title:
XMM-Newton observations of the polars EV UMa, RX J1002-19 and RX
  J1007-20

abstract:
  We present XMM-Newton data of three strongly magnetic cataclysmic variables
(polars) EV UMa, RX J1002-19 and RX J1007-20. These include the polar with the
shortest orbital period (EV UMa) and the polar with one of the highest magnetic
field strengths (RX J1007-20). They exhibit a range of X-ray spectral
characteristics which are consistent with their known magnetic field strength.
We find that two of the systems show evidence for an absorption dip in soft
X-rays. Their profiles are well defined, implying that the stream is highly
collimated. We determine the mass transfer rate for the two systems with known
distances. We determine that the mass of the white dwarf in EV UMa and RX
J1007-20 is ~1Msun while in RX J1002-19 it is closer to ~0.5Msun.


title: The symbiotic star CH Cygni. III. A precessing radio jet

abstract:
  VLA, MERLIN and Hubble Space Telescope imaging observations of the extended
regions of the symbiotic system CH Cygni are analysed. These extensions are
evidence of a strong collimation mechanism, probably an accretion disk
surrounding the hot component of the system. Over 16 years (between 1985 and
2001) the general trend is that these jets are seen to precess. Fitting a
simple ballistic model of matter ejection to the geometry of the extended
regions suggests a period of 6520 +/- 150 days, with a precession cone opening
angle of 35 +/- 1 degrees. This period is of the same order as that proposed
for the orbital period of the outer giant in the system, suggesting a possible
link between the two. Anomalous knots in the emission, not explained by the
simple model, are believed to be the result of older, slower moving ejecta, or
possibly jet material that has become disrupted through sideways interaction
with the surrounding medium.


title: XMM-NEWTON Observation of the Seyfert 2 Galaxy NGC 4138

abstract:
  The XMM-Newton data presented here are the first X-ray observation of the
Seyfert 2 galaxy NGC4138. Although the galaxy has been pointed by ROSAT-HRI, it
was not detected, with a flux upper limit of about 1.1x10^-13 erg cm^-2 s^-1 in
the 0.2-2.4 keV energy band. XMM-Newton performed the observation on 26
November 2001. The source is detected for the first time in X-rays with
F[0.2-2.4]=1.0x10^-13 erg cm^-2 s^-1, in agreement with the upper limit of
ROSAT. The source spectrum is typical of Seyfert 2 galaxies. We find heavy
obscuration (N_H about 8x10^22 cm^-2) and a flat photon index (1.6). The source
intrinsic luminosity is about 5x10^41 erg/s in the 0.5-10 keV energy band.


title: Unifying B2 radio galaxies with BL Lac objects

abstract:
  In an earlier paper we presented nuclear X-ray flux densities, measured with
ROSAT, for the B2 bright sample of nearby low-luminosity radio galaxies. In
this paper we construct a nuclear X-ray luminosity function for the B2 radio
galaxies, and discuss the consequences of our results for models in which such
radio galaxies are the parent population of BL Lac objects. Based on our
observations of the B2 sample, we use Monte Carlo techniques to simulate
samples of beamed radio galaxies, and use the selection criteria of existing
samples of BL Lac objects to compare our simulated results to what is observed.
We find that previous analytical results are not applicable since the BL Lac
samples are selected on beamed flux density. A simple model in which BL Lacs
are the moderately beamed (gamma ~ 3) counterparts of radio galaxies, with some
random dispersion (~ 0.4 decades) in the intrinsic radio-X-ray relationship,
can reproduce many of the features of the radio-selected and X-ray-selected BL
Lac samples, including their radio and X-ray luminosity functions and the
distributions of their radio-to-X-ray spectral indices. In contrast, models in
which the X-ray and radio emission have systematically different beaming
parameters cannot reproduce important features of the radio-galaxy and BL Lac
populations. The redshift distribution and number counts of the X-ray-selected
EMSS sample are well reproduced by our best models, supporting a picture in
which these objects are beamed FRI radio galaxies with intrinsic luminosities
similar to those of the B2 sample. However, we cannot match the redshift
distribution of the radio-selected 1-Jy sample, and it is likely that a
population of FRII radio galaxies is responsible for the high-redshift objects
in this sample. [abridged]


title:
Bose-Einstein condensation in dense nuclear matter and strong magnetic
  fields

abstract:
  Bose-Einstein condensation of antikaons in cold and dense beta-equilibrated
matter under the influence of strong magnetic fields is studied within a
relativistic mean field model. For magnetic fields $> 5 \times 10^{18}$G, the
phase spaces of charged particles are modified resulting in compositional
changes in the system. The threshold density of $K^-$ condensation is shifted
to higher density compared with the field free case. In the presence of strong
fields, the equation of state becomes stiffer than that of the zero field case.


title:
Rapid Variability as a Diagnostic of Accretion and Nuclear Burning in
  Symbiotic Stars and Supersoft X-ray Sources

abstract:
  Accretion disks and nuclear shell burning are present in some symbiotic stars
(SS) and probably all supersoft X-ray binaries (SSXBs). Both the disk and
burning shell may be involved in the production of dramatic outbursts and, in
some cases, collimated jets. A strong magnetic field may also affect the
accretion flow and activity in some systems. Rapid-variability studies can
probe the interesting region close to the accreting white dwarf (WD) in both SS
and SSXBs. I describe fast photometric observations of several individual
systems in detail, and review the results of a photometric variability survey
of 35 SS. These timing studies reveal the first clearly magnetic SS (Z And),
and suggest that an accretion disk is involved in jet production in CH Cyg as
well as in the outbursts of both CH Cyg and Z And. They also support the notion
that the fundamental power source in most SS is nuclear burning on the surface
of a WD, and raise questions about the structure of disks in the SSXBs.
Finally, spectroscopic observations of RS Oph reveal minute-time-scale
line-strength variations, probably due to a hot boundary layer. Taken together,
the rapid timing observations explore the connections between jet-producing WDs
and X-ray binaries, as well as SS, SSXBs, and CVs.


title: On the accretion geometry of Cyg X-1 in the low/hard state

abstract:
  We fit the broad-band RXTE PCA and HEXTE spectrum from 3--200 keV with
reflection models which calculate the vertical ionization structure of an X-ray
illuminated disc. We consider two geometries corresponding to a truncated
disc/inner hot flow and magnetic flares above an untruncated disc. Both models
are able to fit the PCA 3--20 keV data, but with very different spectral
components. In the magnetic flare models the 3--20 keV PCA spectrum contains a
large amount of highly ionized reflection while in the truncated disc models
the amount of reflection is rather small. The Compton downscattering rollover
in reflected emission means that the magnetic flare models predict a break in
the spectrum at the high energies covered by the HEXTE bandpass which is not
seen. By contrast the weakly illuminated truncated disc models can easily fit
the 3--200 keV spectra.


title: Note on the "Dead Zone" in Layered Accretion Models

abstract:
  Current layered accretion models neglect the properties of the ``dead zone''.
However, as argued here from simple considerations, the thickness of this zone
is a critical quantity when the disc is in hydrostatic equilibrium. It controls
not only the structure of the superficial, active layers, but also the
mid-plane density and the total disc mass, and should therefore be introduced
in models of that kind, steady or not. But in the absence of intrinsic heating,
the dead zone must have a tiny size which, given the non-stationary and
turbulent character of the global flow, makes very likely its mixing together
with the two active layers.


title:
Millimeter-wave Searches for Cold Dust and Molecular Gas around T Tauri
  Stars in MBM 12

abstract:
  We report results of a sensitive search for cold dust and molecular gas in
the disks around 8 T Tauri stars in the high-latitude cloud MBM 12.
Interferometric observations of 3 mm continuum emission in 5 fields containing
6 of the objects, and literature values for the remaining two, limit the disk
masses to M_disk < 0.04 - 0.09 M_sun (gas+dust), for a gas:dust mass ratio of
100 and a distance of 275 pc. By coadding the 3 mm data of our five fields, we
set an upper limit to the average disk mass of <M_disk>(N=5) < 0.03 M_sun.
Simultaneous observation of the CS J=2-1 and the N2H+ 1-0 lines show no
emission. Single-dish observations of the 13CO 2-1 line limit the disk mass to
(5 - 10) * 10^-4 M_sun for a standard CO abundance of 2 * 10^-4. Depletion of
CO by up to two orders of magnitude, through freezing out or photodissociation,
can reconcile these limits. These mass limits lie within the range found in the
Taurus-Auriga and rho Oph star-forming regions (0.001 - 0.3 M_sun), and
preclude conclusions about possible decrease in disk mass over the 1 - 2 Myr
age range spanned by the latter two regions and MBM 12. Our observations can
exclude the presence in MBM 12 of T Tauri stars with relatively bright and
massive disks such as T Tau, DG Tau, and GG Tau.


title: On the Misalignment of Jets in Microquasars

abstract:
  We discuss the timescales for alignment of black hole and accretion disc
spins in the context of binary systems. We show that for black holes that are
formed with substantial angular momentum, the alignment timescales are likely
to be at least a substantial fraction of the systems' lifetimes. This result
explains the observed misalignment of the disc and the jet in the microquasar
GRO J 1655-40 and in SAX J 1819-2525 as being likely due to the
Bardeen-Petterson effect. We discuss the implications of these results on the
mass estimate for GRS 1915+105, which has assumed the jet is perpendicular to
the orbital plane of the system and may hence be an underestimate. We show that
the timescales for the spin alignment in Cygnus X-3 are consistent with the
likely misalignment of disc and jet in that system, and that this is suggested
by the observational data.


title:
Difference between Spatial Distributions of the H-alpha Kernels and Hard
  X-Ray Sources in a Solar Flare

abstract:
  We present the relation of the spatial distribution of H-alpha kernels with
the distribution of hard X-ray (HXR) sources seen during the 2001 April 10
solar flare. This flare was observed in H-alpha with the (Sartorius) telescope
at Kwasan Observatory, Kyoto University, and in hard X-rays (HXRs) with the
Hard X-ray Telescope (HXT) onboard Yohkoh. We compared the spatial distribution
of the HXR sources with that of the H-alpha kernels. While many H-alpha kernels
are found to brighten successively during the evolution of the flare ribbons,
only a few radiation sources are seen in the HXR images. We measured the
photospheric magnetic field strengths at each radiation source in the H-alpha
images, and found that the H-alpha kernels accompanied by HXR radiation have
magnetic strengths about 3 times larger than those without HXR radiation. We
also estimated the energy release rates based on the magnetic reconnection
model. The release rates at the H-alpha kernels with accompanying HXR sources
are 16-27 times larger than those without HXR sources. These values are
sufficiently larger than the dynamic range of HXT, which is about 10, so that
the difference between the spatial distributions of the H$\alpha$ kernels and
the HXR sources can be explained.


title: Soft X-ray Emissions from Planets, Moons, and Comets

abstract:
  A wide variety of solar system bodies are now known to radiate in the soft
x-ray energy (<5 keV) regime. These include planets (Earth, Jupiter, Venus,
Saturn, Mars): bodies having thick atmospheres, with or without intrinsic
magnetic field; planetary satellites (Moon, Io, Europa, Ganymede): bodies with
thin or no atmospheres; and comets and the Io plasma torus: bodies having
extended tenuous atmospheres. Several different mechanisms have been proposed
to explain the generation of soft x-rays from these objects, whereas in the
hard x-ray energy range (>10 keV) x-rays result mainly from the electron
bremsstrahlung process. In this paper we present a brief review of the x-ray
observations on each of the planetary bodies and discuss their characteristics
and proposed source mechanisms.


title: Kinematics of Planetary Nebulae in M51's Tidal Debris

abstract:
  We report the results of a radial velocity survey of planetary nebulae (PNe)
located in the tidal features of the well-known interacting system NGC 5194/95
(M51). We find clear kinematic evidence that M51's northwestern tidal debris
consists of two discrete structures which overlap in projection -- NGC 5195's
own tidal tail, and diffuse material stripped from NGC 5194. We compare these
kinematic data to a new numerical simulation of the M51 system, and show that
the data are consistent with the classic ``single passage'' model for the
encounter, with a parabolic satellite trajectory and a 2:1 mass ratio. We also
comment on the spectra of two unusual objects: a high-velocity PN which may be
associated with NGC 5194's halo, and a possible interloping high-redshift
galaxy.


title: General Relativistic Magnetoionic Theory

abstract:
  We have developed methods for tracing rays and performing radiative transfer
through a magnetoactive plasma in a general relativistic environment. The two
electromagnetic plasma modes propagate differently due to a combination of
dispersive and gravitational effects. We have found that, when given an
appropriate environment surrounding the central black hole, it is indeed
possible to generate a significant degree of circular polarisation without an
appreciable amount of linear polarisation due to these effects alone.


title: Observational Properties of Extragalactic Globular Cluster Systems

abstract:
  The superior resolution of HST and the light gathering power of large 8-10m
class telescopes are now providing information on distant globular clusters
(GCs) that is comparable to that obtained in early 1990s for Local Group
systems. Here I summarise what has been learnt from the imaging and limited
spectroscopy of GCs in other galaxies. The GC systems of spirals and
ellipticals reveal remarkable similarities. The vast bulk of GCs appear to have
formed at early epochs, with mergers making a limited contribution to the
overall GC system at later epochs. These observational findings are placed in
the context of galaxy formation.


title: Factors Determining Variability Time in Active Galactic Nucleus Jets

abstract:
  The relationship between observed variability time and emission region
geometry is explored for the case of emission by relativistic jets. The
approximate formula for the jet-frame size of the emission region, $R'=Dc\Delta
t_{\rm obs}$ is shown to lead to large systematic errors when used together
with observed luminosity and assumed or estimated Doppler factor $D$ to
estimate the jet-frame photon energy density. These results have implications
for AGN models in which low-energy photons are targets for interaction of high
energy particles and photons, e.g. synchrotron-self Compton models and hadronic
blazar models, as well as models of intra-day variable sources in which the
photon energy density imposes a brightness temperature limit through Compton
scattering.
  The actual relationship between emission region geometry and observed
variability is discussed for a variety of geometries including cylinders,
spheroids, bent, helical and conical jet structures, and intrinsic variability
models including shock excitation. The effects of time delays due to finite
particle acceleration and radiation time scales are also discussed.


title: A metallicity-flattening relation for dwarf elliptical galaxies

abstract:
  It is shown that bright cluster dwarf ellipticals follow a relation between
metallicity and apparent flattening. Rounder dwarfs tend to be more metal-rich.
The evidence is based on colour as well as spectroscopic line-strength data
from the literature. The large scatter of dEs around the mean
metallicity-luminosity relation, usually ascribed to large observational
errors, turns out to be an ellipticity effect. In the magnitude range $-14 \ga
M_B \ga -18$ the metallicity of dEs depends more strongly on ellipticity than
luminosity. A possible explanation is that galaxies with masses around $10^{9}$
$M_{\odot}$ suffered a partial blowout of metal-enriched gas along their minor
axis, rendering ellipticity a critical parameter for metallicity (De Young &
Heckman 1994).


title:
Another Interpretation of the Power-law type Spectrum of an
  Ultraluminous Compact X-ray Source in IC 342

abstract:
  The ultraluminous compact X-ray sources (ULXs) generally show a curving
spectrum in the 0.7--10 keV ASCA bandpass, which looks like a high temperature
analogue of the disk dominated high/soft state spectra seen in Galactic black
hole binaries (BHBs) at high mass accretion rates. Several ULXs have been seen
to vary, and to make a transition at their lowest luminosity to a spectrum
which looks more like a power law. These have been previously interpreted as
the analogue of the power law dominated low/hard state in Galactic BHBs.
However, the ULX luminosity at which the transition occurs must be at least
10--50 per cent of the Eddington limit assuming that their highest luminosity
phase corresponds to the Eddington limit, while for the Galactic BHBs the
high/soft--low/hard transition occurs at a few per cent of the Eddington limit.
Here we show that the apparently power law spectrum in a ULX in IC342 can be
equally well fit over the ASCA bandpass by a strongly Comptonised optically
thick accretion disk with the maximum temperature of ~1 keV. Recent work on the
Galactic BHBs has increasingly shown that such components are common at high
mass accretion rates, and that this often characterises the very high (or
anomalous) state. Thus we propose that the power law type ULX spectra are not
to be identified with the low/hard state, but rather represent the
Comptonisation dominated very high/anomalous state in the Galactic BHBs.


title: Integral-field Spectroscopy of Galactic Nuclei

abstract:
  High-resolution imaging and long-slit spectroscopy obtained with HST,
combined with ground-based integral-field spectroscopy, provides the kinematics
of stars and gas in nearby galactic nuclei with sufficient accuracy to derive
the intrinsic dynamical structure, and to measure the mass of the central black
hole. This has revealed that many nuclei contain decoupled kinematic components
and asymmetric structures, and that nuclear and global properties of galaxies
are correlated. Higher spatial resolution and significantly increased
sensitivity are required to cover the full range of galaxy properties and
types, including the nearest powerful active radio galaxies, and to study the
evolution of galactic nuclei as a function of redshift. The prospects in this
area are discussed.


title:
Modelling the infrared galaxy evolution using a phenomenological
  approach

abstract:
  To characterise the cosmological evolution of the sources contributing to the
infrared extragalactic background, we have developped a phenomenological model
that constrains in a simple way the galaxy luminosity function evolution with
the redshift, and fits all the existing source counts and redshift
distributions, Cosmic Infrared Background intensity and fluctuations
observations, from the mid-infrared to the submillimetre range. The model is
based on template spectra of starburst and normal galaxies, and on the local
infrared luminosity function. Although the Cosmic Infrared Background can be
modeled with very different luminosity functions as long as the radiation
production with redshift is the right one, the number counts, and the
anisotropies of the unresolved background, imply that the luminosity function
must change dramatically with redshift, with a rapid evolution of the
high-luminosity sources (L>3 10^{11} L_{\odot}) from z=0 to z=1 which then stay
rather constant up to redshift 5. The derived evolution of the IR luminosity
function may be linked to a bimodal star formation process, one associated with
the quiescent and passive phase of the galaxy evolution and one associated with
the starburst phase, trigerred by merging and interactions. The latter
dominates the infrared and submillimetre ouput energy of the Universe.
  The model is intended as a convenient tool to plan further observations, as
illustrated through predictions for Herschel, Planck and ALMA observations. Our
model predictions for given wavelengths, together with some usefull routines,
are available for general use.


title: Hysteresis in the Light Curves of Soft X-ray Transients

abstract:
  Using PCA data from the Rossi X-Ray Timing Explorer (RXTE), we track the
spectral states of the neutron star transient system Aql X-1 through a complete
outburst cycle. We find a hard-to-soft state transition during the very early,
rising phase of the outburst and show that there is a hysteresis effect such
that the transition back to the hard state occurs at a luminosity $\sim $ 5
times {\it lower} than the hard-to-soft transition. This hysteresis effect
rules out the propeller mechanism as the sole cause of state transitions in Aql
X-1. Assuming the propeller mechanism only operates at a luminosity equal to or
below that of the observed soft-to-hard transition requires that the magnetic
field of Aql X-1 be less than $7\times 10^7$ Gauss, the lowest neutron star
field known to date. To compare the state transition behavior of Aql X-1 with
that found in transient black hole systems, we use RXTE ASM data to compute
hardness-intensity diagrams for four black hole candidate transients where the
ASM data should also give us state information throughout much of the outburst
cycles. In all four systems, we find evidence for a hard-to-soft state
transition during the rising outburst phase and for the source staying in a
soft state down to much lower luminosities during the declining phase, i.e., a
hysteresis effect. This similarity suggests a common origin for state
transitions in low magnetic field neutron star and black hole systems, and the
hysteresis effect rules out the ``Strong ADAF Principle'' for determining the
state of an accretion disc. We discuss the general implications of these
observations for current models of state transitions. We note the contrast to
previous observations of the non-transient systems Cygnus X-1 and X-3 which do
not show a hysteresis effect.


title: Atmospheric shower fluctuations and the constant intensity cut method

abstract:
  We explore the constant intensity cut method that is widely used for the
derivation of the cosmic ray energy spectrum, for comparisons of data obtained
at different atmospheric depths, for measuring average shower profiles, and for
estimates of the proton-air cross section from extensive air shower data. The
constant intensity cut method is based on the selection of air showers by
charged particle or muon size and therefore is subject to intrinsic shower
fluctuations. We demostrate that, depending on the selection method, shower
fluctuations can strongly influence the characteristics of the selected
showers. Furthermore, a mixture of different primaries in the cosmic ray flux
complicates the interpretation of measurements based on the method of constant
intensity cuts. As an example we consider data published by the Akeno
Collaboration. The interpretation of the Akeno measurements suggests that more
than 60-70% of cosmic ray primaries in the energy range 10^{16}-19^{17} eV are
heavy nuclei. Our conclusions depend only weakly on the hadronic interaction
model chosen to perform the simulations, namely SIBYLL and QGSjet.


title:
Formation of terrestrial planets in close binary systems: the case of
  Alpha Centauri A

abstract:
  At present the possible existence of planets around the stars of a close
binary system is still matter of debate. Can planetary bodies form in spite of
the strong gravitational perturbations of the companion star? We study in this
paper via numerical simulation the last stage of planetary formation, from
embryos to terrestrial planets in the Alpha Cen system, the prototype of close
binary systems. We find that Earth class planets can grow around Alpha Cen A on
a time-scale of 50 Myr. In some of our numerical models the planets form
directly in the habitable zone of the star in low eccentric orbits. In one
simulation two of the final planets are in a 2:1 mean motion resonance that,
however, becomes unstable after 200 Myr. During the formation process some
planetary embryos fall into the stars possibly altering their metallicity.


title: Scaling laws in decaying helical hydromagnetic turbulence

abstract:
  We study the evolution of growth and decay laws for the magnetic field
coherence length xi, energy E_M and magnetic helicity H in freely decaying 3D
MHD turbulence. We show that with certain assumptions, self-similarity of the
magnetic power spectrum alone implies that xi~t^{1/2}. This in turn implies
that magnetic helicity decays as H~t^{-2s}, where s=(xi_{diff}/xi_H)^2, in
terms of xi_{diff}, the diffusion length scale, and xi_H, a length scale
defined from the helicity power spectrum. The relative magnetic helicity
remains constant, implying that the magnetic energy decays as E_M~t^{-1/2-2s}.
The parameter s is inversely proportional to the magnetic Reynolds number Re_M,
which is constant in the self-similar regime.


title: Extreme X-ray variability in the luminous quasar PDS 456

abstract:
  We present evidence from Beppo-SAX and XMM-Newton of extreme X-ray
variability in the high luminosity radio-quiet quasar PDS 456, the most
luminous known AGN at z<0.3. Repeated X-ray flaring is found in PDS 456, over
the duration of the 340 ksec long Beppo-SAX observation. The X-ray flux doubles
in just 30 ksec, whilst the total energy output of the flaring events is as
high as 10^51 erg. Under the assumption of isotropic emission at the Eddington
limit, this implies that the size of the X-ray emitting region in PDS 456 is
less than 3 Schwarzschild radii, for a 10^9 solar mass black hole. From the
rates of change of luminosity observed during the X-ray flares, we calculate
lower limits for the radiative efficiency between 0.06 and 0.41, implying that
accretion onto a Kerr black hole is likely in PDS 456. We suggest that the
rapid variability is from X-ray flares produced through magnetic reconnection
above the disc and calculate that the energetics and timescale of the flares
are plausible if the quasar is accreting near to the maximum Eddington rate. A
similar mechanism may account for the extreme rapid X-ray variability observed
in many Narrow Line Seyfert 1s. In the case of PDS 456, we show that the X-ray
flaring could be reproduced through a self-induced cascade of about 1000
individual flares over a timescale of the order 1 day.


title: GLAST Dark Matter Search

abstract:
  The GLAST Large Area Telescope, scheduled for launch in 2006, is a next
generation space based gamma ray telescope which will improve in point source
sensitivity by a factor of 30 over that of EGRET below 10 GeV, and extend
beyond EGRET up to 300 GeV. Thus GLAST offers a unique opportunity to discover
WIMP dark matter through precision studies of gamma rays produced in pair
annihilations. The most dense region of dark matter in our galaxy is currently
thought to occur at the center; in particular, dark matter should concentrate
within 3 pc of the putative supermassive black hole located at the SgrA* radio
source. In fact, the 2nd and 3rd EGRET catalogs contain a significant point
source coincident with the Milky Way galactic center within a resolution of 12
arcminutes. The EGRET team has determined that the spectral and temporal
characteristics of this point source are consistent with dark matter WIMP
annihilations. More detailed analysis has determined that the magnitude and
spectrum of the EGRET source is consistent with relic WIMPs concentrated within
3 pc of the central supermassive black hole. Furthermore, the SgrA* radio
emission is consistent with the synchrotron radiation expected from electrons
and positrons produced in WIMP annihilations. If true, then GLAST should be
able to constrain the particle properties of the postulated WIMP with 1 month
of data.


title: Observability of Neutron Stars with Quarks

abstract:
  Recent Chandra observations have raised expectations that the objects RX
J185635-3754 and 3C58 are either bare strange quark stars or stars with
extended quark cores. However, these observations can also be interpreted in
terms of normal neutron stars. Essential requirements for either explanation
are that they simultaneously account for the observed (i) spectral features
(i.e., thermal or nonthermal, possible lines), (ii) bounds on the inferred mass
(M) and radius (R), and (iii) the cooling curves (effective temperatures T and
luminosities L vs. age). Compact stars offer the promise of delineating QCD at
finite baryon density (Lattimer and Prakash, 2001) in a fashion complementary
to relativistic heavy ion collider experiments, which largely address the
finite temperature, but baryon poor regime.


title:
A Radio Survey for Linear and Circular Polarization in Low Luminosity
  Active Galactic Nuclei

abstract:
  We conducted a Very Large Array survey of eleven low luminosity active
galactic nuclei for linear and circular polarization at 8.4 GHz. We detected
circular polarization in one source (M81*) and linear polarization in 3
sources. Sensitivity limits were ~0.1% for both modes of polarization in 9 of
11 sources. The detections confirm the importance of nonthermal emission in
LLAGN. However, detection rates for circular and linear polarization are lower
for these sources than for more powerful AGN. Fractional linear polarization in
detected sources is also lower than in more powerful AGN. The weak linear
polarization in the survey sources indicates their overall similarity to Sgr
A*. Confusion with thermal sources, depolarization and weaker, less extended
jets may contribute to these differences. We detect a rotation measure >~ 7 x
10^4 rad m^-2 for NGC 4579. This may arise from magnetized plasma in the
accretion, outflow or interstellar regions. Inverted spectra are present in
both M81* and Sagittarius A* and absent from all sources in which circular
polarization is not detected. This suggests that optical depth effects are
important in the creation of circular polarization.


title:
Monitoring the Health and Safety of the ACIS Instrument On-Board the
  Chandra X-ray Observatory

abstract:
  The Chandra X-ray Observatory (CXO), NASA's latest ``Great Observatory'', was
launched on July 23, 1999 and reached its final orbit on August 7, 1999. The
CXO is in a highly elliptical orbit, approximately 140,000 km x 10,000 km, and
has a period of approximately 63.5 hours (~2.65 days). Communication with the
CXO nominally consists of 1-hour contacts spaced 8-hours apart. Thus, once a
communication link has been established, it is very important that the health
and safety status of the scientific instruments as well as the Observatory
itself be determined as quickly as possible.
  In this paper, we focus exclusively on the automated health and safety
monitoring scripts developed for the Advanced CCD Imaging Spectrometer (ACIS)
to use during those 1-hour contacts. ACIS is one of the two focal plane
instruments on-board the CXO. We present an overview of the real-time ACIS
Engineering Data Web Page and the alert schemes developed for monitoring the
instrument status during each communication contact. A suite of HTML and PERL
scripts monitors the instrument hardware house-keeping electronics (i.e.,
voltages and currents) and temperatures during each contact. If a particular
instrument component is performing either above or below pre-established
operating parameters, a sequence of email and alert pages are spawned to the
Science Operations Team of the Chandra X-ray Observatory Center so that the
anomaly can be quickly investigated and corrective actions taken if necessary.
We also briefly discuss the tools used to monitor the real-time science
telemetry reported by the ACIS flight software.
  The authors acknowledge support for this research from NASA contract
NAS8-39073.


title: The Interesting Dynamics of the 55 Cancri System

abstract:
  Recent studies of the 55 Cancri system suggest the existence of three planets
with periods of ~15 days, ~45 days, and ~5500 days (Marcy et al. 2002). The
inner two planets are near the 3:1 mean motion commensurability and it is
likely that these two planets became trapped in the resonance while farther
from the star and migrated together. As the innermost planet begins to
dissipate energy through tides the planets break out of the resonance. The
final state of the system gives important information about its past history,
such as the migration timescale that led to capture.


title:
Sacrificial charge and the spectral resolution performance of the
  Chandra Advanced CCD Imaging Spectrometer

abstract:
  Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the
focal plane instruments on the Chandra X-ray Observatory, suffered radiation
damage from exposure to soft protons during passages through the Earth's
radiation belts. The ACIS team is continuing to study the properties of the
damage with an emphasis on developing techniques to mitigate charge transfer
inefficiency (CTI) and spectral resolution degradation. A post-facto CTI
corrector has been developed which can effectively recover much of the lost
resolution. Any further improvements in performance will require knowledge of
the location and amount of sacrificial charge - charge deposited along the
readout path of an event which fills electron traps and changes CTI. We report
on efforts by the ACIS Instrument team to characterize which charge traps cause
performance degradation and the properties of the sacrificial charge seen
on-orbit. We also report on attempts to correct X-ray pulseheights for the
presence of sacrificial charge.


title: The Magellanic Stream, High-Velocity Clouds and the Sculptor Group

abstract:
  The Magellanic Stream is a 100\deg x 10\deg filament of gas which lies within
the Galactic halo and contains ~ 2 x 10^8 \Msun of neutral hydrogen. We present
data from the HI Parkes All Sky Survey (HIPASS) in the first complete survey of
the entire Magellanic Stream and its surroundings. We also present a summary of
the reprocessing techniques used to recover large-scale structure in the
Stream. The Stream properties revealed include: bifurcation along the main
Stream filament; dense, isolated clouds which follow the entire length of the
Stream; head-tail structures; and a complex filamentary web at the head where
gas is being freshly stripped away from the Small Magellanic Cloud and the
Bridge. Debris which appears to be of Magellanic origin extends out to 20\deg
from the main Stream filaments. The large number of elongated Stream clouds
suggests the presence of shearing motions within the Stream, arising from tidal
forces or interaction with the tenuous Galactic halo. Clouds along the
sightline to the less distant half of the Sculptor Group, show anomalous
properties. We argue that these clouds represent halo material, and are not
distant Sculptor Group clouds. This result has significant implications for the
hypothesis that there might exist distant, massive HVCs within the Local Group.
(abridged)


title: Dark matter, density perturbations and structure formation

abstract:
  This paper provides a review of the variants of dark matter (CDM, HDM) which
are thought to be fundamental components of the universe and their role in
origin and evolution of structures.


title: VLT spectroscopy of NGC3115 globular clusters

abstract:
  We present results derived from VLT-FORS2 spectra of 24 different globular
clusters associated with the lenticular galaxy NGC3115. A subsample of 17
globular clusters have sufficiently high signal-to-noise to allow precision
measurements of absorption line-strengths. Comparing these indices to new
stellar population models by Thomas et al. we determine ages, metallicities and
element abundance ratios. Our data are also compared with the Lick/IDS
observations of Milky Way and M31 globular clusters. Unpublished higher order
Balmer lines (HgammaA,F and HdeltaA,F) from the Lick/IDS observations are given
in the Appendix. Our best age estimates show that the observed clusters which
sample the bimodal colour distribution of NGC3115 are coeval within our
observational errors (2-3 Gyr). Our best calibrated age/metallicity diagnostic
diagram (Hbeta vs [MgFe]) indicates an absolute age of 11-12 Gyr. We confirm
with our accurate line-strength measurements that the (V-I) colour is a good
metallicity indicator within the probed metallicity range. The abundance ratios
for globular clusters in NGC3115 give an inhomogeneous picture. We find a range
from solar to super-solar ratios for both blue and red clusters. From our
accurate recession velocities we detect, independent of metallicity, clear
rotation in the sample of globular clusters. In order to explain the
metallicity and abundance ratio pattern, particularly the range in abundance
ratios for the metal rich globular clusters in NGC3115, we favour a formation
picture with more than two distinct formation episodes.(Abridged)


title: Outflows from ellipticals: the role of supernovae

abstract:
  Models of SN driven galactic winds for ellipticals are presented. We assume
that ellipticals formed at high redshift and suffered an intense burst of star
formation. The role of supernovae of type II and Ia in the chemical enrichment
and in triggering galactic winds is studied. In particular, several recipes for
SN feed-back together with detailed nucleosynthesis prescriptions are
considered. It is shown that SNe of type II have a dominant role in enriching
the interstellar medium of elliptical galaxies whereas type Ia SNe dominate the
enrichment and the energetics of the intracluster medium.


title:
Iron Emission Lines from Extended X-ray Jets in SS 433: Reheating of
  Atomic Nuclei

abstract:
  Powerful relativistic jets are among the most ubiquitous and energetic
observational consequences of accretion around supermassive black holes in
active galactic nuclei and neutron stars and stellar-mass black holes in x-ray
binary (XRB) systems. But despite more than three decades of study, the
structure and composition of these jets remain unknown. Here we present
spatially resolved x-ray spectroscopy of arc second-scale x-ray jets from the
XRB SS 433 analized with the Chandra advanced charge-coupled device imaging
spectrometer. These observations reveal evidence for a hot continuum and
Doppler-shifted iron emission lines from spatially resolved regions.
Apparently, in situ reheating of the baryonic component of the jets takes place
in a flow that moves with relativistic bulk velocity even more than 100 days
after launch from the binary core.


title:
A Polarization Sensitive Bolometric Detector for Observations of the
  Cosmic Microwave Background

abstract:
  We have developed a bolometric detector that is intrinsically sensitive to
linear polarization which is optimized for making measurements of the
polarization of the cosmic microwave background radiation. The receiver
consists of a pair of co-located silicon nitride micromesh absorbers which
couple anisotropically to linearly polarized radiation through a corrugated
waveguide structure. This system allows simultaneous background limited
measurements of the Stokes I and Q parameters over ~ 30% bandwidths at
frequencies from ~ 60 to 600 GHz. Since both linear polarizations traverse
identical optical paths from the sky to the point of detection, the
susceptibility to systematic effects is minimized. The amount of uncorrelated
noise between the two polarization senses is limited to the quantum limit of
thermal and photon shot noise, while drifts in the relative responsivity to
orthogonal polarizations are limited to the effect of non-uniformity in the
thin film deposition of the leads and the intrinsic thermistor properties.
Devices using NTD Ge thermistors have achieved NEPs of 2 x 10^{-17} W/sqrt{Hz}
with a 1/f knee below 100 mHz at a base temperature of 270 mK. Numerical
modelling of the structures has been used to optimize the bolometer geometry
and coupling to optics. Comparisons of numerical results and experimental data
are made. A description of how the quantities measured by the device can be
interpreted in terms of the Stokes parameters is presented. The receiver
developed for the Boomerang and Planck HFI focal planes is presented in detail.


title:
Multi-frequency GMRT Observations of the HII regions S 201, S 206, and S
  209 : Galactic Temperature Gradient

abstract:
  We present radio continuum images of three Galactic HII regions, S 201, S
206, and S 209 near 232, 327, and 610 MHz using the Giant Meterwave Radio
Telescope (GMRT). The GMRT has a mix of short and long baselines, therefore,
even though the data have high spatial resolution, the maps are still sensitive
to diffuse extended emission. We find that all three HII regions have bright
cores surrounded by diffuse envelopes. We use the high resolution afforded by
the data to estimate the electron temperatures and emission measures of the
compact cores of these HII regions. Our estimates of electron temperatures are
consistent with a linear increase of electron temperature with Galacto-centric
distance for distances up to 18 kpc (the distance to the most distant HII
region in our sample).


title: Helioseismic limit on heavy element abundance

abstract:
  Primary inversions of accurately measured solar oscillation frequencies
coupled with the equations of thermal equilibrium and other input physics,
enable us to infer the temperature and hydrogen abundance profiles inside the
Sun. These profiles also help in setting constraints on the input physics as
well as on heavy element abundance in the solar core. Using different
treatments of plasma screening for nuclear reaction rates, limits on the
cross-section of proton-proton nuclear reaction as a function of heavy element
abundance in the solar core are obtained and an upper limit on heavy element
abundance in the solar core is also derived from these results.


title:
Acceleration and Enrichment of 3He in Impulsive Solar Flares by Electron
  Firehose Waves

abstract:
  A new mechanism for acceleration and enrichment of 3He during impulsive solar
flares is presented. Low-frequency electromagnetic plasma waves excited by the
Electron Firehose Instability (EFI) can account for the acceleration of ions up
to 1 MeV/amu energies as a single stage process. The EFI arises as a direct
consequence of the free energy stored in a temperature anisotropy
(T_parallel>T_perp) of the bulk energized electron population during the
acceleration process. In contrast to other mechanisms which require special
plasma properties, the EFI is an intrinsic feature of the acceleration process
of the bulk electrons. Being present as a side effect in the flaring plasma,
these waves can account for the acceleration of 3He and 4He while selectively
enhancing 3He due to the spectral energy density built up from linear growth.
Linearized kinetic theory, analytic models and test-particle simulations have
been applied to investigate the ability of the waves to accelerate and
fractionate. As waves grow in both directions parallel to the magnetic field,
they can trap resonant ions and efficiently accelerate them to the highest
energies. Plausible models have been found that can explain the observed
energies, spectra and abundances of 3He and 4He.


title: Supernovae and Neutrinos

abstract:
  A long-standing problem in supernova physics is how to measure the total
energy and temperature of $\nu_\mu$, $\nu_\tau$, $\bar{\nu}_\mu$, and
$\bar{\nu}_\tau$. While of the highest importance, this is very difficult
because these flavors only have neutral-current detector interactions. We
propose that neutrino-proton elastic scattering, $\nu + p \to \nu + p$, can be
used for the detection of supernova neutrinos in scintillator detectors. It
should be emphasized immediately that the dominant signal is on {\it free}
protons. Though the proton recoil kinetic energy spectrum is soft, with $T_p
\simeq 2 E_\nu^2/M_p$, and the scintillation light output from slow, heavily
ionizing protons is quenched, the yield above a realistic threshold is nearly
as large as that from $\bar{\nu}_e + p \to e^+ + n$. In addition, the measured
proton spectrum is related to the incident neutrino spectrum. The ability to
detect this signal would give detectors like KamLAND and Borexino a crucial and
unique role in the quest to detect supernova neutrinos. These results are now
published: J. F. Beacom, W. M. Farr and P. Vogel, Phys. Rev. D {\bf 66}, 033001
(2002) [arXiv:hep-ph/0205220]; the details are given there.


title: Improving X-Ray Resolution with XOSS

abstract:
  Improving angular resolution is one of X-ray astronomy's big challenges.
While X-ray interferometry should eventually vastly improve broad-band angular
resolution, in the near-term, X-ray telescopes will sacrifice angular
resolution for increased collecting area and energy resolution. Natural
occultations have long been used to study sources on small angular scales, but
are limited by short transit times and the rarity of transits. We describe here
how one can make use of an X-ray Occulting Steerable Satellite (XOSS) to
achieve very-high resolution of X-ray sources, conventional X-ray telescopes.
Similar occulting satellites could also be deployed in conjunction with future
space observatories in other wavebands.


title: Detecting Extra-Solar Planets via Microlensing at High Magnification

abstract:
  Extra-solar planets can be efficiently detected in gravitational microlensing
events of high magnification. High accuracy photometry is required over a
short, well-defined time interval only, of order 10-30 hours. Most planets
orbiting the lens star are evidenced by perturbations of the microlensing light
curve in this time.


title:
On the Luminosities and Temperatures of Extended X-ray Emission from
  Planetary Nebulae

abstract:
  We examine mechanisms that may explain the luminosities and relatively low
temperatures of extended X-ray emission in planetary nebulae. By building a
simple flow structure for the wind from the central star during the proto, and
early, planetary nebulae phase, we estimate the temperature of the X-ray
emitting gas and its total X-ray luminosity. We conclude that in order to
account for the X-ray temperature and luminosity, both the evolution of the
wind from the central star and the adiabatic cooling of the post-shocked wind's
material must be considered. The X-ray emitting gas results mainly from shocked
wind segments that were expelled during the early planetary nebulae phase, when
the wind speed was moderate. Alternatively, the X-ray emitting gas may result
from a collimated fast wind blown by a companion to the central star. Heat
conduction and mixing between hot and cool regions are likely to occur in some
cases and may determine the detailed X-ray morphology of a nebula, but are not
required to explain the basic properties of the X-ray emitting gas.


title:
Observational Consequences of Evolution of Primordial Fluctuations in
  Scalar-Tensor Cosmology

abstract:
  Evolution of primordial fluctuations in a Brans-Dicke type scalar-tensor
gravity theory is comprehensively investigated. The harmonic attractor model,
in which the scalar field has its harmonic effective potential in the Einstein
conformal frame and the theory relaxes toward Einstein gravity with time, is
considered. The evolution of adiabatic initial perturbations in flat SCDM
models is examined from the radiation-dominated epoch up to the present. We
discuss how the scalar-tensor gravity affects the evolution of metric and
matter perturbations, mainly focusing on the observational consequences, i.e.,
the matter power spectrum and the power spectrum of cosmic microwave background
temperature. We find that the early time deviation is characterized only by the
large static gravitational constant while the late time behavior is
qualitatively different from that in Einstein gravity because the time
variation of the gravitational constant and its fluctuation have non-negligible
effects. The attracting scalar-tensor gravity affects only small scale modes
due to its attracting nature, the degree of which is far beyond the
post-Newtonian deviation at the present epoch.


title: Criticism of recent calculations of common envelope ejection

abstract:
  We re-examine a recent claim by Han et al. (2002) that the ionization energy
in the envelope has to be included in the ejection criterion of common
envelopes. In particular, we argue that (1) they include a mass loss rate prior
to the onset of the common envelope that is too low; (2) They do not include
the energy radiated by the accreting white dwarf companion, as well as that
emitted by the core of the giant star; and (3) As argued by one of us before,
the opacity in the envelope is too low for the efficient usage of the
ionization energy.


title:
Stellar Envelopes as Sources of Broad Line Region Emission: New
  Possibilities Allowed

abstract:
  In Active Galactic Nuclei (AGNs) the presence of a star cluster around the
central black hole can have several effects on the dynamics and the emission of
the global system. In this paper we analyze the interaction of stellar
atmospheres with a wind outflowing from the central region of the AGN nucleus.
Even a small mass loss from stars, as well as possible star collisions, can
give a non-negligible contribution in feeding matter into the AGN nuclear wind.
Moreover, stellar mass loss can produce envelopes surrounding stars that turn
out to be suitable for reproducing the observed emission from the Broad Line
Region (BLR). In this framework, the envelope can be confined by the bow shock
arising from the interaction between the expanding stellar atmosphere and the
AGN nuclear wind.


title:
A relativistic approach to nonlinear peculiar velocities and the
  Zeldovich approximation

abstract:
  We study the peculiar motion of non-relativistic matter in a fully covariant
way. The exact nonlinear equations are derived and then applied to the case of
pressure-free matter, moving relatively to a quasi-Newtonian Eulerian frame.
Our two-frame formalism facilitates the study of the nonlinear kinematics of
the matter, as the latter decouples from the background expansion and starts to
``turn around'' and collapse. Applied to second perturbative order, our
equations provide a fully covariant formulation of the Zeldovich approximation,
which by construction addresses the mildly nonlinear regime of structure
formation. Employing a dynamical system approach, we show that, just like in
the Newtonian case, the relativistic treatment also predicts that pancakes are
the natural end-structures for any generic overdensity.


title:
Infrared imaging and spectroscopy of companion candidates near the young
  stars HD 199143 and HD 358623 in Capricornius

abstract:
  We present JHK images of the young (~20 Myrs) nearby (~48 pc) stars HD 199143
and HD 358623 to search for (sub-)stellar companions around them. The images
were obtained in JHK with the speckle camera SHARP-I in July 2001 and in H with
SofI in Dec 2000, July 2001, and Dec 2001, all at the ESO 3.5m NTT. We present
a companion candidate with a 2 arc sec offset being almost 2 mag fainter than
HD 358623 with proper motion consistent with the known proper motion of the
primary star HD 358623 A. Then, we obtained a spectrum in the H-band (with SofI
at the NTT) of this companion showing that it has spectral type M1-3,
consistent with being a companion of HD 358623 A (K7-M0). Also, a companion
candidate with a 1 arcsecond offset being 2 mag fainter than HD 199143 is
detected. The JHK colors of this candidate are consistent with a spectral type
M0-2. We determine the ages and masses of all four objects from theoretical
tracks and isochrones, all four stars appear to be co-eval with ~20 Myrs. Our
limits for additional detectable but undetected companions are such that we
would have detected all stellar companions with separations > 0.5 arc sec (24
AU at 48 pc).


title:
The X-ray spectrum of the Seyfert I galaxy Mrk 766: Dusty Warm Absorber
  or Relativistic Emission Lines?

abstract:
  Competing models for broad spectral features in the soft X-ray spectrum of
the Seyfert I galaxy Mrk766 are tested against data from a 130 ks XMM-Newton
observation. A model including relativistically broadened Ly-alpha emission
lines of OVIII, NVII and CVI is a better fit to 0.3-2 keV XMM RGS data than a
dusty warm absorber. Moreover, the measured depth of neutral iron absorption
lines in the spectrum is inconsistent with the magnitude of the iron edge
required to produce the continuum break at 17-18Angstroms in the dusty warm
absorber model. The relativistic emission line model can reproduce the
broad-band (0.1-12 keV) XMM-EPIC data with the addition of a fourth line to
represent emission from ionized iron at 6.7 keV and an excess due to reflection
at energies above the iron line. The profile of the 6.7 keV iron line is
consistent with that measured for the low energy lines. There is evidence in
the RGS data at the 3sigma level for spectral features that vary with source
flux. The covering fraction of warm absorber gas is estimated to be ~12%. Iron
in the warm absorber is found to be overabundant with respect to CNO compared
to solar values.


title: Origin of the torsional oscillation pattern of solar rotation

abstract:
  A model is presented that explains the `torsional oscillation' pattern of
deviations in the solar rotation rate as a geostrophic flow. The flow is driven
by temperature variations near the surface due to the enhanced emission of
radiation by the small scale magnetic field. The model explains the sign of the
flow, its amplitude and the fact that the maxima occur near the boundaries of
the main activity belts. The amplitude of the flow decreases with depth from
its maximum at the surface but penetrates over much of the depth of the
convection zone, in agreement with the data from helioseismology. It predicts
that the flow is axisymmetric only on average, and in reality consists of a
superposition of circulations around areas of enhanced magnetic activity. It
must be accompanied by a meridional flow component, which declines more rapidly
with depth.


title: On the effect of discrete numbers of stars in chemical evolution models

abstract:
  We examine the impact of discrete numbers of stars in stellar populations on
the results of Chemical Evolution Models. We explore the resulting dispersion
in the true yields and their possible relation with the dispersion in
observational data based on a Simple Closed-Box model.
  In this framework we find that the dispersion is larger for the less evolved
or low abundance regions. Thus, the age-metallicity relation may be a tracer of
the Star Formation History of our Galaxy. This theoretical dispersion is
especially high for the relative abundance log(N/O) in regions where the total
number of stars created is still low. This may explain part of the scatter in
the N/O ratio observed in star forming galaxies.
  We have also found a first order theoretical estimation for the goodness of a
linear fit of the Helium abundance vs. 12 + log (O/H) with values of the
regression coefficient between 0.9 and 0.7 (independent of sampling effects).
  We conclude that it is necessary to include these sampling effects in a more
realistic Chemical Evolution Model in order that such a model reproduces, at
the same time, the mean value and the dispersion of observed abundances.


title: Gravitational lensing by spinning and escaping lenses

abstract:
  The effect of currents of mass on bending of light rays is considered in the
weak field regime. Following Fermat's principle and the standard theory of
gravitational lensing, we derive the gravitomagnetic correction to time delay
function and deflection angle caused by a geometrically-thin lens. The cases of
both rotating and shifting deflectors are discussed.


title: A note on gravitational wave lensing

abstract:
  In a recent paper [Ruffa] it was proposed that the massive black hole at the
Galactic center may act as a gravitational lens focusing gravitational wave
energy to the Earth. Considering the gravitational wave signal emitted by
galactic spinning pulsars, an enhancement in the gravitational wave intensity
by a factor of a few thousand is found. For galactic and extra-galactic sources
the intensity enhancement can be as high as 4,000 and 17,000, respectively. In
this note we consider the probability of significant signal enhancement from
galactic and extra-galactic pulsars by the proposed mechanism and find that it
is actually negligible. The lensing effect due to a possible companion object
(a star or the galactic center black hole) of the gravitational wave source is
also investigated in the framework of the classical microlensing theory.


title: Astrometric signatures of self-gravitating protoplanetary discs

abstract:
  We use high resolution numerical simulations to study whether gravitational
instabilities within circumstellar discs can produce astrometrically detectable
motion of the central star. For discs with masses of M_disc = 0.1 M_star, which
are permanantly stable against fragmentation, we find that the magnitude of the
astrometric signal depends upon the efficiency of disc cooling. Short cooling
times produce prominent filamentary spiral structures in the disc, and lead to
stellar motions that are potentially observable with future high precision
astrometric experiments. For a disc that is marginally unstable within radii of
\~10 au, we estimate astrometric displacements of 10-100 microarcsec on decade
timescales for a star at a distance of 100 pc. The predicted displacement is
suppressed by a factor of several in more stable discs in which the cooling
time exceeds the local dynamical time by an order of magnitude. We find that
the largest contribution comes from material in the outer regions of the disc
and hence, in the most pessimistic scenario, the stellar motions caused by the
disc could confuse astrometric searches for low mass planets orbiting at large
radii. They are, however, unlikely to present any complications in searches for
embedded planets orbiting at small radii, relative to the disc size, or Jupiter
mass planets or greater orbiting at large radii.


title:
Moments of inertia for neutron and strange stars: limits derived for the
  Crab pulsar

abstract:
  Recent estimates of the properties of the Crab nebula are used to derive
constraints on the moment of inertia, mass and radius of the pulsar. To this
purpose, we employ an approximate formula combining these three parameters. Our
"empirical formula" I = a(x)MR^2, where x = (M/M_sun)(km/R), is based on
numerical results obtained for thirty theoretical equations of state of dense
matter. The functions a(x) for neutron stars and strange stars are
qualitatively different. For neutron stars a_NS(x) = x/(0.1+2x) for x <= 0.1
(valid for M > 0.2 M_sun) and a_NS(x) = (2/9)(1+5x) for x > 0.1. For strange
stars a_SS(x) = (2/5)(1+x) (not valid for strange stars with crust and M < 0.1
M_sun). We obtain also an approximate expression for the maximum moment of
inertia I_max,45 = (-0.37 + 7.12x_max) (M_max/M_sun)(R_(M_max)/(10 km))^2,
valid for both neutron stars and strange stars. Applying our formulae to the
evaluated values of I_Crab, we derive constraints on the mass and radius of the
pulsar. A very conservative evaluation of the expanding nebula mass, M_neb = 2
M_sun, yields M_Crab > 1.2 M_sun and R_Crab = 10-14 km. Setting the most recent
evaluation ("central value") M_neb = 4.6 M_sun rules out most of the existing
equations of state, leaving only the stiffest ones: M_Crab > 1.9 M_sun, R_Crab
= 14-15 km.


title: The mass-function of primordial star clusters

abstract:
  We use the block model to generate merger trees for the first star clusters
in a LCDM cosmology. Using a simple collapse model and cooling criterion, we
determine which halos are able to form stars before being disrupted by mergers.
We contrast the mass functions of all the resulting star clusters and those of
primordial composition, i.e. star clusters that have not been contaminated by
subclusters inside them. In confirmation of previous work, two generations of
primordial star clusters are identified: low-temperature clusters that cool via
molecular hydrogen, and high-temperature clusters that cool via electronic
transitions. The former dominate by number, but the two populations contain a
similar mass with the precise balance depending upon the details of the model.
We speculate on the current-day distribution of Population III stars.


title: Building Planets with Dusty Gas

abstract:
  We have developed a new numerical technique for simulating dusty-gas flows.
Our unique code incorporates gas hydrodynamics, self-gravity and dust drag to
follow the dynamical evolution of a dusty-gas medium. We have incorporated
several descriptions for the drag between gas and dust phases and can model
flows with submillimetre, centimetre and metre size "dust". We present
calculations run on the APAC* supercomputer following the evolution of the dust
distribution in the pre-solar nebula. *Australian Partnership for Advanced
Computing


title: A Survey of 557 GHz Water Vapor Emission in the NGC 1333 Molecular Cloud

abstract:
  Using NASA's Submillimeter Wave Astronomy Satellite (SWAS) we have examined
the production of water in quiescent and shocked molecular gas through a survey
of the 556.936 GHz transition of ortho-H2O in the NGC 1333 molecular core.
These observations reveal broad emission lines associated with the IRAS~2,
IRAS~4, IRAS~7, and HH7-11 outflows. Towards 3 positions we detect narrow (~2-3
km/s) emission lines clearly associated with the ambient gas. The SWAS
observations, with a resolution of 4', are supplemented with observations from
the Infrared Space Observatory (ISO) and by an unbiased survey of a 17' x 15'
area, with 50" resolution, in the low-J transitions of CO, 13CO, C18O, N2H+,
CH3OH, and SiO.
  Using these combined data sets, with consistent assumptions, we find
beam-averaged o-H2O abundances of > 10^{-6} relative to H2O for all four
outflows. A comparison of SWAS and ISO water data is consistent with
non-dissociative shock models, provided the majority of the 557 GHz emission
arises from cool post-shock material with enhanced abundances. In the ambient
gas the o-H2O abundance is found to lie between 0.1-1 x 10^{-7} relative to H2
and is enhanced when compared to cold pre-stellar molecular cores. A comparison
of the water emission with tracers of dense condensations and shock chemistry
finds no clear correlation. However, the water emission appears to be
associated with the presence of luminous external heating sources which power
the reflection nebula and the photodissociation (PDR) region. Simple PDR models
are capable of reproducing the water and high-J 13CO emission, suggesting that
a PDR may account for the excitation of water in low density undepleted gas as
suggested by Spaans & van Dishoeck (2001).


title: X-ray spectral variability of the Seyfert galaxy NGC 4051

abstract:
  We report on the X-ray spectral variability of the Seyfert 1 galaxy NGC 4051
observed with the Rossi X-ray Timing Explorer (RXTE) during a 1000 day period
between May 1996 and March 1999. The spectra were obtained as part of
monitoring observations and from two long observations using the RXTE
Proportional Counter Array (PCA). During the monitoring period the 2-10 keV
flux of NGC 4051 varied between 10E-12 and 7x 10E11 (cgs). We re-analysed RXTE
PCA observations from a distinct low state in May 1998 using the latest
background and detector response models. The RXTE and BeppoSAX observations of
NGC 4051 during the low state show a very hard spectrum with a strong
unresolved fluorescence line. This emission, probably due to reflection from a
molecular torus, is likely to be constant over long time-scales and is
therefore assumed as an underlying component at all flux states. By subtracting
the torus component we are able to determine the spectral variability of the
primary continuum. In the variable component we observe a strong
anti-correlation of X-ray flux and spectral hardness in the PCA energy band. We
show that the changes in hardness are caused by slope variability of the
primary power law spectrum rather than by changing reflection or variable
photoelectric absorption. The primary spectral index varies between Gamma=1.6
for the faintest states and Gamma=2.3 during the brightest states, at which
level the spectral index approaches an asympotic value. We find that the
response of the flux of the 6.4 keV iron fluorescence line to changes in the
continuum flux depends on the timescale of the observation. The profile of the
line is very broad and indicates an origin in the innermost regions of the
accretion disk.


title: Second-Order Cosmological Perturbations from Inflation

abstract:
  We present the first computation of the cosmological perturbations generated
during inflation up to second order in deviations from the homogeneous
background solution. Our results, which fully account for the inflaton
self-interactions as well as for the second-order fluctuations of the
background metric, provide the exact expression for the gauge-invariant
curvature perturbation bispectrum produced during inflation in terms of the
slow-roll parameters or, alternatively, in terms of the scalar spectral $n_S$
and and the tensor to adiabatic scalar amplitude ratio $r$. The bispectrum
represents a specific non-Gaussian signature of fluctuations generated by
quantum oscillations during slow-roll inflation. However, our findings indicate
that detecting the non-Gaussianity in the cosmic microwave background
anisotropies emerging from the second-order calculation will be a challenge for
the forthcoming satellite experiments.


title: Massive Disks in Low Surface Brightness Galaxies

abstract:
  An update of the set of low surface brightness galaxies is presented which
can be used to set constraints on the otherwise ambiguous decompositions of
their rotation curves into contributions due to the various components of the
galaxies. The selected galaxies show all clear spiral structure and arguments
of density wave theory of galactic spiral arms are used to estimate the masses
of the galactic disks. Again these estimates seem to indicate that the disks of
low surface brightness galaxies might be much more massive than currently
thought. This puzzling result contradicts stellar population synthesis models.
This would mean also that low surface brightness galaxies are not dominated by
dark matter in their inner parts.


title: On the time evolution of the redshift and the luminosity distance

abstract:
  We investigate the temporal evolution of the redshift and the luminosity
distance within the standard Friedmann-Roberston-Walker cosmological model. The
redshift and luminosity distance of sources evolve with time and we show that
they tend to given values, namely the stable equilibrium states associated to
the first order differential equation they verify. This suggests that the
sources concentrate at about these values. Furthermore, as these values depend
only on the cosmological parameters, their measure could provide a new approach
to determine the value of the cosmological constant.


title:
Probing the absorbing haloes around two high-redshift radio galaxies
  with VLT-UVES

abstract:
  We present VLT-UVES echelle spectroscopy of the HI and CIV absorption in the
spatially-extended Lyman-alpha emission around two high-redshift radio galaxies
0200+015 (z=2.23) and 0943-242 (z=2.92). The absorbers in 0943-242 exhibit
little additional structure compared with previous low-resolution spectroscopy
and the main absorber is still consistent with HI column density of ~10^19
cm^-2. This is consistent with a picture in which the absorbing gas has low
density and low metallicity and is distributed in a smooth absorbing shell
located beyond the emission-line gas. However, the main absorbers in 0200+015
are very different. The previous single absorber fit of HI column density
\~10^19 cm^-2, now splits into two ~4 x 10^14 cm^-2 absorbers which extend more
than 15kpc to obscure additional Ly-alpha emission coincident with a radio lobe
in these high-resolution observations. Although consistent with the shell-like
distribution for the absorption systems, 0200+015 requires a much higher metal
enrichment than 0943-242. The metallicity, inferred from the CIV absorption, is
considerably lower in 0943-242 than in 0200+015. We explain these differences
with an evolutionary scenario based on the size of the radio source. In both
sources the HI absorption gas originates from either a gas-rich merger or
pristine cluster gas which cools and collapses towards the centre of the dark
matter halo. The higher metallicity in the larger radio source (0200+015) may
be a result of a starburst driven superwind (concurrent with the triggering of
the radio emission) which has engulfed the outer halo in this older source.


title: Radio pulsar death

abstract:
  Pulsar radio emission is believed to be originated from the electron-positron
pairs streaming out from the polar cap region. Pair formation, an essential
condition for pulsar radio emission, is believed to be sustained in active
pulsars via one photon process from either the curvature radiation (CR) or the
inverse Compton scattering (ICS) seed photons, or sometimes via two photon
process. In pulsars with super-critical magnetic fields, some more exotic
processes, such as magnetic photon splitting and bound pair formation, will
also play noticeable roles. All these effects should be synthesized to discuss
radio pulsar death both in the conventional long-period regime due to the
turnoff of the active gap, and in the high magnetic field regime due to the
possible suppression of the free pair formation. Here I briefly review some
recent progress in understanding radio pulsar death.


title: The Flight Spectral Response of the ACIS Instrument

abstract:
  We discuss the flight calibration of the spectral response of the Advanced
CCD Imaging Spectrometer (ACIS) on-board the Chandra X-ray Observatory (CXO).
The spectral resolution and sensitivity of the ACIS instrument have both been
evolving over the course of the mission. The spectral resolution of the
frontside-illuminated (FI) CCDs changed dramatically in the first month of the
mission due to radiation damage. Since that time, the spectral resolution of
the FI CCDs and the backside-illuminated (BI) CCDs have evolved gradually with
time. We demonstrate the efficacy of charge-transfer inefficiency (CTI)
correction algorithms which recover some of the lost performance. The detection
efficiency of the ACIS instrument has been declining throughout the mission,
presumably due to a layer of contamination building up on the filter and/or
CCDs. We present a characterization of the energy dependence of the excess
absorption and demonstrate software which models the time dependence of the
absorption from energies of 0.4 keV and up. The spectral redistribution
function and the detection efficiency are well-characterized at energies from
1.5 to 8.0 keV. The calibration at energies below 1.5 keV is challenging
because of the lack of strong lines in the calibration source and also because
of the inherent non-linear dependence with energy of the CTI and the absorption
by the contamination layer. We have been using data from celestial sources with
relatively simple spectra to determine the quality of the calibration below 1.5
keV. The analysis of these observations demonstrate that the CTI correction
recovers a significant fraction of the spectral resolution of the FI CCDs and
the models of the time-dependent absorption result in consistent measurements
of the flux at low energies for data from a BI (S3) CCD.


title: Tensor to scalar ratio of perturbation amplitudes and inflaton dynamics

abstract:
  For the inflaton perturbations it is shown that the evolution of the
difference between the spectral indices can be translated into information on
the scale dependence of the tensor to scalar amplitudes ratio, $r$, and how the
scalar field potential can be derived from that information. Examples are given
where $r$ converges to a constant value during inflation but dynamics are
rather different from the power--law model. Cases are presented where a
constant $r$ is not characteristic of the inflationary dynamics though the
resulting perturbation spectra are consistent with the CMB and LSS data.
  The inflaton potential corresponding to $r$ given by a n--th order polynomial
of the e--folds number is derived in quadratures expressions. Since the
observable difference between the spectral indices evaluated at a pivot scale
yields information about the linear term of that polynomial, the first order
case is explicitly written down. The solutions show features beyond the
exponential form corresponding to power--law inflation and can be matched with
current observational data.


title: Methane Opacities in T Dwarf Atmospheres

abstract:
  We present the current status of PHOENIX model atmospheres for dwarfs of the
spectral type T, typical for older field brown dwarfs and low-mass brown
dwarfs. The results are based on new predictions of the CH_4 line opacities
from theoretical calculations with the STDS software package, extrapolating to
transitions from rotational levels up to J=40. While individual line positions
and strengths are reproduced with moderate to fair accuracy, the cumulative
band strength in the region of the IR methane bands is modelled much better
thanks to the inclusion of large numbers of faint lines relevant at high
temperatures.


title: Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga

abstract:
  We present high resolution optical spectra obtained with the HIRES
spectrograph on the Keck I telescope of low mass T Tauri stars and brown dwarfs
(LMTTs) in Taurus-Auriga. Of particular interest is the previously classified
"continuum T Tauri star" GM Tau, which has a spectral type of M6.5 and a mass
just below the stellar/substellar boundary. None of the LMTTs in Taurus are
rapidly rotating (vsini < 30 km/s), unlike low mass objects in Orion. Many of
the slowly rotating, non-accreting stars and brown dwarfs exhibit prominent
H-alpha emission (EWs of 3 - 36 A), indicative of active chromospheres. We
demonstrate empirically that the full-width at 10% of the H-alpha emission
profile peak is a more practical and possibly more accurate indicator of
accretion than either the equivalent width of H-alpha or optical veiling:
10%-widths > 270 km/s are classical T Tauri stars (i.e. accreting), independent
of stellar spectral type. Although LMTTs can have accretion rates comparable to
that of more typical, higher-mass T Tauri stars (e.g. K7-M0), the average mass
accretion rate appears to decrease with decreasing mass. The diminished
frequency of accretion disks for LMTTs, in conjunction with their lower, on
average, mass accretion rates, implies that they are formed with less massive
disks than higher-mass T Tauri stars. The radial velocities, circumstellar
properties and known binaries do not support the suggestion that many of the
lowest mass members of Taurus have been ejected from higher stellar density
regions within the cloud. Instead, LMTTs appear to have formed and are evolving
in the same way as higher-mass T Tauri stars, but with smaller disks and
shorter disk lifetimes.


title: The Influence of Triaxial Halos on Collisionless Galactic Disks

abstract:
  We investigate the effect of rotating, triaxial halos on disk galaxies
through an extensive set of numerical N-body simulations. Our simulations use a
rigid potential field for the halos and bulges and collisionless particles for
the disks. The triaxiality and the rotation rate of the halo are varied, as
well as the masses of all three galaxy components. We analyze both the bar
stability and spiral response of the disk under these conditions.
  We characterize most of our models by the mass ratio of the disk to the halo
at 2.3 disk scale lengths, (M_d/M_h)_Rsun. For models with a mass ratio greater
than 0.8, a halo pattern speed Omega_h = 6.7 km/s/kpc, and an
intermediate-to-major axis ratio q_b=0.85, a strong bar will develop within 3
Gyr, even for models with a bulge mass M_b=0.3M_d. Models in which the bulge
mass is reduced by half develop bars earlier and with lower Omega_h.
  We create an artificial Hubble sequence of galaxies by varying the
bulge-to-disk ratio of our models from 0 to 2.5. The torque induced by a
rotating, non-axisymmetric halo creates bisymmetric spiral structure in the
disk. We find the the pitch angle of the spiral arms in these models follows
the same general trend found in observations of spiral galaxies, namely that
later type galaxies have higher pitch angles. Our simulations follow closely
the observational relation of spiral pitch angle with maximum rotational
velocity of the disk, where galaxies with faster rotation have more tightly
wound spiral arms. This relation is followed in our simulations regardless of
whether the dominating mass component of the galaxy is the disk, the halo, or
the bulge.


title: Chandra Observation of Luminous and Ultraluminous X-ray Binaries in M101

abstract:
  X-ray binaries in the Milky Way are among the brightest objects on the X-ray
sky. With the increasing sensitivity of recent missions, it is now possible to
study X-ray binaries in nearby galaxies. We present data on six luminous
sources in the nearby spiral galaxy, M101, obtained with the Chandra ACIS-S. Of
these, five appear to be similar to ultraluminous sources in other galaxies,
while the brightest source, P098, shows some unique characteristics. We present
our interpretation of the data in terms of an optically thick outflow, and
discuss implications.


title: The Three-Point Correlation Function in Cosmology

abstract:
  With the advent of high-quality surveys in cosmology the full three-point
correlation function will be a valuable statistic for describing structure
formation models. It contains information on cosmological parameters and
detailed halo properties that cannot be extracted from the two-point
correlation function. We use the halo clustering model to analytically
calculate the three-point correlation function (3PCF) for general cosmological
fields. We present detailed results for the configuration dependence of the
3-dimensional mass and galaxy distributions and the 2-dimensional cosmic shear
field. We work in real space, where higher order correlation functions on small
scales are easier to measure and interpret, but halo model calculations get
rapidly intractable. Hence we develop techniques for accurate evaluations of
the 1, 2 and 3-halo contributions to the 3PCF.
  The 3PCF violates the hierarchical ansatz in both its scale and configuration
dependence. We study the behavior of the coefficient Q in the hierarchical
expansion from large, quasilinear scales down to about 20 kpc. We find that the
nonlinear 3PCF is sensitive to the halo profile of massive halos, especially
its inner slope. We model the distribution of galaxies in halos and show that
the 3PCF of red galaxies has a weaker configuration and scale dependence than
the mass, while for blue galaxies it is very sensitive to the parameters of the
galaxy formation model. The 3PCF from weak lensing on the other hand shows
different scalings due to projection effects and a sensitivity to cosmological
parameters.


title: Extinction within 10 degrees of the Galactic Centre using 2MASS

abstract:
  We extract J and K_s magnitudes from the 2MASS Point Source Catalog for
approximately 6 million stars with 8 < K_s < 13 in order to build an A_K
extinction map within 10 degrees of the Galactic centre. The extinction was
determined by fitting the upper giant branch of (K_s, J-K_s) colour-magnitude
diagrams to a dereddened upper giant branch mean locus built from previously
studied Bulge fields. The extinction values vary from A_K=0.05 in the edges of
the map up to A_K=3.2 close to the Galactic centre. The 2MASS extinction map
was compared to that recently derived from DENIS data. Both maps agree very
well up to A_K=1.0. The 2MASS extinction values were also compared to those
obtained from dust emission in the far infrared using DIRBE/IRAS. Several
systematic effects likely to bias this comparison were addressed, including the
presence of dust on the background of the bulk of 2MASS stars used in the
extinction determination. For the region with $3^{\circ}<|b|<5^{\circ}$, where
the dust contribution on the far side of the Galaxy is $\approx$ 5%, the two
extinction determinations correlate well, but the dust emission A_K values are
systematically higher than those from 2MASS. A calibration correction factor of
76% for the DIRBE/IRAS dust emission extinction is needed to eliminate this
systematic effect. Similar comparisons were also carried out for the
$1^{\circ}<|b|<3^{\circ}$ and $|b| < 0.5^{\circ}$ strips. An asymmetry relative
to the Galactic plane is observed in the dust maps, roughly in the sense that
A_K values are 60% smaller in the south than in the north for
$1^{\circ}<|b|<5^{\circ}$. This asymmetry is due to the presence of foreground
dust clouds mostly in the northern region of the Bulge.


title:
New insights in high-resolution spectroscopy: a wide theoretical library
  of R=500000 stellar spectra

abstract:
  We present an extended theoretical library of over 800 synthetic stellar
spectra, covering energy distribution in the optical range (lambda = 3500-7000
angstrom), at inverse resolution R=500000. The library, based on the ATLAS9
model atmospheres, has been computed with the SYNTHE code developed by R.L.
Kurucz. The grid spans a large volume in the fundamental parameter space (i.e.
effective temperature, surface gravity, metallicity), and can be profitably
applied to different research fields dealing both with the study of single
stars and stellar aggregates, through population synthesis models. A
complementary project, in progress, will extend the wavelength range to the
ultraviolet, down to 850 angstrom, at an inverse resolution of R=50000.


title:
The alpha-element abundances in the most oxygen-poor planetary nebula PN
  G 135.9+55.9

abstract:
  We present extensive new spectroscopy and imaging of PN G 135.9+55.9.
  We use these data as constraints to photoionization models to derive limits
on the oxygen abundance. We find that PN G 135.9+55.9 has an oxygen abundance
less than 1/50 of the solar value. Our models favour a value of 12 + \log O/H
between 5.8 and 6.5 dex, confirming that PN G 135.9+55.9 is the most
oxygen-poor planetary nebula known (Tovmassian et al. 2001). We also derive
Ne/O = 0.5 +/- 0.3, S/O < 0.094, and Ar/O < 0.23. Although the value of Ne/O is
nominally high, it need not imply that the progenitor of PN G 135.9+55.9
converted any of its initial oxygen abundance to neon. The helium abundance
appears to be very low, He/H ~ 0.08, but a precise determination will require a
much more detailed study. We find that Ha/Hb is lower than expected and perhaps
variable, a finding for which we have no clear explanation.


title: Methane and the Spectra of T Dwarfs

abstract:
  We have updated our PHOENIX model atmospheres and theoretical spectra for
ultracool dwarfs with new opacity data for methane based on line strength
predictions with the STDS software. By extending the line list to rotational
levels of J=40 we can significantly improve the shape of the near-IR absorption
features of CH_4, and in addition find an enhanced blanketing effect, resulting
in up to 50% more flux emerging in the J band than seen in previous models,
which may thus contribute to the brightening in J and blue IR colors observed
in T dwarfs.


title: Five Dwarf Novae with Orbital Periods Below Two Hours

abstract:
  We give mean spectra and report orbital periods Porb based on radial
velocities taken near minimum light for five dwarf novae, all of which prove to
have Porb less than 2 hr. The stars and their periods are KX Aql, 0.06035(3) d;
FT Cam, 0.07492(8) d; PU CMa, 0.05669(4) d; V660 Her, 0.07826(8) d;, and DM
Lyr, 0.06546(6). The emission lines in KX Aql are notably strong and broad, and
the other stars' spectra appear generally typical for short-period dwarf novae.
We observed FT Cam, PU CMa, and DM Lyr on more than one observing run and
constrain their periods accordingly. Differential time-series photometry of FT
Cam shows strong flickering but rules out deep eclipses. Although dwarf novae
in this period range generally show the superhumps and superoutbursts
characteristic of the SU UMa subclass of dwarf novae, none of these objects
have well-observed superhumps.


title:
BRIGHT lights, BIG city: Massive galaxies, giant Ly-a nebulae, and
  proto--clusters

abstract:
  High redshift radio galaxies are great cosmological tools for pinpointing the
most massive objects in the early Universe: massive forming galaxies, active
super--massive black holes and proto--clusters. We report on deep narrow--band
imaging and spectroscopic observations of several z > 2 radio galaxy fields to
investigate the nature of giant Ly-alpha nebulae centered on the galaxies and
to search for over--dense regions around them. We discuss the possible
implications for our understanding of the formation and evolution of massive
galaxies and galaxy clusters.


title: Observed and Physical Properties of Core-Collapse Supernovae

abstract:
  I use photometry and spectroscopy data for 24 Type II plateau supernovae to
examine their observed and physical properties. This dataset shows that these
objects encompass a wide range of ~5 mag in their plateau luminosities, their
expansion velocities vary by x5, and the nickel masses produced in these
explosions go from 0.0016 to 0.26 Mo. From a subset of 16 objects I find that
the explosion energies vary between 0.6x and 5.5x10^51 ergs, the ejected masses
encompass the range 14-56 Mo, and the progenitors' radii go from 80 to 600 Ro.
Despite this great diversity several regularities emerge, which reveal that
there is a continuum in the properties of these objects from the faint,
low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy,
nickel-rich SN 1992am. This study provides evidence that more massive
progenitors produce more energetic explosions, thus suggesting that the outcome
of the core collapse is somewhat determined by the envelope mass. I find also
that supernovae with greater energies produce more nickel. Similar
relationships appear to hold for Type Ib/c supernovae, which suggests that both
Type II and Type Ib/c supernovae share the same core physics. When the whole
sample of core collapse objects is considered, there is a continous
distribution of energies below 8x10^51 ergs. Far above in energy scale and
nickel production lies the extreme hypernova 1998bw, the only supernova firmly
associated to a GRB.


title:
A search for molecules in damped Lyman-alpha absorbers occulting
  millimetre-loud quasars

abstract:
  We have used the SEST 15-metre and Onsala 20-metre telescopes to perform deep
(r.m.s. >~ 30 mJy) integrations of various molecular rotational transitions
towards damped Lyman-alpha absorption systems (DLAs) known to occult
millimetre-loud quasars. We have observed 6 new systems and improved the
existing limits for 11 transitions. These limits may be approaching the
sensitivities required to detect new systems and we present a small number of
candidate systems which we believe warrant further observation.


title: Extrasolar Planets and Mean-Motion Resonances

abstract:
  The 2:1 orbital resonances of the GJ 876 system can be easily established by
the differential planet migration due to planet-nebula interaction. Significant
eccentricity damping is required to produce the observed orbital
eccentricities. The geometry of the GJ 876 resonance configuration differs from
that of the Io-Europa pair, and this difference is due to the magnitudes of the
eccentricities involved. We show that a large variation in the configuration of
2:1 and 3:1 resonances and, in particular, asymmetric librations can be
expected among future discoveries.


title: The primordial Helium abundance

abstract:
  The primordial abundance of 4He, Y_P, is one of the hottest themes in
present-day astronomy, mostly due to its cosmological relevance. The
disagreement between different determinations has been currently reduced to the
1-2 percent level, but these differences are still large enough to have deep
implications for Big-Bang nucleosynthesis. It is therefore crucial to estimate
precisely the uncertainties involved in the measurement of Y_P. Here, I review
the methods used in the determination of Y_P and the related uncertainties. I
also discuss some recent results, and emphasize the assumptions underlying the
differences among them.


title: The lower mass function of young open clusters

abstract:
  We report new estimates for the lower mass function of 5 young open clusters
spanning an age range from 80 to 150 Myr. In all studied clusters, the mass
function across the stellar/substellar boundary (~0.072 Mo) and up to 0.4 Mo is
consistent with a power-law with an exponent alpha of -0.5 +/- 0.1, i.e., dN/dM
~ M**(-0.5).


title:
A modified version of the Gregory-Loredo method for Bayesian periodic
  signal detection

abstract:
  The detection of planetary transits in stellar photometric light-curves is
poised to become the main method for finding substantial numbers of terrestrial
planets. The French-European mission COROT (foreseen for launch in 2005) will
perform the first search on a limited number of stars, and larger missions
Eddington (from ESA) and Kepler (from NASA) are planned for launch in 2007.
Transit signals from terrestrial planets are small (Delta_F/F approx 10^{-4}),
short (Delta_t approx 10 hours) dips, which repeat with periodicity of a few
months, in time series lasting up to a few years. The reliable and automated
detection of such signals in large numbers of light curves affected by
different sources of noise is a statistical and computational challenge. We
present a novel algorithm based on a Bayesian approach. The algorithm is based
on the Gregory-Loredo method originally developed for the detection of pulsars
in X-ray data. In the present paper the algorithm is presented, and its
performance on simulated data sets dominated by photon noise is explored. In an
upcoming paper the influence of additional noise sources (such as stellar
activity) will be discussed.


title: Far infrared polarimeter with very low instrumental polarization

abstract:
  After a short analysis of the main problems involved in the construction of a
Far Infrared polarimeter with very low instrumental noise, we describe the
instrument that will be employed at MITO telescope to search for calibration
sources and investigate polarization near the CMB anisotropy peaks in the next
campaign (Winter 2002-03).


title:
Effects of quintessence on observations of Type Ia SuperNovae in the
  clumpy Universe

abstract:
  We discuss the amplification dispersion in the observed luminosity of
standard candles, like supernovae (SNe) of type Ia, induced by gravitational
lensing in a Universe with dark energy (quintessence). We derive the main
features of the magnification probability distribution function (pdf) of SNe in
the framework of on average Friedmann-Lemaitre-Robertson-Walker (FLRW) models
for both lensing by large-scale structures and compact objects. The
magnification pdf is strongly dependent on the equation of state, $w_Q$, of the
quintessence. The dispersion increases with the redshift of the source and is
maximum for dark energy with very large negative pressure; the effects of
gravitational lensing on the magnification pdf, i.e. the mode biased towards
de-amplified values and the long tail towards large magnifications, are reduced
for both microscopic DM and quintessence with an intermediate $w_Q$. Different
equations of state of the dark energy can deeply change the dispersion in
amplification for the projected observed samples of SNe Ia by future space-born
missions. The "noise" in the Hubble diagram due to gravitational lensing
strongly affects the determination of the cosmological parameters from SNe
data. The errors on the pressureless matter density parameter, $\Omega_M$, and
on $w_Q$ are maximum for quintessence with not very negative pressure. The
effect of the gravitational lensing is of the same order of the other
systematics affecting observations of SNe Ia. Due to the lensing by large-scale
structures, in a flat Universe with $\Omega_M =0.4$, at $z=1$ a cosmological
constant ($w_Q=-1$) can be interpreted as dark energy with $w_Q <-0.84$ (at
2-$\sigma$ confidence limit).


title: Global 8.4-GHz VLBI observations of JVAS B0218+357

abstract:
  In this paper we present new observations of the gravitational lens system
JVAS B0218+357 made with a global VLBI network at a frequency of 8.4 GHz. Our
maps have an rms noise of 30 microJy/beam and with these we have been able to
image much of the extended structure of the radio jet in both the A and B
images at high resolution (~1 mas). The main use of these maps will be to
enable us to further constrain the lens model for the purposes of H0
determination. We are able to identify several sub-components common to both
images with the expected parity reversal, including one which we identify as a
counter-jet. We have not been successful in detecting either the core of the
lensing galaxy or a third image. Using a model of the lensing galaxy we have
back-projected both of the images to the source plane and find that they agree
well. However, there are small, but significant, differences which we suggest
may arise from multi-path scattering in the ISM of the lensing galaxy. We also
find an exponent of the radial mass distribution of approximately 1.04, in
agreement with lens modelling of published 15-GHz VLBI data. Polarisation maps
of each image are presented which show that the distributions of polarisation
across images A and B are different. We suggest that this results from Faraday
rotation and associated depolarisation in the lensing galaxy.


title: An analytical model for the history of cosmic star formation

abstract:
  We use simple analytic reasoning to identify physical processes that drive
the evolution of the cosmic star formation density in cold dark matter
universes. Based on our analysis, we formulate a model to characterise the
redshift dependence of the star formation history and compare it to results
obtained from a set of hydrodynamic simulations which include star formation
and feedback. At early times, densities are sufficiently high and cooling times
sufficiently short that abundant quantities of star-forming gas are present in
all dark matter halos that can cool by atomic processes. Consequently, the star
formation density generically rises exponentially as z decreases, independent
of the details of the physical model for star formation, but dependent on the
normalisation and shape of the cosmological power spectrum. This part of the
evolution is dominated by gravitationally driven growth of the halo mass
function. At low redshifts, densities decline as the universe expands to the
point that cooling is inhibited, limiting the amount of star-forming gas
available. We find that in this regime the star formation rate scales
approximately in proportion to the cooling rate within halos. We derive
analytic expressions for the full star formation history and show that they
match our simulation results to better than ~10%. Using various approximations,
we reduce the expressions to a simple analytic fitting function that can be
used to compute global cosmological quantities that are directly related to the
star formation history. As examples, we consider the integrated stellar
density, the supernova and gamma-ray burst rates observable on Earth, the metal
enrichment history of the Universe, and the density of compact objects.
(abridged)


title: The Carlsberg Meridian Telescope CCD Drift Scan Survey

abstract:
  This paper contains the general data reduction methods used in processing the
data from the Carlsberg Meridian Telescope CCD Drift Scan Survey. An efficient
method to calibrate the fluctuations in the positions of the images caused by
atmospheric turbulence is described. The external accuracy achieved is 36 mas
in right ascension and declination. A description of the recently released
catalogue is given.


title:
Nuclear Ashes: Reviewing Thirty Years of Nucleosynthesis in Classical
  Novae

abstract:
  One of the observational evidences in support of the "thermonuclear runaway
model" for the classical nova outburst relies on the accompanying
nucleosynthesis. In this paper, we stress the relevant role played by
nucleosynthesis in our understanding of the nova phenomenon by constraining
models through a comparison with both the atomic abundance determinations from
the ejecta and the isotopic ratios measured in presolar grains of a likely nova
origin. Furthermore, the endpoint of nova nucleosynthesis provides hints for
the understanding of the mixing process responsible for the enhanced
metallicities found in the ejecta, and reveals also information on the
properties of the underlying white dwarf (mass, luminosity...).
  We discuss first the interplay between nova outbursts and the Galactic
chemical abundances: Classical nova outbursts are expected to be the major
source of 13C, 15N and 17O in the Galaxy, and to contribute to the abundances
of other species with A < 40, such as 7Li or 26Al. We describe the main nuclear
path during the course of the explosion, with special emphasis on the synthesis
of radioactive species, of particular interest for the gamma-ray output
predicted from novae (7Li, 18F, 22Na, 26Al). An overview of the recent
discovery of presolar nova candidate grains, as well as a discussion of the
role played by nuclear uncertainties associated with key reactions of the
NeNa-MgAl and Si-Ca regions, are also given.