title: Microarcsecond Radio Imaging using Earth Orbit Synthesis

abstract:
  The observed interstellar scintillation pattern of an intra-day variable
radio source is influenced by its source structure. If the velocity of the
interstellar medium responsible for the scattering is comparable to the
earth's, the vector sum of these allows an observer to probe the scintillation
pattern of a source in two dimensions and, in turn, to probe two-dimensional
source structure on scales comparable to the angular scale of the scintillation
pattern, typically $\sim 10 \mu$as for weak scattering. We review the theory on
the extraction of an ``image'' from the scintillation properties of a source,
and show how earth's orbital motion changes a source's observed scintillation
properties during the course of a year. The imaging process, which we call
Earth Orbit Synthesis, requires measurements of the statistical properties of
the scintillations at epochs spread throughout the course of a year.


title: HI 21cm imaging of a nearby Damped Lyman-alpha system

abstract:
  We present Giant Metrewave Radio Telescope (GMRT) HI 21cm emission images of
the z=0.009 damped Lyman-alpha (DLA) absorber towards the QSO HS 1543+5921. The
DLA has been earlier identified as a low surface brightness galaxy SBS 1543+593
at an impact parameter of ~ 400 pc to the QSO line of sight. The extremely low
redshift of the absorber allows us to make spatially resolved images of the
21cm emission; besides the HI mass, this also enables us to determine the
velocity field of the galaxy and, hence, to estimate its dynamical mass.
  We obtain a total HI mass of ~ 1.4x10^9 Msun, considerably smaller than the
value of M*(HI) determined from blind 21cm emission surveys. This continues the
trend of low HI mass in all low redshift DLAs for which HI emission
observations have been attempted. We also find that the QSO lies behind a
region of low local HI column density in the foreground galaxy. This is
interesting in view of suggestions that DLA samples are biased against high HI
column density systems. The dynamical mass of the galaxy is found to be Mdyn ~
5x10^9 Msun.


title: A rapidly variable narrow X-ray iron line in Mkn 841

abstract:
  We report on the detection of a rapidly variable narrow Fe K$\alpha$ line in
Mkn 841. The source has been observed two times by XMM-Newton and
simultaneously with BeppoSAX. The two observations, of about 10ks long each,
were separated by $\sim$ 15 hours. The line flux reaches a maximum during the
first observation and is significantly reduced in the second one. The continuum
shape and flux, instead, keep roughly constant between the two pointings. Such
rapid variability of a narrow (unresolved by the XMM-pn instrument) line has
never been reported in the past. These results are not easily explained in the
standard cold reflection model where the narrow line component is supposed to
be produced far from the primary X-ray source (e.g. from the torus) and is thus
not expected to vary rapidly. Different interpretations are discussed.


title:
ROSAT X-ray sources in the field of the LMC. III.The log N -- log S of
  background AGN and the LMC gas

abstract:
  We use 50 (candidate) background X-ray sources (AGN) in the LMC field
observed in ROSAT PSPC observations to derive the observed log N - log S
relation. We correct for the varying PSPC exposure and the absorption due to
the galactic and the LMC gas. We compare the observed log N - log S with a
theoretical log N - log S of the soft extragalactic X-ray background (AGN and a
cluster of galaxy contribution). We find that the observed log N - log S has a
deficiency with respect to the theoretical log N - log S. Factors which can
account for such a deficiency are: (1) incompleteness of the selected AGN and
cluster of galaxies sample, (2) deviation of the log N - log S in the LMC field
from the log N - log S derived from a large sample of AGN in several fields,
(3) existence of gas additional to the HI represented in the Parkes HI map of
the LMC field. We investigate the likely contribution of these effects and find
that (1) a fraction of at most 30% of the background sources may not have been
found in this analysis and may contribute to the observed deficiency. (2) We
cannot exclude a deviation of the log N - log S in the field of the LMC from a
theoretical log N - log S, especially the cluster of galaxy contribution may
show variations across the sky. (3) If LMC gas (restricted to >10^21 cm^-2
columns) in addition to the HI represented in the Parkes map would be
responsible for the deficiency, then a factor of >0.3 (at 90% confidence) of
additional gas would be required. This would equal a molecular mass fraction of
>21%, which would be larger than, but within the uncertainties consistent with
a molecular mass fraction of ~30% derived from CO observations (for columns
>10^21 cm^-2).


title: A study of convection with delta Scuti stars in open clusters: Pleiades

abstract:
  In this work we propose a preliminary seismic investigation of $\delta$ Scuti
stars in the Pleiades cluster, focusing on potential diagnostics of convection
and core-overshooting. Taking into account the effect of fast rotation in the
modelling, we compare observed frequencies for 4 $\delta$ Scuti stars with
radial linear instability predictions. A satisfying agreement is reached
between the predicted ranges of unstable modes and those derived from
observations for ``low-mass'' stars ($\sim 1.55 M_{\odot}$). However, a strong
disagreement is found for ``high-mass'' stars ($\sim 1.77 M_{\odot}$), whatever
the mixing length $(\alpha)$ value. These results are compared with previous
ones obtained for Praesepe.


title: The effect of mixing on metallicity gradients in the ICM

abstract:
  It is generally argued that most clusters of galaxies host cooling flows in
which radiative cooling in the centre causes a slow inflow. However, recent
observations by Chandra and XMM conflict with the predicted cooling flow rates.
It has been suggested that radio jets that are situated at the centre of
clusters of galaxies can assist in reducing the deposition of cold gas. Radio
jets inflate cavities of hot radio plasma that rise through the cluster
atmosphere and thus stir the intra-cluster medium. In this letter it is
investigated whether this scenario is consistent with the pronounced
metallicity gradients that have been observed in the cores of clusters.


title:
A study of correlation between the oscillation amplitude and stellar
  parameters for delta Scuti stars in open clusters. Toward selection rules for
  delta Scuti stars oscillations

abstract:
  In the present work, we study correlations between stellar fundamental
parameters and the oscillation amplitude for delta Scuti stars. We present this
study for a sample of 17 selected delta Scuti stars belonging to 5 young open
clusters. Taking advantage of properties of delta Scuti stars in clusters, we
correct the photometric parameters of our objects for the effect of fast
rotation. We confirm the benefit of applying such corrections in this kind of
studies. In addition, the technique used for this correction allows us to
obtain an estimation of stellar parameters like the angle of inclination and
the rotation rate, usually not accessible. A significant correlation between
the parameter i' (estimation of the angle of inclination of the star) and the
oscillation amplitude is found. A discussion and interpretation of these a
priori surprising results is proposed, in terms of a possible selection rule
for oscillation modes of delta Scuti stars.


title:
A possible contribution to CMB anisotropies at high l from primordial
  voids

abstract:
  We present preliminary results of an analysis into the effects of primordial
voids on the cosmic microwave background (CMB). We show that an inflationary
bubble model of void formation predicts excess power in the CMB angular power
spectrum that peaks between 2000 < l < 3000. Therefore, voids that exist on or
close to the last scattering surface at the epoch of decoupling can contribute
significantly to the apparent rise in power on these scales recently detected
by the Cosmic Background Imager (CBI).


title: On Optimal Detection of Point Sources in CMB Maps

abstract:
  Point-source contamination in high-precision Cosmic Microwave Background
(CMB) maps severely affects the precision of cosmological parameter estimates.
Among the methods that have been proposed for source detection, wavelet
techniques based on ``optimal'' filters have been proposed.In this paper we
show that these filters are in fact only restrictive cases of a more general
class of matched filters that optimize signal-to-noise ratio and that have, in
general, better source detection capabilities, especially for lower amplitude
sources. These conclusions are confirmed by some numerical experiments.
\keywords{Methods: data analysis -- Methods: statistical


title:
Variability in the Thermal Emission from Accreting Neutron Star
  Transients

abstract:
  The composition of the outer 100 m of a neutron star sets the heat flux that
flows outwards from the core. For an accreting neutron star in an X-ray
transient, the thermal quiescent flux depends sensitively on the amount of
hydrogen and helium remaining on the surface after an accretion outburst and on
the composition of the underlying ashes of previous H/He burning. Because H/He
has a higher thermal conductivity, a larger mass of H/He implies a shallower
thermal gradient through the low density envelope and hence a higher effective
temperature for a given core temperature. The mass of residual H and He varies
from outburst to outburst, so the thermal quiescent flux is variable even
though the core temperature is constant for timescales < 10 000 yr. Heavy
elements settle from a H/He envelope in a few hours; we therefore model the
quiescent envelope as two distinct layers, H/He over heavier elements, and
treat the mass of H/He as a free parameter. We find that the emergent thermal
quiescent flux can vary by a factor of 2 to 3 between different quiescent
epochs. The variation is more pronounced at lower interior temperatures, making
systems with low quiescent luminosities and frequent outbursts, such as SAX
J1808.4-3658, ideal candidates from which to observe this effect. We compute,
for different ash compositions, the interior temperatures of Cen X-4, Aql X-1,
and SAX J1808.4-3658. In the case of Aql X-1, the inferred high interior
temperature suggests that neutrino cooling contributes to the neutron star's
thermal balance.


title: Hubble Space Telescope NICMOS Imaging of the Core of M87

abstract:
  We present broad-band 1.1, 1.6 and 2.2 micron images and a 2.37 micron
narrow-band image of the inner 19" of the nearby radio galaxy M87, obtained
with the Near Infrared Camera and Multi-Object Spectrometer of the Hubble Space
Telescope (HST). The isophotes of the broad-band images are almost perfectly
circular to within approximately 0.5" (~ 50 pc) of the active nucleus, and an
r**1/4 law provides a good fit to the galaxy profile to within the same
distance. This result agrees with predictions that the nuclear supermassive
black hole will produce a nearly spherical distribution of the surrounding
stars within a galaxy crossing time. A difference image formed from the 1.6
micron image and a V-band image obtained with the HST Wide Field Planetary
Camera 2 does not show any clear evidence of a physically thick dusty torus
around the nucleus, consistent with its lack of strong thermal infrared
emission. The images and associated colors also confirm that the regions beyond
the nucleus do not contain strongly concentrated dust,in contrast to many other
radio galaxies. In combination with other recent observations, these results
indicate that M87 represents the dynamically evolved product of past galaxy
mergers, and suggest that its nucleus is in the final stages of activity.


title:
Infrared spectroscopy of the largest known trans-neptunian object 2001
  KX76

abstract:
  We report complete near-infrared (0.9-2.4 $\mu$m) spectral observations of
the largest know trans-neptunian objects (TNO) 28976 = 2001 KX$_{76}$ taken in
two different nights using the new Near Infrared Camera Spectrometer (NICS)
attached to the 3.56m Telescopio Nazionale Galileo (TNG). The spectra are
featureless and correspond to a neutral colored object. Our observations
indicate that the surface of 2001 KX$_{76}$ is probably highly evolved due to
long term irradiation, and that collisional resurfacing processes have not
played an important role in its evolution.


title: VLBA Measurement of Nine Pulsar Parallaxes

abstract:
  We determined the distances to nine pulsars by parallax measurements using
the NRAO Very Long Baseline Array, doubling the number of pulsars with accurate
distance measurements. Broadband phase modeling was used to calibrate the
varying dispersive effects of the ionosphere and remove the resulting phase
errors from the phase-referenced VLBI data. The resulting parallaxes have a
typical accuracy of 100 microarcseconds or better, yielding distances
measurements as accurate as 2%. We also report new proper motion measurements
of these pulsars, accurate to 0.4 mas per year or better.


title: Determining Central Black Hole Masses in Distant Active Galaxies

abstract:
  An empirical relationship, of particular interest for studies of high
redshift active galactic nuclei (AGNs) and quasars, between the masses of their
central black-holes and rest-frame ultraviolet (UV) parameters measured in
single-epoch AGN spectra is presented. This relationship is calibrated to
recently measured reverberation masses of low-redshift AGNs and quasars. An
empirical relationship between single-epoch rest-frame optical
spectrophotometric measurements and the central masses is also presented. The
UV relationship allows reasonable estimates of the central masses to be made of
high-redshift AGNs and quasars for which these masses cannot be directly or
easily measured by the techniques applicable to the lower luminosity, nearby
AGNs. The central mass obtained by this method can be estimated to within a
factor of ~3 for most objects. This is reasonable given the intrinsic
uncertainty of a factor less than 2 in the primary methods used to measure the
central masses of nearby inactive and active galaxies, namely resolved gas and
stellar kinematics in the underlying host galaxy and reverberation-mapping
techniques. The UV relationship holds good potential for being a powerful tool
to study black-hole demographics at high redshift as well as to statistically
study the fundamental properties of AGNs. The broad line region size -
luminosity relationship is key to the calibrations presented here. The fact
that its intrinsic scatter is also the main source of uncertainty in the
calibrations stresses the need for better observational constraints to be
placed on this relationship. The empirically calibrated relationships presented
here will be applied to quasar samples in forthcoming work.


title: Discovery of two infrared supernovae: a new window on the SN search

abstract:
  We report the discovery of two supernovae (SN 1999gw and SN 2001db) obtained
within the framework of an infrared monitoring campaign of Luminous Infrared
Galaxies, aimed at detecting obscured supernovae. SN 2001db, extinguished by
Av~5.5 mag, is the first supernova discovered in the infrared which has
received the spectroscopic confirmation. This result highlights the power of
infrared monitoring in detecting obscured SNe and indicates that optical
surveys are probably missing a significant fraction of SNe, especially in
obscured systems such as starburst galaxies. The preliminary estimate of SN
rate in LIRG galaxies is about an order of magnitude higher than that expected
from optical surveys.


title: The Growth and Structure of Dark Matter Haloes

abstract:
  In this paper, we analyse in detail the mass-accretion histories and
structural properties of dark haloes in high-resolution N-body simulations.
Modeling the density distribution in individual haloes with the NFW profile, we
find, for all main progenitors of a given halo, there is a tight correlation
between its inner scale radius $r_s$ and the mass within it, $M_s$, which is
the basic reason why halo structural properties are closely related to their
mass-accretion histories. This correlation can be used to predict accurately
the structural properties of a dark halo at any time from its mass-accretion
history. We also test our model with a large sample of GIF haloes. The build-up
of dark haloes in CDM models generally consists of an early phase of fast
accretion and a late phase of slow accretion [where $M_h$ increases with time
approximately as the expansion rate]. These two phases are separated at a time
when the halo concentration parameter $c\sim 4$. Haloes in the two accretion
phases show systematically different properties, for example, the circular
velocity $v_h$ increases rapidly with time in the fast accretion phase but
remain almost constant in the slow accretion phase,the inner properties of a
halo, such as $r_s$ and $M_s$ increase rapidly with time in the fast accretion
phase but change only slowly in the slow accretion phase. The potential well
associated with a halo is built up mainly in the fast accretion phase, even
though a large amount of mass (over 10 times) can be accreted in the slow
accretion phase. We discuss our results in connection to the formation of dark
haloes and galaxies in hierarchical models.


title:
The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda
  III

abstract:
  The Hubble Space Telescope WFPC2 camera has been used to image Andromeda III,
a dwarf spheroidal companion (dSph) to M31. The resulting color-magnitude (c-m)
diagrams reveal the morphology of the horizontal branch (HB) in this dwarf
galaxy. We find that like Andromeda I and Andromeda II, and like most of the
Galactic dSph companions, the HB morphology of And III is predominantly red,
redder than that of both And I and And II despite And III having a lower mean
metallicity. We interpret this red HB morphology as indicating that the bulk of
the And III population is ~3 Gyr younger than the age of the majority of
Galactic globular clusters. Nevertheless, the And III c-m diagram does reveal a
few blue HB stars, and a number of RR Lyrae variables are also evident in the
data. This indicates that And III does contain an `old' population of age
comparable to that of the Galactic globular clusters. There is no evidence,
however, for any young stars in And III despite a claimed association between
this dSph and an HI cloud. As was the case for And II, but not And I, no radial
gradient was detected in the And III HB morphology. And III is ~75 kpc from the
center of M31, comparable to the Galactocentric distances of Sculptor and
Draco. Comparison with standard globular cluster red giant branches indicates
<[Fe/H]> = -1.88 +/-0.11, consistent with the absolute-magnitude - mean
abundance relation followed by dSph galaxies. The same comparison yields an
intrinsic abundance dispersion of sigma([Fe/H]) = 0.12, a low value compared to
the Galactic dSphs of comparable luminosity to And III. The list of candidate
variables reveals one definite and one probable Anomalous Cepheid variables.


title:
Detections of SiO Masers from the Large-Amplitude Variables in the
  Galactic Nuclear Disk

abstract:
  We have surveyed known large-amplitude variables within 15' of the Galactic
center in the SiO J=1-0 v=1 and 2 maser lines at 43 GHz, resulting in 79
detections and 58 non-detections. The detection rate of 58 percent is
comparable to that obtained in Bulge IRAS source surveys. SiO lines were also
detected from four other sources near the program objects. The SiO detection
rate increases steeply with the period, particularly for stars with P>500 d,
where it exceeds 80%. We found at a given period that the SiO detection rate is
approximately double that for OH. These facts suggest that the large-amplitude
variables in the Nuclear Disk region are AGB stars similar in their overall
properties to the inner and outer bulge IRAS/SiO sources.


title:
Clementine Observations of the Zodiacal Light and the Dust Content of
  the Inner Solar System

abstract:
  Using the Moon to occult the Sun, the Clementine spacecraft used its
navigation cameras to map the inner zodiacal light at optical wavelengths over
elongations of 3-30 degrees from the Sun. This surface brightness map is then
used to infer the spatial distribution of interplanetary dust over heliocentric
distances of about 10 solar radii to the orbit of Venus. We also apply a simple
model that attributes the zodiacal light as being due to three dust populations
having distinct inclination distributions, namely, dust from asteroids and
Jupiter-family comets (JFCs), dust from Halley-type comets, and an isotropic
cloud of dust from Oort Cloud comets. The best-fitting scenario indicates that
asteroids + JFCs are the source of about 45% of the optical dust cross-section
seen in the ecliptic at 1 AU, but that at least 89% of the dust cross-section
enclosed by a 1 AU radius sphere is of a cometary origin. When these results
are extrapolated out to the asteroid belt, we find an upper limit on the mass
of the light-reflecting asteroidal dust that is equivalent to a 12 km asteroid,
and a similar extrapolation of the isotropic dust cloud out to Oort Cloud
distances yields a mass equivalent to a 30 km comet, although the latter mass
is uncertain by orders of magnitude.


title: Angular Resolution of the Pachmarhi Array of Cerenkov Telescopes

abstract:
  The Pachmarhi Array of Cerenkov Telescopes consists of a distributed array of
25 telescopes that are used to sample the atmospheric Cerenkov Photon showers.
Each telescope consists of 7 parabolic mirrors each viewed by a single
photo-multiplier tube. Reconstruction of photon showers are carried out using
fast timing information on the arrival of pulses at each PMT. The shower front
is fitted to a plane and the direction of arrival of primary particle
initiating the shower is obtained. The error in the determination of the
arrival direction of the primary has been estimated using the {\it split} array
method. It is found to be $\sim 2.4^\prime ~$ for primaries of energy $ > 3
\~TeV$. The dependence of the angular resolution on the separation between the
telescopes and the number of detectors are also obtained from the data.


title:
KiloHertz quasi-periodic oscillations difference frequency exceeds
  inferred spin frequency in 4U 1636-53

abstract:
  Recent observations of the low-mass X-ray binary 4U 1636-53 with the Rossi
X-ray Timing Explorer show, for the first time, a kiloHertz quasi-periodic
oscillation (kHz QPO) peak separation that exceeds the neutron star spin
frequency as inferred from burst oscillations. This strongly challenges the
sonic-point beat frequency model for the kHz QPOs found in low-mass X-ray
binaries. We detect two simultaneous kHz QPOs with a frequency separation of
323.3+-4.3 Hz in an average Fourier power spectrum of observations obtained in
September 2001 and January 2002. The lower kHz QPO frequency varied between 644
Hz and 769 Hz. In previous observations of this source the peak separation
frequency was ~250 Hz when the lower kHz QPO frequency was ~900 Hz. Burst
oscillations occur in 4U 1636-53 at ~581 Hz and possibly at half that frequency
(290.5 Hz). This is the first source where the peak separation frequency is
observed to change from less than (half) the burst oscillation frequency to
more than that. This observation contradicts all previously formulated
implementations of the sonic-point beat frequency model except those where the
disk in 4U 1636-53 switches from prograde to retrograde.


title: Nature of Faint Companions to G type Stars using Adaptive Optics

abstract:
  High spatial resolution (0.30 arcsec) NIR photometric observations using the
adaptive optics of the 100 inch Mt. Wilson Telescope and the Penn State IR
Imager and Spectrograph (PIRIS) have revealed faint companions to HD190067 and
HIP13855. HD190067b is found to be of mass of 0.075$M_{\odot}$ to
0.1$M_{\odot}$ and with an age of 0.5 Gyrs to a few Gyrs. HIP13855b is a low
mass star (age: 100 Myrs to 500 Myrs) of mass range between 0.1$M_{\odot}$ to
0.2$M_{\odot}$. Further NIR spectroscopic observations will be necessary to
classify their spectral type precisely.


title: Tracking quintessential inflation from brane worlds

abstract:
  We analyse the mechanism of quintessential inflation in brane world scenarios
for a number of particle physics inspired scalar potentials. We constrain the
parameter space of those scalar potentials and comment on the likelihood that
we could discriminate these models from standard inflation, based on upcoming
large scale structure and cosmic microwave background observations.


title: X-Ray Resonance Opacity of Oxygen and Iron in AGN MCG--6-30-15

abstract:
  Theoretical differential oscillator strengths related to monochromatic
opacity due to K- and L-shell absorption from oxygen and iron ions are directly
compared with the Chandra and Xmm-Newton spectra of Seyfert~1 galaxy
MCG--6-30-15. We compute the highly resolved continuum with resonances due to O
I - VI and Fe XVI. It is found that the KLn (n --> infty) resonance series
limits in O VI, and the lowest LMM resonance in Fe XVI, lie at the prominent
17.5 A break in the observed spectra. We also calculate and identify, for the
first time, the observed gap in spectral flux at 22-23 A in the Chandra spectra
due to K --> L resonant absorption features from all O-ions O I - VI,
potentially leading to abundance determination of several or all ionization
stages; similar signature gaps may be predicted due to other elements. The
precise atomic parameters are computed in the relativistic close coupling
approximation using the Breit-Pauli R-matrix method. The new X-ray opacities
might possibly distinguish between models of a dusty warm absorber, and/or
gravitational redshift and broadening due to a massive black hole in
MCG--6-30-15.


title:
Chemical composition of carbon-rich, very metal-poor subgiant LP625-44
  observed with the Subaru/HDS

abstract:
  We have obtained a high resolution (R~90,000) spectrum of the carbon- and
s-process-element-rich, very metal-poor ([Fe/H]=-2.7) subgiant LP625-44, as
well as that of HD140283 (a metal-poor subgiant with normal abundance ratio)
for comparison, with the High Dispersion Spectrograph (HDS) for the Subaru
Telescope for detailed abundance study. The oxygen abundance derived from the O
I triplet around 7770A is uncertain, but the excess of oxygen in LP625-44 seems
remarkable (perhaps by nearly a factor 10), in comparison with that of HD140283
derived from the same lines. The Na enhancement in LP625-44 is by about a
factor 50, suggesting hydrogen burning in the 22Ne-rich layer in an asymptotic
giant branch star which produces the abundance pattern of this object. In our
new spectrum of LP625-44, the Pb I lambda 3683A line has been detected, as well
as the Pb I lambda 4057A line which has already been studied, confirming the Pb
abundance (log epsilon(Pb)~1.9) derived by the previous work. The abundance
ratio of s-process elements at the second peak (e.g., La, Ce and Nd) to that at
the third peak (Pb) in LP 625-44 is significantly higher (by a factor 5) than
that in other three s-process element-rich objects recently studied by van Eck
et al.. Recent theoretical works have modeled the s-process nucleosynthesis in
the radiative layer of asymptotic giant branch stars in the inter-pulse phase,
and the above results means that these processes produced a large scatter in
the abundance ratios. Another possiblity is that different processes (e.g.,
s-process nucleosynthesis during thermal pulses) have contributed to heavy
elements in the early Galaxy.


title: SPH compressible turbulence

abstract:
  In this paper an SPH version of the alpha turbulence model devised by Holm
and his colleagues is formulated for compressible flow with a resolution that
varies in space and time. The alpha model involves two velocity fields. One
velocity field is obtained from the momentum equation, the other by averaging
this velocity field as in the version of SPH called XSPH. The particles (fluid
elements) are moved with the averaged velocity. In analogy to the continuum
alpha model we obtain a particle Lagrangian from which the SPH alpha equations
can be derived. The system satisfies a discrete Kelvin circulation theorem
identical to that obtained with no velocity averaging. In addition, the energy,
linear and angular momentum are conserved. We show that the continuum
equivalent of the SPH equations are identical to the continuum alpha model, and
we conjecture that they will have the same desirable features of the continuum
modelincluding the reduction of energy in the high wave number modes even when
the dissipation is zero. Regardless of issues concerning turbulence modelling,
the SPH alpha model is a powerful extension of the XSPH algorithm which reduces
disorder at short length scales and retains the constants of the motion. The
SPH alpha model is simple to implement.


title: X-ray powerful diagnostics for highly-ionized plasmas: He-like ions

abstract:
  The calculations of the ratios of the Helium-like ion X-ray lines from C V to
Si XIII are revisited in order to apply the results to density, temperature and
ionization process diagnostics of data from high-resolution spectroscopy of the
new generation of X-ray satellites: Chandra and XMM-Newton.
  Comparing to earlier computations, Porquet & Dubau (2000), the best
experimental values are used for radiative transition probabilities. The
influence of an external radiation field (photo-excitation), the contribution
from unresolved dielectronic satellite lines and the optical depth are taken
into account.
  These diagnostics could be applied to collision-dominated plasmas (e.g.,
stellar coronae), photo-ionized plasmas (e.g., ``Warm Absorber'' in AGNs), and
transient plasmas (e.g., SNRs).


title: Astrometric Microlensing: A Channel to Detect Multiple Lens Systems

abstract:
  If a source star is gravitationally microlensed by a multiple lens system,
the resulting light curve can have significant deviations from the standard
form of a single lens event. The chance to produce significant deviations
becomes important when the separations between the component lenses are
equivalent to the combined angular Einstein ring radius of the system. For
multiple lens systems composed of more than two lenses, however, this condition
is difficult to meet because the orbits of such systems are unstable. Even if
events are caused by a multiple lens system with stable orbits where a pair of
lenses are closely located and the other component (third body) has a wide
separation from the pair, photometrically identifying the lens multiplicity
will be difficult because the event will be identified either by a binary lens
event caused by the close pair lenses or a single lens event caused by the
third body. In this paper, we show that if a seemingly binary lens event is
astrometrically followed up by using future high precision interferometers, the
existence of an additional third body can be identified via a repeating event.
We show that the signatures of third bodies can be unambiguously identified
from the characteristic distortions they make in the centroid shift
trajectories. We also show that due to the long range astrometric effect of
third bodies, the detection efficiency will be considerable even for third
bodies with large separations from their close lens pairs.


title:
Dynamical state of superclusters of galaxies: do superclusters expand or
  have they started to collapse?

abstract:
  We investigate the dynamical state of superclusters in Lambda cold dark
matter ($\Lambda$CDM) cosmological models, where the density parameter
$\Omega_0=0.2-0.4$ and $\sigma_8$ (the rms fluctuation on the $8h^{-1}$Mpc
scale) is $0.7-0.9$. To study the nonlinear regime, we use N-body simulations.
We define superclusters as maxima of the density field smoothed on the scale
$R=10h^{-1}$Mpc. Smaller superclusters defined by the density field smoothed on
the scale $R=5h^{-1}$Mpc are also investigated. We find the relations between
the radially averaged peculiar velocity and the density contrast in the
superclusters for different cosmological models. These relations can be used to
estimate the dynamical state of a supercluster on the basis of its density
contrast. In the simulations studied, all the superclusters defined with the
$10h^{-1}$Mpc smoothing are expanding by the present epoch. Only a small
fraction of the superclusters defined with $R=5h^{-1}$Mpc has already reached
their turnaround radius and these superclusters have started to collapse. In
the model with $\Omega_0=0.3$ and $\sigma_8=0.9$, the number density of objects
which have started to collapse is $5 \times 10^{-6}h^3$Mpc$^{-3}$. The results
for superclusters in the N-body simulations are compared with the spherical
collapse model. We find that the radial peculiar velocities in N-body
simulations are systematically smaller than those predicted by the spherical
collapse model ($\sim 25$% for the $R=5h^{-1}$Mpc superclusters).


title: The radio-loud plasma in pulsars

abstract:
  The pulsar magnetosphere contains a strongly magnetized, relativistic plasma.
We need to understand the physics of that plasma if we want to connect the data
to the models. Our group in Socorro is mixing theory and observations in order
to study the radio-loud pulsar plasma. In this paper we report on several
aspects of our current work.


title: Subluminous Stars among the FAUST UV sources toward OPHIUCHUS

abstract:
  We present results of an analysis of a UV image in the direction of
Ophiuchus, obtained with the FAUST instrument. The image contains 228 UV
sources. Most of these were identified as normal early-type stars through
correlations with cataloged objects. For the first time in this project we
identified UV sources as such stars by selecting suitable candidates in crowded
fields as the bluest objects in color-color diagrams using observations from
the Wise Observatory. These candidates were then studied using low-resolution
spectroscopy, which allowed the determination of spectral types to an accuracy
of about one-half class, for 60 stars. Synthetic photometry of spectral data
was performed in order to predict the expected UV emission, on the basis of the
photometric information. These results were used along with the Hipparcos/Tycho
information, to search for sub-luminous stars. The comparison of the predicted
emission with the FAUST measured magnitudes allowed us to select twelve stars
as highly-probable evolved hot stars. High signal-to-noise spectra were
obtained for nine of these stars and Balmer line profiles were compared with
the prediction of atmosphere models and with the spectrum of real stellar
atmospheres. Among the nine candidates, six are classified as previously
unrecognized sdB stars and two as white dwarfs. Our result indicates that
indeed more bright subluminous stars are still unrecognized in the existing
samples.


title:
Unveiling the structure of the planetary nebula M 2-48: Kinematics and
  physical conditions

abstract:
  The kinematics and physical conditions of the bipolar planetary nebula M 2-48
are analysed from high and low dispersion long-slit spectra. Previous CCD
narrow-band optical observations have suggested that this nebula is mainly
formed by a pair of symmetric bow-shocks, an off-center semi-circular shell,
and an internal bipolar structure. The bipolar outflow has a complex structure,
characterised by a series of shocked regions located between the bright core
and the polar tips. There is an apparent kinematic discontinuity between the
bright bipolar core and the outer regions. The fragmented ring around the
bright bipolar region presents a low expansion velocity and could be associated
to ejection in the AGB-PN transition phase, although its nature remains
unclear. The chemical abundances of the central region are derived, showing
that M 2-48 is a Type I planetary nebula (PN).


title: Superhumps in Cataclysmic Binaries. XXII. 1RXS J232953.9+062814

abstract:
  We report photometry of 1RXS J232953.9+062814, a recently discovered dwarf
nova with a remarkably short 64.2-minute orbital period. In quiescence, the
star's light curve is that of a double sinusoid, arising from the "ellipsoidal"
distortion of the Roche-lobe-filling secondary. During superoutburst, common
superhumps develop with a period 3-4% longer than P_orb. This indicates a mass
ratio M_2/M_1=0.19+-0.02, a surprisingly large value in so compact a binary.
This implies that the secondary star has a density 2-3 times higher than that
of other short-period dwarf novae, suggesting a secondary enriched by H-burning
prior to the common-envelope phase of evolution. We estimate i=50+-5 deg,
M_1=0.63 (+0.12, -0.09) M_sol, M_2=0.12 (+0.03, -0.02) M_sol, R_2=0.121
(+0.010, -0.007) R_sol, and a distance to the binary of 180+-40 pc.


title: The 2001 Superoutburst of WZ Sagittae

abstract:
  We report the results of a worldwide campaign to observe WZ Sagittae during
its 2001 superoutburst. After a 23-year slumber at V=15.5, the star rose within
2 days to a peak brightness of 8.2, and showed a main eruption lasting 25 days.
The return to quiescence was punctuated by 12 small eruptions, of ~1 mag
amplitude and 2 day recurrence time; these "echo outbursts" are of uncertain
origin, but somewhat resemble the normal outbursts of dwarf novae. After 52
days, the star began a slow decline to quiescence.
  Periodic waves in the light curve closely followed the pattern seen in the
1978 superoutburst: a strong orbital signal dominated the first 12 days,
followed by a powerful /common superhump/ at 0.05721(5) d, 0.92(8)% longer than
P_orb. The latter endured for at least 90 days, although probably mutating into
a "late" superhump with a slightly longer mean period [0.05736(5) d]. The
superhump appeared to follow familiar rules for such phenomena in dwarf novae,
with components given by linear combinations of two basic frequencies: the
orbital frequency omega_o and an unseen low frequency Omega, believed to
represent the accretion disk's apsidal precession. Long time series reveal an
intricate fine structure, with ~20 incommensurate frequencies. Essentially all
components occurred at a frequency n(omega_o)-m(Omega), with m=1, ..., n. But
during its first week, the common superhump showed primary components at n
(omega_o)-Omega, for n=1, 2, 3, 4, 5, 6, 7, 8, 9 (i.e., m=1 consistently); a
month later, the dominant power shifted to components with m=n-1. This may
arise from a shift in the disk's spiral-arm pattern, likely to be the
underlying cause of superhumps.
  The great majority of frequency components ... . (etc., abstract continues)


title:
Deuterated molecules as a probe of ionization fraction in dense
  interstellar clouds

abstract:
  Deuterium fractionation in molecular ions, in particular HCO+, has been
extensively used to estimate the degree of ionization in molecular clouds. This
paper reviews recent work on ionization degree in homogeneous clouds. We will
show that the N(DCO+)/N(HCO+) column density ratio furnishes a measurement of
x(e) only in regions where CO is not significantly depleted, thus in the outer
skirts of dense cloud cores. To probe x(e) deep inside the clouds, one has to
gauge deuterium enhancement in molecular ions with parent species not affected
by depletion (e.g. N2H+), and rely on chemical models which take into account
the cloud density structure. Unlike N(DCO+)/N(HCO+), the N(N2D+)/N(N2H+) column
density ratio is predicted to considerably increase with core evolution (and/or
the amount of CO depletion), reaching large values (> 0.2) in cloud cores on
the verge of forming a star.


title:
Evidence for Orbital Decay of RX J1914.4+2456: Gravitational Radiation
  and the Nature of the X-ray Emission

abstract:
  RX J1914.4+2456 is a candidate double-degenerate binary (AM CVn) with a
putative 569 s orbital period. If this identification is correct, then it has
one of the shortest binary orbital periods known, and gravitational radiation
should drive the orbital evolution and mass transfer if the binary is
semi-detached. Here we report the results of a coherent timing study of the
archival ROSAT and ASCA data for RX J1914.4+2456. We performed a phase coherent
timing analysis using all five ROSAT observations spanning a 4.6 year period.
We demonstrate that all the data can be phase connected, and we show evidence
that the 1.756 mHz orbital frequency is increasing at a rate of 8 +- 3 e-18
Hz/s, consistent with the expected loss of angular momentum from the binary
system via gravitational radiation. In addition to providing evidence for the
emission of gravitational waves, our measurement of the orbital decay
constrains models for the X-ray emission and the nature of the secondary. If
stable mass accretion drives the X-ray flux, then orbital decay is inconsistent
with a degenerate donor. A helium burning dwarf is compatible if indeed such
systems can have periods as short as that of RX J1914.4+2456, an open
theoretical question. Our measurement is consistent with the unipolar induction
model of Wu et al. which does not require accretion to drive the X-ray flux. We
discuss how future timing measurements of RX J1914.4+2456 (and systems like it)
with for example, Chandra and XMM-Newton, can provide a unique probe of the
interaction between mass loss and gravitational radiation. We also discuss the
importance of such measurements in the context of gravitational wave detection
from space, such as is expected in the future with the LISA mission.


title:
Two-dimensional kinematics and stellar populations of early-type
  galaxies: First results from the SAURON survey

abstract:
  We present the SAURON project, which is aimed at studying the morphology,
two-dimensional kinematics and stellar populations of a representative sample
of elliptical galaxies and spiral bulges. SAURON, a dedicated integral-field
spectrograph that is optimized for wide-field observations and has high
throughput, was built in Lyon and is now operated at the WHT 4.2m telescope. At
present, we have observed approximately two thirds of the seventy-two sample
galaxies with SAURON. A comparison with published long-slit measurements
demonstrates that the SAURON-data is of equal or better quality, and provides
full two-dimensional coverage. The velocity and velocity dispersion fields
exhibit a large variety of morphologies: from simple rotating systems to
cylindrical, disky and triaxial velocity fields, bars and decoupled cores. Most
of these kinematical signatures do not have counterparts in the light
distribution. While some galaxies are consistent with axisymmetry, most are
more complex systems than assumed previously. This suggests that the
kinematical properties of nearby E/S0 galaxies do not agree with the often
assumed simplistic two-family model, in which the giant non-rotating triaxial
ellipticals are opposed to the fast-rotating axisymmetric faint ellipticals and
S0s.


title: Detection of the 2175\AA Extinction Feature at z=0.83

abstract:
  We determine the extinction curve in the z_l=0.83 lens galaxy of the
gravitational lens SBS0909+532 from the wavelength dependence of the flux ratio
between the lensed quasar images (z_s=1.38) from 3400 to 9200\AA. It is the
first measurement of an extinction curve at a cosmological distance of
comparable quality to those obtained within the Galaxy. The extinction curve
has a strong 2175\AA feature, a noteworthy fact because it has been weak or
non-existent in most estimates of extinction curves outside the Galaxy. The
extinction curve is fitted well by a standard $R_V=2.1\pm0.9$ Galactic
extinction curve. If we assume standard Galactic extinction laws, the estimated
dust redshift of $z=0.88\pm0.02$ is in good agreement with the spectroscopic
redshift of the lens galaxy. The widespread assumption that SMC extinction
curves are more appropriate models for cosmological dust may be incorrect.


title:
Chandra Observations of the Pleiades Open Cluster: X-ray Emission from
  Late-B to Early-F Type Binaries

abstract:
  We present the analysis of a 38.4 ks and a 23.6 ks observation of the core of
the Pleiades open cluster. The Advanced CCD Imaging Spectrometer on board the
Chandra X-ray Observatory detected 99 X-ray sources in a 17'X17' region,
including 18 of 23 Pleiades members. Five candidate Pleiades members have also
been detected, confirming their cluster membership. Fifty-seven sources have no
optical or near-infrared counterparts to limiting magnitudes V=22.5 and J=14.5.
The unidentified X-ray sources are probably background AGN and not stars. The
Chandra field of view contains seven intermediate mass cluster members. Five of
these, HII 980 (B6 + G), HII 956 (A7 + F6), HII 1284 (A9 + K), HII 1338 (F3 +
F6), and HII 1122 (F4 + K), are detected in this study. All but HII 1284 have
high X-ray luminosity and soft X-ray spectra. HII 1284 has X-ray properties
comparable to non-flaring K-type stars. Since all five stars are visual or
spectroscopic binaries with X-ray properties similar to F-G stars, the
late-type binary companions are probably producing the observed coronal X-ray
emission. Strengthening this conclusion is the nondetection by Chandra of two A
stars, HII 1362 (A7, no known companion) and HII 1375 (A0 + A SB) with X-ray
luminosity upper limits 27-54 times smaller than HII 980 and HII 956, the B6-A7
stars with cooler companions. Despite the low number statistics, the Chandra
data appear to confirm the expectation that late-B and A stars are not strong
intrinsic X-ray sources. The ACIS spectra and hardness ratios suggest a gradual
increase in coronal temperature with decreasing mass from F4 to K. M stars
appear to have somewhat cooler coronae than active K stars.


title: Super-Eddington outburst of V4641 Sgr

abstract:
  X-ray transients provide unique opportunity to probe accretion regimes of at
a vastly different accretion rates. We analyze a collection of the RXTE
observations (Galactic Center scans, ASM monitoring and a pointed observation)
of enigmatic transient source high mass X-ray binary V4641 Sgr and argue that
they broadly support the hypothesis that giant September 1999 outburst was
associated with an episode of super-Eddington accretion onto the black hole.
During the outburst an extended optically thick envelope/outflow has been
formed around the source making the observational appearance of V4641 Sgr in
many aspects very similar to that of SS433. These results suggest that objects
like V4641 Sgr and SS433 indeed represent the class of objects accreting matter
at a rate comparable or above Eddington value and the formation of an
envelope/outflow is a generic characteristic of supercritical accretion.
  When the accretion rate decreased the envelope vanished and the source short
term variability and spectral properties started to resemble those of other
galactic black hole candidates accreting at a rate well below the Eddington
value. Interestingly that during this phase the source spectrum was very
similar to the Cygnus X-1 spectrum in the low state inspite of more than order
of magnitude larger X-ray luminosity.


title: Towards the Secondary Bar: Gas Morphology and Dynamics in NGC 4303

abstract:
  The bulk of the molecular line emission in the double barred galaxy NGC4303
as observed in its CO(1-0) line with the OVRO mm-interferometer comes from two
straight gas lanes which run north-south along the leading sides of the
large-scale primary bar. Inside a radius of ~ 400 pc the molecular gas forms a
spiral pattern which, for the northern arm, can be traced to the nucleus.
Comparison of the OVRO and archival HST data with dynamical models of gas flow
in the inner kiloparsec of single- and double-barred galaxies shows that the
observed global properties of the molecular gas are in agreement with models
for the gas flow in a strong, large-scale bar, and the two-arm spiral structure
seen in CO in the inner kiloparsec can already be explained by a density wave
initiated by the potential of that bar. Only a weak correlation between the
molecular gas distribution and the extinction seen in the HST V-H map is found
in the inner 400 pc of NGC4303: The innermost part of one arm of the nuclear CO
spiral correlates with a weak dust filament in the color map, while the overall
dust distribution follows a ring or single-arm spiral pattern well correlated
with the UV continuum. This complicated nuclear geometry of the stellar and
gaseous components allows for two scenarios: (A) A self-gravitating m=1 mode is
present forming the spiral structure seen in the UV continuum. In this case the
gas kinematics would be unaffected by the small (~ 4'') inner bar. (B) The UV
continuum traces a complete ring which is heavily extincted north of the
nucleus. Such a ring forms in hydrodynamic models of double bars, but the
models cannot account for the UV emission observed on the leading side of the
inner bar. (abridged)


title: The Sunyaev-Zel'dovich Effect Spectrum of Abell 2163

abstract:
  We present an interferometric measurement of the Sunyaev-Zel'dovich effect
(SZE) at 1 cm for the galaxy cluster Abell 2163. We combine this data point
with previous measurements at 1.1, 1.4, and 2.1 mm from the SuZIE experiment to
construct the most complete SZE spectrum to date. The intensity in four
wavelength bands is fit to determine the central Compton y-parameter (y_c) and
the peculiar velocity (v_p) for this cluster. Our results are
y_c=3.56(+0.41/-0.41)(+0.27/-0.19) x 10^-4 and v_p=410(+1030/-850)(+460/-440)
km/s where we list statistical and systematic uncertainties, respectively, at
68% confidence. These results include corrections for contamination by Galactic
dust emission. We find less contamination by dust emission than previously
reported. The dust emission is distributed over much larger angular scales than
the cluster signal and contributes little to the measured signal when the
details of the SZE observing strategy are taken into account.


title:
Understanding the long-term spectral variability of Cygnus X-1 with
  BATSE and ASM observations

abstract:
  We present an analysis of all observations of Cygnus X-1 by the BATSE (20-300
keV) and by ASM (1.5-12 keV) until 2002 June, including 1200 days of
simultaneous data. We find a number of correlations between fluxes and
hardnesses in different energy bands. In the hard state, the variability can be
explained by softening the overall spectrum with a pivot at 50 keV and another,
independent variability pattern where the spectral shape does not change when
the luminosity changes. In the soft state, the variability is caused by a
variable hard tail of a constant shape superimposed on a constant soft
component. These variability patterns are in agreement with the
energy-dependent rms variability in the two states. We also study in detail
recent soft states in 2000-02. The last of them has lasted so far for >200
days. Their spectra are harder in the 1.5-5 keV band but similar or in the 3-12
keV band than those of the 1996 soft state whereas the rms variability is
stronger in all the ASM bands. On the other hand, the 1994 soft state
transition observed by BATSE appears very similar to the 1996 one. We interpret
the variability patterns by theoretical Comptonization models. In the hard
state, the variability appears to be driven mostly by changing flux in seed
photons Comptonized in a hot thermal plasma cloud with an approximately
constant power supply. In the soft state, the variability is consistent with
flares of hybrid, thermal/nonthermal, plasma with variable power above a stable
cold disk. The spectral and timing differences between the 1996 and 2000-02
soft states are explained by a decrease of the color disk temperature. Also,
based on broad-band pointed observations, we find the intrinsic bolometric
luminosity increases by a factor of 3-4 from the hard state to the soft one.


title: What regulates the velocity distribution of interstellar clouds?

abstract:
  Kinetic energy stored in ISM bulk/turbulent motions is a crucial ingredient
to properly describe most properties of observed galaxies. By using Monte Carlo
simulations, we investigate how this energy is injected by supernovae and
dissipated via cloud collisions and derive the corresponding ISM velocity
probability distribution function (PDF). The functional form of the PDF for the
modulus of the velocity dispersion is $$p(v) \propto v^2
\exp[-(v/\sigma)^\beta].$$ The power-law index of the PDF depends only on the
value of the average cloud collision elasticity < \epsilon > as \beta =
2\exp(<\epsilon > -1). If \beta and the gas velocity dispersion \sigma are
known, the specific kinetic energy dissipated by collisions is found to be
\propto \sigma^2 \ln (2 / \beta)/(\beta-0.947); in steady state, this is equal
to the energy input from SNe. We predict that in a multiphase, low metallicity
(Z \approx 5 \times 10^{-3} Z_\odot) ISM the PDF should be close to a
Maxwellian (\beta = 2) with velocity dispersion \sigma \simgt 11$ km s\m; in
more metal rich systems (Z \simgt 5 \times 10^{-2} Z_\odot), instead, we expect
to observe almost exponential PDFs. This is in good agreement with a number of
observations that we review and might explain the different star formation
modes seen in dwarfs and spiral galaxies.


title: Gaussian Spectral Line Profiles of Astrophysical Masers

abstract:
  Calculations are performed to demonstrate the deviations from Gaussian that
occur in the spectral line profiles of a linear maser as a result of the
amplification process. Near-Gaussian profiles are presented for bright,
interstellar 22 GHz water masers obtained from high resolution Very Long
Baseline Array (VLBA) observations of W3 IRS 5. For the profiles to be so close
to Gaussian, the calculations indicate that these masers must originate in
quite hot gas with temperatures greater than 1200 K -- a conclusion that is
supportive of C-type shocks as the origin of these masers. In addition, the
degree of saturation of these masers must be less than approximately one-third,
from which it follows that the beaming angles are less than about 10^{-4} ster
and the actual luminosities are modest. If spectral profiles that are as close
to Gaussian as the profiles presented in this initial investigation are found
to occur widely, they can be valuable diagnostics for the environments of
astrophysical masers.


title:
Detecting gravitational lensing cosmic shear from samples of several
  galaxies using two-dimensional spectral imaging

abstract:
  Studies of weak gravitational lensing by large-scale structures require the
measurement of the distortions introduced to the shapes of distant galaxies at
the few percent level by anisotropic light deflection along the line of sight.
To detect this signal on 1-10 arcmin scales in a particular field, accurate
measurements of the correlations between the shapes of order 1000-10000
galaxies are required. This large-scale averaging is required to accommodate
the unknown intrinsic shapes of the background galaxies, even with careful
removal of systematic effects. Here an alternative is discussed. If it is
possible to measure accurately the detailed dynamical structure of the
background galaxies, in particular rotating disks, then it should be possible
to measure directly the cosmic shear distortion, as it generally leads to a
non-self-consistent rotation curve. Narrow spectral lines and excellent
two-dimensional spatial resolution are required. The ideal lines and telescope
are CO rotational transitions and the Atacama Large Millimeter Array (ALMA)
respectively.


title: Effective Screening due to Minihalos During the Epoch of Reionization

abstract:
  We show that the gaseous halos of collapsed objects introduce a substantial
cumulative opacity to ionizing radiation, even after the smoothly distributed
hydrogen in the intergalactic medium has been fully reionized. This opacity
causes a delay of around unity in redshift between the time of the overlap of
ionized bubbles in the intergalactic medium and the lifting of complete
Gunn-Peterson Lyman alpha absorption. The minihalos responsible for this
screening effect are not resolved by existing numerical simulations of
reionization.


title: New sub-millimeter limits on dust in the 55 Cancri planetary system

abstract:
  We present new, high-sensitivity sub-millimeter observations towards 55
Cancri, a nearby G8 star with one, or possibly two, known planetary
companion(s). Our 850 $\mu$m map, obtained with the SCUBA instrument on the
James Clerk Maxwell Telescope, shows three peaks of emission at the 2.5 mJy
level in the vicinity of the star's position. However, the observed peaks are
25$\arcsec$--40$\arcsec$ away from the star and a deep $R$-band optical image
reveals faint point sources that coincide with two of the sub-millimeter peaks.
Thus, we do not find evidence for dust emission spatially associated with 55
Cancri. The excess 60 $\mu$m emission detected with ISO may originate from one
or more of the 850 $\mu$m peaks that we attribute to background sources. Our
new results, together with the HST/NICMOS coronographic images in the
near-infrared, place stringent limits on the amount of dust in this planetary
system, and argue against the existence of a detectable circumstellar dust disk
around 55 Cnc.


title: The Broadband Afterglow of GRB980329

abstract:
  We present radio observations of the afterglow of the bright gamma-ray burst
GRB980329 made between one month and several years after the burst, a
re-analysis of previously published submillimeter data, and late-time optical
and near-infrared (NIR) observations of the host galaxy. From the absence of a
spectral break in the optical/NIR colors of the host galaxy, we exclude the
earlier suggestion that GRB980329 lies at a redshift of z >~5. We combine our
data with the numerous multi-wavelength observations of the early afterglow,
fit a comprehensive afterglow model to the entire broadband dataset, and derive
fundamental physical parameters of the blast-wave and its host environment.
Models for which the ejecta expand isotropically require both a high
circumburst density and extreme radiative losses from the shock. No low density
model (n << 10 cm^{-3}) fits the data. A burst with a total energy of ~ 10^{51}
erg, with the ejecta narrowly collimated to an opening angle of a few degrees,
driven into a surrounding medium with density ~ 20 cm^{-3}, provides a
satisfactory fit to the lightcurves over a range of redshifts.


title:
Measuring the Boundary Layer and Inner Accretion Disk Temperatures for
  WX Ceti During Superoutburst

abstract:
  We obtained EUV photometry, optical spectroscopy, and multi-color optical
photometry for WX Cet during its 1998 November superoutburst. WX Cet is only
the second short-period, low mass transfer CV (TOAD) to ever be observed in the
EUV. Our determined superhump period is consistent with that found by Kato et
al. (0.059 d) and we confirm that superhumps are grey in the optical. The
optical spectra provide direct evidence that the line emission region is
optically thick and our multi-wavelength photometric measurements are used to
determine the inner accretion disk and boundary layer temperatures during
superoutburst. Using a determined distance to WX Cet of ~130 pc, we find
T$_{ID}$= 21,000K and T_{BL}~72,500K. Both values are in good agreement with
that expected by models of the superoutburst continuum being produced by the
inner disk and boundary layer.


title:
Environmental Dependencies for Star Formation Triggered by Expanding
  Shell Collapse

abstract:
  Criteria for gravitational collapse of expanding shells in rotating, shearing
galaxy disks were determined using three-dimensional numerical simulations in
the thin shell approximation. The simulations were run over a grid of 7
independent variables, and the resultant probabilities for triggering and
unstable masses were determined as functions of 8 dimensionless parameters.
When the ratio of the midplane gas density to the midplane total density is
small, an expanding shell reaches the disk scale height and vents to the halo
before it collapses. When the Toomre instability parameter Q, or a similar
shear parameter, Q_A, are large, Coriolis forces and shear stall or reverse the
collapse before the shell accumulates enough mass to be unstable. With large
values of C=c_sh/(GL)^0.2, for rms velocity dispersion c_sh in the swept-up
matter and shell-driving luminosity L, the pressure in the accumulated gas is
too large to allow collapse during the expansion time. Considering ~5000 models
covering a wide range of parameter space, the common properties of shell
collapse as a mechanism for triggered star formation are: (1) the time scale is
4*sqrt(C/2 pi G rho) for ambient midplane density rho, (2) the total fragment
mass is ~2x10^7 Msun, of which only a small fraction is likely to be molecular,
(3) the triggering radius is ~2 times the scale height, and the triggering
probability is ~0.5 for large OB associations. Star formation triggered by
shell collapse should be most common in gas-rich galaxies, such as young
galaxies or those with late Hubble types.


title: Scintillations and Levy flights through the interstellar medium

abstract:
  Temporal broadening of pulsar signals results from electron density
fluctuations in the interstellar medium that cause the radiation to travel
along paths of different lengths. The Gaussian theory of fluctuations predicts
that the pulse temporal broadening should scale with the wavelength as
lambda^4, and with the dispersion measure (corresponding to distance to the
pulsar) as DM^2. For large dispersion measure, DM > 20 pc/cm^3, the observed
scaling is lambda^4 DM^4, contradicting the conventional theory. Although the
problem has existed for 30 years, there has been no resolution to this paradox.
  We suggest that scintillations for distant pulsars are caused by
non-Gaussian, spatially intermittent density fluctuations with a power-like
probability distribution. This probability distribution does not have a second
moment in a large range of density fluctuations, and therefore the previously
applied conventional Fokker-Planck theory does not hold. Instead, we propose to
apply the theory of Levy distributions (so-called Levy flights). Using the
scaling analysis (confirmed by numerical simulations of ray propagation) we
show that the observed scaling is recovered for large DM, if the density
differences, delta N, have Levy distribution decaying as |delta N|^{-5/3}.


title:
Expected Performance of a Neutrino Telescope for Seeing AGN/GC Behind a
  Mountain

abstract:
  We study the expected performance of building a neutrino telescope, which
targets at energy greater than $10^{14}$ eV utilizing a mountain to interact
with neutrinos. The telescope's efficiency in converting neutrinos into leptons
is first examined. Then using a potential site on the Big Island of Hawaii, we
estimate the acceptance of the proposed detector. The neutrino flux limit at
event rate 0.3/year/half decade of energy is estimated to be comparable to that
of AMANDA neutrino flux limit at above $10^{16}$ eV.


title: Mass transfer from the donor of GRS 1915+105

abstract:
  A scenario for a periodic filling and emptying of the accretion disc of the
microquasar GRS 1915+105 is proposed, by computing the mass transfer rate from
the evolving low mass red giant donor (Greiner at al. 2001) and comparing it
with the observed accretion rate onto the primary black hole. We propose a
duty-cycle with (5-10)(eta/0.1) per cent active ON-state where eta is the
efficiency of converting accretion into radiation. The duration of the
quiescent recurrent OFF-state is identified as the viscosity time scale at the
circularization radius and equals 370(alpha/0.001)^(-4/5) years, where alpha is
the viscosity parameter in the alpha-prescription of a classical disc. If the
viscosity at the outer edge of the disc is small and eta is close to the
maximum available potential energy (per rest mass energy) at the innermost
stable orbit, the present active phase may last another 10 - 20 years.


title: X-ray background measurements with XMM-Newton EPIC

abstract:
  We discuss the methods used to compile a high signal-to-noise dataset
representative of both the instrumental and cosmic background signal measured
at high galactic latitude by the XMM-Newton EPIC cameras. The characteristics
of the EPIC background are described and the potential applications of the
derived dataset in general science analysis are outlined. In the case of the
cosmic X-ray background, the transition between a hard power-law spectrum (due
to the integrated emission of unresolved, largely extragalactic, point sources)
and a softer thermal spectrum (produced by hot plasma associated with the
Galactic plane and halo) is unambiguously detected around ~1keV. We derive a
value for the intensity of the power-law component of 2.15 (+/- 0.26) e-11
erg/sq cm/s/sq deg in the 2-10 keV band (Normalisation at 1keV of 11.1 photons
/sq cm/s/sr/keV). The implication is that recent, very deep Chandra
observations have resolved ~70 - 90% of the 2-10 keV background into discrete
sources. Our measurement is towards the higher end of the range of quoted
background normalisations.


title:
On Equation of Motion for Arbitrarily Shaped Particle under Action of
  Electromagnetic Radiation

abstract:
  Arguments of astronomers against equation of motion for arbitrarily shaped
particle under action of electromagnetic radiation are discussed. Each of the
arguments is commented in detail from the point of view of the required
physics. It is shown that the arguments of astronomers, including referees in
several astronomical and astrophysical journals, are unacceptable from the
physical point of view. Detail explanations should help astronomers in better
physical understanding of the equation of motion. Relativistically covariant
equation of motion for real dust particle under the action of electromagnetic
radiation is derived. The particle is neutral in charge. Equation of motion is
expressed in terms of particle's optical properties, standardly used in optics
for stationary particles.


title: Scale-Adaptive filters for the detection/separation of compact sources

abstract:
  This paper presents scale-adaptive filters that optimize the
detection/separation of compact sources on a background. We assume that the
sources have a multiquadric profile, i. e. $\tau (x) = {[1 +
{(x/r_c)}^2]}^{-\lambda}, \lambda \geq {1/2}, x\equiv |\vec{x}|$, and a
background modeled by a homogeneous and isotropic random field, characterized
by a power spectrum $P(q)\propto q^{-\gamma}, \gamma \geq 0, q\equiv
|\vec{q}|$. We make an n-dimensional treatment but consider two interesting
astrophysical applications related to clusters of galaxies (Sunyaev-Zel'dovich
effect and X-ray emission).


title: Cosmological Tests for a Linear Coasting Cosmology

abstract:
  A strictly linear evolution of the scale factor is a characteristic feature
in several classes of alternative gravity theories. In this article we
investigate the overall viability of an open linear coasting cosmological
model. We report that this model is consistent with gravitational lensing
statistics (within $1\sigma$) and accomodates old high-redshift galaxies. We
finally conclude that such a linear coasting, $\a(t) = t$, is not ruled out on
basis of these observational tests.


title:
New Constraints on Neutron Star Cooling from Chandra Observations of
  3C58

abstract:
  3C58 is a young Crab-like supernova remnant. Historical evidence strongly
suggests an association of the remnant with supernova SN 1181, which would make
3C58 younger than the Crab Nebula. Recent Chandra observations have identified
the young 65 ms pulsar J0205+6449 at its center, embedded in a compact nebula
which, we show here, appears to be confined by the pulsar wind termination
shock. We present new Chandra observations of this compact nebula and embedded
pulsar which set strong upper limits on thermal emission originating from the
neutron star surface. These limits fall far below predictions of standard
neutron star cooling, requiring the presence of exotic cooling processes in the
neutron star core.


title:
A new upper limit on the total neutrino mass from the 2dF Galaxy
  Redshift Survey

abstract:
  We constrain f_nu = Omega_nu / Omega_m, the fractional contribution of
neutrinos to the total mass density in the Universe, by comparing the power
spectrum of fluctuations derived from the 2dF Galaxy Redshift Survey with power
spectra for models with four components: baryons, cold dark matter, massive
neutrinos and a cosmological constant. Adding constraints from independent
cosmological probes we find f_nu < 0.13 (at 95% confidence) for a prior of 0.1<
Omega_m <0.5, and assuming the scalar spectral index n=1. This translates to an
upper limit on the total neutrino mass and m_nu,tot < 1.8 eV for "concordance"
values of Omega_m and the Hubble constant. Very similar results are obtained
with a prior on Omega_m from Type Ia supernovae surveys, and with
marginalization over n.


title: Higher Order Variability Properties of Accreting Black Holes

abstract:
  To better constrain the emission mechanism underlying the hard state of
galactic black hole candidates, we use high-time resolution RXTE lightcurves
for Cyg X-1 and GX 399-4 to compute two higher order variability statistics for
these objects, the skewness and the Fourier bispectrum. Similar analyses, in
particular using the skewness measure, have been attempted before, but the
photon collection area of RXTE allows us to present results of much greater
statistical significance. The results for the two objects are qualitatively
similar, reinforcing the idea that the same basic mechanisms are at work in
both. We find a significantly positive skewness for variability timescales less
than $\sim 1 $ second, and a {\it negative} skewness for timescale $1- 5 $ sec.
Such a skewness pattern cannot be reproduced by the simplest shot variability
models where individual shots have a fixed profile and intensity and are
uncorrelated in time. Further evidence against simple shot models comes from
the significant detection of a non-zero bicoherence for Fourier periods $\sim
0.1-10$ sec, implying that significant coupling does exist between variations
on these timescales. We discuss how current popular models for variability in
black hole systems can be modified to match these observations. Using simulated
light curves, we suggest that the most likely way to reproduce this observed
behavior is to have the variability come in groups of many shots, with the
number of shots per unit time fitting an envelope function which has a rapid
rise and slow decay, while the individual shots have a slow rise and a rapid
decay. Invoking a finite energy reservoir that is depleted by each shot is a
natural way of producing the required shot correlations.


title: Flattening and truncation of stellar discs in edge-on spiral galaxies

abstract:
  We analyse the global structure of the old stellar discs in 34 edge-on spiral
galaxies. The radial and vertical exponential scale parameters of the discs are
obtained by applying an improved two-dimensional decomposition technique to our
I-band photometry. We find a clear increase in the disc scaleheight with
maximum rotational velocity, in accordance with observations of the stellar
velocity dispersions in galaxy discs. The range and maximum of the intrinsic
flattening of the disc light seem to increase with both maximum rotational
velocity and total HI mass. We use the disc flattening to estimate the disc
contribution to the maximum rotational velocity, resulting in an average of
57+-22 percent. The disc light distributions are further investigated for the
presence of radial truncations. We find that the radial light distributions of
at least 20 spirals are truncated, corresponding to 60 percent of the sample.
For small scalelength spirals, which are the most numerous in the local
Universe, the results suggest that the average ratio of disc truncation radius
to disc scalelength is at least four.


title:
The Non-Damped Nature of Twelve Low-Redshift Damped Lyman Alpha
  Candidate Systems

abstract:
  Hubble Space Telescope (HST) UV spectroscopy of 12 candidate low-redshift
damped Lyman alpha (DLA) systems in 11 QSOs (z=0.103 in Q0054+144, z=0.969 and
z=0.987 in Q0302-223, z=0.478 in Q0454-220, z=1.476 in Q1047+550, z=1.070 in
Q1206+459, z=1.228 in Q1247+267, z=0.399 in Q1318+290B, z=0.519 in Q1329+412,
z=0.276 in Q1451-375, z=0.204 in Q2112+059, z=0.263 in Q2251+113) are
presented; the observations demonstrate that they are not DLAs with
$N(HI)\ge2\times10^{20}$ atoms cm$^{-2}$. In all cases except two the systems
either do not exist or are well below the DLA threshold column density; the
exceptions are a z=0.474 system in Q0454-220 which has $N(HI)=3\times10^{19}$
atoms cm$^{-2}$ and a z=1.223 system in Q1247+267 which has
$N(HI)=8\times10^{19}$ atoms cm$^{-2}$. Despite the availability of data in the
HST archives demonstrating that these are not suitable targets, many have
unfortunately been approved for observation with Chandra, Gemini, and/or HST
with the intent of doing followup work on low-redshift DLAs. Furthermore, these
results indicate that the low-redshift DLA statistics derived from IUE spectra
and presented by Lanzetta, Wolfe, & Turnshek (1995) and Wolfe et al. (1995) are
invalid.


title: Rocket Observations of Far-Ultraviolet Dust Scattering in NGC 2023

abstract:
  The reflection nebula NGC 2023 was observed by a rocket-borne long-slit
imaging spectrograph in the 900 -- 1400 Angstrom bandpass on 2000 February 11.
A spectrum of the star, as well as that of the nebular scattered light, was
recorded. Through the use of a Monte Carlo modeling process, the scattering
properties of the dust were derived. The albedo is low, 0.2 -- 0.4, and
decreasing toward shorter wavelengths, while the phase function asymmetry
parameter is consistent with highly forward-scattering grains, g~0.85. The
decrease in albedo, while the optical depth increases to shorter wavelengths,
implies that the far-UV rise in the extinction curve is due to an increase in
absorption efficiency.


title: Local Circumstellar Magnetic Fields Around Evolved Stars

abstract:
  I argue that the presence of magnetic fields around evolved stars, e.g.,
asymptotic giant branch stars, and in PNe, does not necessarily imply that the
magnetic field plays a global dynamical role in shaping the circumstellar
envelope. Instead, I favor magnetic fields with small coherence lengths, which
result from stellar magnetic spots or from jets blown by an accreting
companion. Although the magnetic field does not play a global role in shaping
the circumstellar envelope, it may enhance local motion (turbulent) via
magnetic tension and reconnection. The locally strong magnetic tension may
enforce coherence flow which may favor the masing process.


title:
Slitless Spectroscopy of LMC Planetary Nebulae. A Study of the Emission
  Lines and Morphology

abstract:
  HST STIS slitless spectroscopy of LMC PNs is the ideal tool to study their
morphology and their ionization structures at once. We present the results from
a group of 29 PNs that have been spatially resolved, for the first time, in all
the major optical lines. Images in the light of \ha, \nii, and \oiii are
presented, together with line intensities, measured from the extracted 1D and
2D spectra. A study on the surface brightness in the different optical lines,
the electron densities, the ionized masses, the excitation classes, and the
extinction follows, illustrating an ideal consistence with the previous results
found by us on LMC PNs. In particular, we find the surface brightness decline
with the photometric radius to be the same in most emission lines. We find that
asymmetric PNs form a well defined cooling sequence in the excitation --
surface brightness plane, confirming their different origin, and larger
progenitor mass.


title: Is RX J185635-375 a Quark Star?

abstract:
  Deep Chandra LETG+HRC-S observations of the isolated neutron star candidate
RX J1856.5-3754 have been analysed to search for metallic and resonance
cyclotron spectral features and for pulsation behaviour. As found from earlier
observations, the X-ray spectrum is well-represented by a ~ 60 eV (7e5 K)
blackbody. No unequivocal evidence of spectral line or edge features has been
found, arguing against metal-dominated models. The data contain no evidence for
pulsation and we place a 99% confidence upper limit of 2.7% on the
unaccelerated pulse fraction over a wide frequency range from 1e-4 to 100 Hz.
We argue that the derived interstellar medium neutral hydrogen column density
of 8e19 <= N_H <= 1.1e20 per sq. cm favours the larger distance from two recent
HST parallax analyses, placing RX J1856.5-3754 at ~ 140 pc instead of ~ 60 pc,
and in the outskirts of the R CrA dark molecular cloud. That such a
comparatively rare region of high ISM density is precisely where an isolated
neutron star re-heated by accretion of interstellar matter would be expected is
either entirely coincidental, or current theoretical arguments excluding this
scenario for RX J1856.5-3754 are premature. Taken at face value, the combined
observational evidence -- a lack of spectral and temporal features and an
implied radius at infinity of 3.8-8.2 km that is too small for current neutron
star models -- points to a more compact object, such as allowed for quark
matter equations of state.


title:
Short Timescale Correlations Between Line and Continuum Fluxes in Cygnus
  X-1

abstract:
  We present the results of 16-s time scale spectral fits for Cygnus X-1 in the
soft state and in the transition state, using a Comptonised blackbody plus an
iron line. On these timescales, we find that that the continuum source flux can
vary by factors 2-3 and that the iron line intensity appears to track these
changes well, i.e., the inferred equivalent width of the line remains constant
to within the errors. We also find no significant changes in the seed
(blackbody) photon temperature, while the properties of the Comptonising corona
clearly do vary, with the spectral hardness and flux generally being
correlated. The corona therefore seems to be the overall driver for the rapid
timescale variability observed in the soft and transition states. These results
are consistent with the Fourier resolved spectroscopy results of Gilfanov et
al. (2000) that indicate the iron line shows rapid flux variations while the
blackbody component does not and suggest that the iron line flux in fact tracks
continuum changes down to very short timescales. We extend this work by showing
that not only the variability amplitudes, but also the {\it phases} of the iron
line and continuum components are identical. We note that the short timescale
variability properties of the soft and transition states are actually not very
different from those of the hard state, suggesting that the corona is the main
cause of rapid variability in that state too, and hence that the mechanism
responsible for the corona is similar in all three states.


title: SNe heating and the chemical evolution of the intra-cluster medium

abstract:
  We compute the chemical and thermal history of the intra-cluster medium in
rich and poor clusters under the assumption that supernovae (I, II) are the
major responsible both for the chemical enrichment and the heating of the
intra-cluster gas. We assume that only ellipticals and S0 galaxies contribute
to the enrichment and heating of the intra-cluster gas through supernova driven
winds and explore several prescriptions for describing the feed-back between
supernovae and the interstellar medium in galaxies. We integrate then the
chemical and energetical contributions from single cluster galaxies over the
cluster luminosity function and derive the variations of these quantities as
functions of the cosmic time. We reach the following conclusions: i) while type
II supernovae dominates the chemical enrichment and energetics inside the
galaxies, type Ia supernovae play a predominant role in the intra-cluster
medium, ii) galaxy models, which reproduce the observed chemical abundances and
abundance ratios in the intra-cluster medium, predict a maximum of 0.3-0.4 keV
per particle of energy input, a result obtained by assuming that type Ia
supernovae contribute 100% of their initial blast wave energy whereas type II
supernovae contribute only by a few percents of their initial energy.


title:
Broad Emission Line Shifts in Quasars: An Orientation Measure for
  Radio-Quiet Quasars?

abstract:
  Using a sample of 3814 quasars from the Sloan Digital Sky Survey, we confirm
that high-ionization, broad, emission lines such as CIV are significantly
blueshifted with respect to low-ionization, broad, emission lines such as MgII.
CIV emission line peaks have a range of shifts from a redshift of 500 km/s to
blueshifts well in excess of 2000 km/s as compared to MgII. We confirm previous
results that suggest an anti-correlation between the shift of the CIV emission
line peak and the rest equivalent width of the CIV emission line. Furthermore,
using composite spectra, we are able to show that the apparent shift of the CIV
emission line peak is not a shift so much as it is a lack of flux in the red
wing for the composite with the largest apparent shift. This observation should
strongly constrain models for the broad emission line region in quasars. The
emission line blueshift and equivalent width of CIV are also discussed in light
of the Baldwin Effect and as a function of other quasar properties such as
spectral index, radio and X-ray detection. We find a possible correlation with
both the radio and broad absorption line properties of the quasars that is
suggestive of orientation as the cause of the CIV velocity shifts.


title:
Three-Dimensional Hydrodynamic Simulations of Accretion Tori in Kerr
  Spacetimes

abstract:
  This paper presents results of three-dimensional simulations of global
hydrodynamic instabilities in black hole tori, extending earlier work by Hawley
to Kerr spacetimes. This study probes a three-dimensional parameter space of
torus angular momentum, torus size, and black hole angular momentum. We have
observed the growth of the Papaloizou-Pringle instability for a range of torus
configurations and the resultant formation of m=1 planets. We have also
observed the quenching of this instability in the presence of early accretion
flows; however, in one simulation both early accretion and planet formation
occurred. Though most of the conclusions reached in Hawley's earlier work on
Schwarzschild black holes carry over to Kerr spacetime, the presence of frame
dragging in the Kerr geometry adds an element of complexity to the simulations;
we have seen especially clear examples of this phenomenon in the accretion
flows that arise from retrograde tori.


title:
The Validity of the Adiabatic Contraction Approximation for Dark Matter
  Halos

abstract:
  We use high resolution numerical simulations to investigate the adiabatic
contraction of dark matter halos with a Hernquist density profile. We test the
response of the halos to the growth of additional axisymmetric disk potentials
with various central concentrations and the spherically symmetric potential of
a softened point mass. Adding the potentials on timescales that are long
compared to the dynamical time scale of the halo, the contracted halos have
density profiles that are in excellent agreement with analytical predictions
based on the conservation of the adiabatic invariant $M(r)r$. This is
surprising as this quantity is strictly conserved only for particles on
circular orbits and in spherically symmetric potentials. If the same potentials
are added on timescales that are short compared to the dynamical timescale, the
result depends strongly on the adopted potential. The adiabatic approximation
still works for disk potentials. It does, however, fail for the central
potential.


title: An IR view of mass loss in Long Period Variables

abstract:
  We have investigated the mass loss processes in Long Period Variables, by
combining radiative transfer modeling with mid-IR imaging and spectroscopic
observations. We find a correlation between variability type and temporal
variations in the mass loss rate. Mira variables are more likely to maintain
constant mass loss rates over long period of time. Semiregular and Irregular
variables are characterized by frequent interruptions in their mass loss rate,
on timescales of ~100 yr. High resolution imaging of individual Long Period
Variable sources show departures from spherical symmetry. We present the case
of o Cet (Mira), in which the presence of a low mass companion plays an active
role in shaping the circumstellar environment.


title:
A large atomic hydrogen shell in the outer Galaxy: SNR or stellar wind
  bubble?

abstract:
  We report the detection of a ring like HI structure toward l=90.0, b=2.8 with
a velocity of v_LSR=-99 km/s. This velocity implies a distance of d=13 kpc,
corresponding to a Galactocentric radius of R_gal=15 kpc. The l-v_LSR diagram
implies an expansion velocity of v_exp ~ 15 km/s for the shell. The structure
has an oblate, irregular shell-like appearance which surrounds weak infrared
emission as seen in the 60 micrometer IRAS data. At a distance of 13 kpc the
size of the object is about 110 x 220 pc and placed 500 pc above the Galactic
plane with a mass of 1e5 solar mass. An expanding shell with such a high mass
and diameter cannot be explained by a single supernova explosion or by a single
stellar wind bubble. We interpret the structure as a relic of a distant stellar
activity region powered by the joint action of strong stellar winds from early
type stars and supernova explosions.


title: Detecting Very High Energy Neutrinos by the Telescope Array

abstract:
  We present the cosmic neutrino detecting potential of the Telescope Array for
quasihorizontally downward and upward air showers initiated by very high energy
neutrinos penetrating the air and the Earth respectively. We adopted model
predictions for extraterrestrial neutrino fluxes from active galactic nuclei,
gamma-ray bursters, Greisen photo production, the collapse of topological
defects, and Z-bursts. The Telescope Array, using a large array of bright and
wide field-of-view flourescence telescopes, can esplore these very high energy
cosmic neutrino sources.


title: Calibrating the Cepheid Period-Luminosity relation with the VLTI

abstract:
  The VLTI is the ideal instrument for measuring the distances of nearby
Cepheids with the Baade-Wesselink method, allowing an accurate recalibration of
the Cepheid Period-Luminosity relation. The high accuracy required by such
measurement, however, can only be reached taking into account the effects of
limb darkening, and its dependence on the Cepheid pulsations. We present here
our new method to compute phase- and wavelength-dependent limb darkening
profiles, based on hydrodynamic simulation of Classical Cepheid atmospheres.


title:
A universal probability distribution function for weak-lensing
  amplification

abstract:
  We present an approximate form for the weak lensing magnification
distribution of standard candles, valid for all cosmological models, with
arbitrary matter distributions, over all redshifts. Our results are based on a
universal probability distribution function (UPDF), $P(\eta)$, for the reduced
convergence, $\eta$. For a given cosmological model, the magnification
probability distribution, $P(\mu)$, at redshift $z$ is related to the UPDF by
$P(\mu)=P(\eta)/2|\kappa_{min}|$, where $\eta=1+(\mu-1)/(2|\kappa_{min}|)$, and
$\kappa_{min}$ (the minimum convergence) can be directly computed from the
cosmological parameters ($\Omega_m$ and $\Omega_\Lambda$). We show that the
UPDF can be well approximated by a three-parameter stretched Gaussian
distribution, where the values of the three parameters depend only on
$\xi_\eta$, the variance of $\eta$. In short, all possible weak lensing
probability distributions can be well approximated by a one-parameter family.
We establish this family, normalizing to the numerical ray-shooting results for
a ${\Lambda}$CDM model by Wambsganss et al. (1997). Each alternative
cosmological model is then described by a single function $\xi_\eta(z)$. We
find that this method gives $P(\mu)$ in excellent agreement with numerical
ray-tracing and three-dimensional shear matrix calculations, and provide
numerical fits for three representative models (SCDM, $\Lambda$CDM, and OCDM).
Our results provide an easy, accurate, and efficient method to calculate the
weak lensing magnification distribution of standard candles, and should be
useful in the analysis of future high-redshift supernova data.


title:
Unified Classical and Quantum Radiation Mechanism for Ultra-Relativistic
  Electrons in Curved and Inhomogeneous Magnetic Fields

abstract:
  We analyze the general radiation emission mechanism from a charged particle
moving in a curved inhomogeneous magnetic field. The consideration of the
gradient makes the curved vacuum magnetic field compatible with the Maxwell
equations and adds a non-trivial term to the transverse drift velocity and,
consequently, to the general radiation spectrum. To obtain the radiation
spectrum in the classical domain a general expression for the spectral
distribution and characteristic frequency of an electron in arbitrary motion is
derived by using Schwinger's method. The radiation patterns of the
ultrarelativistic electron are represented in terms of the acceleration of the
particle. The same results can be obtained by considering that the motion of
the electron can be formally described as an evolution due to magnetic and
electric forces. By defining an effective electromagnetic field, which combines
the magnetic field with the fictitious electric field associated to the
curvature and drift motion, one can obtain all the physical characteristics of
the radiation by replacing the constant magnetic field with the effective
field. The power, angular distribution and spectral distribution of all three
components (synchrotron, curvature and gradient) of the radiation are
considered in both classical and quantum domain in the framework of this
unified formalism. In the quantum domain the proposed approach allows the study
of the effects of the inhomogeneities and curvature of the magnetic field on
the radiative transitions rates of electrons between low-lying Landau levels
and the ground state.


title:
Gas Metallicity of Narrow-Line Regions in Narrow-Line Seyfert 1 Galaxies
  and Broad-Line Seyfert 1 Galaxies

abstract:
  We investigate gas metallicity of narrow-line regions in narrow-line Seyfert
1 galaxies (NLS1s) and broad-line ones (BLS1s) in order to examine whether or
not there is a difference in the gas metallicity between the two populations of
Seyfert 1 galaxies. We apply two methods to study this issue. One is to use the
emission-line flux ratio of [N II]6583/H_alpha in combination with some other
optical emission-line flux ratios. This method, which has been often applied to
Seyfert 2 galaxies, suggests that the gas metallicity of narrow-line regions is
indistinguishable or possibly higher in BLS1s than in NLS1s. On the contrary,
the other method in which only forbidden emission-line fluxes are used results
in that NLS1s tend to possess metal-richer gas in the narrow-line regions than
BLS1s. We point out that this inconsistency may be owing to the contamination
of the broad component of permitted lines into the narrow component of ones in
the first method. Since the results derived by using only forbidden
emission-line fluxes do not suffer from any uncertainty of the fitting function
for the broad component of Balmer lines, the results from this method are more
reliable than those derived by using permitted lines. We thus conclude that the
gas metallicity of narrow-line regions tends to be higher in NLS1s than in
BLS1s.


title: X-ray Binaries and Globular Clusters in Elliptical Galaxies

abstract:
  The X-ray emission from normal elliptical galaxies has two major components:
soft emission from diffuse gas and harder emission from populations of
accreting (low-mass) stellar X-ray binaries (LMXB). If LMXB populations are
tied to the field stellar populations in galaxies, their total X-ray
luminosities should be proportional to the optical luminosities of galaxies.
However, recent ASCA and Chandra X-ray observations show that the global
luminosities of LMXB components in ellipticals exhibit significant scatter at a
given optical luminosity. This scatter may reflect a range of evolutionary
stages among LMXB populations in ellipticals of different ages. If so, the
ratio of the global LMXB X-ray luminosity to the galactic optical luminosity,
L_LMXB/L_opt, may be used to determine when the bulk of stars were formed in
individual ellipticals. To test this, we compare variations in L_LMXB/L_opt for
LMXB populations in ellipticals to optically-derived estimates of stellar ages
in the same galaxies. We find no correlation, implying that L_LMXB/L_opt
variations are not good age indicators for ellipticals. Alternatively, LMXBs
may be formed primarily in globular clusters (through stellar tidal
interactions), rather than in the stellar fields of galaxies. Since elliptical
galaxies exhibit a wide range of globular cluster populations for a given
galaxian luminosity, this may induce a dispersion in the LMXB populations of
ellipticals with similar optical luminosities. Indeed, we find that
L_LMXB/L_opt ratios for LMXB populations are strongly correlated with the
specific globular cluster frequencies in elliptical galaxies. This suggests
that most LMXBs were formed in globular clusters.


title: Evidence of fast rotation in dwarf elliptical galaxies

abstract:
  In this Paper we investigate the kinematical properties of early-type dwarfs
by significantly enlarging the scarce observational sample so far available. We
present rotation curves and mean velocity dispersions for four bright dwarf
ellipticals and two dwarf lenticular galaxies in the Virgo cluster. Most of
these galaxies exhibit conspicuous rotation curves. In particular, five out of
the six new galaxies are found to be close to the predictions for oblate
spheroids flattened by rotation. Therefore, and contrary to the previous
observational hints, the present data suggest that an important fraction of
dwarf early-type galaxies may be rotationally supported.


title: Two-temperature coronal flow above a thin disk

abstract:
  We extended the disk corona model (Meyer & Meyer-Hofmeister 1994; Meyer, Liu,
& Meyer-Hofmeister 2000a) to the inner region of galactic nuclei by including
different temperatures in ions and electrons as well as Compton cooling. We
found that the mass evaporation rate and hence the fraction of accretion energy
released in the corona depend strongly on the rate of incoming mass flow from
outer edge of the disk, a larger rate leading to more Compton cooling, less
efficient evaporation and a weaker corona. We also found a strong dependence on
the viscosity, higher viscosity leading to an enhanced mass flow in the corona
and therefore more evaporation of gas from the disk below. If we take accretion
rates in units of the Eddington rate our results become independent on the mass
of the central black hole. The model predicts weaker contributions to the hard
X-rays for objects with higher accretion rate like narrow-line Seyfert 1
galaxies (NLS1s), in agreement with observations. For luminous active galactic
nuclei (AGN) strong Compton cooling in the innermost corona is so efficient
that a large amount of additional heating is required to maintain the corona
above the thin disk.


title: Circumbinary disk evolution

abstract:
  We study the evolution of circumbinary disks surrounding classical T Tau
stars. High resolution numerical simulations are employed to model a system
consisting of a central eccentric binary star within an accretion disk. The
disk is assumed to be infinitesimally thin, however a detailed energy balance
including viscous heating and radiative cooling is applied. A novel numerical
approach using a parallelized Dual-Grid technique on two different coordinate
systems has been implemented.
  Physical parameters of the setup are chosen to model the close systems of DQ
Tau and AK Sco, as well as the wider systems of GG Tau and UY Aur. Our main
findings are for the tight binaries a substantial flow of material through the
disk gap which is accreted onto the central stars in a phase dependent process.
We are able to constrain the parameters of the systems by matching both
accretion rates and derived spectral energy distributions to observational data
where available.


title: The broad band X-ray spectrum of the black hole candidate GRS1758-258

abstract:
  We present the results of a BeppoSAX observation of the black hole candidate
GRS1758-258 carried out in 1997, while the source was in its low/hard state.
The X-ray spectrum, simultaneously observed over the broad energy range from
0.1 to 200 keV, can be well described by a Comptonized emission model with
electron temperature kT_e = 31.4 keV and optical depth of 4.0 (spherical
geometry), although a cut-off power-law and a reflection model cannot be
excluded. Additionally, a broad iron line at 6.4 keV with equivalent width EW =
67 eV has been marginally detected. The 0.1-200 keV luminosity is 1.4x10^37
erg/s for an assumed distance of 8 kpc. The soft and hard luminosities are such
that the source falls inside the so-called "burster box". No evidence for a
soft excess is present.


title: The detection of the donor star in IY UMa

abstract:
  We present the results of a search for the donor star in the high inclination
SU UMa type cataclysmic variable IY UMa. We detect absorption features in the
near infrared consistent with an M type dwarf donor star. Using the skew
mapping technique to exploit the velocity information provided by the 8183-8194
Angstrom Na I absorption doublet, we locate the absorption at the expected
donor velocity of IY UMa.