title: A Model for the Quiescent Phase of the Recurrent Nova U Scorpii

abstract:
  A theoretical light curve is constructed for the quiescent phase of the
recurrent nova U Scorpii in order to resolve the existing distance discrepancy
between the outbursts (6 kpc) and the quiescences (14 kpc). Our U Sco model
consists of a very massive white dwarf (WD), an accretion disk (ACDK) with a
flaring-up rim, and a lobe-filling, slightly evolved, main-sequence star (MS).
The model properly includes an accretion luminosity of the WD, a viscous
luminosity of the ACDK, a reflection effect of the MS and the ACDK irradiated
by the WD photosphere. The B light curve is well reproduced by a model of 1.37
M_sun WD + 1.5 M_sun MS (0.8---2.0 M_sun MS is acceptable) with an ACDK having
a flaring-up rim, and the inclination angle i~80 degree. The calculated color
is rather blue (B-V~0.0) for a suggested mass accretion rate of 2.5 x 10^{-7}
M_sun yr^{-1}, thus indicating a large color excess of E(B-V)~0.56 with the
observational color of B-V=0.56 in quiescence. Such a large color excess
corresponds to an absorption of A_V~1.8 and A_B~2.3, which reduces the distance
to 6-8 kpc. This is in good agreement with the distance estimation of 4-6 kpc
for the latest outburst. Such a large intrinsic absorption is very consistent
with the recently detected period change of U Sco, which is indicating a mass
outflow of ~3 x 10^{-7} M_sun yr^{-1} through the outer Lagrangian points in
quiescence.


title: Advection-Dominated Accretion with Infall and Outflows

abstract:
  We present self-similar solutions for advection-dominated accretion flows
with radial viscous force in the presence of outflows from the accretion flow
or infall. The axisymmetric flow is treated in variables integrated over polar
sections and the effects of infall and outflows on the accretion flow are
parametrised for possible configurations compatible with the self-similar
solution. We investigate the resulting accretion flows for three different
viscosity laws and derive upper limits on the viscosity parameter alpha. In
addition, we find a natural connection to non-rotating and spherical accretion
with turbulent viscosity, which is assumed to persist even without differential
rotation. Positive Bernoulli numbers for advection-dominated accretion allow a
fraction of the gas to be expelled in an outflow and the upper limit on the
viscosity predicts that outflows are inevitable for equations of state close to
an ideal gas.


title:
The WARPS survey - IV: The X-ray luminosity-temperature relation of high
  redshift galaxy clusters

abstract:
  We present a measurement of the cluster X-ray luminosity-temperature relation
out to high redshift (z~0.8). Combined ROSAT PSPC spectra of 91 galaxy clusters
detected in the Wide Angle ROSAT Pointed Survey (WARPS) are simultaneously fit
in redshift and luminosity bins. The resulting temperature and luminosity
measurements of these bins, which occupy a region of the high redshift L-T
relation not previously sampled, are compared to existing measurements at low
redshift in order to constrain the evolution of the L-T relation. We find a
best fit to low redshift (z<0.2) cluster data, at T>1 keV, to be L proportional
to T^(3.15\pm0.06). Our data are consistent with no evolution in the
normalisation of the L-T relation up to z~0.8. Combining our results with ASCA
measurements taken from the literature, we find eta=0.19\pm0.38 (for Omega_0=1,
with 1 sigma errors) where L_Bol is proportional to (1 + z)^eta T^3.15, or
eta=0.60\pm0.38 for Omega_0=0.3. This lack of evolution is considered in terms
of the entropy-driven evolution of clusters. Further implications for
cosmological constraints are also discussed.


title: HS0907+1902: a new 4.2hr eclipsing dwarf nova

abstract:
  We report on follow-up spectroscopy and photometry of the cataclysmic
variable candidate HS0907+1902 selected from the Hamburg Quasar Survey. B, V,
and R photometry obtained during the first observed outburst of HS0907+1902
(V~13) reveals deep eclipses (DeltaV~2.1-2.8) and an orbital period Porb=4.2h
with the eclipse depth decreasing to the red. The outburst eclipse profiles are
symmetric, indicating an axisymmetrical brightness distribution in the
accretion disc. We derive an inclination i~73deg-79deg from the eclipse
duration. The quiescent spectrum obtained with the Hobby-Eberly Telescope shows
double peaked emission lines of HI, HeI and FeI,II and clearly identifies the
system as a dwarf nova. Absorption features of the secondary star are detected
at red wavelengths from which a spectral class M3+-1.5 and a distance of
d=320+-100pc are derived.


title: Type Ia Supernovae

abstract:
  Type Ia Supernovae are in many aspects still enigmatic objects. Recent years
have witnessed a bonanza of supernova observations. The increased samples from
dedicated searches have allowed the statistical investigation of Type Ia
Supernovae as a class. The observational data on Type Ia Supernovae are very
rich, and the uniform picture of a decade ago has been replaced by several
correlations which connect the maximum luminosity with light curve shape, color
evolution, spectral appearance, and host galaxy morphology. These correlations
hold across almost the complete spectrum of Type Ia Supernovae, with a number
of notable exceptions. After 150 days past maximum, however, all observed
objects show the same decline rate and spectrum. Bolometric light curves are a
handy tool to investigate the overall appearance of Type Ia Supernovae. The
nickel masses derived this way show large variations, which combined with the
dynamics from line widths, indicate that the brighter events are also coming
from more massive objects. The lack of accurate distances and the uncertainty
in the correction for absorption are hampering further progress. Improvements
in these areas are vital for the detailed comparison of luminosities and the
determination of nickel masses.


title:
Photometric and kinematic studies of open star clusters. II. NGC 1960 (M
  36) and NGC 2194

abstract:
  We present CCD photometry and proper motion studies of the two open star
clusters NGC 1960 (M 36) and NGC 2194. Fitting isochrones to the colour
magnitude diagrams, for NGC 1960 we found an age of t=16 Myr and a distance of
roughly d=1300 pc and for NGC 2194 t=550 Myr and d=2900 pc, respectively. We
combined membership determination by proper motions and statistical field star
subtraction to derive the initial mass function of the clusters and found
slopes of Gamma=-1.23 +/- 0.17 for NGC 1960 and Gamma=-1.33 +/- 0.29 for NGC
2194. Compared to other IMF studies of the intermediate mass range, these
values indicate shallow mass functions.


title:
The dynamical evolution of the fragmented, bipolar dust shell around the
  carbon star IRC +10216: Rapid changes of a PPN-like structure?

abstract:
  We present high-resolution J-, H-, and K-band observations and the first H-K
color image of the carbon star IRC +10216. The images were reconstructed from
6m telescope speckle interferograms using the bispectrum speckle interferometry
method. The H and K images with resolutions between 70mas and 92mas consist of
several compact components within a 0.2" radius and a fainter asymmetric
nebula. The brightest four components are denoted with A to D in the order of
decreasing brightness in the 1996 image. A comparison of our images from 1995,
1996, 1997, and 1998 gives - almost like a movie of five frames - insight into
the dynamical evolution of the inner nebula. For instance, the separation of
the two brightest components A and B increased from 191 mas in 1995 to 265 mas
in 1998. At the same time, component B is fading and the components C and D
become brighter. The X-shaped bipolar structure of the nebula, most prominently
present in the J-band image, implies an asymmetric mass loss. Such asymmetries
are often present in protoplanetary nebulae but are unexpected for AGB stars.
IRC +10216 is thus likely to be very advanced in its AGB evolution, shortly
before turning into a protoplanetary nebula. The cometary shapes of A in the H
and J images and in the 0.79 micron and 1.06 micron HST images suggest that the
core of A is not the central star, but the southern lobe of a bipolar
structure. The position of the central star is probably at or near the position
of component B, where the H-K color has a value of 4.2. If the star is at or
near B, then the components A, C, and D are likely to be located at the inner
boundary of the dust shell.


title: K-Band Calibration of the Red Clump Luminosity

abstract:
  The average near-infrared (K-band) luminosity of 238 Hipparcos red clump
giants is derived and then used to measure the distance to the Galactic center.
These Hipparcos red clump giants have been previously employed as I-band
standard candles. The advantage of the K-band is a decreased sensitivity to
reddening, and perhaps also a reduced systematic dependence on metallicity. In
order to investigate the latter, and also to refer our calibration to a known
metallicity zero-point, we restrict our sample of red clump calibrators to
those with abundances derived from high-resolution spectroscopic data. The mean
metallicity of the sample is [Fe/H] = -0.18 dex. The data are consistent with
no correlation between M_K and [Fe/H], and only weakly constrain the slope of
this relation. The luminosity function of the sample peaks at M_K = -1.61 +-
0.03 mag. Next, we assemble published optical and near-infrared photometry for
about 20 red clump giants in a Baade's Window field with a mean metallicity
nearly identical to that of the Hipparcos red clump. We derive the distance to
the Galactic center: R = 8.24 +- 0.42 kpc. The uncertainty in this distance
measurement is dominated by the small number of Baade's Window red clump giants
examined here [abridged].


title: Is Galactic Structure Compatible with Microlensing Data?

abstract:
  We generalize to elliptical models the argument of Kuijken (1997), which
connects the microlensing optical depth towards the Galactic bulge to the
Galactic rotation curve. When applied to the latest value from the MACHO
collaboration for the optical depth for microlensing of bulge sources, the
argument implies that the Galactic bar cannot plausibly reconcile the measured
values of the optical depth, the rotation curve and the local mass density.
Either there is a problem with the interpretation of the microlensing data, or
our line of sight to the Galactic centre is highly atypical in that it passes
through a massive structure that wraps only a small distance around the
Galactic centre.


title: "Clocked" Bursts From GS 1826-238

abstract:
  We report on the long term monitoring of the GINGA transient source GS
1826-238 performed with the BeppoSAX Wide Fiels Camera (WFC) instrument, during
four different observing campaigns covering October 1996 - September 1999. WFC
detection of type-I bursting activity from the source ruled out its proposed
black hole candidacy and clearly suggested the compact object related to GS
1826-238 to be a weakly magnetized neutron star. The analysis of the arrival
times of the observed 78 bursts lead to the discovery of a recurrence of ~5.75
hours with a spread of 38 minutes (FWHM) along more than 3 years monitoring
data (Ubertini et al., 1999). We performed a more detailed analysis of the
whole available data, and evidence of shortening of the recurrence time,
together with a drastic narrowing in the spread (down to a few minutes) was
observed on a one year time scale. Possible relation with the source X-ray
persistent emission is discussed.


title:
Depletion curves in cluster lenses: simulations and application to the
  cluster MS1008-1224

abstract:
  When the logarithmic slope of the galaxy counts is lower than 0.4 (this is
the case in all filters at large magnitude), the magnification bias due to the
lens makes the number density of objects decrease, and consequently, the radial
distribution shows a typical depletion curve. In this paper, we present
simulations of depletion curves obtained in different filters for a variety of
different lens models - e.g., a singular isothermal sphere, an isothermal
sphere with a core, a power-law density profile, a singular isothermal
ellipsoid and a NFW profile. The different model parameters give rise to
different effects, and we show how the filters, model parameters and redshift
distributions of the background populations affect the depletion curves. We
then compare our simulations to deep VLT observations of the cluster
MS1008--1224 and propose to constrain the mass profile of the cluster as well
as the ellipticity and the orientation of the mass distribution. This
application is based solely on deep photometry of the faint background
galaxies. We finally give some possible applications of this method, useful for
cluster lenses.


title: Bright X-ray bursts from 1E 1724-3045 in Terzan 2

abstract:
  During about 3 years wide field monitoring of the Galactic Center region by
the WFC telescopes on board the BeppoSAX satellite, a total of 14 type-I X-ray
bursts were detected from the burster 1E 1724-3045 located in the globular
cluster Terzan 2. All the observed events showed evidence for photospheric
radius expansion due to Eddington-limit burst luminosity, thus leading to an
estimate of the source distance (~7.2 kpc). Preliminary results of the analysis
of the bursts are presented.


title:
Massive star formation and evolution in starburst galaxies: mid-infrared
  spectroscopy with ISO-SWS

abstract:
  We present new ISO-SWS data for a sample of 27 starburst galaxies, and with
these data examine the issues of formation and evolution of the most massive
stars in starburst galaxies. Using starburst models which incorporate time
evolution, new stellar atmosphere models for massive stars, and a starburst
model geometry derived from observations of the prototypical starburst M82, we
model the integrated mid-infrared line ratio [NeIII](15.6 microns)/[NeII](12.8
microns). This line ratio is sensitive to the hardness of the stellar energy
distribution and therefore to the most massive stars present.
  We conclude from our models, with consideration of recent determinations of
the stellar census in local, high-mass star forming regions, that the
[NeIII]/[NeII] ratios we measure are consistent with the formation of massive
(~50-100 solar mass) stars in most starbursts. In this framework, the low
nebular excitation inferred from the measured line ratios can be attributed to
aging effects. By including estimates of the ratio of infrared-to-Lyman
continuum luminosity for the galaxies in our sample, we further find that most
starbursts are relatively short-lived (1-10 million years), only a few O-star
lifetimes. We discuss a possible cause of such short events: the effectiveness
of stellar winds and supernovae in destroying the starburst environment.


title: The best unbiased estimator for the CMB angular bispectrum

abstract:
  For those angular multipoles where cosmic variance is an issue,
non-Gaussianities in the Cosmic Microwave Background (CMB) anisotropies will be
hard to detect. Here, we construct explicitly the best unbiased estimator for
the CMB angular bispectrum.


title: Galactic Evolution of Beryllium and Oxygen

abstract:
  We discuss the early evolution of beryllium and oxygen in our Galaxy by
comparing abundances of these elements for halo and disk metal-poor stars.
Both, O and Be rise as we go progressively to more metal-rich stars, showing a
slope 0.41 +-0.09 ([Be/O] vs [Fe/H]) for stars with [Fe/H] < -1. This
relationship provides an observational constraint to the actually proposed
Galactic Cosmic Ray theories.


title:
An H alpha Survey of 8 Abell Clusters: the dependence of tidally-induced
  star formation on cluster density

abstract:
  We have undertaken a survey of H alpha emission in a substantially complete
sample of CGCG galaxies of types Sa and later within 1.5 Abell radii of the
centres of 8 low-redshift Abell clusters. Some 320 galaxies were surveyed, of
which 116 were detected in emission (39% of spirals, 75% of peculiars).
Detected emission was classified as `compact' or `diffuse'. From an analysis of
the full survey sample, we reconfirm our previous identification of compact and
diffuse emission with circumnuclear starburst and disk emission respectively.
The circumnuclear emission is associated either with the presence of a bar, or
with a disturbed galaxy morphology indicative of on-going tidal interactions.
The frequency of such tidally-induced (circumnuclear) starburst emission in
spirals increases from regions of lower to higher local galaxy surface density,
and from clusters with lower to higher central galaxy space density. We
conclude that tidal interactions are likely to be the main mechanism for the
transformation of spirals to S0s in clusters. Finally, for regions of
comparable local density, the frequency of tidally-induced starburst emission
is greater in clusters with higher central galaxy density. This implies that,
for a given local density, morphological transformation of disk galaxies
proceeds more rapidly in clusters of higher central galaxy density. This effect
is considered to be due to subcluster merging and could account for the
previously considered anomalous absence of a significant type - local surface
density relation for irregular clusters at intermediate redshift.


title: Large-Scale Cosmic Shear Measurements

abstract:
  We present estimates of the gravitational lensing shear variance obtained
from images taken at the CFHT using the UH8K CCD mosaic camera. Six fields were
observed for a total of 1 hour each in V and I, resulting in catalogs
containing approximately 20,000$ galaxies per field, with properly calibrated
and optimally weighted shear estimates. These were averaged in cells of sizes
ranging from 1'.875 to 30' to obtain estimates of the cosmic shear variance
$<\bar{\gamma}^2>$, with uncertainty estimated from the scatter among the
estimates for the 6 fields. Our most reliable estimator for cosmic shear is
provided by the cross-correlation of the shear measured in the two passbands.
At scales $\lsim 10'$ the results are in good agreement with those of van
Waerbeke et al. 2000, Bacon et al. 2000 and Wittman et al. 2000 and with
currently fashionable cosmological models. At larger scales the shear variance
falls below the theoretical predictions, and on the largest scales we find a
null detection of shear variance averaged in 30' cells of $<\bar{\gamma}^2 > =
(0.28 \pm 1.84) \times 10^{-5}$.


title:
Correlated mixtures of adiabatic and isocurvature cosmological
  perturbations

abstract:
  The Cosmic Microwave Background (CMB) anisotropies measurements can provide
many clues about the Universe. Although the common belief is that they will
allow a very precise measurement of the cosmological parameters (that is, the
current state of the Universe), they will alternatively give interesting
informations about the state of the initial perturbations (that is, the state
of the Universe at the end of inflation). In this paper, we study the
observational consequences on the CMB anisotropies of some wide set of inital
conditions, with a correlated mixture of adiabatic and isocurvature
perturbations.


title: Clustering statistics on a light-cone in the cosmological redshift space

abstract:
  We summarize a series of our recent work concerning the cosmological
redshift-space distortion and light-cone effects. After briefly describing the
theoretical formalism, we show how those effects are sensitive to the
cosmological parameters. Then we apply this formalism to predict the two-point
correlation functions and power spectra for the X-ray clusters, galaxies and
quasars in future surveys, and discuss their cosmological implications.


title: Nonlinear Analysis of Irregular Variables

abstract:
  The Fourier spectral techniques that are common in Astronomy for analyzing
periodic or multi-periodic light-curves lose their usefulness when they are
applied to unsteady light-curves. We review some of the novel techniques that
have been developed for analyzing irregular stellar light or radial velocity
variations, and we describe what useful physical and astronomical information
can be gained from their use.


title: G328.4+0.2 : A large and luminous Crab-like supernova remnant

abstract:
  We report on radio continuum and HI observations of the radio source
G328.4+0.2 using the Australia Telescope Compact Array. Our results confirm
G328.4+0.2 to be a filled-center nebula with no surrounding shell, showing
significant linear polarization and an almost flat spectral index. These
results lead us to conclude that G328.4+0.2 is a Crab-like, or ``plerionic'',
supernova remnant (SNR), presumably powered by an unseen central pulsar. HI
absorption towards G328.4+0.2 puts a lower limit on its distance of 17.4 +/-
0.9 kpc, making it the largest (D=25 pc) and most luminous (L_R = 3e35 erg/s)
Crab-like SNR in the Galaxy. We infer G328.4+0.2 to be significantly older than
the Crab Nebula, but powered by a pulsar which is fast spinning (P<20 ms) and
which has a comparatively low magnetic field (B<1e12 G). We propose G328.4+0.2,
G74.9+1.2 and N157B as a distinct group of large-diameter, high-luminosity
Crab-like SNRs, all powered by fast-spinning low-field pulsars.


title:
Deriving the Nonlinear Cosmological Power Spectrum and Bispectrum from
  Analytic Dark Matter Halo Profiles and Mass Functions

abstract:
  We present an analytic model for the fully nonlinear power spectrum P and
bispectrum Q of the cosmological mass density field. The model is based on
physical properties of dark matter halos, with the three main model inputs
being analytic halo density profiles, halo mass functions, and halo-halo
spatial correlations, each of which has been well studied in the literature. We
demonstrate that this new model can reproduce the power spectrum and bispectrum
computed from cosmological simulations of both an n=-2 scale-free model and a
low-density cold dark matter model. To enhance the dynamic range of these large
simulations, we use the synthetic halo replacement technique of Ma & Fry
(2000a), where the original halos with numerically softened cores are replaced
by synthetic halos of realistic density profiles. At high wavenumbers, our
model predicts a slope for the nonlinear power spectrum different from the
often-used fitting formulas in the literature based on the stable clustering
assumption. Our model also predicts a three-point amplitude Q that is scale
dependent, in contrast to the popular hierarchical clustering assumption. This
model provides a rapid way to compute the mass power spectrum and bispectrum
over all length scales where the input halo properties are valid. It also
provides a physical interpretation of the clustering properties of matter in
the universe.


title:
Two-dimensional galaxy-galaxy lensing: a direct measure of the
  flattening and alignment of light and mass in galaxies

abstract:
  We propose a new technique to directly measure the shapes of dark matter
halos of galaxies using weak gravitational lensing. Extending the standard
galaxy-galaxy lensing method, we show that the shape parameters of the mass
distribution of foreground galaxies can be measured from the two-dimensional
shear field derived from background galaxies. This enables the comparison of
the ellipticity of the mass distribution with that of the light in galaxies, as
well as an estimate of the degree of alignment between the stellar component
and dark matter. We choose the specific case of an elliptical, isothermal
profile and estimate the feasibility and significance of the detection of this
signal. The prospects for applying this technique are excellent with large
on-going surveys like the Sloan Digital Sky Survey. The expected signal is
smaller, but comparable in significance to that of the mass in standard
galaxy-galaxy lensing analyses. Since shapes of halos depend on the degree of
dissipation and the transfer of angular momentum during galaxy assembly,
constraints obtained from our analysis will provide an important input to
models of galaxy formation.


title:
Testing the multiple supernovae versus gamma-ray burst scenarios for
  giant HI supershells

abstract:
  The energy source of the giant HI supershells in nearby galaxies and in our
own is still an unsettled issue. Proposed scenarios for production of
near-complete ringlike supershells are multiple supernovae (SNe) and gamma-ray
bursts (GRBs). In the late phase of evolution it is difficult to tell these
models apart. We show that, if a supershell has been powered by multiple SNe,
peculiar metal abundances should be found in the medium within the bubble. We
present line diagnostics that could detect such unusual abundances, such as
unusually high ratios of [O]/[Fe] and [Ne]/[Fe]. Among ions of the same
element, a higher enhancement is expected in lines from a high-ionization state
than in lines from a low-ionization state. Identification of the energy source
of HI supershells would set strong constraints on the rates and energetics of
GRBs, as well as on their location within a galaxy.


title: 16 x 25 Ge:Ga Detector Arrays for FIFI LS

abstract:
  We are developing two-dimensional 16 x 25 pixel detector arrays of both
unstressed and stressed Ge:Ga photoconductive detectors for far-infrared
astronomy from SOFIA. The arrays, based on earlier 5 x 5 detector arrays used
on the KAO, will be for our new instrument, the Far Infrared Field Imaging Line
Spectrometer (FIFI LS). The unstressed Ge:Ga detector array will cover the
wavelength range from 40 to 120 microns, and the stressed Ge:Ga detector array
from 120 to 210 microns. The detector arrays will be operated with multiplexed
integrating amplifiers with cryogenic readout electronics located close to the
detector arrays. The design of the stressed detector array and results of
current measurements on several prototype 16 pixel linear arrays are reported.
They demonstrate the feasibility of the current concept. ***This paper does not
include Figures due to astro-ph size limitations. Please download entire file
at http://fifi-ls.mpe-garching.mpg.de/spie.det.ps.gz ***


title: Perspective of long baseline interferometry

abstract:
  This article is a sort of sequel of the earlier extensive review by Saha
(1999a) where emphasis was laid down on the ground based single aperture, as
well as on the working long baseline optical interferometers (LBI) situated at
the various observatories across the globe that are producing a large amount of
astronomical results. Since the future of high resolution astronomy lies with
the new generation of arrays, the numerous technical challenges of developing
such systems are addressed indicating the current trends and the path to future
progress in interferometry. The new generation interferometers such as Palomar
testbed interferometer (PTI), Navy prototype optical interferometer (NPOI),
Keck interferometer, Very large telescope interferometer (VLTI), Center for
high angular resolution astronomy (CHARA) array, Optical very large array
(OVLA), Mitaka optical infrared arrays (MIRA), etc., are being developed. A few
of them, viz., PTI, NPOI, IOTA are producing results. Among the working
interferometers that have been described earlier by Saha (1999a), the expansion
of the Grand interf\'erom\`etre \`a deux (two) t\'elescopes (GI2T), Infrared
and optical telescope array (IOTA) are in progress. The current status of all
these interferometers stated above are enumerated. The data analysis being
carried out using the working interferometers are also described. The space
interferometry programmes are advancing very fast. Among the notable ones are
the Space technology 3 (ST3), Space interferometry mission (SIM), and Darwin;
they have already received funds. The technical details of these
interferometers and their objectives are highlighted.


title: The observation of Delta Sct and Gamma Dor stars by using MONS satellite

abstract:
  The MONS space experiment will be able to verify some of the most important
topics in the asteroseismologic studies of Delta Sct and Gamma Dor stars. We
discuss how the $\gamma$ Doradus can be considered possible "bridges" between
the opacity driven overstable pulsation and the stochastically excited solar
like oscillation. For this reason the possible inclusion of a Gamma Dor
representative in the MONS main target list is presented and discussed. To
study Delta Sct stars, an appropriate frequency resolution, comparable to or
better than what is currently achieved by ground-based observations, is
necessary and hence two runs are recommended. To avoid over-scheduling of the
Main Camera, a possible combination of observations from the Main Camera and
from the Star Trackers is proposed. As a result, key-objects could be
adequately monitored, affording the possibility to enter into details of
amplitude variations. Simultaneously, the same results could be obtained on two
Gamma Dor stars.


title: A far IR study of the CfA Seyfert sample. I. The data

abstract:
  We present mid and far IR ISO data of the CfA Seyfert galaxy sample. These
data allow a detailed study of the far IR Spectral Energy Distribution (SED) of
these galaxies. A Bayesian inversion method has been used to invert the SED of
these sources yielding two fundamental results, namely, that the mid and far IR
SED of Seyfert galaxies can be explained solely through thermal reradiation of
high energy photons by dust, and that this thermal emission is made up of two
or three different independent components, a warm, a cold and a very cold dust
component. These thermal components have been readily explained as produced
respectively by warm dust heated by either the active nucleus or by
circumnuclear starburts, cold dust heated by star forming region in the galaxy
disk, and very cold dust heated by the general interstellar radiation field.
Comparisons between the parameters obtained from the analysis of the IR SEDs
(fluxes, temperatures, luminosities) have been made. Our results suggest that
the emission in the mid IR is anisotropic and the differences found between
Seyfert 1 and Seyfert 2s can be explained with thin molecular tori models.


title: Self-interacting Dark Matter and Invisibly Decaying Higgs

abstract:
  Self-interacting dark matter has been suggested in order to overcome the
difficulties of the Cold Dark Matter model on galactic scales. We argue that a
scalar gauge singlet coupled to the Higgs boson, which could lead to an
invisibly decaying Higgs, is an interesting candidate for this self-interacting
dark matter particle. We also present estimates on the abundance of these
particles today as well as consequences to non-Newtonian forces.


title: Stellar Structure and Evolution: Deductions from Hipparcos

abstract:
  During the last decade, the understanding of fine features of the structure
and evolution of stars has become possible as a result of enormous progress
made in the acquisition of high-quality observational and experimental data and
of new developments and refinements in the theoretical description of stellar
plasmas. The confrontation of high-quality observations with sophisticated
stellar models has allowed many aspects of the theory to be validated, and
several characteristics of stars relevant to Galactic evolution and cosmology
to be inferred. This paper is a review of the results of recent studies
undertaken in the context of the Hipparcos mission, taking benefit of the
high-quality astrometric data it has provided. Successes are discussed, as well
as the problems that have arisen and suggestions proposed to solve them. Future
observational and theoretical developments expected and required in the field
are also presented.


title:
Turbulent mixing, viscosity, diffusion and gravity in the formation of
  cosmological structures: the fluid mechanics of dark matter

abstract:
  Self-gravitational structure formation theory for astrophysics and cosmology
is revised using nonlinear fluid mechanics. Gibson's 1996-2000 theory balances
fluid mechanical forces with gravitational forces and density diffusion with
gravitational diffusion at critical viscous, turbulent, magnetic, and diffusion
length scales termed Schwarz scales. Instability occurs for scales larger than
the largest Schwarz scale rather than only for scales larger than the acoustic
scale introduced by Jeans 1902. From the new theory, the inner-halo-dark-matter
of galaxies consists of dark proto-globular-star-cluster (PGC) clumps of
small-planetary-mass objects called primordial fog particles (PFPs) formed soon
after decoupling at 300,000 years. PFPs explain Schild's 1996 "rogue planets
>... likely to be the missing mass" of a quasar lens-galaxy. WIMP dark matter
fluid is super-diffusive and fragments at large L_SD scales to form
outer-galaxy-halos. In the beginning of structure formation 30,000 years after
the Big Bang the viscous Schwarz scale L_SV matched the horizon scale L_H at
proto-galaxy-supercluster masses, decreasing to proto-galaxy fragments at
300,000 years. WIMP diffusivities from observed outer-halo (L_SD) scales
indicate WIMP particle masses in the neutrino rather than neutralino range.


title: Molecular Abundances in the Atmosphere of the T Dwarf Gl 229B

abstract:
  We present new, high resolution, infrared spectra of the T dwarf Gliese 229B
in the J, H, and K bandpasses. We analyze each of these as well as previously
published spectra to determine its metallicity and the abundances of NH3 and CO
in terms of the surface gravity of Gl 229B, which remains poorly constrained.
The metallicity increases with increasing gravity and is below the solar value
unless Gl 229B is a high-gravity brown dwarf with log g(cgs) ~ 5.5. The NH3
abundance is determined from both the H and the K band spectra which probe two
different levels in the atmosphere. We find that the abundance from the K band
data is well below that expected from chemical equilibrium, which we interpret
as strong evidence for dynamical transport of NH3 in the atmosphere. This is
consistent with the previous detection of CO and provides additional
constraints on the dynamics of the atmosphere of this T dwarf.


title: Cosmic Statistics through Weak Lenses

abstract:
  Many recent studies have demonstrated that scaling arguments, such as the
so-called hierarchical {\em ansatz}, are extremely useful in understanding the
statistical properties of weak gravitational lensing. This is especially true
on small angular scales (i.e. at high resolution), where the usual perturbative
calculations of matter clustering no longer apply. We build on these studies in
order to develop a complete picture of weak lensing at small smoothing angles.
In particular, we study the full probability distribution function, bias and
other multipoint statistics for the ``hot spots'' of the convergence field
induced by weak lensing, and relate these to the statistics of overdense
regions in underlying mass distribution. It is already known that weak lensing
can constrain the background geometry of the Universe, but we further show that
it can also provide valuable information about the statistics of collapsed
objects and the physics of collisionless clustering. Our results are
particularly important for future observations which will, at least initially,
focus on small smoothing angles.


title:
Chandra X-ray Observatory Arcsecond Imaging of the Young, Oxygen-rich
  Supernova Remnant 1E0102.2-7219

abstract:
  We present observations of the young, Oxygen-rich supernova remnant
1E0102.2-7219 taken by the Chandra X-ray Observatory during Chandra's Orbital
Activation and Checkout phase. The boundary of the blast wave shock is clearly
seen for the first time, allowing the diameter of the remnant and the mean
blast wave velocity to be determined accurately. The prominent X-ray bright
ring of material may be the result of the reverse shock encountering ejecta;
the radial variation of O VII vs. O VIII emission indicates an ionizing shock
propagating inwards, possibly through a strong density gradient in the ejecta.
We compare the X-ray emission to Australia Telescope Compact Array 6 cm radio
observations (Amy and Ball) and to archival Hubble Space Telescope [O III]
observations. The ring of radio emission is predominantly inward of the outer
blast wave, consistent with an interpretation as synchrotron radiation
originating behind the blast wave, but outward of the bright X-ray ring of
emission. Many (but not all) of the prominent optical filaments are seen to
correspond to X-ray bright regions. We obtain an upper limit of ~9e33 erg/s (3
sigma) on any potential pulsar X-ray emission from the central region.


title: Lithium-6 from Solar Flares

abstract:
  By introducing a hitherto ignored Li-6 producing process, due to accelerated
He-3 reactions with He-4, we show that accelerated particle interactions in
solar flares produce much more Li-6 than Li-7. By normalizing our calculations
to gamma-ray data we demonstrate that the Li-6 produced in solar flares,
combined with photospheric Li-7, can account for the recently determined solar
wind lithium isotopic ratio, obtained from measurements in lunar soil, provided
that the bulk of the flare produced lithium is evacuated by the solar wind.
Further research in this area could provide unique information on a variety of
problems, including solar atmospheric transport and mixing, solar convection
and the lithium depletion issue, and solar wind and solar particle
acceleration.


title:
The excitation and kinematical properties of H2 and [FeII] in the
  HH46/47 bipolar outflow

abstract:
  Long slit spectra of the molecular outflow Herbig-Haro (HH) 46/47 has been
taken in the J and K near-infrared bands. The observed H2 line emission
confirms the existence of a bright and extended redshifted counter-jet outflow
southwest of HH46. We show that this outflow seems to be composed of two
different emission regions which have distinct heliocentric velocities, in
contrast with the optical appearance, and which implies an acceleration of the
counter-jet. The observed [FeII] emission suggests an average extinction of 7-9
visual magnitudes for the region associated with the counter-jet. Through
position-velocity diagrams, we show the existence of different morphologies for
the H2 and [FeII] emission regions in the northern part of the HH46/47 outflow.
We have detected for the first time high velocity (-250 Km/s) [FeII] emission
in the region bridging HH46 to HH47A. The two strong peaks detected can be
identified with the optical positions B8 and HH47B. The H2 excitation diagrams
for the counter-jet shock suggest an excitation temperature for the gas of Tex
approx. 2600K. The lack of emission from the higher energy H2 lines such as the
4-3S(3) transition, suggests a thermal excitation scenario for the origin of
the observed emission. Comparison of the H2 line ratios to various shock models
yielded useful constraints about the geometry and type of these shocks. Planar
shocks can be ruled out whereas curved or bow-shocks (both J and C-type) can be
parametrised to adjust our data.


title: Luminosity- and morphology-dependent clustering of galaxies

abstract:
  How does the clustering of galaxies depend on their inner properties like
morphological type and luminosity? We address this question in the mathematical
framework of marked point processes and clarify the notion of luminosity and
morphological segregation. A number of test quantities such as conditional
mark-weighted two-point correlation functions are introduced. These descriptors
allow for a scale-dependent analysis of luminosity and morphology segregation.
Moreover, they break the degeneracy between an inhomogeneous fractal point set
and actual present luminosity segregation. Using the Southern Sky Redshift
Survey~2 (da Costa et al. 1998, SSRS2) we find both luminosity and
morphological segregation at a high level of significance, confirming claims by
previous works using these data (Benoist et al. 1996, Willmer et al. 1998).
Specifically, the average luminosity and the fluctuations in the luminosity of
pairs of galaxies are enhanced out to separations of 15Mpc/h. On scales smaller
than 3Mpc/h the luminosities on galaxy pairs show a tight correlation. A
comparison with the random-field model indicates that galaxy luminosities
depend on the spatial distribution and galaxy-galaxy interactions. Early-type
galaxies are also more strongly correlated, indicating morphological
segregation. The galaxies in the PSCz catalog (Saunders et al. 2000) do not
show significant luminosity segregation. This again illustrates that mainly
early-type galaxies contribute to luminosity segregation. However, based on
several independent investigations we show that the observed luminosity
segregation can not be explained by the morphology-density relation alone.


title:
Populations of high-luminosity density-bounded H II regions in spiral
  galaxies? Evidence and implications

abstract:
  (Abridged) We present evidence that the HII regions of high luminosity in
disk galaxies may be density bounded, so that a significant fraction of the
ionizing photons emitted by their exciting OB stars escape from the regions.
The key piece of evidence is the presence, in the H\alpha luminosity functions
(LFs) of the populations of HII regions, of glitches, local sharp peaks at an
apparently invariant luminosity, defined as the Stromgren luminosity (L_ Str),
L_H\alpha = L_Str = 10^38.6 (\pm 10^0.1) erg/s (no other peaks are found in any
of the LFs) accompanying a steepening of slope for L_H\alpha> L_Str. This
behavior is readily explicable via a physical model whose basic premises are:
(a) the transition at L_H\alpha = L_Str marks a change from essentially
ionization bounding at low luminosities to density bounding at higher values,
(b) for this to occur the law relating stellar mass in massive star-forming
clouds to the mass of the placental cloud must be such that the ionizing photon
flux produced within the cloud is a function which rises more steeply than the
mass of the cloud. Supporting evidence for the hypothesis of this transition is
presented. If confirmed, the density-bounding hypothesis would imply that the
density-bounded regions were the main sources of the photons which ionize the
diffuse gas in disk galaxies. We estimate that these regions emit sufficient
Lyman continuum not only to ionize the diffuse medium, but to cause a typical
spiral to emit significant ionizing flux into the intergalactic medium. The low
scatter observed in L_Str, less than 0.1 mag rms in the still quite small
sample measured to date, is an invitation to widen the data base, and to
calibrate against primary standards, with the aim of obtaining a precise
standard candle.


title: Galaxy Morphologies in the Cluster CL1358+62 at z=0.33

abstract:
  We describe the morphological composition of a sample of 518 galaxies in the
field of CL1358+62 at z=0.33, drawn from a large HST mosaic covering 53 sq.
arcmin. The sample is complete to I=22, corresponding to M_V=-18.5 in the rest
frame. The galaxies have been independently classified by the authors of this
paper and by Alan Dressler. For galaxies with I<21, the two sets of classifiers
agree on the total early-type population, but disagree on the S0/E ratio. We
discuss the constraints on morphological evolution and the implication of the
differing S0/E ratios. We use our large body of spectra to make the
correspondence between morphological and spectral type.


title: A Theory of Gamma-Ray Bursts

abstract:
  We present a specific scenario for the link between GRB and hypernovae, based
on Blandford-Znajek extraction of black-hole spin energy. Such a mechanism
requires a high angular momentum in the progenitor object. The observed
association of gamma-ray bursts with type Ibc supernovae leads us to consider
massive helium stars that form black holes at the end of their lives as
progenitors. We combine the numerical work of MacFadyen & Woosley with analytic
calculations, to show that about 1E53 erg each are available to drive the fast
GRB ejecta and the supernova. The GRB ejecta are driven by the power output
through the open field lines, whereas the supernova is powered by closed filed
lines and jet shocks. We also present a much simplified approximate derivation
of these energetics.
  Helium stars that leave massive black-hole remnants in special ways, namely
via soft X-ray transients or very massive WNL stars. Since binaries naturally
have high angular momentum, we propose a link between black-hole transients and
gamma-ray bursts. Recent observations of one such transient, GRO J1655-40/Nova
Scorpii 1994, explicitly support this connection: its high space velocity
indicates that substantial mass was ejected in the formation of the black hole,
and the overabundance of alpha-nuclei, especially sulphur, indicates that the
explosion energy was extreme, as in SN 1998bw/GRB 980425. (abstract shortened)


title:
Blobs in Wolf-Rayet Winds: Random Photometric and Polarimetric
  Variability

abstract:
  Some isolated Wolf-Rayet stars present random variability in their optical
flux and polarization. We make the assumption that such variability is caused
by the presence of regions of enhanced density, i.e. blobs, in their envelopes.
In order to find the physical characteristics of such regions we have modeled
the stellar emission using a Monte Carlo code to treat the radiative transfer
in an inhomogeneous electron scattering envelope. We are able to treat multiple
scattering in the regions of enhanced density as well as in the envelope
itself. The finite sizes of the source and structures in the wind are also
taken into account. Most of the results presented here are based on a parameter
study of models with a single blob. The effects due to multiple blobs in the
envelope are considered to a more limited extent. Our simulations indicate that
the density enhancements must have a large geometric cross section in order to
produce the observed photopolarimetric variability. The sizes must be of the
order of one stellar radius and the blobs must be located near the base of the
envelope. These sizes are the same inferred from the widths of the sub-peaks in
optical emission lines of Wolf-Rayet stars. Other early-type stars show random
polarimetric fluctuations with characteristics similar to those observed in
Wolf-Rayet stars, which may also be interpreted in terms of a clumpy wind.
Although the origin of such structures is still unclear, the same mechanism may
be working in different types of hot stars envelopes to produce such
inhomogeneities.


title: Cosmological Strucure Formation with Topological Defects

abstract:
  Structure formation with topological defects is described. The main
differences from inflationary models are highlighted. The results are compared
with recent observations. It is concluded that all the defect models studied so
far are in disagreement with recent observations of CMB anisotropies.
Furthermore, present observations do not support 'decoherence', a generic
feature of structure formation from topological defects.


title: A new cosmological tracker solution for Quintessence

abstract:
  In this paper we propose a quintessence model with the potential $V(\Phi
)=V_{o}[ \sinh {(\alpha \sqrt{\kappa_{o}}\Delta \Phi})] ^{\beta}$, which
asymptotic behavior corresponds to an inverse power-law potential at early
times and to an exponential one at late times. We demonstrate that this is a
tracker solution and that it could have driven the Universe into its current
inflationary stage. The exact solutions and the description for a complete
evolution of the Universe are also given. We compare such model with the
current cosmological observations.


title: Cold and Fuzzy Dark Matter

abstract:
  Cold dark matter (CDM) models predict small-scale structure in excess of
observations of the cores and abundance of dwarf galaxies. These problems might
be solved, and the virtues of CDM models retained, even without postulating
{\it ad hoc} dark matter particle or field interactions, if the dark matter is
composed of ultra-light scalar particles (m ~ 10^{-22}eV), initially in a
(cold) Bose-Einstein condensate, similar to axion dark matter models. The wave
properties of the dark matter stabilize gravitational collapse providing halo
cores and sharply suppressing small-scale linear power.


title: Lyman Alpha Cooling Radiation from High-Redshift Halos

abstract:
  The baryons inside high-redshift halos with virial temperatures above T=10^4
K cool radiatively as they condense inside dark matter potential wells. We show
that the release of the gravitational binding energy, over the halo assembly
time-scale, results in a significant and detectable Ly alpha flux. At the
limiting line flux of approximately 10^-19 erg/s/cm^2/asec^2 of the Next
Generation Space Telescope, several sufficiently massive halos, with velocity
dispersions above sigma=120 km/s, would be visible per 4'x4' field. The halos
would have characteristic angular sizes of approximately 10 asec, would be
detectable in a broad-band survey out to redshifts z=6-8, and would provide a
direct probe of galaxies in the process of forming. They may be accompanied by
HeII Ly alpha emission at the 10 percent level, but remain undetectable at
other wavelengths. Our predictions are in good agreement with the recent
finding of two Ly alpha ``blobs'' at z=3.1 by Steidel et al. (1999).


title: Chandra, GLAST, and the Galactic Center

abstract:
  Two-temperature spherical accretion flows produce $\approx 100$ Mev
gamma-rays from the decay of neutral pions created in proton-proton collisions
close to the black hole; they also produce $\sim 10$ keV X-rays by
bremsstrahlung emission at large radii. The gamma-ray to X-ray luminosity ratio
is nearly independent of black hole mass and accretion rate. It does depend
sensitively on the radial density profile of the accretion flow through the
parameter a, where $n \propto r^{-a}$. For the canonical Bondi value of a =
3/2, the gamma-ray to X-ray luminosity ratio is $\approx 30$. We interpret a
recent Chandra detection coincident with the massive black hole at the Galactic
Center as being thermal bremsstrahlung emission from the accretion flow. With
this normalization, the expected gamma-ray luminosity is $\approx 10^{35}$ ergs
s$^{-1}$ if a = 3/2. This is nearly two orders of magnitude above the detection
threshold of the GLAST telescope. For $a \approx 1/2$, however, (a value
suggested by recent theoretical arguments), the expected gamma-ray luminosity
is only $\approx 10^{29}$ ergs s$^{-1}$; GLAST should therefore provide an
important probe of the true accretion rate and radial density profile of the
accretion flow onto Sgr A*.


title: Angular Momentum Transport in Particle and Fluid Disks

abstract:
  We examine the angular momentum transport properties of disks composed of
macroscopic particles whose velocity dispersions are externally enhanced
(``stirred''). Our simple Boltzmann equation model serves as an analogy for
unmagnetized fluid disks in which turbulence may be driven by thermal
convection. We show that interparticle collisions in particle disks play the
same role as fluctuating pressure forces and viscous dissipation in turbulent
disks: both transfer energy in random motions associated with one direction to
those associated with another, and convert kinetic energy into heat. The
direction of angular momentum transport in stirred particle and fluid disks is
determined by the direction of external stirring and by the properties of the
collision term in the Boltzmann equation (or its analogue in the fluid
problem). In particular, our model problem yields inward transport for
vertically or radially stirred disks, provided collisions are suitably
inelastic; the transport is outwards in the elastic limit. Numerical
simulations of hydrodynamic turbulence driven by thermal convection find inward
transport; this requires that fluctuating pressure forces do little to no work,
and is analogous to an externally stirred particle disk in which collisions are
highly inelastic.


title:
Additional Information from Astrometric Gravitational Microlensing
  Observations

abstract:
  Astrometric observations of microlensing events were originally proposed to
determine the lens proper motion with which the physical parameters of lenses
can be better constrained. In this proceeding, we demonstrate that besides this
original usage astrometric microlensing observations can be additionally used
in obtaining various important information about lenses. First, we demonstrate
that the lens brightness can be determined with astrometric observations,
enabling one to know whether the event is caused by a bright star or a dark
lens. Second, we show that with additional information from astrometric
observations one can resolve the ambiguity of the photometric binary lens fit
and thus uniquely determine the binary lens parameters. Finally, we propose two
astrometric methods that can resolve the degeneracy in the photometric lens
parallax determination. Since one can measure both the proper motion and the
parallax by these methods, the lens parameters of individual events can be
uniquely determined.


title: On the Physics of Primordial Magnetic Fields

abstract:
  There are at present more then 30 theories about the origin of cosmic
magnetic fields at galactic and intergalactic scales. Most of them rely on
concepts of elementary particle physics, like phase transitions in the early
Universe, string theory and processes during the inflationary epoch. Here we
present some more astrophysical arguments to provide some guidance through this
large number and variety of models. Especially the fact that the evolution of
magnetic fields depends on the spatial coherence scale of the fields leds to
some interesting conclusions, which may rule out the majority of the
theoretical scenarios. In principle one has to distinguish between the
large-scale and small-scale magnetic fields. Large scale fields are defined as
those as becoming sub-horizon at that redshift at which the mass energy density
becomes equal to the photon energy density, which we name as equality. Small
scale fields which are sub-horizon even before equality, i.e. with scales lower
than (present) few Mpc cannot survive the radiation era and cannot reach
recombination, because of the effects of magnetic diffusion and photon
diffusion. Therefore mechanisms based on phase transitions become unlike, as
they provide magnetic fields on scales smaller than the horizon. Thus, the
observed galactic and intergalactic fields, which are small scales in our
terminology must be created after recombination by normal plasma processes
during the protogalactic evolution. The large scale fields instead were
produced during inflation and may have noticeable implications for the
formation of the large scale structure of the Universe. The inclusion of large
scale magnetic fields may improve present Cold Dark Matter theories of
structure formation.


title: On the formation and evolution of the globular cluster Omega Centauri

abstract:
  By means of N-body/hydrodynamical simulations we model the evolution of a
primordial 10^{8} solar masses density peak which ends up in an object closely
resembling the present day globular cluster Omega Centauri. We succeed to
reproduce the main features of the cluster, namely the structure, kinematics
and metallicity distribution. We suggest that Omega Centauri might be a
cosmological dwarf elliptical, formed at high redshift, evolved in isolation
and self-enriched, and eventually fallen inside the potential well of the Milky
Way, in agreement with the Searle-Zinn (1978) paradigm for galactic globular
clusters formation. We finally suggest that Omega Centauri is probably
surrounded by an extended Dark Matter (DM) halo, for which no observational
evidence is at present available. We expect that signatures, if any, of the DM
halo can be found in the kinematics of stars outside about 20 arcmin.


title: NGC 6994: an open cluster which is not an open cluster

abstract:
  We report on CCD photometry in the Johnson B,V and I passbands for 146 stars
in a 9' \times 9' region around the southern aggregate NGC 6994 (C 2056-128),
which appears in the Lynga (1987) catalogue of open star clusters. We argue
that this object is not really an open cluster, but simply a random enhancement
of four bright stars above the background level. This stars sample includes HD
358033 and GSC 05778-0082, together with M 73, which is referred to as a binary
star, but actually represents the whole asterism. Since NGC 6994 is not the
first case (see for instance Carraro and Patat 1995), this raises the
possibility that other open clusters may have been misclassified. We also
suggest that NGC 6994 is unlikely to be an open cluster remnant (OCR).


title: Mode detection from line-profile variations in Delta Scuti stars

abstract:
  The phenomenology associated with line profile variations in delta Scuti
stars is reviewed. The three main techniques adopted to detect pulsation modes,
i.e., the pixel-by-pixel analysis, the analysis of the moment time series and
the Fourier Doppler Imaging are presented and discussed. Their application to
the observational data has allowed the reliable detection of several pulsation
modes, many of them not detectable with photometric observations. The need of
better coordination of simultaneous spectroscopic and photometric campaigns in
order to get the complete pulsation spectra of these stars is pointed out. The
observation in different campaigns of the same objects has proved that dramatic
changes in the mode amplitudes are quite common, even in a couple of years (and
maybe less). In the last part of the paper a recent approach to the mode
detection by direct fit of line profile variations in multiperiodic pulsators
is described.


title:
Discovery of a New Deeply Eclipsing SU UMa-Type Dwarf Nova, IY UMa (=
  TmzV85)

abstract:
  We discovered a new deeply eclipsing SU UMa-type dwarf nova, IY UMa, which
experienced a superoutburst in 2000 January. Our monitoring revealed two
distinct outbursts, which suggest a superoutburst interval of ~800 d, or its
half, and an outburst amplitude of 5.4 mag. From time-series photometry during
the superoutburst, we determined a superhump and orbital period of 0.07588 d
and 0.0739132 d, respectively.


title:
Increase of the pion-kaon Hawking radiation from Schwarzschild black
  holes by Dirac monopoles

abstract:
  An algorithm for numerical computation of the barrier transparency for the
potentials surrounding Schwarzschild black holes is described for massive
scalar particles. It is then applied to calculate the total (including all
particle species and the contributions of twisted field configurations
connected with Dirac monopoles) luminosity for the pion-kaon Hawking radiation
from a Schwarzschild black hole with mass $M=10^{12}$ g. It is found that the
contribution due to monopoles can be of order 11% of the total pion-kaon
luminosity.


title: Cross-correlating CMB polarization with local large scale structures

abstract:
  We study heterogeneous quantities that efficiently cross-correlate the
lensing information encoded in CMB polarization and large-scale structures
recovered from weak lensing galaxy surveys. These quantities allow us to take
advantage of the special features of weak lensing effect on CMB B-polarization
and of the high (40%) cross-correlation between the two data sets. We show that
these objects are robust to filtering effects, have a low intrinsic cosmic
variance (around 8% for small 100 square degrees surveys) and can be used as an
original constraint on the vacuum energy density.


title:
Driven-disk model for binaries with precessing donor star.
  Three-dimensional simulations

abstract:
  We present the results of three-dimensional numerical simulations of mass
transfer in semi-detached binary with a donor star whose rotation vector
precesses around the orbital rotation axis of the binary in the observer's
coordinate frame. The calculations support our previous model of flow without a
`hot spot'. Characteristic features of the flow in this model, such as the
formation of an circumbinary envelope, the absence of a `hot spot' at the edge
of the accretion disk, and the formation of a shock wave along the edge of the
stream, are also present in the solution for a binary with precessing donor
star. The parameters of accretion disk and of the structure of the near-disk
regions recur with the precessional period of the rotation axis of donor star.


title:
Discovery of the optical counterpart and early optical observations of
  GRB990712

abstract:
  We present the discovery observations of the optical counterpart of the
gamma-ray burster GRB990712 taken 4.16 hours after the outburst and discuss its
light curve observed in the V, R and I bands during the first ~35 days after
the outburst. The observed light curves were fitted with a power-law decay for
the optical transient (OT), plus an additional component which was treated in
two different ways. First, the additional component was assumed to be an
underlying galaxy of constant brightness. The resulting slope of the decay is
0.97+/-0.05 and the magnitudes of the underlying galaxy are: V = 22.3 +/- 0.05,
R = 21.75 +/- 0.05 and I = 21.35 +/- 0.05. Second, the additional component was
assumed to be a galaxy plus an underlying supernova with a time-variable
brightness identical to that of GRB980425, appropriately scaled to the redshift
of GRB990712. The resulting slope of the decay is similar, but the
goodness-of-fit is worse which would imply that either this GRB is not
associated with an underlying supernova or the underlying supernova is much
fainter than the supernova associated with GRB980425. The galaxy in this case
is fainter: V = 22.7 +/- 0.05, R = 22.25 +/- 0.05 and I = 22.15 +/- 0.05; and
the OT plus the underlying supernova at a given time is brighter. Measurements
of the brightnesses of the OT and the galaxy by late-time HST observation and
ground-based observations can thus assess the presence of an underlying
supernova.


title: Detection of polarized mm and submm emission from SgrA*

abstract:
  We report the detection of linear polarization from SgrA* at 750, 850, 1350
and 2000 microns which confirms the contribution of synchrotron radiation. From
the lack of polarization at longer wavelengths it appears to arise in the
millimetre/sub-millimetre excess. There are large position angle changes
between the millimetre and sub-millimetre results and these are discussed in
terms of a polarized dust contribution in the sub-millimetre and various
synchrotron models. In the model which best explains the data the synchrotron
radiation from the excess is self-absorbed in the millimetre region and becomes
optically thin in the sub-millimetre. This implies that the excess arises in an
extremely compact source to the order of 2 Schwarzschild radii.


title: Photometric Redshifts based on standard SED fitting procedures

abstract:
  In this paper we study the accuracy of photometric redshifts computed through
a standard SED fitting procedure, where SEDs are obtained from broad-band
photometry. We present our public code hyperz, which is presently available on
the web. We introduce the method and we discuss the expected influence of the
different observational conditions and theoretical assumptions. In particular,
the set of templates used in the minimization procedure (age, metallicity,
reddening, absorption in the Lyman forest, ...) is studied in detail, through
both real and simulated data. The expected accuracy of photometric redshifts,
as well as the fraction of catastrophic identifications and wrong detections,
is given as a function of the redshift range, the set of filters considered,
and the photometric accuracy. Special attention is paid to the results expected
from real data.


title: An outline of radiatively-driven cosmology

abstract:
  A Big Bang universe consisting, before recombination, of H, D, 3He, 4He, 6Li,
and 7Li ions, electrons, photons, and massless neutrinos, at closure density,
with a galaxy-size perturbation spectrum but no large-scale structure, will
evolve into the universe as we now observe it. Evolution during the first
billion years is controlled by radiation. Globular clusters are formed by
radiatively-driven implosions, galaxies are formed by radiatively triggered
gravitational collapse of systems of globular clusters, and voids are formed by
radiatively-driven expansion. After this period the strong radiation sources
are exhausted and the universe has expanded to the point where further
evolution is determined by gravity and universal expansion.


title: On the sources of the late integrated Sachs-Wolfe effect

abstract:
  In some scenarios, the peculiar gravitational potential of linear and mildly
nonlinear structures depends on time and, as a result of this dependence, a
late integrated Sachs-Wolfe effect appears. Here, an appropriate formalism is
used which allows us to improve on the analysis of the spatial scales and
locations of the main cosmological inhomogeneities producing this effect. The
study is performed in the framework of the currently preferred flat model with
cosmological constant, and it is also developed in an open model for
comparisons. Results from this analysis are used to discuss the contribution of
Great Attractor-like objects, voids, and other structures to the CMB
anisotropy.


title: The late afterglow and host galaxy of GRB 990712

abstract:
  We present deep HST imaging, as well as ground-based imaging and
spectroscopy, of the optical afterglow associated with the long-duration
gamma-ray burst GRB 990712 and its host galaxy. The data were obtained 48--123
days after the burst occurred. The magnitudes of the host (R = 21.9, V = 22.5)
and optical afterglow (R = 25.4, V = 25.8, 47.7 days after the burst) favor a
scenario where the optical light follows a pure power-law decay with an index
of alpha ~ -1.0. We find no evidence for a contribution from a supernova like
SN1998bw. This suggests that either there are multiple classes of long-duration
gamma-ray bursts, or that the peak luminosity of the supernova was > 1.5 mag
fainter than SN1998bw. The HST images and EFOSC2 spectra indicate that the
gamma-ray burst was located in a bright, extended feature (possibly a
star-forming region) 1.4 kpc from the nucleus of a 0.2 L^*_B galaxy at z =
0.434, possibly a Seyfert 2 galaxy. The late-time afterglow and host galaxy of
GRB 990712 bear some resemblance to those of GRB 970508.


title:
Cut-off radii of galactic disks: A statistical study on the truncation
  of galactic disks

abstract:
  We present the analysis of a CCD survey of 31 nearby (<= 110 Mpc) edge-on
spiral galaxies. The three-dimensional one-component best fit models provide
their disk-scalelengths h and for the first time their disk cut-off radii
R_{co}. We confirm for this sample the existence of such sharp truncations, and
find a significantly lower mean value of the distance independent ratio
R_{co}/h =2.9 +- 0.7 than the standard value of 4.5 often used in the
literature. Our data show no correlation of these parameters with Hubble type,
whereas we report a correlation between R_{co}/h and the distance based
scalelength in linear units. Compared to the Milky Way we find only lower
values of R_{co}/h, explained either by possible selection effects or by the
completely different techniques used. We discuss our data in respect to present
models for the origin of the cut-off radii, either as a relict of the galaxy
formation process, or as an evolutionary phenomenon.


title:
Explosion Implosion Duality and the Laboratory Simulation of
  Astrophysical Systems

abstract:
  The Euler equations of ideal gas dynamics posess a remarkable nonlinear
involutional symmetry which allows one to factor out an arbitrary uniform
expansion or contraction of the system. The nature of this symmetry (called by
cosmologists the transformation to supercomoving variables) is discussed and
its origin clarified. It is pointed out that this symmetry allows one to map an
explosion problem to a dual implosion problem and vice versa. The application
to laboratory simulations of supernova remnants is considered; in principle
this duality allows the complete three-dimensional evolution of highly
structured explosion ejecta to be modelled using a static target in an
implosion facility.


title: Double-Mode Stellar Pulsations

abstract:
  The status of the hydrodynamical modelling of nonlinear multi-mode stellar
pulsations is discussed. The hydrodynamical modelling of steady double-mode
(DM) pulsations has been a long-standing quest that is finally being concluded.
Recent progress has been made thanks to the introduction of turbulent
convection in the numerical hydrodynamical codes which provide detailed results
for individual models. An overview of the modal selection problem in the HR
diagram can be obtained in the form of bifurcation diagrams with the help of
simple nonresonant amplitude equations that capture the DM phenomenon.


title:
Submillimeter and Far-InfraRed Experiment (SAFIRE): A PI class
  instrument for SOFIA

abstract:
  SAFIRE is a versatile imaging Fabry-Perot spectrograph covering 145 to 655
microns, with spectral resolving powers ranging over 5-10,000. Selected as a
"PI" instrument for the airborne Stratospheric Observatory for Infrared
Astronomy (SOFIA), SAFIRE will apply two-dimensional pop-up bolometer arrays to
provide background-limited imaging spectrometry. Superconducting transition
edge bolometers and SQUID multiplexers are being developed for these detectors.
SAFIRE is expected to be a "First Light" instrument, useable during the initial
SOFIA operations. Although a PI instrument rather than a "Facility Class"
science instrument, it will be highly integrated with the standard SOFIA
planning, observation, and data analysis tools.


title: What if Dark matter is Bosonic and self-interacting

abstract:
  Recently the problem of singular galactic cores and over-abundant formation
of dwarf galaxies, inherent to the standard cold dark matter model, had
attracted a great deal of attention. One scenario which may be free of these
problems invokes a self-interacting Bose-field. We find the limiting core
density in this model due to the self-annihilation of the scalar field into its
own relativistic quanta. The limiting density may correspond to the observable
one if there is only one dark matter component. Alternatively, there may be
more than one dark matter species and the annihilation of one species may be
very efficient with subsequent expansion of the other, thus avoiding the
problem of singular cores.


title:
Modeling Nonaxisymmetric Bow Shocks: Solution Method and Exact Analytic
  Solutions

abstract:
  A new solution method is presented for steady-state, momentum-conserving,
non-axisymmetric bow shocks and colliding winds in the thin-shell limit. This
is a generalization of previous formulations to include a density gradient in
the pre-shock ambient medium, as well as anisotropy in the pre-shock wind. For
cases where the wind is unaccelerated, the formalism yields exact, analytic
solutions.
  Solutions are presented for two bow shock cases: (1) that due to a star
moving supersonically with respect to an ambient medium with a density gradient
perpendicular to the stellar velocity, and (2) that due to a star with a
misaligned, axisymmetric wind moving in a uniform medium. It is also shown
under quite general circumstances that the total rate of energy thermalization
in the bow shock is independent of the details of the wind asymmetry, including
the orientation of the non-axisymmetric driving wind, provided the wind is
non-accelerating and point-symmetric. A typical feature of the solutions is
that the region near the standoff point is tilted, so that the star does not
lie along the bisector of a parabolic fit to the standoff region. The principal
use of this work is to infer the origin of bow shock asymmetries, whether due
to the wind or ambient medium, or both.


title: Mass Segregation in Star Clusters

abstract:
  Star clusters - open and globulars - experience dynamical evolution on time
scales shorter than their age. Consequently, open and globular clusters provide
us with unique dynamical laboratories for learning about two-body relaxation,
mass segregation from equipartition of energy, and core collapse. We review
briefly, in the framework of star clusters, some elements related to the
theoretical expectation of mass segregation, the results from N-body and other
computer simulations, as well as the now substantial clear observational
evidence.


title:
A search for Jovian-mass planets around CM Draconis using eclipse minima
  timing

abstract:
  For the eclipsing binary system CM Draconis, eclipse minimum times have been
monitored with high precision between 1994 and 1999. Periodic deviations of
minimum times from a linear ephemeris may indicate the presence of an orbiting
third body. Individual measurements of 41 eclipse minimum times result in a
standard deviation from linear ephemeris of 5.74 seconds. A power spectral
analysis of the residuals reveals only one periodicity with more then 2 seconds
amplitude. This feature, with a periodicity between 750 and 1050 days has an
amplitude of 2.8+-0.5 seconds, and is also present with similar phases if the
power spectral analysis is performed independently for primary and secondary
eclipses. It would be compatible with a planet of 1.5-3 Jupiter masses at an
orbital distance of 1.1-1.45 AU to the binary barycenter. The assignation of a
planet to the CM Dra system can however only be upheld if this periodicity can
be followed in future observations for several years. For low-mass eclipsing
binary stars, the method of eclipse minimum timing allows one to reach mass
limits for the detection of third bodies well below that feasible by radial
velocity measurements.


title: The MACHO Project: Microlensing Detection Efficiency

abstract:
  The MACHO project is a search for dark matter in the form of massive compact
halo objects (MACHOs). The project has photometrically monitored tens of
millions of stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud
(SMC), and Galactic bulge in search of rare gravitational microlensing events
caused by these otherwise invisible objects. In 5.7 years of observations
toward the LMC some 13-17 microlensing events have been observed by the MACHO
survey, allowing powerful statements to be made about the nature of the dark
population in the halo of our Galaxy. A critical component of these statements
is an accurate determination of the survey's detection efficiency. The
detection efficiency is a complicated function of temporal sampling, stellar
crowding (the luminosity function), image quality, photometry, time-series
analysis, and criteria used to select the microlensing candidates. Such a
complex interdependence is most naturally solved using a Monte Carlo approach.
Here we describe the details of the Monte Carlo used to calculate the
efficiency presented in the MACHO 5.7-year LMC results. Here we correct several
shortcomings of past determinations, including (1) adding fainter source stars
(2.5 magnitudes below our faintest detected "stars"), (2) an up-to-date
luminosity function for the LMC, (3) better sampling of real images in both
stellar density and observing conditions, (4) an improved scheme for adding
artificial microlensing onto a random sample of real lightcurves, and many
other improvements. [Abridged]


title: A Characteristic Scale on the Cosmic Microwave Sky

abstract:
  The current suite of results from Cosmic Microwave Background anisotropy
experiments is fulfilling the promise of providing extraordinary levels of
discrimination between cosmological models. We calculate a binned anisotropy
power spectrum, which we tabulate, along with error bars and bin-to-bin
correlations, so that it can be easily used for constraining models. The
resulting power spectrum is flat at large angles, with a gradual rise to a
prominent peak at around 0.5 degrees and a decrease thereafter. This is
precisely the shape predicted by inflationary-inspired adiabatic models. Within
that class of cosmologies, this characteristic scale imprinted on the CMB sky
can be used to infer that the geometry of the Universe is very close to flat.
The next wave of CMB results should add fuel to the debate about whether or not
the Universe once inflated, as well as beginning in earnest the task of
measuring cosmological parameters.


title: A New Probe of the Molecular Gas in Galaxies: Application to M101

abstract:
  Recent studies of nearby spiral galaxies suggest that photodissociation
regions (PDRs) are capable of producing much of the observed HI in galaxy
disks. In that case, measurements of the HI column density and the
far-ultraviolet (FUV) photon flux provide a new probe of the volume density of
the local underlying H_2. We develop the method and apply it to the giant Scd
spiral M101 (NGC 5457). We find that, after correction for the best-estimate
gradient of metallicity in the ISM of M101 and for the extinction of the
ultraviolet emission, molecular gas with a narrow range of density from 30-1000
cm^-3 is found near star- forming regions at all radii in the disk of M101 out
to a distance of 12' (approximately 26 kpc), close to the photometric limit of
R_25 = 13.5'.
  In this picture, the ISM is virtually all molecular in the inner parts of
M101. The strong decrease of the HI column density in the inner disk of the
galaxy at R_G < 10 kpc is a consequence of a strong increase in the dust-to-gas
ratio there, resulting in an increase of the H_2 formation rate on grains and a
corresponding disappearance of hydrogen in its atomic form.


title: Magellanic Cloud Periphery Carbon Stars IV: The SMC

abstract:
  The kinematics of 150 carbon stars observed at moderate dispersion on the
periphery of the Small Magellanic Cloud are compared with the motions of
neutral hydrogen and early type stars in the Inter-Cloud region. The
distribution of radial velocities implies a configuration of these stars as a
sheet inclined at 73+/-4 degrees to the plane of the sky. The near side, to the
South, is dominated by a stellar component; to the North, the far side contains
fewer carbon stars, and is dominated by the neutral gas. The upper velocity
envelope of the stars is closely the same as that of the gas. This
configuration is shown to be consistent with the known extension of the SMC
along the line of sight, and is attributed to a tidally induced disruption of
the SMC that originated in a close encounter with the LMC some 0.3 to 0.4 Gyr
ago. The dearth of gas on the near side of the sheet is attributed to ablation
processes akin to those inferred by Weiner & Williams (1996) to collisional
excitation of the leading edges of Magellanic Stream clouds. Comparison with
pre LMC/SMC encounter kinematic data of Hardy, Suntzeff, & Azzopardi (1989) of
carbon stars, with data of stars formed after the encounter, of Maurice et al.
(1989), and Mathewson et al. (a986, 1988) leaves little doubt that forces other
than gravity play a role in the dynamics of the H I.


title: Geometric phase in phasing of antenna arrays

abstract:
  The response of a pair of differently polarized antennas is determined by
their polarization states AND a phase between them which has a geometric part
which becomes discontinuous at singular points in the parameter space. Such
phase singularities have been observed in optical polarization experiments
[R.Bhandari, Physics Reports 281 (1997) 1]. It is pointed out that such a phase
is implicit in an equation for the response derived in the sixties [Morris et
al Ap.J. 139 (1964) 551].
  When a source emitting partially polarized radiation is observed with a
correlation interferometer consisting of two antennas with different
polarizations, curiously, fringes can be made to vanish for an appropriate
choice of the polarization states, in general non orthogonal [V Radhakrishnan,
Current Science 67 (1994) 257]. The result follows by considering the
interference as a superposition of two patterns due to the two orthogonal
polarization components of the radiation, which have a phase difference of
magnitude \pi, a geometric phase.


title:
Two-dimensional models of hydrodynamical accretion flows into black
  holes

abstract:
  We present a systematic numerical study of two-dimensional axisymmetric
accretion flows around black holes. The flows have no radiative cooling and are
treated in the framework of the hydrodynamical approximation. The models
calculated in this study cover the large range of the relevant parameter space.
There are four types of flows, determined by the values of the viscosity
parameter $\alpha$ and the adiabatic index $\gamma$: convective flows,
large-scale circulations, pure inflows and bipolar outflows. Thermal conduction
introduces significant changes to the solutions, but does not create a new flow
type. Convective accretion flows and flows with large-scale circulations have
significant outward-directed energy fluxes, which have important implications
for the spectra and luminosities of accreting black holes.


title: Spherical Scalar Field Halo in Galaxies

abstract:
  We study a spherically symmetric fluctuation of scalar dark matter in the
cosmos and show that it could be the dark matter in galaxies, provided that the
scalar field has an exponential potential whose overall sign is negative and
whose exponent is constrained observationally by the rotation velocities of
galaxies. The local space-time of the fluctuation contains a three dimensional
space-like hypersurface with surplus of angle.


title:
Comments on the paper ``Polarimetric Constraints on the Optical
  Afterglow Emission from GRB 990123'' by Hjorth et al. (Science, 26 1999)

abstract:
  GRB 990123 is the most luminous event detected so far, and in an important
paper, Hjorth et al. (1999) reported an upper limit on the degree of linear
polarization of the optical afterglow for this burst (P <2.3%). One of the
interprtations for this small value of P was that the emission was probably due
a relativistic jet with ordered magnetic field, and the viewing angle in the
lab frame theta' <= Gamma^{-1}, where Gamma is the bulk Lorentz factor of the
jet at the time of the optical emission. We point out that this conclusion
resulted from a confusion between the angles measured in the lab frame and in
the plasma rest frame. For ordered magnetic field, one would actually obtain a
large value of P because the above mentioned angle would correspond to a very
large angle, theta <= \pi/2, in the plasma rest frame. And this is probably the
case with the blazars. On the other hand, it is indeed possible to have P ~ 0
if the magnetic field of GRB 990123 was completely chaotic and the viewing
angle was considerably smaller than the semi-angle of the jet.


title: Lyman alpha Absorption Systems and the Intergalactic Medium

abstract:
  The last few years have seen a dramatic improvement in our understanding of
the origin of Lyman alpha absorption systems. Hydrodynamic numerical
simulations of cold dark matter dominated universes have shown that the many
properties of the Lyman alpha absorption systems can be explained by a
photoionized, space-filling, intergalactic medium. Lyman alpha lines offer
promising probes of the photoionizing background, the amplitude of the mass
fluctuations at high redshift and the evolution of the equation of state of the
intergalactic medium.


title:
Massive Stars in the Range $\rm 13-25 M_\odot$: Evolution and
  Nucleosynthesis. II. the Solar Metallicity Models

abstract:
  We present the evolutionary properties of a set of massive stellar models
(namely 13, 15, 20 and 25 $\rm M_\odot$) from the main sequence phase up to the
onset of the iron core collapse. All these models have initial solar chemical
composition, i.e. Y=0.285 and Z=0.02. A 179 isotope network, extending from
neutron up to $\rm ^{68}Zn$ and fully coupled to the evolutionary code has been
adopted from the Carbon burning onward. Our results are compared, whenever
possible, to similar computations available in literature.


title: The Alignment of Clusters using Large Scale Simulations

abstract:
  The alignment of clusters of galaxies with their nearest neighbours and
between clusters within a supercluster is investigated using simulations of
512^{3} dark matter particles for \LambdaCDM and \tauCDM cosmological models.
Strongly significant alignments are found for separations of up to 15h^{-1}Mpc
in both cosmologies, but for the \LambdaCDM model the alignments extend up to
separations of 30h^{-1}Mpc. The effect is strongest for nearest neighbours, but
is not significant enough to be useful as an observational discriminant between
cosmologies. As a check of whether this difference in alignments is present in
other cosmologies, smaller simulations with 256^{3} particles are investigated
for 4 different cosmological models. Because of poor number statistics, only
the standard CDM model shows indications of having different alignments from
the other models.


title: The Anisotropy of MHD Alfv\'{e}nic Turbulence

abstract:
  We perform direct 3-dimensional numerical simulations for magnetohydrodynamic
(MHD) turbulence in a periodic box of size $2\pi$ threaded by strong uniform
magnetic fields. We use a pseudo-spectral code with hyperviscosity and
hyperdiffusivity to solve the incompressible MHD equations. We analyze the
structure of the eddies as a function of scale. A straightforward calculation
of anisotropy in wavevector space shows that the anisotropy is scale-{\it
independent}. We discuss why this is {\it not} the true scaling law and how the
curvature of large-scale magnetic fields affects the power spectrum and leads
to the wrong conclusion. When we correct for this effect, we find that the
anisotropy of eddies depends on their size: smaller eddies are more elongated
than larger ones along {\it local} magnetic field lines. The results are
consistent with the scaling law $\tilde{k}_{\parallel} \sim
\tilde{k}_{\perp}^{2/3}$ proposed by Goldreich and Sridhar (1995, 1997). Here
$\tilde{k}_{\|}$ (and $\tilde{k}_{\perp}$) are wavenumbers measured relative to
the local magnetic field direction. However, we see some systematic deviations
which may be a sign of limitations to the model, or our inability to fully
resolve the inertial range of turbulence in our simulations.


title: The Generation of Magnetic Fields Through Driven Turbulence

abstract:
  We have tested the ability of driven turbulence to generate magnetic field
structure from a weak uniform field using three dimensional numerical
simulations of incompressible turbulence. We used a pseudo-spectral code with a
numerical resolution of up to $144^3$ collocation points. We find that the
magnetic fields are amplified through field line stretching at a rate
proportional to the difference between the velocity and the magnetic field
strength times a constant. Equipartition between the kinetic and magnetic
energy densities occurs at a scale somewhat smaller than the kinetic energy
peak. Above the equipartition scale the velocity structure is, as expected,
nearly isotropic. The magnetic field structure at these scales is uncertain,
but the field correlation function is very weak. At the equipartition scale the
magnetic fields show only a moderate degree of anisotropy, so that the typical
radius of curvature of field lines is comparable to the typical perpendicular
scale for field reversal. In other words, there are few field reversals within
eddies at the equipartition scale, and no fine-grained series of reversals at
smaller scales. At scales below the equipartition scale, both velocity and
magnetic structures are anisotropic; the eddies are stretched along the local
magnetic field lines, and the magnetic energy dominates the kinetic energy on
the same scale by a factor which increases at higher wavenumbers. We do not
show a scale-free inertial range, but the power spectra are a function of
resolution and/or the imposed viscosity and resistivity. Our results are
consistent with the emergence of a scale-free inertial range at higher Reynolds
numbers.


title: BeppoSAX observation of the transient X-ray pulsar GS 1843+00

abstract:
  We present the results from both the timing and spectroscopic analysis of the
transient X-ray pulsar GS 1843+00 observed by the BeppoSAX satellite on 1997
April 4, when the source was at a luminosity of ~10^{37} erg s^{-1}. GS 1843+00
shows a very hard spectrum that is well fitted by an absorbed power law (N_H
\~2.3 10^{22} cm^{-2}) modified by a high energy cut-off above 6 keV. The
source shows a small pulse amplitude in the whole energy band. The pulse
profile evolves with energy from a double-peaked to single-peaked shape. The
barycentric pulse period is 29.477+/-0.001 s.


title: Impulsive and Varying Injection in GRB Afterglows

abstract:
  The standard model of Gamma-Ray Bursts afterglows is based on synchrotron
radiation from a blast wave produced when the relativistic ejecta encounters
the surrounding medium. We reanalyze the refreshed shock scenario, in which
slower material catches up with the decelerating ejecta and reenergizes it.
This energization can be done either continuously or in discrete episodes. We
show that such scenario has two important implications. First there is an
additional component coming from the reverse shock that goes into the
energizing ejecta. This persists for as long as the re-energization itself,
which could extend for up to days or longer. We find that during this time the
overall spectral peak is found at the characteristic frequency of the reverse
shock. Second, if the injection is continuous, the dynamics will be different
from that in constant energy evolution, and will cause a slower decline of the
observed fluxes. A simple test of the continuously refreshed scenario is that
it predicts a spectral maximum in the far IR or mm range after a few days.


title: What can GLAST say about the origin of cosmic rays in other galaxies ?

abstract:
  Gamma rays in the band from 20 MeV to 300 GeV, used in combination with data
from radio and X-ray bands, provide a powerful tool for studying the origin of
cosmic rays in our sister galaxies Andromeda and the Magellanic Clouds.
Gamma-ray Large Area Space Telescope (GLAST) will spatially resolve these
galaxies and measure the spectrum and intensity of diffuse gamma radiation from
the collisions of cosmic rays with gas and dust in them. Observations of
Andromeda will give an external perspective on a spiral galaxy like the Milky
Way. Observations of the Magellanic Clouds will permit a study of cosmic rays
in dwarf irregular galaxies, where the confinement is certainly different and
the massive star formation rate is much greater.


title:
Radio Detection of High Energy Particles: Coherence Versus Multiple
  Scales

abstract:
  Radio Cherenkov emission underlines detection of high energy particles via a
signal growing like the particle-energy-squared. Cosmic ray-induced
electromagnetic showers are a primary application. While many studies have
treated the phenomenon approximately, none have attempted to incorporate all
the physical scales involved in problems with time- or spatially- evolving
charges. We find it is possible to decompose the calculated fields into the
product of a form factor, characterizing a moving charge distribution,
multiplying a general integral which depends on the charge evolution. In
circumstances of interest for cosmic ray physics, the resulting expressions can
be evaluated explicitely in terms of a few parameters obtainable from shower
codes. The classic issues of Frauhofer and Fresnel zones play a crucial role in
the coherence.


title: Photoionization and Recombination

abstract:
  Theoretically self-consistent calculations for photoionization and (e + ion)
recombination are described. An identical eigenfunction expansion for the ion
is employed in coupled channel calculations for both processes, thus ensuring
consistently accurate cross sections and rates in an ab initio manner. The
theoretical treatment of (e + ion) recombination subsumes both the non-resonant
recombination ('radiative recombination'), and the resonant recombination
('di-electronic recombination') processes in a unified scheme. In addition to
the total, unified recombination rates, level-specific recombination rates and
photoionization cross sections are obtained for a large number of atomic
levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling,
calculations are carried out in the close coupling approximation using the
R-matrix method. Although the calculations are computationally intensive, they
yield nearly all photoionization and recombination parameters needed for
astrophysical photoionization models with higher precision than hitherto
possible, estimated at about 10-20 % from comparison with experimentally
available data (including 'experimentally derived DR rates'). Results are
electronically available for over 40 atoms and ions. Photoionization and
recombination of He-, and Li-like C and Fe are described for X-ray modeling.
The unified method yields total and complete (e+ion) recombination rate
coeffcients, that can not otherwise be obtained theoretically or
experimentally. "temp" 23 lines, 1524 characters


title:
Atomic data from the Iron Project.XLIV. Transition probabilities and
  line ratios for Fe VI with fluorescent excitation in planetary nebulae

abstract:
  Relativistic atomic structure calculations for electric dipole E1, electric
quadrupole E2 and magnetic dipole M1 transition probabilities among the first
80 fine-structure levels of Fe VI, dominated by configurations 3d^3, 3d^24s,
and 3d^24p, are carried out using the Breit-Pauli version of the code
Superstructure. Experimental energies are used to improve the accuracy of these
transition probabilities. Employing the 80-level collision-radiative (CR) model
with these dipole and forbidden transition probabilities, and Iron Project
R-matrix collisional data, we present a number of [Fe VI] line ratios
applicable to spectral diagnostics of photoionized H II regions. It is shown
that continuum fluorescent excitation needs to be considered in CR models in
order to interpret the observed line ratios of optical [Fe VI] lines in
planetary nebulae NGC 6741, IC 351, and NGC 7662. The analysis leads to
parametrization of line ratios as function of, and as constraints on, the
electron density and temperature, as well as the effective radiation
temperature of the central source and a geometrical dilution factor. The
spectral diagnostics may also help ascertain observational uncertainties. The
method may be generally applicable to other objects with intensive background
radiation fields, such as novae and active galactic nuclei. The extensive new
Iron Project radiative and collisional calculations enable a consistent
analysis of many line ratios for the complex iron ions.


title:
Electron-Ion Recombination Rate Coefficients and Photoionization Cross
  Sections for Astrophysically Abundant Elements IV. Relativistic calculations
  for C IV and C V for UV and X-ray modeling

abstract:
  The first complete set of unified cross sections and rate coefficients are
calculated for photoionization and recombination of He- and Li-like ions using
the relativistic Breit-Pauli R-matrix method. We present total, unified (e +
ion) recombination rate coefficients for (e + C VI ---> C V) and (e + C V
\longrightarrow C IV) including fine structure. Level-specific recombination
rate coefficients up to the n = 10 levels are also obtained for the first time;
these differ considerably from the approximate rates currently available.
Applications to recombination-cascade coefficients in X-ray spectral models of
K-alpha emission from the important He-like ions is pointed out. The overall
uncertainty in the total recombination rates should not exceed 10-20%.
Ionization fractions for Carbon are recomputed in the coronal approximation
using the new rates.
  The present (e + ion) recombination rate coefficients are compared with
several sets of available data, including previous LS coupling results, and
`experimentally derived' rate coefficients. The role of relativistic fine
structure, resolution of resonances, radiation damping, and interference
effects is discussed. Two general features of recombination rates are noted:
(i) the non-resonant (radiative recombination) peak as E,T ---> 0, and the (ii)
the high-T resonant (di-electronic recombination) peak.


title:
The artificial night sky brightness mapped from DMSP Operational
  Linescan System measurements

abstract:
  We present a method to map the artificial sky brightness across large
territories in astronomical photometric bands with a resolution of
approximately 1 km. This is useful to quantify the situation of night sky
pollution, to recognize potential astronomical sites and to allow future
monitoring of trends. The artificial sky brightness present in the chosen
direction at a given position on the Earth's surface is obtained by the
integration of the contributions produced by every surface area in the
surrounding. Each contribution is computed based on detailed models for the
propagation in the atmosphere of the upward light flux emitted by the area. The
light flux is measured with top of atmosphere radiometric observations made by
the Defense Meteorological Satellite Program (DMSP) Operational Linescan
System.
  We applied the described method to Europe obtaining the maps of artificial
sky brightness in V and B bands.


title: A Giant Glitch in the Energetic 69 ms X-ray Pulsar AXS J161730-505505

abstract:
  We present new results on the recently discovered 69 ms X-ray pulsar AXS
J161730-505505, the sixth youngest sample of all known pulsars. We have
undertaken a comprehensive X-ray observing campaign of AXS J161730-505505 with
the ASCA, SAX, and XTE observatories and follow its long term spin-down history
between 1989 and 1999, using these, archival GINGA and ASCA data sets, and the
radio ephemeris. The spin-down is not simply described by a linear function as
originally thought, but instead we find evidence of a giant glitch (|Delta P/P|
> 10E-6) between 1993 August and 1997 September, perhaps the largest yet
observed from a young pulsar. The glitch is well described by steps in the
period and its first derivative accompanied by a persistent second derivative
similar to those in the Vela pulsar. The pulse profile of AXS J161730-505505
presents a single asymmetric peak which is maintained over all observation
epochs. The energy spectrum is also steady over time, characterized by a highly
absorbed power-law with a photon index 1.4 +/- 0.2, consistent with that found
for other young rotation powered pulsars.