a new model in which gamma-rays and radiation
from the early x-ray afterglow are back-scattered by an electron-positron pair
screen at a distance of about $10^{14}-10^{15}$ cm from the source and
irradiate the expanding outer layers of the supernova ejecta, thereby producing
x-ray lines. The model suffers from fewer problems compared to previous models.
It also has the advantage of requiring only a single explosion to produce both
the GRB and the supernova ejecta, in contrast to most other models for the
lines which require the supernova to go off days or weeks prior to the GRB. The
model, however, has difficulty explaining the $>10^{48}$ ergs of energy emitted
in the x-ray lines, which requires somewhat extreme choices of model
parameters. The difficulties associated with the various models are not
particular to GRB 011211. They are likely to pose a problem for any GRB with
x-ray lines.


title:
Analytic expressions for mean magnification by a quadrupole
  gravitational lens

abstract:
  We derive an analytic expression for the mean magnification due to strong
gravitational lensing, using a simple lens model, a singular isothermal sphere
embedded in an external shear field. We compute separate expressions for
2-image and 4-image lensing. For 4-image lensing, the mean magnification takes
a particularly simple form: <mu>_4 = 3.6/(gamma*(1-gamma^2)), where gamma is
the external shear. We compare our analytic results to a numerical evaluation
of the full magnification distribution. The results can be used to understand
the magnification bias that favors the discovery of four-image systems over
two-image systems in flux-limited lens surveys.


title:
The Cluster Mass Function from Early SDSS Data: Cosmological
  Implications

abstract:
  The mass function of clusters of galaxies is determined from 400 deg^2 of
early commissioning imaging data of the Sloan Digital Sky Survey; ~300 clusters
in the redshift range z = 0.1 - 0.2 are used. Clusters are selected using two
independent selection methods: a Matched Filter and a red-sequence color
magnitude technique. The two methods yield consistent results. The cluster mass
function is compared with large-scale cosmological simulations. We find a
best-fit cluster normalization relation of sigma_8*omega_m^0.6 = 0.33 +- 0.03
(for 0.1 ~< omega_m ~< 0.4), or equivalently sigma_8 = (0.16/omega_m)^0.6. The
amplitude of this relation is significantly lower than the previous canonical
value, implying that either omega_m is lower than previously expected (omega_m
= 0.16 if sigma_8 = 1) or sigma_8 is lower than expected (sigma_8 = 0.7 if
omega_m = 0.3). The best-fit mass function parameters are omega_m = 0.19
(+0.08,-0.07) and sigma_8 = 0.9 (+0.3,-0.2). High values of omega_m (>= 0.4)
and low sigma_8 (=< 0.6) are excluded at >~ 2 sigma.


title: Multiwavelength Searches of Unidentified EGRET Sources

abstract:
  3EG J1835+5918 is the brightest of the so-called unidentified EGRET sources
at intermediate galactic latitude (l,b)=(89,25). We obtained complete radio,
optical, and X-ray coverage of its error box, discovering a faint ultrasoft
X-ray source in the ROSAT All-Sky Survey. Deep optical imaging at the location
of this source, as pinpointed by an observation with the ROSAT HRI, reveals a
blank field to a limit of V > 25.2. The corresponding lower limit on f_X/f_V is
300, which signifies that the X-ray source 3EG J1835+5918 is probably a
thermally emitting neutron star. Here we report on recent Chandra and HST
observations that strengthen this identification. 3EG J1835+5918 may thus
become the prototype of an hypothesized population of older pulsars, born in
the Gould belt, that can account for as many as 40 local EGRET sources. In
addition to 3EG 1835+5918, we review the ongoing multiwalength effort by
members of our group to study other unidentified EGRET sources using X-ray,
optical, and radio data.


title: The Magnetorotational Instability in a Collisionless Plasma

abstract:
  We consider the linear axisymmetric stability of a differentially rotating
collisionless plasma in the presence of a weak magnetic field; we restrict our
analysis to wavelengths much larger than the proton Larmor radius. This is the
kinetic version of the magnetorotational instability explored extensively as
mechanism for magnetic field amplification and angular momentum transport in
accretion disks. The kinetic calculation is appropriate for hot accretion flows
onto compact objects and for the growth of very weak magnetic fields, where the
collisional mean free path is larger than the wavelength of the unstable modes.
We show that the kinetic instability criterion is the same as in MHD, namely
that the angular velocity decrease outwards. However, nearly every mode has a
linear kinetic growth rate that differs from its MHD counterpart. The kinetic
growth rates also depend explicitly on beta, i.e., on the ratio of the gas
pressure to the pressure of the seed magnetic field. For beta ~ 1 the kinetic
growth rates are similar to the MHD growth rates while for beta >> 1 they
differ significantly. For beta >> 1, the fastest growing mode has a growth rate
of sqrt{3} Omega for a Keplerian disk, larger than its MHD counterpart; there
are also many modes whose growth rates are negligible, < beta^{-1/2} Omega <<
Omega. We provide a detailed physical interpretation of these results and show
that gas pressure forces, rather than just magnetic forces, are central to the
behavior of the magnetorotational instability in a collisionless plasma. We
also discuss the astrophysical implications of our analysis.


title: X-ray Arc Structures in Chandra Images of NGC5128 (Centaurus A)

abstract:
  We describe results from our initial study of the diffuse X-ray emission
structures in NGC 5128 (Cen A) using the Chandra X-ray Observatory
observations. The high-angular resolution Chandra images reveal multi-scale
X-ray struct ures with unprecedented detail and clarity. The large scale
structures suggest complex symmetry, including a component possibly associated
with the inner radio lobes, and a separate component with an orthogonal
symmetry that may be associated with the galaxy as a whole. We detect arc-like
soft X-ray structures, extending to ~8 kpc in the direction perpendicular to
the jet. These arcs appear to be tracing an ellipse, or a ring seen in
projection, and ar e enclosed between the dust and HI emitting gas in the
central region of the galaxy, and the optical and HI shell fragments at a
distance of about 8-10 kpc. The diffuse X-ray and the optical emission in the
arcs could originate in a region of interaction (possibly a shock) between the
infalling material from the outer regions of the galaxy, and the cool dust and
HI emitting material in the center, or an equatorial outflow resulting from an
outburst of nuclear activity ~10^7 years ago.


title: Molecular Gas and the Young Starburst in NGC 5253, Revisited

abstract:
  We report the detection of CO(2-1) and 3.1 mm and 1.3 mm continuum emission
towards the extremely young starburst in NGC 5253, with data taken from the
Owens Valley Millimeter Array. Faint CO emission originates in five molecular
clouds distributed along the prominent dust lane seen in visual images. With
the gas, the morphology of NGC 5253 looks much like a dwarf elliptical version
of the ``dust-lane ellipticals'' or ``polar-ring'' class of galaxies. The
molecular gas resides in GMCs well away from the radio-IR super-star
cluster/supernebula seen in the radio and infrared. The millimeter continuum
data confirm that the 2 cm flux from the supernebula is optically thick; the
Lyman continuum rate derived from the 1.3 mm continuum is N$_{Lyc} \sim
6x10^{52} s^{-1}$ for the central ~20''. CO may underestimate the true
molecular column density, as expected for a low metallicity system, although
there are regions along the dust lane that appear to have near-Galactic
conversion factors. We estimate a total molecular gas mass of $M_{H_{2}}\lsim
10^{7} M_{\odot}$. The molecular gas in the dust lane is falling into the
galaxy, supporting an accretion hypothesis. The dust lane gas cannot therefore
be causally associated with the current burst of star formation. A relatively
small amount, $M_{H_{2}}\lsim 5x10^{5} M_{\odot}$, of molecular gas is
associated with the current starburst. We estimate a star formation efficiency
of at least 25 % and more likely ~75 %, consistent with the formation of a
bound cluster. Despite the extreme youth of the starburst, the specific trigger
of the starburst remains elusive, although the infall of gas in the dust lane
suggests that there is more star formation to come in NGC 5253.


title: K-Band Red Clump Distance to the Large Magellanic Cloud

abstract:
  The Hipparcos I-band calibration of horizontal-branch red clump giants as
standard candles has lead to controversial results for the distance to the
Large Magellanic Cloud (LMC). In an attempt to properly ascertain the
corrections for interstellar extinction and clump age and metallicity, we
analyze new multi-wavelength luminosity functions of the LMC red clump. Our
photometry dataset in the K-band was obtained with the SOFI infrared imager at
the European Southern Observatory's New Technology Telescope. In the V and I
passbands, we employ data from WFPC2 onboard the Hubble Space Telescope. The
LMC red clump is first identified in a K,(V-K) color-magnitude diagram. Our
luminosity functions yield apparent magnitudes of K = 16.974, I = 18.206, and V
= 19.233 (+- 0.009_r +- 0.02_s; random and systematic error, respectively).
Compared directly to the Hipparcos red clump calibration (without a correction
for age and metallicity), the LMC clump measurements imply a negative
interstellar reddening correction. This unphysical result indicates a
population difference between clumps. A modified calibration based on
theoretical modeling yields an average reddening correction of E(B-V) = 0.089
+- 0.015_r, and a true LMC distance modulus of 18.493 +- 0.033_r +- 0.03_s. We
reconcile our result with the short distance previously derived from OGLE II
red clump data.


title: T Tauri Stars in the Small Magellanic Cloud

abstract:
  The Small Magellanic Cloud (SMC) is an excellent laboratory to study the
formation of solar-mass stars in a low-metallicity environment, similar to the
conditions expected in the early phases of galactic evolution. Here we present
preliminary results from a search for low-mass pre-main-sequence stars in the
SMC based on Hubble Space Telescope archival data. Candidates are selected on
the basis of their H_alpha emission and location in the [(F675W-F814W), F814W]
color-magnitude diagram. We discuss characteristics of our candidate T Tauri
sample and possible follow up work.


title: A Helical Magnetic Field in the Jet of 3C 273

abstract:
  Both in the Faraday Rotation Measure and the intrinsic polarization angle,
new features are revealed to indicate a helical magnetic field operating along
the jet of the bright active galactic nuclei 3C 273. The helical field has been
suggested to be related to the formation and collimation of jets by
magnetohydrodynamic models. The distribution of the RM shows a systematic
gradient with respect to the jet axis, which is expected by a helical magnetic
field. In addition, the helical field can consistently explain two types in the
direction of the projected magnetic field: parallel and perpendicular to the
jet axis. Further, if the helical magnetic field is generated by winding up of
an initial field by rotation of the accretion disk, we can uniquely determine
the direction of the disk rotation, since the jet is approaching us.


title: A photometric study of the young open cluster NGC 1220

abstract:
  We present UBV CCD observations obtained in the field of the northern open
cluster NGC 1220, for which little information is available. We provide also BV
CCD photometry of a field 5$^{\prime}$ northward of NGC 1220 to take into
account field star contamination. We argue that NGC 1220 is a young compact
open cluster, for which we estimate a core radius in the range $1.5-2.0$
arcmin. We identify 26 likely candidate members with spectral type earlier than
$A5$, down to $V_o$=15.00 mag on the basis of the position in the two-colour
Diagram and in the Colour Magnitude Diagrams (CMDs). By analyzing the
distribution of these stars in the colour-colour and CMDs, we find that NGC
1220 has a reddening E$(B-V)=0.70\pm0.15$ mag, is placed $1800\pm200$ pc
distant from the Sun, and has an age of about 60 Myrs. The cluster turns out to
be located about 120 pc above the Galactic plane, relatively high with respect
to its age.


title:
Variations of the TeV energy spectrum at different flux levels of Mkn
  421 observed with the HEGRA system of Cherenkov telescopes

abstract:
  The nearby BL Lacertae (BL Lac) object Markarian~421 (Mkn~421) at a red shift
z=0.031 was observed to undergo strong TeV Gamma-ray outbursts in the
observational periods from December 1999 until May 2001. The time averaged
energy spectrum is well described by a power law with an exponential cut-off
energy at 3.6(+0.4-0.3)_{stat}(+0.9-0.8)_{sys} TeV.
  The energy spectra derived for different average flux levels ranging from 0.5
to 10 * 10^{-11}ph/cm**2/s follow a clear correlation of photon index and flux
level.
  Generally, the energy spectra are harder for high flux levels. From January
to April 2001 Mkn~421 showed rapid variability (doubling time as short as 20
minutes), accompanied with a spectral hardening with increasing flux level
within individual nights.
  For two successive nights (MJD 51989-51991, March 21-23,2001), this
correlation of spectral hardness and change in flux has been observed within a
few hours. The cut-off energy for the Mkn~421 TeV spectrum remains within the
errors constant for the different flux levels and differs by
2.6+/-0.6_stat+/-0.6_sys TeV from the value determined for Mkn~501. This
indicates that the observed exponential cut-off in the energy spectrum of
Mkn~421 is not solely caused by absorption of multi-TeV photons by
pair-production processes with photons of the extragalactic near/mid infrared
background radiation.


title: Twenty years of TIRGO telescope

abstract:
  We present the characteristics and the current status of the "Telescopio
Infrarosso del Gornergrat" (Tirgo), the national infrared facility operating
from the beginning of the 80s over the swiss alps. We describe its current
instrumentation and resume its activities during its 20 years of life.


title:
ESO Imaging Survey. The Stellar Catalogue in the Chandra Deep Field
  South

abstract:
  (abridged) Stellar catalogues in five passbands (UBVRI) over an area of
approximately 0.3 deg^2, comprising about 1200 objects, and in seven passbands
(UBVRIJK) over approximately 0.1 deg^2, comprising about 400 objects, in the
direction of the Chandra Deep Field South are presented.
  The 90% completeness level of the number counts is reached at approximately U
= 23.8, B = 24.0, V = 23.5, R = 23.0, I = 21.0, J = 20.5, K = 19.0.
  A scheme is presented to select point sources from these catalogues, by
combining the SExtractor parameter CLASS_STAR from all available passbands.
  Probable QSOs and unresolved galaxies are identified by using the previously
developed \chi^2-technique (Hatziminaoglou et al 2002), that fits the overall
spectral energy distributions to template spectra and determines the best
fitting template.
  The observed number counts, colour-magnitude diagrams, colour-colour diagrams
and colour distributions are presented and, to judge the quality of the data,
compared to simulations based on the predictions of a Galactic Model convolved
with the estimated completeness functions and the error model used to describe
the photometric errors of the data.
  The resulting stellar catalogues and the objects identified as likely QSOs
and unresolved galaxies with coordinates, observed magnitudes with errors and
assigned spectral types by the $\chi^2$-technique are presented and are
publicly available.


title:
The Southern Dwarf Hunt: Local Group Dwarf Candidates in the Southern
  Sky

abstract:
  We present observations of 82 Local Group dwarf galaxy candidates, of which
62 were chosen visually from ESO-SRC survey plates of the southern sky (32 of
which were not previously catalogued) and the rest suggested by various sources
in the literature. Two are the Local Group galaxies Antlia and Cetus; nine are
more distant galaxies, though still within a few megaparsecs; 45 are background
galaxies; seven are planetary (or other emission) nebulae; 15 are reflection or
other Galactic nebulae; two are galaxy clusters; one is a Galactic star cluster
and one is a misidentified star. We conclude that there is no large population
of faint Local Group dwarf galaxies of any familiar type awaiting discovery. We
point out the danger of relying on a single type of data to reach conclusions
about an object.


title: H2 formation and excitation in the diffuse interstellar medium

abstract:
  We use far-UV absorption spectra obtained with FUSE towards three late B
stars to study the formation and excitation of H2 in the diffuse ISM. The data
interpretation relies on a model of the chemical and thermal balance in
photon-illuminated gas. The data constrain well the nR product between gas
density and H2 formation rate on dust grains: nR = 1 to 2.2 e-15 s-1. For each
line of sight the mean effective H2 density n, assumed uniform, is obtained by
the best fit of the model to the observed N(J=1)/N(J=0) ratio, since the
radiation field is known. Combining n with the nR values, we find similar H2
formation rates for the three stars of about R = 4 e-17 cm3/s.
  Because the target stars do not interact with the absorbing matter we can
show that the H2 excitation in the J>2 levels cannot be accounted for by the UV
pumping of the cold H2 but implies collisional excitation in regions where the
gas is much warmer. The existence of warm H2 is corroborated by the fact that
the star with the largest column density of CH+ has the largest amount of warm
H2.


title: Cosmology with Varying Constants

abstract:
  The idea of possible time or space variations of the `fundamental' constants
of nature, although not new, is only now beginning to be actively considered by
large numbers of researchers in the particle physics, cosmology and
astrophysics communities. This revival is mostly due to the claims of possible
detection of such variations, in various different contexts and by several
groups. Here, I present the current theoretical motivations and expectations
for such variations, review the current observational status, and discuss the
impact of a possible confirmation of these results in our views of cosmology
and physics as a whole.


title: Cosmological Constraint from the 2dF QSO Spatial Power Spectrum

abstract:
  In this paper we obtain constraints on the cosmological density parameters,
\Omega_m and \Omega_b, by comparing the preliminary measurement of the QSO
power spectrum from the two degree field QSO redshift survey with results from
an analytic technique of power spectrum estimation, described in this paper. We
demonstrate the validity of the analytic approach by comparing the results with
the power spectrum of an N-body simulation. We find a better fit to the shape
of the QSO power spectrum for low density models with \Omega_m= 0.1-0.4. We
show that a finite baryon fraction \Omega_b/\Omega_m=0.2, consistent with
observations of the CMB anisotropies and nucleosynthesis, fits the
observational result of the 2QZ survey better, though the constraint is not
very tight. By using the Fisher matrix technique, we investigate just how a
survey would be required before a significant constraint on the density
parameters can be made. We demonstrate that the constraint could be
significantly improved if the survey was four times larger.


title: Shape Alignments of Satellite Galaxies

abstract:
  We test a sample of satellites of isolated primary galaxies, extracted from
the 2dF Galaxy Redshift Survey (2dFGRS), for any tendency to be aligned along
(or against) the primary-to-satellite radius vector. If tidal effects induce
such an alignment, it would contaminate recent measurements of galaxy halo
masses which use the coherent alignment induced on background galaxies by
gravitational lensing. The mean tangential ellipticity of 1819 satellites
within 500 kpc projected radius is <e_+> = +0.004+-0.008, so no tidal alignment
is detected. This implies at 95% confidence that satellite alignment is less
than a 20% contamination of the alignment signal attributed to galaxy-galaxy
lensing by Smith et al. (2001) and McKay et al. (2001).


title: Optical spectroscopy of radio galaxies in the 7C Redshift Survey

abstract:
  We present optical spectroscopy of all 49 radio galaxies in the 7C-I and
7C-II regions of the 7C Redshift Survey (7CRS). The low-frequency (151 MHz)
selected 7CRS sample contains all sources with flux-densities S_151 > 0.5 Jy in
three regions of the sky; 7C-I and 7C-II were chosen to overlap with the 5C6
and 5C7 surveys respectively, and cover a total sky area of 0.013 sr. The
sample has been completely identified and spectroscopy of the quasars and
broad-lined radio galaxies has been presented in Willott et al. (1998). Only
seven of the radio galaxies do not have redshift determinations from the
spectroscopy, giving a redshift completeness for the sample of >90%. The median
redshift of the 7CRS is 1.1. We present a composite 0.2<z<0.8 7CRS radio galaxy
spectrum and investigate the strengths of the 4000 Angstrom breaks in these
radio galaxies. We find an anti-correlation between the 4000 Angstrom break
strength and emission line luminosity, indicating that departures from old
elliptical galaxy continuum shapes are most likely due to non-stellar emission
associated with the active nucleus.


title:
Tightly Correlated X-ray/H$\alpha$ Emitting Filaments in the Superbubble
  and Large-Scale Superwind of NGC 3079

abstract:
  Using Chandra and HST we show that X-ray and H$\alpha$ filaments that form
the 1.3-kpc diameter superbubble of NGC 3079 have strikingly similar patterns
at 0."8 resolution. This tight match seems to arise from cool disk gas that has
been driven by the wind, with X-rays being emitted from upstream, stand-off
bowshocks or by conductive cooling at the cloud/wind interfaces. We find that
the soft X-ray plasma has thermal and kinetic energies of
$2\times10^{56}\sqrt{\eta_x}$ and $5\times10^{54}\sqrt{\eta_X}$ erg
respectively, where $\eta_X$ is the filling factor of the X-ray gas and may be
small; these are comparable to the energies of the optical line-emitting gas.
X-rays are also seen from the base of the radio counterbubble that is obscured
optically by the galaxy disk, and from the nucleus (whose spectrum shows the Fe
K$\alpha$ line). Hydrodynamical simulations reproduce the obbservations well
using large filling factors within both filament systems; assuming otherwise
seriously underestimates the mass loss in the superwind. The superbubble is
surrounded by a fainter conical halo of X-rays that fill the area delineated by
high angle, H$\alpha$-emitting filaments, supporting our previous assertion
that these filaments form the contact discontinuity/shock between galaxy gas
and shocked wind. About 40\arcsec (3 kpc) above the disk, an X-ray arc may
partially close beyond the bubble, but the north-east quadrant remains open,
consistent with the superwind having broken out into at least the galaxy halo.


title: Charging processes for dust particles in Saturn's magnetosphere

abstract:
  We investigated the electrostatic charging behavior of submillimeter-sized
dust particles located in Saturn's magnetosphere. The charging effects we
considered included electron/ion capture from the magnetospheric plasma,
electron/ion capture from the solar-wind plasma, the photoelectric effect from
solar radiation, and secondary electron emission from energetic electrons. In
our results, we show charging times and equilibrium potentials for particles
located in different regions of Saturn's magnetosphere. We find that charging
in Saturn's magnetosphere is not particularly sensitive to the dust particle's
material properties. The equipotential ranges from $\sim$-2 V at 3.5 R$_S$,
decreasing to $\sim$-5 V at 6 R$_S$, and then increasing to $\sim$-1.5 V at 10
R$_S$. The charging time for micron-sized particles is a few minutes, and for
0.01 micron-sized particles the charging time is 6 hours (or more). The latter
is a significant fraction of Saturn's rotation period.


title: The STACEE-32 Ground Based Gamma-ray Detector

abstract:
  We describe the design and performance of the Solar Tower Atmospheric
Cherenkov Effect Experiment detector in its initial configuration (STACEE-32).
STACEE is a new ground-based gamma ray detector using the atmospheric Cherenkov
technique. In STACEE, the heliostats of a solar energy research array are used
to collect and focus the Cherenkov photons produced in gamma-ray induced air
showers. The large Cherenkov photon collection area of STACEE results in a
gamma-ray energy threshold below that of previous detectors.